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• As a promising preparation strategy for 2D MXenes, the molten-salt-assisted synthesis method has garnered significant attention in recent years owing to its numerous advantages. • Molten-salt-assisted synthesis method is elucidated through the etching mechanism, property regulation, and delamination of multi-layered MXenes. • The applications of 2D MXenes derived from the molten-salt-assisted synthesis method in energy storage and conversion. • The challenges and prospects associated with the synthesis of molten-salt-assisted synthesis methods are put forward. Two-dimensional (2D) MXenes have captured inter-disciplinary interest owing to their exceptional electronic conductivities, adjustable layered structures, and controllable interfacial functional groups. Low-cost, efficient, and amicable techniques are urgently desired for synthesizing high-quality and high-yield 2D MXene materials. Recently, molten-salt-assisted methods have been proven to be the promising processes to construct versatile 2D MXenes with metallic-level conductivity, good mechanical strength, low ion diffusion barrier and rich surface chemistries to meet the criteria for practical applications. Herein, the most up-to-date progress of molten-salt-assisted approaches for manufacturing 2D MXene materials and their synthesis mechanisms are comprehensively summarized, introducing the effect on the physical/chemical properties of the obtained MXenes compared with other common synthesis methods. Meanwhile, typical examples of MXenes obtained by tuning surface termination, interlayer spacing, size, and morphology are presented. Further, the focus turns to their structure–property relationships and applications in electrochemical energy storage and conversion, including supercapacitors, Li-batteries, Zn-ion batteries and electrocatalysis. Finally, a discussion about the challenges and prospects of the molten-salt-assisted approaches is put forward. This review will guide and encourage the future rational design and controllable synthesis of 2D MXenes with high performance based on molten-salt-assisted strategies. [ABSTRACT FROM AUTHOR]

• Ti 3 C 2 T x MXene provides zincophilic sites for dendrite-Free zinc deposition. • The ZnO@MXene anode achieves ultra-long cycle stability at a high rate. • The average discharge specific capacity of this work can attain 625 mAh·g−1. Although Zn-Ni battery is a potential energy storage system, the anode zinc electrode often faces dendrite, passivation and deformation problems, which tend to be exacerbated at high current densities particularly, and severely hamper its practical applications. Zinc oxide was modified with 2D transition metal carbides/nitride (ZnO@MXene) firstly for the purpose of broadening the application scenarios of zinc alkaline secondary batteries. A variety of characterizations and density functional theory (DFT) calculations certify that highly conductive MXene matrix provides a high-speed electron transfer channel and its low ionic diffusion barrier and excellent ionic diffusion mobility of MXene can quickly reduce the ion concentration gradient at the solid–liquid interface, which weakens the concentration polarization. Also, MXene can tune the diffusion behavior to induce homogeneous deposition of zinc via the zinc-oriented-O groups, forming well-dispersed "seed points" to realize uniform nucleation and inhibiting dendrite growth. Therefore, ZnO@MXene as the anode of a Zn-Ni battery can keep its capacity of 594mAh·g−1 after 1500 cycles at 10C. That reaches 90% of its initial capacity (596mAh·g−1), suggesting superb specific capacity, rate performance, and cycle life span. [ABSTRACT FROM AUTHOR]

[Display omitted] • Aerogel-structured MnO 2 was assembled by defect-rich ultrathin nanosheets. • V doping and oxygen vacancies manipulate electronic structure of the MnO 2. • The MnO 2 shows enhanced electrical conductivity and fast Zn2+ diffusion ability. • The MnO 2 cathode presents markedly boosted electrochemical performance. Rechargeable MnO 2 //Zn zinc-ion batteries (ZIBs) gain increasing attention as prospective candidates for large-scale energy storage applications, but MnO 2 cathode materials are afflicted by intrinsic low electrical conductivity, sluggish Zn2+ diffusion kinetics and unstable crystal structure during Zn2+ insertion/extraction. Herein, we report the scalable synthesis of an aerogel-structured MnO 2 (A-MnO 2) assembled by defect-rich ultrathin nanosheets for ZIBs. For the A-MnO 2 , V doping and its induced oxygen vacancies manipulate electronic structure to enhance electrical conductivity and decrease Zn2+ diffusion energy barrier, and meanwhile, the ultrathin nanosheets-assembled aerogel structure favors the exposure of more electrochemically active sites and the shortening of ion diffusion distance. As a consequence, the A-MnO 2 is endowed with markedly boosted electrochemical kinetics and thus superior electrochemical performance than defect-free MnO 2 nanorod counterpart. Furthermore, flexible ZIB devices with both impressive flexibility and outstanding electrochemical properties can be realized using the A-MnO 2 cathode material. This work is expected to promote the practical application of MnO 2 //Zn ZIBs. [ABSTRACT FROM AUTHOR]