Fluorination Modification of Butene Carbonate in High-Voltage Lithium–Metal Batteries: Insights from Quantum Chemical Calculation and Molecular Dynamics Simulation

As an indispensable component of electrolytes, solvents play a crucial role in battery operation. Fluorinated solvents, specifically fluoroethylene carbonate (FEC), have demonstrated significant efficacy in enhancing the energy density of high-voltage lithium metal batteries. Currently, butene carbonate (BC) has been employed as an electrolyte solvent with favorable outcomes. However, there is a lack of in-depth research on the fluorination strategies of BC. To improve the energy density of lithium metal batteries, this study focuses on BC, conducting theoretical investigations on its isomers with varying fluorine substitution positions and quantities. The research findings indicate that the position and number of fluorine substitutions exert directional control over solvent properties. β-position fluorination significantly enhances oxidation stability by substantially lowering the highest occupied molecular orbital (HOMO) energy level and localizing electron distribution, achieving a maximum oxidation potential of 8.38 V (1.34 V higher than nonfluorinated BC). α-position fluorination modulates the reduction potential to 0.76 V by elevating the lowest unoccupied molecular orbital (LUMO) energy level and optimizing electrostatic potential (ESP) distribution. This position-dependent behavior reveals the balancing principle of fluorination degree on performance - moderate fluorination (2-5F) can simultaneously maintain ion transport efficiency and interface stability. The study identified (4R,5R)-4-fluoro-4-(fluoromethyl)-5-(trifluoromethyl)-1,3-dioxolan-2-one (molecule 5,16) as an optimal solvent capable of functioning across the entire voltage range, characterized by a lithium-ion transference number of 0.5369 and a synergistic potential of 8.19 V for oxidation and 0.76 V for reduction, demonstrating exceptional comprehensive performance. This research provides critical insights into the utilization of butene carbonate with varying fluorine substitution positions and quantities as electrolyte solvents.