Hydrated eutectic electrolytes (HEEs) hold promise as green, safe and affordable electrolytes for high-voltage electrochemical energy storage. The water molecules in HEEs participate in the solvation structure of cations, which is critical to the electrolyte performance. We hereby report HEEs consisting of NaClO4, N-methyl acetamide (NMAc) and water. By adjusting the ratio of the ingredients, the optimized HEEs-5 shows a wide electrochemical potential window, lowered viscosity and non-flammability. Spectroscopic analysis and molecular dynamics simulations reveal that NMAc and H2O form the inner solvation shell of Na+, while the free ClO4– result in enhanced ionic conductivity. Moreover, NMAc molecules form a protective barrier on the surface of carbon upon charging, inhibiting the activation-controlled faradaic self-discharge reactions caused by free water molecules. The supercapacitor with HEEs-5 electrolyte shows a high voltage of 2.3 V, ultra-long cycle life and low self-discharge. This work reveals the crucial roles of NMAc, but also shed light on the design and optimization of other HEEs.

中文翻译：

---

用于高电压和低自放电的超级电容器的乙酰胺基水合共晶电解质


水合共晶电解质 （HEE） 有望成为用于高压电化学储能的绿色、安全且经济实惠的电解质。高熵元素中的水分子参与阳离子的溶剂化结构，这对电解质性能至关重要。我们特此报告由 NaClO4、N-甲基乙酰胺 （NMAc） 和水组成的 HEE。通过调整成分的比例，优化的 HEEs-5 显示出较宽的电化学电位窗口、更低的粘度和不易燃性。光谱分析和分子动力学模拟表明，NMAc 和 H2O 形成 Na+ 的内溶剂化壳，而游离 ClO4– 导致离子电导率增强。此外，NMAc 分子在充电时在碳表面形成保护屏障，抑制由游离水分子引起的活化控制的法拉第自放电反应。采用 HEEs-5 电解液的超级电容器具有 2.3 V 的高电压、超长的循环寿命和低自放电。这项工作揭示了 NMAc 的关键作用，但也阐明了其他 HEE 的设计和优化。