| 1. |
- Sobkowiak, Adam, et al.
(författare)
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A Mössbauer spectroscopy study of polyol synthesized tavorite LiFeSO4F.
- 2014
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 226:1-3, s. 229-236
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Tidskriftsartikel (refereegranskat)abstract
- The tavorite polymorph of LiFeSO4F has attracted considerable attention as a cathode material for lithium ion batteries due to interesting structural and electrochemical characteristics. For the analysis of such iron-based electrode materials, Mössbauer spectroscopy has become an important and highly useful tool. In this work, we perform a detailed Mössbauer study of pristine tavoriteLiFeSO4F prepared by an optimized synthesis in tetraethylene glycol as reaction media. In contrast to many reported results, we demonstrate the use of an asymmetric fitting model for the inner doublet of the spectrum, which is coupled to the structural properties of the compound. Moreover, we discuss a new approach of ascribing the Fe2 + -doublets to the two distinct crystallographic iron sites of tavorite LiFeSO4F by comparing the Mössbauer signal intensities with the expected f-factors for the corresponding iron atom.
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| 2. |
- Sobkowiak, Adam, et al.
(författare)
-
Identification of an Intermediate Phase, Li1/2FeSO4F, Formed during Electrochemical Cycling of Tavorite LiFeSO4F
- 2014
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 26:15, s. 4620-4628
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Tidskriftsartikel (refereegranskat)abstract
- Many compounds adopting the tavorite-type crystal structure have attracted considerable attention as cathode materials for lithium ion batteries due to the favorable structural characteristics, facilitating promising electrochemical performance. Recent reports have highlighted the complex mechanism of lithium insertion/extraction in some of these compounds, such as the stabilization of intermediate phases in the LiFeSO4OH and LiVPO4F systems. In the case of tavorite LiFeSO4F, reported density functional theory (DFT) calculations have suggested the possibility of a similar behavior, but thus far, no experimental verification of such a process has, to the best of our knowledge, been successfully demonstrated. In this work, we investigate the structural evolution of LiFeSO4F upon extraction/insertion of lithium ions from/into the host framework. By thorough ex situ characterizations of chemically and electrochemically prepared LixFeSO4F-samples (0 ≤ x ≤ 1), we demonstrate the stabilization of an intermediate phase, Li1/2FeSO4F, for which one possible structural model is proposed. However, results indicating charge ordering on the iron-sites, suggesting the formation of a super structure with a larger unit cell, are also highlighted. Moreover, the degree of formation of Li1/2FeSO4F is shown to be highly dependent on the rate of lithium extraction as a result of an exceptionally small potential separation (similar to 15 mV during charging) of the two subsequently occurring biphasic processes, LiFeSO4F/Li1/2FeSO4F and Li1/2FeSO4F/FeSO4F. Finally, the intermediate phase is shown to be formed both on charge and discharge during battery cycling, even though an apparent asymmetrical electrochemical trace suggests the contrary.
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