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- 2019
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Journal article (peer-reviewed)
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| 2. |
- Mogensen, Ronnie, et al.
(author)
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Evolution of the solid electrolyte interphase on tin phosphide anodes in sodium ion batteries probed by hard x-ray photoelectron spectroscopy
- 2017
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In: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 245, s. 696-704
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Journal article (peer-reviewed)abstract
- In this work the high capacity anode material Sn4P3 for sodium ion batteries is investigated by electrochemical cycling and synchrotron-based hard x-ray photoelectron spectroscopy (HAXPES) in order to elucidate the solid electrolyte interphase (SEI) properties during the first 1.5 cycles. The electrochemical properties of tin phosphide (Sn4P3) when used as an anode material are first established in half cells versus metallic sodium in a 1 M NaFSI in EC: DEC electrolyte including 5 vol% FEC as SEI forming additive. The data from these experiments are then used to select the parameters for the samples to be analysed by HAXPES. A concise series of five cycled samples, as well as a soaked and pristine sample, were measured at different states of sodiation after the initial sodiation and after the following full cycle of sodiation and desodiation. Our results indicate that the SEI is not fully stable, as both significant thickness and composition changes are detected during cell cycling. (C) 2017 Elsevier Ltd. All rights reserved.
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| 3. |
- Hamann, Dathan, et al.
(author)
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Jewellery : alloy composition and release of nickel, cobalt and lead assessed with the EU synthetic sweat method
- 2015
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In: Contact Dermatitis. - : Wiley. - 0105-1873 .- 1600-0536. ; 73:4, s. 231-238
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Journal article (peer-reviewed)abstract
- Background. Several studies have shown nickel and cobalt release from jewellery by using spot tests, but the metal composition of jewellery is largely unknown. Objectives. To evaluate the metal composition of a large worldwide sample of mainly inexpensive jewellery items, and investigate the release of nickel, cobalt and lead from a subsample by using EN 1811: 1998-required methods. Methods. A total of 956 metallic jewellery components were examined with X-ray fluorescence spectroscopy. A subsample of 96 jewellery items purchased in the United States were investigated for nickel, cobalt and lead release by the use of artificial sweat immersion and plasma optical emission spectroscopy. Results. Eighteen elements were detected. The 10 most frequently occurring were, in order of frequency, copper, iron, zinc, nickel, silver, chromium, tin, manganese, lead, and cobalt. Release of nickelwas noted from 79 of the 96 US samples (0.01-98 mu g/cm(2)/week), release of cobalt from 35 samples (0.02-0.5 mu g/cm(2)/week), and release of lead from 37 samples (0.03-2718 mu g/cm(2)/week). Conclusions. We present here a comprehensive list of the most frequently encountered metals in jewellery and fashion accessories. Different allergenic and non-allergenic metals are utilized. We also report the frequent release of nickel, cobalt and lead from these objects, despite legislative restrictions.
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| 4. |
- Jeschull, Fabian, et al.
(author)
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Solid Electrolyte Interphase (SEI) of Water-Processed Graphite Electrodes Examined in a 65 mAh Full Cell Configuration
- 2018
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:10, s. 5176-5188
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Journal article (peer-reviewed)abstract
- Electrode binders, such as sodium carboxymethyl cellulose (CMC-Na), styrene–butadiene rubber (SBR) and poly(sodium acrylate) (PAA-Na) are commonly applied binder materials for the manufacture of electrodes from aqueous slurries. Their processability in water has considerable advantages over slurries based on N-methylpyrrolidone (NMP) considering toxicity, environment and production costs. In this study, water-processed graphite electrodes containing either CMC-Na:SBR, PAA-Na, or CMC-Na:PAA-Na as binders have been prepared on a pilot scale, cycled in graphite||LiFePO4 Li-ion battery cells and analyzed post-mortem with respect to the binder impact on the SEI composition, using in-house (1486.6 eV) and synchrotron-based (2300 eV) photoelectron spectroscopy (PES). The estimated SEI layer thickness was smaller than 11 nm for all samples and decreased in the order: PAA-Na > CMC-Na:SBR > CMC-Na:PAA-Na. The SEI thickness correlates with the surface concentration of CMC-Na, for example, the CMC-Na:PAA-Na mixture showed signs of polymer depletion of the PAA-Na component. The SEI layer components are largely comparable to those formed on a conventional graphite:poly(vinylidene difluoride) (PVdF) electrode. However, the SEI is complemented, by notable amounts of carboxylates and alkoxides, whose formation is favored in water-based negative electrodes. Additionally, more electrolyte salt degradation is observed in formulations comprising PAA-Na. The choice of the binder for the negative electrode had little impact on the surface layer formed on the LiFePO4 positive electrode, except for different contents of sodium salt deposits, as a result of ion migration from the counter electrode.
