Synergistic theoretical and experimental study on the ion dynamics of bis(trifluoromethanesulfonyl)imide-based alkali metal salts for solid polymer electrolytes

25038 | Phys. Chem. Chem. Phys., 2023, 25, 25038–25054 This jou nal is © he Owne Socie ies 2023
Ci e his: Phys. Chem. Chem. Phys.,
2023, 25, 25038
Syne gis ic heo e ical and expe imen al s udy
on he ion dynamics o
bis( i luo ome hanesul onyl)imide-based alkali
me al sal s o solid polyme elec oly es†
B ige e Al hea Fo uin,
abc
Jon O egi,
b
Juan Miguel Lo
´pez del Amo,
a
Se gio Rod iguez Pen
˜a,
ab
Lei e Meabe,
a
Hegoi Manzano, *
b
Ma ı
´a Ma ı
´nez-Iban
˜ez *
a
and Ja ie Ca asco *
ad
Model alida ion o a well-known class o solid polyme elec oly e (SPE) is u ilized o p edic he ionic
s uc u e and ion dynamics o al e na i e alkali me al ions, leading o ad ancemen s in Na-, K-, and
Cs-based SPEs o solid-s a e alkali me al ba e ies. A comp ehensi e s udy based on molecula dynamics
(MD) is conduc ed o simula e ion coo dina ion and he ion anspo p ope ies o poly(e hylene oxide) (PEO)
wi h li hium bis( i luo ome hanesul onyl)imide (LiTFSI) sal ac oss a ious LiTFSI concen a ions. Th ough
alida ion o he MD simula ion esul s wi h expe imen al echniques, we gain a deepe unde s anding o he
ionic s uc u e and dynamics in he PEO/LiTFSI sys em. This compu a ional app oach is hen ex ended
o p edic ion coo dina ion and anspo p ope ies o al e na i e alkali me al ions. The ionic s uc u e in
PEO/LiTFSI is signi ican ly in luenced by he LiTFSI concen a ion, esul ing in diffe en li hium-ion anspo
mechanisms o highly concen a ed o dilu ed sys ems. Subs i u ing li hium wi h sodium, po assium, and
cesium e eals a weake ca ion-PEO coo dina ion o he la ge cesium-ion. Howe e , sodium-ion based
SPEs exhibi he highes ca ion anspo numbe , indica ing he c ucial in e play be ween sal dissocia ion and
ca ion-PEO coo dina ion o achie ing op imal pe o mance in alkali me al SPEs.
1. In oduc ion
The e e -inc easing global ene gy demand ied wi h inc easing
en i onmen al conce ns
1
ega ding clima e change has p o-
g essi ely led owa ds he inco po a ion o enewable ene gy
sou ces, such as wind and sola ene gy, wi hin na ional g ids.
Howe e , conside ing he in e mi en na u e o na u al ene gy
sou ces, ene gy s o age is i al owa ds he ealiza ion o a
sus ainable and efficien ene gy p oducing sec o . The cu en
ma ke leade o ene gy s o age sys ems, he li hium-ion
ba e y (LIB), shows a high po en ial owa ds mi iga ing ene gy
luc ua ions om enewable ene gy sou ces wi hin he g id.
2
Conside ing he apid expansion o he ene gy s o age ma ke
in addi ion o he ising cos and sca ci y o li hium,
3,4
he need
o de eloping al e na i e ba e y echnologies o LIBs, is
essen ial. Fu he mo e, demand o highe ene gy densi y,
inc eased sus ainabili y, abundan and economically iable
ene gy s o age sys ems ha e led o a su ge in he explo a ion
o al e na i e ba e y echnologies beyond LIBs in ecen yea s.
5–7
Pos -li hium-ion ba e ies (pos -LIBs), such as li hium–me al ba -
e ies (LMBs),
8–11
sodium-ion ba e ies (NIBs),
4,12,13
po assium-ion
ba e ies (KIBs),
14–17
and cesium-ion ba e ies (CIBs)
18–20
a e gain-
ing momen um. Nume ous ad an ages o hese pos -LIB echno-
logies include highe edox po en ials; Li
+
/Li (3.04 V s. SHE),
Na
+
/Na (2.71 V s. SHE), K
+
/K (2.93 V s. SHE), and Cs
+
/Cs
(3.03 V s. SHE), along wi h supe io heo e ical speci ic
capaci ies,
21
an abundance o bo h sodium and po assium in
he Ea h’s c us posing an a ac i ely low cos al e na i e o
li hium, and he highe di usion coe icien s (low di usion
ba ie ) o cesium-based elec odes esul ing in hinde ed den-
d i e o ma ion o cesium-ion ba e ies.
20,22
Howe e , despi e
a
Cen e o Coope a i e Resea ch on Al e na i e Ene gies (CIC ene giGUNE),
Basque Resea ch and Technology Alliance (BRTA), Ala a Technology Pa k, Albe
Eins ein 48, 01510 Vi o ia-Gas eiz, Spain. E-mail: jca a[email p o ec ed],
mma inez@cicene gigune.com
b
Depa men o Physics, Uni e si y o he Basque Coun y (UPV/EHU), 48940 Leioa,
Spain. E-mail: [email protected]
c
ALISTORE-Eu opean Resea ch Ins i u e, CNRS FR 3104, Hub de l’Ene gie,
Rue Baudelocque, 80039 Amiens Cedex, F ance
d
IKERBASQUE, Basque Founda ion o Science, Plaza Euskadi 5, 48009 Bilbao,
Spain
†Elec onic supplemen a y in o ma ion (ESI) a ailable: Suppo ing ables and
igu es including o ce ield pa ame e s, chemical s uc u es, li hium-ion specia-
ion analysis, MD-based ionic conduc i i y con e gence es s, MSD, DSC, EIS,
Raman spec oscopy, MAS-NMR spec oscopy, and ac i a ion ene gies o he
anspo mechanisms o he diffe en in es iga ed sys ems. See DOI: h ps://
doi.o g/10.1039/d3cp02989a
Recei ed 26 h June 2023,
Accep ed 31s Augus 2023
DOI: 10.1039/d3cp02989a
sc.li/pccp
PCCP
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i s p omise, alkali me al ba e ies ace high eac i i y, wi h
elec ode and elec oly e componen s spon aneously eac ing
wi h mos pola ap o ic elec oly e sol en s, esul ing in
uns able solid elec oly e in e phases, which may a ec cycle
pe o mance.
21,23
The limi ed s abili y and li e ime challenges
a e u he educed by ailu e mechanisms, such as dend i ic
g ow h on he anode and he cu en collec o , in e nal sho -
ci cui s and elec oly e decomposi ion, esul ing in elec oly e
loss.
21,23,24
Add essing hese challenges, he success ul de elop-
men o al e na i e all-solid-s a e alkali me al ba e y echnologies
necessi a es he ad ancemen o alkali me al sal s, conside ing
hei compa ibili y wi h a ious polyme ma ices and alkali me al-
based elec odes. The e o e, a undamen al unde s anding o ion
coo dina ion as well as ion anspo mechanisms is c ucial o
assessing he o e all pe o mance o hese SPEs.
A omis ic modelling o polyme elec oly es is an effec i e
app oach o accele a e he sea ch owa ds new alkali me al sal s
and alkali me al-based elec oly e componen s, especially con-
