A scaling law to determine phase morphologies during ion intercalation

• Published in: Energy & environmental science 2020-07, Vol.13 (7), p.2142-2152
• Main Authors: Fraggedakis, Dimitrios, Nadkarni, Neel, Gao, Tao, Zhou, Tingtao, Zhang, Yirui, Han, Yu, Stephens, Ryan M, Shao-Horn, Yang, Bazant, Martin Z
• Format: Article
• Language: English
• Subjects: Intercalation; Lithium-ion batteries; Morphology; Performance degradation; Phase diagrams; Phase separation; Rechargeable batteries; Scaling; Scaling laws
• ISSN: 1754-5692; 1754-5706
• DOI: 10.1039/d0ee00653j

Driven phase separation in ion intercalation materials is known to result in different non-equilibrium phase morphologies, such as intercalation waves and shrinking-core structures, but the mechanisms of pattern selection are poorly understood. Here, based on the idea that the coarsening of the slowest phase is the rate limiting step, we introduce a scaling law that quantifies the transition from quasi-equilibrium intercalation-wave to diffusion-limited shrinking-core behavior. The scaling law is validated by phase-field simulations of single Li x CoO 2 particles, in situ optical imaging of single Li x C 6 particles undergoing transitions between stage 1 ( x = 1) and 2 ( x = 0.5) at different rates, and all the available literature data for single-particle imaging of Li x CoO 2 , Li x C 6 and Li x FePO 4 . The results are summarized in operational phase diagrams to guide simulations, experiments, and engineering applications of phase-separating active materials. Implications for Li-ion battery performance and degradation are discussed. A scaling law, based on the coarsening of the slowest phase, determines the morphologies of phase separating intercalation materials.