1µm

Polymer Separator Films for Lithium Ion Batteries:Past, Present, and Future

Patrick BrantExxonMobil Chemical Company

University of TennesseeKnoxville, TNMarch 4, 2010

2

Overview

ExxonMobil organization

Plastics - Polyolefin utility

Catalytic olefin polymerization with metallocenesGas phase polymerization process

Lithium ion batteries and separator film

Summary

Early / Lead Generation Pre-developm ent Developm ent

3

4

POs – Key Features

Polyolefins (POs) – Champions of Thermoplastics a

• Chemically Inert • Low cost• Recyclable / Energy

Recovery• Exceptional Fabrication &

Applications Versatility

• WW Production of Thermoplastics > 350 Billion Pounds / Year

• POs > 50% of all Thermoplastics

• Sustainable? 6-7%, CO2 [2 saved/1 produced] b, downgauging

Paper or plastic? 4x more

POs54%

PS 9%PVC17%

PET 5.0%

ABS3.5%

PU5.5%

PA1.3%

PMMA0.9%

PC0.9%

a G. Gottfreid, Polymeric Materials, Ch. 1

b McKinsey and Company study, reviewed by the Öko Institute

Others

5

Polyolefins in Transportation

About 200 lb of plastics, rubber in typical car

10% Weight Reduction –6.6% Fuel Economy

Advanced motor oils

6

Example of Metallocene Catalyst Impact

Commercialization Challenge

• Introduce new catalyst on world scale UNIPOL™ gas phase PE reactor

• Metallocene catalyst + methylalumoxaneactivator + porous silica support

• 2000 g PE/ g catalyst + complex formulation makes catalyst expensive

• Reactor difficult to start and fouls out / sheets

• Solutions– Simplified catalyst formulation– Careful control of poisons– Right choice of poison scavenger– Right choice of operability aids/additives– Avoid making polymer “death” grades

• Results– Productivities improved to >6000 g PE/ g

catalyst and higher– Stable commercial operations– Less waste, fewer resources– Strong business growth (~30%/year) of

polymers that sell for significantly higher prices

< 500 psi, < 110 °C

Huge reactors > 7000 ft3, >400 Kta

�residence time 3 hr

Low conversion of monomer per cycle

Cooler

Compressor

Monomer

Polymer Discharge

Catalyst

Poly

mer

G

ranu

les

• • ••

•

•• Bed weight:

125T = 727+

Heat removal:94.5 kJ/mol or22.6 kcal/mol

Reactor data:<500 psi <100 ºC>7000 ft3 >400 kTA

Residence time ~ 3 hr

7

Granule Morphology One Key to Gφ Reactor Operation

Neat granules(stereomicroscopy)

Void morphology of granules(oil immersion)

Surface & cross-sectionalviews of granules (SEM)Replication

Particle Diameter

Popu

latio

n

Time

Epoxy

Thin section of granule iPPfollowed by HDPE (TEM)

white = HDPE, gray = iPPWhat happens to the catalyst?

8

Polyethylene – A High Performance Polymer

CC

CC

C

H H

H H

H H

H H

H H

Battery Separator Film

9

Lithium Ion Battery Overview

Past → PresentMotivation for workBattery components and brief historySeparator structure and functions; how they are madeLithium ion battery benefits, impact

FutureDriversOpportunitiesEV, HEV, pHEV considerations Summary

10

Initial Motivation for Work

Two clear fundamental advantages1. Lithium is the lightest metal2. Lithium half reaction standard electrode potential is big †

In principal, fundamental advantages could lead toHigher energy density; weight and volume advantageHigher power density at a given energy densityFewer cells, related parts

Key Hurdles- beginning in 1975CathodeAnodeElectrolyteSeparatorSelf-discharge performanceMemoryCost per W-h and per WAbuse resistanceCold/hot behaviorThermal management (safety)Cycle lifeMarkets?

† “Electrochemical Series” in Handbook of Chemistry and Physics

Ragone Plot

1

10

100

1000

10000

1 10 100 1000

Specific Energy (Wh/kg)

Spec

ific

Pow

er (W

/kg) LIB

Other BatteryOptions

* 1 Wh = 3,600 J or 860.4 cal

11

Basic Components in (Lithium Ion) Battery †

ion transport

* Separator = Battery Separator Film = BSF

Separator *AnodeCathode Electrolyte

Graphitic CarbonLithium Metal Oxide

e-

† And in all batteries

Galleries for Li

ion transport

12

Brief History

Other Cathodes:Li(Ni,Mn,Co)O2Li(Ni,Co,Al)O2

F. Beguin and R. Yazami, Actualite Chimique 2006 295-296, 86-90

Goo

deno

ughetal.

