【作者】 卢雷；

【导师】 左晓希； 李伟善；

【作者基本信息】 华南师范大学 ， 物理化学， 2007， 硕士

【摘要】 聚合物锂离子电池以极佳的热稳定性和机械性能，以及可做成各种形状及安全性能高等特点，引起了人们的深切关注。目前已广泛应用于手机、微型信用卡、笔记本电脑及化学传感器等设备。聚合物电解质是聚合物锂离子电池的重要组成部分，尽管研究者对锂离子聚合物电解质做了大量研究，但全固态聚合物电解质体系在室温下的导电率仍然达不到应用要求。由于凝胶聚合物电解质中无自由移动液体，室温下导电率可达10^-3S cm^-1，因此成为目前的研究重点。为了提高聚合物电解质导电率和机械性能，本课题利用乳液聚合法合成了一种新型聚合物：聚甲基丙烯酸甲酯-醋酸乙烯酯（PMMA-Vac），通过浸泡法将此共聚物覆盖在聚烯烃（PE）隔膜上，制备了聚烯烃多孔膜支撑的聚合物电解质膜，浸泡在电解液中即得到凝胶聚合物电解质。由于PE膜增加了包覆膜的机械性能和安全性能，而电解质膜的微孔可以吸收并固定大量的电解液，因而能有效解决聚合物电解质目前存在的电导率和机械强度等问题。通过差热和热重分析（DSC/TG）及红外光谱（FTIR）等方法研究了共聚型聚合物的性质，通过交流阻抗（AC）、扫描电镜（SEM）、吸液率和电池充放电实验等方法研究了聚合物、聚合物膜和聚合物电解质的性质，得到的结论如下：1、共聚物通过单体MMA及Vac打开C=C的形式得到的；当单体MMA与Vac比例为9：1时，得到的共聚物的转化率97.49％。同时交联剂的加入可以提高聚合物膜的网状结构，有利于吸收更多的电解液及为锂离子的迁移提供更好的通道，从而大大提高了聚合物膜的吸液率和离子电导率。溶剂选择实验表明，相对于以丙酮为溶剂得到的聚合物电解质来说，以N-N二甲基甲酰胺（DMF）为溶剂的聚合物电解质有更好的性能，离子电导率为1.85×10^-3s×cm^-1。扫描电镜表明，聚合物膜有极佳的交错相连的微孔结构，聚合物膜的吸液率高达2000％以上。当共聚物的含量为2％时，得到的聚合物电解质的性能更适合实际应用；同时PMMA-VAc膜具有良好的热稳定性：在380℃范围内保持稳定，适用于锂离子电池；电化学测试表明，以此聚合物电解质制各的聚合物锂离子电池有良好的循环性能和倍率放电性能。2、通过将PMMA-Vac分别与聚偏氟乙烯（PVDF），聚四氟乙烯（PTFE）及PVP-VA64（N-乙烯吡咯烷酮（NVP）与乙酸乙烯酯（VAc）的共混物，简称为V64）共混及溶剂的选择来提高聚合物膜的综合性能，结果发现溶剂为DMF时，共混聚合物膜有较好的吸液率和吸液保持率；同时，相对于PMMA-Vac得到的电解质而言，以PTFE和PMMA-Vac共混后聚合物膜在溶剂中会卷曲，不利于应用；PVDF与PMMA-Vac共混得到的聚合物膜吸液能力及液体保持率均有所下降，同时共混聚合物膜的电化学性能也有所下降；V64的加入有利于提高聚合物电解质的液体保持率，24小时后吸液率仍有800％，并且得到的共混聚合物膜的热稳定性及电化学稳定性良好。电化学性能测试表明，其分解温度及电化学稳定窗口分别可达380℃及4.3V，以该聚合物电解质组装的扣式电池具有良好的循环性能和倍率容量。LiMn₂O₄／电解质／GMS全电池100周循环容量保持率达80.3％。更多还原

【Abstract】 Polymer lithium-ion batteries have been extensively studied in recent years forapplications in various electrochemical devices, such as cellular phones, smart creditcards, laptop computers and chemical sensors, due to their excellent thermal andmechanical stability, flexibility and Safety. Despite extensive researches on lithiumpolymer conductors, the conductivity of pure solid electrolytes （with no liquid） isinsufficient for practical application at room temperature. Most of the recent studieshave been focused on the gel polymer electrolytes in which the liquid electrolyte hasbeen immobilized by incorporating into the polymer matrix because their ionicconductivity can reach 10^-3S cm^-1 at ambient temperature.With the aim to develop polymer membrane with high conductivity andmechanical stability for lithium-ion batteries, this work attempted to synthesize apolymer,poly-methyl metacrylate-vinyl acetate （PMMA-Vac） by emulsion polymeri-zetion with methyl metacrylate （MMA） and vinyl acetate （Vac） as monomers. Withthis polymer, polymer membrane and polymer electrolyte were prepared on the baseof polyethylene （PE） membrane with a dip coating and phase inversion method. ThePE can give mechanical integrity to the electrolyte system and offers enhanced safetyby exhibiting thermal shutdown under condition of severe abuse. While gellablepolymer was coated on PE, it could encapsulate and hold electrolyte.Performances of the synthesized polymer and prepared polymer membrane andelectrolyte were studied with FTIR, DSC/TG, SEM, GPC and battery charging anddischarge experiments. Following results were obtained:1 It is found from FTIR that PMMA-Vac was formed by breaking the doublebonds of monomers. PMMA-Vac can be easily dispersed in mixed carbonates to forma gel. The polymer has best transformation rate of 97.49% and better performancewhen the rate of MMA:Vac is 9:1, Cross-linked reagent can improve porous structure of membrane, which is good for electrolyte absorptivity and supports transfer pathsfor Li⁺, so the polymer membrane has electrolyte absorption of 2000% and betterconductivity. The polymer membrane has better performance when the solvent isDMF in contract of acetone, The ion conductance is 1.85×10^-3s×cm^-1.The bestcontent of PMMA-Vac for polymer membrane is 2% for practical application.Polymer membrane can be stable up to 380℃. The conductivity of the polymerelectrolyte at room temperature is 1.85×10^-3s×cm^-1. With the polymer electrolyte asthe gel polymer electrolyte （GPE） of battery, the battery shows its good cyclicstability and high rate discharge performance.2. Polymer membranes were prepared by mixing PMMA-Vac and PVDF, PTFE,PVP-VA64 with different solvent. It is found the polymer membrane has betterelectrolyte absorption for DMF as solvent. The polymer membrane mixed with PTFEis not fit for lithium-ion battery for its crispation.The polymer membrane mixed withPVDF has lower electrolyte absorption than PMMA-Vac membrane, The polymermembrane mixed with PVP-VA64 has excellent electrolyte retainability and good heatstability, The cells consisting GPE mixed with PMMA-Vac and PVP-VA64 showedgood cycling characteristics and rate capacities.The discharge capacity of the batterybased on LiMn₂O₄/ PMMA-Vac+PVP-VA64 polymer electrolyte/C retains 80.3%after 100 cycles.更多还原