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ab ica ion o high-pe o mance
dual ca bon Li-ion hyb id capaci o :
mass balancing app oach o
imp o e he ene gy-powe densi y
and cycle li e
and a panja1,2, Jon Aju ia1, Noel Díez3, Dh ubajyo i Bha acha jya1, Eide Goikolea2 &
Daniel ca iazo1,4 ✉
Mos li hium-ion capaci o (Lic) de ices include g aphi e o non-po ous ha d ca bon as nega i e
elec ode o en ailing when demanding high ene gy a high powe densi ies. He ein, we in oduce a
new Lic o med by he assembly o polyme de i ed hollow ca bon sphe es (HcS) and a supe ac i a ed
ca bon (AC), as nega i e and posi i e elec odes, espec i ely. The hollow mic os uc u e o HCS and
he ul a la ge speci ic su ace a ea o AC maximize li hium inse ion/di usion and ions adso p ion in
each o he elec odes, leading o indi idual ema kable capaci y alues and a e pe o mances. To
op imize he pe o mance o he Lic no only in e ms o ene gy and powe densi ies bu also om
a s abili y poin o iew, a igo ous mass balance s udy is also pe o med. Op imized LIC, using a 2:1
nega i e o posi i e elec ode mass a io, shows e y good e e sibili y wi hin he ope a i e ol age
egion o 1.5–4.2 V and i is able o deli e a speci ic cell capaci y o 28 mA h−1 e en a a high cu en
densi y o 10 A g−1. This leads o an ene gy densi y o 68 W h kg−1 a an ex eme powe densi y o
30 kW kg−1. Mo eo e , his LIC de ice shows an ou s anding cyclabili y, e aining mo e han 92% o he
ini ial capaci y a e 35,000 cha ge–discha ge cycles.
The sea ch o mo e powe ul ene gy s o age de ices has been in ensi ied in ecen yea s due o he inc easing
ene gy demand om mode n human ac i i y. Thus, bo h he esea ch and he indus ial communi ies a e acing
he challenges o de elop high powe /ene gy sou ces o he as -g owing ma ke o elec ic ehicles, ae ospace
and nex gene a ion po able elec onics. Amongs he di e en ene gy s o age sys ems, li hium-ion ba e ies
(LIBs) and supe capaci o s (SCs) a e he p e e ed ene gy sou ces o high ene gy o high-powe applica ions,
espec i ely. The main ad an ages o LIBs o e SCs a e hei b oad ope a ing po en ial window, hei highe
ene gy densi y (∼200 W h kg−1 s. < 10 W h kg−1 o SCs)1–4. On he o he hand, SCs a e able o supply much
highe powe densi ies and ha e an ex ended cycle li e (o e 106 cycles). Indus ially manu ac u ed LIBs and SCs
s ill show hei limi a ions in ce ain a eas o applica ion demanding bo h high-powe and high-ene gy.
Hyb id elec ochemical capaci o s (HECs), which combine a ba e y- ype nega i e elec ode wi h a capaci-
i e posi i e elec ode, ha e ecen ly a ac ed huge scien i ic and indus ial in e es since hey can p o ide high
ene gy densi ies a high powe . HECs based on di e en me al-ions such as Li+, Na+ o K+ ha e been p oposed
un il da e5–12. In pa icula , in li hium-ion capaci o s (LICs) he in e cala ion/dein e cala ion o Li+ occu s in
he anode side as in a LIB, whils he adso p ion/deso p ion o he coun e ion ( ypically PF6−) akes place a he
su ace o he posi i e elec ode as in an elec ical double laye capaci o (EDLC)5,6. Di e en LIC sys ems (“Dual
ca bon LICs”) combining a high su ace a ea ac i a ed ca bon as he posi i e elec ode wi h a Li-ion in e cala ing
ca bon (g aphi e, ha d ca bons o so ca bons) as he nega i e elec ode ha e been desc ibed in he li e a u e
1Cen 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. 2Uni e sidad del País
Vasco, UPV/EHU, 48080, Bilbao, Spain. 3Ins i u o de Ciencia y Tecnología del Ca bono, INCAR-CSIC. F ancisco
Pin ado Fe, 26, 33011, O iedo, Spain. 4IKERBASQUE, Basque Founda ion o Science, 48013, Bilbao, Spain. ✉e-mail:
[email p o ec ed]
open
The e a e amendmen s o his pape
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showing an ene gy s o age capaci y almos i e imes highe han ha o EDLCs, main aining good esponse
a high powe demand and s abili y upon long cycling.6,9,10–12. Ano he ad an age wi h espec o con en ional
EDLC capaci o s is ha , due o he asymme ic combina ion o anode and ca hode, he LIC de ices su e om a
much lowe sel -discha ge, simila ly o Li-ion ba e ies7,11.
