Defect Chemistry, Sodium Diffusion and Doping Behaviour in NaFeO<sub>2</sub> Polymorphs as Cathode Materials for Na-Ion Batteries: A Computational Study
Minor metal-free sodium iron dioxide, NaFeO<sub>2</sub>, is a promising cathode material in sodium-ion batteries. Computational simulations based on the classical potentials were used to study the defects, sodium diffusion paths and cation doping behaviour in the α- and ^...
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doaj-8ca472137fc44799a7a47fc96977c1842020-11-25T02:16:00ZengMDPI AGMaterials1996-19442019-10-011219324310.3390/ma12193243ma12193243Defect Chemistry, Sodium Diffusion and Doping Behaviour in NaFeO<sub>2</sub> Polymorphs as Cathode Materials for Na-Ion Batteries: A Computational StudyNavaratnarajah Kuganathan0Nikolaos Kelaidis1Alexander Chroneos2Department of Materials, Imperial College London, London SW7 2AZ, UKFaculty of Engineering, Environment and Computing, Coventry University, Priory Street, Coventry CV1 5FB, UKDepartment of Materials, Imperial College London, London SW7 2AZ, UKMinor metal-free sodium iron dioxide, NaFeO<sub>2</sub>, is a promising cathode material in sodium-ion batteries. Computational simulations based on the classical potentials were used to study the defects, sodium diffusion paths and cation doping behaviour in the α- and β-NaFeO<sub>2</sub> polymorphs. The present simulations show good reproduction of both α- and β-NaFeO<sub>2</sub>. The most thermodynamically favourable defect is Na Frenkel, whereas the second most favourable defect is the cation antisite, in which Na and Fe exchange their positions. The migration energies suggest that there is a very small difference in intrinsic Na mobility between the two polymorphs but their migration paths are completely different. A variety of aliovalent and isovalent dopants were examined. Subvalent doping by Co and Zn on the Fe site is calculated to be energetically favourable in α- and β-NaFeO<sub>2</sub>, respectively, suggesting the interstitial Na concentration can be increased by using this defect engineering strategy. Conversely, doping by Ge on Fe in α-NaFeO<sub>2</sub> and Si (or Ge) on Fe in β-NaFeO<sub>2</sub> is energetically favourable to introduce a high concentration of Na vacancies that act as vehicles for the vacancy-assisted Na diffusion in NaFeO<sub>2</sub>. Electronic structure calculations by using density functional theory (DFT) reveal that favourable dopants lead to a reduction in the band gap.https://www.mdpi.com/1996-1944/12/19/3243nafeo<sub>2</sub>defectsna-ion diffusiondopantsatomistic simulation |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Navaratnarajah Kuganathan Nikolaos Kelaidis Alexander Chroneos |
spellingShingle |
Navaratnarajah Kuganathan Nikolaos Kelaidis Alexander Chroneos Defect Chemistry, Sodium Diffusion and Doping Behaviour in NaFeO<sub>2</sub> Polymorphs as Cathode Materials for Na-Ion Batteries: A Computational Study Materials nafeo<sub>2</sub> defects na-ion diffusion dopants atomistic simulation |
author_facet |
Navaratnarajah Kuganathan Nikolaos Kelaidis Alexander Chroneos |
author_sort |
Navaratnarajah Kuganathan |
title |
Defect Chemistry, Sodium Diffusion and Doping Behaviour in NaFeO<sub>2</sub> Polymorphs as Cathode Materials for Na-Ion Batteries: A Computational Study |
title_short |
Defect Chemistry, Sodium Diffusion and Doping Behaviour in NaFeO<sub>2</sub> Polymorphs as Cathode Materials for Na-Ion Batteries: A Computational Study |
title_full |
Defect Chemistry, Sodium Diffusion and Doping Behaviour in NaFeO<sub>2</sub> Polymorphs as Cathode Materials for Na-Ion Batteries: A Computational Study |
title_fullStr |
Defect Chemistry, Sodium Diffusion and Doping Behaviour in NaFeO<sub>2</sub> Polymorphs as Cathode Materials for Na-Ion Batteries: A Computational Study |
title_full_unstemmed |
Defect Chemistry, Sodium Diffusion and Doping Behaviour in NaFeO<sub>2</sub> Polymorphs as Cathode Materials for Na-Ion Batteries: A Computational Study |
title_sort |
defect chemistry, sodium diffusion and doping behaviour in nafeo<sub>2</sub> polymorphs as cathode materials for na-ion batteries: a computational study |
publisher |
MDPI AG |
series |
Materials |
issn |
1996-1944 |
publishDate |
2019-10-01 |
description |
Minor metal-free sodium iron dioxide, NaFeO<sub>2</sub>, is a promising cathode material in sodium-ion batteries. Computational simulations based on the classical potentials were used to study the defects, sodium diffusion paths and cation doping behaviour in the α- and β-NaFeO<sub>2</sub> polymorphs. The present simulations show good reproduction of both α- and β-NaFeO<sub>2</sub>. The most thermodynamically favourable defect is Na Frenkel, whereas the second most favourable defect is the cation antisite, in which Na and Fe exchange their positions. The migration energies suggest that there is a very small difference in intrinsic Na mobility between the two polymorphs but their migration paths are completely different. A variety of aliovalent and isovalent dopants were examined. Subvalent doping by Co and Zn on the Fe site is calculated to be energetically favourable in α- and β-NaFeO<sub>2</sub>, respectively, suggesting the interstitial Na concentration can be increased by using this defect engineering strategy. Conversely, doping by Ge on Fe in α-NaFeO<sub>2</sub> and Si (or Ge) on Fe in β-NaFeO<sub>2</sub> is energetically favourable to introduce a high concentration of Na vacancies that act as vehicles for the vacancy-assisted Na diffusion in NaFeO<sub>2</sub>. Electronic structure calculations by using density functional theory (DFT) reveal that favourable dopants lead to a reduction in the band gap. |
topic |
nafeo<sub>2</sub> defects na-ion diffusion dopants atomistic simulation |
url |
https://www.mdpi.com/1996-1944/12/19/3243 |
work_keys_str_mv |
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1724893481910927360 |