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Visualizing the chemistry and structure dynamics in lithium-ion batteries by in-situ neutron diffraction.

Wang XL, An K, Cai L, Feng Z, Nagler SE, Daniel C, Rhodes KJ, Stoica AD, Skorpenske HD, Liang C, Zhang W, Kim J, Qi Y, Harris SJ - Sci Rep (2012)

Bottom Line: The succession of Li-Graphite intercalation phases was fully captured under an 1C charge-discharge condition (i.e., charge to full capacity in 1 hour).However, the lithiation and dilithiation pathways are distinctively different and, unlike in slowing charging experiments with which the Li-Graphite phase diagram was established, no LiC₂₄ phase was found during charge at 1C rate.Approximately 75 mol. % of the graphite converts to LiC₆ at full charge, and a lattice dilation as large as 4% was observed during a charge-discharge cycle.

View Article: PubMed Central - PubMed

Affiliation: Chemical and Engineering Materials Division, Oak Ridge National Laboratory Oak Ridge, TN 37831-6465, USA. xlwang@cityu.edu.hk

ABSTRACT
We report an in-situ neutron diffraction study of a large format pouch battery cell. The succession of Li-Graphite intercalation phases was fully captured under an 1C charge-discharge condition (i.e., charge to full capacity in 1 hour). However, the lithiation and dilithiation pathways are distinctively different and, unlike in slowing charging experiments with which the Li-Graphite phase diagram was established, no LiC₂₄ phase was found during charge at 1C rate. Approximately 75 mol. % of the graphite converts to LiC₆ at full charge, and a lattice dilation as large as 4% was observed during a charge-discharge cycle. Our work demonstrates the potential of in-situ, time and spatially resolved neutron diffraction study of the dynamic chemical and structural changes in "real-world" batteries under realistic cycling conditions, which should provide microscopic insights on degradation and the important role of diffusion kinetics in energy storage materials.

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Related in: MedlinePlus

Optical micrographs taken from a failed commercial 18650 battery cells to illustrate the nature of heterogeneous failure.The images (a) and (b), each showing a region approximately 2×2 mm2 on the graphite electrode, were taken from different locations (shown as red squares). These regions were shorted to metallic Li and thereby lithiated to the maximum extent possible. Full lithiation (LiC6) turns graphite to a gold color. In (a), taken far from the end caps, the entire region becomes gold, indicating that all of the graphite in this region became lithiated. In (b), taken close to the end cap (about 20 mm away from (a)) the electrode is only partially gold. Black indicates the presence of graphite particles that are not lithiated. They may have become electrically disconnected from the current collector. (The curved white lines in the images are artifacts from collecting the samples.)
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f1: Optical micrographs taken from a failed commercial 18650 battery cells to illustrate the nature of heterogeneous failure.The images (a) and (b), each showing a region approximately 2×2 mm2 on the graphite electrode, were taken from different locations (shown as red squares). These regions were shorted to metallic Li and thereby lithiated to the maximum extent possible. Full lithiation (LiC6) turns graphite to a gold color. In (a), taken far from the end caps, the entire region becomes gold, indicating that all of the graphite in this region became lithiated. In (b), taken close to the end cap (about 20 mm away from (a)) the electrode is only partially gold. Black indicates the presence of graphite particles that are not lithiated. They may have become electrically disconnected from the current collector. (The curved white lines in the images are artifacts from collecting the samples.)

Mentions: In many cases, degradation and failure in large format batteries start locally at inhomogeneities or weak points, rather than uniformly across the entire battery378. Figure 1 highlights the spatial inhomogeneity in the anode of a commercial 18650 battery after it lost a significant amount of capacity under cycling. The graphite anode suffered damage near each end cap. Close examination shows that the central region of the electrode tape is largely homogeneous, while the edge areas appear to be highly fractured with a substantial loss of capacity. The optical micrographs of samples from each region are contrasted in Figure 1. Lithiation of graphite electrodes – the LiC6 phase – turns them to a golden color9 that can be readily observed. The deteriorated region, which cannot be fully lithiated, lost 2/3 of its capacity. Similar results can be expected for large format pouch cell batteries.


