长寿命锰酸锂材料的研究

发布时间：2018-05-01 22:44

本文选题：锂离子电池 + 尖晶石锰酸锂　；参考：《天津大学》2014年硕士论文

【摘要】：近年来由于环境污染和资源短缺,引发了能源汽车的热议,也引起了研究者对汽车动力电池的高度关注,为了满足能源汽车的普及,对锂离子电池的成本和性能稳定性提出了新的要求。尖晶石锰酸锂以储量丰富、价格低廉、安全稳定、绿色无污染等特点被公认为适宜的动力电池正极材料之一,但其高温条件下存在的Jahn-Teller畸变效应而引起的循环容量衰减问题阻碍了其规模化应用。目前的解决方法有合成方法的改变、包覆改性、掺杂改性等,主要的改性方法为引入掺杂离子进行掺杂改性,本文主要对采用高温固相法合成的尖晶石锰酸锂进行金属阳离子掺杂,以改善其循环性能.采用高温固相法溶胶凝胶法制备了锰酸锂材料,XRD研究表明,两种方法所制备的样品均为尖晶石结构,通过SEM分析高温固相法制备的样品颗粒较大,形貌规则,粒度均匀,分散良好,电性能测试中高温固相法样品具有更高的放电容量、平稳的放电平台,良好的循环性能。以Li2CO3和Mn(CH3COO)2为原材料,考察不同的焙烧工艺影响,通过XRD和电性能分析研究表明当焙烧温度为850℃,焙烧时间为20小时所合成的样品具有更好晶体结构和电化学性能,样品首次可逆放电容量为128.7mAh/g,50周后循环保持率为94.2%。通过采用CH3COOLi、LiOH和Li2CO3以及Mn(CH3COO)2、MnSO4、MnCl2、Mn(NO3)2不同的原材料以高温固相法合成尖晶石样品,结果发现不同的原材料合成的样品性能差异较大,以LiOH和Mn(CH3COO)2为原材料合成的样品的结具有典型的尖晶石结构,结晶度高,形貌规则,电化学性能好。采用高温固相合成法以LiOH和Mn(CH3COO)2为原材料,以不同原料配比合成尖晶石锰酸锂,经过XRD、SEM和电性能测试研究发现,在高温焙烧时存在Li盐挥发的现象,锂锰配比要高于化学计量比,以Li/2Mn=1.15合成出的样品首次可逆容量为118.9 mAh/g,50周后循环保持率为97.6%。以LiOH和Mn(CH3COO)2为原材料,引入Co、Cr、Al元素进行掺杂改性,采用高温固相法合成样品,XRD显示,无论是单元掺杂还是多元掺杂锰酸锂材料的晶体结构没有发生变化,均为尖晶石相结构,且无杂相出现。通过电性能测试分析,掺杂Co、Cr、Al单元素后,无论掺杂比例大小,均可引锰酸锂材料可逆容量的降低,循环性能均可得到改善。通过引入Co、Cr、Al多元素掺杂后,合成的锰酸锂材料结构不变,为尖晶石结构。采用DSC分析确定Al元素对提高材料的热稳定性具有明显的效果;Cr元素对改善材料的倍率性能有一定的作用;Co、Cr、Al三者的协同作用可显著提高材料的循环性能尤其是高温循环性能,合成得到Sample-2(LiCo0.1Cr0.05Al0.1Mn1.75O4)样品常温1C循环,500周后容量保持率为89.9%,高温55℃1C循环500周容量保持率仍然可达78.4%。通过对尖晶石LiMn2O4材料与LiCoO2和三元材料进行混合,混合后样品优势互补,在LiCoO2材料中混合一定比例的LiMn2O4材料可以改善其安全稳定性;在尖晶石LiMn2O4材料中混合一定比例的三元材料,可以提高材料的容量,并明显改善LiMn2O4材料的高温性能,混合比例为20%的样品LMMNC-8,45℃循环500周后容量保持率为85.6%,比LMO提高了6.7%。
[Abstract]:In recent years, due to environmental pollution and shortage of resources, the hot discussion of energy vehicles has been caused, and the researchers have attracted the attention of the automotive power battery. In order to meet the popularity of energy vehicles, new requirements for the cost and performance stability of lithium ion batteries are put forward. Spinel lithium manganese acid lithium is rich in reserves, low in price, safe and stable and green. No pollution and other characteristics have been recognized as one of the suitable cathode materials for power batteries, but the problem of cyclic capacity attenuation caused by the Jahn-Teller distortion effect in high temperature conditions hinders its large-scale application. The current solutions include the changes of synthetic methods, coating modification, mixed modification, etc., the main modification method is the introduction of doping. Ion doping modification, this paper mainly doped metal cation of spinel manganate by high temperature solid-phase synthesis to improve its cycling performance. The lithium manganese oxide material was prepared by high temperature solid phase sol-gel method. The XRD study showed that the samples prepared by the two methods were spinel structure, and the high temperature solid phase was analyzed by SEM. The samples prepared by the method have large particles, regular morphology, uniform particle size and good dispersion. High temperature solid state samples have higher discharge capacity, stable discharge platform and good cycling performance in electrical properties test. The effects of different calcination processes are investigated with Li2CO3 and Mn (CH3COO) 2 as raw materials. By XRD and electrical properties analysis, it is shown that roasting The samples with a temperature of 850 C and 20 hours of calcination have better crystal structure and electrochemical properties. The first reversible discharge capacity of the sample is 128.7mAh/g, and the retention rate of the cycle is 94.2%. 