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

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 Na 3 V 1.44 Fe 0.5 Mo 0.06 (PO 4 ) 3 cathode was designed through Fe/Mo dual-doping at the V sites of Na 3 V 2 (PO 4 ) 3 and synthesized via a conventional high-temperature solid-state method. The introduction of Fe 3+ activates the V 4+ /V 5+ redox couple at a high voltage plateau (~ 4.0 V), while also generates additional Fe 2+ /Fe 3+ and V 4+ /V 5+ redox pairs. Meanwhile, the doing of Mo 6+ creates cation vacancies, effectively modulating the electronic structure of vanadium and promoting ionic transport kinetics. Benefiting from this dual-doping strategy, the Na 3 V 1.44 Fe 0.5 Mo 0.06 (PO 4 ) 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. The dual-doping strategy in the NASICON-type Na 3 V 1.44 Fe 0.5 Mo 0.06 (PO 4 ) 3 cathode activates multiple redox centers and generates structural vacancies, thereby enhancing electrochemical performance with outstanding cycling stability and excellent ionic mobility kinetics. • A NASICON-type Na 3 V 1.44 Fe 0.5 Mo 0.06 (PO 4 ) 3 cathode material was successfully designed and synthesized. • Fe 3+ doping activates multiple redox centers; while Mo 6+ introduction induces vacancies, effectively enhancing sodium-ion transport for overall performance. • The Na 3 V 1.44 Fe 0.5 Mo 0.06 (PO 4 ) 3 cathode delivers a remarkable discharge capacity of 123.4 mAh g −1 at 0.2C and a high energy density of 406 Wh kg −1 , and demonstrates outstanding cycling stability with 92 % capacity retention after 2500 cycles at 30C.