Iongel Soft Solid Electrolytes Based on [DEME][TFSI] Ionic Liquid for Low Polarization Lithium-O-2 Batteries

Iongel So Solid Elec oly es Based on [DEME][TFSI] Ionic
Liquid o Low Pola iza ion Li hium-O2Ba e ies
Ma a Al a ez-Ti ado,[a, b] Lau en Cas o,*[b] Au élie Guéguen,[b] and Da id Mece eyes*[a, c]
Li hium-ai /O2ba e ies a e a p omising ba e y echnology o
au omo i e applica ions due o hei high ene gy densi y.
Howe e , many challenges need o be sol ed, pa icula ly he
high eac i i y o he elec oly e wi h oxygen supe oxide
adicals and i s low cyclabili y. In his wo k, we p esen a simple
and as way o p epa e polyme -based iongel so solid
elec oly es. The mally and mechanically s able iongels a e
p epa ed by as UV-pho opolyme isa ion exhibi ing a high
ionic conduc i i y (~1.2×103Scm1a 25°C). When used as
solid elec oly es in li hium symme ical cells, hey can wi h-
s and a c i ical cu en densi y o 0.5 mAcm2. Pe o mance in
LiO2cells showed capaci ies as la ge as 3.3 mAhcm2, and
cycling capabili y o 25 cycles, exceeding esul s on liquid-
coun e pa cells.
In oduc ion
Li hium-O2(LiO2) cells a e a ascina ing class o Li me al-ai
ba e ies ea u ing one o he highes heo e ical speci ic
ene gy densi ies (3500 Whkg1).[1] None heless, he e is s ill a
long jou ney o go un il hei comme cializa ion becomes a
eali y. F om a ma e ial pe spec i e, many e o s ha e been
pu in de eloping mo e e icien elec oly es ha comply wi h
a b oad se o p ope ies such as high ionic conduc i i y o
mo e en i onmen ally iendly elec oly es.[2] In ha sense, ionic
liquids (ILs) seem a good al e na i e o con en ional lammable
o ganic sol en s due o a combina ion o good anspo
p ope ies, non- ola ili y, low oxici y (no e ha his p ope y
needs o be analyzed ca e ully),[3] non- lammabili y and s abili y
o supe oxide adicals.[4,5] The mos in es iga ed ionic liquids in
LiO2ba e ies a e based on imidazolium- and py olidinium-
ca ions[4,6–9] and luo ine-based anions (i.e.,
bis( i luo ome hanesul onyl)imide, TFSI).[10] Recen ly, less com-
monly used e a-alkyl ammonium based ILs, such as N,N-
die hyl-N-me hyl-N-(2-me hoxye hyl)ammonium
bis( i luo ome hanesul onyl)imide ([DEME][TFSI]) has shown
sui able p ope ies o applica ion in his ype o ba e ies. Fo
ins ance, Ulissi and co-wo ke s[11,12] showed ha [DEME][TFSI]
allowed a e e sible, low pola iza ion gal anos a ic cycling in
LiO2cells. In o he wo ks,[13] [DEME][TFSI] was used as elec o-
ly e achie ing 99.5% coulombic e iciency du ing cycling.
