Performance Of Carbon Capsule-based Compound Material For Supercapacitor

Supercapacitors due to its high specific capacitance,high power density,good cycle performance,low pollution and rapid charging process etc.,has attracted the great attention of many researchers.The supercapacitor consists of electrolyte,electrode material,collector and diaphragm.And electrolyte and electrode material are important factors affecting its electrochemical performance.How to optimize the composition and structure of the electrode material has become the key to the development of supercapacitors.There are three types of commonly used supercapacitor electrode materials: carbon-based materials,transition metal oxides,and conductive polymer materials.However,these electrode materials have their own advantages and disadvantages: carbon-based materials have good cycle stability,simple preparation process,and low cost,but the specific capacity is low;the specific capacity of metal oxides is much higher than that of carbon materials,but usually the resistance and the cost is high and the cycle performance is poorer;conductive polymer material has good conductivity,small internal resistance and high specific capacity,but the material is prone to volume expansion and contraction during charge and discharge,and the cycle stability is poor.Therefore,a single electrode material could not meet the need for good electrochemical performance.Researchers focus on composite materials synthesis and and hope to make use of synergistic effect among various materials to improve its electrochemical performance.Carbon capsules not only have the excellent chemical stability and electrical conductivity but alsoa high specific surface area and active sites.Among lots of metal oxide materials,manganese dioxide has high specific capacity,environmental friendliness,and low cost.The spinel Li Mn2O4 has a low preparation cost,simple synthesis method,convenience to commercialization,and less pollution to the environment.Therefore,both manganese dioxide and Li Mn2O4 are ideal materials for supercapacitor electrode materials.In this paper,carbon capsules are compound with Mn O2 and Li Mn2O4 to synthesize the sandwich structure of Mn O2@GCs@Mn O2 and Li Mn2O4@GCs composite material,respectively.This article mainly includes the following aspects of the work:1.Carbon capsules(CCs)were prepared by catalytic electrochemical vapor deposition(CCVD)using commercial Zn O as catalyst and template and acetylene as carbon source.When the carbon layersare less than 10,carbon capsules can be called graphite capsules(GCs).The results of the carbon capsule electrochemical performance are as follows: in sodium sulfate electrolyte,the specific capacitance of carbon capsule atcurrent density of1A/g is about 9F/g.And pure carbon capsules exhibit good electrical conductivity.2.MnO2@GCs@MnO2 sandwich composite was synthesized by microwave chemical reaction withcarbon capsules as precursor.On the basis of Mn O2@GCs@Mn O2 sandwich composites,three kinds of Mn O2/C composites with different proportions of C and Mn O2 were synthesized by changing the molar ratio of the reactant potassium permanganate and carbon capsules.The electrochemical properties of the three sandwich composite materials were studied.The results show that the electrochemical performance of the sandwich composite materials synthesized when the molar ratio of potassium permanganate and carbon capsules is 1:1.The specific capacitance of the composite material reaches 308F/g at a current density of 0.2A/g in neutral electrolyte,and 390F/g at a current density of 0.5A/g in an alkaline solution.The electronic conductivity of the sandwich structure is better than that of commercial manganese dioxide,which is worse than pure carbon capsules..3.Manganese dioxide nanorods were synthesized by hydrothermal method using Mn SO4,(NH4)2S2O8 and(NH4)2SO4 as reactants.Then manganese dioxide nanorods were used as precursors for manganese source and lithium hydroxide was used as lithium source.The short rod spinel lithium manganate was prepared by high temperature solid phase synthesis.Finally,acetylene was used as a carbon source,and a carbon layer was deposited on the surface of short-bar Li Mn2O4 by CCVD to synthesize Li Mn2O4/GCscomposite electrode material.The electrochemical properties of the material were studied.The electronic conductivity of Li Mn2O4/GCscomposites is better than pure Li Mn2O4,and the specific capacitance of Li Mn2O4/GCscomposites is higher under the same test conditions,showing more excellent electrochemical performance.Electrode of lithium Li Mn2O4/GCs sample has a highspecific capacitance up to 451F/g at a current density of 0.5A/g in 0.5mol/L lithiumsulfate electrolyte.