Abstract:

As one of the key components in lithium battery electrolyte additives, fluoroethylene carbonate (FEC) is primarily produced industrially using the halogen exchange process. During the FEC synthesis, a substitution reaction between potassium fluoride (KF) and chloroethylene carbonate (CEC) occurs, the rate of which has been limited by the interphase mass transfer of KF. Meanwhile, the CEC is susceptible to an elimination reaction to form by-product of vinylene carbonate. To address these issues, the effect of phase transfer catalyst (PTC) structure on the interphase mass transfer of KF and reaction energy barriers were investigated. It was revealed that the optimized conditions consist of [bmim][BF₄] (1-butyl-3-methylimidazolium tetrafluoroborate) as the PTC, acetonitrile as the solvent, a reaction temperature of 81.6℃, and a KF∶CEC molar ratio of 2.5∶1. Under the optimized reaction conditions, an unprecedently high yield of FEC (91.94%, molar fraction) was achieved. Density functional theory calculations suggested that the [bmim][BF₄] can form complexes with the KF in acetonitrile to increase the nuclear distance between K⁺ and F^- and decrease the free energy of solvation of KF. As a result, the interphase mass transfer of KF was facilitated and the energy barrier of the substitution reaction between KF and CEC was reduced, which contributed to the efficient production of FEC from CEC.

Key words: ionic liquids, phase transfer catalysis, complexes, mass transfer, fluoroethylene carbonate, density functional theory

摘要：

氟代碳酸乙烯酯（FEC）是锂电池电解液添加剂的重要组分之一，其工业制备方法主要为卤素交换法，即氯代碳酸乙烯酯（CEC）与氟化钾（KF）通过取代反应制备FEC。该工艺中，取代反应速率受限于KF相际传质速率，且CEC易发生消去反应生成碳酸亚乙烯酯副产物。针对上述问题，研究了相转移催化剂（PTC）结构对KF相际传质速率和CEC制FEC主副反应能垒的影响规律和调控机制。优化条件下，PTC为[bmim][BF₄]（1-丁 基-3-甲基咪唑四氟硼酸盐），溶剂为乙腈，反应温度为乙腈回流温度（81.6℃），n（KF）∶n（CEC）=2.5∶1，此时FEC收率高达91.94%（摩尔分数）。密度泛函理论计算表明，在乙腈中[bmim][BF₄]能与KF形成配合物，增加K⁺和F^-的核间距并降低KF的溶解自由能，从而强化相际传质并降低取代反应能垒，实现CEC经KF取代高效制备FEC。

关键词: 离子液体, 相转移催化, 配合物, 传质, 氟代碳酸乙烯酯, 密度泛函理论