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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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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Cars

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Light Trucks

Heavy Vehicles

U.S. Production

Off-Road

4 MCARE 2012 – February 27, 2012

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Annual World Oil

Production

(Billions of Barrels)

Estimates of Remaining Oil Reserves

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Projected Growth in

Light-Duty Vehicle Registrations

Can We Sustain Increasing Consumption?

5 MCARE 2012 – February 27, 2012

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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.

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2.75

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3.75

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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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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