Constructing highly reversible zinc batteries under high depth of discharge & current density conditions via quaternary ammonium cations modulating electric field force and competitive solvation

Aqueous zinc-ion batteries have emerged as a promising alternative to lithium-ion batteries due to their safety, high theoretical energy density, and environmental friendliness. However, several critical challenges – such as the hydrogen evolution reaction (HER) and corrosion induced by active water molecules, as well as the uneven zinc deposition and rampant growth of dendrites caused by high local electric fields – significantly hinder their practical applications. These issues become even more severe under high depth-of-discharge (DoD) conditions, where the reversibility of the zinc anode drastically deteriorates. In this work, we introduce an organic quaternary ammonium salt, tetramethylammonium tetrafluoroborate (TMA–BF), as an electrolyte additive. Theoretical calculations combined with experimental characterization reveal that TMA⁺ incorporates into the EDL, neutralizing the negative charge of Zn deposits. This regulates the local electric field force within the EDL, promoting uniform Zn²⁺ deposition and suppressing dendrite growth by electrostatic screening. Furthermore, the strong affinity between TMA⁺ and water molecules alters the hydrogen-bonding network by competing with Zn²⁺ in solvation (competitive solvation), effectively reducing the amount of active water molecules. As a result, the modified ZIBs exhibit high reversibility: Zn‖Zn symmetric cells achieve over 4000 hours of stable cycling at 2 mA cm⁻² and over 1400 hours at 20 mA cm⁻². Remarkably, even under deep discharge conditions (DoD of 75% and 85%), stable cycling is maintained for more than 700 and 400 hours, respectively – outperforming most reported electrolyte additive strategies. Moreover, the Zn‖MnO₂ full cell retains 92% of its capacity after 8000 cycles, and the Zn‖Br₂ cell also retains 84% of its capacity after 1200 cycles. Finally, the assembled pouch cell exhibited splendid performance, highlighting the practical viability of this strategy.