Lithium-Ion batteries have become the storage medium of choice over the past 5 years in Australia and more recently globally but is the technology really safe?
Many would say that it depends on the topology, LFP, NMC, LCO, LTO and so on. We have all seen video's of a nail being driven into a battery (under test conditions) but is this really going to happen, and what is the scenario? Do the cells have a BMS attached, what are the cell SOC, and why are they driving a nail into the cells?
Lithium-ion cells are safe, provided they are managed by the BMS properly. The BMS should be designed to manage all aspects how the cells are treated under a number of conditions. The BMS must without fail, monitor BS (Battery System) temperature, balance cells, and most importantly manage the charge and discharge current.
Thermal runaway begins when the heat generated within a battery exceeds the amount of heat that is dissipated to its surroundings. If the cause of excessive heat creation is not remedied, the condition will worsen. The BMS should recognise this and reduce current flowing in and out of the battery allowing thermal mass within the cells to dissipate.
Some batteries have a built in mechanical breaker designed to open circuit when the current exceeds set parameters, this is utilised as a secondary form of protection should the BMS not stop or reduce the current flow. These breakers are mostly thermally controlled allowing high current to flow from the battery during surge scenarios i.e. when the PCE is switched on, there are significant in rush currents while the PCE capacitors are energised, this can cause damage to the cells and initiate a thermal runaway scenario.
In summary, the BMS is the integral part of making your lithiu-ion batteries safe, speak to your supplier to ensure that the BMS does stop over charging scenarios 100% of the time, under all operating conditions.