fail safe design for large capacity lithium ion batteries

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.

Fail Safe Design for Large Capacity Lithium-ion Batteries

NREL Commercialization & Tech Transfer Webinar March 27, 2011

Gi-Heon Kim

[email protected]

John Ireland, Kyu-Jin Lee, Ahmad Pesaran

Kandler Smith

[email protected]

Source: A123 Source: GM

NATIONAL RENEWABLE ENERGY LABORATORY

Challenges for Large LIB Systems

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•  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

0 50 100 150 200 250 3003.4

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Time [sec]

Volta

ge [V

]

Reference1Ah40Ah

Outer temperature

Inner temperature

Small cell

Large cell

blog.wellsfargo.com

engadget.com

Short

Short


Barriers for Safe Large LIB Systems

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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


“Fail-safe” concept differentiates:

•  Power line (to be as conductive as possible) and •  Balancing line (to be relatively resistive);

Electrical Current Paths in LIBs

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1) Battery Electric Power Delivery: Charging/Discharging

2) Balancing: Material Utilization

The proposed architecture facilitates early fault detection and isolation features…


Fail-Safe Design

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AAI2 I1

Rf1

Rf2

Rf3

Rf4

AAI2 I1

•  |Signal| >> |Noise|

•  Known reference; (I2 – I1)ref = 0

•  Single measure per module

I2 – I1

Viability of the proposed concept has been inves4gated against various design parameters and opera4on condi4ons

•  Simula4on model •  Ini4al tes4ng

Fault Detection


AAI2I1

AAI4I3

Impact of ISC Resistance on Signal

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Fault Detection

Cell# 1

Cell# 3

Cell# 4

Cell# 2

Cell# 5

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4

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Curre

nt [A

]

Time [sec]

I2-I1 +

I2-I1 -

0 5 10 15 200

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Curre

nt [A

]

Time [sec]

0 5 10 15 200

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Curre

nt [A

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Time [sec]

Rs= 100 mΩ

Rs= 500 mΩ Rs= 2 Ω

40Ah (20Ah+20Ah) Rf= 100 mΩ Module current : 0 A N in series : 5 Shorted Cell # : 2

Magnitude of signal varies with ISC resistance

Rs: 100 mΩ/ 500 mΩ/2Ω


Experiments Confirmed Model Predictions

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Fault Detection

Rs= 200 mΩ Rs= 1 Ω

Experimental implementa4on reproduces the results

AAI2I1

AAI4I3

AAI2I1

AAI4I3

Cell# 1

Cell# 3

Cell# 2

-‐1

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Series1

Series2

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Series1

Series2

16Ah (8Ah+8Ah) Rf= 180 mΩ Module current : 0 A N in series : 3 Shorted Cell # : 3

Rs: 200 mΩ / 1Ω

Cur

rent

[A]

Time [sec] Time [sec]

I2-I1: + I2-I1: -

I2-I1: + I2-I1: -

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0.1

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Series1

Series2

Current through parallel junc4ons


Isolating the Fault

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Fault Suppression

Isolated Fault

AA

Rf1

Rf2

Rf3

Rf4

Reviving “Mitigation technologies valid with small capacity batteries”

Once the faulted electrode is electrically isolated, the subsequent behavior of the faulted electrode depends on the characteristics of individual unit, and not on the pack or module assembly characteristics. Therefore, designing safe packs can possibly be reduced to designing safe unit cells.

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.


Summary & Next Steps

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•  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


Acknowledgements

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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!