钼基纳米材料的合成及其电化学性能研究

发布时间：2018-03-21 22:17

本文选题：氧化钼　切入点：MoO_2/RGO　出处：《新疆大学》2017年硕士论文　论文类型：学位论文

【摘要】：锂离子电池(Li-ion Battery,LIB)因具有较长的循环寿命、较高的能量密度、对环境比较友好而受到广泛应用,小到便携式电子产品(手机、手表)大到电动汽车等生活的各个方面。石墨的成本不高,工作电势比较低,最重要的是它的导电性很好,所以石墨是目前使用最普遍、也是最早商业化的锂电负极材料。然而石墨本身的结构特征使它在脱嵌锂的过程中(富锂状态)下容易生成LiC_6这种计量比的石墨层间化合物,而局限了多个碳原子中只能插入一个锂,从而导致的结果就是可逆容量比较低,只有三百多毫安时每克,在一定程度上不能满足目前的商业要求。所以,当今社会,人们对锂离子电池有了电容量更高这样的要求,这就促使科研人员正在研究比现有技术更先进、性能更好的新型材料。要取得这样的成果,必须要选择容量更高、稳定性更好的电极材料,以期在保证安全的前提下,最大限度的提高电池容量、循环寿命和充放电速率。钼系氧化物和硫化物纳米材料储量比较丰富,而且将其用作LIB负极材料时,表现出了优异的电化学性能,到目前为止已成为电化学方面的研究热点。本文通过溶剂热法合成了不同形貌的氧化钼纳米材料和MoO_2/还原氧化石墨烯复合纳米材料;利用熔融盐焙烧法合成了MoS_2/C复合纳米材料,并对合成的这些样品在锂电方面的应用性进行了研究。首先我们用二水合钼酸钠为钼源,通过两相溶剂热法调控得到了不同形貌和物相的氧化钼纳米材料,再将电化学性能比较好的样品Mo-200(即单斜晶系的MoO_2)与还原氧化石墨烯进行复合,探讨还原氧化石墨烯的加入对该材料在电化学性能上的提高;最后以新疆特色资源腐植酸钾为碳源,利用熔融盐焙烧法成功制备了MoS_2/C复合纳米材料,之后将合成的材料用作LIB负极材料,并且还与商品MoS2在电化学方面的性能进行了对比研究。具体研究内容如下:(1)两相溶剂热法合成不同形貌的氧化钼纳米材料及其电化学性能研究:利用两相溶剂热法,通过改变溶剂热的温度,对产物的物相和形貌进行了调控,并对其进行了电化学性能测试。电化学研究表明:200 o~C水热下得到的样品(Mo-200)即单斜相的MoO_2表现出了最佳的循环稳定性和倍率性能,它在电流密度为100 mA g~-1的条件下循环50圈之后,电化学容量还是能够保持在485.3mAh g~-1,比其他溶剂热温度下(120,150和180 o~C)得到样品的放电比容量要高。(2)两相溶剂热法合成MoO_2/还原氧化石墨烯(MoO_2/RGO)纳米复合材料及其电化学性能研究:将Mo-200与氧化石墨烯(GO)进行复合,在这个过程中,GO被高温水热还原得到还原氧化石墨烯(RGO),最终我们得到MoO_2/RGO复合纳米材料。电化学研究表明,加入一定量的RGO后,MoO_2/RGO复合纳米材料的导电性提高,阻抗变小,表现出了更加优异的电化学性能,在电流密度为100 mA g~-1的条件下循环50圈之后,电化学容量依然能够保持在765.1mAh g~-1,比单一MoO_2的放电比容量高279.8 mAh g~-1。(3)以腐植酸钾为炭源制备MoS_2/C复合纳米材料及其电化学性能研究:利用价格低廉的新疆特色资源腐植酸钾为炭源,直接焙烧得到MoS_2/C复合纳米材料,通过改变焙烧温度,对产物的形貌进行了调控,并对其进行了电化学性能测试。电化学研究表明:700 o~C焙烧得到的MoS_2/C表现出了最佳的循环稳定性和倍率性能,它在电流密度为100 mA g~-1的条件下循环50圈之后,电化学容量依然能够保持在554.9 mAh g~-1。
[Abstract]:Lithium ion battery (Li-ion, Battery, LIB) because the cycle life is longer, higher energy density, more friendly to the environment and has been widely applied to small, portable electronic products (mobile phone, watch) to electric cars and other aspects of life. The graphite cost is not high, the working potential is relatively low, the most important is it a good conductivity, so the graphite is currently the most commonly used, but also the first commercial lithium ion battery anode material. However, due to its structural characteristics of graphite in the process of Li + intercalation (lithium rich state) easy to generate LiC_6 the measurement of graphite layer ratio compounds, and a number of limitations you can only insert a carbon atom in lithium, which is the result of the reversible capacity is relatively low, only more than 300 Ma per gram, can not meet the requirements of the business to a certain extent. So, in today's society, people of a lithium ion battery Higher capacitance of such requirements, which prompted researchers are working on more advanced than the existing technology, new materials with better properties. To achieve such results, we must choose the higher capacity, better stability of electrode materials, in order to ensure the safety of the premise, improve the capacity of the battery to the greatest extent, circulation life and charge discharge rate. Rich molybdenum oxide and reserves, and be used as anode material LIB, showed excellent electrochemical performance, so far has become a research hot point of electrochemistry. This paper through the solvothermal synthesis of different morphologies of molybdenum oxide nano materials and MoO_2/ graphite oxide graphene nanocomposites reduction; MoS_2/C nanocomposites were prepared by molten salt roasting method, and the application of the synthesis of these samples in the aspects of lithium was studied. First, we With two hydrated sodium molybdate as molybdenum source by solvent thermal method regulation with different morphologies were obtained and molybdenum oxide nano material phase, then the samples Mo-200 better electrochemical properties (i.e. monoclinic MoO_2) and reduction of graphene oxide compound, investigation of redox graphene added to improve the material in the electrochemical performance; taking Xinjiang characteristic resources of potassium humate as carbon source, MoS_2/C nanocomposites were prepared by molten salt roasting method was successful. After the synthetic material is used as anode material LIB, and also with the goods in the electric chemical properties of MoS2 was studied. The main research contents are as follows: (1) study of molybdenum oxide nanomaterials with different morphologies and electrochemical properties of synthetic two-phase solvothermal method using two-phase solvothermal method, by changing the solvent thermal temperature, phase and morphology of the products were regulation, And has carried on the electrochemical performance test. Electrochemical studies indicate that 200 o~C hydrothermal samples (Mo-200) namely monoclinic phase MoO_2 showed the best cycle stability and rate capability, after it at a current density of 100 mA g~-1 under the condition of 50 cycles, the electrochemical capacity can still keep in 485.3mAh g~-1, other than the solvothermal temperature (120150 and 180 o~C) to get the discharge specific capacity of the sample is higher. (2) the synthesis of MoO_2/ two-phase solvothermal reduction of graphene oxide (MoO_2/RGO) nano composite material and its electrochemical properties: Mo-200 and graphene oxide (GO) compound, in this process, GO by the reduction of graphene oxide high temperature hydrothermal reduction (RGO), we obtained MoO_2/RGO nanocomposites. The electrochemical studies show that adding a certain amount of RGO, the conductivity of MoO_2/RGO nanocomposites increased, impedance becomes small , showed more excellent electrochemical performance, after the current density is 100 mA g~-1 under the condition of 50 cycles, the electrochemical capacity is still able to maintain in the 765.1mAh g~-1 than single MoO_2 discharge of high specific capacity of 279.8 mAh g~-1. (3) to study the electrochemical properties of MoS_2/C composite nano material and its preparation process of potassium humate as carbon source using cheap Xinjiang characteristic resources of potassium humate as carbon source, directly calcined to obtain MoS_2/C nanocomposites, by changing the calcination temperature on the morphology of the products was regulated, and its electrochemical performance test. Electrochemical studies indicate that 700 o~C roasting MoS_2/C showed optimal cycling stability and rate capability after that, the current density is 100 mA at g~-1 under the condition of 50 cycles, the electrochemical capacity can still maintain at 554.9 mAh g~-1.

【学位授予单位】：新疆大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1;TM912

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