Korean researchers have developed a material that enhances both the performance and stability of sulfide-based solid electrolytes for all-solid-state batteries.
The Korea Institute of Industrial Technology (KITECH) announced Wednesday that a research team led by Senior Researcher Kim Tae-hyo of the Low Carbon Energy Group successfully increased lithium-ion mobility and reduced toxic hydrogen sulfide (H₂S) emissions generated upon exposure to moisture by combining three elements in sulfide-based solid electrolyte materials.
Solid electrolytes serve as the pathway for lithium-ion movement between the cathode and anode inside all-solid-state batteries, with sulfide-based materials considered leading candidates due to their high ionic conductivity.
The research team focused on lithium hexaphosphorus pentasulfide iodide (Li₆PS₅I) among sulfide-based solid electrolytes.
Li₆PS₅I has advantages including low manufacturing costs and the ability to form a lithium iodide (LiI) nano-protective layer when in contact with lithium metal, enhancing cell stability.
However, it has drawbacks of relatively low ionic conductivity among sulfide-based solid electrolytes and vulnerability to humidity, generating toxic hydrogen sulfide when exposed to moisture in the air.
The research team solved this problem by incorporating three elements with different roles—chlorine, antimony, and oxygen—into Li₆PS₅I.
Chlorine (Cl) alters the atomic arrangement inside the material to facilitate lithium-ion movement, while antimony (Sb) and oxygen (O) create bonding structures more resistant to moisture, reducing material decomposition and hydrogen sulfide generation.
The team derived the optimal composition balancing ionic conductivity and structural stability after systematically adjusting the ratios of the three elements and comparing various compositions.
Experimental results showed the developed material achieved ionic conductivity of 1.158 millisiemens per centimeter (mS/cm), approximately 77 times higher than the original.
Hydrogen sulfide emissions decreased by 40% in a 30% relative humidity environment, confirming improved moisture resistance. In a higher 50% relative humidity environment, while the original material deteriorated to a mud-like state after 24 hours of exposure, the developed material maintained its solid state.
Stability with lithium metal also improved.
The critical current density—the threshold before internal short-circuiting in the battery—increased by 86% compared to the original, and stable operation for more than 2,000 hours in contact with lithium metal was confirmed.
The research team notably went beyond material design by assembling pressure cells and verifying cycle performance, achieving technological completeness across the entire process from material development to battery demonstration.
When the developed solid electrolyte was applied, the all-solid-state battery's initial discharge capacity reached 158.4 milliampere-hours per gram (mAh/g), an 18% improvement over the existing Li₆PS₅I-based battery (134.5 mAh/g).
Stable operation was also confirmed in durability tests involving 100 charge-discharge cycles.
"This achievement confirms the feasibility of developing materials that can simultaneously enhance both performance and stability in sulfide-based solid electrolytes," Senior Researcher Kim said. "We plan to accelerate commercialization of all-solid-state batteries through technology transfer to domestic materials, parts, and equipment companies."
The research findings were published in the international academic journal Chemical Engineering Journal in the field of chemical engineering.