Low-temperature behavior of Li-ion cells

Studies on Li-ion cells with and without Li/Li+ reference electrodes confir m that the limiting factor for low-temperature performance is the carbon an ode. The cycling behavior of MCMB (2528)-LiCoO2 cells were studied over the temperature range of -40 degrees C to room temperature, and at all tempera tures 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 me tallic lithium at the anode for temperatures less than or equal to -20 degr eesC causes permanent capacity loss. This loss is not attributed to electro lyte conductivities, which are relatively high over this temperature range, but rather to continual growth of the solid electrolyte interphase resulti ng from solvent/electrolyte reduction at freshly deposited metallic lithium . The studies also reveal that at low temperatures, lithium cannot be compl etely removed or inserted into the coexistence range of dilute stage 1 and stage 4. This may be a simple electrokinetic phenomenon or, more likely, th e limiting solid-state diffusion of lithium in carbon. (C) 2001 The Electro chemical Society.