| 1. |
- Chábera, Pavel, et al.
(författare)
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A low-spin Fe(iii) complex with 100-ps ligand-to-metal charge transfer photoluminescence
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 543:7647, s. 695-699
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Tidskriftsartikel (refereegranskat)abstract
- Transition-metal complexes are used as photosensitizers1, in light-emitting diodes, for biosensing and in photocatalysis2. A key feature in these applications is excitation from the ground state to a charge-transfer state3,4; the long charge-transfer-state lifetimes typical for complexes of ruthenium5 and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron6 and copper7 being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs6,8,9,10, it remains a formidable scientific challenge11 to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered12 photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers13,14,15. Here we present the iron complex [Fe(btz)3]3+ (where btz is 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(iii) d5 complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (2LMCT) state that is rarely seen for transition-metal complexes4,16,17. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.
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| 2. |
- Sobkowiak, Adam, et al.
(författare)
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Identification of an Intermediate Phase, Li1/2FeSO4F, Formed during Electrochemical Cycling of Tavorite LiFeSO4F
- 2014
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 26:15, s. 4620-4628
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Tidskriftsartikel (refereegranskat)abstract
- Many compounds adopting the tavorite-type crystal structure have attracted considerable attention as cathode materials for lithium ion batteries due to the favorable structural characteristics, facilitating promising electrochemical performance. Recent reports have highlighted the complex mechanism of lithium insertion/extraction in some of these compounds, such as the stabilization of intermediate phases in the LiFeSO4OH and LiVPO4F systems. In the case of tavorite LiFeSO4F, reported density functional theory (DFT) calculations have suggested the possibility of a similar behavior, but thus far, no experimental verification of such a process has, to the best of our knowledge, been successfully demonstrated. In this work, we investigate the structural evolution of LiFeSO4F upon extraction/insertion of lithium ions from/into the host framework. By thorough ex situ characterizations of chemically and electrochemically prepared LixFeSO4F-samples (0 ≤ x ≤ 1), we demonstrate the stabilization of an intermediate phase, Li1/2FeSO4F, for which one possible structural model is proposed. However, results indicating charge ordering on the iron-sites, suggesting the formation of a super structure with a larger unit cell, are also highlighted. Moreover, the degree of formation of Li1/2FeSO4F is shown to be highly dependent on the rate of lithium extraction as a result of an exceptionally small potential separation (similar to 15 mV during charging) of the two subsequently occurring biphasic processes, LiFeSO4F/Li1/2FeSO4F and Li1/2FeSO4F/FeSO4F. Finally, the intermediate phase is shown to be formed both on charge and discharge during battery cycling, even though an apparent asymmetrical electrochemical trace suggests the contrary.
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| 3. |
- JOHANSSON, DAVID, et al.
(författare)
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Nanoplasmonic sensing of Pb-acid and Li-ion batteries
- 2016
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Ingår i: Presented at the 2nd International Conference on Sensors and Electronic Instrumental Advances (SEIA), Barcelona, Spain, September 22 – 23, 2016. - : INT FREQUENCY SENSOR ASSOC-IFSA. ; , s. 57-59, s. 57-59
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Konferensbidrag (refereegranskat)abstract
- The increasing sophistication and performance of batteries are connected with more complex chemical and physical battery processes and increase the need of more direct and informative measurements, both in the R&D phase and for monitoring and control during operation of vehicles. Todays potentiometric based measurement sensors are not sufficiently accurate for optimal battery sensing. To avoid the built in wide safety margins new, more informative monitoring signals are therefore desired or needed. In this study the optical technology NanoPlasmonic Sensing (NPS) has been used to in-situ monitor the charge and discharge processes of lead-acid and Li-ion batteries. The optical signals were found to correlate well with charging/discharging of both battery technologies.
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| 4. |
- Sobkowiak, Adam, et al.
(författare)
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Hydrogen absorption and desorption properties of a novel ScNiAl alloy
- 2011
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 104:1, s. 235-238
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Tidskriftsartikel (refereegranskat)abstract
- A new hydrogen absorbing material has been discovered, ScNiAl, which can store 1.5 wt.% hydrogen reversibly. In this compound, hydrogen absorption is a two-step process; solid solution of hydrogen at temperatures below 180A degrees C and decomposition into ScH2 and NiAl at higher temperatures. Detailed analysis of the hydrogen absorption/desorption has been performed using in situ synchrotron radiation powder X-ray diffraction and thermal desorption spectroscopy. The apparent activation energy for hydrogen desorption was determined to be 182 kJ/mol and the material is stable during cycling.
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| 5. |
- Guerrini, Niccolo, et al.
(författare)
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Charging Mechanism of Li2MnO3
- 2020
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 32:9, s. 3733-3740
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Tidskriftsartikel (refereegranskat)abstract
- Operando mass spectroscopy demonstrates quantitatively that lithium extraction from Li2MnO3 is charge compensated by oxygen loss (O-loss) not oxidation of oxide ions that are retained within the structural framework (O-redox). This fact is confirmed by X-ray absorption and emission spectroscopy. Li NMR shows that the two-phase core-shell structure, which forms on charging, is composed of an intact Li2MnO3 core and a highly disordered shell containing no Li, with a composition close to MnO2. Discharge involves Li insertion into the disordered shell. CO2 and O-2 are detected on charging at 15 mA g(-1), whereas charging by galvanostatic intermittent titration technique (GITT) forms only CO2; an observation in agreement with the previously described model of oxygen evolution from high-voltage cathodes producing singlet O-2 that reacts with the electrolyte forming CO2. The dominance of oxygen evolution over O-redox is in accordance with the model of O-loss occurring when the oxide ions are undercoordinated; O in the shell devoid of Li is coordinated by only 2 Mn.