Rega ding he nega i e elec ode, ha d ca bons ha e shown p omising esul s e en doubling he heo e ical
capaci y o g aphi e. Thei diso de ed s uc u e con aining g aphi e-like domains wi h a low deg ee o c ys al-
lini y enables he use o mo e space o he Li+ ion s o age in he ca i ies and mic opo es along wi h in e cala-
ion10,12. Di e en nanos uc u ed ca bon ma e ials, namely ca bon nanoshee s, nanosphe es, ca bon nanopipes
o ca bon nano ibe s among o he s ha e been ecen ly in es iga ed as anodes o LICs. Tuning he mic os uc u e
o he ca bons a he nanoscale b ough abou signi ican imp o emen s in e ms o s uc u al s abili y, anspo
kine ics, cyclabili y, and coulombic e iciency9,12–14. The mo phology o he hollow ca bon sphe es esul s pa icu-
la ly con enien since hey p o ide elec oly e ese oi s and as en Li+ in e cala ion/dein e cala ion p ocesses
h ough he hin ca bon walls15,16. Addi ionally, hei ample inne space can bu e he olume changes unde gone
du ing he cha ge/discha ge p ocesses, hus imp o ing he mechanical s abili y o he elec ode16,17.
As he posi i e elec ode, ac i a ed ca bons a e p e e en ially chosen due o hei la ge speci ic su ace a eas
and open po osi y, which allows as ionic anspo o he whole su ace o he elec ode6,18. In a p e ious wo k,
we ha e in oduced a no el and s aigh o wa d syn he ic ou e o he p epa a ion o ul a-high speci ic su ace
a ea ac i a ed ca bons. This syn hesis s a egy, consis ing on a acile one-s ep p ocess in which polyme iza ion,
ca boniza ion and chemical ac i a ion o he ca bon p ecu so s occu all a once and yields ca bons wi h spe-
ci ic su ace a eas sligh ly abo e 3000 m2 g−1 and a hie a chical mic o-mesopo ous s uc u e. Bo h hei sui able
po ous s uc u e and easy p epa a ion make hem a sui able choice o he posi i e elec ode ma e ial in LIC
sys ems19.
The pe o mance o hyb id supe capaci o s can be imp o ed h ough he op imiza ion o he mass balance
be ween he posi i e and nega i e elec odes20. Thus, di e en mass balances ansla e in o di e en wo king
po en ial spans and, he e o e, a di e en deg ee o u iliza ion o each elec ode, which can be used o maximize
he ene gy densi y o he de ice. Indeed, mos o he scien i ic epo s ocus on he bes -ob ained ene gy/powe
esul s, no paying much a en ion o sa e y and s abili y.
In his epo , we p esen a acile syn he ic ou e owa ds hollow ca bon sphe es by he py olysis o ni ogen
con aining monome s. This ma e ial was coupled in a ull cell wi h ou home-made supe ac i a ed ca bon as
he posi i e elec ode. Op imiza ion o he elec odes mass balance, wi hin an ope a i e po en ial window o
1.5–4.2 V, was also in es iga ed.
Resul s and Discussions
physicochemical cha ac e iza ion. The schema ic diag am included in Fig.1 summa izes he app oach
ollowed o he p epa a ion o he hollow ca bon sphe es ha will se e as nega i e elec ode in his s udy. Fi s ,
polyme ic hollow mic osphe es we e p epa ed by a simple s a egy ha in ol es he in e acial co-polyme iza ion
o aniline and py ole in he p esence o T i on X-10017,21. Due o hei di e en hyd ophobici y, he molecules o
aniline mainly si a he ou e laye o he micelle-wa e in e ace, whe eas he mo e hyd ophobic py ole mole-
cules end o di use owa ds he inne wall o he micella co e.
Polyme iza ion leads o he o ma ion o hollow polyme ic sphe es (HPS) and i s subsequen ca boniza ion
unde ine a mosphe e yields hollow ca bon sphe es (HCS). The HCS main ain he p is ine mic os uc u e o
he HPS bu unde go a sligh sh inkage o hei size (Fig.2a,b).
