Application of a Sodium Sulfur Cell with Dynamic Sulfur Electrode to a Battery System

Abstract

The construction and performance of a sodium sulfur battery system with dynamic sulfur electrodes are described. Three cells were first connected in parallel, then two such groups were connected in series. Each cell included a liquid sodium filled β″‐alumina tube and a system to feed liquid sulfur into the annular cathode. Low‐resistance graphite felt was tightly packed around the β″‐alumina tube. Sodium pentasulfide was removed from the sulfur electrode. The battery was operated automatically and stably charged and discharged in the two‐phase region. The discharged energy was 4372 Wh (capacity 1170 Ah) during a continuous operation of 19.5 h. The discharge/charge energy efficiency of the battery was 82% at an averaged current density of 100 mA/cm² and operating temperature of 350°C. The deviation of the cell current in a parallel chain was less than 7%, and this was induced by the difference in internal resistance. In the daily charge/discharge cycle, cell capacity with the dynamic sulfur electrode was 1.5 times higher than that with the static sulfur electrode using the same active surface of β″‐alumina, because the internal resistance of the former cell was constant regardless of cell capacity. This battery system with a dynamic sulfur electrode can be applied to energy storage systems, such as large scale load leveling systems, electric vehicle batteries, and solar energy systems.