Unveiling the Site-Dependent Effects of Methoxy-Substituted Sulfolane as Electrolyte Additives for High-Voltage...

Sulfone-based solvents such as sulfolane (SL) exhibit excellent oxidative stability for high-voltage lithium batteries, but their practical application is hindered by high viscosity, limited reductive stability, and poor graphite compatibility. Herein, density functional theory (DFT) calculations combined with molecular dynamics (MD) simulations were employed to systematically investigate 26 methoxy-substituted sulfolane derivatives (SLOCH3) with different substitution numbers and positions. The results reveal that methoxy substitution reconstructs the local electronic environment and Li+ solvation behavior rather than intrinsically improving redox stability. A-site substitution strongly weakens the high-voltage framework, whereas B-site substitution better preserves oxidative tolerance while enabling structural tunability. Importantly, methoxy substitution enhances Li+ coordination and can still improve Li+ transport even when the ion-pair structure shifts from SSIPs to CIPs and AGGs. This unusual transport behavior indicates that Li+ migration is dominated by local solvation-shell reorganization rather than conventional ion-pair classification. Moreover, moderate methoxy substitution effectively reduces viscosity and promotes Li+ partial ionic conductivity, demonstrating the synergistic regulation of interfacial chemistry and ion transport. Among all the molecules investigated, two representative candidates were selected. 1a0a'2b0b' exhibits well-balanced overall performance in terms of oxidative stability, Li+ coordination regulation, and ionic transport. 1a0a'1b2b' shows the highest Li+ transference number, highlighting its potential for fast-charging applications. This work provides molecular-level insights into site-dependent methoxy engineering of sulfolane and offers guidance for the rational design of high-voltage lithium-metal battery electrolytes.