铁基纳米材料的制备及其电化学性能研究

发布时间：2018-07-06 14:39

本文选题：熔融盐焙烧法 + Fe_3O_4/C复合物　；参考：《新疆大学》2017年博士论文

【摘要】：追求安全、价格低廉和容量更高的电极材料已经成为了电化学探索领域的一个重要使命。在不同的电极材料中,磁铁矿就是一种很好的选择,因为它资源丰富、价格便宜、环境兼容性好、理论比容量高达约925 m Ah/g。基于此,以氯化铁作为铁源、以油酸钠或腐植酸钾为碳源,通过熔融盐模板法合成出形貌不同和尺寸不同的Fe基纳米颗粒和碳膜的复合物;紧接着对它们的锂离子电池、超级电容器等电化学性能进行了初步的探究。具体内容如下:首先,通过一步熔融盐焙烧法对氢氧化铁@油酸混合物前驱体进行焙烧,合成出了单分散的纳米Fe_3O_4立方体镶嵌在碳膜上的二维纳米复合物。在这个二维纳米复合物中,高分散的四氧化三铁纳米立方体被镶嵌在片状的碳膜载体上。对合成的立方体Fe_3O_4/C纳米复合物进行了系统的电化学性能测试。当样品被应用于超级电容器电极材料时,在1 A/g的电流密度下,600oC焙烧合成的S3-600的电容可以到达253.9 F/g,这是因为在复合物中的碳膜可以防止金属氧化物Fe_3O_4颗粒的团聚,保持住纳米晶体的形状和尺寸,由此来提高Fe_3O_4作为超级电容器的电化学性能。而当样品被用作锂离子电池负极材料时,在100 m A/g的电流密度下S3-600的首次可逆比容量可以高达3924.5 m Ah/g,循环充放电160圈后它的比容量还能达到2238.8 m Ah/g,而且比容量值还有继续增大的趋势;当改变电流密度时(100→1000→100 m A/g),S3-600电极材料的比容量从3092 m Ah/g逐渐降低到326 m Ah/g,而当减小电流密度时其容量又开始升高,达到875 m Ah/g,而且有继续升高的趋势。总体来说,600oC氩气气氛下焙烧后的Fe_3O_4/C复合材料无论是作为超级电容器,还是作为锂电负极材料都具有较好的倍率性能和循环性能,电化学方面有良好的应用前景。第二,通过一步熔融盐焙烧法对氢氧化铁@油酸的混合物直接在氨气气氛中焙烧得到均匀负载在碳膜上的纳米颗粒Fe_3O_4-Fex N(x=1,3)。通过对二维纳米结构的Fe_3O_4-Fe_xN/C复合材料进行形貌表征发现,在反应时不加碱、不加有机溶剂,焙烧温度700oC时得到的产物A3-700具有更加规整的形貌。此时样品形貌是尺寸均匀的立方体均匀镶嵌在碳膜上。将该产物应用于超级电容器电极后,在电流密度500 m A/g时样品的电容可以高达707.9 F/g,而当电流密度增大到3 A/g时,还能有147.4 F/g的电容。二维Fe_3O_4-Fe_xN/C复合材料拥有良好的赝电容性能可以归功于三点,(1)铁基化合物和碳膜之间的协同作用,(2)碳膜的高导电性,(3)氧化还原活性的铁基化合物的存在。在这里,结构规整、连续的碳膜所起的作用是:很好的保持住了金属颗粒的完整性,也增大了电极材料的电导性。这部分工作不仅提供了一条合成Fe_3O_4-Fe_xN/C复合材料的新思路,还证明了该材料应用于电化学方面的优势,为新一代先进能量存储设备的发展提供了可供参考的路径。第三,在该部分采用了二步熔融盐焙烧法,首先对氢氧化铁@油酸的混合物直接焙烧得到形貌均匀的负载在碳膜上的立方相Fe_3O_4,再通过氨气气氛二次焙烧得到二维纳米结构的Fe_3O_4-Fe_3N/C复合材料。将产物应用于锂离子电池负极材料后,结果表明,在100 m A/g时,700oC焙烧得到的样品B1-700的首次可逆容量有1107.1 m Ah/g,循环50圈后可逆比容量还能高达931.9 m Ah/g,比容量的循环维持率有84.2%。而当它们被应用于超级电容器时,在500 m A/g的电流密度下的电容高达480.5 F/g。这种较高的性能提高归因于氮化铁的存在,因为它的存在有利于电子和质量的传递,能够大大增强材料的电导率,也可以在电极材料的反应中防止氧化铁纳米颗粒的体积变化。另外,碳膜的存在也能防止金属颗粒的团聚,可以相应的改善超级电容器的电化学性能。这部分工作所制备的材料拥有结构紧致的形貌,这种形貌也可以降低复合物和电流集合体的接触阻力。最后,以价格廉价的腐植酸钾替代价格相对高的油酸钠作为碳源,通过一步熔融盐焙烧法对氢氧化铁@腐植酸混合物前驱体进行焙烧,成功合成出了纳米结构的Fe_3O_4颗粒镶嵌在碳膜上的二维纳米复合物。对合成的立方体Fe_3O_4/C纳米复合物进行系统的电化学性能测试后发现,碳和Fe_3O_4结合后发生的协同作用可以使材料拥有高的比容量和良好的倍率性。当把它应用到锂离子电池负极时,在0.5 A/g的充电-放电过程中,Fe_3O_4/C-750纳米片在第一圈的放电过程中有一个高达762.7 m Ah/g的储锂容量,充电时的可逆容量为747.3 m Ah/g,初次库伦效率可以高达98%;而在测试倍率性能时,随着电流密度从100 m A/g增大到2000 m A/g,Fe_3O_4/C-750电极材料的容量逐渐从477 m Ah/g降低到248 m Ah/g,当电流密度再返回到100 m A/g时,其容量还可以达到289 m Ah/g。这个结果表明,产物有高的可逆容量、高的首次库伦效率、还有明显增强的循环和倍率性能。最后,将样品应用到超级电容器电极材料时,样品Fe_3O_4/C-750电极在500 m A/g时的电容有265.6 F/g。样品之所以有这么强的电化学性能,主要可以归因于碳膜的存在,也即是Fe_3O_4/C复合材料中引入的导电碳膜可以大大提高金属氧化物的电导性,增强电极材料的电子传递速率和可调的应变性,同时也可以在电极材料的反应中防止氧化铁纳米颗粒的体积变化。
[Abstract]:The electrode materials for the pursuit of safety, low price and higher capacity have become an important mission in the field of electrochemical exploration. Magnetite is a good choice in different electrode materials, because it is rich in resources, low in price and good in environmental compatibility. The theoretical ratio is about 925 m Ah/g., based on this, iron chloride is used as iron. Source, using sodium oleate or potassium humate as carbon sources, Fe based nanoparticles and carbon films of different sizes and sizes are synthesized by molten salt template method. The electrochemical properties of their lithium ion batteries and supercapacitors are preliminarily investigated. The specific contents are as follows: first, by one step melting salt roasting method, Ferric hydroxide @ oleic acid mixture