The hickness o he ca bon walls was o ca. 110 nm (Fig.2d). The XRD pa e n o he ca bonized sample
(Fig.2c) shows wo low in ensi y and b oad X- ay di ac ion peaks a ~26° and ~50°, which co espond o he
(002) and (100) planes cha ac e is ic o diso de ed ca bons wi h a low deg ee o g aphi iza ion. The Raman spec-
um (Fig.2c, inse ) shows wo p edominan bands a ~1356 cm−1 and ~1594 cm−1, which e lec he de ec s
in he ca bon la ice (D-band) and he s e ching ib a ion in C-C bonds (G-band), espec i ely. Addi ionally,
wo b oad and e y low in ense peaks can be iden i ied in he 2500–3000 cm−1 egion, ha a e asc ibed o he
G´ s e ching mode. De ec s in he o ms o edges and su ace impe ec ions like de ec s, c acks, ca i ies, and
ac i e si es ac as ca aly ic si es, which can be ac i e o o ma ion o solid-elec oly e in e ace (SEI) laye as
well as li hia ion-deli hia ion p ocess in he nega i e elec ode o LIC cell22. The high- esolu ion TEM images
(Fig.2e) e idenced he p esence o mic opo es in he ca bon shells. To ge addi ional in o ma ion abou he ex-
u al ea u es o hese ca bon sphe es, ni ogen gas adso p ion-deso p ion measu emen s we e ca ied ou . The
N2 adso p ion-deso p ion iso he m egis e ed o HCS (Fig.2 ) shows a p o ile in be ween ypes I and IV acco d-
ing o IUPAC classi ica ion, wi h a H4 hys e esis loop23. The la ge adso p ion o ni ogen a low ela i e p essu es
con i med he mic opo ous na u e o he ma e ial. Due o he p esence o a la ge amoun o mic opo es, he BET
Figu e 1. Schema ic diag am o he syn hesis p ocess o hollow polyme sphe es (HPS) and hollow ca bon
sphe es (HCS).
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speci ic su ace a ea calcula ed o his ma e ial was 282 m2 g−1. Since he monome s used o he p epa a ion o
he HCS con ain ni ogen we ha e also pe o med he elemen al analysis o he HCS ca bon using Induc i ely
Coupled Plasma Mass Spec ome y (ICP-MS) o de e mine he ni ogen con en in his anode ma e ial. The
analysis showed ha HCS has a high ni ogen con en o 9.1 w .% in i s ca bon amewo k. I is well-known ha
he inco po a ion o ni ogen-con aining g oups in he ca bon ne wo k no only imp o es he elec onic and
ionic conduc i i ies bu also p o ides ac i e si es ha enhance ion adso p ion leading o an inc ease in capaci y
and a e capabili y17,24.
Physicochemical cha ac e iza ion o he supe ac i a ed ca bon p epa ed by he in-si u polyme iza ion, ca -
boniza ion, and ac i a ion o melamine and e eph halaldehyde is included in Fig.3. SEM images (Fig.3a) show
i egula -shaped ca bon u icles wi h a size o ~50 nm and a e y ough su ace. High magni ica ion TEM in es i-
ga ion (Fig.3b) e eals he nanopo es andomly dis ibu ed along wi h he sample. The N2 adso p ion-deso p ion
iso he m egis e ed o his ac i a ed ca bon exhibi s a p o ile in be ween ype I and IV wi h a dis inguishable
capilla y condensa ion s ep in he ela i e p essu e ange o 0.3–0.619. The ab up inc ease o N2 abso p ion a
low ela i e p essu es is indica i e o i s highly mic opo ous s uc u e. Indeed, he speci ic su ace a ea and po e
olume calcula ed o his ma e ial a e as high as 3180 m2 g−1 and 2.8 cm3 g−1, espec i ely. The po e size dis i-
bu ion calcula ed om he iso he m da a (inse in Fig.3c) shows he con ibu ion o wo po e sys ems wi h in
he mic o- and mesopo e ange, cen e ed a ca. 1.0 nm and 2.3 nm, espec i ely. The ul a-la ge speci ic su ace
a ea combined wi h i s hie a chical dis ibu ion o po e sizes is con enien o he physical adso p ion o a la ge
numbe o ions wi h a low esis ance o di usion, esul ing ideal o i s use as an EDLC elec ode. The Raman
spec um in Fig.3d displays he ypical D and G bands a ~1350 cm−1 and ~1590 cm−1, espec i ely, poin ing ou
ha a signi ican amoun o g aphi ic ca bon is s ill p esen in he ca bonaceous ne wo k despi e he la ge con-
cen a ion o de ec s and/o po es in sample24.
elec ochemical cha ac e iza ion
Bo h ca bonaceous ma e ials we e elec ochemically cha ac e ized indi idually. Fi s , he pe o mance o HCS
as anode ma e ial was in es iga ed in a hal -cell con igu a ion (T- ype Swagelok) using Li oil as bo h he coun e
and he e e ence elec ode. The cell was cycled wi hin he po en ial ange o 0.002–2.0 V s. Li+/Li. Figu e4a
illus a es he 1s , 5 h and he 10 h cyclic ol ammog ams (CVs) eco ded a 1 mV s−1. I can be obse ed ha mos
o he capaci y is s o ed below 1.0 V. In he i s CV, a b oad educ ion peak can be dis inguished be ween ~1.0 o
0.3 V, which esembles he o ma ion o a SEI laye due o he ca bona e sol en decomposi ion25. The in e cala-
ion o Li+ in o he HCS akes place be ween 0.3 and 0.01 V, while he dein e cala ion p ocess shows a maximum
cu en peak a 0.23 V. The Gal anos a ic cha ge-discha ge cu es (GCD) pe o med be ween 2.0 V and 0.002 V
a di e en cu en a es a e shown in Fig.4b. The i s discha ge a 0.1 C (C = 372 mA h g−1) om i s open ci cui
Figu e 2. (a) SEM images o HPS and (b) HCS ob ained a e he py olysis o HPS, (c) XRD pa e n eco ded
o HCS (inse : Raman spec um egis e ed o HCS), (d) low magni ica ion TEM image o HCS and (e) high
magni ica ion TEM image o HCS ou e su ace, ( ) N2 adso p ion-deso p ion iso he ms egis e ed o HCS.
