高温长寿命锰酸锂正极材料的合成及其改性研究

发布时间：2018-06-10 00:20

本文选题：锰酸锂 + 四氧化三锰　；参考：《中南大学》2014年博士论文

【摘要】：摘要：能源危机、环境污染、全球变暖等一系列问题严重威胁到人类的生存和发展。为解决以上问题,各国政府纷纷投入大量人力物力开发利用电动汽车。锂离子电池具有体积小、电压高、容量大、寿命长、自放电小、无记忆效应和绿色环保等优点而成为车载动力的首选。磷酸铁锂和锰酸锂作为最可能应用于动力电池的正极材料。然而在我国磷酸铁锂热火朝天的几年里,世界各大主流汽车厂商电动汽车电池正极材料逐步向以日韩为代表的锰系正极材料转移。但是日本以及韩国对动力LiMn2O4正极材料进行封锁,在技术上进行保密,因此,研究开发出性能优越的尖晶石LiMn2O4具有非常重要的现实意义。本文从前驱体入手,提出采用控制结晶一步氧化法制备球形四氧化三锰前驱体,然后联合高温固相法制备球形锰酸锂,并从资源综合利用角度出发,采用液相法进行掺杂改性研究。论述了控制结晶法合成前驱体的理论基础。根据同时平衡原理和质量守恒定律推导,绘制出Mn-NH3-SO42--H2O的φ-pH图,并对晶粒形成和长大机理进行理论分析,为制备形貌单一、粒径分布均匀的球形四氧化三锰前驱体提供理论基础。系统研究了控制结晶一步氧化法制备球形四氧化三锰工艺。研究了反应温度、反应时间、搅拌速度、MnS04摩尔浓度、氨水浓度、氨锰摩尔比、硫酸锰加料速度对前驱体物理化学指标的影响,研究结果表明,在反应温度为70℃、搅拌速度为500r·min-1、反应时间为12h、硫酸锰浓度为1.25mol·L-1、氨水浓度为2mol·L-1、NH3/Mn摩尔比为2.4、硫酸锰加料速度为600mL·h-1。制备的Mn304纯度高达99.74%,粒度分布较好,平均粒径为11.201μm,振实密度达到2.28g·cm-3。拉曼光谱分析表明所有Raman峰与尖晶石Mn304的特征峰完全吻合。系统研究了高温固相法制备球形锰酸锂。研究结果表明最佳烧结工艺为500℃、650℃预烧6h后升温至800℃烧结10h,此条件下合成的LiMn204材料颗粒球形度较好、结晶完善、电化学性能较好,常温0.1C首次放电比容量高达125.5mAh·g-1,1C首次放电比容量为119.9mAh·g-1,循环300次后容量保持率为87.66%,高温(55℃)1C首次放电比容量为114.9mAh·g-1,循环200次后容量保持率为86.24%。LiMn2O4电极循环伏安结果发现两对氧化还原峰,与LiMn204电极的充放电曲线的特征平台表现一致。研究了联合控制结晶一步氧化高温固相法制备球形掺镁锰酸锂。研究发现控制NH3/Mn摩尔比,可以得到Mg含量可控、振实密度较大的球形掺Mg的Mn304前驱体。XRD结果显示经过高温固相反应,Mg取代部分Mn成功进入尖晶石LiMn204晶格。镁掺杂改善了锰酸锂的循环性能,当前驱体中镁含量约为1.5%时,得到的LiMn2-xMgxO4电化学性能最好,常温1C首次放电比容量为113.1mAh·g-1,循环300次后容量保持106.4mAh·g-1；高温1C首次放电比容量为121.4mAh·g-1,循环300次后容量保持99.3mAh·g-1。循环性能基本能满足动力电池要求。为进一步改善锰酸锂的循环性能、降低原料成本、提高资源综合回收利用,采用液相法分别对锰酸锂进行了Ni、Co单一和Ni、Co复合掺杂。XRD结果表明,Ni、Co成功取代部分Mn进入尖晶石LiMn204晶格,减小了材料的晶格常数。钻掺杂锰酸锂具有较高的放电比容量和较好的循环性能,当前驱体中钴含量为8%时,材料1C首次放电比容量为117.3mAh-g-1,循环200周后容量保持率为95.82%；镍掺杂有效改善了LiMn204的循环性能,但是材料的比容量较低；Ni、Co复合掺杂LiMn204具有较高的比容量和较好的循环性能,当前驱体中Ni、Co的百分含量分别为1%左右时,制备的LiMn204常温和高温1C首次放电比容量分别为112.8和118.2mAh-g-1,常温500次循环后容量保持率为97.52%,高温300次循环后容量保持率为90.52%,所有物理化学指标都达到动力电池要求。XPS分析结果表明,Ni、Co复合掺杂提高了锰的平均价态,Ni、Co复合掺杂样品中Mn、Ni、Co的价态分别为+4、+2、+3价。最后对球形锰酸锂及Ni、Co复合掺杂锰酸锂进行中试。中试结果表明锰酸锂具有较好的常温电化学性能,1C首次放电比容量为115.8mAh·g1,循环500次后容量保持率为89.29%；Ni、Co复合掺杂锰酸锂具有优越的电化学性能,常温和高温1C首次放电比容量分别为112.8和111.2mAh-g-1,500次循环后容量保持率分别为91.22%和83.81%。成本分析认为该工艺具有非常好的经济效益。
[Abstract]:Abstract: a series of problems, such as energy crisis, environmental pollution, global warming, seriously threaten the survival and development of human beings. In order to solve the above problems, governments have invested a lot of human and material resources to develop and utilize electric vehicles. Lithium ion batteries have small size, high voltage, large capacity, long life, small self discharge, no memory effect and green environmental protection. It has become the first choice of vehicle power. Lithium phosphate and lithium manganese dioxide are most likely to be used as positive materials for power batteries. However, in the years in China, the positive materials of electric vehicle batteries in the world's major automotive manufacturers have gradually shifted to the manganese cathode materials with Japan and South Korea as their behalf. South Korea has blocked the power LiMn2O4 cathode materials and secrecy in technology. Therefore, it is of great practical significance to study and develop the spinel LiMn2O4 with superior performance. This paper, starting from the former, proposed to prepare spherical four oxidation three manganese precursor by controlled crystallization and one step oxidation method, and then combined with high temperature solid state method to prepare the ball. Lithium manganese oxide is studied from the perspective of comprehensive utilization of resources.
The theoretical basis of controlling the synthesis of precursor by crystallization method is discussed. According to the principle of simultaneous equilibrium and the law of mass conservation, the phi -pH diagram of Mn-NH3-SO42--H2O is drawn, and the mechanism of grain formation and growth is theoretically analyzed to provide a theoretical basis for the preparation of a spherical four oxidation three manganese precursor with single morphology and uniform particle size distribution.
The effects of reaction temperature, reaction time, stirring speed, MnS04 molar concentration, ammonia water concentration, ammonia and manganese molar ratio, manganese sulphate feed rate on precursors physical and chemical indexes are studied. The results show that the reaction temperature is 70 degrees C and the stirring speed is 500r min. The results of the study show that the reaction temperature is 70, and the stirring speed is 500r. Min -1, the reaction time is 12h, the concentration of manganese sulfate is 1.25mol. L-1, the concentration of ammonia water is 2mol. L-1, the NH3/Mn molar ratio is 2.4, the Mn304 purity of Mn304 is 99.74%, the particle size distribution is better and the average particle size is 11.201 mu m. The characteristic peak coincides completely.
