| 1. |
- Mikheenkova, Anastasiia, et al.
(författare)
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Ageing of High Energy Density Automotive Li-Ion Batteries : The Effect of Temperature and State-of-Charge
- 2023
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 170:8
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Tidskriftsartikel (refereegranskat)abstract
- Lithium ion batteries (LIB) have become a cornerstone of the shift to electric transportation. In an attempt to decrease the production load and prolong battery life, understanding different degradation mechanisms in state-of-the-art LIBs is essential. Here, we analyze how operational temperature and state-of-charge (SoC) range in cycling influence the ageing of automotive grade 21700 batteries, extracted from a Tesla 3 long Range 2018 battery pack with positive electrode containing LiNixCoyAlzO2 (NCA) and negative electrode containing SiOx-C. In the given study we use a combination of electrochemical and material analysis to understand degradation sources in the cell. Herein we show that loss of lithium inventory is the main degradation mode in the cells, with loss of material on the negative electrode as there is a significant contributor when cycled in the low SoC range. Degradation of NCA dominates at elevated temperatures with combination of cycling to high SoC (beyond 50%).
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| 2. |
- Butori, Martina, et al.
(författare)
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The effect of oxygen partial pressure and humidification in proton exchange membrane fuel cells at intermediate temperature (80-120 degrees C)
- 2023
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 563, s. 232803-
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Tidskriftsartikel (refereegranskat)abstract
- The integration of proton exchange membrane fuel cells (PEMFCs) in heavy-duty vehicles would be facilitated if operating temperatures above 100 degrees C were possible. In this work, the effect of temperature in the intermediate range of 80-120 degrees C is investigated for a commercial membrane electrode assembly (MEA) through polarization curves and electrochemical impedance spectroscopy. The importance of oxygen partial pressure on voltage is systematically studied by decoupling it from humidity and temperature. The results show that adequate oper-ation at intermediate temperature is achievable if the oxygen partial pressure is sufficient. Although the cathode kinetics is faster with rising temperatures, the voltage gain is counteracted by the decreasing equilibrium po-tential. At intermediate temperature, the water transport is enhanced, levelling out the relative humidity dif-ference between anode and cathode. However, ionic conductivity in the polymer can become limiting at high currents, due to a smaller relative humidity increase at these temperatures. To conclude, a higher operating temperature does not inherently cause a decrease in obtained current density. Rather, the difficulty to simul-taneously have sufficient oxygen partial pressure and high relative humidity causes limitations within the cathode that to some extent can be solved by pressurizing the cell.
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| 3. |
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| 4. |
- Carlson, Annika
(författare)
-
Electrochemical properties of alternative polymer electrolytes in fuel cells
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fuel cells, using hydrogen as energy carrier, allow chemically‑stored energy to be utilized for many applications, including balancing the electrical grid and the propulsion of vehicles. To make the fuel cell technology more accessible and promote a sustainable energy society, this thesis focuses on alternative polymer electrolytes, as they can potentially lead to a lower cost and a more environmentally‑friendly fuel cell. The main subject is anion exchange membrane fuel cells (AEMFCs), for which the importance of gas diffusion electrode morphology and platinum electrode reactions are investigated. Properties of the membrane such as water flux during operation are evaluated. Furthermore, novel polymer electrolytes are studied: variations of poly(phenylene oxide)‑based membranes in AEMFCs; and cellulose‑based membranes in a proton exchange membrane fuel cell (PEMFC). The AEMFC results show that the performance is dependent on the electrode morphology. Electrochemical experiments in a hydrogen/hydrogen cell combined with modelling show that the hydrogen oxidation reaction proceeds through the Tafel‑Volmer reaction pathway on platinum. Application of the model in a hydrogen/oxygen cell shows that the cathode has the slowest reaction rate. During operation, the water flux through the membrane is directed from the anode where water is produced to the cathode where it is consumed. This leads to an increase in water content at both electrodes, which implies that electrode flooding is more likely than dry‑out during operation. The effect of membrane thickness on water flux is shown to be larger than the effect of polymer structure for several different types of poly(phenylene oxide)‑based membranes. The comparison of these polymers also indicates that a high conductivity, for the relative humidity achieved in a fuel cell, promotes increased performance. Finally, the study of cellulose-based membranes in a PEMFC shows that cellulose as a renewable, natural polymer has promising properties, such as stable conductivity for relative humidities above 65 % and a low gas permeability.
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| 5. |
- Carlson, Annika, et al.
(författare)
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Fuel cell evaluation of anion exchange membranes based on poly(phenylene oxide) with different cationic group placement
- 2020
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry. - 2398-4902. ; 4:5, s. 2274-2283
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Tidskriftsartikel (refereegranskat)abstract
- Four novel poly(phenylene oxide)-based anion exchange membranes were investigated for electrochemical performance, ionic conductivity and water transport properties in an operating anion exchange membrane fuel cell (AEMFC), using Pt/C gas diffusion electrodes with Tokuyama ionomer. The poly(phenylene oxide)-membranes have a 1- or 5-carbon alkyl spacer between the backbone and a trimethylalkylammonium (TMA) or piperidinium (Pip) cationic group, and ion-exchange capacities (IECs) between 1.5 and 1.9 mequiv g(-1). The polymer with a 5-carbon alkyl spacer, a TMA cationic group, and a higher IEC showed the highest ion conductivity and performance in the AEMFC. The results also show that introducing a 5-carbon alkyl spacer does not improve performance unless the IEC is increased and that exchanging the TMA with a Pip cationic group results in lower fuel cell performance despite a higher IEC. A discrepancy in ion conductivity between fuel cell and ex situ test was observed for the 5-carbon spacer polymers and is attributed to a higher sensitivity for dehydration. Similar water flux under load, from the anode to the cathode with increased water content at both electrodes, was observed for all membranes and only varied with membrane thickness. The deviation in fuel cell performance observed between the membranes could not be explained by differences in water flux or ionic conduction, suggesting that the electrode-membrane interaction plays a major role. Nevertheless, the study emphasizes that high membrane conductivity (for the lambda-range in a fuel cell) and efficient water transport (obtained by lower membrane thickness) promote higher electrochemical performance.
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| 6. |
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| 7. |
- Carlson, Annika, et al.
(författare)
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Kinetic parameters in anion-exchange membrane fuel cells
- 2019
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Ingår i: ECS Transactions. - : Electrochemical Society Inc.. - 1938-6737 .- 1938-5862. - 9781607685395 ; , s. 649-659
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Konferensbidrag (refereegranskat)abstract
- Understanding limitations in an operating AEMFC is essential to .enhance the technology. Here the electrode processes are studied experimentally as well as by two physics-based models taking the porosity of the electrodes into account. The aim is to use the models to determine kinetic parameters specific for in-situ operation. The models can also be used to explain the experimental .behavior. From the impedance model of a symmetric H2/H2 cell it is shown that the hydrogen oxidation reaction (HOR) proceeds through the Tafel-Volmer reaction pathway, with the hydrogen adsorption as the slower reaction step. Based on the HOR model a •steady-state model of an O2/H2 cell is used to evaluate data from 14 experimental I-V curves, obtained for different gas partial pressures and catalyst loadings, in order to study the effects of the oxygen reduction reaction and overall cell limitations. The results show that the oxygen reduction reaction kinetics limit the cell performance for low current densities. However, at higher currents the uneven current distribution and locally low hydrogen adsorption at the anode increasingly affect the overall performance. Uneven current distribution is also observed at the cathode and likely caused by insufficient effective ionomer conductivity.
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| 8. |
- Carlson, Annika, et al.