Visualizing the chemistry and structure dynamics in lithium-ion batteries by in-situ neutron diffraction.

Wang XL, An K, Cai L, Feng Z, Nagler SE, Daniel C, Rhodes KJ, Stoica AD, Skorpenske HD, Liang C, Zhang W, Kim J, Qi Y, Harris SJ - Sci Rep (2012)

Optical micrographs taken from a failed commercial 18650 battery cells to illustrate the nature of heterogeneous failure.The images (a) and (b), each showing a region approximately 2×2 mm2 on the graphite electrode, were taken from different locations (shown as red squares). These regions were shorted to metallic Li and thereby lithiated to the maximum extent possible. Full lithiation (LiC6) turns graphite to a gold color. In (a), taken far from the end caps, the entire region becomes gold, indicating that all of the graphite in this region became lithiated. In (b), taken close to the end cap (about 20 mm away from (a)) the electrode is only partially gold. Black indicates the presence of graphite particles that are not lithiated. They may have become electrically disconnected from the current collector. (The curved white lines in the images are artifacts from collecting the samples.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3475991&req=5

f1: Optical micrographs taken from a failed commercial 18650 battery cells to illustrate the nature of heterogeneous failure.The images (a) and (b), each showing a region approximately 2×2 mm2 on the graphite electrode, were taken from different locations (shown as red squares). These regions were shorted to metallic Li and thereby lithiated to the maximum extent possible. Full lithiation (LiC6) turns graphite to a gold color. In (a), taken far from the end caps, the entire region becomes gold, indicating that all of the graphite in this region became lithiated. In (b), taken close to the end cap (about 20 mm away from (a)) the electrode is only partially gold. Black indicates the presence of graphite particles that are not lithiated. They may have become electrically disconnected from the current collector. (The curved white lines in the images are artifacts from collecting the samples.)
Mentions: In many cases, degradation and failure in large format batteries start locally at inhomogeneities or weak points, rather than uniformly across the entire battery378. Figure 1 highlights the spatial inhomogeneity in the anode of a commercial 18650 battery after it lost a significant amount of capacity under cycling. The graphite anode suffered damage near each end cap. Close examination shows that the central region of the electrode tape is largely homogeneous, while the edge areas appear to be highly fractured with a substantial loss of capacity. The optical micrographs of samples from each region are contrasted in Figure 1. Lithiation of graphite electrodes – the LiC6 phase – turns them to a golden color9 that can be readily observed. The deteriorated region, which cannot be fully lithiated, lost 2/3 of its capacity. Similar results can be expected for large format pouch cell batteries.

Bottom Line: The succession of Li-Graphite intercalation phases was fully captured under an 1C charge-discharge condition (i.e., charge to full capacity in 1 hour).However, the lithiation and dilithiation pathways are distinctively different and, unlike in slowing charging experiments with which the Li-Graphite phase diagram was established, no LiC₂₄ phase was found during charge at 1C rate.Approximately 75 mol. % of the graphite converts to LiC₆ at full charge, and a lattice dilation as large as 4% was observed during a charge-discharge cycle.

View Article: PubMed Central - PubMed

Affiliation: Chemical and Engineering Materials Division, Oak Ridge National Laboratory Oak Ridge, TN 37831-6465, USA. xlwang@cityu.edu.hk

ABSTRACT
We report an in-situ neutron diffraction study of a large format pouch battery cell. The succession of Li-Graphite intercalation phases was fully captured under an 1C charge-discharge condition (i.e., charge to full capacity in 1 hour). However, the lithiation and dilithiation pathways are distinctively different and, unlike in slowing charging experiments with which the Li-Graphite phase diagram was established, no LiC₂₄ phase was found during charge at 1C rate. Approximately 75 mol. % of the graphite converts to LiC₆ at full charge, and a lattice dilation as large as 4% was observed during a charge-discharge cycle. Our work demonstrates the potential of in-situ, time and spatially resolved neutron diffraction study of the dynamic chemical and structural changes in "real-world" batteries under realistic cycling conditions, which should provide microscopic insights on degradation and the important role of diffusion kinetics in energy storage materials.

Show MeSH
Related in: MedlinePlus