| 1. |
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| 2. |
- Gode, Peter, et al.
(författare)
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In-situ measurements of gas permeability in fuel cell membranes using a cylindrical microelectrode
- 2002
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Ingår i: Journal of Electroanalytical Chemistry. - 0022-0728 .- 1873-2569. ; 518:2, s. 115-122
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Tidskriftsartikel (refereegranskat)abstract
- A new method to study permeation of gases in proton conducting membranes using a cylindrical microelectrode is presented. The focus of this work was to develop an in-situ method to study transport properties of hydrogen and oxygen close to real fuel cell operating conditions. The gas permeability is strongly affected by the change of water content in the membrane and it is therefore of advantage that, by using this method, measurements can be carried out over a wide range of relative humidities. The numerical method makes it possible to separate the diffusion coefficient and the concentration of dissolved gas in the membrane and also allows kinetic limitations to be taken into account. Chronoamperometric measurements on Nafion(R) 117 were successfully evaluated numerically. Experiments at temperatures of 25 and 60 degreesC with respect to oxygen permeation and at 60 degreesC for hydrogen permeation at relative humidities in the range 30-94% are presented. The reproducibility of data was excellent when measuring with different microelectrodes, on the same membrane sample, but differed when measuring on different samples. In general, the permeability increases with increasing temperature and relative humidity.
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| 3. |
- Gode, Peter, et al.
(författare)
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Influence of the composition on the structure and electrochemical characteristics of the PEFC cathode
- 2003
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 48:28, s. 4175-4187
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Tidskriftsartikel (refereegranskat)abstract
- The influence the composition of the cathode has on its structure and electrochemical performance was investigated for a Nafion content spanning from 10 to 70 wt.%. The cathodes were formed on a Nafion membrane by the spray method and using 20 wt.% Pt on Vulcan (E-TEK). Materials characterisation (SEM, STEM, gas and mercury porosimetry, electron conductivity) and electrochemical characterisation (steady-state polarisation curve, impedance spectroscopy in O-2 and current-pulse measurements in N-2) were performed. The impedance spectra were analysed using our dynamic agglomerate model. The results indicate that the agglomerate model is valid until a Nafion content of about 45 wt.%. Pt/C and Nation are homogeneously mixed for any composition and no Nafion film was observed. The cathodes containing 36-43 wt.% Nation display a single or double Tafel slope behaviour ascribed to diffusion limitations in the agglomerates. At larger Nation content, the agglomerate model can describe the curves only by assuming a diffusion coefficient 3-4 decades smaller than that of gases. At such compositions, the porosity was only 10%. These results were interpreted as a blocking of the pores and a non-percolating pore system for too large Nafion contents.
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| 4. |
- Gode, Peter, et al.
(författare)
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Membrane Durability in a PEM Fuel Cell Studied Using PVDF Based Radiation Grafted Membranes
- 2003
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Ingår i: Fuel Cells. - : Wiley. - 1615-6846 .- 1615-6854. ; 3:1-2, s. 21-27
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Tidskriftsartikel (refereegranskat)abstract
- The durability testing of membranes for use in a polymer electrolyte fuel cell (PEFC) has been studied in situ by a combination of galvanostatic steady-state and impedance measurements. The PEFC measurements, which are time consuming, have been compared to fast ex situ testing in 3% H2O 2 solution. For the direct assessment of membrane degradation micro-Raman spectroscopy and determination of ion exchange capacity (IEC) have been used. PVDF based membranes, radiation grafted with styrene and sulfonated, were used as model membranes. By using low degrees of grafting, below about 35%, the durability of this type of membrane can be increased. Degradation in the fuel cell was found to be highly localised. It was found that in situ measurements in the PEFC alone are not sufficient. Measurement of the cell resistance via impedance is not always a reliable indicator of changes in membrane resistance because other resistance changes in the cell can easily interfere and cannot be separated from those caused by the membrane. Micro-Raman is an ideal complementary method to in situ testing, but it is time consuming. For fast pre-screening of membrane durability mass loss measurements during exposure to 3% H2O2 solution combined with the determination of changes in the IEC can be performed.
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| 5. |
- Jaouen, Frédéric, et al.
(författare)
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Adhesive copper films for an air-breathing polymer electrolyte fuel cell
- 2005
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 144:1, s. 113-121
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Tidskriftsartikel (refereegranskat)abstract
- A design for an air-breathing and passive polymer electrolyte fuel cell is presented. Such a type of fuel cell is in general promising for portable electronics. In the present design, the anode current collector is made of a thin copper foil. The foil is provided with an adhesive and conductive coating, which firstly tightens the hydrogen compartment without mask or clamping pressure, and secondly secures a good electronic contact between the anode backing and the current collector. The cathode comprises a backing, a gold-plated stainless steel mesh and a current collector cut out from a printed circuit board. Three geometries for the cathode current collector were evaluated. Single cells with an active area of 2 cm(2) yielded a peak power of 250-300 MW cm(-2) with air and pure H-2 in a complete passive mode except for the controlled flow of H-2. The cells' response was investigated in steady state and transient modes.
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| 6. |
- Svens, Pontus, et al.
(författare)
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Li-Ion Pouch Cells for Vehicle Applications-Studies of Water Transmission and Packing Materials
- 2013
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 6:1, s. 400-410
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Tidskriftsartikel (refereegranskat)abstract
- This study includes analysis of encapsulation materials from lithium-ion pouch cells and water vapour transmission rate (WVTR) measurements. WVTR measurements are performed on both fresh and environmentally stressed lithium-ion pouch cells. Capacity measurements are performed on both the fresh and the environmentally stressed battery cells to identify possible influences on electrochemical performance. Preparation of the battery cells prior to WVTR measurements includes opening of battery cells and extraction of electrode material, followed by resealing the encapsulations and adhesively mounting of gas couplings. A model describing the water diffusion through the thermal welds of the encapsulation are set up based on material analysis of the encapsulation material. Two WVTR equipments with different type of detectors are evaluated in this study. The results from the WVTR measurements show how important it is to perform this type of studies in dry environment and apply a rigorous precondition sequence before testing. Results from modelling confirm that the WVTR method has potential to be used for measurements of water diffusion into lithium-ion pouch cells. Consequently, WVTR measurements should be possible to use as a complement or alternative method to for example Karl Fisher titration.
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| 7. |
- Acevedo Gomez, Yasna, et al.
(författare)
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Effect of nitrogen dioxide impurities on PEM fuel cell performance
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Air is the most practical and economical oxidant to feed to the cathode in a proton exchange membrane fuel cell (PEMFC). However, the air is accompanied by small amounts of impurities that affect the performance of the fuel cell. Among these, nitrogen dioxide is the impurity that has been least investigated, and its effect is not fully understood. In this study, a possible mechanism is proposed based on the contamination of the fuel cell at different concentrations and adsorption potentials, and by employing stripping cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results at different concentrations showed that the catalyst sites are blocked by the adsorption of NO2, and that there is a non-linear relationship between the concentration and degradation. The degradation is suggested to be related to the formation of intermediate species, as also shown by the pseudo-inductive impedance at the concentration of 100 and 200 ppm. Furthermore, the cyclic voltammetry showed that there is an oxidation to NO3- at 1.05 V, followed by the reduction of this specie to NO2- at 0.68 V, and a subsequent reduction of NO2- to N2O and/or NH2OH.
