Boosted electrochemical performance of Na₃V₂(PO₄)₃ at low temperature through synergistical F substitution and construction of interconnected nitrogen-doped carbonaceous network

Benefitting from its unique NASICON-type framework, the Na₃V₂(PO₄)₃ (NVP) cathodes have aroused extensive interest and have been deemed as the promising cathode candidate for sodium-ion batteries (SIBs). Unfortunately, the poor electronic conductivity, combined with the undesirable volume variations, seriously hinders the practical application of NVP cathode, especially at low temperatures. Herein, a dual-strategy, F substitution accompanied by V vacancies and the construction of three-dimensional (3D) nitrogen-doped carbonaceous frameworks (NC), were employed for the NVP cathode (F-NVP/C@3DNC). The former can remarkably decrease the particle size and enhance Na⁺ migration capability, increasing the ionic conductivity. Meanwhile, the electronic connection and effective buffering can be obtained from the latter, strengthening the electrode integrity. Consequently, up to 100 cycles at 0.1 A g^–1, a reversible capacity of 113.8 mAh g^–1, approaching the theoretical value (117 mAh g^–1), is demonstrated, accompanied by impressive capacity retentions at 1.0 (93.75% after 4800 cycles) and 20.0 A g^–1 (92.7% after 1000 cycles). More importantly, even at –20 °C, a superior specific capacity (102.6 mAh g^–1 after 100 cycles at 0.1 A g^–1) and high capacity retention (86.6% at 20.0 A g^–1 up to 1000 cycles) can still be obtained simultaneously. Significantly, the design of F-NVP/C@3DNC provides insights for the fabrication of polyanion cathodes for applications at low temperatures with modified structure stability and reaction kinetics.