Engineering Crystal Growth and Surface Modification of Na V (PO ) F Cathode for High-Energy-Density Sodium-Ion Batteries.

Na V (PO ) F (NVPF) is a suitable cathode for sodium-ion batteries owing to its stable structure. However, the large radius of Na restricts diffusion kinetics during charging and discharging. Thus, in this study, a phosphomolybdic acid (PMA)-assisted hydrothermal method is proposed. In the hydrothermal process, the NVPF morphologies vary from bulk to cuboid with varying PMA contents. The optimal channel for accelerated Na transmission is obtained by cuboid NVPF. With nitrogen-doping of carbon, the conductivity of NVPF is further enhanced. Combined with crystal growth engineering and surface modification, the optimal nitrogen-doped carbon-covered NVPF cuboid (c-NVPF@NC) exhibits a high initial discharge capacity of 121 mAh g at 0.2 C. Coupled with a commercial hard carbon (CHC) anode, the c-NVPF@NC||CHC full battery delivers 118 mAh g at 0.2 C, thereby achieving a high energy density of 450 Wh kg . Therefore, this work provides a novel strategy for boosting electrochemical performance by crystal growth engineering and surface modification.