High Lithium Storage Capacity and Long Cycling Life Fe₃S₄ Anodes with Reversible Solid Electrolyte Interface Films and Sandwiched Reduced Graphene Oxide Shells

Increasing demands for lithium-ion batteries (LIBs) with high energy density and high power density require highly reversible electrochemical reactions to enhance the cyclability and capacities of electrodes. As the reversible formation/decomposition of the solid electrolyte interface (SEI) film during the lithiation/delithiation process of Fe 3 S 4 could bring about a higher capacity than its theoretical value, in the present work, synthesized Fe 3 S 4 nanoparticles are sandwich-wrapped with reduced graphene oxide (RGO) to fabricate highly reversible and long cycling life anode materials for high-performance LIBs. The micron-sized long slit between sandwiched RGO sheets effectively prevents the aggregation of intermediate phases during the discharge/charge process and thus increases cycling capacity because of the reversible formation/decomposition of the SEI film driven by Fe nanoparticles. Furthermore, the RGO sheets interconnect with each other by a face-to-face mode to construct a more efficiently conductive network, and the maximum interfacial oxygen bridge bonds benefit the fast electron hopping from RGO to Fe 3 S 4, improving the depth of the electrochemical reactions and facilitating the highly reversible lithiation/delithiation of Fe 3 S 4 . Thus, the resultant Fe 3 S 4 /RGO hybrid shows a highly reversible charge capacity of 1324 mA h g –1 over 275 cycles at a current density of 100 mA g –1, even retains 480 mA h g –1 over 500 cycles at 1000 mA g –1, which are much higher than reported values.