| 1. |
- Fredi, Giulia, et al.
(author)
-
Graphitic microstructure and performance of carbon fibre Li-ion structural battery electrodes
- 2018
-
In: Multifunctional Materials. - : IOP Publishing. - 2399-7532. ; 1:1
-
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- Carbon fibres (CFs), originally made for use in structural composites, have also been demonstrated as high capacity Li-ion battery negative electrodes.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.
|
|
| 2. |
- Cznotka, E., et al.
(author)
-
3D laser scanning confocal microscopy of siloxane-based comb and double-comb polymers in PVDF-HFP thin films
- 2016
-
In: Journal of Coatings Technology Research. - : Springer Science and Business Media LLC. - 1935-3804 .- 1547-0091. ; 13:4, s. 577-587
-
Journal article (peer-reviewed)abstract
- Currently, atomic force microscopy is the preferred technique to determine roughness on membrane surfaces. In this paper, a new method to measure surface roughness is presented using a 3D laser scanning confocal microscope for high-resolution topographic analysis and is compared to conventional SEM. For this study, the surfaces of eight samples based on a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) host polymer with different liquid interpenetrating components were analyzed. Polymethylhydrosiloxane, triethylene glycolallylmethyether, (3,3,3-trifluoropropyl) methylcyclotrisiloxane (D-3-C2H4CF3), polysiloxane-comb-propyloxymethoxytriglycol (PSx), poly-siloxane-comb-propyl-3,3,3-trifluoro (PSx-C2H4CF3), poly [bis(2-(2-methoxyethoxy) ethoxy) phosphazene, or poly [bis(trifluoro) ethoxy] phosphazene was chosen as interpenetrating compound to investigate the impact of comb and double-comb-structured polymer backbones, as well as their dipolar or fluorous residues on the PVDF-HFP-miscibility. Different phases of the constituting ingredients were identified via their thermal properties determined by DSC. Additionally, the COSMO-RS method supported the experimental results, and with regard to computed sigma-profiles, new modified structures for polysiloxane and polyphosphazene synthesis were suggested.
|
|
| 3. |
- Cznotka, E., et al.
(author)
-
Characterization of semi-interpenetrating polymer electrolytes containing poly(vinylidene fluoride-co-hexafluoropropylene) and ether-modified polysiloxane
- 2016
-
In: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 289, s. 35-47
-
Journal article (peer-reviewed)abstract
- This work presents a detailed study of a semi-interpenetrating polymer network (semi-IPN) consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polysiloxane-comb-propyl(triethylene oxide) (PSx) and lithium bis(trifluoromethane)sulfonimide (LiTFSI) prepared by a solution casting technique. According to differential scanning calorimetry (DSC), formation of the PVDF-HFPs crystalline phase is inhibited by the PSx which results in a significant improvement of tensile strain. A homogeneous distribution of PVDF-HFP and PSx in the membrane is analyzed using micro-FTIR mapping. Since no peak-shift due to mixing of PVDF-HFP and PSx was observed in FTIR second derivative analysis, computational models were applied to investigate the intermolecular interactions between the constituting domains of different polarity. An influence of PVDF-HFP on the Li+ transport in the ion-conducting PSx was determined by calculating the effective conductivities. The highest ionic conductivity of 7.7 × 10- 5 S cm- 1 at room temperature was reached with 15 wt.% LiTFSI. The electrochemical stability window ranges from 0.5 V to 4.6 V vs. Li/Li+ reference electrode.
|
|
| 4. |
- Cznotka, E., et al.
(author)
-
Highly-fluorous pyrazolide-based lithium salt in PVDF-HFP as solid polymer electrolyte
- 2016
-
In: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 292, s. 45-51
-
Journal article (peer-reviewed)abstract
- For the first time, the concept of fluorophilicity f(i) is adapted to the development of a novel solid polymer electrolyte (SPE) by computationally evaluating a new class of lithium salts, the perfluoroalkylated pyrazolides. An SPE consisting solely of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and different concentrations of highly-fluorous lithium [5-(perfluorobutyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl] trifluoroborate (LiPFAPB14) is reported. Membranes with a salt concentration up to 80 wt.% are prepared and are investigated by 3D laser scanning confocal microscopy, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) concerning the correlation between the LiPFAPB14 salt concentrations with the miscibility in PVDF-HFP. Membrane performances as SPE are evaluated by impedance spectroscopy revealing ionic conductivities of 1.4 x 10(-4) S cm(-1) at 90 degrees C with 80 wt.% LiPFAPB14.
|
|
| 5. |
- Drvarič Talian, Sara, et al.
(author)
-
Fluorinated Ether Based Electrolyte for High-Energy Lithium-Sulfur Batteries: Li+ Solvation Role behind Reduced Polysulfide Solubility
- 2017
-
In: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 29:23, s. 10037-10044
-
Journal article (peer-reviewed)abstract
- By employing new electrolytes, the polysulfide shuttle phenomenon, one of the main problems of lithium-sulfur (Li-S) batteries, can be significantly reduced. Here we present excellent Coulombic efficiencies as well as adequate performance of high-energy Li-S cells by the use of a fluorinated ether (TFEE) based electrolyte at low electrolyte loading. The observed altered discharge profile was investigated both by electrochemical experiments and an especially tailored COSMO-RS computational approach, while the details of the discharge mechanism were elucidated by two operando techniques: XANES and UV-vis spectroscopy. A significant decrease of polysulfide solubility compared to tetraglyme is due to different Li+ solvation mode.
|
|
| 6. |
- Flores, Eibar, 1990, et al.
