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Carboni, M., Manzi, J., Armstrong, A. R., Billaud, J., Brutti, S. & Younesi, R. (2019). Analysis of the Solid Electrolyte Interphase on Hard Carbon Electrodes in Sodium-Ion Batteries. Chemelectrochem, 6(6), 1745-1753
Open this publication in new window or tab >>Analysis of the Solid Electrolyte Interphase on Hard Carbon Electrodes in Sodium-Ion Batteries
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2019 (English)In: Chemelectrochem, ISSN 2196-0216, Vol. 6, no 6, p. 1745-1753Article in journal (Refereed) Published
Abstract [en]

The composition, morphology, and evolution of the solid electrolyte interphase (SEI) formed on hard carbon (HC) electrodes upon cycling in sodium‐ion batteries are investigated. A microporous HC was prepared by pyrolysis of d‐(+)‐glucose at 1000 °C followed by ball‐milling. HC electrodes were galvanostatically cycled at room temperature in sodium‐ion half‐cells using an aprotic electrolyte of 1 m sodium bis(trifluoromethanesulfonyl)imide dissolved in propylene carbonate with 3 wt % fluoroethylene carbonate additive. The evolution of the electrode/electrolyte interface was studied by impedance spectroscopy upon cycling and ex situ by spectroscopy and microscopy. The irreversible capacity displayed by the HC electrodes in the first galvanostatic cycle is probably due to the accumulation of redox inactive NaxC phases and the precipitation of a porous, organic‐inorganic hybrid SEI layer over the HC electrodes. This passivation film further evolves in morphology and composition upon cycling and stabilizes after approximately ten galvanostatic cycles at low current rates.

Keywords
electrodes, hard carbon, materials, sodium-ion batteries, solid electrolyte interphase
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-382659 (URN)10.1002/celc.201801621 (DOI)000463752300017 ()
Funder
Swedish Research Council Formas, 2016-01257StandUp
Available from: 2019-05-07 Created: 2019-05-07 Last updated: 2019-05-07Bibliographically approved
Naylor, A. J., Makkos, E., Maibach, J., Guerrini, N., Sobkowiak, A., Björklund, E., . . . Bruce, P. G. (2019). Depth-dependent oxygen redox activity in lithium-rich layered oxide cathodes. Journal of Materials Chemistry A, 7(44), 25355-25368
Open this publication in new window or tab >>Depth-dependent oxygen redox activity in lithium-rich layered oxide cathodes
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2019 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 44, p. 25355-25368Article in journal (Refereed) Published
Abstract [en]

Lithium-rich materials, such as Li1.2Ni0.2Mn0.6O2, exhibit capacities not limited by transition metal redox, through the reversible oxidation of oxide anions. Here we offer detailed insight into the degree of oxygen redox as a function of depth within the material as it is charged and cycled. Energy-tuned photoelectron spectroscopy is used as a powerful, yet highly sensitive technique to probe electronic states of oxygen and transition metals from the top few nanometers at the near-surface through to the bulk of the particles. Two discrete oxygen species are identified, On− and O2−, where n < 2, confirming our previous model that oxidation generates localised hole states on O upon charging. This is in contrast to the oxygen redox inactive high voltage spinel LiNi0.5Mn1.5O4, for which no On− species is detected. The depth profile results demonstrate a concentration gradient exists for On− from the surface through to the bulk, indicating a preferential surface oxidation of the layered oxide particles. This is highly consistent with the already well-established core–shell model for such materials. Ab initio calculations reaffirm the electronic structure differences observed experimentally between the surface and bulk, while modelling of delithiated structures shows good agreement between experimental and calculated binding energies for On−.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-399616 (URN)10.1039/C9TA09019C (DOI)000498556500014 ()
Available from: 2019-12-13 Created: 2019-12-13 Last updated: 2019-12-18Bibliographically approved
Massel, F., Hikima, K., Rensmo, H., Suzuki, K., Hirayama, M., Xu, C., . . . Duda, L. (2019). Excess lithium in transition metal layers of epitaxially grown thin film cathodes of Li2MnO3 leads to rapid loss of covalency during first battery cycle. The Journal of Physical Chemistry C, 123(47), 28519-28526
Open this publication in new window or tab >>Excess lithium in transition metal layers of epitaxially grown thin film cathodes of Li2MnO3 leads to rapid loss of covalency during first battery cycle
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2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 47, p. 28519-28526Article in journal (Refereed) Published
Abstract [en]

