Preparation And Electrochemical Properties Of Sisal Fiber Activated Carbons Composites

With the increasing of environment concerns and the development of electronic devices,there was a growing demands for the lithium ion batteries with high energy density.However,the graphitic carbon which was widely used for the anode materials only had a theoretical specific capacity of 372 mAh/g,which could not meet the demands of high specific capacity lithium ion batteries.So it was necessary to develop green and high specific capacity anode materials for lithium ion batteries.Biomasses contained a large amount of carbon.Biomasses carbons could be prepared at low temperature with the protection of N2 by pyrolysis and hydrothermal treatment.Sometimes physical and chemical activation was necessary for improving their properties.Amorphous carbons obtained from biomass such as coconut shell,rice husk,okara,and cocoon had been reported.Sisal was the characteristic plant in Guangxi,China.Sisal had a long life cycle,rich in source,renewable,easy to degrade and free of pollution.Therefore,the utilization and research of the sisal had the significance of sustainable development for agriculture and environmental protection.Sisal fiber was a major by-product in sisal industry,which was a natural plant polymer materials,rich pore,and it could maintain its fiber morphology after carbonization,therefore sisal fiber had the potential value of high capacity anode materials for lithium ion batteries.In this paper,activated carbons composites were prepared with sisal fiber as anode materials for lithium ion batteries.Studied the influence of preparation process on the structure of sisal fiber activated carbons,explored the optimal conditions for preparation of sisal fiber activated carbons,then tested the sisal fiber activated carbons as anode materials of lithium-ion battery.Studied the electrochemical performance of sisal fiber activated carbons by galvanostatic charge-discharge test,cyclic voltammetry test and electrochemical impedance test.The study provided theoretical and experimental basis for using sisal fiber as anode materials for lithium ion batteries.The main research contents were summarized as follows:1.Sisal fiber activated carbons had been prepared by pyrolysis of sisal fibers at different temperatures and hydrothermal treatment after pyrolysis.The obtained sisal fiber activated carbons?SFACs?were subjected to X-ray powder diffraction?XRD?,BET-surface area,SEM,Cyclic voltammetry,Charge-discharge studies and Electrochemical impedance spectroscopy studies.The structures of the SFACs had been changed with the increased pyrolysis temperature and the hydrothermal treatment.The SFACs pyrolyzed at 900 ?with hydrothermal treatment had more micropores than others.The electrochemical tests showed that the SFACs pyrolyzed at 900 ? with hydrothermal treatment offered an extraordinarily high initial capacity of 998 mAh/g and the charge-transfer resistance of 90 ?.The work highlighted the potential to utilize sisal fibers to produce anode materials for lithium ion batteries.2.Iron oxides/sisal fiber activated carbons composites were synthesized by hydrothermal method.The composites were tested by composites characterization and electrochemical test,The results showed that the structure of iron oxides varied with hydrothermal temperatures.As anode materials for lithium-ion batteries,the composites showed a wonderful synergistic effect on the electrochemical performance,and the composites prepared at 120 ?consisted of ?-FeOOH and ?-Fe2O3 mixture phases and exhibited the higher reversible specific capacity and the better cycling stability.3.The MoSe₂-MoO₂/sisal fiber activated carbons composites were prepared by the hydrothermal and the calcination method as the anode materials for lithium ion batteries.The relationship between the preparation conditions and the structure,the electrochemistry performance of MoSe₂-MoO₂/SFACs composites was also explored,and the best preparation conditions were determined.The test results indicated that the MoSe₂-MoO₂/SFACs composites showed a initial capacity of 724 mAh/g and a reversible capacity of 494 mAh/g over 30 cycle number at a current density of 50 mA/g.4.Elemental sulfur was prepared by the chemical synthesis method in the hydrothermal environment,sulfur/sisal fiber activated carbons composites were prepared,and the sulfur was inner and on the surface of the SFACs.Sulfur which was dispersed in SFACs improved the specific discharge capacity of the cathode materials;the microporous of the SFACs effectively decreased the irreversible dissolution of sulfur and its discharge products in the electrolyte which enhanced the reaction activity and improved the utilization of active materials;Sisal fiber activated carbons improved the conductivity of elemental sulfur with its good electronic conductivity.