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- Aktekin, Burak, et al.
(författare)
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Cation Ordering and Oxygen Release in LiNi0.5-xMn1.5+xO4-y (LNMO)—In Situ Neutron Diffraction and Performance in Li-Ion Full Cells
- 2018
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Konferensbidrag (refereegranskat)abstract
- LiNi0.5Mn1.5O4 (LNMO) is a promising spinel-type positive electrode for lithium ion batteries as it operates at high voltage and possesses high power capability. However, rapid performance degradation in full cells, especially at elevated temperatures, is a problem. There has been a considerable interest in its crystal structure as this is known to affect its electrochemical performance. LNMO can adopt a P4332 (cation ordered) or Fd-3m (cation disordered) arrangement depending on the synthesis conditions. Most of the studies in literature agree on better electrochemical performance for disordered LNMO [1], however, a clear understanding of the reason for this behaviour is still lacking. This partly arises from the fact that synthesis conditions leading to disordering also lead to oxygen deficiency, rock-salt impurities and therefore generate some Mn3+ [2]. Most commonly, X-ray diffraction is used to characterize these materials, however, accurate structural analysis is difficult due to the near identical scattering lengths of Mn and Ni. This is not the case for neutron diffraction. In this study, an in-situ neutron diffraction heating-cooling experiment was conducted on slightly Mn-rich LNMO under pure oxygen atmosphere in order to investigate relationship between disordering and oxygen deficiency. The study shows for the first time that there is no direct relationship between oxygen loss and cation disordering, as disordering starts prior to oxygen release. Our findings suggest that it is possible to obtain samples with varying degrees of ordering, yet with the same oxygen content and free from impurities. In the second part of the study, highly ordered, partially ordered and fully disordered samples have been tested in LNMO∥LTO (Li4Ti5O12) full cells at 55 °C. It is shown that differences in their performances arise only after repeated cycling, while all the samples behave similarly at the beginning of the test. The difference is believed to be related to instabilities of LNMO at higher voltages, that is, in its lower lithiation states.[1] A. Manthiram, K. Chemelewski, E.-S. Lee, Energy Environ. Sci. 7 (2014) 1339.[2] M. Kunduraci, G.G. Amatucci, J. Power Sources. 165 (2007) 359–367.
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| 2. |
- Aktekin, Burak, et al.
(författare)
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Understanding the Capacity Loss in LiNi0.5Mn1.5O4 - Li4Ti5O12 Lithium-Ion Cells at Ambient and Elevated Temperatures
- 2017
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Konferensbidrag (refereegranskat)abstract
- The high voltage spinel LiNi0.5Mn1.5O4 (LNMO) is an attractive positive electrode due to its operating voltage around 4.7 V (vs. Li/Li+) arising from the Ni2+/Ni4+ redox couple. In addition to high voltage operation, a second advantage of this material is its capability for fast lithium diffusion kinetics through 3-D transport paths in the spinel structure. However, the electrode material is prone to side reactions with conventional electrolytes, including electrolyte decomposition and transition metal dissolution, especially at elevated temperatures1. It is important to understand how undesired reactions originating from the high voltage spinel affect the aging of different cell components and overall cycle life. Half-cells are usually considered as an ideal cell configuration in order to get information only from the electrode of interest. However, this cell configuration may not be ideal to understand capacity fading for long-term cycling and the assumption of ‘stable’ lithium negative electrode may not be valid, especially at high current rates2. Also, among the variety of capacity fading mechanisms, the loss of “cyclable” lithium from the positive electrode (or gain of lithium from electrolyte into the negative electrode) due to side reactions in a full-cell can cause significant capacity loss. This capacity loss is not observable in a typical half-cell as a result of an excessive reserve of lithium in the negative electrode.In a full-cell, it is desired that the negative electrode does not contribute to side reactions in a significant way if the interest is more on the positive side. Among candidates on the negative side, Li4Ti5O12 (LTO) is known for its stability since its voltage plateau (around 1.5 V vs. Li/Li+) is in the electrochemical stability window of standard electrolytes and it shows a very small volume change during lithiation. These characteristics make the LNMO-LTO system attractive for a variety of applications (e.g. electric vehicles) but also make it a good model system for studying aging in high voltage spinel-based full cells.In this study, we aim to understand the fundamental mechanisms resulting in capacity fading for LNMO-LTO full cells both at room temperature and elevated temperature (55°C). It is known that electrode interactions occur in this system due to migration of reaction products from LNMO to the LTO side3, 4. For this purpose, three electrode cells have been cycled galvanostatically with short-duration intermittent current interruptions5 in order to observe internal resistance for both LNMO and LTO electrodes in a full cell, separately. Change of voltage curves over cycling has also been observed to get an insight into capacity loss. For comparison purposes, back-to-back cells (a combination of LNMO and LTO cells connected electrically by lithium sides) were also tested similarly. Post-cycling of harvested electrodes in half cells was conducted to determine the degree of capacity loss due to charge slippage compared to other aging factors. Surface characterization of LNMO as well as LTO electrodes after cycling at room temperature and elevated temperature has been done via SEM, XPS, HAXPES and XANES.ReferencesA. Kraytsberg, Y. Ein-Eli, Adv. Energy Mater., vol. 2, pp. 922–939, 2012.Aurbach, D., Zinigrad, E., Cohen, Y., & Teller, H. Solid State Ionics, 148(3), 405-416, 2002.Li et al., Journal of The Electrochemical Society, 160 (9) A1524-A1528, 2013.Aktekin et al., Journal of The Electrochemical Society 164.4: A942-A948. 2017.Lacey, M. J., ChemElectroChem. Accepted Author Manuscript. doi:10.1002/celc.201700129, 2017.
