High-Precision Modeling and Measurement of Core Temperature in Lithium-Ion Battery Cells

Lithium-ion batteries (LIBs) are central to modern energy storage systems, yet accurate monitoring of their internal thermal behavior remains a challenge. This study proposes an advanced method for measuring and predicting core temperature variations in 18650 LIB cells, addressing the limitations of conventional surface-based temperature measurements and thermal imaging techniques. An innovative hermetically sealed measurement fixture was developed to enable direct, localized, and stable internal heat distribution monitoring under vacuum conditions, mitigating electrolyte evaporation and oxidation risks. A refined lumped thermal-electrical model incorporating both radial and axial heat conduction paths was proposed and validated through empirical experiments. The proposed measurement method was conducted to evaluate the feasibility of the method, and the proposed lumped model was also experimentally validated using the IMREN 18650-3500-30A battery (with a nominal capacity of 3500 mAh and a maximum continuous discharge rate of 10 A). The results demonstrated a maximum accuracy improvement of up to 8.23% during the transient period. The proposed approach offers valuable insights for enhancing battery thermal management strategies, improving thermal simulation accuracy, and informing safer, more efficient battery designs.