| 1. |
- Fredi, Giulia, et al.
(author)
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Graphitic microstructure and performance of carbon fibre Li-ion structural battery electrodes
- 2018
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In: Multifunctional Materials. - : IOP Publishing. - 2399-7532. ; 1:1
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Journal article (peer-reviewed)abstract
- Carbon fibres (CFs), originally made for use in structural composites, have also been demonstrated as high capacity Li-ion battery negative electrodes. Consequently, CFs can be used as structural electrodes; simultaneously carrying mechanical load and storing electrical energy in multifunctional structural batteries. To date, all CF microstructural designs have been generated to realise a targeted mechanical property, e.g. high strength or stiffness, based on a profound understanding of the relationship between the graphitic microstructure and the mechanical performance. Here we further advance this understanding by linking CF microstructure to the lithium insertion mechanism and the resulting electrochemical capacity. Different PAN-based CFs ranging from intermediate-to highmodulus types with distinct differences in microstructure are characterised in detail by SEM and HRTEMand electrochemical methods. Furthermore, the mechanism of Li-ion intercalation during charge/discharge is studied by in situ confocal Raman spectroscopy on individual CFs. RamanGband analysis reveals a Li-ion intercalation mechanism in the high-modulus fibre reminiscent of that in crystalline graphite. Also, the combination of a relatively low capacity of the high-modulus CFs (ca. 150 mAh g-1) is shown to be due to that the formation of a staged structure is frustrated by an obstructive turbostratic disorder. In contrast, intermediate-modulus CFs, which have significantly higher capacities (ca. 300 mAh g-1), have Raman spectra indicating a Li-ion insertion mechanism closer to that of partly disordered carbons. Based on these findings, CFs with improved multifunctional performance can be realised by tailoring the graphitic order and crystallite sizes.
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| 2. |
- Jeschke, Steffen, 1986, et al.
(author)
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Catching TFSI: A Computational–Experimental Approach to β-Cyclodextrin-Based Host–Guest Systems as electrolytes for Li-Ion Batteries
- 2018
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In: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 11:12, s. 1942-1949
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Journal article (peer-reviewed)abstract
- Cyclodextrins (CDs) are pyranoside-based macromolecules with a hydrophobic cavity to encapsulate small molecules. They are used as molecular vehicles, for instance in pharmaceutical drug delivery or as solubility enhancer of monomers for their polymerization in aqueous solution. In this context, it was discovered about 10 years ago that the bis(trifluoromethylsulonyl)imide (TFSI) anion forms host–guest complexes with βCD in aqueous media. This sparked interest in using the TFSI anion in lithium-based battery electrolytes open for its encapsulation by βCD as an attractive approach to increase the contribution of the cation to the total ion conductivity. By using semi-empirical quantum mechanical (SQM) methods and the conductor-like screening model for a real solvent (COSMO-RS), a randomly methylated βCD (RMβCD) is here identified as a suitable host for TFSI when using organic solvents often used in battery technology. By combining molecular dynamics (MD) simulations with different NMR and FTIR experiments, the formation of the corresponding RMβCD–TFSI complex was investigated. Finally, the effects of the addition RMβCD to a set of electrolytes on the ion conductivity are measured and explained using three distinct scenarios.
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