| 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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Development of P2 or P2/P3 cathode materials for sodium-ion batteries by controlling the Ni and Mn contents in Na0.7CoxMnyNizO2 layered oxide
- 2023
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 438
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Tidskriftsartikel (refereegranskat)abstract
- Layered oxide cathode materials with the general formula NaxTMO2 (TM = transition metals) have shown promises as electrode materials for future large-scale sodium-ion batteries. However, several challenges including capacity degradation at high voltage, phase transitions as well as structural sensitivity to minor changes in the sodium and transition metal contents during the synthesis process have hampered their development. Herein, we report a systematic investigation of the impact of replacing cobalt by either manganese or nickel on the structural and electrochemical properties of Na0.7CoxMnyNizO2 (x + y + z = 1) layered oxide materials using a variety of analysis and electrochemical techniques. Mixed phases of P2 and P3 cathode materials are obtained through a slight increase of the nickel content, while increasing the manganese content showed little effect on the P2-type structure. Increasing manganese content is shown to lead to lower discharge capacity but excellent capacity retention after 100 cycles, while nickel-rich electrodes exhibit higher discharge capacity approaching 120 mAh/g but poor rate capability performance.
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| 3. |
- Hakim, Charifa, et al.
(författare)
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P-doped Hard Carbon as Anode Material for Sodium-ion Batteries
- 2019
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Ingår i: Proceedings of 2019 7th international renewable and sustainable energy conference (IRSEC). - : IEEE. - 9781728151526 ; , s. 754-756
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Konferensbidrag (refereegranskat)abstract
- The P-doped hard carbon was synthesized using carboxymethyl cellulose and phosphoric acid as the carbon and phosphorus precursors, respectively. The X-ray photoelectron spectroscopy (XPS) analysis reveals that the doped phosphorus atoms can incorporate into the carbon framework and most of them are connecting with carbon atoms to form P-C bonds. When used as anodes in sodium ion batteries, the obtained un-doped and P-doped hard carbon show poor electrochemical performances. The results indicate further optimization of the synthesis process is required. However, this approach opens up new possibilities to improve electrochemical performance of hard carbon anodes.
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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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