Overcoming the Energy–Power Trade‐Off in Fiber Electronics: The Role of Metal‐Ion Hybrid Capacitors

Fiber-based energy storage is integral to realizing smart textiles and soft electronics, where devices must deliver high power and adequate energy while tolerating repeated mechanical deformation. Metal-ion hybrid capacitors-which pair a battery-type faradaic electrode with a capacitive counterpart-offer a pathway to narrow the energy-power gap. While recent progress in metal-ion chemistries and device architecture has improved electrochemical performance and compatibility with wearable formats, the field remains fragmented, and a unified understanding of these rapidly evolving developments is still lacking. Herein, a structured review is presented that first summarizes the broader landscape of fiber-based energy storage systems, with emphasis on device architectures and fabrication strategies. It then outlines metal-ion hybrid capacitors, highlighting their charge-storage mechanisms, performance trade-offs, and ion chemistries. On this basis, the review provides comprehensive knowledge of fiber-based metal-ion hybrid capacitors (FMHCs) across lithium-, sodium-, potassium-, and zinc-ion chemistries, discussing charge-storage mechanisms, materials selection, device architectures, and fabrication routes. Finally, current challenges for practical deployment and future research directions are highlighted, providing a unified framework to guide innovative FMHC design toward practical, high-performance wearable energy storage.