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 other-wise only operations in organic electrolytes previously. The -Nb18W16O93 with lithium-ion intercalation pseudocapacitive behavior exhibits excel-lent rate performance, high areal capacity, and ultra-long cycling sta-bility. 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.