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| 5. |
- Naylor, Andrew J., et al.
(author)
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Depth-dependent oxygen redox activity in lithium-rich layered oxide cathodes
- 2019
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488. ; 7:44, s. 25355-25368
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Journal article (peer-reviewed)abstract
- Lithium-rich materials, such as Li1.2Ni0.2Mn0.6O2, exhibit capacities not limited by transition metal redox, through the reversible oxidation of oxide anions. Here we offer detailed insight into the degree of oxygen redox as a function of depth within the material as it is charged and cycled. Energy-tuned photoelectron spectroscopy is used as a powerful, yet highly sensitive technique to probe electronic states of oxygen and transition metals from the top few nanometers at the near-surface through to the bulk of the particles. Two discrete oxygen species are identified, On− and O2−, where n < 2, confirming our previous model that oxidation generates localised hole states on O upon charging. This is in contrast to the oxygen redox inactive high voltage spinel LiNi0.5Mn1.5O4, for which no On− species is detected. The depth profile results demonstrate a concentration gradient exists for On− from the surface through to the bulk, indicating a preferential surface oxidation of the layered oxide particles. This is highly consistent with the already well-established core–shell model for such materials. Ab initio calculations reaffirm the electronic structure differences observed experimentally between the surface and bulk, while modelling of delithiated structures shows good agreement between experimental and calculated binding energies for On−.
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| 6. |
- Ojwang, Dickson O., et al.
(author)
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Moisture-Driven Degradation Pathways in Prussian White Cathode Material for Sodium-Ion Batteries
- 2021
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:8, s. 10054-10063
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Journal article (peer-reviewed)abstract
- The high-theoretical-capacity (∼170 mAh/g) Prussian white (PW), NaxFe[Fe(CN)6]y·nH2O, is one of the most promising candidates for Na-ion batteries on the cusp of commercialization. However, it has limitations such as high variability of reported stable practical capacity and cycling stability. A key factor that has been identified to affect the performance of PW is water content in the structure. However, the impact of airborne moisture exposure on the electrochemical performance of PW and the chemical mechanisms leading to performance decay have not yet been explored. Herein, we for the first time systematically studied the influence of humidity on the structural and electrochemical properties of monoclinic hydrated (M-PW) and rhombohedral dehydrated (R-PW) Prussian white. It is identified that moisture-driven capacity fading proceeds via two steps, first by sodium from the bulk material reacting with moisture at the surface to form sodium hydroxide and partial oxidation of Fe2+ to Fe3+. The sodium hydroxide creates a basic environment at the surface of the PW particles, leading to decomposition to Na4[Fe(CN)6] and iron oxides. Although the first process leads to loss of capacity, which can be reversed, the second stage of degradation is irreversible. Over time, both processes lead to the formation of a passivating surface layer, which prevents both reversible and irreversible capacity losses. This study thus presents a significant step toward understanding the large performance variations presented in the literature for PW. From this study, strategies aimed at limiting moisture-driven degradation can be designed and their efficacy assessed.
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| 7. |
- Schäfer, David, et al.
(author)
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Multiscale Investigation of Sodium-Ion Battery Anodes: Analytical Techniques and Applications
- 2024
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In: Advanced Energy Materials. - 1614-6840 .- 1614-6832. ; 14:15
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Journal article (peer-reviewed)abstract
- The anode/electrolyte interface behavior, and by extension, the overall cell performance of sodium-ion batteries is determined by a complex interaction of processes that occur at all components of the electrochemical cell across a wide range of size- and timescales. Single-scale studies may provide incomplete insights, as they cannot capture the full picture of this complex and intertwined behavior. Broad, multiscale studies are essential to elucidate these processes. Within this perspectives article, several analytical and theoretical techniques are introduced, and described how they can be combined to provide a more complete and comprehensive understanding of sodium-ion battery (SIB) performance throughout its lifetime, with a special focus on the interfaces of hard carbon anodes. These methods target various length- and time scales, ranging from micro to nano, from cell level to atomistic structures, and account for a broad spectrum of physical and (electro)chemical characteristics. Specifically, how mass spectrometric, microscopic, spectroscopic, electrochemical, thermodynamic, and physical methods can be employed to obtain the various types of information required to understand battery behavior will be explored. Ways are then discussed how these methods can be coupled together in order to elucidate the multiscale phenomena at the anode interface and develop a holistic understanding of their relationship to overall sodium-ion battery function.
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