【作者】 谢辉；

【导师】 唐致远；

【作者基本信息】 天津大学 ， 应用化学， 2009， 博士

【摘要】 本文引入一种新型纳米型无机材料制备出了具有优异电化学性能的复合型聚合物电解质,全面研究了无机纳米填料对聚合物电解质电化学性能的影响并对其作用机理进行分析;首次对聚合物电解质、无机填料和新型锂盐双乙二酸硼酸锂(LiBOB)与铝集流体之间的腐蚀性进行了系统的研究;将LiBOB作为锂盐添加剂,研究其对铝集流体腐蚀性、正极材料的兼容性等性能的作用和影响;最后用本文制备复合型聚合物电解质的方法对生产用的液态锂离子电池隔膜进行改性,制备出型号为383562的航模用聚合物锂离子电池,全面研究了该聚合物锂离子电池的电化学性能和安全性能。本文首次将具有纳米结构的PC-401型气相Al2O3引入到聚合物电解质体系中。以PVDF-HFP共聚物为基体、丙酮/乙醇为溶剂/非溶剂体系,采用倒相法制备出具有优异电化学性能的复合型聚合物电解质。通过多种电化学实验手段表明,由于具有纳米尺寸、较高的比表面积及表面活性基团,无机填料能够较大程度地降低聚合物电解质的结晶度、提高孔隙率、吸液率及离子导电率、锂离子迁移数和与金属锂的界面性能等。对无机填料的含量进行调整以获取最优化的物理和电化学性能。一系列的实验表明,无机填料对共聚物的比为1:10时为最佳值。当PC-401的含量为10%时,聚合物电解质的结晶度从不含无机填料时的23%降至9%左右,降低幅度超过60%;同时,聚合物电解质的孔隙率和吸液率也有较大幅度的提高。聚合物电解质的离子导电率为0.89 mS/cm,能较好地满足锂离子电池的实际需求;锂离子迁移数达到0.47,远远高于液态电解质0.2-0.3的水平。因此该聚合物电解质适合应用于高功率锂离子电池中。本文首次对锂离子电池中铝集流体的腐蚀性行为进行了全面系统的研究,并提出一种新型的等效电路对铝集流体的腐蚀性行为进行分析和拟合。通过电势阶跃法、交流阻抗法、循环伏安法等电化学方法表明,PC-401能够较好地衰减铝集流体的腐蚀电流,而且工作电压越高其抑蚀效果越突出。无机纳米填料的添加能够改变铝集流体上界面钝化层的结构与厚度,从而达到降低铝腐蚀电流的保护作用。全面比较了LiPF6、LiBF4、LiClO4和LiBOB四种常用锂盐对铝集流体的腐蚀性行为。结果表明,LiBOB具有最低的腐蚀电流。不同锂盐对铝箔的稳定性从强到弱的顺序为:LiBOB>LiBF4>LiPF6>LiClO4。LiBOB对铝集流体的高温稳定性非常优异,在70℃下依然对铝箔保持较高的稳定性。这对提高锂离子电池的高温性能具有一定的实际意义。本文首次将LiBOB作为添加剂应用于聚合物电解质中并系统研究了其对各项电化学性能的影响。研究结果表明在LiPF6电解液中添加5%的LiBOB能有效地抑制铝集流体的腐蚀行为。该发现有利于改善电池的循环寿命和储存性能。LiBOB作为锂盐添加剂还能明显改善正极材料的首次充放电效率及其界面膜的稳定性和界面阻抗。LiMn2O4的结构稳定性较差,特别是在高温下,其会逐渐溶解于LiPF6电解液中,从而导致LiMn2O4锂离子电池的循环与高温性能较差。在70℃下存放10天,5%的LiBOB使LiMn2O4锂离子电池的不可逆容量损失从35%降至26%。因而LiBOB添加剂能够显著降低LiMn2O4锂离子电池的自放电速率。这对聚合物锂离子电池的应用也有一定的现实意义。将复合型聚合物电解质的制备方法和体系应用于常规液态锂离子电池使用的隔膜中,对其进行改性。通过SEM清晰地观察到表面和断面的微观形貌,其孔径及厚度分布都较为均匀。选择LiFePO4为正极、复合石墨为负极材料,使用改性后的隔膜制备成使用于航模中的383562型聚合物锂离子电池,其初始容量超过500 mAh。使用该隔膜的电池具有优异的大电流充放电性能,10C放电依然有初始容量的90%,其高功率循环性能也较好,10C充放电循环200次后容量衰减在5%左右。不过其电压平台及高温循环性能欠佳。这主要是受正极材料本身和LiPF6电解液的影响。依据国际通用标准对电池进行各类安全性测试。结果表明,该电池具有优异的安全性能,其抗过放、过充、150℃热冲击及短路性能等都较好,所有安全性实验均未出现漏液、着火或爆炸等现象。更多还原

