Theoretical Insights into the Favorable Functionalized Ti(2)C-Based MXenes for Lithium–Sulfur Batteries

[Image: see text] Because of the high specific surface area, excellent electronic conductivity, facile Li diffusion, and rich functional groups, Ti(2)C-based MXenes have been widely used to improve the electrochemical property of lithium–sulfur batteries. The complex surface functionalization (such as −OH, −S, −F, and −O) of MXenes boosts the performance but also causes controversies about the favorable functionalized surface in the electrochemical reaction during the charge and discharge process. In the present work, a theoretical study based on density functional theory has been carried out to clarify the favorable functionalized surface by comparing pristine Ti(2)C and −OH-, −S-, −F-, and −O-functionalized Ti(2)C surfaces from the aspects of adsorption ability, electronic conductivity, and kinetic conversion ability. It is found that compared with severe polysulfide deformation on pristine Ti(2)C and Ti(2)C(OH)(2) surfaces, Ti(2)CO(2), Ti(2)CS(2), and Ti(2)CF(2) have effective polysulfide adsorption. Ti(2)CO(2) has the largest surface adsorption energy, followed by Ti(2)CS(2), and Ti(2)CF(2) is the weakest. Meanwhile, the narrow-band gap semiconductor property of Ti(2)CO(2) during adsorption indicates worse electronic conductivity than metallic Ti(2)CS(2) and Ti(2)CF(2). In addition, for the kinetic conversion ability, the Ti(2)CS(2) surface has the fastest polysulfide conversion and Li diffusion, followed by Ti(2)CF(2), and Ti(2)CO(2) represents the slowest conversion and diffusion. Accordingly, because of the medium binding energy, good electronic conductivity, and fast polysulfide conversion and Li diffusion, Ti(2)CS(2) is revealed to be the favorable functionalized surface. More importantly, the origin for the Ti(2)CS(2) surface with medium adsorption ability represents the fastest polysulfide conversion, and Li diffusion is further clarified. The great affinity of the Ti(2)CS(2) surface to the product Li(2)S leads to facile polysulfide conversion. The uniform charge distribution on the Ti(2)CS(2) surface contributes to the fast Li diffusion.