side ing he ecen ad ances in compu ing powe .
8,25–29
The
g owing u iliza ion o modelling echniques is d i en by se e al
ac o s, including educed en i onmen al impac compa ed o
expe imen al p ocesses, as e simula ion imes compa ed o
adi ional expe imen al me hods, and he capabili y o acqui e
in o ma ion ha may no be eadily a ainable h ough expe i-
men al cha ac e iza ion echniques.
8,30–34
Ye , a key elemen
o he success ul in eg a ion o compu a ional-based me hods
in ma e ials de elopmen is comp ehensi e model alida ion
agains well-de ined, high-quali y expe imen al da a, which is
o en lacking bu c ucially needed in he ield.
He ein, we p esen a comp ehensi e s udy o he well-known
PEO/LiTFSI SPE as a unc ion o LiTFSI concen a ion. Ou
app oach in ol es p edic ing ion coo dina ion and ion anspo
using a omis ic molecula dynamics (MD) simula ions. A key
aspec o ou s udy is he alida ion o he model, whe e we ha e
aken pa icula ca e o combine h ee diffe en echniques:
Raman, magic angle spinning nuclea magne ic esonance (MAS-
NMR), and elec ochemical impedance spec oscopies. This combi-
na ion o well-de ined expe imen s is c ucial o alida ing ou
heo e ical models and simula ions. No ably, such a syne gis ic
model alida ion s udy has been lacking in he li e a u e on he
PEO/LiTFSI SPEs, and ou wo k ills his impo an gap. Fu he -
mo e, ou alida ed heo e ical app oach p o ides aluable insigh
ha ex ends beyond he PEO/LiTFSI sys em. Speci ically, i allows us
o p edic simila p ope ies o al e na i e alkali me al-based sys-
ems,suchasPEO/XTFSI(X=Na,K,andCs),b oadening hescopeo
ou s udy. These insigh s offe aluable guidance o designing new
sal s o SPEs, hus con ibu ing o he ad ancemen o he ield.
2. Theo e ical and
expe imen al me hods
2.1. Theo e ical me hods and compu a ional de ails
Classical MD simula ions we e conduc ed on PEO
n
/LiTFSI o
ou diffe en EO/Li
+
a ios (n= 6, 16, 20 and 32). To ensu e he
obus ness o ou esul s and elimina e any po en ial bias
a ising om he choice o MD so wa e, we employed wo o
he mos widely used codes in he li e a u e: G omacs
35
and
LAMMPS.
36
Con e gence es s we e me iculously conduc ed o
alida e he consis ency o esul s ob ained om bo h codes.
These es s, based on he o al ionic conduc i i y as a unc ion
o empe a u e, enabled us o iden i y he op imal simula ion
ime and box size o he s udied sys ems (c . Fig. S1–S3, ESI†).
Based on hese es s, a simula ion ime o 100 ns and a
medium-sized box con aining 40 ion pai s and 40 polyme
chains we e deemed su icien o achie e accu a e and compa -
able ou comes.
Conside ing ha LAMMPS gene ally exhibi s slowe simula-
ion pe o mance compa ed o G omacs,
37,38
we selec ed
G omacs o in es iga e he in luence o sal concen a ion on
Li-con aining sys ems. This choice was pa icula ly ad an a-
geous o highly dilu ed sys ems, whe e longe MD simula ions
a e needed o ob ain sui able s a is ical a e ages, making
G omacs he p e e ed op ion due o i s highe speed. In con as ,
LAMMPS was exclusi ely u ilized o s udy one in e media e
concen a ion (n=20)whilealsoexplo ing he oleo diffe en
alkali me als (Li
+
,Na
+
,K
+
,andCs
+
). By adop ing his app oach, we
aimed o ensu e he alidi y and eliabili y o ou indings while
in es iga ing he di e se aspec s o ou esea ch.
Speci ically, we conside ed he ollowing compu a ional
se ups. Fo he simula ions pe o med using G omacs,
35
he
simula ion boxes consis ed o 40 PEO chains wi h 24 EO
epea ing uni s in each chain (M
w
=B1056 g mol
1
), and
160, 60, 48 and 30 LiTFSI ion pai s, o n= 6, 16, 20, and 32,
espec i ely. Ini ial boxes we e gene a ed andomly as imple-
men ed in G omacs. Wi h LAMMPS
36
we examined he ion
coo dina ion and anspo p ope ies o PEO
20
/XTFSI sys ems,
whe eX=Li,Na,K,o Cs.In hiscase, hesimula ionboxes
consis ed o 40 PEO chains wi h 20 EO epea ing uni s in each
chain (M
w
=B880 g mol
1
), and 40 XTFSI ion pai s wi h ini ial
con igu a ions con aining andomly posi ioned molecules,
gene a ed using Packmol.
39
P io o he MD p oduc ion simula ions, an efficien and
mul is ep p o ocol was applied o p epa e and equilib a e he
sys ems. I is wo h no ing ha due o he implemen a ion o
G omacs p og amming, he ini ial simula ion box needs o be
ela i ely la ge, esul ing in low densi ies, e.g.,1.64910
1
gcm
3
o PEO
32
/LiTFSI. To ensu e he app op ia e geome y o he
sys em, he i s s ep in his case in ol es an ene gy minimiza-
ion p ocess whe e he posi ions o he molecules a e adjus ed
o achie e a s a e o minimum ene gy. Acco dingly, an ini ial
NPT s uc u al comp ession s ep was ca ied ou using he
Be endsen he mos a and he Pa inello–Rahman ba os a
(wi h a elaxa ion ime o 5 ps o all cases). This comp ession
was pe o med a 267 1C (10 K) unde a p essu e o 98.99 a m
(100 ba ) o ob ain densi ies close o expe imen al alues, i.e.,
simula ed (expe imen al): 1.352 (1.234) g cm
3
(PEO
6
/LiTFSI),
1.193 (1.188) g cm
3
(PEO
16
/LiTFSI), 1.159 (1.179) g cm
3
(PEO
20
/LiTFSI), and 1.167 (1.164) g cm
3
(PEO
32
/LiTFSI).
Subsequen ly, a g adual hea ing p ocess o 327 1C (600 K) a
1 a m and equilib a ion in an NVT ensemble we e conduc ed o
p e en he o ma ion o possible me as able con igu a ions.
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The empe a u e inc ease ollowed an exponen ial pa e n
based on he ime cons an (1 ps). A e wa ds, he sys ems
unde wen a cooling NPT p ocedu e o each he simula ion
empe a u e o 70 1C (343 K) and p essu e o 1 a m. The inal
con igu a ion was u he equilib a ed o 1 ns unde simila
condi ions. Finally, he p oduc ion MD simula ions we e pe -
o med in he NVT ensemble o 200 ns (PEO
n
/LiTFSI) o 100 ns
(PEO
20
/XTFSI) o ensu e a ully di usi e egime.
All-a om op imized po en ials o liquid simula ions (OPLS-AA)
o ce ield
34,40–44
we e u ilized o desc ibe he ene gy po en ials
o PEO, Li
+
,Na
+
,K
+
,Cs
+
, and TFSI

