polymer separator films for lithium ion batteriesseparator structure and functions; how they are...
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Polymer Separator Films
for Lithium Ion Batteries
Patrick Brant
ExxonMobil Chemical Company
Carnegie Mellon University
Pittsburgh, PA
November 11, 2009
2
Overview
ExxonMobil organization
Polyolefin utility
Lithium ion batteries and separator film
Summary
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%
PU
5.5%
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
Lithium Ion Battery Overview
Past Present
Initial motivation for work
Battery components and brief history
Separator structure and functions; how they are made
Lithium ion battery benefits, impact
Future
Drivers
Opportunities
EV, HEV, pHEV considerations
Summary
7
Initial Motivation for Work
Two clear fundamental advantages
1. Lithium is the lightest metal
2. Lithium half reaction standard electrode potential is big †
In principal, fundamental advantages could lead to
Higher energy density; weight and volume advantage
Higher power density at a given energy density
Fewer cells, related parts
Key Hurdles- beginning in 1975
Cathode
Anode
Electrolyte
Separator
Self-discharge performance
Memory
Cost per W-h and per W
Abuse resistance
Cold/hot behavior
Thermal management (safety)
Cycle life
Markets?† “Electrochemical Series” in Handbook of Chemistry and Physics
Ragone Plot
1
10
100
1000
10000
1 10 100 1000
Specific Energy (Wh/kg)
Sp
ec
ific
Po
we
r (W
/kg
) LIB
Other
Battery
Options
* 1 Wh = 3,600 J or 860.4 cal
Ma
teria
lsP
erf
orm
an
ce
8
Basic Components in (Lithium Ion) Battery
* Separator = Battery Separator Film = BSF
Separator *
AnodeCathode Electrolyte
Graphitic Carbon + Binder
Lithium Metal Oxide+ Binder
e-
Galleries for Li Colle
cto
r Colle
cto
r
9
Brief History
Other Cathodes:
Li(Ni,Mn,Co)O2
Li(Ni,Co,Al)O2F. Beguin and R. Yazami, Actualite Chimique 2006 295-296, 86-90
10
Separator Film Requirements
Permeable (~40-50% void volume) for ready ion
transport, yet insulate electrodes
Small pores (seive) but low resistance
Chemically inert, uniform, free of flaws
2-10+ years in highly reactive environment
Excellent puncture strength
Thin (7-30μ), dimensionally stable
Slitting, compatible w/ manufacturing equipment
Act as safety device if cell becomes too hot
Safety margin: Δ = [meltdown temperature –
shutdown temperature]
The higher the meltdown temperature the better
Lithium dendrite
Porosity
yTortuousiteffR
11
Polyethylene – A High Performance Thermoplastic
C
C
C
C
C
H H
H H
H H
H H
H H
Battery Separator Film
Tg -120C Tm 132-140C
12
How to Make a Classic Monolayer Separator Film
Pennings 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
Biaxially
orient,
extract liquid
hydrocarbon,
dry
1 m 5 m1 mSEM SEMTEM TEM5 m5 m
Collapse of
cell
Fibrillation of
plane stacked
lamella crystal
CellSchematic
diagram
~ 1 m ~10nm
AFM 1 m
13
A Closer Look at Separator Morphology
TEM’s of stained cross-sections show highly uniform, finely textured morphology
TD x ND plane MD x ND plane
Crystalline lamellae
14
Orientation and Crystallinity *
Sample 1: 2 % UHMWPE
0
50
100
150
200
250
300
350
400
450
8 13 18 23
2 (o)
I(2
) (a
.u)
WAXS of a BSF
(110)
(200)
b
c
a
ORTHORHOMBIC
UNIT CELL:
a = 7.36 Å
b = 4.92 A
c = 2.54 Å; chain axis
ab
(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
b
CHAIN FOLDED
CRYSTALLINE
LAMELLAE ª
NONCRYSTALLINE
POLYMER
ª Some extended chains
15
Realizing the Benefits of Lithium Ion Batteries
Higher energy density - nearly 2x higher than Ni-MH; weight advantage Higher 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
Virtually no memory effect
Expect lower cost per W-h and per W Raw material cost can be a big factor
Other key data: Abuse resistance
Cold/hot behavior (-40 to +40C); electrolyte viscosity
Thermal management
Cycle life
16
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
Annu
al C
ell P
rodu
ctio
n, 1
0^9
Year
Growth of LIB Comes with Increasing Demands
Markets: Cellphone, laptop, camcorder, digital camera, power tool, ebikes,…
Increasing capacityDowngauging / higher strength
HEV
Early Li-ion
Battery at EV show
Chicago, ‘77
Invention of
microporous
PE separator
Separator used in
world’s first LIB
1
2
3
1990 1995 2000 2005 2010
Ah
EV
Electrovaya’s Maya-300
220 Ah14 Ah1 Ah 4000+ Ah70 Ah
17
Future – Continuing Growth
Energy and LIB
Opportunities, challenges
EV, HEV, pHEV considerations
Evolving demands on separator
Economy Security
Climate
6 x109 Tons CO2/year
Energy
WSJ, August 6, 2009
18
Global Economics and Energy
0
2
4
6
8
10
1980 2030 2005
0
25
50
75
100
1980 2030 2005
0
50
100
150
200
250
300
350
1980 2030 2005
billion
population GDP energy demandtrillion 2005$ MBDOE
Average Growth / Yr.
