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Operando Observation of Lithiation and Delithiation Reactions of a LiCoO2-Li3BO3 Composite Electrode Formed on a Li6.6La3Zr1.6Ta0.4O12 Solid Electrolyte Sheet by Laboratory-based Hard X-ray Photoelectron Spectroscopy (Supporting Information)

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Version 2 2023-11-28, 04:48
Version 1 2023-11-02, 01:58
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posted on 2023-11-02, 01:58 authored by Tsukasa IWAMA, Tsuyoshi OHNISHI, Takuya MASUDA

A positive electrode composed of LiCoO2 (LCO) and Li3BO3 (LBO) was formed on one side of a Li6.6La3Zr1.6Ta0.4O12 (LLZT) solid electrolyte sheet by applying LCO fine powder to LLZT sheet precoated with a Nb thin layer, placing a droplet of aqueous solution of LiOH and H3BO3, and being annealed at ∼700 °C in an oxygen atmosphere. After binding a negative electrode, a Li metal foil, on the other side of LLZT sheet precoated with a Li thin layer, electrochemical reaction at the LiCoO2-Li3BO3 composite positive electrode was observed in an all-solid-state battery configuration, i.e., a LCO-LBO/Nb/LLZT/Li cell, by a newly-developed laboratory-based hard x-ray photoelectron spectroscopy (HAXPES) apparatus equipped with a Cr-Kα source (5414.9 eV) and bias application system. A sharp main peak and a broad satellite peak characteristic to LCO were observed in the Co 2p3/2 region at the pristine state. During charging, i.e., delithiation from LCO, the main peak was asymmetrically broadened to a higher binding energy due to the partial oxidation of Co3+ ions at 780 eV to Co4+ ions at ∼781 eV. In addition, the full width half maximum (FWHM) of the Co4+ peak increased with increasing the amount of lithium insertion, while that of the Co3+ peak remained unchanged. The decrease of satellite peak further confirms the oxidation of Co3+ ions. During the subsequent discharging, i.e., lithiation of LCO, those recovered to the original states, confirming the reversible reduction of Co4+ ions to Co3+ ions. When all the peaks were calibrated with respect to B 1s peak corresponding to LBO as a bulk electrolyte, the Co3+ peaks shifted consistently with the change in cell voltage during charge/discharge cycles, due to the shift of Fermi level of LCO.

Funding

Ministry of Education, Culture, Sports, Science and Technology

Advanced storage battery research and development base

Japan Science and Technology Agency

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Corresponding author email address

Masuda.Takuya@nims.go.jp

Copyright

© 2023 The Author(s).

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