In Situ Construction of Bimetallic Selenides Heterogeneous Interface on Oxidation-Stable Ti 3 C 2 T x MXene Toward Lithium Storage with Ultrafast Charge Transfer Kinetics.

Ti 3 C 2 T x (MXene) is widely acknowledged as an excellent substrate for constructing heterogeneous structures with transition metal chalcogenides (TMCs) for boosting the electrochemical performance of lithium-ion storage. However, conventional synthesis strategies inevitably lead to poor electrochemical charge transfer due to Ti 3 C 2 T x -derived TiO 2 at the heterogeneous interface between Ti 3 C 2 T x and TMCs. Here, an innovative in situ selenization strategy is proposed to replace the originally generated TiO 2 on Ti 3 C 2 T x with metallic TiSe 2 interphase, clearing the bottleneck of slow charge transfer barrier caused by MXene oxidation. The construction of bimetallic selenide formed by CoSe 2 and TiSe 2 generates intrinsic electric fields to guide the fast ion diffusion kinetics in a heterogeneous interface. Additionally, the CoSe 2 /TiSe 2 /Ti 3 C 2 T x heterogeneous structure with enhanced structural stability and improved rate performance is confirmed by both experiments and theoretical calculations. The engineered heterogeneous structure exhibits an ultra-high pseudocapacitance contribution (73.1% at 0.1 mV s -1 ), rendering it well-suited to offset the kinetics differences between double-layer materials. The assembled lithium-ion capacitor based on CoSe 2 /TiSe 2 /Ti 3 C 2 T x possesses a high energy density and an ultralong life span (89.5% after 10 000 times at 2 A g -1 ). This devised strategy provides a feasible solution for utilizing the performance advantages of MXene substrates in lithium storage with ultrafast charge transfer kinetics.