LixC

oO2

13

Separator Film Requirements

Permeable (~40-50% void volume) for ready ion transport, yet insulate electrodes

Small pores but low resistance

Chemically inert, uniform, free of flaws2-10+ years in highly reactive environment

Excellent puncture strengthThin (7-30µ), dimensionally stable

Slitting, compatible w/ manufacturing equipment

Act as safety device if cell becomes too hot Safety margin: ∆ = [meltdown temperature –shutdown temperature]The higher the meltdown temperature the better

Lithium dendrite

PorosityyTortuousit

peffR

14

How to Make a Classic Monolayer Separator FilmPennings et al, 1965 - 1979: Gel spinning and super drawing of uhmw HDPE filaments

Solution of polyethylene dissolved in hydrocarbon

Gel sheetThin wall cellular structure composed

of stacked lamella crystals

Micro-porous filmUniform fine fibrous network

composed of stacked lamella crystals

Biaxial Biaxial orientation,orientation,extractionextraction

1µm 5µm1µmSEM SEMTEM TEM5µm 5µm

Collapse of Collapse of cellcell

Fibrillation of Fibrillation of plane stacked plane stacked lamella crystallamella crystal

CellCellSchematic diagram

~ 1~ 1µµmm ~10nm~10nm

AFM 1µm

15

A Closer Look at Separator MorphologyTEM’s of stained cross-sections show highly uniform, finely textured morphology

TD x ND plane MD x ND plane

TD

ND

MD

NDMD TD

16

Orientation and Crystallinity

Sample 1: 2 % UHMWPE

0

50

100

150

200

250

300

350

400

450

8 13 18 23

2θ (o)

I(2θ)

(a.u

)

WAXS of a BSF

(110)

(200)

ab

b

c

a

ORTHORHOMBICUNIT CELL:a = 7.36 Åb = 4.92 Ac = 2.54 Å; chain axis

(110) (200)

Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886

17

Realizing the Benefits of Lithium Ion Batteries

Higher energy density - nearly 2x higher than Ni-MH; weight advantageHigher power density at a given energy density

Higher voltage - ~3.6 V vs 1.2 V for Ni-Cd and Ni-MH; fewer cells, connections

Better self-discharge performance - around one tenth of Ni-Cd and Ni-MH

No memory effect

Expect lower cost per W-h and per WRaw material cost can be a big factor

Other key data:Abuse resistanceCold/hot behavior (-40 to +40C)Thermal managementCycle life

18

0

0 . 5

1

1 . 5

2

2 . 5

3

1975

1980

1985

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

Ann

ual C

ell P

rodu

ctio

n, 1

0^9

Y e a r

Growth of LIB Comes with Increasing Demands

Markets: Cellphone, laptop, camcorder, digital camera, power tool, ebikes,…

Increasing capacityDowngauging / higher strength

Early Li-ionBattery at EV show

Chicago, ‘77

Invention of microporousPE separator

Separator used in world’s first LIB

1

2

3

1990 1995 2000 2005 2010

Ah

HEVHEVEVEV

ElectrovayaElectrovaya’’ss MayaMaya--300300

220 Ah14 Ah1 Ah 4000+ Ah70 Ah

19

Future – Continuing Growth

Energy and LIBOpportunities, challengesEV, HEV, pHEV considerationsEvolving demands on separator

Economy Security

Climate6 x109 Tons CO2/year

EnergyWSJ, August 6, 2009

20

Transportation - Global

Power Generation

1.6%

Res/Comm

0.4%Industrial

1.0%

Transportation

1.4%

84.540.4

124.0

61.5

2030: ~310 MBDOE

1.2%

demand by sector2030 demand in MBDOEAverage growth/Yr 2005-2030

0

10

20

30

40

50

60

70

1980 2005 2030

Light-Duty Vehicles

Heavy Duty

Aviation

Marine

Rail 0.7%

2.5%

0.3%

2.0%

1.9%

0

10

20

30

40

50

60

70

1980 2005 2030

Light-Duty Vehicles

0.3%

global transportationby sub-sectorMBDOE Average Growth / Yr.

