Investigation of Valence Mixing in Sodium-Ion Battery Cathode Material Prussian White by Mössbauer Spectroscopy

Ericsson, Tore; Häggström, Lennart; Ojwang, Dickson O.; Brant, William R.

doi:10.3389/fenrg.2022.909549

Cited by 3 publications

(2 citation statements)

References 20 publications

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“…20 The trend in the values between electrodes indicates a lower oxidation state for Fe C as a function of x, meaning a mixed valency, as expected for the redox active cation. 25,26 The Raman spectrum of the uncycled electrode shows main bands at 2173, 2152, and 2092 cm −1 (Fig. 4a), and are very similar to the original pristine sample powder already shown in Fig.…”

Section: Dalton Transactions Papersupporting

confidence: 67%

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Guest water hinders sodium-ion diffusion in low-defect Berlin green cathode material

et al. 2022

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Section: Dalton Transactions Papersupporting

confidence: 67%

“…20 The trend in the values between electrodes indicates a lower oxidation state for Fe C as a function of x , meaning a mixed valency, as expected for the redox active cation. 25,26…”

Section: Resultsmentioning

confidence: 99%

Guest water hinders sodium-ion diffusion in low-defect Berlin green cathode material

et al. 2022

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Dehydration Achieving the Iron Spin State Regulation of Prussian Blue for Boosted Sodium‐Ion Storage Performance

Meng,

Chen,

Lai

et al. 2024

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Prussian blue analogs (PBAs) show promise as cathodes for sodium‐ion batteries due to their notable cycle stability, cost‐effectiveness, and eco‐friendly nature, yet the presence of interstitial water limits the specific capacity and obstructs Na+ mobility within the material. Although considerable experimental efforts are focused on dehydrating water for capacity enhancement, there is still a deficiency of a comprehensive understanding of the low capacity of low‐spin Fe resulting from interstitial water, which holds significance in Na+ storage. This study introduces a novel gas‐assisted heat treatment method to efficiently remove interstitial water from Fe‐based PBA (NaFeHCF) electrodes and combines experiments and theoretical calculations to reveal the iron spin state regulation that is related to the capacity enhancement mechanism. This dehydration strategy significantly enhances battery capacity, especially the portion at higher voltages (3.4–4.0 V). The increase in capacity is attributed to the following factors: an enhanced proportion of Fe2+, reduced water content which facilitates faster charge transfer, and the activation of low spin Fe2+. The optimized NaFeHCF demonstrated impressive half‐cell performance of retaining 87.3% capacity after 2000 cycles at a 5 C rate and achieving 100 mAh g−1 capacity over 200 cycles when being paired with hard carbon, exhibiting its practical potential.

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Determining internal porosity in Prussian blue analogue cathode materials using positron annihilation lifetime spectroscopy

Boras,

Nielsen,

Buckel

et al. 2023

J Mater Sci

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Prussian blue analogues (PBAs), $${{A}_x{M}[{M'}({\text {CN}})_{6}]_{1-{{y}}}\cdot {z} {\text {H}}_{2}{\text {O}}}$$ A x M [ M ′ ( CN ) 6 ] 1 - y · z H 2 O , are a highly functional class of materials with use in a broad range of applications, such as energy storage, due to their porous structure and tunable composition. The porosity is particularly important for the properties and is deeply coupled to the cation, water, and $${[{M'}({\text {CN}})_{6}]^{{{n}}-}}$$ [ M ′ ( CN ) 6 ] n - vacancy content. Determining internal porosity is especially challenging because the three compositional parameters are dependent on each other. In this work, we apply a new method, positron annihilation lifetime spectroscopy (PALS), which can be employed for the characterization of defects and structural changes in crystalline materials. Four samples were prepared to evaluate the method’s ability to detect changes in internal porosity as a function of the cation, water, and $${[{M'}({\text {CN}})_{6}]^{{{n}}-}}$$ [ M ′ ( CN ) 6 ] n - vacancy content. Three of the samples have identical $${[{M'}({\text {CN}})_{6}]^{{{n}}-}}$$ [ M ′ ( CN ) 6 ] n - vacancy content and gradually decreasing sodium and water content, while one sample has no sodium and 25% $${[{M'}({\text {CN}})_{6}]^{{n}-}}$$ [ M ′ ( CN ) 6 ] n - vacancies. The samples were thoroughly characterized using inductively coupled plasma-optical emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Mössbauer spectroscopy as well as applying the PALS method. Mössbauer spectroscopy, XRD, and TGA analysis revealed the sample compositions $${{\text {Na}}_{1.8(2)}{\text {Fe}}^{2+}_{0.64(6)}{\text {Fe}}^{2.6+}_{0.36(10)} [{\text {Fe}}^{2+}({\text {CN}})_{6}]}\cdot 2.09(2){{\text {H}}_{2}{\text {O}}},$$ Na 1.8 ( 2 ) Fe 0.64 ( 6 ) 2 + Fe 0.36 ( 10 ) 2.6 + [ Fe 2 + ( CN ) 6 ] · 2.09 ( 2 ) H 2 O , $${{\text {Na}}_{1.1(2)}{\text {Fe}}^{2+}_{0.24(6)}{\text {Fe}}^{2.8+}_{0.76(6)} [{\text {Fe}}^{2.3+}({\text {CN}})_{6}]}\cdot 1.57(1){{\text {H}}_{2}{\text {O}}}$$ Na 1.1 ( 2 ) Fe 0.24 ( 6 ) 2 + Fe 0.76 ( 6 ) 2.8 + [ Fe 2.3 + ( CN ) 6 ] · 1.57 ( 1 ) H 2 O , $${{\text {Fe}}[{\text {Fe}}({\text {CN}})_{6}]}\cdot$$ Fe [ Fe ( CN ) 6 ] · 0.807(9)$${\text {H}}_{2}{\text {O}}$$ H 2 O , and $${{\text {Fe}}[{\text {Fe}}({\text {CN}})_{6}]_{0.75}}\cdot$$ Fe [ Fe ( CN ) 6 ] 0.75 · 1.5$${{\text {H}}_{2}{\text {O}}}$$ H 2 O , confirming the absence of vacancies in the three main samples. It was shown that the final composition of PBAs could only be unambiguously confirmed through the combination of ICP, XRD, TGA, and Mössbauer spectroscopy. Two positron lifetimes of 205 and 405 ps were observed with the 205 ps lifetime being independent of the sodium, water, and/or $${[{\text {Fe}}({\text {CN}})_{6}]^{{{n}}-}}$$ [ Fe ( CN ) 6 ] n - vacancy content, while the lifetime around 405 ps changes with varying sodium and water content. However, the origin and nature of the 405 ps lifetime yet remains unclear. The method shows promise for characterizing changes in the internal porosity in PBAs as a function of the composition and further development work needs to be carried out to ensure the applicability to PBAs generally. Graphical abstract

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Investigation of Valence Mixing in Sodium-Ion Battery Cathode Material Prussian White by Mössbauer Spectroscopy

Cited by 3 publications

References 20 publications

Guest water hinders sodium-ion diffusion in low-defect Berlin green cathode material

Guest water hinders sodium-ion diffusion in low-defect Berlin green cathode material

Dehydration Achieving the Iron Spin State Regulation of Prussian Blue for Boosted Sodium‐Ion Storage Performance

Determining internal porosity in Prussian blue analogue cathode materials using positron annihilation lifetime spectroscopy

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