Grain Boundary Strengthening Enables Microstructural Regulation of Electrolytes for Robust Zinc Metal Batteries

Rechargeable aqueous zinc metal batteries (ZMBs) suffer from notorious dendrite formation and interfacial side reactions, hindering their long-term stability and practical deployment. Here, a grain boundary strengthening electrolyte (GBSE) is reported featuring numerous boundaries with unique anion-participating interfacial composition of reverse micelle motifs. This microstructural regulation effectively suppresses proton and hydroxyl anion transport via the Grotthuss mechanism, while enhancing zinc ion transfer dynamics. Accompanied by the in situ formation of the high-fluorinated solid-electrolyte interface (SEI), the Zn metal anode achieves a remarkable 99.8% coulombic efficiency and a lifespan of over 3000 h with a cumulative deposition capacity exceeding 12 000 mAh cm^-2, demonstrating excellent dendrite suppression and reversibility in the GBSE. This microstructural design substantially enhances the stability of high-voltage Zn||graphite batteries (310 cycles, 92.5% capacity retention) and the performance of highly safe and practical ampere-hour-scale Zn||Mn-doped V₂O₅ pouch cells, achieving a superior cumulative cycling capacity of 510 Ah over 450 cycles with 96.5% capacity retention and 81.65% depth of discharge. This study features a new insight into microstructural regulation and grain boundary strengthening strategy of electrolytes for high-performance ZMBs. © 2025 Wiley-VCH GmbH