Manipulation of Na <sub>3</sub> V <sub>2</sub> (PO <sub>4</sub> ) <sub>2</sub> F <sub>3</sub> via aluminum doping to alter local electron states toward an advanced cathode for sodium‐ion batteries
Shimin Wang, Jinqi Li, Xu Li, Mengjiao Sun, Wenjin Huang, Qing Liu, Futong Ren, Yongjiang Sun, Lingyan Duan, Hang Ma, Hong Guo
Abstract
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.