Preparation And Modification Of Porous Carbon And Application In Lithium Sulfur Battery

The lithium sulfur battery has attracted wide attention,because the sulfur as the cathode delivers a high theoretical capacity(1675m Ah g^-1),and abundant reserves,low price and no pollution of sulfur.But,the application of lithium-sulfur battery is limited by the low conductivity of sulfur,“shuttle effect”of polysulfide and volume effect,the best way to solve these problems is to optimize the host material of sulfur.And in many host materials,Carbon materials are widely used as sulfur host material because of their excellent conductivity,controllable specific surface area and good ductility.In this paper,carbon/sulfur composite cathode materials were prepared by optimizing carbon materials to improve the electrochemical performance of lithium sulfur battery.The research content is as follows:（1）Nitrogen and sulfur Co-doped porous carbon（NSPC）was successfully obtained using glucose as carbon source,ionic liquid as nitrogen source and sulfur source,potassium chloride and zinc chloride as templates,after mixed grinding and pyrolysis in inert atmosphere.Low temperature N₂ adsorption-desorption curve and pore size distribution curve indicate that NSPC has a high specific surface area(697.19m² g^-1)and abundant pore structure.When NSPC/S used as the cathode material of lithium-sulfur battery after load sulfur,it has good cycle performance and high reversible capacity 768.8m Ah g^-1 at a current density of 167.5m A g^-1.（2）Nitrogen and sulfur Co-doped hierarchical porous carbon（NSHPC-X）was prepared by activating the NSPC with KOH.When the mass ratio of NSPC to KOH is1:3,the specific surface area of the hierarchical porous carbon material（NSHPC-3）increases from 697.19m² g^-1 to 1290.67m² g^-1.When NSHPC-3/S used as the cathode material of lithium-sulfur battery after load sulfur,the specific discharge capacity increases to 1229.2m Ah g^-1 when the current density is 167.5m A g^-1.After rate test on NSHPC-3/S,it is found that when its current density recovers from 3350m A g^-1 to167.5m A g^-1,the charge/discharge specific capacity almost recovers to its initial value,which is 80%of the discharge capacity of the first cycle.At the same time,the polar adsorption experiment also proved that NSHPC-3/S had strong adsorption capacity for polysulfides.（3）Nitrogen and sulfur Co-doped carbon and reduced graphene oxide composites were successfully prepared by hydrothermal method and calcination process（r GO@NSC）.The morphology,structure and element distribution of r GO@NSC were studied by SEM,XRD,XPS and other analytical methods.The results show that r GO@NSC are composed of layered graphene and nitrogen-sulfur co-doped carbon spheres.When r GO@NSC/S used as the cathode material of lithium-sulfur battery after load sulfur,it has an initial specific capacity of 1334.2m Ah g^-1 when current density of 167.5m A g^-1,it still has a capacity of 588.4m Ah g^-1when after 100 cycles,it has smaller impedance and faster diffusion rate of Li⁺.When the current density is reduced from 3350m A g^-1 to 167.5m A g^-1,the reversible capacity is almost restored to its initial capacity.