Solid-state battery researchers reveal important insights into degradation mechanisms

Researchers at UNIST, Seoul National University (SNU), and POSTECH have made significant progress in understanding the degradation mechanisms of solid-state batteries (ASSBs), a promising technology for next-generation electric vehicles and large-scale energy storage.

A study jointly conducted by Professor Donghyuk Kim from UNIST’s School of Energy and Chemical Engineering, Professor Sung-Kyun Jung from the School of Interdisciplinary Innovation at Seoul National University, and Professor Jihyun Hon from POSTECH revealed that interfacial chemical reactions play an important role in the structural damage and performance degradation of sulfide-based ASSBs. The findings are published in the journal Nature Communications.

Unlike traditional lithium-ion batteries, which rely on flammable liquid electrolytes, ASSBs use non-flammable solid electrolytes, which improves safety and increases energy density. However, challenges such as interfacial instability and microstructural degradation hinder commercialization. Until now, detailed understanding of how these phenomena occur has remained limited.

To address this, the research team developed a model system that incorporated a protective coating layer on the cathode surface using lithium difluorophosphate (LiDFP) to suppress chemical degradation at the interface. They employed advanced analytical techniques such as machine learning, digital twin modeling, and state-of-the-art characterization techniques to investigate microstructural evolution and reaction behavior from the particle level to the entire electrode.

Their analysis demonstrated that applying the coating effectively suppresses chemical degradation at the cathode-electrolyte interface, resulting in a more uniform electrochemical reaction between particles and consistent mechanical degradation across the electrode. This uniformity improved capacity retention and long-term stability even under lower operating pressures, a long-standing hurdle in ASSB implementation.

Importantly, this study reveals that the coating layer does more than act as a protective barrier. It also maintains lithium ion conduction paths while suppressing harmful interfacial reactions. This dual functionality not only extends battery life, but also provides new avenues for designing safer, non-explosive solid-state batteries.

“Our study provides a detailed, particle-level understanding of the root causes of ASSB performance degradation,” said lead author Dr. Changhyun Park, former UNIST and now a postdoctoral fellow at Justus Liebig-University Gießen.

“We have demonstrated that the coating layer plays an important role beyond mere surface protection. The coating layer can act as a new lithium ion transport pathway, opening up innovative strategies for battery stabilization and longevity.”