High Energy Rechargeable Li-S
Cells for EV Application.
Status, Challenges and Solutions
Yuriy Mikhaylik, Igor Kovalev, Riley Schock, Karthikeyan
Kumaresan, Jason Xu and John Affinito
Sion Power Corporation
2900 E. Elvira Rd. Tucson AZ 85756 USA
www.sionpower.com
1
Outline
•
Why lithium-sulfur technology?
–
–
–
•
•
•
•
Specific energy.
Rate capability.
Low temperature performance.
Status of lithium-sulfur technology.
Addressing the challenges.
New approach pursued by Sion in
collaboration with BASF for EV applications.
Conclusions.
2
Why Lithium Sulfur Technology?
Charge (Li plating)
Discharge (Li stripping)
Anode
(-)
S
+
S
S
S
Li
S
S
S
Li+
Li
S
S
S
S
Li
S
S
S
Li
Li
S
Li2S6
Li
S
S
S
Li
Li
0
S
Li
Li+
Li
Li2S3
Li+
+
Li
Li+
S
Li
Li2S2
S
Li
S
S
S
Li
S
S
S
Li
Li+
Li
S
S
S
S
S
Li
Li
Li
S
Li
-
Load /
Charger
Li
Li2S
S
S
Polysulfide Shuttle
•
Li2S4
S
S
+
Li
Lithium ions are stripped from
the anode during discharge and
form Li-polysulfides in the
cathode.
– Li2S in the cathode is the result of
complete discharge.
Li2S8
Li
Li
Li
S
S
Li
+
Li+ S8
Li+
Li+
S
•
Li+
Li+
Li
Cathode
(+)
•
On recharge the lithium ions are
plated back onto the anode as
the Li2Sx moves toward S8
High order Li-polysulfides (Li2S3
to Li2S8) are soluble in the
electrolyte and migrate to the
anode scrubbing off any dendrite
growth.
+
Theoretical Energy: ~2800Wh/l and 2500 Wh/kg
3
Why Lithium Sulfur Technology?
Specific Energy
Typical experimental discharge and
charge profiles with strong shuttle.
Charge and discharge profiles with
shuttle inhibitor.
2.5
2.5
Following recharges
2.4
2.4
2.3
2.3
Voltage
Voltage
Following recharge
First discharge
2.2
2.1
First discharge
2.2
2.1
2
2.0
Second and following
discharges
1.9
1.9
Second and following discharges
1.8
1.8
0
200
400
600
800
1000
Specific capacity mAh/g
1200
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Specific capacity, Ah/g
With NO3- additives Sion Power controls shuttle and achieves 100% of high
plateau sulfur utilization, 99.5% charge efficiency and 350 – 450 Wh/kg
4
Why Lithium Sulfur Technology?
Rate Capability
Specific Energy, Wh/kg
450
400
350
300
Sion Power Li-S
250
200
Li-ion 18650
150
Li-ion High Power
100
Ni-MH
Ni-Cd
50
0
0
1000
2000
3000
4000
Specific Power, W/kg
5
Why Lithium Sulfur Technology?
Low Temperature Performance
Work partially support by NASA Glenn Contract NNC06CA85C
Charge and Discharge Profiles at -60 oC
2.5A Discharge Profiles
3.0
3.0
2.5
2.5
o
+ 20 C
Voltage
Voltage
2.0
1.5
1.0
o
- 70 C
Charge
50 mA to 2.95 V
2.0
1.5
1.0
o
- 60 C
Discharge
2500 mA to 1.0 V
0.5
0.5
0.0
0.0
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
Ah
Discharge Capacity, Ah
Batteries with optimized solvent and salt concentrations delivered:
1)~160 Wh/kg at -60oC at 1C,
2)~130 Wh/kg at -70oC at 1C,
3) The battery can be recharged at -60°C.
6
Status of Lithium Sulfur Technology
Power Density (W/L)
400%
Cycle Life
300%
Specific Power (W/kg)
USABC
Sion
200%
Rate Cap @1C (%)
100%
Recharge Time (hr)
0%
Upper Temp(oC)
Lower Temp (oC)
Specific Energy (Wh/kg)
Energy Density (Wh/L)
Limiting Mechanisms: 1) Rough lithium surface during cycling 2) Li/electrolyte depletion.
7
Addressing the Challenges
Keys to the EV Market for Lithium-Sulfur
• Challenges - cycle life and high temperature
stability:
– Dynamics of lithium surface roughness and cycling.
– Solvent depletion chemistry.
8
The Dynamics of Lithium Surface Roughness
Monte-Carlo Simulation
Surface Roughness vs Li DoD
Surface Roughness
0.2
• Initially, surface roughness
increases in direct proportion to
Li depth of discharge (DoD).
• Maximal surface roughness can
be observed at ~50-70% of Li
DoD.
0.1
• The typical scenario is cycling at
low Li DoD.
