Atomic-Scale Understanding of Li Storage Processes in the Ti₄C₃ and Chemically Ordered Ti₂Ta₂C₃ MXenes: A Theoretical and Experimental Assessment

By first-principles calculation and experimental measurements, we investigated the lithiation process in the Ti4C3 and Ti2Ta2C3 MXenes. Our results show the successful synthesis of the Ti2Ta2C3 MXene with an interlayer distance of 0.4 nm, which supposes the correct delamination of the material. Our measurements also demonstrate that the double-ordered alloy Ti2Ta2C3 can store 4 times the amount of lithium than the pristine Ti4C3 MXene. By DFT calculation, we investigated the stability of the TixTa4-xC3 MXenes. According to the calculations, five MXenes are stable, where the most stable 50% Ta/Ti ratio structure (Ti2Ta2C3 ) presents a chemically ordered composition. The Li intercalation process-for Ti4C3 and Ti2Ta2C3 MXenes-is carried out as adatoms on the surface, with the T4 site being the most favorable. The chemically ordered MXenes provide better OCV values and can store more Li atoms than the Ti4C3 MXene. Also, the Li diffusion process demonstrates that Ti2Ta2C3 is a more efficient material to be employed as an anode in batteries since it provides the lowest energy barriers. Our results demonstrate the capability of the Ti2Ta2C3 alloy to be employed in energy storage applications thanks to the high stability and capacity to store Li ions in comparison with pristine Ti4C3 MXene.