Orthorhombic Cobalt Ditelluride with Te Vacancy Defects Anchoring on Elastic MXene Enables Efficient Potassium-Ion Storage.

The fast and reversible potassiation/depotassiation of anode materials remains an elusive yet intriguing goal. Herein, a class of the P-doping-induced orthorhombic CoTe2 nanowires with Te vacancy defects supported on MXene (o-P-CoTe2 /MXene) is designed and prepared, taking advantage of the synergistic effects of the conductive o-P-CoTe2 arrays with rich Te vacancy defects and the elastic MXene sheets with self-autoadjustable function. Consequently, the o-P-CoTe2 /MXene superstructure exhibits boosted potassium-storage performance, in terms of high reversible capacity (373.7 mAh g-1 at 0.2 A g-1 after 200 cycles), remarkable rate capability (168.2 mAh g-1 at 20 A g-1 ), and outstanding long-term cyclability (0.011% capacity decay per cycle over 2000 cycles at 2 A g-1 ), representing the best performance in transition-metal-dichalcogenides-based anodes to date. Impressively, the flexible full battery with o-P-CoTe2 /MXene anode achieves a satisfying energy density of 275 Wh kg-1 and high bending stability. The kinetics analysis and first-principles calculations reveal superior pseudocapacitive property, high electronic conductivity, and favorable K+ ion adsorption and diffusion capability, corroborating fast K+ ion storage. Especially, ex situ characterizations confirm o-P-CoTe2 /MXene undergoes reversible evolutions of initially proceeding with the K+ ion insertion, followed by the conversion reaction mechanism.