Advanced phosphate materials as positive electrodes for Na-ion batteries

Ad anced phospha e ma e ials as posi i e
elec odes o Na-ion ba e ies
Ca los Manuel Be langa C uzado
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(cc) 2025 Ca los Manuel Be langa C uzado (cc by-nc 4.0)
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Ad anced phospha e ma e ials as posi i e
elec odes o Na-ion ba e ies
Depa amen o de Química O gánica e Ino gánica
CIC Ene gigune
A disse a ion submi ed o he Uni e si y o he Basque Coun y in
pa ial ul illmen s o he equi emen s o he deg ee o Ph.D.
By
Ca los Manuel Be langa C uzado
Thesis supe iso s:
D a. Mon se Galce án Mes es
P o . Teó ilo Rojo
Tu o :
P o . Teó ilo Rojo
Oc obe 2025
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The scien is has begun o ealize his social esponsibili y…
J. D. Be nal
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Resumen
Las ba e ías de ion-sodio (NIBs, po sus siglas en inglés) han
eme gido en los úl imos años como una de las al e na i as más
p ome edo as a las ba e ías de ion-li io (LIBs), impulsadas po la
c ecien e p eocupación sob e la disponibilidad limi ada del li io, su
cos e y los p oblemas de sos enibilidad asociados a su ex acción.
Aunque las ba e ías de sodio p esen an una densidad ene gé ica
in e io a la de las de li io, o ecen en ajas signi ica i as en é minos
de cos e, abundancia de ma e ia p ima y meno impac o ambien al.
Es as ca ac e ís icas las con ie en en candida as ideales pa a
aplicaciones de almacenamien o es aciona io de ene gía y en
aquellas donde la al a densidad ene gé ica no esul a p io i a ia.
La p esen e esis doc o al se cen a en el desa ollo de mé odos de
sín esis sos enibles, de bajo cos e y esponsables con el medio
ambien e pa a la ob ención de ma e iales ca ódicos basados en
os a os aplicables a ba e ías de ion-sodio. El abajo busca p omo e
el uso de ma e ias p imas abundan es y no óxicas, educiendo el
impac o económico y ecológico de los p ocesos de p oducción, sin
comp ome e las p es aciones elec oquímicas de los ma e iales
esul an es.
El p oyec o abo da es obje i os undamen ales:
1. Es ablece nue os pa adigmas de sín esis e de pa a
ma e iales ca ódicos os a ados de sodio.
2. P o undiza en la comp ensión es uc u al, mo ológica y
elec oquímica de dichos ma e iales.
3. Sen a las bases pa a su escalado indus ial, consolidando las
NIBs como al e na i as iables a las LIBs.
La in es igación combina en oques expe imen ales di ec os e
indi ec os. Po un lado, se explo an u as de sín esis indi ec a
median e sodiación de ma e iales li iados (LiMn1-yFeyPO4), con
ecupe ación del li io como subp oduc o de alo . Po o o, se
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desa ollan p ocesos de sín esis di ec a de ases Nax(TM)y(PO4)z
(donde TM = Mn, Fe o combinaciones de ambos), analizando cómo
pa áme os como el pH o la elación Mn:Fe in luyen en la o mación
de dis in as ases c is alinas.
El es udio ecu e a écnicas a anzadas de ca ac e ización es uc u al
y espec oscópica (di acción de neu ones, espec oscopías
Mössbaue y de abso ción de ayos X, en e o as) pa a iden i ica y
es udia di e en es polimo os como i ili a, xeno ili a y ma ici a, y
comp ende sus mecanismos de inse ción y ex acción de sodio
du an e el ciclado elec oquímico.
En conjun o, los esul ados de es a esis con ibuyen al conocimien o
undamen al sob e los os a os de sodio como ma e iales ca ódicos y
apo an in o mación cla e pa a el diseño de ma e iales de
almacenamien o ene gé ico de p óxima gene ación, sos enibles y
económicamen e compe i i os.
Capí ulo 1. In oducción
Es e capí ulo con ex ualiza la p esen e esis doc o al. En p ime luga ,
se o ece una desc ipción gene al que jus i ica el in e és cien í ico y
ecnológico en el desa ollo de ba e ías de ion-sodio como al e na i a
sos enible a las de ion-li io. A con inuación, se explica el p incipio de
uncionamien o de las ba e ías eca gables y los undamen os
elec oquímicos que las igen. Finalmen e, se p esen a una isión
gene al del es ado del a e en la in es igación sob e ma e iales pa a
ba e ías de sodio, poniendo especial én asis en los ma e iales
polianiónicos como cá odos, debido a su es abilidad es uc u al,
segu idad y po encial pa a aplicaciones a g an escala.
Capí ulo 2 – Técnicas expe imen ales y de ca ac e ización
El segundo capí ulo desc ibe de mane a de allada las écnicas
expe imen ales empleadas en la in es igación:
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•Técnicas es uc u ales y mo ológicas, incluyendo di acción
de ayos X (XRD), mic oscopía elec ónica de ba ido (SEM) y
ansmisión (TEM), y di acción de neu ones.
•Técnicas ísico-químicas, como la espec oscopía Mössbaue ,
el análisis é mico (TGA/DSC) y la espec oscopía de
abso ción de ayos X (XAS).
•Técnicas elec oquímicas, que aba can desde la
ol ampe ome ía cíclica has a las p uebas de ca ga-desca ga
gal anos á ica.
Es as me odologías pe mi en co elaciona la es uc u a c is alina y
la composición química con el endimien o elec oquímico de los
ma e iales sin e izados, apo ando una isión in eg al de los
enómenos que de e minan su uncionalidad como cá odos en
ba e ías de ion-sodio.
Capí ulo 3 – Sín esis indi ec a de i ili a-NaMn1-yFeyPO4 y
ecupe ación de li io
En es e capí ulo se p esen a un mé odo de sín esis indi ec a pa a la
ob ención de la ase i ili a NaMn1-yFeyPO4 a pa i de p ecu so es
come ciales de LiMn1-yFeyPO4 (p opo cionados po Aleees), con
ecupe ación simul ánea del li io.
El p oceso p opues o sus i uye los eac i os pelig osos y cos osos
empleados adicionalmen e (como NO2BF4 o ace oni ilo bajo
a mós e a ine e) po eac i os económicos y no óxicos (Na2S2O8,
Na2S2O3 y agua), educiendo d ás icamen e la huella ambien al del
p oceso.
Los esul ados demues an que la deli iación-sodiación con olada
pe mi e ob ene ma e iales de es uc u a i ili a con buenas
p opiedades elec oquímicas, al iempo que se ecupe a li io de o ma
e icien e. Es a ap oximación cons i uye un a ance signi ica i o hacia
p ocesos indus iales ci cula es y sos enibles pa a la ab icación de
cá odos de sodio.
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Capí ulo 4 – Sín esis di ec a de polimo os Nax(TM)y(PO4)z y
e ec o de las condiciones expe imen ales
El cua o capí ulo se dedica al es udio de la sín esis di ec a de
di e en es polimo os de os a os sódicos, con la ó mula gene al
Nax(TM)y(PO4)z (TM = Mn, Fe o mezclas de ambos). Se analizan las
condiciones expe imen ales que de e minan la o mación de cada
ase, en especial el pH de la solución y la na u aleza del p ecu so
sódico (NaOH, Na2SO4 o ace a o de sodio).
El obje i o p incipal es log a la sín esis di ec a de la ase i ili a
NaTM(PO4), cuya ob ención se ha conside ado his ó icamen e di ícil,
dado que la ase ma ici a suele o ma se p e e en emen e. El es udio
sis emá ico de las a iables de sín esis pe mi ió iden i ica
condiciones que a o ecen la es abilización de dis in as ases y
p opo cionó in o mación undamen al sob e los mecanismos de
nucleación y c ecimien o en medios acuosos.
Capí ulo 5 – Ca ac e ización a anzada de la ase i ili a
NaMn1-yFeyPO4
En el quin o capí ulo se p esen a un análisis es uc u al y
elec oquímico de allado de la ase i ili a NaMn1-yFeyPO4 ob enida
median e sín esis hid o e mal di ec a. A a és de écnicas a anzadas
como la di acción de neu ones y la espec oscopía Mössbaue , se
de e mina on con p ecisión los pa áme os de celda uni a ia, la
p opo ción Mn:Fe en la ed c is alina y la dis ibución de es ados de
oxidación (Fe2+/Fe3+).
Asimismo, se lle ó a cabo una e aluación exhaus i a de la
mo ología, es abilidad é mica y compo amien o elec oquímico,
e elando cómo la sus i ución pa cial de Mn po Fe modi ica la
capacidad y la ciné ica de inse ción de sodio. Las medidas XAS in si u
y ex si u pe mi ie on segui la e olución del en o no local de los
me ales de ansición du an e el ciclado, apo ando una comp ensión
p o unda de los mecanismos edox implicados.
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Con en s
Lis o igu es xxix
Lis o ables xli
Ac onyms xli
1. In oduc ion
1.1. O e iew o ene gy demand ......................................... 3
1.2. Ba e ies .................................................................... 4
1.3. Na-ion ba e ies .......................................................... 6
1.3.1. Anodes o Na-ion Ba e ies .................................... 9
1.3.1.1. Ha d Ca bon .................................................. 10
1.3.1.2. Alloy-Based Anodes ........................................ 11
1.3.1.3. Me al Oxides and Sul ides ............................... 11
1.3.2. Elec oly e Ma e ials o Na-ion Ba e ies ................. 11
1.3.3.1. O ganic Liquid Elec oly es .............................. 12
1.3.3.2. Ce amic Solid-S a e Elec oly es ...................... 13
1.3.3.3. Gel Polyme Solid-S a e Elec oly es ................. 13
1.3.3. Ca hode o Na-ion ba e ies .................................. 13
1.3.3.1. Laye ed oxides .............................................. 14
1.3.3.2. P ussian blue analogues .................................. 15
1.3.3.3. Polyanionic ma e ials ...................................... 17
1.4. Objec i es and goals ................................................... 26
1.5. Re e ences ................................................................ 28
2. Expe imen al Techniques ........................................... 35
2.1. X-Ray Powde Di ac ion echniques ............................. 36
2.2. Elec on mic oscopy echnique ..................................... 38
2.2.1. Scanning Elec on Mic oscopy ................................ 39
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2.2.2. T ansmission Elec on Mic oscopy ........................... 41
2.3. The mal analysis couple wi h Mass Spec ome y echnique
................................................................................ 41
2.4. Induc i ely Coupled Plasma A omic Emission Spec ome y
echnique ........................................................................... 43
2.5. Raman Spec oscopy echnique .................................... 44
2.6. X-Ray Abso p ion Spec oscopy echnique ..................... 45
2.7. Mössbaue Spec oscopy echnique............................... 46
2.8. Solid S a e Nuclea Magne ic Resonance echnique ......... 47
2.9. Elec ochemical echniques .......................................... 48
2.9.1. Elec ode p epa a ion ........................................... 48
2.9.2. Cell assembly ...................................................... 49
2.9.3. Gal anos a ic expe imen s .................................... 50
2.9.4. Cyclic ol amme y ............................................... 51
2.9.5. Po en ios a ic In e mi en Ti a ion Technique ......... 51
2.10. Re e ences ................................................................ 52
3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s
cha ac e iza ion .................................................................. 53
3.1. In oduc ion............................................................... 54
3.2. Syn hesis and phase iden i ica ion ................................ 54
3.2.1. Chemical oxida ion o LiFePO4 ................................ 55
3.2.2. Chemical oxida ion o LiMn0.65Fe0.35PO4 .................... 56
3.2.3. Chemical educ ion o Mn1-yFeyPO4 .......................... 57
3.2.4. Li-Reco e y and Syn hesis o LiFePO4 ..................... 67
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3.3. S uc u al, mo phological and physicochemical
cha ac e iza ion ................................................................... 69
3.3.1. (Li/Na)FePO4 ma e ials cha ac e iza ion .................. 69
3.3.2. (Li/Na)Mn0.65Fe0.35PO4 ma e ials cha ac e iza ion ...... 77
3.3.3. Reco e ed LiFePO4 ma e ial cha ac e iza ion ............ 80
3.4. Elec ochemical cha ac e iza ion o (Li,Na)Mn1-yFeyPO4 .... 82
3.4.1. Elec ochemical p ope ies o syn hesized NaMn1-
yFeyPO4 82
3.4.2. Elec ochemical p ope ies o egene a ed LiFePO4.... 92
3.5. Summa y and Conclusions ........................................... 93
3.6. Re e ences ................................................................ 95
4. Di ec syn hesis o ansi ion me al phospha e-based
polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe) .......................... 99
4.1. In oduc ion............................................................. 100
4.2. Densi y unc ional heo y........................................... 100
4.3. Solubili y analysis and selec ion o he p ecu so s ........ 103
4.4. Syn hesis and phase iden i ica ion o NaxMn1-yFeyPO4 o (0 ≤
y ≤ 1) .............................................................................. 106
4.4.1. Syn hesis and phase iden i ica ion o na ophili e
NaMnPO4 ....................................................................... 106
4.4.2. Syn hesis and phase iden i ica ion o iphyli e NaMn1-
yFeyPO4 (y = 0.25, 0.50, and 0.75) .................................... 107
4.4.3. E ec o he pH on iphyli e NaMn0.25Fe0.75PO4 ....... 108
4.4.4. Syn hesis o NaMn1-yFeyPO4 subs i u ing Mn wi h Fe
p og essi ely .................................................................. 112
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4.5. Syn hesis o Xenophylli e Na4TM7(PO4)6 (TM = Fe, Mn).... 118
4.6. Co ela ion o pH wi h ob ained polymo phs. ................ 120
4.7. Moni o ing o he hyd o he mal syn hesis ia in-si u
Synch o on XRD ............................................................... 122
4.8. Summa y and Conclusions ......................................... 126
4.9. Re e ences .............................................................. 128
5. Cha ac e iza ion o iphyli e NaMn1-yFeyPO4 (0≤y≤30)
127
5.1. In oduc ion............................................................. 128
5.2. S uc u al, mo phological, and physicochemical
cha ac e iza ion ................................................................. 128
5.3. The mal s abili y ...................................................... 137
5.4. Elec ochemis y Cha ac e iza ion ............................... 138
5.5. Reac ion mechanism: X-Ray abso p ion spec oscopy ... 144
5.6. Summa y and Conclusions ......................................... 148
5.7. Re e ences .............................................................. 149
6. Cha ac e iza ion o xenophylli e Na4TM7(PO4)6 (TM = Fe,
Mn) and i s de i a es ......................................................... 153
6.1. In oduc ion............................................................. 154
6.2. S uc u al, mo phological and physicochemical
cha ac e iza ion ................................................................. 154
6.3. Elec ochemis y ...................................................... 167
6.4. Reac ion mechanism: Mössbaue spec oscopy ............ 168
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6.5. Summa y and Conclusions ......................................... 173
6.6 Re e ences .............................................................. 174
7. Reac ion mechanism o ac i a ed ma ici e NaFePO4 . 177
7.1. In oduc ion............................................................. 178
7.2. Syn hesis and cha ac e iza ion o p is ine compound .... 178
7.2.1. Hyd o he mal syn hesis ...................................... 178
7.2.2. S uc u al, mo phological, and physicochemical
cha ac e iza ion o he syn hesised ma ici e NaFePO4 .......... 179
7.2.3. Elec ochemical cha ac e iza ion o p is ine ma ici e
NaFePO4 ........................................................................ 182
7.3. Elec ochemical e alua ion o mechanically ac i a ed
ma ici e NaFePO4 ............................................................... 183
7.4. E ec s o mechanical ac i a ion on ma ici e NaFePO4 by ball
milling: s uc u e, elec ochemis y, and local en i onmen s ... 186
7.4.1. S uc u al and mo phological cha ac e iza ion ollowing
mechanical ac i a ion ...................................................... 186
7.4.2. Ope ando X-Ray Di ac ion cha ac e iza ion .......... 197
7.4.3. Ope ando and ex-si u spec oscopic cha ac e iza ion ...
........................................................................ 200
7.5. Summa y and Conclusions ......................................... 209
7.6. Re e ences .............................................................. 210
8. Gene al conclusions ................................................. 213
Lis o con ibu ions .......................................................... 217
Publica ions ....................................................................... 217
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Con e ences and exhibi ions ................................................ 218
P ojec s ............................................................................ 218
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Lis o igu es
Figu e 1.1. Cumula i e ins alled capaci y (in GW) and he o ecas .
