Triple-Coupling Regulation Enables Dendrite-Free Subzero Aqueous Zn-Ion Batteries

Aqueous Zn-ion batteries (AZIBs) suffer severe degradation at subzero temperatures due to electrolyte freezing, sluggish Zn²⁺ kinetics, and dendrite-induced interfacial instability. Herein, a triple-coupling regulation strategy integrating solvation structure, interfacial chemistry, and crystallographic orientation through a formamide-ethanol deep eutectic electrolyte (ZEFW2) was developed. Molecular dynamics simulations and spectroscopic analyses reveal that ZEFW2 redistributes the primary Zn²⁺ solvation environment, reducing H₂O and acetate coordination while introducing formamide coordination and maintaining favorable Zn²⁺ transport. Depth-resolved XPS further reveals a chemically reconstructed Zn interphase containing Zn-O-related inorganic species and persistent N- and C-containing electrolyte-derived species. The modified solvation and interfacial environments regulate Zn nucleation and promote preferential Zn deposition along the (101) facet, enabling more homogeneous Zn growth and suppressing dendritic morphology. Consequently, Zn||Zn symmetric cells achieve 1400 h of cycling at -20°C under 1 mA cm^-2 and 10 mAh cm^-2, with a Coulombic efficiency of 99.78% over 1200 cycles. Zn||NVO full cells retain 74% of their initial capacity after 1600 cycles at -20°C, while pouch cells demonstrate stable operation at both room and subzero temperatures. This work establishes a molecular-to-interfacial triple-coupling strategy for temperature-resilient AZIBs.