Preparation Of Three-dimensional Graphene Powder And Its Application In Lithium-sulfur Batteries

Graphene has excellent electrochemical,thermal and optical properties,and has broad application prospects in the fields of energy storage,catalysis and adsorption.Lithium-sulfur battery is a promising lithium battery.Its theoretical en ergy density is 5 times that of current lithium ion.However,the poor conductivity of active material sulfur and the shuttle effect caused by the dissolution of polysulfides in the reaction will cause rapid capacity decay.The three-dimensional graphene structure has a large number of active sites,which is conducive to material loading and reaction,and has a good conductive network,which can promote the transmission of ions and electrons in the battery and accelerate the electrochemical reaction.The preparation of three-dimensional graphene powder and its application in lithium-sulfur battery cathode materials is an effective research direction.This research mainly studies the preparation of three-dimensional graphene powder and its application in lithium-sulfur battery cathode materials.Carbon is deposited on the surface of the silica ball by thermal chemical vapor deposition method,and the surface of the silica is coated with carbon.The methane concentration,growth time and growth temperature were changed to grow vertical graphene sheets on the surface of carbon-coated silica balls.At the growth temperature of 1200 ℃,1100 ℃ and 1050 ℃,and the corresponding methane concentrations are 6.3%,14.3% and 20%,three-dimensional graphene with different morphologies can be grown.With a fixed methane concentration of 14.3% and a growth temperature of 1100 ℃,the three-dimensional graphene sheets prepared by prolonging the growth time are denser,and the graphene morphology composed of vertical graphene sheets is better when the growth time is 4 h.Suitable conditions for making three-dimensional graphene on the surface of carbon-coated silica spheres is the temperature of 1100 ℃,the ratio of methane in the mixture of methane and hydrogen is 14.3%,and growth time of 4 h.After etching the silica balls,a three-dimensional graphene powder can be obtained,and the surface has a densely arranged three-dimensional graphene structure with interconnected sheets.The three-dimensional graphene powder and sulfur are combined to prepare the positive electrode of lithium-sulfur battery,which has better discharge specific capacity and cycle stability than the positive electrode whose host material is carbon ball.The three-dimensional conductive network formed by three-dimensional graphene promotes the transport of ions and electrons.And suitable sulfur load can also improve the electrochemical performance of the positive electrode,which can improve the utilization rate of active substance sulfur.However,the positive electrode composed of pure graphene powder and sulfur has a low specific capac ity after cycling,and the performance is significantly improved after adding molybdenum carbide.The initial discharge specific capacity reaches 1423 m Ah/g at a charge-discharge rate of 0.1 C,and 810 m Ah/g after 140 cycles,the charge transfer resistance is only about 10 Ω and it has good rate performance.