电化学辅助制备大尺寸石墨烯及其在锂电池负极上的应用研究

发布时间：2018-03-17 11:11

本文选题：氧化石墨烯　切入点：锂离子电池　出处：《北京化工大学》2017年博士论文　论文类型：学位论文

【摘要】：自2000年,Poizot及其合作者在Nature期刊上首次报道以纳米级的过渡金属氧化物作为锂离子电池负极材料具有优异的电化学性能后,研究者们开始了过渡金属氧化物作为锂电池负极材料的研究热潮。过渡金属氧化物作为锂离子电池负极材料,具有理论比电容高、储备丰富的优点。但是过渡金属氧化物做锂离子电池负极同样存在很显著的缺点,即导电性差,在锂离子电池充放电过程中因体积变化剧烈导致电极结构遭到破坏从而缩短电池使用寿命。本论文先从石墨烯出发,首先采用电化学辅助Hummers法制备出大尺寸氧化石墨烯(GO),然后通过电沉积的方法将大尺寸GO与针状Mn02复合,从而实现结构与性能的改性,使得所制备的复合材料在锂离子电池中具有优异的电化学性能。以大尺寸GO为基础,通过电沉积法制备出石墨烯基三元复合锡铁氧化物(SnFe204/rGO)复合材料,以此复合材料组装成的锂离子电池电化学性能优异。具体研究内容包括以下几个方面:(1)以鳞片石墨做电极,稀硫酸溶液做电解液,恒压下采用电化学插层制备出尺寸大于300 μm的膨胀石墨粉。该膨胀石墨粉层间距d = 0.64 nm,含氧量是11.82%,碳氧比是C/O = 5.9, D峰和G峰的特征峰强度ID/IG= 0.21。通过电化学插层法预氧化处理后的膨胀石墨层间含有硫酸根离子,含硫量3.79%。酸根离子的存在有助于后期Hummers法制备GO时浓硫酸的插层氧化。以上述膨胀石墨粉为原料,采用改进的Hummers法制备的大尺寸GO,边长尺寸可达300 μm。通过HR-TEM取样50个分析,所制备的GO样品中有90%的层数小于5层。表征结果表明所制备的GO具有很高的氧化程度,D峰和G峰的特征峰强度ID/IG=0.94,碳氧比C/O为2.1,含氧碳的百分含量高达59.37%。(2)以大尺寸GO为基础,通过电化学沉积的方法制备出针状二氧化锰-亚毫米级还原氧化石墨烯(nMnO2-srGO)复合薄膜。将nMnO2-srGO复合薄膜作负极组装成锂离子电池,当nMnO2-sGO中MnO2的质量百分含量为76.9%时,锂离子电池具有最佳的电化学性能。具体表现为:循环稳定性测试中,在0.1 A·g-1的电流密度下,首次放电比电容是1850.7 mA h·g-1,200次循环后的放电比容量是1652.2m Ah·g-1,整个循环过程中比电容呈现明显的自增长趋势。倍率性能测试中,在电流密度分别为0.1 A·g-1,0.2 A· g-1, 0.5 A· g-1, A· g-1, 2 A· g-1 和 4 A· g-1时,对应的放电比容量分别为 946.1 mAh·g-1,877.7 mAh·g-1, 795.9 mAh·g-1,744.4 mAh·g-1, 707.3 mAh·g-1 和 616.8 mAh·g-1。电流密度从 0.1 A·g-1 扩大 40 倍到 4 A·g-1 时,比电容仍保留65.1%。当电流密度再次回到0.1 A·g-1时,其放电比容量是1064.5 mAh·g-1,高于最初10个循环的放电比容量946.1 mAh·g-1,具有明显的自增长现象。通过研究GO边长尺寸对以nMnO2-srGO为负极的锂离子电池的电化学性能的影响,证明了 GO尺寸的减小会导致锂离子电池的循环性能和倍率性能变差,同时证明了选择电沉积法制备nMnO2-srGO复合材料的合理性。(3)以大尺寸GO、Fe(NO3)3·9H2O、SnCl2·2H2O为原材料,通过电化学沉积法制备出新型的石墨烯基三元复合锡铁氧化物(SnFe2O4/rGO)材料。研究结果表明,SnFe2O4/rGO复合膜结构是“rGO-SnFe2O4颗粒-rGO”的多层孔隙结构,作为锂离子电池负极表现出优异的电化学性能。考察Fe(NO3)3·9H20和SnCl2·2H20的初始添加质量对SnFe2O4/rGO结构与性能的影响,结果表明,当二者的初始添加质量分别为202 mg和56.5 mg时,制备的SnFe2O4/rGO复合材料电化学性能最佳。在0.1 A·g-1的电流密度下,首次放电比容量1184.6 mA h·g-1,库伦效率83.1%。在0.1 A·g-1的电流密度下循环200次后比容量1018.5 mA h·g-1。倍率循环中,当电流密度从0.1 A·g-1扩大到4 A·-1后,比电容剩余百分比率高达61.2%,说明SnFe2O4/rGO复合物在大电流密度下的结构稳定性好。考察SnFe2O4/rGO的沉积密度对锂离子电池的电化学性能的影响,结果表明SnFe2O4/rGO的沉积密度对锂离子电池的循环性能和倍率性能无明显影响,但是由于沉积密度的增加,锂离子电池的内阻,尤其是SEI膜电阻和电荷转移电阻明显增大。考察GO尺寸对锂离子电池电化学性能的影响,结果表明随着GO尺寸的减小,以SnFe2O4/rGO为负极的锂离子电池的比电容减小。这一结论同时证明了选择电沉积法制备SnFe2O4/rGO复合材料的合理性。
[Abstract]:Since 2000, the first report of Poizot and its partners in the Nature Journal on transition metal oxide nano as anode materials for lithium ion battery has excellent electrochemical performance, the researchers began the research upsurge of transition metal oxide as anode materials for lithium ion batteries. Transition metal oxides as anode materials for lithium ion batteries, has a theoretical specific capacitance the advantages of high, rich reserves. But the transition metal oxide as the cathode of lithium ion battery are also very significant shortcomings, namely the poor electrical conductivity in the lithium ion battery charge and discharge process of severe electrode structure is destroyed so as to shorten the service life of the battery due to volume change. This paper starts from the first graphene based electrochemical assisted Hummers preparation of large size graphene oxide (GO), and then by the method of electro deposition to a large size of GO and Mn02 composite needle to. The modification of the structure and properties of the composite materials, the preparation has excellent electrochemical performance in lithium ion batteries. The large size GO based by electrodeposition method to prepare graphene based three element composite tin iron oxide (SnFe204/rGO) composite materials, the electrochemical properties of the composite lithium ion battery assembly excellent. The research contents include the following aspects: (1) the graphite electrode as the electrolyte, dilute sulfuric acid solution under constant pressure by electrochemical preparation of expanded graphite powder size larger than 300 m. The intercalation process of expanded graphite powder layer spacing of D = 0.64 nm, the oxygen content is 11.82%, the carbon oxygen ratio is C/O = 5.9, D peak and G peak intensities ID/IG= 0.21. by electrochemical intercalation of pre oxidation treatment of expanded graphite layer containing sulfate ions, the sulfur content of 3.79%. ions is