Ti-Cl bonds decorated Ti2NT (x) MXene towards high-performance lithium-ion batteries

Transition metal carbides or nitrides, collectively known as MXenes, are burgeoning two-dimensional materials for energy conversion and storage. The surface chemistry of MXenes could be specially tuned by the modified surface terminations, which directly influences their physicochemical properties. However, the in-depth study and understanding of the specific microstructure and the influence on the electrochemical performance of these terminations remain lacking. Herein, we present an accordion layered Ti2NT (x) MXene with -Cl and -O terminations obtained from copper chloride molten salt etching at a relatively low temperature. X-ray absorption fine structure and x-ray photoelectron spectroscopy analyses reveal the formation of Ti-Cl and Ti-O bonds on the surface of Ti2NT (x) MXene. Density functional theory calculations further suggest that the surface terminations tend to be replaced by -O terminations after Ti-Cl decoration, which implies promising lithium-ion storage performance due to the high lithium affinity of -O terminations. As a result, the Ti2NT (x) MXene based electrode delivers a high reversible capacity (303.4 mAh g(-1) at 100 mA g(-1)), stable cycling capability (1200 cycles without capacity attenuation), and fast Li+ storage (52% capacity retention at 32 C). This work provides a new vision for MXene surface chemistry and an effective avenue to prepare high-performance nitride electrodes, expanding the diversity and controllability of the MXenes family.