Steric Tuning Enables Room-Temperature Coordination Ionic Liquids for Zn-Metal Batteries

The pursuit of high-energy-density batteries requires molten-salt-like electrolytes, but conventional systems often suffer from high viscosity or elevated operating temperature. Herein, we report a class of room-temperature coordination ionic liquids (CILs) constructed through well-defined coordination between Zn²⁺ and pyridyl ligands. X-ray single-crystal diffraction demonstrates the stoichiometric formation of discrete [Zn(ligand)₄]²⁺ in the solid state, while complementary spectroscopic analyses and theoretical simulations confirm similar coordination environments in the liquid state. Precise steric modification of pyridyl ligands, exemplified by 2,6-dimethoxypyridine (DMOP), balances cation-ligand coordination and cation-anion electrostatic interactions to enable room-temperature fluidity. The unique solvation structure facilitates charge-transfer kinetics, promotes the formation of a stable solid-electrolyte interphase, and suppresses side reactions. Consequently, the DMOP-based CIL enables Zn/V₂O₅ and Zn/NaV₃O₈·1.5H₂O full cells to cycle reversibly with excellent stability under harsh operating conditions. This work establishes steric control of coordination chemistry as an effective strategy for designing advanced liquid-state complex electrolytes and extends the concept of solvate ionic liquids to divalent Zn-based systems.