网状结构离子选择性聚合物电解质对抑制锂硫电池穿梭效应的性能研究

In order to solve the problem of the serious capacity fading and the low coulombic efficiency of lithium-sulfur battery caused by the shuttle effect of polysulfides, the intermediates generated during the charge-discharge process of cathode material, that polysulfides dissolve into electrolyte, pass through separator, migrate to anode and react with it, then migrate back to cathode, this project will prepare the polymer electrolyte with network structure and ion-selective ability by a convenient and workable method to replace with the traditional liquid electrolyte/separator system. The dissolution of polysulfides will be reduced because there is no free liquid electrolyte in the polymer electrolyte. Besides, the ion-selective ability makes the mesh into the special channel: it will promote the transmission of lithium ion in polymer membrane, and prevent polysulfides from passing through separator and migrating to anode, so that the shuttle effect will be restricted. The matrix of the network structure polymer electrolyte will be prepared by sulfonating the poly(ether ether ketone)s and then cross-linking with trimetaphosphate phosphate. The structure-activity relationship between units with different structure and functional groups and their influence on shuttle effect of polysulfides will be researched by experimental characterizations. This project will also establish and optimize the model according to the density functional theory, in order to reveal the general action mechanism between different units with lithium ion and polysulfides, and provide the design idea and theoretical basis of the functional electrolyte membrane with ion-selective ability.

为解决锂硫电池正极充放电中间体聚硫离子溶解于电解液、穿过隔膜迁移至负极并与之反应使其腐蚀，再迁移回正极的往复穿梭行为导致电池容量衰减严重、库伦效率低等问题，本项目通过一种过程简便的方法制备具有离子选择性网孔通道的聚合物电解质膜来替代传统电解液/隔膜体系，聚合物电解质膜不含游离的电解液能够降低聚硫离子的溶解度，同时使网状聚合物中每个网孔成为具有离子选择性的特殊通道，一方面促进电正性锂离子在电解质膜中传输，同时阻碍聚硫阴离子穿过膜体向负极迁移，从而抑制其穿梭行为。网状聚合物电解质膜基体以聚醚醚酮为原料，经磺化、与三偏磷酸盐交联反应制得，通过实验表征研究不同网孔单元结构、官能团组成的电解质膜对聚硫离子穿梭行为影响的构效关系，通过密度泛函理论建立并优化模型，揭示不同网孔单元与电正性锂离子、电负性聚硫离子作用的一般规律，为锂硫电池用功能型离子选择性电解质膜的制备提供设计思路和理论依据。

为解决锂硫电池正极充放电中间体聚硫离子溶解于电解液、穿过隔膜迁移至负极并与之反应使其腐蚀，再迁移回正极的往复穿梭行为导致电池容量衰减严重、库伦效率低等问题，本研究通过一种过程简便的方法制备具有离子选择性网孔通道的聚合物电解质膜来替代传统电解液/隔膜体系，网状聚合物电解质膜基体以聚醚醚酮为原料，经磺化、与三偏磷酸盐交联反应制得。对不同交联度的聚合物膜进行了物理、电化学等性能表征，结果表明聚合物膜呈微孔结构，随交联度增大，聚合物膜更加致密，比表面积降低，膜中无定型程度降低，结晶性增大。电解质膜室温离子传导速率接近液态电解液，随聚合物膜交联度增大其离子传导速率降低，膜中离子传导过程由无定型部分转化为结晶态部分。添加三偏磷酸盐交联剂的聚合物膜锂离子迁移数均接近于1，添加10％交联剂的电解质膜使锂硫电池库伦效率在不同电流密度下均接近100 ％，表明聚硫离子的穿梭效应得到有效抑制。本项目成功得到了穿梭效应得到抑制、循环稳定性优秀的锂硫电池，并为锂硫电池用功能型离子选择性电解质膜的制备提供切实可行的设计思路和参考数据。