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Development of functional polymer systems for use in lithium-ion batteries
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Jolley, Michael James (2022) Development of functional polymer systems for use in lithium-ion batteries. EngD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3930032
Abstract
Silicon is a promising candidate as the anode active material for the next generation of lithium-ion batteries (LIBs), due to its relative abundance and high theoretical capacity. To make silicon a viable commercial option, polymer binder systems must be developed which are both electrochemically stable, and mechanically robust enough to accommodate the dramatic volume expansion experienced during cycling. This Innovation Report explores the innovative approach of developing a binder system which combines polyacrylic acid (PAA) and styrene butadiene rubber (SBR) latex simultaneously. Here, the PAA component would provide the electrode with the necessary adhesion strength, while the SBR component would improve flexibility to assist in accommodating the strain from the volume expansion.
However, as PAA and SBR contain different functional groups, they will phase separate out if they are simply mixed. If used as the binder system this mixture results in electrodes with poor electrochemical performance. To overcome this issue, a PAA-g-SBR copolymer binder system was developed and investigated for use in silicon/graphite anodes. The PAA-g-SBR copolymer was successfully synthesized by grafting tert-butyl acrylate on to SBR, and then hydrolysing away the tert-butyl groups. The resultant PAA-g-SBR copolymer was used as the binder system in silicon/graphite anodes with 80 % partially neutralised Na-PAA in a 1:1 ratio. The Na-PAA was also tested with standard SBR in the same ratio, and polymer films were made of both binder systems. Phase separation was observed to occur between the Na-PAA and SBR in the Na-PAA/SBR sample. However, phase separation was found not to occur with the Na-PAA/PAA-g-SBR sample, indicating that the surfaces of the SBR particles had been made more chemically compatible with Na-PAA.
During electrochemical testing, the Na-PAA/PAA-g-SBR system was found to provide superior electrochemical performances to the Na-PAA/SBR system. This was due to the PAA-g-SBR being more chemically compatible with Na-PAA, meaning less phase separation occurred, and resulted in an overall better quality of electrode coating. The Na-PAA/PAA-g-SBR system also displayed more preferable mechanical properties, with a higher adhesion strength, a lower Young’s modulus value and a larger strain at failure compared to that of the Na-PAA/SBR system. These enhanced mechanical properties allowed the Na-PAA/PAA-g-SBR binder system, to maintain the electrodes microstructure more effectively during cycling. Overall, these findings indicate a promising polymer binder system for the application of silicon/graphite anodes in the next generation of LIBs.
Item Type: | Thesis (EngD) | ||||
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Subjects: | T Technology > TK Electrical engineering. Electronics Nuclear engineering | ||||
Library of Congress Subject Headings (LCSH): | Lithium ion batteries -- Materials, Silicon, Binders (Materials), Electrodes -- Design and construction, Electrodes -- Materials, Polymers | ||||
Official Date: | June 2022 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | EngD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Loveridge, Melanie ; Wan, Chaoying | ||||
Format of File: | |||||
Extent: | xxiii, 155 pages : illustrations (some colour) | ||||
Language: | eng |
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