Effects of State-of-Charge and Charging Rate on Material-Level Thermal Transport within Lithium-Ion Batteries

A comprehensive understanding of thermal transport properties at the material level for Lithium-ion batteries (LIBs) is often overlooked, despite being crucial for accurately reconstructing thermal behavior in macroscopic simulations for LIBs. To address this gap, a nitrogen-protected testing method integrated with an electrochemical cycling platform is first developed to measure the intrinsic thermal conductivity ( k ) of the electrodes and separator in LIBs, as well as the thermal contact resistance ( R c ) between them. The effects of the state of charge (SOC) and the charging rate (C-rate) on both k and R c are systematically evaluated, and the constituent of internal thermal resistance within the unit battery is clarified in detail. Results reveal that the k of the cathode increases monotonically with SOC, while the k of the anode exhibits a non-monotonic relationship whose trend depends on the C-rate. Notably, the R c between electrodes and separator, which constitutes the nonnegligible component of total thermal resistance, is marginally affected by SOC but increases significantly with higher C-rate. Additional experiments examining the effects of the testing environment underscore the necessity of nitrogen protection for accurate measurements of thermal transport properties. These findings provide valuable insights for improving thermal management strategies of LIBs in real-world applications.