Manipulation of Na3V2(PO4)2F3 via aluminum doping to alter local electron states toward an advanced cathode for sodium-ion batteries
摘要
With its unique 3D skeleton structure and exceptional cyclic stability, the Na+ superionic conductor (NASICON)-type Na3V2(PO4)2F3 (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 Na3V2(PO4)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 Na3V1.9Al0.1(PO4)2F3 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.
Graphical abstract