First-Principles Prediction of Two-dimensional Vanadium Carbide (MXene) as the Anode for Lithium Ion Batteries
Exploring two-dimensional anode materials that can promote the storage capacity and diffusion mobility of Li ions is at the heart of lithium ion batteries (LIBs) research. Herein, we report results of ab initio electronic structure calculations on storage capacity and diffusion mobility affinities of Li ions adsorbed onto the nondefective and defective MXene V2C monolayer. It is found that the Li ions strongly chemisorb onto the two sides of the V2C surface with a preferential adsorption site at the hollow center of the honeycomb structure. The binding profile and open-circuit voltage calculations reveal that the Li/V2C structure exhibits the specific capacity as high as 472 mAh/g at the Li2V2C stoichiometry, a value relatively high compared with those of the typical anode materials including graphite (372 mAh/g). Furthermore, the diffusion barrier of a Li ion over the V2C surface is identified to be no more than 0.1 eV, which is a few times smaller attained for the graphene and graphitic anodes. In addition, during the lithiation and delithiation processes, the change in the lateral lattice is quite small, only about 2\% increase at the full lithiation of Li2V2C, implying a good cycling performance. More importantly, these intriguing findings are very robust against the intrinsic structural and atomic defects including local point vacancies and biaxial compressive and tensile strains. More specifically, the presence of a monovanadium vacancy enhances the binding energy up to 3.1 eV per Li ion, which is about 30% enhancement compared with the defect-free Li/V2C structure, and reduces the activation barrier by about 2 meV, while these binding and diffusion mobility features can be even more improved when the lattice constant of the V2C monolayer is expanded. These results thus suggests that MXene V2C could be a promising anode material with high capacity and high rate capability for the next generation high-performance LIBs.