【作者】 孙庆；

【导师】 史鹏飞；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2007， 硕士

【摘要】 锡基材料以它的高比容量(990mAh·g-1)有望取代碳材料作为新型锂离子电池负极材料。本文综述了锂离子电池发展情况,重点介绍了负极材料的研究概况,考察了热处理对SnCo材料性能的影响,并分别用球磨法和化学还原法制备了SnCo材料,并对其电化学性能进行了研究。分别对负极材料中活性物质,活性物质与乙炔黑,活性物质、乙炔黑及PVDF,和整个电极片进行了热处理。通过与未进行过任何热处理的极片性能比较发现不同形式热处理,对极片的性能均有所改善,其中尤以对整个极片进行热处理的方式最佳,极片初始容量有600mAh·g-1,在经过80次循环后容量仍能保持在300mAh·g-1以上。对于锡基材料,对其进行极片热处理不失为一种改善极片电化学性能的有效措施。采用球磨法对Sn:Co原子比分别为1:1、2:1和4:1三种比例进行了掺碳研究。在Sn:Co=1:1(原子比)下掺杂5mass%石墨的样品和在Sn:Co=4:1(原子比)下掺杂20mass%、30mass%乙炔黑两个样品性能均不好,容量不高,且衰减很快。在Sn:Co=2:1(原子比)下掺杂5mass%乙炔黑的样品与掺杂了5mass%石墨的样品,从SEM图中观察到掺杂乙炔黑的样品颗粒比较细小、均匀,而掺杂石墨的样品颗粒较大且石墨呈片状嵌入其中。XRD分析表明,掺杂石墨的样品中有晶体Sn的存在,而掺杂乙炔黑的样品则没有。在电化学性能上,掺杂乙炔黑的样品也明显要优于掺杂石墨的样品。掺杂乙炔黑在60次循环后容量仍能维持在400mAh·g-1以上,相比石墨,乙炔黑作为掺杂碳源更好。在掺杂5mass%乙炔黑的基础上将和膏工序中的乙炔黑也以球磨的形式加入到SnCo中去,这样制得乙炔黑掺杂量为15.5mass%的样品。其性能又大大改善,首次脱锂容量达到680mAh·g-1,循环60次后容量仍有530mAh·g-1。按此方式制备了乙炔黑掺杂比例为20mass%和25mass%的样,但是其性能均不好,将三种比例的性能比较呈现出乙炔黑掺杂比例越高,则容量越低,衰减越快的规律。在球磨法所考察的一系列材料中,向Sn:Co=2:1(原子比)中掺杂15.5mass%乙炔黑的样品性能最好。使用化学还原法制得性能较好的材料,首次不可逆容量损失为28%,首次脱锂容量达到822mAh·g-1,经过80次循环容量仍能维持在630mAh·g-1以上,库仑效率基本维持在97%以上。XRD分析检测到有Sn的氧化物的存在,ICP测试表明材料中含有少量B。对于材料性能较好的原因分析,通过实验排除了材料料径、极片活性物质载量、氧化物的存在这些因素的影响,最终确定反应条件为主要因素。反应条件决定材料中无定形态CoB化合物的含量,从而影响到材料的整体结构及电化学性能。ICP分析表明,pH对B的产生有很大影响,在pH≥12的碱性环境中得到的样品中B的含量是很少的,在酸性环境中得到的样品中B的含量相对较多。在pH相同的情况下,Co存在大大有利于B的生成,在酸性环境中这点更加明显。尝试了如机械球磨,逐步加Sn球磨,球磨与乳化相结合等方式来制备SnCoB三元材料,但性能与化学还原法得到的材料相比均相差太远。本文提出,将Sn分散于无定形态的化合物中,这种结构可以极大地缓解Sn嵌锂时引起的体积膨胀问题,得到容量高,循环性能好的Sn基材料。这为Sn基材料的性能改善提供了一个新的思路。更多还原

【Abstract】 Tin-based material for its high specific capacity (990mAh·g-1) is expected to replace the carbon material as a new Li-ion battery electrode material. This paper reviews the development of lithium-ion batteries, focus on the anode electrode material. The SnCo materials were prepared by both ball-milling and chemical reduction and the electrochemical performances of them were studied.The active material, active material & acetylene carbon, active material & acetylene carbon & PVDF and the entire electrode of anode were heat-treated respectively. Compared with the electrode without any heat-treatment, every kind of heat-treatment was beneficial to the electrochemical performance of the electrode. The electrode that entirely was heat-treated had the best performance, whose capacity was 600mAh·g-1 in 1st cycle and matianed above 300mAh·g-1 after 80 cycles. As to Sn-based material, it was a good measure for improving its electrode property to heat-treat the entire electrode.Three kinds of different atomic ratios of SnCo materials (Sn:Co=1:1, 2:1, 4:1) doped different content of carbon were prepared by the method of ball-milling. The samples of SnCo with 5mass% graphite and Sn4Co with 20mass% and 30mass% acetylene black all had bad properties with low capacity and rapid fading. Compared the sample of Sn2Co added 5mass% acetylene black with the sample of Sn2Co added 5mass% graphite, the SEM images showed the particles of the former were smaller and more homogeneous, and the sheet of graphite embedded into the particles of the latter. XRD indicated there was the crystal Sn in the latter, which wasn’t found in the former. The former had a better electrochemical performance. The sample of 5mass% acetylene black had a capacity of 400mAh·g-1 after 60 cycles. On the basis of the sample doping 5mass% acetylene black, the electric agent acetylene black was also joined into SnCo in the form of milling, the sample contenting 15.5mass% acetylene black had been made. Its performance had been greatly improved: the initial capacity of Li-extraction was 680mAh·g-1, through 60 cycles the capacity was still 530mAh·g-1. The samples of doping 20mass% and 25mass% acetylene black were made by this means too, but their performances were not good. The performance comparison of three samples in which the amount of acetylene black were respectively 15.5mass%, 20mass%, 25mass% revealed the rule that the more the content of acetylene black, the lower the capacity and the faster the decay.Adopting chemical reduction the material of better properties was synthesized. The initial irreversible loss of capacity was 28%, and the first capacity of Li-extraction reached 822mAh·g-1. After 80 cycles the capacity could keep 630mAh·g-1. Coulomb efficiency basically maintained above 97%. Tin oxides were detected in XRD analysis, ICP test showed the material containing a small amount of boron. These factors such as the dimension of particles, the mass of active material in electrode, the existence of tin oxides, had been excluded. Finally reaction condition was confirmed to respond for the good performance. Reaction condition decided the amount of the amorphous compounds CoB, that affected the overall structure of materials and electrochemical properties. ICP analysis indicated that the pH of the reaction system had a great impact on it. In the alkaline environment of pH 12 the content of boron in the sample was small. Contrarily, in an acidic environment it was relatively more. When the pH of the system was same, the existence of cobalt was greatly beneficial for the creation of boron, especially in an acidic environment. Several other approaches such as mechanical milling, milling of stepwise adding tin, the integration of milling and emulsification were attempted to produce ternary materials SnCoB. However, the performances of materials prepared were bad.In this paper, such structure that tin was dispersed into amorphous compound, can greatly alleviate the expansion caused by the Li-inertion. The Sn-based material of high capacity and good cyclic performance was hopefully obtained in this way. This paper provides a novel approach to improve the Sn-based material.更多还原