Several recent RV fires have been blamed on lithium-ion batteries, but not all are created equal. Dr. Matthew Priestley, Lead Technology Translator at the UNSW, explains.
A lithium-ion battery pack is made up of one or more lithium-ion cells. Not every cell is fabricated from the same chemical components.
If you compare two different cells from different manufacturers, then the chemical makeup and hence the performance may be quite different.
One important component inside of a lithium-ion cell is a thing called a cathode. We categorise the type of lithium-ion battery by the chemical properties of the cathode.
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A LiFePo4 battery is a lithium-ion battery where the cathode is constructed from lithium ion phosphate (LiFePo4). Each different cathode chemistry will provide different battery properties.
An LFP (LiFePo4) typically has a good thermal stability, which gives better safety performance than some other battery chemistries such as Lithium Nickel Cobalt Aluminum Oxide (NCA). However, as a trade-off, the energy density of LPF is less than NCA.
For the battery chemistries with worse thermal stability, the efficacy of the battery management system becomes more critical to ensure an adequate level of safety.
LPF batteries do have a higher thermal stability than some other lithium-ion battery chemistries. This means that they have a higher threshold for heat before thermal runaway occurs than some other lithium-ion battery chemistries.
Thermal runaway is a dangerous operating state where the cells are heated to a temperature where exothermic reactions occur, and the battery cooling system can no longer handle the rapid heating of the cells. Here, the battery cell temperature will rapidly increase to very high levels, potentially causing a battery fire.
Any lithium-ion battery can cause a fire if the thermal runaway threshold temperature is exceeded. Hence, it is vital to handle these products, even LFP batteries, with care. Damaging a lithium-ion battery (e.g., dropping it off a rooftop) can cause faults that may eventually lead to a thermal runaway event.
Overcharging a lithium-ion battery is a common cause of thermal runaway. Many devices will have a battery management system (BMS) that cuts off the charging before overcharging can occur. However, a fault to either the charger or BMS may still result in a thermal runaway incident. Hence, it is recommended to avoid leaving lithium-ion batteries to charge overnight or leaving them on charge for long periods of time after they have reached full charge.
A BMS is like a vigilant bodyguard for a lithium-ion battery. It may monitor various battery parameters to ascertain potentially unsafe operating conditions and, in such a situation, will aim to move the battery into a safe state.
A well-made BMS will monitor parameters such as the cell voltages, currents and temperatures. A high-quality BMS is vital for the safety of lithium-ion batteries. Not all BMS products are created equal, and some may only monitor the voltage or temperature across groups of cells, which is not as accurate as monitoring each cell individually.
Lithium-ion batteries have a preferred temperature range of roughly between 10-50 degrees Celsius. However, this temperature range will vary depending on the exact device. So, check the manual for their operating temperature range. I recommend trying to avoid operating any lithium-ion battery outside of the temperature range stated in the manual.
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