Abstract
The anti-fluorite type Li5FeO4 has attracted significant interest as a potential cathode material for Li ion batteries due to its high Li content and electrochemical performance. Atomic scale simulation techniques have been employed to study the defects and Li ion migration in Li5FeO4. The calculations suggest that the most favorable intrinsic defect type is calculated to be the cation anti-site defect, in which Li+ and Fe3+ ions exchange positions. Li Frenkel is also found to be lower in this material (0.85 eV/defect). Long range lithium diffusion paths were constructed in Li5FeO4 and it is confirmed that the lower migration paths are three dimensional with the lowest activation energy of migration at 0.45 eV. Here we show that doping by Si on the Fe site is energetically favourable and an efficient way to introduce a high concentration of lithium vacancies. The introduction of Si increases the migration energy barrier of Li in the vicinity of the dopant to 0.59 eV. Nevertheless, the introduction of Si is positive for the diffusivity as the migration energy barrier increase is lower less than that of the lithium Frenkel process, therefore the activation energy of Li diffusion.
Highlights
The most favorable intrinsic disorder type is the Li-Fe anti-site defect. This suggests that there will be a population of Li ion on Fe sites and Fe on Li sites
We propose experimental investigations and diffusion studies in Li5FeO4 doped with Si and or Ge
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Summary
Energy minimization calculations were performed on antifluorite bulk structure of Li5FeO4 to obtain the equilibrium lattice constants, thereby enabling an assessment (through comparison with experiment) of the quality of the pair potentials used in this study. A series of isolated point defect (vacancy and interstitial) energies were calculated, which were combined to determine the formation energies for Frenkel and Schottky-type defects in Li5FeO4. The diffusion paths in the Li5FeO4 structures have not been established experimentally. The second lowest activation energy channel, Y, has an overall activation barrier of 0.56 eV.
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