Lithium-Ion Battery Safety Study Using Multi-Physics Internal ... - NREL

Lithium-Ion Battery Safety Study Using
Multi-Physics Internal Short-Circuit Model
The 5th Intl. Symposium on
Large Lithium-Ion Battery Technology and Application
in Conjunction with AABC09
June 9-10, 2009, Long Beach, CA
Gi-Heon Kim, Kandler Smith, Ahmad Pesaran
National Renewable Energy Laboratory
Golden, Colorado
This research activity is funded by US DOE’s ABRT program (Dave Howell)
NREL/PR-540-45856
gi-heon.kim@nrel.gov
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Background
• NREL’s Li-ion thermal abuse modeling study was started under the
Advanced Technology Development (ATD) program; it is currently
funded by Advanced Battery Research for Transportation (ABRT)
program.
• NREL’s previous model study
� focused on understanding the interaction between heat transfer
and exothermic abuse reaction propagation for a particular
cell/module design, and
� provided insight on how thermal characteristics and conditions
can impact safety events of lithium-ion batteries.
Total Volumetric Heat Release from Component Reactions
4 8 12 16 20 24 28 32 36 40 sec
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Focus Here: Internal Short-Circuit
• Li-Ion thermal runaway due to internal short-circuit is a major safety
concern.
• Other safety concerns may be controlled by electrical and
mechanical methods.
• Initial latent defects leading to later internal shorts may not be easily
controlled, and evolve into a hard short through various mechanisms:
separator wear-out,
metal dissolution and deposition on electrode surface, or
extraneous metal debris penetration, etc.
• Thermal behavior of a lithium-ion battery system for an internal shortcircuit
depends on various factors such as nature of the short, cell
capacity, electrochemical characteristics of a cell, electrical and
thermal designs, system load, etc.
• Internal short-circuit is a multi-physics, 3-dimentional problem related
to the electrochemical, electro-thermal, and thermal abuse reaction
kinetics response of a cell.
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Approach:
Understanding of Internal Short Circuit Through Modeling
• Perform 3D multi-physics internal short simulation study to
characterize an internal short and its evolution over time
• Expand understanding of internal shorts by linking and integrating
NREL’s electrochemical cell, electro-thermal, and abuse reaction
kinetics models
Electro-Thermal Model
Temperature
Current Density
Abuse Kinetics Model Electrochemical Model
T
Internal Short Model Study
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62
61.5
61
60.5
60
59.5
150
100
Y(mm)
50
0
soc [%]
0
50
100
X(mm)
soc
150
200

Research Focus Is on …
• Understanding electrochemical response for short
• Understanding heat release for short event
• Understanding exothermic reaction propagations
• Understanding function and response of mitigation
technology designs and strategies
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Heating Pattern Change
• A multi-physics model simulation demonstrates that heating patterns
at short events depend on the nature of the short, cell characteristics
such as capacity and rate capability.
Heating Pattern at Different Resistance-Shorts
7 Ω Short
3 min 6min 9 min
Can slow down the evolution?
Can suppress?
30 mΩ Short
4s 8s 12s
Affected by external thermal conditions Undetectable from external probes
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Understanding Heating Response Differences
Heating from Short Circuit = Heat from Cell Discharge + Joule Heat at at Short
R o
V ocv
R s
Short Heating = +
Global Local
7
R o = 100mΩ (0.4Ah)
R o = 1mΩ (40Ah)
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Heat for Cell Discharge [ o C/sec]
15
10
5
0
10 -4
cell size
increase
10 -2
Qd
M
=
10 0
Short Resistance [Ω]
V
R
2 ( R + R ) M
o
2
ocv
s
o
10 2
Small cell
Large cell

