Aqueous hybrid supercapacitors are attracting increasing attention due to their potential low cost, high safety and eco-friendliness. However, the narrow operating potential window of aqueous electrolyte and the lack of suitable negative electrode materials seriously hinder its future applications. Here, we explore high concentrated lithium acetate with high ionic conductivity of 65.5 mS cm⁻¹ as a green “water-in-salt” electrolyte, providing wide voltage window up to 2.8 V. It facilitates the reversible function of niobium tungsten oxide, Nb₁₈W₁₆O₉₃, that otherwise only operations in organic electrolytes previously. The Nb₁₈W₁₆O₉₃ with lithium-ion intercalation pseudocapacitive behavior exhibits excellent rate performance, high areal capacity, and ultra-long cycling stability. An aqueous lithium-ion hybrid capacitor is developed by using Nb₁₈W₁₆O₉₃ as negative electrode combined with graphene as positive electrode in lithium acetate-based “water-in-salt” electrolyte, delivering a high energy density of 41.9 W kg⁻¹, high power density of 20,000 W kg⁻¹ and unexceptionable stability of 50,000 cycles.

水混合超级电容器因其潜在的低成本、高安全性和环境友好性而受到越来越多的关注。然而，水系电解质的工作电位窗口窄以及缺乏合适的负极材料严重阻碍了其未来的应用。在这里，我们探索了具有 65.5 mS cm ^-1高离子电导率的高浓度醋酸锂作为绿色“盐包水”电解质，提供高达 2.8 V 的宽电压窗口。它促进了铌钨氧化物 Nb 的可逆功能₁₈ W ₁₆ O ₉₃ ，否则以前只能在有机电解质中运行。具有锂离子嵌入赝电容行为的Nb ₁₈ W ₁₆ O ₉₃表现出优异的倍率性能、高面积容量和超长循环稳定性。采用 Nb ₁₈ W ₁₆ O ₉₃作为负极，石墨烯作为正极，在醋酸锂基“盐包水”电解液中开发出一种水系锂离子混合电容器，可提供 41.9 W kg 的高能量密度^-如图1所示，20,000 W kg ^-1的高功率密度和50,000次循环的无可挑剔的稳定性。