| 1. |
- Asfaw, Habtom D., et al.
(author)
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Boosting the thermal stability of emulsion–templated polymers via sulfonation : an efficient synthetic route to hierarchically porous carbon foams
- 2016
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In: ChemistrySelect. - : Wiley. - 2365-6549. ; 1:4, s. 784-792
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Journal article (peer-reviewed)abstract
- Hierarchically porous carbon foams with specific surface areas exceeding 600 m2 g−1 can be derived from polystyrene foams that are synthesized via water-in-oil emulsion templating. However, most styrene-based polymers lack strong crosslinks and are degraded to volatile products when heated above 400 oC. A common strategy employed to avert depolymerization is to introduce potential crosslinking sites such as sulfonic acids by sulfonating the polymers. This article unravels the thermal and chemical processes leading up to the conversion of sulfonated high internal phase emulsion polystyrenes (polyHIPEs) to sulfur containing carbon foams. During pyrolysis, the sulfonic acid groups (-SO3H) are transformed to sulfone (-C-SO2-C-) and then to thioether (-C−S-C-) crosslinks. These chemical transformations have been monitored using spectroscopic techniques: in situ IR, Raman, X-ray photoelectron and X-ray absorption near edge structure spectroscopy. Based on thermal analyses, the formation of thioether links is associated with increased thermal stability and thus a substantial decrease in volatilization of the polymers.
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| 2. |
- Lacey, Matthew J., et al.
(author)
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The Li-S battery : an investigation of redox shuttle and self-discharge behaviour with LiNO3-containing electrolytes
- 2016
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In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:5, s. 3632-3641
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Journal article (peer-reviewed)abstract
- The polysulfide redox shuttle and self-discharge behaviour of lithium-sulfur (Li-S) cells containing the electrolyte additive LiNO3 has been thoroughly explored by a range of electrochemical and surface analysis techniques on simple Li-S (i.e., not specifically optimised to resist self-discharge) and symmetrical Li-Li cells. Despite the relatively effective passivation of the negative electrode by LiNO3, fully charged cells self-discharged a quarter of their capacity within 3 days, although in the short-term cells can be recharged without any noticeable capacity loss. The processes governing the rate and reversibility of self-discharge in these cells have been investigated and explained in terms of the reactions of polysulfides occurring at both electrodes during idle conditions.
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| 3. |
- Lindgren, Fredrik, et al.
(author)
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A hard X-ray photoelectron spectroscopy study on the solid electrolyte interphase of a lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide based electrolyte for Si-electrodes
- 2016
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 301, s. 105-112
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Journal article (peer-reviewed)abstract
- This report focuses on the relatively new salt, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), and its functionality together with a silicon based composite electrode in a half-cell lithium ion battery context. LiTDI is a promising alternative to the commonly used LiPF6 salt because it does not form HF which can decompose the oxide layer on Si. The formation of a solid electrolyte interphase (SEI) as well as the development of the active Si-particles are investigated during the first electrochemical lithiation and de-lithiation. Characterizations are carried out at different state of charge with scanning electron microscopy (SEM) as well as hard x-ray photoelectron spectroscopy (HAXPES) at two different photon energies. This enables a depth resolved picture of the reaction processes and gives an idea of the chemical buildup of the SEI. The SEI is formed by solvent and LiTDI decomposition products and its composition is similar to SEI formed by other carbonate based electrolytes. The LiTDI salt or its decomposition products are not in itself reactive towards the active Si-material and no unwanted side reactions occurs with the active Si-particles. Despite some decomposition of the LiTDI salt, it is a promising alternative for electrolytes aimed towards Si-based electrodes.
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| 4. |
- Maibach, Julia, et al.
(author)
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Electric potential gradient at the buried interface between Lithium-ion battery electrodes and the SEI observed using photoelectron spectroscopy
- 2016
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In: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 7:10, s. 1775-1780
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Journal article (peer-reviewed)abstract
- The buried interface between the bulk electrode material and the solid electrolyte interphase (SEI) in cycled Li-ion battery anodes is suggested to incorporate an electric potential gradient. This suggestion is based on photoelectron spectroscopy (PES) results from different anode materials that all show relative binding energy shifts between the components of the SEI and the active anode. Implications of this electric potential gradient on binding energy reference points in PES as well as on charge-transfer kinetics in Li-ion batteries are discussed. Specifically, we show that the separation of surface layer and bulk material spectral contributions (depth profiling) is crucial for consistent data interpretation. We conclude that previous interpretations of lithiation as cause for changes in PES spectra may need to be revised.
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| 5. |
- Renman, Viktor, et al.
(author)
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Ni3Sb4O6F6 and Its Electrochemical Behavior toward Lithium-A Combination of Conversion and Alloying Reactions
- 2016
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 28:18, s. 6520-6527
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Journal article (peer-reviewed)abstract
- A group of oxohalides, where Ni3Sb4O6F6 is one example, has been investigated with respect to its electrochemical reactions toward Li+/Li. In situ and ex situ XRD measurements reveal that the original structure collapses and the material becomes amorphous upon insertion of Li at low potentials versus Li+/Li. With continued cycling, a nanocrystalline phase of NiSb, which reacts reversibly with Li, appears and steadily grows more stable. Electrochemical experiments (i.e., chronopotentiometry and cyclic voltammetry) show that multiple reactions of both conversion- and alloying-type are active in the system. High storage capacities are achieved initially but with rapid fading as a consequence of a limited reversibility of the Ni2+/Ni redox process, as shown by X-ray absorption spectroscopy of the first discharge/charge cycle. Stable cycling can be achieved by optimizing the cutoff potentials (i.e., excluding poorly reversible reactions at high and low voltages, respectively), yielding long-term cycling with a practical gravimetric capacity of similar to 200 mAh g(-1).
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