Ci a ion: Landa-Med ano, I.;
Eguia-Ba io, A.; Sananes-Is ael, S.;
Po che , W.; T ad, K.; Mo e i, A.;
Ca alho, D.V.; Passe ini, S.; de
Mea za, I. Insigh s in o he
Elec ochemical Pe o mance o 1.8
Ah Pouch and 18650 Cylind ical
NMC:LFP|Si:C Blend Li-ion Cells.
Ba e ies 2022,8, 97. h ps://doi.o g/
10.3390/ba e ies8080097
Academic Edi o : Biao Li
Recei ed: 25 July 2022
Accep ed: 16 Augus 2022
Published: 18 Augus 2022
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
Copy igh : © 2022 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
ba e ies
A icle
Insigh s in o he Elec ochemical Pe o mance o 1.8 Ah Pouch
and 18650 Cylind ical NMC:LFP|Si:C Blend Li-ion Cells
Imanol Landa-Med ano 1, Ai o Eguia-Ba io 1, Susan Sananes-Is ael 1, Willy Po che 2, Khiem T ad 3,
A ianna Mo e i 4,5 , Diogo Viei a Ca alho 4,5,† , S e ano Passe ini 4,5 and I a xe de Mea za 1,6,*
1CIDETEC Basque Resea ch and Technology Alliance (BRTA), Paseo Mi amon 196,
20014 Donos ia-San Sebas ian, Spain
2CEA-LITEN, G enoble Uni e si éAlpes, 17 A enue des Ma y s, 38000 G enoble, F ance
3VITO/Ene gyVille, Uni Ene gy Technology, Tho Pa k 8310, 3600 Genk, Belgium
4Helmhol z Ins i u e Ulm (HIU), Helmhol zs asse 11, 89081 Ulm, Ge many
5Ka ls uhe Ins i u e o Technology (KIT), 76021 Ka ls uhe, Ge many
6Depa men o O ganic and Ino ganic Chemis y, Uni e sidad del País Vasco (UPV/EHU),
48080 Bilbao, Spain
*Co espondence: [email p o ec ed]
† Cu en add ess: Johnson Ma hey Technology Cen e, Bloun ’s Cou , Sonning Common,
Reading RG4 9NH, UK.
Abs ac :
Silicon has become an in eg al nega i e elec ode componen o li hium-ion ba e ies
in nume ous applica ions including elec ic ehicles and enewable ene gy sou ces. Howe e , i s
high capaci y and low cycling s abili y ep esen a signi ican ade-o ha limi s i s widesp ead
implemen a ion in high ac ions in he nega i e elec ode. He ein, we assembled high-capaci y
(
1.8 Ah
) cells using a nanopa icula e silicon–g aphi e (1:7.1) blend as he nega i e elec ode ma e ial
and a LiFePO
4
–LiNi
0.5
Mn
0.3
Co
0.2
O
2
(1:1) blend as he posi i e elec ode. Two ypes o cells we e
cons uc ed: cylind ical 18650 and pouch cells. These cells we e subjec ed bo h o calenda and
cycling aging, he la e explo ing di e en wo king ol age windows (2.5–3.6 V,
3.6–4.5 V
, and
2.5–4.5 V)
. In addi ion, one cell was opened and cha ac e ised a i s end o li e by means o X- ay
di ac ion, scanning elec on mic oscopy, and u he elec ochemical es s o he aged elec odes. Si
deg ada ion was iden i ied as he p ima y cause o capaci y ade o he cells. This wo k highligh s
he need o de elop no el s a egies o mi iga e he issues associa ed wi h he excessi e olume ic
changes o Si.
Keywo ds:
li hium-ion ba e ies; silicon g aphi e anodes; LFP; NMC; elec ode manu ac u ing;
cell o ma s
1. In oduc ion
Li hium-ion ba e ies (LIBs) ha e in luenced he echnological de elopmen s o he
las 30 yea s, om po able elec onics o elec ic ehicles (EVs). Rega ding he la e ,
almos all ca manu ac u e s o e an elec ic model based on di e en LIB chemis ies [
1
,
2
].
Ne e heless, i is well known ha many ca use s os e conce ns ega ding ‘d i ing ange
anxie y’, which is caused by he limi ed mileage ha EVs can achie e wi hou echa ging,
he a ailabili y o echa ging poin s, and he sho e d i ing ange unde ce ain clima ic
condi ions (such as low empe a u e) [
1
]. As a esul , i is necessa y o de elop no el
ma e ials capable o p o iding highe capaci ies a highe ol ages, which ansla e in o
highe ene gy densi ies.
