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Preparation Of MOF Derivatives And Its Application In Cathode Material Of Lithium-sulfur Batteries

Posted on:2021-07-01Degree:MasterType:Thesis
Country:ChinaCandidate:J YaoFull Text:PDF
GTID:2531306113993409Subject:Mechanical engineering
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With the increasingly serious energy crisis and the rapid development of energy storage technology,lithium-sulfur(Li-S)batteries have become the most research-oriented research and development projects since lithium-ion battery systems due to their low cost,high energy density,and safety and non-toxicity.Application prospects of energy storage battery systems.However,serious volume expansion,easy loss of active materials,and poor electrical conductivity during charging and discharging cause its poor electrochemical performance,which limits its industrial application.Because of the advantages of adjustable pores,structural diversity,and unsaturated metal sites,metal-organic framework materials(MOFs)have gradually become a focus of research.In order to solve the problems of poor conductivity of the MOF material itself,through the combination of carbonization and carbon material coating and other characteristics of the metal-organic frame material itself,high-performance,high-cycle,long-life lithium-sulfur battery anode materials can be obtained.The main research contents are as follows:(1)The metal-organic framework MIL-88-Fe is used as the base material,and modified by high-temperature carbonization and carbon nanotube composite.The results show that:(a)The metal-organic framework material MIL-88-Fe,the porous MIL-88-Fe-500 composite material obtained at a carbonization temperature of 500℃can obtain good electrochemical performance.The S/Fe2O3@C composite material is The initial discharge specific capacity at 0.05 C is 993.3 m Ah/g,and it can maintain 590.04 m Ah/g after 70cycles.At the same time,the comparison with porous carbon and porous Fe2O3 materials has confirmed that its good electrochemical performance is due to the composite effect of Fe2O3 and C;(b)When the CNT addition amount is 50mg,a good cycle stability cycle can be obtained.Maintaining 398.5 m Ah/g after 96 cycles is better than MIL-88-Fe material.(2)The metal-organic framework pacs-Fe is used as the base material to improve the performance of lithium-sulfur batteries through carbonization modification.Because of the addition of the organic ligand DMPU,pacs-Fe can split the pores,which can ensure the uniform distribution of elemental sulfur,and strengthen the physical restraint on polysulfides.The results show that the S/pacs-Fe composite has an initial discharge specific capacity of 787.5 m Ah/g at 0.1 C and maintains 208.5 m Ah/g higher than MIL-88-Fe battery cycle performance after 100 cycles.After carbonization modification,the initial discharge specific capacity of S/pacs-Fe-500 at 1 C is 366.6 m Ah/g,and it can be maintained to 316.3 m Ah/g after 76 cycles,showing a high high rate charge-discharge performance.(3)With metal-organic framework Fe-soc as the base material,the highly sym-metrical and stable azotetracarboxylic acid can alleviate volume expansion,inhibit polysulfides,and improve battery cycle performance.By adding carbon nanotubes and reduced graphene oxide,battery performance is improved.The results show that:S/Fe-soc@r GO has a high initial discharge specific capacity of 1634.3 m Ah/g at 0.1 C and a good specific capacity retention rate is stable at 865.7 m Ah/g after 100 cycles.A high reversible discharge specific capacity of 638 m Ah/g was obtained after 200 cycle at 0.5C.The article uses three Fe-based metal organic framework materials as substrates to prepare lithium-sulfur battery cathode materials.In terms of MOF,it can be found that Fe-soc is significantly better than the other two MOFs.This is because the symmetric and stable cubic structure can increase sulfur.Utilization while buffering volume expansion.The carboxyl and nitrogen elements in azotetracarboxylic acid can assist in the adsorption of sulfur and polysulfides.Can get higher performance of lithium-sulfur batteries.After modifying them separately,the battery performance has also been improved,but S/Fe-soc@r GO is the best.This is because of the synergistic effect of Fe-soc and r GO,r GO improves the electrical conductivity of the composite itself,and assists Fe-soc to bind sulfur and polysulfide,accelerate electrolyte infiltration,improve the ion electron transfer rate,and thus improve lithium sulfur Battery cycle stability and high rate performance.
Keywords/Search Tags:Lithium-sulfur battery, Cathode material, Metal organic frame material, Composite material
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