An investigation of the effects of a high valence state dopant (Zr4+) and the experimental insertion of two Na+ ions in the NaVOPO4 matrix

In this work, we attempt to incorporate two Na atoms into the NaVOPO4 matrix, which transforms the matrix into Na2VOPO4. To achieve this, we adjusted the phase parameters and used a facile synthesis method like the sol-gel-assisted hydrothermal technique. However, at high temperatures, the oxygen environment around the V atom changes, introducing the new phase Na2V(PO4)2 matrix into NaVOPO4. High valence state ions are required to support the active sites, keep the oxygen environment around them at a high temperature, and function well as a dopant for the NVP matrix. As a result, the Zr4+ is incorporated into the NVP matrix and it significantly enhances the tetragonal phases by enhancing (101), (112) planes. By substituting Zr4+ ion, the specific capacity of NVP is raised from 0.8268 mAh/g to 4.214 mAh/g at the scan rate of 10 mV/s.