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MCARE 2012 – February 27, 2012 1
Materials Science for Automotive Electric Vehicle Transportation
Bob Powell Electrochemical Energy Research Laboratory
General Motors Global Research & Development Center
2 MCARE 2012 – February 27, 2012
Urban Pollution
Global
Climate Change
The Challenges Facing Us…
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Growing
Petroleum Consumption
3 MCARE 2012 – February 27, 2012
Source: Transportation Energy Data Book: Edition 24, ORNL-6973, and EIA Annual Energy Outlook 2005, Preliminary release, December 2004.
USA Transportation Petroleum Use by Mode (1970-2025) 2003 Total = 13.42 mbpd
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1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025
Mil
lio
n b
arr
els
per
day
Marine
Rail
Actual Projection
Cars
Air
Light Trucks
Heavy Vehicles
U.S. Production
Off-Road
4 MCARE 2012 – February 27, 2012
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1930 1935 1940 1950 1960 1965 1970 1973 1975 1980 1985 1990 1991 1993 1994 1996 2000 2010 2020 2030 2040 2050
Annual World Oil
Production
(Billions of Barrels)
Estimates of Remaining Oil Reserves
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1996 2050
Bil
lio
ns o
f V
eh
icle
s
IndustrializedNations
World
Projected Growth in
Light-Duty Vehicle Registrations
Can We Sustain Increasing Consumption?
5 MCARE 2012 – February 27, 2012
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solin
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ers
on
al-
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spo
rta
tio
n c
ust
om
ers
, $U
S/ga
l
Cost of (crude) oil, $US/barrel
¶ Liquid fuels – future price and availability
¶ Efficacy of bio-derived fuels?
¶ What is the relative importance of zero on-vehicle “regulated emissions” vs. fuel cost, CO2 emissions , & energy security?
¶ Fuel cell vision offers
1. Range, short re-charge times, and zero emissions
2. Technical efficacy now
¶ Another vision: EREV with bio-derived fuels
¶ City: EV (~40 miles)…zero emissions
¶ Between cities
Liquid fuel: high Wh/kg
Regulated emissions from ICE range extender, but greatly reduced today and low for highway driving
Energy security, affordability, and reduced unwanted emissions (including CO2)
Really BIG questions
MCARE 2012 – February 27, 2012 6
Hybrid Electric Vehicles (including
Plug-In HEV) IC Engine and Transmission
Improvements
Hydrogen Fuel Cell
Petroleum (Conventional & Alternative Sources)
Alternative Fuels (Ethanol, Bio-diesel, CNG, LPG)
Hydrogen
Electricity (Conventional & Alternative Sources)
Battery Electric Vehicles (E-Rev)
Future vehicles will use alternative energy sources like bio-fuel, grid electricity, and hydrogen
Improved Fuel
Economy and
Emissions
Time and
Energy Diversity
Displace
Petroleum
MCARE 2012 – February 27, 2012 7
Transitioning from Internal Combustion to Electrified Propulsion
Petroleum and Biofuels (Conventional and Alternative Sources)
Increasingly Electrified Powertrains
Electricity and Hydrogen (Zero Emissions Energy Sources)
eAssist Full Hybrid
Extended Range
Electric
Battery Electric
Fuel Cell Electric
Plug-in
Hybrid
Solutions needed for a full range of vehicles that provide customer choice
MCARE 2012 – February 27, 2012 8
Variations on Electric Vehicles
PHEV Pure EV
Plug-in Hybrid Electric Vehicle
Pure Electric Vehicle Electric Vehicle with “Extended-Range”
Chevrolet Volt: The Electric Vehicle with Extended Range
EV with Extended Range
• All-electric for up to 40 miles
• Gas generator for +300 miles extended driving range
• Primary fuel is electricity supplemented with gasoline
(Volt)
• All-electric at low speed/power
• Blended electric/gas at higher speed/power
• Primary fuel is gasoline supplemented with electricity
(typical)
• All-electric for ~100 miles
• Fuel is electricity
(typical)
9 MCARE 2012 – February 27, 2012
Typical Commute
Why Target 40 Miles? 40 Miles Is the Key
Based on U.S. Department of Transportation 2003 Omnibus Household Survey
78% of customers
commute 40 miles or less daily
10 MCARE 2012 – February 27, 2012
Electric Vehicle with RANGE-EXTENDER
Driving EXTENDED-RANGE
HUNDREDS of miles
BATTERY Electric Drive
miles 40 Up to
MCARE 2012 – February 27, 2012 12
Battery Requirements for Vehicle Electrification
¶ Will it fit?
