Yermukhambetova, A; (2017) Development of lithium sulphur battery and insights into its failure mechanism. Doctoral thesis , UCL (University College London).

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Abstract

Lithium–sulphur batteries are considered as a promising battery system due to its high theoretical capacity (1675 A h kg−1), high energy density (~2500 W h kg−1) and the natural abundance of sulphur. However, despite intensive research there are certain limitations to be overcome to bring Li/S to practical application; these limitations stem from the multiple reactions and phase changes in the sulphur cathode. Herein, for the first time to author’s knowledge, the effect of the cathode morphology as a function of charge cycles was studied by a multi-scale 3D in-situ X-ray tomography approach. The microstructural evolution within the same Li/S cell is studied without disrupting the contents and revealing significant changes to the electrode morphology. The uneven distribution of the sulphur phase fraction within the electrode thickness and sulphur agglomeration upon cycling were shown. The advantages of in-situ X-ray tomography are compelling, enabling a non-destructive imaging of battery. Furthermore, the strategies for Li/S optimisation were reflected. A comparative study of the effect of widely available conducting polymers: polyacrylonitrile and polyaniline; and metal oxide additives: Mg0.6Ni0.4O and Al2O3; on the Li/S performance, both capacity and cycle life was conducted. Commercially viable cell configurations were developed by a simple ball milling followed by a heat treatment; the best performance was by S/PANI/ Mg0.6Ni0.4O composite with an initial discharge capacity of 1500 mA h g-1. Many problems arise due to polysulphides solubility; therefore, the optimised cathode was tested with electrolytes to investigate the effect of high concentration and viscosity, as well as LiNO3 addition. It was shown that although increasing the electrolyte concentration leads to the higher battery performance and stability, the similar results could be achieved with the addition of LiNO3. Generally, it was shown the tailoring electrolyte and electrodes parameters for Li/S cell is as important as development of efficient and easy scale-up S electrodes.

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