Defect Engineering of Hexagonal MAB Phase Ti 2 InB 2 as Anode of Lithium-Ion Battery with Excellent Cycling Stability.

Hexagonal MAB phases （h-MAB） have attracted attention due to their potential to exfoliate into MBenes, similar to MXenes, which are predicted to be promising for Li-ion battery applications. However, the high cost of synthesizing MBenes poses challenges for their use in batteries. This study presents a novel approach where a simple ball-milling treatment is employed to enhance the purity of the h-MAB phase Ti 2 InB 2 and introduce significant indium defects, resulting in improved conductivity and the creation of abundant active sites. The synthesized Ti 2 InB 2 with indium defects (V In -Ti 2 InB 2 ) exhibits excellent electrochemical properties, particularly exceptional long-cycle stability at current densities of 5 A g -1 (5000 cycles, average capacity decay of 0.0018%) and 10 A g -1 (15 000 cycles, average capacity decay of 0.093%). The charge storage mechanism of V In -Ti 2 InB 2 , involving a dual redox reaction, is proposed, where defects promote the In-Li alloy reaction and a redox reaction with Li in the TiB layer. Finally, a Li-ion full cell demonstrates cycling stability at 0.5 A g -1 after 350 cycles. This work presents the first accessible and scalable application of V In -Ti 2 InB 2 as a Li-ion anode, unlocking a wealth of possibilities for sustainable electrochemical applications of h-MAB phases.