UNIST, Seoul National University, and POSTECH Joint Research Team Identifies Causes of Degradation in 'Dream Battery' All-Solid-State Battery

Professor Donghyuk Kim from the Department of Energy and Chemical Engineering at Ulsan National Institute of Science and Technology (UNIST, President Park Jongrae), Professor Sungkyun Jung's research team from the Department of Advanced Convergence at Seoul National University (President Yoo Honglim), and Professor Jihyun Hong's research team from Pohang University of Science and Technology (POSTECH, President Kim Sungkeun) have developed an interface stabilization technology for cathode and electrolyte in sulfide-based solid electrolytes for all-solid-state batteries, and have elucidated the degradation behavior of these batteries.

Researchers: Professor Sungkyun Jung, Seoul National University; Professor Donghyuk Kim, Ulsan National Institute of Science and Technology; Professor Jihyun Hong, Pohang University of Science and Technology; Dr. Chanhyun Park; Researcher Jinkyu Choi; Dr. Seojeong Park (all from Ulsan National Institute of Science and Technology). Provided by Ulsan National Institute of Science and Technology.

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This research achievement is considered a significant advancement that could accelerate the commercialization of all-solid-state batteries (ASSB), which are regarded as a core technology for next-generation electric vehicles and large-scale energy storage systems.

Unlike conventional lithium-ion batteries, all-solid-state batteries use non-flammable solid electrolytes instead of flammable liquid electrolytes, making them safer and capable of storing more energy. For this reason, they are often called the "dream battery."

However, at the interface where the cathode and solid electrolyte are in direct contact, chemical decomposition and structural damage occur, leading to rapid declines in performance and lifespan. Comprehensive understanding of these issues has remained insufficient.

To address these challenges, the research team created a model system by forming a coating layer on the cathode surface using lithium difluorophosphate (LiDFP), and conducted a detailed analysis of the degradation behavior of all-solid-state batteries based on this system.

In particular, by introducing machine learning, digital twin technology, and advanced analytical techniques, the team tracked and identified how chemical degradation (decomposition reactions) occurring between the cathode and electrolyte affects the uniformity of reactions among cathode particles and changes in microstructure, from the particle level to the electrode level.

The analysis revealed that in cathodes with the applied coating layer, chemical degradation was significantly suppressed and reactions among particles proceeded more uniformly. In addition, mechanical degradation was evenly distributed across the entire electrode, preventing localized damage, and as a result, a high capacity retention rate was achieved.

This demonstrates that long-term operational stability of all-solid-state batteries can be secured, and also suggests the possibility of overcoming the low operating pressure issue, which has long been pointed out as an obstacle to commercialization.

Unlike previous studies, this research is significant in that it revealed the coating layer not only serves as a protective film covering the surface, but also plays a key role in suppressing chemical reactions at the interface while maintaining lithium-ion transport pathways. This proves that the coating material can contribute not only to extending battery lifespan, but also to improving lithium-ion conductivity.

The model used by the research team to quantitatively identify the cause of degradation.

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Dr. Chanhyun Park, the first author (formerly of UNIST Energy and Chemical Engineering, currently a postdoctoral researcher at Justus-Liebig University Giessen in Germany), explained, "This study is the result of precisely analyzing the causes of performance degradation in all-solid-state batteries from the particle level of the cathode to the electrode level. We have shown that the role of the coating material goes beyond simply suppressing chemical reactions and can act as a new pathway for lithium movement, opening a new chapter in the understanding of degradation behavior in all-solid-state batteries."

The research team expects that these results will provide important clues for understanding the mechanisms of performance degradation in all-solid-state batteries and for designing high-performance, long-life batteries.

This research was supported by the National Research Foundation of Korea's Ministry of Trade, Industry and Energy Technology Innovation Program, the National Research Foundation of Korea's Young Researcher Program, the POSCO Fellowship, the Ministry of Science and ICT, the Korea Institute for Advancement of Technology, the Secondary Battery Innovation Research Center, and Cheonbo, a manufacturer of secondary battery electrolytes. The results were published on the 3rd in the prestigious international journal in the field of energy materials, Nature Communications.

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