Confined Ion Regulation via Synergy of Porosity and Acidity in Molecular Sieves for Lithium‐Metal Batteries

ABSTRACT This work establishes a framework of synergistic solvation structure engineering via pore confinement and acidity modulation, offering a new strategy to regulate solvent structures and SEI formation for safe, long‐life, and high‐rate lithium‐metal batteries. A series of modified separators were fabricated using MCM‐41 and ZSM‐5 molecular sieves with systematically varied pore architectures and Brønsted/Lewis acid site densities. Structural and spectroscopic analyses (ATR‐FTIR, Raman, and 7 Li NMR) reveal that molecular sieves selectively filter solvent macromolecules and adsorb ions, thereby shifting lithium‐ion solvation from solvent‐separated ion pairs (SSIPs) toward contact ion pairs (CIPs) and aggregates (AGGs). Density functional theory calculations further confirm that pore size matching coupled with acidic sites weakens Li + solvation, increases local salt concentration, and releases more free Li + , enhancing the lithium‐ion transference number up to 0.66. Electrochemical testing demonstrates that Li||Li symmetric cells with the optimized small pore/high‐acidity ZSM‐5 separator exhibit stable cycling over 750 h with low polarization (<0.2 V). Full Li||LiFePO 4 cells achieve 95.7% capacity retention after 2900 cycles at 5C with a Coulombic efficiency above 99.8%. Post‐cycling characterizations confirm uniform dendrite‐free lithium deposition and the formation of a compact, inorganic‐rich SEI (LiF/Li 2 O‐dominated) facilitated by the solvation regulation.