Electrochemical Evolution of an Iron Sulfide and Sulfur Based Cathode for All-Solid-State Li-Ion Batteries

In this study we demonstrate an all-solid-state electrode with a maximum specific energy of 928 Wh kg−1. A mechanochemically prepared composite of FeS and S is used as the cathode active material. Capacity in excess of theoretical for the active material is attributed to the partial electrochemical utilization of the Li2S component of the 77.5Li2S:22.5P2S5 glass electrolyte in the composite electrode. This electrode exhibits a complex evolving electrochemistry that can be approximated by the combination of the parallel electrochemistries of FeS, FeS2, and S. Using dQ/dV analysis we present indirect evidence for the electrochemical in-situ formation of a FeS2 phase during charging.