Manipulating chaotropic anion enables lacked H-bond aqueous electrolyte for lithium-ion hybrid capacitor

Aqueous electrochemical energy storages have multiple advantages especially safety performance in the energy storage process. The high concentration aqueous electrolytes with a wide electrochemical stable voltage window (ESW) solves the key problems of aqueous electrochemical energy storages. It effectively breaks the limitation of H2O molecule decomposition to realize aqueous electrochemical energy storage with high operating voltage. However, the slow ion transport and high cost limit their application in power-type storages. Here, the lacked H bond aqueous electrolyte (LHE) is proposed by investigating the structures and properties of aqueous electrolytes with various chaotropic anions. The LHE achieves high conductivity, low viscosity, and low cost while ensuring a wide ESW. These excellent properties originate from the OTf- effect on the solvation structure of cations and the number of H-bonds. An aqueous Li-ion hybrid capacitor (LHC) with the LHE exhibits high operating voltage of 2.5 V and high ESW utilization of 92.6 %. The aqueous cathode electrolyte interphase formed by anions on the cathode surface also achieved a long cycle life for the LHC. It has guided the development of novel electrolytes for electrochemical energy storage.