| With the development of society,the demand for high energy density battery energy storage systems is becoming more and more urgent.Currently,the density of commercial lithium-ion batteries such as lithium iron phosphate,lithium cobaltate,lithium manganate,and ternary lithium are very low.For example,the theoretical specific capacity of lithium iron phosphate is 170 mAh g-1,and the theoretical energy density is about 170 Wh Kg-1,which has been gradually failed to meet the market demand.Therefore,it is necessary to develop a battery energy storage system with high energy density.Lithium-sulfur battery has been extensive focused due to its high theoretical specific capacity and theoretical specific energy,which are 1675 mAh g-11 and 2600 Wh Kg-1,respectively.However,the active substance sulfur in lithium sulfur batteries is an insulator of electrons and ions.During the charge and discharge process,the polysulfide shuttle effect and volume expansion and contraction would occur,and the volume change is as high as 80%,which would cause problems such as collapse of the battery structure.Carbon materials can be used as a holder of sulfur to alleviate the problem of shuttle and sulfur insulation of polysulfide to some extent because of its excellent conductivity and pore structure.In this paper,carbon materials were prepared by using natural polymer rush and self-synthesized polymer polypyrrole as carbon source,and applied to lithium-sulfur batteries.The research on high-energy density lithium-sulfur batteries was carried out.The specific research contents are as follows:（1）Using natural polymer rush as a carbon source,three biomass carbon materials DXC,KOH-DXC,MOF-DXC were prepared by direct carbonization,activation of potassium hydroxide and compounding with MOF materials.And the morphology and structure were analyzed by SEM、Raman and XRD.The results showed that the carbonaceous material obtained from the rush mainly exists in an amorphous state.The rushing grass directly carbonized is tubular carbon.The diameter of the tube is about 10μm.It was carbon sheet when treated with potassium hydroxide.And there were many holes at different sizes on the carbon wall.The pore diameter is basically less than 500 nm.After compounding with MOF material,the shape of the carbon tube still remained.And there were many granules attached to the tube wall at the size of 150nm.The prepared carbon and sulfur were composited by melt method to prepare a high-loading carbon sulfur composite.The sulfur contents of the carbon sulfur composites DXC/S,MOF-DXC/S and KOH-DXC/S were about 82%,81.5%and 79%respectively.The electrochemical performance was analyzed by electrochemical workstation and battery test system.The capacity of KOH-DXC/S composite could reach to1200mAh g-1 at a current density of 0.1C,and the capacity of MOF-DXC/S was 900 mAh g-1.DXC/S capacity was only about 600 mAh g-1,which showed that the performance of the lithium sulfur battery from carbon-based rush could be improved after modified.（2）Nitrogen-doped carbon was prepared by using self-made poly-polypyrrole as carbon source,and nitrogen-phosphorus double-doped carbon material was prepared phosphoric by anhydride as the source of phosphorus.The morphology and structure were analyzed by SEM,Raman,XPS and XRD.The electrochemical properties were analyzed by electrochemical workstation and battery test system.The results showed that the carbon material prepared by using polypyrrole as carbon source is granular and has a high degree of graphitization.The lithium-sulfur battery made of N-doped-carbon has a specific capacity f up to 1660 mAh g-1 at a current density of 0.05 C,and the lithium-sulfur battery prepared by nitrogen-phosphorus double-doped carbon could have a sulfur loading on the electrode of13.2mg cm-2,the area ratio of the battery could reach to over 10mAh cm-2,which is very meaningful for the preparation of high energy density lithium-sulfur batteries practical use. |
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