| 1. |
- Younesi, Reza, et al.
(författare)
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Ether Based Electrolyte, LiB(CN)4 Salt and Binder Degradation in the Li-€“O2 Battery Studied by Hard X-ray Photoelectron Spectroscopy (HAXPES)
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:35, s. 18597-18604
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Tidskriftsartikel (refereegranskat)abstract
- Li-O2 cells composed of a carbon cathode containing an α-MnO2 nanowire catalyst and a Kynar (PVDF-HFP) binder were cycled with different electrolytes containing 0.5 M LiB(CN)4 salt in polyethylene glycol dimethyl ether (PEGDME) or tetraethylene glycol dimethyl ether (Tetraglyme) solvents. All cells exhibited fast capacity fading. To explain this, the surface chemistry of the carbon electrodes were investigated by synchrotron based hard X-ray photoelectron spectroscopy (HAXPES) using two photon energies of 2300 and 6900 eV. It is shown that the LiB(CN)4 salt and Kynar binder were degraded during cycling, forming a layer composed of salt and binder residues on the cathode surface. The degradation mechanism of the salt differed in the two tested solvents and, consequently, different types of boron compounds were formed during cycling. Larger amounts of the degraded salt was observed using Tetraglyme as the solvent. With a nonfluorined Li-salt, the observed formation of LiF, which might be a reason for the observed blockage of pores in the cathode and for the observed capacity fading, must be due to Kynar binder decomposition. The amount of LiF formed in the PEGDME cell was larger than that formed in the Tetraglyme cell. The results indicate that not only the electrolyte solvent, but also electrolyte salt as well as the binder used for the porous cathode must be carefully considered when building a successful rechargeable Li-O2 battery.
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| 2. |
- Younesi, Reza, et al.
(författare)
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Surface Characterization of the Carbon Cathode and the Lithium Anode of Li-O2 Batteries using LiClO4 or LiBOB salts
- 2013
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 5:4, s. 1333-1341
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Tidskriftsartikel (refereegranskat)abstract
- The surface compositions of a MnO2 catalyst containing carbon cathode and a Li anode in a Li–O2 battery were investigated using synchrotron-based photoelectron spectroscopy (PES). Electrolytes comprising LiClO4 or LiBOB salts in PC or EC:DEC (1:1) solvents were used for this study. Decomposition products from LiClO4 or LiBOB were observed on the cathode surface when using PC. However, no degradation of LiClO4 was detected when using EC/DEC. We have demonstrated that both PC and EC/DEC solvents decompose during the cell cycling to form carbonate and ether containing compounds on the surface of the carbon cathode. However, EC/DEC decomposed to a lesser degree compared to PC. PES revealed that a surface layer with a thickness of at least 1–2 nm remained on the MnO2 catalyst at the end of the charged state. It was shown that the detachment of Kynar binder influences the surface composition of both the carbon cathode and the Li anode of Li–O2 cells. The PES results indicated that in the charged state the SEI on the Li anode is composed of PEO, carboxylates, carbonates, and LiClO4 salt.
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| 3. |
- Younesi, S Reza, et al.
(författare)
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Influence of the Cathode Porosity on the Discharge Performance of the Lithium-Oxygen Battery
- 2011
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 196:22, s. 9835-9838
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Tidskriftsartikel (refereegranskat)abstract
- By varying the ratio between the amount of carbon and Kynar binder in the cathode of a lithium-oxygen battery, it could be shown that an increasing amount of binder resulted in a decrease in the discharge capacity, mainly as a result of the decrease in the cathode porosity. It was shown that the Kynar binder blocked the majority of the pores with a width below 300 angstrom as determined by studying the pore volume and pore size distribution by nitrogen adsorption. Three carbonate based electrolytes (PC, PC:DEC (1:1), and EC:DEC (2:1) with 1 M LiPF(6)) were tested with the various cathode film compositions. Generally, the PC:DEC and EC:DEC based electrolytes provided higher capacities than PC. The results indicated that the air electrode composition and its effect on the porosity of the cathode, as well as electrolyte properties, are important when optimizing the discharge capacity.
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| 4. |
- Younesi, Reza, et al.