LiFePO
4
(LFP) is he sa es , s a e-o - he-a ca hode ma e ial o au omo i e applica-
ions. In ac , i has been selec ed by Tesla o he Model 3 [
3
]. LFP can p o ide
170 mAh·g−1
a an a e age ol age o 3.45 V s. Li, oughly p o iding 586 Wh
·
kg
LFP−1
[
4
]. In o de o
inc ease he ene gy densi y o LIBs, many EV manu ac u e s ha e chosen laye ed me al
oxides as ca hode ma e ial ins ead o LFP. Among hese laye ed oxides, LiNi
x
Mn
y
Co
z
O
2
Ba e ies 2022,8, 97. h ps://doi.o g/10.3390/ba e ies8080097 h ps://www.mdpi.com/jou nal/ba e ies
Ba e ies 2022,8, 97 2 o 15
(NMC) and LiNi
x
Co
y
Al
z
O
2
(NCA), bo h wi h x + y + z = 1, ha e been used in di e -
en EV models [
1
,
5
]. Many o hese ma e ials can p o ide highe capaci ies a highe
ol ages, leading o highe ene gy densi ies [
6
,
7
]. In pa icula , esea ch associa ed wi h
NMCs has pu sued a dec ease in cobal con en in he ma e ial eplacing cobal wi h
nickel, which is cheape and can lead o highe capaci ies [
8
,
9
]. In his con ex , NMC111
(
Ni:Mn:Co = 0.33:0.33:0.33
) has been subsequen ly eplaced by NMC532, NMC622, and
ul ima ely NMC811 [
10
,
11
]. Ne e heless, he e is a ade-o be ween he high capaci y
esul ing om high nickel con en and he cycle li e, as well as he he mal s abili y o hese
ma e ials [10,11].
Rega ding he nega i e elec ode, g aphi e, which possesses a 372 mAh·g−1capaci y
and a edox po en ial o 0.1 V s. Li
+
/Li, has been he p edominan ma e ial o he las
25 yea s [
12
]. Only Li
4
Ti
5
O
12
(LTO) has ques ioned he sup emacy o g aphi e, mos ly o
powe applica ions [
13
]. Howe e , i s low discha ge capaci y (175 mAh
·
g
−1
) and high
edox po en ial (1.55 V s. Li
+
/Li) limi i s implemen a ion in high-ene gy applica ions [
4
].
Ne e heless, g aphi e is insu icien o achie e he highes olume ic ene gy densi y
goals [
14
,
15
]. Thus, i has been blended wi h silicon oxide (SiO
x
) and silicon (Si) o enhance
i s capaci y and ene gy densi y [
12
,
16
]. Silicon o e s an excellen capaci y and wo ks a
~0.4 V
s. Li
+
/Li, which makes i an ideal candida e as an anode ma e ial [
17
,
18
]. None he-
less, he d awback o his ma e ial is i s low cycling s abili y; i s immense capaci y is
associa ed wi h a signi ican olume ic expansion (+280%) ha comp omises he mechani-
cal s abili y o Si anodes [
19
,
20
]. The con inuous expansion/con ac ion cycles du ing he
li hia ion/deli hia ion cycles lead o he hickening o he solid elec oly e in e phase (SEI)
and ac u e o he Si pa icles, causing he elec ic disconnec ion o hese pa icles [
18
,
21
].
This loss o ac i e ma e ial causes a g adual capaci y dec ease wi h he numbe o cycles;
hus, Si displays a limi ed cycle li e [
16
,
22
]. Si is usually combined wi h g aphi e in small
ac ions o ob ain a comp omise be ween an inc eased ene gy densi y and an accep able
cycle li e. Ne e heless, he exploi a ion o silicon as an ac i e ma e ial canno be based
on he dec ease in i s concen a ion un il i is unc ional; i is necessa y o de e mine he
eac ions occu ing in he ma e ial upon li hia ion/deli hia ion o op imise i s use.
Theo e ically and a high empe a u es, Si is sequen ially li hia ed om i s o iginal
phase o c ys alline phases Li
12
Si
7
, Li
7
Si
3
, Li
13
Si
4
, and Li
22
Si
5
, p o iding a o al capaci y
o 4200 mAh
·
g
−1
[
23
]. A oom empe a u e and in eal LIBs, howe e , Si unde goes a
wo-phase li hia ion in which he in e media e phases a e amo phous [
24
]. By he end o he
li hia ion, no Li
22
Si
5
is o med; he me as able and c ys alline Li
15
Si
4
is he silicon phase [
23
].
The capaci y ha can be ob ained wi h he li hia ion o Si o Li
22
Si
5
is
3579 mAh·g−1[25].
Du ing subsequen deli hia ion, he c ys alline Li
15
Si
4
is emo ed, and an amo phous
phase is ob ained [
23
]. Thus, analysis by means o X- ay di ac ion (XRD) can p o ide
aluable in o ma ion on he deg ee o li hia ion o Si [26].
