| 1. |
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| 2. |
- Brandell, Daniel, et al.
(författare)
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Conduction Mechanisms in Crystalline LiPF6·PEO6 Doped with SiF62- and SF6
- 2005
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Ingår i: Chem. Mater. - : American Chemical Society (ACS). ; 17:14, s. 3673-3680
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics (MD) simulations have been made under imposed electric fields for crystalline LiPF6·PEO6, (LiPF6)1-x(Li2SiF6)x·PEO6, and (LiPF6)1-x(SF6)x·PEO6 for x = 0.01 under standard pressure and temperature conditions with the aim of identifying the conduction mechanisms in the systems. Contrary to the results of earlier experimental investigations where only cation mobility was observed, ionic transport is here found to occur in regions between the polymer hemi-helices, with a high transference number (0.9-1.0) for the PF6- anions.
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| 3. |
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| 4. |
- Brandell, Daniel, et al.
(författare)
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Molecular Dynamics simulation of the LiPF6∙PEO6 structure
- 2005
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 15:14, s. 1422-1428
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics (MD) simulations have been performed for the crystalline LiPF6·PEO6 system at ambient temperature in an effort to model the detail of its atomic-level structure and dynamics. Start coordinates were taken from the neutron powder diffraction analysis of Gadjourova et al., Chem. Mater., 2001, 13, 1282 (ref. ). Polymer-chain conformation, Li+-ion coordination and thermal displacement parameters are compared with experimentally determined values; the differences found are rationalised in terms of differences between the infinite-chain models investigated (both experimental and theoretical) and the finite chain-length material studied.
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| 5. |
- Brandell, Daniel, et al.
(författare)
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Molecular dynamics simulations of Li- and Na-Nafion membranes
- 2006
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Ingår i: SPIE--The International Society for Optical Engineering Vol 61680G. ; , s. 61680G-
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Konferensbidrag (refereegranskat)abstract
- Molecular Dynamics (MD) techniques have been used to study the structure and dynamics of hydrated Li- and Na-Nafion membranes. The membranes were generated using a Monte Carlo-approach for Nafion 117 oligomers of Mw = 1100 and with water contents of 7.5 and 20 % by weight, equivalent to 5 and 15 water molecules per sulfonate group, respectively. After equilibration, local structural properties and dynamical features such as coordination, cluster stability, solvation and ion conductivity were studied. In a comparison between the two cationic systems, it is shown that the Na-Nafion system is more sensitive than Li-Nafion to the level of hydration, and also show higher ion conductivity. The ionic conductivity is shown to increase with higher level of hydration.
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| 6. |
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| 7. |
- Brandell, Daniel, et al.
(författare)
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Molecular dynamics studies of the Nafion®, Dow® and Aciplex® fuel-cell polymer membrane systems
- 2007
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Ingår i: Journal of Molecular Modeling. - : Springer Science and Business Media LLC. - 1610-2940 .- 0948-5023. ; 13:10, s. 1039-1046
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Tidskriftsartikel (refereegranskat)abstract
- The Nafion, Dow and Aciplex systems – where the prime differences lies in the side-chain length – have been studied by molecular dynamics (MD) simulation under standard pressure and temperature conditions for two different levels of hydration: 5 and 15 water molecules per (H)SO3 end-group. Structural features such as water clustering, water-channel dimensions and topology, and the dynamics of the hydronium ions and water molecules have all been analysed in relation to the dynamical properties of the polymer backbone and side-chains. It is generally found that mobility is promoted by a high water content, with the side-chains participating actively in the H3O+/H2O transport mechanism. Nafion, whose side-chain length is intermediate of the three polymers studied, is found to have the most mobile polymer side-chains at the higher level of hydration, suggesting that there could be an optimal side-chain length in these systems. There are also some indications that the water-channel network connectivity is optimal for high water-content Nafion system, and that this could explain why Nafion appears to exhibit the most favourable overall hydronium/water mobility.
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| 8. |
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| 9. |
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| 10. |
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| 11. |
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| 12. |
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| 13. |
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| 14. |
- Larsson, Peter, et al.
