【作者】 郭晨峰；

【导师】 王殿龙；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2014， 博士

【摘要】 石墨由于具有平坦且较低的嵌锂电势，较低的成本和良好的循环性能成为商品化的负极材料。但是它的理论容量较低所以导致了电池的功率密度较低，而且安全性能较差。氧化硅(SiO)基材料具有体积和质量比容量高，价格低廉以及环境友好等优点，所以通常被认为是Si基材料中极具前景的锂离子电池负极材料。然而在嵌入/脱出锂离子过程中巨大的体积变化以及较低的电导率导致了电池容量的迅速衰减，限制了SiO基材料的实际应用。本研究以SiO为活性物质，石墨烯为缓冲载体，制备了二元复合材料—纳米氧化硅-石墨烯(SiO-石墨烯)复合物、电极体系—纳米三维(3D)氧化硅-石墨烯多层电极、三元复合材料—纳米碳包覆氧化硅-石墨烯(SiOx@C/RGO)复合物以及三元复合材料—纳米氧化硅@氮掺杂碳/氮掺杂石墨烯(SiO@NC/NG)复合物。对SiO基-石墨烯复合材料的制备方法、物理性质、电化学储锂性能及其储锂机制进行了深入的研究。以微米石墨为起始物质，采用改进的Hummers法制备得到了氧化石墨烯，并通过“化学还原法和热还原法结合”和“热处理法”得到还原石墨烯(RGO)和热处理石墨烯(TG)。通过对比实验，发现RGO更适合成为制备SiO基-石墨烯复合材料的良好缓冲载体。采用高速研磨法制备了纳米尺寸的SiO颗粒，相比商品化SiO材料，纳米化的SiO颗粒具有更高的比表面积和更好的循环性能。但纳米SiO颗粒也发生了较快的容量衰减，循环20次后，比容量衰减为0，所以不适合独立作为负极材料应用于锂离子电池中。采用“化学还原法和热还原法结合”和“机械混合法”制备SiO/RGO复合物和SiO+RGO混合物，通过对比实验发现SiO/RGO复合物比SiO+RGO混合物具有更优异的电化学性能。在电流密度为100mA g-1时，经过100次放充电循环后SiO/RGO复合物的可逆容量为774.3mAh g-1。通过倍率性能测试发现，当电流密度为800mA g-1时，SiO/RGO复合物的平均可逆容量只有191.5mAh g-1，其倍率性能还有待提升。通过考察不同石墨烯含量对电极的循环性能的影响，发现SiO与氧化石墨烯按照质量比为1:2进行制备时可以得到最佳的循环性能。此外，利用密度泛函理论计算对SiO基-石墨烯增强SiO电化学储锂性能的机理进行研究,深入到因无法测定Li+在金属性Si-石墨烯材料的界面反应的参数所以不能解释的范围，揭示金属性Si-石墨烯复合材料与Li+的迁移信息，从本源上解释SiO-石墨烯纳米复合物增加SiO的电化学储锂性能的作用机制。以3D多孔泡沫镍为集流体，取代传统的铜集流体，采用“交替粘附”的方法将纳米SiO颗粒和石墨烯负载在泡沫镍集流体上，制成电极体系-纳米3D SiO-石墨烯多层电极。通过对比实验发现纳米3D SiO-石墨烯多层电极的比容量远优于纳米3D SiO电极。在电流密度为100mA g-1时，经过100次循环后，纳米3D SiO-石墨烯多层电极保持了1369.5mAh g-1的可逆容量，400次循环后，可逆容量为1349.1mAh g-1，实现了较好的循环性能。当电流密度为极高的3200mA g-1时，依然有519.5mAh g-1的平均可逆容量。采用了C层和RGO层双层修饰方法设计并制备了三元复合材料-纳米SiOx@C/RGO复合物，并研究了其物理性质及电化学储锂性能。SiOx@C具有纳米级的粒径分布，SiOx@C/RGO具有极大的比表面积和典型的多孔结构。通过对比实验发现SiOx@C/RGO电极的电化学性能优于SiOx@C电极。SiOx@C/RGO电极在电流密度为100mA g-1时，首次放充电容量分别为2402.9mAh g-1和1225.5mAh g-1，首次库伦效率为51%。循环400次后，可逆容量为1264mAh g-1，仅比100次循环后可逆容量减少20mAh g-1，实现了较好的循环性能。当电流密度为极高的3200mA g-1时，依然有419.5mAh g-1的平均可逆容量。采用电化学阻抗测试和扫描电镜对C包覆层和RGO网络的协同储锂机制进行了分析，C包覆层对抑制活性物质的体积变化起着重要作用，C包覆层与RGO的协同效应保证了电极结构的稳定性进而提升了材料的电化学储锂性能。进一步利用C包覆层和RGO对SiO基复合物的作用机制示意图分析了其电化学储锂机制。进一步地分别对C层和RGO层进行氮掺杂修饰，制备得到三元复合材料-纳米SiO@NC/NG复合物，并研究了其物理性质及电化学储锂性能。纳米SiO@NC/NG三元复合物具有比纳米SiOx@C/RGO复合物更优异的电化学储锂性能：在电流密度为100mA g-1时，首次放充电容量分别为2465mA h g-1和1372mA h g-1，首次库伦效率为55.66%。电极经过500次循环，依然有1790mAh g-1的可逆容量。即使当电流密度为极高的3200mA g-1时，依然有580mAh g-1的平均可逆容量。最后，采用电化学阻抗测试和扫描电镜测试分析了纳米SiO@NC/NG电极提高的循环性能的作用机制。更多还原

