Insights into the electrochemical properties of Li 2 FeS 2 after FeS 2 discharging.

All-solid-state lithium-sulfur batteries (ASSLSBs) have high reversible characteristics owing to the high redox potential, high theoretical capacity, high electronic conductivity, and low Li + diffusion energy barrier in the cathode. Monte Carlo simulations with cluster expansion, based on the first-principles high-throughput calculations, predicted a phase structure change from Li 2 FeS 2 ( P 3̄ M 1) to FeS 2 ( PA 3̄) during the charging process. LiFeS 2 is the most stable phase structure. The structure of Li 2 FeS 2 after charging was FeS 2 ( P 3̄ M 1). By applying the first-principles calculations, we explored the electrochemical properties of Li 2 FeS 2 after charging. The redox reaction potential of Li 2 FeS 2 was 1.64 to 2.90 V, implying a high output voltage of ASSLSBs. Flatter voltage step plateaus are important for improving the electrochemical performance of the cathode. The charge voltage plateau was the highest from Li 0.25 FeS 2 to FeS 2 and followed from Li 0.375 FeS 2 to Li 0.25 FeS 2 . The electrical properties of Li x FeS 2 remained metallic during the Li 2 FeS 2 charging process. The intrinsic Li Frenkel defect of Li 2 FeS 2 was more conducive to Li + diffusion than that of the Li 2 S Schottky defect and had the largest Li + diffusion coefficient. The good electronic conductivity and Li + diffusion coefficient of the cathode implied a better charging/discharging rate performance of ASSLSBs. This work theoretically verified the FeS 2 structure after Li 2 FeS 2 charging and explored the electrochemical properties of Li 2 FeS 2 .