Sulfur-Embedded FeS₂ as a High-Performance Cathode for Room Temperature All-Solid-State Lithium–Sulfur Batteries

All-solid-state lithium–sulfur batteries employing sulfur electrodes and a solid electrolyte at room temperature are still a great challenge owing to the low conductivities of sulfur cathodes. In this work, we report room temperature all-solid-state lithium–sulfur batteries using thin sulfur layer-embedded FeS2 (FeS2@S) microsphere composites as active materials in the FeS2@S–Li10GeP2S12-Super P cathode electrode. Setting the cut-off voltage between 1.5 and 2.8 V, only lithiation–delithiation reactions between L2FeS2 and FeSy and direct reaction between Li2S and S will occur, which avoids large volume change of FeS2 caused by the conversion reaction, leading to the structure integrity of FeS2@S. The resultant batteries exhibit excellent rate and cyclic performances, delivering specific capacities of 1120.9, 937.2, 639.7, 517.2, 361.5, and 307.0 mA h g–1 for the FeS2@S composite cathode, corresponding to the normalized capacities of 1645.5, 1252.9, 782.5, 700.2, 478.4, and 363.6 mA h g–1 for sulfur at 30, 50, 100, 500, 1000, and 5000 mA g–1, respectively. Besides, they can retain the normalized capacity of 430.7 mA h g–1 for sulfur at 1000 mA g–1 after 200 cycles at room temperature.