The formation and growth of the Li2O2 discharge product impacts the reversibility of the oxygen evolution and reduction reactions in Li-O2 batteries which may lead to a shorter cycle life. A clear understanding of the surface reactions and the growth mechanism of Li2O2 requires probing dynamic changes on the surface of the positive electrodes in situ during the discharge of a Li-O2 battery. To investigate this, we establish an experimental system by adopting a multi-beam optical sensor (MOS) and developing a custom-made battery cell. First, the accuracy and reliability of the system was demonstrated by analyzing the stress accumulation on the Au negative electrode during Li plating/stripping, and the results were consistent with an earlier single-beam scanning deflectometry report. Then, the Li-O2 battery was discharged in LiNO3 in diglyme electrolyte by applying either linear sweep voltammetry or by applying constant current under an O2 environment. Control experiments in Argon-saturated electrolytes indicate surface stress generation due to charge-induced stress. The stress generation on Au positive electrode is attributed to the formation of Li2O2 reaction products on the Au surface and charge-induced stress.
Bibliographical noteFunding Information:
This work was supported by the Start-up grant provided by Binational Science Foundation (#2018327). Ö. Ö. Ç. conceived the idea and supervised the work. H.D. performed in situ stress measurements and sample preparation. All authors discussed the results. The authors declare that they have no competing interests. Additional data related to this paper may be requested from the authors.
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