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?

Anode (-)

Charge (Li plating) Discharge (Li stripping)

Li+ Li+
S S S S S S S S S Li Li S Li S Li S S Li S Li S Li

Cathode (+)

Li+ Li+
Li

Li+ S8 Li2S8 Li2S6 Li2S4 Li2S3

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.

Li

Li
S S S

Li

S Li

Li S Li S S S

Li+
S

Li

0
Li+ Li Li+
S Li S S Li S S S S S S S Li Li
+

Li+
S Li S S Li S Li S S Li Li

Li2S2 Li2S

Li+

Li

Li

Polysulfide Shuttle

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.

Load / Charger

Theoretical Energy: ~2800Wh/l and 2500 Wh/kg

Why Lithium Sulfur Technology?

Specific Energy
Typical experimental discharge and charge profiles with strong shuttle.
2.5

2.5 2.4 2.3

Charge and discharge profiles with shuttle inhibitor.

Following recharges

Following recharge
2.4 2.3

Voltage

2.2 2.1 2.0 1.9 1.8 0 200 400 600

First discharge

Voltage

2.2 2.1 2

First discharge

Second and following discharges

1.9 1.8
800 1000 1200

Second and following discharges

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Specific capacity mAh/g

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
450 400 350 300 250 200 150 100 50 0 0 1000 2000 3000 4000
5

Specific Energy, Wh/kg

Sion Power Li-S

Li-ion 18650 Li-ion High Power

Ni-MH Ni-Cd

Specific Power, W/kg

Why Lithium Sulfur Technology?

Low Temperature Performance
Work partially support by NASA Glenn Contract NNC06CA85C
2.5A Discharge Profiles
3.0 2.5 2.0
3.0 2.5 Charge and Discharge Profiles at -60 oC

+ 20 C
Voltage

2.0 1.5 1.0 0.5 0.0 0.0 0.5 1.0 1.5

Charge 50 mA to 2.95 V

Voltage

1.5 1.0 0.5 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0
o

- 70 C

- 60 C

Discharge 2500 mA to 1.0 V

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 -60C.
6

Status of Lithium Sulfur Technology

Power Density (W/L) 400% Cycle Life 300% 200% 100% 0% Specific Power (W/kg)

USABC Sion

Rate Cap @1C (%)

Recharge Time (hr)

Upper Temp(oC)

Specific Energy (Wh/kg)

Lower Temp (oC)

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.

The Dynamics of Lithium Surface Roughness

Monte-Carlo Simulation

Surface Roughness vs Li DoD

0.2 Surface Roughness

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. The typical scenario is cycling at low Li DoD.

0.1

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.

The Dynamics of Lithium Surface Roughness

Experimental Observations

30 cycles 26% Li DoD

330cycles 100% Li DoD

352 cycles 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.
11

DOL
2.0 Weight (g)

DME

1.5

1.0

Lithium
0.5

0.0 0 20 40 Cycle 60 80 100

The Chemistry of Solvent Depletion

Products and Effects
Identified depletion products and their impact on battery performance.
O MeOLi Li/Li2Sx O O MeSxLi CH4 O OLi

High amount, highly soluble and highly detrimental for S cathode performance. Moderate amount, low solubility, neutral. Small amount, soluble, consumes S. Traces. Traces.

DME

Identified at Sion Power

O Li/Li2Sx O O R O H2

OLi

Highly soluble and highly detrimental for S cathode performance.

O Li n

Increases anode polarization Traces

DOL

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

Proprietary Anode Design
1600
Charge Current Changed from: an 8-hour charge to a 2.5-hour charge

Specific Capacity, mAh/g

1200
Proprietary design Conventional design

47 um 60 um

800

400

Proprietary design

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 20 mAh 15 10 5 0 0 100 200 Cycle 300 400
Conventional design Proprietary design

24 m

FoM ~34

FoM ~110

Li anode after 450 cycles. Initial and final Li thickness ~24 m.

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

Structurally Stable Cathodes
Cathode structure improvement resulted in sulfur utilization increase from 1.2 Ah/g to 1.45 Ah/g. 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
60 80

Specific Capacity (Ah/g)

1.6 1.4 1.2

Improved structure

Conventional cathode

1.0 0.8 0.6 0 20 40

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
75

Proprietory design

Tcell - THeater, C

55

35

Sion-BASF Protective Layer

Sulfur melting Li melting

15

-5

100

120

140

160

180

Heater Temperature, C

200

220

240

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 Powers lithium-sulfur technology.

19

20