Synergistic Influence of the Separator Microstructure and External Pressure on Dendrite-Induced Battery Failures: The Penetration Mechanism and Mitigation Strategy.

Lithium dendrite-induced internal short circuit (ISC) failures pose a severe safety challenge for lithium-ion batteries of electric vehicles (EVs). Due to the complex electrochemical-mechanical interplays caused by the synergistic influence of the separator microstructure and external pressure, the mechanism of dendrite penetration-induced failures remains unclear, hindering the development of dendrite mitigation strategies and battery design. An electrochemical-mechanical coupled phase-field model with realistic separator microstructures is developed to systematically explore the influence of the external pressure and interior microstructure on dendrite penetration processes. Results show that the penetration process exhibits a stage-specific characteristic, from mechanically dominated Stage 1 to electrochemically dominated Stage 2. Furthermore, two typical penetration modes are identified based on path tortuosity, i.e., low- and high-tortuosity paths. The low-tortuosity path is more sensitive to mechanical conditions, and the suppression effect of pressure on dendrite penetration is highly pronounced as the loading position is closer to dendrite tips. Furthermore, an innovative separator configuration integrating elongated pores and multidirectionally constrained circular pores is proposed, with an elliptical barrier array adjacent to the anode, extending ISC time by threefold without high external pressure. The results provide guidance on the synergistic regulation strategy of the separator microstructure and mechanical pressure for dendrite risk-free lithium-ion batteries in EVs.