Low-temperature characterization of lithium-ion carbon anodes via microperturbation measurement

The low-temperature performance limits of Johnson Matthey (JM) 287 graphite and mesocarbon microbead (MCMB) 6-10 coke were investigated using galvanostatic intermittent titration (GITT) and electrochemical impedance spectroscopy. The poor low-temperature (-30degrees C) performance of graphite insertion anodes results from a low lithium insertion capacity because polarization or overpotential is higher than the stage transformation plateau potential. This results in a shorter plateau potential region containing the lithium-rich stages, e. g., Li0.33C6, Li0.5C6, and Li1C6. Overall, there is an incomplete transformation from Li-poor to Li-rich stages when the cutoff potential is limited to 0.0 V (vs. Li/Li+) to avoid metallic lithium deposition. The good low-temperature performance of MCMB 6-10 coke is attributed to the smooth change of equilibrium Li content as a function of potential. The high polarization only decreases Li insertion capacity by a small percentage. At room temperature, stage transformation is the rate-controlling step of electrochemical Li insertion-extraction kinetics for JM 287 graphite. However, at -30degrees C the resistance of solid electrolyte interphase film increases by a factor of over 27, and becomes limiting. (C) 2002 The Electrochemical Society.