Knowledge Management System Of Institute of process engineering,CAS
|关键词||锂离子电池 负极材料 硅碳复合材料 多孔结构 纳米结构|
硅基材料是未来锂离子电池理想的负极材料，因其可以与锂形成合金并具有较高的理论容量（4200 mAh g-1），相当于商业化石墨碳容量（372 mAh g-1）的十倍多。然而硅在锂离子嵌脱过程中体积变化大（>300%）引起电极的粉化和硅与集流体的电接触减少，导致导电性变差和硅的利用率降低。这些因素导致硅基材料较高的不可逆容量和循环稳定性差等特点。近年来，在提高硅基材料的电化学性能方面取得明显的进步，通过制备纳米结构材料、复合材料和多孔材料来缓解循环过程中的体积变化并改善其导电性。基于此，本论文中，我们制备了多孔和纳米结构的锂离子电池硅碳复合物负极材料，通过物理化学方法表征，并对其电化学性能进行系统性的研究。第一，将工业生产中的废细碳粉回收用于锂离子电池负极材料。以蔗糖为粘结剂采用喷雾造粒的方法，将代表性的细碳粉针状焦和石墨化针状焦制成多孔碳微球。制备得到的多孔碳微球呈现较好的球形结构，其内部具有明显的孔结构和硬碳网络，这些特点都利于改善碳负极的电化学性能。研究发现石墨化多孔碳微球与商业化石墨球的容量相当，但前者具有更优的倍率性能。该部分工作表明可以采用工业废弃的石墨化和非石墨化的细碳粉制备微球形形貌的锂离子电池碳基负极材料，对工业中废弃细碳粉材料的回收利用具有指导意义。第二，由于内部存在孔结构，多孔碳微球的振实密度（0.47-0.56 g mL-1）小于商业化石墨球的振实密度（1.18 g mL-1），从而导致多孔碳微球具有相对较低的体积能量密度。因此，本部分，我们利用石墨化针状焦细碳粉废料和硅纳米颗粒，蔗糖作为粘结剂，通过连续球磨和喷雾造粒的方法制备得到多孔硅碳微球。制得的复合微球在氮气气氛下高温炭化后进行化学气相沉积对表面进行碳包覆。研究发现包覆后的多孔硅碳复合微球的容量明显高于商业化石墨微球，并具有优异的循环稳定性能与倍率性能。该工作证实了采用石墨化细碳粉和硅纳米颗粒制备性能优异的微球形锂离子电池硅碳负极材料的技术可行性。第三，为了进一步提高硅基负极材料的可逆容量，我们设计并发展了一种更简单、更绿色的合成方法来制备多孔硅。在高压反应釜中将冶金级硅粉与乙醇在铜基催化剂存在的条件下直接反应制备多孔硅材料，在其表面进行化学气相沉积碳之后制得多孔硅碳复合物。与其它的制备方法不同，该新的制备方法有效避免了任何昂贵仪器和模板的使用，同时避免了高毒性试剂（如SiH4和HF）的使用和复杂的制备过程（如模板去除和化学刻蚀）。同时，多孔硅材料的孔径、孔形状、孔深度和壁厚、颗粒尺寸和产率可以通过改变合成条件来调控。制备得到的多孔硅碳复合物用作锂离子电池负极材料可逆容量高，循环性能优异，该低成本、易操作和可放大生产的制备高性能硅碳负极材料的方法将有助于下一代锂离子电池的发展。第四，在第三部分的基础上，我们在高压反应釜中铜基催化剂存在的条件下，将冶金级硅粉与更多的乙醇反应更长的时间，结合球磨的方法制备得到硅纳米颗粒。硅纳米颗粒的尺寸可以通过改变反应时间来调控。在硅纳米颗粒表面进行化学气相沉积碳之后制备得到硅碳纳米复合物。该复合物用作锂离子电池负极材料表现出较高的可逆容量和优异的循环稳定性。同时，该方法所用的是铜基催化剂和冶金级硅粉，价格明显低于贵金属，并可回收利用，极大的降低了制备硅纳米材料的成本，使锂离子电池硅基纳米材料的简单和低成本合成成为可能。最后，我们课题组在之前的研究基础上，利用Rochow反应的方法，采用冶金级硅与氯甲烷反应制备得到纳米枝状硅碳复合物。通过在固定床反应器中铜基催化剂存在的条件下将冶金级硅粉与氯甲烷直接反应，硝酸刻蚀回收铜复合物之后制得。该纳米枝状复合物用于锂离子电池负极材料具有优异的电化学性能。该方法简单、低能耗和易放大的特点可以用来大量合成锂离子电池用硅碳纳米复合物。
Silicon (Si) is a very promising candidate anode material for next-generation lithium ion batteries, as it can alloy with lithium and possesses the high theoretical energy storage capacity of 4200 mA h g-1, more than 10 times higher than that of graphitic carbon (372 mA h g-1). However, the large volume change of Si (>300%) during repeated lithium insertion and extraction often causes electrode pulverization and gradual loss of electric contact between Si and the current collector, leading to the decrease of the electrical conductivity and inefficient utilization of Si. In general, the above phenomena can cause serious irreversible capacity and poor cyclability. In recent years, significant progress has been made in improving the electrochemical performance of Si-based anodes through preparing nanostructure materials, composites, and porous materials devoted to alleviating the volume change during cycling and to improving the conductivity. Based on these methods, in this thesis, porous and nano structure silicon/carbon composites anode materials for lithium ion batteries were prepared, characterized by physic and chemical technique, and carried out systematic research on their electrochemical performance.Firstly, in order to develop the carbon anodes from the waste fine carbon powders, we employed the spray drying method to make the porous carbon microspheres from the representative fine needle coke and graphitized needle coke powders using sucrose as the binder. The prepared porous carbon microspheres had not only the preferred spherical morphology, but also the well-developed inner porous structure and hard carbon network, very obvious structural characteristics conducive to the high performance carbon anodes. It was found that the capacity of graphitized microspheres was comparable to that of graphite microspheres but with much better rate performance. The work demonstrated the high technical feasibility of making microspherical carbon-based anode materials in lithium ion batteries from graphitized and non-graphitized fine carbon powders, which had guiding significance for recycling the waste fine carbon powders in industrial production.Secondly, the tap density of porous