A comprehensive cognition for the capacity fading mechanism of FeS2 in argyrodite‐based all‐solid‐state lithium battery

Abstract Sulfide solid state electrolyte (SSE) possesses high ionic conductivity and great processability but suffers from narrow electrochemical window. Conversion sulfide cathode FeS 2 has higher specific capacity and moderate redox potential, making it appropriate toward sulfide SSE. However, the complex reaction pathway and capacity fading mechanism in FeS 2 are rarely studied, especially in all‐solid‐state lithium battery (ASSLB). Herein, argyrodite sulfide SSE is paired with FeS 2 to investigate the electrochemical reaction pathways and the capacity fade mechanism. Instead of single conversion reaction, an anionic redox driven reaction of FeS 2 is revealed. The oxidization of Li 2 S vanishes and large quantity of inactive Li 2 S accumulates to cause the interfacial deterioration, along with the stress concentration during cycling, which leads to the rapid capacity fade of FeS 2 . Finally, a simple strategy of slurry‐coated composite electrode with highly conductive network is proposed to direct the uniform deposition of Li 2 S and alleviate the stress concentration. image