Crystallinity Tuning of Na(3)V(2)(PO(4))(3): Unlocking Sodium Storage Capacity and Inducing Pseudocapacitance Behavior

As a promising cathode material of sodium‐ion batteries, Na(3)V(2)(PO(4))(3) (NVP) has attracted extensive attention in recent years due to its high stability and fast Na(+) ion diffusion. However, the reversible capacity based on the two‐electron reaction mechanism is not satisfactory limited by the inactive M1 lattice sites during the insertion/extraction process. Herein, self‐supporting 3D porous NVP materials with different crystallinity are fabricated on carbon foam substrates by a facile electrostatic spray deposition method. The V(5+)/V(4+) redox couple is effectively activated and the three‐electron reactions are realized in NVP for sodium storage by a proper crystallinity tuning. In a disordered NVP sample, an ultra‐high specific capacity of 179.6 mAh g(−1) at 0.2 C is achieved due to the coexistence of redox reactions of the V(4+)/V(3+) and V(5+)/V(4+) couples. Moreover, a pseudocapacitive charge storage mechanism induced by the disordered structure is first observed in the NVP electrode. An innovative model is given to understand the disorder‐induced‐pseudocapacitance phenomenon in this polyanion cathode material.