Flexible Transparent Symmetric Solid-State Supercapacitors Based on NiO-Decorated Nanofiber-Based Composite Electrodes with Excellent Mechanical Flexibility and Cyclability

We have prepared the flexible and transparent symmetric solid-state supercapacitors based on the nanofiber-based composite (NFC) electrodes decorated with NiO nanoparticles which exhibit better electrochemical performance, optical transmittance, and flexibility compared to the NiO-decorated ITO (NiO@ITO) electrodes as a standard system. The structures, morphologies, and its electrochemical properties of the flexible and transparent NiO-decorated NFC (NiO@NFC) electrodes were investigated. SEM analysis confirmed that the NiO nanoparticles were well coated onto the flexible and transparent NFC electrodes, which were prepared by a simple spin-coating of the silver nanowires (AgNWs) dispersion on the flexible and transparent (>90.3% at 550 nm wavelength) NFC film. The obtained NiO@NFC electrode showed a good optical transmittance of ~75.0%, lower sheet resistivity of ~16 O sq^–1, and excellent mechanical flexibility at a bending radius of 1 mm, which were superior to the NiO@ITO electrodes. The assembled NiO@NFC//NiO@NFC and NiO@ITO//NiO@ITO symmetric devices delivered a maximum capacitance of 161 and 85 F g^–1 at 1.0 A g^–1, respectively. Moreover, the fabricated NiO@NFC//NiO@NFC symmetric device showed excellent capacitance retention of ~96.0% at the higher current density of 10 A g^–1 after 5000 cycles and also a maximum energy density of 22 Wh kg^–1, which was about 2 times higher than the NiO@ITO//NiO@ITO symmetric device (~11.8 Wh kg^–1).