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Open AccessArticle

Anomalous Discharge Behavior of Graphite Nanosheet Electrodes in Lithium-Oxygen Batteries

Institute of Inorganic Chemistry, RWTH Aachen University, 52072 Aachen, Germany
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Materials 2020, 13(1), 43; https://doi.org/10.3390/ma13010043
Received: 28 November 2019 / Revised: 15 December 2019 / Accepted: 17 December 2019 / Published: 20 December 2019
(This article belongs to the Special Issue 2D Materials for Energy Storage and Conversion)
Lithium-oxygen (Li-O2) batteries require rational air electrode concepts to achieve high energy densities. We report a simple but effective electrode design based on graphite nanosheets (GNS) as active material to facilitate the discharge reaction. In contrast to other carbon forms we tested, GNS show a distinctive two-step discharge behavior. Fundamental aspects of the battery’s discharge profile were examined in different depths of discharge using scanning electron microscopy and electrochemical impedance spectroscopy. We attribute the second stage of discharge to the electrochemically induced expansion of graphite, which allows an increase in the discharge product uptake. Raman spectroscopy and powder X-ray diffraction confirmed the main discharge product to be Li2O2, which was found as particulate coating on GNS at the electrode top, and in damaged areas at the bottom together with Li2CO3 and Li2O. Large discharge capacity comes at a price: the chemical and structural integrity of the cathode suffers from graphite expansion and unwanted byproducts. In addition to the known instability of the electrode–electrolyte interface, new challenges emerge from high depths of discharge. The mechanistic origin of the observed effects, as well as air electrode design strategies to deal with them, are discussed in this study. View Full-Text
Keywords: Li-O2; lithium-oxygen batteries; air electrode; graphene; nanographite; exfoliation Li-O2; lithium-oxygen batteries; air electrode; graphene; nanographite; exfoliation
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MDPI and ACS Style

Wunderlich, P.; Küpper, J.; Simon, U. Anomalous Discharge Behavior of Graphite Nanosheet Electrodes in Lithium-Oxygen Batteries. Materials 2020, 13, 43.

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