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Technology Research Of Lithium Iron Phosphate From Iron Phosphate Based On Water

Posted on:2015-09-24Degree:MasterType:Thesis
Country:ChinaCandidate:X G ZhouFull Text:PDF
GTID:2181330431996175Subject:Physical chemistry
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Use FePO4as the raw material to synthesis LiFePO4that used in powerlithium-ion battery. It has the advantage that do not has the issue to be oxidized.Itcan both provide phosphorus source and iron source, its tap density andelectrochemical activity is high. However, the performance of commercial ironphosphate products such as the chemical purity of iron phosphate products, the ratioof iron and phosphorus, the number of crystal water, the content of harmful elementsand the physical property such as primary particle size, secondary particle, particlemorphology, the specific surface area, tap density. It is not clear of the impact toLiFePO4at present. In this paper, the main work is focus ontechnology research oflithium iron phosphate from iron phosphate based on water, including the ratio ofmilling solvent based on water, the types of carbon compounds, sinteringtemperature, the particle size of iron phosphate, the ratio of the raw materials.Themain resultsis as the following:(1)Choice FePO4,LiOH and sucrose as raw material, implore the impact of theelectrochemical performance of LiFePO4,when use a series of different proportionsof the mixed solution of ethanol and water as the milling solvent. The experimenthas shown that with the increasing of water content in the solvent, the dischargeperformance of the material has weakened, the main reason is the generate ofFe(OH)3. The content of Fe(OH)3is higher, the purity of material is lower. Carbonas a reducing agent in the atmosphere is difficult to reduce Fe3+, so it is notconducive to obtain high purity material. Consider from this point,it is agreeable touse LiAc instead LiOH as lithium source to obtain lithium iron phosphate material.(2) When the pH of the solvent that contain water is not adjusted, the capacityof the material is low, the main reason is the generation of Fe(OH)3at higheralkalinity condition, then it affect solid-state reaction process that is the generationof olivine lithium iron phosphate phase.(3) Precursor is calcined at660℃,680℃,700℃,720℃,750℃, and the particle size distribution of the obtained product at different calcining temperature is3.78μm,4.97μm,5.05μm,5.98μm,7.60μm, the initial discharge capacity isrespectively86.2mAh/g,131.0mAh/g,147mAh/g,135mAh/g,119mAh/g at0.1C,so it is better to adopt700℃.(4) Precursor is calcined at700℃for7h,10h,12h respectively, the initialdischarge capacity of the obtained materials is respectively141.6mAh/g,154mAh/g,149.7mAh/g at0.1C. Control the time of high-temperature solid-statereaction around10h is more appropriate.(5) The particle size distribution is respectively0.1~10μm,0.1~14μm,0.1~22.48μm when choose sucrose, glucose, citric acid as the carbon source; theinitial discharge capacity of the materials is respectively142.9mAh/g,140.3mAh/g,79.6mAh/g at0.1C; so it is more appropriate to adopt sucrose as the carbon source.(6) The secondary particle size of iron phosphate material are significantlyreduced after the water-based milling, with the extension of milling time thisreduction trend will gradually become slowly. There is no obvious reaction betweenthe particle size of FePO4and the final particle size of LiFePO4product, the finalparticle size of LiFePO4product may rely on calcining temperature, calcining timeand the ratio of raw materials.(7)Control the use level of raw materials FePO4and LiAc, maintain the ratio ofFe and Li is respectively1:1.04,,1:1.03,1:1.02, then the initial discharge capacityof LiFePO4product is respectively148.2mAh/g,150.1mAh/g,143mAh/g,135.8mAh/g, it is more appropriate to control the ratio of Fe and Li is1:1.036.(8)Control the amount of the residual carbon is5.5%,4.5%,3.5%,3wt%through the content of sucrose, the initial discharge specific capacity of the materialis144.8mAh/g,148.7mAh/g,159mAh/g,154.2mAh/g at0.1Crespectively. Thesample prepared with a residual carbon amount around3.5%has a uniform particlesize distribution and microspherewhich is confirmed by SEM.(9)When controlFe/Li ratio is1:1.036and the carbon content is3.5wt%, thesample prepared at700°Cfor10h delivers a highest capacity of159mAh/g and anexcellent flat potential of3.4V. The capacity retention rate is about96.74%at0.2Cafter10cycles, the capacity retention rate is about92.61%at0.5C after10cycles, the capacity retention rate is about86.76%at1C after10cycles, then come back to0.1C after the above cycles, the capacity has reduced less compared with the initialdischarge capacity.
Keywords/Search Tags:technologicalconditions, FePO4, LiFePO4, particle size, the ratio ofraw materials
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