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Li2O2 quantification in non-aqueous Li-O2 batteries with binder-free cathodes
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. (Ångström Advanced Battery Center)ORCID iD: 0000-0002-8915-3032
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: urn:nbn:se:uu:diva-337652OAI: oai:DiVA.org:uu-337652DiVA, id: diva2:1170480
Opponent
Supervisors
Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2018-01-03Bibliographically approved
List of papers
1. 3-D binder-free graphene foam as cathode for high capacity Li-O2 batteries
Open this publication in new window or tab >>3-D binder-free graphene foam as cathode for high capacity Li-O2 batteries
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2016 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, no 25, p. 9767-9773Article in journal (Other (popular science, discussion, etc.)) Published
Abstract [en]

To provide energy densities higher than those of conventional Li-ion batteries, a Li–O2 battery requires a cathode with high surface area to host large amounts of discharge product Li2O2. Therefore, reversible formation of discharge products needs to be investigated in Li–O2 cells containing high surface area cathodes. In this study, a binder-free oxygen electrode consisting of a 3-D graphene structure on aluminum foam, with a high defect level (ID/IG = 1.38), was directly used as the oxygen electrode in Li– O2 batteries, delivering a high capacity of about 9 *104 mA h g-1 (based on the weight of graphene) at the first full discharge using a current density of 100 mA ggraphene-1 . This performance is attributed to the 3-D porous structure of graphene foam providing both an abundance of available space for the deposition of discharge products and a high density of reactive sites for Li–O2 reactions. Furthermore, the formation of discharge products with different morphologies and their decomposition upon charge were observed by SEM. Some nanoscaled LiOH particles embedded in the toroidal Li2O2 were detected by XRD and visualized by TEM. The amount of Li2O2 formed at the end of discharge was revealed by a titration method combined with UV-Vis spectroscopy analysis. 

National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-291383 (URN)10.1039/C5TA10690G (DOI)000378716900008 ()
Conference
Inorganic Days, Visby, June 15 - 17, 2015
Projects
Swedish Research CouncilSwedish Energy AgencyÅngpanneföreningen’s Foundation for Research and DevelopmentJ. Gust. Richert FoundationState Key Laboratory of Fine Chemicals (KF1413)China Scholarship Council
Funder
Swedish Research Council, 2012-4681; 2011-6512Swedish Energy AgencyÅForsk (Ångpanneföreningen's Foundation for Research and Development)
Available from: 2016-05-02 Created: 2016-05-02 Last updated: 2018-01-03Bibliographically approved
2. Towards an Understanding of Li2O2 Evolution in Li-O2 Batteries: An In-operando Synchrotron X-ray Diffraction Study
Open this publication in new window or tab >>Towards an Understanding of Li2O2 Evolution in Li-O2 Batteries: An In-operando Synchrotron X-ray Diffraction Study
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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.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-313451 (URN)10.1002/cssc.201601718 (DOI)000398838600037 ()28247542 (PubMedID)
Funder
Swedish Research CouncilSwedish Energy AgencyÅForsk (Ångpanneföreningen's Foundation for Research and Development)StandUp
Available from: 2017-01-19 Created: 2017-01-19 Last updated: 2018-01-03

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