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Block Copolymer Electrolytes: Polymers for Solid-State Lithium Batteries
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Polymer Chemistry.ORCID iD: 0000-0002-3009-8884
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of solid polymer electrolytes (SPEs) for lithium battery devices is a rapidly growing research area. The liquid electrolytes that are used today are inflammable and harmful towards the battery components. The adoption of SPEs could drastically improve this situation, but they still suffer from a too low performance at ambient temperatures for most practical applications. However, by increasing the operating temperature to between 60 °C and 90 °C, the electrolyte performance can be drastically increased. The drawback of this approach, partly, is that parasitic side reactions become noticeable at these elevated temperatures, thus affecting battery lifetime and performance. Furthermore, the ionically conductive polymer loses its mechanical integrity, thus triggering a need for an external separator in the battery device.

One way of combining both mechanical properties and electrochemical performance is to design block copolymer (BCP) electrolytes, that is, polymers that are tailored to combine one ionic conductive block with a mechanical block, into one polymer. The hypothesis is that the BCP electrolytes should self-assemble into well-defined microphase separated regions in order to maximize the block properties. By varying monomer composition and structure of the BCP, it is possible to design electrolytes with different battery device performance. In Paper I and Paper II two types of methacrylate-based triblock copolymers with different mechanical blocks were synthesized, in order to evaluate morphology, electrochemical performance, and battery performance. In Paper III and Paper IV a different strategy was adopted, with a focus on diblock copolymers. In this strategy, the ethylene oxide was replaced by poly(e-caprolactone) and poly(trimethylene carbonate) as the lithium-ion dissolving group. The investigated mechanical blocks in these studies were poly(benzyl methacrylate) and polystyrene. The battery performance for these electrolytes was superior to the methacrylate-based battery devices, thus resulting in stable battery cycling at 40 °C and 30 °C.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 68
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1630
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-340856ISBN: 978-91-513-0233-1 (print)OAI: oai:DiVA.org:uu-340856DiVA, id: diva2:1180073
Public defence
2018-03-23, Häggsalen, Ångströmlaboratoriet, Uppsala, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilAvailable from: 2018-02-28 Created: 2018-02-04 Last updated: 2018-04-03
List of papers
1. d8-poly(methyl methacrylate)-poly[(oligo ethylene glycol) methyl ether methacrylate] tri-block-copolymer electrolytes: Morphology, conductivity and battery performance
Open this publication in new window or tab >>d8-poly(methyl methacrylate)-poly[(oligo ethylene glycol) methyl ether methacrylate] tri-block-copolymer electrolytes: Morphology, conductivity and battery performance
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2017 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 131, p. 234-242Article in journal (Refereed) Published
Abstract [en]

A series of deuterated tri-block copolymers with the general structure d(8)-PMMA-POEGMA-d(8)-PMMA, with variation in d(8)-PMMA chain length, were synthesized using sequential controlled radical polymerization (ATRP). Solid polymer electrolytes (SPEs) were produced by blending tri-block copolymers and lithium bis(trifluoro methylsulfonate) (LiTFSI). Small-angle neutron scattering (SANS) was used to study the bulk morphology of the deuterated tri-block copolymer electrolyte series at 25 degrees C, 60 degrees C and 95 degrees C. The lack of a second T-g in DSC analysis together with modelling with the random phase approximation model (RPA) confirmed that the electrolytes are in the mixed state, with negative Flory-Huggins interaction parameters. AC impedance spectroscopy was used to study the ionic conductivity of the SPE series in the temperature interval 30 degrees C-90 degrees C, and a battery device was constructed to evaluate a 25 wt% d(8)-PMMA electrolyte. The Li | SPE | LiFePO4 cell cycled at 60 degrees C, giving a discharge capacity of 120 mAh g(-1), while cyclic voltammetry showed that the SPE was stable at 60 degrees C.

