【作者】 陈喻娟；

【导师】 杭义萍； 阮湘元；

【作者基本信息】 华南理工大学 ， 分析化学， 2010， 硕士

【摘要】 采用水热合成法制备一系列不同晶型结构和形态的二氧化锰粉体材料。利用X射线衍射(XRD)、电感藕合等离子体原子发射光谱(ICP-AES)、傅立叶变换红外光谱(FT-IR)、热重-差热分析议(TG-DTA)、场发射扫描电镜(FESEM)和电化学工作站等技术,并通过改变二价锰盐反应物的类型及掺杂镧元素对材料的结构、形态及电化学性能进行了深入的研究。以KMnO4和MnSO4为反应物,采用水热法制备纳米MnO2粉体。通过改变水热反应的温度、时间和酸度等反应条件,制备出α晶型的MnO2纳米棒。研究表明:水热反应时间及温度对MnO2晶型结构的影响不大,但MnO2的结晶度随反应时间的增加而增加。保持反应时间和温度不变,随着反应体系溶液pH的增加,二氧化锰产物结构由α-MnO2型向无定形MnO2转化,即在碱性条件下,更有利于无定形二氧化锰的形成。用AUTOLab电化学工作站测试不同条件下α-MnO2的放电性能。当水热反应时间为24小时、水热反应温度为140℃、溶液pH为1.5时生成的α-MnO2放电容量最高,为150mAh/g。分别以MnSO4、Mn(NO3)2和MnCl2为还原剂,与KMnO4反应。研究阴离子对产物的晶型结构、形态和电化学性能的影响。研究表明:在含NO3-或Cl-二价锰盐溶液中易形成γ-MnO2,在含SO42-二价锰盐溶液中有利于形成α-MnO2。相同的充放电条件下,含γ-MnO2的α-MnO2的粉体,其电极材料的首次放电容量比单相α-MnO2的容量高,可达203 mAh/g。为提高α-MnO2的循环充放电性能,对α-MnO2进行La元素掺杂改性。当La/Mn摩尔比为0.0029时,能有效的改善α-MnO2循环充放电性能,首次放电容量为122.7 mAh/g,循环放电28次后,放电容量为101 mAh/g,衰减容量占首次放电容量的17.7﹪,远远低于不掺杂La的α-MnO2电极材料,其衰减容量66.4﹪。随着La/Mn摩尔比的增加,掺杂La的α-MnO2的首次放电容量有所降低。研究表明掺杂适量La元素,能有效改善MnO2的循环放电性能,有效抑制MnO2容量的衰减,能够满足电池对材料的要求。更多还原

【Abstract】 In this thesis, manganese dioxide which have a series of different crystal structures and morphologies, have been prepared by a hydrothermal method. The crystal structure, morphology and electrochemical performance of productions have been studied deeply by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric - differential thermal analysis meeting (TG-DTA), field emission scanning electron microscopy ( FESEM) , electrochemical workstation and so on. The conclusion is summarized as follows:Nanomanganese dioxide was synthesized by hydrothermal method which used KMnO4 and MnSO4 as precursors. By investigating the influence of different hydrothermal reaction conditions, such as time, temperature and acidity, on the crystal structure, theα-MnO2 nanoclud was acquired. Results show that reaction time and temperature have little influence on the crystal structure of MnO2, but the Crystallinity of MnO2 increase with increasing reaction temperature. Keep the hydrothermal reaction time and temperature as constant, when increasing acidy of solution, the crystal structure of MnO2 change fromα-MnO2 to amorphous MnO2. Thus under alkaline conditions, it is more conducive to the formation of amorphous manganese dioxide.Discharge performance ofα-MnO2 which made under different conditions was tested by electrochemical workstation. The discharge capacity ofα-MnO2 is 150mAh/g which made under 24 hours, 140℃and solution pH of 1.5, it is the best in all. MnSO4, Mn (NO3)2 and MnCl2 were used as reducing agent, than reacted with KMnO4. Research the influence of anions on the crystal structure, morphologies and electrochemical properties of production. Results indicate that theγ-MnO2 forme only in NO3- or Cl- solution. Under the same concentration of K+, SO42- is propitious to formα-MnO2. The initial discharge capacity ofα-MnO2 which containedγ-MnO2 is 203 mAh / g, higher than single-phaseα-MnO2.To improve the cycle charge-discharge performance ofα-MnO2, we synthesized La-dopingα-MnO2 and studied its charge-discharge capability. La3+ can dope well intoα-MnO2 structure without forming La2O3 phase. When La/Mn was equal 0.0029, La could effectively improve charge-discharge capability ofα-MnO2. The initial charge capacity is 122.7 mAh/g, and then decrease to 101 mAh/g after 28 charge-discharge cycles. Attenuation capacity account for 17.7% of initial discharge capacity, far lower than 66.4﹪of La-undopingα-MnO2. The initial discharge capacity of La-dopingα-MnO2 decrease with increasing La/Mn, and capacity fade seriously.Studies show that doping amount of La element, can improve the cycle charge-diacharge performance of MnO2, and effectively inhibite the capacity of MnO2 to attenuate. It can meet the requirements of the battery material.更多还原