We'll begin by analyzing from an electrical perspective why lithium-ion batteries explode or burn. Combustion or explosion usually occurs because heat accumulates and cannot dissipate, reaching an ignition point, or because heat accumulates to a certain level within a given space. In general, for batteries, these situations typically arise from one of four reasons.
1. Internal short circuit (mostly in large pouch cells): Structural or manufacturing defects lead to issues such as internally inserted tabs, insufficient separator coverage, burrs, or separator folds. Internally inserted tabs often occur in thick batteries with internal parallel connections. Inadequate insulation at the tab position can easily lead to acute internal short circuits during subsequent addition of protection boards or use, resulting in combustion or explosion (internal short circuit: I have personal experience with this, having scrapped over 2,000 batteries of this type; it was essentially a design defect, an acute internal short circuit). However, this situation is now extremely rare, unless caused by external forces.
2. External Short Circuit: Combustion and explosion due to external short circuits in batteries below 1AH are rare. Usually, the battery swells or the tabs are burned off. My personal analysis focuses on combustion caused by external short circuits in power lithium batteries or high-capacity mobile phone batteries. This involves improper customer use, such as not considering tab insulation when installing the battery in a metal casing, leading to abnormal battery smoke and combustion at the installation site. Power lithium batteries also commonly suffer from insufficient structural fixing measures (inadequate consideration). During user use, battery pack shaking can cause damage to the external insulation film or connecting wire sheaths, ultimately leading to a short circuit and combustion.
3. Overcharge explosion: This is the most dangerous and the company's biggest fear, but it still happens occasionally. Based on our understanding, there are two main reasons: a) Users do not use the matching charger as required, thus damaging the protection circuitry. Users often charge without time limits, making an explosion almost inevitable; b) Improper battery packing and a malfunctioning protection board will also result in a complete disaster... The same applies to single-cell batteries.
4. The battery itself is made of substandard materials. Substandard materials may cause overheating under the specified voltage and current, leading to an accident.
