Besides the electronic and ionic transport, the heat transport of composites will be decisive for the safety of a solid-state battery, and the proposed resistor network model needs to account for heat transport, too. To investigate and compare the thermal properties of NCM83, LPSCl and their composites, thermal diffusivities (D) were determined experimentally. The thermal diffusivity is a measure of how quickly temperature spreads through a material. Exceptionally low thermal diffusivities ranging from 0.18 mm 2 s -1 to 0.43 mm 2 s -1 were measured for all compositions (Figure ). In this work, isobaric heat capacities (𝐶 𝑃 ) are approximated by calculated isochoric heat capacities (details in the Supporting Information Section S6). Within the investigated temperature range, all heat capacities show a steady increase with temperature (Figure a, bottom) following the excitation of more vibrational modes with increasing temperatures. While