(författare)
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The Hydrogen Electrode Reaction in the Anion Exchange Membrane Fuel Cell
- 2021
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 168:3
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen electrode in the anion-exchange membrane fuel cell needs further attention to understand the overall cell limitations. In this study, electrochemical impedance spectroscopy and galvanodynamic measurements in combination with a physics-based model are used to determine the kinetic parameters of the hydrogen oxidation reaction and hydrogen evolution reaction on Pt/C porous gas-diffusion electrodes in an AEMFC. Two semicircles are observed in the Nyquist plot of a symmetrical AEM hydrogen cell, indicating a two-step reaction pathway. The fit of the model shows that the Tafel-Volmer pathway describes the kinetics better than the Heyrovsky-Volmer pathway. The reaction rates of the adsorption and charge transfer steps are similar in magnitude implying that both need consideration during modeling and evaluation of the hydrogen electrode. Furthermore, the performance is limited also by the ionic conductivity in the electrode. Comparison of the impedance of the HOR and a hydrogen/oxygen AEMFC indicates that the low-frequency semicircle is mainly associated with the oxygen reduction reaction and the cathode, while the high-frequency semicircle is likely related to a combination of the anode and the cathode. Based on this work, a platform for further studies of losses and total impedance of operating AEMFC has been created.
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| 9. |
- Eriksson, Björn
(författare)
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Electrochemical evaluation of new materials in polymer electrolyte fuel cells
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer electrolyte fuel cells (PEFC) convert the chemical energy in hydrogen to electrical energy and heat, with the only exhaust being water. Fuel cells are considered key in achieving a sustainable energy sector. The main obstacles to wide scale commercialization are cost and durability. The aim of this thesis is to evaluate new materials for PEFC to potentially lower cost and increase durability. To lower the amount of expensive platinum catalyst in the fuel cell, the activities of Pt-rare earth metal (REM) alloy catalysts have been tested. To improve the lifetime of the carbon support, the carbon corrosion properties of multi walled carbon nanotubes have been evaluated. To reduce the overall cost of fuel cell stacks, carbon coated and metal coated bipolar plates have been tested. To increase the performance and lifetime of anion exchange membranes, the water transport has been studied.The results show that the Pt-REM catalysts had at least two times higher specific activity than pure platinum, and even higher activities should be obtainable if the surface structures are further refined.Multi-walled carbon nanotubes had lower carbon corrosion than conventional carbon Vulcan XC-72. However, once severely corroded their porous structure collapsed, causing major performance losses.The carbon coated metallic bipolar plates showed no significant increase of internal contact resistance (ICR) by cycling, suggesting that these coatings are stable in fuel cells. The NiMo- and NiMoP coated bipolar plates showed low ICR, however, presence of the coated bipolar plates caused secondary harmful effects on the polymer membrane and ionomer.Considering the water transport through anion exchange membranes it was found that most membranes showed very similar water transport properties, with more water detected at both the anode and cathode when a current was applied. The most significant factor governing the water transport properties was the membrane thickness, with thicker membranes reducing the backflow of water from anode to cathode.The results indicate that all of the new tested materials have the capability to improve the lifetime and reduce cost and thereby improve the overall performance of PEFC.
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| 10. |
- Eriksson, Björn, et al.
(författare)
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Enhanced oxygen reduction activity with rare earth metal alloy catalysts in proton exchange membrane fuel cells
- 2021
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 387
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Tidskriftsartikel (refereegranskat)abstract
- Alloying platinum is an approach to increase the oxygen reduction reaction (ORR) activity and at the same time reduce the amount of precious platinum catalyst in proton exchange membrane fuel cells (PEMFC). In this work the cathode activity of thin films of rare earth metals (REM) alloys, Pt Y, Pt Gd and Pt Tb, produced by sputter deposition onto gas diffusion layers, are evaluated in a fuel cell by means of polarization curves in O /H , and cyclic- and CO-stripping voltammetry in N /5% H . Prior to evaluation, the model electrodes were acid-treated to obtain a Pt skin covering the PtREM alloy bulk, as was revealed by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The core shell alloys of Pt Y and Pt Gd catalysts show a specific activity enhancement at 0.9 V of 2.5 times compared to pure Pt. The slightly lower enhancement factor of 2.0 for Pt Tb is concluded to be due to leaching of the REM, that resulted in a thicker, and subsequently less strained, Pt overlayer. The high activity, combined with the minor changes in surface composition, achieved in the fuel cell environment shows that PtREM core shell catalysts are promising for the cathode reaction in PEMFC.
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| 11. |
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| 12. |
- Fang, Yuan, et al.
(författare)
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Quantifying lithium lost to plating and formation of the solid-electrolyte interphase in graphite and commercial battery components
- 2022
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Ingår i: Applied Materials Today. - : Elsevier BV. - 2352-9407. ; 28
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Tidskriftsartikel (refereegranskat)abstract
- A key degradation mechanism in lithium-ion batteries (LIBs) is the irreversible loss of cyclable lithium during cycling. At the graphite negative electrode, this loss occurs through the deposition of lithium-containing compounds in the solid-electrolyte interphase (SEI) and through plating of metallic lithium, resulting in so-called dead lithium. The separate quantification of SEI and dead lithium has so far been a challenge in post mortem analysis of commercial LIBs. Here we report a simple and fast 7Li nuclear magnetic resonance spectroscopy (NMR) protocol applied to solid-state samples derived from lab-built batteries to independently quantify these and other lithium species in graphite electrodes without the need for specialized cell design nor knowledge of prior charging history. The metallic lithium content is corroborated by electrochemical calculations; the total amount of lithium is also determined from 7Li liquid-state NMR and inductively coupled plasma optical emission spectroscopy (ICP-OES) in suitably digested samples. Factors influencing accuracy like the sample handling process, the radiofrequency skin effect, and re-intercalation losses are investigated. Measurements on samples from commercial cells aged under realistic conditions demonstrate quantification of dead lithium and remaining ionic species (SEI), and further reveal lithium dendrites entrained in the separator following cell disassembly. The method uses conventional and widely available NMR instrumentation and is applicable to samples from lab-scale test cells or commercial batteries, thereby presenting a vast improvement over prior post mortem methods.
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| 13. |
- Fatima, Masoom, et al.
(författare)
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A review on biocatalytic decomposition of azo dyes and electrons recovery
- 2017
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Ingår i: Journal of Molecular Liquids. - : Elsevier B.V.. - 0167-7322 .- 1873-3166. ; 246, s. 275-281
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Tidskriftsartikel (refereegranskat)abstract
- Discharge of waste water from textile industry during coloring processes contains high concentrations of biologically difficult-to-degrade dye chemicals along with antifouling agents. Azo dyes considered to be the largest class of synthetic dyes used in the textile industries and are present in significant amounts in its effluents. These are highly stable because of its complex aromatic structure and covalent azo bonds. Traditional physico-chemical methods are not considered sufficient because of their high cost, partial degradation and more sludge production. The use of biocatalysts for decolorization is a gaining momentum due to having redox-active molecules. Current review explored techniques for the decomposition of textile dyes, their merits, limitations and recommended the emerging microbial fuel cell technology followed by aerobic treatment for complete degradation of dye intermediate metabolites.
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| 14. |
- Fatima, Masoom, et al.
(författare)
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Application of novel bacterial consortium for biodegradation of aromatic amine 2-ABS using response surface methodology
- 2020
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Ingår i: Journal of Microbiological Methods. - : Elsevier BV. - 0167-7012 .- 1872-8359. ; 174
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Tidskriftsartikel (refereegranskat)abstract
- There is a strong need to develop purification methods for textile industrial wastewater containing toxic azo dyes. The reductive cleavage of azo dyes can be made by anaerobic bacteria, but the products of aromatic amines require an aerobic process. In this study a novel bacterial dye degrading consortium (DDC) of five isolated strains identified with 16S rRNA sequence: Proteus mirabilis (KR732288), Bacillus anthracis (KR732289), Enterobacter hormaechei (KR732290), Pseudomonas aeruginosa (KR732293) and Serratia rubidaea (KR732296) were used to aerobically decompose metabolite 2-aminobenxenesulfonic acid (2-ABS), as a model compound. The effect of three variables: temperature (28-42 degrees C), pH (5.0-8.0) and initial concentration of 2-ABS (5-40 ppm) was investigated in terms of degradation and chemical oxygen demand (COD) removal. Central composite design matrixand response surface methodology (RSM) were used for experimental design to evaluate theinteraction of the three process variables. The results show that up to 95% degradation and COD 90% removal are possible at optimal values of 32.4 ppm 2-ABS, pH 6.6 and a temperature of 35.7 degrees C. The theoretical response variables predicted by the developed RSM model was supported the experimental results. The optimized degradation of 2-ABS and COD removal were further confirmed by UV-HPLC analysis.
