Horizontally oriented 2D skin structures on fiber interface for long-life flexible energy storage devices

This work proposes a novel fiber interface binding method, enabling horizontal growth of 2D materials at the carbon fiber interface. This approach ensures exceptional stability and prolonged cycling life for flexible energy storage devices. • Achieves horizontally oriented 2D skin structures on carbon fiber interfaces. • Overcoming the limitations of traditional vertical growth methods. • Greatly improves interfacial stability and electron transport pathways. • Offers a novel interface design for durable flexible fiber electronics. Fiber-based energy storage devices present distinct advantages over rigid alternatives, particularly for flexible and wearable applications. However, achieving stable integration of electrochemically active materials with fiber substrates remains a significant challenge, especially for carbon fibers (CF), due to their inherent physical smoothness and chemical inertness make them prone to interfacial separation under repeated bending and deformation in practical applications. In this study, we employed a salt template-assisted vapor-phase polymerization method to achieve horizontally oriented growth of 2D conductive polymer complex on CF, thereby forming a bamboo sheath-like structure with a 2D juxtaposed ultrathin nanosheet-coated fiber interface (2D-JUN-FI). The skinned nanosheets on CF ensure maximized interfacial binding in the vertical interfaces through extensive surface coverage and hydrogen bonding interaction, while maintaining the structure integraty in the horizontal plane, thus resulting in both high mechanical robustness and electron mobility under static and dynamic deformations. The synthesized electrode of 2D polypyrrole and amorphous niobium oxide on CF composites (2D Ppy/a-Nb 2 O 5 /CF) demonstrates high specific capacity and an exceptionally long cycling life (88.06 % capacitance retention after 5000 cycles). This template-assisted horizontal growth of the 2D-JUN-FI skinned structure provides a novel approach for developing high-stability and long-life flexible energy storage devices.