Enhanced K-Storage Performance in Ultralong Cycle-Life Potassium-Ion Batteries Achieved Via Carbothermal-Reduction-Synthesized Kvopo4 Cathode

•The development of a novel carbothermal-reduction synthesized approach for the preparation of pure-phase KVOPO4.•The non-destructive DRT method revealed the evolution of the stable electrode/electrolyte interface.•Acquiring the mechanism of the highly reversible K-ion storage through detailed characterization and theory simulation.•Superior cycling stability of KVP-800 for 4 V−class PIBs (63 mAh g − 1 after 1000 cycles, 86% capacity retention).