High-voltage, low-temperature supercapacitors enabled by localized “water-in-pyrrolidinium chloride” electrolyte
Peng Zhang, Weili Zhang, Zhengjie Wang, Xuefei Wang, Qingjuan Ren, Shuai Zhang, Yujia Wang, Liang He, Pan Liu, Qingyin Zhang, Zhiqiang Shi
Abstract
Aqueous electrolytes offer superior prospects for advanced energy storage. “Water-in-salt” (WIS) electrolytes exhibit a wide electrochemical stability window (ESW), but their low conductivity, high viscosity, and precipitation at low temperatures restrict their application. Herein, we report a novel localized “water-in-pyrrolidinium chloride” electrolyte (LWIP; 1 mol/L, N-propyl-N-methylpyrrolidinium chloride/(water and N,N-dimethylformamide, 1:4 by molality)) enabling high-voltage, low-temperature supercapacitors (SCs). The greatly improved ESW (3.451 V) is mainly attributed to the strong solvation between Cl− and water molecules, which broadens the negative stability. This water-binding mechanism is very different from that of a WIS electrolyte based on alkali metal salt. SCs using LWIP electrolytes not only yield a high operating voltage of 2.4 V and excellent capacity retention (82.8% after 15,000 cycles at 5 A g−1) but also operate stably at −20 °C. This work provides new approaches for the design and preparation of novel electrolytes.