2D MXene‐based nanomaterials have attracted tremendous attention because of their unique physical/chemical properties and wide range of applications in energy storage, catalysis, electronics, optoelectronics, and photonics. However, MXenes and their derivatives have many inherent limitations in terms of energy storage applications. In order to further improve their performance for practical application, the nanoengineering of these 2D materials is extensively investigated. In this Review, the latest research and progress on 2D MXene‐based nanostructures is introduced and discussed, focusing on their preparation methods, properties, and applications for energy storage such as lithium‐ion batteries, sodium‐ion batteries, lithium–sulfur batteries, and supercapacitors. Finally, the critical challenges and perspectives required to be addressed for the future development of these 2D MXene‐based materials for energy storage applications are presented.

Sodium-ion batteries (SIBs) have been regarded as the most promising candidates for the next-generation energy storage devices owing to their low price and high abundance. However, the development of SIBs is mainly hindered by the instability of cathode materials. Here, we report a new P2-type manganese-rich cathode material, Na0.66Li0.18Mn0.71Mg0.21Co0.08O2 (P2-NaLiMMCO) with uniform spherical structure prepared via a simple solvothermal method and subsequent solid-state reaction. This P2-NaLiMMCO cathode material with uniform microsize secondary spheres and nanosize primary crystalline particles delivers a high initial discharge capacity of 166 mA h g–1 and superior capacity retention, which are superior to most previously reported results. The improved stability of the cathode material was further investigated by the in situ X-ray diffraction technique, which suggests an enhanced reversibility of the cathode material during the desodiation/sodiation process. With the superior electrochemical performance and stable structures, this new P2-NaLiMMCO can serve as a practical cathode material for SIBs.

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Skeletal rearrangement that changes the connectivity of the molecule via cleavage and reorganization of carbon–carbon bonds is a fundamental and powerful strategy in complex molecular assembly. Because of the lack of effective methods to control the migratory tendency of different groups, achieving switchable selectivity in skeletal rearrangement has been a long-standing quest. Metal-based dyotropic rearrangement provides a unique opportunity to address this challenge. However, switchable dyotropic rearrangement remains unexplored. Herein, we show that such a problem could be solved by modifying the ligands on the metal catalyst and changing the oxidation states of the metal to control the migratory aptitude of different groups, thereby providing a ligand-controlled, switchable skeletal rearrangement strategy. Experimental and density functional theory calculation studies prove this rational design. The rearrangement occurs only when the nickel­(II) intermediate is reduced to a more nucleophilic nickel­(I) species, and the sterically hindered iPrPDI ligand facilitates 1,2-aryl/Ni dyotropic rearrangement, while the terpyridine ligand promotes 1,2-acyl/Ni dyotropic rearrangement. This method allows site-selective activation and reorganization of C–C bonds and has been applied for the divergent synthesis of four medicinally relevant fluorine-containing scaffolds from the same starting material.

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