Asymmetric donor-acceptor molecule-regulated core-shell-solvation electrolyte for high-voltage aqueous batteries

Summary

Salt-concentrated aqueous electrolytes show a wider electrochemical window than conventional aqueous electrolytes, yet still suffer from significant hydrogen evolution reaction (HER) at <1.9 V versus Li⁺/Li. Introducing organic compounds was reported to alleviate HER, but all reported organic additives are flammable, inevitably compromising the safety property. Here, we report a new all-nonflammable-ingredient aqueous electrolyte via hybridizing with nonflammable methylurea. The structurally asymmetric methylurea molecules possessing both donor and acceptor functional groups regulate the hydrogen bonding network, resulting in peculiar nanoscale core-shell-like clusters. Such unique solution structure allows localized super-high salt concentration in the electrolyte and suppresses HER at 0.5 V versus Li⁺/Li, achieving a 4.5 V electrochemical window. Under a harsh testing condition with low electrolyte loading, no excess Li resource, no electrode precoating, and conventional aluminum current collectors, this electrolyte realizes a stable cycling of a rocking-chair NbO₂|LiMn₂O₄ full cell (∼175 Wh kg^–1) without compromising the safety property.