0
0
0.2
0.4
0.6
Li DoD
0.8
1
• The best scenario is cycling Li
anodes at 100% DoD – but only
with a current collector.
9
The Dynamics of Lithium Surface Roughness
Experimental Observations
30 cycles
330cycles
352 cycles
26% Li DoD
100% Li DoD
100% Li DoD
Cycling at 100% DOD of lithium prevents surface roughness
but lithium/electrolyte depletion still occurs.
10
The Chemistry of Solvent Depletion
Experimental Observations
Solvent and metallic Li mass vs.
Cycle Number (2.5 Ah Li-S battery).
2.5
•
1,2-Dimethoxyethane(DME) is
mainly responsible for depletion.
•
Mass of metallic Li in the cell did not
change dramatically.
•
However, visually Li looks
completely depleted at 60-80 cycles
due to roughening and disintegration
of Lithium foil.
•
The slopes suggests that Lithium
and DME may react in a molar ratio
of 1:1 to 1:2. Several Lithium
alcoholates can form by reaction
with DME.
DOL
Weight (g)
2.0
DME
1.5
1.0
Lithium
0.5
0.0
0
20
40
60
Cycle
80
100
11
The Chemistry of Solvent Depletion
Products and Effects
Identified depletion products and their impact on battery performance.
O
High amount, highly soluble and highly
detrimental for S cathode performance.
OLi
MeOLi
Moderate amount, low solubility, neutral.
MeSxLi
Small amount, soluble, consumes S.
CH4
Traces.
Li/Li2Sx
O
O
DME
O
Traces.
Identified at Sion Power
O
Highly soluble and highly detrimental
for S cathode performance.
OLi
Li/Li2Sx
O
O
DOL
R
O
O
H2
O
Li
n
Increases anode polarization
Traces
Identified at Sion Power and by D. Aurbach, J. Electrochem. Soc.156,8. 2009.
12
New Approaches Pursued by Sion in
Collaboration with BASF for EV Application
• Reduction of lithium roughness.
– Proprietary anode design.
• Development of innovative materials
– Structurally stable cathodes.
• Materials developed by Sion/BASF
– Physical protection of lithium with multi-functional
membrane assemblies.
13
Lithium Roughness Development
Specific Capacity, mAh/g
Proprietary Anode Design
Charge Current Changed from:
an 8-hour charge
to a 2.5-hour charge
1600
1200
47 um
60 um
Proprietary
design
800
Proprietary
design
Conventional
design
400
Conventional
design
0
0
50
Cycle
100
150
Experimental batteries cycling behavior
Proprietary design allowed for increased charging rate without
increase in surface roughness.
14
Lithium Roughness Development
Proprietary Anode Design
30
25
mAh
20
15
Proprietary
design
Conventional
design
10
FoM ~110
FoM ~34
5
0
0
100
24 μm
200
Cycle
300
400
Li anode after 450 cycles. Initial
and final Li thickness ~24 µm.
Experimental batteries cycling behavior
Li Figure of Merit (FoM) exceeds 100 at Li DoD ~26-30%.
FoM = DoD x Number of Cycles.
15
Development of Innovative Material
Specific Capacity (Ah/g)
Structurally Stable Cathodes
1.6
• Cathode structure
improvement resulted in
sulfur utilization increase
from 1.2 Ah/g to 1.45 Ah/g.
Improved structure
1.4
1.2
• This development paves the
way to increasing specific
energy from the current 350
Wh/kg to the 550 Wh/kg
needed to achieve a 500 km
EV range
Conventional cathode
1.0
0.8
0.6
0
20
40
60
80
Cycle No.
Experimental batteries cycling behavior
16
Development of Innovative Material
Multi-functional Membrane Assemblies
Thermal Ramp Test of Fully charged Li-S batteries after 20 cycles at 5 oC/min.
95
Conventional
design
o
Tcell - THeater, C
75
Proprietory
design
55
Sion-BASF
Protective
Layer
35
15
Sulfur
melting
Li
melting
-5
100
120
140
160
180
o
200
220
240
Heater Temperature, C
With Sion-BASF protective layer on anode, there is no thermal runaway.
17
Conclusions
Reduction of lithium surface roughness with new anode design,
and better cathode structure, resulted in:
• Recharge time reduced to less than 3 hours.
• Substantial cycle life increase if lithium surface roughness
suppressed.
• Sulfur utilization increased to 87%, or 1.45 Ah/g, paving the
way to 550 Wh/kg Li-S battery.
Innovative anode design, and Sion Power-BASF protective
membranes, increased thermal stability of Li-S cells –
eliminating thermal runaway. Batteries passed the melting
point of the Li without violent events.
18
Takeaway
Sion Power Corporation, in collaboration with
BASF, is very optimistic that the future of all
electric EV applications will be dominated by
Sion Power’s lithium-sulfur technology.
19
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