Issue Date: April 18, 2011
Ion Migration In Electrodes Revealed
In a family of fluorosulfate materials of interest for rechargeable battery cathodes, higher calculated activation energies for sodium-ion movement in NaFeSO4F compared with lithium-ion movement in LiFeSO4F help explain the poor performance of NaFeSO4F as an electrode material (Chem. Mater., DOI: 10.1021/cm200683n). A better understanding of the differences between sodium- and lithium-based materials could point the way to development of sodium-based cathodes, reducing pressure on global lithium supplies. Linda F. Nazar of Canada’s University of Waterloo, M. Saiful Islam of England’s University of Bath, and colleagues studied ion migration pathways within LiFeSO4F and NaFeSO4F. They calculated that the paths for Na+ migration in NaFeSO4F all have higher activation energies than the paths for Li+ migration in LiFeSO4F. Additionally, only one migration path is likely in NaFeSO4F, whereas Li+ can migrate along paths in multiple directions. Such differences in ion mobility, along with the fact that the crystal lattice has to expand more to accommodate the larger Na+ ions, would explain the differences in electrode performance observed experimentally, the researchers say.
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