National Category
Polymer Chemistry
Identifiers
urn:nbn:se:uu:diva-337667 (URN)10.1016/j.polymer.2017.10.044 (DOI)000415014300026 ()
Funder
Swedish Research Council
Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2018-02-22Bibliographically approved
2. Poly(benzyl methacrylate)-Poly[(oligo ethylene glycol) methyl ether methacrylate] Triblock-Copolymers as Solid Electrolyte for Lithium Batteries
Open this publication in new window or tab >>Poly(benzyl methacrylate)-Poly[(oligo ethylene glycol) methyl ether methacrylate] Triblock-Copolymers as Solid Electrolyte for Lithium Batteries
2018 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 321, p. 55-61Article in journal (Refereed) Published
Abstract [en]

A triblock copolymer of benzyl methacrylate and oligo(ethylene glycol) methyl ether methacrylate was polymerized to form the general structure PBnMA-POEGMA-PBnMA, using atom transfer radical polymerization (ATRP). The block copolymer (BCP) was blended with lithium bis(trifluoro methylsulfonate) (LiTFSI) to form solid polymer electrolytes (SPEs). AC impedance spectroscopy was used to study the ionic conductivity of the SPE series in the temperature interval 30 °C to 90 °C. Small-angle X-ray scattering (SAXS) was used to study the morphology of the electrolytes in the temperature interval 30 °C to 150 °C. By using benzyl methacrylate as a mechanical block it was possible to tune the microphase separation by the addition of LiTFSI, as proven by SAXS. By doing so the ionic conductivity increased to values higher than ones measured on a methyl methacrylate triblock copolymer-based electrolyte in the mixed state, which was investigated in an earlier paper by our group. A Li|SPE|LiFePO4 half-cell was constructed and cycled at 60 °C. The cell produced a discharge capacity of about 100 mAh g−1 of LiFePO4 at C/10, and the half-cell cycled for more than 140 cycles.

National Category
Polymer Chemistry
Research subject
Chemistry with specialization in Polymer Chemistry
Identifiers
urn:nbn:se:uu:diva-340851 (URN)10.1016/j.ssi.2018.04.006 (DOI)000437372200009 ()
Funder
Swedish Energy AgencyStandUp
Available from: 2018-02-04 Created: 2018-02-04 Last updated: 2018-10-11Bibliographically approved
3. ε-Caprolactone-based solid polymer electrolytes for lithium-ion batteries: synthesis, electrochemical characterization and mechanical stabilization by block copolymerization
Open this publication in new window or tab >>ε-Caprolactone-based solid polymer electrolytes for lithium-ion batteries: synthesis, electrochemical characterization and mechanical stabilization by block copolymerization
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2018 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 8, no 30, p. 16716-16725Article in journal (Refereed) Published
Abstract [en]

In this work, three types of polymers based on epsilon-caprolactone have been synthesized: poly(epsilon-caprolactone), polystyrene-poly(epsilon-caprolactone), and polystyrene-poly(epsilon-caprolactone-r-trimethylene carbonate) (SCT), where the polystyrene block was introduced to improve the electrochemical and mechanical performance of the material. Solid polymer electrolytes (SPEs) were produced by blending the polymers with 10-40 wt% lithium bis(trifluoromethane) sulfonimide (LiTFSI). Battery devices were thereafter constructed to evaluate the cycling performance. The best performing battery half-cell utilized an SPE consisting of SCT and 17 wt% LiTFSI as both binder and electrolyte; a Li vertical bar SPE vertical bar LiFePO4 cell that cycled at 40 degrees C gave a discharge capacity of about 140 mA h g(-1) at C/5 for 100 cycles, which was superior to the other investigated electrolytes. Dynamic mechanical analysis (DMA) showed that the storage modulus E' was about 5 MPa for this electrolyte.

National Category
Polymer Chemistry
Identifiers
urn:nbn:se:uu:diva-340854 (URN)10.1039/c8ra00377g (DOI)000431814500034 ()
Funder
Swedish Energy Agency, 42031-1EU, Horizon 2020, 685716
Available from: 2018-02-04 Created: 2018-02-04 Last updated: 2018-08-27Bibliographically approved
4. A Mechanical Robust yet highly Conductive Diblock Copolymer-based Solid Polymer Electrolyte for Room Temperature Structural Battery Applications
Open this publication in new window or tab >>A Mechanical Robust yet highly Conductive Diblock Copolymer-based Solid Polymer Electrolyte for Room Temperature Structural Battery Applications
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(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:uu:diva-340855 (URN)
Available from: 2018-02-04 Created: 2018-02-04 Last updated: 2018-02-04

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