Structural impact of Zn-insertion into monoclinic V2(PO4)3: implications for Zn-ion batteries

Abstract

The zinc-ion battery (ZIB) has been a system of particular interest in the research community as a possible alternative to lithium-ion batteries (LIB), and much work has been devoted to finding a suitable host material. In this article, monoclinic V₂(PO₄)₃ is investigated as a host material for reversible insertion of Zn²⁺. Initial chemical assessment via a facile microwave-assisted chemical insertion method indicates the possibility of Zn²⁺ insertion into the host. Electrochemical assessment, however, exhibits a significant capacity fade. In-depth analysis on the average and local structure of Li₃V₂(PO₄)₃, the empty host V₂(PO₄)₃, and the Zn-inserted V₂(PO₄)₃ reveals that heavy distortion is induced upon Zn²⁺ insertion into the V₂(PO₄)₃ framework, which is believed to be a result of a strong host–guest interaction jeopardizing the structural integrity. This is further supported by the dissolution of most of the material during the chemical oxidation of the Zn-inserted V₂(PO₄)₃. The underlying structural inadequacy poses difficulties for monoclinic V₂(PO₄)₃ to be a viable reversible host for Zn-ion batteries. This work suggests that not only the electrostatic repulsions of multivalent ions in a structure during diffusion, but also the structural stability of the host upon insertion of multivalent ions, must be considered for a better design of suitable host materials for multivalent-ion batteries.