Studies of Passive Film on Carbon Electrode of Secondary Lithium Battery

• Main Authors: Yang, Chang-Rung, 楊長榮
• Other Authors: Yung-Yun Wang
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/07123995219853359451

博士 === 國立清華大學 === 化學工程學系 === 85 === This work examines the formation of passive film on the carbon electrode of lithium batteries. According to those results, with a single solvent of EC (ethylene carbonate), the structure of the passive film was found to be (CH2OCOOLi)2 on the carbon electrode''s surface. In the DEC (diethyl carbonate) or DMC(dimethyl carbonate) system, C2H5OCOOLi and Li2 CO3 were formed on the carbon electrode''s surface. According to mass spectra, CO2 gas is the main product when EC is decomposed. In addition , DEC is decomposed into CO and C2H6 and DMC into CO and CH4 as well. Those results suggest the composition ofpassive film depends on the solvent''s property. In a binary solvent system which contains EC, the passive film still contains chiefly (CH2OCOOLi)2, which is identical to a single EC solventsystem. This work examines the interface between carbon electrode and organic electrolyte of lithium ion battery by AC impedance technology. A five RC circuits model was adopted to investigate the interfacial property. It was found in EC or DMC electrolyte system, the total interfacial resistance and the passive film'' s thickness increase with a decreasing intercalation potential. However, in DEC system, the total interfacial resistance and the passive film''s thickness decrease as intercalation proceeds. The porous layer of the passive film obviously affects the total interfacial resistance in a single which organic electrolyte. Furthermore, the total interfacial resistance and the passive film''s thickness remain constant after the initial intercalation. This finding suggests that the passive film''s property is steady in a single electrolyte system. In the binary electrolyte system such as EC/DEC or EC/ DMC system, the effects of porous parts on the total interfacial resistance are slight. However, the total interfacial resistance and the passive film''s thickness are smaller than that in a single electrolytesystem. In addition, the variation of the total interfacial resistance and the passive film''s thickness in EC/DEC (or EC/DMC) electrolyte are similar to DEC (or DMC) electrolyte during intercalation progress, respectively.