Sou ce: EIU, IEA. ............................................................... 3
Figu e 1.2. Map o li hium esou ce a ailabili y and geos a egic
impac s (base map by Daniel Dale ). .................................... 4
Figu e 1.3. The numbe o scien i ic publica ions on Na-ion ba e y
since 2015. ....................................................................... 6
Figu e 1.4. S uc u al pa e ns o a) O3- ype laye ed oxides, b) P2-
ype laye ed oxides, c) O2- ype laye ed oxides. The capi al le e s
(A, B, C) a e used o desc ibe he packing pa e ns o he oxygen-
ion amewo ks. G ey, ed and pu ple colo s co espond o Na, O
and M elemen espec i ely. ............................................... 13
Figu e 1.5. Common ypes o s uc u al complexi y in PBAs: (a)
oc ahed al il s, (b) co ela ed ‘slides’ o A-si e ca ions, (c) Jahn–
Telle dis o ions, (d) A-si e occupancy (dis)o de , (e)
hexacyanome alla e acancies and he esul ing connec ed po e-
ne wo k s uc u e, and ( ) amewo k hyd a ion. ................... 15
Figu e 1.6. C ys al s uc u es o : a) oli ine NaMPO4, b) NASICON
Na3V2(PO 4)3, c) iclinic Na2MP2O7, d) o ho hombic Na2MP2O7, e)
o ho hombic Na4M3(PO4)2P2O7, ) o ho hombic Na2MPO4F, g)
monoclinic Na2MPO4F, and h) e agonal Na3M2(PO4)2F3 (M
ep esen s ansi ion me als). ............................................. 17
Figu e 1.7. The c ys al s uc u e o oli ine-g oup M2XO4. Oc ahed a
in M1 and M2 si es and e ahed a in X si e a e illus a ed. ..... 19
Figu e 1.8. Polyhed al ep esen a ion o he oli ine- ype s uc u es
(a,b) and hei con e sion o he ma ici e (c-e) h ough he
in oduc ion o Na o he M2 si e (c) and he shi o he P posi ion
(d). Red sphe es designa e oxygen a oms, a, b, c a e he uni cell
di ec ions. ........................................................................ 19
Figu e 1.9. Gal anos a ic cha ge and discha ge cu es a C/20 o m-
NFP (g een) and a C/10 -NFP (blue-o ange) and he
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co esponding de i a i e dq/dV plo o -NFP which highligh s he
edox peaks. .................................................................... 22
Figu e 1.10. (a) Vol age e sus ime plo o he XRD in si u
expe imen . (b) 2θ e sus ime plo o he XRD pa e ns
comp ising a ull cycle (cha ge and discha ge). The le el o g ey
indica es he ela i e in ensi y ( he da ke he mo e in ense).
Ho izon al ba s a he igh indica e he posi ion o he B agg
peaks o each o he phases in ol ed. (c) Sum o he in eg a ed
in ensi y o he (020) and (211) e lec ions o each o he phases
in ol ed e sus ime. ........................................................ 23
Figu e 2.1. B uke D8 Disco e di ac ome e deployed in his wo k.
...................................................................................... 37
Figu e 2.2. B agg-B en ano geome y in XRD se up o powde
measu emen s. ................................................................. 37
Figu e 2.3. Scanning Elec on Mic oscope Quan a 200 FEG (FEI)
a ailable a CIC ene giGUNE. ............................................. 40
Figu e 2.4. The mog a ime ic analyze TGA NETZSCH STA 449 F3
Jupi e coupled o a Mass Spec ome e QMS 403 Aëolos Quad o
a ailable a CIC ene giGUNE. ............................................. 42
Figu e 2.5. Ul ima 2 Op ical Emission Spec ome e used in his wo k.
...................................................................................... 43
Figu e 3.1. Gene al p oposed syn hesis app oached o he indi ec
syn hesis o NaMn1-yFeyPO4. ............................................... 54
Figu e 3.2. XRD pa e n o syn hesized DL_01 compa ed o FePO4
om he li e a u e (ICSD code: 92199) o phase iden i ica ion.
...................................................................................... 55
Figu e 3.3. XRD pa e ns o he LiMn0.65Fe0.35PO4 p is ine and he
ob ained compounds a e di e en chemical oxida ion condi ions
compa ed o FePO4 om he li e a u e as e e ence wi h simila
XRD pa e n (ICSD code: 92199) o phase iden i ica ion. ...... 57
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Figu e 3.4. XRD pa e n o he syn hesized SD_A compa ed o FePO4
om he da abase (ICSD code: 92199) o phase iden i ica ion.
...................................................................................... 59
Figu e 3.5. XRD pa e ns o he syn hesized SD_B compa ed wi h
Fe1.375PO4(OH) (ICSD code: 170854) and S8 (ICSD code: 870)
om he da abase o phase iden i ica ion. ........................... 60
Figu e 3.6. XRD pa e n o he syn hesized SD_C compa ed wi h
di e en NaxFePO4 phases (ICSD code: 169118, 169119, 92199)
and S8 (ICSD code: 870) o phase iden i ica ion. ................. 61
Figu e 3.7. XRD pa e n o SD_D compa ed wi h Na0.7FePO4 (ICSD
code: 169119) and S8 (ICSD code: 870) om he da abase o
phase iden i ica ion. .......................................................... 62
Figu e 3.8. XRD pa e n o he syn hesized SD_E. ...................... 63
Figu e 3.9. XRD pa e n o he syn hesized SD_F compa ed wi h
NaFePO4 (ICSD code: 169118) om he da abase o phase
iden i ica ion. ................................................................... 64
Figu e 3.10. Rounded lask o 5 L du ing he syn hesis o a ba ch o
iphyli e C/NaFePO4 using he indi ec syn hesis me hod. ...... 64
Figu e 3.11. XRD pa e ns o syn hesized C/FePO4 and C/NaFePO4
compa ed o he comme cial C/LiFePO4 used as p ecu so . ..... 65
Figu e 3.12. Scheme o he di e en chemical educ ion app oaches
o ob aining NaFePO4. ....................................................... 66
Figu e 3.13. XRD pa e ns o syn hesized C/Fe0.35Mn0.65PO4 and
C/NaFe0.35Mn0.65PO4 compa ed o he comme cial
C/LiFe0.35Mn0.65PO4 used as p ecu so . ................................. 67
Figu e 3.14. Gene al scheme o he syn hesis o C/NaFePO4, including
he eco e y and ecycling o li hium p ocedu e. ................... 68
Figu e 3.15. Rie eld e inemen o he XRD pa e n o he
comme cial C/LiFePO4. Expe imen al pa e n ( ed), calcula ed
p o ile (black), di e ence be ween expe imen al and calcula ed
(blue) and B agg posi ions ( e ical ba s in g een). (RB agg =
2.54% and χ2 = 4.87). ...................................................... 70
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Figu e 3.16. Rie eld e inemen o he XRD pa e n o he
syn hesized C/FePO4. Expe imen al pa e n ( ed), calcula ed
p o ile (black), di e ence be ween expe imen al and calcula ed
(blue) and B agg posi ions ( e ical ba s in g een). (RB agg = 4.35
% and χ2 = 4.06). ............................................................. 70
Figu e 3.17. Rie eld e inemen o he XRD pa e n o he
syn hesized C/NaFePO4. Expe imen al pa e n ( ed), calcula ed
p o ile (black), di e ence be ween expe imen al and calcula ed
(blue) and B agg posi ions ( e ical ba s in g een). (RB agg = 3.91
% and χ2 = 1.59). ............................................................. 71
Figu e 3.18. Raman spec a o he as-syn hesized C/NaFePO4,
C/FePO4 and he p ecu so C/LiFePO4 in (a) ai and (b) a gon
a mosphe e. ..................................................................... 72
Figu e 3.19. (a-c) SEM and (d- ) TEM images o (a,d) C-LiFePO4, (b,e)
C/FePO4 and (c, ) C/NaFePO4. ............................................. 73
Figu e 3.20. TEM images o C/NaFePO4 pa icles in which he c acks
a e highligh ed wi h ci cles. ................................................ 74
Figu e 3.21. The mog a ime ic analysis o C/LiFePO4, C/FePO4 and
C/NaFePO4 in ai . .............................................................. 75
Figu e 3.22. The mog a ime ic analysis and analysis o he ou le
gases (H2O and CO2) de ec ed by mass spec ome y o C/FePO4
in ai . .............................................................................. 76
Figu e 3.23. Mass spec ome y wi h he ou le o gases (H2O and
CO2) o C/FePO4 in ai . ....................................................... 76
Figu e 3.24. Le Bail e inemen o he XRD pa e n o he comme cial
p ecu so C/LiMn0.65Fe0.35PO4. Expe imen al pa e n ( ed),
calcula ed p o ile (black), di e ence be ween expe imen al and
calcula ed (blue) and B agg posi ions ( e ical ba s in g een).
(RB agg = 39.4% and χ2 =5.54)............................................ 77
Figu e 3.25. Le Bail e inemen o he XRD pa e n o he comme cial
p ecu so C/Mn0.65Fe0.35PO4. Expe imen al pa e n ( ed),
calcula ed p o ile (black), di e ence be ween expe imen al and
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Figu e 7.9. XRD pa e ns o NaFePO4/C ob ained by hyd o he mal
syn hesis (NFP_0h) and a di e en ball milling imes (NFP_Xh).
.................................................................................... 187
Figu e 7.10. SEM images o he NaFePO4/C a e di e en ball milling
imes (a) 3h (NFP_3h), (b) 6h (NFP_6h), (c) 9h (NFP_9h) and (d)
12h (NFP_12h). .............................................................. 188
Figu e 7.11. Raman spec a o sample a e ball milling o di e en
ime pe iods. .................................................................. 190
Figu e 7.12. 23Na solid s a e NMR spec a o p is ine NFP_0 and a 3h
and 12h ball milling ime. ................................................. 192
Figu e 7.13. 31P solid s a e NMR spec um o p is ine NFP_0h and a
3h and 12h ball milling ime. ............................................ 192
Figu e 7.14. Mössbaue spec a a di e en ball milling imes (3h, 6h,
9h, 12h). ....................................................................... 193
Figu e 7.15. XAS o p is ine ma ici e NFP_0h and NFP_12h. XAS
cha ac e iza ion a O K-edges (a, b), Fe L-edges (c), and Na K-
edges (d, e). Bo h elec on (TEY) and luo escence (FY) modes o
de ec ion we e shown. Fe L3 su e ed sel -abso p ion in
luo escence de ec ion mode and is no shown. The do ed line
co esponds o he spec a o he p is ine powde (NFP_0h). 196
Figu e 7.16. Schema ic illus a ion o he ball milling e ec on
c ys alline s ick shaped NFP. The ball milling wi h C65 leads o a
c ys alline NFP wi h smalle size and he o ma ion o new mo e
diso de ed species possibly loca ed a he su ace. .............. 197
Figu e 7.17. (a) Vol age e sus ime cu e o ope ando synch o on
XRD expe imen o NFP_12h and (b) selec ed egion o 2D-plo
o 2θ e sus ime o he XRD pa e ns comp ising he i s ull
cha ge and discha ge (wa me colo indica es he mo e in ense
peaks). .......................................................................... 198
Figu e 7.18. (a) Vol age e sus ime cu e o ope ando synch o on
XRD expe imen o NFP_12h and and (b) e olu ion o he uni cell
pa ame e s and occupancy along he ull cycle. .................. 199
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Figu e 7.19. (a) Vol age e sus ime cu es o ope ando Mössbaue
expe imen o NFP_12h, (b) 2D-plo o he e olu ion o he
Mössbaue spec a du ing cycling, (c) e olu ion o he pe cen age
o Fe2+ and Fe3+, (d) e olu ion o he di e en componen s o Fe
du ing cycling measu ed by ope ando Mössbaue Spec oscopy.
No e: Fe2+: equi alen o M1 in ma ici e NaxFePO4, Fe2+ (B):
equi alen o M2 in iphyli e NaxFePO4, Fe3+ (a): equi alen o
M1 in ma ici e NaxFePO4; Fe3+(B): equi alen o M2 in iphyli e
NaxFePO4 o he e osi e FePO4. .......................................... 203
Figu e 7.20. (a) Gal anos a ic cha ge and discha ge cu es o
NFP_12h and (b) bo h elec on and luo escence modes o O K-
edges, Fe L2,3-edges, and Na K-edges. Fe L3 su e ed sel -
abso p ion in luo escence de ec ion mode and is no shown. The
do ed line co esponds o he spec a o NFP_12h a poin 1
(OCV). ........................................................................... 206
Figu e 7.21. (a) Gal anos a ic discha ge and cha ge cu e o
NFP_12h and (b) bo h elec on and luo escence modes o O K-
edges, Fe L2,3-edges, and Na K-edges. Fe L3 su e ed sel -
abso p ion in luo escence de ec ion mode and is no shown. The
do ed line co esponds o he spec a o NFP_12h a poin 1
(OCV). ........................................................................... 207
Figu e 7.22. Gene al scheme o he eac ion mechanism o ac i a ed
ma ici e NaFePO4. ........................................................... 208
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Lis o ables
Table 1-1. Compa ison o di e en aspec s be ween Li-ion and Na-
ion ba e ies. ..................................................................... 7
Table 1-2. Assigna ion o M1, M2 and X si es depending on he
s uc u e and ep esen a i e o mula. .................................. 24
Table 3-1. S a egies o he syn hesis o C/Mn0.65Fe0.35PO4 om
C/LiMn0.65Fe0.35PO4. (modi ica ions included in bold). ............. 56
Table 3-2. Di e en s a egies o he syn hesis o C/NaFePO4 om
C/FePO4 (modi ica ions included in bold). ............................. 58
Table 3-3. Rie eld e ined cell pa ame e s o C/LiFePO4, C/FePO4 and
C/NaFePO4. ...................................................................... 69
Table 3-4. Uni cell pa ame e s o C/LiMn0.65Fe0.35PO4,
C/Mn0.65Fe0.35PO4 and C/NaMn0.65Fe0.35PO4 ob ained by
e inemen . ...................................................................... 79
Table 3-5. Compa a i e able summa izing he elec ochemical
pe o mance o he epo ed -NFP ( iphyli e NaFePO4) and m-
NFP (ma ici e NaFePO4) wi h ou -NFP and -NMFP s udied in his
wo k................................................................................ 87
Table 4-1. Lis o p ecu so s used o he hyd o he mal syn hesis
.................................................................................... 100
Table 4-2. Lis o he possible species o med du ing he syn hesis
.................................................................................... 104
Table 4-3. Equilib ium cons an s o he possible species o med
du ing he syn hesis. ....................................................... 105
Table 4-4. Reagen s a io and ob ained phase o he iphyli e
a ge ed composi ions dec easing he pH. .......................... 110
Table 4-5. Reagen s a io and ob ained phase o he iphyli e
a ge ed composi ions inc easing he pH. ........................... 112
Table 4-6. Reagen s a io and ob ained phase o he di e en
iphyli e a ge ed composi ions eplacing p og essi ely Mn o
Fe. ................................................................................ 114
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Table 4-7. Uni cell pa ame e s o he Reagen s a io and ob ained
phase o he di e en iphyli e a ge ed composi ions eplacing
p og essi ely Mn o Fe .................................................... 117
Table 5-1. C ys allog aphic da a (space g oup, cell pa ame e s,
e inemen ag eemen ac o s, cell olume, a omic posi ions,
iso opic he mal ac o s Biso and si e occupancies) o NaMnPO4
ob ained om he Rie eld e inemen o i s NPD pa e n. .... 132
Table 5-2. C ys allog aphic da a (space g oup, cell pa ame e s,
e inemen ag eemen ac o s, cell olume, a omic posi ions,
iso opic he mal ac o s Biso and si e occupancies) o
NaMn0.90Fe0.10PO4 ob ained om he Rie eld e inemen o i s
NPD pa e n. .................................................................. 132
Table 5-3. C ys allog aphic da a (space g oup, cell pa ame e s,
e inemen ag eemen ac o s, cell olume, a omic posi ions,
iso opic he mal ac o s Biso and si e occupancies) o
NaMn0.80Fe0.20PO4 ob ained om he Rie eld e inemen o i s
NPD pa e n. .................................................................. 133
Table 5-4. C ys allog aphic da a (space g oup, cell pa ame e s,
e inemen ag eemen ac o s, cell olume, a omic posi ions,
iso opic he mal ac o s Biso and si e occupancies) o
NaMn0.70Fe0.30PO4 ob ained om he Rie eld e inemen o i s
NPD pa e n. .................................................................. 133
Table 5-5. La ice pa ame e s o he ob ained iphyli e NaMn1-
yFeyPO4 samples and i s eal composi ion. .......................... 134
Table 6-1. Re ined la ice pa ame e s o he ob ained xenophylli e
Na4Fe7(PO4)6 and Na4Mn7(PO4)6. ....................................... 155
Table 6-2. A e age a omic pe cen age composi ion o Na4Mn7(PO4)6,
labeled as Na4Mn7(PO4)6, measu ed by EDX. ....................... 158
Table 6-3. A e age a omic pe cen age composi ion o xenophylli e
Na4Fe7(PO4)6, measu ed by EDX. ...................................... 159
Table 6-4. A e age a omic pe cen age composi ion o xenophylli e
Na4Fe7(PO4)6 a e ball milling measu ed by EDX. ................ 162
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Table 6-5. Room empe a u e 57Fe Mössbaue spec oscopy
pa ame e s o as syn hesized Na4Fe7(PO4)6 and ball milled
HT_xenFe@C, he isome shi (IS) a e gi en wi h espec o α-
Fe s anda d a 300K. ....................................................... 166
Table 6-6. Mössbaue hype ine pa ame e s o he MCR-ALS pu e
componen s. .................................................................. 169
Table 6-7. Ope ando Mössbaue spec oscopy pa ame e s o six
subspec a iden i ied o HT_xenFe@C and i s p edominance
depending on he s a e o cha ge. ..................................... 172
Table 7-1. Summa y o i s cha ge and discha ge capaci y o he
NaFePO4/C a e di e en ball milling imes 0h (NFP_0h) 3h
(NFP_3h), 6h (NFP_6h), 9h (NFP_9h) and 12h (NFP_12h). ... 186
Table 7-2. Summa y o he uni cell pa ame e s and a e age
c ys alli e size ob ained om he Le Bail e inemen o he XRD
pa e ns o he 5 samples depending on he ball-milling ime.