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| 15. |
- Fatima, Masoom, et al.
(författare)
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Low-Cost Single Chamber MFC Integrated With Novel Lignin-Based Carbon Fiber Felt Bioanode for Treatment of Recalcitrant Azo Dye
- 2021
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Ingår i: Frontiers in Energy Research. - : Frontiers Media SA. - 2296-598X. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- A flow through anaerobic microbial fuel cell (MFC) was designed and optimized for efficient treatment of recalcitrant textile wastewater. The membrane-less MFC was first time fabricated with a unique combination of electrodes, a novel bioanode of synthesized lignin-based electrospun carbon fiber supporting a biofilm of Geobacter sulfurreducens for acetate oxidation and an air-breathing cathode, consisting of a pyrolyzed macrocycle catalyst mixture on carbon bonded by polytetrafluoroethylene (PTFE). The effects of different organic loadings of acetate along with Acid Orange (AO5), operation time and ionic strength of auxiliary salts (conductivity enhancers) were investigated and responses in terms of polarization and degradation were studied. In addition, the decomposition of the organic species and the degradation of AO5 along with its metabolites and degraded products (2-aminobenzenesulfonic acid) were determined by chemical oxygen demand (COD) analysis, UV-Vis spectrophotometry and high-performance liquid chromatography (UV-HPLC) techniques. SEM and TEM images were also used to find out the biocompatibility of the microbes on lignin-based electrospun carbon felt anode and the morphology of the cathode. Reduction and breakage of the azo bond of AO5 occurs presumably as a side reaction, resulting in the formation of 2-aminobenzenesulfonic acid and unidentified aromatic amines. Maximum current density of anode 0.59 Am-2 and power density of 0.12 Wm(-2) were obtained under optimized conditions. As a result, decolouration of AO5 and chemical oxygen demand (COD) removal efficiency was 81 and 58%, respectively. These results revealed that the low-cost MFC assembly can offer significant potential for anaerobic decolouration of recalcitrant textile wastewater.
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| 16. |
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| 17. |
- Grimler, Henrik, et al.
(författare)
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Determination of Kinetic Parameters for the Oxygen Reduction Reaction on Platinum in an AEMFC
- 2021
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 168:12, s. 124501-
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Tidskriftsartikel (refereegranskat)abstract
- To promote the development of anion exchange membrane fuel cells (AEMFC), an understanding of the oxygen reduction reaction (ORR) kinetics in porous gas diffusion electrodes is essential. In this work, experimental polarisation curves for electrodes with different platinum catalyst loadings and oxygen partial pressures at the cathode are fitted to a physics-based porous electrode model in the voltage range from open circuit voltage (OCV) to 0.7 V. Polarisation curves measured with different anode catalyst loadings, and hydrogen partial pressures, were used to verify the model. The reactions are described using a two-step Tafel-Volmer pathway at the anode and concentration-dependent Butler-Volmer kinetics at the cathode. A good fit to experimental data in the kinetic region is obtained with an exchange current density of 1.0.10(-8)Acm(-2), a first order dependency on oxygen partial pressure, and a charge transfer coefficient of 0.8 for the ORR. For lower oxygen partial pressure, hydrogen crossover is needed to explain the downward shift of the polarisation curves in the kinetic region. In the experimental data, the polarisation curves show an apparent limiting current density at lower hydrogen partial pressures, explained by the lower rate of the Tafel step at these conditions.
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| 18. |
- Grimler, Henrik
(författare)
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Limiting processes in anion-exchange membrane fuel cells
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fuel cells allow for converting chemical energy stored in hydrogen into electrical energy, with only heat and water as by-products. In a sustainable energy society, hydrogen may play an important role due to its ability to act both as an energy carrier and as a valuable chemical in the process industry. The main remaining obstacles for widely available commercial fuel cells are durability and cost. One way to potentially decrease the cost is to change the fuel cell environment to an alternative chemistry by replacing the proton-exchange membrane (PEM) with an anion-exchange membrane (AEM). This thesis studies the anode reaction, the cathode reaction and water transport in an anion-exchange membrane fuel cell (AEMFC), to investigate where its performance limitations lies in the system. Electrochemical characterisation techniques together with physics-based modelling have been utilised.The results from the study of the anode, shows that the hydrogen reaction proceeds through the Tafel-Volmer pathway, with the Tafel step starting to limit the reaction as the anode overpotential increases. Combining the anode model with a Butler-Volmer expression for the cathode reaction made it possible to model a H2:O2 fuel cell. Comparing the losses from the different processes in the fuel cell shows that the cathode is still the main contributor, but that the anode contribution cannot be neglected when predicting the fuel cell performance. Low ionic conductivity in the electrode was also identified as responsible for part of the overall resistances, leading to uneven current distribution in the catalyst layers and bad utilisation of the catalytic material.Investigating the water transport properties of AEMs showed that not only electroosmotic drag and diffusion, but also an absorption/desorption step between gas phase and membrane phase, are necessary to get a model that can explain the experimental observations. The choice of gas diffusion layers (GDLs) used on the anode and cathode was found to be of similar importance on the water transport as doubling the membrane thickness, showing that not only the membrane is important for water transport. Under most realistic conditions, the risk of local dry-out in a cell was found to be low, as water readily diffuses from the high humidity side of the membrane to the low humidity side.
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| 19. |
- Grimler, Henrik, et al.
(författare)
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Modelling electrode and membrane processes in an anion-exchange membrane fuel cell
- 2017
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Ingår i: EFC 2017 - Proceedings of the 7th European Fuel Cell Piero Lunghi Conference. - : ENEA. ; , s. 127-128
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Konferensbidrag (refereegranskat)abstract
- To better understand which processes that limits the performance in an anion-exchange membrane fuel cell (AEMFC), a physical performance model has been developed. The model considers a tertiary current distribution and is validated against experimental results. The results show that both the anode and the cathode contributes to significant polarisation in the system.
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| 20. |
- Grimler, Henrik, et al.
(författare)
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Water diffusion, drag and absorption in an anion-exchange membrane fuel cell
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Water is a key factor in anion-exchange membrane fuel cells, since it is botha product, reactant, and humidifies the membrane and ionomer phase. Toenable anion-exchange membrane fuel cells, knowledge about the water trans-port properties is needed, so that operating conditions can be optimised toprevent cathode dry-out or anode flooding. In this work, the water trans-port across an AemionTM membrane is quantified for different applied waterpartial pressure differences and current densities, with the help of humiditysensors. Two membrane thicknesses, 25 and 50 μm, are studied, as well astwo gas diffusion layers of different hydrophobicity: Sigracet 25BC which hasbeen PTFE treated to make it more hydrophobic, and Freudenberg H23C2which has not been PTFE treated, and is hence more hydrophilic. The re-sults show that having a hydrophilic GDL on the cathode and a hydrophobicGDL on the anode gives both the highest electrochemical performance, andthe highest water transport, while a hydrophilic GDL on both sides give thelowest electrochemical performance and the lowest water transport. A wa-ter transport model considering absorption/desorption resistance, electroos-motic drag and diffusion was deployed. The best fit was obtained with adrag coefficient close to two and 30 % increased absorption/desorption ratefor a hydrophobic GDL compared to a hydrophilic one.