Fu he mo e, he IL was able o c ea e a li hium p o ec i e ilm
when i was in con ac wi h a Li1.5 Al0.5Ge1.5 (PO4)3(LAGP) solid
ino ganic ilm; imp o ing in his way ba e y cyclabili y. On he
o he hand, liquid elec oly e ba e ies equi e a po ous
sepa a o and leaking o he elec oly e is s ill a eali y. A
plausible way o u he imp o e his is ia he de elopmen o
gel polyme elec oly es, in which he liquid elec oly e is sa ely
encapsula ed wi hin a polyme ne wo k ac ing as a physical
sepa a o . They a e also known as iongels, ionic liquid gels o
ionogels i an IL-based elec oly e is used.[14] Al hough his
app oach is qui e popula in Li-ion,[15–17] Li-me al,[18–20] sodium-
me al[21,22] o o he ype o ba e ies,[8,23] i has no been la gely
explo ed o LiO2cells. The e a e a ew examples based on
poly(me hyl) me hac yla e (PMMA)[24,25] o poly( inylidene
luo ide-co-hexa luo op opylene) (PVdF-HFP)[26,27] polyme -
based iongels. Fo ins ance, Zhao and co-wo ke s[25] de eloped
by UV an iongel con aining 1-e hyl-3-me hylimidazolium e a-
luo obo a e IL (EMIm-BF4), dime hyl sul oxide (DMSO) and
LiTFSI, encapsula ed in a polyme ma ix o med by PMMA and
a iac yla e. Li hium symme ical cells con aining his iongel
p esen ed o e po en ials <0.1 V o 130 h when cycled a
0.3 mAh1. La ely, [DEME][TFSI] was selec ed o o m a quasi-
solid-s a e elec oly e by he gela ion o his IL when mixed
wi h mul i-wall ca bon nano ubes o solidi ica ion when mixed
wi h Li6·40La3Z 1·40Ta0·60O12 (LLZTO) ce amic nanopa icles ia
non-co alen in e ac ions.[28] Rega ding sal concen a ion in
ionic liquid based elec oly es, ecen s udies ha e shown ha
supe concen a ed IL elec oly es (>1:1 mola a io, IL:sal ) a e
able o p o ide an e icien p o ec ion o li hium-me al[29–32] o
sodium-me al anodes.[33] In e es ingly, e ec o sal concen a-
ion is deeply s udied in IL-based liquid elec oly es o LiO2
applica ions[34–36] bu i is no la gely e alua ed when hese a e
use in solid elec oly es. To he bes o ou knowledge, only
one example could be ound o iongels a high sal
concen a ions o all-solid-s a e sodium cells.[21] In his esea ch,
[a] M. Al a ez-Ti ado, P o . D. Mece eyes
Inno a i e polyme s
POLYMAT Uni e si y o he Basque Coun y UPV/EHU
A enida de Tolosa 72, Donos ia-San Sebas ian 20018, Spain
E-mail: [email p o ec ed]
[b] M. Al a ez-Ti ado, D . L. Cas o, D . A. Guéguen
Ma e ial Enginee ing, Ba e ies
Toyo a Mo o Eu ope Resea ch & De elopmen 2
Hoge Wei 33 B, B-1930 Za en em, Belgium
E-mail: [email p o ec ed]
[c] P o . D. Mece eyes
Ike basque
Basque Founda ion o Science
E-48011 Bilbao, Spain
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an iongel con aining 50 mol% o NaFSI in a py olidinium-
based IL (N-p opyl-N-me hylpy olidinium
bis( luo osul onyl)imide, C3mpy FSI) is used as elec oly e.
When used in sodium symme ical cells, his highly-concen-
a ed iongel was able o suppo highe cu en densi y cycling
han an iongel con aining 20 mol% o NaFSI.
In his wo k, we p esen a ull s udy o ob ain op imized
solid polyme elec oly es o LiO2ba e ies based on a low
pola iza ion ionic liquid ([DEME][TFSI]). E ec s o sal concen-
a ion on a polyme -based elec oly e will be s udied o he
i s ime o LiO2applica ions. By combining p omising esul s
o ecen wo ks, we p esen a simple bu e ec i e way o
p epa ing iongels sui able o LiO2cells ha show mechanical
and he mal s abili y, high ionic conduc i i y and ba e y
pe o mance, demons a ing equal o supe io p ope ies o
he liquid-coun e pa ionic liquid ba e y cells.
Resul s and Discussion
Iongels con aining a liquid elec oly e based on [DEME][TFSI]
ionic liquid and LiTFSI sal (ILE) we e p epa ed by UV-pho o-
polyme isa ion as p e iously shown o Li-ion and sodium-ion
ba e ies.[21,37,38] As shown in Scheme 1, poly(e hylene glycol)
dime hac yla e (PEGDM) was di ec ly mixed wi h he liquid
elec oly e a di e en weigh a ios ( om 50 o 90 w %,
Table S1) in he p esence o 2-hyd oxy-2-me hylp opiophene as
he pho oini ia o . A e UV-i adia ing o less han 2 min on
he d op-cas ed solu ion, sel -s anding and anspa en mem-
b anes we e ob ained. Samples wi h concen a ions o ILE
highe han 90 w % we e oo so (no sel -s anding) and
di icul o handle. In all cases, he deg ee o c oss-linking was
moni o ed ia Fou ie ans o m in a ed spec oscopy (FTIR)
spec a, and con e sions o �95% we e eached (Figu e S1).
