Synthesis And Electrochemical Optimisation Of Novel Inverse Spinels For Lithium-ion Battery Negative Electrode Applications

The ever-increasing global demand for more efficient electrical energy storage solutions, driven by the need to power portable electronics and facilitate the transition to electric vehicles, are the propelling forces behind the significant research effort being directed towards the development of novel electrode materials for lithium-ion batteries. The ubiquitous, commercial graphite anode, possesses a limited theoretical capacity, creating a necessity for alternative materials with superior energy density. In this context, this thesis details the first comprehensive investigation of the novel inverse spinel Li3CrV2O8 as a high-capacity anode material.
Phase-pure Li3CrV2O8 compound was successfully synthesised using a citrate sol–gel method. This was confirmed through detailed Rietveld refinement using the powder X-ray diffraction data. The lithiation and delithiation mechanism was systematically probed using charge photometry technique to understand at particle level, its fundamental electrochemical behaviour. This revealed a complex, multi-step reaction, initiated by a limited lithium intercalation into the spinel structure, and a full conversion reaction at lower potentials.
The electrochemical assessment of this as-synthesised parent material demonstrated a promising initial discharge capacity of 350 mAh g⁻¹. Observation revealed that the material suffered from significant drawbacks, most notably a large first-cycle irreversible capacity loss of 49% and a limited rate capability, which would hinder its practical application.
Therefore, to address these performance limitations, two distinct optimisation strategies were systematically explored. Strategic substitution on the chromium cation site revealed that aliovalent / isovalent co-doping with manganese and iron was the most effective chemical strategy for improving stability, successfully reducing the first-cycle capacity loss to as low as 18%. Subsequently, particle morphology engineering via high-energy mechanical milling was shown to improve specific capacity.
The synergistic combination of these two strategies resulted in the milled Li3Cr0.6Mn0.2Fe0.2V2O8 composition delivering an initial discharge capacity of 520 mAh g⁻¹ while maintaining a much-improved first-cycle loss of 29%.