Showing papers by "T.R. Jow published in 1999"

Diminution of Supercooling of Electrolytes by Carbon Particles

Abstract: A liquid solution composed of a pure or mixed solvent and a dissolved salt is the most common form of electrolyte used in electrochemical devices for energy storage and conversion, such as batteries and capacitors. For such an electrolyte, one of the most important properties is its crystallization temperature, which limits the low-temperature operation of a device containing such an electrolyte. If thermodynamic equilibria were strictly followed, crystallization of an electrolyte would start as soon as it is cooled to its liquidus temperature. But such is seldom the case, as an electrolyte by itself often supercools well below this temperature. This supercooling can delay or even eliminate the crystallization of an electrolyte, thus substantially extending its apparent liquid range. The authors studied the supercooling behavior of a number of solutions of LiPF{sub 6} in ethylene carbonate-ethyl methyl carbonate in 1:1 weight ratio with and without the presence of one of these carbons: activated carbon, carbon black, and mesocarbon microbeads. The results of differential scanning calorimetry (DSC) show that the supercooling of less concentrated solutions 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 typemore » of carbon present. The results of conductivity measurements also indicate precipitation in some of the electrolytes at low temperatures, which correlates well with the DSC results. The authors therefore conclude that the temperature range in which an electrolyte supercools without a nucleating material is unreliable for the operation of an electrochemical device containing such an electrolyte. Instead, the liquidus temperature of an electrolyte should be used as the lower limit of operation if the possibility of its crystallization is to be excluded.« less