, including he o ce ield
pa ame e s (bond s e ching, bond-angle, dihed al angle, and
Lenna d-Jones po en ial). The o ce ield pa ame e s used in
his s udy a e a ailable in he ESI†(Tables S1, S2 and Fig. S4).
The ajec o ies ob ained by he MD simula ions we e analyzed
using T a is analyze .
45,46
We u ilized he de aul a omic cha ges om he OPLS-AA
o ce ield o he PEO a oms. Howe e , o enhance he accu acy
and sui able desc ip ion o ou sys ems, we conduc ed an
op imiza ion o he TFSI

anion’s s uc u e in he gas-phase
and compu ed i s co esponding a omic cha ges using densi y
unc ional heo y (DFT) calcula ions. Subsequen ly, we inco -
po a ed hese ecompu ed cha ges o upda e he o iginal OPLS-
AA o ce ield. The DFT calcula ions we e pe o med wi h he
F i z Habe Ins i u e ab ini io molecula simula ions (FHI-AIMS)
so wa e,
47,48
inco po a ing he Becke’s h ee pa ame e s (B3)
exchange unc ional wi h he Lee–Yang–Pa (LYP) nonlocal
co ela ion unc ional (B3LYP)
49,50
adop ed wi h he ‘‘ ie 2’’
s anda d basis se in he FHI-AIMS code. The pa ial cha ges
o TFSI

we e calcula ed using he elec os a ic po en ial (ESP)
me hod
26,27,30,34,51–54
and scaled o 0.7. The cha ges o Li
+
,
Na
+
,K
+
, and Cs
+
we e also scaled o +0.7 each o main ain
cha ge neu ali y. This scaling ac o is used o accoun o he
e ec s o pola iza ion, which a e no conside ed in con en-
ional classical MD simula ions since he cha ges a e ea ed as
unchangeable poin cha ges. The alue o 0.7 is o en used in
he li e a u e o simula ing simila PEO-based polyme
elec oly es.
26,27,52–54
The cu -o o an de Waals o ces and
he eal space o Ewald summa ion was selec ed o be 10 Å, wi h
he as smoo h pa icle mesh Ewald (PME) elec os a ics
55,56
o
ea Coulomb in e ac ions in pe iodic sys ems.
Conside ing he compu ed MD ajec o ies, he diffusion
coefficien o each species was deduced om i s mean squa e
displacemen (MSD), using he Eins ein ela ion:
57
D¼lim
ð !1Þ
1
6 j i ðÞ i0ðÞj
2
(1)
whe e Dis he diffusion coefficien , is he ime elapsed,
i
( )is
he displacemen a elled o species ia ime , and
i
(0) e e s
o he displacemen o species ia he o igin. Based on eqn (1),
once he diffusion coefficien s we e p ocu ed, he Ne ns –
Eins ein ela ion
57
in eqn (2) was used o deduce he ionic
conduc i i y o each ionic species:
si¼qi2ci
kBTDi(2)
whe e s
i
is de ined as he ionic conduc i i y, q
i
e e s o he
unscaled cha ge o 1 o he s udied ca ion and TFSI

ion,
espec i ely, c
i
he concen a ion, D
i
he di usion coe icien o
species i,T ep esen s he empe a u e o he sys em, and k
B
ep esen s he Bol zmann cons an .
The ca ion anspo numbe s based on MD simula ions
we e calcula ed using eqn (3):
MD
Xþ¼sXþ
s o al
(3)
whe e MD
Xþ ep esen s he ca ion anspo numbe , s
X
+
he
ionic conduc i i y, and s
o al
he o al ionic conduc i i y, de e -
mined om he sum o he ca ion and anion conduc i i ies, o
he espec i e ca ion species (X
+
=Li
+
,Na
+
,K
+
,o Cs
+
) wi h he
TFSI

anion.
2.2. Ma e ials
PEO (M
w
=510
6
g mol
1
), LiTFSI (99.9%), and ace oni ile
(ACN) we e pu chased om Sigma Ald ich. P io o use, LiTFSI
was d ied o e nigh a 100 1C unde acuum. An a gon- illed
glo ebox was u ilized o conduc all he p ocedu es ela ed o
he mois u e o oxygen sensi i e ma e ials (MB aun, H
2
O and
O
2
o0.5 ppm).
2.3. P epa a ion o polyme elec oly e memb anes
We used he sol en -cas ing p epa a ion me hod o ab ica e
i e diffe en PEO
n
/LiTFSI o mula ions, wi h e hylene oxide
(EO)/Li
+
a ios o 6, 16, 20, 32, and 64. The PEO-sys ems we e
dissol ed in ACN and subjec ed o a wo-s ep d ying p ocess o
emo e any esidual sol en : (i) he solu ion was le o d y
unde en ila ion a 35 1C o 24 h, and (ii) i was u he d ied
unde dynamic acuum a 50 1C o an addi ional 24 h. Subse-
quen ly, PEO-based SPEs we e p epa ed using he ho p essing
me hod a 60 1C and 3 ons, wi h a ying p ocessing imes. Fo
he measu emen o ionic conduc i i y, SPEs wi h a a ge
hickness o 300 mm and a diame e o 4 mm we e used.
Meanwhile, li hium symme ic cells we e cons uc ed wi h
SPEs ha ing a hickness o 100 mm and a diame e o 16 mm.
2.4. Diffe en ial scanning calo ime y (DSC)
A DSC Disco e y 2500 (TA Ins umen ) ins umen was used o
s udy he phase ansi ion beha iou o he SPEs om 80 o
100 1C, wi h hea ing and cooling a es o 10 K min
1
. Following
his, he SPE samples (ca. 10 mg) we e sealed in Al c ucibles in
an a gon- illed glo ebox. The mal p ope ies, including he
alues o he glass ansi ion empe a u e (T
g
, midpoin o
he hea capaci y change), mel ing empe a u e (T
m
, maximum
o he endo he mic peak), and mel ing en halpy (DH
m
, a ea
below he endo he mic peak), we e deduced om he second
hea ing scan. The calcula ion o he c ys alline ac ion (w
C
)o
he polyme elec oly es was pe o med using eqn (4):
wC¼DHm
DHmPEO  SPE
100% (4)
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whe e DH
m
he mel ing en halpy o he elec oly e, DH
mPEO
he
mel ing en halpy o 100% c ys alline polyme ma ix (205 J g
1
o PEO
58
), and
SPE
he polyme weigh ac ion o he SPE.
2.5. Ionic conduc i i y and li hium ans e ence numbe
CR2032 ype coin cells we e assembled in an a gon- illed
glo ebox o measu e bo h he ionic conduc i i y and he
li hium-ion ans e ence numbe o he espec i e s udied
sys ems. The ionic conduc i i y was measu ed by using wo
s ainless s eel (SS) blocking elec odes, wi h he con igu a ion
SS|SPE|SS and a SPE a ea o 0.1257 cm
2
, based on elec oche-
mical impedance spec oscopy (EIS), pe o med on a Mul i-
channel VMP3 (Biologic, Claix F ance) wi h a signal ampli ude
o 10 mV o e he equency ange 10
1
–10
6
Hz, a 40 and 70 1C.
A s abiliza ion pe iod o 8 h was employed o he measu emen
a 40 1C, and 2 h o he measu emen a 70 1C. The ollowing
equa ion was employed o calcula e he ionic conduc i i y,
eqn (5):
sDC ¼
Rbulk A(5)
whe e s
DC
co esponds o he di ec cu en ionic conduc i i y,
he hickness o he elec oly e (ca. o 0.3 mm), A ep esen s
he a ea o he elec oly e o 0.1257 cm
2
, and R
bulk
ep esen s
he bulk esis ance o he polyme elec oly e measu ed by EIS.
Li hium-ion symme ic cells we e assembled using a
Li|SPE|Li con igu a ion. The li hium-ion ans e ence numbe
was measu ed ollowing he p ocedu es as desc ibed by B uce
and Vincen e al.,
59
measu ed a 40 and 70 1C. CR2032 ype
coin cells we e employed, sandwiching he SPEs be ween wo
li hium discs, wi h a li hium–me al a ea o 1.54 cm
2
. P io o
EIS measu emen s, he cells we e le o s abilize a 40 1C o
8 h, and a 70 1C o 6 h. Eqn (6) was employed o calcula e he
li hium-ion ans e ence numbe , TEIS
Liþ:
TEIS
Liþ¼Iss DVIiRi;Liþ

