Current shifts towards renewable energy technologies have increased the drive for high performance and cost effective battery systems. Sodium ion batteries present a promising alternative to the commonly used lithium-ion batteries and offer several benefits such as low cost and high availability. While lithium-ion battery systems have been studied intensively, it has become apparent that the interfacial chemistry differs significantly for sodium ion batteries, even when using the same solvents.

In previous work, we have shown that amorphous TiO₂ nanotube electrodes are a suitable anode materials for Na-ion batteries. The optimization of electrolytes is important to develop a system with good solubility, high transport properties, electrochemical and interfacial stability. In this work, we have investigated the electrochemical properties of TiO₂ nanotube electrodes - as a model system - in various electrolytes containing different solvent mixtures (cyclic and acyclic carbonates) with NaClO₄ and NaPF₆ salt. In addition, we have conducted fundamental studies of chemical, thermal, and electrochemical stability of the chosen sodium-based electrolytes with a phosphazene-based additive FM2 as well as the commonly used FEC additive.