锂二次电池用新型聚合物电解质和负极表面改性的研究

发布时间：2018-06-26 20:50

本文选题：锂二次电池 + 聚合物电解质　；参考：《上海交通大学》2014年博士论文

【摘要】：本文从新型聚合物电解质的结构设计和聚合物的负极表面修饰两方面着手，以图改善锂二次电池的综合性能。传统的锂二次电池采用碳酸酯为电解液溶剂和聚烯烃微孔薄膜为隔膜。碳酸酯溶剂易挥发和燃烧，安全性差。而所用的隔膜对电解液不具有良好的润湿性和保液性，易造成电解液泄漏，同时其高温热稳定性比较差，这些因素易导致严重的安全隐患。另一方面，锂二次电池负极在充电的强还原条件下易与电解液发生副反应。例如，虽然钛酸锂（LTO）被认为是下一代锂离子电池负极材料的有力竞争者，特别适合于高功率和长寿命锂离子动力电池。不幸的是，，钛酸锂作负极的锂离子电池不能广泛应用是因为该材料会与电解液发生副反应，尤其在高温环境下（高于50℃）会出现严重的气胀现象。针对上述二次锂电池安全性的关键问题，本文主要开展下列研究工作。（1）设计、制备了一种全固态聚合物电解质和二种凝胶聚合物电解质（多孔的凝胶和纯凝胶）代替液态电解液，测定了聚合物电解质的离子电导率、力学性能、电化学稳定窗口、聚合物电解质/金属锂的界面稳定性，并考察了Li/聚合物电解质/Li对称电池的循环性能，进而用LiFePO4和pPAN-S正极组成全电池，测试其循环稳定性和倍率性能。（2）在LTO颗粒表面包覆一层均匀的聚酰亚胺（PI）保护层，在55℃下系统地探索该保护层抑制LTO与液态电解液的副反应的可行性。具体研究结果如下： 1.用溶剂挥发法首次制备以高含量的聚砜-聚环氧乙烷（PSF-PEO）嵌段共聚物为基体，含低含量的双三氟甲烷磺酰亚胺锂（LiTFSI）和固态增塑剂丁二腈（SN）的新型全固态复合聚合物电解质。研究结果表明：PSF-PEO35+LiTFSI+SN全固态聚合物电解质的室温和80℃下的离子电导率分别为1.6×104S cm1和1.14×103S cm1，在80℃下的电化学稳定窗口为4.2V（对Li/Li+），与金属锂有良好的界面稳定性。另外，该固态电解质在宽的温度范围内表现出良好的力学性能和热稳定性。Li/PSF-PEO35+LiTFSI+SN/Li对称电池在65℃下比Li/PEO+LiTFSI/Li有更长的循环寿命及更低的极化电压。Li/PSF-PEO35+LiTFSI+SN/LiFePO4电池在80℃具有良好的循环稳定性和倍率性能。 2.采用原位交联的方法制备了新型的亲水性聚四氟乙烯膜（PTFE）支撑的交联聚乙二醇-聚甲基丙烯酸甘油酯嵌段共聚物（PEG-b-PGMA）凝胶电解质（GPE），系统地研究了优化的GPE-3的物理性能和电化学性能。研究结果表明：优化的GPE-3中交联共聚物PEG-b-PGMA和孔隙可以吸附的大量电解液，而亲水性的PTFE微孔膜为GPE-3膜提供良好的力学支撑。该电解质的室温最高离子电导率为1.3×103Scm1，能够应用于锂二次电池。其电化学稳定窗口为4.5V（对Li/Li+），并与金属锂有良好的相容性。另外该凝胶电解质膜表现出优秀的润湿性、热尺寸稳定性和不易燃烧性。Li/GPE-3/LiFePO4电池在25℃具有与传统液态电解液组装的电池相近的循环稳定性和倍率性能。Li/GPE-3/pPAN-S电池同样拥有良好的循环稳定性，但比容量高于Li/PE-liquid electrolyte/pPAN-S电池。 3.采用紫外光固化（UV-cured）首次合成了含有聚乙二醇二甲基丙烯酸酯-碳酸亚乙烯酯交联共聚物（PEGDA-co-PVC）和线性聚偏氟乙烯-六氟丙烯（PVDF-HFP）的新型半互穿网络聚合物（Semi-IPN）凝胶电解质，并研究其优化的半互穿网络聚合物凝胶电解质的物理和电化学性能。研究结论如下：该凝胶电解质膜没有孔隙，可避免漏液。其室温离子电导率为1.49×103S cm1，电化学稳定窗口为4.2V（对Li/Li+），与金属锂有优异的界面稳定性。此外，该电解质表现出良好的力学性能和热稳定性，较好的实现了离子电导率和机械性能之间的平衡。Li/Semi-IPN GPE/Li比Li/PE-liquidelectrolyte/Li对称电池在放置和循环过程中具有更低且更稳定的界面阻抗，表现出更低的极化电压。另外，Li/Semi-IPN GPE/LiFePO4电池在25℃具有与传统液态电解液组装的电池相似的循环与倍率性能。 4.鉴于改变电解液组分和在LTO表面包碳的方法对抑制LTO与液态电解液的副反应并未取得明显的效果。本研究通过热亚胺化反应将聚酰亚胺（PI）均匀包覆在LTO表面，并系统研究了该保护层在55℃下抑制LTO与液态电解液的界面副反应的效果。红外光谱和TEM及EDS分析确认PI纳米层均匀地包覆在LTO表面；PI-LTO在55℃下的循环稳定性和倍率性能要比未包覆的LTO更好，比容量也更高；由循环前后LTO极片的SEM图对比可知，PI包覆可以减少副反应发生；PI-LTO首次循环后的界面阻抗略大于LTO的，但是50次循环后，明显小于LTO的界面阻抗。同时PI包覆的LTO与电解液产生的副反应放热焓明显大于未包覆的LTO。而且PI包覆后的LTO的放热反应温度从未包覆LTO的263℃提高到276.6℃，提高了材料的热稳定性。上述结果说明，PI保护层可有效地抑制LTO与电解液的副反应，提高了LTO作负极的锂二次电池的安全性。