We have investigated the initial-cycle battery behavior of epitaxial thin films of Li2MnO3-cathodes by employing resonant inelastic X-ray scattering (RIXS) at the O K- and Mn L3-edges. Thin films (25 nm thickness) with Li/Mn-ratios of 2.06 (stoichiometric) and 2.27 (over-stoichiometric), respectively, were epitaxially grown by pulsed laser deposition and electrochemically cycled as battery cathodes in half-cell setup, stopped at potentials for full charge (delithiation) and complete discharge (relithiation), respectively, for X-ray analysis. Using RIXS, we find that significant anionic reactions take place in both materials upon initial delithiation. However, no signatures of localized oxygen holes are found in O K-RIXS of the Li2MnO3 regardless of Li/Mn-ratio. Instead, the top of the oxygen valence band is depleted of electrons forming delocalized empty states upon delithiation. Mn L-RIXS of the over-stoichiometric cathode material shows a progressive loss of charge transfer state intensity during the first battery cycle, revealing a more rapid loss of Mn--O covalency in the over-stoichiometric material.

Keywords
Li-ion battery, Li-rich lithium manganese oxide cathode, pulsed laser deposition (PLD), thin film, resonant inelastic X-ray scattering (RIXS), soft X-ray absorption spectroscopy (XAS)
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-390620 (URN)10.1021/acs.jpcc.9b06246 (DOI)000500417600001 ()
Funder
Swedish Research Council, 2014-6019Swedish Research Council, 2016-03545Swedish Research Council, 2018-06465StandUpSwedish Energy Agency, 40495-1
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-12-20Bibliographically approved
Ebadi, M., Nasser, A., Carboni, M., Younesi, R., Marchiori, C., Brandell, D. & Araujo, C. M. (2019). Insights into the Li-Metal/Organic Carbonate Interfacial Chemistry by Combined First-Principles Theory and X-ray Photoelectron Spectroscopy. The Journal of Physical Chemistry C, 123(1), 347-355
Open this publication in new window or tab >>Insights into the Li-Metal/Organic Carbonate Interfacial Chemistry by Combined First-Principles Theory and X-ray Photoelectron Spectroscopy
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2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 1, p. 347-355Article in journal (Refereed) Published
Abstract [en]

X-ray photoelectron spectroscopy (XPS) is a widely used technique to study surfaces and interfaces. In complex chemical systems, however, interpretation of the XPS results and peak assignments is not straightforward. This is not least true for Li-batteries, where XPS yet remains a standard technique for interface characterization. In this work, a combined density functional theory (DFT) and experimental XPS study is carried out to obtain the C 1s and O 1s core-level binding energies of organic carbonate molecules on the surface of Li metal. Decomposition of organic carbonates is frequently encountered in electrochemical cells employing this electrode, contributing to the build up of a complex solid electrolyte interphase (SEI). The goal in this current study is to identify the XPS fingerprints of the formed compounds, degradation pathways, and thereby the early formation stages of the SEI. The contribution of partial atomic charges on the core-ionized atoms and the electrostatic potential due to the surrounding atoms on the core-level binding energies, which is decisive for interpretation of the XPS spectra, are addressed based on the DFT calculations. The results display strong correlations between these two terms and the binding energies, whereas electrostatic potential is found to be the dominating factor. The organic carbonate molecules, decomposed at the surface of the Li metal, are considered based on two different decomposition pathways. The trends of calculated binding energies for products from ethereal carbon-ethereal oxygen bond cleavage in the organic carbonates are better supported when compared to the experimental XPS results.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-375877 (URN)10.1021/acs.jpcc.8b07679 (DOI)000455561100036 ()
Funder
Swedish Energy Agency, 39036-1Swedish Research CouncilStandUpCarl Tryggers foundation
Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2019-08-05Bibliographically approved
Björklund, E., Göttlinger, M., Edström, K., Brandell, D. & Younesi, R. (2019). Investigation of dimethyl carbonate and propylene carbonate mixtures for LiNi0.6Mn0.2Co0.2O2-Li4Ti5O12 cells. Chemelectrochem, 6(13), 3429-3436
Open this publication in new window or tab >>Investigation of dimethyl carbonate and propylene carbonate mixtures for LiNi0.6Mn0.2Co0.2O2-Li4Ti5O12 cells
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2019 (English)In: Chemelectrochem, E-ISSN 2196-0216, Vol. 6, no 13, p. 3429-3436Article in journal (Refereed) Published
Abstract [en]