.................................................................................... 188
Table 7-3. Summa y o alence o he i on con ained in he samples
as de e mined om Mössbaue spec oscopy. ..................... 194
Table 7-4. Mössbaue hype ine pa ame e s o he MCR-ALS pu e
componen s. .................................................................. 203
Table 7-5. Summa y o he in si u Mössbaue spec oscopy da a.
E olu ion o he ol age capaci y, ime and alence o he i on.
.................................................................................... 204
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Ac onyms
AM
Ac i e Ma e ial
A
A gon
Co
Cobal
CP-MAS
C oss Pola iza ion Magic Angle Spinning
Cu
Coppe
CSA
Chemical Shi Aniso opy
CV
Cyclic Vol ame y
DEC
Die hyl Ca bona e
DFT
Densi y Func ional Theo y
DMC
Dime hyl Ca bona e
DTA
Di e en ial The mal Analysis
EC
E hylene Ca bona e
EDX
Ene gy Dispe si e X- ay Spec oscopy
EIU
Economis In elligence Uni
EOC
End O Cha ge
EOD
End O Discha ge
Fe
I on
FEC
Fluo oe hylene Ca bona e
FEG
Field Emission Gun
GFID
Gas Flame Ioniza ion De ec o
HAADF
High-Angle Annula Da k Field
HRXRD
High-Resolu ion X-Ray Di ac ion
ICP-AES
Induc i ely Coupled Plasma - A omic Emission
Spec oscopy
ICSD
Ino ganic C ys al S uc u e Da abase
IEA
In e na ional Ene gy Agency
I
In ensi y
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IS
Isome Shi
λ
Wa elengh
Li
Li hium
LIBs
Li hium-Ion Ba e ies
LW
Linewid h
MAS
Magic Angle Spinning
MCR-ALS
Mul i a ia e Cu e Resolu ion - Al e na ing Leas
Squa es
Mn
Manganese
m-NFP
Ma ici e NaFePO4 (Sodium I on phospha e)
MQMAS
Mul iple-Quan um Magic Angle Spinning
MSPD
Ma e ials Science Powde Di ac ion
Na
Sodium
NFP
NaFePO4 (Sodium I on Phospha e)
NFPP
Na2FeP2O7 (Sodium I on Py ophospha e)
NIBs
Sodium-Ion Ba e ies
NMP
N-Me hyl-2-Py olydone
NPD
Neu on Powde Di ac ion
O
Oxygen
OCV
Open Ci cui Vol age
P
Phospho us
PBAs
P ussian Blue Analogues
PC
P opylene Ca bona e
PCA
P incipal Componen Analysis
PEO
Polye hylene Oxide
PITT
Po en ios a ic In e mi en Ti a ion Technique
PVDF
Poly inylidene Fluo ide
QMS
Quad upole Mass Spec ome y
QS
Quad upole Spli ing
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Rh
Rhodium
SEI
Solid Elec oly e In e phase
SEM
Scanning Elec on Mic oscopy
Sb
An imony
Si
Silicon
Sn
Tin
SLI
S a e -Ligh ing-Igni ion
ssNMR
Solid-S a e Nuclea Magne ic Resonance
SXRD
Synch o on X-Ray Di ac ion
TEM
T ansmission Elec on Mic oscopy
TEY
To al Elec on Yield
TFY
To al Fluo escence Yield
TGA
The mog a ime ic Analysis
TM
T ansi ion Me al
-NFP
T iphyli e NaFePO4 (Sodium I on Phospha e)
VC
Vinylene Ca bona e
XAS
X-Ray Abso p ion Spec oscopy
XRD
X-Ray Di ac ion
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1
1. In oduc ion
1.1. O e iew o ene gy demand ......................................... 2
1.2. Ba e ies .................................................................... 3
1.3. Na-ion ba e ies .......................................................... 5
1.3.1. Anodes o Na-ion Ba e ies .................................... 8
1.3.1.1. Ha d Ca bon ................................................... 9
1.3.1.2. Alloy-Based Anodes ........................................ 10
1.3.1.3. Me al Oxides and Sul ides ............................... 10
1.3.2. Elec oly e Ma e ials o Na-ion Ba e ies ................. 10
1.3.3.1. O ganic Liquid Elec oly es .............................. 11
1.3.3.2. Ce amic Solid-S a e Elec oly es ...................... 12
1.3.3.3. Gel Polyme Solid-S a e Elec oly es ................. 12
1.3.3. Ca hode o Na-ion ba e ies .................................. 12
1.3.3.1. Laye ed oxides .............................................. 13
1.3.3.2. P ussian blue analogues .................................. 14
1.3.3.3. Polyanionic ma e ials ...................................... 16
1.4. Objec i es and goals ................................................... 25
1.5. Re e ences ................................................................ 27
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1. In oduc ion
2
1.1. O e iew o ene gy demand
The pos -pandemic eco e y in ene gy consump ion accele a ed o
1.8% g ow h in 2024, up om jus 1.2% in 2023.1 This was
suppo ed by s ong demand in Asia, whe e consump ion was
expec ed o expand by 3.1%, despi e he clouds o e China’s
economic ou look. G ow h in ene gy consump ion has also been
s ong in he Middle Eas , pa icula ly i he clima e he e con inues
o wa m, bols e ing demand o ai condi ioning.
Howe e , i is expec ed ha ene gy demand in Eu ope will eco d i s
hi d consecu i e yea o decline as he egion con inues o ba le
agains high ene gy p ices and limi ed gas supply. Ne e heless, he
si ua ion in Eu ope has imp o ed om 2022-23. G ow h was also only
ma ginal in No h Ame ica and La in Ame ica, wi h so economic
g ow h.
The need o s eng hen ene gy secu i y in he wake o he ene gy
c isis, in addi ion o deca boniza ion e o s, will d i e many
go e nmen s o push ahead e en as e wi h he deploymen o
enewable ene gy. Renewable ene gy con inued expanding quickly in
2024, wi h combined sola and wind ene gy consump ion g owing by
abou 11% yea on yea (Figu e 1.1). Capaci y addi ions se a eco d
high o abou 400 GW in 2023 and o g ew e en mo e in 2024.
The inc easing in eg a ion o enewable ene gy sou ces, such as sola
and wind, in o he powe g id necessi a es he use o e icien and
eliable ene gy s o age solu ions, p ima ily ba e ies. These ene gy
sou ces a e in e mi en , wi h p oduc ion luc ua ions due o wea he
condi ions and ime o day, c ea ing a misma ch be ween ene gy
supply and demand. Ba e ies help b idge his gap by s o ing excess
ene gy gene a ed du ing peak p oduc ion imes and eleasing i when
p oduc ion is low, hus ensu ing a s able and con inuous ene gy
supply. Addi ionally, ba e ies enhance g id esilience, educe he
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1. In oduc ion
9
1.3.1.1. Ha d Ca bon
Ha d ca bon is one o he mos p omising anode ma e ials o NIBs
due o i s high capaci y, good cycling s abili y, and ela i ely low cos .
Unlike g aphi e, which is used in LIBs, sodium does no in e cala e
in o g aphi e e icien ly using con en ional ca bona e-based
elec oly es, posing a signi ican challenge o de eloping e ec i e
NIBs. Ha d ca bon, wi h i s diso de ed s uc u e and high su ace
a ea, p o ides sui able si es o sodium ion s o age, o e coming his
challenge. I s mic os uc u e comp ises a combina ion o bo h
g aphi ic nanodomains and amo phous egions, which acili a e he
e e sible inse ion o sodium ions.
Recen s udies ha e shown ha ha d ca bon can achie e capaci ies
up o 300 mAh g⁻¹, making i a compe i i e candida e o comme cial
applica ions. Fu he mo e, ha d ca bon can be syn hesized om a
a ie y o low-cos p ecu so s, including biomass, which adds o i s
economic a ac i eness. The syn hesis p ocess ypically in ol es
py olysis a high empe a u es, leading o he de elopmen o a
po ous s uc u e ha enhances sodium s o age capaci y. In addi ion
o i s inhe en p ope ies, esea ch has ocused on op imizing he
syn hesis pa ame e s and pos - ea men p ocesses o u he
enhance i s elec ochemical pe o mance, specially hei limi ed i s
ini ial coulombic e iciency.
Elec ochemical cha ac e iza ion o ha d ca bon anodes has
demons a ed s able pe o mance o e nume ous cha ge-discha ge
cycles, wi h minimal capaci y deg ada ion, which is c ucial o he
longe i y o NIBs. The ongoing esea ch aims o add ess he
challenges o ini ial i e e sible capaci y loss and imp o e he o e all
e iciency and pe o mance o ha d ca bon anodes.29
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1.3.1.2. Alloy-Based Anodes
Al hough Silicon (Si) is a p omising anode ma e ial o LIBs, i is no
sui able o NIBs due o he lack o s able Na-Si alloy o ma ion. As a
esul , esea ch has ocused on o he alloy- o ming elemen s ha can
e e sibly eac wi h sodium.
Alloy-based anodes, such as in (Sn), an imony (Sb), and phospho us
(P), o e high heo e ical capaci ies. Fo example, sodium can alloy
wi h in o o m Na15Sn4, p o iding a high heo e ical capaci y o 847
mAh g-1. Howe e , hese ma e ials o en su e om signi ican
olume changes du ing cycling, leading o mechanical deg ada ion
and educed cycle li e. S a egies such as nanos uc u ing and he
use o composi es ha e been employed o mi iga e hese issues.30
1.3.1.3. Me al Oxides and Sul ides
T ansi ion me al oxides and sul ides, such as Fe2O3, Co3O4, and MoS2,
ha e been in es iga ed as anode ma e ials o NIBs. These ma e ials
unde go con e sion eac ions wi h sodium, p o iding high capaci ies.
Howe e , hey also ace challenges ela ed o olume expansion and
poo elec ical conduc i i y. Resea ch is ongoing o imp o e hei
pe o mance h ough ma e ial enginee ing and he inco po a ion o
conduc i e addi i es.31
1.3.2. Elec oly e Ma e ials o Na-ion Ba e ies
Elec oly es play a i al ole in he pe o mance, sa e y, and s abili y
o NIBs. They p o ide he medium o sodium ion anspo be ween
he anode and ca hode du ing cha ging and discha ging cycles.
Se e al ypes o elec oly es ha e been de eloped o NIBs.
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1.3.3.1. O ganic Liquid Elec oly es
Liquid elec oly es, ypically composed o sodium sal s dissol ed in
o ganic sol en s, as used in Li-ion echnology, a e he mos
commonly used in NIBs. These elec oly es play a c ucial ole in
acili a ing he mo emen o sodium ions be ween he anode and
ca hode du ing cha ge and discha ge cycles. Sodium
hexa luo ophospha e (NaPF6) in ca bona e sol en s is a popula
choice due o i s good ionic conduc i i y and s abili y, which a e
essen ial o e icien ba e y ope a ion. The ca bona e sol en s o en
include a mix u e o e hylene ca bona e (EC) and die hyl ca bona e
(DEC), which p o ide a balance be ween high dielec ic cons an and
low iscosi y, enhancing he o e all ionic mobili y wi hin he
elec oly e.
Despi e hei ad an ages, o ganic liquid elec oly es o NIBs ace
se e al challenges. One signi ican issue is he lammabili y o o ganic
sol en s, which poses sa e y isks, especially unde high
empe a u es o in he e en o a sho ci cui . Addi ionally,
elec oly e decomposi ion can occu du ing cycling, leading o he
o ma ion o de imen al byp oduc s ha can deg ade he
pe o mance o he ba e y. This decomposi ion is o en accele a ed
a highe ol ages, limi ing he ope a ing ange o he ba e y.
Fu he mo e, compa ibili y wi h elec ode ma e ials is ano he c i ical
ac o . The elec oly e mus o m a s able solid-elec oly e in e phase
(SEI) laye on he anode o p e en u he decomposi ion and ensu e
long- e m cycling s abili y.
To add ess hese issues, esea che s a e explo ing a ious s a egies.
Addi i es such as luo oe hylene ca bona e (FEC) and inylene
ca bona e (VC) a e commonly added o he elec oly e o mula ion o
imp o e he o ma ion and s abili y o he SEI laye . These addi i es
help o enhance he o e all pe o mance and sa e y o he NIBs by
educing elec oly e decomposi ion and imp o ing he compa ibili y
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wi h elec ode ma e ials. Mo eo e , op imizing he a io o sol en s
and sal s can also lead o be e pe o mance. Fo ins ance,
inc easing he concen a ion o he sodium sal can imp o e ionic
conduc i i y and educe he occu ence o side eac ions.32
1.3.3.2. Ce amic Solid-S a e Elec oly es
Solid-s a e elec oly es o e he p omise o enhanced sa e y and
s abili y compa ed o liquid elec oly es. They include ino ganic
ce amics, such as NASICON- ype (Na3Z 2Si2PO12), β-alumina, and
sul ide-based elec oly es (Na3PS4), as well as polyme elec oly es.
These ma e ials p o ide good ionic conduc i i y and a e non-
lammable. Howe e , challenges ela ed o in e acial esis ance,
mechanical p ope ies, and p ocessing cos s mus be o e come o
p ac ical applica ions. Recen ad ancemen s in ma e ial design and
enginee ing a e showing p omise in add essing hese issues.33
1.3.3.3. Gel Polyme Solid-S a e Elec oly es
Gel polyme elec oly es combine he bene i s o liquid and solid-s a e
elec oly es. They consis o a polyme ma ix swollen wi h a liquid
elec oly e, o e ing high ionic conduc i i y and imp o ed sa e y.
Common polyme s used include polye hylene oxide (PEO) and
poly inylidene luo ide (PVDF). These elec oly es p o ide lexibili y
and ease o p ocessing bu s ill ace challenges ela ed o mechanical
s eng h and long- e m s abili y.34
1.3.3. Ca hode o Na-ion ba e ies
A c i ical componen o NIBs is he ca hode ma e ial, which
signi ican ly in luences hei ene gy densi y, cycling s abili y, and a e
pe o mance. The de elopmen o ad anced ca hode ma e ials wi h
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imp o ed s uc u al s abili y, elec onic conduc i i y, and sodium ion
di usion pa hways is essen ial o enhancing he pe o mance and
comme cializa ion po en ial o NIBs.
1.3.3.1. Laye ed oxides
Na-ion laye ed oxides ypically adop a laye ed c ys al s uc u e
simila o ha o Li-ion coun e pa , gene ally ep esen ed by he
o mula NaxTMO2, whe e TM is a ansi ion me al such as Fe, Ni, Co,
Mn, e c. o a combina ion he eo . These ma e ials c ys allize in ei he
O3 o P2- ype s uc u es, di e en ia ed by he s acking sequence o
Na and MO2 laye s along he c-axis. They also di e in hei sodium
con en : O3- ype s uc u es ypically accommoda e a highe sodium
con en (Na1MO2), while P2- ype s uc u es gene ally ha e a lowe
sodium con en (Na2/3MO2).
In O3- ype ma e ials, Na laye s al e na e wi h oc ahed al MO2 laye s,
while P2- ype ma e ials ea u e p isma ic coo dina ion o Na ions
(Figu e 1.4). The choice o ansi ion me al and he s acking ype
signi ican ly in luence he s uc u al s abili y and elec ochemical
p ope ies o hese ca hodes.35
Figu e 1.4. S uc u al pa e ns o a) O3- ype laye ed oxides, b) P2- ype
laye ed oxides, c) O2- ype laye ed oxides. The capi al le e s (A, B, C) a e
used o desc ibe he packing pa e ns o he oxygen-ion amewo ks. G ey,
ed and pu ple colo s co espond o Na, O and M elemen espec i ely.35
The elec ochemical pe o mance o Na-ion laye ed oxides is closely
ied o hei s uc u al cha ac e is ics. Key pe o mance indica o s
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include speci ic capaci y, cycling s abili y, and a e capabili y. Fo
ins ance, O3- ype NaxNi0.5Mn0.5O2 can deli e a speci ic capaci y up
o 200 mAh g-1, wi h s able cycling a mode a e cu en densi ies. On
he o he hand, P2- ype Na2/3Mn0.5Fe0.5O2 exhibi s excellen a e
capabili ies and s uc u al s abili y upon cycling bu ypically o e s
lowe speci ic capaci ies.36–38
In 2024, laye ed oxides domina ed he ma ke sha e bu aced issues
such as poo high- empe a u e s abili y and eliance on nickel
esou ces. They can each an ene gy densi y o 160 Wh kg-1, bu
ypically has a cycle li e o 3,000 cycles and a 30% capaci y decay a
-20 ºC.39
1.3.3.2. P ussian blue analogues
P ussian Blue Analogues (PBAs) ep esen a class o open- amewo k
ma e ials cha ac e ized by hei cyanide-b idged ansi ion me al
complexes. Known o hei e sa ili y and unique p ope ies in ion
exchange and elec och omism, PBAs ha e eme ged as p omising
ca hode ma e ials o NIBs. Thei open- amewo k s uc u e
acili a es apid and e e sible inse ion/ex ac ion o Na+ ions, which
is c i ical o high-pe o mance ba e ies.
