Kinetics and Thermodynamics of Chemical Reactions in Li / SOCl2 Cells

Abstract

The kinetics of the heat producing processes in undischarged and partially discharged cells under open‐ and closed‐circuit conditions have been measured by heat conduction microcalorimetry. The cells studied, Honeywell Type G2666 reserve cells, were activated as needed, and the rates of open‐ and closed‐circuit heat output were determined as a function of time since activation, temperature, and state of discharge. The results of the open‐circuit measurements on whole cells are described by an equation of the form where is the rate of heat output, is the heat produced per unit of reaction, and are empirical constants, and is the time since activation. Both and are found to be functions of temperature. Heat producing processes occur at both the anode and cathode under open‐circuit, undischarged conditions, but the processes at the carbon cathode produce only a few percent of the total heat. The state of discharge has only a small effect on the open‐circuit rate of heat production. Withdrawing current from cells greatly increases the rate of heat output from noncurrent producing reactions. At short times after activation (i.e., <200h) and at high temperatures, the heat produced by nonfaradaic processes can be several times as large as the heat produced by external current being drawn from the cell. At short times after activation, the excess heat is probably due to corrosion of Li, and, at long times after activation, the excess heat is probably due to the reaction of a long‐lived intermediate in the cell electrolyte. A thermodynamic analysis of the cell gives values of and values of , where and are the enthalpy and entropy changes for the cell reaction occurring at the electrodes.