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

Abstract

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.

Keywords

• Potassium-ion batteries
• Cathode
• Defect chemistry
• KFeSO4F
• Fe–C bond