球形LiNi_(0．5-x)Co_(2x)Mn_(0．5-x)O_2的合成及其电化学性能

Synthesis and Electrochemical Performance of Spherical LiNi_(0.5-x)Co_(2x)Mn_(0.5-x)O_2

以化学共沉淀法制备的球形Ni_(0.5-x)Co_(2c)Mn_(0.5-x)CO_3(x=0.075,0.1,1/6)为前驱体合成了球形锂离子电池正极材料LiNi_(0.5-x)Co_(2x)Mn_(0.5-x)O_2(x=0.075,0.1,1/6),研究了钴含量对LiNi_(0.5-x)Co_(2x)Mn_(0.5-x)O_2的物理性能和电化学性能的影响.SEM研究表明,球形LiNi_(0.5-x)Co_(2x)Mn_(0.5-x)O_2由许多一次颗粒构成,随着钴含量的增加,产物中一次颗粒增大.XRD分析表明,LiNi_(0.5-x)Co_(2x)Mn_(0.5-x)O_2均为具有层状结构的纯相物质.电化学性能测试结果显示,LiNi_(0.5-x)Co_(2x)Mn_(0.5-x)O_2随着钴含量的增加,材料的充放电容量提高,且循环性能变好:0.2C倍率下、2.7～4.3V的电压范围内,LiNi_(0.425)CO_(0.15)Mn_(0.425)O_2的放电比容量为145mAh·g^(-1)、LiNi_(0.4)CO_(0.2)Mn_(0.4)O_2为150mAh·g^(-1)、LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2为158mAh·g^(-1),循环50周期后LiNi_(0.425)CO_(0.15)Mn_(0.425)O_2和LiNi_(0.4)Co_(0.2)Mn_(0.4)O_2的容量衰减率在3%以内,LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2容量无衰减.交流阻抗测试结果表明,随着钴含量的增加,材料阻抗值减小.

Spherical LiNi0.5-xCo2xMno.5-xO2（x=0.075, 0.1, 1/6） powders were synthesized from the co-precipitated carbonate precursor, Nio.5-xCo2xMno.5-xCO3（x=0.075, 0.1, 1/6）. The effects of the Co content on the physics and electrochemical performance of LiNi0.5-xCo2xMn0.5-xO2 were investigated. The SEM images of LiNi0.5-xCo2xMn0.5-xO2 show that the spherical material consists of many primary particles, which sizes increase with the content of Co increasement. The results of X-ray powder diffraction show that all LiNi0.5-xCo2xMno.5-xO2 are pure phase materials with lavered strnctures. The electrochemical tests inclicate that the discharge capacities of LiNi0.5-xCo2xMn0.5-xO2 increase and the cycle performances become better with the content of Co increasing. Under the charge/discharge conditions of 0.2C rate and voltage range of 2.7-4.3V, the discharge properties of spherical LiNio.425Co0.15Mn0.425O2, LiNio.4Co0.2Mno.4O2 and LiNi1/3Co1/3Mn1/3O2 are 145,150 and 158 mAh.g^-1, respectively. The discharge capacity fadings for LiNio.425Co0.15Mno.425O2 and LiNio.4Co0.2Mn0.4O2 are less than 3%, however, there is no fade for that of LiNi1/3Co1/3Mn1/3O2 after 50 cycles. The results of AC impedance show that the impedance decreases with the content of Co increasing.