Study on the deformation and failure mechanisms of lithium-ion battery casings during thermal runaway

The structural integrity of lithium-ion battery (LIB) casings during thermal runaway (TR) is critical for ensuring the safety of energy storage systems. Overcharge abuse can trigger intense internal gas generation and rapid heating, leading to severe deformation or even rupture of the battery casing; however, the underlying failure mechanisms remain insufficiently understood. This paper presents a coupled electro–thermo–mechanical multiphysics model that captures the complete plastic deformation and failure process of a prismatic LIB under overcharge conditions. The model is validated against expansion-force measurements from a commercial LiFePO 4 LIB tested across multiple charge rates. Simulation results show that under typical uniaxial constraints, the suppression of side-wall deformation driven by coupled internal pressure and thermal loads forces the top and bottom plates to bulge outward. This deformation pattern concentrates stress at geometric discontinuities near the corners, resulting in maximum plastic strain and energy dissipation. Quantitative analysis further reveals a transition in failure mechanisms: Although material strengthening initially exceeds thermal softening by 371.6% at the time of valve opening, it is ultimately overtaken by thermal softening, which outweighs strengthening by 45.15%. Based on the identified deformation and failure mechanisms of the battery casing, parametric studies show that selectively increasing the thickness of the top and bottom plates is a more effective and mass-efficient safety strategy than uniform thickening. Increasing the top plate thickness from 1.5 mm to 3.0 mm reduces the maximum plastic strain in critical corner regions by 40.0%. This work provides a physics-based predictive tool and practical design guidelines for optimizing LIB casing structures to enhance intrinsic safety.