掺杂型尖晶石LiMn₂O₄的试验研究及合成

【作者】 王凤；

【导师】 戴永年；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2006， 硕士

【摘要】 随着当今社会科技、信息、网络的高速发展,人们对价格低廉、使用期长的蓄电池提出了更高的要求。低成本、高能量密度、高电压、轻型化且循环寿命长、安全性能好的全新的绿色电源—锂离子二次电池成为人们研究的热点。而尖晶石LiMn₂O₄以其高电压、高安全性、低成本,低污染等特性而有望成为新一代锂离子电池正极材料之一,但其较差的循环性能和高温电性能严重阻碍了其商业化进程。本文综述了锂离子电池的工作原理、发展历程,概述了几种锂离子电池正极材料的研究状况;分析了尖晶石LiMn₂O₄作为正极材料容量衰减的机理及其改进措施,最后简单总结了锰酸锂的多种合成方法。 本文采用两种技术路线对尖晶石LiMn₂O₄进行了掺杂合成研究,并利用X射线衍射分（XRD）、扫描电镜能谱分析（SEM-EDS）、电化学性能测试等现代手段对合成材料进行了分析。（1）采用机械球磨-高温固相法合成了阳离子掺杂化合物Li_1.05Mn_2-xM_xO₄（M=Mg、Ni、Al）和阴、阳离子复合掺杂化合物Li_1.05Mn_1.9M_0.1O_.05F_0.5（M=Mg、Ni、Al）,通过研究发现,不同阳离子掺杂化合物Li_1.05Mn_2-xM_xO₄（M=Li、Al、Mg、Ni）在充放电过程中均存在相同规律:随掺杂量的增大,材料的比容量逐渐降低,而循环性能趋于稳定。富锂尖晶石LiMn₂O₄的循环稳定性要比化学计量的LiMn₂O₄的好。其余阳离子掺杂量中,Ni的最佳掺杂量为0.08,Al的最佳掺杂量为0.04,Mg的最佳掺杂量为0.10。阴阳离子复合掺杂研究中,Li_1.05Mn_1.90Ni_0.1O_3.5F_0.5、Li_1.05Mn_1.90Mg_0.1O_3.5F_0.5、Li_1.05Mn_1.90Al_0.1O_3.5F_0.5的首次放电比容量分别为95.64mAh/g,113.46mAh/g,109.19mAh/g,经过15次循环后容量保持率分别为97.19%,91.18%和88.98%。其中Li_1.05Mn_1.90Ni_0.1O_3.5F_0.5第二次循环后容量达到138.86mAh/g,Li_1.05Mn_1.90Mg_0.1O_3.5F_0.5的综合掺杂效果最佳。（2）采用微波加热技术进行了尖晶石LiMn₂O₄的合成条件探索实验,以期通过微波加热的方式能够制备出性能优良的LiMn₂O₄正极材料,从而解决高温固相法烧结时间长、粒度分布不均的缺点。因为微波功率和合成时间是微波加热最重要的因素,本章就针对这两个因素使用家用微波炉来探索合成LiMn₂O₄的最佳合成条件。研究发现,在700-800℃之间恒温10分钟或600℃保温20分钟均可得到纯LiMn₂O₄更多还原

【Abstract】 Nowadays, with the rapid development of science and technology, communication, network, people have made higher demands on cheap and long life-span batteries. Li-ion batteries has been the study hotspot for people for their favorable advantages of low cost, high energy density, high voltage, light-duty, long cycling life and non-pollution. Spinel LiMn₂O₄ is considered as the most promising positive cathode material for Li-ion batteries because of its high voltage, high safety, low cost, and low contaminated, but its poor cycle performance and stability in high temperature blocked severely the commercialize process. This article summarized the work principle, develop course and of Li-ion Batteries, and summarized the study status of several cathode materials;analyzed the reason about attenuation of Spinel LiMn₂O₄ and illuminated some existing synthesize methods of LiMn₂O₄ to improve the performance of this cathode materials.It was studied the doping and synthesizing of Spinel LiMn₂O₄ adopting two ways. The materials was analyzed by modern means of x-ray diffraction （XRD） scanning electric microscopy （SEM-EDS） and the electrochemical properties was tested.: （1） The compound Li_1.05Mn_2-xM_xO₄（M=Mg, Ni, Al）doping with cations and Li_1.05Mn_1.9M_0.1O_3.5F_0.5 （M=Mg Ni Al） doping with cations and anions was synthesized by the way of machine ball-milling-solid phase in high temperature. The results showed that the electrical properties of the batteries with Li_1.05Mn_2-xM_xO₄（M=Al Mg Ni） doping different cations showed same laws when the batteries were charging and discharging: The specific capacity decrease with the increasing of the amount of doping ions. The circling stability of Spinel Li_1.05Mn₂O₄ are better than those of the pure phase LiMn₂O₄. among the other cation-doping compounds. The optimal doping amount of Ni was 0.08, Al was 0.04, Mg was 0.10. In the studies, the first discharge specific capacity of Li_1.05Mn_1.90Ni_0.1O_3.5F_0.5 Li_1.05Mn_1.90Mg_0.1O_3.5F_0.5 and Li_1.05Mn_1.90Al_0.1O_3.5F_0.5 co-doping were as follows separately: 95.64mAh/g, 113.46mAh/g and 109.19mAh/g and the holding ? ratio of capacity after 15 times cycling were separately 97.19%, 91.18% and 88.98%: The ,highest specific capacity of U1.05Mn1.90Nio.1O3.5Foj of the second cycling process reached 138.86mAh/g. The effect of the co-doping Ui.o5Mni.9oMgo.i03.5Fo.5 is the best. （2） Microwave heat technology was adopted to try to find the appropriate experiments conditions and to preparare excellent performance LiMn2O4 as cathode material, thereby to conquer disadvantage of long time of sintering and uneven of granularity distribution of the way of solid phase in high temperature. The optimal condition to synthesize spinel LiMn2C>4 was explored using family micro-wave oven because the power of microwave and heating time are foremost factors. Studies showed that it was appropriate to heat 10 minutes at 700-800°C or preservation 20 minutes at 600°C to prepare pure phase spinel LiMn2C>4, the latter is better controlling condition. It was found that the stable cycling performance of the cathode material of spinel LiMn2O4 prepared by the way of microwave chemistry possess is better than that of the samples prepared by the way of solid phase in high temperature, but the specific capacity is unideal, the best result of the experiments is only 73mAh/g.更多还原