Ano he key aspec in he de elopmen o high-ene gy LIBs is he o ma o he cells.
The e a e h ee main ca ego ies: p isma ic, cylind ical, and pouch [
4
]. Cylind ical cells
a e he mos widely implemen ed o ma [
27
]. Thei dense con aine helps o p e en
de o ma ion due o swelling in he p esence o side eac ions [
28
]. They a e de ined wi h
a nume ic code (XXYYY) in which he i s wo numbe s (XX) ep esen he diame e in
mm, and he emaining numbe s (YYY) ep esen he heigh o he cell in en hs o mm [
2
]
Among hem, he 18650 cells a e he mos popula ; hese cells we e ini ially manu ac u ed
by Sony o hei came as, and he leng h o 65 mm is due o space limi a ions in such a
de ice designed o be held in he palm o a single adul hand [
29
]. On he o he hand, he
diame e o 18 mm was selec ed due o sa e y easons; i was de e mined as he maximum
size o a oid he mal unaway o a cell o ~1 Ah capaci y [
29
]. Recen ly, TESLA has
announced he shi o 4860 cylind ical cells, despi e he sa e y issues ha can a ise [
30
],
which will p obably ha e an impac on he cell size selec ed by o he EV de elope s.
E en i cylind ical cells a e he i s op ion o indus y, hei low packing densi y and
poo hea anspo mo i a ed ba e y de elope s o sea ch o al e na i es. P isma ic cells,
wi h ha d casings simila o hose o cylind ical cells, p o ide sa e y owa ds swelling wi h
Ba e ies 2022,8, 97 3 o 15
inc eased packing densi y, bu hei ene gy densi y is ~20% lowe han ha o cylind ical
cells [
5
]. In any case, mos manu ac u e s selec his o ma in hei EVs [
27
]. In addi ion, i
is belie ed ha pouch cells (p isma ic cells wi h a so packaging) will be able o ou pe o m
hei compe i o s, becoming he p ima y op ion in he nea u u e [28].
In his wo k, high-ene gy cells wi h 1.8 Ah capaci y we e assembled in wo di e en
o ma s o assess he impac o he cell design and casing/packaging: 18650 cylind ical and
pouch. The anode consis ed o a g aphi e/Si mix ma e ial, while he ca hode comp ised o
an LFP/NMC532 blend. A combina ion o ma e ials was u ilised o inc ease he ene gy
densi y o he elec odes h ough he addi ion o NMC532 and Si o he s able-cycle-li e
LFP and g aphi e, espec i ely. NMC532 was selec ed due o i s good comp omise be ween
high capaci y and s abili y a high ol ages [31]. Bo h ypes o cells we e assembled using
he same ba ch o elec odes and subjec ed o he same cycling p o ocols. The calenda
ageing o some cells was in es iga ed, while he cycling age o he o he cells was s udied
using h ee di e en wo king ol ages. Las ly, one cell was opened and cha ac e ised a he
end o i s cycle li e.
2. Ma e ials and Me hods (Expe imen al)
2.1. Anode Manu ac u ing
The nega i e elec ode o his wo k was p epa ed a CIDETEC’s elec ode manu ac u -
ing line. The componen s o his elec ode we e nanopa icula e silicon (N-100, Tekna, Solli,
Oslo) and g aphi e (MEG-2C, SGL Ca bon, Mei ingen, Ge many) as anode ac i e ma e i-
als, Supe C45 ca bon (Ime ys, Pa is, F ance) as he conduc i e addi i e, ca boxyme hyl
cellulose (CMC, Wallocel DOW, Midland, MI, USA) as he dispe san and binde , and
s y ene bu adiene ubbe (SBR, JSRmic o, Leu en, Belgium) as he co-binde . These compo-
nen s we e mixed in a weigh a io o [Si/G /C45/CMC/SBR] = 10.4/74.6/5/5/5. The
expe imen s pe o med o de ine he anode o mula ion a e shown in Figu e S1.
The componen s we e wa e -p ocessed in a plane a y mixe . In addi ion, he p oce-
du e was adap ed o elimina e agglome a es ia p e-dispe sion o Si in he CMC solu ion
and addi ion o he solids (C45 and g aphi e) a di e en s eps and he SBR la ex a he end.
Unexpec ed low slu y pH was measu ed (pH ~3), which could a ec he polyme (CMC
and especially he SBR) con o ma ion. Thus, he slu y pH was adjus ed o
pH = 6–7
by ad-
di ion o ammonia (NH
4
OH). Finally, a mi o -like we coa ing wi h minimal ish-eye spo s,
s aigh edges, wo-side alignmen wi hin <1 mm, and a ge ed loading
(2.54 mAh/cm2)
o 3.7 mg/cm2wi hin 0.3 mg/cm2de ia ion be ween aces was achie ed.
