[Figure 1. Researchers Involved in the Study]

From left: Dr. Hyesung Jung (Korea Institute of Science and Technology; first author), Dr. Jongho Lee (Korea Institute of Science and Technology; corresponding author), Professor Seongsu Shin (Incheon National University; corresponding author), and Professor Hyungchul Kim (Hongik University; corresponding author)

- 2.5 μm-thick thin-film solid electrolyte applied to an all-solid-state battery with bulk electrodes

- New design combining bulk electrodes with a thin-film solid electrolyte

- Room-temperature operation demonstrated using an integrated bulk electrode and thin-film electrolyte structure

A Korean research team has applied a thin-film solid electrolyte approximately 2.5 μm thick to an all-solid-state battery using bulk electrodes and demonstrated battery operation.

Professor Seongsu Shin’s research team from the Department of Mechanical Engineering at Incheon National University, together with Professor Hyungchul Kim of Hongik University and Dr. Jongho Lee’s research team at the Korea Institute of Science and Technology (KIST), developed an all-solid-state battery design that combines bulk electrodes with a thin-film solid electrolyte.

All-solid-state batteries use solid electrolytes instead of the liquid electrolytes used in conventional lithium-ion batteries. This structure has attracted attention for its potential to improve battery performance and energy density.

In conventional powder-based all-solid-state batteries, solid electrolyte layers can become relatively thick. This increases the proportion of materials that do not directly store energy and increases the distance traveled by lithium ions. Researchers have therefore studied ways to make solid electrolyte layers thinner while maintaining stable battery operation.

Thin-film deposition techniques can form solid electrolytes at the micrometer scale. These thin electrolyte layers can shorten ion transport distances and increase the proportion of active materials within a cell. Conventional thin-film batteries, however, generally use thin-film electrodes as well, which limits the amount of active material that can be included.

[Figure 2. Representative Image of the Paper]

Illustration showing the formation process of the hybrid all-solid-state battery structure developed by the joint INU–Hongik University–KIST research team.

The research team combined the two approaches and developed a hybrid all-solid-state battery structure integrating powder-based bulk electrodes with a thin-film solid electrolyte in a single cell.

The researchers directly formed a thin-film solid electrolyte on a bulk anode substrate through a sputtering process and then placed a thick composite cathode sheet on top. This structure combines the high active-material loading of bulk electrodes with the short ion transport distance provided by a thin-film electrolyte.

The research team also applied a lithium compensation method during fabrication of the thin-film solid electrolyte. TaLLZO and Li2O were deposited together through a co-sputtering process, followed by the application of a Li2O capping layer and heat treatment in an Ar atmosphere. Through this process, the team fabricated a cubic-LLZO thin-film electrolyte.

The film was formed uniformly at a thickness of approximately 2.5 μm and showed an out-of-plane ionic conductivity of 1.91 × 10−2 mS cm−1 at room temperature and an activation energy of 0.45 eV.