| 1. |
- Chai, Zhigang, et al.
(författare)
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Ni–Ag Nanostructure-Modified Graphitic Carbon Nitride for Enhanced Performance of Solar-Driven Hydrogen Production from Ethanol
- 2020
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:10, s. 10131-10138
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Tidskriftsartikel (refereegranskat)abstract
- Solar-driven splitting of alcohol utilizing photocatalysts is a promising route to obtain H2 and fine chemicals. Ni nanoparticles have shown great potential for light-driven splitting of alcohol, and their size, exposed facets, and electronic properties play key roles in the performance of photocatalysts. Therefore, purposefully modifying Ni is of great importance. In this report, Ni–Ag nanostructures were fabricated in situ on graphitic carbon nitride by a sequential photodeposition method. The solar-driven hydrogen production from ethanol was dramatically enhanced on the Ni–Ag nanostructure-modified graphitic carbon nitride compared with pure Ni nanoparticle-modified graphitic carbon nitride. It was found that the beneficial role of Ag is to disperse and stabilize small Ni nanoparticles and, importantly, expose catalytic sites that are less prone to accumulate ethanol decomposition products (acetate species), as proven by in situ diffuse reflectance infrared Fourier transform spectroscopy.
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| 2. |
- 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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| 3. |
- 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
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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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| 4. |
- Ostli, Elise R., et al.
(författare)
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Limitations of Ultrathin Al2O3 Coatings on LNMO Cathodes
- 2021
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 6:45, s. 30644-30655
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Tidskriftsartikel (refereegranskat)abstract
- This study demonstrates the application of Al2O3 coatings for the high-voltage cathode material LiNi0.5–xMn1.5+xO4−δ (LNMO) by atomic layer deposition. The ultrathin and uniform coatings (0.6–1.7 nm) were deposited on LNMO particles and characterized by scanning transmission electron microscopy, inductively coupled plasma mass spectrometry, and X-ray photoelectron spectroscopy. Galvanostatic charge discharge cycling in half cells revealed, in contrast to many published studies, that even coatings of a thickness of 1 nm were detrimental to the cycling performance of LNMO. The complete coverage of the LNMO particles by the Al2O3 coating can form a Li-ion diffusion barrier, which leads to high overpotentials and reduced reversible capacity. Several reports on Al2O3-coated LNMO using alternative coating methods, which would lead to a less homogeneous coating, revealed the superior electrochemical properties of the Al2O3-coated LNMO, suggesting that complete coverage of the particles might in fact be a disadvantage. We show that transition metal ion dissolution during prolonged cycling at 50 °C is not hindered by the coating, resulting in Ni and Mn deposits on the Li counter electrode. The Al2O3-coated LNMO particles showed severe signs of pitting dissolution, which may be attributed to HF attack caused by side reactions between the electrolyte and the Al2O3 coating, which can lead to additional HF formation. The pitting dissolution was most severe for the thickest coating (1.7 nm). The uniform coating coverage may lead to non-uniform conduction paths for Li, where the active sites are more susceptible to HF attack. Few benefits of applications of very thin, uniform, and amorphous Al2O3 coatings could thus be verified, and the coating is not offering long-term protection from HF attack.
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| 5. |
- Salian, Girish D., et al.
(författare)
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Investigation of Water-Soluble Binders for LiNi0.5Mn1.5O4-Based Full Cells
- 2022
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Ingår i: ChemistryOpen. - : John Wiley & Sons. - 2191-1363. ; 11:6
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Tidskriftsartikel (refereegranskat)abstract
- Two water-soluble binders of carboxymethyl cellulose (CMC) and sodium alginate (SA) have been studied in comparison with N-methylpyrrolidone-soluble poly(vinylidene difluoride-co-hexafluoropropylene) (PVdF-HFP) to understand their effect on the electrochemical performance of a high-voltage lithium nickel manganese oxide (LNMO) cathode. The electrochemical performance has been investigated in full cells using a Li4Ti5O12 (LTO) anode. At room temperature, LNMO cathodes prepared with aqueous binders provided a similar electrochemical performance as those prepared with PVdF-HFP. However, at 55 degrees C, the full cells containing LNMO with the aqueous binders showed higher cycling stability. The results are supported by intermittent current interruption resistance measurements, wherein the electrodes with SA showed lower resistance. The surface layer formed on the electrodes after cycling has been characterized by X-ray photoelectron spectroscopy. The amount of transition metal dissolutions was comparable for all three cells. However, the amount of hydrogen fluoride (HF) content in the electrolyte cycled at 55 degrees C is lower in the cell with the SA binder. These results suggest that use of water-soluble binders could provide a practical and more sustainable alternative to PVdF-based binders for the fabrication of LNMO electrodes.
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| 6. |
- Tesfamhret, Yonas, et al.
