| 1. |
- Westman, Kasper, 1990, et al.
(författare)
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Diglyme based electrolytes for sodium-ion batteries
- 2018
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:6, s. 2671-2680
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Tidskriftsartikel (refereegranskat)abstract
- Sodium-ion batteries (SIBs) are currently being considered for large-scale energy storage. Optimization of SIB electrolytes is, however, still largely lacking. Here we exhaustively evaluate NaPF6 in diglyme as an electrolyte of choice, via both physicochemical properties and extensive electrochemical tests including half as well as full cells. Fundamentally, the ionic conductivity is found to be quite comparable to carbonate based electrolytes and to obey the fractional Walden rule with viscosity. We find Na metal to work well as a reference electrode and the electrochemical stability, evaluated potentiostatically for various electrodes and corroborated by DFT calculations, to be satisfactory in the entire voltage range 0-4.4 V. Galvanostatic cycling at C/10 of half and full cells using Na3V2(PO4)(3) (NVP) or Na3V2(PO4)(2)F-3 (NVPF) as cathodes and hard carbon (HC) as anodes indicates rapid capacity fading in cells with HC anodes, possibly originating in a lack of a stable SEI or by trapping of sodium. Aiming to understand this capacity fade further, we conducted a GC/MS analysis to determine electrolyte reduction products and to propose reduction pathways, concluding that oligomer and/or alkoxide formation is possible. Overall, the promising results should warrant further investigations of diglyme based electrolytes for modern SIB development, albeit avoiding HC anodes.
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| 2. |
- Jankowski, Piotr, 1990, et al.
(författare)
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Chemically soft solid electrolyte interphase forming additives for lithium-ion batteries
- 2018
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 6:45, s. 22609-22618
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Tidskriftsartikel (refereegranskat)abstract
- The solid electrolyte interphase (SEI) layer is a key element of lithium-ion batteries (LIBs) enabling stable operation and significantly affecting the cycling performance including life-length. Here we present the concept of chemically soft SEI-forming additives, created by introducing aromatic ring based derivatives of already well-known SEI-formers to render them chemically soft, resulting in 1,3,2-benzodioxathiole 2,2-dioxide (DTDPh), 3H-1,2-benzoxathiole 2,2-dioxide (PSPh), and 1,4,2-benzodioxathiine 2,2-dioxide (PSOPh). A computational DFT based comparison predicts promise with respect to both early and controlled reduction processes. These predictions are verified by basic electrochemical studies targeting appropriate additive reduction potentials i.e. prior to any electrolyte solvent or salt decomposition. In addition, the decomposition paths of the SEI-formers are projected and the end products compared with spectroscopic data for the SEI-layers formed in LIB cells. The SEI-layers formed finally show very good properties in terms of improved capacity retention, improved coulombic efficiency, and reduced resistance for the graphite/electrolyte/LFP full cells made, especially observed for PSOPh. That is due to the preferred C-O bond breaking mechanism, observed also for DTDPh, and supported by the S-C bond breaking mechanism, together resulting in well conductive and good adhesion properties of the SEI-layers. This is expedited by higher softness, eventuating in a formation process stabilizing some of the radicals and/or lowering the kinetic barriers. These positive effects are confirmed both when applying a commercial style electrolyte and for a new generation electrolyte based on the LiTDI salt, where suppression of the TDI anion reduction is truly crucial.
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| 3. |
- Jankowski, Piotr, 1990, et al.
(författare)
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Impact of Sulfur-Containing Additives on Lithium-Ion Battery Performance: From Computational Predictions to Full-Cell Assessments
- 2018
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1, s. 2582-2591
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Tidskriftsartikel (refereegranskat)abstract
- Electrolyte additives are pivotal for stabilization of lithium-ion batteries, by suppressing capacity loss through creation of an engineered solid-electrolyte-interphase-layer (SEI-layer) at the negative electrode and thereby increasing lifetime. Here, we compare four different sulfur-containing 5-membered-ring molecules as SEI-formers: 1,3,2-dioxathiolane-2,2-dioxide (DTD), propane-1,3-sultone (PS), sulfopropionic acid anhydride (SPA), and prop-1-ene-1,3-sultone (PES). Density functional theory calculations and electrochemical measurements both confirm appropriate reduction potentials. For a connection of the protective properties of the SEIs formed to the chemical structure of the additives, the decomposition paths are computed and compared with spectroscopic data for the negative electrode surface. The performance of full-cells cycled using a commercial electrolyte and the different additives reveals the formation of organic dianions to play a crucial beneficial role, more so for DTD and SPA than for PS and PES.
