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Research On The Resin Based Porous Carbon/sulfur Composite Cathod For Lithium-sulfur Batteries

Posted on:2020-04-08Degree:MasterType:Thesis
Country:ChinaCandidate:M M ShiFull Text:PDF
GTID:2381330596979141Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
Lithium-sulfur batteries are expected to become a new generation of energy storage system,because of their high theoretical energy density(2600 Wh/kg)and theoretical specific capacity(1675 mA h/g),abundant sources of sulfur cathode materials,low price and environmental protection However,the poor conductivity of sulfur cathode materials,large volume changes,and the solubilitly of intermediate products during charging and discharging lead to low cycle performance and rate performance,which limit the practical application of Li-S batteries Therefore,sulfur cathode materials are usually combined with various conductive carbon materials to impro,ve their electrochemical properties In this paper,carbon aerogels synthesized from resin based porous carbon materials are used as cathode materials for Li-S batteries Graphene/carbon aerogel composites are prepared by introducing graphene nanosheets,and graphene can provide fast electron channels.At the same time,carbon aerogels are used as c-ontainers for S storage.In addition,rare-earth metal oxide nanoparticles were used to modify the resin carbon aerogels to enhance the chemical adsorption ability of the matrix materials to pol ysulfide The specific work is as follows(1)resorcinol(R)and formaldehyde(F)were used as precursors,and sodium carbonate anhydrous(C)was used as a catalyst to prepare gel in aqueous solution Then,it was freeze-dried and carbonized to form carbon aerogels.The influence of catalyst content on the morphology,specific surface area and pore size distribution of carbon aerolgels was also investigated The carbon aerogels containing mesoporous structure were further activated by KOH,and the hierarchical pore structure containing microporous mesoporous materials was prepared.The S content of the composites was characterized by the traditional melting method,and their electrochemical properties were characterized The results show that the activated carbon material(A-CAs-4)has a large specific surface area(1837.4 m2 g-1)and a large pore volume(2.276 cm3 g-1).The first discharge specific capacity is 1260 mAh g-1 at 0.1 C.After 500 cycles at 1C,the capacity remains at 229 mAh g-1,The performance is superior to that of other materials prepared,due to their hierarchical porous structure.It is worth mentioning that the charge discharge curves of microporous carbon aerogels without KOH activation have three platforms,while the extra low voltage platform is due to the small molecular sulfur(S2-4)in the micropores.(2)The carbon aerogel/graphene composites were formed after freeze-drying and carbonization by introducing different amount of graphene oxide(GO)into the polymerization process of resorcinol and formaldehyde.GO has abundant functional groups,which can be used as the nucleation sites of organic gels,and can also be used as catalysts to change the morphology and affect the pore size distribution and specific surface area.After carbonization,graphene nanosheets can be used as high-speed electron channels,and porous carbon aerogels can be used as storage containers for S.The results show that the specific surface of the carbon aerogel/graphene(CA/GNs0.1)composite is 665.477 m2 g-1 and the pore volume is 0.912 cm3 g-1.The carbon/sulfur composites(CA/GNs0.1/S)were used as cathode materials.The first discharge specific capacity was 1501 mAh g-1 at 0.1 C.The specific capacity could be maintained at 471 mAh g-1 and 341 mAh g-1 after 100 and 500 cycles at 1 C.(3)The preparation of rare earth metal oxide nanoparticles(Gd2O3)embedded in carbon aerogel composites(Gdx-CA)by in-situ polymerization and subsequent pyrolysis process.Gd2O3 nanoparticles(redox potential at 1.58V verse Li/Li+)can provide abundant active sites,bind large amounts of active materies by chemical adsorption,and provides nucleation sites for sulfur and lithium sulfide(Li2S).Despite the strong adsorption capacity of micropores,the open structure can not effectively bind active materials.Therefore,the combination of the two methods can significantly improve the electrochemical performance of sulfur electrodes.The results of electrochemical performance showed that the sulfur cathode with Gd2O3 exhibited more stable cycle performance and excellent rate performance.Especially,for S/Gd2-CA electrodes,the first discharge specific capacity of 1210 mAh g-1 at 0.1 C.The specific capacity of S/Gd2-CA electrodes can be maintained at 317 mAh g-1 and 233 mAh g-1 after 100 and 350 cycles at 1 C.The results show that the addition of rare earth oxide particles can significantly improve the cycling performance of the materials,especially in high rate discharge.
Keywords/Search Tags:Lithium-sulfur batteries, carbon aerogel, graphene nanosheets, rare-earth oxide, electrochemical performan
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