【作者】 王东；

【导师】 温广武；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2013， 硕士

【摘要】 随着混合动力车和便携式电子设备的迅速发展，锂离子电池得到越来越广泛的应用，相应地对其比容量和循环稳定性提出了更高的要求。目前商品化的锂离子电池广泛采用石墨类负极材料，这类负极材料循环性能好，但是理论比容量较低（仅有372mAh/g），因此开发新型锂离子电池负极材料成为了研究热点。SiOC复合材料比容量大，合成工艺简单，但是循环稳定性和导电性有待于提高；膨胀石墨质地柔软，作为载体可缓冲SiOC的体积变化，同时提高负极材料的导电性。本文以含氢硅油、甲基乙烯基环硅氧烷和膨胀石墨为原料，采用裂解先驱体的方法制备了SiOC/膨胀石墨负极材料，对裂解过程以及裂解产物进行了一系列表征，并重点考察了其充放电性能和循环性能。DTA-TG分析表明SiOC/膨胀石墨先驱体裂解产率大约为80%，质量损失主要发生在200~800°C，这一温度段内先驱体内部持续发生断裂重排反应；先驱体以及裂解产物的FTIR光谱表明含氢硅油上的Si-H键与交联剂上的CH=CH2基团发生加成反应，裂解产物SiOC主要由Si-O-C和Si-O基团组成；XRD分析表明SiOC复合材料呈无定形态，与膨胀石墨复合之后，XRD图谱上出现了SiO2和SiC的衍射峰；从SEM照片可以看出SiOC/膨胀石墨负极材料粉末主要呈无规则片状，小颗粒依附于大颗粒，SiOC均匀包覆在膨胀石墨表面，厚度大约为几十至几百纳米，此外还发现了一些纳米线；EDS和XRF分析表明，SiOC中Si、O和C元素含量大约为46%、29%和25%。SiOC负极材料的首次放电比容量可达1300mAh/g，但循环性能较差，与膨胀石墨复合之后，负极材料首次放电比容量虽然略有下降，循环性能大大提高，这主要是因为“柔软”的膨胀石墨有效缓冲SiOC的体积变化。在首次充电和以后的循环过程中均没有发现电压平台，表明Li+脱插负极材料过程中没有发生稳定的氧化还原反应。SiOC/膨胀石墨负极材料掺杂Al之后，首次放电比容量有所下降，但是极大改善了循环性能，并且随着Al加入量的增大，首次放电比容量越来越低，循环性能越来越好。通过XRD分析发现，随着Al加入量的增多，XRD图谱上无定形趋势越来越大。随着SiOC/膨胀石墨负极材料中所采用膨胀石墨膨胀率的增大，其首次放电比容量和循环性能均得到提高，这是因为石墨膨胀率越高，负极材料比表面积越大，同时能更有效缓冲SiOC复合材料在脱插锂时产生的体积变化。实验中还发现采用石墨原粉制备的低膨胀率膨胀石墨，所得SiOC/膨胀石墨负极材料电化学性能好于粗颗粒石墨制备的高膨胀率膨胀石墨。本文还对采用乙二醇作为含氢硅油的交联剂制备SiOC/膨胀石墨负极材料作了简单研究。DTA-TG曲线表明先驱体裂解产率较低，原料间合适的配比有待于进一步确定；随着先驱体裂解温度的提高，负极材料电化学性能越来越好，当石墨膨胀率为47ml/g，裂解温度为1200°C时，SiOC/膨胀石墨负极材料首次放电比容量高达1354.4mAh/g，循环60次之后可逆容量仍高于300mAh/g。更多还原

【Abstract】 Along with the rapid development of hybrid car and portable electronic equipment, Lithium-ion battery is used widely, meanwhile there are higher request for the specific capacity and cycling stability. Now the anode materials of commercial lithium-ion batteries are graphite-based materials, the cycling performance of which is perfect but theoretical capacity(372mAh/g) is very low. So it is a research hotpot to develop new lithium-ion battery anode materials.SiOC compound has high specific capacity and simple synthetic process, but its cycle performance and electrical conductivity are bad. Exfoliated graphite(EG) is very soft, which could relieve volume change and increase electrical conducitivity of SiOC anode compound. Precursor is prepared by mixing hydrogen-containing silicone oil, cross-linking agent and exfoliated graphite. The comoposites of SiOC compound/EG are synthesized by heat treatment of this precursor for1h. The cracking process and pyrolysis product are analysed by XRD, SEM, TG and so on. Charge-discharge properties and cycle performance are studied with emphasis.DTA-TG curves indicate that the productivity of precursor is80%and quality loss mainly occurs between200℃to800℃, in which there are lots of break and rearrangement reaction; the FT-IR spectrum of SiOC compound/EG composites show that it is mainly composed of Si-O-C and Si-O groups; the XRD spectrum show that the composites is amorphous with diffraction peak of SiO2and SiC; from SEM photographs of the composites, we could see that most of the anode materials are irregular flakes with some small particles attached to large particles. Besides that we also find that graphite flakes are coated with a very thin layer of SiOC compounds, with some nanowire; EDX and XRF show that the mass fraction of Si, O and C are approximately46%,29%and25%.The first discharge capacity of SiOC can be almost1300mAh/g, but its cycle performance is bad. After compositing with EG, the first discharge capacity of anode materials decrease a little, but the cycling performance become better. This is mainly due to remission of SiOC compounds’volume expansion by soft exfoliated graphites. Voltage platform isn’t found in the charging procession of the first cycle and later cycles, which shows that in the process of Li+inserting anode materials there is no stable redox reaction.Adding aluminum powder into SiOC compound/EG composites can reduce its first discharge capacity but improve the cycle performance, and with the increasing amount of added Al, the initial discharge capacity become lower, meanwhile the cycle performance becomes better and better. The XRD spectrum of the anode materials with different amount of Al show that with the increaing amount of Al, more and more amorphous states can be found. Both of the first discharge capacity and cycle performance become better with the expansion rate of EG increase, and it is also found that when the EG is prepared by graphite row powder, the anode materials is better than others.The SiOC/EG composites prepared by a new kind of cross-linking agent glycol is also studied in this paper. TG-DTA indicates that the productivity of SiOC compound/EG is very slow. With the pyrolysis temperature become higher, the electrochemical of prepared anode materials become better and better. When the expansion of EG is47ml/g and the temperature of treatment is1200℃, the first discharge capacity of SiOC compound/EG anode materials is1354.4mAh/g, and the reversible capacity after60cycles still retains300mAh/g.更多还原