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Probing three-dimensional sodiation-desodiation equilibrium in sodium-ion batteries by in situ hard X-ray nanotomography.

Wang J, Eng C, Chen-Wiegart YC, Wang J - Nat Commun (2015)

Bottom Line: Efforts to relieve this problem are reliant on the understanding of electrochemical and structural degradation.We find an unusual (de)sodiation equilibrium during multi-electrochemical cycles.The superior structural reversibility during 10 electrochemical cycles and the significantly different morphological change features from comparable lithium-ion systems suggest untapped potential in sodium-ion batteries.

View Article: PubMed Central - PubMed

Affiliation: National Synchrotron Light Source II, Brookhaven National Laboratory, Building 743 Ring Road, Upton, New York 11973, USA.

ABSTRACT
Materials degradation-the main limiting factor for widespread application of alloy anodes in battery systems-was assumed to be worse in sodium alloys than in lithium analogues due to the larger sodium-ion radius. Efforts to relieve this problem are reliant on the understanding of electrochemical and structural degradation. Here we track three-dimensional structural and chemical evolution of tin anodes in sodium-ion batteries with in situ synchrotron hard X-ray nanotomography. We find an unusual (de)sodiation equilibrium during multi-electrochemical cycles. The superior structural reversibility during 10 electrochemical cycles and the significantly different morphological change features from comparable lithium-ion systems suggest untapped potential in sodium-ion batteries. These findings differ from the conventional thought that sodium ions always lead to more severe fractures in the electrode than lithium ions, which could have impact in advancing development of sodium-ion batteries.

No MeSH data available.


Related in: MedlinePlus

3D view and quantitative analysis of surface curvature evolution in NIB.(a) Evolution of the two principal curvatures, convex and concave, during the first electrochemical cycle. (b) Schematic illustration (colour) showing surface curvature change, and the corresponding real cross-section images (grey) of selected particle shown below. The discharge/charge profile is presented as the background. (c) 3D view of surface curvedness evolution during the first electrochemical cycle. The curvedness is calculated on the two principal curvatures, convex and concave feature. See Supplementary Information for details. Scale bar, 10 μm.
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f2: 3D view and quantitative analysis of surface curvature evolution in NIB.(a) Evolution of the two principal curvatures, convex and concave, during the first electrochemical cycle. (b) Schematic illustration (colour) showing surface curvature change, and the corresponding real cross-section images (grey) of selected particle shown below. The discharge/charge profile is presented as the background. (c) 3D view of surface curvedness evolution during the first electrochemical cycle. The curvedness is calculated on the two principal curvatures, convex and concave feature. See Supplementary Information for details. Scale bar, 10 μm.

Mentions: The chemical information change can be quantified with the linear attenuation coefficient20212223. For example, the chemical compositions of LixSn were identified by the attenuation coefficient change21. The X-ray attenuation of Si also decreases with lithiation, referring to the Si→LixSi22. In this work, the decrease of the attenuation coefficient indicates the sodiation process from Sn to NaxSn in NIB. The left high peak (pink background) in Fig. 1f corresponds to the background information (electrolytes, conductive carbon, binder and others), and the right peaks correspond to active materials (Sn or NaxSn). The voltage curve shows three voltage plateaus (Supplementary Fig. 5), which refer to the Na–Sn alloying two-phase reactions of Sn–NaSn5 (∼0.5 V), NaSn5–NaSn (∼0.25 V) and NaSn–Na9Sn4 (∼0.15 V)2324. The tomography data was recorded at the end of the second voltage plateaus, corresponding to a phase of NaxSn (x>1.0). The attenuation coefficient change during the initial sodiation process also indicates the phase transformation. This chemical phase change was also confirmed by the discharge curve shown in Fig. 2. Intriguingly, no obvious morphological change was observed at this step, which indicates that the initial sodiation process, despite contributing to the specific capacity, shows negligible volume change. This feature may be attributed to some amorphous phase formation25, which is similar to the multi-step lithiation process in Si, Ge and Sn in LIB262728. The carbon paper with matrix network structure may also buffer the volume expansion. During the further sodiation process, the voltage plateaus (0.15 V) and the big negative shift in attenuation coefficient suggest the formation of Na9Sn4 or even higher-sodiation NaxSn (x≥2.25) phase, which is also revealed by the drastic morphology change shown in Fig. 1a. This sodiation process was also visualized by an in operando 2D TXM study. The setup was shown in Supplementary Fig. 6 and the morphological evolution was shown in Supplementary Fig. 7 (also see Supplementary Video 3). Despite the discharge plateau and the responding capacity referring to the chemical phase change, the Sn particles show no obvious diameter increase and morphology expansion at the beginning of sodiation. After that, with further sodiation, large morphology expansion and diameter increase happen. Therefore, based on the above studies, the sodiation process is initiated by the formation of a NaxSn (x≈1.3, see Supplementary Note 2) phase with low volume change, and followed by further Na-ion insertion that increasing sodiation-induced stress leads to volume expansion/fracture (Fig. 1g).


