过充电保护添加剂1,4-二甲氧基苯的反应机理

摘要

采用密度泛函理论(B3LYP/6-311+G(d,p))和MP216-311+G(d,p)方法,研究锂离子电池过充电保护添加剂1,4-二甲氧基苯(p-DMOB)的作用机理.计算结果表明,在过充时,p-DMOB优先于溶剂分子(乙基甲基碳酸酯、二甲基碳酸酯、碳酸乙酯)发生氧化反应.用B3LYP和MP2计算所得的p-DMOB理论氧化电位接近,分别为4.12和4.05V (vs Li/Li+).p-DMOB氧化时首先失去一个电子,生成p-DMOB+*正离子自由基,用B3LYP和MP2方法计算所得的相应能量变化分别为701.24和728.27 kJ· mol-1.失去电子后苯环的共轭性受到破坏,随后p-DMOB”苯环上的CH键发生断裂,失去H+并形成p-DMOB·自由基,用B3LYP和MP2方法计算所得的相应能量变化分别为1349.78和1810.99 kJ· mol-1,p-D MOB·自由基很小稳定,会在电极表面发生聚合反应形成聚合物膜,用B3LYP和MP2方法计算所得的相应能量变化分别为-553.37和-1331.20kJ·mol-1.%The reaction mechanism of 1,4-dimethoxybenzene (p-DMOB) as an overcharge protection additive for lithium ion batteries was determined by theoretical calculation of density functional theory (DFT) at the level of B3LYP/6-311 +G(d,p) and MP2/6-311 +G(d,p).It was found that p-DMOB is oxidized prior to the solvents,ethyl methyl carbonate,dimethyl carbonate,and ethylene carbonate,when the lithium ion battery is overcharged.The calculated oxidative potentials of p-DMOB by B3LYP and MP2 methods are well in agreement at 4.12 and 4.05 V (vs Li/Li+),respectively.The initial oxidation of p-DMOB involves a one-electron transfer resulting in a radical cation p-DMOB+*.The corresponding energy variations were 701.24 and 728.27 kJ.mol-1 from B3LYP and MP2 calculations,respectively.The p-DMOB+* species then loses one proton forming a radical p-DMOB- through the breaking of a C-- H bond on the benzene ring,with the corresponding energy variations of 1349.78 and 1810.99 kJ·mol-1 for B3LYP and MP2,respectively.The p-DMOB·species is unstable and copolymerizes forming an insulated polymer with the corresponding energy variations of -553.37 and -1331.20 kJ.mol-~ for B3LYP and MP2,respectively.