Process Optimization Of Soymealderived Activated Carbon Used In Supercapacitors And Synthesis Of Its Composites

As a novel energy storage device,supercapacitorshave attached great importance by the researchers around the world,owing to itsexcellent properties,such as high power density,long cycle life,short time of charge and discharge,instantaneous large current and so on.The great influence of the electrode material on supercapacitors' functions makes it a focus and hotspot to research the supercapacitors.The biomass-based activated carbons with the high specific surface area,adjustable microporous structure,good electrical conductivity and electrochemical stability are widely used to prepare the supercapacitor electrode materials.The carbon source is soymeal which is common on the market and low in price.On the basis of the existing research phase,further optimization of the process was carried out to obtain soymeal-derived actived carbon with high specific surface area and excellent electrochemical performance.The main research works and results are listed as following:?1?In the preparation stage of soymeal-derived actived carbon,we choose different pre-carbonization temperaturesasa variable,basing on the existing research stage.Researching the influences of the pre-carbonization temperatures on the pore structures and electrochemical performances of the soymeal-derived actived carbons in the activation ratio of 1: 3,activation temperature of 800 ?,activation time of 1h and other unchanged activation conditions.Finally,we put the soymeal-derived actived carbons with different pore structures into 6 mol L^-1KOH electrolyte to test their electrochemical properties.Results show that:At first,with the increase of pre-carbonization temperature,the specific capacitance of soymeal-derived actived carbon is gradually increased,reaching a maximum specific capacitance of 312 F g^-1at 460 ?,then with the further increase of the pre-carbonization temperature,the specific capacitance of soymeal-derived actived carbon begins to decrease.The sample AC-460 has stable cycle characteristics and has a 79.8%retention of specific capacitance after 10000 cycles in aqueous.The sample AC-460 composed by micro-and meso-structure with a high specific surface area of 3551m2 / g is an ideal material for preparing supercapacitor electrode materials.But its power characteristic is poor.Its specific capacitance drops to 97 F g^-1at 500 mV s^-1 scan rate.?2?We compositehigh specific surface area sample AC-460 which is prepared at pre-carbonization temperature of 460? with RGO?PRGO and DG graphene sheets to research the influences on the specific capacitances and the power characteristics of the soymeal-derived actived carbons.And further,the different size graphenes as the starting materials are composited with the soymeal-derived actived carbons to study the effects ofthe graphenes' sizes on the electrochemical performances of the composited samples.Results show that: The power characteristics of the soymeal-derived actived carbons composited with RGO or PRGO are significantly improved while the specific capacitanceshave a slight increase.Their specific capacitances are increased from the original value 312 F / g to 316 F / g and 317 F / g,respectively.And the capacitance retention rates are increased from the original 31.1% to 45.5% and 39.4% at 500 mV s^-1 scan rate,respectively.The specific capacitance of the soymeal-derived actived carbons composited with DG is decreased to 283 F / g,but the power characteristics has been greatly improved with the capacitance retention rate of 48.1%at 500 mV s^-1 scan rate.This is because DGprepared by liquid stripping method has a complete structure and keeps a high conductivity.So it is easy for ionsto transferre in the charge-discharge process and the power characteristics of the composited samples are greatly improved.But at the same time due to DGcan not be completely stripped by the liquid stripping method,the layers are stacked together.So the specific capacitance of the soymeal-derived actived carbons composited with DG has a slight decline.And the graphenesizes have a huge impact on the electrochemical properties of the composited samples.The electrochemical performances of the soymeal-derived actived carbons composited with RGO prepared from 5000 mesh graphiteis better than that prepared from 300 mesh and 50 mesh graphite.The reason is that when the size of the graphite is large,the oxidation stripping is not sufficient withthe Hummers and the graphene layers are thick and the specific surface area can not be effectively utilized.Therefore,the electrochemical performances of the composite material AC-460 are poor.Therefore,the smaller the graphenesize,the better the compositedsamples.