High‐Entropy Doped KTiOPO ₄ ‐Type Vanadium‐Based Fluorophosphate Cathodes for High‐Energy Sodium‐Ion Batteries

Abstract The development of high‐energy‐density and high‐power cathode materials represents a critical requirement for advancing practical sodium‐ion battery (SIB) technologies. In this work, a high‐entropy‐doped KTiOPO ₄ (KTP)‐type NaV _0.95 (Fe, Mn, Ni, Al, Ca) _0.05 PO ₄ F (HE‐NVPF) cathode material is presented, designed to enhance reaction kinetics, operation voltage, and energy density through single‐crystal phase formation and improved electronic/ionic conductivity. The high‐entropy doping strategy enables the elimination of inductive nucleation agents while promoting single‐crystal growth of HE‐NVPF during low‐temperature hydrothermal synthesis. The KTP‐type crystal structure facilitates complete Na ion utilization and enables a solid‐solution Na storage mechanism in HE‐NVPF cathodes, accompanied by minimal lattice volume changes (4%). When tested in half cells in combination with Na metal anode, the HE‐NVPF cathodes exhibit a remarkably high energy density of 532 Wh kg ⁻¹ with an average operating voltage of 4.0 V, an exceptional long cycle life of 3 000 cycles, and high capacity retentions at 30 C (2 min per charge). Its practical feasibility is demonstrated in graphite//HE‐NVPF full cells, which present power densities of above 10 000 W kg ⁻¹ and energy densities of over 342 Wh kg ⁻¹ for 1000 cycles. This work offers new insights into designing high‐entropy doped cathode materials for long‐life and fast‐charging SIBs.