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Preparation And Modification Of Polyanion-Type Lithium-Ion Battery Cathode Materials

Posted on:2019-07-13Degree:MasterType:Thesis
Country:ChinaCandidate:M LiFull Text:PDF
GTID:2321330569495703Subject:Engineering
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The rapid development of science and technology has not only brought about a rapid increase in people's living standards,but also an increased demand for resources and energy.While limited fossil energy sources are gradually depleted,energy and environmental issues have become increasingly prominent.As a result,new clean primary energy technologies are constantly being developed by people,and energy storage equipment problems have followed.Lithium-ion batteries have become the most promising electrochemical energy storage devices today and in the future thanks to their clean,environment-friendly,high-quality,high-efficiency and other advantages.Especially in this century's new energy automotive revolution,lithium-ion batteries will be the most important.One of the characters.The cathode material is the most important part of the lithium-ion battery,which determines the voltage platform,specific capacity of the battery and affects many other electrochemical properties.In the decades of research,polyanion-type positive electrode materials have gradually emerged,among which phosphate-based lithium iron phosphate?LiFeO4?and lithium vanadium phosphate?Li3V2?PO4?3?have attracted the most attention.They have a very high specific capacity and voltage platform,structural stability,and excellent cycle performance,non-toxic environmental protection,low cost,is the most promising potential for lithium-ion battery cathode material.However,they still have the disadvantages of low electron conductivity and low lithium ion diffusion efficiency.This is also the main research point of the people.First of all,the Li3V2?PO4?3 material is studied from the perspective of the preparation process.V2O5,Li2CO3 and NH4H2PO4 were used as vanadium source,lithium source and phosphorus source respectively,and tartaric acid was used as reducing agent and carbon source to prepare Li3V2?PO4?3/C material by sol-gel method.First,different calcination temperatures?700?and 750??were used to investigate the effect on the phase of the material sample;after the liquid phase reaction,different acid and alkali conditions?PH=4 and PH=9?were used to examine the difference.The phase difference and electrochemical performance of the sample under different conditions.XRD,SEM and various electrochemical testing methods were used in the experiment.Finally,the acidic condition?PH=4?was obtained,and the sample obtained under the calcination condition of 750?.had the best performance.At the 1C rate,the initial discharge specific capacities of 106.3 mAh/g and 133.4 mAh/g were obtained in the voltage ranges of 3.0 to 4.3 V and 3.0 to 4.8 V,respectively.Then,this paper innovatively introduces hydrotalcite-like?LDHs?materials to surface-enhance modification of LiFeO4.First,under the carbothermal method,LiFeO4 was prepared with Li2CO3,FePO4·4H2O and NH4H2PO4 as the main raw materials.NiNO3·6H2O,Al?NO3?3·9H2O and CO?NH2?2 were used as raw materials to prepare Ni-Al-LDHs by one-step hydrothermal method.Afterwards,LDHs were mixed into LiFeO4 at different mass fractions?20%,40%,and 50%?by mechanical milling.The resulting composites were subjected to a series of characterization analyses and electrochemical tests.Finally,it is concluded that when the mass fraction of LDHs is 20%,the composite has the best electrochemical performance,the difference of the oxidation peak and reduction peak potential is significantly reduced,and the electrochemical reversibility is strengthened.At a 1C rate,the discharge specific capacity reached 142 mAh/g,which was significantly higher than that of the original lithium iron phosphate material.Finally,lithium source was introduced into the LDHs material to prepare ternary Li-Ni-Al-LDHs materials,and the modification effect of LDHs materials on lithium iron phosphate materials was further explored.In the experimental part,similar to the previous chapter,the materials of LiFeO4 and LDHs were prepared using the carbothermal reduction method and one-step hydrothermal method,respectively.Subsequently,according to the new mass fraction?10%,15%,20%?,the new LDHs and Li Fe O4 were mixed by ball milling.After a series of electrochemical tests,15%of the samples showed the best performance.Under the 1C rate,the discharge specific capacity reached 150.2mAh/g.
Keywords/Search Tags:Lithium-ion battery, lithium iron phosphate, LDHs, lithium vanadium phosphate, surface coating
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