First-Principles Investigation of Ti <sub>2</sub> CSO and Ti <sub>2</sub> CSSe Janus MXene Structures for Li and Mg Electrodes
Edirisuriya M. Dilanga Siriwardane, Jianjun Hu
Abstract
While lithium battery electrodes are constantly being improved in terms of their performance, discovering new materials with alternative energy carriers such as Mg is 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. Previous experimental studies showed that Janus MoSSe nanosheets provide promising performance for battery electrodes. However, it is not fully understood how MXenes with different surface terminations affect the electrochemical properties and the diffusion barriers of ions. Here, we address this problem by studying 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 and 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 mA h/g) compared to that of other Janus MXenes considered in this paper. For Ti2CSSeLix, we obtained a higher capacity (230.45 mA h/g) and a lower diffusion barrier (0.191 eV) than those of most of the Li-adsorbed S-functionalized MXenes.