Effect of Internal AC Heating on the Temperature Homogeneity of Different Size Battery Cells

Rapidly warming up batteries is an important challenge both for conventional lithium-ion batteries, which operate best over 15 °C, and for most solid-state batteries, which currently require operating temperatures over 60 °C. Internal heating using an alternating current (AC) has been proposed as a possible solution in automotive applications, with faster heating rates possible than conventional external heating methods. This paper investigates the performance of internal AC heating on cells of different sizes, for both cylindrical and pouch formats. A novel experimental arrangement is used in which two cells are tested in series while connected with opposing polarity to create a zero-voltage string, allowing the use of less expensive testing equipment. The results show that larger cells exhibit a considerably greater distribution of surface temperature than smaller format cells during internal heating. This is likely due to the more extreme spatial variation in current density in the current collectors, causing an uneven distribution of internal heat generation. This highlights a significant difference compared to external heating methods, which are not affected by this, and has important implications for temperature measurement and battery management if this type of internal heating is to be used, since temperature sensors must be placed in hot spots or supplemented by validated models to ensure all parts of the battery stay within safe temperature limits.