Efficient and Effective Synthesis of CaV6O16·2.7H2O as High-Performance Cathode Material for Aqueous Zinc Metal Batteries

Abstract

Vanadium oxide-based materials are considered to be among the most promising positive electrode candidates for aqueous zinc-metal batteries (AZMBs). However, complex processes, high costs, and insufficient yields of their preparation methods limit further application. Herein, an efficient and effective oil bath method is presented for the preparation of CaV₆O₁₆·2.7H₂O (CaVO), offering promising performance as cathode material for AZMBs. With commercial crystalline V₂O₅, Ca(CH₃COO)₂, and water as raw materials, phase-pure CaVO with 42.8 g per batch and a yield of 98.8% can be obtained through the reaction at 90 °C for 6 h. It is further demonstrated that the pre-intercalated Ca²⁺ and H₂O not only expand the interlayer spacing from 4.38 Å for V₂O₅ to 8.21 Å for CaVO but also stabilize the interlayer structure of vanadium oxides, promoting the reversibility of CaVO toward the de-/intercalation of Zn²⁺/H⁺. In addition, density-functional theory calculations show that the introduction of Ca²⁺ and H₂O effectively improves the diffusion kinetics of Zn²⁺ in CaVO. As a result, CaVO provides high specific capacity (379 mAh g⁻¹ at 0.05 A g⁻¹) and promising long-term cyclability (94.4% capacity retention after 2200 cycles at 1 A g⁻¹), demonstrating the efficient and effective synthesis of vanadium oxide-based cathode materials for high-performance AZMBs.