The gene ic o mula o P ussian Blue Analogues is
AxTMy[Fe(CN)6]z·nH2O, whe e TM is a ansi ion me al such as Fe, Co,
Ni, o Mn, and A is a mono alen ca ion, ypically Na+. The ansi ion
me als a e linked by cyanide g oups o ming [TM-Fe(CN)6]
amewo ks (Figu e 1.5). The colo ─and, hence, he name─ o he
PBA compounds end o a y depending on he sodium con en , being
ypically g een o he desodia ed s a e (Be lin G een, BG), blue o
pa ially sodia ed s a e (P ussian Blue, PB), and whi e o ully
sodia ed s a e (P ussian Whi e, PW).40
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Figu e 1.5. Common ypes o s uc u al complexi y in PBAs: (a) oc ahed al
il s, (b) co ela ed ‘slides’ o A-si e ca ions, (c) Jahn–Telle dis o ions, (d)
A-si e occupancy (dis)o de , (e) hexacyanome alla e acancies and he
esul ing connec ed po e-ne wo k s uc u e, and ( ) amewo k hyd a ion.41
The unique aspec o PBAs is he p esence o la ge oids wi hin he
c ys al s uc u e, which can accommoda e a a ie y o ca ions and
wa e molecules. This po osi y is c ucial o he apid di usion o Na+
ions du ing ba e y ope a ion.
PBAs a e known o hei low-cos , non- oxici y, and especially hei
obus edox ac i i y. The elec ochemical beha io o PBAs is
p ima ily go e ned by he edox eac ions o he ansi ion me als in
he cyanide amewo k. These ma e ials can exhibi high heo e ical
capaci ies, ypically anging om 100 o 170 mAh g-1. Mo eo e , hei
open- amewo k s uc u e con ibu es o excellen a e capabili ies
and cycling s abili y, as he la ge channels allow o quick and
e icien Na+ anspo .41
Despi e hei ad an ageous p ope ies, PBAs ace se e al challenges.
One signi ican issue is he po en ial o cyanide leaching, which
aises en i onmen al and sa e y conce ns. Mo eo e , he hyd a ion
wa e p esen in he c ys al s uc u e can be a iable, which a ec s
he elec ochemical consis ency and s abili y o he ma e ial.40
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To add ess hese issues, ecen esea ch has ocused on modi ying
he chemical composi ion and syn hesis me hods o PBAs. S a egies
such as pa ial subs i u ion o cyanide wi h o he ligands o coa ing
he PBA pa icles wi h p o ec i e laye s ha e been explo ed o
enhance s abili y and sa e y. Addi ionally, he syn hesis o wa e - ee
PBAs could po en ially imp o e he elec ochemical pe o mance and
add ess he a iabili y caused by hyd a ion.
1.3.3.3. Polyanionic ma e ials
Polyanionic compounds, cha ac e ized by hei polyanion g oups such
as phospha es (PO4), sul a es (SO4), and silica es (SiO4), ha e
a ac ed a en ion in he ield o NIBs due o hei excellen he mal
s abili y and sa e y p o iles. These ma e ials o e a di e se ange o
s uc u es and p ope ies ha a e c i ical o de eloping ad anced
ca hode ma e ials. This sec ion del es in o he s uc u al and
elec ochemical cha ac e is ics o polyanionic compounds and
discusses hei signi icance in he con ex o Na-ion ba e y
echnology.
Polyanionic compounds ea u e a obus h ee-dimensional
amewo k composed o me al ions coo dina ed by polyanionic
g oups. This amewo k esul s in s ong co alen bonding wi hin he
s uc u e, which signi ican ly enhances he he mal and chemical
s abili y o he ma e ial. An addi ional bene i o hese compounds is
he posi i e induc i e e ec o he polyanionic g oups, which aises
he wo king po en ial o he ma e ial by s abilizing he edox couple
and inc easing he ene gy densi y. Common examples include
NASICON-like s uc u es (e.g., Na3V2(PO4)3) and oli ine- ype
phospha es (e.g., NaFePO4) (Figu e 1.6). These amewo ks allow o
s able cycling, a key challenge in ba e y ma e ial s abili y.35
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Figu e 1.6. C ys al s uc u es o : a) oli ine NaMPO4, b) NASICON Na3V2(PO
4)3, c) iclinic Na2MP2O7, d) o ho hombic Na2MP2O7, e) o ho hombic
Na4M3(PO4)2P2O7, ) o ho hombic Na2MPO4F, g) monoclinic Na2MPO4F, and
h) e agonal Na3M2(PO4)2F3 (M ep esen s ansi ion me als).35
The elec ochemical pe o mance o polyanionic compounds is
ma ked by hei s able ol age pla eaus, which a e conduci e o
p edic able and s eady ene gy ou pu . Ma e ials like Na3V2(PO4)3 can
o e good speci ic capaci ies (up o 120 mAh g-1) and exhibi
excellen cycling s abili y wi h low-capaci y ade o e many cycles.
This s abili y is due o he s ong co alen bonds in he polyanion
g oups, which help main ain he in eg i y o he c ys al s uc u e
du ing Na+ inse ion and ex ac ion.35,42
Addi ionally, he polyanionic amewo k ends o lowe he
en i onmen al isk associa ed wi h ba e y ma e ials, as hey a e
mo e esis an o eleasing ha m ul subs ances upon decomposi ion.
Despi e hei ad an ages, polyanionic compounds ace se e al
challenges ha need add essing o op imize hei u ili y in NIBs. One
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signi ican issue is hei inhe en ly lowe elec onic and ionic
conduc i i y, which can limi ion anspo and educe he o e all a e
pe o mance.
Eme ging esea ch has ocused on add essing hese limi a ions
h ough a ious s a egies. Doping wi h di e en me al ions o
c ea ing composi e ma e ials a e common app oaches o enhance
elec ical conduc i i y. Ano he p omising s a egy in ol es
op imizing he syn hesis p ocess o p oduce nanos uc u ed
ma e ials, which can o e sho e ion di usion pa hways and la ge
su ace a eas o imp o ed a e capabili ies.43
Oli ine is a silica e mine al wi h an oli e-g een hue, ypically
ep esen ed by he app oxima e composi ion (Mg,Fe)2SiO4 has been
a subjec o in ense in es iga ion among geoscien is s o yea s. I is
widely ega ded as he p edominan mine al in he Ea h's uppe
man le and is pi o al in egula ing a wide ange o pe ogene ic
p ocesses and he Ea h's physical p ope ies.44–46 The geochemical
and he moba ome ic da a de i ed om oli ine p o ide a aluable
esou ce o unde s anding ock o ma ion, li hosphe ic man le
geodynamics, and he genesis and explo a ion o magma ic o es and
deep-o igin mine als such as py oxenes and ga ne s. Cu en ly, he
plu al e m oli ines is b oadly used o desc ibe a g oup o mine als
con o ming o he gene al o mula M2XO4 (whe e M can be an s-, p-,
o d-block me al o a acancy, and X is ypically Al, Si, o P) (Figu e
1.7), all o which exhibi he undamen al oli ine- ype s uc u e.
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1.4. Objec i es and goals
The p ima y objec i e o his hesis is o de elop and op imize new,
cos -e ec i e syn hesis me hods o a ious phospha e ca hode
ma e ials sui able o sodium-ion ba e ies. The ocus is on c ea ing
en i onmen ally iendly syn hesis ou es ha u ilize abundan and
non- oxic componen s while minimizing p oduc ion cos s. A
comp ehensi e unde s anding o he syn hesis and elec ochemical
mechanisms is c ucial o ad ancing he applica ion o phospha e
ca hodes in sodium-ion ba e ies, wi h an emphasis on a o dabili y
and ma e ial e iciency.
The o e a ching goals o his PhD esea ch a e o:
1. Es ablish a new pa adigm o he syn hesis o phospha e
ca hode ma e ials ha p io i izes en i onmen al sus ainabili y
wi hou comp omising ma e ial pe o mance o cos -
e ec i eness.
2. Enhance he heo e ical and p ac ical unde s anding o
phospha e ma e ials as ca hodes in sodium-ion ba e ies,
se ing a ounda ion o hei u u e indus ial applica ion.
3. Con ibu e o he global e o in ad ancing sodium-ion ba e y
echnologies by p o iding iable al e na i es o cu en
li hium-ion sys ems, pa icula ly o applica ions whe e cos ,
a ailabili y, and en i onmen al impac a e c i ical
conside a ions.
By achie ing hese objec i es and goals, his esea ch aims o
add ess some o he c i ical challenges in he ield o ene gy s o age
ma e ials and pa e he way o he nex gene a ion o sodium-ion
ba e ies. The ou comes a e expec ed no only o en ich he academic
unde s anding o phospha e-based ca hode ma e ials bu also o
a ec (in luence) he b oade landscape o ene gy s o age
echnologies in a sus ainable and cos -e ec i e manne .
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The hesis will be s uc u ed, apa om his ini ial in oduc ion
chap e , o he ollowing chap e s:
Chap e 2, whe e he expe imen al cha ac e iza ion echniques will
be explained, including s uc u al/mo phological, physico-chemical
and elec ochemical echniques.
In chap e 3, an indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 will be
de ailed s a ing om comme cial LiMn1-yFeyPO4 and wi h a me hod
ha enables he eco e y o li hium in he p ocess.
Chap e 4 is dedica ed o he s udy o he di ec syn hesis o di e en
polymo phs wi h he o mula Nax(TM)y(PO4)z (TM = Mn, Fe o
combina ion o bo h) and unde s anding he di e ence o he a ious
expe imen al condi ions (as he pH) o ob aining di e en phases.
Chap e s 5 and 6 consis o he deepe cha ac e iza ions o he
syn hesized ma e ials, including he use o ad anced echniques such
as XAS and Mössbaue spec oscopy, o he iphyli e and
xenophylli e espec i ely ob ained in chap e 4.
Chap e 7 de ails he eac ion mechanism o he ma ici e NaFePO4
using a ious ad anced cha ac e iza ion echniques ollowing i s
ac i a ion by ball milling wi h ca bon.
Chap e 8 summa izes he gene al conclusions o his wo k.
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1.5. Re e ences
(1) Ene gy Ou look 2024.
(2) Da ling on Eze Ekechukwu; Pe e Simpa. A Comp ehensi e
Re iew o Inno a i e App oaches in Renewable Ene gy S o age.
In . J. Appl. Res. Soc. Sci. 2024, 6 (6), 1133–1157.
h ps://doi.o g/10.51594/ija ss. 6i6.1176.
(3) A. Vol a. Philosophical T ansac ions, 90:403–431, 1800.
(4) G. Plan e. The S o age o Elec ical Ene gy. Paul Bed o d, 1859.
(5) Bhawna; Phoga , P.; Sh eya; Singh, N. L.; Singh, S. Ad ancing
Ene gy S o age: A Compa a i e Re iew o Nickel–Cadmium,
Nickel–Me al Hyd ide, and Sodium-Ion Ba e ies. Reac . Chem.
Eng. 2025, 10.1039.D5RE00156K.
h ps://doi.o g/10.1039/D5RE00156K.
(6) Huang, Z.; Jaumaux, P.; Sun, B.; Guo, X.; Zhou, D.;
Shanmuka aj, D.; A mand, M.; Rojo, T.; Wang, G. High-Ene gy
Room-Tempe a u e Sodium–Sul u and Sodium–Selenium
Ba e ies o Sus ainable Ene gy S o age. Elec ochem. Ene gy
Re . 2023, 6 (1), 21. h ps://doi.o g/10.1007/s41918-023-
00182-w.
(7) Xu, J.; Cai, X.; Cai, S.; Shao, Y.; Hu, C.; Lu, S.; Ding, S. High‐
Ene gy Li hium‐Ion Ba e ies: Recen P og ess and a P omising
Fu u e in Applica ions. ENERGY En i on. Ma e . 2023, 6 (5),
e12450. h ps://doi.o g/10.1002/eem2.12450.
(8) Dixi , M.; Wi he spoon, B.; Mu alidha an, N.; Mench, M. M.;
Kweon, C.-B. M.; Sun, Y.-K.; Belha ouak, I. Insigh s in o he
C i ical Ma e ials Supply Chain o he Ba e y Ma ke o Enhanced
Ene gy Secu i y. ACS Ene gy Le . 2024, 3780–3789.
h ps://doi.o g/10.1021/acsene gyle .4c01300.
(9) Shah, A. M.; Liu, G.; Huo, Z.; Yang, Q.; Zhang, W.; Meng, F.;
Yao, L.; Ulgia i, S. Assessing En i onmen al Se ices and
Disse ices o U ban S ee T ees. an Applica ion o he Eme gy
Accoun ing. Resou . Conse . Recycl. 2022, 186, 106563.
h ps://doi.o g/10.1016/j. escon ec.2022.106563.
(10) Ou aoui, I.; Ahai ou , A. In es iga ion o he Feasibili y and
Po en ial Use o Sun T acking Solu ions o Concen a ed
Pho o ol aic Case S udy Fez Mo occo. Ene gy Rep. 2022, 8,
1412–1425. h ps://doi.o g/10.1016/j.egy .2022.08.071.
(11) G osjean, C.; Mi anda, P. H.; Pe in, M.; Poggi, P. Assessmen
o Wo ld Li hium Resou ces and Consequences o Thei
Geog aphic Dis ibu ion on he Expec ed De elopmen o he
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2.2.2. T ansmission Elec on Mic oscopy
A T ansmission Elec on Mic oscope (TEM) has a high ol age o 100
KeV o highe (up o 1 MeV) and p o ides bo h image and di ac ion
in o ma ion abou he samples. In a TEM he elec on beam emi ed
by a ca hode is ocused on a specimen using se e al condense lenses
causing an enla ged e sion o appea on a luo escen sc een. This
elec on beam ca ies in o ma ion abou he specimen.
Unlike SEM, he elec on beam c osses he sample and, he e o e,
he key equi emen is a low hickness o he sample. Besides he
highe esolu ion compa ed wi h SEM imagining, one o he main
ad an ages o TEM imaging is he possibili y o do local elec on
di ac ion pa e ns, which gi es in o ma ion abou he c ys alline
s uc u e o he sample.
TEM measu emen s ha e been done in a FEI Tecnai G2 ope a ed a
200kV ield emission gun (FEG) high esolu ion and equipped wi h
High Angle Annula Da k Field (HAADF) de ec o and X- ay Dispe si e
Ene gy (EDX) spec ome e . The samples we e ul asonica ed unde
ace one and he esul ing dispe sion o he powde was ans e ed
o a quan i oil ca bon ilm ixed on a 3 mm coppe g id (200 mesh).
2.3. The mal analysis couple wi h Mass
Spec ome y echnique
The mal analysis is a g oup o echniques ha s udy he p ope ies
o ma e ials as hey change wi h he empe a u e.
The mog a ime ic analysis is an analy ical echnique used o
de e mine he he mal s abili y o he sample. I measu es changes
in he weigh o a ma e ial as a unc ion o he empe a u e. The
changes obse ed in he mass a e ela ed o chemical o physical
p ocesses ha occu upon hea ing he sample.
Di e en ial he mal analysis is an analy ical echnique ha moni o s
he di e ence in empe a u e be ween he sample and a e e ence
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2. Expe imen al Techniques
42
ma e ial agains ime o empe a u e while he empe a u e o he
sample, in a speci ied a mosphe e, is p og ammed. The obse ed
peaks in he empe a u e di e ence cu e a e ela ed o endo he mic
o exo he mic p ocesses, such a phase ansi ions ha don’ imply
any weigh a ia ion.
Fo his pu pose, TGA NETZSCH STA 449 F3 Jupi e couple wi h he
Mass Spec ome e QMS 403 Aëolos Quad o was used o collec he
he mog a ime ic cu e and he DTA cu e (Figu e 2.4). Mass
spec ome y is an analy ical echnique used o measu e he masses
o molecules, iden i y he chemical s uc u es o compounds wi hin a
sample, and quan i y he amoun o hese compounds.
The sample is ionized, which means he molecules a e con e ed in o
cha ged pa icles (ions). The gene a ed ions a e hen sepa a ed
based on hei mass- o-cha ge a io (m/z) using an analyze . A e
sepa a ion, he ions a e de ec ed, usually by a de ec o ha coun s
ion hi s and measu es hei in ensi y, which co ela es o he
abundance o each ion. The da a collec ed by he de ec o is used o
gene a e a mass spec um.
Figu e 2.4. The mog a ime ic analyze TGA NETZSCH STA 449 F3 Jupi e
coupled o a Mass Spec ome e QMS 403 Aëolos Quad o a ailable a CIC
ene giGUNE.
