【作者】 崔振宇；

【导师】 徐又一；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2008， 博士

【摘要】 隔膜是锂离子电池的重要组成部分,聚偏氟乙烯（PVDF）由于具有良好的热稳定性、力学性能、化学和电化学稳定性而比较适合作为隔膜材料。Tellcordia公司开发的多孔基质相转变-活化技术是目前制备锂离子电池隔膜的主要方法。该技术包括多孔膜骨架的制备和活化形成（隔膜/聚合物电解质）体系两步。在以往的研究中,多孔膜骨架通常是采用浸没沉淀技术获得,该方法存在不容易实现多孔膜的结构可控性,并且所制备多孔膜的力学强度不够理想以及膜孔径分布宽等缺点。用热致相分离技术制备多孔膜,不仅比较容易控制膜的聚集态结构和膜孔结构,而且所制备的多孔膜具有力学强度较好、孔径分布比较窄等优点。但是目前几乎没有将其应用在锂离子电池隔膜方面的报导。本文采用热致相分离技术制备PVDF多孔膜、PVDF-HFP多孔膜、PVDF/PMMA以及PVDF/PEO-PPO-PEO共混多孔膜,并将多孔膜浸入电解液中活化得到（隔膜/聚合物电解质）体系。研究了碳酸乙烯酯、三乙酸甘油酯、环丁砜和邻苯二甲酸二丁酯这四种稀释剂对多孔膜结构和性能的影响,实验结果表明热致相分离过程中,聚合物/稀释剂体系发生固-液分相。相比而言,环丁砜是比较适合作为PVDF的稀释剂,因为用该稀释剂不仅能够制备出力学性能较好的多孔膜、而且还能够制备出PVDF共混多孔膜。以环丁砜为稀释剂,采用热致相分离技术制备了PVDF多孔膜,研究了聚合物分子量、聚合物初始浓度、淬冷速率以及萃取剂等工艺参数对多孔膜的聚集态结构、膜孔结构以及力学性能等方面的影响。并将多孔膜浸入电解液活化得到（隔膜/聚合物电解质）体系,考察了多孔膜的聚集态结构和膜孔结构对电导率和吸液率的影响。发现在一定条件下制备的多孔膜具有比较好的力学性能以及贯通性良好的孔结构,基于这种膜活化得到的（隔膜/聚合物电解质）体系,电导率超过1.0×10^-3S/cm（20℃）、电化学稳定窗口为0～4.7 V（vs Li⁺/Li）,电导率与温度的关系符合阿仑尼乌斯方程。计算表明,无定形区对（隔膜/聚合物电解质）体系的吸液率的贡献为33～46%,而对电导率的贡献只占7.4～19.3%,这说明载流子的迁移主要发生在充满电解液的孔隙中。采用PVDF-HFP共聚物来降低PVDF的结晶度,用热致相分离技术制备了PVDF-HFP多孔膜,研究了聚合物初始浓度和淬冷速率对多孔膜的聚集态结构、膜孔结构以及力学性能等方面的影响。并将多孔膜浸入电解液活化得到（隔膜/聚合物电解质）体系,研究了多孔膜的聚集态结构和膜孔结构对电导率和吸液率的影响。实验结果表明,多孔膜中球状粒子与网状孔结构共存。比较了PVDF与PVDF-HFP为基质的两种（隔膜/聚合物电解质）体系的性能,发现PVDF-HFP体系具有更高的电导率(2.93×10^-3S/cm,20℃)和更好的保液能力。电导率与温度的关系符合VTF方程。计算表明,无定形区对（隔膜/聚合物电解质）体系的吸液率的贡献为50～60%,对电导率的贡献为30～40%,这说明载流子在被电解液溶胀的无定形区中的迁移不能忽略。根据PMMA与PVDF具有较好的相容性,并能降低PVDF的结晶度、增大吸液率。采用共混手段,利用热致相分离技术制备了PVDF/PMMA共混多孔膜,研究了聚合物质量配比和淬冷速率对共混多孔膜的聚集态结构、膜孔结构以及力学性能等方面的影响。实验结果表明,随共混膜中PMMA比例的增加,共混膜的结晶度降低、孔隙率升高,但力学性能降低。与PVDF多孔膜相比,共混多孔膜经电解液活化后,保液能力增强、电导率增大(2.59×10^-3S/cm,20℃)。电化学稳定窗口为0～4.5V（vs Li⁺/Li）。利用PEO-PPO-PEO共聚物中的PPO链段与PVDF有较好的相容性,且两端的PEO链段与电解液具有良好的亲和性,采用共混手段,用热致相分离技术将其与PVDF共混制备锂离子电池隔膜,考察了聚合物质量配比和淬冷速率对共混多孔膜的聚集态结构、膜孔结构以及力学性能等方面的影响。实验结果表明,共混入PEO-PPO-PEO后,球状粒子形状变规整。体系在非等温结晶过程中存在着二次结晶（熔融-再结晶）,二次结晶随共混膜中PEO-PPO-PEO比例的增加而变强,这说明PVDF与PEO-PPO-PEO之间存在相互作用。与PVDF多孔膜相比,共混多孔膜经电解液活化后,保液能力增强、吸液率明显增加、电导率增大(2.94×10^-3S/cm,20℃)。电化学稳定窗口为0～4.5V（vs Li⁺/Li）,电导率与温度的关系满足阿仑尼乌斯方程。将多孔膜活化后组装成电池,测试表明,PVDF-HFP共聚物、PVDF/PMMA、PVDF/PEO-PPO-PEO体系的循环性能和放电容量优于PVDF体系。更多还原

