Battery Failure Investigation
Should a battery fail in a manner that results in electrical malfunction, thermal damage, case rupture, or combustion, a number of questions typically arise:
- Was the failure induced by external forces, such as severe mechanical damage or excessive heat exposure? And if so, what were the nature and magnitude of such forces? Should changes be made to improve the robustness of the product? Was the failure the result of cell, protection circuitry, or battery design? And if so, what types of design modification should be considered?
- Was the failure the result of an internal cell fault or a battery-manufacturing flaw that was not detected by the quality control procedures put in place by the manufacturer? And if so, what additional procedures should be implemented?
- Does the failure represent a random occurrence or is it an early sign of a developing trend?
- If a product recall is warranted, which manufacturing lots should be recalled?
Differentiating between the potential causes of any failure can be difficult, particularly when the failed product or system has been heavily damaged. Based on numerous lithium-ion battery failure analysis investigations, Exponent has developed a systematic investigation approach that has proven effective in identifying the particular causes of any given failure and developing recommendations for corrective action as appropriate.
This method may include techniques such as:
- Damage pattern documentation and analysis
- Battery pack/cell disassembly
- X-ray examination
- Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM /EDS) analysis
- Material and metallographic examination
- Computed Tomographic (CT) scanning
- System analysis and testing
- Charge/discharge testing
- Battery protection circuit analysis and testing
- AC adaptor electrical testing
- Printed circuit board (PCB) propagating fault analysis
- Contact resistance analysis
- Infrared camera thermal measurements
- Burn injury assessment (thermesthesiometer testing)
- Failure replication testing
- Statistical analysis of failure rates and times (risk analysis)
Exponent routinely conducts testing to explore various aspects of lithium-ion battery safety including response to mechanical thermal and electrical abuse, cell thermal runaway propagation, and fire suppression. Some Exponent reports on this type of testing are available on the Portable Rechargeable Battery Association’s (PRBA) website:http://www.prba.org/prba/publications/battery_studies_and_reports/Default.ashx
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