O e all, 75 m was p oduced in wo di e en coa ing wid hs (130 and 205 mm, on o
250 mm-wid h
and 10
µ
m hick Cu oil, Schlenk, Ro h, Ge many) o each o he cell o ma s
(cylind ical and pouch cells, espec i ely).
The anodes wi h 205 mm wid h o so packaged pouch cells did no need sli ing.
Elec odes we e die-cu di ec ly ( ou anodes on 14 cm wide shee ) a e calende ing, o he
s acked design o 100
×
61 mm coa ed a ea, by CIDETEC. The anode olls manu ac u ed in
130 mm wid h coa ing we e sli by CEA o cylind ical cells. To limi was e, CEA used a lab
sli ing equipmen o sli he anode coa ing.
The calende ing s ep o he anodes was aimed a an expec ed op imum po osi y
o 32% (1.41 g/cm
3
). Con ol o lexibili y pe o med by bending es (no damage when
he elec ode was wound on mand els wi h dec easing diame e ) e ealed no c acks on
he
2 mm
diame e mand el. This coupled wi h he 90
◦
peel es s eng h (67
±
2 N/m)
p o ided sa is ac o y mechanical esul s wi h e y high adhesion o he Cu cu en collec o .
2.2. Ca hode Manu ac u ing
The posi i e elec ode in he cu en wo k was de eloped in CEA and hen upscaled,
adap ing iscosi y wi h coa ing equipmen capabili y o 50 L o slu y and a coa ing
machine wi h an o en o 5 m leng h (Meg ec, De Pe e, WI, USA). The posi i e elec ode con-
sis ed o LiFePO
4
(LFP, beLi e, Dnip ope o sk, Uk aine) and LiNi
0.5
Mn
0.3
Co
0.2
O
2
(NMC532) as
ac i e ma e ials, Supe C65 ca bon black (Ime ys, Pa is, F ance) as he conduc i e addi i e, and
Ba e ies 2022,8, 97 4 o 15
poly inylidene luo ide (PVDF, Sol ay Sole
®
5130, B ussels, Belgium) as he binde . The weigh
a io o hese componen s was
[LFP/NMC/C45/PVDF] = 45.25/45.25/5/4.5
. Finally, CEA
coa ed 380 m o wo-sided elec ode om he slu y on o an aluminium cu en collec o o
20
µ
m hickness and a wid h o 30 cm (Hyd o, Oslo, No way). The loading o his coa ing
was 14.4 mg/cm
2
(2.3 mAh/cm
2
). Du ing he sli ing s ep, he elec ode wid h was adjus ed
by cu ing he coils. Then, he ca hode was calende ed o 36% po osi y (
2.3 g/cm3
). A e
calende ing, a con ol o lexibili y (sa is ac o y a 4 mm diame e bending) and adhesion
s eng h (260 ±21 N/m) was applied.
2.3. Cell Manu ac u ing
In o de o compa e he wo cell designs, bo h he cylind ical and he pouch cells con-
sis ing o he same componen s (excep he sepa a o which was speci ic o he assembly)
we e condi ioned wi h he same p o ocol. The sepa a o was a i-laye Celga d 2325 g ade
(Cha lo e, NC, USA) o he cylind ical ha d-case cells, while he s acked so packaging
cells we e assembled wi h a modi ied Celga d ECT-2015 g ade (same hickness) sui able
o he speci ic lamina ion/winding p ocess on he cell-assembly line. The elec oly e was
composed o e hylene ca bona e and dime hyl ca bona e (EC:DMC) in a olume p opo -
ion o 1:1 wi h 1 M li hium hexa luo ophospha e (LiPF
6
) and a blend o addi i es: 10%
luo oe hylene ca bona e (FEC), 2% li hium bis( i luo ome hanesul onyl)imide (LiTFSI),
and 2% inylene ca bona e (VC). The elec oly e was pu chased om UBE Indus ies.
2.3.1. Assembly o 18650 Cylind ical Cells
Cell assembly was pe o med on semiau oma ic winding equipmen inside a d y
oom wi h a dew poin o
−
40
◦
C. Each cell consis ed o a double-side coa ed 55 mm
wide ca hode and a 57 mm wide anode wi h wo 60 mm wide sepa a o s. Elec odes and
sepa a o s we e wound a ound a mand el, and he esul an jelly oll was d ied in a acuum
o en o e nigh . A e welding o he abs on he bo om and he cap o he anode and
ca hode, espec i ely, and g oo ing, he cells we e placed in an A - illed glo e box o
elec oly e illing and c imping. A pic u e o he componen s used o he assembly o
18650 cells is shown in Figu e S2.