(author)
-
Solvation structure in dilute to highly concentrated electrolytes for lithium-ion and sodium-ion batteries
- 2017
-
In: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 233, s. 134-141
-
Journal article (peer-reviewed)abstract
- The solvation structure of several lithium and sodium based electrolytes are explored as a function of salt concentration over a wide range via a detailed PM7 computational study. The cation coordination shells are found to be well-defined and solvent rich for dilute electrolytes, while disordered and anion rich for the more concentrated electrolytes. The Na-based electrolytes display larger cation coordination shells with a more pronounced presence of fluorine as compared to the Li-based electrolytes. The origins of the structural differences are discussed as well as their consequences for properties of battery electrolytes and battery usage-especially targeting the current large interest in highly concentrated electrolytes.
|
|
| 7. |
- Jeschke, Steffen, 1986, et al.
(author)
-
Catching TFSI: A Computational–Experimental Approach to β-Cyclodextrin-Based Host–Guest Systems as electrolytes for Li-Ion Batteries
- 2018
-
In: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 11:12, s. 1942-1949
-
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.
|
|
| 8. |
- Jeschke, Steffen, 1986, et al.
(author)
-
Predicting the Solubility of Sulfur: A COSMO-RS-Based Approach to Investigate Electrolytes for Li-S Batteries
- 2017
-
In: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 23:38, s. 9130-9136
-
Journal article (peer-reviewed)abstract
- Lithium-sulfur (Li-S) batteries are, in theory, considering their basic reactions, very promising from a specific energy density point of view, but have poor power rate capabilities. The dissolution of sulfur from the C/S cathode in the electrolyte is a rate-determining and crucial step for the functionality. To date, time-consuming experimental methods, such as HPLC/UV, have been used to quantify the corresponding solubilities. Here, we use a computational fluid-phase thermodynamics approach, the conductor-like screening model for real solvents (COSMO-RS), to compute the solubilities of sulfur in different binary and ternary electrolytes. By using both explicit and implicit solvation approaches for lithium bistrifluoromethanesulfonimidate (LiTFSI)-containing electrolytes, a deviation of
|
|
| 9. |
- Jeschke, Steffen, 1986, et al.
(author)
-
Supervised Machine Learning-Based Classification of Li-S Battery Electrolytes
- 2021
-
In: Batteries and Supercaps. - : Wiley. - 2566-6223. ; 4:7, s. 1156-1162
-
Journal article (peer-reviewed)abstract
- Machine learning (ML) approaches have the potential to create a paradigm shift in science, especially for multi-variable problems at different levels. Modern battery R&D is an area intrinsically dependent on proper understanding of many different molecular level phenomena and processes alongside evaluation of application level performance: energy, power, efficiency, life-length, etc. One very promising battery technology is Li-S batteries, but the polysulfide solubility in the electrolyte must be managed. Today, many different electrolyte compositions and concepts are evaluated, but often in a more or less trial-and-error fashion. Herein, we show how supervised ML can be applied to accurately classify different Li-S battery electrolytes a priori based on predicting polysulfide solubility. The developed framework is a combined density functional theory (DFT) and statistical mechanics (COSMO-RS) based quantitative structure-property relationship (QSPR) model which easily can be extended to other battery technologies and electrolyte properties.
|
|
| 10. |
- Kerner, Manfred, 1984, et al.
(author)
-
Towards more thermally stable Li-ion battery electrolytes with salts and solvents sharing nitrile functionality
- 2016
-
In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 332, s. 204-212
-
Journal article (peer-reviewed)abstract
- The overall safety of Li-ion batteries is compromised by the state-of-the-art electrolytes; the thermally unstable lithium salt, lithium hexafluorophosphate (LiPF6), and flammable carbonate solvent mixtures. The problem is best addressed by new electrolyte compositions with thermally robust salts in low flammability solvents. In this work we introduce electrolytes with either of two lithium nitrile salts, lithium 4,5-dicyano-1,2,3-triazolate (LiDCTA) or lithium 4,5-dicyano-2-trifluoromethylimidazolide (LiTDI), in solvent mixtures with high flashpoint adiponitrile (ADN), as the main component. With sulfolane (SL) and ethylene carbonate (EC) as co-solvents the liquid temperature range of the electrolytes are extended to lower temperatures without lowering the flashpoint, but at the expense of high viscosities and moderate ionic conductivities. The anodic stabilities of the electrolytes are sufficient for LiFePO4 cathodes and can be charged/discharged for 20 cycles in Li/LiFePO4 cells with coulombic efficiencies exceeding 99% at best. The excellent thermal stabilities of the electrolytes with the solvent combination ADN:SL are promising for future electrochemical investigations at elevated temperatures (> 60 degrees C) to compensate the moderate transport properties and rate capability. The electrolytes with EC as a co-solvent, however, release CO2 by decomposition of EC in presence of a lithium salt, which potentially makes EC unsuitable for any application targeting higher operating temperatures.
|
|
