4.8 Article

In Situ AFM Imaging of Li-O2 Electrochemical Reaction on Highly Oriented Pyrolytic Graphite with Ether-Based Electrolyte

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JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 135, 期 29, 页码 10870-10876

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AMER CHEMICAL SOC
DOI: 10.1021/ja405188g

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  1. RIKEN
  2. RIKEN International Program Associate (IPA)
  3. RIKEN RNC Industrial Cooperation Team

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Understanding the lithium oxygen (Li-O-2) electrochemical reaction is of importance to improve reaction kinetics, efficiency, and mitigate parasitic reactions, which links to the strategy of enhanced Li-O-2 battery performance. Many in situ and ex situ analyses have been reported to address chemical species of reduction intermediate and products, whereas details of the dynamic Li-O-2 reaction have not as yet been fully unraveled. For this purpose, visual imaging can provide straightforward evidence, formation and decomposition of products, during the Li-O-2 electrochemical reaction. Here, we present real-time and in situ views of the Li-O-2 reaction using electrochemical atomic force microscopy (EC-AFM). Details of the reaction process can be observed at nano-/micrometer scale on a highly oriented pyrolytic graphite (HOPG) electrode with lithium ion-containing tetraglyme, representative of the carbon cathode and ether-based electrolyte extensively employed in the Li-O-2 battery. Upon oxygen reduction reaction (ORR), rapid growth of nanoplates, having axial diameter of hundreds of nanometers, length of micrometers, and similar to 5 nm thickness, at a step edge of HOPG can be observed, which eventually forms a lithium peroxide (Li2O2) film. This Li2O2 film is decomposed during the oxygen evolution reaction (OER), for which the decomposition potential is related to a thickness. There is no evidence of byproduct analyzed by X-ray photoelectron spectroscopy (XPS) after first reduction and oxidation reaction. However, further cycles provide unintended products such as lithium carbonate (Li2CO2), lithium acetate, and fluorine-related species with irregular morphology due to the degradation of HOPG electrode, tetraglyme, and lithium salt. These observations provide the first visualization of Li-O-2 reaction process and morphological information of Li2O2, which can allow one to build strategies to prepare the optimum conditions for the Li-O-2 battery.

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