The C=C s e ching ib a ion o he ac ylic g oups (1640–
1635 cm1) o he PEGDM dime hac yla e monome signi i-
can ly dec eased/disappea ed a e he UV-i adia ion, con i m-
ing high monome con e sion.[39]
Fi s , he impac o LiTFSI sal concen a ion on he physico-
he mal p ope ies o he iongels was assessed. Up o ou
di e en mola concen a ions o sal wi hin he iongel we e
s udied, including 13 mol%, 20 mol%, 32 mol % and 52 mol%
o LiTFSI in [DEME][TFSI]. I is wo h no ing ha only ILE in
which he mola a io o he sal is 52 mol%, is a supe -
concen a ed one. Thus, an iongel wi h a 20 mol % o LiTFSI
and 80% o ILE will be named as Iongel-20 mol%-80. All
combina ions a e desc ibed in Table S1.
The he mal s abili y o hese iongels was e alua ed
h ough he mal g a ime ical analysis, TGA. Iongels con aining
up o 90 w % o ionic liquid elec oly e ILE we e s udied. As
shown in Figu e 1(a), all memb anes did no p esen any
he mal deg ada ion un il 315°C due o he ema kable high
he mal s abili y o [DEME][TFSI] ionic liquid (~325°C decom-
posi ion empe a u e).[40] Fu he mo e, he p esence o highe
LiTFSI concen a ions did no signi ican ly impac he esul s.
On he o he hand, hei mechanical s eng h was e alua ed
h ough dynamic mechanical he mal analysis (DMTA), Fig-
u e 1(b). Resul s showed ha he modulus and he memb anes
a e s able om oom empe a u e o high empe a u e (100°C)
due o i s c osslinked na u e wha e e he ILE con en . La ge
con en o polyme in he o mula ion p o oked an inc ease o
he memb ane modulus (e.g., om 2×105Pa o 4×105Pa o
Iongel-20 mol%-90 and Iongel-20 mol%-80, espec i ely). Ac-
co ding o he Tanδde i a i e, Tgdec eased om 22.6 o
43.2°C o Iongel-TFSI-80 and Iongel-TFSI-90, espec i ely.
Hence, iongels wi h highe ILE con en showed a lowe glass
ansi ion alue. O e all, he low Tgo hese iongels and hei
mechanical obus ness, e en a e y high ILE con en s, oge he
wi h hei e y high he mal s abili y, make hese polyme
elec oly es in e es ing ma e ials o ba e y es ing.
To down-selec he mos p omising iongel composi ions,
hei ionic conduc i i y (σ) a di e en empe a u es was
e alua ed. As a baseline, [DEME][TFSI] based iongels wi h
di e en ILE weigh a ios bu a ixed sal concen a ions we e
assessed. Then, he mos p omising o mula ion ( ixed ILE:
polyme weigh a e) was used o e alua e he impac o sal
concen a ion. Acco dingly, iongels a inc easing ILE weigh
a ios (50 w %, 75 w %, 80 w %, 85 w % and 90 w %) we e
p epa ed a a ixed mola concen a ion o 13 mol% o LiTFSI in
[DEME][TFSI] (Table S1). As shown in Figu e 2(a), inc easing
Scheme 1. Schema ic ep esen a ion o he apid UV-pho opolyme isa ion p ocess unde aken o ob ain he c oss-linked iongel elec oly es.
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weigh a ios o he ILE leads o highe σ alues. The e was a
di e ence o one o de o magni ude be ween Iongel-
13 mol%-50 and Iongel-13 mol%-90, achie ing o he las
composi ion a conduc i i y as high as 1.19×103Scm1a
25°C, e y close o he alue o he liquid-coun e pa a he
same empe a u e (1.96×103Scm1). The same end was
ound in iongels a 20 mol% LiTFSI mola concen a ion
con aining 80 w %, 85 w % and 90 w % o LE (Figu e S2),
whe e Iongel-20 mol%-90 had he highes σ(9.99×104Scm1
a 25°C). Hence, iongels con aining 90 w % o ILE was he
chosen composi ion o u he cha ac e iza ion.
