| 1. |
- Sun, Bing, et al.
(författare)
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Ion transport in polycarbonate based solid polymer electrolytes : experimental and computational investigations
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:14, s. 9504-9513
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Tidskriftsartikel (refereegranskat)abstract
- Among the alternative host materials for solid polymer electrolytes (SPEs), polycarbonates have recently shown promising functionality in all-solid-state lithium batteries from ambient to elevated temperatures. While the computational and experimental investigations of ion conduction in conventional polyethers have been extensive, the ion transport in polycarbonates has been much less studied. The present work investigates the ionic transport behavior in SPEs based on poly(trimethylene carbonate) (PTMC) and its co-polymer with epsilon-caprolactone (CL) via both experimental and computational approaches. FTIR spectra indicated a preferential local coordination between Li+ and ester carbonyl oxygen atoms in the P(TMC20CL80) co-polymer SPE. Diffusion NMR revealed that the co-polymer SPE also displays higher ion mobilities than PTMC. For both systems, locally oriented polymer domains, a few hundred nanometers in size and with limited connections between them, were inferred from the NMR spin relaxation and diffusion data. Potentiostatic polarization experiments revealed notably higher cationic transference numbers in the polycarbonate based SPEs as compared to conventional polyether based SPEs. In addition, MD simulations provided atomic-scale insight into the structure-dynamics properties, including confirmation of a preferential Li+-carbonyl oxygen atom coordination, with a preference in coordination to the ester based monomers. A coupling of the Li-ion dynamics to the polymer chain dynamics was indicated by both simulations and experiments.
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| 2. |
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| 3. |
- Gogoi, Neeha, et al.
(författare)
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Silyl-Functionalized Electrolyte Additives and Their Reactivitytoward Lewis Bases in Li-Ion Cells br
- 2022
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 34:8, s. 3831-3838
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Tidskriftsartikel (refereegranskat)abstract
- Silyl groups are included in a wide range of electrolyteadditives to enhance the performance of state-of-the-art Li-ion batteries. Arecognized representative thereof is tris-(trimethylsilyl)phosphate(TMSPa) which, along with the similarly structured phosphite, has beenat the center of numerous electrolyte studies. Even though the silyl grouphas already been widely reported to be specifically reactive towardsfluorides, herein, a reactivity towards several Lewis bases typically found inLi-ion cells is postulated and investigated with the aim to establish a moresimplified and generally applicable reaction mechanism thereof. Bothgaseous and electrolyte soluble reactants and products are monitored bycombining nuclear magnetic resonance and injection cell-coupled massspectrometry. Experimental observations are supported by computationalmodels. The results clearly demonstrate that the silyl groups react withwater, hydroxide, and methoxide and thereby detach in a stepwise fashion from the central phosphate in TMSPa. Intermolecularinteraction between TMSPa and the reactants likely facilitates dissolution and lowers the free energy of reaction. Lewis bases are wellknown to trigger side reactions involving both the Li-ion electrode and electrolyte. By effectively scavenging these, the silyl group canbe explained to lower cell impedance and prolong the lifetime of modern Li-ion batteries.
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| 4. |
- Pogorilyi, Roman, et al.
(författare)
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New product from old reaction : uniform magnetite nanoparticles from iron-mediated synthesis of alkali iodides and their protection from leaching in acidic media
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:43, s. 22606-22612
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Tidskriftsartikel (refereegranskat)abstract
- Iron-mediated synthesis of alkali metal iodides was quite unexpectedly demonstrated to be able to serve as a cost-efficient and reliable source of spherical single crystalline near-stoichiometric magnetite (Fe3O4) nanoparticles as revealed by TEM and XRD studies and also by XANES spectroscopic quantification of the Fe2+-content. Using the particles as nuclei for the Stoeber synthesis of silica nanoparticles, core-shell magnetic material has been produced. The nature of the magnetic component was probed by XANES spectroscopy. The size of the particles is dependent on the synthesis conditions and Si : Fe ratio but can be kept below 100 nm. It is the Si : Fe ratio that determines the stability of the particles in acidic medium. The latter was investigated spectrophotometrically as leaching of Fe3+-cations. Considerable stability was observed at Si : Fe > 10, while at Si : Fe >= 20 no measurable leaching could be observed in over 10 days. Magnetic nanoparticles with improved stability in acidic medium provide an attractive basis for creation of adsorbent materials for applications in harsh media.
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| 5. |
- Renier, Olivier, et al.
(författare)
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Shape Preserving Single Crystal to Amorphous to Single Crystal Polymorphic Transformation Is Possible
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:48, s. 20202-20206
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Tidskriftsartikel (refereegranskat)abstract
- Many crystalline materials form polymorphs and undergo solid–solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)2 which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms.
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| 6. |
- 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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| 7. |
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| 8. |
- 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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| 9. |
- 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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| 10. |
- Iurchenkova, Anna A., 1997-, et al.
(författare)
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MWCNT buckypaper/polypyrrole nanocomposites for supercapasitor application
- 2020
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 335
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Tidskriftsartikel (refereegranskat)abstract
- In this work MWNT/polypyrrole nanocomposites were synthesized and investigated as electrode materials for supercapasitor application. The MWNT were synthesized by CCVD-method and precipitated as buckypaper film (NTBP). The polypyrrole was precipitated on the NTBP surface by chemical (sample NTBP_PPy_Chem) and electrochemical (sample NTBP_PPy_Elect) polymerization. The morphology and functional composition of individual and hybrid materials were investigated by microscopic and spectroscopic methods. It was obtained that the deposition method and presence of NTBP affects the polymer morphology. It was shown that PPy chemical deposition leads to the precipitation of a large amount of an amorphous polymer on a buckypaper surface. At the same time electrochemical deposition method promotes the synthesis of uniform polymer layers. In the second case, the mass of the precipitated polymer is smaller. It was found that both deposition methods are suitable for the polypyrrole deposition and can increase the buckypaper capacity almost twice. The material long cycling showed that the NTBP_PPy_Elect sample has the greatest stability. Thus, in this study, the relationship between morphology, functional composition and electrochemical properties of materials was studied. It was shown that the synthesis method allows controlling the morphology and/or functional composition of the materials. Also it was demonstrated that the synthesized structures are promising for use as supercapacitor electrodes due to the high specific capacitance and stability.
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