The large-scale production of solid-state batteries necessitates the development of alternative routes for processing air-sensitive thiophosphate-based solid electrolytes. To set a basis for this, we investigate the chemical stability and ionic conductivity of the LGPS-type lithium-ion conductor tetra-Li7SiPS8 (LiSiPS) processed with various organic solvents. We elucidate the nature of colorful polysulfides that arise during solvent treatment and trace back their origin to the dissolution of the Li3PS4-type amorphous side phase typically present in LiSiPS. We find that water and alcohols decompose LiSiPS by the nucleophilic attack into oxygen-substituted thiophosphates and thioethers and propose a reaction mechanism for the latter. Moreover, we confirm that quaternary thiophosphates can be recrystallized from MeOH solutions upon subsequent high-temperature treatment. Aprotic solvents with donor numbers smaller than 15 kcal mol–1 are suitable for wet-processing quaternary thiophosphates because both the crystal structure of the electrolyte and a high ionic conductivity of >1 mS cm–1 are retained. Using anisole as a case study, we clarify that a residual water content of up to 800 ppm does not lead to a significant deterioration in the ionic conductivity when compared to dry solvents (≤5 ppm). Additionally, we observe a decrease in ionic conductivity with an increasing amount of the solvent residue, which depends not only on the donor number of the solvent but also on the vapor pressure and interactions between the solvent molecules and thiophosphate groups in the solid electrolyte. Thus, optimization of solvent-processing methods of thiophosphate electrolytes is a multifaceted challenge. This work provides transferable insights regarding the stability of LiSiPS against organic solvents that may enable competitive and large-scale thiophosphate-based solid electrolyte processing.

Heterovalently substituting toxic lead is an increasingly popular design strategy to obtain environmentally sustainable variants of the exciting material class of halide perovskites. Perovskite nanocrystals (NCs) obtained through solution‐based methods exhibit exceedingly high optical quality. Unfortunately, most of these synthesis routes still require reaction under inert gas and at very high temperatures. Herein a novel synthesis routine for lead‐free double perovskite (LFDP) NCs is presented. An approach based upon the hot injection and ligand‐assisted reprecipitation (LARP) methods to achieve a low‐temperature and ambient atmosphere‐based synthesis for manganese‐doped Cs2NaBiCl6 NCs is presented. Mn incorporation is critical for the otherwise non‐emissive material, with a 9:1 Bi:Mn precursor ratio maximizing the bright orange photoluminescence (PL) and quantum yield (QY). Higher synthesis temperatures slightly increase the material's performance, yet NCs synthesized at room temperature are still emissive, highlighting the versatility of the synthetic approach. While the material's indirect bandgap limits its appeal for optoelectronics, this feature could benefit photocatalysis due to longer carrier lifetimes. Moreover, the developed synthesis is facile and can rapidly be adapted to other more viable material compositions and up‐scaled to realize applications directly.

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