IiDVIssRss;Liþ
(6)
whe e I
i
and I
ss
ep esen he ini ial and s eady-s a e cu en ,
espec i ely; R
i,Li
+
and R
ss,Li
+
ep esen he ini ial and s eady-
s a e li hium in e acial esis ance, espec i ely; and DV ep e-
sen s he o al pola iza ion ol age (10 mV).
2.6. Raman spec oscopy
Raman spec a we e collec ed using a Renishaw inVia con ocal
Raman spec ome e (se ial numbe 16H981) wi h an inciden
lase wi h a wa eleng h o 532 nm (lase spo size: 0.8 m; spa ial
esolu ion: 0.4 m). The Raman spec a, collec ed in he ange
o 3000–300 cm
1
, we e eco ded a 25, 40, and 70 1C wi h
inc easing empe a u e, and a s abiliza ion ime o 2 h (40 1C)
and 1 h (70 1C). To inc ease he signal- o-noise a io (S/N), each
plo ed spec um is he a e age o 10 accumula ions o app oxi-
ma ely 3 minu es each. The spec a shown has been no malized
om 0 o 1. The samples we e placed in a sealed, ai - igh cell
buil wi h a Raman-inac i e glass window and assembled in an
a gon- illed glo ebox o p e en con amina ion om ambien
a mosphe e (e.g., ai , wa e ).
2.7. MAS-NMR spec oscopy
7
Li MAS-NMR spec oscopy was employed o de e mine he
chemical en i onmen s o li hium-ion upon concen a ion
changes wi hin he PEO ma ix. The expe imen s we e eco ded
using a WB 500 MHz B uke Ad ance III spec ome e equipped
wi h a 2.5 mm p obe and was conduc ed on LiTFSI powde ,
concen a ed PEO
6
/LiTFSI and dilu ed PEO
32
/LiTFSI SPEs.
All samples we e spun a a magic angle wi h a MAS equency
o 20 kHz. The
7
Li MAS-NMR spec a we e eco ded by using a
single pulse expe imen (3 ms pulse), wi h i s chemical shi
e e enced o a 0.1 M solu ion o LiCl. The empe a u e-
a ia ion NMR spec a we e eco ded by a ying he empe a-
u e, om 40 o 80 1C, wi h a s abiliza ion ime o app oxi-
ma ely 1 h in be ween measu emen s. DMFIT so wa e was
used o analyze he spec a.
60
3. Resul s and discussion
Ion coo dina ion, li hium-ion specia ion, and ion anspo
p ope ies we e assessed h ough MD simula ions, ocusing
on pa icle densi y changes a ound li hium ca ion o TFSI

anions wi hin he PEO polyme ma ix. The MD simula ions
we e conduc ed a 70 1C, as classical MD simula ions a e
limi ed o s udying molecula kine ics and canno p ope ly
simula e he he modynamic p ope ies o semic ys alline
egions ha migh be p esen a lowe empe a u es. Mo eo e ,
he modelling o he PEO
64
/LiTFSI sys em was excluded since
longe ime and leng h scales a e equi ed o sui ably accoun
o he diffusi i y o ionic species wi hin PEO a such low
concen a ions.
53,54,61,62
The compu a ional amewo k was alida ed a 70 1C using
expe imen al echniques, including DSC o analyze polyme
chain dynamics, Raman, and NMR spec oscopies o p obing
he ion coo dina ion en i onmen s, and EIS o examining ion
anspo p ope ies.
The alida ion o he compu a ional amewo k enabled he
p edic ion o a ious p ope ies o al e na i e alkali me al-ions.
MD simula ions we e pe o med on PEO
20
/XTFSI, in es iga ing
he effec s o subs i u ing li hium wi h sodium, po assium, o
cesium ca ions on ionic anspo mechanisms. The analysis
included ion coo dina ion, ion conduc i i y, and ion anspo ,
which a e c i ical ac o s in luencing he pe o mance o SPEs
in all-solid-s a e ba e ies.
3.1. Model alida ion o PEO
n
/LiTFSI SPEs
3.1.1. Modelling li hium-ion sol a ion and mobili y. The
local ion coo dina ion en i onmen o PEO
n
/LiTFSI sys ems
was analyzed by calcula ing he adial dis ibu ion unc ion
(RDF) and he co esponding coo dina ion numbe s (CNs) a
diffe en LiTFSI sal concen a ion, offe ing insigh s in o he
ex en o sal dissocia ion. RDFs desc ibe he p obabili y o
inding a pa icle a a speci ic dis ance om a e e ence
pa icle, indica ing he deg ee o associa ion be ween wo
species o in e es . The CN is hen ob ained by in eg a ing
he p obabili y cu e, ep esen ing he numbe o e e ence
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pa icles ound wi hin he coo dina ion sphe e ange o he
species o in e es .
Fig. 1(a) and (b) displays bo h he RDFs and CNs o in e -
ac ion o he e e ence pa icle, li hium, wi h ei he PEO, deno ed
as Li
+
O

