铁基氧化物的制备与电极界面性能研究
发布时间：2018-09-04 10:16
【摘要】：简单过渡金属氧化物如MnO2、α-Fe2O3、Fe3O4、Cr2O3、Co3O4、MnO、Cu2O因能提供高达700mAh/g以上的可逆容量而受到广泛的关注，是极具潜力的新一代锂离子电池电极材料。其中，铁的氧化物（Fe2O3、Fe3O4）作为锂离子电池负极材料因具有较高的理论比容量和廉价、环境友好等优点受到较多的研究。但是铁的氧化物导电性能较差和在充放电过程中体积变化较大，用作负极时出现很差的循环性能和倍率性能，进而限制了铁的氧化物作为负极材料的应用。最常见的，也是最有效的解决方法是与碳材料进行复合或者制备具有特殊形貌结构的材料。基于以上两点，本文通过将不同种类的碳材料与铁的氧化物进行复合及制备特殊形貌结构铁的氧化物，旨在寻求此类高能密度正极材料的改性方案；重点运用电化学阻抗谱技术，探讨电极动力学过程及其电极界面的性能，寻求此类电极的容量衰减的机理。主要研究内容和结果如下： （1）利用高温固相反应法制备α-Fe2O3/C复合材料。运用X射线衍射（XRD）、扫描电子显微镜、充放电测试、电化学阻抗谱对其结构和电化学性能进行了表征。充放电测试结果显示，α-Fe2O3/C电极循环50周时可逆充电容量为935.3mAh/g，循环性能较商品化α-Fe2O3有显著改善。电化学阻抗谱测试结果显示，α-Fe2O3/C电极在首次嵌锂过程中分别出现了锂离子通过固体电解质相界面膜（SEI膜）的迁移、材料的电子电导率、电荷传递过程相关的半圆，并详细分析了它们的变化规律。 （2）采用水热合成的方法分别制备了α-Fe2O3/GNS、α-Fe2O3/CNTs复合材料和亚微米颗粒α-Fe2O3，系统研究了不同碳源对α-Fe2O3的形貌、结构和电化学性能影响。测试结果表明，α-Fe2O3/GNS和α-Fe2O3/CNTs电极有较高的可逆容量、倍率性能及在大电流下较长的循环寿命。复合材料电化学性能的提高归结于三个方面：一方面碳材料可以缓解由体积变化产生的应力及活性颗粒团聚现象；另一方面，复合材料具有的较大的表面积，使得电极/电解液接触充分；此外，碳材料可以提高电极的电子电导率。 （3）采用水热法制备了空心纳米结构的α-Fe2O3。随着反应时间的延长，α-Fe2O3出现了从棒状到管状的演变过程。通过对这一系列产物进行表征，得出管状的形成是由棒状从两端开始“溶解”再结晶的过程，且“溶解”的方向是沿着[001]晶向指数（C轴）。采用了不同反应物浓度（PO43-）制备α-Fe2O3，随着PO43-浓度的减少，α-Fe2O3出现了从桶状到环状的演变过程。通过对这一系列产物进行表征，得出阴离子（PO43-和SO42-）对产物形貌的调控作用是有所差别的。即，PO43-易于控制前驱体生长，SO42-更倾向于加速α-Fe2O3的“溶解”过程。对所制备的α-Fe2O3进行了电化学性能测试，表明管状的α-Fe2O3有最好的电化学性能。经过65周循环之后，纳米管状的α-Fe2O3电极可逆容量为1131mAh/g，容量保持率在83%。且在不同充放电电流下，管状的α-Fe2O3具有较好可逆容量和倍率性能，这与其特殊结构密切相关。 （4）采用水热法制备了Fe@Fe2O3核壳纳米颗粒与GNS、CNTs复合材料，Fe@Fe2O3/GNS电极在100mA/g下经过90周循环后，仍有959.3mAh/g的可逆容量，容量保持率在86.4%。在大电流密度下，经过280周循环后，Fe@Fe2O3/GNS电极的可逆容量仍然有515mAh/g。电化学阻抗谱测试结果显示，在首次嵌锂过程中，EIS的Nyquist图出现三个半圆，即高频区域的一个圆弧(HFA)，中频区域的一个半圆(MFS)和低频区域的一个半圆(LFS)，，并对每部分的归属进行了探讨，详细分析了它们的变化规律。 在100mA/g下经过60周循环后，Fe@Fe2O3/CNTs电极仍有702.7mAh/g的可逆容量。Fe@Fe2O3/CNTs电极具有较好的倍率性能，且在大电流充放电下，仍然具有较好的可逆容量。电化学阻抗谱测试结果显示，金属Fe和CNTs的存在有利于降低锂离子通过SEI膜和电荷传递电阻，进而使得Fe@Fe2O3/CNTs复合材料具有较好的电化学性能。 （5）采用溶剂热合成的方法合成了Fe3O4-HSs和Fe3O4-HSs/CNTs复合材料。在100mA/g下，Fe3O4-HSs/CNTs电极循环70周后，可逆容量高达1153.8mAh/g，容量保存率在87.8%；在10.0A/g大电流下，Fe3O4-HSs/CNTs电极经过350周长周期循环后，可逆容量仍然能够保持在552.7mAh/g。 采用水热、固相烧结的合成方法分别制备了Fe3O4/CNTs和Fe3O4/C复合材料。充放电测试显示：Fe3O4/CNTs、Fe3O4/C和商品化Fe3O4电极的首次放电容量分别为1421mAh/g、1651mAh/g和2104mAh/g，循环到55周时可逆容量分别为1030mAh/g、513mAh/g和280mAh/g。EIS测试表明，Fe3O4/CNTs电极在首次放电过程中，出现了高频区域与SEI膜相关的一个半圆，中频区域与电荷传递过程相关的一个半圆，低频区域与相变电阻相关的一个圆弧。