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2. Expe imen al Techniques
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2.4. Induc i ely Coupled Plasma A omic
Emission Spec ome y echnique
The induc i ely coupled plasma a omic emission spec oscopy (ICP-
AES) is an analy ical echnique used o elemen al de e mina ions. I
is a ype o mass spec ome y ha uses induc i ely coupled plasma
o ionize he sample, c ea ing a omic and small polya omic ions,
which emi elec omagne ic adia ion a wa eleng hs cha ac e is ic o
a pa icula elemen . The concen a ion o he elemen wi hin he
sample is indica ed by he in ensi y o his emission.
The ICP-AES equipmen used was an Ul ima 2 Ho iba Yobin Y on
(Figu e 2.5). Since he samples ha e o be liquid p io o being
analyzed, he powde samples a e p e iously diges ed in an acid
solu ion o HNO3 and hen hea ed a 190 °C o 15 minu es.
Figu e 2.5. Ul ima 2 Op ical Emission Spec ome e used in his wo k.
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2. Expe imen al Techniques
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2.5. Raman Spec oscopy echnique
Raman spec oscopy is a non-des uc i e ib a ional spec oscopic
echnique used in chemis y o collec a spec um wi h a unique
inge p in o molecules. Each molecule has a di e en se o
ib a ional ene gy le els, and he emi ed pho ons ha e unique
wa eleng h shi s, allowing he iden i ica ion o wha is in a sample.
When a pho on (elec omagne ic adia ion o speci ic equency ν)
eaches a molecule, i in e ac s wi h he pola izable elec on densi y
and he bonds o he molecule, exci ing he molecule o a so-called
i ual ene gy s a e o a sho pe iod o ime. Then, he pho on o
equency ν (Rayleigh sca e ing o elas ic sca e ing) as well as ha
o equency ± i (“Raman sca e ing” o inelas ic sca e ing), whe e
i ep esen s a ib a ional equency o he molecule, a e sca e ed.
Raman sca e ing is much weake han Rayleigh sca e ing, hus only
a e y small ac ion o molecules unde goes inelas ic sca e ing. The
esul ing inelas ically sca e ed pho on can be o ei he lowe o
highe ene gy han he incoming pho on. In case he sca e ed
pho on exhibi ed highe equency han he inciden adia ion, a blue
shi is obse ed, gene a ing wha is known as an i-S okes lines. On
he con a y, i he sca e ed pho on exhibi s a lowe equency han
he inciden adia ion, a ed shi occu s, and hese bands a e e e ed
o as S okes lines. In he spec um, he di e en peaks co espond
o di e en Raman exci a ions.
Raman analyses we e conduc ed in he ange 100 - 4,000 cm-1 using
a Renishaw InVia spec ome e equipped wi h a 532 nm g een lase
ope a ed a a powe o 0.5 mW a ailable a CIC ene giGUNE. The
lase spo size was app oxima ely 1 mm in diame e .
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2.6. X-Ray Abso p ion Spec oscopy
echnique
The X-Ray Abso p ion Spec oscopy (XAS) echnique uses a wide
ange o unable X- ays p o ided by synch o on acili ies o iden i y
he oxida ion s a e o ions in di e en samples. Inciden pho on
ene gies i adia ing he samples a e scanned ac oss an abso p ion
edge c ea ing a co e hole s a e. The a ea unde nea h an abso p ion
spec um ep esen s he pa ial densi y o unoccupied s a es abo e
he Fe mi le el. The spec a can be sepa a ed in o h ee di e en
egions: he p e-edge egion desc ibes co e elec on exci a ion o
unoccupied s a es close o he Fe mi le el, he main-edge p obes he
uppe quasi-bound s a es, and he pos -edge which leads o
exci a ion abo e he ioniza ion h eshold.
The esponse o each inciden pho on ene gy can be de ec ed as
ei he ansmi ed X- ays, luo escence o elec on yield. The e a e
di ec and indi ec de ec ion modes. T ansmission mode is a di ec
de ec ion mode, which iden i ies i s -o de abso p ion p ocesses.
Due o he sho a enua ion leng hs o so X- ays, XAS
measu emen s in ansmission mode a e only ele an o hin
samples, and no o common ba e y ma e ials. The e o e, indi ec
de ec ion modes a e mo e sui able o ba e y analysis and ely on
seconda y p ocesses which a e sepa a ed in o adia i e and non-
adia i e elaxa ion.
In he la e case, he gene a ed co e hole s a e elaxes back o he
g ound s a e by illing he co e-hole wi h an elec on om a highe
ene gy le el ia he emission o an Auge elec on. The Auge
elec on can hen sca e inelas ically and c ea e low ene gy
seconda y elec ons which lea e he sample. The gene a ed numbe
o co e holes is p opo ional o he d ain cu en o eplace he los
pho oelec ons, which is measu ed by a high p ecision amme e . This
de ec ion mode is su ace sensi i e, wi h p obing dep hs o 2-10 nm.
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due o he sho a enua ion leng h o he sca e ed elec ons and is
called he o al elec on yield (TEY). Ano he mode o indi ec
de ec ion is o al luo escence yield (TFY). The exci ed sys em elaxes
back o he g ound s a e by illing he co e hole wi h a alence le el
elec on ia he emission o a pho on wi h he ene gy di e ence o
he wo ene gy le els. The TFY de ec ion is mo e bulk sensi i e (up
o 100 nm), because pho ons ha e a longe a enua ion leng h han
elec ons.
Measu emen s we e pe o med a BL29-BOREAS beam ime in ALBA
(Ba celona). XAS da a we e collec ed in bo h o al elec on and
luo escence yield mode. Signals om TEY mode co espond o he
chemical s a e o he su ace laye o he ma e ial, whe eas FY
co esponds o app oxima ely 100 nm in o he pa icle, hus ha ing
a no able con ibu ion om he bulk c ys al s uc u e, especially
conside ing he pa icle size o he ma e ials.
2.7. Mössbaue Spec oscopy echnique
The Mössbaue Spec oscopy is a echnique which is based on he
ene gy le el ansi ions ha nuclei unde go in a oms. These ene gy
le els ansi ions can p o ide in o ma ion abou he local
en i onmen o an a om as hey depend on he elec onic and
magne ic en i onmen . The Mössbaue e ec consis s o he ecoil-
ee emission o a gamma- ay om a nucleus (sou ce) in he exci ed
s a e and he esonan abso p ion by an iden ical nucleus (abso be
o sample). This e ec is only obse ed in a limi ed numbe o
iso opes, being 57Fe he mos commonly s udied.
In 57Fe Mossbaue spec oscopy, a 57Co sou ce is used. This sou ce
decays o an exci ed s a e o 57Fe by elec on cap u e and hen, i
subsequen ly decays o a g ound s a e emi ing he desi ed gamma-
ay (o 14.4 keV), ha can be abso bed by a 57Fe nucleus in he
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sample. In o de o une he ene gy, he sou ce is mo ed in a ange
o eloci ies using a linea mo o , p oducing he Dopple e ec .4
In he esul ing spec a, gamma- ay in ensi y is plo ed as a unc ion
o he sou ce eloci y. A eloci ies co esponding o he esonan
ene gy le els o he sample, a ac ion o he gamma- ays is
abso bed, esul ing in a d op in he measu ed in ensi y and a
co esponding dip in he spec um.
57Fe Mössbaue spec a we e measu ed a oom empe a u e (293 K)
wi h a 57Co:Rh sou ce and a K gas p opo ional coun e . The
spec ome e was ope a ed wi h a iangula eloci y wa e o m, and
he spec a we e i ed wi h supe posi ions o app op ia e se s o he
Lo en zian lines using NORMOS p og am o powde measu emen
and PC-MOS compu e p og am o ope ando measu emen s.5,6
Isome shi alues a e gi en ela i e o α-Fe me al. In he ope ando
Mössbaue spec oscopy measu emen s, he cell was cycled be ween
4.5 and 1.5 V s. Na+/Na.
2.8. Solid S a e Nuclea Magne ic Resonance
echnique
Solid-s a e nuclea magne ic esonance (ssNMR) spec oscopy is a
aluable ool o cha ac e izing local en i onmen s in complex
ma e ials, pa icula ly hose con aining nuclei such as 23Na and 31P.
The 23Na nucleus, wi h a spin o 3/2, is quad upola and hus highly
sensi i e o local elec ic ield g adien s and coo dina ion symme y.
I s spec a o en exhibi b oad ea u es due o quad upola
in e ac ions, bu hese can be signi ican ly na owed using magic-
angle spinning (MAS), quad upola echo, o mul iple-quan um MAS
(MQMAS) echniques. These me hods enable he esolu ion o dis inc
sodium si es, p o iding insigh s in o s uc u al o de and local
chemical en i onmen s in ma e ials such as ion conduc o s, glasses,
and biological sys ems.
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In con as , 31P is a spin-1/2 nucleus wi h 100% na u al abundance
and no quad upola in e ac ion, esul ing in sha p, well- esol ed
spec a unde MAS. I is widely employed in he s udy o phospha e-
based sys ems, including ino ganic solids, biomine als, and lipid
memb anes. The use o c oss-pola iza ion (CP-MAS) enhances
sensi i i y, pa icula ly in sys ems whe e phospho us is p esen a
low concen a ions. Analysis o chemical shi aniso opy (CSA) and
dipola couplings in 31P ssNMR u he p o ides de ailed in o ma ion
on molecula o ien a ion, local geome y, and dynamic p ocesses.
Toge he , 23Na and 31P ssNMR o e complemen a y insigh s in o he
s uc u e and unc ion o complex solid-s a e ma e ials.
Magic Angle Spinning Nuclea Magne ic Resonance (MAS NMR)
expe imen s we e pe o med a 52.9 MHz, on a B uke -300
spec ome e cha ged o a ield o 4.7 T using a 1.3 mm MAS p obe
a o o spinning speed o 50 kHz. A o o synch onized spin−echo
pulse sequence (90°−τ−180°−τ1−acquisi ion) was used wi h ypical
90° and 180° pulses o 1.2 and 2.4 μs o 23Na and 1.5 and 4 μs, o
31P espec i ely. Recycle day o 1s was used o all expe imen s. The
numbe o scans was se o 4k o 23Na and 6k o 31P expe imen s.
2.9. Elec ochemical echniques
2.9.1. Elec ode p epa a ion
Fo he elec ode p epa a ion, ac i e ma e ials and addi i es ha e
been mixed using N-Me hyl-2-py olidone (NMP) as sol en . In o de
o inc ease he adhesion o he elec ode composi e o he aluminum
oil, Poly inylidene luo ide (PVdF) has been used. Fi s , PVdF has
been dissol ed in NMP. A e wa ds, he ac i e ma e ial and ca bon
black (Supe C65), which has been used as conduc ing addi i e o
inc ease he elec onic conduc i i y, ha e been added and mixed wi h
he magne ic s i e o 1 hou un il a homogeneous slu y is
ob ained. The slu ies p epa ed o his wo k consis o a (ac i e
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ma e ial:conduc i e addi i e:binding polyme ) a io o 8:1:1 o C-
coa ed powde s as C/ -NaFePO4 and 7:2:1 o non C-coa ed powde s
as -NaMn1-yFeyPO4. The slu y has been pou ed on an aluminum oil
(20 µm, Hohsen) and cas using a Doc o Blade coa ing machine
se ing a heigh o 150 µm. The lamina es ha e been d ied unde
acuum o e nigh a 120 °C and elec odes discs wi h a diame e o
12 mm ha e been punched and p essed wi h 4 ons cm-2. Finally,
be o e assembling he elec ochemical cells, he elec odes has been
d ied unde acuum a 120°C o e nigh .
2.9.2. Cell assembly
Hal -cells ha e been assembled o he s udy o ca hode ma e ial,
whe e he ca hode elec ode is assembled e sus a cons an ol age
ma e ial. In his wo k, me allic sodium has been used bo h as a
coun e elec ode and e e ence elec ode in he case o he h ee
elec ode cells. A Wha man glass- ibe sepa a o (GF/D) is placed
be ween he ca hode ma e ial and me allic Na a e being soaked wi h
he elec oly e. 1M NaPF6 EC:PC 1:1 W.% (e hylene ca bona e:
p opylene ca bona e) has been used as s anda d elec oly e unless
o he wise indica ed.
Gal anos a ic da a o coin cells CR2032 we e ypically collec ed wi h
he Macco Ba e y es e and he VMP3 po en ios a /gal anos a was
used o collec ing gal anos a ic da a, cyclic ol ammog ams and
PITT da a in he case o wo-elec ode and h ee-elec ode Swagelok
con igu a ion cell.
In he ope ando Mössbaue spec oscopy measu emen s, he
Mössbaue abso be s we e p epa ed as sel -s anding elec odes o
he ca hode ac i e ma e ial (p e iously ball milled wi h C65) mixed
wi h PTFE binde and moun ed in a speci ically designed in si u
elec ochemical cell.7
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In he ope ando XRD measu emen s, he pa e ns we e collec ed a
a wa eleng h λ = 0.825890 Å using ou homemade ope ando
elec ochemical cell equipped wi h a Be yllium (Be) window as a
cu en collec o and using a anspa en plunge also equipped wi h
a Be window o ansmission geome y.2 Elec ode discs we e
p epa ed by mixing he ca hode ac i e ma e ial wi h ca bon C65
(Ime ys) in a a io o 62: 8 using Wha man GF/D bo osilica e glass
as sepa a o , a 1.0 M sodium hexa luo ophospha e (NaPF6, Sigma-
Ald ich) in a 1 : 1 ol. mix u e o e hylene ca bona e (EC, Ac os) and
dime hyl ca bona e (DMC) as elec oly e and high pu i y Na me al
(Sigma-Ald ich) as nega i e elec ode.
2.9.3. Gal anos a ic expe imen s
The elec ochemical pe o mances o he cells ha e been e alua ed
wi h a gal anos a ic cycling, whe e a cons an cu en is applied wi h
po en ial limi a ions. The e o e, he amoun o exchanges cha ges is
quan i ied and compa ed wi h he heo e ical capaci y.
The ol age o a ba e y V0 depends on he chemical po en ials o he
posi i e and nega i e elec odes. In gal anos a ic cyclic cha ge-
discha ge measu emen s, Vol age is po ed agains ime.
Ne e heless, in he ba e y ield, he p esen a ion o he esul s
usually en ails he con e sion o ime o speci ic capaci y (mAh) o o
g a ime ic speci ic capaci y (mAh g-1), being he las one he amoun
o elec ici y (mAh) ha can 1 g o a ma e ial deli e in a single
cha ge/discha ge a a de e mined C- a e. C- a e (in A g-1 o mA g-1)
is a measu e o he a e a which a ba e y is cha ged o discha ge
ela ed o i s maximum capaci y. A 1C means ha he discha ge
cu en will discha ge he ba e y com ple ely in 1 hou . Gal anos a ic
cyclic cha ge-discha ge expe imen s a a de e mined C- a e
depending on he ma e ials and C- a e capabili y a es ha e been
ca ied ou .
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Figu e 3.3. XRD pa e ns o he LiMn0.65Fe0.35PO4 p is ine and he ob ained
compounds a e di e en chemical oxida ion condi ions compa ed o FePO4
om he li e a u e as e e ence wi h simila XRD pa e n (ICSD code: 92199)
o phase iden i ica ion.
3.2.3. Chemical educ ion o Mn1-yFeyPO4
Fi s ly, o op imize he sodia ion p ocess, a ious syn hesis
app oaches ha e been employed o success ully ob ain he
C/NaFePO₄ pu e phase om he ob ained C/FePO₄. Fo his
chemical educ ion, sodium hiosul a e (Na2S2O3) has been selec ed
as he educing agen due o i s mode a e educing p ope ies. This
is expec ed o minimize damage o he ca bon coa ing o
decomposi ion in o undesi ed p oduc s, since Na2S2O3 p o ides a
milde educ ion en i onmen compa ed o s onge educ an s. The
s a egies implemen ed (Table 3-2) include:
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Table 3-2. Di e en s a egies o he syn hesis o C/NaFePO4 om C/FePO4
(modi ica ions included in bold).
S a egy
Reducing
agen
Ra io
Concen a ion
(M)
T
(°C)
S i ing
ime (h)
a
Na2S2O3
4:1
0.134
80
24
b
Na2S2O3
4:1
0.532
80
24
c
Na2S2O3
4:1
0.532
60
24
d
Na2S2O3
+ Na2SO4
4:1
0.532
60
24
e
Na2S2O4
1:2
0.133
60
24
Na2S2O3
6:1
0.8
60
24
a) Using dilu ed Na2S2O3 as educing agen a 80 ºC
The i s ial was pe o med using dilu ed Na2S2O3 (0.134 M) in
aqueous media, wi h a mola a io (Na2S2O3:FePO4) o 4:1, a a
empe a u e o 80 ºC o 24 hou s. The empe a u e was inc eased
wi h he idea o a o ing he eac ion kine ically.
The powde is ob ained as pu e un eac ed C/FePO4 (SD_A, see
Figu e 3.4), sugges ing ha he eac ion ime o Na2S2O3 can be e y
slow.
