Development and characterisation of next-generation electrode materials for sodium-ion batteries

Abstract

Increased global demand for efficient and sustainable energy storage solutions has pushed the search for battery technologies beyond Li-ion batteries. Sodium-ion batteries are an attractive alternative, utilising low-cost and abundant materials such as Mn/Fe-based layered oxides as positive electrodes and hard carbon materials as negative electrodes. However, these materials have inherent performance limitations. This thesis aims to develop materials with enhanced electrochemical performance and perform characterisation techniques to rationalise the observed performance.

Cu doping of P3-type Mn/Fe layered oxide is studied and shown to exhibit a reversible Fe redox process and migration to tetrahedral sites in the Na layer. The Cu-doped material has higher specific capacities and stable cycling over a large potential window. The anionic redox process is shown to be activated through a reductive coupling mechanism. Biphasic P2/P3 MnFeNiCu layered oxide is investigated and found to have an enhanced sodium diffusivity over the single-phase P2 and P3 materials, enhancing its rate performance. Cycling beyond 4.2 V vs Na⁺/Na, the material exhibited anionic redox process causing increased specific capacities on cycling.

Composites of hard carbon and sodium organic dicarboxylates were investigated, demonstrating synergistic effects of the individual components on electrochemical performance. The composite with an optimised ratio of the components exhibited improved rate performance, effectively overcoming the high-rate performance limitations of hard carbon. Compared to the organic dicarboxylate, the composite required reduced amounts of conductive carbon additive, achieved higher initial Coulombic efficiency, and demonstrated enhanced cycling stability. Additionally, the composite material exhibited excellent cyclability in a full-cell setup and was shown to be cost-effective through a high-level technoeconomic analysis. The potential of microwave-assisted synthesis as a sustainable method for producing these composites was also demonstrated.

This thesis addressed key performance limitations of existing electrode materials and demonstrated approaches for efficient, sustainable, and cost-effective sodium-ion battery electrode materials.

Date of Award	3 Jul 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Robert Armstrong (Supervisor) & Russell Edward Morris (Supervisor)