[Abstract]:Simple transition metal oxides such as MnO2, alpha-Fe2O3, Fe3O4, Cr2O3, Co3O4, MnO and Cu2O have attracted much attention because they can provide reversible capacities up to 700 mAh/g. They are potential electrode materials for lithium-ion batteries. Among them, iron oxides (Fe2O3, Fe3O4) have high theoretical specific capacities as anode materials for lithium-ion batteries. However, the poor conductivity of iron oxides and the large volume change during charging and discharging process lead to poor cycling and rate performance when used as negative electrode, which limits the application of iron oxides as negative electrode materials. Based on the above two points, in this paper, different kinds of carbon materials are compounded with iron oxides and iron oxides with special morphology are prepared. The purpose of this paper is to find the modification scheme of this kind of high energy density cathode materials. The dynamic process of the electrode and the performance of the electrode interface are discussed, and the mechanism of capacity decay of the electrode is explored.
(1) Alpha-Fe2O3/C composites were prepared by high-temperature solid-state reaction method. The structure and electrochemical properties of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge test and electrochemical impedance spectroscopy (EIS). The electrochemical impedance spectroscopy (EIS) results show that there are lithium ions migrating through the solid electrolyte phase interfacial film (SEI film) during the first lithium intercalation, the electronic conductivity of the material and the semicircle related to the charge transfer process.
(2) Alpha-Fe2O3/GNS, alpha-Fe2O3/CNTs composites and submicron particles of alpha-Fe2O3 were synthesized by hydrothermal method. The effects of different carbon sources on the morphology, structure and electrochemical properties of alpha-Fe2O3 were studied systematically. The improvement of the electrochemical properties of the composites can be attributed to three aspects: on the one hand, carbon materials can alleviate the stress caused by volume change and agglomeration of active particles; on the other hand, the large surface area of the composites makes the electrode/electrolyte contact fully; on the other hand, carbon materials can improve the electrode performance. Electronic conductivity.
