THE CORRELATION BETWEEN THE SURFACE-CHEMISTRY AND THE PERFORMANCE OF LI-CARBON INTERCALATION ANODES FOR RECHARGEABLE ROCKING-CHAIR TYPE BATTERIES

The correlation between the electrochemical properties of Li carbon intercalation electrodes and their surface chemistry in solutions was investigated. The carbons investigated were primarily graphite and petroleum coke, and the solvent systems included methyl formate (MF), propylene and ethylene carbonates, ethers and their mixtures. The surface chemistry of the electrodes was studied using mainly diffuse reflectance Fourier transform infrared spectroscopy. The following aspects were studied: (i) the effect of temperature on the buildup of the surface films; (ii) the effect of additives (e.g., CO2, crown ethers), (iii) the behavior when the passive layer is built in one solution followed by cycling in another; and (iv) the effect of cosolvent in MF solutions. The results obtained further prove that the electrochemical behavior of these systems is surface film controlled. An understanding of the surf ace chemistry of these electrodes enables judicious optimization of carbon-solution systems for use in rechargeable Li batteries.