(PEO), o TFSI

ions, deno ed as Li
+
O

(TFSI

), ia
hei espec i e oxygen a oms. Compa ing he RDFs o he
li hium-polyme (Li
+
O

(PEO)), and li hium-TFSI

(Li
+
O

(TFSI

)
in e ac ions, Li
+
O

(PEO) possesses a signi ican ly highe RDF
peak in ensi y and an a e age CN o 5 compa ed o he la e
Li
+
O

(TFSI

). A i s glance, based on he CNs, nea ly com-
ple e LiTFSI dissocia ion is obse ed o mos o he in es iga ed
sys ems, a ibu ed o he p e e en ial sol a ion o he oxygen
dense EO uni s om PEO.
28,30,34,54,63
The incomple e LiTFSI dissocia ion obse ed a highly con-
cen a ed PEO
6
/LiTFSI s ongly sugges s he o ma ion o ion
pai s. This phenomenon can be a ibu ed o wo p ima y
ac o s. Fi s ly, he inc eased p obabili y o elec os a ic in e -
ac ions leads o a highe likelihood o ion clus e o ma ion.
Secondly, he educed numbe o EO coo dina ion si es
a ailable o li hium-ion sol a ion plays a signi ican ole. This
scena io becomes e iden a such high sal concen a ion,
whe e he EO/Li
+
a io is a ound 6, causing he coo dina ion
be ween e he oxygen a oms and Li ions o app oach sa u a-
ion. Consequen ly, i is na u al o some Li ions o coo dina e
wi h TFSI

oxygen a oms ins ead.
Ad ancing he p edic ion o a mo e in-dep h analysis ega d-
ing he li hium-ion coo dina ion en i onmen , li hium-ion
molecula specia ion analysis is pe o med as a unc ion o
LiTFSI sal concen a ion. Based on RDF analysis, he local
minimum o he i s RDF peak, o bo h Li
+
O

(PEO)
and Li
+
O

(TFSI

) coo dina ion ypes, is obse ed a 3 Å
(c . Fig. 1(a) and (b)).
This local minimum co esponds o he edge o he i s
sol a ion shell o Li
+
-ions, he e o e, i is selec ed as he cu -off
dis ance o he li hium-ion molecula specia ion analysis. The
effec s o LiTFSI sal concen a ion upon he ypes o ionic
species, such as polyme –Li
+
, polyme –polyme , and a ious
ion–ion in e ac ion in e dependencies a e plo ed in Fig. 1(c) as
Fig. 1 RDFs (solid line) and CNs (dashed line) o PEO
n
/LiTFSI SPEs, indica ing he Li
+
–O

in e ac ion be ween li hium-ions and (a) PEO, o (b) TFSI

ions.
(c) Li hium-ion molecula specia ion analysis wi h li hium-ion as he e e ence species. The di e en ypes o li hium-ion specia ion a e ep esen ed by
di e en colou s: isola ed Li
+
(blue), Li
+
O

(PEO) (g een), LiþOðTFSI
PEO Þ(pu ple), and Li
+
O

(TFSI

) ( ed). RDFs and li hium-ion molecula specia ion
analyses we e calcula ed om MD simula ions conduc ed a 70 1C.
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pe cen age p obabili y. The li hium-ion molecula specia ion
emains consis en ega dless o he EO/Li
+
a io, in good ag ee-
men wi h RDF analyses and p e ious li e a u e indings.
26,52–54
P edominan ly, li hium ions in e ac wi h PEO ia i s oxygen
a oms, deno ed in he ollowing as Li
+
O

(PEO). The occu -
ence o Li
+
O

(PEO) specia ion inc eases as he LiTFSI sal
concen a ion dec eases, obse ed in bo h PEO
20
/LiTFSI and
PEO
32
/LiTFSI (99%), and simila ly in PEO
16
/LiTFSI (98%).
Howe e , he e is a signi ican dec ease in his specia ion o
highly concen a ed PEO
6
/LiTFSI (77%) (c . Table S3, ESI†).
Addi ionally, a second ype o li hium-ion molecula specia ion,
whe e li hium ions in e ac wi h he oxygen a oms om bo h
TFSI

anions and PEO chains, is exclusi ely p esen in PEO
6
/
LiTFSI (23%), deno ed as LiþOTFSI
PEO

. The ela i ely highe
LiTFSI sal concen a ion and lowe PEO concen a ion in
PEO
6
/LiTFSI limi he a ailable PEO oxygen sol a ion si es,
which hinde s LiTFSI dissocia ion and may p omo e ion clus e
o ma ion,
26,52
since li hium ions a e p e e en ially sol a ed by
he oxygen a oms om PEO,
64–67
he e is a highe p obabili y o
LiþOðTFSI
PEO Þspecia ion in his case.
The s udy o ion anspo inco po a es MSD analysis, a
use ul ool o examining he displacemen o pa icles o e
ime. MSD analysis allows compu a ion o diffusion coefficien s
(eqn (1)) and li hium-ion anspo numbe s (eqn (3)). As shown
in Fig. 2(a), i is e iden ha TFSI

anions exhibi g ea e
displacemen han li hium ions ega dless o he EO/Li
+
a io
o he SPEs.
Upon close inspec ion, i is e iden ha highe ion mobi-
li ies a e obse ed o PEO
20
/LiTFSI, closely ollowed by PEO
16
/
LiTFSI. In con as , o PEO
6
/LiTFSI, he effec s o ion pai
o ma ion become e iden h ough no ably lowe Li
+
and TFSI

ion mobili ies in his highly concen a ed sys em, as e ealed
by RDF analyses. When compa ing he MSD o li hium ions o
he oxygen a oms om PEO, as depic ed in Fig. S5 (ESI†),
i becomes appa en ha li hium-ion mobili y is p ima ily
limi ed by polyme chain mo emen , as he MSD peaks o
he espec i e a oms consis en ly co ela e. In mode a ely and
highly dilu ed PEO
n
/LiTFSI sys ems, he MSD cu es o
li hium-ion mobili y a e lowe compa ed o he displacemen
o oxygen a oms om PEO. Rema kably, o he highly con-
cen a ed PEO
6
/LiTFSI, he li hium-ion anspo appea s o be
nea ly equi alen o PEO mo ion, sugges ing he p esence o a
dis inc li hium-ion anspo mechanism in his case.
Sel -diffusion coefficien s as a unc ion o LiTFSI concen-
a ion, plo ed in Fig. 2(b), end o be highe o TFSI

