Swelling in lithium-ion batteries is a serious issue caused by internal chemical or physical damage, often linked to the release of gas during abnormal reactions. One primary cause is overcharging. When a battery is charged beyond its rated capacity, the electrolyte breaks down into flammable gases like hydrogen and carbon dioxide. This gas buildup creates pressure inside the sealed casing, leading to swelling. Overcharging can occur due to faulty chargers, damaged charging circuits, or leaving the battery plugged in for excessively long periods after reaching full capacity.

Physical damage is another common trigger. Dropping the battery, puncturing it, or exposing it to extreme impacts can damage the separator—a thin layer that keeps the positive and negative electrodes apart. If the separator tears, the electrodes come into direct contact, causing a short circuit. This short circuit generates intense heat, breaking down the electrolyte and producing gas. Even minor dents or cracks in the casing can compromise the separator over time, leading to gradual swelling.

High temperatures accelerate swelling. Exposing lithium-ion batteries to heat above 60°C (e.g., leaving them in a hot car or near a heat source) disrupts the stability of the electrolyte and electrodes. The heat increases the rate of side reactions, such as the decomposition of the solid electrolyte interphase (SEI) layer—a protective film on the anode. As the SEI layer breaks down, more electrolyte is consumed, releasing gas and weakening the battery’s structure.

Manufacturing defects can also cause swelling. Poor quality control during production may result in uneven electrode coating, contaminated electrolytes, or improperly placed separators. These flaws create localized hotspots where abnormal reactions occur, leading to gas buildup. Counterfeit or low-quality batteries are particularly prone to such defects, as they often skip rigorous testing and use substandard materials.

Once a lithium-ion battery swells, it is no longer safe to use. The gas inside is potentially flammable, and further use or charging can lead to rupture, leakage, or even fire. Users should stop using the swollen battery immediately, avoid puncturing it, and dispose of it at a designated recycling facility to prevent environmental hazards.

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