Then, iongels wi h di e en LiTFSI concen a ions we e
p epa ed (Figu e 2b). As only iongels con aining 90 w % o ILE
a e s udied om his poin , only he mola a io will be
indica ed in he nomencla u e o he samples o simplici y
(i.e., Iongel-52 mol%). As shown in Figu e 2(b), iongels wi h
lowe sal concen a ions lead o ionic conduc i i ies wo
o de s o magni ude highe han supe concen a ed Iongel-
52 mol% (~1.19×103Scm1 e sus 6.35×105S cm1a 25°C
o Iongel-13 mol% and Iongel-52 mol%, espec i ely). Rele an
alues a 25°C and 60°C a e shown in Table S2.
In opposi ion o in ui i e esul s, in which a highe
concen a ion o ions would d i e o highe ionic conduc i -
i ies, he much highe iscosi y o he supe concen a ed ILE
played a dominan ole, leading o a highe esis ance and
slowe ion anspo .[4,41] Simila conclusions we e ound in
li e a u e, whe e he inc ease in he [DEME][TFSI]-LiTFSI liquid
elec oly e conduc i i y was di ec ly ela ed o a dec ease in
iscosi y as pe he Vogel-Fulche -Tammann (VFT) model.[11]
O e all, iongels wi h 90 w % o ILE and in e media e sal
concen a ions (13 o 20 mol%) showed he highes ionic
conduc i i ies, di ec ly compa able o hei liquid coun e pa s.
Addi ionally, he pseudo-ac i a ion ene gy alues o he ionic
conduc ion p ocess o hese iongels we e calcula ed ollowing
he A henius-model o he mally ac i a ed p ocesses[42] (Fig-
u e S3). The calcula ed pseudo-ene gy alues inc eased wi h
highe sal concen a ion, and hey we e 0.31, 0.31, 0.33 and
0.48 eV o Iongel-13 mol%, Iongel-20 mol%, Iongel-32 mol%
and Iongel-52 mol%, espec i ely (Figu e S4). Hence, mo e
dilu ed elec oly es (e.g., Iongel-13 mol% o Iongel-20 mol%)
a o ed he dec ease o Ea, acili a ing ion anspo . Fu he -
mo e, he ac ion o cu en ca ied exclusi ely by he Li+ions,
was also e alua ed h ough he calcula ion o he li hium
Figu e 1. a) TGA analysis unde ni ogen a mosphe e a 10°Cmin1o iongel
memb anes con aining 90 w % liquid elec oly e; and b) DMTA analysis a
comp ession om 0 o 100 °C o Iongel-20 mol% memb anes con aining 80
and 90 w % o liquid elec oly e wi h same sal concen a ion (20 mol%).
Figu e 2. a) Ionic conduc i i y e sus empe a u e o Liquid-13 mol% elec oly e and Iongel-13 mol% memb anes con aining inc easing amoun s o liquid
elec oly e, om 50 o 90 w %; and b) ionic conduc i i y e sus empe a u e o iongel memb anes con aining 90 w % o liquid elec oly e a inc easing LiTFSI
mola concen a ions, om 13 mol% o 52 mol%. Inse : image o Ionogel-20 mol % memb ane a 90 w % liquid elec oly e.
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ans e ence numbe ( Li +) on li hium symme ical cells a
60°C. This was done ollowing he well-known E ans-Vincen -
B uce me hod,[43] whe e he cell is pola ized by a small DC
du ing a ch onoampe ome y (Figu e S5). The esul s showed
Li+ anging be ween 0.10 and 0.14 (Figu e 3a), inc easing wi h
inc easing LiTFSI mola concen a ion. This same endency was
epo ed in o he s udies,[31,44] in which he Li +imp o ed om
0.1 o 0.2 using highly-concen a ed elec oly es sugges ing
di e en li hium-ion anspo mechanisms o high concen-
a ed sys ems.[31] In lowe concen a ed ILE he ion pai s
o med (Li – [TFSI]2), do no a ou Li anspo and lowe s Li+;
howe e , in highe concen a ed elec oly es, Li+would be
a ou ed ia he LiO a oms coo dina ion o med be ween
hese TFSI-based agg ega es.[34]
To de e mine he s abili y o hese iongels agains li hium
me al, s ipping/pla ing cycles a inc easing cu en densi ies
we e pe o med on li hium symme ical cells a 60°C a e 3 h
condi ioning a OCV.
