Nov 04: A Korean research team has developed a transfer printing process that enables solid electrolytes, a key component of solid-state batteries, to be fabricated as very thin, uniform, and defect-free layers over large areas. The technology is expected to provide a foundation for the large-area manufacturing of high-energy-density solid-state batteries.
A research team led by Principal Researcher Yongku Kang and Senior Researcher Myung-Soo Park at the Korea Research Institute of Chemical Technology (KRICT, President Seokmin Shin) developed a transfer printing technology using the garnet-type oxide solid electrolyte LLZTO, in which a solid electrolyte layer is first fabricated on a separate substrate and then transferred onto an electrode.
Solid-state batteries use solid-based electrolytes instead of liquid electrolytes, offering the potential to reduce fire risks and increase energy density. To achieve high energy density, the solid electrolyte must be thinner than 20 micrometers (µm) while maintaining uniform thickness over a large area.
Conventional methods for fabricating solid electrolytes as freestanding films require thicknesses of 70–120 µm to prevent tearing. Directly coating an electrolyte slurry onto an electrode also presents problems because the liquid-state slurry can infiltrate the porous electrode, causing electrode deformation and nonuniform electrolyte thickness.
The research team applied a transfer printing method in which a solid electrolyte slurry is coated and dried on a PET-PDMS substrate, after which only the completed thin layer is pressure-laminated with a roller and transferred onto the electrode like a sticker. Rather than testing numerous material combinations through trial and error, the team used Hansen solubility parameters to quantify the affinity between materials and design optimal conditions for both the coating and transfer processes.
During the coating step, the researchers selected material combinations with high affinity to allow the slurry to spread uniformly across the substrate. During the transfer step, combinations with low adhesion were selected so that the dried layer could be cleanly detached from the substrate. In this way, the researchers established a generalizable and quantitative design principle for rationally selecting material combinations without repeated trial-and-error experiments.
As a result, the team fabricated a uniform solid electrolyte layer over an area of 6 × 20 cm, or 120 cm², with an average thickness of 15 µm and a thickness deviation of approximately 1 µm. By comparison, direct coating onto an electrode resulted in nonuniform film thicknesses ranging from 10 to 25 µm, even over a smaller area of 6 × 11 cm.
The electrolyte performance was also improved. At 25°C, the ionic conductivity of the hybrid solid electrolyte reached 2.83 × 10⁻⁴ S/cm, approximately 50% higher than the 1.69 × 10⁻⁴ S/cm measured for a control in which the same polymer electrolyte was incorporated into a polyethylene (PE) separator widely used in conventional batteries. The Li⁺ transference number was also 0.69, nearly twice the 0.36 of the control. This improvement resulted from the LLZTO-rich electrolyte layer itself serving as a continuous pathway for Li⁺ transport.
To evaluate the effectiveness of transfer printing, the researchers compared it with direct coating. After 100 charge-discharge cycles, the cell fabricated by transfer printing retained 83.6% of its capacity, whereas the directly coated cell retained only 36.1%.
Safety was also improved. In a pouch-cell test conducted at 150°C for 2 hours and 30 minutes, the transfer-printed cell maintained a stable voltage. In contrast, the conventional PE separator-based cell experienced an internal short circuit caused by separator shrinkage, resulting in a rapid voltage drop after approximately 10 minutes.
The research team expects that accumulating data on the Hansen solubility parameters of different materials together with actual coating, adhesion, and transfer results could eventually enable AI-based research to prescreen suitable combinations from among numerous candidate materials.
The study was published in the international materials science journal Advanced Functional Materials (IF: 19.9) in September 2026. Post-Master’s Researcher Seul Gi Chu participated as the first author, while Principal Researcher Yongku Kang and Senior Researcher Myung-Soo Park served as corresponding authors.