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리튬공기전지 소재 기술 개발 현황Recent Development of Advanced Materials For Li-Air Batteries

1. 전해질 (Electrolyte)

정 훈 기

한국과학기술연구원

hungi@kist.re.kr

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Reaction  routes.  Expected  :  O2  and  Li2O2  should  be  obtained  under  charge  and  discharge.    Actual:  decomposition  of  organic  carbonate  solvents!    

Electrolyte Issues in Li-Air batteries

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Electrolyte Issues in Li-Air batteries

J.  Read,  J.  .Electrochem.  Soc.,  149  (2002)  A1190-‐A1195.  

ε η (25 oC) O2 solubility b.p.

[ cP ] [ µmol cm-3 ] [ oC ]tetrahydrofuran (THF) 7.4 0.46 8.82 66dimethyl sulfoxide (DMSO) 48 1.948 1.86 189acetonitrile (ACN) 36.64 0.361 8.10 82tetraethylene glycol dimethyl ether 7.79 4.05 4.70 275-2761,2-dimethoxyethane (DME) 7.2 0.46 9.56 84ethylene carbonate (EC) 89.78 1.90 (40 oC) 1.70 248Propylene carbonate (PC) 64.92 2.53 3.20 242Diethyl carbonate (DEC) 2.805 0.75 7.91 126Dimethyl carbonate (DMC) 3.107 0.59 (20 oC) 7.28 91

solvent

•  Properties of Common Organic Solvent!

•  Stability upon the contact with the metallic lithium!•  High O2 solubility and diffusion coefficient, D (∝ 1/η )!•  Low volatility (low vapor pressure)!•  Stability at high anodic overpotential!•  Stability under superoxide radicals (O2-)!

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OO

OO2-

1(PC)

-1/2 O2

oxidative decomposition reaction

O

O- Li+CO2 H2O

(1)

(2)

O2 + e- O2-

2

(3)OO-O

O

O

Li+

OO

Li+

(4)

CO2Li+e-

-O

O

OO

Li+-O

O

O

O-Li+

3 4

O2

O

O- Li+

(5)2O2- + 2CO2 C2O62- + O2

(6)C2O62- + O2- + 4Li+ 2Li2CO3 + 2O2

•  FT-IR!

P.  G.  Bruce  et  al.,  J.  Am.  Chem.  Soc.,133  (2011)  8040-‐8047  

•  FT-IR!

•  XRD!

P.  G.  Bruce  et  al.,  Angew.  Chem.  Int.  Ed.,  50  (2011)  8609-‐8613  

•  Similar results for DME, DOL, 2-Me-THF…!

•  Other alkyl carbonates also decompose!

- Li2O2 is visible up to 10 cycles in XRD"- other amides are not stable with superoxide "P.  G.  Bruce  et  al.,  J.  Am.  Chem.  Soc.,134  (2012)  7952-‐7957  

Ø  Propylene Carbonate (PC) Ø  dimethylether (DME)

Ø  Dimethylformamide (DMF)

충전 반응 중 전해질 분해 문제

리튬공기전지의 전해질 분해 문제

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전해질 - TEGDME

Tetraethyleneglycol dimethylether (TEGDME)

H.-‐G.  Jung  et  al.,  Nature    Chemistry,  4  (2012)  579  H.-‐G.  Jung  et  al.,  Nano  Le=ers  12  (2012)  4333.    

0 1000 2000 3000 4000 5000

1.6

2.4

3.2

4.0

4.8

Vol

tage

/ V

Capacity / mAh g-1

1st cycle 2nd cycle 3rd cycle 10th cycle 20th cycle 30th cycle

at  5,000  mAh  gcarbon  -‐1

•  Ultra high capacity and long cycling!

•  Discharge (formation of Li2O2 )-charge (dissolution of Li2O2) cycle using TEGDME electrolyte !

40 45 50 70 750

1000

2000

3000

4000

5000

Li2CO3+ (73.89)

Li2O2+ (46.02)

To

tal c

ount

s

m/z

Charged electorde0

1000

2000

3000

4000

5000

Discharged electrode

Li2CO3+ (73.89)

Tota

l cou

nts

Li2O2+ (46.02)

•  Stable Li2O2 formation and decomposition!

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전해질 - DMSO

P.  G.  Bruce  et  al.,  Science,337  (2012)  563-‐566  

•  FT-IR! •  SERS!•  Electrochemistry with porous gold electrode!

•  Electrochemistry with carbon black!

•  Stability upon the direct contact with the metallic lithium and Li2O2!

dimethyl sulfoxide (DMSO)

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전해질 - dimethylformamide (DMF)

The  stability  toward  reduced  O2  species  is  not  sufficient!!!  

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전해질 – Polymer Electrolyte

Polyethylene  oxide-‐based  (PEO20LiCF3SO3-‐10%w  ZrO2):    -‐   The  polymer  electrolyte  is  prepared  by  solvent  free  procedure  by  hot  pressing  the  dry    components  at  90  oC  -‐   The  solid  polymer  is  plas;cized  with  polyethylene  glycol  

Advantages:  -‐   High  stability  of  PEO  ether  linkage  -‐   PEO  is  excellent  solva;ng  agent  for  oxygen  and  reac;on  products  -‐   Stability  in  the  solid  state  configura;on  of  the  triple  contact  between  carbon,  electrolyte  and  surrounding  O2  

J. Hassoun, F. Croce, M. Armand & B. Scrosati, Angew. Chem. Int. Ed., 2011, 50, 2999

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리튬공기전지 소재 기술 개발 현황Recent Development of Advanced Materials For Li-Air Batteries

2. Li2O2 Morphology

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Li2O2 Morphology

100 nm

(b)

500 nm

(a)

1 µm

(d)

500 nm

(b)

500 nm

(c)

500 nm

(a)

500 nm

(b)

500 nm

(c)

500 nm

(d)

400 nm

(a)

400 nm

(a)

Li2O2  parYcles    progressively  dissolve  

H.-‐G.  Jung  et  al.,  Nano  Le[er  12,  4333-‐4335  (2012).    

TEM  images  of  an  oxygen  electrode  at  a  discharge  (formaYon  of  Li2O2  )-‐  charge  (dissoluYon  of  Li2O2)  cycle  in  a  lithium  cell  

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Li2O2 Morphology

TEM  images  of  different  parts  of  the  oxygen  electrode  discharged  using  TEGDME  and  PC    

H.-‐G.  Jung  et  al.,  Nano  Le[er  12,  4333-‐4335  (2012).    

IniYal  stage  of  discharge  

Final  stage  of  discharge  

400 nm

(a)

100 nm

(b)

10 nm

(c)400 nm

(a)

100 nm

(b)

10 nm

(c)

400 nm

(a)

100 nm

(b)

10 nm

(c)

   

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Li2O2 Morphology

Influence  of  Temperature  on  Lithium−Oxygen  Ba[ery  Behavior

Room  Temperature

50  °C 70  °CY.-‐K.  Sun  et  al.,  Nano  Le[.  2013,  13,  2971−2975  

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Y.  Shao-‐Horn  et  al.,  Energy  &  Environmental  Science  4  (8)  2011,  2952-‐2958    

Li2O2 Morphology

K.  Kang  et  al.,  Adv.  Mater.,2013