【Abstract】 In this dissertation, we prepared composite polymer electrolytes (CPE) with high electrochemical performances by introducing a unique nano-sized inorganic material. The effects of inorganic fillers on the electrochemical performances of CPE and the mechanism were fully studied and analyzed, as well as the effects of the inorganic fillers and lithium salts on aluminum current collector’s corrosion at both room and high temperature. The unique lithium salt-lithium bis(oxalate) borate (LiBOB) was applied as lithium salt additive, and its effect on aluminum corrosion, the compatibility with cathode active materials were thoroughly studied. We also combined the theoretical research and knowledge with practical application, applied the CPE preparation system to modify the separator used in commercial liquid Li-ion batteries. 383562-typed polymer Li-ion batteries used in airplane models were assembled. The electrochemical and safety performances of the battery were systematically studied.PC-401-a nano-sized fumed alumina with ultra-fine surface structure-was firstly introduced into the CPE system. CPE were prepared through phase inversion method. PVDF-HFP copolymer was used as matrix host, acetone and ethanol as solvent/non-solvent system and PC-401 as inorganic filler. The results revealed that the addition of inorganic fillers can significantly affect the physical and electrochemical performances of the composite polymer electrolyte, such as cystallinity, porosity, electrolyte uptake rate, as well as the ionic conductivity, Li ion transference number and the compatibility with metallic lithium. Through adjusting the content of inorganic fillers in the polymer electrolyte can optimize these properties. Series experiments showed that the inorganic fillers to copolymer ratio of 1:10 is optimization. With this ration, the crystallinity of the PE decreases from 23% (no filler is added) to 9%; in the meanwhile, the porosity and electrolyte uptake ration are also enhanced with similar extent. The ionic conductivity of the PE is 0.89 mS/cm, which can meet the practical application in commercial Li-ion batteries properly. The Li ion transference number is as high as 0.47, much higher than the liquid electrolytes with values in the level of 0.2-0.3. Therefore, the PE we prepared can be used in high power Li-ion batteries which ask for high rate charge and discharge.The aluminum corrosion behavior in Li-ion batteries was systematically studied for the first time. A novel equivalent circuit to analyze the aluminum corrosion behavior was proposed. The results obtained through various electrochemical methods show that the inorganic filler acts as a good inhibitor of aluminum corrosion behavior. And the higher of the working voltage, the better of the inhibiting effect. The research revealed that the addition of the inorganic filler can modify the composition, construction and the thickness of the passivation layer in the interface between the PE and aluminum. All these factors result in the protection of aluminum from corroding.We compared the aluminum corrosion behaviors of different lithium salts, the results showed that LiBOB exhibits the lowest corrosion current. Moreover, the high temperature stability of LiBOB towards aluminum foil is quite high: the corrosion current remains relatively low at temperatures as high as 70℃. The order of the stability of different lithium salts with aluminum is: LiBOB>LiBF4>LiPF6>LiClO4.The LiBOB was used as additive in commercial electrolytes and it’s effect on the performance of the electrolyte was studied. It is shown that only 5% of LiBOB in LiPF6 electrolytes can greatly inhibit the aluminum corrosion behavior. This fact is beneficial to improve the cycle life and storage performance of the batteries. As additive, LiBOB can also enhance the initial cycle efficiency, as well as the stability and impedance of the interface layer of cathode material.The structural stability of LiMn2O4 is relatively low, especially at high temperatures. LiMn2O4 will dissolve in the LiPF6-based electrolyte and results in poor high temperature performances of LiMn2O4 Li-ion batteries. Storing at for 10 days, addition of 5% LiBOB can decrease the irreversible capacity loss of LiMn2O4 Li-ion batteries from 35% to 26%. It means that LiBOB can effectively decrease the self-discharge rate of LiMn2O4 Li-ion batteries. This fact is of certain practical importance to the application of polymer Li-ion batteries.We applied our preparation method and system of composite polymer electrolyte into modifying the separator used in commercial liquid Li-ion batteries. The SEM graphs clearly display the micrographic morphology of the surface and cross-section of the modified separator. 383562-typed polymer Li-ion batteries were assembled using the modified separator, LiFePO4 and complex graphite were used as cathode and anode active materials, respectively. The initial nominal capacity of the battery is over 500 mAh. The prepared battery performs well in high current rate charge and discharge. The discharge capacity at 10 C remains 90% of initial capacity. The high power cycle performance of the battery is very good, the capacity fading after 200 cycles at 10 C is about 5% of initial capacity. However, the discharge plateau at high rates and the high temperature performance of the battery is relatively poor. This is mainly limited by the cathode active material and the electrolyte based on LiPF6.The battery has high safety performance. It survives after various safety testings, including overdischarge to 0V, overcharge at 3 C to 10V and heat shock at 150℃for 1h and external short circuit. There was no electrolyte leakage, fire or explosion after all these tests.更多还原