(författare)
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Structural and electrochemical aspects of Mn substitution into Li2FeSiO4 from DFT calculations
- 2010
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 47:3, s. 678-684
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Tidskriftsartikel (refereegranskat)abstract
- DFT calculations are presented which probe the effect of low-concentration Mn substitution of the Fe-sites in Li2FeSiO4: the promising new and potentially cheap cathode material for upscaled Li-ion battery applications. The LixFe0.875Mn0.125SiO4 System investigated could be achieved by replacing 12.5% of the Fe-sites in 2 x 2 x 1 and 2 x 2 x 2 supercells by Mn ions. The evolution of Bader charges and partial densities of states (DOS) have been followed under a stepwise delithiation process. A clear structural distortion is seen to occur at the Mn-site on delithiation, suggesting possible structural instability. Oxidation of Mn beyond 3+ is calculated to occur at potentials in excess of 4.7 V, implying that oxidation of well separated (>10 angstrom) low-concentration Mn ions to Mn4+ is energetically unfavourable in the LixFe0.875Mn0.125SiO4 structure. This, together with previous DFT results for higher levels of Mn substitution into Li2FeSiO4, indicates that capacity increase in Li2Fe1 (-) yMnySiO4 through a > 1 electron redox reaction may not be so readily attainable in practice, either for high or low Mn concentrations.
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| 15. |
- Lasri, Karime, et al.
(författare)
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Intercalation and conversion reactions in Ni0.5TiOPO4 Li-ion battery anode materials
- 2013
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 229, s. 265-271
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Tidskriftsartikel (refereegranskat)abstract
- The Ni0.5TiOPO4/C composite Li-ion battery anode material has been prepared by a sol-gel method with a subsequent pyrolysis step for the formation of C-coating. The resulting sub-micronsized particles displayed a narrow particle size distribution and a corresponding high electrochemical activity which, in turn, facilitates in-depth analysis of the electrochemical behavior of the material. It is shown that by limiting the degree of lithiation in the material, the redox potential in subsequent cycles is substantially affected. Ex-situ XRD reveals a gradual evolution of the structure during cycling of the material, with lower crystallinity after the first discharge cycle. By correlating the electrochemical properties with the structural studies, new insights into the electrochemical behavior of the Ni0.5TiOPO4/C anode material are achieved, suggesting a combination of intercalation and conversion reactions.
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| 16. |
- Li, Cuiyan, et al.
(författare)
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Microwave-solvothermal synthesis of Fe3O4 magnetic nanoparticles
- 2013
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Ingår i: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 107, s. 23-26
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Tidskriftsartikel (refereegranskat)abstract
- Fe3O4 magnetic nanoparticles were successfully synthesized by the microwave-solvothermal method in a simple reaction system during significantly shorter time than traditional solvothermal or hydrothermal methods. In this synthetic system, ethylene glycol acts as solvent, microwave mediate, and reductant; trisodium citrate works as assistant reductant and electrostatic stabilizer, which makes the Fe3O4 rianoparticles well dispersed in the solution; NH4Ac is the nucleating agent. In the process, a burst of "hot-spots" induced by quick microwave irradiation can create a condition for uniform seeding in the precursor solution, and accelerate the formation of Fe3O4 nanocrystals. F4(3)O(4) nanoparticles prepared by the microwave-solvothermal method showed a higher saturation magnetization than the sample synthesized by the conventional solvothermal method, which can be ascribed to the fact that the former has smaller particle sizes than the later.
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| 17. |
- Liivat, Anti, et al.
