Enhanced electrode kinetics and properties via anionic regulation in polyanionic Na3+xV2(PO4)3−x(P2O7)xcathode material

Mixing polyanion cathode materials are promising candidates for the development of next-generation batteries, owing to their structural robustness and low-volume changes, yet low conductivity of polyanion hinders their practical capacity. Herein, the anion-site regulation is proposed to elevate the electrode kinetics and properties of polyanionic cathode. Multivalent anion P2O74−is selected to substitute the PO43−in Na3V2(PO4)3(NVP) lattice and regulate the ratio of polyanion groups to prepare Na3+xV2(PO4)3−x(P2O7)x(NVPPx, 0 ≤ x ≤ 0.15) materials. The optimal Na3.1V2(PO4)2.9(P2O7)0.1(NVPP0.1) material can deliver remarkably elevated specific capacity (104 mAh g−1at 0.1 C, 60 mAh g−1at 20 C, respectively), which is higher than those of NVP. Moreover, NVPP0.1exhibits outstanding cyclic stability (91% capacity retention after 300 cycles at 1 C). Experimental analyses reveal that the regulation of anions improves the structure stability, increases the active Na occupancy in the lattice and accelerates the Na+migration kinetics. The strategy of anion-site regulation provides the researchers a reference for the design of new high-performance polyanionic materials.