It has recently been shown that ethylene carbonate (EC) experience poor stability at high potentials in lithium-ion batteries, and development of electrolytes without EC, not least using ethyl methyl carbonate (EMC), has therefore been suggested in order to improve the capacity retention. In this context, we here explore another alternative electrolyte system consisting of propylene carbonate (PC) and dimethyl carbonate (DMC) mixtures in NMC-LTO (LiNi0.6Mn0.2Co0.2O2, Li4Ti5O12) cells cycled up to 2.95 V. While PC experience wettability problems and DMC has difficulties dissolving LiPF6 salt, blends between these could possess complementary properties. The electrolyte blend showed superior cycling performance at sub-zero temperatures compared to EC-containing counterparts. At 30 degrees C, however, the PC-DMC electrolyte did not show any major improvement in electrochemical properties for the NMC-LTO cell chemistry. Photoelectron spectroscopy measurements showed that thin surface layers were detected on both NMC (622) and LTO electrodes in all investigated electrolytes. The results suggest that both PC and EC will react on the electrodes, but with EC forming thinner layers comprising more carbonates. Moreover, the electrochemical stability at high electrochemical potentials is similar for the studied electrolytes, which is surprising considering that most are free from the reactive EC component.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-381546 (URN)10.1002/celc.201900672 (DOI)000475512500026 ()
Funder
Swedish Energy Agency, 37725-1StandUp
Available from: 2019-04-11 Created: 2019-04-11 Last updated: 2019-08-19Bibliographically approved
Lindgren, F., Rehnlund, D., Pan, R., Pettersson, J., Younesi, R., Xu, C., . . . Nyholm, L. (2019). On the Capacity Losses Seen for Optimized Nano-Si Composite Electrodes in Li-Metal Half-Cells. Advanced Energy Materials, 9(33), Article ID 1901608.
Open this publication in new window or tab >>On the Capacity Losses Seen for Optimized Nano-Si Composite Electrodes in Li-Metal Half-Cells
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2019 (English)In: Advanced Energy Materials, ISSN 1614-6832, Vol. 9, no 33, article id 1901608Article in journal (Refereed) Published
Abstract [en]

While the use of silicon‐based electrodes can increase the capacity of Li‐ion batteries considerably, their application is associated with significant capacity losses. In this work, the influences of solid electrolyte interphase (SEI) formation, volume expansion, and lithium trapping are evaluated for two different electrochemical cycling schemes using lithium‐metal half‐cells containing silicon nanoparticle–based composite electrodes. Lithium trapping, caused by incomplete delithiation, is demonstrated to be the main reason for the capacity loss while SEI formation and dissolution affect the accumulated capacity loss due to a decreased coulombic efficiency. The capacity losses can be explained by the increasing lithium concentration in the electrode causing a decreasing lithiation potential and the lithiation cut‐off limit being reached faster. A lithium‐to‐silicon atomic ratio of 3.28 is found for a silicon electrode after 650 cycles using 1200 mAhg−1 capacity limited cycling. The results further show that the lithiation step is the capacity‐limiting step and that the capacity losses can be minimized by increasing the efficiency of the delithiation step via the inclusion of constant voltage delithiation steps. Lithium trapping due to incomplete delithiation consequently constitutes a very important capacity loss phenomenon for silicon composite electrodes.

