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Lithium-ion batteries (Li-ion) are revolutionising the automotive industry by powering electric vehicles (EVs), offering high energy density, lightweight design, and sustainable mobility solutions. However, alongside their benefits, understanding and mitigating the fire risks associated with these batteries is crucial for ensuring the safety of EVs and their passengers.
These vehicles, under certain conditions, can pose fire risks due to a phenomenon known as thermal runaway. Thermal runaway is a process where heat builds up uncontrollably within the battery cells, potentially leading to a chain reaction and causing the battery pack to catch fire or even explode. This process is akin to a snowball effect, where heat continues to escalate, similar to a snowball rolling downhill, but with heat instead of snow. Factors such as short circuits, overcharging, or mechanical damage can trigger thermal runaway in an electric vehicle’s battery pack.
Once initiated, thermal runaway can spread rapidly to neighbouring cells, exacerbating the situation. While the effects of thermal runaway may resemble an arc flash due to the intense heat and rapid escalation, it is important to note that thermal runaway is distinct from an arc flash. Understanding and implementing appropriate safety measures are crucial for mitigating the risks associated with thermal runaway in electric vehicles.
Here is video of Thermal Runaway:
As this video has described when a lithium-ion battery in an electric vehicle catches fire, a series of events unfold, often beginning with thermal runaway. As temperatures rise, electrolyte decomposition occurs, releasing flammable gases and increases internal pressure. This can lead to cell rupture, exposure of reactive lithium components to oxygen, and ignition of the electrolyte.
While fires pose a risk in EV batteries, battery manufacturers must collaborate closely with car manufacturers to conduct rigorous quality tests and prevent such incidents from occurring. Fires can be triggered by various factors, which should be mitigated by battery designers and car manufacturers to prevent such things as mechanical damage, manufacturing defects, and external factors like high temperatures and overcharging. Tests to prevent damage and thermal runaway should include performance and abuse testing, such as subjecting batteries to high temperatures, mechanical stress, and overcharging, to ensure they meet the safety standards and can withstand extreme conditions they will likely encounter. Such things like humidity and vibration testing should also be conducted to simulate real-world environments.
Below are some of the safety standards vehicle batteries should comply with to name a few:
- ISO 6469-1 – Electrically propelled road vehicles – safety specifications – part 1: on-board rechargeable energy storage system (RESS)
- GB 38031 – Electric vehicles traction battery safety requirements
- SAND 2005-3123 – Electrical energy storage system abuse test manual for electric and hybrid electric vehicle applications
- IEC 62619 – Safety requirements for secondary lithium cells and batteries, for use in industrial application
- UL 2580 – Standard for safety – batteries for use in electric vehicles
While we’ve addressed the causes of lithium battery fires and the standards they must meet, it’s crucial to emphasise quality standards during manufacturing should also be taken into account to reduce the risks of fires even further. Strict quality controls should be in place throughout the production process, by battery and car manufacturers, in order to detect and rectify defects to ensure consistent and reliable battery performance.
Here is a video showing one simple example of such Quality Checks (from Underwriters Laboratory).
If all the aforementioned measures are carried out, mitigation of the risk for lithium-ion batteries catching fire should be at a minimum. It should not go unmentioned that EVs also undergo crashworthiness tests, providing an opportunity to assess the robustness of the battery enclosure and vehicle structure in preventing mechanical damage during collisions. If all the strict standards for design and production is not enough to keep fire risks in EV’s to a minimum, then it should not go unmentioned that EV batteries be carefully monitored after install and throughout they useful life.
EV batteries are generally equipped with Battery Management Systems (BMS) to monitor battery health. These systems oversee battery temperature, voltage, and state of charge, implementing protective measures like cell balancing and thermal management. BMS combined with thermal management systems are vital for regulating battery temperature and preventing overheating. While Tesla EVs come equipped with such systems, it’s important to research the management systems employed by different car and battery manufacturers. Typically, effective thermal management systems utilise liquid or air cooling, or a combination of both.
Despite occasional reports of EV fires, the likelihood of such incidents occurring in the UK remains relatively low compared to traditional internal combustion engine vehicles.
Whether you’re a user or a supplier entering the EV technology space, prioritising these preventive measures and safety protocols is essential. By doing so, the electric vehicle industry can enhance the safety and reliability of lithium-ion battery systems, facilitating the continued advancement and adoption of electric mobility solutions.