¶ How far can you go?
¶ How well does it accelerate?
¶ Will it start quickly from -30°C?
¶ Will it run well at 40°C?
¶ Will it last 150k miles and 10 years?
¶ How fast can you refill?
¶ How much will it cost to buy and refuel the vehicle?
MCARE 2012 – February 27, 2012 14
Energy-Power Plot of Requirements and Systems
(Venkat Srinivasan, Almaden Conf. 2009: “The Batteries for Advanced Transportation Technologies (BATT) Program.”)
• Lithium ion battery energy density is sufficient for HEV/PHEV/EREV options • Approximately factor of two improvement needed to meet EV goal (USABC) • Reducing cost at same or improved durability is needed for all systems
Fuel Cell Systems
17 MCARE 2012 – February 27, 2012
Lithium ion battery challenges
¶Cost
¶Can we size pack closer to end-of-life requirements?
¶Can we reduce materials & processes costs?
¶Life
¶How do electrodes fail?
¶Can we develop an accelerated life test?
¶Temperature tolerance
¶Can we improve low temperature power?
¶Why is battery life shorter at higher temperatures?
19 MCARE 2012 – February 27, 2012
V
PF6-
Charging Mechanism (Li-Ion cells are fabricated in fully discharged)
PF6-
PF6-
PF6-
Li+
Li+
Li+ Li+
Positive is full of lithium in
discharged state
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
PF6-
Li+
PF6-
Li+
PF6-
Li+
PF6-
Li+
PF6-
Li+
(+) Metal oxide, Separator (Solvent + Salt) (-) Carbon,
phosphate, or silicate titanate, Si Charging energy forces lithium out of positive
into negative electrode.
Li+ e-
20 MCARE 2012 – February 27, 2012
Positive electrode materials (ceramics)
¶ LiMO2 (with M = Ni, Co, Mn, Al … or combinations thereof) is the most used positive material (includes LiCoO2, NCM, LNCA)
¶ LiMn2O4 (spinel) is low cost and provides high power density along with good abuse tolerance
¶ LiMPO4 (with M = Fe, Mn, Mg, … or combinations thereof)
¶ Li2MnO3-Li(NixMnyNiz)O2 (with x + y + z = 1) is of strong interest currently
¶ LiMSiO4 (with M = Fe, Mn, … or combinations thereof) is showing promise as a low cost, high capacity positive
The positive electrode material is a major cost driver in Li-Ion batteries
The potential for solvent oxidation at the positive electrode leads to abuse tolerance concerns
21 MCARE 2012 – February 27, 2012
“This result indicates
volume change causes
the increase in
resistance.”
POSITIVE
ELECTRODE
22 MCARE 2012 – February 27, 2012
23 MCARE 2012 – February 27, 2012
FIBS analysis of NCM + LiMn2O4 (From Mike Balogh of GM Research and Development)
24 MCARE 2012 – February 27, 2012
O map
F map SEM image
S map
K map Ni map
Co map
Mn map
weak x-rays
shadowed region
weak x-rays
shadowed region
C map
NCM +
LiMn2O4
and carbon
conductive
additive
C map
25 MCARE 2012 – February 27, 2012
Understanding Voltage Decay of HE-NMC Cathode Materials Yan Wu (a), Miaofang Chi (b), and Zicheng Li (a) (a) General Motors Global R&D, Electrochemical Energy Research Lab (b) Oak Ridge Nation Laboratory Presented at the 15th Israel Materials Engineering Conference, Feb 28, 2012
Layered Li[Li1/3Mn2/3]O2 – LiMO2 (M = Mn, Ni, and
Co) materials possess almost doubled capacity
value as compared with LiCoO2 due to an oxidation
of the oxide ions and an irreversible loss of oxygen
from the lattice during first charge. During the
subsequent first discharge, the oxygen vacancies in
the lattice facilitate the reduction of the transition
metal ions to lower oxidation states than they
possessed in the initial material, resulting in high
discharge/charge capacities in subsequent cycles.
