| 1. |
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| 2. |
- Aktekin, Burak, et al.
(författare)
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How Mn/Ni Ordering Controls Electrochemical Performance in High-Voltage Spinel LiNi0.44Mn1.56O4 with Fixed Oxygen Content
- 2020
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Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:6, s. 6001-6013
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of LiNi0.5O4 (LNMO) can adopt either low-symmetry ordered (Fd (3) over barm) or high-symmetry disordered (P4(3)32) space group depending on the synthesis conditions. A majority of published studies agree on superior electrochemical performance of disordered LNMO, but the underlying reasons for improvement remain unclear due to the fact that different thermal history of the samples affects other material properties such as oxygen content and particle morphology. In this study, ordered and disordered samples were prepared with a new strategy that renders samples with identical properties apart from their cation ordering degree. This was achieved by heat treatment of powders under pure oxygen atmosphere at high temperature with a final annealing step at 710 degrees C for both samples, followed by slow or fast cooling. Electrochemical testing showed that cation disordering improves the stability of material in charged (delithiated) state and mitigates the impedance rise in LNMO parallel to LTO (Li4Ti5O12) and LNMO parallel to Li cells. Through X-ray photoelectron spectroscopy (XPS), thicker surface films were observed on the ordered material, indicating more electrolyte side reactions. The ordered samples also showed significant changes in the Ni 2p XPS spectra, while the generation of ligand (oxygen) holes was observed in the Ni-O environment for both samples using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). Moreover, high-resolution transmission electron microscopy (HRTEM) images indicated that the ordered samples show a decrease in ordering near the particle surface after cycling and a tendency toward rock-salt-like phase transformations. These results show that the structural arrangement of Mn/Ni (alone) has an effect on the surface and "nearsurface" properties of LNMO, particularly in delithiated state, which is likely connected to the bulk electronic properties of this electrode material.
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| 3. |
- Hakim, Charifa, et al.
(författare)
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Anionic Redox and Electrochemical Kinetics of the Na2Mn3O7 Cathode Material for Sodium-Ion Batteries
- 2022
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 36:7, s. 4015-4025
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Tidskriftsartikel (refereegranskat)abstract
- Manganese-based layered oxides have gained wide attention as cathode materials for sodium-ion batteries due to their cost-effectiveness and nontoxicity. Among them, Na2Mn3O7, which shows promising electrochemical properties as a host material for sodium ions, has been extensively investigated recently. However, the charge compensation mechanisms during battery operation are still ambiguous. Herein, we investigate the electronic structure of Na2Mn3O7 using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering techniques. Mn L-II,L-III-edge XAS spectra show that manganese ions do not undergo any oxidation reaction during the first charge process, suggesting that sodium removal is instead charge compensated by oxygen-ion redox reactions. This, in turn, has an impact on the cycling performances delivered by the material, especially the capacity retention over cycles and also the electrochemical kinetics of sodium ions in Na2Mn3O7.
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| 4. |
- Hakim, Charifa, et al.
(författare)
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Understanding the redox process upon electrochemical cycling of the P2-Na0.78Co1/2Mn1/3Ni1/6O2 electrode material for sodium-ion batteries
- 2020
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Ingår i: Communications Chemistry. - : NATURE PUBLISHING GROUP. - 2399-3669. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- The inclusion of nickel and manganese in layered sodium metal oxide cathodes for sodium ion batteries is known to improve stability, but the redox behaviour at high voltage is poorly understood. Here in situ X-ray spectroscopy studies show that the redox behaviour of oxygen anions can account for an increase in specific capacity at high voltages. Rechargeable sodium-ion batteries have recently attracted renewed interest as an alternative to Li-ion batteries for electric energy storage applications, because of the low cost and wide availability of sodium resources. Thus, the electrochemical energy storage community has been devoting increased attention to designing new cathode materials for sodium-ion batteries. Here we investigate P2- Na0.78Co1/2Mn1/3Ni1/6O2 as a cathode material for sodium ion batteries. The main focus is to understand the mechanism of the electrochemical performance of this material, especially differences observed in redox reactions at high potentials. Between 4.2 V and 4.5 V, the material delivers a reversible capacity which is studied in detail using advanced analytical techniques. In situ X-ray diffraction reveals the reversibility of the P2-type structure of the material. Combined soft X-ray absorption spectroscopy and resonant inelastic X-ray scattering demonstrates that Na deintercalation at high voltages is charge compensated by formation of localized electron holes on oxygen atoms.
