Recent advances in MXene-based nanocomposites for supercapacitors.

MXene materials have become a competitive candidate for electrochemical energy storage due to their unique two-dimensional layered structure, high density, metal-like conductivity, fast ion intercalation, tunable surface terminal groups, and good mechanical flexibilities, showing unique application advantages in the field of supercapacitors. With widely research of MXene in energy storage applications, plenty of studies in synthesis strategies of MXene, including etching, intercalation and exfoliation processes, and its charge storage mechanism in supercapacitors have been conducted. However, the restacking of two-dimensional MXene nanosheets severely affects their electrochemical performance. To prevent the stacking of MXene, MXene-based nanocomposite electrode materials have been developed with remarkable electrochemical performance by incorporating conventional active capacitive materials, including metal oxides/sulfides and conductive polymers, with MXene. This review summarizes the etching strategies of MXenes and selection of intercalants, also discusses the charge storage mechanism of MXenes in aqueous and nonaqueous electrolytes. It mainly expounds the preparation strategies and applications of MXene-based nanocomposites in supercapacitors, including MXene/metal oxide, MXene/metal sulfide, MXene/conducting polymer, and MXene/carbon-based composites. Additionally, the advantages of combining MXene with other active materials in supercapacitor applications, which support its promising prospects, are discussed. Finally, the critical challenges faced by MXene-based nanocomposites in long-term research are mentioned.