However, cell voltage
decreases during
cycling; compromising
cell energy, cycling
stability, and creates
difficulty for battery
state estimation.
26 MCARE 2012 – February 27, 2012
Stoichiometric and nonstoichiometric LNMO structures synthesized by molten salt methods.
Ni and Mn when disordered in the spinel structure manifests superior rate capacity than
when Ni and Mn order and change the structure from spinel to simple cubic. Ongoing work
at GM is investigated order/disorder in high voltage spinel.
27 MCARE 2012 – February 27, 2012
28 MCARE 2012 – February 27, 2012
Natural graphite coated with
Al2O3 by means of atomic
layer deposition (ALD)
29 MCARE 2012 – February 27, 2012
Graphite|iron-phosphate cell…excellent power density, life, and potential for low cost. Challenged on energy density.
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5
Cell
pote
ntial, V
Cell capacity, Ah
P0
P5
Graphite|FePO4 cell45oC, C/2, 90% DOD
Cell capacity loss
963 cycles
New
Charged, FePO4 & Li~0.8C6 Discharged, LiFePO4 & C6
30 MCARE 2012 – February 27, 2012
Iron phosphate vs. Li
- Little voltage variation
Graphite vs. Li
- Voltage variations
31 MCARE 2012 – February 27, 2012
¶ Peak broadening indicating reduction in crystallite size
Analysis of FePO4/ graphite cells
New
50% DOD, 6C,
45oC,1376 cycles
Conventional differential voltage spectroscopy, but here on the full FePO4-graphite cell
Peaks result from graphite staging (next slide)
32 MCARE 2012 – February 27, 2012
¶ Same as previous plot with the exception that origin now is at the fully discharged state…clear that distance between graphite peaks is nearly constant
¶ Conclusion: lithium consumption (at the negative electrode surface) is leading to capacity decline
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0.8
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1.4
1.6
1.8
2
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5
d(C
ell
po
ten
tia
l, V
)/d
(Ca
pa
city,
Ah
)
Cell capacity, Ah
P0
P5
Graphite|FePO4 cell45oC, C/2, 90% DOD
Cell capacity loss
963 cycles
New
Discharged Charged
Utility of dV/dQ vs Q, uniform shifting of peaks for graphite/FePO4 cells
33 MCARE 2012 – February 27, 2012
Electrode microstructure
Anode charge reaction
1. Lithium ion is reduced at the
electrode surface:
Li+ + e- Li0
2. Lithium diffuses rapidly into
host electrode through
vacancies • Opposite reactions takes place
at cathode particle surfaces
• Porous electrodes (~100
mm thick) composed of
host particles (~1 to 5 mm
diameter) are used to
1. increase the surface
area for reaction
2. reduce lithium
diffusion resistance
Li0
Li+ + e- Li0
~100 mm ~25 mm
V
PF 6 -
PF 6 -
PF 6 -
PF 6 -
Li +
Li +
Li + Li +
Li + e
-
Li + e
-
Li + e
-
Li + e
-
Li + e
-
Li + e
-
Li + e
-
Li + e
-
Li + e
-
Li + e
-
PF 6 -
Li +
PF 6 -
Li +
PF 6 -
Li +
PF 6 -
Li +
PF 6 -
Li +
Li + e -
Li
~5 mm
~3 Å
34 MCARE 2012 – February 27, 2012
What is SEI?
Ele
ctrod
e
http://www.cmt.anl.gov/cees/index.html
Porous Phase Dense Phase
Solid Electrolyte Interphace
Ele
ctroly
te
Solid Electrolyte Interphase (SEI): -Formed on the surface of electrode materials during the first few cycles -Due to reduction or oxidation of electrolyte -Loss of Li can not be recovered Why SEI is important? - Protective layer due to electrolyte decomposition - Further electrolyte decomposition (capacity loss) - Li+ transport (power loss) - Battery life and safety
35 MCARE 2012 – February 27, 2012
Formation of the SEI…solvent reduction (ethylene carbonate)
¶ Example reactions only…many others contribute to the formation of the solid electrolyte layer
¶ For computed IR spectra of surface species in an EC electrolyte, see S. Matsuta, T. Asada, and K. Kitaura. J. Electrochem. Soc. 147(2000)1695-1702…dimers found to be lowest energy
¶ Experimental FTIR data indicates predominance of for EC and EC+DEC systems with 1M LiPF6, see C. R. Yang, Y. Y. Wang, C. C. Wan, J. Power Sources, 72(1998)66.