【Abstract】 Graphite has been considered as the commercial anode material because of its flat and low insertion potential of Li+, low cost and preferable cycling performance. However, it suffers from safety issues, low theoretical capacity (leding to the low power density of batteries). SiO-based materials have been considered as promising Li-ion battery anode material among Si-based material owing to their high volume capacity and weight capacity, low cost and environmentally friendly properties. Nevertheless, the application of SiO-based has been limited due to the fast capacity fading, which arises from the large volume variation during the Li+insertion/deinsertion process and its low electrical conductivity. In this work, SiO material has been used as active material and graphene has been utilized as the buffered carrier to prepare binary composite material-nano-SiO-graphene composites, electrode system-nano-3D SiO-graphene multilayered electrode, ternary composite material-nano-SiOx@C/RGO composites and the ternary composite material-nano-SiO@NC/NG composites. The preparation strategy, physical properties, electrochemistry lithium storage properties and lithium storage mechanism of SiO-based-graphene composite material have been researched deeply. Graphene oxide was synthesized by a modified Hummers’ method, microngraphite was used as the starting material. The reduced graphene oxide(RGO) and high temperature treated graphene(TG) were prepared though the “the approach combinated chemical reduction method and thermal reduction method” and “method of heat treatment”. By comparison, RGO was founded as a more suitable buffering carrier in the preparation of SiO-based-graphene composite material. Nano-size SiO particles were prepared using the high speed grinding method which caused a higher specific surface area and better cycling performance than the commercial SiO particles. But the nano-SiO particles also have showed rapid capacity fading, and the specific capacity was reduced to0after20cycles, so it is not suitable for using nano-SiO particles independently as anode material for lithium-ion batteries. The SiO/RGO composites and SiO+RGO compounds were prepared though the “the approach combinated chemical reduction method and thermal reduction method” and “method of heat treatment”. The electrochemical properties of SiO/RGO composites were superior to SiO+RGO compounds according to the result of comparative experiment. The as-prepared composites exhibited a reversible capacity of774.3mAh g-1after100cycles at a current density of100mA g-1. Rate capability tests indicated that the composites exhibited weak high rate properties, and the reversible capacity was as low as191.5mAh g-1at800mA g-1, and the rate performance needs to be improved. By compared studying the effect of different content of graphene on cycling performance, we could get the best cycling performance through adjusting SiO and graphene oxide in accordance with mass ratio of1:2. The mechanism of the enhanced lithium storage performance of SiO-graphene compared with SiO was investigated by density functional theory.3D porous nickel foam current collector was used to replace traditional copper collector, an “alternating conglutination” method was developed to fabricate electrode system-nano-3D SiO-graphene multilayered electrode by loading nano-SiO paticles and graphene. The specific capacity of nano-3D SiO-graphene multilayered electrode were much better than the counterpart of nano-3D SiO electrode according to the results of comparative experiment. The reversible capacity of nano-3D SiO-graphene multilayered electrode was1369.5mAh g-1after100cycles at the current density of100mA g-1. After400cycles at the same current density, the reversible capacity was1349.1mAh g-1, which could realize a better cycling performance and the average reversible capacity was as high as519.5mAh g-1even at3200mA g-1.Ternary composite material-nano-SiOx@C/RGO composites was designed and prepared via a co-modification strategy. The physical properties and electrochemistry lithium storage properties of the composites were also investigated. SiOx@C shows nanosized particle size distributions, and SiOx@C/RGO typically shows the properties of enormous specific surface area and porous structure. The electrochemical performance of SiOx@C/RGO was better than the counterpart of SiOx@C according to the results of comparative experiment. Specifically, SiOx/C@RGO anode delivers a capacity of2402.9mAh g-1in the first discharge and1225.5mAh g-1in the first charge process, exhibiting an initial coulombic efficiency of51%. The reversible capacity of SiOx/C@RGO after400cycles is observed to be1264mAh g-1, which is only20mAh g-1less than that after100cycles and realizing a better cycling performance. The synergistic lithium storage mechanism between carbon coating layer and graphene was investigated by electrochemical impedance spectroscopy and FESEM, and mechanism of carbon coating layer and RGO on SiO-based composite materials was also proposed.Based on the co-modification strategy, a further modification action was operated to improve the double modification layer. Ternary composite material-nano-SiO@NC/NG composites was prepared. The physical properties and electrochemistry lithium storage properties of the composites were also investigated. The electrochemical performance of nano-SiO@NC/NG composites was better than the counterpart of SiOx@C/RGO. Nano-SiO@NC/NG anode delivers a capacity of2465mAh g-1in the first discharge and1372mAh g-1in the first charge process at the current density of100mA g-1, exhibiting an initial coulombic efficiency of55.66%. The reversible capacity of nano-SiO@NC/NG after500cycles is observed to be1790mAh g-1and the average reversible capacity was as high as580mAh g-1even at3200mA g-1. At last, mechanism of improved cycling performance of electrode of nano-SiO@NC/NG was investigated by electrochemical impedance spectroscopy and FESEM.更多还原