Solvent-Dependent Size Regulation of Li₆PS₅Cl Synthesized through Precipitation-Dissolution-Reprecipitation Processes

Solid-state electrolytes (SSEs) have received significant attention as a means to improve the energy density and safety of lithium (Li) batteries. However, their electrochemical performance is critically dependent on the quality of interfacial contact between constituent particles, particularly within the cathode composite. To ensure intimate contact between the SSE and the cathode active material, the use of small SSE particles in 1-3 μm dimensions is essential. Here, we report a one-pot synthesis of argyrodite-type Li₆PS₅Cl (LPSCl) particles with an average size of ∼2 μm, achieved without any post-processing steps. The key strategy was the use of a solvent with strong Li⁺ solvation capability, specifically 1,2-dimethoxyethane (DME), based on the reaction of Li⁺ with naphthalene-derived radical anions. The Li⁺ solvation in DME prevents the formation of aggregative ion pairs between Li⁺ and anionic intermediates, such as polysulfides, polythiophosphates, and chlorides. This stabilization of free Li⁺ governed nucleation and evolution of LPSCl particles via a precipitation-dissolution-reprecipitation process. The use of DME enabled the synthesis of smaller and also higher purity particles compared to weaker solvating solvents such as tetrahydrofuran (THF) and 2-methyl-THF, leading to superior ionic conductivity (3.3 mS cm^-1 at 30 °C) and a high critical current density (1.75 mA cm^-2). When applied in full cells using LiNbO₃-coated NCM811 cathodes, the cells demonstrated remarkable cycling stability, retaining 99.7% of their capacity after 1000 cycles at 1.0 C and 55 °C, providing excellent contact between the small-size LPSCl and NCM811.