Comprehensive Study on Cell Components in High‐Voltage Pouch Cells with Lithium Perchlorate: Decomposition, Transesterification, Chlorination, Deposition, and Self‐Discharge

Abstract Battery development has traditionally focused on high energy and long lifetime cells, but there is now a shift towards their sustainability and safety. One example of this trend is the search for fluorine‐free conductive salts. The overwhelming majority of lithium‐ion conductive salts contain fluorine, which is critical regarding their environmental impact, sustainability, and toxicology. In this study, we perform a comprehensive investigation of the performance and aging mechanisms of cell components with LiClO 4 as conductive salt in high‐voltage NMC622‖Graphite pouch cells. The cells containing LiClO 4 show poorer electrochemical performance compared to their LiPF 6 equivalents. However, to the best of our knowledge, a mechanistic understanding of the effect of LiClO 4 on the aging of electrode and electrolyte components for high‐voltage cells is largely missing. Developing such an understanding will pave the way toward designing alternative salts to LiPF 6 , ultimately leading to fluorine‐free and more sustainable battery cells. Our results show, that the chlorination of ethyl methyl carbonate at both methyl and ethyl groups and the formation of large (Li w )Al x O y Cl z composite deposits on the cathode surface result from perchlorate degradation at the cathode. This leads to increased cell resistance, reduced capacity retention, and accelerated degradation of the LiClO 4 ‐containing electrolytes.