precursor was roasted and a monodisperse nano Fe_3O_4 cube embedded in the carbon film was synthesized. In this two-dimensional nanocomposite, highly dispersed ferric oxide nanoscubes were embedded in a sheet like carbon membrane carrier. The composite cube Fe_3O_4/C nanocomposites were synthesized. The electrochemical performance test of the system was carried out. When the sample was applied to the supercapacitor electrode material, the capacitance of the S3-600 produced by 600oC roasting at the current density of 1 A/g could reach 253.9 F/g, because the carbon film in the compound could prevent the agglomeration of the metal oxide Fe_3O_4 particles and keep the shape and ruler of the nanocrystalline. In order to improve the electrochemical performance of Fe_3O_4 as a supercapacitor, the initial reversible specific capacity of S3-600 at 100 m A/g can be as high as 3924.5 m Ah/g when the sample is used as a lithium ion battery anode material, and its specific capacity can reach 2238.8 m Ah/g after the cycle charge and discharge 160 cycles, and the specific capacity continues to continue. Increasing trend; when the current density is changed (100 to 1000 to 100 m A/g), the specific capacity of the S3-600 electrode material is gradually reduced from 3092 m Ah/g to 326 m Ah/g, and when the current density decreases, its capacity begins to rise, reaching 875 m Ah/g, and has a trend to continue to rise. Generally speaking, Fe_3O_4/C composites are baked in 600oC argon atmosphere. Either as a supercapacitor or as a lithium anode material, it has good multiplier performance and cycle performance, and has a good application prospect in electrochemistry. Second, a single step melting salt roasting method was used to roast the mixture of ferric hydroxide @ oleic acid directly in the ammonia atmosphere to get the nanoparticles Fe_ on the carbon film. 3O_4-Fex N (x=1,3). Through the characterization of the two-dimensional nanostructured Fe_3O_4-Fe_xN/C composite, it is found that the product A3-700 has a more regular morphology when the reaction is not added, without organic solvents, and the calcination temperature 700oC. At this time, the sample morphology is uniform in the size of the cube embedded in the carbon film. After the supercapacitor electrode, the capacitance of the sample can be as high as 707.9 F/g at the current density of 500 m A/g, and the capacitance of 147.4 F/g when the current density increases to 3 A/g. The good pseudo capacitance of the two-dimensional Fe_3O_4-Fe_xN/C composite can be attributed to three points, (1) the synergism between the iron base compound and the carbon film, (2) the carbon film. High conductivity, (3) the existence of redox active iron based compounds. Here, the structure regularization, continuous carbon film plays the role of keeping the integrity of the metal particles and increasing the conductivity of the electrode material. This part of the work not only provides a new way to synthesize Fe_3O_4-Fe_xN/C composites, but also proves that The application of the material to the electrochemical advantages provides a reference path for the development of a new generation of advanced energy storage equipment. Third, the two step molten salt roasting method is used in this