Effects of inhomogeneous temperature distribution during aging on the thermophysical properties of lithium-ion battery electrodes

The thermophysical properties of lithium-ion batteries are crucial for the optimized and safe design of battery thermal management systems. This paper presents an experimental investigation of aging-induced changes in the thermophysical properties of the electrodes of a commercial 20 Ah pouch cell during cyclic aging. The results show that the thermophysical properties can change significantly compared to the beginning of life, depending on the thermal aging conditions. This should be taken into account when optimizing the system design for the entire lifetime. In addition to the influence of the aging temperature, this study focuses on the influence of internal temperature inhomogeneities during aging. It can be shown that temperature inhomogeneities during aging result in inhomogeneous thermophysical properties of the electrodes and that the changes depend on the local average aging temperature, the global temperature gradient over the cell and the local temperature gradients over individual electrodes. Furthermore, it is shown that the direction of the gradient (in- or through-plane) can have a decisive impact on the changes, and thermal through-plane gradients can lead to a self-reinforcing behavior. In order to correlate the individual changes in the anode and cathode with aging mechanisms, an additional post-mortem analysis was performed.