Unveiling the Local Structure and the Ligand Field of Organic Cation Preintercalated Vanadate Cathode for Aqueous Zinc-Ion Batteries

Abstract

Layered vanadium-based materials have been extensively studied as promising cathode materials for aqueous zinc-ion batteries (AZIBs). However, challenges remain to achieve the desired high energy conversion efficiency and energy densities as well as long cycling stability requiring an in-depth understanding of the local and the electronic structure of a vanadium-based cathode, especially concerning the impacts on electrochemical potential and mass transfer in the electrochemical process. In this work, 1-butyl-1-methylpyrrolidinium cations are preintercalated into the layered hydrate vanadium pentoxide (V₂O₅·nH₂O) and partially replace the electroneutral structural water, changing the local atomic environment. X-ray absorption spectroscopies demonstrate the V–O bond elongation and the distortion in the [VO₆] octahedra, which alter the ligand field and brings the V 3d state to a lower energy level, ultimately leading to an increase in the electrochemical potential. It is also revealed that the preintercalated organic cations exert electrostatic interaction with lattice oxygen, stabilizing the layered structure and buffering lattice strain during cycling. Consequently, the modified cathode achieves a superior specific capacity of 412 mAh/g at 0.5 A/g and a capacity retention of 97% after 3000 cycles at 8 A/g. The unveiled correlation between local structure and electrochemical performance paves the way for optimizing the cathode materials by manipulating the local coordination environment.