Advanced materials for flexible and wearable energy storage devices

The rapid advancement of wearable electronics has intensified the need for lightweight, flexible, deformable, and self-sustaining energy-storage systems. Flexible supercapacitors (FSCs) have emerged as promising options for wearable energy-storage applications due to their high-power density, short charge-discharge times, long cycling stability, and mechanical flexibility. Recent advancements in materials engineering, additive manufacturing, and self-sustaining systems have improved the electrochemical and mechanical efficacy of FSCs. This review discusses recent advancements in improved materials, fabrication techniques, and integrated self-charging systems for next-generation wearable supercapacitors. It covers most of the reported materials, including conductive polymers, carbon nanomaterials, MXenes, metal oxides, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and hybrid nanocomposites. Advanced fabrication techniques, such as three-dimensional (3D) printing, microfluidic spinning, wet spinning, dry spinning, coating deposition, screen printing, laser writing, and hybrid UV-assisted 3D printing, are highlighted concerning their impact on electrode structure, ion transport, conductivity, and mechanical integrity. Hybrid material that integrate electrical double-layer capacitance (EDLC) with pseudocapacitive charge-storage processes are highlighted as efficient approaches to improve energy density and electrochemical performance. Furthermore, recent developments in wearable self-charging power systems that integrate triboelectric generators (TENGs) with FSCs are highlighted, illustrating the viability of harvesting biomechanical energy to enable uninterrupted, autonomous device operation.