Reasons for Combustion or Explosion of 18650 Lithium Batteries
1. Internal short circuit: Structural or process defects leading to excessive insertion of the terminal ear, insufficient membrane wrapping, burrs, membrane breakage, etc. Insertion of polar ears often occurs in thick batteries and structures with internal parallel connections. If the insulation of the polar ear position is not in place, it is easy to cause internal acute short circuits and combustion or explosion in subsequent products or during use. However, this situation is almost rare now, unless there are external factors.
2. External short circuit: Explosion after combustion caused by external short circuit of lithium batteries below 1AH is not common, usually resulting in bulging or simply burning off the terminal ear. Personally, I have analyzed that combustion is caused by external short circuit of power batteries or large capacity mobile phone batteries. This involves improper use by the customer - when installing the metal outer box, the ear insulation was not considered, resulting in abnormal battery smoke and combustion at the installation site; Insufficient structural fixation measures are also common in power batteries (due to inadequate consideration), which can cause damage to the external insulation protective film or connection wire skin of the battery due to shaking of the battery pack during user use, ultimately leading to short circuit combustion.
3. Overcharging explosion: This is the most dangerous and feared by businesses, but it still occasionally occurs. From the understanding, there are two points: a. Users do not use the matching charger as required, which damages the protective circuit, and users often charge without time limit, which is difficult to avoid; b. If the 18650 lithium battery is improperly assembled and the protective board fails, it will also explode in a mess. The same applies to a single battery.
4. When the 18650 lithium battery is heated, the reactions inside the battery form a reaction chain, where each reaction promotes each other and proceeds sequentially. Firstly, the decomposition of SEI film releases heat to heat the battery, which promotes the reaction between the negative electrode and the solvent to release more heat, resulting in the reaction between the negative electrode and the binder, solvent decomposition. Then, the positive electrode begins to undergo thermal decomposition reaction, releasing a large amount of heat and gas, ultimately leading to the combustion or explosion of the lithium battery.
5. Manufacturing process. The manufacturing process of 18650 lithium batteries is also an important factor affecting the safety performance of batteries, among which the three main factors are the positive and negative electrode capacity ratio, slurry uniformity control, and coating quality control.
6. Temperature. There are many factors that affect the safety of lithium batteries, among which battery materials have a significant impact on the safety of lithium batteries. Battery materials generally have thermal activity, and when the temperature of the battery continues to rise, many thermal reactions will occur inside. When the heat cannot be dissipated in time, it is easy to cause battery safety accidents. Therefore, the selection of positive and negative electrode materials for lithium batteries has an important impact on the safety performance of batteries.
