CIFRE PhD position at LOF

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Lieu : Solvay/CNRS/University of Bordeaux

Contexte : Study of surface, interface and rheological properties in slurries of ionically conductive particles for all-solid next-generation batteries.

Profil : The candidate should be a reactive and motivated person, with a background in chemistry or physical chemistry and strongly attracted by experimental work specially using gloveboxes; notions of rheology and of programming in Python or in Matlab would be desirable. Experimental work will be performed at the Laboratoire du Futur (LOF UMR CNRS Solvay 5258, https://www.lof.cnrs.fr/en/homepage/) and at Solv

Description:

All-solid-state batteries (ASSB) are promising candidates to significantly surpass the energy densities of lithium-ion batteries currently used. During the fabrication process of an ASSB, the preparation of a paste or of a concentrated slurry is essential to fabricate the electrodes and the separator of the battery, depending on the manufacturing process envisioned; however, one of the main obstacles during this process is the poor compatibility of electrode-electrolyte interface (J. Zhang, 2018) as well as the optimization of the active material content in the electrode. The design of a correct interface with good compatibility is critical to increase the entire performance of ASSB.

Specifically, during a ASSB fabrication via wet processes one of the challenges is to handle concentrated suspensions of ionically conductive particles with the highest possible particle content: after the solvent removal, the solid state electrolyte separator layer should have a close to zero porosity and the contacts between conductive particles should be maximal to ensure a high conductivity. Same challenge is present for electrodes, the system being more complex as it involves active materials particles, solid electrolyte particles and electronic conductive particles. The rheology of concentrated suspensions poses multiple issues such as shear-thickening, jamming, and the possible development of shear-induced inhomogeneities (A. Fall et al. 2015, D. J. Hodgson et al. 2019). The maximum solid fraction that can be dispersed will depend strongly on the details of the particle-surface physicochemical properties and of its interaction with the solvent: further understanding of these points is key in the design of concentrated suspensions.

Together with this, interfacial issues between the electrolyte and the electrodes and separators arise from, among others, the physical contact between the solid electrolyte and the electrodes and from the intercalation between the conductive particles/catholyte or the conductive particles/separator interfaces in the slurry (S. Wang 2020). Indeed, interactions among the particles or between the particles and the other constituents of the slurry, such as electrostatic repulsion, steric hindrance or flocculation, could form different microstructures in slurries, thus yielding uniformities and compromising the overall stability and performance. The final microstructures and the overall performance are determined by the microstructure formed by the components and its interactions in the slurry (L. Ouyang 2020). A deep understanding and study of the chemistry of the surface of ionically conductive particles, and the interactions between the different constituents of the slurry as well as the impact of these interactions on the rheology and consequently on the shaping processes of the final materials are needed in order to improve the performance of the battery.

As well, and from a theoretical point of view, modeling of phenomena involved in solid-state batteries has started to be developed (K. Chayambuka 2019, N. Kazemi, 2019), with the aim to understand internal battery dynamics, there is to date no relevant study reported linking the properties of solid state layers (separator and catholyte) with the initial slurry properties. This field is, even in traditional Li-ion technologies, still in its infancy (A.Franco 2019, A. Franco 2020) and pioneering work will then be performed here.

In this context, this PhD thesis subject proposes to study the effect of the chemistry of surface of conductive particles and the different interactions that exist in concentrated slurries used to fabricate an ASSB and that impact the performance of the battery through 1) the study of the surface chemistry of conductive particles to explain and improve interfacial phenomena, 2) the study of the rheological behavior of the obtained suspensions, and 3) to study these effects from a theoretical point of view through the use and application of physical models.

For that, studies of surface chemistry through FTIR and Raman spectroscopy and rheological measurements for various flow histories will be conducted. A model will be proposed to take into account the link between the properties of the solid state layers and the slurry properties.

Contacts :

Yaocihuatl Medina-Gonzalez, (CR CNRS) yaocihuatl.medinagonzalez-ext@solvay.com
Guillaume Ovarlez (DR CNRS), guillaume.ovarlez@u-bordeaux.fr
Julien Jolly (IR Solvay), julien.jolly@solvay.com
Marc-David Braida (IR Solvay) marc-david.braida@solvay.com