Yamada Koki, Yuasa Shohei, Matsuoka Riho, Sai Ryansu, Katayama Yu, Tsutsumi Hiromori
Department of Applied Chemistry, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Tokiwadai, Ube 755-8611, Japan.
Phys Chem Chem Phys. 2021 Apr 28;23(16):10070-10080. doi: 10.1039/d1cp00852h.
Polymeric materials are considered as promising electrolytes for all-solid-state secondary lithium batteries with superior energy and power densities, long cycle lives, and high safety. To further improve the ionic conductivity of polymer electrolytes, the development of a simple and efficient method that enables precise tuning of the three key factors, polymer segmental dynamics, Li+ coordination structure, and salt dissociability, is desired. In this study, we focus on an amidation reaction, which is a simple reaction with broad applicability, to explore the impact of the side-chain structure on the intermolecular interactions within the polymer, which dictates the aforementioned key factors. We synthesized a series of polyoxetane-based polymers having different branched side-chains, i.e., methyl (PtBuOA) and bulky cyanoethoxy (P3CEOA) groups, via amidation reaction. Spectro(electro)chemical analysis verified that the large steric hindrance of the cyanoethoxy side-chain effectively breaks the hydrogen bond network and dipole interaction within the polymer, both of which decrease the polymer segmental mobility, leading to better long-range Li+ conduction. Furthermore, the unique Li+ coordination structure consisting of a cyano group, ether/carboxyl oxygen, and TFSA anion in P3CEOA electrolytes has moderate stability, which effectively promotes the short-range Li+ conduction. The amide group, with a relatively high dielectric constant, improves the dissociability of lithium salt. We confirmed a more than three orders of magnitude improvement in ionic conductivity by introducing the cyanoethoxy side-chain, than that obtained by introducing the PtBuOA electrolyte with a methyl side-chain. This work provides a holistic picture of the effect of the side-chain structure on the intermolecular interaction and establishes the new design strategy for polymer electrolytes, which enables the precise tuning of the molecular interaction using the side-chain structure.
聚合物材料被认为是全固态二次锂电池很有前景的电解质，具有优异的能量和功率密度、长循环寿命和高安全性。为了进一步提高聚合物电解质的离子电导率，需要开发一种简单有效的方法，能够精确调节聚合物链段动力学、Li⁺配位结构和盐解离性这三个关键因素。在本研究中，我们聚焦于酰胺化反应，这是一种适用性广泛的简单反应，以探究侧链结构对聚合物分子间相互作用的影响，而这种相互作用决定了上述关键因素。我们通过酰胺化反应合成了一系列具有不同支化侧链的聚氧杂环丁烷基聚合物，即甲基（PtBuOA）和庞大的氰乙氧基（P3CEOA）基团。光谱（电化学）分析证实，氰乙氧基侧链的大空间位阻有效地破坏了聚合物内的氢键网络和偶极相互作用，这两者都会降低聚合物链段迁移率，从而实现更好的长程Li⁺传导。此外，P3CEOA电解质中由氰基、醚/羧基氧和TFSA阴离子组成的独特Li⁺配位结构具有适度稳定性，这有效地促进了短程Li⁺传导。具有相对较高介电常数的酰胺基团提高了锂盐的解离性。我们证实，通过引入氰乙氧基侧链，离子电导率比引入具有甲基侧链的PtBuOA电解质提高了三个多数量级。这项工作全面展示了侧链结构对分子间相互作用的影响，并建立了聚合物电解质的新设计策略，该策略能够利用侧链结构精确调节分子相互作用。
