Battery explosions, though rare, occur due to a chain reaction  known as thermal runaway, driven by chemical and physical failures. In  lithium-ion batteries, the primary trigger is the breakdown of the  separator—a thin membrane between  the anode and cathode that prevents direct contact. If the separator is damaged  (e.g., by punctures, overheating, or manufacturing defects), the anode and  cathode short-circuit, releasing large amounts of heat.

Overcharging is a common precursor. When a battery is charged  beyond its rated voltage (typically above 4.2V for lithium-ion), lithium metal  plating occurs on the anode. These metallic deposits can pierce the separator,  causing internal short circuits. The heat from the short circuit accelerates  chemical reactions, including the decomposition of the electrolyte (a flammable  organic solvent) into gases like carbon dioxide and hydrogen fluoride. As  pressure builds inside the battery casing, it can rupture, releasing flammable  gases that ignite when exposed to oxygen.

High temperatures also contribute. Exposure to fire, direct  sunlight, or operating in hot environments (above 60°C) weakens the separator and increases  electrolyte volatility. Physical damage, such as crushing or dropping a battery,  can deform the casing and breach the separator, initiating the short circuit.  Poorly manufactured batteries with inconsistent electrode materials or  inadequate separators are particularly vulnerable, as they lack the structural  integrity to withstand normal stress.

Furthermore, using uncertified chargers can cause overcurrent or  overvoltage, bypassing the BMS and overwhelming the battery’s safety mechanisms. Once thermal runaway  begins, it generates enough heat to ignite adjacent batteries in a pack, leading  to cascading failures. Proper handling, avoiding overcharging, and using  approved chargers are critical to preventing these dangerous  incidents.

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