Preparation And Electrical Conductivity Of Cotton Stalk Based Biochar

Since the development of lithium-ion battery,it has become the most widely used energy storage medium in the world by virtue of its long life,high charge discharge voltage and excellent energy density.With the continuous growth of human demand for energy storage materials and media,and the continuous improvement of the performance requirements of lithium-ion batteries,the global graphite reserves can not meet people’s demand for the preparation of energy storage materials in the future.Therefore,it is necessary to find a new anode material to replace graphite.Cotton straw is a common agricultural waste,and its utilization rate is very low.Using cotton straw as anode material to prepare lithium-ion battery,on the one hand,it can realize the resource reuse of agricultural waste,on the other hand,it can also reduce environmental pollution,which has high ecological and environmental protection value.In this paper,the waste cotton straw around Tarim University was used as raw material to prepare biochar by direct pyrolysis method and activator activation method,and the morphology of biochar was characterized.Then the samples prepared by these two methods were used as anode of lithium-ion battery,and the conductivity of lithium-ion battery was tested.The main research contents and conclusions are as follows:（1）The electrical conductivity of the biochar of cotton stalk was prepared by direct pyrolysis:remove the root and branch of cotton straw,take the main part of cotton straw as raw material,and put it into muffle furnace to pyrolysis at 550,650 and 750℃.The physicochemical properties of the biomass carbon from cotton straw were analyzed,and the electrochemical properties of the carbon were analyzed based on the analysis.The specific surface area of the samples were 1.89,2.09 and 1.72 m²·g^-1,,and the pore sizes were 6.88,7.21 and 3.63nm respectively.The lithium-ion battery was prepared as the negative electrode material.After 100 charging and discharging with a small current density of 0.1C,the specific discharge capacity of the battery was 49.1,157.2 and 62.1 m A·h/g respectively.Then,500 charging and discharging were carried out with 1C high current.The discharge specific capacity of the three samples at different temperatures was 65.3,104.4,79.2 m A·h/g.The results show that the electrochemical properties of the materials are positively related to the physical and chemical properties.（2）The electrical conductivity of cotton straw biochar was prepared by activator activation method:the porous biomass carbon based on cotton straw was prepared by using cotton straw as raw material and anhydrous calcium chloride as activator.The micro morphology and structure of the samples were characterized by different characterization methods,and the electrochemical properties of the samples were tested and analyzed.The results showed that the specific surface area of the pyrolysis cotton straw at650℃reached 487.68 m²·g^-1,while the average pore size,total pore volume and microporous volume were 5.97nm,0.67 cm³·g^-1and 0.1 cm³·g^-1respectively,which showed that the structure of the pore had better pore structure.The first discharge capacity of lithium-ion battery was 1533.5 m A·h/g at a low current density of 0.1C.The specific discharge capacity of the lithium-ion battery was 570.1 m A·h/g after100 cycles.The discharge specific capacity of the battery was 596.1 m A·h/g after 500 cycles at high current 1C ratio,which showed that the sample had good ratio performance and cycle performance.（3）The effects of anhydrous calcium chloride on the physicochemical properties and electrochemical properties of cotton straw based porous biochar were studied.The results show that the samples prepared by the two pyrolysis methods are amorphous carbon structure.The graphitization degree,specific surface area and pore size of the samples prepared by the activation method are better than those prepared by the direct pyrolysis method.The samples prepared by the direct pyrolysis method have larger pore size,higher disorder degree and better stability.Due to the change of specific surface area and mesoporous structure of biochar by activator,the electrochemical performance of biochar prepared by activation method is much better than that prepared by direct pyrolysis method.