Exploring the Potentials of Ti₃CN_2-T (i = 0, 1, 2)-MXene for Anode Materials of High-Performance Sodium-Ion Batteries

Two-dimensional (2D) MXenes, including carbides, nitrides, and carbonitrides MXene, have been proved to be a possible candidate as anode materials of sodium-ion batteries. This paper focuses on the electronic properties and the electrochemical performance of nitrides MXene. First, density functional theory simulations were utilized to disclose the geometric structure and electronic properties, Na diffusion path, and storage behaviors of titanium carbonitrides Ti₃CNT, nitrides MXene Ti₃N₂T, and carbides MXene Ti₃C₂T with oxygen terminations, predicting the more excellent performance of Ti₃N₂O₂ than Ti₃C₂O₂. Also, then the structure characterization and electrochemical performance experiments of Ti₃C₂T and Ti₃CNT were conducted to verify the theoretical predictions and test the cycling performances. The superior performance of Ti₃N₂O₂ originates from the stronger connection of O-Ti-N than that of O-Ti-C, resulting in the stackings of Ti₃N₂O₂ being tighter and the interlayer spacings being larger than that of Ti₃C₂O₂, which is advantageous to sodiation and desodiation. The capacity of Ti₃CNT increased again to 145 mAh/g after 35 cycles at a current density of 20 mA/g, which demonstrated a better rate performance than Ti₃C₂T corroborated by the diffusion barriers of the theoretical calculation results. Ti₃CNT exhibits a good cycling performance of 110 mAh/g (≈60% of the initial value) after 200 cycles, which is better than that of 87 mAh/g (≈51% of the initial value) of Ti₃C₂T. It is worth noting that all these performances ensure that nitride MXene is more suitable as the anode material of Na-ion batteries than carbide MXene. These findings are conducive to expanding the MXene family and promoting their application in energy storage applications.