This es ing empe a u e was selec ed ollowing he
op imiza ion wo k done by o he esea ch g oup wi h liquid
cells using an ILE based on [DEME][TFSI].[11] Cu en densi ies
we e inc eased om 0.01 o 1 mAcm2, cycled 3 imes a each
cu en wi h 1 h dwell. The a e age po en ial (in absolu e
alue) achie ed a each a e o each iongel cell is plo ed in
Figu e 3(b). Cells wi h lowe sal -concen a ed iongel (i.e.,
Iongel-13 mol%, Iongel-20 mol% and Iongel-32 mol% cells) led
o lowe o e po en ials, wi hs anding a c i ical cu en densi y
(CCD, chosen when po en ial exceeds 1 V) o 0.5 mAcm2.
Unexpec edly, he supe concen a ed Iongel-52 mol% cell had
he lowes CCD (0.2 mAcm2). Highly-concen a ed ILE a e
usually explo ed o imp o e he s abili y agains li hium me al,
mi iga ing dend i es g ow h and imp o ing s abili y o he solid
elec oly e in e ace laye (SEI).[31,44] The limi ed pe o mance o
he supe concen a ed Iongel-52 mol% cell compa ed o
li e a u e could be ela ed o he use o polyme ic s uc u es in
his s udy, which migh impac he SEI in e acial s uc u e
o med in pu e supe concen a ed liquid elec oly e cells,[33,45]
baseline o he good pe o mance o hese sys ems. Cells we e
u he cycled (1 h pla ing, 1 h s ipping) in gal anos a ic
mode a hei CCD (Figu e S6a). Iongel-13 mol% and Iongel-
20 mol% cells beha ed e y simila ly, wi h ~0.7 V o e po en-
ials a e 27 and 18 h, espec i ely. Then, hey su e ed om a
“so ” sho -ci cui , showed o by ol age d ops caused by
li hium dend i es g ow h.[46–48] Highe concen a ed Iongel-
32 mol% cells had lowe o e po en ial (~0.2 V) o 14 h, and
hen showed a sha p pola iza ion inc ease un il cell dea h.
Same es was also done on liquid equi alen cells (Figu e S6b).
They had a cons an o e po en ial o ~0.2 V o e cycling.
Liquid-20 mol% cell was s able o 22 h, Liquid-32 mol% cell
o 45 h and Liquid-13 mol% cells, he bes ou o he liquid
cells, o 154 h; being in acco dance wi h simila epo ed
esul s.[11]
Be o e es ing in LiO2cells, he s abili y window o uppe
po en ials o he iongels we e in es iga ed in Li0/Iongels/
S ainless s eel cells by cyclic ol amme y a a scan a e o
0.2 mVs1a 60°C (Figu e S7). No signi ican di e ences we e
obse ed be ween Iongel-13 mol%, Iongel-20 mol% and Ion-
gel-32 mol% cells, in which no oxida ion cu en s occu ed up
o 3.72–3.78 V. The cell con aining supe concen a ed
ILE(Iongel-52 mol%) showed a highe anodic s abili y, up o
3.98 V, in ag eemen o o he s udies on supe concen a ed
DEME-TFSI liquid cells.[29,31] Following hese esul s, cu -o
po en ials o 2 and 3.6 V we e es ablished o LiO2cycling.
Swagelok LiO2ba e ies we e assembled and discha ged
in a dynamic mode a 60°C o de e mine he maximum cu en
a e a which he cells can ope a e (Figu e 4a and b). Inc easing
cu en densi ies ( om 5 μAcm2 o 0.28 mAcm2) we e
applied o 15 min pe a e. S eady po en ials achie ed a each
a e a e plo ed in Figu e 4a o all iongel cells (a e age o 3
cells pe ype). When he cells a e discha ged, he po en ial
eaches a pla eau a 2.96 V s. Li0/Li+(Eeq), which is he edox
po en ial o he eac ion:[49]
2Li þO2þ2e!Li2O2
This po en ial is usually ~0.3 V below and 0.5 V abo e he
Eeq (a discha ge and cha ge, espec i ely) due o ene gy loses.
Resul s showed ha cells con aining in e media e sal concen-
a ions ILE could be cycled a highe cu en a es
(100 μAcm2 o Iongel-20 mol% and Iongel-32 mol% cells)
han Iongel-13 mol% and Iongel-52 mol% cells (~75 μAcm2).
