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Exploring the Frontiers of Polymer Electrolytes for Battery Applications: From Surface to Bulk
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. (Ångström Advanced Battery Centre)ORCID iD: 0000-0002-3374-2276
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lithium-ion batteries have dominated the market since their inception in 1991 due to their unparalleled energy and power densities, but are now faced with new challenges. Growing demand for battery materials for energy intense applications and large-scale interim energy storage have emphasized the need for safe and sustainable battery electrolytes. In this context, non-flammable solid polymer electrolytes (SPEs) are a promising alternative to address the shortcomings of conventional liquid electrolytes. Despite its significance, little research has thus far been devoted to understanding the electrochemical stability of SPEs under the harsh conditions exerted by next-generation electrode materials.

In this thesis, the stability and ramifications of interfaces in polycarbonate- and polyester-based SPEs have been investigated. The polycarbonate exhibited severe degradation upon contact with lithium compared to its ester counterpart. Volatile species stemming from polycarbonate and salt decomposition were observed independent of irreversible current response, thus also highlighting the limitations of voltammetry techniques to determine the electrochemical stability. Two novel techniques were thus devised to evaluate electrochemical stability of SPEs under more realistic conditions. Characterization of the electrode−polyester interface revealed formation of highly resistive interfacial layers composed of polymer, salt and impurity derivatives. The emergence of a detrimental resistance emanating from the polymer−polymer interface was also observed, thus identifying a crucial hurdle for double-layer SPEs as a strategy to extend the stability window.

The application of polycarbonate/polyester-based polymer electrolytes for sodium-ion batteries was also studied. Sodium is far more abundant than lithium, and thereby an excellent chemistry platform to develop new sustainable battery materials. The polycarbonate exhibited an exceptional ability to dissolve large quantities of sodium salt without compromising the mechanical stability. Spectroscopic and thermal measurements revealed the emergence of an alternative ionic transport mechanism at concentrations within the polymer-in-salt regime, which was decoupled from the segmental motion of the polymer chains. By incorporating flexible polyester moieties in polycarbonates, an SPE with better transport properties compared to its individual subunits, and polyether counterparts, was obtained. Optimal salt concentration in this copolymer was dependent on the degree of crystallinity, determined by the portion of polyester. Finally, the practical application of these polymer electrolytes was demonstrated in solid-state sodium-ion batteries.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2021. , p. 67
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2044
Keywords [en]
Lithium-ion batteries, solid-state polymer electrolytes, electrochemical stability window, interfaces, ionic conductivity, polycarbonate, polyester, sustainability, sodium-ion
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-440905ISBN: 978-91-513-1214-9 (print)OAI: oai:DiVA.org:uu-440905DiVA, id: diva2:1546297
Public defence
2021-06-11, Room Å2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2021-05-19 Created: 2021-04-21 Last updated: 2021-06-23
List of papers
1. Early-Stage Decomposition of Solid Polymer Electrolytes in Li-Metal Batteries
Open this publication in new window or tab >>Early-Stage Decomposition of Solid Polymer Electrolytes in Li-Metal Batteries
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2021 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 9, no 39Article in journal (Refereed) Published
Keywords
Lithium-ion batteries; solid polymer electrolytes; electrochemical stability window; solid electrolyte interphase; X-ray photoelectron spectroscopy
National Category
Materials Chemistry Polymer Chemistry
Research subject
Chemistry with specialization in Materials Chemistry; Chemistry with specialization in Polymer Chemistry
Identifiers
urn:nbn:se:uu:diva-440869 (URN)10.1039/D1TA05015J (DOI)000700542000001 ()
Available from: 2021-04-21 Created: 2021-04-21 Last updated: 2023-10-17Bibliographically approved
2. Decomposition of Carbonate-Based Electrolytes: Differences and Peculiarities for Liquids vs. Polymers Observed Using Operando Gas Analysis
Open this publication in new window or tab >>Decomposition of Carbonate-Based Electrolytes: Differences and Peculiarities for Liquids vs. Polymers Observed Using Operando Gas Analysis
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2021 (English)In: Batteries & Supercaps, E-ISSN 2566-6223, Vol. 4, no 5, p. 785-790Article in journal (Refereed) Published
Abstract [en]

Direct tracking of solid polymer electrolyte (SPE) decomposition in comparison to a liquid analogue was accomplished by monitoring the evolution of volatile species using online electrochemical mass spectrometry (OEMS). Reduction of a poly(trimethylene carbonate)-based SPE was dominated by CO2 formation. Detection of CO2 and an absence of CO confirms a preferred reduction degradation pathway involving C−O bond cleavage at the carbonyl carbon, in correlation with earlier suggestions. In contrast, the alkyl carbonate-based liquid electrolyte exhibited extensive ethylene formation. Trace quantities of H2 evolution ascribed to water impurities were also observed in both systems. During oxidation, the SPE and liquid electrolyte exhibited CO2, CO and SO2 evolution synonymous with electrolyte solvent and salt degradation, albeit at different potentials. Overall, gas evolution rates and redox currents were lower in the SPE system. OEMS revealed significant gas formation independent of current response, as such highlighting the limitations of the voltammetry technique commonly used today to assess electrochemical stability.

