Low-temperature behavior of Li-ion cells

Studies on Li-ion cells with and without Li/Li+ reference electrodes confirm that the limiting factor for low-temperature performance is the carbon anode. The cycling behavior of MCMB (2528)-LiCoO2 cells were studied over the temperature range of -40 degrees C to room temperature, and at all temperatures it is the polarization of the anode which limits performance. Even at modest (C/5) to low (C/10) rates of charge and discharge, deposition of metallic lithium at the anode for temperatures less than or equal to -20 degreesC causes permanent capacity loss. This loss is not attributed to electrolyte conductivities, which are relatively high over this temperature range, but rather to continual growth of the solid electrolyte interphase resulting from solvent/electrolyte reduction at freshly deposited metallic lithium. The studies also reveal that at low temperatures, lithium cannot be completely removed or inserted into the coexistence range of dilute stage 1 and stage 4. This may be a simple electrokinetic phenomenon or, more likely, the limiting solid-state diffusion of lithium in carbon. (C) 2001 The Electrochemical Society.