2.2 V wearable asymmetric supercapacitors based on Co oxide//Mn oxide electrodes and a PVA-KOH-urea-LiClO4 alkaline gel electrolyte

In this study, redox-active polyvinyl alcohol (PVA)-KOH-urea-LiClO4 alkaline gel electrolyte was prepared and used to assemble a Co oxide//Mn oxide wearable asymmetric supercapacitor (WASC). This experiment was achieved by choosing a deep eutectic solvent, urea-LiClO4, as the redox additive and aid a broad operating voltage, alongside an alkaline KOH-PVA gel to enhance redox performance and as plasticizer. The nanoporous Co oxide and Mn oxide electrodes were prepared using electroplating. The Co oxide//Mn oxide WASC with a PVA-KOH-urea-LiClO4 gel electrolyte can operate with an output voltage of 2.2 V and produce a high energy density of 125 Wh/kg at 2200 W/kg. The WASC showed good performance (186 F/g at 2 A/g) and 89.5% capacitance retention after 6000 charging/discharging cycles. Additionally, the WASC can maintain its electrochemical performance at various bending angles. Studied as the WASC electrode, in-situ/operando X-ray absorption near-edge spectroscopy revealed that the Co oxide suffers a reversible oxidation state-alteration reaction related to the redox pseudocapacitance reaction in PVA-KOH-urea-LiClO4. To show real life application, the WASCs were successfully applied to power a light-emitting diode and a digital watch.