(3) Alpha-Fe2O3 hollow nanostructures were synthesized by hydrothermal method. With the extension of reaction time, the evolution from rod-like to tubular morphology of alpha-Fe2O3 was observed. Index (C axis). Alpha-Fe2O3 was prepared with different PO43 -. With the decrease of PO43 -, a process from barrel-like to ring-like appeared in the formation of alpha-Fe2O3. SO42-tends to accelerate the "dissolution" of alpha-Fe2O3. The electrochemical properties of the prepared alpha-Fe2O3 were tested and the results show that the tube-like alpha-Fe2O3 has the best electrochemical performance. After 65 weeks of cycling, the reversible capacity of the nanotube-like alpha-Fe2O3 electrode is 1131 mAh/g, and the capacity retention rate is 83%. The -Fe2O3 has good reversible capacity and multiplying property, which is closely related to its special structure.
(4) Fe@Fe2O3 core-shell nanoparticles and GNS, CNTs composites were prepared by hydrothermal method. After 90 weeks of cycling at 100 mA/g, the reversible capacity of Fe@Fe2O3/GNS electrode was 959.3 mAh/g and the capacity retention rate was 86.4%. At high current density, after 280 weeks of cycling, the reversible capacity of Fe@Fe2O3/GNS electrode was 515 mAh/g. The results show that in the first lithium insertion process, three semicircles appear in the Nyquist diagram of EIS, namely, an arc in the high frequency region (HFA), a semicircle in the intermediate frequency region (MFS) and a semicircle in the low frequency region (LFS). The attribution of each part is discussed and their changing rules are analyzed in detail.
After 60 weeks of cycling at 100 mA/g, the reversible capacity of Fe@Fe2O3/CNTs electrode was still 702.7 mAh/g. Fe@Fe2O3/CNTs electrode had good rate-doubling performance, and still had good reversible capacity at high current charge-discharge. The results of EIS showed that the presence of Fe and CNTs was beneficial to the reduction of lithium ion passing through SEI film and electrochemistry. The charge transfer resistance makes Fe@Fe2O3/CNTs composites have better electrochemical performance.
(5) Fe3O4-HSs and Fe3O4-HSs/CNTs composites were synthesized by solvothermal synthesis. After 70 weeks of cycling at 100 mA/g, the reversible capacity of the Fe3O4-HSs/CNTs electrode was as high as 1153.8 mAh/g, and the capacity retention rate was 87.8%. At 10.0A/g high current, the reversible capacity of the Fe3O4-HSs/CNTs electrode remained at 552.7 m after 350 cycles. Ah/g.
Fe_3O_4/CNTs and Fe_3O_4/C composites were synthesized by hydrothermal and solid-phase sintering methods. Charge and discharge tests showed that the first discharge capacities of Fe_3O_4/CNTs, Fe_3O_4/C and commercialized Fe_3O_4 electrodes were 1421 mAh/g, 1651 mAh/g and 2104 mAh/g, respectively. The reversal capacities were 1030 mAh/g, 513 mAh/g and 280 mAh/g. EIS at 55 weeks. During the first discharge of the Fe_3O_4/CNTs electrode, a semicircle in the high frequency region related to the SEI film, a semicircle in the middle frequency region related to the charge transfer process, and an arc in the low frequency region related to the phase change resistance.
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912.9
本文编号：2221787
[Abstract]:Simple transition metal oxides such as MnO2, alpha-Fe2O3, Fe3O4, Cr2O3, Co3O4, MnO and Cu2O have attracted much attention because they can provide reversible capacities up to 700 mAh/g. They are potential electrode materials for lithium-ion batteries. Among them, iron oxides (Fe2O3, Fe3O4) have high theoretical specific capacities as anode materials for lithium-ion batteries. However, the poor conductivity of iron oxides and the large volume change during charging and discharging process lead to poor cycling and rate performance when used as negative electrode, which limits the application of iron oxides as negative electrode materials. Based on the above two points, in this paper, different kinds of carbon materials are compounded with iron oxides and iron oxides with special morphology are prepared. The purpose of this paper is to find the modification scheme of this kind of high energy density cathode materials. The dynamic process of the electrode and the performance of the electrode interface are discussed, and the mechanism of capacity decay of the electrode is explored.
(1) Alpha-Fe2O3/C composites were prepared by high-temperature solid-state reaction method. The structure and electrochemical properties of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge test and electrochemical impedance spectroscopy (EIS). The electrochemical impedance spectroscopy (EIS) results show that there are lithium ions migrating through the solid electrolyte phase interfacial film (SEI film) during the first lithium intercalation, the electronic conductivity of the material and the semicircle related to the charge transfer process.
