Diffusion mechanism in the sodium-ion battery material sodium cobaltate

T J Willis (1) , D. G Porter (2) , D J Voneshen (1) , S. Uthayakumar (3) , F. Demmel (4) , M. Gutmann (4) , M. Roger (5) , K. Refson (6) , J. P. Goff (1)

1 University of London [London]
2 DIAMOND Light source
3 RHUL - Royal Holloway [University of London]
4 ISIS - ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ISIS Neutron and Muon Source
5 GMT - Groupe Modélisation et Théorie
6 RAL - STFC Rutherford Appleton Laboratory

High performance batteries based on the movement of Li ions in Li x CoO2 have made possible a revolution in mobile electronic technology, from laptops to mobile phones. However, the scarcity of Li and the demand for energy storage for renewables has led to intense interest in Na-ion batteries, including structurally-related Na x CoO2. Here we have determined the diffusion mechanism for Na0.8CoO2 using diffuse x-ray scattering, quasi-elastic neutron scattering and ab-initio molecular dynamics simulations, and we find that the sodium ordering provides diffusion pathways and governs the diffusion rate. Above T ~ 290 K the so-called partially disordered stripe superstructure provides channels for quasi-1D diffusion, and melting of the sodium ordering leads to 2D superionic diffusion above T ~ 370 K. We obtain quantitative agreement between our microscopic study of the hopping mechanism and bulk self-diffusion measurements. Our approach can be applied widely to other Na- or Li-ion battery materials.

Domaines: Physique [physics]

T J Willis, D. G Porter, D J Voneshen, S. Uthayakumar, F. Demmel, et al.. Diffusion mechanism in the sodium-ion battery material sodium cobaltate. Scientific Reports, 2018, 8 (1), pp.3210 - 3210. ⟨10.1038/s41598-018-21354-5⟩. ⟨hal-01847278⟩