High-voltage,low-temperature supercapacitors enabled by localized“water-in-pyrrolidinium chloride”electrolyte

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,Ndimethylformamide,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℃.This work provides new approaches for the design and preparation of novel electrolytes.