A Novel Wet Synthesis Method of High-Conductivity Sulfide Solid Electrolytes with Controlled Particle Size for All-Solid-State Batteries
Authors: Park Jun-Woo , Sung Junghwan , Heo Junyoung , Kim Dong-Hee , Gu Hawon , Park Heetaek , Park Jun-Ho , Ha Yoon-Cheol , Kim Doohun 
Published: December 2024

Growing safety concerns regarding commercial lithium-ion batteries arise from the use of flammable organic liquid electrolytes. Consequently, all-solid-state batteries (ASSBs), free from such electrolytes and therefore posing no fire risk, are attracting significant attention as the next-generation battery system. Among various solid electrolytes (SEs), sulfide-based SEs stand out as promising candidates for commercialization due to their high ionic conductivity and superior processability. For the commercialization of ASSBs, a scalable and efficient wet synthesis process for mass production of solid electrolytes is essential.

In previous research, we developed a novel method for preparing bulk-type argyrodite Li6PS5Cl (LPSCl) SEs with high ionic conductivity approaching 2 mS cm-1 using solution-phase synthesis with an additive and no high-energy ball-milling processes. Additionally, we investigated various solvents to understand the relationship between solvent properties and the purity of LPSCl SEs, finding that the characteristics of organic solvents play a significant role in lithium polysulfide formation. Despite these advancements, limitations in large-scale SE production may arise due to the use of petrochemical-derived toxic solvents. Therefore, we explored scalable production of cost-effective LPSCl-based sulfide SEs with high ionic conductivities exceeding 2 mS cm-1 using various green and sustainable solvents. However, the wet synthesis method introduced previously often produces SEs with large particle sizes, necessitating additional pulverization processes. This leads to increased costs and time, posing limitations to commercialization.

This study introduces a novel, scalable, and cost-efficient wet synthesis approach for producing superionic conductive sulfide-based SEs. This pioneering process enables the creation of fine solid electrolyte particles by controlling the nucleation rate and strategically introducing Cl excess to enhance ionic conductivity. The synthesized Li5.5PS4.5Cl1.5 SE features a uniform size distribution (with an average particle diameter of 7 μm) and a high ionic conductivity of 4.98 mS cm-1, comparable to those produced by dry processes. The ability to control particle size allows the direct integration of these SEs with electrodes, eliminating the need for additional pulverization and facilitating the commercialization of ASSBs. The simulation results, including density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, confirm that the experimental data trends align with theoretical predictions. By utilizing green and sustainable solvents, we significantly reduced the environmental footprint of the production process, highlighting the importance of environmentally friendly methods in the sustainable commercialization of ASSBs.

In conclusion, the novel wet synthesis method introduced in this study represents a major advancement in the field of ASSBs. By achieving high ionic conductivity through Cl excess and ensuring fine particle size control, we have addressed key barriers to commercialization. The ability to integrate these SEs directly with electrodes without additional pulverization processes further enhances the practical applicability of this method. As ASSBs continue to gain traction as the next-generation battery system, our findings provide a robust foundation for future developments and large-scale production. This study not only contributes to the technical advancement of battery technology but also underscores the importance of sustainable practices in the quest for high-performance energy storage solutions.