Customizing the water-scarce, zinc ion-rich Helmholtz plane of a zinc anode for Ah-scale Zn metal batteries

Reconstructing the Helmholtz plane (HP) on the zinc anode is a fundamental approach to suppress side reactions and dendrite growth, where the key is to redesign the HP to minimize the presence of water dipoles and ensure a uniform distribution of Zn ion flux. Herein, we propose a strategy to create a water-scarce inner Helmholtz plane (IHP) and a Zn ion-enriched outer Helmholtz plane (OHP) through the in situ development of a PEDOT:PSS hydrogel layer. This layer is doped with ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) on the surface of zinc foil (Zn@IL&PPS). The hydrophobic EMIM⁺ in the lean-water IHP effectively blocks the adverse reactions between water dipoles and metallic zinc. Concurrently, the zincophilic TFSI⁻ and PSS⁻ in the OHP regulate and expedite the flux and diffusion of Zn ions at the anode-electrolyte interface, reducing electrochemical polarization. As a result, the Zn@IL&PPS electrode exhibits an impressive lifespan of 800 h at 30 mA cm⁻² and 15 mA h cm⁻². Additionally, the I₂‖Zn@IL&PPS pouch cell with 1 A h capacity demonstrates excellent cycling stability. This study explores targeted surface modifications to refine HP, paving the way for the development of advanced zinc metal batteries.