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 FeS₂ has higher specific capacity and moderate redox potential, making it appropriate toward sulfide SSE. However, the complex reaction pathway and capacity fading mechanism in FeS₂ are rarely studied, especially in all‐solid‐state lithium battery (ASSLB). Herein, argyrodite sulfide SSE is paired with FeS₂ to investigate the electrochemical reaction pathways and the capacity fade mechanism. Instead of single conversion reaction, an anionic redox driven reaction of FeS₂ is revealed. The oxidization of Li₂S vanishes and large quantity of inactive Li₂S accumulates to cause the interfacial deterioration, along with the stress concentration during cycling, which leads to the rapid capacity fade of FeS₂. Finally, a simple strategy of slurry‐coated composite electrode with highly conductive network is proposed to direct the uniform deposition of Li₂S and alleviate the stress concentration. image