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Structural Lithium Ion Battery Electrolytes
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology.ORCID iD: 0000-0003-0618-1730
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A major challenge in the electrification of vehicles in the transport industry is that batteries are heavy, which reduces their effectiveness in mobile applications. A solution to this is structural batteries, which are batteries that can carry mechanical load while simultaneously storing energy. This can potentially lead to large weight savings on a systems level, since they may allow replacement of load bearing structures with structural batteries. Carbon fibers are suitable for structural batteries because they have superb mechanical properties and readily intercalate lithium ions, i.e. they can be used as electrodes in a lithium ion battery. However, to utilize carbon fibers in structural batteries, a polymer (matrix) is needed to form a composite battery. The polymer is required to have high modulus and high ion transport properties, which are inversely related, to function as an electrolyte. This thesis focuses on the development and characterization of such polymer electrolytes.

The first study was performed on a homogenous polymer electrolyte based on plasticized polyethylene glycol-methacrylate. The influence of crosslink density, salt concentration and plasticizer concentration on the mechanical and electrochemical properties were investigated. Increases in both ionic conductivity and storage modulus were obtained when, compared to non-plasticized systems. However, at high storage modulus (E’>500 MPa) the ionic conductivity (𝜎<10-7 S cm-1) is far from good enough for the realization of structural batteries.

In a second study, phase separated systems were therefore investigated. Polymerization induced phase separation (PIPS) via UV-curing was utilized to the produce structural battery electrolytes (SBE), consisting of liquid electrolyte and a stiff vinyl ester thermoset. The effect of monomer structure and volume fraction of liquid electrolyte on the morphology, electrochemical and mechanical properties were investigated. High storage modulus (750 MPa) in combination with high ionic conductivity (1.5 x 10-4 S cm-1) were obtained at ambient temperature. A SBE carbon fiber lamina half-cell was prepared via vacuum infusion and electrochemically cycled vs lithium metal. The results showed that both ion transport and load transfer was enabled through the SBE matrix.

In the third study the mechanical and electrochemical properties of the SBE-carbon fiber lamina were investigated and the multifunctional performance was evaluated. A new formulation of SBE, with a small addition of thiol monomer, were prepared with improved electrochemical and mechanical properties. The mechanical properties of the SBE carbon fiber lamina did not deteriorate after electrochemical cycling. The capacity of the SBE carbon fiber lamina half-cell was 232 ± 26 mAh g-1, at a C/20 charge rate. Furthermore, the lamina displayed multifunctional performance, compared to the monofunctional properties of its constituents.

In the final study, a new curing method was investigated, since UV-curing cannot be used to prepare full-cell carbon fiber composite structural batteries. Thermal curing was investigated to prepare the SBE. The PIPS was not adversely affected by the change in curing method, and the length scale of the phase separation in the SBE was slightly larger compared to UV-cured SBEs. The thermally cured SBEs exhibited improved thermomechanical properties without a reduction in the electrochemical properties. Thermal curing did not affect the electrochemical properties of the SBE carbon fiber lamina, however the type of carbon fiber utilized was found to negatively affect the cycling performance.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. , p. 55
Series
TRITA-CBH-FOU ; 2019:17
Keywords [en]
Structural batteries, Structural battery electrolyte, Lithium ion batteries, Polymerization induced phase separation, Carbon fibers
National Category
Polymer Chemistry
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-247270ISBN: 978-91-7873-152-7 (print)OAI: oai:DiVA.org:kth-247270DiVA, id: diva2:1298075
Public defence
2019-04-26, F3, Lindstedtsvägen 26, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, 37712-1
Note

QC 20190325

Available from: 2019-03-26 Created: 2019-03-21 Last updated: 2019-03-26Bibliographically approved
List of papers
1. Improved performance of solid polymer electrolytes for structural batteries utilizing plasticizing co-solvents
Open this publication in new window or tab >>Improved performance of solid polymer electrolytes for structural batteries utilizing plasticizing co-solvents
2017 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 134, no 23, article id 44917Article in journal (Refereed) Published
Abstract [en]

This study describes the formulation, curing, and characterization of solid polymer electrolytes (SPE) based on plasticized poly(ethylene glycol)-methacrylate, intended for use in structural batteries that utilizes carbon fibers as electrodes. The effect of crosslink density, salt concentration, and amount of plasticizer has been investigated. Adding a plasticizing solvent increases the overall performance of the SPE. Increased ionic conductivity and mechanical performance can be attained compared to similar systems without plasticizer. At ambient temperature, ionic conductivity (sigma) of 3.3 x 10(-5) Scm(-1), with a corresponding storage modulus (E) of 20 MPa are reached.