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| 5. |
- Kim, Eun Jeong, et al.
(författare)
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Importance of Superstructure in Stabilizing Oxygen Redox in P3-Na0.67Li0.2Mn0.8O2
- 2022
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Ingår i: Advanced Energy Materials. - : John Wiley & Sons. - 1614-6832 .- 1614-6840. ; 12:3
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Tidskriftsartikel (refereegranskat)abstract
- Activation of oxygen redox represents a promising strategy to enhance the energy density of positive electrode materials in both lithium and sodium-ion batteries. However, the large voltage hysteresis associated with oxidation of oxygen anions during the first charge represents a significant challenge. Here, P3-type Na0.67Li0.2Mn0.8O2 is reinvestigated and a ribbon superlattice is identified for the first time in P3-type materials. The ribbon superstructure is maintained over cycling with very minor unit cell volume changes in the bulk while Li ions migrate reversibly between the transition metal and Na layers at the atomic scale. In addition, a range of spectroscopic techniques reveal that a strongly hybridized Mn 3d-O 2p favors ligand-to-metal charge transfer, also described as a reductive coupling mechanism, to stabilize reversible oxygen redox. By preparing materials under three different synthetic conditions, the degree of ordering between Li and Mn is varied. The sample with the maximum cation ordering delivers the largest capacity regardless of the voltage windows applied. These findings highlight the importance of cationic ordering in the transition metal layers, which can be tuned by synthetic control to enhance anionic redox and hence energy density in rechargeable batteries.
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| 6. |
- Kim, Eun Jeong, et al.
(författare)
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Oxygen Redox Activity through a Reductive Coupling Mechanism in the P3-Type Nickel-Doped Sodium Manganese Oxide
- 2020
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Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:1, s. 184-191
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Tidskriftsartikel (refereegranskat)abstract
- Increasing dependence on rechargeable batteries for energy storage calls for the improvement of energy density of batteries. Toward this goal, introduction of positive electrode materials with high voltage and/or high capacity is in high demand. The use of oxygen chemistry in lithium and sodium layered oxides has been of interest to achieve high capacity. Nevertheless, a complete understanding of oxygen-based redox processes remains elusive especially in sodium ion batteries. Herein, a novel P3-type Na0.67Ni0.2Mn0.8O2, synthesized at low temperature, exhibits oxygen redox activity in high potentials. Characterization using a range of spectroscopic techniques reveals the anionic redox activity is stabilized by the reduction of Ni, because of the strong Ni 3d-O 2p hybridization states created during charge. This observation suggests that different route of oxygen redox processes occur in P3 structure materials, which can lead to the exploration of oxygen redox chemistry for further development in rechargeable batteries.
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| 7. |
- Linnell, Stephanie F., et al.
