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.

中文翻译：

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基于“乙腈/盐中的水”混合电解质的安全高效的超级电容器†

电解质的性质是电能存储装置的整体性能和安全性的主要因素。高浓度的“盐中水”（WIS）电解质本质上是不可燃的，耐湿的，并具有宽广的电化学稳定性窗口，这使其成为用于高性能能量存储设备的有希望的电解质。但是，WIS电解质本质上具有低电导率和高粘度，通常会损害许多储能设备（尤其是超级电容器（SC））的高倍率性能。此外，WIS电解质在低温下不可避免地会析出盐，从而缩小了其适用的温度范围。这里，我们将乙腈作为助溶剂引入典型的“盐包水”电解质中，以配制“乙腈/盐包水”（AWIS）混合电解质，在保持上述条件的同时，可显着提高电导率，降低粘度并扩大适用温度范围WIS电解质的重要理化特性。在模型SC上使用AWIS电解质可显着提高高倍率性能，同时在10 A g时电容增加2.4倍相对于原始WIS电解液为^-1。在2.2 V的高工作电压下，这种AWIS电解质还可以使SC型SC在超过14000个循环中具有稳定的长期循环能力。