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

Abstract

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.