高端球形尖晶石锰酸锂正极材料的制备及其改性研究

发布时间：2018-06-18 00:19

本文选题：锂离子电池 + 尖晶石锰酸锂正极材料　；参考：《湘潭大学》2014年硕士论文

【摘要】：尖晶石锰酸锂材料因具有储量资源丰富、环境友好、价格低廉、良好的热稳定性、适宜的充放电平台、容易制备等优点受到越来越多研究者的关注，成为当前最具前景的锂离子电池正极材料之一。然而，受制于其在高温（55oC以上）下较差的循环性能，尖晶石锰酸锂正极材料尚未得到大规模的工业化应用。研究表明，导致这一现象的主要原因为Jahn-Teller效应，电解液中锰的溶解，工业化生产原料纯度较低。针对尖晶石锰酸锂正极材料的缺点，本文做了以下四点研究：首先使用FeF3·3H2O对尖晶石锰酸锂合成原料MnSO4·H2O进行除杂，制备高纯硫酸锰；其次，用高纯硫酸锰、硫酸铝和碳酸钠为沉淀剂，利用共沉淀法合成具有良好球形形貌的高端尖晶石锰酸锂；然后，对尖晶石锰酸锂进行Al掺杂改性，利用共沉淀法合成球形尖晶石LiAlxMn2-xO4材料；最后，利用锆酸锂包覆对尖晶石锰酸锂进行改性，合成锆酸锂包覆的球形尖晶石锰酸锂材料。主要工作如下： (1)基于FeF3·3H2O中的氟离子可以沉淀溶液中的钙、镁离子，铁离子可以与钾、钠离子生成易沉淀的硫酸配盐，多余的铁离子水解形成的Fe(OH)3具有显著的絮凝效果，因此将FeF3·3H2O作为一种新型硫酸锰除杂剂，通过调整溶液的pH值，使钙、镁、钾、钠离子先后沉淀，从而分离普通硫酸锰中较难分离的钙、镁、钾、钠离子。除杂后的高纯硫酸锰产品中，钙、镁、钾、钠离子含量均低于100ppm，铁离子含量低于10ppm，得到的产品可以达到电池级或电子级锰基原料生产所需的高纯硫酸锰对钙、镁、钾、钠离子纯度的要求。 (2)以高纯硫酸锰和碳酸钠为沉淀剂，氨水为络合剂，利用共沉淀法合成了具有良好球形形貌的碳酸锰前驱体，并对反应中的pH值、搅拌速率、温度、氨的浓度四个条件进行了讨论。之后将前驱体与碳酸锂混合、煅烧，合成了球形度良好的高端尖晶石锰酸锂。测试结果表明，合成的高端尖晶石锰酸锂振实密度高，首次放电容量和循环性能均有明显优势。 (3)以高纯硫酸锰、硫酸铝和碳酸钠为沉淀剂，氨水为络合剂，利用共沉淀法合成了具有良好球形形貌的尖晶石LiAlxMn2-xO4系列材料并对其电化学性能进行了研究。研究表明分子式为LiAl0.06Mn1.94O4的材料具有最好的高温循环稳定性能。在55oC、1C倍率条件下，该样品100次充放电后的放电容量仍有113.9mAh g1，容量保持率高达97.0%。 (4)以锆酸锂为包覆层，成功合成了锆酸锂包覆的球形尖晶石锰酸锂。实验结果表明基于锆酸锂良好的锂离子传导性和化学惰性，以锆酸锂为包覆层可有效阻止电解液中HF对锰的溶解，同时不阻碍锂离子的嵌入/脱出过程。电化学测试表明包覆量为3wt.%的材料具有最好的常温和高温电化学性能，25oC,1C倍率条件下，首次放电容量为126.7mAh g1，100次充放电后容量保持率为99.0%；55oC,1C倍率条件下，首次放电容量为129.5mAh g1，100次充放电后容量保持率为90.2%，并且电荷转移阻抗Rct值仅为34.2，，均优于未包覆锰酸锂材料。
[Abstract]:Spinel lithium manganese dioxide is one of the most promising cathode materials for lithium ion batteries because of its abundant reserves, friendly environment, low price, good thermal stability, suitable charging and discharging platform and easy preparation. However, it is subject to the poor evidence-based process under high temperature (above 55oC). The study shows that the main cause of this phenomenon is Jahn-Teller effect, the dissolution of manganese in the electrolyte and the low purity of the raw materials in industrial production. The following four points are studied in this paper: first of all, the use of Fe F3. 3H2O is used to prepare high purity manganese sulfate by removing impurities from spinel lithium manganate synthetic material MnSO4 H2O. Secondly, high purity Spinel Manganese manganese oxide with good spherical morphology is synthesized with high purity manganese sulfate, aluminum sulfate and sodium carbonate as precipitants. Then, Al doped spinel lithium manganese acid is modified by Al and co precipitation method is used. Spherical spinel LiAlxMn2-xO4 material; finally, lithium manganese zirconate was used to modify spinel lithium manganate, and lithium zirconate coated spinel lithium manganese dioxide was synthesized. The main work is as follows:
