Cotton textile enabled, all-solid-state flexible supercapacitors

A hierarchical NiCo₂O₄@NiCo₂O₄ core/shell nanostructure was grown on flexible cotton activated carbon textiles (ACTs) to fabricate NiCo₂O₄@NiCo₂O₄/ACT electrodes. After dipping with PVA/KOH polymer gel which served as both the solid state electrolyte and separator, the flexible NiCo₂O₄@NiCo₂O₄/ACT hybrid electrode exhibited an exceptional combination of electrochemical and mechanical properties in terms of specific capacitance (1929 F g^-1, based on the mass of NiCo₂O₄), energy density (83.6 Wh kg^-1), power density (8.4 kW kg^-1), cycling stability, and mechanical robustness (the tensile strength is 6.4 times higher than that of pure ACT). The outstanding electrochemical performance is ascribed to the unique core/shell nanostructure with high active-surface area, morphological stability, and short ion transport path. Such hierarchical core/shell nanostructure of the same material on a cotton-enabled flexible substrate should inspire us to develop flexible solid-state textile energy storage devices for future wearable electronics.