[Abstract]:In this paper, two aspects of the structure design of the polymer electrolyte and the surface modification of the negative electrode of the polymer are made in order to improve the comprehensive performance of the lithium two battery. The traditional lithium two battery uses carbonate as the electrolyte solvent and the polyolefin microporous membrane as the diaphragm. The carbonate solvent is easy to volatilize and burn, and the safety is poor. The electrolyte does not have good wettability and liquid retention, and it is easy to cause electrolyte leakage, and its thermal stability is poor at the same time. These factors easily lead to serious safety problems. On the other hand, the lithium two battery anode is liable to react with the electrolyte under the condition of strong reduction. For example, lithium titanate (LTO) is considered as the next generation. A strong competitor for anode materials for lithium ion batteries is particularly suitable for high power and long life lithium ion batteries. Unfortunately, lithium titanate as a negative lithium ion battery can not be widely used because the material will react with the electrolyte, especially in high temperature environment (higher than 50 degrees C). The key problems of the safety of the two lithium battery are discussed. The following research work is carried out in this paper. (1) a all solid polymer electrolyte and two kinds of gel polymer electrolytes (porous gel and pure gel) are prepared instead of liquid electrolyte. The ionic conductivity, mechanical properties and electrochemical stability window of the polymer electrolysis are measured. The interfacial stability of polymer electrolyte / lithium metal was investigated and the cycling performance of Li/ polymer electrolyte /Li symmetric battery was investigated. The cycle stability and multiplying performance of the battery were made up of LiFePO4 and pPAN-S positive electrodes. (2) a uniform polyimide (PI) protective layer was coated on the surface of LTO particles, and the protection was systematically explored at 55 degrees C. The feasibility of inhibiting the side reaction between LTO and liquid electrolyte is shown.
