高容量锂离子电池硅负极材料及其电化学性能研究

发布时间：2018-04-01 22:25

本文选题：纳米Si　切入点：多壁碳纳米管　出处：《南昌大学》2017年硕士论文

【摘要】：硅由于其极高的理论比容量(4200mAh/g)、较低的嵌锂电压、资源丰富等优势成为新一代最有潜力的锂离子电池负极活性材料。但是其电导率低和充放电过程中高达4倍的体积效应导致的循环性能差问题严重阻碍了硅在锂离子电池中的商业应用。本文选用粒径为100 nm的纳米Si粉为硅源,采用人造石墨(G)或多壁碳纳米管(MWCNTs)与纳米Si粉复合、以CNT导电纸代替传统铜箔集流体、预锂化处理等手段对硅基锂离子电池进行改性,观察其形貌和结构,组装成扣式半电池后,通过恒流充放电、电化学阻抗等方法研究其电化学性能。主要研究成果如下:(1)将比容量高,循环稳定性、导电性差的纳米Si与循环稳定性、导电性好,比容量低的人造石墨(G)复合涂于铜箔集流体,发现石墨片间搭筑的空间可为纳米Si的体积膨胀提供良好地缓冲作用。Si-G复合电极在低电流密度下放电比容量高,材料利用率最高可达85%。但是电池在较大电流密度下循环时,电池比容量衰减迅速。(2)将MWCNTs与纸纤维通过抽滤制备的CNT导电纸代替铜箔集流体负载MWCNTS-纳米Si复合材料。CNT导电纸具有导电性良好,面密度低,接触面积大,吸液性强等一系列优点,以CNT导电纸为集流体的硅基锂离子电池在80mA/g电流密度下比容量稳定在约1000mAh/g;1000mA/g电流密度下电池比容量达500mAh/g。尤其值得关注的是,对比铜箔硅基电池循环后电化学阻抗的急剧升高,导电纸电池的电化学阻抗在循环后不升反降。因此CNT导电纸作为集流体代替铜箔可有效改善Si的体积膨胀效应。(3)采用稳定金属锂粉(SMLP)预嵌锂的方法改善硅基导电纸电池不可逆容量大的问题。预锂化的电池在静置过程中可自发完成SEI膜的形成,且由于其自发缓慢的SEI膜形成过程,形成的SEI膜更为致密和稳定,不但有效减少电池的不可逆容量,还使得电池的整体容量略高于未锂化的硅电池。
[Abstract]:Due to its extremely high theoretical specific capacity of 4200mAh / g, low lithium intercalation voltage and abundant resources, silicon has become the most promising anode active material for lithium-ion batteries.However, the low conductivity and the volume effect of up to 4 times during charge and discharge lead to poor cycling performance, which seriously hinders the commercial application of silicon in lithium ion batteries.In this paper, silicon based lithium-ion battery was modified by using 100nm nano-Si powder as silicon source, using artificial graphite (G) or multi-walled carbon nanotube (MWCNTs) as composite with nano-Si powder, using CNT conductive paper instead of traditional copper foil to collect fluid, pre-lithiation treatment and so on.The morphology and structure of the cells were observed, and the electrochemical properties of the cells were studied by constant current charge / discharge and electrochemical impedance.The main research results are as follows: (1) Nanocrystalline Si with high specific capacity, cyclic stability and poor electrical conductivity is coated on copper foil with high specific capacity, good electrical conductivity and low specific capacity.It is found that the space between graphite sheets can provide a good buffer for volume expansion of nanocrystalline Si. Si-G composite electrode has a high discharge capacity at low current density and the highest material utilization ratio can reach 85.However, when the battery circulates at a high current density, the specific capacity of the battery decreases rapidly. (2) the CNT conductive paper prepared by MWCNTs and paper fiber, instead of copper foil collector loaded MWCNTS- nanocrystalline silicon composite, has good conductivity and low surface density.There are a series of advantages such as large contact area and strong liquid absorption. The specific capacity of silicon-based lithium-ion battery with CNT conductive paper as a fluid collector at 80mA/g current density is stable at about 1000mAh/ g ~ 1000mA-1 路g / g current density, and the specific capacity of the battery is 500mAh/ g.In particular, compared with the rapid increase of electrochemical impedance of copper foil silicon based cells, the electrochemical impedance of conductive paper cells does not rise but drop after the cycle.The formation of SEI film can be completed spontaneously in the static process of pre-lithiated battery, and because of its spontaneous slow formation of SEI film, the formed SEI film is denser and more stable, which not only reduces the irreversible capacity of the battery, but also reduces the irreversible capacity of the battery.The overall capacity of the battery is slightly higher than that of the non-lithium silicon cell.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912;TB332

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