Interlayer Regulatory Engineering of NiO₂ by Introducing H⁺ for High-Rate Mg Ion Storage

Abstract

Magnesium ion batteries (MIBs) are considered as potential next-generation energy-storage systems. However, Mg 2+ has high polarization ability, causing it to be difficult to diffuse in cathode materials and leading to poor rate performance of materials. Herein, we propose that the modification strategy of introducing interlayer cations into layered transition metal oxides achieves the enhancement of Mg 2+ migration by weakening the Coulombic interactions between the host material and Mg 2+ . Based on first-principles calculations, the electrochemical properties of NiO 2 and Ni(OH) 2 formed by the introduction of the interlayer cation H + into NiO 2 as cathode materials for MIBs are comprehensively investigated. The results show that the introduction of H + effectively shields the interaction between the host material and Mg and reduces the diffusion barrier of Mg 2+ in the material from 1.26 to 0.67 eV, which is conducive to the subsequent ion insertion. Thus, the introduction of interlayer cations successfully activated the highly reversible and fast Mg 2+ storage properties in the material. Furthermore, the presence of H + can not only significantly improve the electrical conductivity of the material and promote the transformation of the material from semiconductor to metal during ion insertion but also alleviate the volume expansion caused by Mg 2+ insertion and promote the stability and integrity of the structure. Thus, the interlayer regulation strategy of introducing interlayer cations into the material can realize the control of various aspects of electron transport and ion diffusion, and structural stabilization of the materials endows the materials with excellent electrochemical properties.