The preparation of spherical lithium manganate by high temperature solid state method is systematically studied. The results show that the optimum sintering process is 500 degrees C, the temperature of 6h at 650 C is heated to 800 C for 10h. Under this condition, the particles have better sphericity, perfect crystallization and better electrochemical performance, and the first discharge ratio of 0.1C at normal temperature is up to the first discharge ratio of 125.5mAh. G-1,1C. The capacity is 119.9mAh g-1 and the capacity retention rate is 87.66% after 300 cycles. The initial discharge ratio of 1C at high temperature (55 C) is 114.9mAh. G-1. After 200 cycles, the capacity retention rate is two pairs of redox peaks of 86.24%.LiMn2O4 electrode cyclic voltammetry, which is in accordance with the characteristic platform of the charge discharge curve of LiMn204 electrode.
Study on the preparation of spherical magnesium manganese doped lithium manganese oxide by a combined controlled crystallization and one step oxidation. It is found that the control of the NH3/Mn molar ratio can be controlled by the Mg content. The.XRD results of a spherical Mg doped Mn304 precursor show that the Mg substituted part of Mn has successfully entered the spinel LiMn204 lattice after a high temperature solid reaction. The magnesium doping is improved. The cycle performance of lithium manganate, when the content of magnesium is about 1.5% in the current drive, has the best electrochemical performance of LiMn2-xMgxO4. The first discharge specific capacity of 1C at normal temperature is 113.1mAh. G-1, and the capacity is 106.4mAh. G-1 after 300 cycles. The first discharge ratio of 1C is 121.4mAh. G-1 at high temperature 1C, and the capacity maintains 99.3mAh. G-1. cycle performance base after 300 cycles. Instinct meets the power battery requirements.
In order to further improve the cycle performance of lithium manganate, reduce the cost of raw materials and improve the comprehensive recovery and utilization of resources, Ni, Co single and Ni, and Co compound.XRD have been carried out by liquid phase method, respectively. The results show that Ni and Co have succeeded in replacing partial Mn into the spinel LiMn204 lattice and reducing the lattice constant of the material. The doping of lithium manganate is higher. The discharge specific capacity and good cycling performance of the current drive are 8%, the initial discharge ratio of 1C is 117.3mAh-g-1, and the capacity retention rate is 95.82% after 200 weeks. The nickel doping improves the cycle performance of LiMn204 effectively, but the specific capacity of the material is low; Ni, Co composite LiMn204 has higher specific capacity and comparison. With good cyclic performance, when the content of Ni and Co in the current drive is about 1% respectively, the initial discharge specific capacity of LiMn204 at normal temperature and high temperature 1C is 112.8 and 118.2mAh-g-1 respectively. The capacity retention rate is 97.52% after 500 cycles at normal temperature and 90.52% after 300 cycles of high temperature, and all physical and chemical indexes reach the power battery. The results of.XPS analysis showed that the average valence state of manganese was increased by Ni and Co composite doping. The valence states of Mn, Ni and Co in Ni and Co composite doped samples were +4, +2, and +3, respectively.
The results showed that lithium manganate and Ni, Co compound doped lithium manganate were in the middle test. The results showed that lithium manganate had good electrochemical performance at normal temperature. The initial discharge specific capacity of 1C was 115.8mAh. G1, and the capacity retention rate was 89.29% after 500 cycles; Ni, Co compound doped lithium manganate had excellent electrochemical performance, and the first discharge at normal temperature and high temperature 1C was the first discharge. The capacity retention rate after 112.8 and 111.2mAh-g-1500 cycles respectively is 91.22% and 83.81%. cost analysis shows that the process has very good economic benefits.
【学位授予单位】：中南大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912

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