Si基纳米复合微球的构建及其储锂性能研究

发布时间：2018-06-25 03:05

  本文选题：锂离子电池 + 负极材料　； 参考：《湖南大学》2016年硕士论文

【摘要】：硅因为具有高的理论比容量(4200mAh/g)和丰富的资源而被作为锂离子电池最有前景的负极材料之一。但是硅负极材料低的导电率和严重的体积效应限制了其商业化应用。而碳材料,包括无定形碳和石墨烯等都具备导电导锂性能,在充放电过程中体积变化很小,而且具备优良的延展性,可以有效地缓冲硅在充放电过程中的体积变化,因此制备硅与碳材料的复合材料有望得到高性能的新型锂离子电池负极材料。本文分别采用微乳液法、喷雾热解法和喷雾干燥法制备无定型碳或石墨烯与硅的复合微球做为锂离子电池负极材料,并对制备的复合材料进行表征及电化学性能测试分析。通过微乳液法加镁热还原的两步法制备了Graphene/Si复合材料,对复合材料采用扫描电镜、X射线衍射等进行表征,并将其作为锂离子电池负极材料进行电化学性能测试,研究了不同石墨烯含量以及碳包覆对其电化学性能的影响。研究表明,Graphene/Si复合材料在石墨烯与Si02的比例为1:1时的电化学性能是最好的,100个循环后稳定在600mAh/g;对石墨烯与Si02的比例为1:2的样品进行碳包覆处理,碳包覆前的样品90个循环后容量不足400mAh/g,碳包覆之后90个循环后容量仍有700mAh/g。通过简单的超声喷雾热解和部分镁热还原的两步法成功制备了多孔的SiO2/Si/graphene/C微球。这种3-D结构的微球中,碳包覆的Si/SiO2纳米颗粒(5-10纳米)镶嵌于石墨烯的三维网络结构中,石墨烯不但可以提高微球的导电性,而且可以增强微球的结构强度。复合微球中的孔结构既可以容纳硅在嵌锂和脱锂时的体积膨胀和收缩,又可以为电解液提供存储的空间。将多孔微球做为锂离子电池负极材料,其表现出优异的循环稳定性,在0.1 mA/cm2的电流密度下,第二个循环的放电容量达到1104.9mAh/g,200个循环之后仍有1141.6mAh/g,容量保留率超过100%,使得复合微球成为很有前景的锂离子电池负极材料。通过喷雾干燥法成功制备了SiO2/graphene/C空心多孔微球,使用XRD、扫描电镜等手段对其进行了表征,并研究了不同比例的石墨烯含量对负极材料电化学性能的影响。将其作为锂离子电池负极材料测试其电化学性能,研究表明,随着微球中石墨烯含量的上升,负极材料的电化学性能越好,当Si02、蔗糖和氧化石墨烯的质量比为2:1:0.8时多孔微球的循环性能最好,100个循环后容量达到270mAh/g,而不含石墨烯的样品100个循环后容量只有80mAh/g。
[Abstract]:Silicon is regarded as one of the most promising anode materials for lithium ion batteries because of its high theoretical specific capacity (4200mAh/g) and abundant resources. However, the low conductivity and severe volume effect of silicon anode materials restrict their commercial application. However, carbon materials, including amorphous carbon and graphene, have the properties of conducting lithium, little change in volume during charge and discharge, and excellent ductility, which can effectively buffer the volume change of silicon during charge and discharge. Therefore, the composite materials of silicon and carbon are expected to obtain high performance cathode materials for lithium ion batteries. In this paper, amorphous carbon or graphene / silicon composite microspheres were prepared by microemulsion method, spray pyrolysis method and spray drying method, respectively. The composite materials were characterized and their electrochemical properties were analyzed. The Graphene / Si composite was prepared by two step method of microemulsion and magnesium thermal reduction. The composite was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The composite was used as anode material of lithium ion battery for electrochemical performance test. The effects of different graphene content and carbon coating on electrochemical properties were studied. The results show that the electrochemical performance of Graphene / Si composite is the best when the ratio of graphene to SiO2 is 1:1, and the 100 cycles are stabilized at 600mAh/ g, and the samples with the ratio of graphene to SiO2 are treated with carbon coating at 1:2. Before carbon coating, 90 samples have less than 400mAh/ g capacity after cycling, and 90 samples after carbon coating still have a capacity of 700mAh/ g. Porous Sio _ 2 / Si _ (2 / R) -C microspheres were prepared by simple ultrasonic spray pyrolysis and partial magnesium thermal reduction. In the 3-D microspheres, the carbon-coated Si / Sio _ 2 nanoparticles (5-10 nm) are embedded in the three-dimensional network structure of graphene. Graphene can not only improve the electrical conductivity of the microspheres, but also enhance the structural strength of the microspheres. The pore structure in the composite microspheres can not only accommodate the volume expansion and contraction of silicon in lithium intercalation and delithium removal, but also provide storage space for electrolyte. When the porous microspheres are used as anode materials for lithium ion batteries, they exhibit excellent cycling stability at the current density of 0. 1 mA/cm2. The discharge capacity of the second cycle is 1104.9mAh/ g, and after 200 cycles there are still 1141.6mAh/ g, and the capacity retention is more than 100, which makes the composite microspheres a promising cathode material for lithium ion batteries. SiO2 / graphene / C hollow porous microspheres were prepared by spray drying method and characterized by XRD and SEM. The effects of graphene content in different proportion on electrochemical properties of anode materials were studied. The electrochemical properties of the anode materials for lithium ion batteries were tested. The results showed that the better the electrochemical performance of the anode materials was with the increase of graphene content in the microspheres. When the mass ratio of sucrose to graphene oxide is 2: 1: 0.8, the porous microspheres have the best cycling performance, with the capacity of 270 mg / g after 100 cycles, while the capacity of 100 samples without graphene is only 80 mg / g.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB332;TM912
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本文编号：2064256