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| 8. |
- Acevedo Gomez, Yasna
(författare)
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On Gas Contaminants, and Bipolar Plates in Proton Exchange Membrane Fuel Cells
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The proton exchange membrane (PEM) fuel cell is an electrochemical device that converts chemical energy into electrical energy through two electrocatalytic reactions. The most common catalyst used is platinum on carbon (Pt/C), which has shown the best performance in the fuel cell until now. However, the drawback of this catalyst is that it does not tolerate impurities, and both hydrogen and oxygen may carry small amounts of impurities depending on the production sources. The purpose of this thesis is to understand the effect of two impurities that are less investigated, i.e., ammonia, which may accompany the hydrogen rich reformates from renewable sources, and nitrogen dioxide, which may come from air pollution. The mechanism of contamination and an adequate recovery method for the respective contaminant are studied. Additionally, electroplated bipolar plates with Ni-Mo and Ni-Mo-P coatings were tested as alternatives to stainless steel and carbon materials.The results show that ammonia not only provokes changes in the polymer membrane but also in the oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR) and catalyst ionomer in both electrodes. The extent of performance recovery after the contamination depends on the concentration used and the exposure time. In contrast, nitrogen dioxide affects the catalyst in the electrode directly; the contamination is related to side reactions that are produced on the catalyst’s surface. However, NO2 is not attached strongly to the catalyst and it is possible to restore the performance by using clean air. The time the recovery process takes depends on the potential applied and the air flow.Finally, the evaluation of electroplated Ni-Mo and Ni-Mo-P on stainless steel by ex situ and in situ studies shows that these coatings reduce the internal contact resistance (ICR) and the corrosion rate of the stainless steel considerably. However, the in situ experiments show that phosphorus addition to the coating does not improve the fuel cell performance; thus, the Ni-Mo alloy is found to be a promising choice for electroplating stainless steel bipolar plates.
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| 9. |
- Acevedo Gomez, Yasna, et al.
(författare)
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Performance recovery after contamination with nitrogen dioxide in a PEM fuel cell
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- While the market of fuel cell vehicles is increasing, these vehicles will still coexist with combustion engine vehicles on the roads and will be exposed to an environment with significant amounts of contaminants that will decrease the durability of the fuel cell. In order to investigate different recovery methods, a PEM fuel cell is in this study contaminated with 100 ppm of NO2 at the cathode side. The possibility to recover the cell performance is studied by using different airflow rates, different current densities, and by subjecting the cell to successive polarization curves. The results show that the successive polarization curves are the best choice for recovery; it took 35 min to reach full recovery of cell performance, compared to 4.5 hours of recovery with pure air at 0.5 A cm-2 and 110 ml min-1. However, the performance recovery at a current density of 0.2 A cm-2 and air flow 275 ml min-1 was done in 66 min, which is also a possible alternative. Additionally, two operation techniques are suggested and compared during 7 h of operation; air recovery and air depletion. The air recovery technique shows to be a better choice than the air depletion technique.
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| 10. |
- Acevedo Gomez, Yasna, et al.
(författare)
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Performance Recovery after Contamination with Nitrogen Dioxide in a PEM Fuel Cell
- 2020
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Ingår i: Molecules. - : MDPI. - 1431-5157 .- 1420-3049. ; 25:5
-
Tidskriftsartikel (refereegranskat)abstract
- While the market for fuel cell vehicles is increasing, these vehicles will still coexist with combustion engine vehicles on the roads and will be exposed to an environment with significant amounts of contaminants that will decrease the durability of the fuel cell. To investigate different recovery methods, in this study, a PEM fuel cell was contaminated with 100 ppm of NO2 at the cathode side. The possibility to recover the cell performance was studied by using different airflow rates, different current densities, and by subjecting the cell to successive polarization curves. The results show that the successive polarization curves are the best choice for recovery; it took 35 min to reach full recovery of cell performance, compared to 4.5 h of recovery with pure air at 0.5 A cm(-2) and 110 mL min(-1). However, the performance recovery at a current density of 0.2 A cm(-2) and air flow 275 mL min(-1) was done in 66 min, which is also a possible alternative. Additionally, two operation techniques were suggested and compared during 7 h of operation: air recovery and air depletion. The air recovery technique was shown to be a better choice than the air depletion technique.
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| 11. |
- Acevedo Gomez, Yasna, et al.
(författare)
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PERFORMANCE RECOVERY FROM NO2 EXPOSURE IN PEM FUEL CELL
- 2017
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Ingår i: EFC 2017 - Proceedings of the 7th European Fuel Cell Piero Lunghi Conference. - : ENEA. ; , s. 157-158
-
Konferensbidrag (refereegranskat)abstract
- The hydrogen fuel cell vehicle market is projected to increase in the coming years, and fuel cell vehicles will operate in an environment where they coexist with combustion engine vehicles. In this context, the PEM fuel cell will be exposed to significant amounts of contaminants on the roads that will decrease its performance and durability. In the present study the PEM fuel cell is exposed to 100 ppm of nitrogen dioxide in the airflow. Different methods for recovery of performance were tested; recovery during constant current load and by subjecting the cell to successive polarization curves. The results showed that the successive polarization curves are the best choice for recovery. However, recovery at low current density and high potential is also a good alternative.
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| 12. |
- Acevedo Gomez, Yasna, et al.
(författare)
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Reformate from biogas used as fuel in a PEM fuel cell
- 2013
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Ingår i: EFC 2013 - Proceedings of the 5th European Fuel Cell Piero Lunghi Conference. ; , s. 163-164
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Konferensbidrag (refereegranskat)abstract
- The performance of a PEM fuel cell can be easily degraded by introducing impurities in the fuel gas. Since reformate of biogas from olive mill wastes will contain at least one third of carbon dioxide, its influence was studied on a PtRu catalyst. A clean reformate gas for the anode (67% H2 and 33% CO2) without any traces of other compounds was used and electrochemical measurements showed that the performance of the fuel cell was hardly affected. However, diluting the hydrogen with higher amounts of CO2 will reduce the performance remarkably.
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| 13. |
- Ahlberg Tidblad, Annika, et al.
(författare)
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Surface analysis with ESCA and GD-OES of the film formed by cathodic reduction of chromate
- 1991
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Ingår i: Electrochimica Acta. ; 36:10, s. 1605-1610
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Tidskriftsartikel (refereegranskat)abstract
- In the chlorate process, a small addition of chromate to the electrolyte results in the formation of a cathode film, which inhibits the reduction of the intermediate hypochlorite ions. To enable surface characterization of the chromium film, it was grown by cathodic reduction onto gold and platinum substrates in hydroxide and chlorate solution. Surface analyses of this film by ESCA and GD-OES indicate that it has a distinct and constant chemical composition during growth given by the formula Cr(OH)3·xH2O. The film is thin, less than 50 Å on platinum and 80 Å on gold. It exhibits poor conductivity and covers the entire cathode surface. © 1991.
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| 14. |
- Ajpi, Cesario, et al.
(författare)
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Crystal structure and Hirshfeld surface analysis of poly[tris(mu(4)-benzene-1,4-dicarboxylato)tetrakis(di-methylformamide)tr inickel(II)] : a two-dimensional coordination network
- 2019
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Ingår i: Acta Crystallographica Section E: Crystallographic Communications. - : International Union of Crystallography. - 2056-9890. ; 75, s. 1839-1843
-
Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of the title compound, [Ni-3(C8H4O4)(3)(C3H7NO)(4)], is a two-dimensional coordination network formed by trinuclear linear Ni-3(tp)(3)(DMF)(4) units (tp = terephthalate = benzene-1,4-dicarboxylate and DMF = dimethyl-formamide) displaying a characteristic coordination mode of acetate groups in polynuclear metal-organic compounds. Individual trinuclear units are connected through tp anions in a triangular network that forms layers. One of the DMF ligands points outwards and provides interactions with equivalent planes above and below, leaving the second ligand in a structural void much larger than the DMF molecule, which shows positional disorder. Parallel planes are connected mainly through weak C-H center dot center dot center dot O, H center dot center dot center dot H and H center dot center dot center dot C interactions between DMF molecules, as shown by Hirshfeld surface analysis.