The p esence o small shoulde s in he XRD pa e n may sugges he
onse o a sligh sodia ion p ocess, indica ing pa ial inco po a ion o
sodium in o he FePO4 amewo k.
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Figu e 3.4. XRD pa e n o he syn hesized SD_A compa ed o FePO4 om
he da abase (ICSD code: 92199) o phase iden i ica ion.
b) Inc emen o concen a ion
The ollowing es was ca ied ou using a high concen a ion o
Na2S2O3 (0.532 M), wi h a mola a io (Na2S2O3:FePO4) o 4:1, a a
empe a u e o 80 ºC o 24 hou s.
The ob ained powde consis s o a mix u e o Fe1.375PO(OH), which
is no he a ge ed p oduc , and S8 (SD_B, Figu e 3.5), showing ha
a his highe concen a ion o Na2S2O3 all he Fe is s ill in oxida ion
s a e (III) a ec ing somehow he C/FePO4. This sugges ha a his
empe a u e Fe2+ migh no be s able and could be easily e-oxidized
o Fe3+. The p esence o S8 can be a ibu ed o a common side-
p oduc o eac ions whe e Na2S2O3 is in ol ed.
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Figu e 3.5. XRD pa e ns o he syn hesized SD_B compa ed wi h
Fe1.375PO4(OH) (ICSD code: 170854) and S8 (ICSD code: 870) om he
da abase o phase iden i ica ion.
c) Dec ease in empe a u e
To analyze he e ec o he empe a u e on his eac ion,
expe imen s a lowe empe a u e (60 ºC) o 24 hou s we e ca ied
ou using an excess o Na2S2O3 wi h he same concen a ion (0.532
M), and a mola a io (Na2S2O3:FePO4) o 4:1.
The ob ained powde , called SD_C is a mix u e o NaFePO4,
Na0.7FePO4, FePO4 and S8 (see Figu e 3.6), sugges ing ha ,
al hough he a ge ed NaFePO4 is inally ob ained, he p esence o
o he impu i ies indica es ha he educing/sodia ion eac ion is no
comple ely e ec i e.
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Figu e 3.6. XRD pa e n o he syn hesized SD_C compa ed wi h di e en
NaxFePO4 phases (ICSD code: 169118, 169119, 92199) and S8 (ICSD code:
870) o phase iden i ica ion.
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d) Addi ion o Na2SO4 as ex a sodium sal
To imp o e he oxida ion p ocess and compensa e he sodium
de iciency in he p oduc s, a simila expe imen o he c) p e iously
desc ibed was ca ied ou wi h he addi ion o sodium sulpha e,
Na2SO4. In his case, he ob ained powde , SD_D was a mix u e o
Na0.7FePO4 and S8 (see Figu e 3.7), showing ha al e na i e
expe imen al condi ions s ill need o be ound.
Figu e 3.7. XRD pa e n o SD_D compa ed wi h Na0.7FePO4 (ICSD code:
169119) and S8 (ICSD code: 870) om he da abase o phase iden i ica ion.
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e) Using Na2S2O4 as educing agen
An al e na i e educing agen , sodium di hioni e, Na2S2O4, known o
be a s onge educing agen , was used in he new syn hesis. The
eac ion was ca ied ou using an aqueous solu ion o Na2S2O4 wi h a
concen a ion o 0.133 M and a mola a io (Na2S2O4:FePO4) o 1:2
a 25 ºC o 24 hou s. Howe e , in his case, he ob ained phase,
SD_E was ound o be amo phous (see Figu e 3.8). This esul is
likely due o he s ong educing cha ac e o Na2S2O4, which gi es
ise o he amo phiza ion o he ob ained compound. Consequen ly,
Na2S2O4 was disca ded as sodia ion agen .
Figu e 3.8. XRD pa e n o he syn hesized SD_E.
) Imp o e he educing p ocess by using concen a ed
Na2S2O3,
Based on he p e ious esul s, we decided o make use o Na2S2O3
ins ead o Na2S2O4. To imp o e he e iciency o i s educing ac i i y,
he mola a io (Na2S2O3:FePO4) was inc eased om 4:1 o 6:1, and
he concen a ion om 0.532 o 0.8 M, while main aining he
empe a u e and ime pa ame e s (60 ºC o 24 hou s). To a oid he
o eseeable p esence o S8 in he inal p oduc , he powde was
washed wi h oluene a 60ºC o 1 hou . Finally, he pu e C/NaFePO4
phase hence o h: SD_F, was inally ob ained by il a ion unde
hese condi ions, as shown by he XRD pa e n in Figu e 3.9. The by-
p oduc Na2S4O6 is soluble and would emain dissol ed in he
wa e wa e .
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Figu e 3.9. XRD pa e n o he syn hesized SD_F compa ed wi h NaFePO4
(ICSD code: 169118) om he da abase o phase iden i ica ion.
Summa izing, he pu e C/NaFePO4 phase was ob ained by he
chemical sodia ion o C/FePO4 wi h a 0.8M Na2S2O3 aqueous (Sigma-
Ald ich, 99%) solu ion educing agen in a (Na2S2O3:FePO4) a io o
6:1, a he empe a u e o 60 ºC o 24 h. (Figu e 3.10). Using his
app oach, 150 g ams o -C/NaFePO4 can be ob ained in one ba ch,
wi h a yield o 91%.
Figu e 3.10. Rounded lask o 5 L du ing he syn hesis o a ba ch o iphyli e
C/NaFePO4 using he indi ec syn hesis me hod.
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The XRD pa e ns sequence o he ull indi ec syn hesis is shown in
Figu e 3.11 and a schema ic desc ip ion o he di e en app oaches
used o ob ain he C/NaFePO4 pu e phase om C/FePO4 is shown
in Figu e 3.12, which summa izes he expe imen al s a egies
showed in Table 3-2.
Figu e 3.11. XRD pa e ns o syn hesized C/FePO4 and C/NaFePO4 compa ed
o he comme cial C/LiFePO4 used as p ecu so .
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Figu e 3.12. Scheme o he di e en chemical educ ion app oaches o
ob aining NaFePO4.
To alida e his s a egy, he same chemical educ ion p ocedu e
(s a egy F, Figu e 3.12) was employed o syn hesize
C/NaMn0.35Fe0.65O4 om he p e iously ob ained phase
C/Mn0.35Fe0.65PO4 phase, as de ailed p e iously in Sec ion 3.2.2.
This p ocess in ol ed he selec i e educ ion o Fe and Mn p ecu so s
wi hin he ca bon-coa ed amewo k, enabling he ans o ma ion
while p ese ing he s uc u al in eg i y o he ma e ial. The XRD
pa e ns o he syn hesized C/NaMn0.35Fe0.65O4 con i med i s
success ul o ma ion as a pu e phase, wi h no de ec able seconda y
phases o impu i ies (Figu e 3.13). This indica es ha he educ ion
p ocedu e is e ec i e o ailo ing he ma e ial's composi ion while
main aining i s c ys allini y.
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3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s
cha ac e iza ion
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The mo phology and size o he C/LiFePO4, C/FePO4 and
C/NaFePO4 pa icles we e cha ac e ized by SEM, e ealing ha all
h ee compounds exhibi good homogenei y and a simila pa icle size
dis ibu ion wi hin 50-300 nm o diame e (Figu e 3.19.a-c). In
addi ion, TEM images show ha he pa icles a e uni o mly ca bon
coa ed a e he oxida ion and educ ion ea men s (Figu e 3.19.d-
), indica ing ha he oxida ion/ educ ion eac ion does no al e he
sample mo phology om su ace o bulk. A highe magni ica ion TEM
image o C/NaFePO4 (Figu e 3.20) clea ly con i ms he p esence o
c acks, which a e highligh ed in pu ple. This can be a ibu ed o he
ex ac ion and inse ion o Li+ and Na+ du ing he chemical syn hesis,
p ima ily due o he signi ican olume misma ch be ween
FePO4/NaFePO4 (18%), compa ed o LiFePO4/FePO4 (7%).3
Figu e 3.19. (a-c) SEM and (d- ) TEM images o (a,d) C-LiFePO4, (b,e)
C/FePO4 and (c, ) C/NaFePO4.
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3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s
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Figu e 3.20. TEM images o C/NaFePO4 pa icles in which he c acks a e
highligh ed wi h ci cles.
The pe cen age o ca bon in he esul ing C/NaFePO4 we e
de e mined by TGA measu emen s in ai (see Figu e 3.21), expec ing
he combus ion o ca bon libe a ed as CO2. This is impo an because
he pe cen age o ca bon di ec ly a ec s he accu a e no maliza ion
o elec ochemical capaci y, ensu ing ha he epo ed pe o mance
e lec s only he ac i e LiFePO4 phase. Howe e , a empe a u es
abo e 200 ºC, he hea ing o C/NaFePO4 gi es ise o an inc ease
in he mass ha can be a ibu ed o he decomposi ion o NaFePO4
in o species such as Na3Fe2(PO4)3 and Fe2O3 due o he oxida ion
p ocesses o Fe2+ o Fe3+. A simila phenomenon is obse ed wi h
C/LiFePO4.8
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Figu e 3.21. The mog a ime ic analysis o C/LiFePO4, C/FePO4 and
C/NaFePO4 in ai .
Fo his eason, o e alua e he pe cen age o ca bon i was measu ed
C/FePO4, whe e Fe is al eady in he oxida ion s a e (III). When
C/FePO4 is hea ed, a small ac ion o humidi y H2O is libe a ed in
he ange o RT-150ºC. Then, a weigh loss o app oxima ely 2% is
obse ed in he ange o 350-520 ºC (Figu e 3.22), which is
a ibu ed o he Ca bon-coa ing laye in he samples. This loss was
co obo a ed by he measu emen s pe o med in he Mass
Spec ome e coupled o he TGA and assigned o he libe a ion o
CO2 (Figu e 3.23).
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Figu e 3.22. The mog a ime ic analysis and analysis o he ou le gases
(H2O and CO2) de ec ed by mass spec ome y o C/FePO4 in ai .
Figu e 3.23. Mass spec ome y wi h he ou le o gases (H2O and CO2) o
C/FePO4 in ai .
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3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s
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77
3.3.2. (Li/Na)Mn0.65Fe0.35PO4 ma e ials
cha ac e iza ion
Le Bail e inemen s o he C/LiMn0.65Fe0.35PO4, C/Mn0.65Fe0.35PO4
and C/NaMn0.65Fe0.35PO4 ob ained a e chemical deli hia ion and
sodia ion a e shown in Figu e 3.24, Figu e 3.25 and Figu e 3.26
espec i ely. I can be no iced ha he C/Mn0.65Fe0.35PO4 peaks a e
shi ed o a highe 2 compa ed o hose o he C/LiMn0.65Fe0.35PO4
peaks, due o he cell con ac ion ha esul s om deinse ion o
li hium ions. Howe e , he inse ion o sodium ions in o FePO4 o o m
NaFePO4 s uc u e leads o la ge uni cell pa ame e s, and hus he
peaks a e shi ed o lowe 2. This e ec is simila han he obse ed
wi h (Li,Na)FePO4 componds. These compounds c ys allize in he
o ho hombic sys em wi h Pnma space g oup. The Le Bail e ined cell
pa ame e s o C/LiMn0.65Fe0.35PO4, C/Mn0.65Fe0.35PO4 and
C/NaMn0.65Fe0.35PO4 a e shown in Table 3-4 and a e in good
ag eemen wi h he expec ed alues.9
Figu e 3.24. Le Bail e inemen o he XRD pa e n o he comme cial
p ecu so C/LiMn0.65Fe0.35PO4. Expe imen al pa e n ( ed), calcula ed p o ile
(black), di e ence be ween expe imen al and calcula ed (blue) and B agg
posi ions ( e ical ba s in g een). (RB agg = 39.4% and χ2 =5.54).
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3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s
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Figu e 3.25. Le Bail e inemen o he XRD pa e n o he comme cial
p ecu so C/Mn0.65Fe0.35PO4. Expe imen al pa e n ( ed), calcula ed p o ile
(black), di e ence be ween expe imen al and calcula ed (blue) and B agg
posi ions ( e ical ba s in g een). (RB agg = 1.11% and χ2 = 4.04).
Figu e 3.26. Le Bail e inemen o he XRD pa e n o he comme cial
p ecu so C/NaMn0.65Fe0.35PO4. Expe imen al pa e n ( ed), calcula ed p o ile
(black), di e ence be ween expe imen al and calcula ed (blue) and B agg
posi ions ( e ical ba s in g een). (RB agg =3.60 % and χ2 =2.42).
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3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s
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Table 3-4. Uni cell pa ame e s o C/LiMn0.65Fe0.35PO4, C/Mn0.65Fe0.35PO4 and
C/NaMn0.65Fe0.35PO4 ob ained by e inemen .
a (Å)
b (Å)
c (Å)
V (Å3)
C/LiMn0.65Fe0.35PO4
10.3936(4)
6.0646(2)
4.7290(2)
298.09(2)
C/Mn0.65Fe0.35PO4
9.6973(3)
5.8870(2)
4.7788(1)
272.891(1)
C/NaMn0.65Fe0.35PO4
10.4800(3)
6.2555(1)
4.9715(1)
325.92(1)
The SEM images (Figu e 3.27) depic he mo phology o (a, b) C-
LiMn0.65Fe0.35PO4, (c, d) C/Mn0.65Fe0.35PO4, and (e, )
C/NaMn0.65Fe0.35PO4. Uni o m sphe ical pa icles wi h a ying sizes
a e obse ed, indica ing success ul o ma ion o he ma e ials. The
mo phology e eals a bimodal size dis ibu ion, comp ising p ima y
pa icle in he ange o 1-5 µm and la ge seconda y pa icles in he
ange o 10-30 µm. The images a highe magni ica ions (b, d, )
e eal a smoo h su ace ex u e wi h some agglome a ion.
Figu e 3.27. SEM images o (a),(b) C-LiMn0.65Fe0.35PO4, (c),(d)
C/Mn0.65Fe0.35PO4 and (e),( ) C/NaMn0.65Fe0.35PO4.
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3.3.3. Reco e ed LiFePO4 ma e ial cha ac e iza ion
A cha ac e iza ion o he eco e ed Li3PO4 and syn hesized LiFePO4
(sec ion 3.2.4) was pe o med o analyze hei s uc u al amewo k,
mo phological ea u es, which a e impo an o unde s anding hei
pe o mance. XRD pa e ns o he eco e ed Li3PO4 and he
syn hesized LiFePO4 a e shown in Figu e 3.28 and Figu e 3.29
espec i ely. Bo h compounds c ys allize in he o ho hombic sys em,
wi h a Pmn21 space g oup o he Li3PO4 and Pmna o LiFePO4. The
uni cell pa ame e s de e mined by Le Bail e inemen a e a =
6.1282(5) Å, b = 5.2499(4) Å, c = 4.88226(4) Å and a = 10.3309(3)
Å, b = 6.00860(15) Å, c = 4.69534(11) Å, o Li3PO4 and LiFePO4,
espec i ely, and a e in good ag eemen wi h hose epo ed in he
li e a u e.10,11
Figu e 3.28. Le Bail Re inemen o Li3PO4 ob ained om Li+ con aining
was ewa e (Sec ion 3.2.4). Expe imen al pa e ( ed), calcula ed p o ile
(black), di e ence be ween expe imen al and calcula ed (blue) and B agg
posi ions e ical ba s in g een).
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3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s
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Figu e 3.29. Le Bail Re inemen o LiFePO4 ob ained om ecycled Li3PO4.
Expe imen al pa e ( ed), calcula ed p o ile (black), di e ence be ween
expe imen al and calcula ed (blue) and B agg posi ions e ical ba s in
g een).
The mo phology o he pa icles o he eco e ed Li3PO4 and he
syn hesized LiFePO4 was also cha ac e ized by scanning elec on
mic oscopy (SEM), which showed a homogeneous dis ibu ion o
agglome a es (≈ 50µm) o pa icles (600-700 nm) in he case o
Li3PO4 and a homogeneous pa icle size dis ibu ion (0.5-2 µm) in he
case o he LiFePO4 (Figu e 3.30).
Figu e 3.30. SEM imaged o (a) ecycled Li3PO4 and (b) LiFePO4 ob ained
om ecycled Li3PO4.
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3.4. Elec ochemical cha ac e iza ion o
(Li,Na)Mn1-yFeyPO4
3.4.1. Elec ochemical p ope ies o syn hesized
NaMn1-yFeyPO4
Following he syn hesis and comp ehensi e s uc u al,
mo phological, and physicochemical cha ac e iza ion o he
syn hesized C/NaFePO4 and C/NaMn0.65Fe0.35PO4 in sec ion 3.2.3,
i is essen ial o e alua e hei elec ochemical beha io unde
applica ion- ele an condi ions. Fo he elec ochemical es ing, he
slu ies p epa ed consis ed o (C/NaMn1-yFeyPO4:C65:PVDF) wi h a
a io o 8:1:1.
