Jason ZhangPacific Northwest National Laboratory

Richland, Washington, U.S.A.

3rd China-US Electric Vehicle and Battery Technology Workshop, Beijing, China

March 14-15, 2011

1

Challenges and Opportunities in Li-Air Batteries

Outline

2

1. Advantages of Li-air Batteries

2. Development of Primary Li-air Batteries

3. Rechargeable Mechanism in Li-air Batteries

4. Challenges and Opportunities

3

Practical Li-air Batteries

Li/O2 Reaction in Different Electrolyte

Theoretical voltage

Theoretical specific energy based on metal

Theoretical specific energy

based on reactants

(excluding O2)

Theoretical specific

energy based on reaction products

Specific energy based on full reaction

V Wh/kg Wh/kg Wh/kg Wh/kgWith precipitation

Li + ½ O2 ↔ ½ Li2O2 3.10 11972 11972 3622 2790*

Li + 0.25 O2+ 1.5 H2O ↔ LiOH.H2O

3.44 13285 2717 2198 1500

Li + 0.25O2 + HCl ↔LiCl +0.5H2O

4.27 16491 2637 2227 1607

With no precipitation

Li + 0.25 O2+ 11.14 H2O ↔ LiOH+10.64H2O* 3.44 13285 444 428 444

Li + 0.25O2 + HCl +2.29H2O↔LiCl +2.79H2O* 4.27 16491 1352 1236 1353

*J. P. Zheng et al, J. Electrochem. Soc., 158 (1), A43- A46 (2011).

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2. Development of Primary Li-air Batteries

Air Electrode Optimization Electrolyte Selection Li-air Batteries with O2 Diffusion Membranes Graphene Based High Capacity Air Electrode

5

Carbon-based Air Electrode

Separator

Li Metal

Package

Air

Anode Current Collector

Cathode Current Collector+

-

Gas Diffusion Membrane

Air-Stable Electrolyte

O2 Diffusion Membrane/moisture & electrolyte barrier

PNNL Approaches:

Nanostructured Carbon with High Mesoporous Volume

Basic Structure:

Design of Primary Li-air Batteries

Initial cell configuration:Type 2325 coin cells

Test in dry box (RH ~ 1%)

Insulation Gasket

Can

Anode Cap

Nickel Mesh(Spot welded to can)

Air Electrode

Separator

Lithium Metal

Air Access Hole Gas Diffusion Barrier

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Comparison of Carbon Sources

The specific capacity increases with increasing mesopore volume of the carbon used in the air electrode.

Air Electrode Optimization

0

100

200

300

400

500

600

700

800

900

1000

Carbon Sources

Spec

ific

Cap

acity

(mA

h/g)

Calgon Ball MilledKB BP2000 JMC

Denka

Coin cell tested in dry air box

Ketjenblack carbon

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0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 100 200 300 400 500 600 700 800 900 1000Specif ic Capacity (mAh/g)

Vol

tage

(V

)

55%KB+30%MnO2+15%Teflon

55%KB+30%V2O5+15%Teflon

55%KB+30%CFx+15%Teflon

85%KB+15%Teflon

(a) 0.1 mA/cm2

Comparison of Hybrid Air Electrodes

Jie Xiao, Wu Xu, Deyu Wang, and Ji-Guang Zhang, J. Electrochem. Soc. 157, A294 (2010).

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0

0.4

0.8

1.2

1.6

2

2.4

2.8

3.2

3.6

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Volta

ge (V

)

Cell capacity (Ah)

Operated in ambient air (~20% RH) for 33 daysTotal weight of the complete battery: 8.387 gSpecific energy: 362 Wh/kg

2340 mAh/g carbon

Performance of Li-air Batteries0.8 mil polymer membrane

Metal mesh 0.7 mm KB carbon electrode

0.5 mm Li foil1 mil separator with binding layer

Cu mesh

+-

Footprint: 4.6 cm x 4.6 cm; thickness = 3.8 mm

0%

10%

20%

30%

40%

50%

60%

70%

80%

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Weight Distribution of a Practical Li-air Battery

New challenge in practical Li-air batteries: high-performance carbon (Ketjen black) expends more than 80% after soaked with electrolyte and absorbs much more electrolyte than previous prediction.

