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Influence of inactive electrode components on degradation phenomena in nano-Si electrodes for Li-ion batteries
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Structure and Molecular Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Structure and Molecular Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Structure and Molecular Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Structure and Molecular Biology.
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2016 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 325, 513-524 p.Article in journal (Refereed) Published
Abstract [en]

The electrode morphology and electrochemistry of silicon nanocomposite electrodes containing either carboxymethyl cellulose (CMC-Na) or poly(acrylic acid) (PAA) binders are examined in context of their working surface area. Using porous carbon (Ketjenblack) additives, coatings with poor adhesion properties and deep cracks were obtained. The morphology is also reflected in the electrochemical behavior under capacity-limited conditions. Mapping the differential capacity versus potential over all cycles yields detailed insights into the degradation processes and shows the onset of cell failure with the emergence of lithium-rich silicon alloys at low potentials, well before capacity fading is observed. Fading occurs faster with electrodes containing PAA binder. The surface area of the electrode components is a major cause of increased irreversible reaction and capacity fade. Synchrotron-based X-ray photoelectron spectroscopy on aged, uncycled electrodes revealed accelerated conversion of the native SiOx-layer to detrimental SiOxFy in presence of Ketjenblack. In contrast, a conventional carbon black better preserved the SiOx-layer. This effect is attributed to preferred adsorption of binder on high surface area electrode components and highlights the role of binders as 'artificial SEI-layers'. This work demonstrates that optimization of nanocomposites requires careful balancing of the surface areas and amounts of all the electrode components applied.

Place, publisher, year, edition, pages
2016. Vol. 325, 513-524 p.
Keyword [en]
Silicon anode, Carbon black, Binder, Artificial solid-electrolyte interface, X-ray photoelectron spectroscopy
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-307859DOI: 10.1016/j.jpowsour.2016.06.059ISI: 000381165600059OAI: oai:DiVA.org:uu-307859DiVA: diva2:1048921
Funder
Swedish Research Council, 2012-3837Swedish Energy Agency
Available from: 2016-11-22 Created: 2016-11-22 Last updated: 2017-03-17Bibliographically approved
In thesis
1. Polymers at the Electrode-Electrolyte Interface: Negative Electrode Binders for Lithium-Ion Batteries
Open this publication in new window or tab >>Polymers at the Electrode-Electrolyte Interface: Negative Electrode Binders for Lithium-Ion Batteries
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We are today experiencing an increasing demand for high energy density storage devices like the lithium-ion battery for applications in portable electronic devices, electric vehicles (EV) and as interim storage for renewable energy. High capacity retention and long cycle life are prerequisites, particularly for the EV market. The key for a long cycle life is the formation of a stable solid-electrolyte interphase (SEI) layer on the surface of the negative electrode, which typically forms on the first cycles due to decomposition reactions at the electrode-electrolyte interface. More control over the surface layer can be gained when the layer is generated prior to the battery operation. Such a layer can be tailored more easily and can reduce the loss of lithium inventory considerably. In this context, water-soluble electrode binders, e.g. sodium carboxymethyl cellulose (CMC-Na) and poly(acrylic acid) (PAA), have proven themselves exceptionally useful. Since the binder is a standard component in composite electrodes anyway, its integration into the electrode fabrication process is easily accomplished.

This thesis work investigates the parameters that govern binder distribution in elec-trode coatings, control the stability and electrochemical performance of the elec-trode and that determine the composition of the surface layer. Several commonly used electrode materials (graphite, silicon and lithium titanate) have been applied in order to study the impact of the binder on the electrode morphology and the differ-ent electrode-electrolyte interfaces. The results are correlated with the electrochemi-cal performance and with the SEI composition obtained by in-house and synchro-tron-based photoelectron spectroscopy (PES).

The results demonstrate that the poor swellability of these water-soluble binders leads to a protection of the active material, given that the surface coverage is high and the binder evenly distributed. Although on the laboratory scale electrode formu-lations with a high binder content are common, they have little practical use in commercial devices due to the high content of inactive material. As the binder con-tent is decreased, complete surface coverage is more difficult to achieve and the binder distribution is more strongly coupled to the particle-binder interactions during the preparation process. Moreover, it is demonstrated in this thesis how these inter-actions are related to the surface area of the electrode components applied, the surface composition and the electrochemistry of the electrode. As a result of the smaller binder contents the benefits provided by CMC-Na and PAA at the electrode surface are compromised and the performance differs less distinctly from electrodes fabricated with the conventional binder, i.e. poly(vinylidene difluoride) (PVdF). Composites of alloying and conversion materials, on the other hand, typically em-ploy binders in larger amounts. Despite the frequently noted resiliency to volume expansion, which is also a positive side effect of the poor swellability of the binder in the electrolyte, the protection of the surface and the formation of a more stable interface are the major cause for the improved electrochemical behaviour, com-pared to electrodes employing PVdF binders.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 84 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1490
Keyword
binder, CMC-Na, PAA, graphite, silicon, lithium-ion battery, photoelectron spectros-copy
National Category
Chemical Sciences
Research subject
Chemistry with specialization in Materials Chemistry; Chemistry with specialization in Polymer Chemistry; Chemistry with specialization in Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-317739 (URN)978-91-554-9855-9 (ISBN)
Public defence
2017-05-05, Ång/10132, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2017-04-11 Created: 2017-03-17 Last updated: 2017-04-21

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