2005 – 2030
0.9%
Average Growth / Yr.
2005 – 2030
3.0%
Average Growth / Yr.
2005 – 2030
1.2%
19
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 sector
2030 demand in MBDOE
Average 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 transportation
by sub-sector
MBDOE Average Growth / Yr.
2005 – 2030
1.4%
22
Batteries in Transportation
100
101
102
103
104
105
106
107
Specific
Pow
er
(W/k
g)
0.01 0.1 1 10 100 1000
Specific Energy (Wh/kg)
Capacitors
Batteries Fuel
Cells
Combustion
Electrochemical
Capacitors
Engines
Ele
ctr
oly
tic
Ragone Plot
LIB
Gasoline LIB
Energy Density,
kWh† /kg
13 a* 0.17 *
Energy Efficiency ~15-20% * 85-90% *
Efficiency of
Producing Fuel
0.9 ~0.4-0.5 b
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 – 1000 V)
% of Work Done by
Batteries
[Be
ne
fit
/ C
os
t]
1 = break even
high
energy
high
powerHEV
EV
Drive Cycle
Ve
locity
IC
EV = 100% of cycle
HEV < 100%
Energy capture
24
Evolving Separator Demands
Higher temperature stability - ~ 200 250+C
Retain sufficient dimensional stability
Coatings and higher temperature polymers
• Blends, co-extrusion
Increasing puncture resistance
w/ appropriate permeability
Lower shutdown temperature
~10+ year life
Delivered flawlessly at lower cost
for larger battery formats (stacked, prismatic), and
bigger battery packs…. but emphases vary according
to LIB chemistry and module or pack control
Co-extruded Separator
Monolayer
Wet
Process
Coex
Technology
Polymer
Design
25
Improved Thermal Stability
: E25MMS (mono-layer)
: New Commercial Grade (co-extruded)Permeability
Puncture
Thermal
Stability
Shutdown
Temperature
Meltdown
Temperature
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
hri
nk
ag
e
TD shrinkage at 105'C, 8 hrs TD shrinkage at 130'C, 30mins
Lower TD shrinkage allows
more flexible LIB designs
27
Summary
Lithium ion batteries power the portable electronics revolution
Polyolefin separators a key part of this success story
Lithium ion batteries for transportation: ebikes, EV/p-HEV, HEV
Major commitments already
• Battery and auto manufacturer announcements
Continuing improvements, especially to reduce cost, increase life
• Once again, separators critical to performance
Can be a key part of overall drive to increase energy efficiency
Uninterrupted power supplies
Fixed energy storage
More technology breakthroughs are critical
Exciting research and development opportunities
28
Thank you
Many contributors to this talk
JoAnn Canich, Alan Vaughan
Koichi 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
eabili
ty (
rela
tive)
D evelopm entalgrade 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-0
4
Mar
-04
May
-04
Jul-0
4
Sep-0
4
Nov-
04
Jan-0
5
Mar
-05
May
-05
Jul-0
5
Sep-0
5
Nov-
05
Jan-0
6
Mar
-06
May
-06
Jul-0
6
Sep-0
6
Nov-
06
Jan-0
7
Mar
-07
May
-07
Jul-0
7
Sep-0
7
Nov-
07
Jan-0
8
Mar
-08
May
-08
Ga
so
lin
e P
ric
e (
$/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
. M
on
thly
HE
V S
ale
s
Gas Price HEV Sales
US accounts for ~70% of all HEV sales
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