Understanding Heating Response Differences
Heating from Short Circuit = Heat from Cell Discharge + Joule Heat at at Short
R o
V ocv
R s
Short Heating = +
Global Local
Qualitative Representation for Heating Pattern
10 mΩ Short 10 Ω Short
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Heat for Cell Discharge [ o C/sec]
Heat at Short [W]
15
10
5
0
10 4
10 2
10 0
10 -4
10 -2
10 -4
cell size
increase
10 -2
R o = 100mΩ (0.4Ah)
R o = 1mΩ (40Ah)
10 -2
Qd
M
=
10 0
Short Resistance [Ω]
Q
10 0
Short Resistance [Ω]
2 ( R + R ) M
s
=
V
o
2
ocv
V
2
ocv
( ) 2
R + R
o
R
s
o
R
10 2
Small cell
Large cell
s
s
10 2

Understanding Heating Response Differences
Heating from Short Circuit = Heat from Cell Discharge + Joule Heat at at Short
R o
V ocv
R s
Short Heating = +
Qualitative Representation for Heating Pattern
10 mΩ Short 10 Ω Short
Large cell: localized heating
Small cell: global heating
Global Local
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Heat for Cell Discharge [ o C/sec]
Heat at Short [W]
15
10
5
0
10 4
10 2
10 0
10 -4
10 -2
10 -4
cell size
increase
10 -2
R o = 100mΩ (0.4Ah)
R o = 1mΩ (40Ah)
10 -2
Qd
M
=
10 0
Short Resistance [Ω]
Q
10 0
Short Resistance [Ω]
2 ( R + R ) M
s
=
V
o
2
ocv
V
2
ocv
( ) 2
R + R
o
R
s
o
R
10 2
Small cell
Large cell
s
s
10 2

Understanding Heating Response Differences
Heating from Short Circuit = Heat from Cell Discharge + Joule Heat at at Short
R o
V ocv
R s
Short Heating = +
Qualitative Representation for Heating Pattern
10 mΩ Short 10 Ω Short
Large cell: localized heating
Small cell: global heating
Global Local
Same local heating, and
Negligible global heating for both
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Heat for Cell Discharge [ o C/sec]
Heat at Short [W]
15
10
5
0
10 4
10 2
10 0
10 -4
10 -2
10 -4
cell size
increase
10 -2
R o = 100mΩ (0.4Ah)
R o = 1mΩ (40Ah)
10 -2
Qd
M
=
10 0
Short Resistance [Ω]
Q
10 0
Short Resistance [Ω]
2 ( R + R ) M
s
=
V
o
2
ocv
V
2
ocv
( ) 2
R + R
o
R
s
o
R
10 2
Small cell
Large cell
s
s
10 2

Observations from Literature:
Various Short Resistances
small resistance short
(metal to metal)
Heat for Discharge Joule Heat at Short
cell
shut-down
Short Resistance
medium resistance short
(bypassing cathode)
large resistance short
(flow through cathode)
John Zhang, Celgard, AABC08
*Small Cell with Shut-Down Separator
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Observations from Literature:
Various Short Resistances
small resistance short
(metal to metal)
Heat for Discharge Joule Heat at Short
cell
shut-down
Short Resistance
medium resistance short
(bypassing cathode)
large resistance short
(flow through cathode)
large resistance short (>5Ω)
John Zhang, Celgard, AABC08
*Small Cell with Shut-Down Separator
Delayed Separator Breakdown
short With observed No Cell Runaway without (1 thermal amp current) runaway
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Temperature (C)
Peter Roth, SNL, ATD presentation
200
180
160
140
120
100
80
60
40
20
0
Gen3 Electrodes
Celgard Separator
EC:EMC\LiPF6
0 500 1000 1500 2000
Time (s)
Pos. Term. Temp
OCV Voltage
Literature cases with wide range of internal short resistances are observed
30
25
20
15
10
5
0
Cell Voltage (V)

