Characteristics of surface films formed at a mesocarbon microbead electrode in a Li-ion battery

An investigation is made on the interfacial phenomena of commercially avail able mesocarbon microbeads (MCMB) as the carbon lithium electrode in an ele ctrolyte, which consists of 1 M LiPF6 dissolved in an equal mixture of ethy lene carbonate (EC) and diethyl carbonate (DEC). Once the charge-discharge of lithium (Li) proceeds, a surface film is formed on the MCMB carbon elect rode, and ifs thickness increases with cycle number. The growth of the surf ace film with cycle number is observed by a scanning electron microscope an d the surface resistance by means of AC impedance measurements. A continuou s decrease in the charge capacity with cycle number is found and is related to film growth. The surface films are composed of solvated Li compounds, a s shown by surface-sensitive Fourier transform infrared (FT-LR) spectroscop y. (C) 2000 Elsevier Science S.A. All rights reserved.