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| 21. |
- Guccini, Valentina, et al.
(författare)
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Highly proton conductive membranes based on carboxylated cellulose nanofibres and their performance in proton exchange membrane fuel cells
- 2019
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 7:43, s. 25032-25039
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Tidskriftsartikel (refereegranskat)abstract
- The performance of thin carboxylated cellulose nanofiber-based (CNF) membranes as proton exchange membranes in fuel cells has been measured in situ as a function of CNF surface charge density (600 and 1550 μmol g−1), counterion (H+ or Na+), membrane thickness and fuel cell relative humidity (RH 55 to 95%). The structural evolution of the membranes as a function of RH, as measured by Small Angle X-ray Scattering, shows that water channels are formed only above 75% RH. The amount of absorbed water was shown to depend on the membrane surface charge and counter ions (H+ or Na+). The high affinity of CNF for water and the high aspect ratio of the nanofibers, together with a well-defined and homogenous membrane structure, ensures a proton conductivity exceeding 1 mS cm−1 at 30 °C between 65 and 95% RH. This is two orders of magnitude larger than previously reported values for cellulose materials and only one order of magnitude lower than Nafion 212. Moreover, the CNF membranes are characterized by a lower hydrogen crossover than Nafion, despite being ≈30% thinner. Thanks to their environmental compatibility and promising fuel cell performance the CNF membranes should be considered for new generation proton exchange membrane fuel cells.
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| 22. |
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| 23. |
- Kanninen, Petri, et al.
(författare)
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Carbon corrosion properties and performance of multi-walled carbon nanotube support with and without nitrogen-functionalization in fuel cell electrodes
- 2020
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 332
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Tidskriftsartikel (refereegranskat)abstract
- Pt-supported on multi-walled carbon nanotubes (MWCNT) and N-modified MWCNT (N-MWCNT) catalysts are synthesized by pyrolysis from emeraldine solution and microemulsion. Their electrochemical properties and carbon corrosion resistance in a Proton Exchange Membrane Fuel Cell (PEMFC) are compared with a commercial Pt/Vulcan catalyst through I–V curves, cyclic voltammetry and CO stripping. The initial fuel cell performances of the Pt/(N-)MWCNT catalysts are superior to Pt/Vulcan. The corrosion of the catalysts is quantified by the continuous measure of the CO2 release by online-mass spectrometry during potentiodynamic cycling between 0.1 and 1.6 V at 80 °C. The results show that Pt/MWCNT (with the lowest double-layer capacity) is the most stable catalyst followed by Pt/N-MWCNT and Pt/Vulcan, initially losing carbon at a rate of 1.1, 3.4 and 4.7 μgC (mg Ctot)−1 cycle−1, respectively. After about 30% carbon loss (50–70 cycles) all catalysts corrode at an approximate rate of 5.5 μgC mg−1 cycle−1. At this stage, all show similar electrochemical surface area and double-layer capacity. However, the substantial diminution of the initially very thick and porous Pt/(N-)MWCNT catalyst layers after corrosion consequences in lower fuel cell performance compared to the structurally less affected Pt/Vulcan electrode. The results clearly reveal that CNT-based catalyst supports are more corrosion resistant compared to state-of-the-art Vulcan. Moreover, the performance of the corroded electrodes envisages the importance of electrode porosity.
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| 24. |
- Khataee, Amirreza, et al.
(författare)
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Asymmetric cycling of vanadium redox flow batteries with a poly(arylene piperidinium)-based anion exchange membrane
- 2021
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 483
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Tidskriftsartikel (refereegranskat)abstract
- The potential application of a 50 μm thick anion exchange membrane prepared based on poly(terphenyl piperidinium-co-trifluoroacetophenone) (PTPT) is investigated for vanadium redox flow batteries (VRFBs). The PTPT exhibits a considerably lower vanadium permeation than Nafion 212. Therefore, the self-discharge duration of the VRFB based on PTPT is much longer than the VRFB based on Nafion 212. Besides, PTPT shows oxidative stability almost as good as Nafion 212 during immersion in an ex-situ immersion test for more than 400 h. Comparing the VRFB performance when symmetric and asymmetric electrolyte volumes are used yields interesting results. The results show that asymmetric cycling is more effective and efficient for the VRFB assembled with PTPT than Nafion 212 as the capacity fade of 0.03% cycle−1, and the highest coulombic efficiency of 98.8% is attained. Furthermore, the color change of the membrane during cycling can be reversed using a straightforward post-treatment method.
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| 25. |
- Khataee, Amirreza, et al.
(författare)
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Poly(arylene alkylene)s functionalized with perfluorosulfonic acid groups as proton exchange membranes for vanadium redox flow batteries
- 2023
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 671
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Tidskriftsartikel (refereegranskat)abstract
- With the aim to develop vanadium redox flow battery (VRFB) membranes beyond state of the art, we have in the present work functionalized poly(p-terphenylene)s with highly acidic perfluorosulfonic groups and investigated their performance as proton exchange membranes (PEMs). Consequently, two poly(p-terphenylene alkylene)s tethered with perfluoroalkylsulfonic acid and perfluorophenylsulfonic acid, respectively, were synthesized through superacid-mediated polyhydroxyalkylations and cast into PEMs. Compared with Nafion 212, the PEM carrying perfluorophenylsulfonic acid groups (PTPF-Phenyl-SA) was found to exhibit higher ionic conductivity and eight times lower vanadium (IV) permeation rate. The latter explains the longer self-discharge duration of the VRFB based on the PTPF-Phenyl-SA. In addition, the VRFB assembled with the PTPF-Phenyl-SA PEM exhibited a high average coulombic efficiency of 99.6% for over 100 cycles with a capacity fade of 0.24% per cycle, which was 50% lower than when Nafion 212 was used. More importantly, excellent capacity retention was achieved through electrochemical rate performance experiments at different current densities.
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| 26. |
- Kim, Hyeyun, 1986-, et al.
(författare)
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Feasibility of chemically modified cellulose nanofiber membrane as lithium ion battery separator
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Chemical modification of cellulose contributes to its fibrillation to nanofibers and consequently production of a mesoporous membrane, desirable for lithium ion battery separator. Nevertheless, the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidized cellulose nanofibers (TOCN) based separator with high charge density (650 μmol COO-/gCNF) has high risk of cell failure in lithium ion battery (LIB), compared to the counterpart with lower charge density (350 μmol/g). In this study, the influence of sodium carboxylate or carboxylic acid functional groups in TOCN as lithium ion battery separator was investigated. In-operando mass spectrometry measurements were used to elucidate the cause of cell failure by analyzing the gas evolved, from batteries containing different types of separators. For the TOCN separator with sodium carboxylate functional groups, it seems that Na deposition is the dominant reason for poor electrochemical stability of the cell thereof. The poor performance of the protonated TOCN separator is attributed to a high amount of gas evolution, mostly H2, originating from the reduction of trace water and H+ released from COOH and OH surface groups. Nonetheless, the electrochemical performance of the separator could be dramatically improved by adding 2 wt% of vinylene carbonate (VC) to the electrolyte, which effectively suppressed the generation of gas. Furthermore, the separator demonstrated excellent cycling stability in the pouch cell and sufficiently high specific capacity at ≈ 2C of discharging rate.
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| 27. |
- Kim, Hyeyun, 1986-, et al.
