Carbon materials, including graphite, hard carbon, soft carbon, graphene, and carbon nanotubes, are widely used as high‐performance negative electrodes for sodium‐ion and potassium‐ion batteries (SIBs and PIBs). Compared with other materials, carbon materials are abundant, low‐cost, and environmentally friendly, and have excellent electrochemical properties, which make them especially suitable for negative electrode materials of SIBs and PIBs. Compared with traditional carbon materials, modifications of the morphology and size of nanomaterials represent effective strategies to improve the quality of electrode materials. Different nanostructures make different contributions toward improving the electrochemical performance of electrode materials, so the synthesis of nanomaterials is promising for controlling the morphology and size of electrode materials. This paper reviews the progress made and challenges in the use of carbon materials as negative electrode materials for SIBs and PIBs in recent years. The differences in Na+ and K+ storage mechanisms among different types of carbon materials are emphasized.

In 2011, Gogotsi et al. discovered a new type of two‐dimensional transition metal carbides and nitrides, called MXenes, which have become a dazzling new star in the energy storage industry. MXenes are endowed with a series of fascinating properties due to their unique structures and tunable surface chemical functional groups. The application of MXenes in electrochemical energy storage has attracted special attention, especially showing great potential in supercapacitor applications. Compared with other materials, MXenes have high mechanical flexibility, high energy density, and good electrochemical performance, so they are especially suitable as electrode materials for supercapacitors. However, similar to other 2D materials, due to the strong van der Waals forces, MXene layers inevitably undergo stacking agglomeration, resulting in severe loss of electrochemically active sites. If the self‐stacking of MXenes layers can be effectively suppressed, their electrochemical performance will be enhanced. Structural optimization of MXenes and composite doping of MXenes with other materials are two strategies with significant effects. This review summarizes recent advances in MXene synthesis, fundamental properties, and composite materials, focusing on the latest electrochemical performance of MXene‐based electrodes/devices, and puts forward the challenges and new opportunities that MXenes face in this emerging energy storage field.

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