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

Li, Qinghao; Qiao, Ruimin; Wray, L. Andrew; Chen, Jun; Zhuo, Zengqing; Chen, Yanxue; Shen, Yan; Hussain, Zahid; Yang, Wanli

doi:10.1088/0022-3727/49/41/413003

Cited by 105 publications

(152 citation statements)

References 53 publications

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“…12). Such evolutions in the Co L-edges over charge/discharge are analogous to Li x CoO 2 , 48,49 thus confirming some Co 3+/4+ activity. Complete oxidation of Co to 4+ in these layered oxides is unlikely as it is now well admitted, based on the early prediction of oxygen’s redox participation in Li 0 CoO 2 50 that was confirmed later via several characterizations 7 , that O competes with Co for charge compensation at stages of high delithiation.…”

Section: Resultsmentioning

confidence: 53%

Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes

et al. 2017

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Reversible anionic redox has rejuvenated the search for high-capacity lithium-ion battery cathodes. Real-world success necessitates the holistic mastering of this electrochemistry’s kinetics, thermodynamics, and stability. Here we prove oxygen redox reactivity in the archetypical lithium- and manganese-rich layered cathodes through bulk-sensitive synchrotron-based spectroscopies, and elucidate their complete anionic/cationic charge-compensation mechanism. Furthermore, via various electroanalytical methods, we answer how the anionic/cationic interplay governs application-wise important issues—namely sluggish kinetics, large hysteresis, and voltage fade—that afflict these promising cathodes despite widespread industrial and academic efforts. We find that cationic redox is kinetically fast and without hysteresis unlike sluggish anions, which furthermore show different oxidation vs. reduction potentials. Additionally, more time spent with fully oxidized oxygen promotes voltage fade. These fundamental insights about anionic redox are indispensable for improving lithium-rich cathodes. Moreover, our methodology provides guidelines for assessing the merits of existing and future anionic redox-based high-energy cathodes, which are being discovered rapidly.

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Section: Resultsmentioning

confidence: 53%

Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes

et al. 2017

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“…4Spatial separation of O oxidation and TM reduction. a Maps of the two Mn end-member spectra (left) obtained by NMF throughout the first discharge and second charge, showing the reversible reduction of Mn only at the particle surfaces upon discharge to 2.00 V. The Mn oxidation states are assigned based on previous literature 88 . Scale bar is 500 nm.…”

Section: Resultsmentioning

confidence: 99%

Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides

et al. 2017

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Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li1.17–xNi0.21Co0.08Mn0.54O2, these properties arise from a strong coupling between anion redox and cation migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.

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“…54 Due to the different mean free path of electrons and photons, total electron yield (TEY) and fluorescence yield (FY) modes yield chemical information at a depth of 10 nm and ∼100 nm from the particle surface, respectively. As shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Elucidating anionic oxygen activity in lithium-rich layered oxides

et al. 2018

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Recent research has explored combining conventional transition-metal redox with anionic lattice oxygen redox as a new and exciting direction to search for high-capacity lithium-ion cathodes. Here, we probe the poorly understood electrochemical activity of anionic oxygen from a material perspective by elucidating the effect of the transition metal on oxygen redox activity. We study two lithium-rich layered oxides, specifically lithium nickel metal oxides where metal is either manganese or ruthenium, which possess a similar structure and discharge characteristics, but exhibit distinctly different charge profiles. By combining X-ray spectroscopy with operando differential electrochemical mass spectrometry, we reveal completely different oxygen redox activity in each material, likely resulting from the different interaction between the lattice oxygen and transition metals. This work provides additional insights into the complex mechanism of oxygen redox and development of advanced high-capacity lithium-ion cathodes.

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

Cited by 105 publications

References 53 publications

Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes

Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes

Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides

Elucidating anionic oxygen activity in lithium-rich layered oxides

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