Place, publisher, year, edition, pages
John Wiley & Sons, 2021
Keywords
electrochemical stability window, gas evolution, online electrochemical mass spectrometry, solid-state electrolytes, solid polymer electrolytes
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-440842 (URN)10.1002/batt.202000307 (DOI)000613731100001 ()
Funder
StandUpEU, Horizon 2020, 875514
Note

De två första författarna delar förstaförfattarskapet

Available from: 2021-04-21 Created: 2021-04-21 Last updated: 2024-01-15Bibliographically approved
3. Going beyond sweep voltammetry: Alternative approaches in search of the elusive electrochemical stability of polymer electrolytes
Open this publication in new window or tab >>Going beyond sweep voltammetry: Alternative approaches in search of the elusive electrochemical stability of polymer electrolytes
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2021 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 168, no 10, article id 100523Article in journal (Refereed) Published
Abstract [en]

Solid polymer electrolytes (SPEs) are promising candidates for solid-state lithium-ion batteries. Potentially, they can be used with lithium metal anodes and high-voltage cathodes, provided that their electrochemical stability is sufficient. Thus far, the oxidative stability has largely been asserted based on results obtained with sweep voltammetry, which are often determined and reliant on arbitrary assessments that are highly dependent on the experimental conditions and do not take the interaction between the electrolyte and the electrode material into account. In this study, alternative techniques are introduced to address the pitfalls of sweep voltammetry for determining the oxidative stability of SPEs. Staircase voltammetry involves static conditions and eliminates the kinetic aspects of sweep voltammetry, and coupled with impedance spectroscopy provides information of changes in resistance and interphase layer formation. Synthetic charge–discharge profile voltammetry applies the real voltage profile of the active material of interest. The added effect of the electrode active material is investigated with a cut-off increase cell cycling method where the upper cut-off voltage during galvanostatic cycling is gradually increased. The feasibility of these techniques has been tested with both poly(ethylene oxide) and poly(trimethylene carbonate) combined with LiTFSI, thereby showing the applicability for several categories of SPEs.

National Category
Materials Chemistry Polymer Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-440872 (URN)10.1149/1945-7111/ac2d8b (DOI)000709097900001 ()
Funder
EU, European Research Council, 771777
Available from: 2021-04-21 Created: 2021-04-21 Last updated: 2023-03-05Bibliographically approved
4. Dissecting the solid polymer electrolyte–electrode interface in the vicinity of electrochemical stability limits
Open this publication in new window or tab >>Dissecting the solid polymer electrolyte–electrode interface in the vicinity of electrochemical stability limits
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2022 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 14, no 25, p. 28716-28728Article in journal (Refereed) Published
Abstract [en]

Proper understanding of solid polymer electrolyte–electrode interfacial layer formation and its implications on cell performance is a vital step toward realizing practical solid-state lithium-ion batteries. At the same time, probing these solid–solid interfaces is extremely challenging as they are buried within the electrochemical system, thereby efficiently evading exposure to surface-sensitive spectroscopic methods. Still, the probing of interfacial degradation layers is essential to render an accurate picture of the behavior of these materials in the vicinity of their electrochemical stability limits and to complement the incomplete picture gained from electrochemical assessments. In this work, we address this issue in conjunction with presenting a thorough evaluation of the electrochemical stability window of the solid polymer electrolyte poly(ε-caprolactone):lithium bis(trifluoromethanesulfonyl)imide (PCL:LiTFSI). According to staircase voltammetry, the electrochemical stability window of the polyester-based electrolyte was found to span from 1.5 to 4 V vs Li+/Li. Subsequent decomposition of PCL:LiTFSI outside of the stability window led to a buildup of carbonaceous, lithium oxide and salt-derived species at the electrode–electrolyte interface, identified using postmortem spectroscopic analysis. These species formed highly resistive interphase layers, acting as major bottlenecks in the SPE system. Resistance and thickness values of these layers at different potentials were then estimated based on the impedance response between a lithium iron phosphate reference electrode and carbon-coated working electrodes. Importantly, it is only through the combination of electrochemistry and photoelectron spectroscopy that the full extent of the electrochemical performance at the limits of electrochemical stability can be reliably and accurately determined.

Place, publisher, year, edition, pages
American Chemical Society (ACS)American Chemical Society (ACS), 2022
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-440873 (URN)10.1021/acsami.2c02118 (DOI)000820935600001 ()35708265 (PubMedID)
Available from: 2021-04-21 Created: 2021-04-21 Last updated: 2024-01-15Bibliographically approved
5. Overcoming the Obstacle of Polymer–Polymer Resistances in Double Layer Solid Polymer Electrolytes
Open this publication in new window or tab >>Overcoming the Obstacle of Polymer–Polymer Resistances in Double Layer Solid Polymer Electrolytes
2021 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 12, no 11, p. 2809-2814Article in journal (Refereed) Published
Abstract [en]