Conside ing all cells, 50 μAcm2was selec ed as he maximum
cu en densi y o u he gal anos a ic es ing wi h an a e age
discha ge po en ial o ~2.6 V. Wi hin liquid cells (Figu e 4b),
Figu e 3. Tes s on li hium symme ical cells: a) Ionic conduc i i ies a 60°C
agains li hium ans e ence numbe ; and b) a e age po en ials achie ed a
inc easing cu en densi ies. Cu en densi ies we e inc eased om 0.01 o
1 mAcm2a 60°C, cycled 3 imes a each cu en wi h 1 h dwell.
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in e media e sal concen a ions cells had he highes alues
(125 μAcm2 o Liquid-20 mol % and Liquid-32 mol% cells),
simila ly o iongel-based cells. This es was also ca ied ou a
25°C on cells wi h he lowes sal concen a ions (13 mol% and
20 mol%, bo h liquid and polyme ic cells) (Figu e S8b). In hese
condi ions, 20 μA cm2seemed o be he maximum accep able
a e. Those a es we e simila o he ones epo ed in li e a u e
o [DEME][TFSI] liquid cells a oom empe a u e.[11]
As seen in p e ious wo ks,[37] when a dynamic discha ge
loop is comple ed (Loop x1, Figu e S9a), only a small po ion o
he cell discha ge capaci y is used (Figu e S9b). Subsequen ly,
as soon as he cell is no longe pola ized (OCV), he po en ial
ends o each equilib ium o e ime, wi h dEWE/d ~0 (E1eq,
E2eq, e c.). Once he po en ial is s able (usually closed o ini ial
cell po en ial a OCV), cells can be discha ged again. This
ope a ion (dynamic discha ge) was epea ed se e al imes (i. e.,
Loop× 2, Loop×3, …, Loop ×150), un il no capaci y was le
and Eeq �2 V. In e e y loop, cells we e able o discha ge un il a
speci ic cu en densi y, named as imax1,imax2, e c. These wo se s
o da a – e.g., E1eq and imax1 – we e used o analyze u he he
cells (Figu es 4c, d and S9c, d). When he equilib ium pola -
iza ion po en ials a OCV (E1eq,E2eq, e c.) we e plo ed agains
he cumula i e discha ge capaci ies o he cell, he shape o he
cu e mimic he one o a gal anos a ic discha ge (Figu e 4c).
Acco ding o he esul s, cells wi h highe sal concen a ions
ILE led o highe cumula i e capaci ies (32 mol% cells
>20 mol% cells >13 mol% cells). This could be explained as
he equilib ium po en ials a e p opo ional o he amoun o
mobile ions p esen in he elec oly e (highe pola iza ion e ec
o highe ion-concen a ed ILE). This ule was no longe
applied on he supe concen a ed ILE (52 mol%), in which he
iscosi y kep being he dominan esis ance o ce o ion
anspo and ion mobili y was hen signi ican ly educed (low
pola iza ion). Fu he mo e (Figu e S9c), iongel-based cells p e-
sen ed lowe pola iza ions han liquid cells (lowe cumula i e
capaci ies) and 0.1 V di e ence in equilib ium po en ials (2.7
and 2.8 V o iongel and liquid cells, espec i ely). On he o he
hand, he maximum cu en s achie ed on each loop (imax1,imax2,
e c.) played an impo an ole oo in he inal cumula i e
discha ge capaci y. Figu es 4(d) and S6(d) show how hese
cu en a es we e much highe du ing he ull cell discha ge
o Iongel-20 mol% and Iongel-32 mol% cells, wi h maximums
o 225 μAcm2(~125 μAcm2 o he es o he cells), and
ma ching p e ious esul s.
A e wa ds, LiO2iongel cells we e ully discha ged/cha ged
in gal anos a ic mode a he selec ed a e (50 μAcm2),
empe a u e (60°C), using 100 μL o ca holy e (Figu e S8a) and
a e 3 h condi ioning a OCV. Figu e 5(a) shows ha he
absolu e discha ge capaci y o Iongel-13 mol% cell
(3.3 mAhcm2) was he highes o he g oup and h ee imes
highe han supe concen a ed Iongel-52 mol % cell. Howe e ,
Iongel-20 mol% cell has he highes Coulombic e iciency
(100%, 2.5 mAhcm2). This ully discha ged/cha ged es was
also done a a highe a e (0.1 mAcm2), ob aining lowe
capaci ies (~0.7 mAhcm2, iongel cells) and con i ming he
op imiza ion esul s ob ained on he dynamic discha ge es
(Figu e S10a, b). Due o hei lack o pe o mance, supe -
concen a ed cells we e no es ed u he . Las ly, LiO2cells
Figu e 4. Dynamic discha ge o LiO2cells a 60 °C ( a e es ): discha ge po en ial agains cu en densi y a inc easing LE sal concen a ions o a) iongel cells
and b) liquid cells; c) equilib ium pola iza ion po en ial a OCV (E1eq,E2eq, e c.) agains cumula i e discha ge capaci y o Iongel cells achie ed a e each
consecu i e loops; and d) maximum cu en densi ies (imax1,imax2, e c.) achie ed a he end o each discha ge loop o he Iongel cells.