2.3.2. Assembly o Pouch Cells
Elec odes we e cu o size in a semiau oma ic die-cu ing uni (MTI Co p., Richmond,
CA, USA) o 14 cm shee s om he elec ode olls. The ca hodes and anodes we e cu o
di e en sizes (10 cm
×
6.1 cm and 9.8
×
5.9 cm o he anodes and ca hodes, espec i ely).
Pic u es o he die-cu ing uni , a schema ic ep esen a ion o he cells, and a pic u e o he
inal cell a e shown in Figu e S3.
The s acked so -packaging cell was designed comp ising eigh ca hodes and nine
anodes pe cell. The assembly was ca ied ou in a d y oom (dew poin
−
50
◦
C) by manual
s acking o he elec odes a e acuum-d ying a 120–140
◦
C o 12 h. The p ocess, using a
guiding ool o gua an ee s ack alignmen , is depic ed by he pho og aphic sequence in
Figu e S4.
Elec ode langes ( abs) we e ul asonically welded o e minal abs (100
µ
m hick
Al (+)
and Ni-pla ed Cu (
−
)) and hen placed be ween wo hal -shells o aluminium lami-
na ed oil (ALF) pouch ma e ial (wi hou dep h- o ming) and hea sealed on h ee sides
be o e he illing s ep.
The cells we e illed wi h 11.5 g (9 mL) o elec oly e, and he emaining side was
he mally sealed unde
−
850 mba using a acuum chambe seale . The cells we e hen
eady o be o med (see Sec ion 2.4) unde ex e nal p essu e applied by sandwiching he
cell be ween wo s ainless-s eel pla es.
A e his o ma ion, he cells we e degassed and inally sealed unde ull acuum o
g ading cha ac e isa ion.
Ba e ies 2022,8, 97 5 o 15
2.4. Elec ochemical Tes s
2.4.1. Condi ioning (Fo ma ion)
The condi ioning expe imen s we e pe o med inside a empe a u e chambe se a
45
◦
C. A e a es ing pe iod o 2 h, a 1 C p e-cha ge pulse o 10 s was applied, which was
ollowed by a 3 h es pe iod o he imp egna ion o he elec oly e. A e ha , a C/10
cons an cu en cycle be ween 4.5 and 2.5 V was conduc ed, including a cons an ol age
s ep by he end o he cha ge a 4.5 V un il he cu en dec eased o C/20. A e wa ds,
he cells we e emo ed om he chambe , wai ing un il hei empe a u e d opped below
30
◦
C. A e his o ma ion, he pouch cells we e degassed and inally sealed unde ull
acuum o g ading cha ac e isa ion.
2.4.2. Calenda Ageing
A e condi ioning, ou cells pe o ma we e cha ged o 3.6 V ( wo cells pe o ma )
and 4.5 V ( wo cells pe o ma ) and s o ed a 25
◦
C o 58 days ( o he pouch cells) and
96 days
(cylind ical cells). The cells we e kep a an open-ci cui ol age s a e. The capaci y
e olu ion du ing calenda ageing was de e mined a e wo consecu i e cycles wi h a 0.3 C
cha ge and discha ge cu en a e.
2.4.3. Elec ochemical Ageing
The cycling ageing es s we e applied on cylind ical and pouch cells. Cycle ageing was
pe o med wi h a cu en o 0.3 C o bo h cha ging and discha ging wi hin h ee di e en
ol age windows: (i) be ween he minimum and maximum ol age limi s (2.5–4.5 V), which
includes he ansi ion be ween LFP and NMC and be ween wo in e media e ol ages,
(ii) 3.6–4.5 V, and (iii) 2.5–4.5 V o in es iga e he ageing deg ada ion on he di e en LFP
and NMC ol age wo king ange. Each es was ca ied ou on wo cells om he same
ba ch o ensu e he es esul epea abili y. Elec ochemical es s we e pe o med wi h a
Basy ec Cell Tes Sys em po en ios a a 25
◦
C
±
1
◦
C (a CIDETEC acili ies, Donos ia-San
Sebas ian, Spain), a Macco cycle S4000 (a Helmhol z Ins i u e Ulm, Ulm, Ge many), and
a PEC SBT0550 ba e y cycle (a CEA, G enoble, F ance).
2.5. Pos -Mo em Cha ac e isa ion
One cylind ical cell was opened o conduc pos -mo em cha ac e isa ion o i s elec-
odes. This cell was p e iously cycled a 25
◦
C and wi hin he ol age ange 2.5 V–4.5 V
un il i eached 70% s a e o heal h (SOH) a e 44 cycles. The cell was hen ully discha ged
(0% s a e o cha ge, SOC) and in oduced in an a gon- illed glo e box (MB aun, München,
Ge many) wi h O
2
and H
2
O concen a ion below 1 ppm, espec i ely. The en ing was
pie ced o e alua e he in e nal p essu e, he ee elec oly e was eco e ed by he en -
ing, and he cell case was cu . A e wa d, he elec ode oll was ex ac ed and unwound.