(författare)
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A DFT study of VO43- polyanion substitution into the Li-ion battery cathode material Li2FeSiO4
- 2010
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 50:1, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- Density Functional Theory (DFT) has here been used to study the substitution of SiO44- for VO43- polyanions in the orthosilicate Li-ion battery cathode material Li2FeSiO4, in order to enhance electron transfer between the TM-ions and thereby achieve a capacity increase from the potential redox activity of the orthovanadate polyanion. Comparison of results for five different model structures for LiFeXO4, X = Si, P and V, reveals that VO43- substitution destabilizes the tetrahedral structures towards olivine- or spinel-type structures. Our modelling of lithiation of the hypothetical 100% substituted system LiFeVO4 to Li2FeVO4 predicts the reduction of V5+ in the VO43- anion to V4+ at a potential of 2.1 V. While complete delithiation of LiFeVO4 to FeVO4 is accompanied by Fe2+/Fe3+ oxidation at similar to 3.1 V. These lithiation and delithiation processes trigger changes in the unit-cell volume: -6% and +10%, respectively. Notably, only minor structural distortions were observed in both VO43- and the more exotic VO44- tetrahedra. Thermodynamically feasible VO43- substitution levels are also shown to be <30%. This is exemplified for a 12.5% VO4-substituted system which exhibits similar to 50% smaller band-gap and increased capacity at an average deintercalation potential of similar to 3.2 V compared to the un-substituted system.
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| 18. |
- Liivat, Anti, et al.
(författare)
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A molecular dynamics study of ion-conduction mechanisms in crystalline low-Mw LiPF6·PEO6
- 2007
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 17:37, s. 3938-3946
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics (MD) simulation has been used to probe ion-conduction mechanisms in crystalline LiPF6.PEO6 for smectic- and nematic-ordered models of methyl-terminated short-chain monodisperse poly(ethylene oxide) chains with the formula CH3-(OCH2CH2)23-OCH3; Mw = 1059. The effect of aliovalent substitution of the PF6- anion by ca. 1% SiF62- has also been studied. External electric fields in the range 3-6 x 106 V m-1 have been imposed along, and perpendicular to, the chain direction in an effort to promote ion transport during the short timespan of the simulation. Ion-migration barriers along the polymer channel are lower for the nematic models than for the smectic, with anions migrating along the channels more readily than Li-ions. Ion mobility within the smectic interface could also be confirmed, but at a higher field-strength threshold than along the chain direction. Li-ion migration within the smectic plane appears to be suppressed by ion pairing, while Li-ion transport across the smectic gap is facilitated by uncoordinated methoxy end-groups. Interstitial Li-ions introduced into the PEO channel through SiF62- doping are also shown to enhance Li-ion conduction.
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| 19. |
- Liivat, Anti, et al.
(författare)
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A Molecular Dynamics Study of Short-Chain Ordering in Crystalline LiPF6PEO6
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 48:21, s. 6448-6456
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics (MD) simulations have been made of the crystalline short-chain LiPF6·PEO6 system to probe structural ordering for different chain-end arrangements for a methyl-terminated monodisperse poly(ethylene oxide) (EO23 Mw = 1059) host polymer. Five different start structures have been studied, two "smectic" and three "nematic", to represent different types of relative alignment of the end-groups between adjacent PEO chains, and different chain-end coordination situations to the Li-ions. One particular situation is found to result effectively in Li-ion bridging between PEO chains along the chain axes, thereby creating continuous ion transport pathways across the chain breaks. This situation is also found to give rise to Li+-PF6- ion-pairing and Li-O coordination instabilities in the end-group regions, where coordination to Li-ions would appear to have a more radical influence on local structure than the issue of smectic vs. nematic end-group alignment. It could be that such structural situations involving bridging Li-ions (in both smectic and nematic arrangements) are a necessary condition for the promotion of Li-ion transport in the chain direction. Comparison of simulated and experimental XRD profiles is concluded to be an inappropriately crude and uncertain technique for distinguishing between possible short-chain ordering models.
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| 20. |
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| 21. |
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| 22. |
- Liivat, Anti, et al.
(författare)
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Development of a force field for Li2SiF6
- 2005
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Ingår i: Journal of Computational Chemistry. - : Wiley. - 0192-8651 .- 1096-987X. ; 26:7, s. 716-724
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Tidskriftsartikel (refereegranskat)abstract
- A force field has been developed for Li2SiF6 for subsequent use in Molecular Dynamics (MD) simulations involving Li+ and SiF ions in a polymer electrolyte host. Both ab initio calculations and available empirical data have been used. The force field has been verified in simulations of the crystal structure of Li2SiF6 in two different space groups: P321 and Pm1. The use of MD simulation to assess the correct space group for Li2SiF6 shows that it is probably P321.
