Exploring the Potentials of TiCNT ( = 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 TiCNT, nitrides MXene TiNT, and carbides MXene TiCT with oxygen terminations, predicting the more excellent performance of TiNO than TiCO. Also, then the structure characterization and electrochemical performance experiments of TiCT and TiCNT were conducted to verify the theoretical predictions and test the cycling performances. The superior performance of TiNO originates from the stronger connection of O-Ti-N than that of O-Ti-C, resulting in the stackings of TiNO being tighter and the interlayer spacings being larger than that of TiCO, which is advantageous to sodiation and desodiation. The capacity of TiCNT increased again to 145 mAh/g after 35 cycles at a current density of 20 mA/g, which demonstrated a better rate performance than TiCT corroborated by the diffusion barriers of the theoretical calculation results. TiCNT 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 TiCT. 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.