Efficient and Effective Synthesis of CaV${}_6$ O${}_{16}$ · 2.7H${}_2$O as High‐Performance Cathode Material for Aqueous Zinc Metal Batteries

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 CaV6 O16·2.7H2 O
(CaVO), offering promising performance as cathode material for AZMBs. With
commercial crystalline V2 O5 , Ca(CH3 COO)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 Ca 2+ and H2 O not only expand the interlayer spacing from
4.38 Å for V2 O5 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 Ca 2+ and H2 O effectively improves
the diffusion kinetics of Zn 2+ in CaVO. As a result, CaVO provides high
specific capacity (379 mAh g−1 at 0.05 A g−1 ) and promising long-term
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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.