Characterisation, modelling and management of lithium-sulphur batteries for spacecraft applications

The lithium-sulphur couple has such a high theoretical energy density that, in principle, it could contribute significant weight and cost savings for launching a spacecraft. The principle aim of this study was to determine the suitability of lithium-sulphur cell technology for space industry applications by considering all areas of performance, modelling and electronic protection requirements. This thesis is split into three main areas. Firstly, after examining the background material, the current state of the lithium-sulphur electrochemistry is analysed in detail. It is of great importance to have a clear understanding of the cell’s electrochemical and chemical interactions as they can be used to explain the performance characteristics of the cell later in the work. On completion of the electrochemical analysis the thesis then goes on to describe a set of electrical and thermal characterisation tests, the results of which are used to establish a novel equivalent circuit model of a Li-S battery. The equivalent circuit modelling method was chosen mainly for its ease of implementation into a full power system model and for its adaptability to future cell variations, both of which are important for the intended application. The resultant model uses electrical, thermal and “split capacity” domains to successfully predict cell performance. Further characterisation testing results are then analysed with a view to specifying the electrical protection requirements of a Li-S battery management system suitable for different space industry applications. It was determined that the Li-S cell has safety and protection needs that exceed that of lithium-ion batteries, as well as requiring a robust housing structure, reducing the energy density of the battery pack. The conclusion of the work is that, although the Li-S cell holds promise for the future, the current state of the cell’s degradation characteristics prevents it from competing with lithium-ion cells in its current forma