compa ed o Li
+
ions, i espec i e o he LiTFSI concen a ion.
Disce nably, mo e dilu e EO/Li
+
a ios o 20 : 1 and 32 : 1 display
highe Li
+
and TFSI

ion sel -diffusion coefficien s, subs an-
ia ed by RDF analyses which indica e nea ly comple e LiTFSI
dissocia ion o hese a ios. Fig. 2(b) addi ionally displays he
li hium-ion anspo numbe MD
Liþ. The MD
Liþ end emains
ela i ely consis en , excep o PEO
6
/LiTFSI, which shows
he lowes alue o 0.21. Fo he o he s udied PEO
n
/LiTFSI
sys ems, MD
Liþonly sligh ly inc eases, wi h PEO
16
/LiTFSI (0.31),
PEO
20
/LiTFSI (0.31), and PEO
32
/LiTFSI (0.30) displaying com-
pa able alues (c . Table S4, ESI†). In e es ingly, he modelled
ion pai effec s p edic ed o PEO
6
/LiTFSI do no seem o
signi ican ly al e he ion anspo effec s.
The li hium-ion anspo mechanism can be deduced om
he analysis shown in Fig. S6(a) and (b) (ESI†), whe e a
e e ence li hium-ion is selec ed o demons a e li hium-ion
diffusion conce ning he oxygen a oms om PEO, e e ed o as
he O index, o he oxygen a oms om he TFSI

anions,
deno ed as he TFSI index. The MD ajec o y in ol ed 24 EO
monome s o ep esen 40 PEO chains in he sys em, which
included ei he 160 (PEO
6
/LiTFSI) o 30 (PEO
32
/LiTFSI) addi-
ional Li-TFSI ion pai s. Each single PEO chain is isualized
sepa a ed by delinea ed dash lines in Fig. S6 (ESI†), and
simila ly, each TFSI

ion is sepa a ed acco dingly. I is impo -
an o emphasize ha while we ocus on a single Li
+
ion in he
analysis displayed in Fig. S6 (ESI†) o illus a e he diffusion
mechanism, he same mechanism applies when conside ing
o he Li
+
ions as e e ence. Essen ially, he li hium-ion ans-
po mechanism a high concen a ions is in e ed om he
Fig. 2 (a) MSD unc ions o li hium- (solid line) and TFSI

ions (dashed line) as a unc ion o LiTFSI sal concen a ion. (b) Sel -diffusion coefficien s o
he s udied EO/Li
+
a ios, o Li
+
(solid column) and TFSI

(s iped column) as well as li hium-ion anspo numbe s, MD
Liþ

(solid line). MSDs, sel -
diffusion coefficien s, and li hium-ion anspo numbe s we e calcula ed om MD simula ions conduc ed a 70 1C.
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collec i e da a p esen ed in Fig. 1(c) and Table S3 (ESI†), and
he da a used in Fig. S6 (ESI†) se es as a ep esen a i e
example. I is obse ed ha he li hium-ion dissocia es om
TFSI

ions a he beginning o he simula ion, mo es owa ds a
PEO chain, and in e ac s wi h oxygen a oms om bo h he
TFSI

ions and PEO. E en ually, he li hium-ion diffuses along
a single polyme chain while emaining coo dina ed wi h TFSI

ions o he emainde o he simula ion ime. This e i ies ha
li hium-ion diffusion o concen a ed PEO
6
/LiTFSI occu s ia
diffusion along a single polyme chain. In he case o PEO
32
/
LiTFSI, he li hium-ion ba ely in e ac s wi h TFSI

ions, clea ly
jumping om one PEO chain o ano he , con i ming ha
he li hium-ion anspo mechanism o mode a ely dilu e
PEO
n
/LiTFSI sys ems occu s ia an ion-hopping mechanism.
3.1.2. Expe imen al alida ion o li hium-ion coo dina ion
and dynamics. Polyme chain lexibili y plays a c ucial ole in
unde s anding ion dynamics, which can be explo ed by s udy-
ing he c ys alline-amo phous phase ansi ion using DSC. The
DSC aces o he s udied SPEs (Fig. S7, ESI†) exhibi an
inc ease in he glass ansi ion empe a u e, T
g
, as he LiTFSI
con en ises (c . Table S5, ESI†). This can be linked o he
highe LiTFSI concen a ion, which inc eases he numbe o
li hium ions coo dina ed o PEO, impac ing he hea capaci y
nea T
g
. Addi ionally, he inc eased LiTFSI concen a ion also
aises he numbe o cha ge ca ie s, which slows down he
segmen al mo ion o he polyme chains.
68,69
Consequen ly,
PEO
6
/LiTFSI possesses he highes T
g
o 26 1C, indica ing
slowe polyme segmen al mo ion and slowe ion dynamics, as
p edic ed by he MD simula ions.
In he case o highly dilu ed PEO
64
/LiTFSI, he absence o a
T
g
can be asc ibed o se e al ac o s: he excep ionally low
LiTFSI con en and signi ican ly high PEO con en esul in a
highly c ys alline SPE (56%); addi ionally, he T
g
dependency
on he empe a u e sweep a e
70
may also con ibu e o he
absence o a T
g
signal.
The s udied SPEs wi h EO/Li
+
a ios o 16 and 20 display
compa able T
g
alues o 35 1C, howe e , he sligh ly mo e
dilu ed PEO
32
/LiTFSI exhibi s he lowes T
g
(43 1C), indica ing
imp o ed polyme chain lexibili y. Lowe empe a u es a e
equi ed o expedi e polyme mo ion in his case, leading o
enhanced polyme mobili y and, consequen ly, as e ion
dynamics and Li
+
-ion mobili y, as suppo ed by he MSD
analysis om he MD simula ions.
The mel ing ansi ion empe a u e, T
m
, supplies in o ma-
ion ega ding he empe a u e ange a which he SPE is
mol en and i s long- ange s uc u e ansi ions o a diso de ed
amo phous sys em (c . Fig. S7 and Table S5, ESI†). Con a y o
he end o he T
g
, he T
m
inc eases sligh ly as LiTFSI con en
dec eases, om T
m
=49 o621C, o PEO
16
/LiTFSI and PEO
64
/
LiTFSI, espec i ely, which indica es ha he li hium sal
p omo es he amo phiza ion o he c ys alline domains esul -
ing in lowe mel ing empe a u es. Addi ionally, he en halpy o
he mel ing ansi ion, DH
m
, has been used o es ima e he
c ys allini y deg ee, w
c
, o he s udied PEO-based SPEs, which
ep esen s he ac ion o he polyme ha is in a ela i ely
o de ed s a e. Based on he da a p esen ed in Table S5 (ESI†), a
clea end eme ges, showing an inc ease in w
c
wi h dec easing
LiTFSI concen a ion. This obse a ion can be a ibu ed o he
inc ease in he p opo ion o semi-c ys alline PEO and he
co esponding dec ease in he amoun o LiTFSI sal . This
end con i ms he amo phiza ion effec o pola LiTFSI wi hin
he PEO ma ix.
P oceeding wi h he alida ion o he model, Raman and
MAS-NMR spec oscopies we e u ilized o e alua e he accu acy
o he compu a ional p edic ions conce ning he impac o sal
concen a ion on he li hium-ion coo dina ion en i onmen .
Raman spec a we e ob ained o a ious EO/Li
+
a ios a
empe a u es o 25 1C(c . Fig. S8(a), ESI†), 40 1C(c .
Fig. S8(b), ESI†), and 70 1C (Fig. 3(a)). Peak decon olu ion
was hen pe o med o quan i y he ex en o LiTFSI associa ion
as a unc ion o LiTFSI concen a ion and empe a u e, wi h
esul s shown o PEO
6
/LiTFSI in Fig. 3(b) (c . Table S6, ESI†).
Fo u he insigh , we conduc ed MAS-NMR measu emen s on
wo dis inc SPE sys ems: a highly concen a ed PEO
6
/LiTFSI
and a highly dilu ed PEO
32
/LiTFSI (see Fig. 4 and Table S7,
ESI†). These measu emen s allowed us o disce n no able
dissimila i ies in ion dynamics as a unc ion o concen a ion
and empe a u e.
Analysis o he Raman spec a e eals dis inc ib a ional
peaks o he S–N–S ib a ion a 70 1C. Coo dina ed LiTFSI ion
pai s o m, as e idenced by he signal a 747 cm
1
, while ee
ion pai s appea a 740 cm
1
, consis en wi h p e ious
s udies.
30,34,71–74
Upon a dec ease in LiTFSI sal concen a ion,
om highly concen a ed PEO
6
/LiTFSI o highly dilu ed PEO
64
/
LiTFSI, a clea downshi is obse ed om 743 o 741 cm
1
,
co esponding o coo dina ion ha changes om pa ially
coo dina ed Li
+
–TFSI

