| 1. |
- Asfaw, Habtom Desta, Dr. 1986-, et al.
(författare)
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A polymeric cathode-electrolyte interface enhances the performance of MoS2-graphite potassium dual-ion intercalation battery
- 2022
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Ingår i: Cell Reports Physical Science. - : Elsevier. - 2666-3864. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Anion intercalation in the graphite cathode of a dual-ion battery (DIB) occurs at unusually high voltage (>4.5 V K+/K). This exacerbates electrolyte degradation and corrosion of Al current collectors, leading to poor coulombic efficiency (CE), typically <90%, and short cell life as a result. These limitations can be mitigated if a stable cathode-electrolyte interface layer (CEI) can form on the graphite electrode. In this study, we demonstrate that the performance of a potassium-based DIB can be improved with a triallyl phosphate (TAP) monomer added in 6 m KN(SO2CF3)2 (KTFSI)-dimethyl carbonate (DMC) electrolyte. The TAP additive forms a stable polymeric CEI on the graphite particles and thus increases the CE of the cell to 97%–99%. Together with MoS2-negative electrodes with a pre-formed solid electrolyte interphase (SEI) layer, the DIB concept has been shown to offer specific capacities from ∼40 to 80 mAh g−1 with an average discharge voltage of 3.7 V.
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| 2. |
- Asfaw, Habtom Desta, Dr. 1986-, et al.
(författare)
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Electrochemical performance of supercapacitor electrodes based on carbon aerogel-reinforced spread tow carbon fiber fabrics
- 2023
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- Fabric-based supercapacitor electrodes were fabricated by embedding spread tow carbon fiber fabrics, in monolithic, bicontinuous carbon aerogels (CAG). The incorporation of CAG, at less than 30 wt%, increased the specific surface area of the CAG-CF fabric to above 230 m2 g−1 and the pore volume to about 0.35 cm3 g−1, orders of magnitude higher than that for the as-received carbon fibres. The presence of the CAG not only improves the electrochemical performance of the composite electrodes but may enhance the mechanical response due to the high stiffness of the aerogel structure. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance measurements were performed on symmetric supercapacitor cells consisting of two CAG-reinforced fabrics in an ionic liquid electrolyte. The specific capacitance of the symmetric supercapacitor was determined to be in the range 3–5 F g−1, considerably higher than that for the plain carbon fibers. Since optimum structural electrolytes are not yet available, this value was normalized to the total mass of both electrodes to place an upper bound on future structural supercapacitors using this spread tow CAG-CF system. The maximum specific energy and specific power, normalized to the total mass of the electrodes, were around 2.64 W h kg−1 and 0.44 kW kg−1, respectively. These performance metrics demonstrate that the thin CAG-modified spread tow fabrics are promising electrodes for future use in structural supercapacitors. In principle, in future devices, the reduced ply thickness offers both improved mechanical properties and shorter ion diffusion distance, as well as opportunities to fabricate higher voltage multicell assemblies within a given component geometry.
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| 3. |
- 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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| 4. |
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| 5. |
- 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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| 6. |
- Asfaw, Habtom Desta
(författare)
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Multifunctional Carbon Foams by Emulsion Templating : Synthesis, Microstructure, and 3D Li-ion Microbatteries
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 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. |
- Asfaw, Habtom Desta, 1986-, et al.
(författare)
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Over-Stoichiometric NbO2 Nanoparticles for a High Energy and Power Density Lithium Microbattery
- 2017
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Ingår i: ChemNanoMat. - : Wiley. - 2199-692X. ; 3:9, s. 646-655
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Tidskriftsartikel (refereegranskat)abstract
- Effective utilization of active materials in microbatteries can be enhanced by rational design of the electrodes. There is an increasing trend of using 3D electrodes that are coated in nanosized active materials to boost both energy and power densities. This article focuses on the fabrication of 3D electrodes based on monolithic carbon foams coated in over-stoichiometric NbO2 nanoparticles. The electrodes exhibit remarkable energy and power densities at various current densities when tested in lithium microbatteries. An areal capacity of around 0.7mAhcm(-2) and energy density up to 45mWhcm(-3) have been achieved. More than half of the areal capacity can be accessed at a current density of about 11mAcm(-2), with the corresponding energy and power densities being 21mWhcm(-3) and 1349mWcm(-3). These values are comparable to those of microsupercapacitors containing carbon and MnO2 nanomaterials. Furthermore, the electrochemical reversibility improves progressively upon cycling along with substantial increase in the charge transfer kinetics of the electrode. Based on impedance analyses almost a fourfold decrease in the charge transfer resistance has been observed over 25 cycles. Such enhancement of the electronic properties of NbO2 can account for the high electrochemical rate performance of the 3D electrodes.
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| 9. |
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| 10. |
- Asfaw, Habtom Desta, Dr. 1986-, et al.
(författare)
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Tailoring the Microstructure and Electrochemical Performance of 3D Microbattery Electrodes Based on Carbon Foams
- 2019
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Ingår i: Energy Technology. - : Wiley. - 2194-4288 .- 2194-4296.
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Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional (3D) carbon electrodes with suitable microstructural features and stable electrochemical performance are required for practical applications in 3D lithium (Li)-ion batteries. Herein, the optimization of the microstructures and electrochemical performances of carbon electrodes derived from emulsion-templated polymer foams are dealt with. Exploiting the rheological properties of the emulsion precursors, carbon foams with variable void sizes and specific surface areas are obtained. Carbon foams with an average void size of around 3.8 mu m are produced, and improvements are observed both in the coulombic efficiency and the cyclability of the carbon foam electrodes synthesized at 2200 degrees C. A stable areal capacity of up to 1.22 mAh cm(-2) (108 mAh g(-1)) is achieved at a current density of 50 mu A cm(-2). In addition, the areal capacity remains almost unaltered, i.e., 1.03 mAh cm(-2) (91 mAh g(-1)), although the cycling current density increases to 500 mu A cm(-2) indicating that the materials are promising for power demanding applications.
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