1D Nanostructured Na7V4(P2O7)4(PO4) as High-Potential and Superior-Performance Cathode Material for Sodium-Ion Batteries

Tailoring materials into nanostructure offers unprecedented opportunities in the utilization of their functional properties. High-purity Na7V4(P2O7)(4)(PO4) with 1D nanostructure is prepared as a cathode material for rechargeable Na-ion batteries. An efficient synthetic approach is developed by carefully controlling the crystal growth in the molten sodium phosphate. Based on the XRD, XPS, TG, and morphological characterization, a molten-salt assisted mechanism for nanoarchitecture formation is revealed. The prepared Na7V4(P2O7)(4)(PO4) nanorod has rectangle sides and preferential [001] growth orientation. GITT evaluation indicates that the sodium de/intercalation of Na7V4(P2O7)(4)(PO4) nanorod involves V3+/V4+ redox reaction and Na5V43.5+(P2O7)(4)(PO4) as intermediate phase, which results in two pairs of potential plateaus at the equilibrium potentials of 3.8713 V (V3+/V3.5+) and 3.8879 V (V3.5+/V4+), respectively. The unique nanoarchitecture of the phase-pure Na7V4(P2O7)(4)(PO4) facilitates its reversible sodium de/intercalation, which is beneficial to the high-rate capability and the cycling stability. The Na7V4(P2O7)(4)(PO4) cathode delivers 80% of the capacity (obtained at C/20) at the 10 C rate and 95% of the initial capacity after 200 cycles. Therefore, it is feasible to design and fabricate an advanced rechargeable sodium-ion battery by employment of 1D nanostructured Na7V4(P2O7)(4)(PO4) as the cathode material.