On safety of swelled commercial lithium-ion batteries: A study on aging, swelling, and abuse tests

Lithium-ion battery technology has advanced significantly, making these power sources essential for portable electronic devices such as smartphones. In 2023, global smartphone shipments reached nearly 1.2 billion units, underscoring the widespread reliance on these batteries. However, as batteries age, they may swell and potentially pose explosion risks. To investigate the safety of swollen batteries, this study conducts accelerated aging and swelling tests on lithium-ion batteries from five leading brands, which together represent over half of the global smartphone market share. The research involves a series of comprehensive tests, including Accelerated Rate Calorimeters (ARC) test, mechanical, electrical, and thermal abuse tests in accordance with Chinese national standards, as well as gas composition and theoretical flammability analyses on both new and swollen batteries. The findings indicate that swollen batteries generally exhibit safer behavior under floating charging conditions, and both new and swollen batteries pass the abuse tests within the standard framework. This study suggests that the safety of swollen lithium-ion batteries cannot be categorically labeled as dangerous or safe and should be assessed within the context of specific environments.