Dual Electrolyte Additives Suppress Hydrogen Evolution in Aqueous Li-Ion Batteries

Aqueous Li-ion batteries suffer from parasitic hydrogen evolution due to limited cathodic stability. We introduce in this work a dual-additive strategy combining a persulfate and a fluorinated acrylate in a 21 mol kg^–1 LiTFSI aqueous electrolyte. The additives promote the formation of a bilayer solid electrolyte interphase (SEI) comprising an inorganic LiF-rich inner layer and a hydrophobic organic-rich outer layer, which effectively suppresses hydrogen evolution and inhibits SEI dissolution. With this formulation, a LiMn₂O₄/Li₄Ti₅O₁₂ cell is shown to retain over 80% of its initial capacity after 300 cycles, outperforming both the baseline and single-additive controls. The persulfate–acrylate pair likewise improves the cycling stability in other aqueous electrolytes. We also extended the concept to alternative initiator–monomer combinations, demonstrating its versatility in interfacial engineering. By enabling robust SEI formation, this strategy addresses a key limitation of aqueous Li-ion batteries and supports their practical deployment.