Fi s , he elec ochemical pe o mance o C/NaFePO4 was e alua ed
in Na-hal cells in he ol age window 1.5 – 4.0 V ( s. Na+/Na). Figu e
3.31 illus a es he cyclabili y o C/NaFePO4 a C/10 a e o he i s
50 cycles a 25ºC. The capaci y a he end o he i s discha ge was
132 mAh g-1, which co esponds o 86% o he heo e ical capaci y
(154 mAh g-1). Despi e he ini ial cha ge-discha ge disc epancy (only
in he i s cycle) and he signi ican olume misma ch be ween end
membe s (NaFePO4 and FePO4), he ma e ial deli e s a coulombic
e iciency o 100% ha was main ained a e 50 cycles,
demons a ing a good cycling s abili y (87% o capaci y e en ion)
(Figu e 3.31).
The cha ge and discha ge p o iles, depic ed in Figu e 3.32, we e
asymme ical, displaying wo dis inc pla eaus a app oxima ely 3.1
and 2.95 V e sus Na+/Na in cha ge, and only one pla eau a ound
2.80 V in discha ge. This beha io aligns wi h he di e en p ocesses
occu ing, as p e iously desc ibed.2,3,12,13 Addi ionally, he
pola iza ion dec eased om 0.42 V ( i s cycle) o 0.28 V in
subsequen cycles. The highe ini ial pola iza ion in he i s cycle
could be a ibu ed o he o ma ion o di e en species on he
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3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s cha ac e iza ion
89
Phase
Syn hesis me hod
Reagen s
Disch.
capaci y
(mAh g-1)
C-
a e
Commen s
Re .
-NFP
Elec ochemical
syn hesis
LiFePO4 and AlF3 as coa ing
117
0.1C
Impossibili y o scaling-up: no indus ial
in e es .
Ac i e ma e ial:ace ylene black:PTFE
(80:10:10 w %)
Jeong e al.19
99
0.2C
89
0.5C
74
1C
54
2C
-NFP
Elec ochemical
syn hesis
LiFePO4
125
0.5C
Impossibili y o scaling-up: no indus ial
in e es .
Ac i e ma e ial:Ca bon black:PVdF (w %
no speci ied)
Heubne e
al.20
-NFP
Redox eac ion
(sol en : ace oni ile)
LiFePO4,
NO2BF4 and
NaI
141
0.07C
NaFePO4 was w apped wi h Poly hiophene.
NaFePO4:Ca bon black:PVdF (80:10:10
w %)
Ali e al.6
128
0.16C
119
0.32C
93
0.65C
77
1.3C
48
1.95C
-NFP
Redox eac ion
(sol en : ace oni ile)
LiFePO4,
NO2BF4 and
NaI
89
0.1C
Aqueous elec oly e
C-NaFePO4:Supe C65:PVdF
(75:20:5 w %)
Fe nández-
Rope o e
al.21
81
0.2C
51
1C
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3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s cha ac e iza ion
90
Phase
Syn hesis me hod
Reagen s
Disch.
capaci y
(mAh g-1)
C-
a e
Commen s
Re .
39
2C
114
0.2C
106
0.5C
96
1C
84
2C
66
5C
46
10C
-NFP
Sol o he mal
syn hesis (sol en :
e hanol)
LiFePO4, Na2S2O8, and NaOH
125
0.1C
Sol o he mal empe a u es be ween 160
and 180 °C
C-NaFePO4:C65:PVdF (80:10:10 w %)
Xu e al.22
110
0.2C
90
0.5C
72
1C
55
2C
38
5C
-NFP
Redox eac ion in
aqueous media
LiFePO4, Na2S2O8 and Na2S2O3
132
0.1C
Eco- iendly, low cos and scalable
syn hesis.
Excellen pe o mance a high C- a es (>C)
C-NaFePO4:C65:PVdF (80:10:10 w %)
This wo k
114
0.2C
106
0.5C
96
1C
84
2C
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3. Indi ec syn hesis o iphyli e-NaMn1-yFeyPO4 and i s cha ac e iza ion
91
Phase
Syn hesis me hod
Reagen s
Disch.
capaci y
(mAh g-1)
C-
a e
Commen s
Re .
66
5C
-
NMFP
Redox eac ion in
aqueous media
LiMn0.65Fe0.35PO4, Na2S2O8 and
Na2S2O3
108
0.1C
Eco- iendly, low cos and scalable
syn hesis.
C-NaMn0.65Fe0.35PO4:C65:PVdF (80:10:10
w %)
This wo k
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92
3.4.2. Elec ochemical p ope ies o egene a ed
LiFePO4.
The elec ochemical pe o mance o he egene a ed LiFePO4
ob ained om eco e ed Li3PO4 de ailed in sec ion 3.2.4 was also
e alua ed wi hin he ol age window o 2.5 - 4.2 V ( s. Li+/Li) (Figu e
3.35). In he i s cycle, a discha ge capaci y o 143 mAh g-1 was
obse ed which inc eased o app oxima ely 160 mAh g-1 a e i e
cycles. The ini ial coulombic e iciency was ela i ely low (90%),
al hough, i apidly imp o ed, s abilizing o close o 100% a e he
hi d cycle. This beha io , oge he wi h he slopping p o ile obse ed
a end o he discha ge cu e (Figu e 3.35 inse ), may sugges limi ed
elec onic conduc i i y o he LiFePO4 pa icles. Such a limi a ion can
be a ibu ed o he absence o a conduc i e ca bon sou ce du ing
syn hesis, which ypically plays a c ucial ole in enhancing elec on
anspo in oli ine- ype ca hodes. The p og essi e imp o emen in
capaci y upon cycling may also indica e pa ial ac i a ion o he
elec ode ma e ial and imp o ed in e pa icle con ac o e ime. Fo
compa ison, comme cial ca bon-coa ed LiFePO4 om Aleees1
ypically deli e s capaci ies g ea e han 156 mAh g-1 and coulombic
e iciencies highe han 95% in he i s cycle a C/10.
Figu e 3.35. Discha ge capaci y s. cycle numbe o he C/LiFePO4 ob ained
om eco e ed Li3PO4 in hal cell a C/20. The cha ge/discha ge cu e
co esponding o he second cycle is shown in he inse .
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3.5. Summa y and Conclusions
A cos -e ec i e, was e- ee, en i onmen ally iendly, and po en ially
scalable indi ec me hod o syn hesizing iphyli e-C/NaFePO4 and
iphyli e-C/NaMn0.35Fe0.65PO4 has been demons a ed and con i med.
The in e media e C/FePO4 was syn hesized by chemical oxida ion o
comme cial C/LiFePO4 using an aqueous solu ion Na2S2O8 as he
oxidizing agen a oom empe a u e.
The success ul syn hesis o he in e media e NaMn0.35Fe0.65PO4
equi ed doubling he amoun o oxidizing agen and main aining he
eac ion a 60 °C.
The iphyli e C/NaFePO4 and C/NaMn0.65Fe0.35PO4 we e ob ained by
he chemical sodia ion o C/FePO4 and C/Mn0.65Fe0.35PO4 wi h aqueous
solu ion o he educing agen Na2S2O3 in a a io (Na2S2O3:FePO4)
a io o 6:1, a he empe a u e o 60 ºC.
The mo phological cha ac e iza ion con i med ha he Ca bon
Coa ing laye did no disappea du ing he syn hesis p ocess and ha
he opo ac ical eac ion did no al e he sample mo phology om
su ace o bulk.
T-C/NaFePO4 demons a es excellen elec ochemical pe o mance,
deli e ing a capaci y o 132 mAh g-1 a C/10 and e aining
app oxima ely 101 mAh g-1 wi h 100% coulombic e iciency o 100%
a e 200 cycles. Mo eo e , i s ma kedly supe io a e capabili y,
achie ing 84 mAh g-1 a 2C, su passes p e iously epo ed alues (39
o 54 mAh g-1), es ablishing i as one o he op-pe o ming
C/NaFePO4 o da e.
T-C/NaMn0.35Fe0.65PO4 shows a lowe elec ochemical pe o mance
compa ed o i s analogue, wi h an ini ial capaci y o 108 mAh g-1, and
a e en ion o app oxima ely 100 mAh g-1 a e 10 cycles. This
diminished pe o mance is likely a ibu ed o i s in insically lowe
elec onic conduc i i y and educed s uc u al s abili y caused by he
Jahn-Telle dis o ion.
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The li hium ex ac ed du ing he syn hesis can be eco e ed om
was ewa e by syn hesizing Li3PO4, which can hen be u he
con e ed in o a C/LiFePO4 p oduc wi h ou s anding elec ochemical
pe o mance (app oxima ely 155 mAh g-1, equi alen o 94% o he
heo e ical capaci y).
Consequen ly, he p oposed syn hesis me hod o ge C/NaFePO4 and
he excellen elec ochemical pe o mance can make his ma e ial o
be conside ed as a p omising candida e as ca hode o u u e
indus ial applica ions in sodium-ion ba e ies.
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3.6. Re e ences
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(2) Mo eau, P.; Guyoma d, D.; Gaubiche , J.; Bouche , F. S uc u e
and S abili y o Sodium In e cala ed Phases in Oli ine FePO4.
Chem. Ma e . 2010, 22 (14), 4126–4128.
h ps://doi.o g/10.1021/cm101377h.
(3) Casas-Cabanas, M.; Rodda is, V. V.; Sau el, D.; Kubiak, P.;
Ca e e o-González, J.; Paloma es, V.; Se as, P.; Rojo, T.
C ys al Chemis y o Na Inse ion/Deinse ion in FePO4–
NaFePO4. J. Ma e . Chem. 2012, 22 (34), 17421.
h ps://doi.o g/10.1039/c2jm33639a.
(4) Zhu, Y.; Xu, Y.; Liu, Y.; Luo, C.; Wang, C. Compa ison o
Elec ochemical Pe o mances o Oli ine NaFePO4 in Sodium-Ion
Ba e ies and Oli ine LiFePO4 in Li hium-Ion Ba e ies. Nanoscale
2013, 5 (2), 780–787. h ps://doi.o g/10.1039/C2NR32758A.
(5) Wongi ha om, N.; Lee, T.-C.; Wang, C.-H.; Wang, Y.-C.; Chang,
J.-K. Elec ochemical Pe o mance o Na/NaFePO4 Sodium-Ion
Ba e ies wi h Ionic Liquid Elec oly es. J. Ma e . Chem. A 2014,
2 (16), 5655. h ps://doi.o g/10.1039/c3 a15273a.
(6) Ali, G.; Lee, J.-H.; Susan o, D.; Choi, S.-W.; Cho, B. W.; Nam,
K.-W.; Chung, K. Y. Poly hiophene-W apped Oli ine NaFePO4 as
a Ca hode o Na-Ion Ba e ies. ACS Appl. Ma e . In e aces
2016, 8 (24), 15422–15429.
h ps://doi.o g/10.1021/acsami.6b04014.
(7) Lepage, D.; Sobh, F.; Kuss, C.; Liang, G.; Schougaa d, S. B.
Deli hia ion Kine ics S udy o Ca bon Coa ed and Ca bon F ee
LiFePO4. J. Powe Sou ces 2014, 256, 61–65.
h ps://doi.o g/10.1016/j.jpowsou .2013.12.054.
(8) Ni, J.; Wang, Y. Tempe a u e-D i en S uc u al E olu ion o
Ca bon Modi ied LiFePO4 in Ai . RSC Ad . 2015, 5 (39), 30537–
30541. h ps://doi.o g/10.1039/C5RA04744G.
(9) Ouaneche, T.; S ie ano, L.; Moncondui , L.; Gué y, C.; Soug a i,
M. T.; Recham, N. Oli ine NaMn0.66 Fe0.34 PO4 as a Ca hode
Ma e ial o Ad anced Sodium Ion Ba e ies. Ba e . Supe caps
2024, e202400214. h ps://doi.o g/10.1002/ba .202400214.
(10) Ke e , C.; Mighell, A. D.; Maue , F.; Swanson, H. E.; Block,
S. C ys al S uc u e o Twinned Low-Tempe a u e Li hium
Phospha e. Ino g. Chem. 1967, 6 (1), 119–125.
h ps://doi.o g/10.1021/ic50047a027.
(11) Padhi, A. K.; Nanjundaswamy, K. S.; Goodenough, J. B.
Phospho‐oli ines as Posi i e‐Elec ode Ma e ials o Recha geable
Li hium Ba e ies. J. Elec ochem. Soc. 1997, 144 (4), 1188–
1194. h ps://doi.o g/10.1149/1.1837571.
(12) Galce an, M.; Sau el, D.; Acebedo, B.; Rodda is, V. V.; Ma in,
E.; Rojo, T.; Casas-Cabanas, M. The Mechanism o NaFePO4
(de)Sodia ion De e mined by in Si u X-Ray Di ac ion. Phys
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cha ac e iza ion
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Chem Chem Phys 2014, 16 (19), 8837–8842.
h ps://doi.o g/10.1039/C4CP01089B.
(13) Whi eside, A.; Fishe , C. A. J.; Pa ke , S. C.; Sai ul Islam, M.
Pa icle Shapes and Su ace S uc u es o Oli ine NaFePO4 in
Compa ison o LiFePO4. Phys Chem Chem Phys 2014, 16 (39),
21788–21794. h ps://doi.o g/10.1039/C4CP02356K.
(14) Wang, D.; Wu, Y.; L , J.; Wang, R.; Xu, S. Ca bon
Encapsula ed Ma ici e NaFePO4 Nanopa icles as Ca hode
Ma e ial o Sodium-Ion Ba e ies. Colloids Su . Physicochem.
Eng. Asp. 2019, 583, 123957.
h ps://doi.o g/10.1016/j.colsu a.2019.123957.
(15) Kim, J.; Seo, D.-H.; Kim, H.; Pa k, I.; Yoo, J.-K.; Jung, S.-K.;
Pa k, Y.-U.; Godda d Iii, W. A.; Kang, K. Unexpec ed Disco e y
o Low-Cos Ma ici e NaFePO4 as a High-Pe o mance Elec ode
o Na-Ion Ba e ies. Ene gy En i on. Sci. 2015, 8 (2), 540–545.
h ps://doi.o g/10.1039/C4EE03215B.
(16) Liu, Y.; Zhang, N.; Wang, F.; Liu, X.; Jiao, L.; Fan, L.
App oaching he Downsizing Limi o Ma ici e NaFePO4 owa d
High‐Pe o mance Ca hode o Sodium‐Ion Ba e ies. Ad . Func .
Ma e . 2018, 28 (30), 1801917.
h ps://doi.o g/10.1002/ad m.201801917.
(17) Hwang, J.; Ma sumo o, K.; O ikasa, Y.; Ka ayama, M.; Inada,
Y.; Nohi a, T.; Hagiwa a, R. C ys alline Ma ici e NaFePO4 as a
Posi i e Elec ode Ma e ial o Sodium Seconda y Ba e ies
Ope a ing a In e media e Tempe a u e. J. Powe Sou ces 2018,
377, 80–86. h ps://doi.o g/10.1016/j.jpowsou .2017.12.003.
(18) Ma, X.; Xia, J.; Wu, X.; Pan, Z.; Shen, P. K. Rema kable
Enhancemen in he Elec ochemical Ac i i y o Ma ici e NaFePO4
on High-Su ace-A ea Ca bon Clo h o Sodium-Ion Ba e ies.
Ca bon 2019, 146, 78–87.
h ps://doi.o g/10.1016/j.ca bon.2019.02.004.
(19) Jeong, S.; Kim, B. H.; Pa k, Y. D.; Lee, C. Y.; Mun, J.; T on,
A. A i icially Coa ed NaFePO4 o Aqueous Recha geable Sodium-
Ion Ba e ies. J. Alloys Compd. 2019, 784, 720–726.
h ps://doi.o g/10.1016/j.jallcom.2019.01.046.
(20) Heubne , C.; Heiden, S.; Schneide , M.; Michaelis, A. In-Si u
P epa a ion and Elec ochemical Cha ac e iza ion o Submic on
Sized NaFePO4 Ca hode Ma e ial o Sodium-Ion Ba e ies.
Elec ochimica Ac a 2017, 233, 78–84.
h ps://doi.o g/10.1016/j.elec ac a.2017.02.107.
(21) Fe nández-Rope o, A. J.; Sau el, D.; Acebedo, B.; Rojo, T.;
Casas-Cabanas, M. Elec ochemical Cha ac e iza ion o NaFePO4
as Posi i e Elec ode in Aqueous Sodium-Ion Ba e ies. J. Powe
Sou ces 2015, 291, 40–45.
h ps://doi.o g/10.1016/j.jpowsou .2015.05.006.
(22) Xu, Y.; Dai, R.; Wang, X.; Qiao, Z.; Wen, H.; Ruan, D.; Wang,
Y. High-Pe o mance T iphyli e-NaFePO4 Syn hesized by
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97
Sol o he mal Sodium Inse ion P ocess o Sodium-Ion Ba e ies.
Chem. Phys. Le . 2024, 834, 140983.
h ps://doi.o g/10.1016/j.cple .2023.140983.
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4. Di ec syn hesis o ansi ion me al phospha e-based
polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
105
Table 4-3. Equilib ium cons an s o he possible species o med du ing he
syn hesis.
