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Research And Development Of Ni-Mn Spinel Cathode Material For High Power Lithium Ion Battery

Posted on:2014-05-05Degree:MasterType:Thesis
Country:ChinaCandidate:S H LiFull Text:PDF
GTID:2251330425480971Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Spinel LiNi0.5Mn1.5O4has received extensive attention as a promising cathode materialfor lithium ion batteries, because of its high operating voltage (4.7V vs. Li) and thus highpower density. This spinel cathode material has two kinds of crystal structures: Fd3m spacegroup structure and P4332space group structure. Since the electrochemical properties aredifferent for the two distinct space group structure, control of the crystal structure through theoptimation of synthesis process is worthy of detailed investigation.In this paper, a series of synthesis methods, including solid state method, coprecipitationmethod, solgel method and hydrothermal method were used to prepare spinel cathodematerial LiNi0.5Mn1.5O4. Based on the optimation of synthesis method, ions dopingmodification has been employed to further improve the electrochemical performance, and theoptimal doping schemes were discussed. Moreover, the coating modification ofLiNi0.5Mn1.5O4with LiV3O8was investigated in detail.First of all, the synthesis processes for cathode material LiNi0.5Mn1.5O4with differentmethods were optimized. The properties of as prepared materials were characterized usingXray powder diffraction (XRD), scanning electron microscope (SEM) and electrochemicalperformance tests. For coprecipitation method, the best sinter process should be20h at800°C.As to solgel method, the optimal molar ratio between the metal ions and the oxalic acid is1:2.Secondly, the spinel material LiNi0.5Mn1.5O4was doping modified with different ions,Series LiMxNi0.5-x/2Mn1.5-x/2O4-yNy(M:one or more cations among (Al,Fe,Co,Cr,Mg) Al, Fe,Co,Cr and Mg; N:one or more anions F;x=0,0.02,0.04,0.07,0.10,0.20; y=0,0.02,0.04,0.07,0.10,0.20) materials were synthesized with different optimized methods. Theeffects of doping modification on the structure, morphology and electrochemical performanceof corresponding materials were discussed in this paper. In conclusion, the moderate dopingmodification has effects on crystallinity and particle uniformity of as prepared materials.Improved cycle performance and rate capability were obtained through ion modification.Thirdly, LiV3O8coated material LiNi0.5Mn1.5O4/LiV3O8was synthesized with differentprocess. The structure, morphology and electrochemical properties of LiNi0.5Mn1.5O4/LiV3O8materials were characterized with XRD, SEM and electrochemical performance analysis. Itshowed that LiV3O8coating results in the reduced the transmission path of lithium ion. Thecycle performance and rate capability were apparently improved by LiV3O8coating.Finally, the cathode material industrialization process was designed on the basis of thecoprecipitation synthetic route in the laboratory.
Keywords/Search Tags:Lithium ion batteries, cathode material, spinel, LiNi0.5Mn1.5O4, high voltage
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