Takenaka Norio, Inagaki Taichi, Shimada Tatau, Yamada Yuki, Nagaoka Masataka, Yamada Atsuo
Graduate School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Institute for Molecular Science, Myodaiji, Okazaki, Aichi 444-8585, Japan.
J Chem Phys. 2020 Mar 31;152(12):124706. doi: 10.1063/5.0003196.
Aqueous electrolytes have the potential to overcome some of the safety issues associated with current Li-ion batteries intended for large-scale applications such as stationary use. We recently discovered a lithium-salt dihydrate melt, viz., Li(TFSI)(BETI)·2HO, which can provide a wide potential window of over 3 V; however, its reductive stability strongly depends on the electrode material. To understand the underlying mechanism, the interfacial structures on several electrodes (C, Al, and Pt) were investigated by conducting molecular dynamics simulation under the constraint of the electrode potential. The results showed that the high adsorption force on the surface of the metal electrodes is responsible for the increased water density, thus degrading the reductive stability of the electrolyte. Notably, the anion orientation on Pt at a low potential is unfavorable for the formation of a stable anion-derived solid electrolyte interphase, thus promoting hydrogen evolution. Hence, the interfacial structures that depend on the material and potential of the electrode mainly determine the reductive stability of hydrate-melt electrolytes.
水性电解质有潜力克服一些与当前用于大规模应用（如固定用途）的锂离子电池相关的安全问题。我们最近发现了一种锂盐二水合物熔体，即Li(TFSI)(BETI)·2H₂O，它可以提供超过3V的宽电位窗口；然而，其还原稳定性强烈依赖于电极材料。为了理解潜在机制，通过在电极电位约束下进行分子动力学模拟，研究了几种电极（C、Al和Pt）上的界面结构。结果表明，金属电极表面的高吸附力导致水密度增加，从而降低了电解质的还原稳定性。值得注意的是，低电位下Pt上的阴离子取向不利于形成稳定的阴离子衍生固体电解质界面，从而促进析氢。因此，取决于电极材料和电位的界面结构主要决定了水合物熔体电解质的还原稳定性。
