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Towards an Understanding of Li2O2 Evolution in Li-O2 Batteries: An In-operando Synchrotron X-ray Diffraction Study
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0002-8915-3032
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0003-2538-8104
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Beijing Forestry Univ, Coll Mat Sci & Technol, Beijing Key Lab Lignocellulos Chem, Beijing 100083, Peoples R China..
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2017 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 10, no 7, p. 1592-1599Article in journal (Refereed) Published
Abstract [en]

One of the major challenges in developing high-performance Li-O-2 batteries is to understand the Li2O2 formation and decomposition during battery cycling. In this study, this issue was investigated by synchrotron radiation powder X-ray diffraction. The evolution of Li2O2 morphology and structure was observed under actual electrochemical conditions of battery operation. By quantitatively tracking Li2O2 during discharge and charge, a two-step process was suggested for both growth and oxidation of Li2O2 owing to different mechanisms during two stages of both oxygen reduction reaction and oxygen evolution reaction. From an observation of the anisotropic broadening of Li2O2 in XRD patterns, it was inferred that disc-like Li2O2 grains are formed rapidly in the first step of discharge. These grains can stack together so that they facilitate the nucleation and growth of toroidal Li2O2 particles with a LiO2-like surface, which could cause parasitic reactions and hinder the formation of Li2O2. During the charge process, Li2O2 is firstly oxidized from the surface, followed by a delithiation process with a faster oxidation of the bulk by stripping the interlayer Li atoms to form an off-stoichiometric intermediate. This fundamental insight brings new information on the working mechanism of Li-O-2 batteries.

Place, publisher, year, edition, pages
2017. Vol. 10, no 7, p. 1592-1599
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-313451DOI: 10.1002/cssc.201601718ISI: 000398838600037PubMedID: 28247542OAI: oai:DiVA.org:uu-313451DiVA, id: diva2:1067034
Funder
Swedish Research CouncilSwedish Energy AgencyÅForsk (Ångpanneföreningen's Foundation for Research and Development)StandUpAvailable from: 2017-01-19 Created: 2017-01-19 Last updated: 2018-01-03
In thesis
1. Li2O2 quantification in non-aqueous Li-O2 batteries with binder-free cathodes
Open this publication in new window or tab >>Li2O2 quantification in non-aqueous Li-O2 batteries with binder-free cathodes
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The non-aqueous Li-air (Li-O2) battery has been emerging as one of the most promising high-energy storage systems to meet the requirements for electric vehicle applications due to its high theoretical energy density. In order to uncover the underlying electrochemistry and enable an informed battery design, it is crucial to gain a detailed understanding of the cell´s chemical components as well as its behavior during cycling.

    These two fundamental tasks are reflected in this thesis’ structure: First, advanced characterization techniques are demonstrated in the search for a novel cathode material for Li-O2 batteries. Second, the electrochemical reactions occurring within the battery upon cycling are studied by in operando powder X-ray diffraction.

    In the first part, a novel free-standing oxygen cathode was prepared by a facile and efficient solution-process followed by a low-temperature exfoliation, which displayed a 3-D structure arrangement of graphene foam (GF) derived from a graphene oxide (GO) gel on an aluminum substrate (GF@Al). The as prepared GF@Al was directly used as cathode in Li-O2 batteries without any binder and catalyst, delivering a high capacity about 9×104 mA h·g-1 (based on the weight of graphene) or about 60 mAh·g-1 (based on the weight of the whole electrode) at the first discharge with a current density of 100 mA·ggraphene-1. Furthermore, electrodes have been investigated by X-ray diffraction (XRD), Fourier-transform infrared reflection (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis spectroscopy titration. The formation of a discharge product and its decomposition upon charge as well as different morphologies of discharge products on the electrode were observed by SEM and TEM.

    In the second part, the evolution of Li2O2 was investigated by synchrotron radiation powder X-ray diffraction (SR-PXD). By quantitatively tracking Li2O2 under the actual electrochemical conditions, a two-step process during growth and oxidation is observed for Li2O2. This is due to different evolution steps during the two stages of both oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). By analyzing the anisotropic broadening of Li2O2 X-ray diffraction peaks, anisotropic disc-like Li2O2 grains were found to be formed rapidly in the first step of discharge, followed by a nucleation and growth of toroidal Li2O2 particles with a LiO2-like surface. During the charging process, Li2O2 was oxidized from the surface first, followed by an oxidation process with a higher decomposition rate for the bulk. This new analysis technique brings additional information on the evolution of Li2O2 in Li-O2 batteries.

Place, publisher, year, edition, pages
Uppsala universitet, 2017
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-337652 (URN)
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Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2018-01-03Bibliographically approved

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