o he ee TFSI

o m. These expe i-
men al esul s align wi h he p edic ions om he MD simula-
ions, con i ming he accu acy o he compu a ional model.
Essen ially, he inc eased dissocia ion o LiTFSI a lowe LiTFSI
sal concen a ions is e iden om he Raman ends, u he
alida ing he simula ed coo dina ion en i onmen .
The quan i ica ion o he effec o bo h LiTFSI concen a ion
and empe a u e changes upon he li hium-ion coo dina ion
en i onmen was a ained by pe o ming peak decon olu ion o
he s udied PEO
n
/LiTFSI SPEs a a ious empe a u es o 25 1C,
40 1C and 70 1C(c . Table S6 and Fig. S8, ESI†). The empe a u e
effec p o es o p oduce signi ican changes in he quan i ica-
ion o he wo diffe en coo dina ion en i onmen s p incipally
de ec ed o LiTFSI.
71,72
I is impo an o highligh ha he
Raman spec a collec ed a 25 1C in his s udy was pe o med
p io o a p ehea ing ea men s ep,
71
o which non-p ehea ed
and p ehea ed SPEs’ spec a may show conside able diffe -
ences in he S–N–S ib a ion window o mo e concen a ed
PEO
6
/LiTFSI, assigned o he small amoun o ion pai s p esen
in he amo phous phase.
71
Examining he effec o concen-
a ion changes, mainly PEO
6
/LiTFSI and PEO
16
/LiTFSI display
no able diffe ences, wi h he emaining SPEs showing compa -
able esul s, i.e., comple e LiTFSI dissocia ion. A mode a e
con ibu ion om coo dina ed LiTFSI is seen o PEO
6
/LiTFSI
a 40 1C (15%), signi ican ly inc eased a 70 1C (23%). Clea ly,
he local ionic s uc u e o highly concen a ed PEO
6
/LiTFSI is
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affec ed by he mel ing ansi ion o he SPE.
71,72
Con e sely, in
he case o PEO
16
/LiTFSI, a negligible dec ease in he coo di-
na ed LiTFSI o m is obse ed, ansi ioning om 7% a 40 1C
o 4% a 70 1C. These esul s sugges ha mo e dilu e PEO
n
/
LiTFSI sys ems (n46) end o e ain hei ionic s uc u e
despi e changes in empe a u e.
MAS-NMR spec oscopy is a well-es ablished echnique o
p obe bo h ion and polyme dynamics a sho - ange o de
leng h scales (1–2 Å) o a gi en nucleus. This echnique o e s
de ailed in o ma ion abou chemical en i onmen s and hei
empo al luc ua ions. Thus, we used
7
Li solid-s a e NMR
o gain a deepe unde s anding o he changes in he local
li hium-ion s uc u e and dynamics
75,76
as a unc ion o
li hium sal concen a ion a a ious empe a u es. The line
b oadening obse ed in he
7
Li MAS-NMR esonances can be
co ela ed o he a es and ampli udes o local luc ua ions in
he Li
+
en i onmen s, a ising om dynamic a e aging o local
dipola and quad upola in e ac ions. Slowe polyme and
li hium-ion dynamics esul in b oade NMR signals, whils
as e dynamics lead o na owe signals.
75,77
In Fig. 4, he
a iable empe a u e
7
Li MAS-NMR spec a o PEO
32
/LiTFSI
exhibi a ansi ion om a wo- o a one-componen sys em,
wi h bo h signals becoming na owe as he empe a u e
inc eases. The b oade componen e en ually disappea s in
he empe a u e ange o 60–70 1C. In con as , he a iable
empe a u e
7
Li MAS-NMR spec um o PEO
6
/LiTFSI emains
consis en wi h a p edominan ly wo-componen sys em, whe e
he b oade componen becomes na owe and inc eases in
quan i y wi h ising empe a u e.
The decon olu ion o he
7
Li MAS-NMR spec a om Fig. 4
was pe o med o quan i y he espec i e con ibu ions om
each componen (c . Table S7, ESI†). A wo-componen sys em
is obse ed o PEO
32
/LiTFSI, comp ising a mino con ibu ion
o as e li hium-ion dynamics as a na owe componen a
40 1C (46%), inc easing consis en ly up o 60 1C (63%), and
subsequen ly inc easing signi ican ly as he empe a u e is
inc eased o 70 1C (100%), no ably anspi ing a he mel ing
phase ansi ion empe a u e (T
m
=561C). Conside ing ha
li hium-ions a e p e e en ially sol a ed by PEO, as p edic ed by
he RDF and MSD analyses om MD simula ions, li hium-ion
mobili y is in e linked wi h PEO segmen al mo ion, hence, wo
modes o li hium-ion anspo a e ega ded: (1) li hium-ion
anspo ia ion hopping be ween he coo dina ion si es
be ween diffe en PEO chains o segmen s, o (2) li hium-ion
anspo wi hou a change o coo dina ion si e and ia seg-
men al mo ion o he polyme .
30,54,78,79
Since PEO
32
/LiTFSI is a
ela i ely dilu e SPE sys em, and LiTFSI is en i ely dissocia ed
wi hin he PEO ma ix a 70 1C, he as e li hium-ion dynamics
(na owe
7
Li MAS-NMR signals in Fig. 4) a e e iden ly a ib-
u ed o he Li
+
–PEO coo dina ion, as de ec ed by MD simula-
ions and con i med by Raman spec oscopy. Re iewing he
Raman peak decon olu ion esul s a 40 1C, LiTFSI is once
again de e mined o be comple ely dissocia ed, in e ing ha
he wo-componen li hium-ion dynamics deduced by NMR a e
solely a ibu ed o li hium-ions coo dina ed o PEO, occu ing
by ei he one o he wo li hium-ion anspo modes. Based on
MD simula ions (c . Fig. S6(b), ESI†) and simila MD simula-
ions pe o med on PEO/LiTFSI sys ems om li e a u e,
54,78
li hium-ion mobili y be ween di e en coo dina ion si es
be ween di e en PEO chains is as e han li hium-ion mobi-
li y a ising by he li hium-ion coo dina ion ia PEO segmen al
mo ion. The e o e, he na owe componen ep esen ing
as e li hium-ion dynamics, occu s dis inc ly ia li hium-ion
anspo be ween di e en PEO coo dina ion si es and di e -
en polyme chains o PEO
32
/LiTFSI a 70 1C.
Con inuing wi h his easoning, i is in e es ing o no e an
opposi e end o PEO
6
/LiTFSI, wi h he mino con ibu ion o
as e li hium-ion dynamics om he wo-componen sys em
p oceeding o dec ease wi h inc easing empe a u e. Howe e ,
conside ing he signi ican ly lowe numbe o PEO coo dina-
ion si es p esen due o he high LiTFSI sal concen a ion,
addi ional li hium-ion anspo modes may p e ail. Based on
he li hium-ion anspo mechanism deduced in Fig. S6(a)
Fig. 3 Raman spec a o he 730 (720)–760 cm
1
ib a ional window
illus a ing he (a) S–N–S ib a ion o PEO
n
/LiTFSI SPEs a 70 1C, wi h
spec a o nea LiTFSI and nea PEO a 25 1C. The g ey a ow ep esen s
he downshi obse ed upon dec eased LiTFSI concen a ion. Raman
spec a o (b) PEO
6
/LiTFSI a 40 (bo om) and 70 1C ( op). The solid black
line ep esen s eco ded spec a, he solid g een line wi h symbols
co esponds o he cumula i e i o Voig cha ac e pe o med by peak
decon olu ion analysis, wi h he con ibu ion om he coo dina ed cha -
ac e (o ange) and he ee TFSI