CH2
O
C
O
H2C
O 2Li+ + 2e- +
Li2CO3 + H2C=CH2
LiCH2CH2(OCOO)Li
Inorganic
Layer (1st)
Gassing
(ethylene)
Organic layer
+ H2C=CH2
Gassing
(ethylene) Organic layer
[Li(OCOO)CH2]2
Li+ + 2e- = Li
Vcell ~ mLi ~ ln(SOC)
(Calendar life influence)
36 MCARE 2012 – February 27, 2012
Negative electrode…the solid electrolyte interface (SEI)
• Solvent reduction at ~0.8V vs Li
on first cycle
• Then ~100% Coulombic efficiency
37 MCARE 2012 – February 27, 2012
On the importance of Coulombic efficiency I
Cycle Capacity
1 (Ah0)I
2 [(Ah0) I ]I
3 [(Ah0) I I ]I
N (Ah0)(I)N
For N = 5000 cycles and a 12/16 or 75% capacity retention,
the current efficiency per cycle must be such that
[Ah0(I)N ]/Ah0 > 0.75, or I > (0.75)(1/5000) , hence I > 0.99994.
• This is why very low rates of lithium-consuming reactions can lead to premature
cell failure. The rates can be so low that they are not measureable in terms of
seeing current maxima associated with solvent reduction.
• Note: high capacity negatives (Si, Sn based)…large challenge!
2
1
2
1Li+ + e- + LiCH2CH2OCO2Li→
38 MCARE 2012 – February 27, 2012
cD
Ree
cckkB
I
UVfUVf
ca
)()()1(
1
ref ,LiLi)]/([)(
----
-
-
39 MCARE 2012 – February 27, 2012
Chemical-mechanical degradation at the negative electrode
Expansion &
contraction
upon charge
& discharge,
respectively.
223 CHCHLiCO S S]-[Li
...gassesSEIO-H-RS]-[Li
Increased disorder and cracking.
d002 peak-width at half max
amplitude increases with cycling.
Supported by Raman analyses.
• Consistent with loss of active
lithium.
Electrode isolation and
loss of active material
when cracks join
• Consistent with
additional loss of
negative capacity
Cracks
via cycling
SEI forms
on newly
exposed
surfaces
(cracks)
40 MCARE 2012 – February 27, 2012
Current and next generation
negative electrodes
LiC6
372 mAh/g (theoretical)
Si: clear
“theoretical winner”
Dominique Larcher, Shane Beattie, Mathieu Morcrette, Kristina Edström,
Jean-Claude Jumas and Jean-Marie Tarascon, “Recent findings and
prospects in the field of pure metals as negative electrodes for Li-ion
batteries,” J. Mater. Chem., 2007, 17, 3759 – 3772
41 MCARE 2012 – February 27, 2012
Current vs. Future Negative Electrode Materials
Graphite:
¶ Specific capacity: 320 mAh/g
¶ Commercially available
Si-based negative electrode materials:
¶ Large specific capacity: 600~4000 mAh/g
¶ Significant SEI (solid electrolyte interphase) formation: first cycle irreversible capacity → capacity loss
¶ Large volume change (300%): cracking & delamination of electrode → poor cyclability
¶ Small tap density: low active material loading (graphite: 1.3g/ml, Si-nanoparticle: <0.2g/ml)→ affects volumetric energy density
¶ Still at R&D stage
10µm micro-Si particle( Aldrich), vs. Li metal coin cell, room temperature
A.Appleby, etc. JPS, 163, 2007,1003-1039
Thin film Si
After 1 cycle: film cracking
After 30 cycles: film cracking and active material loss
42 MCARE 2012 – February 27, 2012
Utilizing Si in Negative Electrode Materials
ASI: Si-carbon nanofiber
Si
C
Composite
Si
C
Open structures Chemistry: 1: Li+ + e- + Si → LixSi (x≤ 4.4)
2: Li+ + e- + C→ LiC6
(small contribution to capacity)
Confined structures
Si Si
Amprius: Double wall Si nanotube
H.Li (Institute of Physics, Chinese Academy of Sciences IOP-CAS): Core-shell nano size spherical particle
