Superionic conductors (SICs) are of great importance for substantial applications such as energy storage and conversion, and conductance switching. In contrast to typical SICs which have three-dimensional inter-connected ion diffusion pathways, here, we report a two-dimensional layered LiInP₂S₆, which theoretically possesses a low ionic conductivity but realistically achieves an anomalous superionic behavior. We demonstrate that this conductor spontaneously absorbs water molecules upon exposure to humid air, resulting in the formation of a hydrated crystal, which triggers a significant increase of room-temperature ionic conductivity as high as 5.3 × 10⁻³ S cm⁻¹, over 4 orders higher than that of the anhydrous phase. Furthermore, the uptake/release of water molecules is highly reversible without any structural degradation. Structure analysis and theoretical calculations verify that the interlayer molecules would relocate the charge distribution and reduce the ion migration energy barrier (from 0.64 to 0.25 eV) to contribute a three-dimensional continuous pathway for fast Li⁺ diffusion. We reveal that such a molecule-assisted ionic migration behavior essentially follows a solid-state migration mechanism, in spite of its ionic conductivity up to the liquid electrolyte level, which endows a useful ionic conductivity in hydrated LiInP₂S₆ even when cooled to −40 °C. Our work can provide new insights for the development of superionic conductors.

中文翻译：

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由层间分子引发的范德华硫代磷酸锂的反常超离子电导率

超离子导体（SIC）对于能量存储和转换以及电导切换等实际应用非常重要。与具有三维互连离子扩散路径的典型碳化硅相比，我们在这里报道了一种二维层状LiInP ₂ S ₆，它理论上具有较低的离子电导率，但实际上实现了异常的超离子行为。我们证明，这种导体在暴露于潮湿空气时会自发吸收水分子，从而形成水合晶体，从而引发室温离子电导率显着增加，高达 5.3 × 10 ^-3 S cm ^-1，超过 4级数高于无水相。此外，水分子的吸收/释放是高度可逆的，不会发生任何结构降解。结构分析和理论计算验证了层间分子会重新定位电荷分布并降低离子迁移能垒（从0.64到0.25 eV），为快速Li ⁺扩散提供三维连续路径。我们发现，这种分子辅助的离子迁移行为本质上遵循固态迁移机制，尽管其离子电导率高达液体电解质水平，这使得水合LiInP ₂ S ₆具有有用的离子电导率，即使冷却到 - 40°C。我们的工作可以为超离子导体的发展提供新的见解。