Conductive two-dimensional titanium carbide ‘clay’ with high volumetric capacitance

Intercalation and delamination of two-dimensional solids in many cases is a requisite step for exploiting their unique properties. Herein we report on the intercalation of two-dimensional Ti3C2, Ti3CN and TiNbC-so called MXenes. Intercalation of hydrazine, and its co-intercalation with N,N-dimethylformamide, resulted in increases of the c-lattice parameters of surface functionalized f-Ti3C2, from 19.5 to 25.48 and 26.8 Å, respectively. Urea is also intercalated into f-Ti3C2. Molecular dynamics simulations suggest that a hydrazine monolayer intercalates between f-Ti3C2 layers. Hydrazine is also intercalated into f-Ti3CN and f-TiNbC. When dimethyl sulphoxide is intercalated into f-Ti3C2, followed by sonication in water, the f-Ti3C2 is delaminated forming a stable colloidal solution that is in turn filtered to produce MXene 'paper'. The latter shows excellent Li-ion capacity at extremely high charging rates.

Density functional theory (DFT) computations were performed to investigate the electronic properties and Li storage capability of Ti(3)C(2), one representative MXene (M represents transition metals, and X is either C or/and N) material, and its fluorinated and hydroxylated derivatives. The Ti(3)C(2) monolayer acts as a magnetic metal, while its derived Ti(3)C(2)F(2) and Ti(3)C(2)(OH)(2) in their stable conformations are semiconductors with small band gaps. Li adsorption forms a strong Coulomb interaction with Ti(3)C(2)-based hosts but well preserves its structural integrity. The bare Ti(3)C(2) monolayer exhibits a low barrier for Li diffusion and high Li storage capacity (up to Ti(3)C(2)Li(2) stoichiometry). The surface functionalization of F and OH blocks Li transport and decreases Li storage capacity, which should be avoided in experiments. The exceptional properties, including good electronic conductivity, fast Li diffusion, low operating voltage, and high theoretical Li storage capacity, make Ti(3)C(2) MXene a promising anode material for Li ion batteries.