| As a new type of energy storage device between the traditional capacitor and the battery,supercapacitor has been widely used in electric vehicles and other fields.However,the bottleneck problem of supercapacitor—low energy density,hinders its extensive development.In this paper,the electrode material of MnO2 based supercapacitor electrode was prepared by liquid co-precipitation and solvothermal method.The specific energy of electrode material was improved to improve the energy density.First of all,amorphous hydrated MnO2 was prepared by liquid co-precipitation in the presence of non-ionic surfactant Polyvinylpyrrolidone(PVP).In order to comparing the performance,amorphous hydrated MnO2 were also prepared by the above mentioned method with adding the widely used surfactants,polyethylene glycol(PEG)and sodium dodecylbenzensulfonate(SDBS)surfactant.The effect of different surfactants on the morphology,crystal structure and electrochemical properties of the prepared electrode materials were investigated.The experimental results showed that the performance of the electrode materials prepared with nonionic surfactants(PEG,PVP)is better than that of ionic surfactant SDBS.The order of the surfactants was as follows:PVP>PEG>SDBS.The largest specific surface area(196.64 m2/g)and the highest capacitance(246.3 F/g)all came from the MnO2 electrode by adding PVP.Compared with the sample prepared without surfactants,the specific surface area and capacitance of the sample prepared with PVP improved by 92.2%,and 58.0%,respectively.Moreover,the electrode showed good cycle stability at 120 mA/g.After 500 cycles,the specific capacitance still remained 91.8%.What's more,we focused on improving the electrical conductivity and capacitive properties of MnO2.MnO2 was prepared by low-temperature liquid-phase reaction.Then the samples were thermally treated(300?-700?)under nitrogen atmosphere.Crystal structure,porosity,conductivity,microstructure and the electrochemistry properties of thermal treated MnO2 electrode were measured.The measured maximum specific capacitance is 368.2F/g in a 6mol/L KOH electrolyte at lA/g for the prepared electrode annealed at 400?,which has doubled compared with that of the untreated sample.Further observation of MnO2 electrode's microstructure showed that oxygen deficiency-induced phase transformation during thermal treatment under nitrogen leads to co-existence of multivalent Mn,which effectively improves its electrical conductivity and capacitive properties.For further study,the heat treatment atmosphere was changed from nitrogen to air.It was found that the improvement of the properties of the prepared samples was mainly attributed to the change of the crystal form of the product from the amorphous structure to the partly amorphous phase.Subsequently,different morphologies and excellent performance of CoO@MnO2 core/shell composite electrode materials were synthesized by controlling the content of NH4F with using solvothermal classification.Due to non-existent with conductive agent and binder,unique hierarchical structure and excellent electronic transmission network,the prepared composite electrode materials show a good rate capability,excellent capacitance,electrode reaction resistance and low charge transfer/diffusion resistance.The change regulation of specific capacity of the sample was as follows(adding Co2+:NH4F):1:2>1:5>1:0>1:10.The prepared CoO@MnO2 sample by adding Co2+:NH4F=1:2 exhibited the maximum specific capacitance of 1505.7 F/g in a 6mol/L KOH electrolyte at 1A/g,and the specific capacitance of the electrode keeps stable at the initial stage,and still remains 97.5%of the initial value at 5A/g after 1200 cycles.Meanwhile,Coulombic efficiency was close to 100%all the time.The prepared electrode materials showed ideal Conductivity,favorable pore structure,and excellent comprehensive properties,so it is applicable to be used as electrode material for supercapacitors. |
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