Suppressing water clusters by using "hydrotropic" ionic liquids for highly stable aqueous lithium-ion batteries

The state-of-the-art water-in-salt electrolytes exhibit a wider electrochemical window than conventional dilute aqueous electrolytes. However, the extended electrochemical stability window via increasing the salt concentration has reached a bottleneck. An alternative approach is to effectively suppress H2O activity using multi-functional components. Here, we design an isolated water-in-salt solvation structure in aqueous electrolytes with the "hydrotropic" ionic liquid 1-methyl-1-propylpiperidinium bis(fluorosulfonyl)imide (PP13FSI). The addition of PP13FSI suppresses H2O clusters via the hydrophobic PP13+ cations and lithium-philic FSI- anions, showing a greatly extended electrochemical stability window up to 4.9 V. A robust alkaline-based organic-inorganic hybrid solid electrolyte interface is achieved on a low-voltage Li4Ti5O12 anode, which further extends kinetics stability of aqueous electrolytes. Aqueous Li4Ti5O12||LiMn2O4 full cells demonstrate stable cycling over 1000 cycles at 2C rate and a capacity retention of 70% with an average coulombic efficiency of 99.7%. This work provides new avenues to explore effective approaches for the development of next-generation highly stable aqueous lithium-ion batteries.