Investigating sulfide-based all solid-state cells performance through P2D modelling

All solid-state batteries, combining metallic lithium with a solid-state electrolyte, are now considered as a very promising answer to the growing need for higher energy density in safer batteries. While research interests are quickly raising on this topic, the number of experiments to perform in order to find the best combination of active material and solid electrolyte composition could be infinite. Therefore, an easy and low computational-cost model forecasting all solid-state cells performance could accelerate the optimization and lower the number of experiments, reaching more rapidly an up scalable solution. In this work, an innovative electrochemical model for a metallic lithium – argyrodite Li6PS5Cl – NMC622 cell is developed. In particular, two important aspects, characterizing this new battery generation, are implemented inside a P2D model. The first aspect is the implementation of a solid-state electrolyte, in substitution to liquid electrolyte, which means using the single ion conducting electrolyte theory, according to which Ohm's law is the only equation to be solved in the electrolyte domain. This reduces the number of parameters characterizing the electrolyte from three, for the liquid electrolyte (ionic conductivity, transference number, and mean molar activity coefficient), to only one, for the solid electrolyte (ionic conductivity). The second aspect regards the anode side, lithium metal is chosen, in substitution to graphite, and this implies a different treatment from an electrochemical point of view, which is to consider the anode as a boundary condition instead of a porous electrode. Such drastic simplification of the P2D model allows, after careful calibration and validation based on experimental data, to obtain reliable charge/discharge profiles at C/10 and C/5 for lithium – argyrodite Li6PS5Cl – NMC622 cells.