(författare)
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Influence of Al2O3 Coatings on HF Induced Transition Metal Dissolution from Lithium-Ion Cathodes
- 2022
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 169:1
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal (TM) dissolution from oxide cathode materials is a major challenge limiting the performance of modern Li-ion batteries. Coating the cathode materials with thin protective layers has proved to be a successful strategy to prolong their lifetime. Yet, there is a lack of fundamental understanding of the working mechanisms of the coating. Herein, the effect of the most commonly employed coating material, Al2O3, on suppressing hydrofluoric acid(HF)-induced TM dissolution from two state-of-the-art cathode materials, LiMn2O4 and LiNi0.8Mn0.1Co0.1O2, is investigated. Karl Fischer titration, fluoride selective probe and inductively coupled plasma optical emission spectrometry are coupled to determine the evolution of H2O, HF and TM concentrations, respectively, when the active materials come in contact with the aged electrolyte. The coating reduces the extent of TM dissolution, in part due to the ability of Al2O3 to scavenge HF and reduce the acidity of the electrolyte. Delithiation of the cathode materials, however, increases the extent of TM dissolution, likely because of the higher vulnerability of surface TMs in +IV oxidation state towards HF attack. In conclusion, the current study evidences the important role of acid-base reactions in governing TM dissolution in Li-ion batteries and shows that coatings enhance the chemical integrity of the cathode towards an acidic electrolyte.
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| 7. |
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| 8. |
- Tesfamhret, Yonas, et al.
(författare)
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On the Manganese Dissolution Process from LiMn2O4 Cathode Materials
- 2021
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Ingår i: ChemElectroChem. - : John Wiley & Sons. - 2196-0216. ; 8:8, s. 1516-1523
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal (TM) dissolution is a process experienced by most cathode materials based on lithium transition metal oxides. Spinel LiMn2O4 (LMO) is the best-known cathode material that suffers from TM dissolution. Therefore, LMO is selected here to understand the dissolution process and derive an inductively coupled plasma optical emission spectroscopy (ICP-OES) method for quantifying dissolved metal ions. Furthermore, the LMO powder is coated with thin Al2O3 films of different thicknesses using atomic layer deposition (ALD) in an attempt to suppress the dissolution of Mn. Two different types of counter electrodes, lithium iron phosphate (LFP) and Li-metal, were used to investigate the role of the counter electrode on Mn dissolution. HF is identified as the lead cause of Mn dissolution, through comparisons of cells containing LiPF6 or LiClO4 based electrolytes. The results show that Li-metal counter electrode effectively minimizes the dissolution process via likely consuming HF and H2O impurity. In contradiction to the purpose of the protective Al2O3 thin film coating, surface coated LMO showed higher dissolution of Mn compared to pristine LMO, both in LFP||LMO and Li||LMO configurations. Al2O3 is proposed to generate H2O when reacts with HF. H2O could have the possibility to migrate back in the electrolyte and participate in the hydrolysis of LiPF6, resulting in more HF and thereby more Mn dissolution.
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| 9. |
- Tesfamhret, Yonas, et al.
(författare)
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Revealing capacity fading in Sb-based anodes using symmetric sodium-ion cells
- 2021
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 2515-7639. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical performance of negative active materials employed in sodium-ion batteries is dependent on the amount of Na+ available in the test cells. As such, electrodes that exhibit long cycle-life and high coulombic efficiency (CE) in half-cells could suffer from fast capacity fading in full-cells as a result of unstable solid electrolyte interphase (SEI) and mechanical degradation leading to loss of active materials. In this work, the performance of Sb–graphite composite active materials prepared by extended ball-milling was evaluated in sodium half-cells and various types of symmetric cells (SCs). In half-cell tests, the composite electrodes provided specific capacities in the range 350–600 mAh g−1 at C/20 with initial CE of 82%. A stable capacity of 380 mAh g−1 was observed in the subsequent 100 cycles with the CE increasing to nearly 99%. However, self-discharge tests on half-cells and galvanostatic cycling of SCs revealed poor capacity retention as a result of parasitic reaction occurring through the SEI layer. Contrary to half-cells, the SCs revealed that Sb electrodes suffered from sharp capacity losses when a limited amount of Na+ ions was available in the cells. This is also characteristic of full-cells in which the sodium ions are supplied by the positive electrode.
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| 10. |
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| 11. |
- Tesfamhret, Yonas, et al.
