Investigation of active heating systems for polymer-solid-state cells in an automotive battery module

The ionic conductivity of electrolytes, fluid or solid, in lithium-ion cells is essential for the high-performance application in the automotive field. In colder temperatures, the literature shows the polymer solid-state approach has a weakness connected to ionic conductivity (Grundish et al., 2021; Kamaya and et al., 2011; Manthiram et al., 2017) [1-3]. At elevated temperatures the ionic conductivity rises and becomes attractive for the automotive usage. In this work, it is investigated how large automotive pouch cells, with polymer electrolyte and lithium-metal anode, can be heated up. Different heating systems and boundary conditions, as ambient temperature and heating power are investigated. Due to the anisotropic thermal conductivity in- and through-plane of the cell, a high variance in the heating time with different heating systems occurs, with up to 13% difference. A reciprocal effect of heating time and temperature spread inside one cell is observed - the shorter the heating time, the higher the temperature spread. Also, a strong influence of the ambient temperature can be seen. With lower surrounding temperature the heating time rises strongly. In comparison between the ambient temperatures -25 °C and 10 °C the heating time can be reduced by 17%. This work shows that the thermal behavior of new cell technologies needs to be investigated more closely.