(författare)
-
Feasibility of Chemically Modified Cellulose Nanofiber Membranes as Lithium-Ion Battery Separators
- 2020
-
Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 12:37, s. 41211-41222
-
Tidskriftsartikel (refereegranskat)abstract
- Chemical modification of cellulose is beneficial to produce highly porous lithium-ion battery (LIB) separators, but introduction of high charge density adversely affects its electrochemical stability in a LiNi1/3Mn1/3Co1/3O2 (NMC)/graphite full cell. In this study, the influence of carboxylate functional groups in 2,2,6,6-tetramethylpiperidine-1-oxyl-mediated oxidized cellulose nanofibers (TOCNs) on the electrochemical performances of the LIB separator was investigated. X-ray photoelectron spectroscopy and in operando mass spectrometry measurements were used to elucidate the cause of failure of the batteries containing TOCN separators in the presence and absence of sodium counterions in the carboxylate groups and additives. For the TOCN separator with sodium carboxylate functional groups, it seems that Na deposition is the dominant reason for poor electrochemical stability of the cell thereof. The poor performance of the protonated TOCN separator, attributed to a high amount of gas evolution, is dramatically improved by adding 2 wt % of vinylene carbonate (VC) because of suppressed gas evolution. Unveiling the failure mechanism of the TOCN separators and successively implementing the strategies to improve performance, for example, removing Na, adding VC, and adjusting cycling rates, enable a remarkable cycling performance in the NMC/graphite full cell at approximate to 2 C (3 mA/cm(2)) of a fast discharging rate. Despite the aforementioned efforts and compromises required, an increased charge density of the TOCN is beneficial to acquire a mechanically stronger separator. In conclusion, the manufacturing process of cellulose nanofibers needs to be carefully adjusted to acquire a desired separator property. To the best of our knowledge, it is first reported to perform operando gas evolution measurements to systematically investigate the electrochemical stability of nanocellulose as an LIB separator material. The results elucidate not only the challenges for extensive applications of hygroscopic biomaterials for commercial LIBs but also the practical solutions to achieve high electrochemical stability of the materials.
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| 28. |
- Kim, Hyeyun, 1986-, et al.
(författare)
-
Spray-coated nanocellulose based separator/electrode assembly
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A separator-electrode assembly (SEA) made of wood-based cellulose nanofibers (CNF) and Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was fabricated by a facile spray-coating process. CNF building blocks were prepared by homogenizing enzymatically pretreated cellulose fibers dispersed in a non-hazardous solvent, 2-propanol (IPA). The porous composite separator was made by spray-coating thin layers CNF-IPA, followed by a PVDF-HFP spray coating, on a lithium ion battery electrode. A CNF substrate was crucial for making a highly porous and thermally stable separator and PVDF-HFP coating enhanced its mechanical stability. The SEA maintained dimensional integrity when subjected to high temperature and when used in lithium ion batteries. A CNF-LiNi1/3Co1/3Mn1/3O2 (NMC) SEA showed excellent electrochemical stability, especially at fast charging/discharging rate, whereas a graphite counterpart showed poor electrochemical performance, resulting in cell failure. A SiO2 layer overcoated on the top of CNF-NMC SEA enabled its application for a proof-of-concept lithium metal battery and for a high energy‐density LiNi0.6Co0.2Mn0.2O2 (NMC622) lithium‐ion battery with excellent electrochemical stability and performances. The utilization of biodegradable materials and non-hazardous solvents such as IPA and acetone makes the development of the CNF based SEA attractive, as an eco-friendly lithium ion battery manufacturing process.
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| 29. |
- Marra, Eva, et al.
(författare)
-
ORR activity and stability of carbon supported Pt3Y thin films in PEMFCs
- 2023
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 472
-
Tidskriftsartikel (refereegranskat)abstract
- In order to investigate stability of oxygen reduction reaction (ORR) on a Pt3Y thin film under relevant fuel cell conditions, we performed an accelerated stress test (AST) consisting of 3600 potential cycles between 0.4 and 1.4 V at 1 V s−1 in a single proton exchange membrane fuel cell (PEMFC). The ORR activities were evaluated via polarization curves before and after the AST. Electrochemical active surface area (ECSA) was obtained by CO-stripping voltammetry whereas the morphological changes were monitored by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Variations in surface composition and electronic structures were evaluated by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). After AST, the polarization curves show loss of ORR activity in all voltages for both Pt and Pt3Y. Except at very high voltages (E > 0.85 VRHE), the ORR activity of Pt3Y after AST is very close to that of Pt before AST. This correlates well with the results from the deconvolution of Pt-4f XPS spectra where the binding energy of metallic Pt in Pt3Y is comparable to pure Pt (71.22 eV). SEM and TEM images demonstrate that the morphologies of the aged Pt3Y and as-sputtered Pt are similar, whereas EDX results confirm a steady bulk composition of Pt3Y thin films throughout the entire electrochemical test. By correlating all these results, we conclude that the loss of ORR activity for Pt3Y is due to an increase in the thickness of the Pt overlayer which induces a relaxation of the Pt overlayer decreasing the compressive strain effect. For pure Pt, the loss of ORR activity is associated with a growth of the Pt domains associated with Ostwald ripening process.
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| 30. |
- Marra, Eva, et al.
(författare)
-
Oxygen reduction reaction kinetics on a Pt thin layer electrode in AEMFC
- 2022
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 435, s. 141376-141376
-
Tidskriftsartikel (refereegranskat)abstract
- The study of the catalytic activity in a fuel cell is challenging, as mass transport, gas crossover and the counterelectrode are generally interfering. In this study, a Pt electrode consisting of a thin film deposited on the gasdiffusion layer was employed to study the oxygen reduction reaction (ORR) in an operating Anion Exchange Membrane Fuel Cell (AEMFC). The 2D Pt electrode was assembled together with a conventional porous Pt/Ccounter electrode and an extra Pt/C layer and membrane to reduce the H2 crossover. Polarization curves atdifferent O2 partial pressures were recorded and the resulting reproducible ORR activities were normalized withrespect to the active surface area (ECSA), obtained by CO stripping. As expected, decreasing the O2 partialpressure results in a negative shift in open circuit voltage (OCV), cell voltage and maximum attainable currentdensity. For cell voltages above 0.8 V a fairly constant Tafel slope of 60 mV dec−1 was recorded but at lowervoltages the slope increases rapidly. The observed Tafel slope can be explained by a theoretical model with anassociative mechanism where charge- and proton-transfer steps are decoupled, and the proton transfer is the rate-determining step. A reaction order of 1 with respect to O2 was obtained at 0.65 V which corresponds well withthe mechanism suggested above. Based on the obtained catalyst activities, the electrode performance is comparable to good porous electrodes found in the field. The methodology presented in this study is expected to beuseful in future kinetic studies of other catalysts for AEMFC.
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| 31. |
- Mattinen, Ulriika, et al.
(författare)
-
Gas evolution in commercial Li-ion battery cells measured by on-line mass spectrometry – Effects of C-rate and cell voltage
- 2020
-
Ingår i: Journal of Power Sources. - : Elsevier B.V.. - 0378-7753 .- 1873-2755. ; 477
-
Tidskriftsartikel (refereegranskat)abstract
- Gas evolution in lithium ion batteries (LIB) caused by degradation of the battery cell components, is not only detrimental to cell performance, it is also a major safety risk. Understanding the connection between cell usage and gas evolution at different states of health of the battery is of utmost importance for the improvement of cell components as well as user protocols for LIBs. In this work, an electrochemical mass spectrometric in-operando cell house, capable of hosting a cylindrical 18650 cell, was developed and used to study the gas evolution at increasing cycle C-rates (from C/20 to 4C) between 2.6 V and 4.2 V and during stepwise increased/decreased cell voltages ranging from 2.2 V to 4.4 V. The cell under study was a commercial 1.5 Ah NMC-LMO/Graphite cell, pierced inside an Ar-filled glove box and mounted to the gas-tight cell house before being connected to the On-Line Electrochemical Mass Spectrometer (OEMS). The results show that the large capacity fade observed at high C-rate is associated to major evolution of ethylene gas. The voltage step experiments revealed that CO2 is the main gas evolving at high voltages (>4.15 V) and H2 at low (<2.8 V). Despite significant gas evolution at these extreme voltages, the cell capacity remained stable.
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| 32. |
- Mikheenkova, Anastasiia, et al.
