Three-Dimensional Visualization of Chemical Stratification and Pathological Redistribution in Aqueous Zinc Batteries

The deployment of aqueous zinc batteries in next-generation energy storage is hindered by interfacial instability of the zinc anode, closely linked to the spatiotemporal evolution of interfacial chemical fields. Herein, an in-situ 3D pH visualization platform directly reveals a spontaneous and persistent gravity-aligned pH gradient at the zinc-electrolyte interface, reaching ∼0.6 between the upper and lower regions. Coupled multiphysics simulations show that electrochemically induced electrolyte density stratification drives natural convection, dominating ion and proton transport and sustaining pH and Zn2+ gradients. The resulting vertical chemical stratification spatially decouples interfacial reactions, leading to directional zinc redistribution. As a proof of concept, suppressing convection using a mixed-salt electrolyte homogenizes the interfacial pH (ΔpH < 0.1) and extends the cycling lifetime of symmetric zinc batteries by over 75%. This work reveals a gravity-coupled mechanism governing interfacial chemical field evolution, providing general physical principles for stabilizing aqueous metal anodes.