part. First, the mixture of ferric hydroxide @ oleic acid is directly roasted to get a cubic phase Fe_3O_4 with a uniform negative load on the carbon film, and then through the ammonia gas. The Fe_3O_4-Fe_3N/C composite of two-dimensional nano structure was obtained at two times. After applying the product to the anode material of the lithium ion battery, the results showed that the first reversible capacity of B1-700 was 1107.1 m Ah/g, and the reversible specific volume of B1-700 was up to 931.9 m Ah/g after 50 cycles at 100 m. When the rate is 84.2%., when they are applied to the supercapacitor, the higher capacity of the capacitor at the current density of 500 m A/g is up to 480.5 F/g., which is attributed to the existence of iron nitride, because its existence is beneficial to the transmission of electrons and mass, can greatly enhance the electrical conductivity of the material, and can also prevent oxygen in the reaction of the electrode material. In addition, the presence of the carbon film also prevents the agglomeration of the metal particles, and can improve the electrochemical performance of the supercapacitor. The materials prepared in this part have the structure compact morphology, which can also reduce the contact resistance of the composite and electric current aggregation. Finally, the price is cheap. Potassium humate is replaced by potassium humate as a carbon source, and a two-dimension nanocomposite with nanostructured Fe_3O_4 particles embedded in the carbon film is successfully synthesized by a one-step melting salt roasting method to roast the precursor of ferric hydroxide @ humic acid mixture. The chemical performance test found that the synergistic effect of the combination of carbon and Fe_3O_4 can make the material have high specific capacity and good multiplier. When applying it to the negative electrode of the lithium ion battery, in the 0.5 A/g charging and discharging process, there is a 762.7 m Ah/g of Chu Lirong in the first lap of the Fe_3O_4/C-750 nanoscale. The reversible capacity of the charge is 747.3 m Ah/g, and the initial Kulun efficiency can be as high as 98%. While the current density increases from 100 m A/g to 2000 m A/g, the capacity of the Fe_3O_4/C-750 electrode materials gradually decreases from 477 m Ah/g to 248 m Ah/g. When the current density returns to 100 m, the capacity can also reach 289. Ah/g. results show that the product has a high reversible capacity, high first Kulun efficiency, and obviously enhanced circulation and multiplying performance. Finally, when the sample is applied to the electrode material of the supercapacitor, the capacitance of the sample Fe_3O_4/C-750 electrode at 500 m A/g has such strong electrochemical properties, which can be mainly attributed to the sample. Because of the presence of carbon film, that is, the conductive carbon film introduced in the Fe_3O_4/C composite can greatly improve the conductivity of metal oxide, enhance the electron transfer rate and adjustable change of the electrode material, and prevent the volume change of the iron oxide nanoparticles in the reaction of the electrode materials.
【学位授予单位】：新疆大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1;TM53

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