Scientific direction Development of key enabling technologies
Transfer of knowledge to industry

PhD : selection by topics

Technological challenges >> Physical chemistry and electrochemistry
1 proposition(s).

Selection and optimisation of silicon anodes for all solid state batteries

Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN)

Laboratoire Matériaux

01-01-2020

SL-DRT-20-0864

cedric.haon@cea.fr

The success of energy transition will depend strongly on mobility. Electric vehicles will reduce CO2 emissions but the deployment of e-cars is linked to improvements of actual Li-ion batteries in term of energy density, cycle life and safety. In general, conventional Li-ion batteries (LIB) contain a cathode (lithiated Ni-Mn-Co oxide), anode (graphite), liquid electrolyte (carbonate based solvents containing lithium salt) and separator (to avoid short-circuit and allow the shuttling of Li+ ions). LIBs raise safety issues due to their volatile and flammable electrolytes. In addition, low specific capacity of graphite (372 mAh g-1) also hampers the wider acceptance of current LIB, as in electric vehicles. In terms of safety, SSBs are an efficient and viable alternate to conventional LIBs as they do not contain any flammable organic electrolyte. Beside, SSE often show a wide electrochemical potential window, an advantage to increase the energy density of the battery. Many SSBs have been demonstrated using metallic lithium (Li) as anode for simplicity, but Li proved instable against nearly all developed solid-state electrolyte (SSE) and to form dendrites, and is difficult to plate in very thin films. As these detrimental issues are specific to Li metal, a replacement with alloy-based anodes sounds appropriate in developing SSBs. For example, silicon (Si) based anodes are handled in air and high temperature tolerant. Largely Earth abundant, Si can deliver a very high theoretical capacity of 3579 mAh.g-1 or 8303 mAh.cm-3 at an operating voltage of 0.4 V vs Li+/Li. However, the mechanical integrity of the electrodes in SSBs might get severely affected by the large volume changes (>300%) of Si during cycling, resulting in the formation of cracks, pulverization and delamination, which is a critical point. Thus, establishing and maintaining a good contact between electrode and electrolyte throughout cycling is the prerequisite for high energy density SSBs with Si anode. Research and development (R&D) of Si-based SSBs has focus on thin film form of Si as it is expected to address the mechanical issue and charge transfer resistance at interfaces. However, thin film anodes deliver a very low areal capacity (0.3 mAh.cm-2) compared to those of commercial anodes of LIBs (2-5 mAh.cm-2) due to the poor loading of active material. The proposed work deals with the research of silicon materials ? solid electrolytes couples and understanding of chemical and mechanical stability at the interfaces. Silicon materials will be tuned to change particle size and morphology and surface chemistry. Several types of silicon materials will be studied based on our know-how. One or several solid electrolytes will be selected at the beginning of the Ph.D. Understanding of reactivity and fracture mechanisms at the interfaces will be based on in-situ electrochemical characterizations and post-mortem analyses.

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