The properties of the electrolyte are the dominant factors for the overall performance and safety of electrical energy storage devices. Highly concentrated “water in salt” (WIS) electrolytes are inherently non-flammable, moisture-tolerant, and exhibit wide electrochemical stability windows, making them promising electrolytes for high-performance energy storage devices. However, WIS electrolytes possess intrinsically low conductivity and high viscosity, which usually impair the high-rate performance of many energy storage devices, especially supercapacitors (SCs). Additionally, the inevitable salt precipitation at low temperature for WIS electrolytes narrows down their applicable temperature range. Here, we introduce acetonitrile as a co-solvent to a typical “water in salt” electrolyte to formulate an “acetonitrile/water in salt” (AWIS) hybrid electrolyte that provides significantly improved conductivity, reduced viscosity and an expanded applicable temperature range while maintaining the aforementioned important physicochemical properties of WIS electrolytes. Using the AWIS electrolyte for a model SC remarkably enhances the high-rate performance, accompanied by a 2.4 times capacitance increase at 10 A g⁻¹ with respect to the original WIS electrolyte. This AWIS electrolyte also enables a stable long-term cycling capability of the model SC for over 14 000 cycles at a high operation voltage of 2.2 V.

The interlayer modification and the intercalation pseudocapacitance have been combined in vanadium oxide electrode for aqueous zinc‐ion batteries. Intercalation pseudocapacitive hydrated vanadium oxide Mn_1.4V₁₀O₂₄·12H₂O with defective crystal structure, interlayer water, and large interlayer distance has been prepared by a spontaneous chemical synthesis method. The inserted Mn²⁺ forms coordination bonds with the oxygen of the host material and strengthens the interaction between the layers, preventing damage to the structure. Combined with the experimental data and DFT calculation, it is found that Mn²⁺ refines the structure stability, adjusts the electronic structure, and improves the conductivity of hydrated vanadium oxide. Also, Mn²⁺ changes the migration path of Zn²⁺, reduces the migration barrier, and improves the rate performance. Therefore, Mn²⁺‐inserted hydrated vanadium oxide electrode delivers a high specific capacity of 456 mAh g⁻¹ at 0.2 A g^–1, 173 mAh g^–1 at 40 A g^–1, and a capacity retention of 80% over 5000 cycles at 10 A g^–1. Furthermore, based on the calculated zinc ion mobility coefficient and Zn(H₂O)_n²⁺ diffusion energy barrier, the possible migration behavior of Zn(H₂O)_n²⁺ in vanadium oxide electrode has also been speculated, which will provide a new reference for understanding the migration behavior of hydrated zinc‐ion.