Tailored Polymer‐Inorganic Bilayer SEI with Proton Holder Feature for Aqueous Zn Metal Batteries

Conventional SEI in aqueous Zn-ion batteries mainly acts as a physical barrier to prevent HER, which is prone to structural deterioration stemming from uneven Zn deposition at high current densities. Herein, we propose an in-situ structural design of polymer-inorganic bilayer SEI with a proton holder feature by aniline-modulated electrolytes. The inner ZnF2 with high stiffness and strength effectively suppresses Zn dendrites. And the outer PANI regulates the current distribution and delays the Sand's time of dendrites growth. The =N- in PANI is capable of reversible proton holder, thereby inhibiting HER. With this bilayer SEI, the Zn anode achieves an impressive cycle life of 126 h under 40 mA cm-2 & 40 mAh cm-2 (DOD=70.8%), solving the bottleneck of single-layer inorganic SEI that could not be cycled under these conditions. The Zn||NaVO pouch battery with bilayer SEI exhibits a high capacity of 1.2 Ah and a cycle life of 350 h with 78% capacity retention. At -30°C, the battery delivers a capacity of 335 mAh and a cycle life of 507 h with 72% capacity retention. Our findings offer profound insights into the design of SEI with tailored structure and functionality, paving the way for the next generation of advanced batteries.