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Experimental visualization of the diffusion pathway of sodium ions in the Na 3 [Ti 2 P 2 O 10 F] anode for sodium-ion battery

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ABSTRACT

Sodium-ion batteries have attracted considerable interest as an alternative to lithium-ion batteries for electric storage applications because of the low cost and natural abundance of sodium resources. The materials with an open framework are highly desired for Na-ion insertion/extraction. Here we report on the first visualization of the sodium-ion diffusion path in Na3[Ti2P2O10F] through high-temperature neutron powder diffraction experiments. The evolution of the Na-ion displacements of Na3[Ti2P2O10F] was investigated with high-temperature neutron diffraction (HTND) from room temperature to 600°C; difference Fourier maps were utilized to estimate the Na nuclear-density distribution. Temperature-driven Na displacements indicates that sodium-ion diffusion paths are established within the ab plane. As an anode for sodium-ion batteries, Na3[Ti2P2O10F] exhibits a reversible capacity of ~100 mAh g−1 with lower intercalation voltage. It also shows good cycling stability and rate capability, making it promising applications in sodium-ion batteries.

No MeSH data available.


Unit cell of Na3[Ti2P2O10F] including the Na delocalization observed by Fourier Synthesis; Na are delocalized in octagonal rings places in the interlayer space between PO4-TiO5F sheets.
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f4: Unit cell of Na3[Ti2P2O10F] including the Na delocalization observed by Fourier Synthesis; Na are delocalized in octagonal rings places in the interlayer space between PO4-TiO5F sheets.

Mentions: In order to clarify the Na distribution and how Na ion is transported in the framework, we have undertaken a high-temperature neutron diffraction (HTND) of Na3[Ti2P2O10F] from RT to 600°C. No structural transition was observed in the temperature range studied; the crystal structures can be refined within the same tetragonal structural model. Figure 1b illustrates the goodness of the fit at 600°C; the atomic parameters for the refinements and the Rietveld plots at 200 and 400°C are shown in Table S2 and Figure S1 in the Supporting Information. An interesting insight into the Na ion motion was achieved by removing Na atoms from the structural model at 600°C and performing a difference Fourier synthesis from the observed and calculated NPD data. The difference contains information of the missing scattering density (in this case nuclear density). Figure 3 shows a difference Fourier map corresponding to the z = 0 section where strong positive peaks corresponding to the 8h sites for Na1 are observed, and some intermediate nuclear density is observed between both peaks, indicating that Na is partially delocalized at intermediate positions. It can be visualized clearly in Figure 4, where Na atoms are delocalized in octagonal rings within the interlayer space, suggesting that the diffusion is two dimensional (2D), since there is no residual Na scattering through the layers even at an elevated temperature of 600°C.


Experimental visualization of the diffusion pathway of sodium ions in the Na 3 [Ti 2 P 2 O 10 F] anode for sodium-ion battery
Unit cell of Na3[Ti2P2O10F] including the Na delocalization observed by Fourier Synthesis; Na are delocalized in octagonal rings places in the interlayer space between PO4-TiO5F sheets.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384114&req=5

f4: Unit cell of Na3[Ti2P2O10F] including the Na delocalization observed by Fourier Synthesis; Na are delocalized in octagonal rings places in the interlayer space between PO4-TiO5F sheets.
Mentions: In order to clarify the Na distribution and how Na ion is transported in the framework, we have undertaken a high-temperature neutron diffraction (HTND) of Na3[Ti2P2O10F] from RT to 600°C. No structural transition was observed in the temperature range studied; the crystal structures can be refined within the same tetragonal structural model. Figure 1b illustrates the goodness of the fit at 600°C; the atomic parameters for the refinements and the Rietveld plots at 200 and 400°C are shown in Table S2 and Figure S1 in the Supporting Information. An interesting insight into the Na ion motion was achieved by removing Na atoms from the structural model at 600°C and performing a difference Fourier synthesis from the observed and calculated NPD data. The difference contains information of the missing scattering density (in this case nuclear density). Figure 3 shows a difference Fourier map corresponding to the z = 0 section where strong positive peaks corresponding to the 8h sites for Na1 are observed, and some intermediate nuclear density is observed between both peaks, indicating that Na is partially delocalized at intermediate positions. It can be visualized clearly in Figure 4, where Na atoms are delocalized in octagonal rings within the interlayer space, suggesting that the diffusion is two dimensional (2D), since there is no residual Na scattering through the layers even at an elevated temperature of 600°C.

View Article: PubMed Central - PubMed

ABSTRACT

Sodium-ion batteries have attracted considerable interest as an alternative to lithium-ion batteries for electric storage applications because of the low cost and natural abundance of sodium resources. The materials with an open framework are highly desired for Na-ion insertion/extraction. Here we report on the first visualization of the sodium-ion diffusion path in Na3[Ti2P2O10F] through high-temperature neutron powder diffraction experiments. The evolution of the Na-ion displacements of Na3[Ti2P2O10F] was investigated with high-temperature neutron diffraction (HTND) from room temperature to 600°C; difference Fourier maps were utilized to estimate the Na nuclear-density distribution. Temperature-driven Na displacements indicates that sodium-ion diffusion paths are established within the ab plane. As an anode for sodium-ion batteries, Na3[Ti2P2O10F] exhibits a reversible capacity of ~100 mAh g−1 with lower intercalation voltage. It also shows good cycling stability and rate capability, making it promising applications in sodium-ion batteries.

No MeSH data available.