Regulating the Inner Helmholtz Plane with a High Donor Additive for Efficient Anode Reversibility in Aqueous Zn-Ion Batteries

The performance of aqueous Zn ion batteries (AZIBs) is highly dependent on inner Helmholtz plane (IHP) chemistry. Notorious parasitic reactions containing hydrogen evolution reactions (HER) and Zn dendrites both originate from abundant free H₂ O and random Zn deposition inside active IHP. Here, we report a universal high donor number (DN) additive pyridine (Py) with only 1 vol. % addition (Py-to-H₂ O volume ratio), for regulating molecule distribution inside IHP. Density functional theory (DFT) calculations and molecular dynamics (MD) simulation verify that incorporated Py additive could tailor Zn²⁺ solvation sheath and exclude H₂ O molecules from IHP effectively, which is in favor of preventing H₂ O decomposition. Consequently, even at extreme conditions such as high depth of discharge (DOD) of 80 %, the symmetric cell based on Py additive can sustain approximately 500 h long-term stability. This efficient strategy with high DN additives furnishes a promising direction for designing novel electrolytes and promoting the practical application of AZIBs, despite inevitably introducing trace organic additives.