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Synthesis And Electrochemical Performance Of Biomass Carbon-based Cathode Materials For Lithium-sulfur Batteries

Posted on:2024-07-26Degree:MasterType:Thesis
Country:ChinaCandidate:W H LiuFull Text:PDF
GTID:2531307100961729Subject:Biology and Medicine
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Lithium-sulfur(Li-S)batteries exhibit high theoretical specific capacity(1675m Ah·g-1)and energy density(2600 Wh·kg-1),thus they are considered as one of the most promising high energy density storage systems.In spite of these significant advantages,there are several problems and challenges that have to be solved for Li-S batteries.For example,the low electron conductivity of sulfur,shuttle effect and loss of active substances caused by the dissolution and diffusion of polysulfides in electrolyte,and the volume expansion of sulfur intermediates during the delithium/lithium intercalation reaction,which directly leads to poor electrochemical performance.Due to the advantages of high conductivity,large specific surface area,heterogeneous element doping and low price,natural biomass-derived carbon materials are widely used as encapsulated sulfur matrix in cathode materials of Li-S batteries,which can greatly improve the sulfur utilization and suppress the shuttle effect.In this thesis,based on natural biomass materials,it is modified by pore-making,polar metal nanoparticles doping and heteroatomic doping,and a reasonable design of sulfur matrix applied in Li-S batteries.The main research contents and results are as follows:1.Nickel nanoparticle-doped corn-derived carbon materials(Ni/PC)were synthesized by instantaneous expansion,nickel salt treatment and high-temperature calcination using corn kernels as precursors,which exhibit excellent electrical conductivity and interlaced multilayer pore structure.The unique porous structure can not only shorten the electron transfer distance and enhance the electrical conductivity,but also relieve the volume expansion of the cathode.The strong interaction between polar metallic nickel nanoparticles and polysulfides can chemically adsorb polysulfides.The modified S@Ni/PC-2 composite cathode has an initial specific capacity of 1103.6m Ah·g-1 at the discharge rate of 0.5 C,and the capacity remains at 579.3 m Ah·g-1 after500 cycles.At 0.1 C,the capacity of the electrode can reach 1288 m Ah·g-1,and the capacity can reach 1189 m Ah·g-1 after continuous charging/discharging at different discharge rates and restored to 0.1 C again.2.Nitrogen-doped bamboo-structure carbon nanotubes(BCNTs)were synthesized using dicyandiamide,nickel nitrate and biomass-derived carbon(PC material without treated with nickel salt in the previous experiment).BCNTs were used as sulfur substrates,and sulfur nanoparticles were chemically in-situ synthesized on their surface to prepare S@BCNTs composite cathode materials.BCNTs have thin tubular walls of only about 8carbon layers,showing high specific surface area and high electrical conductivity.The chemically in-situ synthesized sulfur nanoparticles are small in size,so they can be uniformly distributed on the surface of BCNTs and in close contact with them.The nitrogen atom doping can act as adsorption sites for polysulfides and inhibit their dissolution and diffusion.The S@BCNTs-2 composite cathode with a sulfur content of62.2 wt.%provides an initial specific capacity of 1008.4 m Ah·g-1 at 0.1 C.In addition,when tested at different discharge rates,the S@BCNTs-2 composite cathode still provides a reversible capacity of 964.6 m Ah·g-1 when restored again to 0.1 C.3.BCNTs were first acidified,and then mixed evenly with polyvinylidene fluoride in a certain proportion and pyrolyzed at high temperature.The surface of BCNTs was fluorinated,and finally,they were combined with sulfur to prepare S@FBCNTs-A composite cathode material.Effective doping of fluorine atoms can be performed at the defects,which are caused by the destruction of BCNTs by acidification process.The strong electronegativity of fluorine atoms can improve the electrical conductivity of carbon materials,while exhibiting a stronger affinity for polysulfides and suppressing the shuttle effect.The modified S@FBCNTs-A1 cathode shows a high initial specific capacity of 1407.5 m Ah·g-1(0.2 C).When the discharge rate is increased to 5 C,the capacity can still be maintained at 622.3 m Ah·g-1,and when it is restored to 0.1 C again,its discharge capacity can be restored to 1318.6 m Ah·g-1.
Keywords/Search Tags:lithium-sulfur battery, biomass carbon, cathode, electrochemical performance
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