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| 23. |
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| 24. |
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| 25. |
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| 26. |
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| 27. |
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| 28. |
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| 29. |
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| 30. |
- Liivat, Anti, et al.
(författare)
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Li-ion migration in Li(2)FeSiO(4)-related cathode materials : A DFT study
- 2011
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 192:1, s. 58-64
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Tidskriftsartikel (refereegranskat)abstract
- The orthosilicate family of materials Li(2)MSiO(4) for M = Fe, Mn and Co are coming to be seen as potentially cheap cathode materials for large-scale Li-ion batteries, not least through the possibility for significant capacity gains if more than one Li-ion can be removed per formula unit. To gain insights into possible Li-ion migration pathways and diffusion barriers for Li-ions, model systems for Li(x)FeSiO(4)(x approximate to 1.2) are here studied using the Density Functional Theory (DFT) approach. Li-ion and ion-vacancy migration barriers are calculated for a number of model systems. The results help explain why the Li/Fe site-mixing observed during electrochemical cycling of Li(2)FeSiO(4) does not lead to any noticeable loss in cell performance, despite the increased tortuosity introduced into the Li-migration pathways by this ion-mixing process.
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| 31. |
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| 32. |
- Liivat, Anti, et al.
(författare)
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Minerals as a source of novel Li-ion battery electrode materials
- 2015
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Ingår i: Macedonian Journal of Chemistry and Chemical Engineering. - 1857-5552 .- 1857-5625. ; 34:1, s. 145-149
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Tidskriftsartikel (refereegranskat)abstract
- As a tribute to the major contribution made by Academician Gligor Jovanovski to the field of Mineralogy in Macedonia, this paper promotes the potential role that minerals can have as a future source of inspiration in identifying novel materials for sustainable energy storage in general, and for advanced Li-ion batteries in particular. We exemplify this by indicating the innovative use of polyanions in novel Li-ion battery cathode materials such as the olivine lithium iron phosphate (LiFePO4), and in an even newer material - the orthosilicate lithium iron silicate (Li2FeSiO4). Both materials have strong intrinsic links to mineralogy and - illustrate well how mineralogy can lead to new material breakthroughs in this and other areas of modern technology.
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| 33. |
- Liivat, Anti
(författare)
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New crystalline NaAsF(6)-PEO(8) complex : A Density Functional Theory study
- 2011
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 57, s. 244-249
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Tidskriftsartikel (refereegranskat)abstract
- DFT calculations of new polymer salt complex NaAsF(6)center dot PEO(8) have been carried out in its low-temperature (LT) phase for the purpose of understanding the relationship between the structure and ionic transport in this material. Both relaxation at OK and finite-temperature ab initio molecular dynamics approach up to 273 K reproduced the LT structure very well. Nudged elastic band method has been used for estimating the migration barriers for collective migration of cations or anions in PEO tunnel-direction. The migration barriers were 1.25 eV per anion and 1.6 eV per cation which could explain the lower t(+) value as reported from experiments. AsF(6)(-) anion exhibits rotational disorder about the three crystallographic directions of which the y-direction is least hindered.
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| 34. |
- Liivat, Anti, et al.
