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Preparation And Application Of Polyaniline/Activated Carbon Composite Material And Modified Lithium Iron Phosphate

Posted on:2020-07-23Degree:MasterType:Thesis
Country:ChinaCandidate:T HanFull Text:PDF
GTID:2381330611499635Subject:Chemical engineering
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As the most widely used conductive polymer,polyaniline(PANI)has the advantages of low cost,environmental friendliness and good redox reversibility.However,pure polyaniline has a serious agglomeration due to its poor conjugate ability,which greatly affects its electrochemical performance.Lithium iron phosphate(LiFePO4)is currently the most popular cathode material for lithium batteries.It has the advantages of high safety,environmental friendliness and wide source of materials.However,its low conductivity and poor diffusion of lithium ions limit its performance.Based on this,the PANI/AC and PANI/AC/CNTs composites were synthesized by using activated carbon(AC)and carbon nanotubes(CNTs)as templates to improve the electrochemical performance of polyaniline.LiFePO4/PANI composites were formed by polyaniline modified LiFePO4 to investigate the effect of polyaniline on the properties of LiFePO4.Firstly,PANI/AC composites were prepared with different contents of activated carbon as template,and a series of state treatments were carried out to obtain composite materials with different states.The optimum electrolyte was prepared by research,and the electrolyte composition was an EC:DEC electrolyte having a lithium ion concentration of 1.6 mol/L.Physical characterization indicates that the reduced composites have higher crystallinity,better morphology and higher specific surface area.CV and EIS tests have shown that the reduced PANI/AC(5%)composite has the best electrochemical performance.The battery charge and discharge test also proved this,the discharge specific capacity reached 154.5 mAh/g at 0.2 C rate,and the capacity retention rate after 100 cycles was 91%.Secondly,CNTs were added to the PANI/AC composites.Polyaniline was modified by AC and CNTs.Different PANI/AC/CNTs composites were prepared by controlling the content of CNTs.Functionalization(carboxylation and benzene sulfonation)of carbon nanotubes was used to synthesize functionalized PANI/AC/CNTs composites.FE-SEM and TEM showed relatively good morphological characteristics when the CNTs content was 5%.FT-IR and XRD indicate that the amount of CNTs in the composite is different and the peak intensity is different.The results of CV and EIS showed that the composites had the best reversibility and capacity performance when the CNTs was 5%,and the battery conductivity was the best.At a current density of 0.2 C,the specific capacity of the 5%CNTs composite reached 160 mAh/g,and the 100 cycle capacity was almost unchanged.Functionalized composites have higher specific capacity,and the discharge capacity of benzenesulfonated PANI/AC/CNTs composites can reach 165 mAh/g at 0.2 C,and only 5%decay in 100 cycles.The poly aniline was formed in situ on the surface of LiFePO4 to synthesize LiFePO4/PANI composite.And it is subjected to dedoping and reduction treatment to obtain composite materials in different states.The polyaniline in different states was mechanically combined with LiFePO4 in different proportions to form a composite material.Physical characterization indicates that the addition of polyaniline changes the functional group,crystallinity and surface structure of LiFePO4 to some extent,in the materials synthesized in situ.The mechanical mixing material has not changed.Among them,the oxidized LiFePO4/PANI(10%)composite has the best comprehensive performance.The discharge specific capacity can reach 158mAh/g at 0.2C current density,and the 100-cycle capacity retention rate is 98%.Hydrochloric acid doped LiFePO4/PANI(5%)composites have the best rate performance,and also have a capacity of 114.6 mAh/g at 0.5C.Finally,the market analysis of the prepared materials,compared with other cathode materials,polyaniline composite materials have the advantages of low cost,low pollution,simple process,etc.,and have broad development space.
Keywords/Search Tags:lithium ion battery, composite material, Polyaniline, activated carbon, Carbon nanotube, lithium iron phosphate
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