Self-Regulated Gradient Hydrogel Electrolyte with Ultrafast Ion Channels for Robust Zinc-Ion Batteries

Hydrogel electrolytes are crucial for advancing safe and flexible aqueous zinc-ion batteries. However, conventional homogeneous hydrogels suffer a trade-off between fast Zn²⁺ transport and stable Zn/electrolyte interfaces. Herein, we report a surface energy-driven self-regulated gradient hydrogel electrolyte (SRG-HE) that resolves this conflict via a spatially modulated polymer network. The SRG-HE shows dense layers at the Zn/SRG-HE interfaces provide robust passivation, while a low-density bulk supports rapid Zn²⁺ diffusion. During in situ polymerization, amphiphilic Triton X-100 induces spontaneous component migration and surface enrichment, forming a symmetric surface-bulk-surface gradient. The dense surface layers suppress free-water activity to stabilize interfaces, whereas the hydrated bulk delivers high ionic conductivity (97.7 mS cm^{- 1}). Polar groups in SRG-HE further immobilize OTf^-, enabling selective Zn²⁺ transport with a high transference number of 0.88. Consequently, Zn||Zn cells cycle stably for 1365 h at 4 mA cm^{- 2} with uniform (002)-textured deposition. When paired with V₂O₅ cathodes, the full cells maintain a reversible capacity of 234 mAh g^{- 1} after 2000 cycles at 1000 mA g^{- 1}, achieving near 100% Coulombic efficiency. Even under mechanical deformation, SRG-HE-based pouch cells retain functionality, underscoring their potential for durable, high-performance energy storage systems.