ion cha ac e (pu ple). The wo e ical
do ed lines co espond o he coo dina ed con ac ion pai posi ion a
747 cm
1
(o ange) and he ee ion pai posi ion a 740 cm
1
(pu ple),
espec i ely.
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(ESI†) and a simila s udy pe o med o PEO/LiTFSI sys ems,
54
a high LiTFSI concen a ions, li hium-ions p e e en ially
coo dina e wi h PEO due o he p esence o ion pai s and ion
clus e s. Howe e , despi e his p e e ence, he coo dina ion o
li hium ions o TFSI

anions enhances li hium-ion anspo .
No ably, ion pai s and ion clus e s offe he mos s able
s uc u e o anspo ing li hium ca ions, esul ing in highe
li hium-ion mobili ies compa ed o li hium ions solely coo di-
na ed o PEO.
54
Consequen ly, he limi ed polyme segmen al
mo ion induced by he high LiTFSI concen a ion leads o he
as e li hium-ion dynamics obse ed as a mino i y. A 40 1C,
his mino i y cons i u es 47%, dec easing o 32% a 70 1C.
These as e li hium-ion dynamics a e no iceably dis inguished
as li hium ions in he o m o ion pai s and ion clus e s. This
obse a ion inds u he suppo ed om MD simula ions and
Raman spec oscopy, whe e he mino i y o he li hium ions is
ound o be associa ed wi h TFSI

anions.
Conside ing ha empe a u es highe han he T
m
o he
PEO
6
/LiTFSI SPE lead o a g ea e p esence o amo phous
egions, acili a ing p edominan ly a ou ed li hium-PEO coo -
dina ion, he e is an obse ed inc ease in slowe li hium-ion
dynamics ( eaching 68% a 70 1C). This obse a ion is u he
con i med by Raman spec oscopy, which indica es he p esence
o dissocia ed LiTFSI species, and MD simula ions, which show
Li
+
–PEO coo dina ion.
Asce aining he accu acy o he model’s abili y o p edic
he effec s o concen a ion on he li hium-ion anspo , s udy-
ing he empe a u e dependence o he ionic conduc i i y may
con ey in o ma ion abou he p ima y cha ge ca ie s and hei
anspo p ope ies wi hin he s udied sys ems. The A henius
plo in Fig. 5(a) displays he ionic conduc i i y o he s udied
PEO
n
/LiTFSI sys ems a 40 1C and 70 1C. The semic ys alline
na u e o PEO is appa en since he ionic conduc i i ies a
40 1C, a lowe empe a u e han he mel ing phase ansi ion
empe a u es (c . Table S5, ESI†), a e signi ican ly lowe com-
pa ed o he ionic conduc i i ies a 70 1C, a which comple ely
amo phous beha iou o he SPEs a e obse ed. Obse ing he
effec o LiTFSI concen a ion, a empe a u es lowe han he
mel ing phase ansi ion, i.e.,401C, bo h he c ys allini y
deg ee and he ex en o LiTFSI concen a ion a e ac o s which
may affec he ionic conduc i i y. An inc eased c ys allini y
deg ee signi ies an inc eased ac ion o o de ed polyme
chains, dec easing ionic conduc i i y, whils an upsu ge in
LiTFSI concen a ion may p oduce inc eased ion–ion in e -
dependen in e ac ions, gene ally es ic ing ion mobili y o a
g ea e magni ude. This a ionale ollows o mo e concen-
a ed SPEs, whe e PEO
6
/LiTFSI possesses lowe ionic conduc-
i i y (4.2 10
6
7.7 10
7
Scm
1
) compa ed o highly
dilu ed PEO
64
/LiTFSI (1.6 10
5
26 10
6
Scm
1
).
Rega ding mode a ely dilu e sys ems, a end o inc easing
Fig. 4
7
Li MAS-NMR spec a o (a) PEO
6
/LiTFSI and (b) PEO
32
/LiTFSI a 40 1C, 50 1C, 60 1C, 70 1C, and 80 1C. The solid black line ep esen s he
eco ded spec a, he dashed ed lines ep esen he peak i ing, whils he solid pu ple and cyan lines in (a), and he solid g een and blue lines in (b), bo h
espec i ely ep esen wo dis inc li hium-ion dynamics.
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