4.6 V高电压钴酸锂正极材料Al-Zn共掺杂研究

Study on Al-Zn co-doping of 4.6 V high voltage lithium cobalt oxide cathode materials

钴酸锂具有高达274 mA·h/g的理论容量,是最早商业化的锂离子电池正极材料之一。然而,钴酸锂层状结构在高电压下的不稳定性使其实际充电电压很难超过4.45 V(vs.Li),这大大限制了其容量发挥。针对上述问题,采用小半径铝离子与大半径锌离子共掺杂的方法来提升钴酸锂正极材料在高电压下的结构稳定性。通过高分辨透射电子显微镜及X射线衍射证明了Al-Zn共掺杂可增大钴酸锂晶面间距;扫描电镜-元素分布分析证明了Al-Zn的均匀掺杂;电化学阻抗谱证明了共掺杂对界面副反应的抑制作用。结果表明,通过调控晶体结构和界面副反应,可以有效增强高电压下钴酸锂的电化学稳定性。通过软包金属锂电池的组装发现,Al-Zn共掺杂的钴酸锂正极材料在4.6 V充电截止电压、0.2C倍率下,充放电比容量可达218.8 mA·h/g,循环600次后容量保持率可达83.3%,且其综合电化学性能远高于铝掺杂及未改性的钴酸锂正极材料。

Lithium cobalt oxide has a theoretical capacity of up to 274 mA·h/g and it is one of the earliest commercialized cathode materials for lithium-ion batteries.However,the instability of the layered structure of lithium cobalt oxide at high voltage makes it difficult for its actual charging voltage to exceed 4.45 V(vs.Li),thus greatly limiting its capacity.In response to the above problems,the method of co-doping with small-radius aluminum ions and large-radius zinc ions was used to improve the structural stability of lithium cobalt oxide cathode materials at high voltage.High-resolution transmission electron microscopy and X-ray diffraction proved that Al-Zn co-doping could increase the interplanar spacing of lithium cobalt oxide.The scanning electron microscopy-element distribution analysis proved the uniform doping of Al-Zn.And the electrochemical impedance spectroscopy proved the inhibitory effect of co-doping on interfacial side reactions.The results showed that the electrochemical stability of lithium cobalt oxide at high voltage could be effectively enhanced by regulating the crystal structure and interfacial side reactions.Through the assembly of soft-pack metal lithium batteries,it was found that the Al-Zn co-doped lithium cobalt oxide cathode material has a charge and discharge specific capacity of 218.8 mA·h/g at a charge cut-off voltage of 4.6 V and a rate of 0.2C.The capacity retention rate could reach 83.3%after 600 cycles,and its comprehensive electrochemical performance was much higher than that of aluminum-doped and unmodified lithium cobalt oxide cathode materials.