Structural and electrochemical studies of novel sodium-ion battery electrode materials

The DPhil project involves the synthesis and characterisation of novel sodium-ion battery electrode materials. While lithium-ion batteries have transformed and, in many ways, helped define our globally-connected world, there are resource and performance limits to the extent in which they can pervade our society much beyond digital electronics. As a consequence, sodium-ion batteries are becoming of increasing importance because they offer a more sustainable, cost effective and safer energy storage solution than both current and future lithium-ion battery technologies. Sodium-ion batteries have reached higher energy densities than commercial lithium iron phosphate batteries at operating temperatures between 20oC and 60oC. Originally targeted at stationary applications, such as grid-based storage, these recent developments suggest that sodium-ion batteries may also impact on the transportation industry. The material in a sodium-ion battery cathode is more complex than its lithium-ion cathode material equivalent. The cathode materials to be explored in this project have two very distinct crystalline components consisting of a phase (O3) with octahedrally co-ordinated Na+ and a second phase (P2) where the Na+ co-ordination is trigonal prismatic. The anode materials to be explored in this project are hard carbons. These are analogous to graphite, but with the graphene layers turbostratically disordered. Sodiation of the anode occurs in two different mechanisms - ionic intercalation and metallic nano-sodium clustering in the pores. The thesis aims are: 1) to develop a comprehensive understanding of the chemical and structural evolution of these materials under operating conditions using a combination of thermodynamic, crystallographic and electrochemical techniques 2) to explore the nature of non-stoichiometry and structural disorder in the cathode materials and correlate these properties with battery performance 3) to propose and synthesise novel battery cathode compositions which optimise power and energy density and materials cost 4) to understand and optimise sodiation and desodiation mechanisms in the anode. This project falls within the EPSRC Energy research area, specifically energy storage. It is funded half by EPSRC and half by Faradion Ltd. Faradion is pioneering the next generation of advanced, low-cost battery materials using sodium-ion technology for stationary large-format applications.