carbon microspheres (0.47-0.56 g mL-1) was less than that of graphite microspheres (1.18 g mL-1) because of the existence of inner porosity, leading to relatively low volume energy density of porous carbon microspheres. Therefore，in this section, we prepared porous Si/C microspheres by the successive ball milling and spray drying procedures using waste fine graphitized needle coke as the primary carbon resource, and Si nanoparticles as the Si source, as well as sucrose as the binder. The obtained spheres were carbonized in high temperature calcination in N2 and further deposited with carbon by the chemical vapor deposition method. It was found that the reversible capacity of carbon-coated porous Si/C microspheres was significantly more than graphite microspheres, as well as excellent cycling performance and rate performance. This work demonstrated the high technical feasibility of making high-performance micro-spherical Si/C anode materials for lithium ion batteries from graphitized fine carbon powders and Si nanoparticles.Thirdly, for further improving the reversible capacity of Si-based anode materials, we designed and developed a simpler and greener approach for the preparation of porous Si by directly reacting metallurgical-grade Si powders with ethanol in the presence of Cu-based catalysts in an autoclave. The Si/C composites were obtained after chemical vapor deposition of carbon. Differing from the established synthetic routes, this new route effectively avoided the use of any expensive equipment and template, highly toxic reactants (e.g., SH4 and HF) and complicated processing steps (e.g., template removal and chemical etching) needed to produce Si anodes with comparable cost and scalability to graphite anodes. Furthermore, the pore size, shape, depth and wall thickness, particle size, and the yield of porous Si materials could be readily tuned by varying the synthesis conditions. The synthesized Si/C composites were used as anode materials for lithium ion batteries which showed both high reversible capacity and good cycle life. This low-cost, easy-handling and scalable fabrication process of the high performance porous Si/C anode materials should contribute to the next generation lithium ion batteries.Fourthly, based on the section 3, we prepared Si nanoparticles by directly reacting metallurgical-grade Si powders with more ethanol and more reaction time in the presence of Cu-based catalysts in an autoclave, followed by ball milling. The size of Si nanoparticles could be controlled by adjusting the reaction time. The Si/C nanocomposites could be obtained after chemical vapor deposition of carbon on the surface of Si nanoparticles. When used as anode materials of lithium ion batteries, the Si/C nanocomposites exhibited high reversible capacity and excellent cycling stability. More importantly, the use of Cu composite and metallurgical-grade bulk Si, which was much cheaper than the noble metals and could be recycled, was expected to significantly lower the cost of Si nanostructure materials, making it possible for facile and low-cost production of Si nanostructure materials for applications in lithium ion batteries.At last, based on our previous research, we prepared Si/C nano branches via Rochow reaction by reacting metallurgical-grade Si powders with CH3Cl. Si/C nano branches were fabricated by directly reacting metallurgical-grade Si powders with CH3Cl in the presence of Cu-based catalysts in a fixed bed, followed by acid etching of Cu compounds. The obtained Si/C nano branches as anode materials of lithium ion batteries showed good electrochemical performance. The overall method was simple, energy-efficient and easy to scale-up for fabrication of Si/C nano-composites for lithium ion batteries.
|任文锋. 锂离子电池硅碳复合负极材料的合成及电化学性能研究[D]. 北京. 中国科学院研究生院,2016.|
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