(författare)
-
Ageing of High Energy Density Automotive Li-ion Batteries: The Effect of Temperature and State-of-Charge
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Lithium ion batteries (LIB) have become a cornerstone of the shift to electric transportation. In an attempt to decrease the production load and prolong battery life, understanding different degradation mechanisms in state-of-the-art LIBs is essential. Here, we analyze how operational temperature and state-of-charge (SoC) range in cycling influence the ageing of automotive grade 21700 batteries, extracted from a Tesla 3 Long Range 2018 battery pack with positive electrode containing LiNixCoyAlzO2 (NCA) and negative electrode containing SiOx-C. In the given study we use a combination of electrochemical and material analysis to understand degradation sources in the cell. Herein we show that loss of lithium inventory is the main degradation mode in the cells, with loss of material on the negative electrode as there is a significant contributor when cycled in the low SoC range. Degradation of NCA dominates at elevated temperatures with combination of cycling to high SoC (beyond 50%).
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| 33. |
- Mussa, Abdilbari, et al.
(författare)
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Fast-charging effects on ageing for energy-optimized automotive LiNi1/3Mn1/3Co1/3O2/graphite prismatic lithium-ion cells
- 2019
-
Ingår i: Journal of Power Sources. - : ELSEVIER SCIENCE BV. - 0378-7753 .- 1873-2755. ; 422, s. 175-184
-
Tidskriftsartikel (refereegranskat)abstract
- The reactions in energy-optimized 25 Ah prismatic NMC/graphite lithium-ion cell, as a function of fast charging (1C-4C), are more complex than earlier described. There are no clear charging rate dependent trends but rather different mechanisms dominating at the different charging rates. Ageing processes are faster at 3 and 4C charging. Cycling with 3C-charging results in accelerated lithium plating but the 4C-charging results in extensive gas evolution that contribute significantly to the large cell impedance rise. Graphite exfoliation and accelerated lithium inventory loss point to the graphite electrode as the source of the gas evolution. The results are based on careful post-mortem analyses of electrodes using: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). SEM results show particle cracking independent of the charging rate used for the cycling. XPS and EIS generally indicate thicker surface film and larger impedance, respectively, towards the edge of the jellyrolls. For the intended application of a battery electric inner-city bus using this type of cell, charging rates of 3C and above are not feasible, considering battery lifetime. However, charging rates of 2C and below are too slow from the point of view of practical charging time.
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| 34. |
- Mussa, Abdilbari, et al.
(författare)
-
Inhomogeneous active layer contact loss in a cycled prismatic lithium-ion cell caused by the jelly-roll curvature
- 2018
-
Ingår i: Journal of Energy Storage. - : Elsevier Ltd. - 2352-152X .- 2352-1538. ; 20, s. 213-217
-
Tidskriftsartikel (refereegranskat)abstract
- Internal resistance is a key parameter that affects the power, energy, efficiency, lifetime, and safety of a lithium-ion battery. It grows due to chemical and mechanical battery wear during ageing. In this work, the effect of the jelly-roll winding curvature on impedance rise is investigated. NMC electrode samples, harvested from the curved as well as the flat regions of the jelly-roll from cycle-aged and calendar-aged prismatic cells (25 Ah, hard casing) are investigated by electrochemical impedance spectroscopy. After cycling, larger impedance rise is observed at the outer radius (concave) of the curved region compared to the inner radius (convex) or the flat region of the jelly-roll, and the difference increases with a decrease in the jelly-roll radius of curvature, from the cell skin towards the core. To identify the causes behind the observed difference in the impedance rise, investigations at different external compression (0 and 2.5 MPa) and temperature (5 and 25 °C) are performed. The results show that contact loss between the current collector and the active layer is the main source of the difference in impedance rise. Mechanical mechanisms that may cause the contact loss are discussed and design recommendations to mitigate the rise in impedance are given.
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| 35. |
- Novalin, Timon, et al.
(författare)
-
Demonstrating the absence of metal ion contamination in operando PEM fuel cells utilizing unmodified stainless steel bipolar plates
- 2023
-
Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 349
-
Tidskriftsartikel (refereegranskat)abstract
- Using stainless steel as material for bipolar plates (BPPs) in proton exchange membrane fuel cells (PEMFCs) carries a perceived risk of corrosion and subsequent metal ion contamination of the membrane electrode as-sembly (MEA). However, assessments in literature on this hazard to PEMFC systems have been based on ex-situ corrosion studies, where general assumptions made on the BPP environment might not be a correct simulation of real on-site conditions. In this contribution, uncoated BPPs from stainless steel grades 304 L, 316 L and 904 L were subjected to in-situ hybrid endurance/stress testing to simulate realistic conditions in operating fuel cell systems and re-evaluate the need of additional corrosion protection. A post analysis of the plates showed no signs of surface dissolution on any of the tested samples and the concentration of iron in the MEA averaged 7 to 10 ppm for uncoated samples and 7 to 11 ppm for coated and graphitic reference tests, displaying a negligible amount of trace metals compared to critical thresholds found in literature. Contact resistance values were stable for all samples and observable changes in cell performance and voltage degradation was confirmed to be un-related to the presence of uncoated bipolar plates. The combined effects of decoupling of bipolar plate surface potentials from electrode potentials and operational control of stable gas flow compositions to sustain stainless steel surface passivation, were identified as explanation for the experimentally observed corrosion resistance of uncoated stainless steel plates in PEMFCs.
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| 36. |
|
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| 37. |
- Novalin, Timon
(författare)
-
Electrochemical characterization of materials for next generation polymer electrolyte fuel cells
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer electrolyte fuel cells occupy a key position in implementing the hydrogen economy on a global scale. However, assessments of cost, availability and sustainability of materials currently used to manufacture state-of-the-art fuel cell stacks have given cause for concern. Platinum and platinum-group metals are prohibitively expensive and of low abundance. The benchmark ion-conductive polymer NafionTM and related perfluorosulfonic acid-based polymers are difficult to synthesize and environmentally persistent to extreme degrees. Graphitic and carbon composite bipolar plates are unsuitable for mass production and have low recycling potential. In the compiled works, alternative materials were evaluated both for the acidic and alkaline variations of polymer electrolyte fuel cells. Electrochemical characterization was carried out in single cell tests with a focus on finding the limitations in terms of ohmic, charge transfer and transport resistances in the cell, through polarization and impedance measurements.Carbon coated stainless steel bipolar plates were tested operando in a proton exchange membrane fuel cell (PEMFC) under realistic conditions based on the New European Drive Cycle. Observed trace metal contamination of the MEA was linked to metal dissolution from coating defects caused by manufacturing (Paper I). A theoretical understanding of observed metal dissolution was confirmed experimentally and a concept for preventing metal dissolution was developed for PEMFC bipolar plates (Paper II). The developed concept was extended to uncoated stainless steel bipolar plates and tested successfully for three stainless steel types in operando PEMFC (Paper III)Anion exchange polymers based on poly(arylene piperidinium) (PAP) were tested as both membranes and ionomers in a comparative study with a commercial reference material, showing higher performance and the significance of ionomer-carbon support interactions (Paper IV). PAP-based ionomers with varying ion exchange capacities were studied to optimize electrodes in anion exchange membrane fuel cells (AEMFC). A combination of high ion exchange capacity ionomer on both cathode and anode was best performing, linked to small water transport resistance in cathode and increased kinetic contribution of the anode HOR (Paper V). The effects of modifying the catalyst layer through the introduction of crosslinked PAP particles were studied in operando AEMFCs. A positive impact on charge transfer and diffusion resistances in electrodes containing particles could be observed. (Paper VI).Silver nanoparticles were used as catalyst material in the cathode of previously optimized membrane electrode assemblies in AEMFC. The results showed promising performance compared to platinum electrodes based on monetary and sustainability considerations, but also challenges regarding catalyst stability and detrimental silver-ionomer interactions. (Paper VII).
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| 38. |
- Novalin, Timon, et al.
