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 LiClO₄ as conductive salt in high-voltage NMC622‖Graphite pouch cells. The cells containing LiClO₄ show poorer electrochemical performance compared to their LiPF₆ equivalents. However, to the best of our knowledge, a mechanistic understanding of the effect of LiClO₄ 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 LiPF₆, 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_xO_yCl_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 LiClO₄-containing electrolytes.