Interface defect induced upgrade of K-storage properties in KFeSO4F cathode: From lowered Fe-3d orbital energy level to advanced potassium-ion batteries

KFeSO4F (KFSF) is considered a potential cathode due to the large capacity and low cost. However, the inferior electronic conductivity leads to poor electrochemical performance. Defect engineering can facilitate the electron/ion transfer by tuning electronic structure, thus providing favorable electrochemical performance. Herein, through the regulation of surface defect engineering in reduced graphene oxide (rGO), the Fe-C bonds were formed between KFSF and rGO. The Fe-C bonds formed work in regulating the Fe-3d orbital as well as promoting the migration ability of K ions and increasing the electronic conductivity of KFSF. Thus, the KFSF@rGO delivers a high capacity of 119.6 mAh g-1. When matched with a graphite@pitch-derived S-doped carbon anode, the full cell delivers an energy density of 250.5 Wh kg-1 and a capacity retention of 81.5% after 400 cycles. This work offers a simple and valid method to develop high-performance cathodes by tuning defect sites.