The posi i e and nega i e elec odes we e sepa a ed, and samples o pos -mo em and
ex ended elec ochemical analyses we e cu ou om he middle pa o he eco e ed
shee s (a oiding he ex e nal pa s o he elec odes). These samples we e insed wi h
DMC sol en ; insing ba hs o sol en we e used, in which each sample was soaked o
app oxima ely 30 s. P is ine samples we e s udied in pa allel.
Scanning elec on mic oscopy (SEM) imaging and ene gy-dispe si e X- ay spec-
oscopy (EDX) was pe o med on a ca bon-spu e ed sample using a JSM 7600F (JEOL,
Tokyo, Japan). The c ys allog aphic analysis o he di e en samples was pe o med by
means o powde XRD, using a B uke D8 Disco e di ac ome e (Cu K
α
adia ion,
λ= 0.154 nm
, Bille ica, MA, USA) equipped wi h a LynxEye PSD de ec o (S ockholm,
Sweden). The di ac og ams we e eco ded be ween 2
θ
= 10
◦
and 80
◦
a 0.003
◦·
s
−1
. XRD
and SEM analyses we e pe o med using an ine ans e chambe o p o ec he sample
om he ex e nal a mosphe e.
Las ly, some samples we e also used o assemble hal coin cells (HCCs, CR2032
con igu a ion) using li hium me al (Rockwood Li hium, 500
µ
m hick, F ank u , Ge many)
as he coun e elec ode. Elec odes o 1.13 cm
2
we e punched and assembled in an a gon-
Ba e ies 2022,8, 97 6 o 15
illed glo e box (H
2
O < 0.1 ppm, O
2
< 0.1 ppm) e sus li hium, using Wha man, GF/D
sepa a o (Maids one, UK), and 120
µ
L o 1 M o LiPF
6
in EC:DMC (1:1) + 10% FEC, 2%
LiTFSI, and 2% VC elec oly e. These cells we e subjec ed o wo cycles a C/20 ollowed by
a a e capabili y es and 150 cycles a C/3 ( o he hal coin cells wi h eco e ed nega i e
elec ode) o 1 C ( o he hal coin cells wi h eco e ed posi i e elec ode). The es s we e
conduc ed a 20
◦
C. The po en ial windows o posi i e and nega i e elec ode HCCs we e
4.3 V–2.6 V and 1.0 V–10 mV, espec i ely.
2.6. Th ee-Elec ode Cells
Th ee-elec ode cells we e assembled o moni o he po en ial o each o he elec odes
upon gal anos a ic cycling. Th ee-elec ode Swagelok cells we e assembled in an MB aun
a gon- illed glo e box wi h oxygen and wa e con en s below 1 ppm. Li hium me al oil
(Rockwood Li hium, F ank u , Ge many) was used as e e ence elec ode along wi h glass
ib e sepa a o s (Wha man, Cy i a, Maids one, UK), soaked wi h 1 M LiPF
6
in EC:DMC
(1:1) + 10% FEC, 2% LiTFSI, and 2% VC elec oly e.
3. Resul s
3.1. Condi ioning Resul s
Figu e 1shows a ep esen a i e condi ioning cycle o one o he cells.
Figu e 1.
Cha ac e is ic condi ioning cycle o he cells. (
a
) Vol age s. ime ep esen a ion and
(
b
) ol age s. capaci y ep esen a ion. Elec ochemical p ocesses a each s ep o he p o ile a e
indica ed in (a).
The condi ioning cycle a 45
◦
C is di ided in o di e en s eps in Figu e 1a. Ini ially,
a 1 C pulse o 10 s was in oduced in be ween wo es ing pe iods o 2 and 3 h. The aim
o hese es ing pe iods was o achie e an e icien imp egna ion o he elec odes and he
sepa a o wi h he elec oly e, while he pulse was applied o a oid coppe oxida ion a
~0 V
.
A e wa ds, a C/10 C- a e was applied h oughou he cha ge s ep. The po en ial ini ially
inc eased apidly un il ~2.5 V, a which poin he SEI was o med [
32
]. The deli hia ion
o he LFP, oge he wi h he li hia ion o he anode, was he eac ion co esponding o
he pla eau be ween 3.35 and 3.5 V. E en i i is easy o asc ibe his pla eau o LFP in he
ca hode, i is no i ial o iden i y he anode ac i e ma e ial (Si o g aphi e) unde going
he educ ion eac ion. This analysis was pe o med using a h ee-elec ode cell and is
discussed in Sec ion 3.3. The deli hia ion o NMC532 and he li hia ion o he anode we e
he main eac ions occu ing abo e 3.5 V. Mos o he cha ge capaci y was ob ained in his
las egion (~1.3 Ah), wi h he capaci y in he LFP deli hia ion egion being only ~0.45 Ah
(Figu e 1b).
