Manipulation of Na 3 V 2 (PO 4 ) 2 F 3 via aluminum doping to alter local electron states toward an advanced cathode for sodium‐ion batteries

Abstract With its unique 3D skeleton structure and exceptional cyclic stability, the Na + superionic conductor (NASICON)‐type Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) has been considered as a competitive cathode material for advanced Na‐ion batteries. However, the release of fluorine during the heat treatment leads to the formation of an additional phase Na 3 V 2 (PO 4 ) 3 (NVP), which results in a low‐voltage plateau and compromises the energy density. Herein, we modulate the local electronic states of the V site by aluminum substitution to strengthen the stability of F. The results confirm that the aluminum introduction not only changes the local electron states of V sites, significantly reducing the formation of NVP by‐product from 6.71 wt% to 1.01 wt%, but also effectively reduces the band gap, improving the electronic conductivity of NVPF. The optimized Na 3 V 1.9 Al 0.1 (PO 4 ) 2 F 3 exhibits higher energy density of 340 Wh·kg −1 and excellent rate performance of 106.7 mAh·g −1 at 10C compared with the pristine cathode.