Lithium-Ion Battery Simulation for Greener Ford Vehicles

Dawn Bernardi, Ph.D.,

October 13 , 2011

COMSOL Conference 2011 Boston, MA

2

Outline

� Vehicle Electrification at Ford from Nickel/Metal-Hydride to Lithium-Ion Batteries

– The Hybrid Electric Vehicle (HEV)

– The Plug-in Hybrid Electric Vehicle (PHEV)

– The Battery Electric Vehicle (BEV)

� Li-Ion Battery Chemistry

� Li-Ion Battery Modeling (HEV)

– Comparison of model calculations to experimental pulse/rest behavior

– Contributions to overvoltage during pulse and rest periods

– Model calculations of lithium distribution

– Sensitivity of voltage relaxation to particle characteristics

– Sensitivity of initial overvoltage to anisotropy in solid-state Li diffusivity

3

Ford’s current HEV lineup utilizes Nickel/Metal Hydride Battery Technology

4

• Fusion

• C-max • Escape

Ford’s Next-Generation HEVs will use Lithium-Ion Battery Technology

5

Advanced lithium-

ion battery provides up to 30 miles all-

electric range

Ford’s Plug-In Hybrid Electric Vehicleswill use Lithium-Ion Battery Technology

• C-max Energi

6

Ford’s All-Electric Vehicles

• Focus

• Transit Connect

7

Li+e−

Li+e−

Li+e−

Li+e−

CHARGE DISCHARGE

V

PF6−

Lithium-Ion Battery Chemistry

PF6−

PF6−

PF6−

Li+

Li+

Li+Li+

Li+e−

Li+e−

Li+e−

Li+e−

PF6−

Li+

PF6−

Li+

PF6−

Li+

PF6−

Li+

PF6−

Li+

Carbon Electrolyte Metal oxide

Li+e−

(+)(-)

Li+e−

Li+e−

Li+e−

Li+e−

8

Journal of Power Sources, 196, 412-427 (2011)

Lithium-Ion Cell Model(-) (+)

9

Discharge Current Pulse: Model vs. Experiment

OCV

(65% SOC)

rest

10

Charge Current Pulse: Model vs. Experiment

rest

OCV

(65% SOC)

11

Discharge Current Pulse: Model vs. Experiment

rest

OCV

(65% SOC)

12

What are the significant contributors to the overvoltage, especially during the rest period?

The voltage

relaxation

period is

about 200 s.

Current Pulse: Calculated Overvoltage Behavior

13

Calculated Overvoltage

Primary contributors

1. electronic resistance of solid active material at the positive terminal

2. resistance to solid-state lithium transport in positive active material

3. separator resistance

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0.5

0.55

0.6

0.65

0.7

0 0.2 0.4 0.6 0.8 1

Electrode Dimensionless Distance, L_pos

y i

n

Liy

(NC

A)O

2_su

rf

40.1

s

40 s

46 s

>100 s

42 s

60 s

40.6

s

0.03

s

0.003

s

0 s

5 s

10.2

s

20.2 s

0.5

0.55

0.6

0.65

0.7

0.75

0 0.2 0.4 0.6 0.8 1

Electrode Dimensionless Distance, L_neg

x_

av

g

in L

ixC

6_

su

rf 5 s40 s 10.2

s

>100 s

42 s

20.2

s

14.2

s

60 s

0.03 s

0 s

Cu foil Al foil

Separator

Negative:

Positive:

Reaction starts at the separator interface

Reaction starts at the Al current-collector interface

Negative

Positive

Dim

ensio

nle

ss L

ithiu

m C

oncentr

ation

Dim

ensio

nle

ss L

ithiu

m C

oncentr

ation

Calculations: Solid-Phase Li Composition (at Particle Surfaces) Throughout the Electrodes

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0.5

0.55

0.6

0.65

0.7

0 0.2 0.4 0.6 0.8 1

Particle Dimensionless Radial Distance

y in

L

iy(N

CA

)O2

40.1 s

40 s

46 s

100 s

42 s

60 s

40.6 s

0.03 s

0 s

5 s10.2 s

20.2 s

Calculations: Solid-Phase Li Composition Throughout a Particle at the Al Current-Collector Interface in the Positive Electrode

Center of Particle Surface of Particle

These concentration variations are responsible for the overvoltage that persists during the rest period.

Dim

ensio

nle

ss L

ithiu

m C

oncentr

ation

16

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0 0.2 0.4 0.6 0.8 1

Particle Dimensionless Radial Distance

x_

av

g in

Lix

C6

0

10

20

30

40

50

60

% L

iC6

5 s

40 s

10.2 s

100 s

42 s

20.2 s

60 s

0.03 s

0 s

50 s

Center of Particle Surface of Particle

These composition variations are not responsible for overvoltage

(because of the two-phase nature of the negative-electrode active material).

Calculations: Solid-Phase Li Composition Throughout a Particle at the Separator Interface in the Negative Electrode

Dim

ensio

nle

ss L

ithiu

m C

oncentr

ation

17

Calculations: 2-Dimensional Animation of Solid-Phase Li Composition Throughout Positive and Negative Electrodes

Part

icle

Dim

ensio

nle

ss R

adia

l D

ista

nce

Negative Positive

Sep.

Cu foil Al foil

18

Calculations: Voltage relaxation time as a function of positive-electrode particle characteristics

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Current Pulse: Model vs. Experiment (in the first 3 seconds)

Could anisotropy of DLipos explain the experimental behavior?

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Current Pulse: Model vs. Experiment (in the first 3 seconds)

“Fixing” the diffusivity at the particle periphery would reduce overvoltage.

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Summary and Future Directions

� Weight, volume, and cost are driving the shift from nickel/metal-hydride to lithium-ion battery technology for automotive propulsion.

� Battery models can implicate resistive factors that reduce fuel economy.

– Positive electrode: electronic resistance of active material

– Positive electrode: solid-state lithium transport

� Low lithium diffusivity at particle peripheries may explain the initial steep voltage descent

� When compared to behavior throughout life, models can implicate life-limiting mechanisms.

Thank you for your

attention!

Back-up slides

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From Nickel/Metal Hydride to Lithium-Ion Batteries

0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80 100 120 140 160

Specific Energy (Wh/kg)

Sp

ecif

ic P

ow

er

(W/k

g)

NiMH High Power