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| 3. |
- Aktekin, Burak, et al.
(författare)
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Understanding the Rapid Capacity Fading of LNMO-LTO Lithium-ion Cells at Elevated Temperature
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The high voltage spinel LiNi0.5Mn1.5O4 (LNMO) has an average operating potential around 4.7 V vs. Li/Li+ and a gravimetric charge capacity of 146 mAh/g making it a promising high energy density positive electrode for Li-ion batteries. Additionally, the 3-D lithium transport paths available in the spinel structure enables fast diffusion kinetics, making it suitable for power applications [1]. However, the material displays large instability during cycling, especially at elevated temperatures. Therefore, significant research efforts have been undertaken to better understand and improve this electrode material.Electrolyte (LiPF6 in organic solvents) oxidation and transition metal dissolution are often considered as the main problems [2] for the systems based on this cathode material. These can cause a variety of problems (in different parts of the cell) eventually increasing internal cell resistance, causing active mass loss and decreasing the amount of cyclable lithium.Among these issues, cyclable lithium loss cannot be observed in half cells since lithium metal will provide almost unlimited capacity. Being a promising full cell chemistry for high power applications, there has also been a considerable interest on LNMO full cells with Li4Ti5O12 (LTO) used as the negative electrode. For this chemistry, for an optimized cell, quite stable cycling for >1000 cycles has been reported at room temperature while fast fading is still present at 55 °C [3]. This difference in performance (RT vs. 55 °C) is beyond most expectations and likely does not follow any Arrhenius-type of trend.In this study, a comprehensive analysis of LNMO-LTO cells has been performed at different temperatures (RT, 40 °C and 55 °C) to understand the underlying reasons behind stable cycling at room temperature and rapid fading at 55 °C. For this purpose, testing was made on regular cells (Figure 1a), 3-electrode cells (Figure 1b) and back-to-back cells [4] (Figure 1c). Electrode interactions (cross-talk) have been shown to exist in the LTO-LNMO system [5] and back-to-back cells have therefore been used to observe fading under conditions where cross-talk is impossible [4]. Galvanostatic cycling combined with short-duration intermittent current interruptions [6] was performed in order to separately observe changes in internal resistance for LNMO and LTO electrodes in a full cell. Ex-situ characterization of electrodes have also been performed using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES).Our findings show how important the electrode interactions can be in full cells, as a decrease in lithium inventory was shown to be the major factor for the observed capacity fading at elevated temperature. In this presentation, the effect of other factors – active mass loss and internal cell resistance – will be discussed together with the consequences of cross-talk.References[1] A. Kraytsberg et al. Adv. Energy Mater., vol. 2, pp. 922–939,2012.[2] J. H. Kim et al., ChemPhysChem, vol. 15, pp. 1940–1954, 2014.[3] H. M. Wu et al. J. E. Soc., vol. 156, pp. A1047–A1050, 2009.[4] S. R. Li et al., J. E. Soc., vol. 160, no. 9, pp. A1524–A1528, 2013.[5] Dedryvère et al. J. Phys. C., vol. 114 (24), pp. 10999–11008, 2010.[6] M. J. Lacey, ChemElectroChem, pp. 1–9, 2017.
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| 9. |
- Etman, Ahmed, et al.
