Partially Etched Ti₃ AlC₂ as a Promising High-Capacity Lithium-Ion Battery Anode

MXenes, a family of two-dimensional transition-metal carbide and nitride materials, are thought to be promising materials in energy storage because of their high electronic conductivity, hydrophilic surfaces, and low diffusion barriers. MXenes are generally prepared by removing the "A" elements (A=Al, Si, Sn, etc.) from their corresponding MAX phases by using hydrofluoric acid (HF) and other etching agents, although these "A" elements usually have great volumetric and gravimetric capacities. In a study of the etching progress of Ti₃ AlC₂ and evaluation of their anode performance in lithium-ion batteries, a partially etched sample (0.5 h-pe Ti₃ C₂ T_x ) is found to have much higher capacity (160 mAh g^-1 , 331.6 mAh cm^-3 at 1C) when compared with the fully etched Ti₃ C₂ T_x (110 mAh g^-1 , 190.3 mAh cm^-3 at 1C). Moreover, a 99 % capacity retention was observed even after 1000 cycles in the 0.5 h-pe Ti₃ C₂ T_x anode. This interesting result can be explained, at least in part, by the alloying of the residual Al during lithiation.