Development of carbon-based materials for improved sodium-ion battery anodes

Abstract

Sodium-ion batteries (SIBs) are an important future technology for large-scale grid energy storage due to the abundance and lower cost of sodium compared to lithium. However, there are many challenges that continue to hamper their commercial development, including sluggish reaction kinetics, large volume expansions during cycling, and unstable solid-electrolyte interface (SEI) formation. Additionally, more work needs to be done to understand the storage mechanisms of sodium ions in anode materials and to understand what material properties are important for high performance. This thesis focuses on two areas: the development of a new anode material made of red phosphorus nanoparticles (RPNPs) wrapped in reduced graphene oxide (rGO) sheets and an in-depth investigation into the impact of rGO material characteristics on its performance as a SIB anode. In the first section, the synthesis of an rGO@RPNP composite through a scalable spray drying process provides increased performance when compared to the individual components or when the individual components are simply mixed together. This proof of concept is the starting point for future work on increasing red phosphorus loading within the core-shell structures, improving the reduction process to maximize the conductivity of the composite, and investigating methods to improve the initial coulombic efficiency (ICE) through optimization of material properties. The second section attempts to decouple the effects of rGO chemistry and oxygen content from its surface area to understand the effect of the material characteristics on its electrochemical performance. It is found that a non-exfoliated sample slowly reduced to a low temperature of 400 ℃ provides the best performance in terms of desodiation capacity (216 mAh g-1 at 100 mA g-1), and stability (85% retention over 200 cycles) while reducing the irreversible capacity loss by two to threefold compared to previous literature.