(2) Alpha-Fe2O3/GNS, alpha-Fe2O3/CNTs composites and submicron particles of alpha-Fe2O3 were synthesized by hydrothermal method. The effects of different carbon sources on the morphology, structure and electrochemical properties of alpha-Fe2O3 were studied systematically. The improvement of the electrochemical properties of the composites can be attributed to three aspects: on the one hand, carbon materials can alleviate the stress caused by volume change and agglomeration of active particles; on the other hand, the large surface area of the composites makes the electrode/electrolyte contact fully; on the other hand, carbon materials can improve the electrode performance. Electronic conductivity.
(3) Alpha-Fe2O3 hollow nanostructures were synthesized by hydrothermal method. With the extension of reaction time, the evolution from rod-like to tubular morphology of alpha-Fe2O3 was observed. Index (C axis). Alpha-Fe2O3 was prepared with different PO43 -. With the decrease of PO43 -, a process from barrel-like to ring-like appeared in the formation of alpha-Fe2O3. SO42-tends to accelerate the "dissolution" of alpha-Fe2O3. The electrochemical properties of the prepared alpha-Fe2O3 were tested and the results show that the tube-like alpha-Fe2O3 has the best electrochemical performance. After 65 weeks of cycling, the reversible capacity of the nanotube-like alpha-Fe2O3 electrode is 1131 mAh/g, and the capacity retention rate is 83%. The -Fe2O3 has good reversible capacity and multiplying property, which is closely related to its special structure.
(4) Fe@Fe2O3 core-shell nanoparticles and GNS, CNTs composites were prepared by hydrothermal method. After 90 weeks of cycling at 100 mA/g, the reversible capacity of Fe@Fe2O3/GNS electrode was 959.3 mAh/g and the capacity retention rate was 86.4%. At high current density, after 280 weeks of cycling, the reversible capacity of Fe@Fe2O3/GNS electrode was 515 mAh/g. The results show that in the first lithium insertion process, three semicircles appear in the Nyquist diagram of EIS, namely, an arc in the high frequency region (HFA), a semicircle in the intermediate frequency region (MFS) and a semicircle in the low frequency region (LFS). The attribution of each part is discussed and their changing rules are analyzed in detail.
After 60 weeks of cycling at 100 mA/g, the reversible capacity of Fe@Fe2O3/CNTs electrode was still 702.7 mAh/g. Fe@Fe2O3/CNTs electrode had good rate-doubling performance, and still had good reversible capacity at high current charge-discharge. The results of EIS showed that the presence of Fe and CNTs was beneficial to the reduction of lithium ion passing through SEI film and electrochemistry. The charge transfer resistance makes Fe@Fe2O3/CNTs composites have better electrochemical performance.
(5) Fe3O4-HSs and Fe3O4-HSs/CNTs composites were synthesized by solvothermal synthesis. After 70 weeks of cycling at 100 mA/g, the reversible capacity of the Fe3O4-HSs/CNTs electrode was as high as 1153.8 mAh/g, and the capacity retention rate was 87.8%. At 10.0A/g high current, the reversible capacity of the Fe3O4-HSs/CNTs electrode remained at 552.7 m after 350 cycles. Ah/g.
Fe_3O_4/CNTs and Fe_3O_4/C composites were synthesized by hydrothermal and solid-phase sintering methods. Charge and discharge tests showed that the first discharge capacities of Fe_3O_4/CNTs, Fe_3O_4/C and commercialized Fe_3O_4 electrodes were 1421 mAh/g, 1651 mAh/g and 2104 mAh/g, respectively. The reversal capacities were 1030 mAh/g, 513 mAh/g and 280 mAh/g. EIS at 55 weeks. During the first discharge of the Fe_3O_4/CNTs electrode, a semicircle in the high frequency region related to the SEI film, a semicircle in the middle frequency region related to the charge transfer process, and an arc in the low frequency region related to the phase change resistance.
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912.9
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