50 weeks later by using CH3COOLi, LiOH and Li2CO3 and Mn (CH3COO) 2, MnSO4, MnCl2, Mn (NO3) 2 different raw materials to synthesize spinel by high temperature solid phase method. The results show that the properties of the samples synthesized by different raw materials are different. The samples synthesized by LiOH and Mn (CH3COO) 2 as the raw materials have typical spinel structure, high crystallinity, regular morphology and good electrochemical properties. LiOH and Mn (CH3COO) 2 are used as raw materials to synthesize spinel with different raw materials. Lithium manganate, after XRD, SEM and electrical properties test, found that there is a phenomenon of Li salt volatilization at high temperature, and the ratio of lithium and manganese is higher than that of stoichiometry. The first reversible capacity of the samples produced by Li/2Mn=1.15 is 118.9 mAh/g, and the retention rate of the Li/2Mn=1.15 is 97.6%. with LiOH and Mn (CH3COO) 2 as the raw material, and Co, Cr, Al elements are introduced. Modified, high temperature solid state method was used to synthesize the samples. XRD showed that the crystal structure of both unit and multi doped lithium manganese oxide material did not change, and all of them were spinel phase structure, and no heterozygous phase appeared. The reversible capacity of lithium manganese oxide material can be induced by doping Co, Cr and Al by electrical properties test. Through the introduction of Co, Cr, Al multielement doping, the structure of the synthesized lithium manganese dioxide is unchanged and the structure of spinel. The DSC analysis is used to determine the Al element to improve the thermal stability of the material; the Cr element has a certain effect on the improvement of the material multiplier performance; the coordination of Co, Cr, Al three. The function can significantly improve the cyclic performance of the material, especially the high temperature cycling performance. The Sample-2 (LiCo0.1Cr0.05Al0.1Mn1.75O4) sample at normal temperature 1C cycle is synthesized, the capacity retention rate is 89.9% after 500 weeks, and the 500 week capacity retention rate of the high temperature 55 C 1C cycle is still up to 78.4%. through mixing the spinel LiMn2O4 material with LiCoO2 and three yuan material. After mixing, the sample has complementary advantages. Mixing a certain proportion of LiMn2O4 material in LiCoO2 material can improve its safety and stability. Mixing a certain proportion of three yuan material in the spinel LiMn2O4 material can improve the capacity of the material, and obviously improve the high temperature performance of the LiMn2O4 material. The sample of the mixture ratio of 20% is LMMNC-8,45 centigrade for 500 weeks. The post capacity retention rate is 85.6%, which is higher than LMO by 6.7%.

【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TQ131.11;TM912

【参考文献】