Place, publisher, year, edition, pages
WILEY, 2017
Keywords
lithium ion, plasticizer, solid polymer electrolyte, structural battery, thermoset
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-206228 (URN)10.1002/app.44917 (DOI)000397614000016 ()2-s2.0-85012878893 (Scopus ID)
Note

QC 20170517

Available from: 2017-05-17 Created: 2017-05-17 Last updated: 2019-03-21Bibliographically approved
2. Structural lithium ion battery electrolytes via reaction induced phase-separation
Open this publication in new window or tab >>Structural lithium ion battery electrolytes via reaction induced phase-separation
Show others...
2017 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 48, p. 25652-25659Article in journal (Refereed) Published
Abstract [en]

For the realization of structural batteries, electrolytes where both higher ionic conductivity and stiffness are combined need to be developed. The present study describes the formation of a structural battery electrolyte (SBE) as a two phase system using reaction induced phase separation. A liquid electrolyte phase is combined with a stiff vinyl ester based thermoset matrix to form a SBE. The effect of monomer structure variations on the formed morphology and electrochemical and mechanical performance has been investigated. An ionic conductivity of 1.5 x 10(-4) S cm(-1), with a corresponding storage modulus (E') of 750 MPa, has been obtained under ambient conditions. The SBEs have been combined with carbon fibers to form a composite lamina and evaluated as a battery half-cell. Studies on the lamina revealed that both mechanical load transfer and ion transport are allowed between the carbon fibers and the electrolyte. These results pave the way for the preparation of structural batteries using carbon fibers as electrodes.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-220591 (URN)10.1039/c7ta04684g (DOI)000417953100058 ()2-s2.0-85038213596 (Scopus ID)
Note

QC 20180117

Available from: 2018-01-17 Created: 2018-01-17 Last updated: 2019-03-21Bibliographically approved
3. Multifunctional performance of a carbon fiber UD lamina electrode for structural batteries
Open this publication in new window or tab >>Multifunctional performance of a carbon fiber UD lamina electrode for structural batteries
Show others...
2018 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 168, p. 81-87Article in journal (Refereed) Published
Abstract [en]

In electric transportation there is an inherent need to store electrical energy while maintaining a low vehicle weight. One way to decrease the weight of the structure is to use composite materials. However, the electrical energy storage in today's systems contributes to a large portion of the total weight of a vehicle. Structural batteries have been suggested as a possible route to reduce this weight. A structural battery is a material that carries mechanical loads and simultaneously stores electrical energy and can be realized using carbon fibers both as a primary load carrying material and as an active battery electrode. However, as yet, no proof of a system-wide improvement by using such structural batteries has been demonstrated. In this study we make a structural battery composite lamina from carbon fibers with a structural battery electrolyte matrix, and we show that this material provides system weight benefits. The results show that it is possible to make weight reductions in electric vehicles by using structural batteries. 

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Carbon fibers, Electrodes, Electrolytes, Vehicles, Battery electrode, Electric transportation, Electrical energy, Electrical energy storages, Mechanical loads, Multifunctional performance, Structural batteries, Weight reduction, Secondary batteries
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-236594 (URN)10.1016/j.compscitech.2018.08.044 (DOI)000452342800010 ()2-s2.0-85053778783 (Scopus ID)
Note

QC 20181126

Available from: 2018-11-26 Created: 2018-11-26 Last updated: 2019-04-08Bibliographically approved
4. Bicontinuous electrolytes via thermally initiated polymerization for structural lithium ion batteries.
Open this publication in new window or tab >>Bicontinuous electrolytes via thermally initiated polymerization for structural lithium ion batteries.
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
Research subject
Fibre and Polymer Science; Energy Technology
Identifiers
urn:nbn:se:kth:diva-247267 (URN)
Note

QC 20190325

Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-03-26Bibliographically approved

Open Access in DiVA

The full text will be freely available from 2020-03-25 10:42
Available from 2020-03-25 10:42

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Ihrner, Niklas

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