Research Of Self-supported Carbon Based/ Transition Metal Oxide Composite Electrode For All-Solid-State-Supercapacitors

Carbon electrode materials have been widely studied and applied to supercapacitors because of their high power density,good cycling stability and excellent rate performance.The transition metal oxide also can be used as supercapacitor electrode material.Compared with the double layer capacitance provided by carbon materials,metal oxide can provide pseudopotential,and its theoretical capacity is several times or even tens times higher than that of carbon material.But its stability and rate performance are not as good as that of carbon materials.In this paper,a simple and efficient hydrothermal method is used to prepare three-dimensional self-supported graphene-based metal pseudocapacitor composites.And assembled All-solid-state supercapacitors with solid electrolyte.In order to improve materials flexibility and processability,a biomass?ramie?carbonated substrate was used to replace the graphene.The transition metal oxide is carried on the surface by water heat.The specific research contents include the following three aspects:?1?The carbon/pseudocapacitor composite?GA/CoO?was prepared by one step hydrothermal method.The raw materials are commercial graphene oxide?GO?aqueous solution prepared by Hummer method,ascorbic acid?Vc?,Co?OAc?₂·4H₂O and urea.The structure and electrochemical properties of the electrode materials obtained by pure reduction graphene oxide,doped Vc and doped CoO are mainly explored.The comparison results show that adding appropriate Vc can effectively improve the three-dimensional self-supported structure of the material,while adding a small amount of Co?OAc?₂·4H₂O can make the GA doped CoO pseudocapacitor,effectively improve the specific capacitance performance without damaging its self-supported structure.The electrochemical test shows that it has good supercapacitor performance.At 1 A/g current density,the specific capacity is up to 222 F/g,which is 79 F/g higher than that of pure GA.?2?GA/MnCo₂O₄ composite electrode was synthetized via the one-step hydrothermal method.The raw materials are GO aqueous solution,ascorbic acid,Co?OAc?₂·4H₂O,Co?OAc?₂·4H₂O and urea.When tested as supercapacitor electrodes,the GA/MnCo₂O₄ delivered a high specific capacitance of 289.2 F/g at 1 A/g and it still maintained at a value of 152 F/g even at 20 A/g.At the same time,three methods of preparing solid state electrolyte PVA/KOH were studied,and all solid state supercapacitors were assembled with GA/MnCo₂O₄.The energy density and power density of the 1.5 V working voltage reach 15.98 Wh/kg and 2.7 kW/kg,the self-discharge rate is slower,the leakage current is only 42?A,and the capacitance after 3000 cycles of charging and discharging has no obvious change.?3?A natural and environmentally friendly biomass material,ramie fiber,is used as a carbon source.Simply treated and made into thin film like fiber.Then a flexible self-supported carbonated substrate was prepared by high temperature carbonization.The co-manganese spinel was grown on carbonized ramie fiber by hydrothermal method to obtain the RCF/MnCo₂O₄.The results showed that RCF/MnCo₂O₄ had good self-support and flexibility.When tested as supercapacitor electrodes,the Fe/NPC delivered a large specific capacitance of 329.6 F/g at 1 A/g and it still maintained at a value of 148 F/g even at 20 A/g,showing high rate performance.The energy density and power density of the flexible all solid state supercapacitor assembled with the working voltage of 1 V can reach 6.75Wh/kg and 1.8 kW/kg.The supercapacitors self-discharge rate is slow,and the leakage current is only40?A,which has good circulation stability and shows good flexibility.