Mg和Na共掺杂对富锂正极材料结构和电性能影响研究

采用溶胶—凝胶法制备了Na和Mg共掺杂的无钴富锂锰基正极材料,通过透射电子显微镜(HRTEM)、X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)、充放电测试仪和电化学工作站对所制备样品的形貌、结构和电化学性能进行了测试。结果表明,所有样品颗粒大小约100nm,呈近似球形,样品均无杂相峰出现,都具有良好的层状结构,Na~+和Mg~(2+)对Ni和Mn离子的氧化状态没有影响。LNi018具有最好的电化学性能,初始放电容量为225.5mAh/g,库伦效率为78.0%,循环250周后容量保持率为83.1%。LNi018样品中Ni含量相对于其它样品较少,Ni ~(2+)和Mg~(2+)的价态相同,离子半径近似(Ni ~(2+)6.9nm,Mg~(2+)7.2nm),在晶格中Mg~(2+)取代了Ni~(2+)的位置,同时较大半径的Na~+(10.2nm)增大锂层间距,使晶体结构在充放电循环过程中更加稳定,因而能保持较高的放电电压和容量。

Effect of Mg and Na Co-doping on Structure and Electrochemical Performance of Li-rich Cathode Materials

Cobalt free Li-rich manganese based cathode materials with Na and Mg co-doping were prepared by sol-gel method. Morphology, microstructure and electrochemical properties of cobalt free Li-rich manganese based cathode materials were tested by transmission electron microscopy (HRTEM), X ray diffractometer (XRD), X ray photoelectron spectroscopy (XPS), charge discharge tester and electrochemical workstation. The results show that particle size of all samples is about 100 nm with near-spherical. There are no heterophase peaks in samples, all of them have good layered structure, and Na+ and Mg2+ has no effect on oxidation state of Ni and Mn ions. LNi018 has best electrochemical performance with initial discharge capacity of 225.5 mAh/g and coulombic efficiency of 78.0%, and capacity retention rate is 83.1% after 250 cycles. Ni content in LNi018 sample is less than that of other samples, valence states of Ni2+ and Mg2+ are the same, and ionic radius is approximate (Ni2 + 6.9 nm, Mg2+ 7.2 nm), Mg2+ takes place of Ni2+ in lattice. At the same time, the larger radius of Na+ (10.2 nm) rises lithium layer spacing, which makes crystal structure more stable during charge discharge cycle, thus maintaining a higher discharge voltage and capacity.