Novel materials for high capacity sulphur based batteries

Sammanfattning: Batteries have become a vital part of our everyday lives and are used in a wide range of portable electronic devices (e.g. mobile phones, laptops, toy, and power tools). With the increased problems of environmental pollution, due to the use of fossil fuels for electric energy and transportation, there is an increased need for high capacity batteries for load levelling in renewable energy systems (wind, solar, tidal, etc.) and for electric vehicles. Li-ion batteries are currently very successful in portable applications. However, the specific capacity of current systems (< 250 mAh/g, < 120 Wh/kg), typically based on lithiated graphite anodes and metal oxide cathodes, is not sufficient for large-scale applications. In addition, there is also a need to improve battery technology in terms of price and sustainability concerning the raw of materials used. This has motivated research on next generation battery technology based on other chemistries.   One of the most promising chemistries for next generation batteries is based on the conversion of sulphur. As an example, the theoretical discharge capacity of a lithium-sulphur cell is 1675 mAh/g or 2500 Wh/kg. Sulphur can also be coupled to sodium or used in the form a metal sulphide (e.g. FeS2), still with superior capacity compared to Li-ion technology. Considering that the active material, sulphur, has a low cost and is abundant brings also the potential for a low cost and sustainable technology. However, even though sulphur-based batteries are very promising their theoretical capacity has so far not been realised in practice in a cell with long cycle life and high charge/discharge efficiency.   In this thesis, I present new materials concepts aiming to enable next generation high capacity batteries based on the conversion of sulphur. The main target has been to improve the capacity, but the materials used have also good perspective in terms of sustainability and price. A key to improve the properties has been to tailor materials on the nanoscale. One example is the fibre-based materials prepared by electrospinning. These include carbon structures for high capacity and high rate electrodes as well as gel-polymer electrolyte membranes. The results presented in the thesis show that high discharge capacity and good cycle performance can be achieved with the new materials concepts. The functional mechanisms behind the concepts is discussed and the role of different material aspects is revealed.