UNIST Professor Lee Hyun-wook's team, pressure change
Distinguishing side reactions that reduce the life of all-solid-state batteries
Contributing to the development of all-solid-state batteries without explosion risk


A diagnostic technology that identifies side reactions that reduce the lifespan of all-solid-state batteries has been developed domestically.

On the 7th, Professor Hyunwook Lee's research team from the Department of Energy and Chemical Engineering at Ulsan National Institute of Science and Technology (UNIST) and the research team of Professor Matthew T. McDowell from Georgia Institute of Technology in the U.S. succeeded in distinguishing the secondary phase and dendritic material generation reactions in a sulfide all-solid-state battery by analyzing pressure changes.

Professor Lee Hyun-wook said, “Unlike expensive X-ray technology, this diagnostic method can be used for everything from small batteries to commercialized large-capacity batteries,” and expressed his expectations, saying, “It will enable simpler and more precise performance evaluation and prediction of solid-state batteries.” Solid-state batteries are next-generation batteries that have no risk of explosion by replacing the internal liquid electrolyte with a solid.

The joint research team conducted the study based on the idea that there may be differences in volume changes within the battery when secondary materials or lithium dendritic materials are created. This is the principle that the pressure measured externally decreases as the volume of the material within the battery decreases. To demonstrate this, two types of sulfide-based solid electrolytes with different side reactions within the battery were used.

Sulfide-based solid electrolytes containing tin metal ions tend to change into unstable secondary phases when they come into contact with lithium metal electrodes of batteries. On the other hand, sulfide-based solid electrolytes without metal ions tend to form pointed lithium dendrites that penetrate into the electrolyte on the electrode surface.

“The secondary phase, which has a smaller volume than the existing electrolyte, is formed across the entire cross-section of the electrolyte, which results in a large pressure reduction, but the lithium dendrite is formed by filling the small pores inside the solid electrolyte, which results in less pressure reduction,” said Chanhee Lee, a doctoral candidate in the Department of Energy and Engineering at UNIST and the first author of the paper. “We observed this form during an actual charging experiment.”

The key to commercializing all-solid-state batteries is to find a solid that has ionic conductivity as good as that of a liquid. Sulfide-based solids are the materials with the best ionic conductivity among solid electrolytes that have been developed so far.

The research team also conducted the above analysis experiment by varying the pressure applied in the production of sulfide-based solid electrolytes. The results of the experiment showed that the higher the pressure applied in the process of making electrolyte by agglomerating powdered sulfide, the more the lithium dendrite formation was suppressed and the longer the battery life was.

This research was conducted with the support of the Korea Institute of Energy Technology Evaluation and Planning and the National Research Foundation of Korea’s New Researcher Program. The research results were published online on August 24 in ACS Energy Letters, an international academic journal in the energy field, and are awaiting publication.