| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Kim, Eun Jeong, et al.
(författare)
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Vacancy-Enhanced Oxygen Redox Reversibility in P3-Type Magnesium-Doped Sodium Manganese Oxide Na0.67Mg0.2Mn0.8O2
- 2020
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Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:11, s. 10423-10434
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Tidskriftsartikel (refereegranskat)abstract
- Lithium-rich layered oxides and sodium layered oxides represent attractive positive electrode materials exhibiting excess capacity delivered by additional oxygen redox activity. However, structural degradation in the bulk and detrimental reactions with the electrolyte on the surface often occur, leading to limited reversibility of oxygen redox processes. Here, we present the properties of P3-type Na0.67Mg0.2Mn0.8O2 synthesized under both air and oxygen. Both materials exhibit stable cycling performance in the voltage range of 1.8-3.8 V, where the Mn3+/Mn4+ redox couple entirely dominates the electrochemical reaction. Oxygen redox activity is triggered for both compounds in the wider voltage window 1.8-4.3 V with typical large voltage hysteresis from nonbonding O 2p states generated by substituted Mg. Interestingly, for the compound prepared under oxygen, an additional novel reversible oxygen redox activity is shown with an exceptionally small voltage hysteresis (20 mV). The presence of vacancies in the transition-metal layers is shown to play a critical role not only in forming unpaired O 2p states independent of substituted elements but also in stabilizing the P3 structure during charge with reduced structural transformation to the O'3 phase at the end of discharge. This study reveals the important role of vacancies in P3-type sodium layered oxides to increase energy density using both cationic and anionic redox processes.
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| 6. |
- 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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| 7. |
- 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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| 8. |
- Ma, Le Anh, 1992-, et al.
(författare)
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Capacity losses due to solid electrolyte interphase formation and sodium diffusion in sodium-ion batteries
- 2021
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Knowledge about capacity losses due to the formation and dissolution of the solid electrolyte interphase (SEI) layer in sodium-ion batteries (SIBs) is still limited. One major challenge in SIBs is the fact that the SEI generally contains more soluble species than the corresponding SEI layers formed in Li-ion batteries. By cycling carbon black electrodes against Na-metal electrodes, to mimic the SEI formation on negative SIB electrodes, this study studies the associated capacity losses in different carbonate electrolyte systems. Using electrochemical testing and synchrotron-based X-ray photoelectron (XPS) experiments, the capacity losses due to changes in the SEI layer and diffusion of sodium in the carbon black electrodes during open circuit pauses of 50 h, 30 h, 15 h and 5 h are investigated in nine different electrolyte systems. The different contributions to the open circuit capacity loss were determined using a new approach involving different galvanostatic cycling protocols. It is shown that the capacity loss depends on the interplay between the electrolyte chemistry and the thickness and stability of the SEI layer. The results show, that the Na-diffusion into the bulk electrode gives rise to a larger capacity loss than the SEI dissolution. Hence, Na-trapping effect is one of the major contribution in the observed capacity losses. Furthermore, the SEI formed in NaPF6-EC:DEC was found to become slightly thicker during 50 h pause, due to self-diffused deintercalation of Na from the carbon black structure coupled by further electrolyte reduction. On the other hand, the SEI in NaTFSI with the same solvent goes into dissolution during pause. The highest SEI dissolution rate and capacity loss was observed in NaPF6-EC:DEC (0.57 μAh/hpause) and the lowest in NaTFSI-EC:DME (0.15 μAh/hpause).
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| 9. |
- Ma, Le Anh, 1992-, et al.
