Role and Evolution of FeS₂ Cathode Microstructure in Argyrodite-Based All-Solid-State Lithium–Sulfur Batteries

High Resolution Image Download MS PowerPoint Slide All-solid-state lithium–sulfur batteries (ASSLSBs) are emerging as a promising alternative for green energy storage, offering high theoretical capacities and energy densities by using inexpensive materials. To date, ASSLSBs commonly suffer from poor cycle life and sluggish reaction kinetics. A promising active material for ASSLSBs is iron disulfide, FeS 2, due to its natural abundance, low cost, and high theoretical capacity (894 mAh·g –1 ). It undergoes a displacement reaction with significant volume changes whose effects can be locally constrained by using small particles. Here, the influence of the positive electrode microstructure on the electrochemical performance of FeS 2 -based ASSLSBs with Cl-rich argyrodite, Li 5.5 PS 4.5 Cl 1.5, a mechanically soft sulfide solid electrolyte with high ionic conductivity, is investigated. Composites with different microstructures were prepared using three different processing methods ( i.e., hand grinding, ball mill, and mini mill). Their impact on the electrochemical performance was evaluated, revealing that homogeneously submicro-structured composites achieve higher capacities (up to 4.28 mAh·cm –2 ) and capacity retention (87.2% at the 50 th cycle). Furthermore, finely structured composites enhance the in situ formation of active material from the solid electrolyte and increase its accessible reversible capacity. Ex situ analyses ( i.e., SEM-EDS and XPS) at different states of charge show that the morphology of FeS 2 evolves forming core–shell like submicro-structures.