| Climate change and the limited availability of fossil fuels have greatly affected the world ecology and economy.With a fast-growing market for portable electronic devices and the development of hybrid electric vehicles,there has been an ever increasing and urgent demand for environmentally friendly,high-power energy resources.Supercapacitors,also known as electrochemical capacitors or ultracapacitors,have attracted much attention because of their high-power density,long cycle life,and environmentally friendly.Carbon materials are considered prospective electrode materials for industrialization because of their abundance,lower cost,easy processing,non-toxicity,higher specific surface area,good electronic conductivity,high chemical stability,and wide operating temperature range.In recent years,the shortage of mineral resource have greatly limited the carbon materials development and application.Biomass resources are regarded as important raw material for preparation of various carbon materials because of their source wide,renewable,environmentally friendly and low cost.Besides the general advantage of the biomass resources,starch category is numerous as an important biomass.Nowdays,most of the researches of starch-based carbon materials focused on the activation time,different mass ratios of KOH/C and activator kinds while few studies on carbonization temperature and activation methods.Carbonization temperature and activation method as the core-block of the preparation of carbon materials,has an important effec the structure of carbon materials and its electrochemical performance.We have studied the influence of different carbonization and activation temperature on the electrochemical performance of cassava starch-based activated carbon as supercapacitor electrode materials,and determined the optimum technology of prepared cassava starch-based activated carbon.On this basis,highly graphite and carbon nanosheets modified porous and hollow cassava starch-based activated carbon microsphere was obtained by adjusting the activation method.The formation mechanism of carbon nanosheets were investigated,and electrochemical performance of porous and hollow cassava starch-based activated carbon microsphere was investigated.To obtained highly graphite cassava starch-based activated carbon microsphere at low temperature,hierarchical holes and high graphite of cassava starch-based activated carbon microspheres was prepared by catalyst with nickel acetate and activator with KOH at 850?,and its electrochemical performance was investigated.(1)Cassava starch-based activated carbon were preparated by cassava starch,and 400 ?,500 ? and 600 ? were used as cassava starch carbonization temperature.Et4NF4/PC as electrolyte,assembly into a button type 2025 type supercapacitor,evaluating the electrochemical properties of cassava starch based activated carbon as supercapacitor electrode materials.500 ? as carbonization temperature of cassava starch to prepare cassava starch-based activated carbon,and its showed excellent electrochemical performance.The discharge specific capacity up to 94 F/g at the current density of 0.1 A/g,when the current density was up to 1 A/g,but also keep good rate performance with the discharge specific capacity can reach 93 F/g.The cassava starch carbon contains a large number of organic matter,which was not fully be carbonized at 500?.In the activation process the part of the organic matter further cracking under the action of alkali,therefore,to the formation of mesoporous.The increase of the mesoporous ratio of activated carbon can urge ion rapidly diffuse,and then to the promotion ratio performance of supercapacitor.(2)Cassava starch-based activated carbon were preparated by cassava starch,and 850 ?,900? and 950? were used as cassava starch activation temperature.Et4NF4/PC as electrolyte,assembly into a button type 2025 type capacitor,evaluating the electrochemical properties of cassava starch based activated carbon,950?as activation temperature of cassava starch to prepare cassava starch-based activated carbon,and its showed excellent electrochemical performance.The discharge specific capacity was 112 F/g and 109 F/g at the current density of 0.1 A/g and 1 A/g,keeping good rate performance.Cassava starch activated carbon obtained maximum specific surface area 2190.79 m2 g-1 and high rate of mesoporous when activation temperature at 950?.The specific capacity can maintain 89%at current density of 1 A/g after 1000 cycle.(3)Highly graphitized porous and hollow cassava starch-based activated carbon microsphere with carbon nanosheets modified were prepared via petroleum coke buried method using cassava starch as raw material.During the activated process,cracking gas(e.g.,CO and CO2)were produced by KOH react with carbon,at the same time deposited on the surface of activated carbon microsphere to form carbon nanosheet in the closed space.The cracking gas and closed space is a key factor in the preparation of carbon nanosheet.Porous and hollow carbon cassava starch-based activated carbon microsphere obtained maximum specific surface area 1931.14 m2 g-1 and wide distribution porous 3-100 nm when activation temperature at 950?.6 M KOH as electrolyte,assembly into a button type 2032 type capacitor,studied the electrochemical performance of carbon nanosheets modified porous and hollow carbon cassava starch-based activated carbon microsphere obtained at 950 ?,and its showed excellent electrochemical performance.The discharge specific capacity up to 275 F/g at the current density of 1 A/g,when the current density was up to 20 A/g,but also keep good rate performance with the discharge specific capacity can reach 220 F/g.The specific capacity with no obvious attenuation after 10000 cycles of at the current density of 1 A/g.Highly graphited porous hollow carbon microspheres with carbon nanosheets modified and prepared by starch shows excellent electrochemical performance as supercapacitor electrode material,which has not been reported.(4)Cassava starch-based activated carbon microsphere were prepared via petroleum coke buried method using KOH as activator,and cassava starch absorbed with nickel ion and bare cassava starch as raw material.XRD results showed that the activated carbon microsphere prepared by cassava starch absorbed with nickel ion displayed higher graphitization degree than the bare starch.specific surface area and pore structure results showed that the activated carbon microsphere prepared by cassava starch absorbed with nickel ion displayed higher mesoporous rates than the bare starch.Et4NF4/PC as electrolyte,assembly into a button type 2025 type capacitor,The electrochemical test results showed that the activated carbon microsphere prepared by cassava starch absorbed with nickel ion displayed a better electrochemical performance than the bare starch.The discharge specific capacity up to 129 F/g,122 F/g and 116 F/g at the current density of 0.1 A/g,0.5 A/g and 1 A/g,showed excellent rate performance.However,the activated carbon microsphere prepared by bare cassava starch was 91 F/g at the current density of 1 A/g.The specific capacity of the activated carbon microsphere prepared by cassava starch absorbed with nickel ion can maintain 94%after 1000 cycles of at the current density of 1 A/g,and the activated carbon microsphere prepared by bare cassava starch was only 76%.The activated carbon microsphere prepared by cassava starch absorbed with nickel ion are more suitable for as supercapacitor electrode materials. |
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