Structure and Electrochemical Properties of Magnesium Ion Intercalation into Vanadium Dioxide

Abstract

Magnesium-ion Batteries (MIBs) offer a promising energy density, safety, and low-cost energy storage due to the large abundance of magnesium on Earth. However, only limited candidates have been proposed for MIBs cathode materials. In this study, the structure and electrochemical properties of magnesium ion intercalation into vanadium dioxide (VO2(B)) has been unveiled. VO2(B) was synthesized using a facile hydrothermal method, and confirmed by XRD, HR FE-SEM and TEM as a monoclinic structure with the space group of C 2/m, and a nano-belt morphology. The material shows reversible magnesium intercalation with a discharge capacity of 51.0 mAh g-1 at 25oC at current density of 20 mA g-1 in nonaqueous electrolyte (0.5 M Mg(ClO4)2 in AN). It shows good rate performance at 25, 30, 40, and 50 mA g-1. The cycle performance of VO2(B) still need improvement, as it delivered 62% of the initial capacity after 25 cycles, due to the structural degradation and vanadium dissolution in the electrolyte. VO2(B) also shows magnesium intercalation with a discharge capacity of 114.8 mAh g-1 with an average voltage of ~2.47 V (vs Mg/Mg2+) at 60oC in nonaqueous electrolyte. The structural evolution at pristine, discharge, and charge state revealed the magnesium ion intercalation into VO2(B). The crystal structure of Mg0.11VO2 and detail magnesium ion position in VO2(B) is determined for the first time. It has monoclinic structure with space group of C 2/m and the magnesium ion is located in the largest cavity of VO2(B). TEM-EDX mapping and XPS result also revealed the reversible magnesium intercalation into the material.