(författare)
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Li-O-2 Battery Degradation by Lithium Peroxide (Li2O2): A Model Study
- 2013
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 25:1, s. 77-84
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Tidskriftsartikel (refereegranskat)abstract
- The chemical stability of the Li-O-2 battery components (cathode and electrolyte) in contact with lithium peroxide (Li2O2) was investigated using X-ray photoelectron spectroscopy (XPS). XPS is a versatile method to detect amorphous as well as crystalline decomposition products of both salts and solvents. Two strategies were employed. First, cathodes including carbon, alpha-MnO2 catalyst, and Kynar binder (PVdF-HFP) were exposed to Li2O2 and LiClO4 in propylene carbonate (PC) or tetraethylene glycol dimethyl ether (TEGDME) electrolytes. The results indicated that Li2O2 degrades TEGDME to carboxylate containing species and that the decomposition products, in turn, degraded the Kynar binder. The alpha-MnO2 catalyst was unaffected. Second, Li2O2 model surfaces were kept in contact with different electrolytes to investigate the chemical stability and also the resulting surface layer on Li2O2. Further, the XPS experiments revealed that the Li salts such as LiPF6, LiBF4, and LiC!
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| 5. |
- Asfaw, Habtom Desta, et al.
(författare)
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Emulsion-templated bicontinuous carbon network electrodes for use in 3D microstructured batteries
- 2013
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Ingår i: Journal of Materials Chemistry. - United Kingdom. - 0959-9428 .- 1364-5501. ; 1:44, s. 13750-13758
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Tidskriftsartikel (refereegranskat)abstract
- High surface area carbon foams were prepared and characterized for use in 3D structured batteries. Twopotential applications exist for these foams: firstly as an anode and secondly as a current collector supportfor electrode materials. The preparation of the carbon foams by pyrolysis of a high internal phase emulsionpolymer (polyHIPE) resulted in structures with cage sizes of 25 mm and a surface area enhancement pergeometric area of approximately 90 times, close to the optimal configuration for a 3D microstructuredbattery support. The structure was probed using XPS, SEM, BET, XRD and Raman techniques; revealingthat the foams were composed of a disordered carbon with a pore size in the <100 nm range resultingin a BET measured surface area of 433 m2 g-1. A reversible capacity exceeding 3.5 mA h cm2 at acurrent density of 0.37 mA cm-2 was achieved. SEM images of the foams after 50 cycles showed thatthe structure suffered no degradation. Furthermore, the foams were tested as a current collector bydepositing a layer of polyaniline cathode over their surface. High footprint area capacities of500 mA h cm-2 were seen in the voltage range 3.8 to 2.5 V vs. Li and a reasonable rate performancewas observed.
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| 6. |
- Asfaw, Habtom Desta, Dr. 1986-, et al.
(författare)
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Facile synthesis of hard carbon microspheres from polyphenols for sodium-ion batteries : insight into local structure and interfacial kinetics
- 2020
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Ingår i: Materials Today Energy. - : Elsevier BV. - 2468-6069. ; 18
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Tidskriftsartikel (refereegranskat)abstract
- Hard carbons are the most promising negative active materials for sodium ion storage. In this work, a simple synthesis approach is proposed to produce hard carbon microspheres (CMSs) (with a mean diameter of ~1.3 μm) from resorcinol-formaldehyde precursors produced via acid-catalyzed polycondensation reaction. Samples prepared at 1200, 1400, and 1500 oC showed different electrochemical behavior in terms of reversible capacity, initial coulombic efficiency (iCE), and the mechanism of sodium ion storage. The specific capacity contributions from the flat voltage profile (<0.1 V) and the sloping voltage region (0.1–1 V) showed strong correlation to the local structure (and carbonization temperature) determined by the interlayer spacing (d002) and the Raman ID/IG ratio of the hard carbons (HCs) and the rate of cycling. Electrochemical tests indicated that the HC synthesized at 1500 oC performed best with an iCE of 85–89% and a reversible capacity of 300–340 mAh g−1 at 10 mA g−1, with the majority of charge stored below 0.1 V. The d002 and the ID/IG ratio for the sample were ~3.7 Å and ~1.27, respectively, parameters indicative of the ideal local structure in HCs required for optimum performance in sodium-ion cells. In addition, galvanostatic tests on three-electrode half-cells cells revealed that sodium metal plating occurred as cycling rates were increased beyond 80 mA g−1 leading to considerably high capacity and poor coulombic efficiency, a point that must be considered in full-cell batteries. Pairing the hard CMS electrodes with Prussian white positive electrode, a proof-of-concept cell could provide a specific capacity of almost 100 mAh g−1 maintained for more than 50 cycles with a nominal voltage of 3 V.
