层状LiNi_0.8Co_0.2O₂正极材料掺杂研究

【作者】 胡正；

【导师】 彭文杰；

【作者基本信息】 中南大学 ， 冶金物理化学， 2009， 硕士

【摘要】 目前,已大规模商业化的层状锂离子电池正极材料有LiCoO₂,但因为钴价格昂贵和毒性等问题,研究者一直致力于寻找其他替代材料。钴和镍的各种性质非常相近,能以任意比例形成固溶体,同时LiNi_1-yCo_yO₂体系兼有钴酸锂和镍酸锂两者的优点而受到了人们的广泛研究。在LiNi_1-yCo_yO₂体系中,LiNi_0.8Co_0.2O₂的前景被看好。通过对共沉淀法制备前驱体、前驱体预处理和高温固相反应过程各种影响因素进行分析和优化,确定了合成LiNi_0.8Co_0.2O₂正极材料的较优的工艺条件:以镍钴混合液为原液、碳酸氢钠为沉淀剂、氨水为络合剂调节溶液pH值8附近制备前躯体,锂盐过量5%、750℃烧结15小时,在空气气氛中较成功地合成了具有较好层状结构和电化学性能的LiNi_0.8Co_0.2O₂正极材料。在2.7-4.3V范围,以0.1C放电,首次放电容量达179.2mAh·g^-1。循环10次后容量变为167 mAh·g^-1,容量保持率为93.2 %。以0.2C充电、0.5C放电,第一次循环后容量为159.7 mAh·g^-1,循环30次后容量衰减到112.3 mAh·g^-1,容量保持率为70.3%。本文对LiNi_0.8Co_0.2O₂进行了掺杂改性研究,探讨了Fe、Al、Mg等掺杂离子的影响。得到了Li(Ni_0.8Co_0.2)_0.95Al_0.05O₂,Li[(Ni_0.8Co_0.2)_0.95Al_0.05]_1-xFe_xO₂（x=0.02, 0.05, 0.1, 0.2）,Li[(Ni_0.8Co_0.2)_0.95Al_0.05]_1-xMg_xO₂（x=0.02, 0.05）正极材料中以Li(Ni_0.8Co_0.2)_0.95Al_0.05O₂正极材料的性能最好,以0.1C充放电,Li(Ni_0.8Co_0.2)_0.95Al_0.05O₂的比容量达到155.7 mAh·g^-1,前10次循环容量保持率达到98.3%。以0.2C充电、0.5C放电时。在前30次循环中,Li(Ni_0.8Co_0.2)_0.95Al_0.05O₂的比容量从142.8 mAh·g^-1下降到131.8 mAh·g^-1,容量保持率达到92.3%。而Fe、Mg掺杂均导致材料性能变差。更多还原

【Abstract】 LiCoO₂ has been widely used as a cathode material in commercial lithium ion battery layed .But due to the high cost and toxicity of Co , many efforts have been made to replace it. In practice, it is regularly argued that LiNi_0.8Co_0.2O₂ is a promising cathode materials to replace LiCoO₂, because it possess the merit of LiCoO₂ and LiNiO₂.The reaction conditions in co-precipitation process, pretreatment process and calcination process were analyzed and optimized. The precussor was prepared by control the pH value about 8、the ammonia concentration. Layered LiNo_0.8Co_0.2O₂ was synthesized with 5 % excess lithium under 750℃for 15h in atmosphere. The results of LiNo_0.8Co_0.2O₂ indicated that the LiNo_0.8Co_0.2O₂ delivered 179.2 mAh·g^-1at the rate of 0.1C during the voltage range of 2.7-4.3V.The capacity retention rateswas 93.2% after 10 cycles. The material shows an initial discharge capacity of 159.7 mAh·g^-1at the rate of 0.2C charge and 0.5C discharge during the voltage range of 2.7-4.3V. The capacity retention rates were 70.3% after 30 cycles.Doped LiNi_0.8Co_0.2O₂ were studied. The effect of Fe、Mg、Al on the performance of LiNi_0.8Co_0.2O₂ were explored. in Li (Ni_0.8Co_0.2) _0.95Al_0.05O₂、Li[(Ni_0.8Co_0.2)_0.95Al_0.05]_1-xFe_xO₂（x=0.02, 0.05, 0.1, 0.2）、Li[(Ni_0.8Co_0.2)_0.95Al_0.05]_1-xMg_xO₂（x=0.02, 0.05）. The performance of Li (Ni_0.8Co_0.2)_0.95Al_0.05O₂ was the best. The prepared Li (Ni_0.8Co_0.2) _0.95Al_0.05O₂ delivered the intial capacity of 155.7 mAh·g^-1 at 0.1C. The capacity retention rate was 98.3% after 10 cycles at the rate of 0.1C. it delivered the intial capacity of 142.8 mAh·g^-1 at the rate of 0.2C charge and 0.5C discharge during the voltage range of 2.7-4.3V. The capacity retention rate was 92.3% after 30 cycles.The doping of Fe and Mg deteriorates the performance of Li (Ni_0.8Co_0.2)_0.95Al_0.05O₂.更多还原