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| 15. |
- Ajpi, Cesario, et al.
(författare)
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Crystal structure and Hirshfeld surface analysis of poly[tris-(μ4-benzene-1,4-di-carboxyl-ato)tetra-kis-(di-methyl-formamide)-trinickel(II)] : a two-dimensional coordination network.
- 2019
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Ingår i: Acta crystallographica. Section E, Crystallographic communications. - 2056-9890. ; 75:Pt 12, s. 1839-1843
-
Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of the title compound, [Ni3(C8H4O4)3(C3H7NO)4], is a two-dimensional coordination network formed by trinuclear linear Ni3(tp)3(DMF)4 units (tp = terephthalate = benzene-1,4-di-carboxyl-ate and DMF = di-methyl-formamide) displaying a characteristic coordination mode of acetate groups in polynuclear metal-organic compounds. Individual trinuclear units are connected through tp anions in a triangular network that forms layers. One of the DMF ligands points outwards and provides inter-actions with equivalent planes above and below, leaving the second ligand in a structural void much larger than the DMF mol-ecule, which shows positional disorder. Parallel planes are connected mainly through weak C-H⋯O, H⋯H and H⋯C inter-actions between DMF mol-ecules, as shown by Hirshfeld surface analysis.
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| 16. |
- Ajpi Condori, Cesario, 1978-
(författare)
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Hybrid materials for lithium-ion batteries
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Lithium‐ion batteries are the most important power source for electronic devices as electronics, storage and the different electric vehicles. The research and development of new materials for different applications has increased, especially in the development of materials with better electrochemical properties (Specific capacity, rate capability, high energy density and cyclability). Inorganic materials such as LiFePO4, LiMn2O4 and organic materials such as Li4C6O6, quinones and anthraquinones, polyaniline (PANI) and others have been extensively studied. Improvement of the electrochemical properties involve different aspects as: control in the particle size of the materials, doping with other elements and the combination of the different properties of the organic an inorganic materials. The development of hybrids materials with improved electrochemical properties need a combination between of inorganic and organic structures. This type of hybrids materials are a very attractive option for the development of advanced materials. For the design of this type of hybrid materials it is necessary to form interactions between the inorganic and organic part (supramolecular chemistry). This opens up for using an immense amount of organic materials such as conductive polymers and PANI (Polyaniline) are attractive alternatives in the development of hybrid materials due to their excellent electronic conductivity. Other attractive types of hybrid materials are compounds based on metal-organic frameworks (MOF), coordination polymers (CP) and coordination networks (CN).This thesis work is focused in the synthesis, structural characterization and electrochemical characterization of two groups of hybrid materials: 1) LiFePO4-PANI synthetized by different methods.2) Metal-organic compounds M-BDC-DMF with M=Ni2+, Fe2+, C8H4O2=Terephthalate=BDC=Benzene dicarboxylate, DMF=N,N-dimethylformamide.The materials were synthesized by chemical oxidation methods combined with thermal treatment (LiFePO4-PANI-Li hybrid powder) and by solvothermal methods (M-BDC-DMF). The materials were characterized by SCXRD, PXRD, FTIR, SEM and electrochemical methods and the electrochemical characterization was carried out using CV, EIS and galvanostatics methods. The specific capacities of PANI was 95 mAh/g, of LiFePO4 was 120 mAh/g and of LiFePO4-PANI was 145 mAh/g at 0.1C. At 2C the capacity of LiFePO4 was 70 mAh/g and LiFePO4-PANI was 100 mAh/g. The specific capacities of Ni3(C8H4O4)3(C3H7NO)4 is ~50 mAh/g and Fe-BDC-DMF was ~175 mAh/g. The work has shown that PANI can improve the performance of LFP also at higher discharges rates. For M-BDC-DMF stability seems to be an issue which should be studied more in the future.
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| 17. |
- Ajpi Condori, Cesario, et al.
(författare)
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Synthesis and Characterization of LiFePO4-PANI Hybrid Material as Cathode for Lithium-Ion Batteries
- 2020
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:12
-
Tidskriftsartikel (refereegranskat)abstract
- This work focuses on the synthesis of LiFePO4-PANI hybrid materials and studies their electrochemical properties (capacity, cyclability and rate capability) for use in lithium ion batteries. PANI synthesis and optimization was carried out by chemical oxidation (self-assembly process), using ammonium persulfate (APS) and H3PO4, obtaining a material with a high degree of crystallinity. For the synthesis of the LiFePO4-PANI hybrid, a thermal treatment of LiFePO(4)particles was carried out in a furnace with polyaniline (PANI) and lithium acetate (AcOLi)-coated particles, using Ar/H(2)atmosphere. The pristine and synthetized powders were characterized by XRD, SEM, IR and TGA. The electrochemical characterizations were carried out by using CV, EIS and galvanostatic methods, obtaining a capacity of 95 mAhg(-1)for PANI, 120 mAhg(-1)for LiFePO(4)and 145 mAhg(-1)for LiFePO4-PANI, at a charge/discharge rate of 0.1 C. At a charge/discharge rate of 2 C, the capacities were 70 mAhg(-1)for LiFePO(4)and 100 mAhg(-1)for LiFePO4-PANI, showing that the PANI also had a favorable effect on the rate capability.
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| 18. |
- Ajpi Condori, Cesario, et al.
(författare)
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Synthesis and spectroscopic characterization of Fe3+-BDC metal organic framework as material for lithium ion batteries
- 2023
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Ingår i: Journal of Molecular Structure. - : Elsevier B.V.. - 0022-2860 .- 1872-8014. ; 1272
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Tidskriftsartikel (refereegranskat)abstract
- This work presents synthesis and spectroscopic characterization of a new metal-organic framework (MOF). The compound Fe-BDC-DMF was synthetized by the solvothermal method and prepared via a reaction between FeCl3.6H2O and benzene-1,4-dicarboxylic acid (H2BDC) or terephthalic acid using N,N-dimethylformamide (DMF) as solvent. The powder was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR) analysis. The electrochemical properties were investigated in a typical lithium-ion battery electrolyte by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charging and discharging. The synthetized Fe-BDC-DMF metal-organic framework (MOF) contains a mixture of three phases, identified by PXRD as: MOF-235, and MIL-53(Fe) monoclinic with C2/c and P21/c space groups. The structure of the Fe-BDC is built up from Fe3+ ions, terephalates (BDC) bridges and in-situ-generated DMF ligands. The electrochemical measurements conducted in the potential range of 0.5–3.5 V vs. Li+/Li0 show the voltage profiles of Fe-BDC and a plateau capacity of around 175 mAh/g. © 2022 The Author(s)
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| 19. |
- Ajpi Condori, Cesario, et al.
