Synergistic gallium and silicon co-doping for high-performance NASICON-type cathodes for sodium-ion batteries

Sodium superionic conductor (NASICON)-type Na 3 V 2 (PO 4 ) 3 (NVP) is widely regarded as a promising cathode material for sodium-ion batteries (SIBs); however, its practical application is hindered by limited specific capacity and pronounced volume shrinkage during cycling Herein, a rational multi-component design is proposed through simultaneous cationic and anionic substitution, yielding Na 3+x V 1.5 Ga 0.5 (PO 4 ) 3−x (SiO 4 ) x (0 ≤ x ≤ 0.3) cathode materials. Partial substitution of V 3+ by Ga 3+ enables reversible activation of the high-voltage V 4+ /V 5+ redox couple (~4.0 V), while replacement of PO 4 3− with SiO 4 4− introduces additional electroactive Na + and expands ion-transport pathways, thereby extending the voltage plateau and enhancing specific capacity. Among the investigated compositions, Na 3.1 V 1.5 Ga 0.5 (PO 4 ) 2.9 (SiO 4 ) 0.1 exhibits optimal electrochemical performance, delivering a high reversible specific capacity of 116.2 mAh g −1 within a voltage window of 2.2–4.2 V and retaining 96.6% of its initial capacity after 500 cycles at 10C. Ex situ X-ray diffraction reveals that the Na + insertion/extraction proceeds via a combined solid-solution and phasic reaction mechanism with a remarkably small volume change of only 4.7%, ensuring excellent structural stability. This work demonstrates that synergistic multi-site regulation of cations and anions is an effective strategy for designing high-energy-density and long-life phosphate cathode materials for advanced SIBs.