Electrochemical Mechanical Failure Caused by Rotational Stacking Faults in Layered Oxide Cathodes

Background

Electrochemical mechanical degradation is one of the primary causes of capacity decline in high energy density cathode materials, especially those based on intercalated layered oxides. This paper reveals the presence of Rotational Stacking Faults (RSFs) in layered lithium transition metal oxides. These defects, which arise from specific stacking sequences at various angles, significantly affect the material’s structure and electrochemical stability. The study shows that RSFs promote oxygen dimerization and transition metal migration, leading to the formation and propagation of microcracks, thus causing cumulative electrochemical mechanical degradation during cycling. The paper also explores thermal defect elimination as a potential solution, showing that it can suppress RSFs, reduce microcracks, and enhance the cycling life of lithium-rich layered cathodes. The prevalent but previously overlooked RSFs introduce a new synthetic guideline for high energy density layered oxide cathodes.

Source of Paper

The study was conducted by Donggun Eum, Sung-O Park, Ho-Young Jang, Youngjun Jeon, Jun-Hyuk Song, Sangwook Han, Kyoungoh Kim, and Kisuk Kang, primarily from the Department of Materials Science and Engineering, Institute of Innovative Research on Rechargeable Batteries, Center for Nanoparticle Research of the Institute for Basic Science, School of Engineering, and School of Chemical and Biological Engineering at Seoul National University, Korea. The research was published in the journal “Nature Materials” in 2024, with the DOI https://doi.org/10.1038/s41563-024-01899-9.

Detailed Research Process

a) Experimental Procedure

The research involved several key steps:

1. Design of Model System: Single-crystal O2-type lithium-rich layered oxide was selected as the model system to analyze the impact of RSFs on structural stability.
2. Density Functional Theory (DFT) Calculations: DFT calculations were used to study the structural changes induced by RSFs, particularly the effects on transition metal migration and oxygen dimer formation during the charging process.
3. Experimental Observations: Techniques such as Scanning Transmission Electron Microscopy (STEM) and Geometric Phase Analysis (GPA) were employed to observe the manifestation of RSFs in the structure and the formation and propagation of cracks.

b) Main Results

1. Detection of RSFs: Through electron microscopy, numerous RSFs in various stacking sequences were observed, which were validated using DFT calculations showing these defects’ behavior at different angles.
2. Electrochemical Degradation Caused by RSFs: DFT calculations and Ab Initio Molecular Dynamics (AIMD) simulations revealed that RSFs-induced structural slippage accelerates oxygen dimerization and transition metal migration, leading to microcrack formation.
3. Effects of Thermal Defect Elimination: High-temperature annealing demonstrated that RSFs could be partially eliminated, alleviating internal microstrain and improving the material’s mechanical strain capability, thereby extending the battery’s cycling life.

c) Conclusion

The study concludes that RSFs in layered lithium transition metal oxides play a significant role. Through thermal treatment, RSFs can be significantly reduced, improving the electrochemical stability of cathode materials. This research provides a new direction for manufacturing high-energy layered cathodes, aiding in solving issues of voltage and capacity decay in lithium-rich layered cathodes.

d) Research Highlights

1. Key Role of RSFs Discovered: RSFs are identified and validated as a major factor causing electrochemical mechanical degradation in layered oxide cathodes.
2. Thermal Defect Elimination Strategy: A specific thermal treatment method effectively reduces RSFs, enhancing mechanical and electrochemical performance.
3. Comprehensive Application Prospects: The proposed RSFs management strategy is significant for materials research and provides practical guidance for actual battery design.

Significance of the Research

The research reveals the critical impact of RSFs on high energy density layered cathode materials, emphasizing the importance of managing these defects. This discovery provides new approaches and methods for designing more stable and efficient battery materials in the future. Further studies might find similar phenomena in other types of layered cathode materials, broadening the application scope of this research direction.

By deeply investigating RSFs and proposing effective defect management strategies, this paper significantly enhances the electrochemical performance of layered lithium transition metal oxide cathode materials, laying a solid foundation for the future development of high-performance battery materials.