Li/SOCl2 cells for high temperature applications

The capacity of Li/SOCl2 cells operating at temperatures as high as 150 °C has been measured at discharge rates up to 5 mA/cm2. The results indicate the unique chemical and electrochemical stability of the system, manifested by its ability to be discharged continuously at 150 °C for more than 2 months while obtaining 70% of the cell nominal capacity. The capacity-temperature plot shows a maximum at 50 °C. Above 50 °C the capacity decreases as a result of the increase in the self-discharge current at higher temperature. An anomalous capacity increase is found at temperatures above 100 °C. Above this temperature it has been shown that thermal decomposition products may increase the cathodic reaction rate and modify the structure of the passivation layer on the anode surface. Over the 100 – 150 °C temperature range the lithium chloride film morphology, as analysed by SEM, tends to be of a smaller crystal size the higher the temperature. This trend is in opposition to that found at the lower temperature range, e.g., −40 to 70 °C. In addition, the decomposition product, e.g., SO2, improves the transport properties of the electrolyte and thus increases the carbon cathode efficiency.