Mg和Na共掺杂对富锂正极材料结构和电性能影响研究

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

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。

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 100nm with near-spherical.There are no heterophase peaks in samples,all of them have good layered structure,and Na^(+)and Mg^(2+)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 250cycles.Ni content in LNi018 sample is less than that of other samples,valence states of Ni^(2+)and Mg^(2+)are the same,and ionic radius is approximate(Ni^(2+)6.9nm,Mg^(2+)7.2nm),Mg^(2+)takes place of Ni^(2+)in lattice.At the same time,the larger radius of Na^(+)(10.2nm)rises lithium layer spacing,which makes crystal structure more stable during charge discharge cycle,thus maintaining a higher discharge voltage and capacity.