First-Principles Investigation of Ti2CSO and Ti2CSSe Janus MXene Structures for Li and Mg Electrodes

While lithium battery electrodes are constantly being improved in terms of their properties, discovering new materials with alternative energy carriers like Mg are important to lower the cost of production and to enhance the energy density. MXenes are a type of highly investigated materials with promising energy applications due to their excellent electronic conductivity and good mechanical and dynamical stability. Experimentally realized Janus MoSSe nanosheets provided promising results for battery electrodes. It is known that the surface terminations of MXenes highly affect on the electrochemical properties and the diffusion barriers of ions. Inspired by this, we studied Ti2CSO and Ti2CSSe Janus MXenes for Li and Mg electrodes. Our density functional theory-based, first-principles calculations indicate that both monolayers are thermodynamically, mechanically, and dynamically stable. We calculated that the average voltages for Li and Mg adsorbed Ti2CST (T = O, Se) MXenes are approximately 0.95 and 0.2 V, respectively. The maximum voltage for Ti2CSTLix is about 2 V, and that for Ti2CSTMgx is around 0.45 V. The Mg adsorbed Ti2CSO monolayer exhibits the highest gravimetric capacity (524.54 mAh/g) compared to that of other Janus MXenes considered in this paper. For Ti2CSSeLix, we obtained a higher capacity (230.45 mAh/g) and a lower diffusion barrier (0.191 eV) than that of most of the Li adsorbed S-functionalized MXenes.