OPTIMIZING AND DESIGNING POSITIVE ELECTRODE MATERIALS FOR SODIUM ION BATTERIES

Abstract

Sodium ion batteries have the potential to be a more sustainable alternative to the widely-used lithium ion batteries. Layered sodium transition metal oxides as positive electrode materials have been a focus of research. However, most sodium transition metal oxide materials suffer from low operating voltage, unstable crystal structure, poor cycling performance, and air-sensitivity. In order for sodium ion batteries to have practical application, more studies on positive electrodes are required.

This work focuses on the investigation of strategies to improve the behavior of positive electrode materials in sodium ion batteries. Some examples were given using transition metal layer substitution to develop novel positive electrode materials. Doping with certain elements significantly enhances the performance and alleviates some of the aforementioned problems. The possible role of dopant elements, specifically titanium or copper, was investigated. The structural and electrochemical performance of some nickel rich materials, which are possibly high-capacity materials, namely Na3Ni2BiO6 and NaNi0.8Co0.15Al0.05O2 were also studied. Besides transition metal layer doping, other methods were employed to modify the positive electrode materials. Washing NaNi0.5Mn0.5O2 with ethanol removes most of the sodium residues on the surface, resulting in improved air stability, smaller hysteresis and higher capacity. Doping in the sodium layer with calcium leads to improved cycling performance, higher coulombic efficiency, and better air-stability. Finally, a preliminary study of using mechanofusion method to coat electrode materials with nanoparticles was demonstrated. Future directions of research are discussed.