(författare)
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The role of ethylene carbonate (EC) and tetramethylene sulfone (SL) in the dissolution of transition metals from lithium-ion cathodes
- 2023
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 13, s. 20520-20529
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal (TM) dissolution is a direct consequence of cathode-electrolyte interaction, having implications not only for the loss of redox-active material from the cathode but also for the alteration of solid electrolyte interphase (SEI) composition and stability at the counter electrode. It has widely been reported that the limited anodic stability of typical carbonate-based electrolytes, specifically ethylene carbonate (EC)-based electrolytes, makes high-voltage cathode performance problematic. Hence, the more anodically stable tetramethylene sulfone (SL) has herein been utilized as a co-solvent and a substitute for EC in combination with diethyl carbonate (DEC) to investigate the TM dissolution behavior of LiN0.8C0.17Al0.03 (NCA) and LiMn2O4 (LMO). EC|DEC and SL|DEC solvents in combination with either LiPF6 or LiBOB salts have been evaluated, with LFP as a counter electrode to eliminate the influence of low potential anodes. Oxidative degradation of EC is shown to propagate HF generation, which is conversely reflected by an increased TM dissolution. Therefore, TM dissolution is accelerated by the acidification of the electrolyte. Although replacing EC with the anodically stable SL reduces HF generation and effectively mitigates TM dissolution, SL containing electrolytes are demonstrated to be less capable of supporting Li-ion transport and thus show lower cycling stability.
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| 12. |
- Tesfamhret, Yonas
(författare)
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Transition metal dissolution from Li-ion battery cathodes
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium-ion batteries (LIBs) have become reliable electrochemical energy storage systems due to their relative high energy and power density, in comparison to alternative battery chemistries. The energy density of current LIBs is limited by the average operating voltage and capacity of oxide-based cathode materials containing a variety of transition metals (TM). Furthermore, the low anodic stability of "conventional" carbonate-based electrolytes limits further extension of the LIBs voltage window. Here, ageing mechanisms of cathodes are investigated, with a main focus on TM dissolution and on strategies to tailor the cathode surface and the electrolyte composition to mitigate TM dissolution.Atomic layer deposition (ALD) coatings of the cathode surface with electrically insulating Al2O3 and TiO2 coatings is employed and investigated as a method to stabilize the cathode/electrolyte interface and minimize TM dissolution. The thesis illustrates both the advantages and limitations of amorphous oxide coating materials during electrochemical cycling. The protective oxide layer restricts auto-catalytic salt degradation and the consequent propagation of acidic species in the electrolyte. However, a suboptimal coating contributes to a nonhomogeneous cathode surface ageing during electrochemical cycling. Furthermore, the widely accepted concept of charge disproportionation as the fundamental cause of TM dissolution is demonstrated to be a minor factor. Rather, a chemical dissolution mechanism based on acid-base/electrolyte-cathode interaction underlies substantial TM dissolution.The thesis demonstrates LiPF6, and by implication HF, as the principal source of TM dissolution. In addition, the oxidative degradation of ethylene carbonate (EC) solvent contributes indirectly to generation of HF. Thus, an increase in electrolyte oxidative degradation products accelerates TM dissolution. Substituting EC and LiPF6 with a more anodically stable solvent (e.g., tetra-methylene sulfone) and a non-fluorinated salt (e.g., LiBOB or LiClO4) or addition of TM scavenging additives like lithium difluorophosphate (LiPO2F2) are here investigated as strategies to either i) mitigate TM dissolution, ii) supress TM migration and deposition on the anode surface, or iii) supress formation of acidic electrolyte degradation products and thereby TM dissolution. The thesis also highlights the necessity of taking precautions when attempting to replace the components, as reducing TM dissolution may come at the expense of electrochemical cycling performance.
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| 13. |
- Østli, Elise R., et al.
(författare)
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On the Durability of Protective Titania Coatings on High‐Voltage Spinel Cathodes
- 2022
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Ingår i: ChemSusChem. - : John Wiley & Sons. - 1864-5631 .- 1864-564X. ; 15:12
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Tidskriftsartikel (refereegranskat)abstract
- TiO2-coating of LiNi0.5-xMn1.5+xO4 (LNMO) by atomic layer deposition (ALD) has been studied as a strategy to stabilize the cathode/electrolyte interface and mitigate transition metal (TM) ion dissolution. The TiO2 coatings were found to be uniform, with thicknesses estimated to 0.2, 0.3, and 0.6 nm for the LNMO powders exposed to 5, 10, and 20 ALD cycles, respectively. While electrochemical characterization in half-cells revealed little to no improvement in the capacity retention neither at 20 nor at 50 °C, improved capacity retention and coulombic efficiencies were demonstrated for the TiO2-coated LNMO in LNMO||graphite full-cells at 20 °C. This improvement in cycling stability could partly be attributed to thinner cathode electrolyte interphase on the TiO2-coated samples. Additionally, energy-dispersive X-ray spectroscopy revealed a thinner solid electrolyte interphase on the graphite electrode cycled against TiO2-coated LNMO, indicating retardation of TM dissolution by the TiO2-coating.
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