PhD defense, Louise FRENCK

The lithium-air (Li-air) technology developed by EDF uses an air electrode which works with an aqueous electrolyte, which prevent the use of unprotected lithium metal electrode. A Li+ ionic conductor glass ceramic is used to separate the aqueous electrolyte compartment from the negative lithium electrode. However, this glass-ceramic is not stable in contact with lithium, it is thus necessary to add a protective buffer layer. In another hand, this protection should ideally resist to lithium dendritic growth. It is in this context that this research project which has as goal the development of a protective buffer layer based on block copolymer electrolytes (BCE) between the lithium metal and the lithium ionic conductor ceramic, for lithium-air battery.
In a first part, the BCE is studied in lithium-lithium symmetric cells, in order to determine their properties such as their ionic conductivities, their transference number, and their resistance to dendritic growth. Several characterization techniques are employed and especially the hard X-ray micro-tomography to analyze the lithium morphology before and after cycling. For single-ion BCE, we expect to suppress dendritic growth, however, we report here for the first time, the visualization of a homogeneous growth of lithium but the formation of dense lithium objects.
In another part, the composite BCE-ceramic is studied by electrochemical impedance spectroscopy. The cycling of composite-lithium symmetric cells and the analysis of the EIS measurements after each cycle permit to determine if the dendrites have cross the electrolyte and are in contact with the ceramic. Besides, the quantification of the polarization loss at the interface polymer-ceramic is evaluated by polarization experiments. This contributions is found to be small.