Exploring the insertion properties of Mg2+ in H2V3O8 as a function of the water content in the organic electrolyte

Abstract

Magnesium-ion batteries (MIBs) are potential alternatives to lithium-ion batteries (LIBs) due to the high abundance of magnesium. However, the strong polarization of the divalent charge of Mg2+ hinders fast ion-diffusion for most cathode materials in comparison to monovalent ions such as Li+. By adding water to dry organic electrolytes, improved electrochemical properties are observed for some electrode materials in MIBs. H2V3O8 is a promising high-capacity cathode material for various battery types such as LIBs and MIBs. We show that both the kinetic and the electrochemical properties of H2V3O8 are improved by adding water to dry organic electrolyte leading to an initial specific capacity of 303 mAh·g−1 at a current density of 50 mA·g−1. This value is approximately four times higher than capacities measured in cells with dry electrolyte. In addition to in depth electrochemical characterization, the structural changes of H2V3O8 are explored by in-operando X-ray diffraction during galvanostatic cycling as a function of the water content in the organic electrolyte. Furthermore, the distribution of Mg2+ in H2V3O8 is investigated postmortem by transmission electron microscopy. Based on these results a mechanism for Mg2+insertion into H2V3O8 is proposed and how it is changed by adding water to the organic electrolyte.