Cu
Cu
Cu
Prismatic Stack Cell Short Simulation
Al
Al
Modeling Objectives
•Characterize short natures
•Predict cell responses
•Predict onset of thermal runaway
Assumptions
•Short remains same
•Structurally intact
•No venting and no combustion
• 20 Ah
• P/E ~ 10 h -1
• Stacked prismatic
• Form factor: 140 mm x 200 mm x 7.5 mm
• Layer thickness: (Al-Cathode-Separator-Anode-Cu)
15 µm-120 µm-20 µm-135 µm-10 µm
• Multi-physics model parameters
� Electrochemistry model: a set evaluated at NREL
� Exothermic kinetics: Hatchard and Dahn (1999)
� Electronic conductivity: Srinivasan and Wang (2003)
Negative Tab
Positive Tab
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Shorted Spot
200 mm
140 mm
7.5 mm
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Short Between Al & Cu Current Collector Foils
• Shorted area: 1 mm x 1 mm
• e.g.,
� metal debris penetration through electrode & separator layers
� contact between outermost bare Al foil and negative-bias can
Cu
Al
R short ~ 10 mΩ
I short ~ 300 A (15 C-rate)
electric potential distribution
at shorted metal foil layers
14
current density field near short
diverging current
at Cu foil
converging current
at Al foil
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Short Between Al & Cu Current Collector Foils
Joule Heat for Short Temperature @10 sec after short
• Joule heat release is localized for converging current near short
• Localized temperature rise is observed.
• Temperature of Al tab appears to reach its melting temperatures (~600 o C)
15
surface temperature
internal temperature
800 o C
25 o C
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Short Between Al & Cu Foils: Reaction Propagation
Exothermic Reaction Heat [kW]
12
10
8
6
4
2
0
0 10 20 30
Time [sec]
40 50 60
30 sec
T
Q
40 sec
T
Q
10 sec
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T
Q
T : Temperature
Q: Reaction Heat
50 sec
T
Q
20 sec
60 sec
T
Q
T
Q

Short Between Cathode and Anode Electrodes
• Shorted area: 1 mm x 1 mm
• e.g.,
� separator puncture
� separator wearout under electrochemical environment
Anode
Cathode
R short ~ 20 Ω
I short ~ 0.16 A (< 0.01 C-rate)
current density field near short
• Electron current is still carried mostly by metal current collectors
• Short current should get through the resistive electrode layers
• Potential drop occurs mostly across positive electrode
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Anode
potential near short
Cathode
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Temperature ( o C)
Short Between Electrodes: Temperature
Temperature at Short
Cell Average Temperature
0 200 400 600 800 1000 1200
Time (sec)
surface temperature
18
Temperatures at 20 min after Short
internal temperature
43.1°C
25.5°C
• Thermal signature of the short is hard to detect from the surface
• The short for simple separator puncture is not likely to lead to an immediate
thermal runaway
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Observations: Simple Separator Puncture
Celina Mikolajczak, Exponent, NASA Aerospace Battery Workshop 2008
• Wear and puncture or degradation of separator
• Local degradation of electrode materials
? Issue on Structural Integrity of Separator
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Short Between Electrodes: Impact of Short Area
Impact of Separator Structural Integrity
Exothermic Heat [W]
Separator Hole Propagation
1 mm x 1 mm � 3 cm x3 cm
R short ~ 20 Ω
I short ~ 0.16 A (< 0.01 C-rate)
Time [sec]
R short ~ 30 mΩ
I short ~ 100 A (5 C)
3cm x 3cm Separator Hole
Joule Heat @ cathode layer
Joule Heat @ foils
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Myung Hwan Kim, LG Chem, AABC08
Temperature at 1min after short
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Observations:
Y. Baba, Sanyo Electric, PRIME 2008 (214 th ECS)
Structurally Reinforced Separator
• Ceramic coated (one-side) functional separator was tested.
• Improvements in safety were NOT observed clearly against typical abuse tests.
• Slight performance improvements were reported.
Myung Hwan Kim, LG Chem, AABC08
• Mn-spinel based cathode, ceramic coated separator, and laminated packaging
provide good abuse-tolerance against typical abuse tests.
Nail Penetration Test
vs
NOTE:
An abuse test such as nail-penetration is not likely to represent the process of formation
and evolution of internal short-circuits.
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Rationale: metal plating – lowering R s
Celina Mikolajczak,
Exponent, NASA Aerospace
Battery Workshop 2008
Li plating on Anode Surface
Short Resistance (Rs) Decrease
With increase in plating area and depth
Metal plating provides a potential site for low resistance short formation.
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Short Between Anode and Al Foil
Temperature ( o C)
• Shorted area: 1 mm x 1 mm
• e.g.,
� metal particle inclusion in cathode slurry
� deep copper deposition on cathode during overdischarge
Anode
R short ~ 2Ω
I short ~ 1.8A (< 0.1C)
Temperature at Short
Cell Average Temperature
Time ( x 10sec)
Al
• Temperature at short quickly reaches over 200oC. • This type of short is likely to evolve into a hard short in relatively short time.
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23
Temperatures at 1 hr after short
surface temperatures
internal temperatures
250°C
37°C
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Observations: Cathode Layer Bypassing
Takefumi Inoue, GS YUASA, NASA Aerospace Battery Workshop 2008
Explanation published by SONY and presented by GS YUASA
The mechanism of the fire accident on the DELL PC / SONY Lithium-Ion battery published
by SONY in “Nikkei Electronics, Nov. 6, 2006”.
Metal particle enters into the
triangle zone at the edge of
positive electrode where bare
Al foil is exposed.
Metal particle dissolves and
deposits on anode surfaces.
Lithium dendrite grows back
on the deposited nickel.
Low resistance short forms.
NOTE:
A short formed through or bypassing a resistive cathode layer would result in relatively low
resistance short and ,highly likely, evolve quickly into a more severe short leading to a
safety incident.
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Small Cell (0.4 Ah) Short: metal to metal
Cu
• 0.4 Ah cell
• Shorted area: 1 mm x 1 mm
R short ~ 7 mΩ
I short ~ 34 A (85 C-rate)
140
130
120
110
100
surface temperature
Al
25
Shorted Spot
Large cell (20Ah)
Rshort ~ 10 mΩ
Ishort ~ 300 A (15 C-rate)
40 mm
35 mm
3 mm
0
100 110 120 130 140
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volume fraction volume fraction
0.2
0.1
0.2
0.1
0
100 110 120 130 140
temperature [ o C]

