| 1. |
- Ericsson, Tore, et al.
(författare)
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Investigation of Valence Mixing in Sodium-Ion Battery Cathode Material Prussian White by Mossbauer Spectroscopy
- 2022
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Ingår i: Frontiers in Energy Research. - : Frontiers Media S.A.. - 2296-598X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Prussian white (PW), Na2Fe [Fe(CN)(6)], is a highly attractive cathode material for sustainable sodium-ion batteries due to its high theoretical capacity of similar to 170 mAhg(-1) and low-cost synthesis. However, there exists significant variability in the reported electrochemical performance. This variability originates from compositional flexibility possible for all Prussian blue analogs (PBAs) and is exasperated by the difficulty of accurately quantifying the specific composition of PW. This work presents a means of accurately quantifying the vacancy content, valence distribution, and, consequently, the overall composition of PW via Mossbauer spectroscopy. PW cathode material with three different sodium contents was investigated at 295 and 90 K. The observation of only two iron environments for the fully sodiated compound indicated the absence of [Fe(CN)(6)](4-) vacancies. Due to intervalence charge transfer between iron centers at 295 K, accurate determination of valences was not possible. However, by observing the trend of spectral intensities and center shift for the nitrogen-bound and carbon-bound iron, respectively, at 90 K, valence mixing between the iron sites could be quantified. By accounting for valence mixing, the sum of iron valences agreed with the sodium content determined from elemental analysis. Without an agreement between the total valence sum and the determined composition, there exists uncertainty around the accuracy of the elemental analysis and vacancy content determination. Thus, this study offers one more stepping stone toward a more rigorous characterization of composition in PW, which will enable further optimization of properties for battery applications. More broadly, the approach is valuable for characterizing iron-based PBAs in applications where precise composition, valence determination, and control are desired.
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| 2. |
- Khasevani, Sepideh G., et al.
(författare)
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The beauty of being complex: Prussian blue analogues as selective catalysts and photocatalysts in the degradation of ciprofloxacin
- 2022
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Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 410, s. 307-319
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the performance of four Prussian blue analogues (PBAs) as catalysts for the selective degradation of ciprofloxacin in water, under both dark and illumination conditions. We show that no light is actually needed to induce a selective degradation of the molecular target, while light irradiation spurs the process, without, however, resulting in the commonly reported photolysis-supported breaking down. We present a systematic characterization of the PBAs aiming at interpreting the catalytic outcomes in the light of a classic coordination chemistry analysis, empowered by the most recent findings in literature. We show that varying the transition metal binding the N atom of the cyanide bridge is key to promote photoinduced charge generation and transfer, which effectively disrupts the molecular target. The analysis of the materials before and after the irradiation with solar simulated light results in a change of the lattice parameters, indicating the possibility of a light-induced spin cross-over.
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| 3. |
- Menon, Ashok S., et al.
(författare)
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Synthesis-structure relationships in Li- and Mn-rich layered oxides : phase evolution, superstructure ordering and stacking faults
- 2022
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:11, s. 4435-4446
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Tidskriftsartikel (refereegranskat)abstract
- Li- and Mn-rich layered oxides are promising positive electrode materials for future Li-ion batteries. The presence of crystallographic features such as cation-mixing and stacking faults in these compounds make them highly susceptible to synthesis-induced structural changes. Consequently, significant variations exist in the reported structure of these compounds that complicate the understanding of how the crystallographic structure influences its properties. This work investigates the synthesis-structure relations for three widely investigated Li- and Mn-rich layered oxides: Li2MnO3, Li1.2Mn0.6Ni0.2O2 and Li1.2Mn0.54Ni0.13Co0.13O2. For each compound, the average structure is compared between two synthetic routes of differing degrees of precursor mixing and four annealing protocols. Furthermore, thermodynamic and synthesis-specific kinetic factors governing the equilibrium crystallography of each composition are considered. It was found that the structures of these compounds are thermodynamically metastable under the synthesis conditions employed. In addition to a driving force to reduce stacking faults in the structure, these compositions also exhibited a tendency to undergo structural transformations to more stable phases under more intense annealing conditions. Increasing the compositional complexity introduced a kinetic barrier to structural ordering, making Li1.2Mn0.6Ni0.2O2 and Li1.2Mn0.54Ni0.13Co0.13O2 generally more faulted relative to Li2MnO3. Additionally, domains with different degrees of faulting were found to co-exist in the compounds. This study offers insight into the highly synthesis-dependent subtle structural complexities present in these compounds and complements the substantial efforts that have been undertaken to understand and optimise its electrochemical properties.
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| 4. |
- Nielsen, Ida, et al.
(författare)
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Water driven phase transitions in Prussian white cathode materials
- 2022
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Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 2515-7655. ; 4:4
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Tidskriftsartikel (refereegranskat)abstract
- Prussian white (PW, Na2Fe [Fe(CN)(6)] center dot zH(2)O) is a promising cathode material for use in sodium-ion batteries for large-scale energy storage applications, which demand long cycling life-times. However, for non-aqueous battery applications PW must not contain any water, and yet dehydration induces a large volume change destabilizing the structure and reducing the cycling life. The material undergoes multiple phase transitions as a function of both the sodium and water content, however, the mechanism behind is poorly understood. Here, we use neutron diffraction to explore the influence of water on the structure of PW. For the first time, two structures for a single composition of PW were observed near room temperature independent of the synthesis method. These structures differ in the FeN6 and FeC6 octahedral tilting configurations, which is connected to the ordering of water in the framework. The removal of water modulates the magnitude of pre-existing structural distortions, if it is itself disordered within the structure, rather than modifying the nature of the distortions. These results provide a robust fundamental understanding of the chemical driving force impacting the nature and magnitude of structural distortions in Prussian blue analogues. The insights provide guidance for designing tilt-engineering ultimately enabling new materials with enhanced long-term electrochemical performance in battery applications.
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| 5. |
- Ojwang, Dickson O., 1985-, et al.
(författare)
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Guest water hinders sodium-ion diffusion in low-defect Berlin green cathode material
- 2022
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 51:38, s. 14712-14720
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Tidskriftsartikel (refereegranskat)abstract
- Among Prussian blue analogues (PBAs), NaxFe[Fe(CN)(6)](1-y)center dot nH(2)O is a highly attractive cathode material for sodium-ion batteries due to its high theoretical capacity of similar to 170 mA h g(-1) and inexpensive raw materials. However, concerns remain over its long-term electrochemical performance and structural factors which impact sources of resistance in the material and subsequently rate performance. Refined control of the [Fe(CN)(6)] vacancies and water content could help in realizing its market potential. In this context, we have studied a low-defect Berlin green (BG) Na0.30(5)Fe[Fe(CN)(6)](0.94(2))center dot nH(2)O with varied water content corresponding to 10, 8, 6, and 2 wt%. The impact of water on the electrochemical properties of BG was systematically investigated. The electrodes were cycled within a narrow voltage window of 3.15-3.8 V vs. Na/Na+ to avoid undesired phase transitions and side reactions while preserving the cubic structure. We demonstrate that thermal dehydration leads to a significantly improved cycling stability of over 300 cycles at 15 mA g(-1) with coulombic efficiency of >99.9%. In particular, the electrode with the lowest water content exhibited the fastest Na+-ion insertion/extraction as evidenced by the larger CV peak currents during successive scans compared to hydrated samples. The results provide fundamental insight for designing PBAs as electrode materials with enhanced electrochemical performance in energy storage applications.
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