Flexible free-standing Ni–Mn oxide antenna decorated CNT/nanofiber membrane for high-volumetric capacitance supercapacitors

Abstract

There is growing demand for lightweight flexible supercapacitors with high electrochemical performance for wearable and portable electronics. Here, we spun nanoparticles of nickel–manganese oxides along with carbon nanotubes into carbon nanofibers and engineered a 3D networked Ni–Mn oxides/CNT@CNF free-standing membrane for flexible supercapacitor applications. The electrospinning process controlled the nanoparticle aggregation while subsequent heat treatment generates nanochannels in the fibres, resulting in a very porous tubular nanocomposite structure. The preparation process also enabled good interfacial contact between the nanoparticles and the conductive carbon network. The resulting Ni–Mn oxides/CNT@CNF membrane displays high mass loading (Ni–Mn oxides) of 855 mg cm⁻³ and low CNT incorporation of ∼0.4%. The outstanding porous structure, synergy of the carbon with Ni–Mn oxides, and fast and facile faradaic reactions on the electrode were responsible for the superior volumetric capacitance of 250 F cm⁻³ at 1 A cm⁻³, energy density as high as 22 mW h cm⁻³ and an excellent power density of 12 W cm⁻³. Despite the low CNT loading, the hybrid electrode exhibits excellent cycling performance with capacitance retention of 96.4% after 10 000 cycles evidencing a well-preserved Ni–manganese oxide nanostructure throughout the cycling. The resulting outstanding electrochemical performances of the Ni–Mn oxides/CNT@CNF synergic system offer new insights into effective utilization of transition metal oxides for establishing high-performance flexible supercapacitors within a confined volume.