All-solid-state batteries using sulfide-based electrolytes are among the most extensively studied, in order to improve energy density, safety and fast charging. Although lithium metal was initially the preferred choice for the anode, the difficulties encountered in its implementation and the performance achieved suggest that alternatives should be proposed. Silicon offers an interesting compromise in terms of energy density and lifetime. However, further improvements are still needed. An initial thesis on the subject highlighted the benefits of using silicon nanomaterials in combination with argyrodite L6PS5Cl. This work also enabled us to switch from 0.8 mAh cells made from compacted powders to 16 mAh cells made from coated electrodes, while significantly reducing cycling pressure from over 125 MPa to 1 MPa and improving lifetime (90% capacity retention after 160 cycles). However, several questions remain unanswered. The reactivity between argyrodite and silicon, which depends on the surface chemistry, and the mechanisms that enable coated electrodes to cycle at pressures as low as 1 MPa need to be elucidated
To answer these questions, we propose to use XPS to characterize the interfaces between the electrolyte and various silicon materials during the life of the battery. Secondly, to measure cell deformation during cycling. These characterizations, coupled with standard physico-chemical and electrochemical characterizations, will help to improve cell performance. These improvements will be based on the use of high-performance silicon nanowire/graphite composites synthesized at IRIG for the anode, NMC with a coating for the cathode, and electrode formulation development work. Initial tests with silicon/graphite composites have been conclusive, but the impact of these materials' characteristics on performance remains to be assessed, in particular wire diameter, silicon content, surface chemistry and choice of graphite. The production of coated electrodes, initiated in the thesis of M. Grandjean in collaboration, remains to be developed. In particular, there is a need to increase surface capacity and power performance, and to do this we need to increase the proportion of active material and evaluate different types of carbon for the electrical conductive network.
This work will help maintain CEA's momentum on the subject and propose a solution for generation 4a batteries, which could succeed current batteries thanks to a better understanding of operating and degradation mechanisms.