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Thesis Advisor陈仕谋 ; 张锁江  
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline应用化学
Keyword锂离子电池 负极 离子液体电沉积法

当前已经商业化的锂电池负极材料,主流产品为人造石墨和改性天然石墨,还有少量产业化应用的钛酸锂,可以基本满足一般电子产品、储能电池的要求。但由于它们的理论容量均不高,不能满足对电池储能具有更高要求的电动汽车及混合动力汽车等领域的发展需求。因此需要开发更多的具有高容量的电极材料,来提升电池能量密度。本课题选取锗作为研究对象,它的理论储锂容量高达1600mAh/g,远远高于石墨(372mAh/g),非常有潜力提高锂电池的性能。然而,锗负极材料在应用到锂电池中时,也面临着较大的问题与挑战,即在充放电过程中,随着Li+在电极材料中的嵌入与脱出,电极材料会发生体积变化,并且膨胀高达370%。这会直接引起材料的内部相互挤压,导致材料破碎并从集流体脱离下来,使锂电池的循环稳定性大幅度降低。本课题通过电沉积的方法,从离子液体中直接将锗离子还原,沉积到具有特殊结构的集流体上,得到Ge镀层/特殊结构集流体的复合电极。电化学测试表明,这种方法制备的负极可以较大程度地改善锗的电化学性能,主要工作包括:(1)以铜网集流体作为沉积基底,通过离子液体电沉积的方法,实现了在其表面上电沉积上一层致密的锗层。以此锗/铜网复合物直接作为锂电池的负极,研究材料结构对电池电化学性能的影响。经沉积的锗层由致密的纳米颗粒组成,且与铜网之间的结合比较牢固,不易脱离。研究表明,从第2次起到第55次循环,容量衰退减缓,比容量由原来的873mAh/g下降到了672mAh/g,容量保持率为76.9%。(2)以碳布集流体作为沉积基底,同样以离子液体电沉积的方法,制备锗/碳布复合电极。扫描电镜表征发现,在碳布纤维表面沉积的锗层具有“内疏外密”的双层结构。这种双层结构的锗镀层材料,不仅具有较高的比容量,还有效地缓解了材料在充放电过程中的体积变化严重的问题,使得材料的结构稳定性得以完善。电化学测试表明,在循环100次以后,电池的容量仍然高达989 mA h g-1,具有较高的容量保持率。

Other Abstract

Artificial graphite and modified natural graphite are the main commercialized lithium battery anode material. And a small amount use of lithium titanate is also applied in lithium batteries. These anode material can basically meet the requirements of general electronics and energy storage batteries. However, for the capacity of the commercial ones is not so high that cannot meet the rapid development of electric cars and hybrid vehicles, we need to find more electrode material with high capacity to improve the battery energy density . We choose germanium as the research object for its theoretical capacity as high as 1600 mAh/g, more than the graphite (372mAh/g), making it as an attractive electrode material for lithium batteries.However, similar to other electrode material that with high capacity, the key drawback of the Ge is the large volume change (up to 370%) during Li+ insertion/extraction, which leads to the pulverization of the electrode material and peeling off from the current collector. In this research, we syntheses the Ge-based material by ionic liquid electrodeposition method, to electrodeposit Ge from an ionic liquid on different current collector with special structure. Compared with the common method that by mixing adhesive, conductive material and electrode material together and then coating on the current collector, the Ge-based anode material by the ionic liquid electrodeposition method can be directly used as the integrated anode without using the adhesive and conductive material, which also simply the process of the synthesis of the electrode.The electrochemical tests show that this method can greatly improve the electrochemical performance of Ge-based material. The main research contents and achievements were summarized as follows:(1) A Ge/copper wire mesh anode has been successfully synthesized and characterized. The germanium layer deposited on the copper wire mesh is dense and consists of Ge nanoparticles. There is a firm contact between the Ge film and the surface of the copper wire mesh. Electrochemical tests shows that from the 2nd cycle to 55th cycle, the capacity drops from 873 mAh/g to 672 mAh/g slowly, remain at a rate of 76.9%.(2) The carbon cloth is also used as current collector to prepare the integrated anode by electrodepositing germanium on carbon cloth. The scanning electron microscopy (SEM) characterization shows that the Ge film on the surface of the carbon fiber has a double- layered structure: a porous inner layer of Ge island arrays and a compact Ge film outer layer. The double-layer structure can effectively buffer the volume change in the process of charging and discharging caused by the Li+ insertion/extraction, which further improves the cycle stability of the electrode. Electrochemical tests show that after 100 cycle, the capacity of the battery is still as high as 989 mAh/g, with a high retention of capacity. 

Document Type学位论文
Recommended Citation
GB/T 7714
张小红. 离子液体电沉积法制备锗基锂电池负极材料[D]. 北京. 中国科学院研究生院,2017.
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