Experimental determinations of thermophysical parameters for lithium-ion batteries: A systematic review

Thermophysical parameters, including the specific heat and thermal conductivity of lithium-ion batteries (LIBs), are the key parameters for the design of battery thermal management systems in electric vehicles. The evaluations of internal temperature distribution and even the thermal safety characteristics of the batteries depend highly on these thermophysical parameters under either live operation or repose condition. In this paper, the experimental studies of the specific heat and thermal conductivity of LIBs are reviewed and discussed. This review classifies the experimental studies into ex-situ and in-situ measurements. The ex-situ measurements, based on the dissection of the battery, may differ from realistic scenarios and thus the obtained parameters may not be fully applicable for thermal prediction of practical battery systems. Contrarily, in-situ measurements better represent the realistic characteristics without dismantling the battery, which can be further categorized into weighted average method, heat flow method, dedicated equipment including accelerating rate calorimeter (ARC), calibration calorimeter in insulation, self-made calorimeter method, and so on. Due to the short test time and good size adaptability, unsteady-state in-situ measurement techniques, including the calibration calorimeter and quasi-steady state techniques, are becoming the promising research directions in the future, especially for the simultaneous determination of multiple thermal parameters. The large data scatterings are pointed out based on the existing results, and the underlying mechanisms are scrutinized. To guarantee measurement accuracy, it is indispensable to calibrate the heat loss and benchmark with standard sample tests together with rigorous uncertainty analysis. The thermophysical parameters should be determined under different temperatures, states of charge (SOC) and aging conditions to enable accurate prediction of temperature profiles and degradation for LIBs with ever increasing energy density and safety risk.