Preparation Of Carbon Electrode Materials By Fix-Point Activation And Its Structure And Electrochemical Properties

With the continuous upgrading of industrial technology in recent years,people's demand for advanced energy storage technology and equipment is more and more urgent.Although supercapacitors play an important role in energy conversion due to their high-power density,fast charging and discharging speed and long cycle life,their relatively low energy density severely limits their application scope.How to improve the capacitance to provide sufficient energy for high power output has become the critical problem to be solved.The electrode material is the storage location of the supercapacitor,so it is the key to design and improve the structure to achieve high energy storage.From the perspective of practical application,the improvement of the capacitance of supercapacitors can be directly improved by increasing the mass ratio capacitance of electrode materials,or by improving the quality of electrode materials per unit area to achieve the purpose of improving the capacitance of supercapacitors.In this paper,mesoporous carbon was synthesized by hydrothermal synthesis method as the precursor,and its electrochemical properties were tested after one-step fixed-point activation treatment.The controllability and pore diameter distribution of electrode materials by one-step fixed-point activation were investigated.In addition,bamboo with straight axial pores was used as electrode material to explore the effect of the porous structure on the thickness of electrode material.The directional straight pore structure of bamboo material effectively increases the quality of electrode material per unit area.On the basis of the above results,the one-step fixed-point activation method was applied to bamboo,which could improve the electrochemical performance of bamboo and increase the capacitance per unit area by several orders of magnitude while retaining the bamboo's directional straight hole structure.The main contents of this paper were summarized as follows:Mesoporous carbon was synthesized by hydrothermal method with m-aminophenol and hexamethylenetetramine as raw materials,F127 as soft template,trimethylbenzene as pore reamer,sulfuric acid as pH regulator.Then the mesoporous carbon was blended with KOH solution,the reaction of phenolic hydroxyl with KOH was used to realize the fixation of K ions,and the whole activation of porous carbon was realized by one-step fixed-point activation method at high temperature.The results demonstrated that the morphology of activated products could be effectively controlled by controlling the distribution of phenolic hydroxyl groups and regulating the amount of KOH added.The effect of one-step activation conditions on the morphology and structure of the products was systematically investigated.It was shown that the mesoporous carbon materials were gradually changed from coral-like spherical morphology to 3D flake interconnection network structure with the increase of the amount of KOH.The morphology,microstructure,crystal structure,specific surface area,pore size distribution,and surface element composition of the material were further studied by SEM,TEM,XRD,nitrogen adsorption and desorption and XPS tests,and the one-step fixed-point activation mechanism was proposed.Compared with the coral-like spherical morphology by traditional activation,3D flake interconnection network structure by one-step fixed-point activation was more conducive to the contact between electrolyte and electrode materials,which was more conducive to ion diffusion and improved the electrical properties of the electrode materials.In the three-electrode system,the specific capacitance of the fixed-point activated sample reached 375 F g-1 at the current density of 0.5 A g-1,and the mass specific capacitance of 276 F g-1 was still retained when the current density rose to 20 A g-1,which was better than that of the traditional activated sample.Excellent energy density and power density under high current density and excellent cycling stability were shown by symmetrical supercapacitors,which were assembled by fixed point activated sample.In order to explore the influence of the straight axial pore structure of bamboo on electrochemical properties of the electrode materials at different carbonization temperatures,carbon electrode material was directly carbonized at different temperature by using bamboo as the raw material.When bamboo carbon material was used as an electrode,the radial area of bamboo was used as the electrode area of the electrode material and the axial length was used as the thickness of the electrode material.The effects of different carbonization temperatures on the morphology,microstructure,crystal structure,specific surface area and pore diameter distribution,surface element composition and other aspects were investigate by SEM,TEM,XRD,Raman spectrum,nitrogen adsorption and desorption and XPS tests.The results showed that the morphology and structure of the prepared carbon materials were not changed with the increase of carbonization temperature,and the straight axial pore structure of bamboo could be retained completely.When the carbonized bamboo materials were used as electrode materials,the electrode materials prepared at different carbonization temperatures exhibited excellent area specific capacitance.Different from traditional powder electrode materials,the axial straight pore of carbonized bamboo material could significantly reduce the transport resistance of electrolytes and ions in the axial direction of carbon material,and further increased the effective thickness of electrode materials,which significantly improved the electrochemical energy storage capacity of electrode materials in per unit area.When the samples prepared at different carbonization temperatures were used as electrode materials under the current density of 1mA cm-2.the area-specific capacitance of samples were bigger than 20 F cm-2.In order to achieve the overall activation while retaining the morphology and structure of bamboo,one-step fixed-point activation was applied to bamboo through alkalizing the cellulose in the bamboo by KOH.By means of SEM,TEM,XRD,Raman spectrum,nitrogen adsorption and desorption,XPS and electrochemical performance test characterization of carbon materials prepared at different activation temperatures,the optimal activation conditions for fixed-point activation of bamboo materials were explored.The results showed that the bamboo carbon material retained the straight pore morphology and exhibited the maximum specific suface area,pore capacity and area specific capacitance when the sample was activated at 700?.With the increase of activation temperature,the specific surface area,pore capacity and area specific capacitance of the sample were decreased.When the samples were used as electrode material in 6M KOH electrolyte with current density of 1mA cm-2 in the three-electrode test,the mass specific capacitance of the electrode material was kept nearly constant with the thickness when the thickness was less than 2.5mm.Meanwhile,the area specific capacitance was up to 40000 mF cm-2 when the thickness was 2.5mm,which was 40 times higher than that of the traditional powder electrode.Therefore,one-step fixed point activation could be used to activate the material on the basis of retaining the straight pore structure of bamboo,significantly increasing the specific capacitance of the material and greatly improving the energy storage capacity of the materials.