An Oligomeric Additive Bridges Inner and Outer Helmholtz Planes to Enable Reversible Zn Anodes via Spatial and...

Precise molecular engineering of the electrode/electrolyte interface remains a key bottleneck for aqueous Zn-ion batteries (ZIBs). Here, we report an oxidative polymerization strategy to synthesize oligomeric chromotropic acid disodium salt (OCAD) as a multifunctional additive. The oligomeric architecture bridges the inner and outer Helmholtz planes (IHP and OHP), shifting regulation from IHP-localized adsorption to full IHP/OHP coverage. The expanded dimeric framework (1.51 vs. 0.65 nm) displaces water molecules and promotes Zn²⁺ desolvation at the OHP via steric hindrance and hydrophobic effects, while sulfonic and phenolic hydroxyl groups repel SO₄ ^2- and buffer pH at the IHP through electrostatic repulsion and proton donation. This functional decoupling overcomes the consumption-driven failure of conventional small-molecule additives, suppressing side reactions and guiding uniform Zn deposition. Consequently, symmetric cells with OCAD-modified Zn anodes achieve exceptional cycling stability exceeding 4300 h at 1 mA cm^-2/1 mAh cm^-2 and operate at an 85.6% depth of discharge. A full battery paired with a Na₂V₆O₁₆ cathode retains 81.6% capacity after 4700 cycles at 20 A g^-1. The performance translates effectively to high‑mass‑loading cathodes and pouch cells, underscoring practical viability. This work establishes molecular oligomerization as a versatile paradigm for long‑range interface regulation in durable aqueous ZIBs.