Fe₃S₄@Li₇P₃S₁₁ nanocomposites as cathode materials for all-solid-state lithium batteries with improved energy density and low cost

All-solid-state lithium batteries are considered as one of the most promising alternatives to traditional lithium-ion batteries because of their high safety and high energy density. In order to further improve the energy density of all-solid-state lithium batteries, sulfide electrodes with high theoretical capacities and solid electrolytes with high ionic conductivities have been widely explored and successfully demonstrated in all-solid-state lithium batteries. However, the interfacial resistance arising from poor interfacial compatibility and loose contact seriously hinders the electrochemical performances of all-solid-state lithium batteries. Fe₃S₄ ultrathin nanosheets with a thickness of 15 nm are synthesized by a facile polyvinyl alcohol-assisted precipitation method. In order to achieve intimate contact between sulfide electrodes and sulfide solid electrolytes, Fe₃S₄ nanosheets are in situ coated with Li₇P₃S₁₁ and employed as cathode materials in Li/75% Li₂S-24% P₂S₅-1% P₂O₅/Li₁₀GeP₂S₁₂/Fe₃S₄@Li₇P₃S₁₁ all-solid-state lithium batteries to investigate their electrochemical performances. Fe₃S₄@Li₇P₃S₁₁ nanocomposite electrodes exhibit higher discharge capacity and better rate capability than pristine Fe₃S₄ nanosheets. After 200 cycles, the discharge capacity remained at a high value of 1001 mA h g^-1 at a current density of 0.1 A g^-1. The superior cycling stability could be ascribed to intimate contact and low charge transfer resistance at the interface between electrodes and solid electrolytes.