XJIPC OpenIR  > 材料物理与化学研究室
Thesis Advisor陈朝阳
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline材料工程
Keyword镍钴锰酸锂 电化学性能 表面改性 锂离子电池

镍钴锰酸锂(LiNi1/3Co1/3Mn1/3O2)三元正极材料自发现以来,就引起了研究者的广泛关注。由于其比容量高、循环性能,低毒性等特点,在动力电池市场具有很好的应用前景,被认为是最有希望取代钴酸锂LiCoO2的锂离子电池正极材料。为了进一步推广镍钴锰酸锂在动力电池市场的应用,其大电流快速充放电性能和极端温度条件下的循环性能有待进一步提高。本论文首先使用水热法和共沉淀法两种不同的方法,制备了镍钴锰酸锂正极材料,并根据电化学性能测试结果,不断优化镍钴锰酸锂正极材料的制备工艺。为了改善镍钴锰酸锂正极材料的循环性能和倍率性能,实验使用悬浮混合法制备了导电陶瓷(Ti3SiC2)改性镍钴锰酸锂正极材料。通过导电陶瓷对镍钴锰酸锂的表面修饰,有效增加了锂离子和电子的扩散速率,减小了锂离子和电子材料的界面阻抗和电荷转移阻抗,从而显著改善了镍钴锰酸锂正极材料的循环性能和倍率性能。经过100次循环,镍钴锰酸锂正极材料放电比容量降到48.5 mAh g?1,改性后材料放电容量仍然保持在114.7 mAh g?1。为了进一步改善镍钴锰酸锂正极材料的倍率性能和低温性能,实验通过液相法和高温烧结法(500 ℃),制备了玻璃态锂快离子导体 ( (42.5-x) Li2O: 57.5B2O3: xLi2SO4) 包覆镍钴锰酸锂的复合材料。由于锂快离子导体在镍钴锰酸锂表面形成了稳定的保护层,并且有效降低了材料的电荷转移阻抗,从而改善了镍钴锰酸锂正极材料在大倍率和低温下的电化学性能。在1C倍率条件下循环100次后,包覆后材料的放电比容量达到141.7 mAh g?1,远高于镍钴锰酸锂材料的放电比容量54.0 mAh g?1。在-20 ℃,包覆后材料的放电比容量为127.7 mAh g-1,相比于初始材料的86.4 mAh g?1,表现出了较好的低温性能。

Other Abstract

Since ternary cathode material LiNi1/3Co1/3Mn1/3O2 was proposed, it attracts wide attention of the researchers. Compared with the LiCoO2, the poor performance of the ternary cathode material at rate capability and low temperature limits its further application. In this work,LiNi1/3Co1/3Mn1/3O2 materials were prepared by using hydrothermal method and co-precipitation method. The samples prepared by both methods have typical LiNi1/3Co1/3Mn1/3O2 material characteristic peaks. In the electrochemical performance tests, the samples prepared by co-precipitation have better electrochemical properties than the samples prepared by hydrothermal method. In addition, LiNi1/3Co1/3Mn1/3O2 materials prepared by the co-precipation method had the smallest electrode polarity and the highest lithium ion diffusion coefficient in the cyclic voltammetry tests. LiNi1/3Co1/3Mn1/3O2 materials prepared by co-precipation are highly ordered and have good cycle performance and rate performance. Then the Ti3SiC2 modified LiNi1/3Co1/3Mn1/3O2 was prepared by suspension mixing method, and compared with LiNi1/3Co1/3Mn1/3O2 by the morphology and electrochemical performance, in order to improve the magnification performance of the material by surface modification. The morphology of Ti3SiC2 modified LiNi1/3Co1/3Mn1/3O2 material is that NCM distributed on Ti3SiC2 surface, forming the point and surface distribution model. The surface modification of LiNi1/3Co1/3Mn1/3O2 by conductive ceramics Ti3SiC2 effectively increases the diffusion rate of lithium ions and reduces the transfer impedance of ions between materials, thus significantly improving the multiplier performance of LiNi1/3Co1/3Mn1/3O2.Finally, (42.5-x) Li2O: 57.5B2O3: xLi2SO4 modified LiNi1/3Co1/3Mn1/3O2 cathode materials are prepared via solution method followed by heat-treatment at 500°C. The lithium fast ion conductors (42.5-x) Li2O: 57.5B2O3: xLi2SO4 provide a stable surface protection for LiNi1/3Co1/3Mn1/3O2. The results indicate that (42.5-x) Li2O: 57.5B2O3: xLi2SO4 modified LiNi1/3Co1/3Mn1/3O2 exhibits improved electrochemical performances at high rate and low temperature. Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) have confirmed a thin Li2O-B2O3-Li2SO4 coating layer (about 10 nm) on the original structure of LiNi1/3Co1/3Mn1/3O2. (42.5-x) Li2O: 57.5B2O3: xLi2SO4 (x=10) modified LiNi1/3Co1/3Mn1/3O2 sample shows the highest discharge capacity of 176.1mAh g-1 at the rate of 0.2 C,0.5 C, 1 C, 2 C, 5 C, and 0.2 C in sequence after 30 cycles at ambient temperatures, and keeps a capacity retention of 98.4%, higher than 87.4% for LiNi1/3Co1/3Mn1/3O2 at the same conditions. In -20°C,(42.5-x) Li2O: 57.5B2O3: xLi2SO4 (x=10) modified LiNi1/3Co1/3Mn1/3O2 samples deliver higher initial discharge capacity of 127.7mAh g-1 and exhibits a better rate performance compared with the pristine LiNi1/3Co1/3Mn1/3O2.

Document Type学位论文
Recommended Citation
GB/T 7714
吕丁丁. Li-Ni-Co-Mn-O系正极材料的制备及其表面改性研究[D]. 北京. 中国科学院大学,2018.
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