Double-layer solid polymer electrolytes (DLSPEs) comprising one layer that is stable toward lithium metal and one which is stable against a high-voltage cathode are commonly suggested as a promising strategy to achieve high-energy-density lithium batteries. Through in-depth EIS analysis, it is here concluded that the polymer–polymer interface is the primary contributor to electrolyte resistance in such DLSPEs consisting of polyether-, polyester-, or polycarbonate-bad SPEs. In comparison to the bulk ionic resistance, the polymer–polymer interface resistance is approximately 10-fold higher. Nevertheless, the interfacial resistance was successfully lowered by doubling the salt concentration from 25 to 50 wt % LiTFSI owing to improved miscibility at the interface of the two polymer layers.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2021
National Category
Materials Chemistry Polymer Chemistry
Research subject
Chemistry with specialization in Materials Chemistry; Chemistry with specialization in Polymer Chemistry
Identifiers
urn:nbn:se:uu:diva-440868 (URN)10.1021/acs.jpclett.1c00366 (DOI)000635441500015 ()33710889 (PubMedID)
Funder
EU, European Research Council, 771777
Available from: 2021-04-21 Created: 2021-04-21 Last updated: 2024-01-15Bibliographically approved
6. Stable Cycling of Sodium Metal All-Solid-State Batteries with Polycarbonate-Based Polymer Electrolytes
Open this publication in new window or tab >>Stable Cycling of Sodium Metal All-Solid-State Batteries with Polycarbonate-Based Polymer Electrolytes
2019 (English)In: ACS APPLIED POLYMER MATERIALS, ISSN 2637-6105, Vol. 1, no 4, p. 825-832Article in journal (Refereed) Published
Abstract [en]

Solid polymer electrolytes based on high-molecular-weight poly(trimethylene carbonate) (PTMC) in combination with NaFSI salt were investigated for application in sodium batteries. The polycarbonate host material proved to be able to dissolve large amounts of salt, at least up to a carbonate:Na+ ratio of 1:1. Combined DSC, conductivity, and FTIR data indicated the formation of a percolating network of salt clusters along with the transition to a percolation-type ion transport mechanism at the highest salt concentrations. While the highest total ionic conductivities were seen at the highest salt concentrations (up to a remarkable 5 x 10(-5) S cm(-1) at 25 degrees C at a 1:1 carbonate:Na+ ratio), the most stable battery performance was seen at a more moderate salt loading of 5:1 carbonate:Na+, reaching >80 cycles at a stable capacity of similar to 90 mAh g(-1) at 60 degrees C in a sodium metal/Prussian blue cell. The results highlight the importance of the choice of salt and salt concentration on electrolyte performance as well as demonstrate the potential of utilizing polycarbonate-based electrolytes in sodium-based energy storage systems.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
polymer electrolytes, polycarbonates, sodium, batteries, ionic conductivity
National Category
Polymer Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-392889 (URN)10.1021/acsapm.9b00068 (DOI)000476966800025 ()
Funder
EU, European Research Council, 771777 FUN POLYSTORE
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2021-04-22Bibliographically approved
7. Towards room temperature operation of all-solid-state Na-ion batteries through polyester-polycarbonate-based polymer electrolytes
Open this publication in new window or tab >>Towards room temperature operation of all-solid-state Na-ion batteries through polyester-polycarbonate-based polymer electrolytes
2019 (English)In: Energy Storage Materials, ISSN 2405-8289, E-ISSN 2405-8297, Vol. 19, p. 31-38Article in journal (Refereed) Published
Abstract [en]

In an ambition to develop solid-state Na-ion batteries functional at ambient temperature, we here explore a novel electrolyte system. Polyester-polycarbonate (PCL-PTMC) copolymers were combined with sodium bis(fluorosulfonyl) imide salt (NaFSI) to form solid polymer electrolytes for Na-ion batteries. The PCL-PTMC:NaFSI system demonstrated glass transition temperatures ranging from -64 to -11 degrees C, increasing with increasing salt content from 0 to 35 wt%, and ionic conductivities ranging from 10(-8) to 10(-5) S cm(-1) at 25 degrees C. The optimal salt concentration was clearly dependent on the level of crystallinity, which was largely determined by the CL content. At 70 and 80 mol% CL, the PCL-PTMC:NaFSI system was fully amorphous and exhibited high conductivities at lower salt concentrations. When the CL content was increased to 100 mol%, high ionic conductivities were instead observed at high salt concentrations. A decent transference number of ca. 0.5 at 80 degrees C was obtained for a polymer film containing 20 mol% CL units and 25 wt% NaFSI. Finally, a HC vertical bar 80-20(25)vertical bar Na2-xFe(Fe(CN)(6)) all-solid-state polymer electrolyte full cell was assembled to demonstrate the practical application of the material and cycled for more than 120 cycles at similar to 22 degrees C.

Keywords
All-solid-state batteries, Solid polymer electrolyte, Room temperature cycling, Sodium-ion
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-387602 (URN)10.1016/j.ensm.2019.03.022 (DOI)000469207500004 ()
Funder
EU, European Research Council, 771777 FUN POLYSTORE
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2021-10-26Bibliographically approved

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