(författare)
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Synthesis and spectroscopic characterization of NiII coordination network : Poly-[tris(µ4-Benzene-1,4-dicarboxylato)-tetrakis(µ1-dimethylformamide-κ1O)-trinickel(II)] as material for lithium ion batteries
- 2022
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Ingår i: Journal of Molecular Structure. - : Elsevier B.V.. - 0022-2860 .- 1872-8014. ; 1265
-
Tidskriftsartikel (refereegranskat)abstract
- The compound Ni3(C8H4O4)3(C3H7NO)3, poly-[tris(µ4-Benzene-1,4-dicarboxylato)-tetrakis(µ1-dimethylformamide-κ1O)-trinickel(II)], was synthesized by the solvothermal method prepared via reaction between NiCl2•6H2O and terephthalic acid using N,N-dimethylformamide (DMF) as solvent. The structure was characterized by powder X-ray diffraction and infrared spectroscopy analyses. The electrochemical properties as a potential active material in lithium-ion batteries were characterized by electrochemical impedance spectroscopy and galvanostatic charge-discharge curves in a battery half-cell. The characterization results show that the coordination network contains one independent structure in the asymmetric unit. It is constructed from Ni2+ ions, terephthalate bridges and in-situ-generated DMF ligands, forming two similar two-dimensional (2D) layer structures. These similar 2D layers are in an alternating arrangement and are linked with each other by dense H—H interactions (45%) to generate a three-dimensional (3D) supramolecular framework with ordered and disordered DMF molecules. The electrochemical measurements, conducted in the potential range of 0.5–3.5 V vs Li/Li+, show that Ni3(C8H4O4)3(C3H7NO)4 has good electrochemical properties and can work as anode in lithium-ion batteries. The material presents an initial specific capacity of ∼420 mAh g−1, which drops during consecutive scans but stabilizes at ∼50 mAh g−1. However, due to the wide potential range there are indications of a gradual collapse of the structure. The electrochemical impedance spectroscopy shows an increase of charge transfer resistance from 24 to 1190 Ohms after cycling likely due to this collapse.
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| 20. |
- Andersson, Malin, et al.
(författare)
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Electrochemical model-based aging-adaptive fast charging of automotive lithium-ion cells
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Fast charging of electric vehicles remains a compromise between charging time and degradation penalty. Conventional battery management systems use experience-based charging protocols that are expected to meet vehicle lifetime goals. Novel electrochemical model-based battery fast charging uses a model to observe internal battery states. This enables control of charging rates based on states such as the lithium-plating potential but relies on an accurate model as well as accurate model parameters. However, the impact of battery degradation on the model’s accuracy and therefore the fitness of the estimated optimal charging procedure is often not considered. In this work, we therefore investigate electrochemical model-based aging-adaptive fast charging of automotive lithium-ion cells. First, an electrochemical model is identified at the beginning of life for 6 automotive prototype cells and the electrochemically constrained fast-charge is designed. The model parameters are then periodically re-evaluated during a cycling study and the charging procedure is updated to account for cell degradation. The proposed method is compared with two reference protocols to investigate both the effectiveness of selected electrochemical constraints as well as the benefit of aging-adaptive usage. Finally, post-mortem characterization is presented to highlight the benefit of aging-adaptive battery utilization.
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| 21. |
- Andersson, Malin, et al.
(författare)
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Electrochemical model-based aging-adaptive fast charging of automotive lithium-ion cells
- 2024
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 372
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Tidskriftsartikel (refereegranskat)abstract
- Fast charging of electric vehicles remains a compromise between charging time and degradation penalty. Conventional battery management systems use experience-based charging protocols that are expected to meet vehicle lifetime goals. Novel electrochemical model-based battery fast charging uses a model to observe internal battery states. This enables control of charging rates based on states such as the lithium-plating potential but relies on an accurate model as well as accurate model parameters. However, the impact of battery degradation on the model's accuracy and therefore the fitness of the estimated optimal charging procedure is often not considered. In this work, we therefore investigate electrochemical model-based aging-adaptive fast charging of automotive lithium-ion cells. First, an electrochemical model is identified at the beginning of life for 6 automotive prototype cells and the electrochemically constrained fast-charge is designed. The model parameters are then periodically re-evaluated during a cycling study and the charging procedure is updated to account for cell degradation. The proposed method is compared with two reference protocols to investigate both the effectiveness of selected electrochemical constraints as well as the benefit of aging-adaptive usage. Finally, post-mortem characterization is presented to highlight the benefit of aging-adaptive battery utilization.
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| 22. |
- Andersson, Malin, et al.
(författare)
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p Parametrization of physics-based battery models from input-output data : A review of methodology and current research
- 2022
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 521, s. 230859-
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Forskningsöversikt (refereegranskat)abstract
- Physics-based battery models are important tools in battery research, development, and control. To obtain useful information from the models, accurate parametrization is essential. A complex model structure and many unknown and hard-to-measure parameters make parametrization challenging. Furthermore, numerous applications require non-invasive parametrization relying on parameter estimation from measurements of current and voltage. Parametrization of physics-based battery models from input-output data is a growing research area with many recent publications. This paper aims to bridge the gap between researchers from different fields that work with battery model parametrization, since successful parametrization requires both knowledge of the underlying physical system as well as understanding of theory and concepts behind parameter estimation. The review encompasses sensitivity analyses, methods for parameter optimization, structural and practical identifiability analyses, design of experiments and methods for validation as well as the use of machine learning in parametrization. We highlight that not all model parameters can accurately be identified nor are all relevant for model performance. Nonetheless, no consensus on parameter importance could be shown. Local methods are commonly chosen because of their computational advantages. However, we find that the implications of local methods for analysis of non-linear models are often not sufficiently considered in reviewed literature.
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| 23. |
- Asp, Leif, 1966, et al.
(författare)
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A structural battery and its multifunctional performance
- 2021
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Ingår i: Advanced Energy and Sustainability Research. - : Wiley. - 2699-9412. ; 2:3
-
Tidskriftsartikel (refereegranskat)abstract
- Engineering materials that can store electrical energy in structural load paths can revolutionize lightweight design across transport modes. Stiff and strong batteries that use solid-state electrolytes and resilient electrodes and separators are generally lacking. Herein, a structural battery composite with unprecedented multifunctional performance is demonstrated, featuring an energy density of 24 Wh kg-1 and an elastic modulus of 25 GPa and tensile strength exceeding 300 MPa. The structural battery is made from multifunctional constituents, where reinforcing carbon fibers (CFs) act as electrode and current collector. A structural electrolyte is used for load transfer and ion transport and a glass fiber fabric separates the CF electrode from an aluminum foil-supported lithium–iron–phosphate positive electrode. Equipped with these materials, lighter electrical cars, aircraft, and consumer goods can be pursued.
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| 24. |
- Asp, Leif E, et al.
(författare)
-
Carbon Fibre Composite Structural Batteries: A Review
- 2019
-
Ingår i: Functional Composites and Structures. - : Institute of Physics (IOP). - 2631-6331.
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a comprehensive review of the state-of-the-art in structural battery composites research. Structural battery composites are a class of structural power composites aimed to provide mass-less energy storage for electrically powered structural systems. Structural battery composites are made from carbon fibres in a structural electrolyte matrix material. Neat carbon fibres are used as a structural negative electrode, exploiting their high mechanical properties, excellent lithium insertion capacity and high electrical conductivity. Lithium iron phosphate coated carbon fibres are used as the structural positive electrode. Here, the lithium iron phosphate is the electrochemically active substance and the fibres carry mechanical loads and conduct electrons. The surrounding structural electrolyte is lithium ion conductive and transfers mechanical loads between fibres. With these constituents, structural battery half-cells and full-cells are realised with a variety in device architecture. The paper also presents an overview of material modelling and characterisation performed to date. Particular reference is given to work performed in national and European research projects under the leadership of the authors, who are able to provide a unique insight into this emerging and exciting field of research.
