【作者】 王闰冬；

【导师】 刘晓旸；

【作者基本信息】 吉林大学 ， 无机化学， 2011， 硕士

【摘要】 二氧化锰(MnO2)材料因其复杂的多孔结构而被广泛应用于电池、分子筛及催化等领域,受到了人们的广泛关注。同时MnO2作为电池阴极材料,价格低廉且对环境友好,已被研究多年,但目前实际应用中的MnO2的放电比容量与其理论容量相比尚有较大的提升空间,且因其循环性能不理想而在可充电池中的应用方面受到限制。它们的电化学活性取决于许多因素,但主要决定于二氧化锰的晶体结构。因此合成出晶体结构良好的二氧化锰材料具有重要的意义。传统的合成二氧化锰的方法主要有氧化还原沉淀法、水热法、低温固相法和溶胶-凝胶法等,但这些方法所合成出来的二氧化锰的尺寸普遍比较小,以纳米尺寸为主。利用高压技术可以得到许多常压下难以合成的新物质以及一些其他的具有特殊形貌和晶体结构的物质,助熔剂的使用可以降低反应的温度,使固体在熔融状态下发生反应,更有利于大单晶体的合成。因此,本论文主要研究了层状二氧化锰材料的合成及其结构的表征和电化学性能的测量,旨在通过高压方法合成出尺寸较大且电化学性能良好的二氧化锰电极材料。本文以MnO2为起始原料,以KOH作为助熔剂,在压力为100 MPa,温度为400℃的条件下,反应24 h,合成了新型层状化合物K0.33MnO162·0.4H2O。并对产物进行了XRD、EDS、TG、SEM和IR表征,以及电化学性能测量。化合物为片状单晶体,厚度大约为3-4μm,最大长度可以达到40-50μm,而且它具有很好的热稳定性,可以在700℃以下稳定存在；通过对其进行表征和性质测试,发现其具有良好的电化学性质,这也为制备大容量且性能良好的电池提供了新的途径。详细讨论了反应时间、反应温度、反应压力以及助熔剂摩尔比对K0.33MnO162·0.4H20组成和形貌的影响。实验结果表明,随着反应时间的增加,合成实验先生成δ-MnO2,之后会有少量的Mn304生成,当反应达到一定时间后,则全部转化为目标产物。而产物的形貌由小尺寸逐渐长成尺寸较大的片状单晶体。随着反应温度的升高,产物由Ko.33Mn0162·0.4H20逐渐转变为δ-MnO2,而且有少量的Mn304生成。产物的形貌由尺寸较大的片状晶体,逐渐变为尺寸较小的长条状晶体。在低配比时,反应物没有发生反应,随着配比的增加反应物逐渐反应,当配比达到1:20时反应物全部转化为产物,而且产物的晶体尺寸随着反应物配比的增加而增大。只有在高压下才能合成出Ko.33Mn0162·0.4H2O,并且高压产物的晶体尺寸也要明显大于常压产物的晶体尺寸。此外,本文采用高压助熔剂法还成功合成了δ-MnO2,并对其进行了结构的表征和性质的测试。与传统的合成方法相比,高压助熔剂法能合成出尺寸较大的δ-MnO2单晶体。X-射线粉末衍射测试表明,δ-MnO2的结晶度良好,属单斜晶系,空间群为C2/m,层间距约为0.72 nm；通过扫描电子显微镜观察其形貌,发现δ-MnO2为均一的圆形片状单晶体,厚度约为2-3μm,最大长度可达30-40μm；通过热重曲线分析得出,其具有良好的热稳定性,可以在800℃以下稳定存在；本文还通过红外光谱谱图初步分析了δ-MnO2的结构信息。更多还原

【Abstract】 Manganese oxide (MnO2) has been investigated widely because of its applications in batteries, separation and catalysis, and used as cathodes for batteries for long time due to its good economy and low toxicity. However, the specific capacity of MnO2 in practical Li/MnO2 batteries is lower compared to its theoretical value, and its cyclic performance is not good for application in rechargeable batteries. Their electrochemical activity depends on many factors, but mainly on the crystal structure of manganese dioxide. Therefore, the synthesis of the manganese dioxide with good crystal structure is of great importance.The traditional method for the synthesis of manganese dioxide include redox precipitation, hydrothermal, low-temperature solid state method and sol-gel method, etc. However, the size of manganese dioxide synthesized by these methods is generally nano size-based. By means of high pressure technology, many new substances or substances with some special morphology and crystal structure can be made up. The flux, which can reduce the reaction temperature, is more conducive to the synthesis of a large single crystal. Therefore, this paper investigated the synthesis of the layered manganese oxide and its structure characterization and electrochemical properties. The manganese dioxide synthesized by high pressure methods, has large size and good electrochemical performance.MnO2 was used as the starting material, KOH as the flux, and the reaction is under the conditions of 100 MPa,400℃and 24 h. In this paper, it is the first synthesis of a novel layered compound, K0.33MnO1.62··0.4H2O. The crystal structure, morphology and electrochemical properties have been studied deeply by means of powder X-ray diffraction (XRD), energy dispersive spectrometer (EDS), thermogravimetric (TG), scanning electron microscopy (SEM), and infrared spectroscopy (IR), ect. The product is flaky crystal, its thickness could reach about 3-4μm, and the largest diameter was 40-50μm Meanwhile, it also has good thermal stability, which is stable up to 700℃. And it shows that, it has good electrochemical performance, which offers a new way for preparation of the batteries of high capacity and good performance.In addition, we also discussed the influences of the reaction time, reaction temperature, pressure and reactant ratio on the composition and morphology of K0.33MnO1.62·0.4H2O. With increasing reaction time,δ-MnO2 was first generated, and then a small amount of Mn3O4 would appear. When a certain time is reached, they all converted into the target product, and the size of the product also increases. With rising reaction temperature, the K0.33MnO1.62·0.4H2O gradually transformed intoδ-MnO2, and a small amount of Mn3O4 was found, and the size of the product would be reduced. The starting materials could not be reacted with each other at the low ratio, and they gradually reacted with increasing the ratio. They would be all transformed into the product when the ratio reaches 1:20. The crystal size of the product increases with increasing of the ratio of reactants. K0.33MnO1.62·0.4H2O can only be synthesized by high pressure, and the crystal size of product synthesized by high pressure was significantly larger than that synthesized under the room pressure.We successfully synthesizedδ-MnO2 by high pressure flux, and characterized its structure and properties. Compared with the conventional synthetic methods, the single crystal ofδ-MnO2 synthesized by high pressure flux has a larger size. The corresponding X-ray diffraction results show that the crystallinity ofδ-MnO2 is good, and it is with monoclinic, space group C2/m, and the distance between the layers is about 0.72 nm. Its scanning electron microscopy shows that,δ-MnO2 was homogeneous single crystal with circular sheet, the thickness was about 2-3μm, the maximum diameter was 30-40μm. The TG curve shows that it has good thermal stability, and can be stable up to 800℃. By means of the infrared spectroscopy, we preliminarily analyzed the local structure information ofδ-MoO2.更多还原