Rechargeable non-aqueous lithium-oxygen (Li-O2) cells (also known as lithium-air cells) could surpass the stored energy of today’s most advanced lithium-ion cells. Significant challenges exist that must be overcome to bring Li-O2 batteries into a real-world application. These challenges include stability against reactive intermediates and products, stability against singlet oxygen, the recharge and cyclability efficiency, finding an optimised electrolyte, materials development and improvements in fundamental understanding of the electrochemical and chemical reactions that take place within the cell.
In general, for non-aqueous Li-O2 cells , Li+ produced at the lithium metal negative electrode (anode) during discharge, diffuse across the electrolyte and into the pores of the open structure of the positive electrode (described widely in the literature as an air cathode). The electrolyte commonly consists of a lithium salt that has appreciable solubility in an organic solvent. Dioxygen gas (O2) from the atmosphere enters the positive electrode, and dissolves into the electrolyte within its pores. The dissolved O2 is then reduced to initially form superoxide (O2-) at the porous positive electrode surface by electrons from the external circuit and combines with Li+ from the electrolyte, finally resulting in the formation of lithium peroxide (Li2O2) as the final solid discharge product. During the charging step the reaction is, to varying degrees, reversible. Li2O2 can be electrochemically oxidised, releasing oxygen gas, Li+ and electrons. The discharge and charge steps can be recurrently cycled, making these reactions the basis for a high-energy storage device. However, oxidising Li2O2 commonly requires high energies/overpotentials that both reduce efficiency of cells and promote parasitic reactions that accelerate cell failure. The application of redox mediator additives is a key strategy in mitigating these challenges as these materials can act effectively as soluble catalysts to promote/control (dis)charging steps to improve efficiencies and stabilities.
This PhD project will focus on the synthesis of redox mediator (RM) families and will initially target derivatives of TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxyl) and aromatic amines. Both these families provide a wide scope for design to optimise the efficacy of the RM functionality within Li-O2 cells in order to lower the voltage gap. Li-O2 cells will be fabricated using benchmarked carbon paper electrodes as the air-cathode and lithium metal. Fundamental electroanalytical chemistry through to advanced operando techniques (for example Raman microscopy and differential electrochemical mass spectroscopy) on full cells will be carried out to characterise the nature of the electrochemical reactions.
The student would be trained in organic synthesis of redox mediators, characterisation and analytical techniques, electrochemistry, and frontier battery research. The PhD studentship is fully sponsored by Lubrizol and the student will have the opportunity to be hosted at Lubrizol to work alongside Lubrizol research scientists in materials for Li-air batteries.
The start date of PhD position is 01/10/2023 with the duration for 4 years.https://www.liverpool.ac.uk/study/postgraduate-research/how-to-apply/.
Please ensure you include the project title in your online application and quote reference CCPR067.
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