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The typical two-dimensional layered structure materials, MXenes, are widely used in energy conversion and storage due to their high conductivity, ion transport ability, and rich surface structures. Recently, MXenes and their composites have been widely employed in secondary batteries, especially sodium-ion batteries (SIBs), with obvious performance improvement. As anodic materials, MXenes, metal oxides, metal sulfides, and other materials contain certain advantages in Na+ storage, but they individually also suffer from some issues and challenges, such as low conductivity and serious volume change, as well as the associated low capacity and poor cyclability. By virtue of the advantages of MXenes, with their high conductivity and ultrathin two-dimensional structures, the construction of surface-functionalized MXenes and MXene-based composites could effectively improve the conductivity and mass-transport properties of composites, alleviate volume expansion, and, thus, enhance the capacity properties, rate performances, and cycle stability of SIBs. Herein, we review the latest research status of the structural design of MXenes and Mxene-based materials, as well as their applications in SIBs. We briefly introduce the research background and introduce MXenes and SIBs, and focus on their structural designs and corresponding applications in SIBs. Finally, the important challenges of MXene-based materials applied to SIBs are discussed, and the future prospects of MXene-based composite developments in SIBs are presented.

Due to the advantages of rich resources, low cost, high energy conversion efficiency, long cycle life, and low maintenance fee, sodium–ion batteries have been regarded as a promising energy storage technology. However, their relatively low energy density compared with the commercialized lithium–ion batteries still impedes their application for power systems. Anode–free rechargeable sodium–metal batteries (AFSMBs) pose a solution to boost energy density and tackle the safety problems of metal batteries. At present, researchers still lack a comprehensive understanding of the anode-free cells in terms of electrolytes, solid–electrolyte interphase (SEI), and current collectors. This review is devoted to the field of AFSMBs, and outlines the breakthroughs that have been accomplished along with our perspective on the direction of future development for AFSMBs and the areas that warrant further investigation.