PhD Position : Study of reduction and oxidation mechanisms of sulfur in lithium-sulfur batteries in the presence of transition metal sulfides

The thesis aims to investigate the relationship between structure and reactivity of transition metal sulfide within lithium-sulfur batteries. Lithium-sulfur batteries have theoretically very important assets (specific energy three times higher than lithium-ion, low cost, low toxicity) yet they are penalized by some limitations. Among them, a strong redox shuttle, short lithium polysulfides that leads to self-discharge and severe capacity loss. Transition metal sulfides such as MoS₂ are known to trap and catalyze the transformation of these lithium polysulfides. Yet, the details of the mechanisms of the transformations or the optimal structure of these transition metal sulfides for this purpose are not deeply studied.

The tasks and objectives given to the PhD student are thus to:

• Synthetize different structures of transition metal sulfides.

• Produce positive electrodes doped with these metal sulfides and assemble them in button cells.

• Characterize the cells with electrochemical methods and post-mortem techniques.

• Embed the positive electrodes materials in dedicated cells to proceed to operando characterization in synchrotron and neutron sources.

• Gather characterization results to establish the relationship between structure and reactivity of the metal sulfides.

This multidisciplinary research work is in the framework of a partnership between IFPEN (Solaize), CEA SyMMES (Grenoble) and CNRS LEPMI (Grenoble).

Keywords: lithium-sulfur battery, electrochemistry, neutron and synchrotron sources, transition metal sulfides