两性树枝状液晶嵌段共聚物电解质设计及其锂离子通道调控

The solid polymer electrolyte is considered to have a good stability and reliability for lithium ion battery, and it is important to design a polymer electrolyte with high conductivity. Novel star dendritic liquid crystalline (LC) copolymers containing Poly(ethylene glycol) (PEG) and polymethacrylate with cyanobiphenyl mesogenic pendants are put forward to synthesize in this project. The effect of mesogen on ions conductivity of star copolymers with PEG segment at main chain or side chain will be studied. The solid polymer electrolytes were prepared by mixing of dendritic LC copolymers and lithium salt. Star-shaped copolymers are expected to exhibit unique physical properties and morphologies that are not observed in the corresponding linear polymers. In particular, the crystallinity and degree of chain entanglement of polymers are smaller than those of the linear polymers. The strong assembly of mesogens induces the copolymers with enantiotropic mesophase, even after doped with Li+ ions. The lamellar structures will be achieved by cooperative assembly of mesogen-containing polymethacrylate groups and the amorphous PEG nanoscale aggregation. The effects of structural variations on the properties will be studied. It will systematically explore the characterization of star copolymers in terms of their microphase structure, thermal properties, and electrochemical performance as solid polmyer electrolytes (SPEs). And the relationship between microphase structure and the electrochemical properties of the SPEs on temperature, LC thermal annealing and magnetic field strength will also be investigated. It is promising to get high performance all-solid polymer lithium-ion batteries.

合成高电导率的全固态聚合物电解质是制备高效、稳定、可靠锂离子电池的关键。本项目拟将氰基联苯共轭液晶基元以侧链形式引入到支化聚合物中，与PEG共聚得树枝状液晶性嵌段共聚物。研究聚合物中液晶基元对主链型PEG及侧链型PEG链段运动性能的影响，考察与锂盐共混聚合物电解质的离子电导率。树枝状结构的引入，可以有效防止链段结晶，提高PEG分子链段的运动能力。利用液晶分子自发取向的特性驱动共聚物有序组装，赋予聚合物良好的微观相分离结构，促使PEG链段在固定区域内有效缠绕，构筑具有固定离子传输通道的高性能全固态聚合物电解质。研究树枝状液晶性嵌段共聚物分子构型和液晶取向行为（退火处理或在一定的磁场条件下）对聚合物电解质相分离、相形态结构有序性调控的影响，考察聚合物电解质离子电导率的各向异性及电化学性能。优化电解质膜的结构，组装高性能的锂离子电池。

锂离子电池聚合物电解质具有稳定、可靠、设计灵活、总体质量轻等优点而成为一种研究趋势。但该类电解质的最大问题是电导率低导致大电流放电性能差，扩散系数小导致电池易产生浓差极化界面。为此，本项目利用嵌段、支化、交联等方法来抑制聚合物链段的结晶性，并通过引入液晶基元形成固定离子传输通道，设计合成一系列新型聚合物电解质。. 第一，合成八臂液晶嵌段共聚物和聚甲基丙烯酸酯咪唑鎓盐结构，后引入交联剂，得复合型全固态聚合物电解质，考察了固态聚合物电解质的微观形貌，研究了液晶嵌段共聚或离子液晶对聚合物电解质诱导组装调控，通过改变液晶含量，在微观区域内形成离子传输通道，得到独立成膜性好、电化学性能稳定的复合型全固态聚合物电解质。退火处理后电解质电室温电导率值可达10-4 S cm-1，在95 ℃下可达10-3 S cm-1。. 第二，研究了支化结构对聚氧化乙烯或聚咪唑鎓盐结晶性、热性能的影响，并与电纺丝膜复合，得到固态或类固态聚合物电解质。支化及梳型结构确保聚合物处于无定形态，分子链段运动能力达到最大化，有利于对锂离子的传输，提高离子电导率。与电纺丝膜复合以提高电解质的安全性和力学性能。通过SEM、TGA、DSC、EIS以及LSV对聚合物电解质的形貌、热学性能、电导率以及电化学稳定窗口进行了表征，该系列电解质表现出良好的机械性能和电化学性能，组装成软包装电池具有很好的可穿刺和弯曲折叠性。. 以上研究提供了一系列电化学性能良好的聚合物电解质，为组装高效、稳定的聚合物锂离子电池提供了有效的途径。