Thermal runaway in lithium iron phosphate batteries is primarily caused by the internal heat generation rate being far higher than the heat dissipation rate. This results in a large accumulation of heat inside the lithium-ion battery, which triggers a chain reaction, leading to battery fire and explosion.
(1) Overheating triggers thermal runaway
Overheating of power lithium iron phosphate batteries can be caused by improper battery selection and thermal design, external short circuits leading to temperature increases, or loose cable connections. Solutions should address both battery design and battery management. From a battery material design perspective, materials to prevent thermal runaway can be developed to block the runaway reaction. From a battery management perspective, different temperature ranges can be predicted to indicate different safety levels, enabling tiered alarms.
(2) Overcharging triggers thermal runaway
Overcharge-triggered thermal runaway refers to a situation where the lithium iron phosphate battery management system (BMS) lacks proper overcharge protection, causing the battery to continue charging even though the BMS has malfunctioned. To address this type of overcharge, the first step is to identify charger malfunctions, which can be resolved by implementing full redundancy in the charger. Secondly, it's crucial to examine the battery management system for proper operation, such as whether the voltage of each individual cell is being monitored.
(3) Internal short circuit triggers thermal runaway
Impurities from battery manufacturing, metal particles, expansion and contraction during charging and discharging, and lithium plating can all cause internal short circuits. These internal short circuits occur slowly over a very long period, and it's unknown when thermal runaway will occur. Experiments cannot replicate the process. Currently, experts worldwide have not yet found a way to reproduce the internal short circuit process caused by impurities, and research is ongoing.
To solve the internal short circuit problem, the first step is to find a battery manufacturer with high-quality products and select lithium iron phosphate batteries and battery cell capacity. The second step is to conduct safety prediction of internal short circuits and identify cells with internal short circuits before thermal runaway occurs.
(4) Mechanically triggered thermal runaway
Collisions are a typical way to mechanically trigger thermal runaway. If we were to simulate a collision in the lab, the closest approximation would be a needle penetration test. By conducting needle penetration tests on ternary lithium-ion batteries and lithium iron phosphate batteries to study the thermal runaway process, it was found that lithium iron phosphate batteries did not exhibit the same severe heat release as ternary lithium-ion batteries during this process. Experiments show that different materials react differently upon needle penetration, with lithium iron phosphate being relatively safer.
