Preparation Of Oxygen-riched Carbon Materials For Supercapacitors

Supercapacitor is a new type of energy storage device with the advantages of fast charge and discharge capacity,long cycle life and environmental protection.As the core component of supercapacitor,electrode restricts the performance of supercapacitor.Therefore,the development of new electrode materials with excellent electrochemical performance is of great significance for the development of supercapacitors.Biomass materials are rich in reserves,high in carbon content,cheap and easy to obtain,and are ideal materials for supercapacitor electrodes.In addition,biomass materials also contain heteroatoms such as nitrogen,oxygen,and phosphorus that can produce pseudocapacitance,thereby increasing the total specific capacitance of the material.In this paper,starch,a high oxygen content biomass raw material,was used to obtainO-riched carbon materials by sulfuric acid carbonization at a lower temperature.At the same time,theO-riched carbon material was compounded with other materials to assemble a variety of new supercapacitors,and showed good electrochemical performance.The specific research contents are as follows:1.AnO-riched and highly graphitized carbon material（OSC）（Raman spectrum I_D/I_G=0.75）was prepared by carbonization of starch with concentrated H₂SO₄at a relatively low temperature（100℃）.On this basis,we choose dicyandiamide as the nitrogen source,and grow N-doped carbon nanotubes on the surface ofOSC by vapor deposition.Thus,a carbon material rich inO and N（named NOSC）was prepared.When the current density reaches 1 A g^-1,the NOSC electrode has a specific capacitance of 759 F g^-1.After 10000 cycles,95.8%of the capacitance is still retained.An all-solid-state symmetric supercapacitor（SSC）is assembled,which can achieve a wide voltage window of 1.8 V.At the same time,the specific capacitance of the SSC is 91 F g^-1.When the energy density is 41.12 Wh kg^-1,the power density is 449.95 W kg^-1.2.The SnO₂/OSC composite was obtained by a simple hydrothermal method to combine theO-riched carbon materialOSC with the metal oxide SnO₂.OSC can effectively prevent the aggregation of SnO₂particles and ensure the stability of the structure,so as to better promote the transmission of electrons.By optimizing the ratio of the two,the SOSC-2electrode showed the best electrochemical performance.When the current density reaches 1 A g^-1,the composite exhibits a specific capacitance value of 689 F g^-1.After 10000charge-discharge cycles,it exhibits excellent cycle performance with a capacitance loss of2.2%.The solid-state symmetric supercapacitor can achieve a wide voltage window of 2 V.When the energy density is 43.47 Wh kg^-1,the power density is 500 W kg^-1.3.Further mixed acid oxidation of OSC was carried out to obtain thinner and smaller oxygen-enriched carbon particles HOSC.The oxidation conditions were optimized to obtain the HOSC-85 with the best electrical performance.The HOSC-85 was compounded with graphene oxide（GO）,and the GSC composite flexible membrane electrode was prepared by vacuum filtration.The addition ofOSC effectively suppresses the stacking of graphene due to theπ-πinteraction between layers.After optimizing the ratio of the two components,the obtained GSC-1 electrode has an area specific capacitance of 566 m F cm^-2at a current density of 1 m A cm^-2.After 10000 cycles of charge and discharge,the capacitance retention rate is90.8%.The GO/MnO₂//GSC asymmetric supercapacitor was assembled with GO/MnO₂film as the positive electrode,GSC-1 film electrode as the negative electrode and PVA-KOH gel as the electrolyte.The operating voltage of the device was 1.4 V and the area specific capacitance was 150 m F cm^-2.When the energy density is 0.0408 m Wh cm^-2,the power density is 0.699 m W cm^-2.