(författare)
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Fundamental Understanding and Quantification of Capacity Losses Involving the Negative Electrode in Sodium-Ion Batteries
- 2024
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Ingår i: Advanced Science. - : Wiley-VCH Verlagsgesellschaft. - 2198-3844. ; 11:6
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge about capacity losses related to the solid electrolyte interphase (SEI) in sodium-ion batteries (SIBs) is still limited. One major challenge in SIBs is that the solubility of SEI species in liquid electrolytes is comparatively higher than the corresponding species formed in Li-ion batteries. This study sheds new light on the associated capacity losses due to initial SEI formation, SEI dissolution and subsequent SEI reformation, charge leakage via SEI and subsequent SEI growth, and diffusion-controlled sodium trapping in electrode particles. By using a variety of electrochemical cycling protocols, synchrotron-based X-ray photoelectron spectroscopy (XPS), gas chromatography coupled with mass spectrometry (GC-MS), and proton nuclear magnetic resonance (1H-NMR) spectroscopy, capacity losses due to changes in the SEI layer during different open circuit pause times are investigated in nine different electrolyte solutions. It is shown that the amount of capacity lost depends on the interplay between the electrolyte chemistry and the thickness and stability of the SEI layer. The highest capacity loss is measured in NaPF6 in ethylene carboante mixed with diethylene carbonate electrolyte (i.e., 5 µAh h−1/2pause or 2.78 mAh g·h−1/2pause) while the lowest value is found in NaTFSI in ethylene carbonate mixed with dimethoxyethance electrolyte (i.e., 1.3 µAh h−1/2pause or 0.72 mAh g·h−1/2pause).
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| 10. |
- Ma, Le Anh, 1992-, et al.
(författare)
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Na-ion mobility in P2-type Na0.5MgxNi0.17-xMn0.83O2 (0 <= x <= 0.07) from electrochemical and muon spin relaxation studies
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 23:42, s. 24478-24486
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Tidskriftsartikel (refereegranskat)abstract
- Sodium transition metal oxides with a layered structure are one of the most widely studied cathode materials for Na+-ion batteries. Since the mobility of Na+ in such cathode materials is a key factor that governs the performance of material, electrochemical and muon spin rotation and relaxation techniques are here used to reveal the Na+-ion mobility in a P2-type Na0.5MgxNi0.17-xMn0.83O2 (x = 0, 0.02, 0.05 and 0.07) cathode material. Combining electrochemical techniques such as galvanostatic cycling, cyclic voltammetry, and the galvanostatic intermittent titration technique with mu+SR, we have successfully extracted both self-diffusion and chemical-diffusion under a potential gradient, which are essential to understand the electrode material from an atomic-scale viewpoint. The results indicate that a small amount of Mg substitution has strong effects on the cycling performance and the Na+ mobility. Amongst the tested cathode systems, it was found that the composition with a Mg content of x = 0.02 resulted in the best cycling stability and highest Na+ mobility based on electrochemical and mu+SR results. The current study clearly shows that for developing a new generation of sustainable energy-storage devices, it is crucial to study and understand both the structure as well as dynamics of ions in the material on an atomic level.
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| 11. |
- Ma, Le Anh, 1992-, et al.
(författare)
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Oxygen redox activity in Na0.67Ni0.25Mg0.05Mn0.7O2
- 2018
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Ingår i: Abstract for 5th international conference of sodium batteries 2018 in St. Malo, France (ICNaB 2018) 12th - 15th November 2018..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 12. |
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| 13. |
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| 14. |
- Ma, Le Anh, 1992-, et al.
(författare)
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Strategies for Mitigating Dissolution of Solid Electrolyte Interphases in Sodium-Ion Batteries
- 2021
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Ingår i: Angewandte Chemie International Edition. - : John Wiley & Sons. - 1433-7851 .- 1521-3773. ; 60:9, s. 4855-4863
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial reactions in sodium-ion batteries (SIBs) are not well understood yet. The formation of a stable solid electrolyte interphase (SEI) in SIBs is still challenging due to the higher solubility of the SEI components compared to lithium analogues. This study therefore aims to shed light on the dissolution of SEI influenced by the electrolyte chemistry. By conducting electrochemical tests with extended open circuit pauses, and using surface spectroscopy, we determine the extent of self-discharge due to SEI dissolution. Instead of using a conventional separator, beta-alumina was used as sodium-conductive membrane to avoid crosstalk between the working and sodium-metal counter electrode. The relative capacity loss after a pause of 50 hours in the tested electrolyte systems ranges up to 30 %. The solubility of typical inorganic SEI species like NaF and Na2CO3 was determined. The electrolytes were then saturated by those SEI species in order to oppose ageing due to the dissolution of the SEI.
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| 15. |
- 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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