A Review of Failure Modes and Safety Strategies of Lithium-Ion Batteries from Materials to Systems.

Lithium-ion batteries (LIBs) have rapidly proliferated due to their high energy density, fast charging capability, and long cycle life. However, intrinsic thermal instability poses serious safety concerns, as failures can trigger fires or explosions, hindering large-scale deployment in electric vehicles and energy storage systems. This review examines thermal runaway mechanisms of LIBs by dividing them into sequential stages involving anode-electrolyte interface breakdown, separator shrinkage, electrolyte decomposition, and cathode oxygen release, and by analyzing how multiphysical couplings among thermal, electrochemical, mechanical, and chemical factors govern cascade evolution. Furthermore, the review explores safety enhancement strategies across multiple scales, ranging from material-level improvements such as surface coating and doping of Ni-rich cathodes, ceramic-based separators, and non-flammable electrolyte additives, to structural designs of cells, modules, and packs, as well as system-level diagnostics and control frameworks utilizing battery management systems, artificial intelligence, and digital twin-based prediction models. Addressing the increasing risks associated with LIB applications remains a critical challenge in battery and fire safety engineering. This review therefore proposes a cascade-aware safety framework that links quantitative, stage-specific failure indicators to material-, cell-, module-, pack- and system-level interventions for intrinsic safety design in high-energy-density LIBs.