The subsequen discha ge was ini ia ed wi h he deli hia ion o he anode and he
li hia ion o he NMC532 (~1.1 Ah), ollowed by a s able pla eau be ween 3.1 and 2.5 V o
LFP li hia ion and he deli hia ion o he anode.
Ba e ies 2022,8, 97 7 o 15
The discha ge capaci y and coulombic e iciency ob ained o he pouch cells we e
1.81
±
0.05 Ah and 82.3%
±
0.5%, espec i ely, whe eas 1.93
±
0.02 Ah and 86.6%
±
0.3%
we e ob ained o he 18650 cells (Table 1). The highe discha ge capaci y ob ained in he
18650 cells p obably o igina es om he di e en beha iou owa ds he esidual wa e
con en du ing cell assembly. Fo he i s poin , all he cells we e assembled in a d y oom,
paying a en ion o d y all he componen s be o e assembly. I is easonable o conside
ha he cylind ical con igu a ion is mo e esilien a main aining p essu e on he elec ode
and o a oid he pa icles om disconnec ing e en i he pouch cells a e o med be ween
wo pla es.
Table 1.
A e age i s cycle discha ge capaci y (a C/10) and coulombic e iciency, second cycle
discha ge capaci y (a 1 C), and AC esis ance o he pouch and he 18650 cylind ical cells assembled.
1s Cycle—Discha ge C/10 1s Cycle—Coulombic
E iciency 2nd Cycle—Discha ge 1 C AC Resis ance a 1 kHz
18650 1931 ±17 mAh 86.6 ±0.3% 1807 ±29 mAh 76 ±7 mΩ(50% SOC)
Pouch 1810 ±50 mAh 82.3 ±0.5% 1630 ±30 mAh 26 ±7 mΩ(30% SOC)
3.2. Calenda Ageing
Figu e 2shows he e olu ion o SOH a he end o he calenda ageing es o bo h he
cylind ical and he pouch cells a 3.6 and 4.5 V. The SOH was calcula ed using Equa ion (1).
SOH (%) = 100 −(C0−Ci)
C0
×100, (1)
whe e
Ci
is he discha ge capaci y measu ed a he end o he ageing es , and
C0
is he
discha ge capaci y measu ed be o e he ageing es (ini ial capaci y), bo h ob ained a a
0.3 C- a e.
Figu e 2.
SOH e olu ion upon calenda aging a 25
◦
C o cylind ical (ci cles) and pouch (squa es)
cells a 3.6 V (blue ma ke s) and 4.5 V ( ed ma ke s). E o ba s indica e he s anda d de ia ion
be ween he wo cells pe expe imen .
The capaci y o he cells s o ed a 3.6 V seems o dec ease mo e slowly han ha o he
cells s o ed a he highe ol age o 4.5 V. This is because he elec oly e deg ades as e a
highe ol age, i.e., when he cell is ully cha ged. On he o he hand, he deg ada ion is
highe in pouch o ma when aged a 4.5 V. No no able di e ences we e obse ed be ween
he wo cell o ma s a 3.6 V calenda aging.
Ba e ies 2022,8, 97 8 o 15
3.3. Cycling Aging: E ec o he Vol age Cycling Window on he Capaci y Fade Ra e
Figu e 3shows he e olu ion o he SOH e sus he o al capaci y h oughpu (cumu-
la i e capaci y du ing he cycle li e) o he cylind ical and pouch cells a 25
◦
C. The ci cles,
iangles, and squa es indica e he cells cycled in he 2.5–3.6 V, 3.6–4.5 V, and 2.5–4.5 V
ol age windows, espec i ely.
Figu e 3.
SOH e olu ion wi h he o al capaci y h oughpu o cylind ical (ci cle ma ke s) and
pouch (squa e ma ke s) cells cycled in he 3.6–4.5 V (blue ma ke s), 2.5–3.6 V (o ange ma ke s), and
2.5–4.5 V (g een ma ke s) ol age windows.
Simila o wha was obse ed o he calenda ageing es s, he pouch cells seemed o
deg ade as e han he cylind ical cells.
Fo bo h cell o ma s, he cells cycled wi hin he 3.6 o 4.5 V ol age window showed
he slowes ageing a e, compa ed o he cells cycled wi hin he ol age windows o 2.5
o 3.6 V and 2.5 o 4.5 V. Fo he la e wo cases, he e was a minimal di e ence be ween
he capaci y o he cylind ical cells, which showed sligh ly highe capaci y e en ion.
