Bidirectional multi-physics modeling of failure in 18650 lithium-ion batteries under quasi-static indentation: Implications for bionic underwater vehicle power systems

Localized mechanical compression of lithium-ion batteries (LIBs) poses a potential safety concern in flexible bionic underwater vehicles (BUVs) with spatially constrained battery compartments. Motivated by this application, a three-dimensional multi-physics model is developed for a single 18650 LIB subjected to quasi-static radial indentation. The framework enables bidirectional coupling among mechanical deformation, electrical response, internal short circuit (ISC), and thermal evolution. Unlike conventional models employing a fixed ISC threshold, the model incorporates a dynamically updated nonlinear mechanical-thermal composite criterion that represents the combined effects of local separator deformation, stress state, and temperature on ISC initiation and evolution. An inverse method based on temperature residuals is used to reconstruct an effective residual heat-generation rate primarily associated with high-temperature side reactions. The parameters of the electrical model are identified from hybrid pulse power characterization data, while the coupled framework is calibrated against quasi-static indentation data at 10% state of charge. Idealized parametric simulations are subsequently performed by varying the indenter diameter and axial loading position. The simulations indicate that contact geometry alters the relative contributions of shear, bending, and compression to LIB deformation, thereby affecting ISC initiation and evolution, voltage response, and heat accumulation. Within the present 10% SOC simulations, reconstructed residual heat generation follows ISC initiation, while loading geometry has a stronger influence on ISC timing and voltage response than on predicted peak temperature. These findings provide model-based insights into LIB failure and response for subsequent investigations of mechanical protection, thermal management, and safety monitoring in BUV battery modules and packs.