, Volume 18, Issue 8, pp 2071-2075
Date: 25 Mar 2014

Understanding the structural and electronic properties of the cathode material NaFeF3 in a Na-ion battery

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Abstract

Na-ion battery cathode material NaFeF3 and the corresponding desodiated products were investigated by using first-principle density functional theory calculations within the generalized gradient approximation (GGA) + U framework. Our results show that Na0.5FeF3 is the only energetically stable intermediate phase among the cases considered in the present work (x = 0.75, 0.5, 0.25), leading to theoretically two voltage plateaus, i.e., 2.63 V (1 ≥ x ≥ 0.5) and 2.82 V (0.5 ≥ x ≥ 0) in Na x FeF3, respectively. The mean charge voltage of the extraction of the first 0.5 Na ions agrees well with the experimental value, but the one of the extraction of the second 0.5 Na ions exhibits a relatively low value comparing to the experimental results, indicating that another end phase exists, which is consistent with the recent experiments. Furthermore, the electronic structures upon the desodiation are also discussed, and charge localization into distinct Fe2+ and Fe3+ is found in the intermediate-phase Na0.5FeF3.