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Porosity Blocking in Highly Porous Carbon Black by PVdF Binder and Its Implications for the Li-S System
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 45, 25890-25898 p.Article in journal (Refereed) Published
Abstract [en]

In this work, the influence of cathode binders on the porosity of composite electrodes for lithiumsulfur (LiS) batteries employing high surface area carbon blacks has been closely scrutinized. This has been accomplished by comparison of PVdF with the related copolymer, PVdF-HFP. Analysis of carbon black porosity after addition of binder in NMP solution reveals that PVdF(-HFP) fills pores of almost any size in carbon black, which can effect a severe reduction in pore volume and surface area accessible to the electrolyte in a LiS cell. Noting the different swelling behavior of both binders, the implications of pore filling by the binder on the electrochemistry of LiS cells can be determined. Because of the low swellability of PVdF in dimethoxyethane:dioxolane (DME:DOL)-based electrolytes, access of the electrolyte to the carbon surface area and pore volume is restricted, with potentially severe detrimental effects on the available capacity of the cell. Furthermore, this effect is still clearly significant for common binder loadings and with preinfiltration of sulfur; this study is therefore a clear demonstration that PVdF is an unsuitable choice of binder for the lithiumsulfur system and that alternatives must be considered.

Place, publisher, year, edition, pages
2014. Vol. 118, no 45, 25890-25898 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-239773DOI: 10.1021/jp508137mISI: 000344978000009OAI: oai:DiVA.org:uu-239773DiVA: diva2:775172
Available from: 2014-12-30 Created: 2014-12-30 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Functional Binders at the Interface of Negative and Positive Electrodes in Lithium Batteries
Open this publication in new window or tab >>Functional Binders at the Interface of Negative and Positive Electrodes in Lithium Batteries
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, electrode binders as vital components in the fabrication of composite electrodes for lithium-ion (LIB) and lithium-sulfur batteries (LiSB) have been investigated.

Poly(vinylidene difluoride) (PVdF) was studied as binder for sulfur-carbon positive electrodes by a combination of galvanostatic cycling and nitrogen absorption. Poor binder swelling in the electrolyte and pore blocking in the porous carbon were identified as origins of low discharge capacity, rendering PVdF-based binders an unsuitable choice for LiSBs. More promising candidates are blends of poly(ethylene oxide) (PEO) and poly(N-vinylpyrrolidone) (PVP). It was found that these polymers interact with soluble lithium polysulfide intermediates generated during the cell reaction. They can increase the discharge capacity, while simultaneously improving the capacity retention and reducing the self-discharge of the LiSB. In conclusion, these binders improve the local electrolyte environment at the electrode interface.

Graphite electrodes for LIBs are rendered considerably more stable in ‘aggressive’ electrolytes (a propylene carbonate rich formulation and an ether-based electrolyte) with the poorly swellable binders poly(sodium acrylate) (PAA-Na) and carboxymethyl cellulose sodium salt (CMC-Na). The higher interfacial impedance seen for the conventional PVdF binder suggests a protective polymer layer on the particles. By reducing the binder content, it was found that PAA-Na has a stronger affinity towards electrode components with high surface areas, which is attributed to a flexible polymer backbone and a higher density of functional groups.

Lastly, a graphite electrode was combined with a sulfur electrode to yield a balanced graphite-sulfur cell. Due to a more stable electrode-electrolyte interface the self-discharge of this cell could be reduced and the cycle life was extended significantly. This example demonstrates the possible benefits of replacing the lithium metal negative electrode with an alternative electrode material.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2015. 58 p.
Keyword
binder, lithium-sulfur batteries, graphite, lithium-ion batteries
National Category
Physical Chemistry Polymer Chemistry Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-267557 (URN)
Presentation
2015-12-16, 2005, Department of Chemistry - Ångström, Lägerhyddsvägen 1, Uppsala, 16:15 (English)
Opponent
Supervisors
Available from: 2015-11-26 Created: 2015-11-24 Last updated: 2015-11-26Bibliographically approved

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Lacey, Matthew J.Jeschull, FabianEdström, KristinaBrandell, Daniel

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