Diminution of supercooling of electrolytes by carbon particles

We studied the supercooling behavior of a number of solutions of LiPF6 in e thylene carbonate-ethyl methyl carbonate in 1:1 weight ratio with and witho ut the presence of one of these carbons: activated carbon, carbon black, an d mesocarbon microbeads. The results of our experiments of differential sca nning calorimetry (DSC) show that the supercooling of less concentrated sol utions is significantly diminished by the presence of a carbon, the degree and the nature of which depends on the concentration of the electrolyte and the type of carbon present. The results of our conductivity measurement al so indicate precipitation in some of the electrolytes at low temperatures, which correlates well with the DSC results. We therefore conclude that the temperature range in which an electrolyte supercools without a nucleating m aterial is unreliable for the operation of an electrochemical device contai ning such an electrolyte. Instead, the liquidus temperature of an electroly te should be used as the lower limit of operation if the possibility of its crystallization is to be excluded. (C) 1999 The Electrochemical Society. S 0013-4651(99)03-011-6. All rights reserved.