Shut-Down Separator
Li
STOP
+
Li + e -
Large Cell
Representation
Li
STOP
+
26
• Thermally triggered
• Block the ion current in circuit
Difficult to apply in
• Large capacity system
• High voltage system
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Thermal Behavior of a Small Cell
800
600
400
200
149
123
244
Even with a small cell,
in some conditions,
shutdown separator may not function
213 555
0
0 2 4 6 8 10 12 14 16 18
In some conditions,
shutdown separator will function
131
126
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359
without shut-down
shut-down functioned
130
126

Summary
• NREL performed an internal short model simulation study to characterize an
internal short and its evolution over time by linking and integrating NREL’s
electrochemical cell, electro-thermal, and abuse reaction kinetics models.
• Initial heating pattern at short events depends on various physical
parameters such as nature of short, cell size, rate capability.
• Temperature rise for short is localized in large-format cells.
• Electron short current is carried mostly by metal collectors.
• A simple puncture in the separator is not likely to lead to an immediate
thermal runaway of a cell.
• Maintaining the integrity of the separator seems critical to delay short
evolution.
• Electrical, thermal, and electrochemical responses of a shorted cell change
significantly for different types of internal shorts.
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Future Work
• Perform in depth analysis for evaluating recommended safety
designs such as structurally intact separators and shutdown
featured device/strategy in relation to cell design parameters
(materials, electrode thickness, cell capacity, etc.)
• Design experimental apparatus for model validation through the
collaboration with other national labs (Sandia National
Laboratory)
• Partner with cell manufacturers and auto industries to help
them design safer lithium-ion battery system that appears
critical to realize technologies for green mobility
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Acknowledgments
Vehicle Technology Program at DOE
Advanced Battery Research for Transportation program
• Dave Howell
• Gary Henriksen
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