固体电解质界面膜(Solid Electrolyte Interphase,SEI)在钠离子电池(Sodium Ion Battery,NIB)中扮演着重要作用.迄今为止,对于钠离子电池SEI膜的探索仍然十分有限.本研究利用电化学原子力显微镜(Electrochemical AFM,EC-AFM),通过循环伏安法研究了钠离子电池负极材料高定向热解石墨(Highly Oriented Pyrolytic Graphite,HOPG),在碳酸乙烯酯(Ethylene Carbonate,EC)和氟代碳酸乙烯酯(Fluoroethylene Carbonate,FEC)电解液中首次充放电过程SEI膜的结构变化.通过纳米刻蚀的方法,进一步获得首次充放电结束后SEI的厚度.结合X射线光电子能谱(X-ray Photoelectron Spectroscopy,XPS)分析了HOPG在EC和FEC电解液中所形成的SEI膜的化学组成区别.研究结果表明,在EC电解液中,所生成的SEI膜在HOPG表面非台阶处较薄,但在HOPG的台阶处较厚;在FEC电解液中,所生成的SEI膜很厚,具有明显的双层结构.其中上层是由体积较大的颗粒组成,下层则由致密的小颗粒组成.
Chemical and morphological structures of solid electrolyte interphase (SEI) play a vital role in so-dium-ion battery (NIB). Up to date, SEI remains the least understood component in NIB due to its trace presence, delicate chemical nature, heterogeneity in morphology, elusive formation mechanism, and lack of reliablein situ quantitative characterization tools. SEI morphological evolution during the first cyclic voltammetry and the thick-ness of SEI after first discharging-charging cycle on highly oriented pyrolytic graphite (HOPG) surface were inves-tigated by using in situ electrochemical atomic force microscopy (EC-AFM). Complemented by anex situ XPS analysis, the differences in interfacial features and fundamental constitution of SEI formation in ethylene carbonate (EC) and fluoroethylene carbonate (FEC)-based electrolytes on HOPG electrode surface were revealed. In 1 mol/L NaClO4/EC/DMC electrolyte, dense films were formed at the step edges, while thinner films were observed on the basal plane. In 1 mol/L NaClO4/EC/DMC electrolyte, stable films with doubled layer structures were formed on HOPG electrode after initial electrochemical cycling. The upper layer was composed of large particles, which was soft and easy to be scrapped off by AFM tip while the under layer was composed of dense small particles.
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