First-Principles Study on the Structural, Electronic, and Lithium Storage Properties of Ti3C2T2 (T = O, F, H, OH) MXene.

The structures of bare Ti3C2 and functionalized Ti3C2T2 (T = O, F, H, OH) MXenes were constructed, and the effect of surface functional groups T2 (T = O, F, H, OH) on the structural, electronic, and lithium storage properties were investigated by first-principles calculations. The results show that the proximity of surface functional groups will induce some lattice distortion of Ti3C2T2 MXene. The degree of lattice distortion depends mainly on the adsorption position of functional groups and the types of surface functional groups. From the point of view of forming energy, the surface functional groups tend to be located at the CCP site. From the energy band and DOS results, the presence of surface functional groups has a significant effect on the valence band, while it has a slight impact on the conduction band. In terms of lithium storage, lithium atom adsorption starts from the HCP position for bare Ti3C2, while functionalized Ti3C2T2 starts from the CCP position. The double-layer lithium storage capacity of bare Ti3C2 and Ti3C2O2 were 639.78 mAh/g and 537.22 mAh/g, respectively. And the single-layer lithium storage capacity of Ti3C2F2 was 130.77 mAh/g.