Multiple redox Centers and defect engineering in Fe/Mo dual-doped Na3V2(PO4)3 cathodes for high-performance sodium-ion batteries

Abstract

Sodium superionic conductor (NASICON)-type phosphates cathodes have attracted considerable attention due to their high operational voltage and robust three-dimensional (3D) framework; however, the poor intrinsic electronic conductivity and low energy density hinder their broader application. Herein, a novel NASICON-type Na₃V_1.44Fe_0.5Mo_0.06(PO₄)₃ cathode was designed through Fe/Mo dual-doping at the V sites of Na₃V₂(PO₄)₃ and synthesized via a conventional high-temperature solid-state method. The introduction of Fe³⁺ activates the V⁴⁺/V⁵⁺ redox couple at a high voltage plateau (∼ 4.0 V), while also generates additional Fe²⁺/Fe³⁺ and V⁴⁺/V⁵⁺ redox pairs. Meanwhile, the doing of Mo⁶⁺ creates cation vacancies, effectively modulating the electronic structure of vanadium and promoting ionic transport kinetics. Benefiting from this dual-doping strategy, the Na₃V_1.44Fe_0.5Mo_0.06(PO₄)₃ cathode delivers a high capacity of 123.4 mAh g⁻¹ at 0.2C and an impressive energy density of 406 Wh kg⁻¹ within 2.2–4.2 V. Moreover, it exhibits outstanding cycling stability, presenting a capacity retention of 92 % after 2500 cycles at 30C. This work highlights a viable strategy for advancing high-performance NASICON-type cathodes through complex metal ion doping.