Probing three-dimensional sodiation-desodiation equilibrium in sodium-ion batteries by in situ hard X-ray nanotomography.

Wang J, Eng C, Chen-Wiegart YC, Wang J - Nat Commun (2015)

3D view and quantitative analysis of surface curvature evolution in NIB.(a) Evolution of the two principal curvatures, convex and concave, during the first electrochemical cycle. (b) Schematic illustration (colour) showing surface curvature change, and the corresponding real cross-section images (grey) of selected particle shown below. The discharge/charge profile is presented as the background. (c) 3D view of surface curvedness evolution during the first electrochemical cycle. The curvedness is calculated on the two principal curvatures, convex and concave feature. See Supplementary Information for details. Scale bar, 10 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4491187&req=5

f2: 3D view and quantitative analysis of surface curvature evolution in NIB.(a) Evolution of the two principal curvatures, convex and concave, during the first electrochemical cycle. (b) Schematic illustration (colour) showing surface curvature change, and the corresponding real cross-section images (grey) of selected particle shown below. The discharge/charge profile is presented as the background. (c) 3D view of surface curvedness evolution during the first electrochemical cycle. The curvedness is calculated on the two principal curvatures, convex and concave feature. See Supplementary Information for details. Scale bar, 10 μm.
Mentions: The chemical information change can be quantified with the linear attenuation coefficient20212223. For example, the chemical compositions of LixSn were identified by the attenuation coefficient change21. The X-ray attenuation of Si also decreases with lithiation, referring to the Si→LixSi22. In this work, the decrease of the attenuation coefficient indicates the sodiation process from Sn to NaxSn in NIB. The left high peak (pink background) in Fig. 1f corresponds to the background information (electrolytes, conductive carbon, binder and others), and the right peaks correspond to active materials (Sn or NaxSn). The voltage curve shows three voltage plateaus (Supplementary Fig. 5), which refer to the Na–Sn alloying two-phase reactions of Sn–NaSn5 (∼0.5 V), NaSn5–NaSn (∼0.25 V) and NaSn–Na9Sn4 (∼0.15 V)2324. The tomography data was recorded at the end of the second voltage plateaus, corresponding to a phase of NaxSn (x>1.0). The attenuation coefficient change during the initial sodiation process also indicates the phase transformation. This chemical phase change was also confirmed by the discharge curve shown in Fig. 2. Intriguingly, no obvious morphological change was observed at this step, which indicates that the initial sodiation process, despite contributing to the specific capacity, shows negligible volume change. This feature may be attributed to some amorphous phase formation25, which is similar to the multi-step lithiation process in Si, Ge and Sn in LIB262728. The carbon paper with matrix network structure may also buffer the volume expansion. During the further sodiation process, the voltage plateaus (0.15 V) and the big negative shift in attenuation coefficient suggest the formation of Na9Sn4 or even higher-sodiation NaxSn (x≥2.25) phase, which is also revealed by the drastic morphology change shown in Fig. 1a. This sodiation process was also visualized by an in operando 2D TXM study. The setup was shown in Supplementary Fig. 6 and the morphological evolution was shown in Supplementary Fig. 7 (also see Supplementary Video 3). Despite the discharge plateau and the responding capacity referring to the chemical phase change, the Sn particles show no obvious diameter increase and morphology expansion at the beginning of sodiation. After that, with further sodiation, large morphology expansion and diameter increase happen. Therefore, based on the above studies, the sodiation process is initiated by the formation of a NaxSn (x≈1.3, see Supplementary Note 2) phase with low volume change, and followed by further Na-ion insertion that increasing sodiation-induced stress leads to volume expansion/fracture (Fig. 1g).

Bottom Line: Efforts to relieve this problem are reliant on the understanding of electrochemical and structural degradation.We find an unusual (de)sodiation equilibrium during multi-electrochemical cycles.The superior structural reversibility during 10 electrochemical cycles and the significantly different morphological change features from comparable lithium-ion systems suggest untapped potential in sodium-ion batteries.

View Article: PubMed Central - PubMed

Affiliation: National Synchrotron Light Source II, Brookhaven National Laboratory, Building 743 Ring Road, Upton, New York 11973, USA.

ABSTRACT
Materials degradation-the main limiting factor for widespread application of alloy anodes in battery systems-was assumed to be worse in sodium alloys than in lithium analogues due to the larger sodium-ion radius. Efforts to relieve this problem are reliant on the understanding of electrochemical and structural degradation. Here we track three-dimensional structural and chemical evolution of tin anodes in sodium-ion batteries with in situ synchrotron hard X-ray nanotomography. We find an unusual (de)sodiation equilibrium during multi-electrochemical cycles. The superior structural reversibility during 10 electrochemical cycles and the significantly different morphological change features from comparable lithium-ion systems suggest untapped potential in sodium-ion batteries. These findings differ from the conventional thought that sodium ions always lead to more severe fractures in the electrode than lithium ions, which could have impact in advancing development of sodium-ion batteries.

No MeSH data available.


Related in: MedlinePlus