Space-confined intercalation expansion strategy for simple and rapid synthesis of kish-based expanded graphite for aluminum ion batteries

The practical application of graphite cathodes in aluminum ion batteries (AIBs) is hindered by poor cycle and rate performance of graphite, due to serious structural degradation. In this work, different types of kish-expanded graphite (KEG) with different expansion volumes were prepared simply and rapidly using low-cost solid waste kish graphite (KG) as precursor, and K2S2O8 and concentrated H2SO4 as oxide intercalation agents by space-confined intercalation expansion strategy. By adjusting the mass ratio of K2S2O8 to KG, the macrostructure and microstructure of KEG can be effectively controlled. Specifically, KEG6, synthesized with the mass ratio of K2S2O8 to KG of 6, exhibited a large expansion volume, graphene nanosheets with numerous graphite microcrystalline layer structures, and micro-nano interlayer pore structures resulting from the cross-linking of graphene nanosheets, along with abundant oxygen-containing functional groups. KEG6, as a cathode material for AIBs, exhibited outstanding electrochemical performance, including superior specific capacity (141.1 mA h/g at 50 mA/g), good rate capability (119.8 mA h/g at 1000 mA/g, 85.6 mA h/g at 2000 mA/g) and remarkable cycle stability (134.0 mA h/g with 99.1% Coulombic efficiency after 10,000 cycles at 1000 mA/g). This study provides a simple and rapid method for the large-scale synthesis of KEG as a potential candidate for AIBs.