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Preparation Of Biomass Porous Carbon And Its Application In Lithium-sulfur Batteries

Posted on:2019-06-05Degree:MasterType:Thesis
Country:ChinaCandidate:Q L LiFull Text:PDF
GTID:2321330566468064Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
With the emergence of new technologies,new energy products have attracted more and more attention,therefore,people have put forward higher requirements for the energy density and fast charging-discharging capacity of commercial batteries.The current commercial lithium ion batteries are not meet peoples demand due to theirs low energy density.However,when the sulfur is used as cathode material,the theoretical energy density of the battery is up to 2600 Wh/kg,and the theoretical specific capacity is 1675 mAh/g,and sulfur is abundant in natural world and low cost,therefore,the researchers consider that lithium sulfur battery is the most potential secondary energy storage system.But the sulfur cathode is facing the problems,such as poor conductivity of sulfur,the dissolution of intermediate products polysulfide ion and the volumetric strain during the process of charging-discharging.Porous carbon materials have high specific surface area and abundant pore size,which can provide sufficient sites of adhering for active substances,and the micropores have strong capillary action,the porous carbon have restrictive function for polysulfide ions,and the carrier is flexible and porous,which can relieve the volume change of the cathode during the cycle process,it is expected to improve the cycle performance of the battey.Therefore,this paper uses the cheap and renewable agricultural waste as the carbon source to prepare the biomass porous carbon by simple chemical activation method,and then compounded with the elemental sulfur to prepare the sulfur/carbon composites,and the electrochemical performance was studied.Finally,the process of preparation for sulfur/carbon composites was discussed.The concrete content of the work is as follows:(1)Using corn bracts as carbon source,KOH as activator,two kinds of biomass porous carbons were prepared by one step carbonization and two step carbonation respectively.The porous carbon(T-ACBs)was prepared by the two carbonization method has ultrahigh specific surface area(1330.0 m2/g)and rich pore volume,and lamellar structure like graphene.The initial discharge capacity of S/T-ACBs composites can reach 1056 mA h/g at room temperature at the rate of 0.1 C,after 50 cycles,the capacity retention rate is 57%,the cells show good cycling performance in the cycle process.(2)Two kinds of biomass carbon were prepared by one step carbonization and two step carbonization,using the corn core as the carbon source,and KOH as activator.Compared with the biomass carbon material(T-ACC)was prepared by the two carbonization process,the biomass carbon material(O-ACC)was prepared by the first activation method has a high specific surface area(1207.5 m2/g),rich pore size and thinner carbon wall,and then composited with elemental sulfur,the S/O-ACC composites materials were obtained.The S/O-ACC electrode has good cycling performance and Kulun efficiency,and its first discharge capacity can reach 1050 mA h/g,after 50 cycles,the capacity retention rate was 49.5%at the rate of 0.1 C,and the coulombic efficiency is above 98%.(3)Two kinds of biomass porous carbon were prepared by one step carbonization and two step carbonization with banana peels as carbon source and KOH as activator,the carbon material(T-ABPs)was prepared by two carbonization has ultrahigh specific surface area(2044.6 m2/g),and the carbon material with holes in the present hole,cooperation development of big and small hole size,the carbon wall with ravine sags and crests.And then composited with elemental sulfur,the S/T-ABPs composites materials were obtained.The first discharge specific capacity of the S/T-ACBs electrode can reach 1351 mA h/g at 0.1 C and can maintain 351 mA h/g after 300 cycles at 1 C.The rate performance of the battery was tested,after 10 times every rate,the cell shows good reversible capacities of about 960 mAh/g?790 mAh/g?600 mAh/g?400 mA h/g and 300 mA h/g at 0.1 C,0.5 C,1 C,2 C,and 3 C,respectively.What is more,after 5 C rate,when the rate is switched to 0.1 C again,the capacity of the electrode resumes to approximately 940 mA h/g.It shows that the electrode has stable structure and good specific capacity reversibility.(4)The above loading sulfur methods were melting method.T-ABPs with excellent structure was used as carbon source,and then composited with elemental sulfur by ball milling,chemical method and high temperature heating treatment,and the electrochemical properties of these electrode materials were tested.It is found that the sulfur content is near the standard volume(60%)when the active substance sulfur is 1.5 times of theoretical content,the specific capacity of the battery only reducted 16%after 5 cycles,and shows 50%capacity retention over 50 cycles.That sulfur/carbon composites were prepared by melting method were treated at high temperature for 2 h,the cycle performance of the battery is obviously improved.
Keywords/Search Tags:lithium sulfur battery, biomass porous carbon, sulfur/carbon composites materials, loading sulfur method, electrochemical performance
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