First-principle study of electronic properties and quantum capacitance of lithium adsorption on pristine and vacancy-defected O-functionalized Ti2C MXene

Abstract

The electronic structure, surface charge storage and quantum capacitance of lithium adsorption on pristine and vacancy-defected Ti2CO2 MXene are theoretically investigated by density functional theory. Negative adsorption energies (Eads) of pristine Ti2CO2 (PT) and C-vacancy Ti2CO2 (VT) monolayers adsorbed by Li atom indicate that the adsorption processes of Li atom on systems are exothermic and favorable to adsorption. The most stable configurations are confirmed for the Li-adsorbed PT and VT monolayers. Pristine Ti2CO2 (PT) monolayer is a semiconductor with the bandgap of 0.2035 eV, while C-vacancy Ti2CO2 (VT) monolayer has the metallic nature. The adsorption of Li atom on PT monolayer makes the system undergo the semiconductor-metal transition, while the adsorption of Li atom on VT monolayer doesn’t change the metal nature. The magnetism is observed for the system with Li atom directly adsorbed on top of hollow site (VT-LH), and the total magnetic moments is 0.18 μB. Charge density differences of the adsorption of Li atom on PT and VT monolayers are further explored. The introduction of C-vacancy improves the quantum capacitances of the Li-adsorbed systems at 0 V, and Li-adsorbed PT and VT monolayers have high quantum capacitance because of the large density of states near Fermi level, and are suitable for cathode material.