Structural Design And Application Of High-performance Supercapacitors

With the continuous development of science and technology,self-powered wearable monitoring system is regarded as one of the key technologies of the next generation of intelligent electronics.However,energy devices that power these smart electronics have been a constant focus of our efforts.In order for these smart electronics to be flexible and comfortable to wear,we have to give up the bulky and rigid external power supply system.This means that flexible,skin-friendly and integrated power supply units will become the focus of our research.Because of its small size,high safety and comfortable wearing,micro-supercapacitors have become one of the choices of integrated energy storage devices.However,there are still many deficiencies in the application of wearable integrated systems,which requires us to develop new electrode materials and optimize device structure to improve its performance and practical application value.The main research results of this paper are as follows:Firstly,Co3O4@NiCo2O4 composite was synthesized on nickel foam substrate by two-step hydrothermal method.Due to their synergistic effect,the electrochemical properties were significantly improved compared with those of Co3O4 or NiCo2O4 monomers.The area specific capacitance of a single electrode calculated to be 9.12 F·cm-2 in charging-discharging test at the current density of 2 mA·cm-2.The symmetrical supercapacitor assembled by two Co3O4@NiCo2O4 electrodes delivered an area specific capacity of 486 mF·cm-2 at the current density of 5 mA·cm-2.After 5000 galvanostatic charge-discharge cycles,the capacitance maintained 98.6%of the initial capacity still.The asymmetric supercapacitor device based on Co3O4@NiCo2O4 electrode and active carbon electrode extend to a voltage window of 1.6 V.The area specific capacity was measured to be 1343.7 mF·cm-2 at the current density of 2 mA·cm-2 and the capacitance maintained 99.6%of the initial value inlulstrating the excellent energy storage performance of the device based on Co3O4@NiCo2O4 composite materials electrode.Then,piezoelectric self-charging supercapacitor(PSCS)was fabricated by using PDMS-rGO/C film as positive and negative electrods,piezoelectric P(VDF-TrFE)as the separator.The PSCS device could convert the weak mechanical energy of the human finger joints into electrical energy and store it in the supercapacitor.For this device,the work mechanism was concluded as piezoelectric potential-driven double electrical layer behavior(non-faraday process).Under the bended deformation,the PSCS could achieve a potential window of 0.5 V and the discharge last about 15.8 seconds,the biggest current is 6.5 ?A·cm-2 at the same time.In addition,in order to achieve the self-powered health monitoring system,we integrated a micro-supercapacitor array and biosensor on the PET substrate which could realize the qualitative analysis of metabolites in human sweat,so as to provide reference data for human daily health.The assembled concentric circle micro-supercapacitor based on NiCo2O4 electrodes delivered an area specific capacitance of 18.8 mF·cm-2.The designed wearable sweat monitoring system showed the sensitivities of 0.5 ?A ?M-1 for glucose,0.031 nF/mM for[Na+]and 0.056 nF/mM for[K+],respectively.