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po en ial shows wo dis inc pla eaus a ~1.0 V and ~0.25 V co esponding o SEI o ma ion and Li+ in e cala ion,
which a e in good ag eemen wi h he CV. The i s discha ge shows a e y la ge speci ic capaci y o ca. 910 mA h
g−1, whe eas he i s cha ge shows a speci ic capaci y o 523 mA h g−1 co esponding o an i e e sible capaci y
loss o ~43%. Such high i e e sible capaci y loss measu ed in he i s cycle is a ibu ed no only o he o ma ion
o he SEI laye caused by he decomposi ion o ca bona e elec oly e bu also due o he i e e sible eac ion
o Li+ wi h oxygen-con aining unc ional g oups p esen in he HCS26. I can be obse ed in he second and
ou h cha ge-discha ge cu es ha an addi ional cha ge s o age occu s be ween 1.5 and 0.25 V in addi ion o
he Li+ in e cala ion be ween 0.25 and 0.01 V. This explains he high speci ic discha ge capaci y alues o 500 and
430 mA h g−1, espec i ely. This addi ional speci ic capaci y alues a e a ibu ed o he highly diso de ed na u e
o HCS ca bon ha p omo es Li+ s o age h ough o he mechanisms such as excess bulk s o age, s o age in ca -
i ies and nanopo es, in e acial/su ace s o age and he e ec o he e oa oms, which g adually dec eases du ing
he subsequen cycles s abilizing a e he i h cycle27. The HCS anode showed excellen capaci y e en ion a
inc eased cu en a es (Fig.4d). Thus, 173 mA h g−1 and 100 mA h g−1 we e achie ed a 10 C and 30 C (measu ed
in he 5 h cycle egis e ed a each cu en a e), which co esponds o a e en ion o he ini ial capaci y o ~40%
and ~24%, espec i ely. E en a e es ing a he e y high cu en a e o 100 C, 87% o he ini ial capaci y was
e ie ed when he cu en a e was se again o 0.1 C. The SEM images egis e ed o an anode con aining HCS
and he binde show ha he ca bon sphe es a e well dispe sed, which ensu es ha li hium ions can easily access
all he a ailable mic opo ous ca bon su aces (Fig.4c). Addi ionally, he mic os uc u e o he HCS is undoub -
edly esponsible o such ad anced a e pe o mance. Bo h he in e pa icle space and he sphe ical oids in he
co e o he HCSs ac as ion-bu e ing ese oi s, which sho en he di usion pa h owa ds he hin mic opo ous
ca bon shell16,17. I is also no ewo hy ha al hough he CE in he i s cycle was me ely 57%, i quickly aised up
o 95% in he second cycle and s abilized a a alue o 98% in he subsequen cycles e en a high cu en a es.
Such high CE indica es ha his ca bon a chi ec u e is e y capable o endu ing he mechanical s ess induced a
ha sh cu en a es.
Figu e 3. (a) SEM image, (b) TEM image, (c) N2 adso p ion-deso p ion iso he ms (inse : po e size dis ibu ion
cu e) and (d) Raman spec um egis e ed o he ac i a ed ca bon (AC).
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The capaci i e pe o mance o he supe ac i a ed ca bon was e alua ed in he po en ial ange o 1.5–4.2 V s.
Li+/Li using LiPF6 in 1:1 (EC:DMC) as he elec oly e. Figu e5a,b include he CV cu es egis e ed a 5 and
100 mV s−1. A he lowes scan a e, he plo is squa e-shaped and e y symme ic, e idencing he capaci i e
beha io o he ma e ial. Gene ally, he open ci cui po en ial o ac i a ed ca bon ca hodes alls in be ween he
po en ial ange o 3.0–3.1 V s. Li+/Li in a Li-ion elec oly e. The e o e, he elec ical double laye s o es ions o
opposi e cha ge depending on he po en ial ange, i.e. i adso bs
−
PF6
anions om 3 V o 4.2 V and Li+ ca ions
om 3 V o 1.5 V. E en a he high sweep a e o 100 mV s−1 he plo shows he cha ac e is ic ec angula -shaped
p o ile, poin ing ou he as and e ec i e pola iza ion unde gone due o he cha ge sepa a ion a he elec ode/
elec oly e in e ace. Figu e5c shows he GC-GD p o iles o he AC ca hode a di e en cu en densi ies. The
symme ic iangula -shaped GC-GD cu es showing almos 100% o CE con i m he pu ely capaci i e beha io
o he supe ac i a ed ca bon. In e es ingly, his AC achie ed a speci ic capaci ance o 208 F g−1 a 1 A g−1, and
e ained 203 F g−1 a a high discha ge a e o 10 A g−1 (Fig.5d). Such good capaci ance e en ion is a o ed by he
ex emely high speci ic su ace a ea o he AC combined wi h i s hie a chical and in e connec ed po ous ne wo k,
which allows he unimpeded di usion o elec oly e ions on o he ac i e ca bon su ace19,20. The excellen a e
capabili y obse ed oge he wi h he absence o ohmic d op a he beginning o he discha ge b anches poin ou
his ac i a ed ca bon as a p omising posi i e elec ode ma e ial o LIC sys ems.
