Insights into Tiny High-Entropy Doping Promising Efficient Sodium Storage of Na3V2(PO4)2O2F toward Sodium-Ion Batteries

Abstract

Both high operation voltage and theoretical capacity promise polyanion-type fluorophosphate Na₃V₂(PO₄)₂O₂F as a competitive cathode toward high-energy-density sodium-ion batteries (SIBs). However, the intrinsic low kinetic characteristics seriously influence its high-power property and service life. To well address this, a creative tiny high-entropy (HE) doping methodology is purposefully developed to fabricate nanoscale Na₃V_1.94(Cr, Mn, Co, Ni, Cu)_0.06(PO₄)₃O₂F (NVPOF-HE) as the advanced cathode materials for SIBs. The grain refinement effect induced by collaborative regulations from polyvinyl pyrrolidone and tiny HE heteroatomic doping is reasonably proposed for nanosizing particle dimension of NVPOF-HE. Systematic experiments and theoretical calculations authenticate that the HE doping efficiently promotes the electronic/ionic transport and high-voltage capacity contribution, and weakens the lattice expansion over Na⁺-(de)intercalation processes. Thanks to the appealing virtues mentioned here, the nano NVPOF-HE, compared to single-ion/dual-ion/triple-ion doped cases, achieves even better Na⁺-storage performance in terms of both high-rate capacities and long-term cycling stability. Furthermore, the NVPOF-HE assembled full SIBs deliver a high materials-level energy density of 463 Wh kg⁻¹ and electrochemical stability of ≈93.8% capacity retention after 1000 cycles at 5 C rate. More essentially, the fundamental insights gained here provide a significant scientific and technological advancement in high-performance and durable polyanionic cathodes toward next-generation SIBs.