A Theoretical Study on Tailoring the Nitrile Substitution Strategy in Carbonates for Lithium-Ion Batteries

Improving the operating voltage is an effective strategy for enhancing the energy density of lithium-ion batteries. However, this approach raises critical challenges, including oxidative decomposition of the electrolyte and degradation of electrode materials, which urgently require solutions. In this context, nitrile compounds, characterized by their strong electron-withdrawing effect, high dielectric constant, and excellent oxidation stability, have emerged as ideal materials for optimizing high-voltage electrolytes. While some studies have reported the impact of linear nitrile compounds on battery performance, research on cyclic nitrile compounds remains scarce. To address this research gap, we designed a series of nitrile-substituted cyclic carbonates based on ethylene carbonate (EC) and propylene carbonate (PC) and conducted quantum chemical calculations and molecular dynamics simulations. Quantum chemical calculation results demonstrate that introducing a cyano group (-CN) at the methylene or methine position can form a conjugation effect with the C═O group, thereby enhancing the molecular oxidation stability. With the same number of nitrile substituents, the substitution position (methylene vs methine) or cis/trans configuration has a minor influence on the oxidation potential, but the reduction potential of the cis configuration is higher than that of the trans configuration. Geminal disubstitution and methyl-permethyl substitution significantly increase the reduction potential due to synergistic effects. Molecular dynamics simulation results indicate that the introduction of cyano groups restructures the solvation shell, influencing the kinetics of lithium-ion coordination and transport. This work emphasizes the importance of selecting the number and position of nitrile substituents in cyclic carbonates. Based on quantum chemical and molecular dynamics calculation results, we provide candidate molecule screening recommendations for cathode/anode film-forming additives and solvents, aiming to offer practical strategies for improving the electrochemical performance of high-voltage lithium metal/lithium-ion batteries.