Synergetic Effect of Multicomponent Phosphate and Rich Grain‐Boundary in Solid/Electrolyte Interphase Boosts Rapid Ion Transport Toward Fast Aqueous Zinc Metal Batteries

Abstract The development of fast‐charging aqueous zinc (Zn) metal batteries is crucial for large‐scale energy storage applications. However, in pursuit of fast‐charging capability under a high current density (>10 mA cm −2 ), the intensified Zn 2+ flux imbalance at the electrolyte/anode interphase will cause more uncontrolled dendrite growth. Herein, with experimental and simulation results, a theoretical formulation is proposed to reveal a current density‐dependent failure mechanism that elucidates how space‐charge‐induced Zn 2+ accumulation triggers cascading dendrite formation. To mitigate this kinetic mismatch, a fast‐ion‐conducting solid/electrolyte interphase (SEI) model system with multicomponent phosphate and rich grain‐boundary is established, by which the Zn 2+ transference number increases from 0.25 to 0.82 and the migration energy barrier at the interphase decreases from 3.80 to 1.35 eV. Consequently, this designed interfacial remodeling enables Zn||Zn cells to exhibit ultrahigh‐rate capability and extended durability (achieving 13 000 cycles at 40 mA cm −2 and 4000 h at 0.5 mA cm −2 ). More significantly, full cells retain 86% capacity after 2000 cycles at 2 A g −1 , while industrial‐scale 4 × 6 cm 2 pouch cells maintain 90.3% capacity over 100 cycles. Collectively, these findings establish a universal interfacial design principle for high‐power aqueous metal batteries by correlating grain‐boundary ion dynamics with effective dendrite suppression.