Unrecoverable lattice rotation governs structural degradation of single-crystalline cathodes

• Published in: Science (American Association for the Advancement of Science) Vol. 384; no. 6698; pp. 912 - 919
• Main Authors: Huang, Weiyuan, Liu, Tongchao, Yu, Lei, Wang, Jing, Zhou, Tao, Liu, Junxiang, Li, Tianyi, Amine, Rachid, Xiao, Xianghui, Ge, Mingyuan, Ma, Lu, Ehrlich, Steven N., Holt, Martin V., Wen, Jianguo, Amine, Khalil
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 24.05.2024; AAAS
• Subjects: Cathodes; Cobalt; Crystal lattices; Crystal structure; Crystals; Degradation; Electrochemistry; Electron microscopy; Grain boundaries; Manganese; MATERIALS SCIENCE; Metal crystals; Nickel; Rotation; Single crystals; Statistical analysis; Statistical methods; X-ray diffraction
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.ado1675

Transitioning from polycrystalline to single-crystalline nickel-rich cathodes has garnered considerable attention in both academia and industry, driven by advantages of high tap density and enhanced mechanical properties. However, cathodes with high nickel content (>70%) suffer from substantial capacity degradation, which poses a challenge to their commercial viability. Leveraging multiscale spatial resolution diffraction and imaging techniques, we observe that lattice rotations occur universally in single-crystalline cathodes and play a pivotal role in the structure degradation. These lattice rotations prove unrecoverable and govern the accumulation of adverse lattice distortions over repeated cycles, contributing to structural and mechanical degradation and fast capacity fade. These findings bridge the previous knowledge gap that exists in the mechanistic link between fast performance failure and atomic-scale structure degradation. In theory, larger metal crystals in high-nickel-content nickel-manganese-cobalt (NMC) cathodes should have a higher practical capacity than polycrystalline ones because of the absence of grain boundaries and heterogeneous volume changes. However, in practice, single-crystalline NMC particles with more than 70% nickel exhibit worse performance with more rapid capacity fade. Huang et al . developed a technique to capture both statistical and individual lattice distortions in an ensemble of particles, thus bridging between the information provided by x-ray diffraction and electron microscopy methods. The authors observed that lattice rotation, a frequently occurring but often underdetected lattice distortion, is a primary factor initiating structural and electrochemical degradation in single-crystal cathode particles. —Marc S. Lavine