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| 25. |
- Asp, Leif, 1966, et al.
(författare)
-
Realisation of structural battery composite materials
- 2015
-
Ingår i: ICCM International Conferences on Composite Materials. - : International Committee on Composite Materials.
-
Konferensbidrag (refereegranskat)abstract
- This paper introduces the concept of structural battery composite materials and their possible devices and the rationale for developing them. The paper presents an overview of the research performed in Sweden on a novel structural battery composite material. The research areas addressed include: carbon fibre electrodes, structural separators, multifunctional matrix materials, device architectures and material functionalization. Material characterization, fabrication and validation are also discussed. The paper focuses on a patented battery composite material technology. Here, carbon fibres are employed as combined negative battery electrodes and reinforcement, coated with a solid polymer electrolyte working simultaneously as electrolyte and separator with ability to transfer mechanical loads. The coated fibres are distributed in a conductive positive cathode material on an aluminium electron collector film. Efficient Li-ion transport between the electrodes is achieved by the solid polymer electrolyte coating being only a few hundred nanometres thick. Finally some outstanding scientific and engineering challenges are discussed. Such challenges, calling for further research are related to manufacture, development of new solid polymer electrolytes for improved multifunctionality and the lack of material models.
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| 26. |
- Asp, Leif, 1966, et al.
(författare)
-
Structural Battery Composites: A Review, Functional Composites and Structures
- 2019
-
Ingår i: Functional Composites and Structures. - : IOP Publishing. - 2631-6331. ; 1
-
Forskningsöversikt (refereegranskat)abstract
- This paper presents a comprehensive review of the state-of-the-art in structural battery composites research. Structural battery composites are a class of structural power composites aimed to provide mass-less energy storage for electrically powered structural systems. Structural battery composites are made from carbon fibres in a structural electrolyte matrix material. Neat carbon fibres are used as a structural negative electrode, exploiting their high mechanical properties, excellent lithium insertion capacity and high electrical conductivity. Lithium iron phosphate coated carbon fibres are used as the structural positive electrode. Here, the lithium iron phosphate is the electrochemically active substance and the fibres carry mechanical loads and conduct electrons. The surrounding structural electrolyte is lithium ion conductive and transfers mechanical loads between fibres. With these constituents, structural battery half-cells and full-cells are realised with a variety in device architecture. The paper also presents an overview of material modelling and characterisation performed to date. Particular reference is given to work performed in national and European research projects under the leadership of the authors, who are able to provide a unique insight into this emerging and exciting field of research.
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| 27. |
- Benavente Araoz, Fabian Andres, et al.
(författare)
-
An Aging Study of NCA/Si-Graphite Lithium-Ion Cells for Off-Grid Photovoltaic Systems in Bolivia
- 2021
-
Ingår i: Journal of the Electrochemical Society. - : IOP Publishing Ltd. - 0013-4651 .- 1945-7111. ; 168:10
-
Tidskriftsartikel (refereegranskat)abstract
- Performance and aging of lithium-ion 18650 cylindrical cells containing NCA and Si-graphite composite electrodes are investigated during long-term low current rate (∼0.1C) cycling protocol resembling charge/discharge profile of off-grid photovoltaic battery system. The cells are cycled within 30% and 75% state-of-charge ranges (SOC) with low, middle and high cut-off voltages. Electrochemical impedance spectroscopy data of full cylindrical cells exhibit severe aging for cells that have been cycled at higher cut-off voltage of 4.2 V. Symmetric cell impedance from each electrode shows that aging of NCA is dominant over aging of Si-graphite. Using a Newman-based impedance model, the NCA symmetrical cells' impedance spectra are parameterized to evaluate the aging modes. The resulting parameterization confirms increased particles' surface film resistance due to possible electrolyte oxidation and tortuosity increase at high cut-off voltages. Cycling the cells with middle and low cut-off voltages causes few significant changes when compared to calendar-aged samples. This opens up the possibility to significantly increase battery lifetime for small photovoltaic battery systems in rural areas of Bolivia. © 2021 The Author(s).
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| 28. |
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| 29. |
- Benavente Araoz, Fabian Andres, 1985-, et al.
(författare)
-
Effect of Partial Cycling of NCA/Graphite Cylindrical Cells in Different SOC Intervals
- 2020
-
Ingår i: Journal of the Electrochemical Society. - : Institute of Physics Publishing. - 0013-4651 .- 1945-7111. ; 167:4
-
Tidskriftsartikel (refereegranskat)abstract
- A quasi-realistic aging test of NCA/graphite lithium-ion 18650 cylindrical cells is performed during a long-term low c-rate cycling and using a new protocol for testing and studying the aging. This to emulate a characteristic charge/discharge profile of off-grid PV-battery systems. The cells were partially cycled at four different cut-off voltages and two state of charge ranges (ΔSOC) for 1000 and 700 cycles over 24 months. Differential voltage analysis shows that a combination of loss of active material (LAM) and loss of lithium inventory (LLI) are the causes of capacity loss. Cells cycled with high cut-off voltages and wide ΔSOC (20% to 95%) were severely affected by material degradation and electrode shift. High cut-off voltage and narrow ΔSOC (65% to 95%) caused greater electrode degradation but negligible cell unbalance. Cell impedance is observed to increase in both cells. Cells cycled with middle to low cut-off voltages and narrow ΔSOC (35%-65% and 20% to 50%) had comparable degradation rates to calendar-aged cells. Cycling NCA/graphite cells with low c-rate and high cut-off voltages will degrade the electrode in the same way high c-rate would do. However, low c-rate at low and middle cut-off voltages greatly decrease cell degradation compared to similar conditions at middle to high c-rate, therefore increasing battery lifetime. © 2020 The Author(s).
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| 30. |
- Benavente Araoz, Fabian Andres, 1985-, et al.
(författare)
-
Evaluation of the battery lifetime impact on PV systems techno-economic design
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Battery cycle life is a determining factor to enable the sustainability and reliability of off-grid photovoltaic (PV)/battery systems installed in rural communities. External circumstances such as remote localization and disperse distribution of communities, make the replacement and/or maintenance of battery systems with short cycle life rather difficult. Using experimental data of capacity retention from lithium-ion commercial batteries, we calculate the optimized loss of power supply probability (LPSP) and life cycle cost (LCC) for three applications operating in three locations of Bolivia. PV power and battery capacity design are estimated through optimization under the influence of suppressed demand. Optimization results show favorable LCCs when the location offers high solar irradiance in general. Suppressed demand has a marked impact on LPSP for cases where battery cycle life is limited due to aging. This is more evident for the household case, where the seasonal effect on the solar irradiance profile is considered. For the school and health center applications, a uniform load profile has positive impacts on the resulting LCC values.
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| 31. |
- Benavente Araoz, Fabian Andres, et al.
