Thermal response and aging behavior of lithium-ion batteries for new-energy locomotives under complex operating conditions

Abstract Lithium-ion batteries have become a mainstream energy storage technology owing to their high energy density and long cycle life. however, their thermal safety and aging issues remain critical challenges to reliable operation. In this study, an electrochemical-thermal-SEI film growth multi-physics coupled model is developed to simulate and analyze the thermal and aging behaviors of a single lithium-ion cell under different charge/discharge C-rates and ambient temperature conditions. The spatial nonuniformity of the coupled thermal-aging response within the cell is further analyzed. The results show that, as the discharge rate increases, the terminal voltage decreases more rapidly, the discharge duration is shortened, the discharge curves after cycling shift leftward, and the available capacity declines. Under the high-rate 4C condition, the temperature rise rate is 2.26 times that under the low-rate condition, and the increase in SEI film thickness is 2.23 times that under the low-rate condition, indicating that high-rate operation substantially intensifies electrochemical polarization, internal heat generation, and SEI-related side reactions. Ambient temperature also has a pronounced influence on battery aging: high-temperature operation leads to severe SOH degradation and a marked increase in the temperature nonuniformity coefficient. These findings reveal the coupled effects of rate, temperature, and spatial distribution on battery aging, providing a theoretical basis for thermal management optimization and lifetime prediction of traction batteries in new-energy locomotives.