Preparation And Electrochemical Performance Of Porous Carbon Materials For Lithium-sulfur Battery Cathode Materials

Lithium-sulphur batteries,as the next generation lithium batteries,have the advantages of high specific capacity(1675 mAh?g^-1)and energy density(2500Wh?Kg^-1)that traditional lithium-ion batteries can not achieve.At the same time,sulphur,the cathode materials of lithium-sulphur batteries,also have the advantages of abundant reserves,easy access,low price and environmental friendliness.Therefore,it is necessary to study lithium-sulphur batteries at a time when traditional lithium-ion batteries are hardly to meet the needs of high-speed developing modern electrical appliances.Due to the limitation of the characteristics of sulfur,it is hardly to use sulfur as lithium-sulfur battery cathode materials directly.The lithium-sulfur battery cathode needs special composite materials designed to make the lithium-sulfur battery show better electrochemical performance.In this paper,several kinds of carbon composites were designed,fabricated and applied to lithium-sulphur batteries.By evaluating the electrochemical performance of lithium-sulphur batteries fabricated by composite materials,continuously optimizing the preparation process,materials with good electrochemical properties were obtained and characterized by XRD,SEM,EDS,BET and FT-IR.The main contents are as follows:1.Cobalt-carbon-nitrogen uniformly distributed composite carbon material was obtained by heat treatment and carbonization of metal-organic frame material.The influence of various variables in heat treatment on the composite material was discussed by controlling variable method.The results showed that the material prepared had the best electrochemical performance by heating at 5°C·min^-1 to 900°C for 3 h and treating with CO₂ gas for 1 h.The first discharge point specific capacity of lithium-sulphur batteries prepared by composite materials can reach 106.32 mAh?g^-1.After 50 cycles,the discharge specific capacity of lithium-sulphur batteries can keep 614.29 mAh?g^-1.2.Sol gel method was used to grow spherical phenolic resin on the surface of carbon nanotubes.Carbon nanotubes and mesoporous carbon spheres were successfully prepared through a series of heat treatment processes.The composition and structure of carbon nanotubes and mesoporous carbon sphere composites were analyzed.Finally,the effects of various variables on the composites were discussed.It was found that the heterogeneity of space stacking of carbon nanotubes and mesoporous carbon spheres composites increased compared with pure mesoporous carbon nanospheres NMC.However,due to the restraint of carbon nanotubes,the structural stability of the composites was enhanced,and the optimum heat treatment process was 800°C.The first discharge capacity of CNT-NMC is 1293.49 mAh?g^-1 after holding for 3 hours,then heating up to 900°C and treating with CO₂ gas for 1 hour.The cycle stability of CNT-NMC is better than that of NMC after the fifth cycle.3.Metal-organic framework materials were adsorbed on the surface of carbon nanotubes by chemical adsorption and heat treatment.CNT-Co-N-C,a cobalt-containing and nitrogen-containing porous carbon composite joined by carbon nanotubes,was successfully obtained.Finally,CNT-Co-N-C under the optimal heat treatment process was obtained by exploring the heat treatment process.Compared with Co-N-C,it was found that its electrochemical properties were improved for the first time.The specific discharge capacity is 1405.73 mAh?g^-1,and still reaches 998.67 mAh?g^-1 after five cycles.It has good electrochemical performance.