beneficial to later prepared by Hummers GO The intercalation of concentrated sulfuric acid. The oxidation of graphite powder as raw material, the large size GO improved Hummers preparation, size up to 300 m. through 50 HR-TEM sampling analysis, the 90% GO prepared in a sample of less than 5 layers. The characterization results show that the prepared GO has a degree the oxidation is very high, ID/IG=0.94 characteristic peak intensity of D peak and G peak, carbon oxygen ratio of C/O is 2.1, the percent content of oxygen and carbon containing up to 59.37%. (2) to the large size of GO as the foundation, through electrochemical deposition method and preparation of manganese dioxide - acicular sub millimeter reduced graphene oxide (nMnO2-srGO) composite film. NMnO2-srGO composite film as cathode assembly of lithium ion battery, when the mass fraction of nMnO2-sGO in MnO2 was 76.9%, lithium ion battery has the best electrochemical performance. The specific performance: the cycle stability test, the current density of 0.1 A - g-1, for the first time The electrical capacitance is 1850.7 mA H - g-1200 cycles, the discharge specific capacity is 1652.2m Ah g-1, the whole cycle capacitance showed obvious growth trend. The rate performance test, the current density was 0.1 A - g-1,0.2 A - g-1 0.5 A - g-1, A - g-1, 2 A 4 - g-1 and A - g-1, the corresponding discharge was 946.1 mAh - g-1877.7 mAh - g-1 795.9 mAh - g-1744.4 capacity, mAh - g-1, 707.3 mAh g-1 and 616.8 mAh g-1. current density from 0.1 A g-1 to expand 40 times to 4 A - g-1, the specific capacitance remained when 65.1%. the current density returned to 0.1 A - g-1, the discharge capacity is 1064.5 mAh g-1, higher than the first 10 cycles the discharge capacity of 946.1 mAh / g-1, with self growth obviously. The effect of GO size on the electrochemical performance of nMnO2-srGO as anode materials for lithium ion batteries. The proof of the GO The decrease in size will lead to lithium ion battery cycling performance and rate variation, and proves that the electric nMnO2-srGO composite prepared by deposition method. The rationality of (3) to the large size of GO, Fe (NO3) 3 - 9H2O, SnCl2 - 2H2O as raw materials, through the electrochemical deposition of graphene based model the three element composite tin oxide (SnFe2O4/rGO) material. The results show that the SnFe2O4/rGO composite membrane structure is multi pore structure of rGO-SnFe2O4 particles, -rGO as anode for lithium ion batteries exhibit excellent electrochemical performance. The effects of Fe (NO3) 3 - 9H20 and SnCl2 - the initial 2H20 effects on the structure and quality. The results show that the performance of SnFe2O4/rGO, when the initial two additions were 202 mg and 56.5 mg, prepared by the electrochemical performance of SnFe2O4/rGO composites. The optimal current density of 0.1 A - g-1, the first discharge capacity of 1184.6 mA H g-1, Kulun 83.1%. efficiency of circulation in the current density of 0.1 A - g-1 under 200 times than the capacity of 1018.5 mA h g-1. circulation, when the current density increased from 0.1 A to 4 A - g-1 - -1, the specific capacitance of the remaining percentage as high as 61.2%, shows the structure stability of SnFe2O4/rGO complex in under the current density. The electrochemical performance of the SnFe2O4/rGO deposition density of lithium ion batteries. The results showed that no significant influence of deposition density of SnFe2O4/rGO lithium ion battery cycle performance and rate performance, but due to the increase of deposition density, the internal resistance of the lithium ion battery, especially SEI film resistance and charge transfer resistance increased obviously. The effects of GO size on electrochemical performance of lithium ion battery. The results show that with the decrease of the size of GO, with SnFe2O4/rGO as the ratio of capacitance decreases as anode materials for lithium ion batteries. This conclusion also proved that the choice of The rationality of SnFe2O4/rGO composites prepared by electrodeposition method.

【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM912;TQ127.11

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