Phonon assisted ion diffusion in electrochemically cycled NaxCoO2

Le résumé fourni par la source

Understanding ion diffusion mechanisms in layered materials is critical for advancing next-generation battery technologies. Using the well-characterized Na x CoO 2 (NCO) system as a model platform, we investigated the temperature-dependent diffusion properties across a broad compositional range ( x = 0 . 33 − 0 . 89 ) using muon spin relaxation ( μ + SR). Unexpected low-temperature internal magnetic field fluctuations were observed, systematically varying with Na content and appearing well before the onset of long-range diffusion. These fluctuations are attributed to phonon-assisted local Na motion, as suggested by a systematic increase in A with x , concurrent with a decreasing activation energy. The diffusion coefficient was calculated based on the crystal structure using a tailored diffusion model accounting for two inequivalent Na sites, yielding values consistent with those found in other layered battery materials. This work highlights the crucial role of phonon-coupled diffusion mechanisms in enabling ion transport at the microscopic scale, providing new insights into ion dynamics in layered solid-state conductors and their relevance to sodium-ion battery technology. • Low-energy ion motion observed before long-range diffusion in layered Na cobaltates. • Local sodium hopping linked to phonon interactions at low temperatures. • Diffusion increases despite lattice contraction with higher sodium content. • Study reveals a new phonon-assisted diffusion mechanism in battery materials.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.