Tailoring the Electric Double Layer with Trace PEG400 for Ultra‐Stable Zn Anodes

Developing stable aqueous zinc-ion batteries (AZIBs) requires suppressing interfacial water-induced side reactions and dendrite growth at Zn anodes. Electrolyte additives present a viable strategy, but conventional electrolyte additives often require high concentrations that compromise ionic conductivity and bring about toxic and flammable issues. In this work, trace amounts (0.8 vol%) of polyethylene glycol 400 (PEG400) is introduced to operate as an effective electric double layer (EDL) regulator. The minimal additive loading uniquely restructures the EDL without changing bulk electrolyte properties (ionic conductivity and Zn²⁺ ions solvation structure). A competitive adsorption mechanism is elucidated, wherein PEG400, possessing stronger adsorption energy than H₂O, preferentially occupies the Zn anode surface, forming a H₂O-poor EDL that suppresses water-induced side reactions and improves nucleation kinetics to enable dendrite-free deposition. AZIBs with the addition of PEG400 achieve exceptional cycling stability for 440 h under harsh test conditions of 30 mA cm^-2 and 180 h even at a higher current density of 40 mA cm^-2. Full batteries coupled with NH₄V₄O₁₀ (NVO) cathodes deliver 351 mAh g^-1 at 1 A g^-1, corresponding to a capacity retention of 90% for 1000 cycles.