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Martine Grandjean

Selection and optimization of silicon anodes for all-solid-state batteries

Published on 22 November 2023
Thesis presented November 22, 2023

Abstract:
All-solid batteries are considered as a promising next-generation rechargeable energy storage system, with the possibility to enhance energy density in comparison to their liquid electrolyte counterparts. Among the range of solid electrolytes, those containing sulfide compounds have shown great potential due to their high ionic conductivity and appropriate mechanical properties. However, solid-state batteries with sulfide-based electrolyte only cycle correctly when maintained at high pressure, which imposes significant limitations on cell design. Additionally, the reactivity of these sulfides with lithium metal remains a significant challenge to their development. Silicon as the negative electrode material presents an appealing compromise in terms of cost, compatibility, and energy density when compared to lithium metal. Nevertheless, its use remains constrained by its substantial volume expansion during lithiation, a limitation that can be mitigated through structural enhancements in both the electrode and the material itself.
This PhD thesis focuses on the selection and optimisation of silicon anodes for all-solid-state batteries. After the identification of the key parameters of the system used and its optimisation, I studied the compatibility between various silicon materials and sulfide-based solid electrolytes. Different silicon sizes and morphologies are compared in this study, using both commercial and synthesised materials. The degradation mechanisms of composite electrodes depending on the silicon material used were highlighted and identified by using electrochemical characterisation techniques such as galvanostatic cycling and electrochemical impedance spectroscopy. The impact of the silicon's surface condition on the solid electrolyte's decomposition was also examined by combining electrochemical characterisation techniques with XPS analysis. Another aspect of our work involves the implementation of all-solid state batteries with sulfide-based electrolyte into a “pouch cell” configuration. In collaboration with the electrode and cell prototyping laboratory (L2PC) at CEA Grenoble, we have developed a process for the coating of the composite electrodes and the solid electrolyte layer, compatible with standard industrial LIB assembly techniques. We could build 10 cm2 solid-state lithium-ion batteries, which cycle under a pressure of 1 MPa only. These cells have achieved a capacity of 16 mAh, a significant improvement compared to the previously used all-pelletized format, which only yielded 0.8 mAh. Furthermore, there has been a remarkable enhancement in the capacity retention, with 79 % of the initial discharge capacity after 160 cycles.

Keywords:
Silicon, all-solid-state batteries,​ sulfide-based solid electrolyte