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.