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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
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Challenges and Opportunities in Li-Air Batteries
Outline
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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
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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.
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: