Single-ion conducting gel polymer electrolytes possess both unity lithium ion transference numbers (∼0.98) and high ionic conductivities (∼5.8 mS cm−1).

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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.

MXene, an emerging family of 2D transition metal carbides/nitride (MXene) materials, has attracted growing attention since its initial discovery in 2011. Owing to their extraordinary electrical conductivity, high mechanical stability, various functional groups, and large interlayer space, MXene and MXene‐based nanomaterials have shown significant energy‐storage capability. Firstly, research progress on the preparation strategies and properties of MXene are summarized. Secondly, the current state‐of‐the‐art advances of MXene and MXene‐based nanomaterials as advanced electrodes for energy storage devices, including lithium‐ion batteries, sodium‐ion batteries, potassium‐ion batteries, and supercapacitors are reviewed. Finally, the key challenges and perspectives for further enhancing their electrochemical performances are also outlined. This Progress Report offers a reference and scientific inspiration for the design and preparation of high‐performance MXene and MXene‐based nanomaterials to meet the increasing need for next‐generation energy‐storage systems.