1. Source: A123 Source: GM
Fail Safe Design
for Large Capacity Lithium-ion Batteries
NREL Commercialization & Tech Transfer Webinar
March 27, 2011
Kandler Smith Gi-Heon Kim
kandler.smith@nrel.gov gi-heon.kim@nrel.gov
John Ireland, Kyu-Jin Lee, Ahmad Pesaran
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.

2. Challenges for Large LIB Systems
• Li-ion batteries are flammable, require expensive manufacturing to reduce defects
• Small-cell protection devices do not work for large systems
• Difficult to detect faults in large cells before catastrophe
Outer temperature
Short
Inner temperature
Short
4
blog.wellsfargo.com
3.9
3.8
Large cell
Voltage [V]
3.7
3.6
Reference
Small cell
3.5 1Ah
40Ah
3.4
0 50 100 150 200 250 300
engadget.com Time [sec]
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3. Barriers for Safe Large LIB Systems
1) Early Fault Detection
• The faults leading to a field accident are believed to grow from a
latent defect over time
• Signals of an early-stage-fault are difficult to detect in large
capacity LIB systems
2) Electrical Isolation of Fault
• To limit further electric current feed energizing the fault
• Neither active nor passive circuit breaker is directly applicable in
large capacity LIB systems
3) Suppression of Fault preventing Propagation
• Pack fault response depends on pack integration characteristics
as well as individual cell safety characteristics
• Using safe cells does not guarantee the safety of a pack
consisting of them
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4. Electrical Current Paths in LIBs
1) Battery Electric Power Delivery: “Fail-safe” concept differentiates:
Charging/Discharging • Power line (to be as conductive as
possible) and
• Balancing line (to be relatively
resistive);
2) Balancing:
Material Utilization
The proposed architecture facilitates
early fault detection and isolation features…
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5. I1 I2 I1 I2 Fail-Safe Design
A A A A
Fault Detection
Rf1 I2 – I1
• |Signal| >> |Noise|
Rf2
• Known reference; (I2 – I1)ref = 0
• Single measure per module
Rf3
Viability
of
the
proposed
concept
has
been
inves4gated
against
Rf4 various
design
parameters
and
opera4on
condi4ons
• Simula4on
model
• Ini4al
tes4ng
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6. Impact of ISC Resistance on Signal
Fault Detection
Magnitude
of
signal
varies
with
ISC
resistance
A A
I1 I2
Rs=
100
mΩ
Cell# 5
40Ah
(20Ah+20Ah)
8
Rf=
100
mΩ
Module
current
:
0
A
6
Current [A]
Cell# 4 N
in
series
:
5
4
Shorted
Cell
#
:
2
I2-I1 +
2
Rs:
100
mΩ/
500
mΩ/2Ω
I2-I1 -
Cell# 3 0
0 5 10 15 20
Time [sec]
Rs=
500
mΩ
Rs=
2
Ω
Cell# 2 8 8
6 6
Current [A]
Current [A]
4 4
Cell# 1
I3 I4 2 2
A A
0 0
0 5 10 15 20 0 5 10 15 20
Time [sec] Time [sec]
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7. Experiments Confirmed Model Predictions
Fault Detection
Experimental
implementa4on
reproduces
the
results
Current
through
parallel
junc4ons
16Ah
(8Ah+8Ah)
1
Rf=
180
mΩ
0.9
Module
current
:
0
A
0.8
0.7
N
in
series
:
3
0.6
A A
Shorted
Cell
#
:
3
0.5 Series1
I1 I2 0.4 Series2
0.3
Rs:
200
mΩ
/
1Ω
0.2
0.1
0
0 20 40 60 80
A A Rs=
200
mΩ
Rs=
1
Ω
I1 I2 7 1.4
Cell# 3 6 1.2
5
I2-I1: + 1
I2-I1: +
I2-I1: - I2-I1: -
Current [A]
4 0.8
Cell# 2 Series1 S
3 0.6 S
Series2
2 0.4
1 0.2
Cell# 1
I3 I4 0 0
A A 0 20 40 60 80 0 20 40 60 80
-­‐1
Time [sec] Time [sec]
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8. Isolating the Fault
Fault Suppression
Isolated Fault
Reviving “Mitigation technologies valid with A A
small capacity batteries”
Once the faulted electrode is electrically Rf1
isolated, the subsequent behavior of the
faulted electrode depends on the
characteristics of individual unit, and not on Rf2
the pack or module assembly characteristics.
Therefore, designing safe packs can possibly Rf3
be reduced to designing safe unit cells.
Rf4
Multi-series-branch configuration of the proposed design
still allows partial power delivery from the pack even
after the local-shut down for fault isolation is executed.
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9. Summary & Next Steps
• Proposed “Fail-safe design for large capacity LIB system” is promising
to address the barriers identified: Early fault detection, Electrical
isolation, Fault suppression.
• Simulation models have demonstrated the viability of the proposed
concept against various battery design parameters and operation
conditions
• Collaborate with others for further evaluation, development and
embodiment of the design and the methodologies proposed
• Develop/refine computational tools for specific designs
• Build prototypes and test
• Demonstrate safety improvement of the proposed design against
various failure modes of vehicle battery systems
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10. Acknowledgements
Vehicle Technology Program at DOE
• Dave Howell
• Brian Cunningham
NREL Energy Storage Task Lead
• Ahmad Pesaran
NREL Colleagues
• John Ireland
• Matthew Keyser
• Jeremy Neubauer
Thank you for your attention!
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