Electrolyte weight dominates battery weight structure.

5.78% 5.12%

70%

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Hierarchically Porous Graphene as a Lithium-Air Battery Electrode

a and b, SEM images of as-prepared graphene-based air electrodes

c and d, Discharged air electrode using FGS with C/O = 14 and C/O = 100, respectively.

e, TEM image of discharged air electrode.

f, Selected area electron diffraction pattern (SAED) of the particles: Li2O2.

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Graphene as a Lithium-Air Battery Electrode Record Capacity of 15,000 mAh/g

3. Rechargeable Mechanism in Li-air Batteries

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O2 in

Teflon container

- +

Mass Spec---CO2?

GC---CO2?

Compressed O2, 2 atm

Li/air coin cells filled with 1M LITFSI in PC/EC (low vapor pressure electrolyte )

Coin cells holder

In situ analysis

X-rayFTIRNMR

ex situ analysis

Developed unique characterization tools

2Li + O2 Li2O2 ?

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XRD patterns of the air electrodes discharged at different DOD, with comparisons of the standard chemicals of KB carbon, Teflon, Li2CO3, LEDC, LPDC, Li2O2 and Li2O.

Carbonate Based Electrolytes Decomposes During Li-O2 Reduction Process

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1

2

3

4

5

Cel

l vol

tage

(V) (f) Li2O

1

2

3

4

5

Cel

l vol

tage

(V) (e) Li2O2

1

2

3

4

5

Cel

l vol

tage

(V) (d) LPDC

1

2

3

4

5

Cel

l vol

tage

(V)

(c) LEDC

1

2

3

4

5

Cel

l vol

tage

(V) (b) Li2CO3

1

2

3

4

5

0 10 20 30 40 50 60 70 80 90 100Test time (hour)

Cel

l vol

tage

(V)

(a) SP

Rechargeability of Related Compounds

Li2O2: highly oxidizable (>93%) Lithium alkylcarbonates (LEDC and LPDC) are oxidizable (~42-69%) and

is responsible for apparent recharge-ability reported before. Li2O and Li2CO3: Not rechargeable

Is Li-O2 Battery Rechargeable?

Yes. > 93% of Li2O2 has been decomposed and led to O2 release

2Li + O2 Li2O2 ?

Can Li-O2 Battery Produce Li2O2 During Discharge?

PC-EC

E1

Teflon

Carbon

Li2O2

Li2CO3

Li2O E5

E4

E3

E2

Yes. If the right electrolytes are used

2Li + O2 Li2O2 ?

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Progress Summary

1.Developed primary Li-air batteries to operate in ambient air for 33 days with a specific energy of ~362 Wh/kg for the complete battery.

2.Developed ultra-high capacity air electrode (~15,000 mAh/g) for next generation Li-air batteries.

3.Discovered reaction mechanism in Li-air batteries using carbonate based electrolyte

4.Developed new electrolyte which enables rechargeable reaction in Li-air batteries.

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4. Challenges and Opportunities

Improve the power rate. Develop a stable electrolyte. Improve the reversibility (bifunctional catalyst) Develop an oxygen selective membrane. Prevent Li dendrite growth. Improve cell design to increase practical specific

energy.

Wu Xu, Jie Xiao, Deyu Wang, R. E. Williford, Vilayanur V. Viswanathan, Silas A. Towne, Jianzhi Hu, Zimin Nie, Donghai Mei, Xiaolin Li, Laxmikant V. Saraf, Ilhan A. Aksay, Gordon L. Graff, Jun Liu

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Acknowledgments

Financial support: •Defense Advanced Research Program Agency•Laboratory Directed R&D Program of PNNL

Team Members and Collaborators: