Lithiation and Magnesiation Mechanism of VOCl: First-Principles Moleculardynamics Simulation

Abstract

The layered metal oxide VOCl is a kind of promising electrode material for rechargeable batteries. It is the first time that the thermodynamic, electronic, and kinetic properties of lithiated and magnesiated VOCl were systematically investigated. The upper limit of Li and Mg topological intercalation into VOCl is xLi = 1 and xMg = 0.5, respectively. Beyond the critical value, further lithiation and magnesiation will cause the phase evolution of layered VOCl. Upon lithiation, four discharge plateaus are observed at 2.10, 2.23, 1.62 and 1.23 V vs Li+/Li in the concentration range of 0 ≤ xLi ≤ 1. Upon magnesiation, the average voltage reaches 1.10 V vs Mg2+/Mg in the concentration range of 0 ≤ xMg ≤ 0.25, which are consistent with the experimental values. The pair correlation function (PCF) diagrams display the formation of V metal at high concentration of xLi and xMg, proving the occurrence of conversion reaction. The diffusion energy barriers of Li ions and Mg ions in VOCl are 0.22 and 0.72 eV, respectively, which are much lower than those of other intercalation materials. The layered VOCl bulk is a high-rate capability cathode material for lithium-ion battery. Based on the thermodynamic/kinetic properties and the AIMD simulation results, the electrochemical mechanism of layered VOCl is an intercalation-conversion reaction during the lithiated and magnesiated processes. The conversion-type cathodes have the potential to circumvent the sluggish solid-state Mg diffusion and improves the performance of Mg rechargeable batteries with high-energy density and high-rate capability.