Concentrated aqueous electrolytes have been widely explored for high-voltage aqueous batteries. To achieve higher voltage, even higher alkali-ion molalities are being pursuit up to 55.5 mol kg⁻¹ (m) that corresponds to monohydrate, but the sacrificially lowered ionic conductivity is problematic. Here we report a 61.7 m K-ion aqueous electrolyte composed of KN(SO₂F)₂ (KFSI) and KSO₃CF₃ (KOTf). The pioneered beyond-monohydrate realm is unique to K-ion systems, in which [FSI]⁻ anion is stable to hydrolysis. The K-ion electrolyte has two-order higher ionic conductivity (12 mS cm⁻¹ at 30 °C) than a comparable 55.5 m Li-ion system (0.1 mS cm⁻¹) while exhibiting a 2.7 V potential window on Pt being among the widest in all alkali-ion aqueous electrolytes. This work suggests the superior overall performance of aqueous K-ion batteries over other alkali-ion batteries.

浓缩水性电解质已被广泛地用于高压水性电池。为了获得更高的电压，甚至追求更高的碱金属离子摩尔^数，达到相当于一水合物的55.5 mol kg ^-1（m），但是牺牲地降低离子电导率是有问题的。在这里，我们报告了由KN（SO ₂ F）₂（KFSI）和KSO ₃ CF ₃（KOTf）组成的61.7 m K离子水性电解质。开创性的超越一水合物领域是K离子系统独有的，其中[FSI] ^-阴离子对水解稳定。与可比的55.5 m锂离子系统（0.1 mS cm ^-1）相比，K离子电解质的离子电导率（30°C下为12 mS cm ^-1）高两倍。），而在所有碱离子水性电解质中，Pt上的2.7 V电位窗口最大。这项工作表明水性K离子电池的整体性能优于其他碱离子电池。