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CHPC student graduates with a doctorate in Physics

Cliffton Masedi, a CSIR Centre for High Performance Computing (CHPC) student, has graduated with a Doctor of Philosophy: Physics from the University of Limpopo.

Now formally addressed as Dr Cliffton Masedi, his thesis is titled: Computational Modelling Studies of Discharge Products of Advanced Lithium-Sulphur Batteries and was supervised by Professor Phuti Ngoepe (University of Limpopo) and co-supervised by Dr Happy Sithole (Director: Centre for High Performance Computing).

Cliffton was one of two PhD students supported by the CHPC, with the second candidate currently pursuing his through the University of Cape Town. He is excited about his future prospects and expresses deep gratitude to the CSIR and CHPC: “My three-year studentship covered 100% of my university fees, included a stipend, travelling allowances to beneficial workshops which included one in Germany where I needed to learn how to use a new component of the Media-UNCLE code called Cluster Extension and which was critical to my research”.

“I love the field and as it not so developed in South Africa means I can still grow and develop broad use of high performance computing”, said Dr Masedi.

Dr Cliffton Masedi’sthesis citation

Lithium sulphur (Li/S) and Li air (Li/O) batteries have a potential to provide two to five times the energy density of the current Lithium-ion battery systems. However, Li/S suffers from low conductivity of sulphur and the solubility of intermediary polysulfide species during cycling. Mixed sulphur-selinium (SxSey) represents an attractive new class of cathode materials with promising electrochemical performance in reactions with both lithium and sodium ions. Notably, unlike existing Li/S batteries that only operate at high temperature, these new Se and Li/SexSy electrodes are capable of room temperature cycling. Cliffton’s major contribution is employment of cluster expansion and Monte Carlo techniques to investigate phase separating behaviour of Li2S1-x-Sex.

His study predicted a phase diagram of such system and proposed a phase change at a relatively low temperature of 350K for Li2S0.5Se0.5. In the absence of associated experimental details on Li/SexSy systems, he invoked an unrelated simulation approach, classical molecular dynamics, for which he developed new models, to validate his results. The work provides valuable insights on where phase separation and mixed phases tend to occur in Li2S1-x-Sex systems, over an entire range of sulphur and selenium contents, which will guide designs of future experiments.

Clifftonhas presented 27 papers at local and international conferences and was awarded prizes for best PhD presentations at local conferences. He has published a paper on the work and two more papers have been prepared for publication.

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