Coupling mechanism of internal polarization evolution and 3D thermal behavior in lithium-ion batteries under high-rate discharge

The spatial heterogeneity of multi-physics fields induced by high-rate discharge affects the safety performance of large-format lithium-ion batteries (LIBs). In this work, Quasi-4D electrochemical-thermal (ECT) coupled model is developed for lithium-ion battery to analyze the spatiotemporal evolution of internal mass transport, electrochemical polarization, and temperature fields under different discharge rates (1C, 3C, and 5C). The analysis indicates that an increase in the discharge rate elevates the liquid-phase mass transport resistance within the porous electrodes. At the end of the 5C discharge, the maximum concentration difference of the electrolyte along the electrode thickness direction is approximately 1000 mol/m 3 ; the liquid-phase mass transport limitation drives the charge transfer reactions toward the current collector side, causing the local overpotential to rise to approximately 0.30 V. Multi-source heat generation analysis shows that as the discharge rate increases from 1C to 5C, the total heat generation power of the battery increases non-linearly, the energy proportion of irreversible polarization heat decreases from 86.39% to 65.95%, and the proportion of liquid-phase ionic ohmic heat increases from 7.95% to 12.59%. Regarding macroscopic 3D thermal behaviors, due to the combined effects of localized polarization heat generation and in-plane electronic ohmic heat generation in the current collectors, the maximum temperature regions are concentrated at the tabs and their roots. Under the 5C condition, the maximum battery temperature reaches 314.6 K, with a global temperature rise of 16.4 K, and the maximum internal temperature difference is 3.5 K. Furthermore, a quantitative evaluation reveals a critical internal heat transfer bottleneck, demonstrating that relying solely on localized tab cooling severely enlarges the spatial temperature gradient. Consequently, effective thermal management must integrate localized tab cooling with global large-surface active cooling. This work quantitatively resolves the ECT coupling evolution inside the battery under high-rate discharge, providing a rigorous basis for optimizing battery thermal management systems and evaluating thermal safety boundaries.