(författare)
-
Experimental Investigation and Electrochemical Modeling of Aging Mechanisms on NCA and Si-graphite Electrodes Harvested from Off-grid PV Lithium-ion Cells
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Performance and aging of lithium-ion 18650 cylindrical cells containing NCA and Si-graphite composite electrodes are investigated during a long-term cycling process applying low current rates and different state of charge (SOC) ranges and cut-off voltages. Firstly, electrochemical impedance spectroscopy (EIS) is used to periodically extract impedance data from cylindrical cells. Secondly, NCA and Si-graphite electrode samples are reassembled into symmetrical cells to separate the impedance contribution from NCA and Si-graphite. Finally, using a physics-based impedance model, the symmetrical cells’ impedance spectra are parameterized to evaluate the aging modes. We introduce an additional pseudo-dimension to the model to distribute double layer capacitances on electrode-electrolyte interface, combined with a probability distribution function for total volumetric current, to fit the depressed semicircle in EIS spectra. The parameterization results show that high cut-off voltages cause increased particles’ surface film resistance of the NCA electrode and tortuosity increase in its structure. In Si-graphite electrodes, high cut-off voltages combined with wide ΔSOC range lead to increased surface film resistance attributed to the SEI layer and local limitations in solid lithium intercalation. Cycling the cells with middle and low cut-off voltages causes few significant changes when compared to calendar-aged samples. This opens up the possibility to significant increase of battery lifetime for applications such as small PV-battery systems.
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| 32. |
- Benavente Araoz, Fabian Andres, et al.
(författare)
-
Photovoltaic/battery system sizing for rural electrification in Bolivia : Considering the suppressed demand effect
- 2019
-
Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 235, s. 519-528
-
Tidskriftsartikel (refereegranskat)abstract
- Rural electrification programs usually do not consider the impact that the increment of demand has on the reliability of off-grid photovoltaic (PV)/battery systems. Based on meteorological data and electricity consumption profiles from the highlands of Bolivian Altiplano, this paper presents a modelling and simulation framework for analysing the performance and reliability of such systems. Reliability, as loss of power supply probability (LPSP), and cost were calculated using simulated PV power output and battery state of charge profiles. The effect of increasing the suppressed demand (SD) by 20% and 50% was studied to determine how reliable and resilient the system designs are. Simulations were performed for three rural application scenarios: a household, a school, and a health centre. Results for the household and school scenarios indicate that, to overcome the SD effect, it is more cost-effective to increase the PV power rather than to increase the battery capacity. However, with an increased PV-size, the battery ageing rate would be higher since the cycles are performed at high state of charge (SOC). For the health centre application, on the other hand, an increase in battery capacity prevents the risk of electricity blackouts while increasing the energy reliability of the system. These results provide important insights for the application design of off-grid PV-battery systems in rural electrification projects, enabling a more efficient and reliable source of electricity.
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| 33. |
- Benavente-Araoz, Fabian, et al.
(författare)
-
Loss-of-load probability analysis for optimization of small off-grid PV-battery systems in Bolivia
- 2017
-
Ingår i: Proceedings of the 9th International Conference on Applied Energy. - : Elsevier. ; 142, s. 3715-3720
-
Konferensbidrag (refereegranskat)abstract
- This study evaluates the use of energy storage technologies coupled to renewable energy sources in rural electrification as a way to address the energy access challenge. Characteristic energy demanding applications will differently affect the operating conditions for off-grid renewable energy systems. This paper discusses and evaluates simulated photovoltaic power output and battery state of charge profiles, using estimated climate data and electricity load profiles for the Altiplanic highland location of Patacamaya in Bolivia to determine the loss of load probability as optimization parameter. Simulations are performed for three rural applications: household, school, and health center. Increase in battery size prevents risk of electricity blackouts while increasing the energy reliability of the system. Moreover, increase of PV module size leads to energy excess conditions for the system reducing its efficiency. The results obtained here are important for the application of off-grid PV-battery systems design in rural electrification projects, as an efficient and reliable source of electricity.
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| 34. |
- Benavente, Fabian, 1985-
(författare)
-
Lithium-ion batteries for off-grid PV-systems
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis provides a comprehensive and detailed analysis on the effect ofthe battery operation strategy on the lifetime of commercial lithium-ionbatteries and on the economics of off-grid photovoltaic (PV)-batterysystems.Lithium-ion batteries play a key role in the transition to a fossil-freesociety. Compared to electric vehicles, stationary energy storage hasdifferent requirements for the performance and lifetime of batteries.Although optimal battery design is critical to achieve high energy densityand longer lifetime, operation plays an important role in preventingpremature performance degradation. Understanding the effects ofsuppressed demand, geographical location, and application on system lifecycle costs also enables optimal system design.Load profiles for three applications were estimated and implemented in asimulation model, along with meteorological data for three locations andthe suppressed demand (SD) effect. Using the hourly state of charge (SOC)profiles, four battery operation strategies were designed using partialcycling with different cut-off voltages and two state of charge windows(ΔSOC). Commercial cells were used for the experimental tests. After over1000 cycles a post-mortem characterization was performed.The experiments revealed the cause of premature degradation at high SOCoperation to be a combination of impedance rise in the positive electrodeand loss of lithium inventory at the negative electrode leading to decreaseof capacity. Studies on the impedance spectra of the cells using physicsbasedmodeling revealed a loss of conductivity between particles in thepositive electrode. At system level, as the SD increases, so does theoperational ΔSOC width, while the reliability of the system decreases. Wedefined the reliability as loss of power supply probability. Finally,optimization of cost and reliability, revealed that an optimal system designfavors a battery operation strategy with wider ΔSOC instead of batterylifetime.
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| 35. |
- Bergman, B., et al.
(författare)
-
Contact corrosion resistance between the cathode and current collector plate in the molten carbonate fuel cell
- 2001
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 148:1, s. A38-A43
-
Tidskriftsartikel (refereegranskat)abstract
- The corrosion layer Formed in the contact between the cathode and the current collector is one factor limiting the cathode performance in molten carbonate fuel cells (MCFC). In order to investigate the contribution to the total polarization of the contact resistance, electrochemical experiments were performed in a laboratory-scale fuel cell unit with a specially designed current collector. Two cathode materials, NiO and LiCoO2, were investigated to elucidate the impact of the cathode material on the formed corrosion layer. Polarization measurements as well as electrochemical impedance spectroscopy were used. The method works well for NiO electrodes. However, due to the poor electronic conductivity in the LiCoO2 electrode, the experimental results become difficult to evaluate due to a nonuniform potential distribution. The contact resistance between the cathode and the current collector contributes with a large value to the total cathode polarization. The corrosion layer in case of the LiCoO2 cathode was iron-rich and has a thickness of about 20 mum after 8 weeks operation of the fuel cell. Ln the case of the NiO cathode, a nickel-rich corrosion layer of about 15 mum was formed after 5 weeks operation of the fuel cell.
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| 36. |
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| 37. |
|
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| 38. |
- Bessman, Alexander, et al.
(författare)
-
Aging effects of AC harmonics on lithium-ion cells
- 2019
-
Ingår i: Journal of Energy Storage. - : Elsevier. - 2352-152X .- 2352-1538. ; 21, s. 741-749
-
Tidskriftsartikel (refereegranskat)abstract
- With the vehicle industry poised to take the step into the era of electric vehicles, concerns have been raised that AC harmonics arising from switching of power electronics and harmonics in electric machinery may damage the battery. In light of this, we have studied the effect of several different frequencies on the aging of 28 Ah commercial NMC/graphite prismatic lithium-ion battery cells. The tested frequencies are 1 Hz, 100 Hz, and 1 kHz, all with a peak amplitude of 21 A. Both the effect on cycled cells and calendar aged cells is tested. The cycled cells are cycled at a rate of 1C:1C, i.e., 28 A during both charging and discharging, with the exception of a period of constant voltage at the end of every charge. After running for one year, the cycled cells have completed approximately 2000 cycles. The cells are characterized periodically to follow how their capacities and power capabilities evolve. After completion of the test about 80% of the initial capacity remained and no increase in resistance was observed. No negative effect on either capacity fade or power fade is observed in this study, and no difference in aging mechanism is detected when using non-invasive electrochemical methods of post mortem investigation.
