Distorting Local Structures to Modulate Ligand Fields in Vanadium Oxide for High-Performance Aqueous Zinc-Ion Batteries

Abstract

Layered hydrate vanadates are promising cathode materials for aqueous zinc-ion batteries (AZIBs). Various intercalants have been preinserted into the interplanar space of hydrate vanadates with significantly enhanced kinetics and stabilized structures. However, such an enhancement is induced by various intercalants, and the relationship between the property enhancement and the type of intercalant still needs to be revealed. In this work, the distortion of octahedra induced by the preintercalation of benzyltrimethylammonium (BTA⁺) cations into hydrate vanadium pentoxide (V₂O₅·nH₂O, VOH) and the change in ligand field are studied using synchrotron X-ray pair distribution function (PDF) and X-ray absorption fine structure (XAFS). Variations in the local coordination of vanadium alter the ligand field, decreasing the energy of the lowest unoccupied orbitals (e*), which leads to an increased electrochemical potential. Additionally, the introduced BTA⁺ facilitates fast ion diffusion and stabilizes the layer structure. A cathode with a distorted local structure delivers a specific capacity of 408 mAh/g at 0.5 A/g, with a capacity retention of 95% after 3000 cycles at 8 A/g.