Sulfide Solid Electrolyte with Better Safety and Cost Reduction

All-solid-state batteries are viable alternatives to conventional batteries employing organic electrolytes because of their benefits, i.e., high power density, high energy density, long-life operation and safety. These advantages stem from the great features of inorganic solid electrolytes, which are single ion conductor, so a high lithium-ion transport number, and no-liquid nature. Solid oxide or sulfide are largely studied to allow the emergence of all-solid state batterie based on solid electrolyte ceramic. In particular, the sulfide-based solid electrolytes possess favorable mechanical properties, high ionic conductivity comparable to liquid electrolytes but suffer of moisture exposure that could induce H₂S generation and very expensive precursor.<br/>Sulfide-based solid-electrolytes can potentially be employed in conjunction with a lithium metal negative electrode and 5V-class high voltage positive electrode material. Different families of sulfide electrolyte as glass ceramic, thio-LISICON, LGPS, argyrodites are synthetized by similar precursor as Li₂S-P₂S₅ and other component in function of composition. The composition must be designed to create stable passivating interface with lithium metal. In parallel, the sulfide solid electrolyte reacts with all components constituting the positive electrode as active material, electronic conductor, binder, current collector… Hence, the optimal composition is a key issue. To hope for an emergence of this type of materials within all-solid batteries, it is necessary to avoid the use of heavy and expensive elements but also to improve the resistance of these materials towards humidity. This is possible thanks to the studies carried out on surface modification of sulfide electrolyte or the use of oxy-sulfide in the literature. Nevertheless, all these materials are based on the same precursor: Li₂S: very expensive and unsafe material. The ideal sulfide material would be one that is stable at high potential and low potential with lithium metal, a strong resistance to humidity allowing the handling of the material as well as its safe use in batteries with a low cost synthesis method in a minimum of steps using the minimum of expensive precursors.<br/>In this field and since a few years, Hydro-Quebec has decided to conduct specific research on all-solid ceramic batteries and especially in the field of sulfide-based ceramic electrolytes. A specific study has been carried out to (1) optimize the composition of sulfide solid electrolyte with cheaper precursors to maintain or increase the properties as ionic conductivity and electrochemical stability, (2) better understand the reactivity at various dew points. Safety being in Hydro-Québec's DNA, emphasis has been placed on safety with a minimum step process as well as precise monitoring of H₂S generation of the precursors and the final material depending on temperature and humidity level. The complementarity between synthesis process, compositions, NMR analyses, XRD analyses, ionic conductivity, electrochemical stability, and safety measurements will be presented for the first time on sulfides prepared at Hydro-Quebec.