In iew o he good pe o mances exhibi ed by bo h ca bonaceous ma e ials, LIC ull cells we e assembled
using HCS and AC as anode and ca hode elec odes, espec i ely. As a ule o humb, in asymme ic capaci o
con igu a ion he e should be cha ge balance be ween anode and ca hode based on he speci ic capaci y and
po en ial window28. Howe e , his ule does no always esul in op imum pe o mance in he case o a Li-ion
capaci o . This is because he e is s a k di e ence be ween he kine ics o a adaic li hia ion in anode and
non- a adaic
−
PF6
adso p ion on ca hode. This di e ence esul s in con as ing speci ic capaci y pe o mance o
anode and ca hode a low and high cu en densi y (Figu eS3 o Supplemen a y in o ma ion), which make i
almos impossible o es ima e he cha ge balance e ec i ely only by conside ing he speci ic capaci y a low cu -
en . The e o e, o e alua e and op imize he elec ochemical pe o mance o he ull cell as well as o achie e bes
pe o mance in e ms o speci ic capaci y, cycling s abili y and sa e y, a a ia ion o he elec ode mass a io was
in es iga ed. Thus, ou LIC cells we e assembled using anode/ca hode elec ode mass a ios o 1.1, 1.3, 1.7 and
2.0. In Fig.6a,b ha e compa ed he GC-GD cu es eco ded o hese ou LIC cells a 0.1 and 10 A g−1, espec-
i ely, in he 1.5–4.2 V po en ial ange. A he lowes cu en densi y, a p og essi e dec ease o he discha ge ime
was obse ed when he mass a io was inc eased om 1.1:1 o 2:1. This end is in e ed when he cu en densi y
is inc eased o 10 A g−1. A his cu en a e, a p ominen dec ease in he ohmic d op combined wi h an inc ease
in he discha ge ime (almos wo- old highe ) is obse ed when he mass a io is inc eased om 1.1 o 2. This
Figu e 4. Elec ochemical cha ac e iza ion o hollow ca bon sphe es as an anode in hal -cell con igu a ion
es ed be ween 0.002 and 2.0 V; (a) CVs s. Li/Li+, (b) GC-GD s. Li/Li+, (c) SEM image o HCS elec ode
su ace and (d) a e capabili y and coulombic e iciency.

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di e ence in mass a ia ion pe o mance is also clea ly exhibi ed om Ohmic d op s. cu en densi y plo s o all
LIC cells is shown in Figu eS1 o he Supplemen a y In o ma ion. The be e elec ochemical pe o mance o he
high mass a io LIC cell seems o be he deepe u iliza ion (la ge ope a ing ol age) o he EDLC elec ode du ing
he as anionic adso p ion-deso p ion p ocess. Figu e6c shows he e olu ion o he speci ic capaci y wi h he
cu en densi y o he LIC cells using di e en elec ode mass a ios. I can be obse ed ha a cu en densi ies
below 1 A g−1 he LIC cell wi h he lowe mass a io (1.1:1) shows he highes speci ic capaci y, whe eas he LIC
cell assembled using he 2:1 elec ode mass a io shows he bes a e capabili y and he la ges alue o speci ic
capaci y a high cu en a es, achie ing 28 mA h g−1 a a cu en densi y o 10 A g−1. The same end wi h espec
o he mass a ia ion is also no iced in case o speci ic cell capaci ance (F g−1) alues, which a e included in he
Figu eS2 (Supplemen a y In o ma ion). Figu e6d ep esen s he compa a i e Ragone plo s calcula ed o he
LICs wi h di e en elec ode mass a ios. A he lowes cu en densi y, he 1.1:1 cell achie ed an ene gy densi y
o 141 Wh kg−1, and his alue sligh ly dec eased wi h he inc ease o he mass a io down o he 117 Wh kg−1
eached by he 2:1 cell. Wi h he inc ease o he applied cu en , he di e ences be ween he di e en cells become
mo e no iceable. Indeed, a he highes cu en densi y (8 seconds o discha ge) he LIC wi h he highes loading
in he nega i e elec ode ob ained an ene gy densi y as high as 68 Wh kg−1 a a powe densi y o 30 kW kg−1.
