Prediction of Halogenated MXenes as Electrode Materials for Halide-Ion Batteries

Exploring and developing new rechargeable halide-ion batteries plays an important role in the advancement and growth of the ion battery family. Here, we systematically explored the feasibility of single-layer MXenes and their hydrogenated derivatives as electrode materials for halide-ion batteries via first-principles theory. The calculated results indicate that halide ions (T ions) can be stably and efficiently adsorbed on the surfaces of M₂X and M₂XH₂, with theoretical specific capacities ranging from 227 to 497 mAh g^-1. The diffusion barriers of the T ion on MXenes are from 0.55 to 0.10 eV, comparable to those of the Li ion in graphite and LiCoO₂. The electronegativity of halide anions displays significant impacts on their discharge voltage plateaus on M₂X, with the highest voltage up to 5.60 V for the F ion. As a comparison, the hydrogenation of M₂XH₂ with less surface activity raises a 2-3 V voltage reduction. All MXene-based full cells of T_xTi₂C|T_yTi₂CH₂ (where x = 0-2 and y = 2-0) and T_xTi₂N|T_yTi₂NH₂ (where x = 0-2 and y = 2-0) demonstrated high full battery specific energies for F-, Cl-, and Br-ion batteries, up to 462 Wh kg^-1. These results demonstrate the potential of new halide-ion battery designs, paving the way for future research and innovation in battery technology.