Enhanced electrode kinetics and properties via anionic regulation in polyanionic Na3+xV2(PO4)3−x(P2O7)x cathode 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−1 at 0.1 C, 60 mAh g−1 at 20 C, respectively), which is higher than those of NVP. Moreover, NVPP0.1 exhibits 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.