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 available mesocarbon microbeads (MCMB) as the carbon lithium electrode in an electrolyte, which consists of 1 M LiPF₆ dissolved in an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). Once the charge-discharge of lithium (Li) proceeds, a surface film is formed on the MCMB carbon electrode, and its thickness increases with cycle number. The growth of the surface film with cycle number is observed by a scanning electron microscope and the surface resistance by means of AC impedance measurements. A continuous 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, as shown by surface-sensitive Fourier transform infrared (FT-IR) spectroscopy.