In o de o ge deepe insigh s in o he elec ochemical pe o mance o he LICs, he pe o mance o each
elec ode was moni o ed. The GC-GD p o iles egis e ed o he AC ca hodes and he HCS anodes (plo ed s. Li/
Li+) a a cu en densi y o 1 A g−1 a e shown in Fig.7a–d. In he 1.1:1 LIC cell (Fig.7a) he anode po en ial swing
is signi ican ly high (~1.85 V), which e idences a high u iliza ion o he anode o he Li+
in e cala ion-dein e cala ion p ocess. The e o e, his con igu a ion allows ex ac ion o he highes amoun o
cha ge s o ed hus deli e ing he highes speci ic capaci y. Howe e , since he anodic p ocess is kine ically much
slowe han he adso p ion-deso p ion o
−
PF6
occu ing in he posi i e elec ode, his con igu a ion limi s he
cha ge ex ac ion a high cu en densi ies. This anode po en ial swing is g adually dec eased om ~1.38 o
~0.34 V, as i can be obse ed om Fig.7b–d, wi h an inc ease in anode/ca hode mass a io. This dec ease esul s
in a less u iliza ion o he anode bu esul s in less pa icle olume expansion, elec oly e decomposi ion and li h-
ium consump ion. On i s behal , wi h he inc ease in anode/ca hode mass a io, he po en ial swing in he ca hode
inc eased signi ican ly om 1.0 V (1.1:1 cell) o 2.38 V (2:1 cell) hus g adually enhancing he ca hode capaci y.
The e o e, he 2:1 elec ode mass a io gua an ees he bes a e capabili y o he cell aking ad an age o a highe
u iliza ion o he po ous elec ode su ace. On he o he hand, he lowe pola iza ion egis e ed in he anode
limi s he ope a i e capaci y o he anode hus esul s in less speci ic capaci y o ull cell. Howe e , concu en ly
his lowe anode pola iza ion a oids he chances o li hium pla ing, which is bene icial in e ms o sa e y as well
as du abili y.
Figu e8a and Figu eS4 in supplemen a y in o ma ion show he GC-GD plo s o each elec ode as well as
he co esponding LIC o all cell combina ions a a cu en densi y o 10 A g−1. These igu es almos mi o he
Figu e 5. Elec ochemical cha ac e iza ion o AC ca hode in hal -cell con igu a ion es ed be ween 1.5 o 4.2 V;
(a) & (b) CVs a low and high scan a e o 5 mV s−1 and 100 mV s−1 ( s. Li/Li+), (c) GC-GDs s. Li/Li+, and (d)
capaci y s. cu en densi y ( a e pe o mance).
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obse a ion e ealed om Fig.7a–d wi h addi ional e idence. Figu e8a e eals ha he 2:1 LIC cell is s ill ully
ope a i e wi hin he 1.5–4.2 V po en ial ange e en a such a high cu en a e. Mo eo e , he anode po en ial
swing is s ill limi ed o ~0.38 V. Howe e , he 1.1:1 LIC cell (Figu eS4a) shows a signi ican inc ease in anode
po en ial swing up o ~2.26 V. This esul s in se e e Li+ pla ing on he anode (yellow colo ma ked a ea in
Figu eS4), which no only deg ades he cell pe o mance bu also agg a a es sa e y issues. The o he wo mass
a io LIC cells show a g adual dec ease in he anode po en ial swing, hus enhancing he powe pe o mance.
F om all hese GC-GD esul s, i was ound ha he 2:1 LIC cell shows he bes pe o mance in e ms o bo h spe-
ci ic capaci y and a e capabili y. This is due o a s eady ca hode po en ial window combined wi h he con ended
use o he anode (i s CE is e y close o 100%), which allows he s able pe o mance o he ull cell. So, his 2:1 LIC
cell is selec ed o in es iga e he long- e m s abili y by pe o ming GC-CD cycles a a cu en densi y o 10 A g−1.
The esul an cyclic s abili y plo in Fig.8b shows ha his LIC cell exhibi ed an ou s anding cycling pe o mance,
e aining 98.7% o i s ini ial capaci y a e 10,000 cycles, and 92% a e 35,000 cycles. The po en ial swing o each
elec ode du ing he cycling es is plo ed in Fig.8c. As can be seen, he ca hodic po en ial window shows a small
upwa d shi ing, bu emains s eady du ing he whole es , which alida es he s able pe o mance o he ull cell.
