锂离子电池正极材料球形LiNi_0.7Co_0.15Mn_0.15O₂的制备及表面包覆改性研究

【作者】 谭欣欣；

【导师】 唐有根；

【作者基本信息】 中南大学 ， 应用化学， 2010， 硕士

【摘要】 近年来,LiNixCoyMnzO2三元材料由于具有电压高、比能量密度高、价格较LiCoO2低廉等优点,一直被认为是LiCoO2的最佳替换材料。本文详细考查了三元材料的研究进展,并以LiNi0.7Co0.15Mn0.15O2为研究对象,对三元材料前驱体共沉积过程的机理和工艺条件、LiNi0.7Co0.15Mn0.15O2的合成以及表面包覆改性进行了研究。(1)通过对比分析Me(Ⅱ)-OH--H2O体系与Me(Ⅱ)-NH3-OH--H2O体系中三种金属离子的共沉积机理得知：加入氨水络合剂,使得三种金属离子在同一pH值范围内达到同时沉降,在热力学上保证了三元前驱体在化学组成上的均一性。考察了pH值、氨水浓度等对Ni0.7Co0.15Mn0.15(OH)2前驱体物理和化学性能的影响,发现制备球形Ni0.7Co0.15Mn0.15(OH)2前驱体的最佳工艺条件为：pH=10.5,氨水浓度为0.4M。(2)以球形Ni0.7Co0.15Mn0.15(OH)2为前驱体,用固相合成技术制备了高密度球形LiNi0.7Co0.15Mn0.15O2正极材料。研究了不同焙烧制度、焙烧温度和配锂量对合成材料性能的影响。确定了最佳合成条件为：Li/Me=1.05,在500℃下预烧6h,再于750℃烧结12h。得到的LiNi0.7Co0.15Mn0.15O2正极材料表现了良好的物理性能和电化学性能：粒度分布均匀；振实密度高达2.32 g/cm3；在3.0-4.3V电压区间的初始放电容量为185.2 mAh/g；循环50轮后,容量保持率为94.77%。(3)研究了LiCoO2/LiAlO2包覆对LiNi0.7Co0.15Mn0.15O2性能的影响。结果表明,LiCoO2/LiAlO2包覆后材料的首轮充放电容量几乎没有改变,但包覆有效地抑制了电解液对LiNi0.7Co0.15Mn0.15O2材料的侵蚀,从而改善了材料的循环性能。同时,包覆LiCoO2/LiAlO2后,LiNi0.7Co0.15Mn0.15O2材料在高电压区间的循环性能也得到了明显的提高。LiCoO2的包覆量为3%,LiAlO2的包覆量为0.7%时,包覆后的LiNi0.7Co0.15Mn0.15O2材料表现出了最佳的电化学性能。更多还原

【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.更多还原