【作者】 李立朝；

【导师】 宋怀河；

【作者基本信息】 北京化工大学 ， 高分子化学与物理， 2007， 博士

【摘要】 自1990年Sony公司实现锂离子电池商业化以来，锂离子二次电池以其优越的性能受到各国研究工作者和企业的普遍重视。尽管人们广泛研究与开发别的替代产品，但炭电极材料以其高度的结构稳定性和良好的循环性能仍成为目前唯一实现商业化应用的锂离子电池负极材料。球形炭材料(也称炭微球)具有规则的形貌、光滑的表面、可控制的晶体结构和高的堆积密度，是一类极具优势和潜力的锂离子电池负极材料，其研究开发日益受到重视。针对目前以煤或石油芳烃重油为原料制备球形炭存在工艺路线复杂、球形度难以控制、颗粒大小不匀、成本高等不足，本论文立足于聚合物基可石墨化炭球的制备、结构及电化学性能研究。选用容易由分散聚合法合成得到的聚苯乙烯微球作为原料，其经过交联和高温处理后，可获得高度石墨化的碳材料。聚苯乙烯基炭微球制备的关键是提高其热稳定性和保持其在高温热处理中的球形形态。这里采用两种方法将聚苯乙烯微球交联成热固性的树脂：一是三氯化铝催化交联；二是与二乙烯基苯共聚后氧化交联。交联后的聚苯乙烯树脂经炭化、石墨化处理获得适宜作为锂离子电池负极材料的炭球。此外，研究并提出两种交联方式的反应机理；并测试聚苯乙烯基炭微球的电化学性能，获得比容量和炭结构间的关系，为新型球形炭材料的制备和广泛应用奠定基础。通过分散聚合法合成得到聚苯乙烯微球；以三氯化铝为催化剂、四氯化碳为交联剂对微球进行交联处理，得到热固性聚苯乙烯树脂；经炭化处理后获得粒径在3μm左右的中空和实心的两种炭微球。同时，经过交联处理，聚苯乙烯微球的炭化收率大大提高，由大约1％提高到30％。用XRD和IR对样品在改性处理前后结构和官能团的变化进行研究，提出三氯化铝为催化剂、四氯化碳为交联剂对聚苯乙烯改性的反应机理。在三氯化铝存在下，四氯化碳和聚苯乙烯间存在溶解和交联固化平衡，适量四氯化碳促进聚苯乙烯表面及内部发生交联反应。在较高的交联程度下，四氯化碳难以渗入聚苯乙烯微球内部，从而形成外层高交联-内部低交联的核壳结构聚合物微球，经炭化得到中空炭微球。聚苯乙烯经改性处理、炭化及石墨化处理后，0.2mA／cm~2下30循环后其锂离子电池的比容量稳定在360mA·h／g，0.8mA／cm~2下20循环后稳定在280mA·h／g，显示出高的比容量和良好的大电流充放性能。以二乙烯基苯为共聚单体，通过分散聚合制备了苯乙烯／二乙烯苯共聚微球，研究了二乙烯苯添加量对样品形貌和热性能的影响。对二乙烯苯添加量为0％、30％、50％、70％、100％的样品进行氧化、炭化和石墨化处理，结果表明，聚二乙烯基苯微球直接炭化后不能保持球形，氧化处理使聚二乙烯基苯微球在700℃炭化后保持球形。提出了氧化交联的机理：在热空气中，氧气和交联聚合物中的不饱和双键发生加成-氧化反应，生成羧酸基团和羟基，活泼基团进一步发生酯化反应得到更高交联度的聚合物。以炭化的样品作为锂离子电池的负极材料，研究了二乙烯基苯添加量对样品石墨化前后电化学性能的影响，样品PD50在0.2mA／cm~2下30循环后其锂离子电池的比容量稳定在250mA·h／g，0.8mA／cm~2下20循环后稳定在220mA·h／g。此外，研究了PVC基炭微球石墨化后的形貌变化和电化学性能，小电流(0.2mA／cm~2)30循环后其锂离子电池的比容量稳定在235mA·h／g，大电流(0.8mA／cm~2)下20循环后其锂离子电池的比容量稳定在215mA·h／g，显示很好的大电流充放电性能。并初步制备出聚二乙烯基苯包覆纳米硅粉和二氧化钛复合微球及聚苯乙烯包覆二氧化锡复合纳米球。更多还原