Fo he sake o compa ison, Fig.8d collec s he Ragone plo o ou op imized LIC as well as hose o o he
ep esen a i e LIC sys ems ecen ly epo ed. I is wo h o highligh he excellen ene gy densi y measu ed o
ou selec ed LIC, especially in he high-powe egion in which mos o he p e iously epo ed LICs su e om
an ab up decay o hei ene gy densi ies5,10,13,14,18,29,30.
conclusions
Mic o-sized hollow ca bon sphe es ha e been syn hesized by an easy p ocedu e. This ma e ial exhibi s imp o ed
pe o mance in he li hium inse ion-ex ac ion p ocess especially a e y high cu en a es, which poin i as
a p omising candida e o i s use as he nega i e elec ode in li hium-ion capaci o s. LICs we e assembled by
coupling his mic o-s uc u ed hollow ca bon sphe es e sus a supe ac i a ed mic o-mesopo ous ca bon using
di e en elec ode mass a ios. The hollow ca bon sphe es a e able o esis he olume changes du ing epe i i e
li hia ion-deli hia ion cycles, while he hie a chical po osi y o he supe ac i a ed ca bon o e ing e y low esis -
ance o ion di usion assu ed a good esponse a high cu en a es. I was ound ha he bes nega i e/posi i e
elec ode mass a io in his LIC sys em is 2:1, a which he cell deli e s a maximum g a ime ic ene gy densi y
o 117 Wh kg−1 a 0.34 kW kg−1 and s ill 68 Wh kg−1 a an ex eme powe densi y o 30 kW kg−1. The obus ness
o he LIC was con i med by i s ema kable long- e m s abili y o e 35000 cycles wi h only 8% o capaci y decay
egis e ed. This ou s anding pe o mance makes ou p oposed LIC a p omising ene gy s o age sys em s anding
ou among i s pee s.
Figu e 6. Compa a i e elec ochemical cha ac e iza ion o HCS//AC ull cells wi h di e en elec ode mass
a ios: GC/GDs a a cu en densi y o (a) 0.1 A g−1 and (b) 10 A g−1, (c) a e capabili y and (d) Ragone plo .
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Expe imen al Sec ion
Syn hesis. The hollow ca bon sphe es (HCS) we e syn hesized by he ca boniza ion o polyme ic hollow
sphe es unde a dynamic ine a mosphe e. Fo he syn hesis o he co-polyme ic hollow nanosphe es, 0.08 g o
T i on-X-100 was dispe sed in 50 ml deionized wa e , and hen 0.456 ml o aniline and 0.346 ml o py ole we e
added o he mix u e unde con inuous s i ing ha was kep un il comple e dissolu ion. Then, he solu ion was
kep unde con inuous s i ing in an ice ba h o main ain a empe a u e o 3–5 °C. Fo he oxida i e polyme iza-
ion, aqueous ammonium pe sul a e (0.8 g was dissol ed in 1 ml DI wa e ) was p ecooled a 3–5 °C and added o
he abo e solu ion. The mix u e was s i ed o a ew minu es and he esul ing solu ion was kep in he e ige -
a o o 24 h a 4 °C. Finally, he ob ained da k g eenish polyme p ecipi a e was collec ed by cen i uga ion and
washed wi h DI wa e se e al imes. The p oduc was eeze-d ied o main ain he mic oscopic s uc u e o he
polyme ic hollow sphe es and hen ca bonized a 800 °C in A a mosphe e o 2 h using a hea ing a e o 3 °C
min−1.
The supe ac i a ed ca bon (AC) was syn hesized ollowing he syn he ic ou e desc ibed in de ail in ou p e-
ious epo 19. B ie ly, 1.24 g o melamine, 1.36 g o e eph haladehyde and 5.0 g o KOH we e g ounded using an
aga e mo a and he mix u e was ca bonized unde A a mosphe e. The empe a u e was i s aised up o 250 °C
o 3 h and hen inc eased o 800 °C o 1 h using hea ing amps o 1 °C min−1. (CAUTION: ce ain amoun o
po assium cyanide may be o med du ing he ca boniza ion p ocess, so ca bon should be ca e ully manipula ed,
and he was es ea ed acco dingly). Then he inal p oduc was washed se e al imes wi h 3 M HCl and DI wa e
ollowed by d ying a 120 °C in an o en.
physicochemical cha ac e iza ions. X- ay di ac ion (XRD) pa e ns o he syn hesized powde ed sam-
ples we e eco ded on a B uke D8 X- ay di ac ome e and he da a we e a ained a 40 kV and 30 mA using
CuKα adia ion o e 2θ wi hin he ange om 5 o 90° a s eps o 0.02° wi h a esidence ime o 5 seconds.
