New insights into the interactions between electrode materials and electrolyte solutions for advanced nonaqueous batteries

In this paper we review some recent work with Li metal and Li-graphite anod es and LixMOy cathodes (M = transition metals such as Ni, Co, Mn). The emph asis was on the study of surface phenomena using in situ and ex situ FTIR s pectroscopy, atomic force microscopy tin situ AFM), electrochemical quartz crystal microbalance (EQCM) and impedance spectroscopy (EIS). The performan ce of Li metal and Li-carbon anodes in secondary batteries depends on the n ature of the surface films that cover them. The use of Li metal anodes requ ires the formation of highly uniform and elastic surface films. Thus, most of the commonly used liquid electrolyte solutions are not suitable for Li m etal-based rechargeable batteries. In the case of Li-C-based batteries, the passivating films need not be elastic. Channeling the Li-C electrode surfa ce chemistry towards the formation of Li2CO3 surface films provides adequat e passivation for these electrodes. This can be achieved through the use of EC-based solutions of low EC concentration (cosolvents should be less reac tive than EC). An interesting finding is that the behavior of many commonly used cathodes also depends on their surface chemistry, and that their over all Li insertion processes include the step of Li ion migration through sur face films. Their origin is discussed herein, as well as possible oxidation processes of the relevant solutions. (C) 1999 Elsevier Science S.A. All ri ghts reserved.