MXenes as a Versatile Platform for High‐Energy‐Density Asymmetric Supercapacitors

ABSTRACT Supercapacitors have emerged as promising candidates for next‐generation power devices due to their fast charge–discharge rates and excellent cycling stability; however, their relatively low energy density remains a critical limitation, necessitating a paradigm shift in the design of advanced electrode materials. In this context, MXenes have attracted substantial attention owing to their high electrical conductivity (20,000–24,000 S cm ⁻¹ ), exceptional electrochemical properties, mechanical robustness (Young's modulus: 484 ± 13 GPa, tensile strength: 15.4 ± 1.9 GPa), and tunable surface chemistry with various functional groups (e.g., –OH, –O, and –F). This review highlights the unique advantages of MXenes as electrode materials for asymmetric supercapacitors (ASCs), emphasizing their rich interlayer ion diffusion pathways and abundant redox‐active sites that enable superior pseudocapacitive behaviors. We examine various synthesis strategies, particularly the selective etching of MAX‐phase precursors, and discuss how these approaches affect the structure and performance of MXenes. In addition, we explore advanced material engineering techniques, including surface functionalization, interlayer spacing modulation, and defect engineering, that further enhance ion transport and charge storage. Recent developments in MXene‐based composites and hybrid architectures are also reviewed, with a focus on enhancing energy density, improving cycling life, and improving structural stability. Finally, sustainable synthesis and recycling approaches are discussed as critical for the practical implementation of MXene‐based ASCs. By bridging the gap between energy density and durability, MXenes offer a versatile and scalable platform for next‐generation energy storage technologies.