A comprehensive review on MXenes: synthesis, stability, properties and their functionalization for M-ion batteries and supercapacitors

Owing to their dimensional dependence, two-dimensional (2D) materials with single- or few-layered atomic structures exhibit unique physicochemical properties that differ significantly from their three-dimensional (3D) bulk counterparts. Among these, MXenes - a novel family of 2D transition-metal carbides, nitrides, and carbonitrides - were first reported by Gogotsi et al. in 2011. Since then, MXenes have emerged as a highly promising class of materials for electrochemical energy storage. Their distinctive layered structures and tunable surface terminations provide exceptional properties, including high electrical conductivity, mechanical flexibility, and versatile surface chemistry. In particular, MXenes have shown great potential in supercapacitor applications due to their high energy density, excellent rate capability, and long-term cycling stability. This review presents a comprehensive overview of MXene synthesis and exfoliation methods, and highlights their physicochemical properties. In addition, recent advances in their applications to metal-ion (M-ion) batteries and supercapacitors are critically discussed, with emphasis on the structural features and surface functionalities that underpin their superior electrochemical performance. Furthermore, scalable fabrication approaches for producing industry-relevant MXene-based films and composites are examined. Finally, the review highlights current challenges, emerging opportunities, and future research directions in this rapidly evolving field.