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Polymers at the Electrode-Electrolyte Interface: Negative Electrode Binders for Lithium-Ion Batteries
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. (Struturkemi)
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. , p. 84
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1490
Keywords [en]
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: urn:nbn:se:uu:diva-317739ISBN: 978-91-554-9855-9 (print)OAI: oai:DiVA.org:uu-317739DiVA, id: diva2:1082653
Public defence
2017-05-05, Ång/10132, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilAvailable from: 2017-04-11 Created: 2017-03-17 Last updated: 2017-04-21
List of papers
1. Functional binders as graphite exfoliation suppressants in aggressive electrolytes for lithium-ion batteries
Open this publication in new window or tab >>Functional binders as graphite exfoliation suppressants in aggressive electrolytes for lithium-ion batteries
2015 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 175, p. 141-150Article in journal (Refereed) Published
Abstract [en]

A comparative study of various electrode binders for graphite electrodes was conducted in a carbonate-based electrolyte with a high content of propylene carbonate (PC) as a means to evaluate anode degradation in presence of different binders. Because of its direct contact with the active material, a binder can be interpreted as an interfacial layer and as a local part of the electrolyte, the properties of which greatly depend on the interaction with the liquid electrolyte. In this work we demonstrate how a carefully chosen binder can create a specific surface environment that can protect graphite from exfoliation when the binder exhibits poor solubility in the electrolyte solvent and good surface adhesion to the active material. The exceptional stability of graphite electrodes containing poly(acrylic acid) sodium salt (PAA-Na) and carboxymethyl cellulose sodium salt (CMC-Na), respectively, in a PC-rich electrolyte is explained through the understanding of binder swelling and functionality. Interfacial resistances and electrochemical stability were investigated with impedance spectroscopy and galvanostatic cycling. Electrode morphologies and distributions of material were analysed with SEM and EDX. Evidence is presented that the surface selectivity increases with concentration of functional groups and polymer flexibility. Therefore only the less selective, stiff polymer with less functional groups, CMC-Na, provides sufficient protection at low binder contents.

Keywords
Binder, graphite exfoliation, CMC, propylene carbonate, SEI
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-262960 (URN)10.1016/j.electacta.2015.03.072 (DOI)000360178600019 ()
Funder
Swedish Research Council, 2012-3837
Available from: 2015-09-29 Created: 2015-09-23 Last updated: 2017-12-01Bibliographically approved
2. A stable graphite negative electrode for the lithium-sulfur battery
Open this publication in new window or tab >>A stable graphite negative electrode for the lithium-sulfur battery
2015 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 51, no 96, p. 17100-17103Article in journal (Refereed) Published
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-267760 (URN)10.1039/C5CC06666B (DOI)000367469400011 ()26451894 (PubMedID)
Funder
Swedish Research Council, 2012-3837VINNOVAStandUp
Available from: 2015-11-26 Created: 2015-11-26 Last updated: 2017-12-30
3. Influence of inactive electrode components on degradation phenomena in nano-Si electrodes for Li-ion batteries
Open this publication in new window or tab >>Influence of inactive electrode components on degradation phenomena in nano-Si electrodes for Li-ion batteries
Show others...
2016 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 325, p. 513-524Article 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.

Keywords
Silicon anode, Carbon black, Binder, Artificial solid-electrolyte interface, X-ray photoelectron spectroscopy
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-307859 (URN)10.1016/j.jpowsour.2016.06.059 (DOI)000381165600059 ()
Funder
Swedish Research Council, 2012-3837Swedish Energy AgencyStandUp
Available from: 2016-11-22 Created: 2016-11-22 Last updated: 2017-12-30
4. Binder content dependence of electrochemical properties and interphase composition in Graphite:PVdF-HFP electrodes.
Open this publication in new window or tab >>Binder content dependence of electrochemical properties and interphase composition in Graphite:PVdF-HFP electrodes.
(English)Manuscript (preprint) (Other academic)
Abstract
Keywords
Li-ion battery, binder, poly(vinylidene difluoride), photoelectron spectroscopy
National Category
Chemical Sciences
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-317199 (URN)
Funder
Swedish Research CouncilStandUp
Available from: 2017-03-11 Created: 2017-03-11 Last updated: 2018-01-03
5. The Effects of Binders on Interface Layer Formation on Li4Ti5O12 Electrodes
Open this publication in new window or tab >>The Effects of Binders on Interface Layer Formation on Li4Ti5O12 Electrodes
Show others...
(English)Manuscript (preprint) (Other academic)
Keywords
Li-ion battery, Li4Ti5O12 anode, binder, interface layer, photoelectron spectroscopy
National Category
Chemical Sciences
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-317200 (URN)
Funder
Swedish Research CouncilStandUpSwedish Energy Agency, Batterifonden
Available from: 2017-03-11 Created: 2017-03-11 Last updated: 2017-12-30
6. Water-Soluble Binders for Lithium-Ion Battery Graphite Electrodes: Slurry Rheology, Coating Adhesion and Electrochemical Performance
Open this publication in new window or tab >>Water-Soluble Binders for Lithium-Ion Battery Graphite Electrodes: Slurry Rheology, Coating Adhesion and Electrochemical Performance
2017 (English)In: Energy technology: generation, conversion, storage, distribution, E-ISSN 2194-4296, Vol. 5, no 11, p. 2108-2118Article in journal (Refereed) Published
Abstract [en]

Water-processable composite electrodes are attractive both ecologically and economically. The binders sodium carboxymethyl cellulose (CMC-Na) and poly(sodium acrylate) (PAA-Na) were shown to have improved electrochemical performance over conventional binders. In many studies, a binder content of approximately 10 wt % has been applied, which is not suitable for large-scale electrode production due to viscosity and energy-density considerations. Therefore, we examined herein three electrode formulations with binder contents of 4 wt %, namely, CMC-Na:SBR (SBR=styrene butadiene rubber), PAA-Na, and CMC-Na:PAA-Na, on both laboratory and pilot scales. The formulations were evaluated on the basis of slurry rheology, coating adhesion, and electrochemical behavior in half- and full-cells. CMC-Na:SBR composites provided the best coating adhesion, independent of the mass loading and scale, and also showed the best capacity retention after 100 cycles. Previously reported merits of better cycling efficiencies and solid–electrolyte interphase formation for graphite–PAA composites appeared to vanish upon reducing the binder content to realistic levels.

Keywords
Li-ion battery, Graphite, Binder, Rheology, Electrode Coating
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-317257 (URN)10.1002/ente.201700200 (DOI)000417576700024 ()
Funder
Swedish Research Council
Available from: 2017-03-12 Created: 2017-03-12 Last updated: 2018-03-09Bibliographically approved
7. Analysis of the solid-electrolyte interphase of water-processed graphite electrodes by photoelectron spectroscopy
Open this publication in new window or tab >>Analysis of the solid-electrolyte interphase of water-processed graphite electrodes by photoelectron spectroscopy
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract
Keywords
Li-ion battery, XPS, HAXPES, CMC-Na, PAA, graphite
National Category
Chemical Sciences
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-317258 (URN)
Funder
Swedish Research CouncilStandUp
Available from: 2017-03-12 Created: 2017-03-12 Last updated: 2018-01-03

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