锂硫电池中碳酸乙烯酯与硫簇反应拉曼光谱的理论研究

Theoretical Study of Reactions Between Polysulfides and Ethylene Carbonate and Raman Spectra in Lithium-sulfur Battery

通过密度泛函理论(DFT)计算了锂硫电池中多硫阴离子(S2-n)和碳酸乙烯酯(EC)的2种反应机理,并对其反应物和主要产物的拉曼光谱进行了理论分析.计算结果表明,2种反应路径中,S2-n进攻EC分子烷基碳所需活化能和Gibbs自由能均较低.多硫基团有很强的拉曼特征谱峰,与EC分子相关的部分拉曼谱亦发生显著变化.锂离子的存在影响反应产物的结构和拉曼光谱.密度泛函理论计算提供了锂硫电池中锂、多硫阴离子和电解液反应前后的结构变化和反应信息.

Two mechanisms of the reaction between polysulfides（ S2-n,n = 2—4） and ethylene carbonate（ EC） and Raman spectra of the reactants and main products were investigated by density functional theory（ DFT） method. The results showed that the reaction of polysulfides attacking the ethyl carbon of EC is more favorable than that attacking the carbonyl carbon of EC in terms of the activation energies and Gibbs free energies. Sulfur groups in polysulfides display strong Raman signals,so that simulated Raman spectra of the products of the S2-n＋ EC reaction significantly change after the reaction. The coordination effect of Li＋cation also influenced the simulated Raman spectra of reaction products. DFT results and Raman spectroscopic analysis provide a new insight on structural stability of polysulfides and EC electrolyte in the lithium sulfur battery.