Understanding the partial substitution effect of Mg in Zn-V aqueous batteries

Although vanadium dioxide with various valence states, high theoretical capacity and low cost have been demonstrated as the ideal cathode materials for aqueous zinc-ion batteries (AZIBs), its unstable structure inhibits its further development. Herein, a structurally stable magnesium doped vanadium dioxide (Mg0.16VO2·0.34H2O) was prepared by a simple hydrothermal reaction. The regular of pre-intercalation Mg2+ on the structural and electrochemical properties of cathode was further explored through varying the doping amount of Mg2+. According to the experimental results, a small amount of Mg2+ insertion is not sufficient to stabilize the cathode, while excessive Mg2+ insertion will reduce capacity. The optimal parameter was obtained when the doping content of Mg2+ was 2 mmol, MgHVO/Zn batteries get specific capacity (315.4 mAh/g at a current density of 1 A/g) and outstanding long circulation stability (the capacity retention of 86.36 % over 10,00 cycles even at 5 A/g). And the electrochemical mechanism was explained by a series of in situ tests. This work reveals the regulation of the cathode structure by pre-intercalation Mg2+ and provides some insights for future pre-intercalation cathode regulation.