1. |
|
|
2. |
|
|
3. |
- Costa, Luciano T., et al.
(author)
-
Polymer-ionic liquid ternary systems for Li-battery electrolytes : Molecular dynamics studies of LiTFSI in a EMIm-TFSI and PEO blend
- 2015
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 143:2
-
Journal article (peer-reviewed)abstract
- This paper presents atomistic molecular dynamics simulation studies of lithium bis(trifluoromethane) sulfonylimide (LiTFSI) in a blend of 1-ethyl-3-methylimidazolium (EMIm)-TFSI and poly(ethylene oxide) (PEO), which is a promising electrolyte material for Li- and Li-ion batteries. Simulations of 100 ns were performed for temperatures between 303 K and 423 K, for a Li:ether oxygen ratio of 1:16, and for PEO chains with 26 EO repeating units. Li+ coordination and transportation were studied in the ternary electrolyte system, i.e., PEO16LiTFSI center dot 1.0 EMImTFSI, by applying three different force field models and are here compared to relevant simulation and experimental data. The force fields generated significantly different results, where a scaled charge model displayed the most reasonable comparisons with previous work and overall consistency. It is generally seen that the Li cations are primarily coordinated to polymer chains and less coupled to TFSI anion. The addition of EMImTFSI in the electrolyte system enhances Li diffusion, associated to the enhanced TFSI dynamics observed when increasing the overall TFSI anion concentration in the polymer matrix. (C) 2015 AIP Publishing LLC.
|
|
4. |
- Ek, Gustav, et al.
(author)
-
Li-ion batteries using electrolytes based on mixtures of poly(vinyl alcohol) and lithium bis(triflouromethane) sulfonamide salt
- 2017
-
In: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 246, s. 208-212
-
Journal article (peer-reviewed)abstract
- Poly(vinyl alcohol) (PVA) has, to a limited degree, previously been investigated as an alternative host material to the dominating poly(ethylene oxide)-(PEO)-based polymer electrolytes used in electrochemical applications. These PVA-materials were found to be highly ionically conducting for a number of different salts at temperatures below the glass transition temperature, but in the presence of DMSO (dimethyl sulfoxide) residues. Here, we investigate the PVA:LiTFSI (lithium bis(triflouromethane) sulfonamide) electrolytes system, thereby for the first time using the salt most commonly explored in PEO-based systems also in PVA. It is shown that this results in significantly higher conductivities than for alternative Li salts. Comparisons between electrolytes casted in DMSO, H2O and hot-pressed samples confirm the necessity of solvent residues present in the DMSO casted films for the ionic transport, although no obvious liquid phase is formed. Moreover, we also show the feasibility of PVA-based electrolytes by construction of functional Li-metal broken vertical bar PVA-LiTFSI (DMSO) broken vertical bar LiFePO4 batteries operating at 60 degrees C, displaying stable capacities of 136 mAh/g LiFePO4 at a rate of C/20. (C) 2017 Elsevier Ltd. All rights reserved.
|
|
5. |
|
|
6. |
|
|
7. |
|
|
8. |
- Jeschull, Fabian, et al.
(author)
-
Functional binders as graphite exfoliation suppressants in aggressive electrolytes for lithium-ion batteries
- 2015
-
In: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 175, s. 141-150
-
Journal article (peer-reviewed)abstract
- 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.
|
|
9. |
- Jeschull, Fabian, 1989-
(author)
-
Functional Binders at the Interface of Negative and Positive Electrodes in Lithium Batteries
- 2015
-
Licentiate thesis (other academic/artistic)abstract
- 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.
|
|
10. |
- Jeschull, Fabian, et al.
(author)
-
Influence of inactive electrode components on degradation phenomena in nano-Si electrodes for Li-ion batteries
- 2016
-
In: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 325, s. 513-524
-
Journal article (peer-reviewed)abstract
- 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.
|
|