Regulating interface electric field to stabilize high-voltage KVPO4F positive electrode for sustainable potassium-ion batteries

Fluorophosphates have garnered widespread attention in potassium-ion batteries due to their robust three-dimensional frameworks and high operating voltage. However, their practical implementation is restricted by inherent limitations, including low conductivity and an unstable cathode electrolyte interface. Herein, we propose an interfacial electric field regulating strategy to stabilize the cathode electrolyte interface of the KVPO4F positive electrode material. Based on theoretical calculations and in situ characterization, we find that the enhanced interfacial electric field can simultaneously optimize the transport of electrons and K+, improve the stability of the crystal structure, and facilitate the formation of a thin (~2.7 nm), stable cathode electrolyte interface layer. The designed composite material of KVPO4F and nitrogen-doped carbon nanotubes achieves a high specific energy of 454.8 Wh kg−1 (based on the mass of the positive electrode) in the voltage window of 2.0–5.0 V at 0.5 C (1 C = 131 mA g−1). The relevant full cell also exhibits good cycling stability, with a capacity retention of 80.6% after 2000 cycles at 1 C. Furthermore, this interfacial electric field regulation strategy can also be extended to other polyanionic systems such as KFeSO4F and KTiPO4F, demonstrating practical application potential. This study elucidates an interfacial electric field regulation approach and provides alternative insights for the development of high-energy-density and long-cycle-life potassium-ion batteries. Potassium-ion batteries face stability issues at high voltages. Here, authors use nitrogen-doped nanotubes to regulate the interfacial electric field of a polyanionic KVPO4F positive electrode. This stabilizes the structure and interface, enabling a specific energy of 454.8 Wh kg−1 and a cycling lifespan over 2000 cycles.