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| 4. |
- Jankowski, Piotr, 1990, et al.
(författare)
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New boron based salts for lithium-ion batteries using conjugated ligands
- 2016
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 18:24, s. 16274-16280
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Tidskriftsartikel (refereegranskat)abstract
- A new anion design concept, based on combining a boron atom as the central atom and conjugated systems as ligands, is presented as a route for finding alternative Li-salts for lithium-ion batteries. The properties of a wide range of novel anions designed in this way have been evaluated by DFT calculations focusing on three different fundamental success factors/measures: the strength of the cation-anion interaction, ultimately determining both the solubility and the ionic conductivity, the oxidation limit, determining their possible use vs. high voltage cathodes, and the reduction stability, revealing a possible role of the anion in the SEI-formation at the anode. For a few anions superior properties vs. today's existing or suggested anions are predicted, especially the very low cation-anion interaction strengths are promising features. The design route itself is shown to be versatile in determining the correlation between different choices of ligands and the resulting overall properties - where the most striking feature is the decreased lithium cation interaction energy upon using the (1Z,3Z)-buta-1,3-diene-1,2,3,4-tetracarbonitrile ligands. This also opens avenues for the further design of novel anions beyond those with a boron central atom.
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| 5. |
- Jankowski, Piotr, 1990, et al.
(författare)
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SEI-forming Electrolyte Additives for Lithium-ion Batteries: Development and Benchmarking of Computational Approaches
- 2017
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Ingår i: Journal of Molecular Modeling. - : Springer Science and Business Media LLC. - 0948-5023 .- 1610-2940. ; 23:1
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Tidskriftsartikel (refereegranskat)abstract
- SEI-forming additives play an important role in lithium-ion batteries, and the key to improving battery functionality is to determine if, how, and when these additives are reduced. Here, we tested a number of computational approaches and methods to determine the best way to predict and describe the properties of the additives. A wide selection of factors were evaluated, including the influences of the solvent and lithium cation as well as the DFT functional and basis set used. An optimized computational methodology was employed to assess the usefulness of different descriptors.
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| 6. |
- Jankowski, Piotr, 1990, et al.
(författare)
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TFSI and TDI Anions: Probes for Solvate Ionic Liquid and Disproportionation-Based Lithium Battery Electrolytes
- 2017
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 8:15, s. 3678-3682
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Tidskriftsartikel (refereegranskat)abstract
- Highly concentrated electrolytes based on Li-salts and chelating solvents, such as glymes, are promising as electrolytes for lithium batteries. This is due to their unique properties, such as higher electrochemical stabilities, compliance with high-voltage electrodes, low volatility and flammability, and inertness toward aluminum current collector corrosion. The nature of these properties originates from the molecular-level structure created in either solvate ionic liquids (Sits) or the less common ionic aggregates by disproportionation reactions. The nature of the anion plays a crucial role, and here, we present a computational study using TFSI and TDI anions as probes, revealing increasing differences upon increased salt concentration. TFSI-based electrolytes preferably form SILs, while TDI-based electrolytes form ionic aggregates. The latter lead to an unexpected creation of "free" cationic species even at (very) high salt concentrations and thus promise of ample lithium ion transport.
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| 7. |
- Jankowski, Piotr, 1990, et al.
(författare)
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Understanding of Lithium 4,5-Dicyanoimidazolate-Poly(ethylene oxide) System: Influence of the Architecture of the Solid Phase on the Conductivity
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:41, s. 23358-23367
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Tidskriftsartikel (refereegranskat)abstract
- Solid polymer electrolytes (SPEs) with high lithium conductivity are very beneficial as a safe material for lithium battery applications. Herein we present new set of a SPEs based on lithium 2-trifluoromethyl-4,5-dicyanoimidazolate (LiTDI) with wide range of ether oxygen to lithium molar ratios. The phase composition was characterized in detail with thermal, diffraction, and spectroscopic techniques, and its influence on conductivity behavior was examined. Two detected crystalline phases of LiTDI poly(ethylene oxide) (PEO) were simulated with computational methods. The obtained results allowed insight into the structure of these electrolytes and helped us to understand on the molecular level factors influencing electrochemical properties and phase behavior. It was shown that ability to form a low-melting phase can be used to lower the temperature window of operation. That made it possible to keep such SPEs amorphous at 30 degrees C during 80 days. The thermal stability of the samples was checked to prove the safety of the electrolytes.
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