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- Ciosek Högström, Katarzyna, 1984-, et al.
(author)
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Impact of the flame retardant additive triphenyl phosphate (TPP) on the performance of graphite/LiFePO4 cells in high power applications
- 2014
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 256, s. 430-439
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Journal article (peer-reviewed)abstract
- This study presents an extensive characterization of a standard Li-ion battery (LiB) electrolyte containing different concentrations of the flame retardant triphenyl phosphate (TPP) in the context of high power applications. Electrolyte characterization shows only a minor decrease in the electrolyte flammability for low TPP concentrations. The addition of TPP to the electrolyte leads to increased viscosity and decreased conductivity. The solvation of the lithium ion charge carriers seem to be directly affected by the TPP addition as evidenced by Raman spectroscopy and increased mass-transport resistivity. Graphite/LiFePO4 full cell tests show the energy efficiency to decrease with the addition of TPP. Specifically, diffusion resistivity is observed to be the main source of increased losses. Furthermore, TPP influences the interface chemistry on both the positive and the negative electrode. Higher concentrations of TPP lead to thicker interface layers on LiFePO4. Even though TPP is not electrochemically reduced on graphite, it does participate in SEI formation. TPP cannot be considered a suitable flame retardant for high power applications as there is only a minor impact of TPP on the flammability of the electrolyte for low concentrations of TPP, and a significant increase in polarization is observed for higher concentrations of TPP. (C) 2014 Elsevier B.V. All rights reserved.
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| 2. |
- Leijonmarck, Simon, et al.
(author)
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Direct electropolymerization of polymer electrolytes onto carbon fibers - A route to structural batteries?
- 2014
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In: 16th European Conference on Composite Materials, ECCM 2014. - : European Conference on Composite Materials, ECCM. - 9780000000002
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Conference paper (peer-reviewed)abstract
- In an effort to further reduce weight of carbon fibre reinforced composites, the concept of structural batteries has arisen. A structural battery is a multifunctional material managing both energy storage and enabling of structural integrity. More specific, the carbon fibres in the composites are used as negative electrode in a Li-ion battery. A crucial part of such a battery is the preparation of a thin, ionically conductive and stiff polymer matrix. One route to realize this is the use of electropolymerization, which can cover each individual fibre with polymer. In this study, the surface morphology of coated carbon fibres is investigated with electron microscopy and atomic force microscopy. Additionally, the curing degree as a function of process temperature during polymerization is tested.
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| 3. |
- Willgert, Markus, et al.
(author)
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Cellulose nanofibril reinforced composite electrolytes for lithium ion battery applications
- 2014
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 2:33, s. 13556-13564
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Journal article (peer-reviewed)abstract
- The present study describes the synthesis and characterization of a series of four composite electrolytes for lithium ion battery applications. The two-phase electrolytes are composed of a soft, ionic conductive poly(ethylene glycol) (PEG) matrix having stiff nanofibrillated cellulose (CNF) paper as reinforcement to provide mechanical integrity. The reinforcing CNF is modified in order to create covalent bonds between the phases which is particularly beneficial when swelling the composite with a liquid electrolyte to enhance the ionic conductivity. After swelling the composite polymer electrolyte, forming a gelled structure, values of ionic conductivity at 5 x 10(-5) S cm(-1) and an elastic modulus around 400 MPa at 25 degrees C are obtained.
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| 4. |
- Öberg, Henrik
(author)
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Electronic structure and spectroscopy calculations in fuel cell catalysis
- 2011
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Licentiate thesis (other academic/artistic)abstract
- This thesis presents joint experimental and theoretical studies of surface phenomena at an electronic structure level in proton exchange membrane fuel cells (PEM-FC's). The fuel cell activity can be related to the oxygen reduction taking place at the cathodic surface through the oxygen reduction reaction (ORR). Under certain conditions the dissociative adsorption of O2 becomes the rate limiting reaction step and may therefore affect the overall fuel cell activity. Using core-level spectroscopy in terms of X-ray Photoemission Spectroscopy (XPS), the O2 dissociation barrier on Pt(111) has been determined and density functional theory (DFT) calculations reproduce the estimate well, using structure models that account for lateral adsorbate-adsorbate interactions, a finding that may have implications on the approach to calculate electronic structure properties of heterogeneous surface catalysis. Through a Brønsted-Evans-Polanyi (BEP) relation, the activation barrier for dissociation can be connected to the chemisorption energy of the atomic oxygen binding to the Pt surface. By affecting this energy, the activity of the fuel cell can be tuned; straining the Pt lattice weakens the O-Pt bond according to the Nørskov-Hammer d-band model which relates the adsorbate-substrate chemisorption energy to the position of the d-band center relative the Fermi level. X-ray Absorption (XAS) and Emission Spectroscopy (XES) have been used together with DFT to investigate the electronic structure effect in Pt due to strain, by depositing overlayers of Pt on Cu(111). The d-band model can to some extent be employed to describe the strain effect - but the discrepancies between the calculations and the experiments remain an open question at present. Furthermore, the oxidation of the Pt(111) surface have been studied using XPS and XAS. DFT calculations support the experimental picture and suggest an oxidation resulting in an α-PtO2 type of surface-oxide.
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