1. a new all solid state composite polymer electrolyte with high content of polysulfone polyepoxide (PSF-PEO) block copolymer with low content of double three fluoranimimide lithium (LiTFSI) and solid plasticizer Ding Erjing (SN) was first prepared by solvent evaporation method. The results showed that the solid state polymer electrolyte of PSF-PEO35+LiTFSI+SN was all solid. The ionic conductivity at room temperature and 80 C is 1.6 x 104S CM1 and 1.14 x 103S CM1 respectively. The electrochemical stability window at 80 C is 4.2V (Li/Li+) and has good interfacial stability with metal lithium. In addition, the solid electrolyte shows good mechanical properties and thermal stability.Li/PSF-PEO35+LiTFSI+SN/Li symmetry in a wide temperature range. The battery has longer cycle life and lower polarization voltage than Li/PEO+LiTFSI/Li at 65 C. The.Li/PSF-PEO35+LiTFSI+SN/LiFePO4 battery has good cycling stability and multiplying performance at 80.
2. a new type of hydrophilic polytetrafluoroethylene membrane (PTFE) supported polyethylene glycol polyglyceryl methacrylate block copolymer (PEG-b-PGMA) gel electrolyte (GPE) supported by a hydrophilic polytetrafluoroethylene membrane was prepared by in-situ crosslinking method. The physical properties and electrochemical properties of the optimized GPE-3 were systematically studied. The results showed that the optimized Crosslinking Copolymerization in GPE-3 was carried out. PEG-b-PGMA and pores can adsorb a large amount of electrolyte, and the hydrophilic PTFE microporous membrane provides good mechanical support for the GPE-3 membrane. The electrolyte has the highest ionic conductivity of 1.3 x 103Scm1 at room temperature and can be applied to the lithium two battery. The electrochemical stability window is 4.5V (Li/Li +), and it has good compatibility with the metal lithium. The gel electrolyte membrane exhibits excellent wettability, thermal stability and non combustibility of.Li/GPE-3/LiFePO4 batteries at 25 degrees centigrade, which have similar cyclic stability and multiplex performance with conventional liquid electrolytes..Li/GPE-3/pPAN-S batteries have good cyclic stability, but the specific capacity is higher than Li/PE-liquid electrolyte/. PPAN-S battery.
3. a new semi interpenetrating polymer (Semi-IPN) gel electrolysis containing polyethylene glycol two methacrylate ethylene carbonate crosslinked copolymer (PEGDA-co-PVC) and linear polyvinylidene fluoride (PVDF-HFP) was synthesized by UV curing (UV-cured) for the first time, and its optimized semi interpenetrating network polymer gel electrolysis was studied. The results are as follows: the gel electrolyte membrane has no pores and can avoid leakage. The ionic conductivity at room temperature is 1.49 x 103S CM1, the electrochemical stability window is 4.2V (to Li/Li+), and it has excellent interfacial stability with the metal lithium. In addition, the electrolyte shows good mechanical properties and thermal stability, and is better. The equilibrium.Li/Semi-IPN GPE/Li between the ionic conductivity and the mechanical properties has a lower and more stable interface impedance in the placement and circulation process than the Li/PE-liquidelectrolyte/Li symmetric cell, showing a lower polarization voltage. In addition, the Li/Semi-IPN GPE/LiFePO4 battery has the electricity assembled with the traditional liquid electrolyte at 25. The pool is similar to the cycle and multiplying performance.
4. in view of the change of the electrolyte component and the side reaction of the carbon in the LTO surface to inhibit the side reaction of the LTO and the liquid electrolyte, the polyimide (PI) was uniformly coated on the LTO surface by the thermo amamination reaction, and the effect of the protective layer at the interface of the LTO and the liquid electrolyte at 55 centigrade was studied. The infrared spectrum and TEM and EDS analysis confirmed that the PI nano layer was uniformly coated on the LTO surface; the cyclic stability and multiplying performance of PI-LTO at 55 C was better than that of the uncoated LTO and higher than that of the uncoated LTO; the PI encapsulation could reduce the occurrence of the side reaction and the interfacial resistance after the first cycle of PI-LTO. The resistance is slightly greater than LTO, but after 50 cycles, it is obviously less than the interface impedance of LTO. At the same time, the enthalpy of the side reaction of the PI coated LTO and the electrolyte is obviously greater than that of the uncoated LTO., and the exothermic reaction temperature of the LTO after the PI coating has never been raised to 276.6 degrees C, and the thermal stability of the material is raised. The above results indicate that PI is guaranteed. The protective layer can effectively inhibit the side reaction of LTO and electrolyte, and improve the safety of lithium secondary batteries with LTO as negative electrode.
【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912

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