混合水系锂离子电池二氧化硅胶体电解液的性能研究

发布时间：2018-08-30 14:23

【摘要】：锂离子电池系统(LiBs)具有能量密度大、功率密度高、循环寿命长、重量轻等优点已经被证明是一种最有前途的固定电源,这吸引了科学家的注意并展开了广泛的研究。尽管具有了卓越的性能,但是LiBs在电解液的制备时采用的剧毒、易燃的有机溶剂在使用不当时会产生安全隐患。而且,由于电解液对水分和空气很敏感,导致了制造工艺的复杂和昂贵。这些具有挑战性的问题依旧制约着锂离子电池在大规模储能系统的应用。1994年,Dahn报道了一种新型的可充电锂离子电池,用基于水的电解液替代了有机电解液,这种新的改进系统即水系可充电锂离子电池(ARLBs)。最近,混合水系锂离子电池(ReHABs)的概念被提出了,这种电池采用LiMn2O4作为正极、锌箔为负极和含有Zn2+和Li+的水系电解液。但是为了确保这一体系可以投放到市场前必须要解决几个技术问题。首先,ReHABs在长期充放电过程中在Zn负极的一侧发生可逆的氧化还原反应而容易发生锌沉积而形成树突晶体,会穿透隔膜和损失效率而造成电池短路。第二,与其它电池系统类似,ReHABs也面临着自放电的问题。另一方面,例如在不间断电源(Uninterrupted Power Supply)方面的应用,电池在完成完全充电后,在恒定充电下会继续消耗电力,这是由于电池内存在一个反向电流也就是浮充电流。在ReHABs中,浮充电流过大时会在高工作电压下分解大量的水产生氧气。最后,ReHABs较差的保水能力会导致pH值和电解液浓度变化而导致电池容量的迅速下降。本文构造了二氧化硅胶体电解液体系,探索了各种二氧化硅胶体电解液的物理化学性质进行测试,并组装电池进行电化学分析测试,探讨了二氧化硅胶体电解液对ReHABs性能的影响,主要研究内容包括:(1)纳米二氧化硅掺杂的混合水系锂离子电池电解液的研究及性能评价制备纳米二氧化硅掺杂的水系电解液并将其用于混合水系锂离子电池中,纳米二氧化硅掺杂进电解液的最初目的是为了得到二氧化硅胶体电解液。但是,5%和10%掺杂的二氧化硅电解液就具有粘性并能够在几分钟内进入到吸附式玻璃纤维棉(Absorbed Glass Mat,AGM)内,由于纳米级二氧化硅颗粒具有良好的保水性,将含有二氧化硅掺杂电解液的AGM在空气放置数周仍保持湿润。使用纳米二氧化硅掺杂的电解液,可以抑制锌枝状晶体的沉积、降低浮充电流和自放电,提高电池的放电比容量,在0.2 C的倍率下为140mAh?(g LiMn2O4)-1,与传统电解液相比还能提高ReHABs的循环性能。电池700次循环后的XRD结果表明纳米二氧化硅掺杂的电解液的存在可以保护电池的负极。(2)混合水系锂离子电池不同二氧化硅胶体电解液的研究及性能评价通过向传统水系电解液中加入5种二氧化硅凝胶剂得到了不同的二氧化硅胶体电解液,并将其用于混合水系锂离子电池中。一系列研究表明:孔隙度较高的二氧化硅在制备胶体电解液时需要的数量更少、成胶时间更短。采用了胶体电解液的电池展现了相近或者略高的放电容量,提高了大约10%的倍率性能。此外,所有的胶体电池的开路电压降均减小了,这表明其具有了更长的保质期。Sigma Aldrich气相二氧化硅得到的胶体电解液更适用于ReHABs和其他水系可充电锂离子电池成为廉价安全的商业能源存储系统。(3)混合水系锂离子中气相二氧化硅与β-环糊精胶体电解液的研究及性能评价采用触变的胶凝剂气相二氧化硅与非触变的胶凝剂?-环糊精共同使用来得到新的胶体电解液体系。热重分析表明胶体电解在AGM隔膜中的保水性是高于传统的电解液的。采用这种胶体电解液的ReHABs的放电比容量提高了大约10%,并表现出更高的倍率性能和循环性能。此外,SEM和计时电流法的研究表明使用这种胶体电解液可以抑制锌枝晶的产生从而保护了电极。相比于采用单一的触变的胶凝剂,触变的和非触变的胶凝剂共同使用能够展现出更好的协同作用。(4)混合水系锂离子中气相二氧化硅与聚乙烯醇胶体电解液的研究及性能评价采用气相二氧化硅与聚乙烯醇制备了胶体电解液并应用在ReHABs。研究表明这种胶体电解液可以有效地减少ReHABs的开路电位的下降和自放电率。当在ReHABs使用气相二氧化硅与聚乙烯醇胶体电解液时,能得到更高的比容量、低自放电率、低浮充电流密度、高倍率性能和更好的循环能力。此外,这种电解液能够使ReHABs负极上的Zn的沉积层更加平缓和光滑,有效地避免生成树枝状晶体,从而大大减小了电池短路的可能性。
[Abstract]:Lithium-ion battery system (LiBs) has been proved to be one of the most promising fixed power sources with the advantages of high energy density, high power density, long cycle life and light weight, which attracts the attention of scientists and has been extensively studied. Improper use of organic solvents poses potential safety hazards. Moreover, electrolytes are sensitive to water and air, resulting in complex and expensive manufacturing processes. These challenging problems still limit the use of lithium-ion batteries in large-scale energy storage systems. In 1994, Dahn reported a new type of rechargeable lithium-ion batteries. Water-based electrolytes are used instead of organic electrolytes, a new improved system called water-based rechargeable lithium-ion batteries (ARLBs). Recently, the concept of mixed-water-based lithium-ion batteries (ReHABs) has been proposed, which use LiMn2O4 as the positive electrode, zinc foil as the negative electrode and water-based electrolytes containing Zn2+ and Li +. Several technical problems must be solved before it can be put on the market. First, ReHABs are prone to form dendritic crystals by reversible redox reactions on the side of the Zn negative electrode during long-term charging and discharging, which can penetrate the diaphragm and cause short circuit of the battery. Second, similar to other battery systems, ReHABs are also facing problems. On the other hand, for example, in Uninterrupted Power Supply applications, the battery continues to consume power when fully charged, because there is a reverse current in the