Researchers in Korea have a developed novel, scalable, and cost-efficient wet synthesis approach to produce superionic conductive sulfide-based solid electrolytes (SEs). This method uses careful regulation of the nucleation rate and strategic substitution of elements to control particle size and enhance ionic conductivity.

The resultant Li_5.5PS_4.5Cl_1.5 SEs synthesized show a uniform size distribution (average particle diameter = 7 μm), coupled with a high ionic conductivity of 4.98 mS cm⁻¹. This level of ionic conductivity is either comparable to or exceeds those produced through dry processes.

A paper on their work is published in the journal Energy Storage Materials.

Solid electrolyte powder (left) produced by the wet synthesis process and a prototype of an all-solid-state battery using it. Credit Korea Electrotechnology Research Institute

Significant research endeavors have been dedicated to synthesizing high-quality sulfide SEs with desirable properties to attain high-performance ASSBs. Typically, sulfide SEs can be synthesized through three methods: melt quenching, mechanical ball milling, and wet-chemical processing. The electrochemical performance of the SEs is heavily affected by the manufacturing process employed. While melt quenching and mechanical ball milling each offer unique advantages, wet-chemical processing is desirable due to its simplicity, cost-effectiveness, scalability, and flexibility in establishing practical applications of ASSBs. Many studies have delved into various wet synthesis methods, such as sol-gel, hydrothermal, co-precipitation, and other chemical processes. However, several hurdles persist in commercializing this synthesis method.

One of the significant challenges lies in achieving high ion conductivity in wet-synthesized SEs. Conventional wet synthesis techniques, such as sol-gel and co-precipitation, introduce impurities, defects, and grain boundaries during the synthesis process, leading to a decrease in ion conductivity by approximately 0.1 mS cm⁻¹. Furthermore, controlling the particle size and morphology of the synthesized SEs poses an additional challenge. The formation of agglomerates or inconsistent particle sizes adversely affects the mechanical and electrochemical properties of the SEs. Particle size inconsistency hampers the electrolyte-electrode contact, resulting in increased interfacial resistance and reduced electrochemical performance. Consequently, battery researchers have long sought a novel wet synthesis method capable of simultaneously achieving high ion conductivity and controlled particle size in sulfide SEs, aiming to fulfill this coveted goal.

… In response to these challenges, we propose an innovative wet-synthesis method for fabricating sulfide SEs that can simultaneously accomplish superior ion conductivity and controlled particle size.

—Sung et al.

The Korea Electrotechnology Research Institute (KERI) has submitted numerous patent applications on this method, anticipating considerable interest from the all-solid-state battery industry. The institute plans to engage in technology transfer agreements with companies expressing demand. Furthermore, KERI aims to synergize this accomplishment with a previous development—a special wet synthesis technique designed to mass-produce solid-state electrolytes at one-tenth the raw materials cost, using a patented special additive. KERI hopes that this strategy will position it as a frontrunner in the low-cost mass production of high-quality solid-state electrolytes.

KERI is a government-funded research institute under the National Research Council of Science & Technology of the Ministry of Science and ICT. The research project was funded by the KERI Basic Project and the Innovative Nano Convergence Technology Development Project of the Ministry of Trade, Industry and Energy.

Resources

• Junghwan Sung, Hae Gon Lee, Yung-Soo Jo, Dong-Hee Kim, Heetaek Park, Jun-Ho Park, Doohun Kim, Yoon-Cheol Ha, Kang-Jun Baeg, Jun-Woo Park (2024) “Size-controlled wet-chemical synthesis of sulfide superionic conductors for high-performance all-solid-state batteries,” Energy Storage Materials doi: 10.1016/j.ensm.2024.103253