Film formation at positive electrodes in lithium-ion batteries

Post mortem scanning electron microscopy was used to study the surface film formation on different cathode materials for lithium-ion batteries. The effect of the kind of oxide, the type of solvent and conducting salt, as well as the influence of additives on this process was investigated. In the case of an electrolyte containing ethylene carbonate (EC) and propylene carbonate (PC) (1: 1, w/w) with 1 M LiPF6, film formation was observed on LiCoO2, LiMn2O4, and especially pronounced on LiNiO2 oxide materials. In contrast, with EC, dimethyl carbonate (1: 1, w/w) 1 M LiPF6 containing electrolyte, no solid electrolyte interface formation was detected. The substitution of LiClO4 for LiPF6 with PC-based electrolytes leads to a less prominent layer. If 2% vinylene carbonate was added to the PC-based electrolyte a pronounced film, presumably consisting of polymerization products of this additive, was created. (C) 2004 The Electrochemical Society.