1. Overcharging
During charging, lithium ions move from the positive electrode and are stored in the negative electrode. If charging continues beyond the battery’s safe voltage or capacity limits, the negative electrode may no longer accommodate the incoming lithium effectively. This can accelerate electrolyte decomposition, gas generation and lithium plating, including dendrite formation, all of which can contribute to cell swelling and create a safety risk.
2. Excessive discharge
During initial charging and discharging, electrode materials react with the electrolyte at the solid-liquid interface and form a passivation layer. This layer limits the passage of electrolyte molecules while allowing lithium ions to move through it. It is known as the solid electrolyte interphase (SEI).
The SEI layer changes during charging and discharging. Excessive discharge can damage this protective layer, contribute to electrode degradation and promote gas generation or swelling.
3. Manufacturing defects
Manufacturing defects such as uneven electrode coating or inconsistent assembly can contribute to cell swelling.
4. Long-term use can contribute to swelling
Cell aging and repeated cycling can increase internal degradation and gas generation. A swollen battery should be removed from service and assessed using the manufacturer’s safety procedures.