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Issue 48, 2019
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Operando soft X-ray emission spectroscopy of the Fe2O3 anode to observe the conversion reaction

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Abstract

Drastic electronic-structure changes in an Fe2O3 thin film anode for a Li-ion battery during discharge (lithiation) and charge (delithiation) processes were observed using operando Fe 2p soft X-ray emission spectroscopy (XES). The conversion reaction forming metallic iron due to the lithiation reaction was confirmed by operando XES in combination with the analysis using full-multiplet calculation. The valence of Fe at the open-circuit voltage (OCV) before the second cycle was not Fe3+, but Fe2+ with a weak p–d hybridization, suggesting a considerable irreversibility upon the first discharge–charge cycle and a weakened Fe–O bond after the first cycle. Moreover, we revealed that the Fe 3d electronic-structure change during the second cycle was to some extent reversible as Fe2+ (2.7 V vs. Li/Li+: open circuit voltage) → Fe0 (0.1 V vs. Li/Li+: discharged) → Fe(2+δ)+ (3.0 V vs. Li/Li+: charged). This operando Fe 2p XES in combination with the full-multiplet calculation provides detailed information for redox chemistry during a discharge–charge operation that cannot be obtained by other methods such as crystal-structure and morphology analyses. XES is thus very powerful for investigating the origin and limitation of the lithiation function of anodes involving conversion reactions.

Graphical abstract: Operando soft X-ray emission spectroscopy of the Fe2O3 anode to observe the conversion reaction

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Publication details

The article was received on 11 Sep 2019, accepted on 15 Nov 2019 and first published on 18 Nov 2019


Article type: Paper
DOI: 10.1039/C9CP05036A
Phys. Chem. Chem. Phys., 2019,21, 26351-26357

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    Operando soft X-ray emission spectroscopy of the Fe2O3 anode to observe the conversion reaction

    D. Asakura, Y. Nanba, M. Okubo, H. Niwa, H. Kiuchi, J. Miyawaki, M. Oshima, E. Hosono and Y. Harada, Phys. Chem. Chem. Phys., 2019, 21, 26351
    DOI: 10.1039/C9CP05036A

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