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| 39. |
- Bessman, Alexander, 1989-, et al.
(författare)
-
Challenging Sinusoidal Ripple-Current Charging of Lithium-Ion Batteries
- 2018
-
Ingår i: IEEE Transactions on Industrial Electronics. - : IEEE Press. - 0278-0046 .- 1557-9948. ; 65:6, s. 4750-4757
-
Tidskriftsartikel (refereegranskat)abstract
- Sinusoidal ripple-current charging has previously been reported to increase both charging efficiency and energy efficiency and decrease charging time when used to charge lithium-ion battery cells. In this paper, we show that no such effect exists in lithium-ion battery cells, based on an experimental study of large-size prismatic cells. Additionally, we use a physics-based model to show that no such effect should exist, based on the underlying electrochemical principles.
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| 40. |
- Bessman, Alexander
(författare)
-
Interactions between battery and power electronics in an electric vehicle drivetrain
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electric machine and power electronics in electric and hybrid electric vehicles inevitably cause AC harmonics on the vehicle's DC-link. These harmonics can be partially filtered out by large capacitors, which today are overdimensioned in order to protect the vehicle's battery pack. This is done as a precaution, since it is not known whether ripple-current has any harmful effect on Li-ion cells.We have measured and analyzed the ripple-current present in a hybrid electric bus, and found that a majority of the power was carried by frequencies in the range 100~Hz to 1~kHz. The single most energetic harmonic in this particular vehicle is believed to have been caused by a misaligned resolver in the motor.We have also designed and built an advanced experimental set-up in order to study the effect of ripple-current on Li-ion cells in the lab. The set-up can cycle up to 16 cells simultaneously, with currents of up to 50~A including a superimposed AC signal with a frequency of up to 2~kHz. The cells' temperatures are controlled by means of a climate chamber. The set-up also includes a sophisticated safety system which automatically acts to prevent dangerous situations before they arise.Using this set-up we tested whether superimposing AC with a specific frequency improves the charging performance of Li-ion cells. Statistical analysis found no improvement over regular DC cycling, and a physics-based model explains the experimental findings.We have also investigated whether ripple-current accelerates the aging of Li-ion cells. Twelve cells were either calendar or cycle aged for one year, with some cells being exposed to superimposed AC with a frequency of 1~Hz, 100~Hz, or 1~kHz. No effect was observed on any of capacity fade, power fade, or aging mechanism.Finally we also tested whether it is possible to heat Li-ion cells from low temperatures using only AC. We propose a method for AC heating of Li-ion cells, and open the discussion for generalizing the technique to larger battery packs.In conclusion, ripple-current has negligible effect on Li-ion cells, except for heating them slightly.
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| 41. |
- Bessman, Alexander, et al.
(författare)
-
Investigating the aging effect of current ripple on lithium-ion cells
- 2015
-
Ingår i: ECS Transactions. - : Electrochemical Society. - 1938-6737. - 9781607685395 ; , s. 101-106
-
Konferensbidrag (refereegranskat)abstract
- We have built an experimental setup which exposes twelve cells to a well-defined ripple current. It consists of a system for cycling high capacity cells in parallel with a triangular current waveform superimposed on top of the direct current. The frequency of the waveform is variable up to 50 Hz, and the sum of the DC and AC components can have a magnitude of -40 A to 40 A. Current is measured over a 500 μω shunt resistor. The voltage and current of each cell is read simultaneously at a sample rate up to 4 MS/s, allowing for precise impedance measurements even for high frequency harmonics. The cells are cycled at 40 °C. The experiment has been designed to eliminate indirect effects of the AC harmonics as far as possible. This system is being used to test whether or not AC harmonics affect Li-ion aging.
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| 42. |
- Birgersson, E., et al.
(författare)
-
Reduced two-dimensional one-phase model for analysis of the anode of a DMFC
- 2003
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 150:10, s. A1368-A1376
-
Tidskriftsartikel (refereegranskat)abstract
- An isothermal two-dimensional liquid phase model for the conservation of mass, momentum, and species in the anode of a direct methanol fuel cell (DMFC) is presented and analyzed. The inherent electrochemistry in the DMFC anode active layer is reduced to boundary conditions via parameter adaption. The model is developed for the case when the geometry aspect ratio is small, and it is shown that, under realistic operating conditions, a reduced model, which nonetheless describes all the essential physics of the full model, can be derived. The significant benefits of this approach are that physical trends become much more apparent than in the full model and that there is considerable reduction in the time required to compute numerical solutions, a fact especially useful for wide-ranging parameter studies. Such a study is then performed in terms of the three nondimensional parameters that emerge from the analysis, and we subsequently interpret our results in terms of the dimensional design and operating parameters. In particular, we highlight their effect on methanol mass transfer in the flow channel and on the current density. The results indicate the relative importance of mass-transfer resistance in both the flow channel and the adjacent porous backing.
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| 43. |
- Birgersson, Erik, et al.
(författare)
-
Reduced two-phase model for analysis of the anode of a DMFC
- 2004
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 151:12, s. A2157-A2172
-
Tidskriftsartikel (refereegranskat)abstract
- An isothermal two-phase ternary mixture model that takes into account conservation of momentum, mass, and species in the anode of a direct methanol fuel cell (DMFC) is presented and analyzed. The slenderness of the anode allows a considerable reduction of the mathematical formulation, without sacrificing the essential physics. The reduced model is then verified and validated against data obtained from an experimental DMFC outfitted with a transparent end plate. Good agreement is achieved. The effect of mass-transfer resistances in the flow field and porous backing are highlighted. The presence of a gas phase is shown to improve the mass transfer of methanol at higher temperatures (>30 degreesC). It is also found that at a temperature of around 30 degreesC, a one-phase model predicts the same current density distribution as a more sophisticated two-phase model. Analysis of the results from the two-phase model, in combination with the experiments, results in a suggestion for an optimal flow field for the liquid-fed DMFC.
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| 44. |
- Bodén, Andreas, et al.
(författare)
-
A Model for Mass Transport of Molten Alkali Carbonate Mixtures Applied to the MCFC
- 2006
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 153:11, s. A2111-A2119
-
Tidskriftsartikel (refereegranskat)abstract
- A one-dimensional model based on the Stefan-Maxwell formulation for mass transfer of the main components of a binary molten carbonate electrolyte, including all of the nonidealities, was formulated and applied to the molten carbonate fuel cell (MCFC). The Stefan-Maxwell diffusion coefficients were determined from literature transport data; still, a narrow parameter window in electrolyte composition and temperature had to be used to keep the integrity of the fits. The model for calculation of the electrolyte composition was combined with equations describing the current distribution in the electrodes and the electrolyte. The calculated results of the electrolyte composition changes show that they depend predominantly on the current density and the total electrolyte filling degree. It was also concluded that the electrolyte composition changes are less then two percent for Li/K and five percent for Li/Na. This model demonstrates how experimental data measured at equilibrium conditions may be used to determine Stefan-Maxwell diffusion coefficients and then applied to a transport model for the electrolyte, in this case an MCFC.
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| 45. |
- Bodén, Andreas, et al.
