Core Material for All-Solid-State Batteries Applied Like a Sticker... Boosts Charge-Discharge Performance [Reading Science]

KRICT Uniformly Produces 15-Micrometer-Thick Solid Electrolyte Across 120 cm2
Retains 83.6% Capacity After 100 Charge-Discharge Cycles... Potential for Large-Area Production Confirmed

A technology has been developed to make a key material for all-solid-state batteries, which are attracting attention as next-generation batteries, by attaching it like a sticker. Instead of applying the solid electrolyte directly to an electrode, the material is made into a thin layer on a separate substrate and then transferred to the electrode. The process reduces thickness irregularities and electrode deformation caused by conventional manufacturing methods, while significantly improving capacity retention after charging and discharging.

The Korea Research Institute of Chemical Technology (KRICT) announced on October 26 that a research team led by Principal Researcher Kang Younggu and Senior Researcher Park Myungsoo had developed a transfer printing technology to transfer oxide-based hybrid solid electrolytes onto electrodes.

Overview of the transfer-printing process for oxide-hybrid solid electrolytes. Provided by the research team.

All-solid-state batteries use solid electrolytes instead of liquid electrolytes, reducing the risk of fire and enabling higher energy density. To achieve high energy density, however, the solid electrolyte must be made thinner than 20 micrometers (μm; one-millionth of a meter) while maintaining uniform thickness over a large area.

Previously, when solid electrolytes were made as separate films, they had to be 70 to 120 μm thick to prevent them from tearing easily. Applying a liquid electrolyte slurry directly to an electrode could cause the slurry to seep into the electrode, deforming its structure and creating uneven thickness.

The research team first made a solid electrolyte film on a separate substrate using garnet-type oxide materials that conduct lithium ions. They then pressed the film with rollers and transferred only the finished film onto the electrode. The process works much like peeling a sticker and applying it to a desired surface.

In particular, the team used the Hansen solubility parameter (HSP), which quantifies the compatibility between materials, to design material combinations suitable for coating and transfer. The team adjusted the adhesion properties so that the electrolyte slurry would spread evenly across the substrate during coating and the dried film would detach easily during transfer.

Solid electrolyte before transfer coating (right) and after transfer (left). Provided by the research team.

As a result, the team produced a uniform solid electrolyte film with an average thickness of 15 μm and a variation of about 1 μm across an area measuring 6 cm by 20 cm, or 120 cm². By contrast, the direct coating method produced uneven thicknesses ranging from 10 to 25 μm even across an area of just 66 cm².

Retains 83.6% of capacity after 100 charge-discharge cycles; high-temperature safety also confirmed

The battery made using transfer printing retained 83.6% of its initial capacity after 100 charge-discharge cycles. The capacity retention rate of the battery made using direct coating was just 36.1%, a difference of 47.5 percentage points.

Lithium-ion conductivity was also measured at 2.83 × 10^-4 S/cm at room temperature (25°C), about 67% higher than that of an electrolyte based on a polyethylene (PE) separator used as a control.

The batteries also differed in high-temperature safety tests. When pouch cells were tested at 150°C, the transfer-printed cell maintained a stable voltage for 2 hours and 30 minutes. In contrast, the voltage of the conventional cell with a PE separator dropped sharply after about 10 minutes because separator shrinkage caused an internal short circuit.

However, this achievement reflects tests of the electrolyte manufacturing process and battery performance at the laboratory scale. Further testing is needed to assess long-term charge-discharge stability and production yields in mass manufacturing before the technology can be applied to large batteries for electric vehicles.

Research team photo. (From left) Kang Younggu, principal researcher; Chu Seulgi, post-master’s researcher; and Park Myeongsu, senior researcher at the Korea Research Institute of Chemical Technology. Photo provided by the institute.

The research team expects the technology to be applicable to roll-to-roll processing, a continuous production method. The team also plans to use artificial intelligence (AI) to predict the coating and adhesion properties of different materials and identify optimal material combinations.

Kang Younggu, a principal researcher at KRICT, said, "This technology can reduce defects that occur when the film is applied directly to the electrode, making it possible to reduce defects and improve production yields in large-area manufacturing."

Post-master’s researcher Chu Seulgi participated in the study as the first author. The findings were published in September in the international journal Advanced Functional Materials.

This content was produced with the assistance of AI translation services.