碳酸酯接枝聚合物电解质的合成与性能研究

The interest in the study of polymer electrolyte system is continually growing, because of the potential application of these materials in a great variety of electrochemical devices including lithium ion batteries and electrochromic devices. The property of the electrolyte effects the life time, energy density and use of these devices. The polymeric property of polymer electrolyte gives it advantages over liquid electrolytes and rigid mineral electrolytes in terms of density, flexibility, processability, design possibility and safety. Polymer electrolyte composes of polymer and lithium salt. Though the mechanical property of polymer electrolyte is good, the ionic conductivity is lower than liquid electrolyte with several orders of magnitude. In spite of variety of strategies applied, the low conductivity exhibited by polymer electrolytes modified by ceramic fillers, polymer blending, additives and polar plasticizers, has not yet provided an adequate basis for commercial systems. The ionic conductivity and mechanical property can not reached the demand with the same electrolyte. The main reason is the configuration difference between the polymer and plasticizer is too great. The plasticizers merging in the polymer is a kind of physical behavior, it enhances the ionic conductivity and reduces the mechanical property as well. The lithium ion battery with such electrolyte will encounter the same disadvantage as liquid electrolyte. We thought the problem could be solved by using chemical bonding of carbonate functional group which is the main working group in liquid electrolyte and plasticizers to edge out physical adsorption, reducing the difference between polymer and plasticizers. In this project, a set of supermolecules composed of glycerol carbonate and polymers grafted with carbonate group will be synthesized. Polymer electrolytes composed of one kind of grafted monomers, two kinds of monomers will be produced and characterized. The polymers will be soaked with lithium salt dissolved in propylene carbonate, ethylene carbonate or synthesized supermolecules to produce gel polymer electrolyte as well. Because both of polymer and plasticizer have carbonate group, the molecular weight of the plasticizers increased, the similarity of the matrix and plasticizers will increase. According to the theory that substances with similar configuration can be easily dissolved in each other, the swelling percentage of the plasticizers could be increased and the mechanical strength will be kept. The ionic conductivity, lithium transference number and electrochemical stability of the electrolyte will be tested.Lithium transference mechanism will be investigated by characterizing the lithium position in the electrolyte. The mechanical properties and stability of grafted polymer electrolytes will also be tested. The polymer electrolyte with high ionic conductivity and good mechanical properties will be used to prepare lithium ion batteries and electrochromic devices.

聚电解质是锂离子电池和电致变色器件的关键组成部分，其性能优劣直接关系到锂离子电池、电致变色器件的寿命、功率及应用范围。目前聚电解质存在机械加工与离子导电性能无法兼顾的难题。原因是聚合物与增塑剂的分子结构差异较大，及它们物理混合造成的相分离。我们的策略是通过化学键合替代物理掺杂，且使聚合物与增塑剂结构接近。本课题设计合成一系列含有液体电解质碳酸酯基团的超分子和高分子，制备单一组分、两种或多种共混聚合物。它们可作为增塑剂、聚电解质载体或作为提高增塑剂掺杂量的相转移物质。由于该类体系具有聚合物和碳酸酯双重特点，基于相似相溶原理预测：在保持聚电解质机械强度下可提高碳酸酯基的掺杂比例和掺杂量。通过电导率、离子迁移数、机械性能的测试，对其离子迁移机理的研究，及组装锂离子电池和电致变色器件的应用探讨，评估该体系的机械加工和离子导电性能。旨在获取优良的聚电解质，推动锂离子电池的全固化和电致变色器件发展。

聚合物电解质是锂离子电池和电致变色器件的关键组成部分，其性能优劣直接关系到锂离子电池、电致变色器件的寿命和功率。本课题合成了一系列含有碳酸丙烯酯/亚硫酸丙烯酯基团的超分子，利用TG-FTIR、结合Gaussian理论计算，系统研究了这些化合物热稳定性，并且提出了其裂解可能过程。同时，用作锂离子电池电解液添加剂，采用倍率测试、恒流充放电测试、交流阻抗测试和扫描电子显微镜测试等手段研究了这些化合物对锂离子电池工作性能的影响。结果表明：通过对循环20周前后球化石墨电极形貌的对比，球化石墨电极表面相对于空白电解液可形成一层致密而稳定的固体电解质中间相膜（SEI），从而优化电极⁃电解液的界面性能，改善电池的倍率性能。此外，本课题也合成了含有碳酸丙烯酯基团的高分子，如聚2,3-环碳酸甘油酯甲基丙烯酸酯和聚2,3-环碳酸甘油酯丙烯酸酯。为了控制聚合物分子量、分子量分布，系统研究了聚合条件的影响。在此基础上，制备了多孔凝胶聚乙烯-聚2,3-环碳酸甘油酯甲基丙烯酸酯/聚2,3-环碳酸甘油酯丙烯酸酯复合物电解质膜，离子电导率高达10-3 S/cm，并且，这种多孔凝胶电解质复合膜可以有效提高锂离子电池的工作性能。