| 1. |
- Ebadi, Mahsa, et al.
(författare)
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Restricted Ion Transport by Plasticizing Side Chains in Polycarbonate-Based Solid Electrolytes
- 2020
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 53:3, s. 764-774
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Tidskriftsartikel (refereegranskat)abstract
- Increasing the ionic conductivity has for decades been an overriding goal in the development of solid polymer electrolytes. According to fundamental theories on ion transport mechanisms in polymers, the ionic conductivity is strongly correlated to free volume and segmental mobility of the polymer for the conventional transport processes. Therefore, incorporating plasticizing side chains onto the main chain of the polymer host often appears as a clear-cut strategy to improve the ionic conductivity of the system through lowering of the glass transition temperature (T-g) This intended correlation between Tg and ionic conductivity is, however, not consistently observed in practice. The aim of this study is therefore to elucidate this interplay between segmental mobility and polymer structure in polymer electrolyte systems comprising plasticizing side chains. To this end, we utilize the synthetic versatility of the ion-conductive poly(trimethylene carbonate) (PTMC) platform. Two types of host polymers with side chains added to a PTMC backbone are employed, and the resulting electrolytes are investigated together with the side chain-free analogue both by experiment and with molecular dynamics (MD) simulations. The results show that while added side chains do indeed lead to a lower Tg, the total ionic conductivity is highest in the host matrix without side chains. It was seen in the MD simulations that while side chains promote ionic mobility associated with the polymer chain, the more efficient interchain hopping transport mechanism occurs with a higher probability in the system without side chains. This is connected to a significantly higher solvation site diversity for the Li+ ions in the side-chain-free system, providing better conduction paths. These results strongly indicate that the side chains in fact restrict the mobility of the Li+ ions in the polymer hosts.
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| 2. |
- Eriksson, Therese, 1992-, et al.
(författare)
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Carbonyl-Containing Solid Polymer Electrolyte Host Materials : Conduction and Coordination in Polyketone, Polyester, and Polycarbonate Systems
- 2022
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 55:24, s. 10940-10949
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Tidskriftsartikel (refereegranskat)abstract
- Research on solid polymer electrolytes (SPEs) is now moving beyond the realm of polyethers that have dominated the field for several decades. A promising alternative group of candidates for SPE host materials is carbonyl-containing polymers. In this work, SPE properties of three different types of carbonyl-coordinating polymers are compared: polycarbonates, polyesters, and polyketones. The investigated polymers were chosen to be as structurally similar as possible, with only the functional group being different, thereby giving direct insights into the role of the noncoordinating main-chain oxygens. As revealed by experimental measurements as well as molecular dynamics simulations, the polyketone possesses the lowest glass transition temperature, but the ion transport is limited by a high degree of crystallinity. The polycarbonate, on the other hand, displays a relatively low coordination strength but is instead limited by its low molecular flexibility. The polyester performs generally as an intermediate between the other two, which is reasonable when considering its structural relation to the alternatives. This work demonstrates that local changes in the coordinating environment of carbonyl-containing polymers can have a large effect on the overall ion conduction, thereby also showing that desired transport properties can be achieved by fine-tuning the polymer chemistry of carbonyl-containing systems.
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| 3. |
- Eriksson, Therese, 1992-
(författare)
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Cation Conduction and Coordination in Carbonyl-Containing Compounds : Li+ Transport in Alternative Polymer Electrolyte Host Materials
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The field of solid polymer electrolytes (SPEs) used to create safer lithium-ion batteries has been dominated by polyethylene oxide (PEO) since the discovery of its ion-conducting properties in the 1970s. In this thesis, as an alternative, the ion coordination and conduction properties of SPEs based on polyketones, polyesters and polycarbonates are investigated. Instead of having only an ether oxygen on the backbone (like PEO) the functional group in all three of these polymer classes contains a carbonyl oxygen, which is the main coordinating motif on the polymer backbone. The polyesters and polycarbonates do, however, have one or two more oxygens in the functional group compared to the polyketones. This was shown to have a great effect on the SPE properties. The key properties that have been studied in this work are the ionic conductivity, glass transition temperature, degree of crystallinity, coordination strength, and the transport number. The polymers are both studied individually and comparatively. The polyketone electrolytes studied in this thesis are novel to the solid polymer electrolyte field, and not as established as the polyesters and polycarbonates. The polyketone-based electrolytes have a high degree of crystallinity and the lithium coordination strength is quite high, therefore the ion transport is significantly reduced. Results with a higher salt concentration, however, suggest that with a more amorphous polyketone electrolyte, the transport properties could be significantly improved. The challenge with the polycarbonates is not the degree of crystallinity, as most of the ones studied herein are amorphous, but instead the high glass transition temperature. They are thereby restricted by the low degree of segmental motion present. This problem could not be solved by lowering the glass transition temperature by the addition of side-chains, as the side-chains instead block the pathway of the lithium ions. A positive aspect seen in the polycarbonate-based electrolytes was the high lithium transference number, which is significantly higher than both the polyketones’ and the polyester’s. The polyester is also semi-crystalline; the degree of crystallinity can be reduced by the addition of salt or nanoparticles though. Synthesising a polyester-polycarbonate copolymer is also an option to create an amorphous polymer. The polyester is somewhat of a midway between the polyketone and polycarbonate, both in its molecular structure as well as in its physical and ion transport properties. It does, however, show the highest ionic conductivity out of the three as it has a rather low glass transition temperature and not too strong ion coordination. This work highlights the physical, coordination and conduction properties found in carbonyl-containing polymer host materials. Even though the polyketones, polyesters and polycarbonates are structurally quite similar, their properties can vary significantly. They are, however, all likely candidates for tomorrow’s solid-state lithium-ion batteries.
