The potential application of 2D Ti2CT2 (T = C, O and S) monolayer MXenes as anodes for Na-ion batteries: A theoretical study

First-principle calculations are performed to study the electronic properties and Na-ion storage capabilities of two-dimensional Ti2C MXene monolayers. The surface derivatives, namely Ti2CC2, Ti2CO2, and Ti2CS2, are also considered. The results demonstrate that the bare and terminated monolayers are metallic in character with high electrical conductivity. We find that these monolayers are stable, with Ti2C and Ti2CO2 offering the most stable configurations overall. We also consider functionalized Ti2C MXenes terminated with-C and-O and find that, compared to S-terminated surfaces, these display better activation adsorption. Theoretical results underscore the excellent adsorption properties of Ti2CC2 and Ti2CO2 and reveal that they have lower energy barriers for sodium diffusion than Ti2C. In addition, the results showed that sodium ion adsorption on Ti2C monolayers achieved a high adsorption energy (-2.5 to -0.4 eV) during sodiation, which could enhance the motion capabilities of bare and oxide systems. The structural transformation behaviors of bare and terminated Ti2C monolayers were confirmed during sodiation by ab initio molecular dynamic simulations. In view of its outstanding capacity, electrical conductivity and high Na-ion diffusivity, we conclude that Ti2C and its surface termination groupbased monolayers have excellent potential for use as anodes in Na-ion batteries.