Toward flexible energy storage: MXene frameworks from synthesis principles to device applications

The rapid proliferation of wearable, portable, and foldable electronics has exposed critical limitations in conventional energy storage technologies, particularly in terms of mechanical adaptability and miniaturization. Addressing these challenges necessitates the development of energy storage systems that are not only electrochemically robust but also mechanically flexible and scalable. MXenes, an emerging class of two-dimensional transition metal carbides, nitrides, and carbonitrides, have emerged as compelling candidates for flexible energy storage applications owing to their distinctive structural and physicochemical attributes (electrical conductivity, tunable surface chemistries, and intrinsic mechanical flexibility). This review critically examines recent advances in the synthesis and structural modulation of MXenes tailored for flexible energy storage systems. Emphasis is placed on their integration with complementary materials, such as carbon nanostructures (e.g., nanotubes and nanofibers), transition metal oxides (e.g., V₂O₃, VO₂, and TiO₂), and porous matrices. The discussion encompasses a broad spectrum of device chemistries, ranging from diverse flexible battery applications to supercapacitors, and highlights the mechanistic roles of MXenes in charge transport, ion diffusion, and mechanical resilience. Key challenges, including structural degradation under strain, interfacial stability, and scalable processing, are identified. Alongside strategic design principles to guide the future development of mechanically compliant and high-end Mxene based flexible energy technologies are highlighted.