Root cause analysis of battery swelling: gas generation, SEI decomposition, overcharge. Complete 8D corrective action guide.
What Is Battery Swelling? Battery swelling is the irreversible expansion of a lithium-ion cell caused by internal gas generation or electrode growth. It is one of the most visible and most dangerous degradation modes in EV, consumer and energy-storage packs: a swollen pouch cell loses capacity fast, raises internal pressure, and can eventually rupture or vent. In 8D terms, swelling is almost always a D4 problem that spans material, thermal and electronic control (BMS) factors at the same time. Symptoms Visible bulging of the pouch, prismatic can or module frame Internal pressure above the design limit (pouch cells often exceed 0.5 MPa) Accelerated capacity fade — SOH drops below 80% within months instead of years Abnormal temperature rise during charge (10-20 °C above baseline) Sweet solvent or electrolyte odour near the pack Soft, spongy compression pads that no longer return to their original thickness Affected Components Li-ion pouch cells (consumer electronics, EV modules) Prismatic cells (automotive, stationary storage) Cylindrical 18650 / 21700 cells Battery management system (BMS) and its voltage and temperature derating logic Thermal management system (liquid cold plate, air cooling, compression foam) Detection Methods Dimensional check: micrometer thickness measurement against nominal, plus visual inspection at the cell edges...