Keywords
asymmetric cycling, hard X-ray photoelectron spectroscopy, lithium trapping, silicon, solid electrolyte interphase layer
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-398839 (URN)10.1002/aenm.201901608 (DOI)000477265600001 ()
Funder
Swedish Research Council, VR-2015-04421Swedish Research Council, VR-2017-06320StandUp
Note

De 2 första författarna delar förstaförfattarskapet.

Available from: 2019-12-11 Created: 2019-12-11 Last updated: 2019-12-11Bibliographically approved
Brant, W., Mogensen, R., Colbin, S., Ojwang, D. O., Schmid, S., Häggstrom, L., . . . Younesi, R. (2019). Selective Control of Composition in Prussian White for Enhanced Material Properties. Chemistry of Materials, 31(18), 7203-7211
Open this publication in new window or tab >>Selective Control of Composition in Prussian White for Enhanced Material Properties
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2019 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 31, no 18, p. 7203-7211Article in journal (Refereed) Published
Abstract [en]

Sodium-ion batteries based on Prussian blue analogues (PBAs) are ideal for large-scale energy storage applications due to the ability to meet the huge volumes and low costs required. For Na2-xFe[Fe(CN)(6)](1-y)center dot zH(2)O, realizing its commercial potential means fine control of the concentration of sodium, Fe(CN)(6) vacancies, and water content. To date, there is a huge variation in the literature of composition leading to variable electrochemical performance. In this work, we break down the synthesis of PBAs into three steps for controlling the sodium, vacancy, and water content via an inexpensive, scalable synthesis method. We produce rhombohedral Prussian white Na1.88(5)Fe[Fe-(CN)(6)]center dot 0.18(9)H2O with an initial capacity of 158 mAh/g retaining 90% capacity after 50 cycles. Subsequent characterization revealed that the increased polarization on the 3 V plateau is coincident with a phase transition and reduced utilization of the high-spin Fe(III)/Fe(II) redox couple. This reveals a clear target for subsequent improvements of the material to boost long-term cycling stability. These results will be of great interest for the myriad of applications of PBAs, such as catalysis, magnetism, electrochromics, and gas sorption.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-395840 (URN)10.1021/acs.chemmater.9b01494 (DOI)000487859200012 ()
Funder
StandUpSwedish Research Council, 2016-03441ÅForsk (Ångpanneföreningen's Foundation for Research and Development)
Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved
Björklund, E., Naylor, A. J., Brant, W., Brandell, D., Younesi, R. & Edström, K. (2019). Temperature dependence of electrochemical degradation in LiNi1/3Mn1/3Co1/3O2/Li4Ti5O12 cells. Energy Technology, 7(9), Article ID 1900310.
Open this publication in new window or tab >>Temperature dependence of electrochemical degradation in LiNi1/3Mn1/3Co1/3O2/Li4Ti5O12 cells
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2019 (English)In: Energy Technology, ISSN 2194-4288, Vol. 7, no 9, article id 1900310Article in journal (Refereed) Published
Abstract [en]

Aging mechanisms in lithium‐ion batteries are dependent on the operational temperature, but the detailed mechanisms on what processes take place at what temperatures are still lacking. The electrochemical performance and capacity fading of the common cell chemistry LiNi1/3Mn1/3Co1/3O2 (NMC)/Li4Ti5O12 (LTO) pouch cells are studied at temperatures 10, 30, and 55 °C. The full cells are cycled with a moderate upper cutoff potential of 4.3 V versus Li+/Li. The electrode interfaces are characterized postmortem using photoelectron spectroscopy techniques (soft X‐ray photoelectron spectroscopy [SOXPES], hard X‐ray photoelectron spectroscopy [HAXPES], and X‐ray absorption near edge structure [XANES]). Stable cycling at 30 °C is explained by electrolyte reduction forming a stabilizing interphase, thereby preventing further degradation. This initial reaction, between LTO and the electrolyte, seems to be beneficial for the NMC–LTO full cell. At 55 °C, continuous electrolyte reduction and capacity fading are observed. It leads to the formation of a thicker surface layer of organic species on the LTO surface than at 30 °C, contributing to an increased voltage hysteresis. At 10 °C, large cell‐resistances are observed, caused by poor electrolyte conductivity in combination with a relatively thicker and LixPFy‐rich surface layer on LTO, which limit the capacity.

