A review of recent advances in MXene-based flexible energy storage materials: theoretical and experimental perspective

Abstract

The rapid depletion of fossil fuels and the pressing demand for clean, durable, and adaptable energy storage systems have accelerated research into advanced nanomaterials for next-generation devices. Transition metal carbides, nitrides, and carbonitrides, classified as two-dimensional (2D) materials, have emerged as a rapidly expanding category since the identification of Ti ₃ C ₂ in 2011. MXenes exhibit excellent physicochemical properties, including high metallic conductivity, hydrophilic surfaces, tunable interlayer spacing, and diverse surface chemistry characterised by functional terminations such as –O, –OH, and –F. Due to these characteristics, MXenes are effective for energy storage. Beyond their general capabilities, a significant aspect is their application in the production of flexible energy storage sheets. These sheets are increasingly significant for the operation of wearable electronics, portable devices, roll-up displays, and soft robotics. MXenes are utilised in flexible energy storage systems due to their ability to integrate mechanical strength with superior electrochemical performance. MXene can be fabricated into freestanding films or hybrid composites that exhibit excellent rate capability, and cycling stability, all while maintaining mechanical flexibility. Methods such as vacuum filtration, self-assembly, electrospinning, and coating can be employed for this purpose. Surface terminations, porosity tuning, and structural changes significantly influence ion mobility, charge capacity, and the overall flexibility of the device. MXene-based flexible sheets exhibit the ability to bend and twist while maintaining conductivity and energy density, contrasting significantly with conventional rigid electrodes. This creates new opportunities for multifunctional energy storage systems. Despite significant advancements, challenges remain in achieving scalable and environmentally friendly synthesis, regulating flake thickness, optimising surface terminations, and ensuring material stability under standard conditions. Future research directions include the exploration of fluorine-free and environmentally friendly etching techniques, large-scale production of single-layer MXenes, covalent functionalisation for tailored flexibility, and the development of low-dimensional heterostructures (0D/2D, 1D/2D, and 3D architectures) to achieve synergistic performance. The integration of MXenes into hybrid flexible devices may accelerate their advancement towards commercial viability, particularly for applications requiring lightweight, flexible, and durable power sources. Recent developments in MXene-based hybrid architectures and surface engineering techniques are also covered, emphasizing how oxide–MXene heterostructures, interlayer spacing modulation, and controlled surface terminations enhance ion transport pathways and electrochemical stability in flexible configurations. In order to enable dependable functioning of flexible and wearable energy storage devices, the review also looks at how these structural and interfacial alterations support stable electrochemical performance under mechanical deformation. This review focuses on MXene-based flexible energy storage sheets, emphasizing the connections between fabrication techniques, structural engineering, mechanical flexibility, and electrochemical performance in deformable devices, in contrast to earlier MXene reviews that cover general energy storage or sensing applications.