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| 6. |
- Mindemark, Jonas, et al.
(författare)
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Mechanical Stabilization of Solid Polymer Electrolytes through Gamma Irradiation
- 2016
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Konferensbidrag (refereegranskat)abstract
- Recent research efforts into solid polymer electrolytes (SPEs) beyond the polyether paradigm have broadened the research field with new materials that offer improvements in performance as well as opportunities for tailoring materials for specific applications. In particular materials based on polycarbonates and polyesters have shown to fulfil this promise, as shown for systems based on both the poly(ethylene carbonate) [1,2] and the poly(trimethylene carbonate) [3,4] backbone structures. This has ultimately led to the development of SPEs that can be used in Li batteries operational at room temperature. [1,4] Since ion conduction in these materials – at least at moderate salt concentrations – is coupled to the polymer chain dynamics, the performance of these electrolytes is inherently a compromise between mechanics and ion dynamics. While this is not necessarily an issue at room temperature, it becomes notable at elevated temperatures and we have observed migration of the electrolyte during long-term battery operation under such conditions, ultimately leading to failure of the electrolyte membrane to act as a separator between the electrodes with concomitant battery failure. A solution to this is to chemically crosslink the material in order to stabilize it mechanically. For the poly(ε-caprolactone-co-trimethylene carbonate) host material we have already successfully used in high-performance Li battery cells, [4] this can be done through γ-irradiation. [5] Here, we have explored this treatment in the context of SPEs and show the effects of γ-irradiation on the mechanical properties, ionic conductivity and battery cell performance at room temperature and beyond. Figure 1. Viscoelastic properties (left) and ionic conductivity (right) of pristine and γ-irradiated SPEs. References[1] K. Kimura, M. Yajima, Y. Tominaga, Electrochem. Commun. 66 (2016) 46-48.[2] M. D. Konieczynska, X. Lin, H. Zhang, M. W. Grinstaff, ACS Macro Lett. 4 (2015) 533-537.[3] J. Mindemark, B. Sun, D. Brandell, Polym. Chem. 6 (2015) 4766-4774.[4] J. Mindemark, B. Sun, E. Törmä, D. Brandell, J. Power Sources 298 (2015) 166-170.[5] E. Bat, J. A. Plantinga, M. C. Harmsen, M. J. A. van Luyn, Z. Zhang, D. W. Grijpma, J. Feijen, Biomacromolecules 9 (2008) 3208–3215
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| 7. |
- Mindemark, Jonas, et al.
(författare)
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Mechanical Stabilization of Solid Polymer Electrolytes through Gamma Irradiation
- 2017
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Ingår i: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 230, s. 189-195
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Tidskriftsartikel (refereegranskat)abstract
- Attaining sufficient mechanical stability is a challenge for high-performance solid polymer electrolytes, particularly at elevated temperatures. We have here characterized the viscoelastic properties of the nonpolyether host material poly(epsilon-caprolactone-co-trimethylene carbonate) with and without incorporated LiTFSI salt. While this electrolyte material performs well at room temperature, at 80 degrees C the material is prone to viscous flow. Through gamma-irradiation at a dose of 25 kGy, the material stabilizes such that it behaves as a rubbery solid even at low rates of deformation while retaining a high ionic conductivity necessary for use in solid-state Li batteries. The performance of the irradiated electrolyte was investigated in Li polymer half-cells (Li vs. LiFePO4) at both 80 degrees C and room temperature. In Contrast with the notably stable battery performance at low temperatures using the non-irradiated material, during cycling of the irradiated electrolytes detrimental instabilities were noted at both 80 degrees C and room temperature. The possible effects of both radiation damage to the electrolyte and impaired interfacial contacts due to the crosslinking indicate that a different procedure may be necessary in order to stabilize these electrolytes for use in battery cells capable of stable long-term operation.
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| 8. |
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| 9. |
- Blidberg, Andreas, 1987-, et al.
(författare)
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Identifying the Electrochemical Processes in LiFeSO4F Cathodes for Lithium Ion Batteries
- 2017
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Ingår i: ChemElectroChem. - : Wiley. - 2196-0216. ; 4:8, s. 1896-1907
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The electrochemical performance of tavorite LiFeSO4F can be considerably improved by coating the material with a conducting polymer (poly(3,4-ethylenedioxythiophene); PEDOT). Herein, the mechanisms behind the improved performance are studied systematically by careful electrochemical analysis. It is shown that the PEDOT coating improves the surface reaction kinetics for the Li-ion insertion into LiFeSO4F. For such coated materials no kinetic limitations remain, and a transition from solid state to solution-based diffusion control was observed at 0.6 mA cm−2 (circa C/2). Additionally, the quantity of PEDOT is optimized to balance the weight added by the polymer and the improved electrochemical function. Post mortem analysis shows excellent stability for the LiFeSO4F-PEDOT composite, and maintaining the electronic wiring is the most important factor for stable electrochemical cycling of LiFeSO4F. The insights and the methodology used to determine the rate-controlling steps are readily transferable to other ion-insertion-based electrodes, and the findings are important for the development of improved battery electrodes.
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| 10. |
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