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| 7. |
- Asfaw, Habtom Desta, 1986-, et al.
(författare)
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Nanosized LiFePO4-decorated emulsion-templated carbon foam for 3D micro batteries : a study of structure and electrochemical performance
- 2014
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Ingår i: Nanoscale. - Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 6:15, s. 8804-8813
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we report a novel 3D composite cathode fabricated from LiFePO4 nanoparticles deposited conformally on emulsion-templated carbon foam by a sol–gel method. The carbon foam is synthesized via a facile and scalable method which involves the carbonization of a high internal phase emulsion (polyHIPE) polymer template. Various techniques (XRD, SEM, TEM and electrochemical methods) are used to fully characterize the porous electrode and confirm the distribution and morphology of the cathode active material. The major benefits of the carbon foam used in our work are closely connected with its high surface area and the plenty of space suitable for sequential coating with battery components. After coating with a cathode material (LiFePO4nanoparticles), the 3D electrode presents a hierarchically structured electrode in which a porous layer of the cathode material is deposited on the rigid and bicontinuous carbon foam. The composite electrodes exhibit impressive cyclability and rate performance at different current densities affirming their importance as viable power sources in miniature devices. Footprint area capacities of 1.72 mA h cm−2 at 0.1 mA cm−2 (lowest rate) and 1.1 mA h cm−2 at 6 mA cm−2(highest rate) are obtained when the cells are cycled in the range 2.8 to 4.0 V vs. lithium.
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| 8. |
- Ebadi, Mahsa, et al.
(författare)
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Insights into the Li-Metal/Organic Carbonate Interfacial Chemistry by Combined First-Principles Theory and X-ray Photoelectron Spectroscopy
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:1, s. 347-355
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) is a widely used technique to study surfaces and interfaces. In complex chemical systems, however, interpretation of the XPS results and peak assignments is not straightforward. This is not least true for Li-batteries, where XPS yet remains a standard technique for interface characterization. In this work, a combined density functional theory (DFT) and experimental XPS study is carried out to obtain the C 1s and O 1s core-level binding energies of organic carbonate molecules on the surface of Li metal. Decomposition of organic carbonates is frequently encountered in electrochemical cells employing this electrode, contributing to the build up of a complex solid electrolyte interphase (SEI). The goal in this current study is to identify the XPS fingerprints of the formed compounds, degradation pathways, and thereby the early formation stages of the SEI. The contribution of partial atomic charges on the core-ionized atoms and the electrostatic potential due to the surrounding atoms on the core-level binding energies, which is decisive for interpretation of the XPS spectra, are addressed based on the DFT calculations. The results display strong correlations between these two terms and the binding energies, whereas electrostatic potential is found to be the dominating factor. The organic carbonate molecules, decomposed at the surface of the Li metal, are considered based on two different decomposition pathways. The trends of calculated binding energies for products from ethereal carbon-ethereal oxygen bond cleavage in the organic carbonates are better supported when compared to the experimental XPS results.
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| 9. |
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| 10. |
- Younesi, Reza, et al.
(författare)
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The Cathode Surface Composition of a Cycled Li–O2 Battery : A Photoelectron Spectroscopy Study
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:39, s. 20673-20680
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Tidskriftsartikel (refereegranskat)abstract
- A layer of reaction products, dominantly built up of C and O in the form of ethers and lithium alkyl carbonates, is formed on the surface of the carbon cathode during discharge of a Li–O2 battery in an electrolyte of 1 M LiPF6 in PC. The results are based on a detailed surface analysis combining the use of in house X-ray photoelectron spectroscopy (XPS) and synchrotron based hard X-ray photoelectron spectroscopy (HAXPES). The Li–O2 batteries were investigated at uncycled state (stored), after the first discharge, after the first charge, and at the end of life (discharge state). The results showed little to no Li2O2 and/or Li2O among the discharge products. The surface layers on the cathode were dominantly removed during charging of the battery. At the end of battery life, no complete discharge product layer is formed. The cathodes showed a strong indication of binder decomposition during cycling of the Li–O2 cell. Overall, the results obtained in this investigation show that the whole cathode formulation as well as the electrolyte composition need a completely new approach for the realization of a recyclable Li–O2 battery.
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