clamping layer
Chemistry: 1: Li+ + AB→ LiAB
(AB is Li ion conductor) 2: Li+ + e- + Si→ LixSi (x≤4.4)
G. Yushin (Georgia Institute of Technology): Si-C nanocomposite granule
43 MCARE 2012 – February 27, 2012
Background: nanowire electrodes
44 MCARE 2012 – February 27, 2012
Uncoated Alumina ALD Coated
(SIMS analyses)
(GM Research & Development Center, Warren, MI)
45 MCARE 2012 – February 27, 2012
Separators and ceramics
¶ Function
¶ “Zero” electronic conduction Requires mechanical integrity
Low porosity helps to mitigate dendrite shorting
¶ Facile ionic conduction High porosity is desired
Wetted by conventional solvent+salt systems (e.g., LiPF6 in EC+DEC)
¶ Strong element of cell abuse-tolerance strategy
¶ Current separator costs are significant
¶ Poly(propylene) and poly(ethylene)
¶ Relatively new development:
¶ Ceramic enhancement
Conventional separator
PP or PP|PE|PP
46 MCARE 2012 – February 27, 2012
V
PF6-
Charging Mechanism (divalent Mn can also migrate)
PF6-
PF6-
PF6-
Li+
Li+
Li+ Li+
Positive is full of lithium in
discharged state
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
Li+e-
PF6-
Li+
PF6-
Li+
PF6-
Li+
PF6-
Li+
PF6-
Li+
(+) Metal oxide, Separator (Solvent + Salt) (-) Carbon,
phosphate, or silicate titanate, Si Charging energy forces lithium out of positive
into negative electrode.
Li+ e-
47 MCARE 2012 – February 27, 2012
Mn Dissolution – cell degradation
Mn dissolution leads to cell degradation by forming Mn metal dendrites (short circuit), blocking Li ion transport (capacity fade) and decomposing electrolyte (gassing, capacity fade)
Approaches to solve degradation due to Mn dissolution:
• New cathode materals • ALD coatings to protect surface of the cathode particle • Functionalized separators
• Use a LiPF6 -free electrolytes
48 MCARE 2012 – February 27, 2012
Summary and Challenges
Electrification is an essential component of future transportation systems
Batteries, whether for HEV, PHEV, EREV, or BEV, are “now” and will carry us forward
Battery materials and processes have a critical role to play
Ceramic technology is enabling lithium ion batteries
Challenges
Lower cost materials and processing/manufacturing
Higher specific energy/power and higher energy/power density
Higher voltage-stable positives and electrolytes – prevent Mn dissolution
Higher Li storage negatives with cycling durability (fatigue)
Reliable performance and safety under all operating conditions
49 MCARE 2012 – February 27, 2012
Acknowledgments
GM Global Research&Development
Mark Verbrugge, Mark Mathias, Yan Wu, Jung-Hyun Kim, Meng Jiang, Ion Halalay, Xingcheng Xiao, Curt Wong
GM Volt Team
Hughes Research Laboratories
Ping Liu
MCARE 2012
Jack Simon
50 MCARE 2012 – February 27, 2012
Thank you
52 MCARE 2012 – February 27, 2012
Lithium-Ion Battery
Engine Generator
Charge Port
Electric Drive Unit
53 MCARE 2012 – February 27, 2012
North American Car of the Year for 2011
Motor Trend 2011 Car of the Year
Green Car Journal 2011 Green Car of the Year
Car and Driver 10 Best for 2011
Ward’s AutoWorld 10 Best Engines for 2011
AUTOMOBILE Magazine 2011 Automobile of the Year
2010 Breakthrough Technology, by Popular Mechanics
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