battery, i.e. floating charge current. Finally, the poor water-holding capacity of ReHABs leads to the rapid decrease of cell capacity due to the change of pH value and electrolyte concentration. In this paper, a silica gel electrolyte system is constructed, and the physical and chemical properties of various silica gel electrolytes are tested, and the cells are assembled for electrochemical separation. The influence of silica gel electrolyte on the performance of ReHABs was discussed. The main research contents include: (1) The research and performance evaluation of nano-silica-doped mixed-water lithium-ion battery electrolyte and the preparation of nano-silica-doped aqueous electrolyte and its application in mixed-water lithium-ion battery, nano-silica The initial purpose of doping into the electrolyte was to obtain silica gel electrolyte. However, the 5% and 10% doped silica electrolyte was viscous and could enter into the adsorbed glass wool (AGM) within a few minutes. Because the nano-silica particles had good water retention, it would contain dioxide. AGM of silicon-doped electrolyte remained wet in air for several weeks. Nano-silicon dioxide-doped electrolyte could inhibit the deposition of zinc dendrite, reduce floating charge current and self-discharge, and increase the specific discharge capacity of the battery. At the rate of 0.2 C, it was 140 mAh? (g LiMn2O4) -1. Compared with traditional electrolyte, it could also improve the cycle of ReHABs. Performance. XRD results after 700 cycles show that the existence of nano-silica doped electrolyte can protect the negative electrode of the battery. (2) Study and performance evaluation of different silica gel electrolytes for mixed-water lithium-ion batteries Silicon gel electrolyte is used in mixed-water lithium-ion batteries. A series of studies have shown that silica with higher porosity needs less amount and shorter gelation time in preparing colloidal electrolyte. In addition, the open-circuit voltage drop of all colloidal batteries decreased, indicating a longer shelf life. The colloidal electrolyte obtained from Sigma Aldrich vapor-phase silicon dioxide is more suitable for ReHABs and other rechargeable lithium-ion batteries in water systems as a cheap and safe commercial energy storage system. (3) Vapor-phase silicon dioxide in mixed-water lithium-ion batteries. Study and performance evaluation of colloidal electrolyte with beta-cyclodextrin The discharge specific capacity of eHABs was increased by about 10% and exhibited higher rate performance and cycling performance. In addition, SEM and chronoamperometry studies showed that the use of this colloidal electrolyte could inhibit the formation of zinc dendrites and consequently protect the electrode. (4) Study and performance evaluation of gas-phase silica and polyvinyl alcohol colloidal electrolyte in mixed water lithium ion system Decreasing and self-discharging rates. When using fumed silica and polyvinyl alcohol colloidal electrolyte in ReHABs, higher specific capacity, lower self-discharging rate, lower floating charge current density, higher rate performance and better cycling capacity can be obtained. In addition, this electrolyte can make the deposition of Zn on the negative electrode of ReHABs more smooth and smooth, effectively avoiding. The formation of dendritic crystals greatly reduces the possibility of battery shorting.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM912

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