High-performance flexible solid-state supercapacitors based on MnO ₂-decorated nanocarbon electrodes

Flexible energy storage units are highly desired to meet the ever-increasing demands for flexible electronics. In this paper, highly flexible solid-state supercapacitors are fabricated using MnO₂-decorated nanocarbon electrodes and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide-poly(vinylidene fluoride)-hexafluoropropylene ([EMIM][NTf2]-PVdF(HFP)) gel electrolytes. The flexible electrodes are prepared by electrodepositing MnO₂ onto the carbon nanotube/carbon nanoonion (CNT/CNO) films. CNT/CNO films have a large surface area for MnO₂ deposition and work as mechanical supports with high flexibility and light weight. CNOs act as spacers to separate CNTs, introducing mesopores inside the CNT/CNO films for preventing pore blocking during MnO₂ deposition. The supercapacitor exhibits enhanced electrochemical performance with an energy density of 16.4 W h^-1 kg^-1 at a power density of 33.3 kW kg^-1 by using the [EMIM][NTf2]-PVdF(HFP) gel electrolyte. Moreover, the supercapacitors can exhibit high electrochemical performance under large mechanical stress, making the devices suitable for flexible electronics.