(författare)
-
Conductivity of SDC and (Li/Na)2CO3 composite electrolytes in reducing and oxidising atmospheres
- 2007
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 172:2, s. 520-529
-
Tidskriftsartikel (refereegranskat)abstract
- Composite electrolytes made of samarium-doped cerium oxide and a mixture of lithium carbonate and sodium carbonate salts are investigated with respect to their structure, morphology and ionic conductivity. The composite electrolytes are considered promising for use in so called intermediate temperature solid oxide fuel cells (IT-SOFC), operating at 400-600 degrees C. The electrolytes are tested in both gaseous anode (reducing) and cathode (oxidising) environments and at different humidities and carbon dioxide partial pressures. For the structure and morphology measurements, it was concluded that no changes occur to the materials after usage. From measurements of melting energies, it was concluded that the melting point of the carbonate salt phase decreases with decreasing fraction of carbonate salt and that a partial melting occurs before the bulk melting point of the salt is reached. For all the composites, two regions may be observed for the conductivity, one below the carbonate salt melting point and one above the melting point. The conductivity is higher when electrolytes are tested in anode gas than when tested in cathode gas, at least for electrolytes with less than half the volume fraction consisting of carbonate salt. The higher the content of carbonate salt phase, the higher the conductivity of the composite for the temperature region above the carbonate melting point. Below the melting point, though, the conductivity does not follow this trend. Calculations on activation energies for the conductivity show no trend or value that indicates a certain transport mechanism for ion transport, either when changing between the different composites or between different gas environments.
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| 46. |
- Bodén, Andreas, et al.
(författare)
-
Influence of the anode pore-size distribution and total electrolyte filling degree on the MCFC performance
- 2008
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 155:2, s. B172-B179
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Experimental data of the total cell reaction resistance as a function of the total electrolyte filling degree was measured to investigate how more electrolyte initially may be added to get as long a cell lifetime as possible. The reaction resistance of each electrode was also measured using two gas compositions and various total electrolyte filling degrees. A theoretical model for the distribution of electrolyte between the anode and the cathode as a function of the total electrolyte filling degree was used to compare the experimental data in this study with data from a symmetrical cell setup. The model takes into account the electrode pore-size distributions and considers two cases for the contact angle between the electrode and the electrolyte for the anode: a zero wetting angle (fully wetted) or reported experimental values for the wetting angle on pure Ni. It was concluded that after the cathode initially has been sufficiently filled with electrolyte the anode pores have to be smaller than the remaining ones of the cathode to allow having the anode act as a reservoir to prolong cell lifetime. The results from the experimental data and the theoretical model for electrolyte distribution were compared with results from a symmetrical setup.
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| 47. |
- Bodén, Andreas, et al.
(författare)
-
Mass transport in molten alkali carbonate mixtures
- 2006
-
Ingår i: Proc. Electrochem. Soc.. - 9781566775144 ; , s. 151-161
-
Konferensbidrag (refereegranskat)abstract
- A one-dimensional model based on Stefan-Maxwell theory of mass transfer was used to calculate the composition changes of the electrolyte in MCFC. Stefan-Maxwell diffusivities were calculated from conductivity and transport number data and used in the model. The composition changes calculated agreed with experimental results for lithium-potassium carbonate but less for lithium-sodium. The time dependent change of composition was also calculated but this could not explain the difference. In addition, the influence of the porosity of the fuel cell components, together with the electrolyte filling degree, was calculated and this showed a large influence on the composition change.
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| 48. |
- Bodén, Andreas, 1977-
(författare)
-
The anode and the electrolyte in the MCFC
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A goal of the Swedish government is to increase the usage of renewable fuels and biomass-based fuels. Fuel cells, and especially the MCFC, are useful for these types of fuels. The Swedish market may benefit from the MCFC in two ways: increased efficiency of the biofuels and also utilisation of produced heat in district heating. Most of the commercial MCFC systems today are optimised for use with methane. The possibility to utilise biomass in Sweden makes it important to study how the MCFC may be adapted or optimised for good performance and low degradation with gas produced from biomass or other renewable fuels. This thesis is focused on methods that may be used to investigate and evaluate MCFC electrodes and electrolytes with renewable fuels i.e. CO2-containing gases. The methods and results are both experimental and mathematically modelled. The objectives of this thesis are to better understand how the performance of the anode is dependent on different fuels. Anode kinetics and the water-gas shift reaction have been investigated as well as the possibility to increase cell lifetime by increasing the initial electrolyte amount by having the anode as a reservoir. The effect of segregation of cations in the electrolyte during operation has also been studied. It was found that if the gas composition at the current collector inlet is in equilibrium according to the water gas-shift reaction the gas composition inside the electrode is almost uniform. However, if the gas is not in equilibrium then the concentration gradients inside the current collector have a large effect on the gas composition inside the electrode. The conversion of the gas in the gas flow channels according to the water-gas shift reaction depends on the gas flow rate. For an anode used in a gas mixture of humidified hydrogen and carbon dioxide that are not in equilibrium some solubility of Ni in a (Li/Na)2CO3 mixture was found. To have the anode act as an electrolyte reservoir to prolong cell lifetime the anode pore size should be carefully matched with that of the cathode and a bimodal pore-size distribution for the anode is preferable to have as good performance as possible for as large electrolyte filling degree interval as possible. Modelling results of segregation of cations in the electrolyte during operation indicate that the electrolyte composition changes during operation and that the lithium ions are enriched at the anode for both types of electrolyte used for the MCFC. The electrolyte composition changes are small but might have to be considered in long-time operation. The results from this thesis may be used to better understand how the MCFC may be used for operation with renewable fuels and how electrodes may be designed to prolong cell lifetime.
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| 49. |
- Bodén, Andreas, et al.
(författare)
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The solubility of Ni in molten Li2CO3–Na2CO3 (52/48) in H2/H2O/CO2 atmosphere
- 2007
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 166:1, s. 59-63
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Tidskriftsartikel (refereegranskat)abstract
- In this work the solubility of a Ni-Al anode for MCFC has been studied at atmospheric pressure and two different temperatures using various gas compositions containing H-2/H2O/CO2. It is well known that nickel is dissolved at cathode conditions in an MCFC. However, the results in this study show that nickel can be dissolved also at the anode, indicating that the solubility increases with increasing CO2 partial pressure of the inlet gas and decreasing with increasing temperature. This agrees with the results found by other authors concerning the solubility of NiO at cathode conditions. The dissolution of Ni into the melt can proceed in two ways, either by the reduction of water or by the reduction of carbon dioxide.
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| 50. |
- Bouton, Karl, et al.
(författare)
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A structural battery with carbon fibre electrodes balancing multifunctional performance
- 2024
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 256
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Tidskriftsartikel (refereegranskat)abstract
- Structural multifunctional materials have the potential to transform current technologies by implementing several functions to one material. In a multifunctional structural battery, mass saving and energy efficiency are created by the synergy between the mechanical and electrochemical properties of the material's constituents. Consequently, structural batteries could e.g. mitigate electric vehicle overweight or enable thinner portable electronics. This requires combining the best composite and battery manufacturing practices. In the present work this is achieved through the infusion of a stack of carbon fibre-based electrodes with a hybrid polymer-liquid electrolyte. The realised full cell structural battery is based on carbon fibre electrodes with a lithium iron phosphate (LiFePO4) coating on the positive side. This battery laminate shows a very good balance between energy density, stiffness and strength of 33.4 Wh/kg, 38 GPa and 234 MPa, respectively. To push these performances further, different improvement strategies are discussed, and the results are compared with previously published target performances. Ultimately, we demonstrate the feasibility of designing and manufacturing all-fibre solid-state structural batteries as a material solution for future lightweight electric commodities.
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