| 1. |
- Hollmark, Håkan M., et al.
(author)
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Resonant Soft X-Ray Emission Spectroscopy and X-Ray Absorption Spectroscopy on the Cathode Material LiNi0.65Co0.25Mn0.1O2
- 2010
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In: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 157:8, s. A962-A966
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Journal article (peer-reviewed)abstract
- We present a study of the charge-state behavior of the Li-ion battery cathode material LixNi(0.65)Co(0.25)Mn(0.1)O(2) as observed by X-ray absorption spectroscopy (XAS) and resonant soft X-ray emission (RSXE). A set of six identical Li//LixNi0.65Co0.25Mn0.1O2 batteries has been cycled and is studied in different states of charge in the range of x = 1.0, ... ,0.2 before disassembly in an Ar glove box. Site and symmetry selective information about the electronic structure of the conduction and valence bands reveals that Ni as well as Co ions participate in the uptake and release of the extra electron charge that the inserted Li ions provide, but the Ni ion is much less than expected. The net amount of charge on the oxygen varies approximately 0.24 charge units in the range of x, and dramatic changes in the hybridization are evident in XAS and in particular in RSXE at the O K edge. We attribute this to a strong screening behavior of the Li ions between the oxide layers. Structural integrity effects limit the extraction of Li ions to a value of about x = 0.2-0.4. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3454739] All rights reserved.
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| 2. |
- Younesi, Reza, et al.
(author)
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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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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:35, s. 18597-18604
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Journal article (peer-reviewed)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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| 3. |
- Younesi, Reza, et al.
(author)
-
Surface Characterization of the Carbon Cathode and the Lithium Anode of Li-O2 Batteries using LiClO4 or LiBOB salts
- 2013
-
In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 5:4, s. 1333-1341
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Journal article (peer-reviewed)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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| 4. |
- Asfaw, Habtom Desta
(author)
-
Multifunctional Carbon Foams by Emulsion Templating : Synthesis, Microstructure, and 3D Li-ion Microbatteries
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- Carbon foams are among the existing electrode designs proposed for use in 3D Li-ion microbatteries. For such electrodes to find applications in practical microbatteries, however, their void sizes, specific surface areas and pore volumes need be optimized. This thesis concerns the synthesis of highly porous carbon foams and their multifunctional applications in 3D microbatteries. The carbon foams are derived from polymers that are obtained by polymerizing high internal phase water-in-oil emulsions (HIPEs).In general, the carbonization of the sulfonated polymers yielded hierarchically porous structures with void sizes ranging from 2 to 35 µm and a BET specific surface area as high as 630 m2 g-1. Thermogravimetric and spectroscopic evidence indicated that the sulfonic acid groups, introduced during sulfonation, transformed above 250 oC to thioether (-C-S-) crosslinks which were responsible for the thermal stability and charring tendency of the polymer precursors. Depending on the preparation of the HIPEs, the specific surface areas and void-size distributions were observed to vary considerably. In addition, the pyrolysis temperature could also affect the microstructures, the degree of graphitization, and the surface chemistry of the carbon foams.Various potential applications were explored for the bespoke carbon foams. First, their use as freestanding active materials in 3D microbatteries was studied. The carbon foams obtained at 700 to 1500 oC suffered from significant irreversible capacity loss during the initial discharge. In an effort to alleviate this drawback, the pyrolysis temperature was raised to 2200 oC. The resulting carbon foams were observed to deliver high, stable areal capacities over several cycles. Secondly, the possibility of using these structures as 3D current collectors for various active materials was investigated in-depth. As a proof-of-concept demonstration, positive active materials like polyaniline and LiFePO4 were deposited on the 3D architectures by means of electrodeposition and sol-gel approach, respectively. In both cases, the composite electrodes exhibited reasonably high cyclability and rate performance at different current densities. The syntheses of niobium and molybdenum oxides and their potential application as electrodes in microbatteries were also studied. In such applications, the carbon foams served dual purposes as 3D scaffolds and as reducing reactants in the carbothermal reduction process. Finally, a facile method of coating carbon substrates with oxide nanosheets was developed. The approach involved the exfoliation of crystalline VO2 to prepare dispersions of hydrated V2O5, which were subsequently cast onto CNT paper to form oxide films of different thicknesses.
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| 5. |
- Younesi, S Reza, et al.
(author)
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Influence of the Cathode Porosity on the Discharge Performance of the Lithium-Oxygen Battery
- 2011
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 196:22, s. 9835-9838
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Journal article (peer-reviewed)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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| 6. |
- Younesi, Reza, et al.
(author)
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Li-O-2 Battery Degradation by Lithium Peroxide (Li2O2): A Model Study
- 2013
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 25:1, s. 77-84
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Journal article (peer-reviewed)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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| 7. |
- Asfaw, Habtom Desta, et al.
(author)
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Emulsion-templated bicontinuous carbon network electrodes for use in 3D microstructured batteries
- 2013
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In: Journal of Materials Chemistry. - United Kingdom. - 0959-9428 .- 1364-5501. ; 1:44, s. 13750-13758
-
Journal article (peer-reviewed)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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| 8. |
- Roberts, Matthew, et al.
(author)
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3D lithium ion batteries-from fundamentals to fabrication
- 2011
-
In: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 21:27, s. 9876-9890
-
Journal article (peer-reviewed)abstract
- 3D microbatteries are proposed as a step change in the energy and power per footprint of surface mountable rechargeable batteries for microelectromechanical systems (MEMS) and other small electronic devices. Within a battery electrode, a 3D nanoarchitecture gives mesoporosity, increasing power by reducing the length of the diffusion path; in the separator region it can form the basis of a robust but porous solid, isolating the electrodes and immobilising an otherwise fluid electrolyte. 3D microarchitecture of the whole cell allows fabrication of interdigitated or interpenetrating networks that minimise the ionic path length between the electrodes in a thick cell. This article outlines the design principles for 3D microbatteries and estimates the geometrical and physical requirements of the materials. It then gives selected examples of recent progress in the techniques available for fabrication of 3D battery structures by successive deposition of electrodes, electrolytes and current collectors onto microstructured substrates by self-assembly methods.
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| 9. |
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| 10. |
- Asfaw, Habtom Desta, 1986-, et al.
(author)
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Nanosized LiFePO4-decorated emulsion-templated carbon foam for 3D micro batteries : a study of structure and electrochemical performance
- 2014
-
In: Nanoscale. - Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 6:15, s. 8804-8813
-
Journal article (peer-reviewed)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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