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Sodiation and Desodiation via Helical Phosphorus Intermediates in High-Capacity Anodes for Sodium-Ion Batteries
journal contribution
posted on 2018-06-18, 20:50 authored by Lauren
E. Marbella, Matthew L. Evans, Matthias F. Groh, Joseph Nelson, Kent J. Griffith, Andrew J. Morris, Clare P. GreyNa-ion batteries are promising alternatives
to Li-ion systems for
electrochemical energy storage because of the higher natural abundance
and widespread distribution of Na compared to Li. High capacity anode
materials, such as phosphorus, have been explored to realize Na-ion
battery technologies that offer comparable performances to their Li-ion
counterparts. While P anodes provide unparalleled capacities, the
mechanism of sodiation and desodiation is not well-understood, limiting
further optimization. Here, we use a combined experimental and theoretical
approach to provide molecular-level insight into the (de)sodiation
pathways in black P anodes for sodium-ion batteries. A determination
of the P binding in these materials was achieved by comparing to structure
models created via species swapping, ab initio random
structure searching, and a genetic algorithm. During sodiation, analysis
of 31P chemical shift anisotropies in NMR data reveals
P helices and P at the end of chains as the primary structural components
in amorphous NaxP phases. X-ray diffraction
data in conjunction with variable field 23Na magic-angle
spinning NMR support the formation of a new Na3P crystal
structure (predicted using density-functional theory) on sodiation.
During desodiation, P helices are re-formed in the amorphous intermediates,
albeit with increased disorder, yet emphasizing the pervasive nature
of this motif. The pristine material is not re-formed at the end of
desodiation and may be linked to the irreversibility observed in the
Na–P system.
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Na x P phases31 P chemical shift anisotropiesHigh capacity anode materialssodiationLi-ionelectrochemical energy storagedesodiationfield 23 Na magic-angleSodium-Ion Batteries Na-ion batteriesHelical Phosphorus IntermediatesNMRNa 3 P crystal structurere-formedX-ray diffraction dataP helicesNa-ion battery technologiesP anodes
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