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Tengstedt, Carl
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Blidberg, A., Gustafsson, T., Tengstedt, C., Björefors, F. & Brant, W. R. (2017). Monitoring LixFeSO4F (x = 1, 0.5, 0) Phase Distributions in Operando To Determine Reaction Homogeneity in Porous Battery Electrodes. Chemistry of Materials, 29(17), 7159-7169
Åpne denne publikasjonen i ny fane eller vindu >>Monitoring LixFeSO4F (x = 1, 0.5, 0) Phase Distributions in Operando To Determine Reaction Homogeneity in Porous Battery Electrodes
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2017 (engelsk)Inngår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 29, nr 17, s. 7159-7169Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Increasing the energy and power density simultaneously remains a major challenge for improving electrochemical energy storage devices such as Li-ion batteries. Understanding the underlying processes in operating electrodes is decisive to improve their performance. Here, an extension of an in operando X-ray diffraction technique is presented, wherein monitoring the degree of coexistence between crystalline phases in multiphase systems is used to investigate reaction homogeneity in Li-ion batteries. Thereby, a less complicated experimental setup using commercially available laboratory equipment could be employed. By making use of the intrinsic structural properties of tavorite type LiFeSO4F, a promising cathode material for Li-ion batteries, new insights into its nonequilibrium behavior are gained. Differences in the reaction mechanism upon charge and discharge are shown; the influence of adequate electronic wiring for the cycling stability is demonstrated, and the effect of solid state transport on rate performance is highlighted. The methodology is an alternative and complementary approach to the expensive and demanding techniques commonly employed for time-resolved studies of structural changes in operating battery electrodes. The multiphase behavior of LiFeSO4F is commonly observed for other insertion type electrode materials, making the methodology transferable to other new energy storage materials. By expanding the possibilities for investigating complex processes in operating batteries to a larger community, faster progress in both electrode development and fundamental material research can be realized.

sted, utgiver, år, opplag, sider
American Chemical Society, 2017
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-338351 (URN)10.1021/acs.chemmater.7b01019 (DOI)000410868600017 ()
Tilgjengelig fra: 2018-01-08 Laget: 2018-01-08 Sist oppdatert: 2018-01-25bibliografisk kontrollert
Aktekin, B., Lacey, M., Nordh, T., Younesi, R., Tengstedt, C., Zipprich, W., . . . Edström, K. (2017). Understanding the Capacity Loss in LiNi0.5Mn1.5O4 - Li4Ti5O12 Lithium-Ion Cells at Ambient and Elevated Temperatures. In: : . Paper presented at 232nd ECS MEETING. , Article ID MA2017-02 105.
Åpne denne publikasjonen i ny fane eller vindu >>Understanding the Capacity Loss in LiNi0.5Mn1.5O4 - Li4Ti5O12 Lithium-Ion Cells at Ambient and Elevated Temperatures
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2017 (engelsk)Konferansepaper, Poster (with or without abstract) (Fagfellevurdert)
Abstract [en]

The high voltage spinel LiNi0.5Mn1.5O(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 interruptionsin 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.

References

  1. A. Kraytsberg, Y. Ein-Eli, Adv. Energy Mater., vol. 2, pp. 922–939, 2012.

  2. Aurbach, D., Zinigrad, E., Cohen, Y., & Teller, H. Solid State Ionics, 148(3), 405-416, 2002.

  3. Li et al., Journal of The Electrochemical Society, 160 (9) A1524-A1528, 2013.

  4. Aktekin et al., Journal of The Electrochemical Society 164.4: A942-A948. 2017.

  5. Lacey, M. J., ChemElectroChem. Accepted Author Manuscript. doi:10.1002/celc.201700129, 2017. 

HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-337963 (URN)
Konferanse
232nd ECS MEETING
Tilgjengelig fra: 2018-01-05 Laget: 2018-01-05 Sist oppdatert: 2018-01-05
Aktekin, B., Lacey, M., Nordh, T., Tengstedt, C., Brandell, D. & Edström, K. (2017). Understanding the Rapid Capacity Fading of LNMO-LTO Lithium-ion Cells at Elevated Temperature. In: : . Paper presented at 2nd International Symposium on Materials for Energy Storage and Conversion, September 26-28, 2017, Ortahisar, Turkey.
Åpne denne publikasjonen i ny fane eller vindu >>Understanding the Rapid Capacity Fading of LNMO-LTO Lithium-ion Cells at Elevated Temperature
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2017 (engelsk)Konferansepaper, Oral presentation with published abstract (Annet vitenskapelig)
Abstract [en]

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.

HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-337964 (URN)
Konferanse
2nd International Symposium on Materials for Energy Storage and Conversion, September 26-28, 2017, Ortahisar, Turkey
Tilgjengelig fra: 2018-01-06 Laget: 2018-01-06 Sist oppdatert: 2018-02-23bibliografisk kontrollert
Nordh, T., Younesi, R., Hahlin, M., Duarte, R. F., Tengstedt, C., Brandell, D. & Edström, K. (2016). Manganese in the SEI layer of Li4Ti5O12 studied using combined NEXAFS and HAXPES techniques. The Journal of Physical Chemistry C, 120(6), 3206-3213
Åpne denne publikasjonen i ny fane eller vindu >>Manganese in the SEI layer of Li4Ti5O12 studied using combined NEXAFS and HAXPES techniques
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2016 (engelsk)Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 6, s. 3206-3213Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

A combination of hard X-ray photoelectron spectroscopy (HAXPES) and near edge X-ray absorption fine structure (NEXAFS) are here used to investigate the presence and chemical state of crossover manganese deposited on Li-ion battery anodes. The synchrotron based experimental techniques-using HAXPES and NEXAFS analysis on the same sample in one analysis chamber-enabled us to acquire complementary sets of information. The Mn crossover and its influence on the anode interfacial chemistry has been a topic of controversy in the literature. Cells comprising lithium manganese oxide (LiMn2O4, LMO) cathodes and lithium titanate (Li4Ti5O12, LTO) anodes were investigated using LP40 (1 M LiPF6, EC:DEC 1:1) electrolyte. LTO electrodes at lithiated, delithiated, and open circuit voltage (OCV-stored) states were analyzed to investigate the potential dependency of the manganese oxidation state. It was primarily found that a solid surface layer was formed on the LTO electrode and that this layer contains deposited Mn from the cathode. The results revealed that manganese is present in the ionic state, independent of the lithiation of the LTO electrode. The chemical environment of the deposited manganese could not be assigned to simple compounds such as fluorides or oxides, indicating that the state of manganese is in a more complex form.

HSV kategori
Forskningsprogram
Kemi med inriktning mot materialkemi
Identifikatorer
urn:nbn:se:uu:diva-267788 (URN)10.1021/acs.jpcc.5b11756 (DOI)000370678700012 ()
Forskningsfinansiär
Swedish Energy Agency
Tilgjengelig fra: 2015-11-26 Laget: 2015-11-26 Sist oppdatert: 2017-12-01bibliografisk kontrollert
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