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Preparation of ( 0.15 ) O_2 Surface coating study of lithium ion battery cathode material spherical LiNi_ (0.7) Co_ (0.15 ) Mn_

Author: TanXinXin
Tutor: TangYouGen
School: Central South University
Course: Applied Chemistry
Keywords: Li-ion battery cathode material LiNi0.7Co0.15Mn0.15O2 co precipitation coated
CLC: TM912
Type: Master's thesis
Year: 2010
Downloads: 384
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Abstract


The LiNixCoyMnzO2 system was reported to be the best choice to replace LiCoO2 as Li-ion battery cathode materials due to its high voltage, high energy density and lower cost at present. The research development of LiNixCoyMnzO2 system was summarized, this dissertation emphasizes on layered LiNi0.7Co0.15Mn0.15O2 cathode material. The mechanism and conditions of NixCoyMnz(OH)2 co precipitation process, the preparation of LiNi0.7Co0.15Mn0.15O2 and coating performance were studied.(1) The mechanism of three metal ion co precipitation propcess in Me(Ⅱ)-OH--H2O system and Me(Ⅱ)-NH3-OH--H2O system were contrastively analyzed. The results show that three metal ion would be co precipitated in a same pH range by introduce NH4OH chelating agent, which assured the precursor have a uniform chemical composition. This paper represents details of the optimized spherical Ni0.7Co0.15Mn0.15(OH)2 formation process by control pH, amount of chelating agent. The results indicated that the optimum conditions for spherical Ni0.7Co0.15Mn0.15(OH)2 were that the pH of the aqueous solution is 10.5, and the concentration of NH4OH is 0.4M.(2) Spherical LiNi0.7Co0.15Mn0.15O2 cathode materials with high tap-density were successfully synthesized by mixing uniform co-precipitated spherical Ni0.7Co0.15Mn0.15(OH)2 and LiOH·H2O followed by heat-treatment. The effects of calcination method, temperature and the ratio of Li/Me on layered LiNi0.7Co0.15Mn0.15O2 cathode materials were studied. On this basis, the best synthesis conditions were obtained: Li/Me=1.05, the mixed materials were calcined at 500℃for 6h and then calcined at 750℃for 12h. The obtained LiNi0.7Co0.15Mn0.15O2 cathode material exhibits good physical and electrochemical performance with uniform particle size distribution, high tap-density (2.32 g/cm3), Initial discharge capacity is 185.2 mAh/g in 3.0-4.3V and the capacity retention is 94.77% after 50 cycles.(3) With LiCoO2 or LiA102 coated, coating effects on the performance of layered cathode material LiNi0.7Co0.15Mn0.15O2 were studied. The results showed that the initial charging/discharging capacity almost has no charged after LiCoO2 or LiA102 coated. However, the LiCoO2 or LiA102 coated materials effectively restrain the erosion between electrolyte and LiNi0.7Co0.15Mn0.15O2 cathode material, accordingly, the cycling performance was enhanced. At the same time, the cycling performance in high voltage range of LiNi0.7Co0.15Mn0.15O2 cathode material has been improved by coating LiCoO2 or LiAlO2. The sample coated with 3% LiCoO2 or 0.7% LiAlO2 exhibit good electrochemical properties.

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