Chemical transformation of MgH2/V2O5 composite to Mg-V-O rock salt and its influence on the electrochemical Li conversion and hydrogen storage characteristics of MgH2

TL;DR

This paper explores the chemical transformation of MgH2/V2O5 composites into Mg-V-O rock salt structures and examines how this affects lithium conversion and hydrogen storage, revealing key electrochemical behaviors and limitations.

Contribution

It demonstrates the formation of magnesium vanadium oxide with a rock salt structure and links this to changes in electrochemical performance in lithium and hydrogen storage.

Findings

Formation of magnesium vanadium oxide with rock salt structure confirmed.

Small oxide additive improves initial discharge capacity.

Electrolyte degradation is not the main issue; charge transfer is limiting.

Abstract

This study investigates the lithium conversion behavior of a hydrogen storage material based on vanadium oxide added magnesium hydride. To understand the chemical interaction between vanadium oxide and magnesium hydride, detailed X ray diffraction and X ray photoelectron spectroscopy analyses were performed on ball milled composites with varying compositions. The results confirm the formation of a combined magnesium vanadium oxide with a rock salt structure, indicating strong chemical interaction between the components. It is further shown that the presence of a small amount of this oxide additive significantly influences the lithium reaction with magnesium hydride, leading to a high initial discharge capacity and limited recharge capacity in lithium ion coin cells. Post use analyses confirm the presence of magnesium hydride, suggesting that volume expansion is not responsible for the observed irreversibility. Electrochemical impedance spectroscopy using differential function of relaxation times indicates that electrolyte degradation is not a major issue. Instead, slow charge transfer processes are identified as the limiting factor, and these are sensitive to the composition of the additive. These findings highlight that improving electrode and electrolyte compatibility is essential for enhancing performance in this system.