This PhD project focuses on all-solid-state batteries (ASSBs) that are thought as one of the future energy storage technologies. However, there is still a limited understanding in regard to mechanisms available to strengthen these solid electrolyte properties at the appropriate length scale, improve stability, and mitigate fatigue during cycling. To address these points this PhD work aims at studying the correlation between the spatially resolved chemical and morphological evolutions of the interfaces between the composite electrolyte and electrodes during  the  ASSB  operation  in  order  to   pinpoint   key   parameters   governing  electrochemical  and  electrical   responses. To achieve complementary information at different scales, three sets of operando characterization techniques (XPS, confocal Raman spectroscopy and FIB-SEM) with various spatial resolution and that can potentially be successively applied on the same electrodes/electrolyte stack will be developed in hope to gain a unified understanding of a 'living' ASSB. The ability to probe these features in real time using an electrochemical cell is barely reported, and will rely on the top-facility characterization platforms of IMN (France) and CIC Energigune (secondment-Spain) while benefiting from an ongoing collaboration with the Californian San Diego University who will provide up-to-date ASSB cells targeting bath Li and Na technologies by using coated cathode materials paired with various ceramic electrolytes. Upon optimization of operando cells and experimental conditions confocal Raman microscopy that provides improved contrast to Raman maps and a better depth resolution (compared to the traditional wide-field optical microscope) will be firstly developed to follow the SEI formation and degradation mechanisms in the ceramics. Resufts will be combined with operando XPS to probe the chemical composition and evolution at the extreme surface of the SEI. FIB-SEM will be investigated as an ultimate operando characterization tool by cross sectioning and contacting the sample with a nanomanipulator. 30 reconstruction of the bulk samples near the  interface will be performed to reinforce the understanding of the impact of evolving nanostructuration parameters (porosity, phase network continuity, etc...) on the electrochemical and impedance responses. This microscope is also equipped with a cryogenic setup as well as EDS chemical mapping and coupled with Raman spectroscopv to complement chemical analysis during cycling. The student will spend 3 months in CIC to learn about XPS and conduct preliminary in-situ characterizations, and 1-2 months at Californian San Diego University making and testing ASSB to better understand their experimental pitfalls.

Supervisor(s) contact: Gaubicher Joël, joel.gaubicher@cnrs-irm.fr