On he o he hand, he pouch cells showed simila capaci y deg ada ion a hose wo
ol age windows.
To p o ide u he insigh in o he cause o he di e ences in he capaci y e en ion
o he cells depending on he ol age window, a h ee-elec ode Swagelok cell wi h Li as
he e e ence was assembled and cycled be ween 2.5 and 4.5 V. The elec ochemical esul s
ob ained wi h his cell a e shown in Figu e 4.
The cu e o he capaci y e olu ion wi h he cycle coun (Figu e 4a) showed an almos
linea and s eep capaci y decay a e he wo ini ial C/20 cycles. These wo ini ial cycles
a e analysed in de ail in Figu e 4b, whe e he con ibu ion o he anode and he ca hode
we e ob ained h ough he use o he e e ence elec ode included in he cell. Bo h cycles
displayed ha he discha ge capaci y o he ull cell was limi ed by he deli hia ion o he
anode in he ol age window selec ed (2.5–4.5 V). The di e en ial analysis o he li hia ion
and deli hia ion cu es o he anode in hese wo cycles a e shown in Figu e 4c, whe e he
peaks associa ed wi h he (de)li hia ion o g aphi e and silicon a e di e en ia ed. I can
be obse ed ha he deli hia ion o silicon occu ed a ~0.4 V, which is close o he lowe
cu -o ol age o he ull cell (below 3 V in Figu e 4b). This con ibu ion disappea ed in
he DVA cu e wi h he epe i i e li hia ion/deli hia ion s eps a C/3, as highligh ed in
Figu e 4d. Thus, he cells cycled wi hin he ol age window o 3.6–4.5 V we e cycled in a
ange ha a oided deep Si li hia ion/deli hia ion. These esul s explain he highe cycle
li e obse ed in cells cycled a he 3.6–4.5 V ol age window.
Ba e ies 2022,8, 97 9 o 15
Figu e 4.
Expe imen s wi h a h ee-elec ode cell consis ing o an NMC-LFP ca hode, a G /Si anode,
and a Li e e ence elec ode cycled a 25
◦
C be ween 2.5 and 4.5 V a a C/3 C- a e. (
a
) Discha ge
capaci y wi h he cycle coun . (
b
) Vol age p o iles a C/20. Di e en ial capaci y plo a (
c
) C/20
and (d) C/3 o he anode ol age p o iles. Deli hia ion ea u es associa ed wi h g aphi e and silicon
u ilisa ion in (
c
) a e highligh ed in yellow and g een, espec i ely. E idence o a lack o silicon ac i i y
a e 50 cycles in (d) is highligh ed in pu ple.
3.4. Pos -Mo em Cha ac e isa ion
One o he cylind ical cells cycled in he ol age window 2.5–4.5 V was disman led
(Figu e S5) and subjec ed o ma e ial and elec ochemical cha ac e isa ion, pa icula ly o
he elec odes. On ini ial isual analysis, he nega i e elec ode p esen ed la ge de-bonding
a eas, as shown in Figu e S6. The zones s ongly adhe ed o he sepa a o we e whi e/g ey,
while no d as ic colou change was obse ed o he sepa a o which mainly emained
whi e (Figu e S7). The jelly oll was s ill well soaked by he elec oly e du ing disman ling.
The posi i e elec ode unexpec edly showed a e y high deg ee o debonding, as shown
in Figu e S8. Usually, no (o e y-low le el) debonding occu s o he posi i e elec odes.
Ne e heless, undamaged samples o his elec ode showed a e y high adhesion o a ound
100 N/m.
3.4.1. SEM-EDX
The SEM images o he posi i e elec ode a e gi en in Figu e S9. The posi i e pos -
mo em elec ode was composed o a mix u e o pa icles wi h small (Ø < 1
µ
m) and
la ge (1
µ
m<Ø<5
µ
m) pa icle sizes. Some ca bon ib es we e also obse ed. The
mo phology o he posi i e elec ode was homogeneous in la ge zones, as shown in he
lowes -magni ica ion SEM pic u e.
EDX analysis, co esponding o a ec angula zone (~40
×
55
µ
m), is p esen ed in
Figu e S10. The posi i e elec ode was mainly composed o C, O, Fe, and P elemen s. Mn
and Ni we e also de ec ed, bu in smalle amoun s. The Co signal was no de ec ed, bu i
could ha e been masked by he Fe main peak, as i appea ed in he same ene gy domain.
The EDX analysis was also pe o med in h ee di e en zones, as desc ibed in Figu e S11.
The EDX spec a a e compa ed in Figu e S12; Poin 1 co esponds o an a ea wi h a la ge
pa icle size (1
µ
m<Ø<5
µ
m). EDX analysis e ealed he main composi ion o Mn, Ni,
