Elucidating critical origin for capacity fading in High-voltage coin cell with FSI-based electrolyte

F-containing functional electrolytes have been extensively investigated to improve the performance of Li-metal batteries as they generate stable LiF-based solid–electrolyte interphase layers, improving Li deposition/dissolution efficiency. However, these imide-based electrolytes corrode not only the Al current collector but also the stainless steel (SS) component of the coin cell at high operating voltages. Additionally, deciding upon which part of the corrosion has a greater effect on the performance degradation remains a topic of debate. In this study, through systematic cell design exposing SS to LiFSI-based electrolyte, it is found that SS corrosion is a more dominant cause of capacity fading than the Al case. Moreover, the computational study reveals that the electron transfer from Al to SS decomposes FSI^– and the resulting byproducts finally corrode Al. To develop stable cells by removing corrosion factors, the SS and Al-free pouch-type cells are proposed by integrating carbon current collectors and locally high-concentration electrolyte and exhibit 430 cycles with a coulombic efficiency of 99.93%. This study demonstrates the importance of careful selection of cell components and systematic cell design to ensure a robust interface at the cathode side, suggesting the necessity to develop a new testing cell to replace the current coin-cell platform.