【Abstract】 Separator is an important part in lithium ion battery,Poly（vinylidene fluoride） （PVDF） is a kind of suitable material to be used as separator due to its excellent thermal stability,mechanical properties,chemical and electrochemical stability.At present,the main technology to prepare separator for lithium ion battery is microporous matrix phase inversion-activation method explored by Tellcordia Co.Ltd. This technique is composed of two steps:the preparation of microporous matrix and activation.In previous studies,microporous matrix was usually obtained by immersion precipitation process.This technique is not only difficult to control porous structure of membrane,but also not excellent mechanical properties and wide pore size distribution.The main advantages of thermally induced phase separation process （TIPS） are easily porous structure control,good mechanical properties and narrow pore size distribution.However,little researches have been carried out to apply microporous membranes prepared via TIPS process in separator of lithium ion battery. In this work,PVDF and PVDF-HFP microporous membranes,PVDF/PMMA and PVDF/PEO-PPO-PEO blend porous membranes were prepared via TIPS process and （separator/polymer electrolyte） systems based on microporous membranes were prepared by activation.Ethylene carbonate,triacetin,sulfolane and dibutyl phthalate were introduced to research the effect on porous structure and properties of microporous membranes.The result indicated that solid-liquid phase separation occurred for polymer/diluent system during TIPS process.Sulfolane is a good candidate for PVDF,because not only microporous membranes with good mechanical properties,but also PVDF-based blend membranes can be obtained using sulfolane as the diluent.PVDF microporous membranes were prepared and the influences of polymer molecular weight,polymer concentration,quenching condition and extractant on the aggregation structure,porous structure and mechanical properties were studied. （Separator/polymer electrolyte） system was obtained by activation.How the aggregation structure and porous structure influence ionic conductivity and electrolyte uptake were investigated.It was found that microporous membranes with spherulites prepared at certain condition processed good mechanical properties and well-interconnected porous structure.Ionic conductivity was beyond 1.0×10^-3S/cm at 20℃,electrochemical stability was in the range of 0～4.7 V（vs Li⁺/Li ）,logσand 1/T showed a linear variation and followed Arrhenius-type behavior.The contribution of amorphous domains to electrolyte uptake and ionic conductivity is in the range of 33～44%and 7.4～19.3%,which means that the transfer of carrier ions is mainly through pores filled electrolyte.PVDF-HFP was used to decreases the crystallinity of PVD,PVDF-HFP prepared via TIPS process.Polymer concentration and quenching condition were used to control the aggregation structure,porous structure and mechanical properties of microporous membranes.（Separator/polymer electrolyte） system was obtained by activation.The effects of aggregation structure and porous structure on ionic conductivity and electrolyte uptake were investigated.The experimental results showed that compared with PVDF system,PVDF-HFP system has higher ionic conductivity(2.93×10^-3S/cm,20℃) and better electrolyte maintenance,logσand 1/T followed VTF equation.The contribution of amorphous domains to electrolyte uptake and ionic conductivity is in the range of 50～60%and 30～40%,which means that the transfer of carrier ions within the gel phase should not be ignored.Considering the good compatibility between PMMA and PVDF,the addition of PMMA will decrease the crystallinity of PVDF and increase electrolyte uptake. PVDF/PMMA blend microporous membranes were prepared via TIPS process.The effects of polymer weight fraction and quenching condition on the aggregation structure,porous structure and mechanical properties of microporous membranes were studied.The experimental results revealed that the addition of PMMA decreased the crystallinity,mechanical properties and increased porosity.Compared with PVDF microporous membrane,after activation,the blend membranes processed higher ionic conductivity(2.59×10^-3S/cm,20℃) and better electrolyte maintenance.The electrochemical stability was in the range of 0～4.5V（vs Li⁺/Li）.Due to good compatibility between PVDF and PPO segment,and good affinity between PEO and liquid electrolyte,PVDF/PEO-PPO-PEO blend microporous membranes were prepared via TIPS process.The effects of polymer weight fraction and quenching condition on the aggregation structure,porous structure and mechanical properties of microporous membranes were studied.The experimental results revealed that spherulites became regular with the addition of PEO-PPO-PEO. It was found that secondary crystallization existed in the process of non-isothermal crystallization and enhanced by increasing PEO-PPO-PEO content,which meant that there existed interaction between the two polymers.Compared with PVDF microporous membrane,after activation,the blend membranes processed higher ionic conductivity(2.59×10^-3S/cm,20℃) and better electrolyte maintenance.The electrochemical stability was in the range of 0～4.5V（vs Li⁺/Li）.logσand 1/T followed Arrhenius-type behavior.The cell measurement revealed that the charge-discharge efficiency and discharge capacity of PVDF-HFP,PVDF/PMMA and PVDF/PEO-PPO-PEO system were better than that of PVDF system.更多还原