(författare)
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One-pot Synthesis of MoO3-x Nanosheets for Supercapacitor Applications
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Molybdenum oxide nanosheets are interesting materials for energy storage, catalysis, and gas sensor applications.1 However, they are traditionally prepared via a variety of approaches which require the use of high temperature or organic solvents.2,3 Herein, we report the synthesis of MoO3-x nanosheets (where x denotes oxygen vacancy) via a one-step water based exfoliation strategy using bulk molybdenum oxides precursors.4 Scanning and transmission electron microscopy show that the MoO3-x has a typical nanosheet morphology with a few nanometer thickness. The MoO3-x nanosheets display localized surface plasmon resonance (LSPR), which can be enhanced by modifying the morphology and the amount of oxygen vacancies (x) using chemical and/or photochemical treatments.The aqueous suspension of the MoO3-x nanosheets was drop-cast onto carbon paper and this material was then used as binder free electrodes for supercapacitor applications. The electrodes showed promising performance regarding capacitance and rate capability in acidified sodium sulphate solutions. The facile green synthesis of MoO3-x nanosheets coupled with their significant photochemical and electrochemical properties pave the way for the use of the nanosheets in a variety of applications.References:(1) de Castro, I. A.; Datta, R. S.; Ou, J. Z.; Castellanos-Gomez, A.; Sriram, S.; Daeneke, T.; Kalantar-zadeh, K. Molybdenum Oxides - From Fundamentals to Functionality. Adv. Mater. 2017, 29 (40), 1701619.(2) Xiao, X.; Song, H.; Lin, S.; Zhou, Y.; Zhan, X.; Hu, Z.; Zhang, Q.; Sun, J.; Yang, B.; Li, T.; Jiao, L.; Zhou, J.; Tang, J.; Gogotsi, Y. Scalable Salt-Templated Synthesis of Two-Dimensional Transition Metal Oxides. Nat. Commun. 2016, 7, 11296.(3) Alsaif, M. M. Y. A.; Field, M. R.; Daeneke, T.; Chrimes, A. F.; Zhang, W.; Carey, B. J.; Berean, K. J.; Walia, S.; van Embden, J.; Zhang, B.; Latham, K.; Kalantar-zadeh, K.; Ou, J. Z. Exfoliation Solvent Dependent Plasmon Resonances in Two-Dimensional Sub-Stoichiometric Molybdenum Oxide Nanoflakes. ACS Appl. Mater. Interfaces 2016, 8 (5), 3482–3493.(4) Etman A. S.; Abdelhamid H. N.; Yuan Y.; Wang L.; Zou X.; Sun J. Facile Water Based Strategy for Synthesizing MoO3-x Nanosheets: Efficient Visible Light Photocatalyst for Dye Degradation. ACS Omega. in Press.
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| 10. |
- Etman, Ahmed S., et al.
(författare)
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Simple and Green Method for Fabricating V2O5·nH2O Nanosheets for Lithium Battery Application
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- During the last few years, the synthesis of inorganic two dimensional (2D) materials tremendously increased, due to their promising surface area1,2. However, the synthesis of these 2D materials can significantly influence our environment, by the use of harmful chemicals and severe reaction conditions3,4.Herein, we report on a simple and green strategy for fabricating hydrated vanadium pentoxide (V2O5.nH2O) nanosheets from commercially available vanadium oxides precursors via water based exfoliation technique. Operando and ex situ X-ray diffraction (XRD) studies were conducted to track the structural changes during the exfoliation process. The vanadium oxidation states and the water content of the material were determined by X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA), respectively. Electron microscopy and atomic force microscopy (AFM) showed that the V2O5.nH2O is composed of a few nanometer thick nanosheets. A composite material of the V2O5∙nH2O nanosheets and multi-walled carbon nanotube (MW-CNT) were fabricated and then tested as a free standing electrodes (FSE) and conventionally casted electrodes (CCE) for lithium battery. Both electrodes showed promising capacities and rate capabilities for lithium-ion intercalation.References:(1) Nicolosi, V.; Chhowalla, M.; Kanatzidis, M. G.; Strano, M. S.; Coleman, J. N. Liquid Exfoliation of Layered Materials. Science (80-. ). 2013, 340 (6139), 1226419.(2) Etman, A. S.; Asfaw, H. D.; Yuan, N.; Li, J.; Zhou, Z.; Peng, F.; Persson, I.; Zou, X.; Gustafsson, T.; Edström, K.; Sun, J. A One-Step Water Based Strategy for Synthesizing Hydrated Vanadium Pentoxide Nanosheets from VO2 (B) as Free-Standing Electrodes for Lithium Battery Applications. J. Mater. Chem. A 2016, 4 (46), 17988–18001.(3) Wei, Q.; Liu, J.; Feng, W.; Sheng, J.; Tian, X.; He, L.; An, Q.; Mai, L. Hydrated Vanadium Pentoxide with Superior Sodium Storage Capacity. J. Mater. Chem. A 2015, 3, 8070–8075.(4) Zhou, K.-G.; Mao, N.-N.; Wang, H.-X.; Peng, Y.; Zhang, H.-L. A Mixed-Solvent Strategy for Efficient Exfoliation of Inorganic Graphene Analogues. Angew. Chem. Int. Ed. Engl. 2011, 50 (46), 10839–10842.
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