Dr. R. SchmidtDr. R. Schmidt, Dr. A. Panchenko, Dr. B. Ewald, Dr. S. , Dr. A. Panchenko, Dr. B. Ewald, Dr. S. IvanoviciIvanovici, Dr. , Dr. R. Oesten (BFB)R. Oesten (BFB)BASF SE, 67056 Ludwigshafen, GermanyBASF SE, 67056 Ludwigshafen, Germany

Electrode Development @ BASF for Electrode Development @ BASF for Lithium/Sulfur BatteriesLithium/Sulfur Batteries

44thth Symposium on Energy Storage: Symposium on Energy Storage: Beyond Lithium IonBeyond Lithium IonPacific Northwest National LaboratoryJune 8, 2011

2

BASF Lithium/Sulfur Research Partner

� Since 2009 joint development agreement with world-leading lithium/sulfur company Sion Power

� Sion Power major developer of Li/S battery systems and protected lithium anode technology

� Acceleration of Li/S research and development with BASF expertise as chemical solution provider

3

Outstanding superiority of Li/S in respect of gravimetric energy density

Comparison Li-Ion vs. Li/S batteries

Li/S – The Battery System Beyond Li-ion

Today Future Theory

0

3000

2000

1000

Li-Ion Li/SGravimetric Energy

[Wh/kg]

Li-Ion Li/SVolumetric Energy

[Wh/l]

Advantages:

� High gravimetric energydensity

� Low cost and abundantraw materials

� Ideal battery system for fullelectric vehicle application

� Operability at very lowtemperatures

� High potential of improvement

4

Potential and Challenges

� “Life” of Li/Sbatteries endscurrently too earlyafter 50-100 cycles (< 800 mAh)

� Goal: > 500 cycles

� Observed capacityfive times higherthan lithium-ionbatteries

Comparison of cycle data of Li/S cell (red = discharging, blue = charging)and lithium-ion battery (LIB).

Li/S

Cycle no.5040302010

Capacity (mAh/g)1.200

1.000

800

600

400

200

00

LIB

Five times higher capacity than Li-ion technology

5

Discharging:

� Li is stripped from anode and lithium sulfides are formed in the cathode

Charging:

� Re-plating of Li and re-formation of elemental sulfur

Speciality of Li/S: (Partly) dissolving electrodes during cycling

Model of Lithium/Sulfur battery

Working Principle of Li/S System

Li+

Li+

Li+

Li+

Li+

Li+

Li+

Li+

Li+

Li+

Li+

Li+

Sep

arat

or

Li0

Li2S3

Li2S6

Li2S

Li2S8

PolysulfideShuttle

Anode(–)

Cathode(+)

Charge (Li plating)

Discharge (Li stripping)

LiSS S S

S S SSLi

Carbon

Sulfur

Binder

LiSS S S

S S SSLiLiS

SS

SLi

LiSSLi

LiSS

SSLi

LiSS

SSLi

LiSS S

S SSLi

SLi

SSLi

6

Discharge Curve

Second Stage

� Precipitation of Li2S

� Formation of smaller polysulfides

� 65-75 % of sulfur usage

First Stage

� Elemental sulfur is reduced

� Polysulfide up to Li2S4 are formed

2.4

Potential (V) vs Li/Li+

2.3

2.2

2.1

2.0

1.9

1.8

Specific capacity (mAh/g Sulfur)0 400 800 1200 1600

First stage

Theoreticalcapacity

Second stage

Speciality of Li/S: (Partly) dissolving electrodes during cycling

7

State of the art Li/S battery with Teflon binder

Special requirements:� Sulfur cathode sensitive to

drying under vacuum� Partly dissolving cathode� Carbon particles responsible

for structural stability

5040302010

1.400

1.000

800

600

400

200

00

1.200

Cycle no.

Cap

acity

[mA

h/g]

capacity drop ~ 50 %

Binder and carbon development is key factor for optimized cathode

Approach:� Utilization of new carbon

materials� Pretreatment of carbon and

sulfur material

Cathode Development

8

� Intercalated graphites: Intercalation of Lewis acid guest molecules (e.g. SO3)

intercalate

IntercalatedGraphite:

Graphite:

Intercalation: e.g.+ NOx / H2SO4

Intercalation: e.g.+ NOx / H2SO4

Expanded Graphites

Intercalation is key to expansion

9

Graphite Expanded Graphite “Pockets” for sulfur uptake

� Expanded graphites can lead to better cell performance

� Highly conductive and light material

� Fixation of sulfur in pockets

Expanded Graphites

Micropockets

10

� Temperature / gradient controlled expansion:

Expanded Graphites

Temperature is key factor for optimized structure

11

Expanded Graphites

Highly stable performance for first 50 cycles

� Over 1100 mAh/g sulfur over 50 cylces

� Consumption of electrolyte responsiblefor cell failure after 60 cycles

� Testing in 110 mAh cells

� Up to 40% expandedgraphites in cathode

5040302010

1.400

1.000

800

600

400

200

00

1.200

Cycle no.

Cap

acity

[mA

h/g]

Charge/discharge capacity of cell with improved cathode

12