Ebadi Mahsa, Eriksson Therese, Mandal Prithwiraj, Costa Luciano T, Araujo C Moyses, Mindemark Jonas, Brandell Daniel
Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, SE-751 21 Uppsala, Sweden.
Instituto de Química-Departamento de Físico-química, Universidade Federal Fluminense, Outeiro de São João Batista s/n, CEP 24020-150 Niterói, RJ, Brazil.
Macromolecules. 2020 Feb 11;53(3):764-774. doi: 10.1021/acs.macromol.9b01912. Epub 2020 Jan 31.
Increasing the ionic conductivity has for decades been an overriding goal in the development of solid polymer electrolytes. According to fundamental theories on ion transport mechanisms in polymers, the ionic conductivity is strongly correlated to free volume and segmental mobility of the polymer for the conventional transport processes. Therefore, incorporating plasticizing side chains onto the main chain of the polymer host often appears as a clear-cut strategy to improve the ionic conductivity of the system through lowering of the glass transition temperature ( ). This intended correlation between and ionic conductivity is, however, not consistently observed in practice. The aim of this study is therefore to elucidate this interplay between segmental mobility and polymer structure in polymer electrolyte systems comprising plasticizing side chains. To this end, we utilize the synthetic versatility of the ion-conductive poly(trimethylene carbonate) (PTMC) platform. Two types of host polymers with side chains added to a PTMC backbone are employed, and the resulting electrolytes are investigated together with the side chain-free analogue both by experiment and with molecular dynamics (MD) simulations. The results show that while added side chains do indeed lead to a lower , the total ionic conductivity is highest in the host matrix without side chains. It was seen in the MD simulations that while side chains promote ionic mobility associated with the polymer chain, the more efficient interchain hopping transport mechanism occurs with a higher probability in the system without side chains. This is connected to a significantly higher solvation site diversity for the Li ions in the side-chain-free system, providing better conduction paths. These results strongly indicate that the side chains in fact restrict the mobility of the Li ions in the polymer hosts.
几十年来，提高离子电导率一直是固体聚合物电解质发展中的首要目标。根据聚合物中离子传输机制的基本理论，对于传统传输过程，离子电导率与聚合物的自由体积和链段迁移率密切相关。因此，在聚合物主链上引入增塑侧链通常被视为一种明确的策略，通过降低玻璃化转变温度（ ）来提高体系的离子电导率。然而，在实际中并未始终观察到 与离子电导率之间的这种预期关联。因此，本研究的目的是阐明在包含增塑侧链的聚合物电解质体系中链段迁移率与聚合物结构之间的这种相互作用。为此，我们利用了离子导电聚碳酸三亚甲酯（PTMC）平台的合成多功能性。采用了两种在PTMC主链上添加侧链的主体聚合物，并通过实验和分子动力学（MD）模拟对所得电解质以及无侧链类似物进行了研究。结果表明，虽然添加的侧链确实会导致 降低，但无侧链的主体基质中的总离子电导率最高。在MD模拟中可以看到，虽然侧链促进了与聚合物链相关的离子迁移率，但在无侧链的体系中，更有效的链间跳跃传输机制发生的概率更高。这与无侧链体系中锂离子的溶剂化位点多样性显著更高有关，从而提供了更好的传导路径。这些结果有力地表明，侧链实际上限制了聚合物主体中锂离子的迁移率。
