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

Abstract

The thermodynamic, electronic, and kinetic properties were systematically investigated during the process of Li and Mg atoms into VOCl. The upper limit of Li and Mg intercalation into VOCl is xLi =1 and xMg=0.5, respectively. At high concentration, the further lithiation and magnesiation will cause the phase evolution. The pair correlation function (PCF) diagrams prove the formation of V metal at high concentration of xLi and xMg. The four discharge plateaus of lithiation are observed at 2.10, 2.23, 1.62 and 1.23 V vs. Li+/Li in the concentration range of 0≤xLi≤1, while the average voltage of the embedded Mg is 1.10 V vs. Mg2+/Mg in the concentration range of 0≤xMg≤0.25, which are consistent with the experimental values. 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. Based on the thermodynamic/kinetic properties and the AIMD simulation results, the electrochemical process of layered VOCl is an intercalation-conversion reaction process upon the lithiation and magnesiation processes.

Lattice Distortions and Magnetic Interactions in Single-Layer VOCl

“…A larger U eff -value will reduce the monoclinic angle, while expanding the lattice. In the bulk, the value U eff = 2 eV has been shown to simultaneously reproduce structural, electronic and magnetic properties reasonably well [20,26]. We have calculated the U eff -parameter with density functional perturbation theory (DFPT) [44], which resulted in the value U eff =5.67 eV for both monolayers as well as the bulk.…”

“…At room temperature, bulk VOCl is a paramagnetic insulator, but a twofold antiferromagnetic (AFM) superstructure develops below the Néel temperature, T N ≈ 80 K [16,17]. The large vdW gap makes VOCl suitable for intercalation applications, and it is currently being considered for novel transistors [18] and battery archi- * marcus.ekholm@liu.se tectures, with a demonstrated stability to air exposure and cyclic ion shuttling [19][20][21].…”