草酸盐共沉淀法制备锂离子电池正极材料LiNi0.5Mn0.5O2及其电化学性能

Electrochemical Performance of LiNi_(0.5)Mn_(0.5)O_2 as Cathode Material for Lithium-Ion Batteries Prepared by Oxalate Co-Precipitation Method

使用草酸盐共沉淀法合成了LiNi0.5Mn0.5O2,并研究了共沉淀时的pH条件对终产物的结构、形貌及电化学性能的影响.采用X射线衍射(XRD)和扫描电镜(SEM)表征了在pH值为4.0、5.5、7.0和8.5时得到的共沉淀和终产物LiNi0.5Mn0.5O2的结构和形貌.使用充放电实验研究了不同pH条件下得到的LiNi0.5Mn0.5O2的电化学性能.结果表明,pH为7.0时,合成的材料颗粒更小、分布最均匀,材料具有良好的层状特征,且材料中锂镍的混排程度最小.电化学测试结果印证了pH为7.0时合成的材料具有更好的电化学性能,在0.1C的倍率下,材料的首次放电比容量达到了185 mAh.g-1,在循环20周后,放电比容量仍然保持在160 mAh.g-1.X射线光电子能谱(XPS)测试结果表明,pH为7.0时合成的LiNi0.5Mn0.5O2中Ni为+2价,Mn为+4价.

The oxalate co-precipitation method was used to synthesize LiNi0.5Mn0.5O2.The effects of pH on the structure,morphology,and electrochemical performance of LiNi0.5Mn0.5O2 were investigated.The crystal structures and surface morphologies of the oxalate precursor and LiNi0.5Mn0.5O2 obtained at pH=4.0,5.5,7.0,8.5 were characterized by X-ray diffraction（XRD） and scanning electron microscopy（SEM） methods.The electrochemical performance of LiNi0.5Mn0.5O2 was evaluated by galvanostatic charge/discharge tests.Results show that the LiNi0.5Mn0.5O2 obtained at pH=7.0 has a smaller particle size,more uniform distribution,better layered characteristics and a smaller degree of cation mixing.Electrochemical tests confirmed that the sample obtained at pH =7.0 had the best electrochemical performance.At 0.1C rate,its discharge capacity reached 185 mAh.g-1 at the first cycle and remained over 160 mAh.g-1 after the 20th cycle.X-ray photoelectron spectroscopy（XPS） results indicated that the oxidation states of Ni and Mn in the LiNi0.5Mn0.5O2 obtained at pH=7.0 were ＋2 and ＋4,respectively.