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.
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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