铁酸锌复合纳米纤维材料的制备和电化学性能研究

发布时间：2018-09-09 13:18

【摘要】：近年来,环保问题如能源危机、环境恶化等由于其危害引起了广泛关注。相比于其他电池,锂离子电池由于优异的电化学性能以及绿色无污染等优点被认为是解决传统化石燃料短缺的有效途径。然而电动汽车和新型储能电站的发展对锂离子电池的性能提出了更高的要求,负极材料作为决定电池性能的主要部分,是研究人员的研究重点。由于过渡金属氧化物较高的理论比容量和静电纺纤维的高比表面、高孔隙率等的特点,将它们应用在锂离子电池的负极材料领域会有很好的前景。基于这一思路,本论文通过纳米化、碳材料复合或导电高聚物复合等手段制备得到铁酸锌纳米纤维(ZnFe_2O_4)、铁酸锌/石墨烯复合纳米纤维(ZnFe_2O_4/G)和铁酸锌/聚苯胺复合纳米纤维(ZnFe_2O_4/PANI)材料。其中ZnFe_2O_4纳米纤维作为主要储锂主体,文中研究了ZnFe_2O_4纤维的改性方法,分析了改性后的复合纳米纤维作为负极材料的电化学性能,并通过比较复合前后电化学性能差异得出性能改善原因。研究内容包括:(1)结合静电纺丝和高温煅烧的方法,首先利用静电纺丝法制得PAN/PVP/Zn(CH_3COO)2/Fe(NO_3)_3前驱体复合纳米纤维毡,然后分别在600 ℃和800 ℃条件下制得了ZnFe_2O_4纳米纤维。由XRD的表征图可知,相较于600 ℃,800 ℃条件温度下制得的ZnFe_2O_4纳米纤维具有更高的结晶度,SEM图像显示ZnFe_2O_4纳米纤维拥有粗糙的表面,由无数纳米颗粒构成,取向度良好,且粗细均匀,平均直径为150 nm左右。随后利用BET、TG、FTIR以及电化学性能测试等对所得纳米纤维样品进行了分析表征,实验结果表明,首次循环时ZnFe_2O_4纳米纤维具有较高的放电容量(1278mAh/g),循环50周之后仍保持550 mAh/g的容量。表明纳米化后的纤维具有较大比表面积和丰富孔隙,有利于锂离子嵌入/脱出,增强储锂性能,提高了材料的电化学性能。(2)为了进一步提高ZnFe_2O_4纳米纤维的性能,结合静电纺丝技术和水热还原法,通过添加氧化石墨烯制成ZnFe_2O_4/G复合纳米纤维。石墨烯拥有柔软的片层结构,包覆在纳米纤维表面后,能阻挡电极和电解液直接接触的同时,还能有效缓解充放电过程中金属氧化物的团聚,保持复合纤维的结构稳定。石墨烯良好的导电性也弥补了ZnFe_2O_4的性能缺陷,两种材料结合后能发挥很好的协同作用。实验结果表明,在300 mA/g下循环100周后容量稳定保持在900 mAh/g左右,当电流密度高达5000 mA/g时,可逆容量仍达711 mAh/g,显示良好的倍率性能。(3)结合静电纺丝和原位聚合法,制备了包覆不同质量比例苯胺的ZnFe_2O_4/PANI复合纳米纤维。电化学测试结果表明,PANI含量为15%时,电化学性能最佳,首次循环时放电容量达到1467.7 mAh/g,循环50周之后,仍能保持在1180 mAh/g,当电流密度提升到2000 mA/g时,可逆容量可达738 mAh/g,倍率性能优良。PANI的添加增加了材料的导电性,特殊的包覆结构为电化学反应时提供更多的活性位点,也为ZnFe_2O_4纳米纤维在反应过程中产生的体积膨胀压力提供了缓冲屏障。
[Abstract]:In recent years, environmental problems such as energy crisis and environmental deterioration have attracted much attention due to their harmfulness. Compared with other batteries, lithium-ion batteries are considered to be an effective way to solve the shortage of traditional fossil fuels due to their excellent electrochemical performance and green pollution-free. However, the development of electric vehicles and new energy storage power plants has brought lithium into the market. Because of the high theoretical specific capacity of transition metal oxides and the high specific surface area and high porosity of electrospun fibers, the application of transition metal oxides in the field of anode materials for lithium-ion batteries will be possible. Based on this idea, zinc ferrite nanofibers (ZnFe_2O_4), zinc ferrite/graphene composite nanofibers (ZnFe_2O_4/G) and zinc ferrite/polyaniline composite nanofibers (ZnFe_2O_4/PANI) were prepared by nanocrystallization, carbon composite or conductive polymer composite. In this paper, the modification methods of ZnFe_2O_4 fiber were studied, and the electrochemical properties of the modified composite nanofibers as anode materials were analyzed. The reasons for the improvement were obtained by comparing the electrochemical properties before and after the modification. PAN/PVP/Zn(CH_3COO)2/Fe(NO_3)_3 precursor composite nanofiber felt was prepared by spinning method. ZnFe_2O_4 nanofibers were prepared at 600 C and 800 C, respectively. The XRD characterization showed that ZnFe_2O_4 nanofibers had higher crystallinity than those prepared at 600 C and 800 C. SEM images showed that ZnFe_2O_4 nanofibers had higher crystallinity than those prepared at 800 C. The nanofibers were characterized by BET, TG, FTIR and electrochemical properties. The results showed that ZnFe_2O_4 nanofibers had high discharge capacitance at the first cycle. The results show that the nanofibers have large specific surface area and rich porosity, which is beneficial to lithium ion intercalation / detachment, lithium storage and electrochemical properties of the materials. (2) In order to further improve the properties of ZnFe_2O_4 nanofibers, electrospinning technology and water are combined. ZnFe_2O_4/G composite nanofibers were prepared by thermal reduction method with graphene oxide. Graphene has a soft lamellar structure. Graphene coated on the surface of nanofibers can block the direct contact between electrodes and electrolyte, at the same time, it can effectively alleviate the agglomeration of metal oxides during charging and discharging and maintain the structural stability of the composite fibers. The experimental results show that the capacity of ZnFe_2O_4 can be maintained at about 900 mAh/g after 100 weeks of cycling at 300 mA/g. When the current density is as high as 5000 mA/g, the reversible capacity still reaches 711 mAh/g, showing good rate performance. ZnFe_2O_4/PANI composite nanofibers coated with different mass ratios of aniline were prepared by spinning and in-situ polymerization. The electrochemical test results showed that the electrochemical properties of the composite nanofibers were the best when the content of PANI was 15%. The discharge capacity reached 1467.7 mAh/g at the first cycle and remained at 1180 mAh/g after 50 weeks of cycling. When the current density increased to 2000 mA/g, The reversible capacity can reach 738 mAh/g, and the rate performance is excellent. The addition of PANI increases the conductivity of the material. The special coating structure provides more active sites for the chemical reaction, and provides a buffer barrier for the volume expansion pressure of ZnFe_2O_4 nanofibers.
【学位授予单位】：江南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ340.64

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