Keywords
aging, lithium-ion batteries, photoelectron spectroscopy
National Category
Energy Engineering Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-381545 (URN)10.1002/ente.201900310 (DOI)000483721900011 ()
Available from: 2019-04-11 Created: 2019-04-11 Last updated: 2019-12-09Bibliographically approved
Sångeland, C., Younesi, R., Mindemark, J. & Brandell, D. (2019). Towards room temperature operation of all-solid-state Na-ion batteries through polyester-polycarbonate-based polymer electrolytes. ENERGY STORAGE MATERIALS, 19, 31-38
Open this publication in new window or tab >>Towards room temperature operation of all-solid-state Na-ion batteries through polyester-polycarbonate-based polymer electrolytes
2019 (English)In: ENERGY STORAGE MATERIALS, ISSN 2405-8297, Vol. 19, p. 31-38Article in journal (Refereed) Published
Abstract [en]

In an ambition to develop solid-state Na-ion batteries functional at ambient temperature, we here explore a novel electrolyte system. Polyester-polycarbonate (PCL-PTMC) copolymers were combined with sodium bis(fluorosulfonyl) imide salt (NaFSI) to form solid polymer electrolytes for Na-ion batteries. The PCL-PTMC:NaFSI system demonstrated glass transition temperatures ranging from -64 to -11 degrees C, increasing with increasing salt content from 0 to 35 wt%, and ionic conductivities ranging from 10(-8) to 10(-5) S cm(-1) at 25 degrees C. The optimal salt concentration was clearly dependent on the level of crystallinity, which was largely determined by the CL content. At 70 and 80 mol% CL, the PCL-PTMC:NaFSI system was fully amorphous and exhibited high conductivities at lower salt concentrations. When the CL content was increased to 100 mol%, high ionic conductivities were instead observed at high salt concentrations. A decent transference number of ca. 0.5 at 80 degrees C was obtained for a polymer film containing 20 mol% CL units and 25 wt% NaFSI. Finally, a HC vertical bar 80-20(25)vertical bar Na2-xFe(Fe(CN)(6)) all-solid-state polymer electrolyte full cell was assembled to demonstrate the practical application of the material and cycled for more than 120 cycles at similar to 22 degrees C.

Keywords
All-solid-state batteries, Solid polymer electrolyte, Room temperature cycling, Sodium-ion
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-387602 (URN)10.1016/j.ensm.2019.03.022 (DOI)000469207500004 ()
Funder
EU, European Research Council, 771777 FUN POLYSTORE
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-06-26Bibliographically approved
Ma, L. A., Massel, F., Naylor, A. J., Duda, L. & Younesi, R. (2019). Understanding charge compensation mechanisms in Na0.56Mg0.04Ni0.19Mn0.70O2. Communications chemistry, 2, Article ID 125.
Open this publication in new window or tab >>Understanding charge compensation mechanisms in Na0.56Mg0.04Ni0.19Mn0.70O2
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2019 (English)In: Communications chemistry, E-ISSN 2399-3669, Vol. 2, article id 125Article in journal (Refereed) Published
Abstract [en]

Sodium-ion batteries have become a potential alternative to Li-ion batteries due to the abundance of sodium resources. Sodium-ion cathode materials have been widely studied with particular focus on layered oxide lithium analogues. Generally, the capacity is limited by the redox processes of transition metals. Recently, however, the redox participation of oxygen gained a lot of research interest. Here the Mg-doped cathode material P2-Na0.56Mg0.04Ni0.19Mn0.70O2 is studied, which is shown to exhibit a good capacity (ca. 120 mAh/g) and high average operating voltage (ca. 3.5 V vs. Na+/Na). Due to the Mg-doping, the material exhibits a reversible phase transition above 4.3 V, which is attractive in terms of lifetime stability. In this study, we combine X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy techniques to shed light on both, cationic and anionic contributions towards charge compensation.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-390622 (URN)10.1038/s42004-019-0227-z (DOI)000494732500002 ()
Funder
EU, Horizon 2020, 730872Swedish Research Council Formas, 2016-01257StandUp
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-11-25Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2538-8104

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