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Thermal Runaway and Li-ion Battery Safety
Thermal Runaway and Li-ion Battery Safety
Li-ion batteries (LIBs) are an essential technology for enabling the UK, and other countries alike, to achieve Net Zero targets by enabling electrified transport and supporting renewable energy sources on the grid. However, on rare occasions, Li-ion batteries can undergo thermal runaway.
Li-ion battery thermal runaway process. Copyright Peter Bugryniec. Source: link.
Under normal operation, the heat generated by charging/discharging a battery can easily be dissipated and the cell remains at a safe temperature. However, during the thermal runaway event, additional heat from an abuse event, such as a short circuit, can lead to excessive heat that cannot effectively be dissipated. This can lead to a temperature rise where exothermic decomposition reactions of the cell's materials begin. This leads to further heat generation and temperature rise, causing a positive feedback loop that speeds up reactions and finally leads to intense heat and temperatures. These temperatures can reach over 1000℃ and temperature rates above 1000’s℃/min which cannot be controlled by practical battery thermal management systems.
The failure of one cell can propagate to others in the module, then from module to module, leading to the destruction of the entire battery system as well as being a hazard to people and assets within the vicinity.
Li-ion Battery Fire and Toxicity Hazards
Li-ion Battery Fire and Toxicity Hazards
Li-ion Battery Thermal Runaway Off-Gas Hazards. Copyright Peter Bugryniec.
Further, the decomposition reactions lead to flammable and toxic gas generation. This can cause significant fires that are difficult to extinguish, as well as the potential to cause explosions. While carbon monoxide and fluorinated gas species present a serious toxicity hazard.
More details on this topic can be found here.
Reducing Lithium-ion Battery Hazards
Reducing Lithium-ion Battery Hazards
Core Principles for Reducing the Hazard Caused by Thermal Runaway. Copyright Peter Bugryniec. Source: link.
The 4 core principles for reducing the hazards caused by thermal runaway (TR) in batteries:
Intrinsic safety – anti-TR properties of cells, governed by materials modification and cell design.
Early detection – sensing and BMS integration to warn of a fault.
Passive defence design – to reduce secondary damage under abuse to maintain integrity even if one cell or module fails it should not propagate.
Once TR occurs, countermeasures should be activated to reduce the secondary hazard, such as TR propagation or fire propagation. Postponing TR propagation is valuable because it means there is increased time to respond to the incident, i.e. for passengers to evacuate a vehicle or for firefighters to reach a stationary BESS system.
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