Realization of Sodium-ion Batteries : From Electrode to Electrolyte Materials

Sammanfattning: Batteries are among the most important technologies required to enable the world to move beyond fossil fuels towards a more efficient and environmentally friendly society based on electricity from renewable sources. Unfortunately, the rapidly increasing number and size of batteries that the world needs in order to perform this paradigm shift is putting enormous strain on the supply of traditional raw materials for batteries, such as lithium and cobalt. Batteries built using only earth abundant elements could guarantee that the supply of energy storage will be available to everyone at reasonable prices. Sodium-ion batteries are among the most popular candidates to achieve battery systems that can provide performance close to or on par with lithium-ion batteries at a lower cost and environmental impact. Although the sodium-ion and lithium-ion batteries share many properties, there is a lot of research required before sodium-ion batteries can compete with the highly optimised lithium-ion batteries. This work explores the stability of the solid electrolyte interphase (SEI) formed on the anode in sodium-ion batteries through means of electrochemical measurements and x-ray photoelectron spectroscopy (XPS) analysis. The fundamental properties in regards to solubility and electrochemical stability of the surface layer on model anodes as well as on anode materials like hard carbon and tin-phosphide is discussed. The synthesis and electrochemical performance of Prussian white comprising of all earth abundant elements for use as a low-cost and high-performance cathode material is demonstrated. The work also includes several investigations of alternative solvents and salts for electrolytes that have been analysed in conjunction with sodium-ion cells based on hard carbon and Prussian white. The electrolytes studied possess a wide spectrum of different opportunities such as high ionic conductivity, non-flammability, fluorine-free composition and improved low and high-temperature performance.