Characterization of TFSI and FSI based polymer electrolytes for sodium batteries

Abstract: Lithium ion batteries (LIBs) are today dominating the field of rechargeable batteries for portable devices. Recently also other LIBs applications have been considered, such as electromobility and large-scale grid storage. With the growing demand of lithium and its limited resources, it is advantageous to consider other chemistries to complement/replace LIBs. Sodium, being abundant and similar to lithium, is a suitable alternative. In addition, in order to fulfill new applications (e.g. electromobility) the batteries also need to meet stringent safety requirements. The concept of an all solid state battery, for example using a polymer electrolyte rather than a liquid organic solvent based electrolyte, is a promising option in this context. A known drawback of such electrolytes is, however, the low ionic conductivities obtained at room temperature, which perhaps can be improved by choosing suitable material combinations. In this thesis, an overview of non aqueous electrolytes for sodium batteries operating close to room temperature is given, together with descriptions of the preparation and characterization of several different novel sodium based polymer electrolytes. These comprise both solid polymer electrolytes (SPEs) – based on PEO with either NaTFSI or NaFSI salt dissolved – and ternary polymer electrolytes – including also an appropriate ionic liquid (IL). All systems were characterized in terms of ionic conductivity, thermal properties, and ionic speciation.