Why Do Lithium-ion Batteries Catch Fire?
Lithium-ion (Li-ion) batteries can catch fire or explode due to thermal runaway, often triggered by overcharging, physical damage, or manufacturing defects. Thermal runaway is a dangerous chain reaction where an increase in temperature causes further temperature increase, often resulting in a fire. It can be triggered by many types of abuse, such as, but not limited to: overcharging, deep over-discharging, and charging at too high rates (especially critical at low temperatures), discharging at too high rates, crush and other structural damages, external heating, external short circuiting. A contamination during manufacturing can also cause a thermal runaway to happen even years later when the battery is in its application. Once thermal runaway starts, it can quickly escalate, causing the battery to combust. Implementing robust safety measures can significantly reduce these risks and ensure safer use of Lithium-ion battery technology.
- LITHIUM-ION BATTERY OPERATION
Lithium-ion (Li-ion) batteries have 2 terminals, a positive and a negative one. These terminals are connected electronically to the electrodes inside a Li-ion battery. Inside the battery, we find 2 different electrodes: cathode and anode. When discharging the battery, Li-ions get on their way inside the battery, from anode to cathode. Outside of the battery we have a current during discharge, and electrons move from anode to cathode and during charge, Li-ions and electrons take the opposite way. There is a separator between cathode and anode to avoid an internal short circuit.
Figure1: Short circuits may occur between anode and cathode
- INTERNAL SHORT CIRCUITS
Internal short circuits occur when there’s an internal physical connection between the anode and cathode. This can be caused by manufacturing defects, physical damage, or the growth of Lithium dendrites – tiny, needle-like structures that can pierce right through the separator and cause an internal short. When this happens, large currents can flow internally, the battery can overheat, leading to a fire or explosion. The risk of Li-dendrite growth is especially critical when charging at too high rates at too low temperatures.
- OVERCHARGING
Overcharging occurs when a battery is charged beyond its maximum capacity. This would then cause the electrolyte to break down and lead to heat and gas development. Of course, battery management systems (BMS) are designed to control voltage limits to prevent overcharging, but a faulty BMS could lead to an overcharge scenario.
- MECHANICAL DAMAGE
Physical impacts, punctures, or crushing can damage Li-ion battery to an extend leading to internal short circuits and thermal runaway. For example, puncturing a battery during a car accident can obviously cause the battery to catch fire.
- LITHIUM IRON PHOSPHATE (LFP) BATTERIES
Lithium Iron Phosphate (LFP) batteries are known for their excellent safety and long cycle life. They are commonly used in stationary energy storage systems and electric vehicles. The Lithium Iron Phosphate (LFP) batteries are often portrayed as safer battery technology as they tend to produce less gas during thermal runaway, which makes them safer in some way. LFP cathodes collapse at way higher temperatures compared to Lithium Nickel Manganese Cobalt Oxide (NMC) battery cathodes.
- RECOMMENDATIONS & CONCLUSION
The causes of lithium battery explosions involve internal short circuits, thermal runaway, long-term overcharging of the battery cell, external short circuits, external high temperatures, mechanical vibration or damage, charging problems, and other aspects. Therefore, when using and maintaining lithium batteries, it is necessary to strictly abide by relevant safety regulations to ensure the safety and stability of the battery. At the same time, strengthening safety supervision and preventive measures are also important means to prevent lithium battery explosions.
Stakeholders are advised to ensure that the lithium batteries they procure are compliant to IEC standards which were adopted by the country. These standards are set to be enforced by the proposed, Energy (Solar Products and Installations) Regulations which are soon to be promulgated. The lithium batteries for use in Zimbabwe should be complaint to the two IEC standards below:
- IEC 62619 is an international standard that specifies the requirements and tests for secondary lithium cells and batteries used in industrial applications, including stationary applications. It focuses on safety requirements and ensures the reliable operation of these batteries in various industrial contexts.
- IEC 62281 is an International Standard that focuses on the safety of primary and secondary lithium cells and batteries during transport. It outlines test methods and requirements to ensure the safe handling and transportation of these types of batteries.
Stakeholders are encouraged to procure lithium batteries from reputable suppliers as opposed to buying smuggled or second-hand batteries were the safety and warranties of those batteries cannot be guaranteed.