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High-Energy Lithium-Sulfur Batteries Hui Wang and Chengdu Liang
Center for Nanophase Material Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37830 Contact information: Chengdu Liang ([email protected]), (865)456-9185
Overview and Scope of Project This project investigates solid-state Li-S chemistry as high energy batteries for electric grid applications. In this design, solid electrolytes will replace conventional liquid electrolytes and separators. Lithium ion-conducting sulfur compounds will be cycled at the solid state as the cathode. The anode will be pure metallic lithium. The use of a solid electrolyte is a key innovation of solid-state Li-S batteries as opposed to conventional Li-S batteries in which liquid electrolytes cause intrinsically short cycle-life, low energy density, and safety concerns. The goal of the project is to achieve long-lived stable cycling of high-energy solid-state Li-S batteries through the discovery of new functional materials and the innovation of electrode and battery structures.
Why Li-S batteries
Li-S Batteries Research Is Motivated by Their High Energy and Low Cost
Lithium-ion conducting cathode materials are key to solid-state batteries
Impart ionic conductivity to S-rich compounds Lithium
polysulfidophosphates (LPSP)
2 3 4 5 6 7 8-5.4
-5.1
-4.8
-4.5
-4.2
-3.9
-3.6
Li3PS4+n
n
Log
σ (S
cm-1)
Room temperature conductivity as a function of S-S bonds in LPSP
2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5-5.0
-4.8
-4.6
-4.4
-4.2
-4.0
-3.8
-3.6
log
σ (S
cm-1)
1000/T (K-1)
Ea = 0.37 eV
Li3PS4+5
90 80 70 60 50 40 30 20t / oC
Room temperature ionic conductivity of Li3PS4+5 is 107 times higher than that of Li2S!
0 50 100 150 200 250 3000
200
400
600
800
1000
1200
1400
1600
Discharge Charge Discharge Charge
Cycle number
RT
60 oC
0
100
200
300
400
500
600
700
Cap
acity
(mA
h g-1
, nor
mal
ized
to S
)
Capacity (m
Ah g
-1, normalized to Li3 PS
4+n )
Conclusions • Newly developed composite electrolyte of LiI-LPS is promising
• High ionic conductivity >10-4 Scm-1 at room temperature • Wide electrochemical window up to 10V • Extremely stable with lithium metal anode
• Li+-conducting sulfur cathode enables all-solid Li-S batteries • Ionic conductivity is key to battery cycling • TiS2 functions as the binder, electronic and ionic conductor, and capacity
contributor
• Slurry coating method provide thin solid electrolyte membrane • Cell resistance has been reduced because of a thin membrane • Energy density can be improved
FY15 plan for grid applications • Explore the additive effect with metal sulfides as the
electronic and ionic conductor for the optimization of cathode compositions.
• Construct large cells to demonstrate the high energy density of solid-state Li-S batteries.
• Optimize the membrane synthesis procedure for large pouch cells.
• Enhance the cell rate performance by using high conduction solid electrolytes.
Contact Information: PI: Chengdu Liang, [email protected], (865) 456-9185
High energy density Theoretic: 2550 Wh/kg, 2862 Wh/l
Low cost Sulfur is free Cell cost is low: $100/kWh
Development of high performance solid electrolyte has a high ionic conductivity and excellent compatibility with metallic lithium anode
2.6 2.8 3.0 3.2 3.4
-4.0
-3.5
-3.0
-2.5
-2.0
2 Li3PS4 : 1 LiILi3PS4
log
σ / S
cm
-1
1000 T-1 / K-1
0 2 4 6 8 10
-0.04
-0.02
0.00
0.02
0.04
Curr
ent /
mA
Voltage / V vs Li/Li+
-0.2 0.0 0.2 0.4
-0.02
0.00
0.02
Cur
rent
/ m
A
Voltage / V vs Li/Li+
0V
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0-0.020
-0.015
-0.010
-0.005
0.000
0.005
0.010
0.015
0.020
Volta
ge /
V
Capacity (mAh/cm2)
Cycle # 20-1000
Cycle # 2 • 2 LPS·LiI has the best electrochemical stability among reported Li-ion conductors
• DC conductivity = AC conductivity Low charge transfer resistance
• DC polarization is linear up to a current density of 1.26 mA cm-2
• 10V electrochemical window
a, before cycling b, after first discharge cycle c, after first charge cycle
Charge/ Discharge Mechanism
Li3PS4+n Li3PS4 Li2S
S-S bonds are key to the electrochemical function.
Li3PS4+n
Li3PS4 Li2S
Li3SP4+n
Key development for high-energy and high power solid-state batteries
A B
0.0 0.4 0.8 1.21.5
2.0
2.5
3.0
Volta
ge (V
)
Capacity (mAh)
Discharge Charge
0 5 10 15 20 25 30 350.0
0.5
1.0
1.5
Capa
city (
mAh
)
Cycle No.
Charge Capacity Discharge Capacity
Stable cycling of LPSP with TiS2 at the solid state
Thin solid electrolyte membranes are crucial for high energy density and excellent cell performance. A slurry coating method has been developed to create free-standing membranes of 2” diameter and 20 µm thickness.
TiS2 has been identified as a mixed conductor to carry out three functions: (1) inorganic binder, (2) electronic and ionic conductor, and (3) contributor to total capacity.
