C Lourenço Tuanan, Ebadi Mahsa, J Panzer Matthew, Brandell Daniel, T Costa Luciano
MolMod-CS, Instituto de Química, Universidade Federal Fluminense, Rio de Janeiro, Brazil.
Department of Chemistry-Ångström Laboratory, Uppsala University, Uppsala, Sweden.
J Comput Chem. 2021 Sep 5;42(23):1689-1703. doi: 10.1002/jcc.26706. Epub 2021 Jun 14.
The development of polymer electrolytes (PEs) is crucial for advancing safe, high-energy density batteries, such as lithium-metal and other beyond lithium-ion chemistries. However, reaching the optimum balance between mechanical stiffness and ionic conductivity is not a straightforward task. Zwitterionic (ZI) gel electrolytes comprising lithium salt and ionic liquid (IL) solutions within a fully ZI polymer network can, in this context, provide useful properties. Although such materials have shown compatibility with lithium metal in batteries, several fundamental structure-dynamic relationships regarding ionic transport and the Li coordination environment remain unclear. To better resolve such issues, molecular dynamics simulations were carried out for two IL-based electrolyte systems, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][TFSI]) with 1 M LiTFSI salt and a ZI gel electrolyte containing the IL and a ZI copolymer: poly(2-methacryloyloxyethyl phosphorylcholine-co-sulfobetaine vinylimidazole), poly(MPC-co-SBVI). The addition of ZI polymer decreases the [TFSI] -[Li] interactions and increases the IL ion diffusivities, and consequently, the overall ZI gel ionic conductivity. The structural analyses showed a large preference for lithium-ion interactions with the polymer phosphonate groups, while the [TFSI] anions interact directly with the sulfonate group and the [BMP] cations only display secondary interactions with the polymer. In contrast to previous experimental data on the same system, the simulated transference numbers showed smaller [Li] contributions to the overall ionic conductivities, mainly due to negatively charged lithium aggregates and the strong lithium-ion interactions in the systems.
聚合物电解质（PEs）的发展对于推进安全、高能量密度电池至关重要，如锂金属电池和其他超越锂离子化学体系的电池。然而，在机械刚度和离子电导率之间达到最佳平衡并非易事。在这种情况下，由锂盐和离子液体（IL）溶液组成的两性离子（ZI）凝胶电解质，在完全由ZI聚合物网络构成的体系中，可以提供有用的性能。尽管这类材料在电池中已显示出与锂金属的兼容性，但关于离子传输和锂配位环境的几个基本结构 - 动力学关系仍不明确。为了更好地解决这些问题，对两个基于IL的电解质体系进行了分子动力学模拟，一个是含有1 M LiTFSI盐的N - 丁基 - N - 甲基吡咯烷鎓双（三氟甲基磺酰）亚胺（[BMP][TFSI]），另一个是含有IL和ZI共聚物的ZI凝胶电解质：聚（2 - 甲基丙烯酰氧基乙基磷酰胆碱 - 共 - 磺基甜菜碱乙烯基咪唑），聚（MPC - 共 - SBVI）。ZI聚合物的加入减少了[TFSI]⁻与[Li]⁺的相互作用，增加了IL离子扩散率，进而提高了整个ZI凝胶的离子电导率。结构分析表明，锂离子与聚合物膦酸酯基团的相互作用具有很大的偏好性，而[TFSI]⁻阴离子直接与磺酸酯基团相互作用，[BMP]阳离子仅与聚合物表现出次级相互作用。与先前关于同一体系的实验数据相反，模拟的迁移数显示[Li]⁺对总离子电导率的贡献较小，这主要是由于体系中带负电荷的锂聚集体和强烈的锂离子相互作用。