2005 – 2030 1.4%

21

Gasoline ~ 25 cents / gallon

22

Batteries in Transportation

100101102103104105106107

Spe

cific

Pow

er (W

/kg)

0.01 0.1 1 10 100 1000Specific Energy (Wh/kg)

Cap

acito

rs

Batteries FuelCells

Combustion

ElectrochemicalCapacitors

Engines

Ele

ctro

lytic

Ragone Plot

LIB

~0.4-0.5 b0.9Efficiency of Producing Fuel

85-90% *~15-20% *Energy Efficiency

0.17 *13 a*Energy Density, kWh† /kg

LIBGasoline

Diversification and more efficient use of hydrocarbons: 13.8 MBbl oil/day for transportation in US

Reduce carbon dioxide emissions

Part of integrated set of solutions

a 3x the energy density of sugarb For production of e- from coal or NG † 1 kWh = 3,600 kJ or 860.4 kcal

Gasoline versus LIB

* Deutsche Bank, Auto Manufacturing Electric Cars: Plugged in, 9 June 2008

23

Relative LIB Benefit / Cost

Rough estimate: LIB size for EV ~200 kg (80 -1,000 V)

% of Work Done by Batteries

[Ben

efit

/ Cos

t]

1 = break even

high energy

high power

HEV

EV

Drive Cycle

Vel

ocity

HEV

HEV

IC

EV = 100% of cycle

HEV < 100%Energy capture

24

Evolving Separator Demands

Higher temperature stability - ~ 200-250+CRetain sufficient dimensional stabilityCoatings and higher temperature polymers

• Blends, co-extrusion

Increasing puncture resistancew/ appropriate permeability

Lower shutdown temperature

~10+ year life

Delivered flawlessly at lower cost

for larger battery formats, and bigger battery packs….but emphases vary according to LIB chemistry and module or pack control

Co-extruded Separator

Monolayer

Wet ProcessWet

Process

CoexTechnology

CoexTechnology

Polymer Design

Polymer Design

25

Improved Thermal Stability

: E25MMS (mono-layer)

: New Commercial Grade (co-extruded)Permeability

Puncture

ThermalStability

ShutdownTemperature

MeltdownTemperature

Power

Mechanical Safety

Thermal Safety

Tensile Balance

New commercial grade has superior thermal stability, higher permeability and meltdown temperature than standard mono-layer

26

Lower TD Shrinkage

TD Shrinkage

0

10

20

30

40

E25MMS V25EKD V25CGD Developmental grade 1

Grades

% s

hrin

kage

TD shrinkage at 105'C, 8 hrs TD shrinkage at 130'C, 30mins

Lower TD shrinkage allowsmore flexible LIB designs

27

Summary

Lithium ion batteries power the portable electronics revolutionPolyolefin separators a key part of this success story

Lithium ion batteries for transportation: ebikes, EV/p-HEV, HEVMajor commitments already

• Battery and auto manufacturer announcementsContinuing improvements, especially to reduce cost

• Once again, separators critical to performance

Can be a key part of overall drive to increase energy efficiencyUninterrupted power supplies

Continuing technology breakthroughs are criticalExciting research and development opportunities

28

Thank you

Many contributors to this talkJoAnn Canich, Alan VaughanKoichi Kono, Jack Tan, Takeshi Ishihara, Jeff Brinen, Zerong Lin, …..

29

Shutdown Performance

0

50

100

150

200

100 110 120 130 140

Temperature / oC

Perm

eab

ility

(re

lative

)

Developmentalgrade 2

V25EKD

Developmental grade 2 is designed for earlier pore closure with complete shutdown at 128˚C, potentially prevent exothermic reaction which leads to thermal runaway in the event of internal shorts or overcharging

30

Economics Lesson: Hybrid Sales Linked to Fuel Price

U.S. Gasoline Price and Hybrid Sales (2004-2008)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Jan-04

Mar-04

May-04

Jul-0

4Sep

-04Nov-0

4Ja

n-05Mar-

05May

-05Ju

l-05

Sep-05

Nov-05

Jan-06

Mar-06

May-06

Jul-0

6Sep

-06Nov-0

6Ja

n-07Mar-

07May

-07Ju

l-07

Sep-07

Nov-07

Jan-08

Mar-08

May-08

Gas

olin

e Pr

ice

($/g

al)

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

N.A

. Mon

thly

HEV

Sal

es

Gas Price HEV Sales

US accounts for ~70% of all HEV sales