Liquid electrolytes with high ionic conductivity, high transference number for the target ions, and excellent electrochemical, chemical, and thermal stability are essential for electrochemical energy storage devices. Water-in-salt (WIS) electrolytes, in which the salt-water ratio is larger than one, are gaining intensive attention in the electrochemical community. Here, we review the recent work on WIS and the closely-related water-in-ionic liquids electrolytes. We highlight the fact that many properties of these electrolytes, in bulk and at electrolyte-electrode interfaces, are underpinned by the physics and chemistry of the interfaces formed between water and ions (or aggregated water/ion clusters). Manipulating these interfaces by tailoring the selection of ions and water-ion ratio opens up new dimensions in the optimization of liquid electrolytes but also poses new challenges. We conclude the review by highlighting several directions for research on WIS electrolytes, in particular, the study of WIS electrolyte-electrode interfaces using surface force measurements.

具有高离子电导率，目标离子的高转移数以及优异的电化学，化学和热稳定性的液体电解质对于电化学储能装置至关重要。盐水比大于1的盐包水（WIS）电解质在电化学界引起了广泛关注。在这里，我们回顾了有关WIS和与之密切相关的离子液体中水电解质的最新工作。我们强调了一个事实，即这些电解质的整体和电解质-电极界面的许多特性都受到水和离子（或聚集的水/离子簇）之间形成的界面的物理和化学作用的支持。通过调整离子的选择和水离子比率来操纵这些界面，在优化液体电解质方面开辟了新的领域，但同时也带来了新的挑战。在总结本综述时，我们重点介绍了WIS电解质研究的几个方向，特别是使用表面力测量研究WIS电解质-电极界面的方法。