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| 4. |
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| 5. |
- Eriksson, Therese, 1992-, et al.
(författare)
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Effects of nanoparticle addition to poly(epsilon-caprolactone) electrolytes : Crystallinity, conductivity and ambient temperature battery cycling
- 2019
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Ingår i: Electrochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0013-4686 .- 1873-3859. ; 300, s. 489-496
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Tidskriftsartikel (refereegranskat)abstract
- It has previously been shown that nanoparticle additives can, in a simple way, significantly improve the ionic conductivity in solid polymer electrolyte systems with the semi-crystalline poly(ethylene oxide) (PEO) as a host material. It has been suggested that the improved ionic conductivity is a result of reduced degree of crystallinity and additional conductivity mechanisms occurring in the material. In this work, this principle is applied to another semi-crystalline polymer host: poly(epsilon-caprolactone) (PCL). This is a polymer with comparable properties (T-g, T-m, etc.) as PEO, and constitute a promising material for use in solid polymer electrolytes for lithium ion batteries. 15 wt% of the respective nanoparticles TiO2, Al2O3 and h-BN have been added to the PCL-LiTFSI solid polymer electrolyte in an attempt to increase the conductivity and achieve stable room temperature cyclability. The crystallinity, ionic conductivity and electrochemical properties were investigated by differential scanning calorimetry, electrochemical impedance spectroscopy and galvanostatic cycling of cells. The results showed that with an addition of 15 wt% Al2O3, the degree of crystallinity is reduced to 6-7% and the ionic conductivity increased to 6-7 x 10(-6) S cm(-1) at room temperature, allowing successful cycling of cells at 30 degrees C, while h-BN did not contribute to similar improvements. The effect of nanoparticles, however, differ significantly from previous observations in PEO systems, which could be explained by different surface-polymer interactions or the degree of ordering in the amorphous phases of the materials.
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| 6. |
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| 7. |
- Eriksson, Therese, 1992-, et al.
(författare)
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Polyketones as Host Materials for Solid Polymer Electrolytes
- 2020
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Ingår i: Journal of the Electrochemical Society. - : ELECTROCHEMICAL SOC INC. - 0013-4651 .- 1945-7111. ; 167:7
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Tidskriftsartikel (refereegranskat)abstract
- While solid polymer electrolytes (SPEs) have great potential for use in future lithium-based batteries, they do, however, not display conductivity at a sufficient level as compared to liquid electrolytes. To reach the needed requirements of lithium batteries it is therefore necessary to explore new materials classes to serve as novel polymer hosts. In this work, SPEs based on the polyketone poly(3,3-dimethylpentane-2,4-dione) were investigated. Polyketones are structurally similar to several polycarbonate and polyester SPE hosts investigated before but have, due to the lack of additional oxygen atoms in the coordinating motif, even more electronwithdrawing carbonyl groups and could therefore display better properties for coordination to the salt cation. In electrolyte compositions comprising 25-40 wt% LiTFSI salt, it was observed that this polyketone indeed conducts lithium ions with a high cation transference number, but that the ionic conductivity is limited by the semi-crystallinity of the polymer matrix. The crystallinity decreases with increasing salt content, and a fully amorphous SPE can be produced at 40 wt% salt, accompanied by an ionic conductivity of 3 x 10(-7) S cm(-1) at 32 degrees C. This opens up for further exploration of polyketone systems for SPE-based batteries.
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| 8. |
- Eriksson, Therese, 1992-, et al.
(författare)
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The Role of Coordination Strength in Solid Polymer Electrolytes: Compositional Dependence of Transference Numbers in thePoly(ε-Caprolactone)–Poly(Trimethylene Carbonate) System
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 23:45, s. 25550-25557
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Tidskriftsartikel (refereegranskat)abstract
- Both polyesters and polycarbonates have been proposed as alternatives to polyethers as host materials for future polymer electrolytes for solid-state lithium-ion batteries. While being comparatively similar functional groups, the electron density on the coordinating carbonyl oxygen is different, thereby rendering different coordinating strength towards lithium ions. In this study, the transport properties of poly(epsilon-caprolactone) and poly(trimethylene carbonate) as well as random copolymers of systematically varied composition of the two have been investigated, in order to better elucidate the role of the coordination strength. The cationic transference number, a property well-connected with the complexing ability of the polymer, was shown to depend almost linearly on the ester content of the copolymer, increasing from 0.49 for the pure poly(epsilon-caprolactone) to 0.83 for pure poly(trimethylene carbonate). Contradictory to the transference number measurements that suggest a stronger lithium-to-ester coordination, DFT calculations showed that the carbonyl oxygen in the carbonate coordinates more strongly to the lithium ion than that of the ester. FT-IR measurements showed the coordination number to be higher in the polyester system, resulting in a higher total coordination strength and thereby resolving the paradox. This likely originates in properties that are specific of polymeric solvent systems, e.g. steric properties and chain dynamics, which influence the coordination chemistry. These results highlight the complexity in polymeric systems and their ion transport properties in comparison to low-molecular-weight analogues, and how polymer structure and steric effects together affect the coordination strength and transport properties.
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