锂离子电池正极材料锂镍钴氧的制备及改性研究

【作者】 禹萍；

【导师】 苏玉长；

【作者基本信息】 中南大学 ， 材料物理与化学， 2002， 硕士

【摘要】 本论文采用固相混合和液相化学法在高温热处理下制备了锂离子二次电池用的具有层状结构的LiNi_1-xCo_xO₂正极材料及LiNi_0.7Co_0.3-xM_xO₂（M=Al，Mn）材料；利用X射线衍射法、扫描电镜、微电极循环伏安法及恒电流充放电测试等，研究了合成材料的结构和电化学性能，主要结论如下： 1．比较了两种不同制备方法制得的LiNi_1-xCo_xO₂正极材料结构和电化学性能发现，采用液相化学法制得的LiNi_1-xCo_xO₂固溶体材料其固溶效果、阳离子有序度及电化学测试容量、循环性能均明显优于采用固相混合制得的LiNi_1-xCo_xO₂材料； 2．对不同热处理烧结工艺制得的LiNi_1-xCo_xO₂固溶体的结构和电化学性能研究发现，认为750℃下热处理20小时为最合适的合成工艺；对不同掺Co量的LiNi_1-xCo_xO₂固溶体的研究发现，当x=0.4时，LiNi_1-xCo_xO₂材料的电化学综合性能最好；但研究发现，制备的LiNi_1-xCo_xO₂正极材料在恒电流充放电过程中存在一定的极化现象，且材料的结构仍不稳定，循环性能仍有待于进一步提高。 3．固相法制备的LiNi_0.7Co_0.3-xM_xO₂（M=Al，Mn）样品具有与层状结构LiNiO₂相同的晶体结构。研究发现在锂镍钴化合物中掺Al虽可稳定化合物的结构，但掺入量不宜太多，认为掺入量x应小于或等于0.10；750℃是最适宜的合成温度，在这个温度下制备的样品的结构和电化学循环性能较好； 4．随着Mn固溶量x的增加，I_（003）／I_（104）的比值减小，阳离子的无序度增加，因此在LiNi_0.7Co_0.3O₂中掺Mn量x也不宜超过0.10。电化学测试发现，掺Mn量为0.10的LiNi_0.7Co_0.3-xMn_xO₂样品和LiNi_0.7Co_0.3O₂相比，充放电平台上升，充放电容量增加，且循环性能也明显增强。更多还原

【Abstract】 Layered structure LiNi_1-xCo_xO₂ positive materials and LiNio LiNi_0.7Co_0.3-xM_xO₂ （M=A1, Mn） materials of lithium ion secondary batteries were prepared by solid phase mixing reaction and liquid phase chemical methods in this paper. Their crystal structures and electrochemical performances were studied by using XRD, SEM, micro-electrode cyclic voltammetry, galvanostatic charge/discharge test and measurement and so on. The conclusions were showed as following:1. Compared the crystal structures and electrochemical properties of LiNi1_xCoxO2 positive materials which were synthesized by different methods, it could be discovered that the effect of solid solution, the degree of order of cations, charge-discharge capability and cyclic performances of LiNi1-xCoxO2 solid solution prepared by liquid phase chemical method were superior to those of LiNi1_xCoxO2 prepared by solid phase mixing reactio.2. The characters of LiNi1-xCoxO2 solid solution synthesized by different technological conditions, including XRD and electrochemical behavior were studied. The results showed that the optimum heat treatment technological condition was 750 C for 20 hour. As to different x values of LiNi1-xCoxO2 solid solution ,we found that electrochemical behaviors of LiNi0.6Co0.4O2 were better than the others. But obviously polarizations of LiNi1-xCoxO2 solid solution were occurred in the process of galvanostatic charge/discharge. The cyclic performances should be improved.3. LiNio.7Co0.3-xMxO2（M=Al, Mn） prepared by solid phase mixing reaction had the same crystal structures with LiNiO2 layered structure. It revealed that mixing Al to LiNi1-xCoxO2 composition can stabilize their layered structure, but the values of x should be less than 0.10; 750 C were the optimum temperature because that LiNi1-xCoxO2 composition prepared at this temperature showed better structure and electrochemical behavior;4. With x of mixing Mn increasing, the ratio of I（003）/I（104） decreased, the degree of order of cation increased. From the electrochemical behavior, we could conclude, compare to LiNi0.7Co0.3O2, LiNi0.7Co0.20Mn0.10O2 had higher charge-discharge platforms, more.更多还原