Local Heat Generation in a Single Stack Lithium Ion Battery Cell

Abstract

The local heat generation in a single stack lithium ion battery cell was investigated as a function of the C-rate and state of charge (SoC). For that purpose, a custom build electrochemical cell design developed for local in-operando temperature measurements is used. The local temperature evolution in both electrodes and the separator is compared with local heat generation rates calculated from galvanostatic intermittent titration technique (GITT) measurements. The impact of reversible and irreversible heats is evaluated as a function of the C-rate and the SoC. The results reveal substantial differences in the local heat generation rates of the individual components of the battery cell related to their kinetic and thermodynamic properties. Significant SoC dependencies of the local reversible and irreversible heat generation are reflected by both the local temperature measurements and the heat generation rates calculated from GITT. A distinct asymmetry between charging and discharging is revealed which results from the intrinsic asymmetry of the reversible heat as well as differences in the kinetic limitations of the lithiation and delithiation of active materials. This study indicates, that the heat generation rates of the individual cell components should be considered accurately in order to build up basics for targeted material-, design- and thermal management optimization to handle thermal issues in large battery packs.