Flexible Supercapacitors Fabricated by Growing Porous NiCo₂O₄ In Situ on a Carbon Nanotube Film Using a Hyperbranched Polymer Template

The lightweight carbon nanotube (CNT) has been attracting great attention in the field of flexible electronics, but it is still a challenge to increase both high capacitance and high energy density. Here, we report the use of an epoxy-ended hyperbranched polymer (EHP) as a reactive template in an in situ preparation of porous NiCo2O4 on a pristine CNT film. The resultant porous NiCo2O4 has a core–shell nanostructure and possesses higher surface area and electrochemical performance in comparison to NiCo2O4 prepared without CNT film. As an electrode material, the CNT@NiCo2O4 film showed a high specific volume capacitance of 281.7 F cm–3. The flexible symmetric supercapacitor assembled from the CNT@NiCo2O4 film displayed high volume capacitance (23.3 F cm–3), 95.6% retention in capacitance after 5000 charging–discharging cycles and bending performance, and high energy density (3.2 mWh cm–3). The CNT film served as a flexible current collector, and porous NiCo2O4 supplied high electrochemical performance. The reaction mechanism using the epoxy-ended hyperbranched polymer as a reactive template in the preparation of porous NiCo2O4 has been investigated using FT-IR, XRD, and TG.