(1) the fluorine ions based on FeF3 / 3H2O can precipitate calcium, magnesium ions in the solution, iron ions can produce precipitate sulphuric acid with potassium and sodium ions, and Fe (OH) 3, formed by the hydrolysis of excess iron ions, has significant flocculation effect. Therefore, FeF3 / 3H2O is used as a new type of manganese sulphate impurity removing agent, and by adjusting the pH value of the solution, calcium, magnesium, potassium is made. Sodium ions are precipitated successively to separate calcium, magnesium, potassium and sodium ions, which are more difficult to separate from ordinary manganese sulfate. In the high purity manganese sulphate products, the content of calcium, magnesium, potassium and sodium ions is lower than 100ppm, and the content of iron ions is lower than 10ppm. The products obtained can reach the high purity manganese sulfate for the production of battery grade or electronic grade manganese base. The requirements for the purity of potassium and sodium ions.
(2) using high pure manganese sulfate and sodium carbonate as precipitant and ammonia as complexing agent, the precursor of manganese carbonate with good spherical morphology was synthesized by coprecipitation method. The pH value, stirring rate, temperature and ammonia concentration in the reaction were discussed. The precursor was mixed with lithium carbonate and calcined, and the high end of the sphericity was synthesized. Spinel lithium manganate. The test results show that the synthetic high end spinel lithium manganese oxide has high density of compaction, and has obvious advantages in the first discharge capacity and cycle performance.
(3) with high purity manganese sulfate, aluminum sulfate and sodium carbonate as precipitant and ammonia as complexing agent, the spinel LiAlxMn2-xO4 series materials with good spherical morphology were synthesized by coprecipitation method and their electrochemical properties were studied. The study shows that the material with molecular formula for LiAl0.06Mn1.94O4 has the best high temperature cycling stability. In 55oC, Under the condition of 1C ratio, the discharge capacity of the sample after 100 charge and discharge is still 113.9mAh G1, and the capacity retention rate is as high as 97.0%.
(4) lithium zirconate coated lithium manganese zirconate was successfully synthesized with lithium zirconate as coating layer. The experimental results show that lithium zirconate is good in lithium ion conductivity and chemical inertness. Lithium zirconate as coating can effectively prevent the dissolution of manganese in the electrolyte, and it does not obstruct the insertion / release process of lithium ion. The electrochemical test shows that lithium ion is not obstructed. The material with a coating amount of 3wt.% has the best electrochemical and high temperature electrochemical properties. Under the condition of 25oC and 1C multiplying, the capacity retention rate of the first discharge capacity of 126.7mAh g1100 is 99%; 55oC and 1C multiplying condition, the initial discharge capacity is 90.2% after 129.5mAh g1100 charge discharge, and the charge transfer impedance Rct is 90.2%. The value is only 34.2, which is better than that of the uncoated lithium manganese material.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

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