【Abstract】 Since Sony Company commercialized lithium ion batteries in 1990, lithium ion battery has been paid much attention by researchers and companies due to their advantages in electrochemical properties. Despite the considerable efforts to find other substituents, carbon materials still remain the only commercial anode for lithium ion batteries because of their steady structure and good circular properties. Among carbon materials, sphere-shaped carbon particles （or called carbon microbeads） are a kind of promising anode materials for Li-ion batteries owing to their regular morphologies, controllable crystal structure, smooth surface and high packing density.Mesocarbon microbead prepared from coal tar pitch or petroleum heavy oil is an attractive and competitive anode material for Li-ion batteries. However, there are some disadvantages, e.g., complicated process, wide size distribution and high cost. This thesis focused on the preparation, structure and electrochemical properties of carbon microbeads from polystyrene （PS） microspheres. Choosing polystyrene microspheres as the starting materials is based on their facile synthesis via the dispersion polymerization and the highly graphitizable ability when they are cross-linked and carbonized at high temperature. The key factor for the preparation of polystyrene-based carbon microbeads is how to realize the stabilization when PS microspheres are heat treated in inert gas atmosphere. Two kinds of techniques were tried to crosslink PS into thermosetting PS resin, i.e., AlCl3 and DVB modification. Carbon microbeads were obtained as anode materials for Li-ion batteries by carbonization and graphitization of the cross-linked polystyrene microspheres. In addition, the reaction mechanism for cross-linking of two-types was elucidated. The electrochemical properties of carbon microbeads were analyzed to find the relation between the structure of microbeads and the specific capacities. The above research provided a guide for preparation and wide applications of new kinds of spherical carbon materials.PS microbeads were prepared by dispersion polymerization. The thermosetting PS resin were obtained via the cross linking by CCl₄ under the catalysis of AlCl₃, and two kinds of carbon microbeads （solid or hollow spheres） with the diameter of 3μm were obtained by carbonization. Meanwhile, the carbonization yield of cross-linked PS microbeads was greatly improved from 1% to 30%. The changes of structure and functional groups of samples before and after modification were characterized by XRD and IR, and it was indicated that PS microbeads were modified by the cross-linked agent of CCl₄ under the catalysis of A1C1₃. With the aid of A1C1₃, there was a balance between the dissolution and solidification of cross-linking for PS microbeads and CCl₄, and the cross-linking reaction on the surface of and inner of PS was promoted by proper amount of CC1₄. It is difficult for CC1₄ to penetrate into the center of PS microbeads with high cross-linking degree, under which polymer microbeads with core-shell structure were obtained, and therefore hollow carbon microbeads were prepared by further carbonization. As anode materials for Li-ion batteries, the specific capacity of PS-based carbon sample after graphitization kept a stable value of 360 mA·h/g after 30 circles under the current density of 0.2 mA/cm² and of 280 mA·h/g after 20 circles under the current density of 0.8 mA/cm², suggesting the material possesses the high specific capacity and a high-rate charge-discharge capabilitis.Microbeads from the styrene--divinylbenzene copolymer were prepared by dispersion copolymerization, and the effect of DVB content on the morphology and thermostability of product were investigated. The results of oxidation, carbonization and graphitization of product with DVB content of 0%, 30%, 50%, 70% and 100% show that the spherical shape of copolymer microbeads could not be maintained after direct carbonization, while could be kept after oxidation and then carbonization at 700℃. The mechanism of cross-linking reaction induced by oxidation was proposed, i.e., during heat-treatment the oxidation crosslinking reaction took place between oxygen and pendant double-bonds in copolymers in air to form carboxyl and hydroxyl groups; and polymer with high degree of cross-linking were obtained by the esterification of active groups. The effect of DVB content on the electrochemical properties of carbonized and graphitized products were studied and the results show that the PD50 kept a stable specific capacity of 250 mA·h/g after 30 circles under the current density of 0.2 mA/cm² and of 220 mA·h/g after 20 circles under the current density of 0.8 mA/cm².In addition, the morphology and electrochemical properties of PVC-based carbon microbeads after graphitization were studied and the results show, that the specific capacity of the product kept a stable specific of 235 mA·h/g after 30 circles under small current density and of 215 mA·h/g after 20 circles under large current density.更多还原