Vanadium oxides obtained by chimie douce reactions: The influences of transition metal species on crystal structures and electrochemical behaviors in zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) have received increasing attention due to cost-effectiveness and inherent safety. A wide variety of advanced cathode materials have been revealed with promising performance in RAZIBs. However, these materials usually require sophisticated procedures at high temperatures, which greatly limit further practical application. Herein, a chimie douce approach is adopted to prepare vanadium oxides from V₂O₅ suspension with the addition of various transition metal cations (Mn²⁺, Zn²⁺, Ag⁺, and Fe³⁺) by simple liquid-solid mixing under ambient conditions. For the cases of Mn²⁺ and Zn²⁺, the dissolution-recrystallization process takes place leading to layered Mn_0.31V₃O₇·1.40H₂O (MnVO) and Zn_0.32V₃O₇·1.52H₂O (ZnVO). The use of Ag⁺ forms tunneled Ag_0.33V₂O₅ (AgVO), and the present of Fe³⁺ stays mainly unreacted V₂O₅. The underlying reaction chemistries are proposed, for which the pH values of precursor solutions are found to be a key factor. Among the prepared materials, layered vanadium oxides exhibit promising battery performance. Particularly, MnVO delivers 340 and 217 mAh g^-1 at 1 and 8 A g^-1, respectively. A specific capacity of 164 mAh g^-1 can be retained after 500 cycles at 1 A g^-1. By contrast, AgVO and FeVO demonstrate inferior performance with retaining only 89 and 20 mAh g^-1 after 500 cycles.