Post on 13-Dec-2015
description
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
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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
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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
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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