Raman spec a da a we e collec ed using a Renishaw spec ome e (Nanonics Mul i iew 2000) which was ope -
a ed wi h an exci a ion wa eleng h o 532 nm unde an A ion lase wi h an exposi ion ime o 10 seconds. The
nanos uc u e o he syn hesized samples was in es iga ed on a Scanning elec on mic oscope (SEM) in a ield
emission Quan a 200 FEG mic oscope. Tecnai G2 ansmission elec on mic oscope (TEM, FEI) was used o
he mic os uc u al cha ac e iza ion. Fo TEM analysis, samples we e homogeneously dispe sed in 1 ml e hanol
o 10–15 min by ul asonica ion. A e ha , a ew d ops o he solu ion we e cas on a Cu g id deco a ed wi h
holey ca bon ilms. N2 adso p ion-deso p ion expe imen s we e ca ied ou a −196 °C using an ASAP 2020
ins umen om Mic ome i ics. The alues o speci ic su ace a ea we e calcula ed using he B unaue , Emme ,
and Telle (BET) equa ion wi hin a ela i e p essu e ange o 0.05–0.2. The o al po e olume (VT) was calcula ed
by he amoun o ni ogen adso bed a р/po = 0.95. Po e size dis ibu ions (PSD) we e e alua ed based on he
Figu e 7. Compa a i e gal anos a ic cha ge-discha ge p o iles o each elec ode in LICs wi h di e en
elec ode mass a ios a a cu en densi y o 1 A g−1. The cells we e un in he 1.5–4.2 V po en ial ange.
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N2 adso p ion b anch da a by using he wo-dimensional nonlocal densi y unc ional heo y (2D-NLDFT). The
ni ogen con en in he HCS ca bon was de e mined by induc i ely coupled plasma mass spec ome y (ICP-MS).
Elec ode p epa a ion, cell assembly, and elec ochemical cha ac e iza ion echniques. The
nega i e elec ode slu y was p epa ed by mixing 90 w % o hollow sphe ical ca bon (HCS) wi h 5 w % Supe -C
C65 ca bon black (Ime ys G aphi e & Ca bon, Willeb oek, Belgium) and 5% poly inylidene luo ide (PVdF)
in N-me hyl-2-py olidone (NMP). The componen s we e mixed unde igo ous s i ing o a leas 1 h using
a magne ic s i e . The ob ained HCS-based slu y was coa ed on o a coppe oil cu en collec o . Fo he pos-
i i e elec ode slu y, he ac i a ed ca bon, Supe -C C65, and PVdF we e mixed in a weigh mass a io o 90:5:5
in NMP solu ion unde con inuous s i ing o 1 h and hen he AC-based slu y was lamina ed on o an alu-
minum oil. Lamina es we e placed immedia ely in o a acuum o en o d ying a 80 °C o 12 h unde con-
s an acuum. The mass loading o he posi i e elec ode was o 1–1.3 mg cm−2 while he loading in he nega i e
elec ode anged om 1.4 o 2.6 mg cm−2. The elec ochemical cha ac e iza ion o he anode was e alua ed in a
h ee-elec ode con igu a ion using an ai igh Swagelok T-cell. Me allic Li was used as bo h he coun e and he
e e ence elec ode, and he anode was cycled wi hin he po en ial ange o 0.002 V o 2 V. The same cell assembly
p ocedu e was ollowed o pe o m he elec ochemical cha ac e iza ion o he ca hode wi hin he 1.5–4.2 V
po en ial ange.
Li hium hyb id supe capaci o ull cells (HCS//AC) we e assembled using ou di e en nega i e- o-posi i e
elec ode mass a ios: (1.1:1), (1.3:1), (1.7:1) and (2:1). A h ee-elec ode con igu a ion (Swagelok T-cell) wi h
a me allic Li e e ence was chosen in o de o eco d he indi idual elec ode po en ial changes. S ainless s eel
cu en collec o s and a po ous glass ibe sepa a o (Wha man GFB) we e used and he elec oly e used was 1 M
LiPF6 in EC:DMC (1:1). Be o e es ing, he nega i e and posi i e elec odes we e p econdi ioned o maximize
he ou pu ol age. Thus, he HCS elec ode was cycled a leas i e imes be ween 0.002 and 2 V s. Li/Li+ a
0.1 C a e o o m a solid elec oly e in e phase (SEI) and supply enough li hium o compensa e he ini ial i e-
e sible cycles. A e ha , a cu -o po en ial o 0.2 V s. Li/Li+ was se o e ade any chances o li hium pla ing.
The AC elec ode was also cha ged up o a cu -o po en ial o 4.2 V s. Li/Li+. A e his p e-li hia ion p ocess,
he LICs ull cells we e buil o hei ex ensi e elec ochemical cha ac e iza ion. Cyclic ol amme y (CV), and
Gal anos a ic cha ge-discha ge (GC-GD) measu emen s we e pe o med using a mul ichannel VMP3 gene a o
(Biologic, F ance).
Figu e 8. Elec ochemical pe o mance o he 2:1 LIC: (a) GD-GC p o ile o each elec ode and he ull cell
po en ial window a a cu en densi y o 10 A g−1; (b) cycling s abili y; (c) po en ial swings o each elec ode
du ing he cycling es ; (d) compa a i e Ragone plo s o ou 2:1 LIC and o he ep esen a i e LICs epo ed in
he li e a u e.