Quantitative probe of the transition metal redox in battery electrodes through soft x-ray absorption spectroscopy

Qinghao Li, Ruimin Qiao, L. Andrew Wray, Jun Chen, Zengqing Zhuo, Yanxue Chen, Shishen Yan, Feng Pan, Zahid Hussain, Wanli Yang

    Research output: Contribution to journalReview articlepeer-review

    Abstract

    Most battery positive electrodes operate with a 3d transition-metal (TM) reaction centre. A direct and quantitative probe of the TM states upon electrochemical cycling is valuable for understanding the detailed cycling mechanism and charge diffusion in the electrodes, which is related with many practical parameters of a battery. This review includes a comprehensive summary of our recent demonstrations of five different types of quantitative analysis of the TM states in battery electrodes based on soft x-ray absorption spectroscopy and multiplet calculations. In LiFePO4, a system of a well-known two-phase transformation type, the TM redox could be strictly determined through a simple linear combination of the two end-members. In Mn-based compounds, the Mn states could also be quantitatively evaluated, but a set of reference spectra with all the three possible Mn valences needs to be deliberately selected and considered in the fitting. Although the fluorescence signals suffer the self-absorption distortion, the multiplet calculations could consider the distortion effect, which allows a quantitative determination of the overall Ni oxidation state in the bulk. With the aid of multiplet calculations, one could also achieve a quasi-quantitative analysis of the Co redox evolution in LiCoO2 based on the energy position of the spectroscopic peak. The benefit of multiplet calculations is more important for studying electrode materials with TMs of mixed spin states, as exemplified by the quantitative analysis of the mixed spin Na2-xFe2(CN)6 system. At the end, we showcase that such quantitative analysis could provide valuable information for optimizing the electrochemical performance of Na0.44MnO2 electrodes for Na-ion batteries. The methodology summarized in this review could be extended to other energy application systems with TM redox centre for detailed analysis, for example, fuel cell and catalytic materials.

    Original languageEnglish (US)
    Article number413003
    JournalJournal of Physics D: Applied Physics
    Volume49
    Issue number41
    DOIs
    StatePublished - Sep 16 2016

    Keywords

    • Li-ion batteries
    • Na-ion batteries
    • soft x-ray absorption spectroscopy
    • transition-metal redox

    ASJC Scopus subject areas

    • Electronic, Optical and Magnetic Materials
    • Condensed Matter Physics
    • Acoustics and Ultrasonics
    • Surfaces, Coatings and Films

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