(författare)
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Novel insights into higher capacity from the Li-ion battery cathode material Li2FeSiO4
- 2017
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 223, s. 109-114
-
Tidskriftsartikel (refereegranskat)abstract
- A highly reactive composite cathode material incorporating nano-particles of the popular Li-ion battery cathode material Li2FeSiO4 (LFS) is here studied to probe the activation of the controversial Fe3+/Fe4+ redox couple in exploiting the second Li-ion in the formula unit - for use in rechargeable Li-ion batteries. A novel form of in situ Mossbauer spectroscopy is used to monitor the oxidation state of the Fe-ions in symmetric LFS LFS cells. This is based on mapping the poorly resolvable Mossbauer spectra from the expected Fe3+/Fe4+ redox couple in the working electrode onto the highly resolvable Fe2+/Fe3+ spectra from the counter electrode. Comparison of such data from half-delithiated Li(1)Fe3+SiO4 parallel to Li(1)Fe3+SiO4 and almost lithium-free "Li(0)Fe4+SiO4 parallel to Li(0)Fe4+SiO4" symmetric cells is demonstrated - to distinguish the electrode reactions from the those involving the electrolyte. Lithium is shown to cycle reversibly in the symmetric cells. However, a large proportion of the cycled lithium (similar to 70%) does not derive from the bulk of the electrodes, but is rather a result of high-V electrolyte degradation, where charge balance is maintained by leaching lithium from the electrolyte and inserting it into the electrodes.
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| 35. |
- Liivat, Anti, 1974-
(författare)
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Ordering in Crystalline Short-Chain Polymer Electrolytes
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer electrolytes are the most obvious candidates for safe "all-solid" Li-ion batteries and other electrochemical devices. However, they still have relatively poor ionic conductivities, which limits their wider adoption in commercial applications. It has earlier been the conventional wisdom that only amorphous phases of polymer electrolytes show usefully high ionic conduction, while crystalline forms are insulators. However, this has been challenged in the last decade by the discovery of highly organized, low-dimensional ion-conducting materials. Specifically, the crystalline phases of LiXF6.PEO6 exhibit higher ionic conductivities than their amorphous counterparts, with the Li-ion conduction taking place along the PEO channels. Polymer chain-length and chain-end registry has emerged as potentially significant in determining ionic conduction in these materials. Molecular Dynamics simulations have therefore been made of short-chain, monodisperse (Mw~1000), methoxy end-capped LiPF6.PEO6 to examine relationships between ion conduction and mode of chain-ordering. Studies of smectic and nematic arrangements of PEO chains have revealed that ion-transport mechanisms within the smectic planes formed by cooperative chain-end registry appear to be more suppressed by ion-pairing than in-channel conduction. Disorder phenomena in the chain-end regions emerge as a critical factor in promoting Li-ion migration across chain-gaps, as does the structural continuity of the PEO channels. Simulations incorporating ~1% aliovalent SiF62- dopants further suggest an increase in Li-ion conduction when the extra Li-ions reside within the PEO channels, with the anion influencing charge-carrier concentration through enhanced ion-pair formation. XRD techniques alone are shown to be inadequate in ascertaining the significance of the various short-chain models proposed; atomistic modelling is clearly a helpful complement in distinguishing more or less favourable situations for ion conduction. Though providing valuable insights, it must be concluded that this work has hardly brought us significantly closer to breakthroughs in polymer electrolyte design; the critical factors which will make this possible remain as yet obscure.
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| 36. |
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| 37. |
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| 38. |
- Liivat, Anti
(författare)
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Structural changes on cycling Li 2FeSiO 4 polymorphs from DFT calculations
- 2012
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 228, s. 19-24
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Tidskriftsartikel (refereegranskat)abstract
- Cation mixing has been demonstrated experimentally in the Li-ion battery cathode material Li 2FeSiO 4. This feature is investigated here using DFT calculations. It is shown that full reversal of Li/Fe site occupations is energetically favoured on delithiation for all three electrochemically active Li 2FeSiO 4 polymorphs. The common layered topology in the arrangement of SiO 4 and FeO 4 tetrahedra in all three polymorphs transforms into a 3D-framwork. Calculations show here that such a change in structure leads to a lowering of electrochemical insertion potential from ~ 3.1 to ~ 2.8 V, in good agreement with experimental data. Calculations also predict the correct anisotropy in the cell expansion on delithiation on Li/Fe site reversals. Partial mixing of Li and Fe site occupations is energetically less favourable, which supports a two-phase transformation mechanism.
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| 39. |
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| 40. |
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| 41. |
- Mussa, Abdilbari, et al.
