A two-dimensional assembly of ultrafine cobalt oxide nanocrystallites anchored on single-layer TiCT nanosheets with enhanced lithium storage for Li-ion batteries.

Recently, Ti-based MXenes were expected to compete with graphene and other carbonaceous materials towards Li-ion batteries (LIBs) due to their two-dimensional (2D) open structure, cost efficiency, superior conductivity and low Li diffusion barrier. However, the relatively moderate capacity and aggregation tendency hamper their practical applications in next-generation LIBs. Herein, we explore for the first time a scalable bottom-up approach to fabricate a series of CoO@single-layer TiCT (s-TiCT) hybrids, where numerous homogeneous CoO nanocrystallites (NCs), serving both as a spacer and electroactive phase, are anchored uniformly on the surface of s-TiCT nanosheets (NSs) through the Co-O-Ti interfacial bonds. Furthermore, detailed experimental analyses clearly shed light upon the formation mechanism of the hybrid CoO@s-TiCT NSs. Thanks to the structural and compositional merits, the 2D CoO@s-TiCT NSs even exhibit a remarkable high-rate capacity of ∼223 mA h g at an ultra-high current density of 10 A g, and a long-span cycle life with a high reversible capacity of 550 mA h g at 1 A g after 700 consecutive cycles. Corresponding density functional theory calculation further confirms that the Co-O-Ti interfacial function leads to an even higher pseudocapacitive contribution and faster lithium storage behavior due to the enhanced interfacial electron transfer.