Geometric Matching Effect of Tetrahedral Cation Adsorption Enables Reliable Interfacial Engineering toward Stable Aqueous Zinc-Ion Batteries

Geometry-driven molecular design provides a promising route for controlling electrode/electrolyte interfaces in aqueous zinc-ion batteries (AZIBs), yet rational additive selection remains challenging. This study demonstrates the effectiveness of molecular point group theory as a screening principle for high-performance electrolyte additives. The tetrahedral quaternary phosphonium cation (P₄₄₄₄⁺) stands out for its inherently high T_d symmetry and localized polarization, compared with asymmetric cations. Combined experimental and theoretical results reveal that P₄₄₄₄⁺ maintains a stereochemically locked T_d → C_3v adsorption geometry, assembling into a uniform and gradient protective layer (cation-rich inner/anion-rich outer) that displaces interfacial water. This ordered interphase transforms in situ into a ZnP/ZnF₂-enriched solid electrolyte interphase (SEI), effectively suppressing hydrogen evolution, mitigating corrosion, and channeling Zn²⁺ flux into planar and dendrite-free deposition. Consequently, Zn//Zn cells with P₄₄₄₄⁺ additives achieve extended cycle life exceeding 3000 h at 1 mA cm^-2 and 1200 h at 5 mA cm^-2, while Zn//polyaniline (PANI) full cells maintain 86.2% capacity after 2000 cycles at 1.0 A g^-1. These findings reveal a strong correlation between molecular symmetry and interfacial stability, which offers insights for next-generation additive design and advancing high-performance, durable AZIBs.