Cathode

In the idealized model of the disordered rocksalt structure, lithium and transition metal ions randomly occupy every cation site, making it isotropic (i.e., the same in all directions). In Raman spectroscopy, signals are forbidden in a perfectly isotropic cubic structure. A team from the University of New Mexico and NTNU demonstrated that Li1+xNbxMn1–2xO2 and Li1+xNbxFe1–2xO2 with XRD peaks corresponding to the disordered rocksalt structure do give several Raman signals. Layered domains within the disordered rocksalt phase can explain their results. Layered compounds like LCO and NMC with 1:1 Li:transition metal ratios have native lithium diffusion planes between the layers. Disordered rocksalts do not have lithium diffusion pathways unless the Li:transition metal ratio is > 1 (closer to 1.2). Importantly, the authors note that lithium excess compositions are still required for ion transport, even with the presence of layered domains.

(a) Isotropic disordered structures with no Raman signals. (b) Raman signals from cubic disordered rocksalts. (c) Structure models for DRX with layered domains.

Research: Cathode Source: Wang, Huang, Raji-Adefila, Outka, Wang, and Chen

Volta Foundation

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