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we e cycled wi h limi ed capaci y (0.2 mAcm2) a 50 μAcm2
and 2–3.6 V cu -o po en ials. Figu e 5(b) displays he dis-
cha ge capaci y e en ion o he h ee iongel cells. The bes
ones, Iongel-13 mol% and Iongel-20 mol % cells s a ed o ade
a e 25 cycles, al hough he ading o he 20 mol% one is
sligh ly smoo he . In e ms o Coulombic e iciency, CE, (Fig-
u e S10d), he Iongel-20 mol % cell had a 100% CE o a ew
cycles mo e han Iongel-13 mol% cell. The cyclabili y o he
liquid cells was also unde aken o compa ison (Figu e S10c).
Liquid-13 mol% cell was he bes one, keeping 100% o he
discha ge capaci y o 22 cycles. Thus, based on all hese
elec ochemical es s, we can conclude ha in ou case iongel-
based cells had highe cyclabili y han liquid cells.
Conclusion
In his wo k we p esen a s ep o wa d in he de elopmen o
sa e elec oly e designs o LiO2ba e ies by he use o so
solid iongel elec oly es based on a low pola iza ion ionic liquid
elec oly e. Taking he bes o p e ious esea ch wo ks, iongel
polyme ic elec oly es ha e been op imized by a ying he
polyme : ionic liquid elec oly e a ios, and he sal concen-
a ion, including supe concen a ed elec oly es. The iongels
can be p epa ed in an easy bu e ec i e manne ( as UV-
polyme iza ion) as lexible and sel -s anding memb anes. The
ionic na u e o he liquid elec oly e made hese iongels
excep ionally he mally s able (no deg ada ion un il 315 °C),
and su icien ly obus (~105Pa) o ba e y cells ope a ions.
E en u he , he op imiza ion o he o mula ion allowed
inding iongels wi h an ionic conduc i i y close o he liquid
coun e pa (~1.2×103Scm1a 25°C). In e media e sal -
concen a ed iongels (20 mol%), showed excellen pe o m-
ance in li hium symme ical cells, exceeding he liquid cells
esul s. O e all, Iongel-20 mol % LiO2cells exhibi ed a com-
p omising pe o mance amongs he es o he cells: one o
he maximum cu en a es, highe numbe o cycles and
highes Coulombic e iciency. The indings would also con i m
he capabili y and pe o mance o he polyme ic-based elec o-
ly es in his ype o ba e ies, which is di ec ly compa able o
liquid cells. This op imized and as p epa a ion me hod o ionic
liquid solid elec oly es could be used as he baseline o u u e
wo ks in which iongel p ope ies could be uned o applica ion
in LiO2 echnology.
Expe imen al Sec ion
Comp ehensi e expe imen al de ails including syn hesis and
cha ac e iza ions can be ound in he Suppo ing In o ma ion.
Acknowledgemen s
This wo k was suppo ed by he Eu opean Commission's unded
Ma ie Skłodowska-Cu ie p ojec POLYTE-EID (P ojec No. 765828).
The manusc ip was w i en h ough con ibu ions o all au ho s
ha ha e gi en app o al o he inal e sion.
Con lic o In e es
The au ho s decla e no con lic o in e es .
Da a A ailabili y S a emen
The da a ha suppo he indings o his s udy a e a ailable
om he co esponding au ho upon easonable eques .
Keywo ds: iongel ·li hium-O2ba e y ·li hium me al ·polyme
elec oly e ·solid-s a e ba e y
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Manusc ip ecei ed: Janua y 28, 2022
Re ised manusc ip ecei ed: Ma ch 11, 2022
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