Supercapacitors Preparation And Properties Of The Carbon Electrode Material

Rice husk active carbon with high specific surface area and high content of mesopore was prepared as electrode active materials to meet the prerequirements of the manufacture of supercapacitors.Sulfur-free expanded graphite was also prepared as a novel conductive agent.Both of the materials were used to make the electrode slices,and their electrochemical properties were studied.We used rice husk as raw material,NaOH as activing agent to prepare activated carbon with high specific surface area and high content of mesopore.The optimized synthesis conditions were obtained,including the reaction temperature,alkline/carbon ratio and activition time,in a method of the orthogonal experiment and single factor optimization.The activated carbon obtained with a alkali/carbon mass ratio of 3:1 after activation at 750℃for 1.5h exhibites the best iodine adsorption and methylene blue adsorbtion properties.According to the nitrogen adsorption test,the specimen obtained at this condition exhibit a content of mesopore of 61.15%and an average pore size of 2.6 nm,and a specific area 2164 m~2/g,which fits the supercapacitor's requirement pretty well.The sulfur-free expanded graphite with high expantion volume ratio was obtained by sork the flake graphite into a solution of concentrated phosphate and nitrate,and addition of potassium permanganate after that.The expanded graphite obtained with a phosphate/nitrate ratio of 3:1,and a acid mixture volume/graphite mass ratio of 5:1(ml/g),and a potassium permanganate/ graphite mass ratio at 0.1:1,and a reaction time of 1h,has a high expanxion volume of 223 ml/g.The model supercapacitor was assemblied using electrode slices made from activated rice husk carbon and common conductive graphite,which act as electrode active material and conductive agent,respectively.And the electrochemistry performance of the model supercatacitor was tested.The electrode slices showed good capacitance characteristics with a specific capacity of 98 F/g at the recharging/ discharging current of 0.1 A/g,and a ESR of 4.6Ωand a drain current of 0.50 mA/cm~2,which indicates that the rice husk obtained can be used as the electrode materials for supercapacitor.The electrode slices was prepared with activated rice husk carbon and expanded graphite,which act as electrode active material and conductive agent,respectively. And the electrochemistry performance of the derived model supercapacitor was tested in comparasion with that of electrode using common graphite.The electrode slices showed good capacitance characteristics with a specific capacity of 123 F/g at the recharging/discharging current of 0.1 A/g,which is 25.51%higher than conductive graphite competators.Also the slices exhibit a ESR of 4.2Ωand a drain current of 0.37 mA/cm~2,with low energy losses.