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 Tx ) 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 Tx (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 Tx anode. This interesting result can be explained, at least in part, by the alloying of the residual Al during lithiation.