(författare)
-
Electrochemical performance of poly(arylene piperidinium) membranes and ionomers in anion exchange membrane fuel cells
- 2021
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 507
-
Tidskriftsartikel (refereegranskat)abstract
- Awakening interest in anion exchange membrane fuel cells (AEMFC) for low temperature applications has led to an increased demand for high-performing polymers stable under alkaline conditions. In this study a poly(p-terphenylene piperidinium)-based (PAP) membrane and ionomer was synthesised and applied in membrane electrode assemblies (MEAs), with porous gas-diffusion electrodes based on Pt catalysts supported by VULCAN® and high surface area carbon, respectively. The MEAs were evaluated in AEMFC single-cell tests. In order to identify specific beneficial characteristics of the polymer, the results were compared to reference tests using a commercial Aemion™-polymer. Steady-state polarisation performance measurements were carried out as well as electrode characterisations via cyclic voltammetry and electrochemical impedance spectroscopy, in addition to ex-situ characterisation of the polymer and the membrane electrode assemblies. PAP-based membranes showed great potential with an in-situ measured average ohmic resistance of 0.09 Ω cm2. Mass transport limitations at higher current densities were observed for high surface area carbon electrodes, leading to an overall higher performance with the use of VULCAN®. Properties of the ionomer related to water uptake capabilities were observed to inhibit performance as well. The higher water uptake of PAP-based ionomers appears to be a key property for increasing electrode performance.
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| 39. |
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| 40. |
|
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| 41. |
- Novalin, Timon, et al.
(författare)
-
Trace-metal contamination in proton exchange membrane fuel cells caused by laser-cutting stains on carbon-coated metallic bipolar plates
- 2021
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 46:26, s. 13855-13864
-
Tidskriftsartikel (refereegranskat)abstract
- Trace-metal contamination poses a threat to performance and stability of proton exchange membrane fuel cells (PEMFCs). In this study the source of origin and degree of metal dissolution from carbon-coated 316L bipolar plates (BPPs) are evaluated after a long-term PEMFC test run under conditions resembling a real-life automotive application. Despite intact carbon-coating, metal dissolution occurs from uncoated oxycarbide stains on the plates? surface. Which correlates with post-mortem detection of chromium, iron and nickel in the membrane electrode assembly. The rate of cell voltage decrease throughout the high current operations is found to be twice as high in the presence of metal ions. Metal dissolution can be correlated with transients in cell voltage during dynamic current load cycling as a result of temporary global fuel starvation. The observed difference in metal dissolution on the anode and cathode BPP indicates weak galvanic coupling between the bipolar plate(s) and the electrode layer(s). ? 2020 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).
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| 42. |
- Ohrelius, Mathilda, et al.
(författare)
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Lifetime Limitations in Multi-Service Battery Energy Storage Systems
- 2023
-
Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 16:7
-
Tidskriftsartikel (refereegranskat)abstract
- A reliable power grid system based on renewable energy sources is a crucial step to restrict the climate crisis. Stationary battery energy storage systems (BESS) offer a great potential to repel power fluctuations in the grid at different timescales. However, for a reliable operation and cost estimation, the degradation in the batteries needs to be understood. We present an accelerated battery degradation study, on single as well as multi-service applications, of NCM532/Gr lithium-ion battery cells. Frequency regulation (FR) was the least harmful for the battery, with an expected lifetime of 12 years, while peak shaving (PS) resulted in an expected lifetime of 8 years. The combined cycle (FRPS) accelerated the capacity loss, and degradation of the positive electrode was induced from the start of cycling, causing power limitations after only 870 equivalent full cycles (EFC). Tracking the 1C-rate discharge capacity was proven to be a good indication of the accelerated cell polarization, and it can serve as a useful method to evaluate the internal battery state of health (SOH).
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| 43. |
- Roy Chowdhury, Niladri, 1989, et al.
(författare)
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Influence of state of charge window on the degradation of Tesla lithium-ion battery cells
- 2024
-
Ingår i: Journal of Energy Storage. - : Elsevier BV. - 2352-152X .- 2352-1538. ; 76
-
Tidskriftsartikel (refereegranskat)abstract
- The Tesla Model 3 is currently one of the most popular electric vehicle (EV) and was the best selling EV in 2020. In this article, performance and degradation of 21700 cylindrical cells, taken from a new vehicle, were studied by cycling within 10% State of charge (SOC) windows. Cells tested in either very high and very low SOC windows show faster degradation than at moderate SOC. In particular, the shortest service life was for cells cycled below 25% SOC. The ageing mechanisms of the cells cycled in these most extreme windows have been monitored by non-destructive electrochemical methods including analyses of differential voltage, incremental capacity, and voltage hysteresis. The combination of loss of lithium inventory (LLI) accelerated in early cycling by SiOx utilization, paired with loss of active material (LAM) of SiOx are responsible for the most rapid ageing, which is observed in the cells cycled in the 5%–15% SOC window. Calendar ageing, however, is not accelerated by storage at low SOC. The results from this study offer an understanding of the distinct, SOC-dependent ageing patterns observed in the cells. This understanding of the ageing mechanisms in different cycling and storage conditions can be used to recommend improved customer usage patterns and substantially extend the lifetime of lithium-ion batteries in operation.
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| 44. |
- Roy Chowdhury, Niladri, et al.
(författare)
-
The state of charge dependence of degradation in lithium-ion cells from a Tesla Model 3
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The Tesla Model 3 is currently one of the most popular electric vehicles (EV)and was the best selling EV in 2020. In this article, performance and degradation are studied for 21700 cylindrical cells from a Tesla Model 3 cycledwithin nine, sequential state of charge (SOC) windows, each using 10% ofthe cell capacity is studied. Cells tested in either very high and very low SOCwindows show faster degradation than at moderate SOC. In particular, theshortest service life was for cells cycled below 25% SOC. The ageing mechanisms of the cells cycled in these most extreme windows have been monitoredby non-destructive electrochemical methods including analyses of differentialvoltage, incremental capacity, and voltage hysteresis. The combination ofloss of active material (LAM) and loss of lithium inventory (LLI) are responsible for the most rapid ageing observed in the cells cycled in the 5-15%SOC window. Calendar ageing, however, is not accelerated by storage atlow SOC. The results from this study offer an understanding of the distinct,SOC-dependent ageing patterns observed in the cells. This understanding ofthe ageing mechanisms in different cycling and storage conditions can be usedto recommend improved customer usage patterns and substantially extendthe lifetime of lithium-ion batteries in operation.
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| 45. |
- Salmeron-Sanchez, Ivan, et al.
(författare)
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Zwitterionic poly(terphenylene piperidinium) membranes for vanadium redox flow batteries
- 2023
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 474
-
Tidskriftsartikel (refereegranskat)abstract
- Over recent years, non-fluorinated ion exchange membranes based on poly(terphenylene) backbones carrying different functional groups have shown potential application for vanadium redox flow batteries (VRFBs). Generally, the ion exchange membrane in VRFBs is a critical component in terms of the output power, long-term stability and cost. Yet, the shortcomings of commercial membranes (e.g., Nafion) have become a substantial barrier to further commercializing VRFBs. After successfully fabricating and testing poly(terphenylene)-based membranes carrying piperidinium and sulfonic acid groups, respectively, for VRFBs, we have in the present work combined both these ionic groups in a single zwitterionic membrane. A series of poly(terphenylene)-based membranes containing zwitterionic (sulfoalkylated piperidinium) and cationic (piperidinium) groups in different ratios (40–60%) were synthesized and investigated. The VRFB using the zwitterionic membranes showed competitive performance compared to Nafion 212 regarding ionic conductivity, capacity retention, and chemical stability. In addition, it was shown that the VRFB performance was improved by increasing the content of zwitterionic groups within the membrane. A self-discharge time of more than 800 h and 78.7% average capacity retention for 500 VRFB cycles were achieved using a membrane with an optimized ratio (60% zwitterionic and 40% piperidinium groups). Furthermore, the chemical stability was promising, as there was no change in the chemical structure after 500 cycles. Our results represent a critical step for developing novel and competitive ion exchange membranes as an excellent alternative to the Nafion benchmark.