(författare)
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Fast-charging effects on ageing for energy-optimized automotive LiNi1/3Mn1/3Co1/3O2/graphite prismatic lithium-ion cells
- 2019
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Ingår i: Journal of Power Sources. - : ELSEVIER SCIENCE BV. - 0378-7753 .- 1873-2755. ; 422, s. 175-184
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Tidskriftsartikel (refereegranskat)abstract
- The reactions in energy-optimized 25 Ah prismatic NMC/graphite lithium-ion cell, as a function of fast charging (1C-4C), are more complex than earlier described. There are no clear charging rate dependent trends but rather different mechanisms dominating at the different charging rates. Ageing processes are faster at 3 and 4C charging. Cycling with 3C-charging results in accelerated lithium plating but the 4C-charging results in extensive gas evolution that contribute significantly to the large cell impedance rise. Graphite exfoliation and accelerated lithium inventory loss point to the graphite electrode as the source of the gas evolution. The results are based on careful post-mortem analyses of electrodes using: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). SEM results show particle cracking independent of the charging rate used for the cycling. XPS and EIS generally indicate thicker surface film and larger impedance, respectively, towards the edge of the jellyrolls. For the intended application of a battery electric inner-city bus using this type of cell, charging rates of 3C and above are not feasible, considering battery lifetime. However, charging rates of 2C and below are too slow from the point of view of practical charging time.
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| 42. |
- Renman, Viktor, et al.
(författare)
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Manganese pyrosilicates as novel positive electrode materials for Na-ion batteries
- 2018
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 2:5, s. 941-945
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Tidskriftsartikel (refereegranskat)abstract
- A carbon-coated pyrosilicate, Na2Mn2Si2O7/C, was synthesized and characterized for use as a new positive-electrode material for sodium ion batteries. The material consists of 20-80 nm primary particles embedded in a approximate to 10 nm-thick conductive carbon matrix. Reversible insertion of Na+ ions is clearly demonstrated with approximate to 25% of its theoretical capacity (165 mA h g(-1)) being accessible at room temperature at a low cycling rate. The material yields an average potential of 3.3 V vs. Na+/Na on charge and 2.2 V on discharge. DFT calculations predict an equilibrium potential for Na2Mn2Si2O7 in the range of 2.8-3.0 V vs. Na+/Na, with a possibility of a complete flip in the connectivity of neighboring Mn-polyhedra - from edge-sharing to disconnected and vice versa. This significant rearrangement in Mn coordination (approximate to 2 angstrom) and large volume contraction (>10%) could explain our inability to fully desodiate the material, and illustrates well the need for a new electrode design strategy beyond the conventional down-sizing/coating procedure.
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| 43. |
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| 44. |
- Soolo, Endel, et al.
(författare)
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Force field generation and molecular dynamics simulations of Li+-Nafion
- 2010
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 55:8, s. 2587-2591
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Tidskriftsartikel (refereegranskat)abstract
- A new molecular dynamics force field for Nafion (R) containing Li+ ions has been generated using Density Functional Theory calculations (B3LYP) on a Nafion side-chain, a Li+ ion and a H2O molecule. The depth of the potential energy well between Li+ and the sulphonate group was decreased with similar to 10 kcal/mol and the optimal Li-S distance 0.5 angstrom shorter, as compared to force fields generated without water present. Molecular dynamics simulations based on the new force field result in a self-diffusion coefficient for Li+ of 8.0 x 10(-8) cm(2)/s at 353 K, which is closer to experimental result than previous simulations using force fields based on pure Nation-cation interactions.
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| 45. |
- Soolo, Endel, et al.