Chemical equilib ium
Equilib ium cons an
(K) exp ession
Value
o K
H2O ⇋H++OH-
Ke=[H+]·[OH-]
10-14
H++SO4
2- ⇋HSO4
-
K2=[HSO4
-]
[H+]·[SO4
2-]
101.99
H++HSO4
-⇋ H2SO4
K3=[H2SO4]
[H+]·[SO4
2-]
10-3
H++PO4
3- ⇋ HPO4
2-
K4=[HPO4
2-]
[H+]·[PO4
3-]
1012.38
H++HPO4
2- ⇋ H2PO4
-
K5=[H2PO4
-]
[H+]·[HPO4
2-]
107.2
H++H2PO4
- ⇋ H3PO4
K6=[H3PO4]
[H+]·[H2PO4
-]
102.15
OH-+Na+⇋ NaOH
β7=[NaOH]
[OH-]·[Na+]
10-0.2
SO4
2-+Na+⇋ NaSO4
-
β8=[NaSO4
-]
[SO4
2-]·[Na+]
100.7
CH3COO-+Na+⇋ NaCH3COO-
β9=[NaCH3COO]
[CH3COO-]·[Na+]
10−4.74
OH-+Mn2+⇋ MnOH+
β10=[MnOH+]
[OH-]·[Mn2+]
104.6
Mn2++SO4
2- ⇋ MnSO4
β11=[MnSO4]
[SO4
2-]·[Mn2+]
102.67
3Mn2++2PO4
3- ⇋ Mn3(PO4)2
β12=[Mn3(PO4)2]
[PO4
3-]2·[Mn2+]3
10-25
Mn2++HPO4
2- ⇋ MnHPO4
β13=[MnHPO4]
[HPO4
2-]·[Mn2+]
10-12.95
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4. Di ec syn hesis o ansi ion me al phospha e-based
polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
106
4.4. Syn hesis and phase iden i ica ion o
NaxMn1-yFeyPO4 o (0 ≤ y ≤ 1)
4.4.1. Syn hesis and phase iden i ica ion o
na ophili e NaMnPO4
The hyd o he mal syn hesis o na ophili e NaMnPO4 was ca ied ou
by adap ing he expe imen al condi ions p e iously epo ed o he
syn hesis o he isos uc u al li hiophili e LiMnPO4.2 An aqueous
solu ion was p epa ed by dissol ing NaOH, MnSO4·H2O and H3PO4 in
a mola a io o 3:1:1, co esponding o 1.456 g o NaOH, 2.420 g o
MnSO4·H2O and 1.384 g o H3PO4 in a o al olume o 30 ml o H2O.
The p ecu so solu ion was ans e ed o a 45 ml PTFE-line ha was
hen sealed wi hin a PARR s ainless s eel au ocla e. Then, he
au ocla e was placed in o a mu le u nace and hea ed up o 180 ºC
o 4h. A e comple ion o he eac ion, he au ocla e was cooled o
oom empe a u e and he ob ained solu ion was il e ed and insed
wi h dis illed wa e o emo e any esidual soluble species. The
powde ob ained, he ea e e e ed o as HT_NaMn, was
cha ac e ized by XRD as shown in Figu e 4.2, con i ming he
success ul o ma ion o pu e na ophili e NaMnPO4.
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4. Di ec syn hesis o ansi ion me al phospha e-based
polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
107
Figu e 4.2. XRD pa e n o he syn hesized HT_NaMn ma ching wi h he
epo ed na ophili e NaMnPO4 (ICSD code: 36249).
4.4.2. Syn hesis and phase iden i ica ion o
iphyli e NaMn1-yFeyPO4 (y = 0.25, 0.50, and 0.75)
The syn hesis o iphyli e NaMn1-yFeyPO4 (y = 0.25, 0.50 and 0.75)
solid solu ion was p epa ed using he same hyd o he mal syn hesis
p o ocol p e iously desc ibed o na ophili e NaMnPO4. Fo each
a ge composi ion, he amoun o MnSO4·H2O was pa ially eplaced
by FeSO4·7H2O in acco dance wi h he desi ed Mn:Fe s oichiome y.
The eac ion condi ions, including he mola a io o eac an s, o al
sol en olume, au ocla e ype, and hea ing empe a u e (180 °C),
we e kep cons an o ensu e compa abili y. The esul ing ma e ials
we e labeled as HT_ Mn75Fe25 (y = 0.25), HT_ Mn50Fe50 (y =
0.50), HT_ Mn25Fe75 (y = 0.75).
A e ca e ul analysis o he XRD pa e ns o he ob ained compounds
(see Figu e 4.3), i was obse ed ha in HT_ Mn75Fe25 and
HT_ Mn50Fe50 he iphyli e phase is ob ained along wi h Fe3O4
impu i ies, while in HT_ Mn25Fe75 an uniden i ied phase is
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4. Di ec syn hesis o ansi ion me al phospha e-based
polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
108
ob ained ins ead. These indings will be u he discussed la e in
sec ion 4.5.
Figu e 4.3. XRD pa e ns o he syn hesized samples HT_ Mn75Fe25,
HT_ Mn50Fe50 and HT_ Mn25Fe75 compa ed wi h he epo ed na ophili e
NaMnPO4 (ICSD code: 36249).
4.4.3. E ec o he pH on iphyli e
NaMn0.25Fe0.75PO4
4.4.3.1. E ec o dec easing he pH
In an e o o explo e he in luence o pH on he phase o ma ion
du ing hyd o he mal syn hesis, a ge ed modi ica ions we e made o
he eac ion mix u e o p omo e he c ys alliza ion o he iphyli e
NaMn0.25Fe0.75PO4 phase. This s a egy was designed o lowe he pH
o he solu ion o de e mine whe he his adjus men could
he modynamically a o he o ma ion o he a ge ed iphyli e
phase, pa icula ly wi h high Fe con en (such as NaMn0.25Fe0.75PO4).
In he i s app oach, NaOH (used as he p ima y sodium sou ce in
p e ious syn heses) was eplaced by Na2SO4. This modi ica ion
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4. Di ec syn hesis o ansi ion me al phospha e-based
polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
109
signi ican ly educed he pH o he eac ion mix u e (below 6), as
Na2SO4 is a neu al sal compa ed o he s ongly basic NaOH. To
accoun o he di e ence in sodium con en (Na2SO4 p o iding wo
Na equi alen s pe o mula uni ), he mola a ion o Na2SO4:H3PO4
mola a io was adjus ed o 1.5:1 ins ead o 3:1 a ion used in he
o iginal syn hesis using NaOH. The ob ained compound, labeled as
HT75_Na2SO4 (whe e HT e e s o hyd o he mal syn hesis, and
“75” indica es he Fe con en o 0.75), was cha ac e ized by XRD.
The XRD pa e n (Figu e 4.4) indica ed he o ma ion o he
alluaudi e NaMn(Mn,Fe)2(PO4)3 phase, which c ys allizes in he
monoclinic sys em wi h C2/c space g oup. No ace no e idence o
he iphyli e phase was obse ed.
Figu e 4.4. XRD pa e n o syn hesized HT75_Na2SO4 ma ching wi h he
epo ed alluaudi e NaMnFe2(PO4)3 (ICSD code: 261050).
In he second app oach, NaCH3COO as a weake base compa ed
NaOH, was used as a sodium sou ed. Gi en ha NaCH3COO p o ides
he same numbe o Na+ equi alen s pe uni o mula as NaOH, he
NaCH3COO:H3PO4 mola a io was main ained a 3:1, consis en wi h
he o iginal expe imen (1). The esul ing p oduc , labeled
HT75_NaCH3COO, was also cha ac e ized by XRD. Simila o he
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4. Di ec syn hesis o ansi ion me al phospha e-based
polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
110
p e ious expe imen wi h Na2SO4, he XRD pa e n (Figu e 4.5) also
co esponded o he alluaudi e NaMn(Mn,Fe)2(PO4)3 phase
(monoclinic sys em wi h C2/c as a space g oup). A se o addi ional
peaks co esponding o uniden i ied impu i y phases we e obse ed.
Figu e 4.5. XRD pa e n o he syn hesized HT75_NaCH3COO ma ching wi h
he epo ed alluaudi e NaMnFe2(PO4)3 (ICSD code: 261050).
Summa izing, hese esul s sugges ha lowe ing he pH o he
eac ion mix u e h ough subs i u ion o he sodium sou ce wi h
ei he Na₂SO₄ o NaCH₃COO does no p omo e he o ma ion o he
iphyli e phase a high Fe con en . Ins ead, bo h app oaches a o
he c ys alliza ion o he alluaudi e- ype NaMn(Mn,Fe)2(PO4)3
s uc u e. The expe imen al pa ame e s and esul s o he wo
app oaches a e summa ized in Table 4-4.
Table 4-4. Reagen s a io and ob ained phase o he iphyli e a ge ed
composi ions dec easing he pH.
Syn hesis
conde
Ta ge ed
composi ion
Na Sou ce
( a io)
MnSO4·
H2O
FeSO4·
7H2O
H3PO4
Ob ained
phase
HT_Na2SO
4
NaMn0.25Fe0.75PO4
Na2SO4
(1.5)
0.25
0.75
1
Alluaudi e
HT_NaCH3
COO
NaMn0.25Fe0.75PO4
NaCH3COO
(3)
0.25
0.75
1
Alluaudi e
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4. Di ec syn hesis o ansi ion me al phospha e-based
polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
111
4.4.3.2. E ec o inc easing he pH
To encou age he o ma ion o he iphyli e NaMn1-yFeyPO4 phase, we
sys ema ically examined he e ec o pH by adjus ing he
NaOH:H3PO4 mola a io. An alkaline syn hesis en i onmen , such as
hose c ea ed by a NaOH:H3PO4 a io o 4:1, is conside ed a o able
o iphyli e s abiliza ion. The ob ained samples we e labeled
acco ding o hei a ge ed composi ion: HT_ Mn75Fe25pH10-12
o NaMn0.75Fe0.25PO4, HT_ Mn50Fe50pH10-12 o
NaMn0.50Fe0.50PO4 and HT_ Mn25Fe75pH10-12 o
NaMn0.25Fe0.75PO4.
The inal syn hesized compounds we e analyzed by XRD (Figu e 4.6.)
e ealing he success ul o ma ion o iphyli e polymo phs o he
a ge ed composi ions NaMn1-yFeyPO4 in he ange 0.25 ≤ y ≤ 1
(Table 4-5).
Figu e 4.6. XRD pa e ns o he syn hesized HT_ Fe25pH10, HT_ Fe50pH10
and HT_ Fe75pH10, ma ching wi h he na ophili e/ iphyli e NaMnPO4 phase
(ICSD code: 36249).
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4. Di ec syn hesis o ansi ion me al phospha e-based
polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
112
Table 4-5. Reagen s a io and ob ained phase o he iphyli e a ge ed
composi ions inc easing he pH.
Syn hesis
code
Ta ge ed
composi ion
NaOH
MnSO4·
H2O
FeSO4
·7H2O
H3PO4
Ob ained
phase
HT_ Mn75Fe
25pH10-12
NaMn0.75Fe0.25PO4
4
0.75
0.25
1
T iphyli e
HT_ Mn50Fe
50pH10-12
NaMn0.50Fe0.50PO4
4
0.5
0.5
1
T iphyli e
HT_ Mn25Fe
75_pH10-12
NaMn0.25Fe0.75PO4
4
0.25
0.75
1
T iphyli e
O e all, hese obse a ions indica e ha highe pH alues a o he
s abiliza ion o he iphyli e phase, a end ha emains e iden e en
wi h inc easing Fe con en in he ma e ial.
4.4.4. Syn hesis o NaMn1-yFeyPO4 subs i u ing Mn
wi h Fe p og essi ely
To sys ema ically in es iga e he e ec o p og essi e Fe subs i u ion
on he iphyli e NaMn1-yFeyPO4 phase, a se ies o composi ions wi h
inc emen al Fe con en (Δy = 0.05) was syn hesized unde he same
hyd o he mal condi ions as desc ibed in sec ion 4.4.2. The a ge ed
composi ions spanned he ange 0.25 > y > 0.90.
As Figu e 4.7 shows, XRD analysis con i med he o ma ion o
iphyli e phase o a ge ed composi ions in he ange o 0.25 ≥ y ≥
0.60. Howe e , inc easing Fe con en , he p esence o Fe3O4 peaks
becomes p og essi ely mo e p ominen in he XRD pa e ns. This
sugges incomple e inco po a ion o Fe in o he iphyli e NaMn1-
yFeyPO4 phase and implies ha he ac ual Fe con en in he
syn hesized phases is lowe han he nominal a ge . Fu he mo e,
o composi ions wi h y > 0.60, he XRD pa e ns exhibi addi ional
di ac ion peaks ha do no ma ch any known iphyli e o
na ophili e phases, indica ing he o ma ion o an uniden i ied
seconda y phase. Table 4-6 summa izes all he esul s.
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4. Di ec syn hesis o ansi ion me al phospha e-based polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
113
Figu e 4.7. XRD pa e ns o NaMn1-yFeyPO4 samples subs i u ing Mn wi h Fe p og essi ely compa ed wi h na ophili e NaMnPO4
om he da abase (ICSD code: 36249).
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4. Di ec syn hesis o ansi ion me al phospha e-based polymo phs Nax(TM)y(PO4)z (TM = Mn, Fe)
114
Table 4-6. Reagen s a io and ob ained phase o he di e en iphyli e a ge ed composi ions eplacing p og essi ely Mn o
Fe.
Syn hesis code
Ta ge ed composi ion
NaOH
MnSO4·H2O
FeSO4·7H2O
H3PO4
Ob ained phase
HTp og_ NaMnPO4
NaMnPO4
3
1
0
1
Na ophili e
HTp og_ Mn75Fe25
NaMn0.75Fe0.25PO4
3
0.75
0.25
1
T iphyli e, Fe2O3
HTp og_ Mn70Fe30
NaMn0.70Fe0.30PO4
3
0.70
0.30
1
T iphyli e, Fe2O3
HTp og_ Mn65Fe35
NaMn0.65Fe0.35PO4
3
0.65
0.35
1
T iphyli e, Fe2O3
HTp og_ Mn60Fe40
NaMn0.60Fe0.40PO4
3
0.60
0.40
1
T iphyli e, Fe2O3
HTp og_ Mn55Fe45
NaMn0.55Fe0.45PO4
3
0.55
0.45
1
T iphyli e, Fe2O3
HTp og_ Mn50Fe50
NaMn0.50Fe0.50PO4
3
0.50
0.50
1
T iphyli e, Fe2O3
HTp og_ Mn45Fe55
NaMn0.45Fe0.55PO4
3
0.45
0.55
1
T iphyli e, Fe2O3
HTp og_ Mn40Fe60
NaMn0.40Fe0.60PO4
3
0.40
0.60
1
T iphyli e, Fe2O3, Unde e mined
HTp og_ Mn35Fe65
NaMn0.35Fe0.65PO4
3
0.35
0.65
1
Unde e mined
HTp og_ Mn30Fe70
NaMn0.30Fe0.70PO4
3
0.30
0.70
1
Unde e mined
HTp og_ Mn25Fe75
NaMn0.25Fe0.75PO4
3
0.25
0.75
1
Unde e mined
HTp og_ Mn20Fe80
NaMn0.20Fe0.80PO4
3
0.20
0.80
1
Unde e mined
HTp og_ Mn15Fe85
NaMn0.15Fe0.85PO4
3
0.15
0.85
1
Unde e mined
HTp og_ Mn10Fe90
NaMn0.10Fe0.90PO4
3
0.10
0.90
1
Unde e mined
HTp og_ Fe100
NaFePO4
3
0
1
1
Unde e mined
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Lis o con ibu ions
218
Con e ences and exhibi ions
XXXVI Reunión Bienal de la Real Sociedad Española de
Química (Si ges, 2017), wi h an O al Communica ion: Sín esis ácil
y económica de NaFePO4 oli ino como elec odo posi i o en ba e ías
de ion sodio.
Powe ou u u e 2017 (Vi o ia-Gas eiz, 2017), wi h a pos e
Easy and low-cos syn hesis and elec ochemical pe o mance o
oli ine NaFePO4 as posi i e elec ode o sodium-ion ba e ies.
E-MRS 2019 Sp ing Mee ing - IUMRS-ICAM In e na ional
(Nice, 2019) Con e ence on Ad anced Ma e ials, wi h an O al
Communica ion: A no el low-cos syn hesis o oli ine NaFePO4 as
posi i e elec ode o
sodium-ion ba e ies.
Powe ou u u e 2019 (Vi o ia-Gas eiz, 2019), wi h a pos e :
G een and low-cos syn hesis o oli ine NaFePO4 as posi i e
elec odes o sodium-ion ba e ies.
CIRMAT (Mad id, 2022): wi h a pos e : Sus ainable syn hesis o
iphyli e NaFePO4 as posi i e elec ode o sodium ion ba e ies:
om ma e ials o ecycling.
The Ba e y Show 2023 (2023, S u ga )
Ad anced Au omo i e Ba e y Con e ence (2024, S asbou g)
P ojec s
Ibe d ola P ojec (2020-2021): Analysis o he Posi i e Impac o
he Applica ion o Sus ainable Sodium-Ion Ba e ies in he Elec ic
G id. (P.I.: Ca los Manuel Be langa C uzado)
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