(författare)
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Effect of Ti-Substitution on the Properties of P3 Structure Na2/3Mn0.8Li0.2O2 Showing a Ribbon Superlattice
- 2022
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Ingår i: ChemElectroChem. - : Wiley-Blackwell. - 2196-0216. ; 9:19
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen anion redox offers an effective strategy to enhance the energy density of layered oxide positive electrodes for sodium- and lithium-ion batteries. However, lattice oxygen loss and irreversible structural transformations over the first cycle may result in large voltage hysteresis, thereby impeding practical application. Herein, ribbon superstructure ordering of Li/transition-metal-ions was applied to suppress the voltage hysteresis combined with Ti-substitution to improve the cycling stability for P3-Na0.67Li0.2Ti0.15Mn0.65O2. When both cation and anion redox reactions are utilized, Na0.67Li0.2Ti0.15Mn0.65O2 delivers a reversible capacity of 172 mA h g(-1) after 25 cycles at 10 mA g(-1) between 1.6-4.4 V vs. Na+/Na. Ex-situ X-ray diffraction data reveal that the ribbon superstructure is retained with negligible unit cell volume expansion/contraction upon sodiation/desodiation. The performance as a positive electrode for Li-ion batteries was also evaluated and P3-Na0.67Li0.2Ti0.15Mn0.65O2 delivers a reversible capacity of 180 mA h g(-1) after 25 cycles at 10 mA g(-1) when cycled vs. Li+/Li between 2.0-4.8 V.
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| 8. |
- Ma, Le Anh, 1992-
(författare)
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Anti-Ageing Strategies : How to avoid failure in sodium-ion batteries
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to move away from fossil fuels, batteries are one of the most important technologies to store energy from renewable sources. The rapid demands of battery applications put pressure on supply chains of raw materials, such as lithium, nickel, copper, aluminium and cobalt. There is a concern about the availability of such elements in the future. Sodium-ion batteries based on naturally abundant elements have become an attractive alternative to lithium-ion batteries due to their potential to reduce the cost and to improve the sustainability of batteries. A low electrochemical cycling stability of these Na-ion batteries can hinder long-term implementation in large-scale applications. It is necessary to understand what can lead to ageing and electrochemical cycling failure in sodium-ion batteries and how such detrimental side-reactions can be prevented. Compared to lithium-ion batteries, the research on sodium-ion batteries is not as mature yet.This thesis work sheds light on the ageing mechanisms at the electrode/electrolyte interfaces and in the bulk of electrode materials with the help of a variety of spectroscopic and electrochemical methods. The electrochemical properties at the anode/electrolyte interface have been carefully investigated with different galvanostatic cycling protocols and x-ray photoelectron spectroscopy (XPS). The solid electrolyte interphase (SEI) in sodium-ion batteries is known to be inferior to its Li-analogue and hence, its long-term stability needs to be thoroughly investigated in order to improve it. Fundamental properties of the SEI in regards to formation, growth and dissolution are investigated on platinum and carbon black electrodes in different electrolyte systems. As well as the use of unconventional additives have proven to saturate the electrolyte and to mitigate SEI dissolution. This work shows one of the few studies highlighting SEI dissolution using electrochemical cycling tests coupled with pauses, in order to detect SEI ageing in batteries. Ageing mechanisms in manganese-based cathodes have also been studied due to the abundance of manganese and their electrochemical performance at high voltages with synchrotron-based XPS, x-ray absorption spectroscopy (XAS), resonant inelastic x-ray scattering (RIXS) and muon spin relaxation measurements coupled with electrochemical techniques. Surface-sensitive studies revealed how capacity losses stem from electrolyte degradation which results in a redox gradient between surface and bulk electrode. The work also shows how anionic redox contributions and incomplete phase transitions are reasons of additional capacity losses observed in manganese-based cathodes. Furthermore, it shows how a low Na-mobility is also an indicator for inferior long-term cycling properties leading capacity losses.
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| 9. |
- Ma, Le Anh, 1992-, et al.
(författare)
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Understanding charge compensation mechanisms in Na0.56Mg0.04Ni0.19Mn0.70O2
- 2019
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Ingår i: Communications Chemistry. - : Springer Science and Business Media LLC. - 2399-3669. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Massel, Felix, et al.
(författare)
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Excess lithium in transition metal layers of epitaxially grown thin film cathodes of Li2MnO3 leads to rapid loss of covalency during first battery cycle
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:47, s. 28519-28526
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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