Researchers Reveal Degradation in Solid-State Batteries

Abstract

Achieving a comprehensive understanding of battery systems necessitates multi-length scale analysis, from the atomic- to macro-scale, to grasp the complex interplay of phenomena influencing performance. However, studies to understand these phenomena in all-solid-state batteries (ASSBs) poses significant challenges due to the complex microstructural evolution involved, including the pore formation and contact loss resulting from cathode material breathing, chemical degradation at interfaces, and their interplay. Herein, we investigate the impact of chemical degradation on the reaction behavior and microstructural evolution of Ni-rich cathode particle (LiNi0.6Co0.2Mn0.2O2) within composite cathodes of sulfide-based ASSBs, using a well-defined model system incorporating Li-In alloy anodes and a non-decomposable coating layer that solely alters the interfacial chemical reactivity. By using lithium difluorophosphate (LiDFP) to suppress chemical degradation, we observed that this suppression enhances the reaction uniformity among particles and homogenizes mechanical degradation, albeit increasing pore formation and tortuosity. In addition, unbridled chemical degradation induces significant reaction heterogeneity and non-uniform mechanical degradation, with fewer pores and lower tortuosity. These findings complement the understanding of mechanical degradation, which is traditionally described using the metrics of contact loss and tortuosity, and underscore the critical role of coating layers in promoting lithium conduction by maintaining contact with the cathode surface.

Researchers from UNIST, Seoul National University (SNU), and POSTECH have made a significant breakthrough in understanding the degradation mechanisms of all-solid-state batteries (ASSBs), a promising technology for next-generation electric vehicles and large-scale energy storage. Jointly led by Professor Donghyuk Kim at UNIST's School of Energy and Chemical Engineering, Professor Sung-Kyun Jung at SNU's School of Transdisciplinary Innovations, and Professor Jihyun Hong from POSTECH, their findings reveal that interfacial chemical reactions play a critical role in structural damage and performance decline in sulfide-based ASSBs.

Unlike conventional lithium-ion batteries that rely on flammable liquid electrolytes, ASSBs use non-flammable solid electrolytes, offering enhanced safety and higher energy density. However, challenges such as interface instability and microstructural deterioration have impeded their commercialization. Until now, the detailed understanding of how these phenomena occur has remained limited.

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

Their analysis demonstrated that applying the coating effectively inhibits chemical degradation at the cathode-electrolyte interface, resulting in more uniform electrochemical reactions across particles and consistent mechanical degradation throughout the electrode. This uniformity led to improved capacity retention and long-term stability, even under lower operational pressures-a longstanding obstacle in ASSB deployment.

Importantly, the study uncovered that the coating layer does more than serve as a protective barrier; it also maintains lithium-ion conduction pathways while suppressing detrimental interfacial reactions. This dual function not only prolongs battery life but also offers new pathways for designing safer, explosion-free solid-state batteries.

Lead author Dr. Chanhyun Park, formerly of UNIST and now a postdoctoral researcher at Justus-Liebig University Giessen, commented, "Our research provides a detailed, particle-level understanding of the root causes of ASSB performance degradation." He further noted, "We demonstrated that the coating layer plays a vital role beyond mere surface protection-it can serve as a new lithium-ion transport pathway, opening up innovative strategies for battery stabilization and longevity."

Their findings have been published in the October 2025 issue of Nature Communications. This research has been supported by the funding from the National Research Foundation of Korea (NRF), the Ministry of Trade, Industry and Energy (MOTIE), the POSCO Science Fellowship of POSCO TJ Park Foundation, and the Korea Institute for Advancement of Technology (KIAT).

Journal Reference

Chanhyun Park, Jingyu Choi, Seojoung Park, et al., "Interfacial chemistry-driven reaction dynamics and resultant microstructural evolution in lithium-based all-solid-state batteries," Nat. Commun., (2025).