(författare)
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Molecular dynamics simulations of EMI-BF4 in nanoporous carbon actuators
- 2012
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Ingår i: Journal of Molecular Modeling. - : Springer Science and Business Media LLC. - 1610-2940 .- 0948-5023. ; 18:4, s. 1541-1552
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Tidskriftsartikel (refereegranskat)abstract
- An artificial muscle composite material consisting of carbide derived carbon (CDC) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) ionic liquid was modeled using molecular dynamics (MD) simulations, in order to determine the molecular structural rearrangements causing actuation. CDC was represented as separate curved graphene-like flakes with charges of +2, 0 or -2 on each flake, with 24-27 aromatic rings each. The charge distribution in the flakes was determined by PM6 semi-empirical optimization. The pore size distribution of CDC and the density of the material were comparable to experimental data. Molecular structure analysis revealed a preferential parallel orientation for the cations over the negatively charged CDC surfaces, while cationic rotations and reorientations could be observed for positively charged CDC. Changes in the pore occupancy for each ionic type were observed for pore sizes between 4 and 7 angstrom, which, together with the replacement of large cations with smaller anions, could explain the volume decrease in the anodes (and, vice versa, the volume increase in the cathodes) in this type of actuator.
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| 46. |
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| 47. |
- Valvo, Mario, et al.
(författare)
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Detecting voltage shifts and charge storage anomalies by iron nanoparticles in three-electrode cells based on converted iron oxide and lithium iron phosphate
- 2023
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 440
-
Tidskriftsartikel (refereegranskat)abstract
- Noticeable voltage shifts have been observed in the charge/discharge profiles of a three-electrode cell with a lithium metal reference electrode and having a deeply lithiated iron oxide (Fe/Li2O) negative electrode galvanostatically cycled in a limited potential range against a positive LiFePO4 counterpart. The origin of such shifts has been attributed to charge storage anomalies in the Fe/Li2O nanocomposite due to characteristic reduced Fe nanoparticle sizes. These shifts also affected the extreme points of the voltage profiles of the positive electrode, which was also independently monitored. A combined evaluation of voltage profile slippages with possible changes in internal resistance and/or Li+ inventory loss, including an aimed analysis of current interruptions at the end of each lithiation/de-lithiation half-cycle to monitor the internal resistance and diffusion resistance coefficient of the Fe/Li2O electrode, has enabled a clarification of its altered charge storage. An asymmetric behaviour of the Fe/Li2O electrode during Li+ uptake/release has been revealed, highlighting a progressive, diffusion-controlled-type voltage drift at low potentials vs. Li+/Li, and an unusual tendency to slight oxidation with capacitive variations during the reverse electrochemical processes at higher voltages, instead.
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| 48. |
- Valvo, Mario, et al.
(författare)
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Iron-Based Electrodes Meet Water-Based Preparation, Fluorine-Free Electrolyte and Binder : A Chance for More Sustainable Lithium-Ion Batteries?
- 2017
-
Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 10:11, s. 2431-2448
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Tidskriftsartikel (refereegranskat)abstract
- Environmentally friendly and cost-effective Li-ion cells are fabricated with abundant, non-toxic LiFePO4 cathodes and iron oxide anodes. A water-soluble alginate binder is used to coat both electrodes to reduce the environmental footprint. The critical reactivity of LiPF6-based electrolytes toward possible traces of H2O in water-processed electrodes is overcome by using a lithium bis(oxalato) borate (LiBOB) salt. The absence of fluorine in the electrolyte and binder is a cornerstone for improved cell chemistry and results in stable battery operation. A dedicated approach to exploit conversion-type anodes more effectively is also disclosed. The issue of large voltage hysteresis upon conversion/de-conversion is circumvented by operating iron oxide in a deeply lithiated Fe/Li2O form. Li-ion cells with energy efficiencies of up to 92% are demonstrated if LiFePO4 is cycled versus such anodes prepared through a prelithiation procedure. These cells show an average energy efficiency of approximately 90.66% and a mean Coulombic efficiency of approximately 99.65% over 320 cycles at current densities of 0.1, 0.2 and 0.3 mAcm(-2). They retain nearly 100% of their initial discharge capacity and provide an unmatched operation potential of approximately 2.85 V for this combination of active materials. No occurrence of Li plating was detected in three-electrode cells at charging rates of approximately 5C. Excellent rate capabilities of up to approximately 30C are achieved thanks to the exploitation of size effects from the small Fe nanoparticles and their reactive boundaries.
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