Bare Mo-Based Ordered Double-Transition Metal MXenes as High-Performance Anode Materials for Aluminum-Ion Batteries

Using the SCAN-rVV10 density functional, the electrochemical properties of bare Mo-based ordered double-transition metal MXenes (Mo₂MC₂, M = Sc, Ti, V, Zr, Nb, Hf, Ta) as aluminum-ion battery anode materials are studied. By calculating the average adsorption energy for each layer in a symmetric multilayer adsorption configuration, we find that all investigated MXene structures could adsorb three layers of Al atoms on both upper and lower surfaces, leading to the high theoretical capacities ranging from 888.98 mAh g^–1 (Mo₂TaC₂) to 1170.33 mAh g^–1 (Mo₂ScC₂). The formation of a multilayer adsorption configuration for Al atoms on Mo-based MXenes is mainly attributed to the gradual decreasing of the valence charge transfer from the adsorption layer to the substrate. Then, the CI-NEB method is used to assess the diffusion performance of Al atoms adsorbed on MXenes for energy favorable zig-zag like migration pathways. It is revealed that the migration energy barrier is no larger than 0.20 eV for all seven Mo-based MXenes. Therefore, the intrinsic Mo-based double-transition metal MXenes are promising anode materials possessing both high energy storage density and fast ion diffusion dynamics for Al-ion batteries.