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| 46. |
- Smith, Alexander J., et al.
(författare)
-
Expanded In Situ Aging Indicators for Lithium-Ion Batteries with a Blended NMC-LMO Electrode Cycled at Sub-Ambient Temperature
- 2021
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 168:11, s. 110530-
-
Tidskriftsartikel (refereegranskat)abstract
- An important step toward safer and more reliable lithium-ion battery systems is the improvement of methods for detection and characterization of battery degradation. In this work, we develop and track aging indicators over the life of 18650-format lithium-ion batteries with a blended NMC532-LMO positive electrode and graphite negative electrode. Cells are cycled until reaching 80% of their original capacity under combinations of four cycling conditions: ambient and sub-ambient temperatures (29 degrees C and 10 degrees C) and fast and mild rates (2.7 and 1.0C). Loss of lithium inventory dominates aging for all cases, with additional loss of NMC capacity under the combination of sub-ambient temperature and mild rate. A novel, easily acquired polarization factor complements capacity fade analysis; it correlates well with impedance and galvanostatic cycle life and indicates changes in active aging processes. These processes are further revealed by differential voltage analysis (DVA) and incremental capacity analysis (ICA). New indicators and aging scenarios are evaluated for these techniques and supported by post mortem analysis. From in operando cycling data and a single, slow discharge curve, these four methods (capacity fade, polarization factor, DVA, and ICA) comprise a simple, explanatory, and non-invasive toolbox for evaluating aging in lithium-ion battery systems.
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| 47. |
- Smith, Alexander J., et al.
(författare)
-
Localized lithium plating under mild cycling conditions in high-energy lithium-ion batteries
- 2023
-
Ingår i: Journal of Power Sources. - : Elsevier. - 0378-7753 .- 1873-2755. ; 573
-
Tidskriftsartikel (refereegranskat)abstract
- Conditions such as the temperature and pressure experienced by lithium-ion battery components are dependent on cell geometry and can vary widely within a large cell. The resulting uneven degradation is challenging to study at the full cell level but can be revealed upon disassembly and post mortem analysis. In this work, we report localized lithium plating in automotive-grade, prismatic lithium-ion cells, also under cycling conditions generally considered to be mild (e.g., 5–65 %SOC, 23 °C, 0.5C cycle rate). Dead lithium content is quantified using 7Li nuclear magnetic resonance spectroscopy in both electrode and separator samples, corresponding to substantial capacity fade (26–46%) of the full cells. Severe lithium plating is typically initiated in regions near the positive tab, in which both the separators and negative electrodes are ultimately deactivated. High pressure arises during cycling, and we propose a deactivation mechanism based on high local stress due to electrode expansion and external constraint. Further, we develop a model to demonstrate that component deactivation can result in lithium plating even under mild cycling conditions. Notably, components harvested from regions with no detected lithium plating maintained adequate electrochemical performance.
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| 48. |
- Smith, Alexander J.
(författare)
-
Tools for characterizing performance degradation in lithium-ion batteries
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium-ion batteries have enabled vast societal changes, ranging in scale from the adoption of personal electronics to electromobility and grid-scale, renewable energy storage. However, all applications face performance fade over time, observed as losses of battery capacity and power. This gradual degradation is most often due to electrochemical aging processes inside the cell, including phenomena causing a loss of cyclable lithium (e.g., lithium plating, growth of the solid‑electrolyte interphase or SEI), a loss of active material (e.g., particle cracking), and/or a loss of ionic or electronic conductivity. In the compiled works, many individual batteries have been aged and analyzed to better understand the conditions contributing to aging in different cell designs. The cells studied include lab-built pouch cells, commercial cylindrical cells (with electrodes LiNixMnyCo1‑x‑yO2‑LiMn2O4/C6 and LiNixCoyAl1‑x‑yO2/C6‑SiOx), and larger automotive-grade prismatic cells (LiNixMnyCo1‑x‑yO2/C6).Complementary in situ and post mortem methods are developed, with relevance for both battery research and battery control systems. Excellent characterization can often be achieved by a combination of differential voltage and incremental capacity analyses. Obtained from a simple, slow cycle, the derivatives of the voltage profile reveal many features that can be tracked over aging. This thesis particularly develops these techniques for blended electrodes, deconvoluting the aging of individual components. Dynamic performance is resolved with a novel polarization factor, impedance spectroscopy, and tools based on current pulses/interruptions. Finally, a protocol based on nuclear magnetic resonance spectroscopy is developed, enabling fast and direct quantification of lithium plating and SEI on harvested battery components. With such tools, we can improve how batteries are used and monitored, paving the way for efficient research and safer, more reliable batteries.
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| 49. |
- Svens, Pontus, 1970-, et al.
(författare)
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Evaluating Performance and Cycle Life Improvements in the Latest Generations of Prismatic Lithium-Ion Batteries
- 2022
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Ingår i: IEEE TRANSACTIONS ON TRANSPORTATION ELECTRIFICATION. - : Institute of Electrical and Electronics Engineers (IEEE). - 2332-7782. ; 8:3, s. 3696-3706
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Tidskriftsartikel (refereegranskat)abstract
- During the last decade, the market interest for electrified vehicles has increased considerably alongside global climate initiatives. This has coincided with vast improvements in automotive-grade, lithium-ion battery performance. This has increased the range of battery electric vehicles and plug-in hybrids, but lifetime remains a challenge. Aging during fast charging is especially difficult to understand due to its nonlinear dependence on charge rate, state-of-charge, and temperature. We present results from fast charging of several energy-optimized, prismatic lithium-ion battery cell generations with a nickel manganese cobalt (NMC)/graphite chemistry through comparison of capacity retention, resistance, and dQ/dV analysis. Changes in cell design have increased energy density by almost 50% over six years of cell development and acceptable cycle life can be expected, even under fast charging, when restricting the usage of the available capacity. Even though this approach reduces the useable energy density of a battery system, this tradeoff could still be acceptable for vehicle applications where conventional overnight charging is not possible. The tested cell format has been used for a decade in electrified vehicles. The ongoing development and improvement of this cell format by several cell manufacturers suggests that it will continue to be a good choice for future vehicles.
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| 50. |
- Wang, Huan, et al.
(författare)
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MnO2/Mn2+ chemistry: Charging protocol and electrolyte regulation
- 2023
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Ingår i: Energy Storage Materials. - : Elsevier BV. - 2405-8289 .- 2405-8297. ; 63
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous rechargeable Zn-MnO2 batteries based on the dissolution/deposition mechanism of MnO2/Mn2+are gaining increasing attention due to their high capacity and structural simplicity. One of the major concerns is the Mn2+/Mn3+side reaction, which hampers the coulombic efficiency (CE) due to Mn3+(aq) disproportionation. However, factors affecting Mn3+ formation have not been systematically investigated. In this study, we utilized in situ optical microscopy and Scanning Electron Microscopy (SEM) to evaluate the formation of Mn3+ by observing its disproportionation product: the randomly deposited MnO2. We found that an excessively high charging voltage and a low electrolyte pH (pH<4.2) were shown to adversely accelerate Mn3+ formation. Most reports on the Mn2+/MnO2 cathode indicate a coulombic efficiency of only 80 % on carbon felt (thickness: 2.5 mm) at 2 mAh/cm2 due to the inherently low electrical conductivity of MnO2. Here with the optimized charging protocol and the utilization of the anode-friendly, methanesulfonic acid (MSA)-containing electrolyte, we achieved a CE of nearly 100 % for up to 200 cycles at 2 mAh/cm2. This work gives guidelines on the electrolyte design and charging protocol optimization towards high-performance MnO2/Mn2+cathodes.
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