TOPIC 14 - Positive Electrode Materials for Sodium-Ion Batteries: Ion Transport and Redox Properties

In the critical area of sustainable energy storage, sodium batteries have emerged as a promising alternative for large-scale grid storage applications due to the low cost and high abundance of sodium. Phosphate-containing materials are being studied intensively as promising positive electrode materials for sodium-ion batteries owing to their high stability and fast ionic mobility. Among such materials, the mixed-anion Na₃V₂(PO₄)₂F_3-yO_y and mixed-cation Na₃(V,M)₂(PO₄)₂F₃ (M = Fe, Mn) systems are attractive electrode materials due to their high voltage for two Na⁺ ion extraction and high energy densities. Iron-contaning compositions around Na₂FePO₄F and NaFePO₄ are other alternatives that we would like to screen as well. Our proposed PhD project relates to key questions that are not fully understood in these sodium battery materials in relation to defect, transport and electronic properties so as to improve their electrochemical performance. The new PhD project will encompass advanced atomistic modelling work at Bath to investigate the following inter-linking aspects: (i) how the nature of the substituent (M) and the distribution of vanadyl bonds influence Na⁺ ion diffusion and redox activity; (ii) the atomic-scale distribution of ionic defects and the modification of electronic structure; (iii) understanding the irreversible transition at high voltage and the effect of the vanadyl bond and local coordination units. The modelling results will feed back to the experimental programme and vice versa so that there will be close contact between the two. The partner institutions and research labs at Picardie led by Prof Christian Masquelier and at Bordeaux led by Dr. Laurence Croguennec will allow the PhD student to carry out complementary experimental studies including: (a) materials synthesis using coprecipitation routes (b) characterization work using state-of-the-art X-ray diffraction, temperature-controlled synchrotron X-Ray and neutron diffraction, electron microscopy, NMR spectroscopy and electrochemical experiments

Supervisor(s) contact: Prof Saiful ISLAM, Dr Ben MORGAN, m.s.islam@bath.ac.uk; bjm42@bath.ac.uk