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

A double layer δ-NH 4 V 4 O 10 , 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 V 2 O 5 , 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 )NH 4 V 4 O 10 . 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-NH 4 V 4 O 10 . 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-NH 4 V 4 O 10 . The scheme of theoretical cyclic voltammetry presented here will be useful for addressing issues of cyclability and energy rate in other electrode materials. A double layer δ-NH 4 V 4 O 10 , 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.