Structural transformation during Li/Na insertion and theoretical cyclic voltammetry of the δ-NH4V4O10 electrode: a first-principles study

Abstract

A double layer δ-NH₄V₄O₁₀, due to its high energy storage capacity and excellent rate capability, is a very promising cathode material for Li-ion and Na-ion batteries for large-scale renewable energy storage in transportation and smart grids. While it possesses better stability, and higher ionic and electronic conductivity than the most widely explored V₂O₅, the mechanisms of its cyclability are yet to be understood. Here, we present a theoretical cyclic voltammetry as a tool based on first-principles calculations, and uncover structural transformations that occur during Li⁺/Na⁺ insertion (x) into (Li_x/Na_x)NH₄V₄O₁₀. Structural distortions associated with single-phase and multi-phase structural changes during the insertion of Li⁺/Na⁺, identified through the analysis of voltage profile and theoretical cyclic voltammetry are in agreement with the reported experimental electrochemical measurements on δ-NH₄V₄O₁₀. We obtain an insight into its electronic structure with a lower band gap that is responsible for the high rate capability of (Li_x/Na_x) δ-NH₄V₄O₁₀. The scheme of theoretical cyclic voltammetry presented here will be useful for addressing issues of cyclability and energy rate in other electrode materials.