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Ab initio structure search and in situ 7Li NMR studies of discharge products in the Li-S battery system.

See KA, Leskes M, Griffin JM, Britto S, Matthews PD, Emly A, Van der Ven A, Wright DS, Morris AJ, Grey CP, Seshadri R - J. Am. Chem. Soc. (2014)

Bottom Line: We suggest that during the first discharge plateau, S is reduced to soluble polysulfide species concurrently with the formation of a solid component (Li2S) which forms near the beginning of the first plateau, in the cell configuration studied here.The NMR data suggest that the second plateau is defined by the reduction of the residual soluble species to solid product (Li2S).A ternary diagram is presented to rationalize the phases observed with NMR during the discharge pathway and provide thermodynamic underpinnings for the shape of the discharge profile as a function of cell composition.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry and Materials Research Laboratory and ∥Materials Department, University of California, Santa Barbara (UCSB) , Santa Barbara, California 93106, United States.

ABSTRACT
The high theoretical gravimetric capacity of the Li-S battery system makes it an attractive candidate for numerous energy storage applications. In practice, cell performance is plagued by low practical capacity and poor cycling. In an effort to explore the mechanism of the discharge with the goal of better understanding performance, we examine the Li-S phase diagram using computational techniques and complement this with an in situ (7)Li NMR study of the cell during discharge. Both the computational and experimental studies are consistent with the suggestion that the only solid product formed in the cell is Li2S, formed soon after cell discharge is initiated. In situ NMR spectroscopy also allows the direct observation of soluble Li(+)-species during cell discharge; species that are known to be highly detrimental to capacity retention. We suggest that during the first discharge plateau, S is reduced to soluble polysulfide species concurrently with the formation of a solid component (Li2S) which forms near the beginning of the first plateau, in the cell configuration studied here. The NMR data suggest that the second plateau is defined by the reduction of the residual soluble species to solid product (Li2S). A ternary diagram is presented to rationalize the phases observed with NMR during the discharge pathway and provide thermodynamic underpinnings for the shape of the discharge profile as a function of cell composition.

No MeSH data available.


Related in: MedlinePlus

Calculated quadrupolar coupling constants, CQ, for the 7Li nuclei of the low-energycompoundsin the series LixS1–x. The distributions of CQ values for each Li atom in 28 stoichiometries found by AIRSS areshown as histogram plots with the height of the line indicating thenumber of atoms exhibiting that CQ.
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fig2: Calculated quadrupolar coupling constants, CQ, for the 7Li nuclei of the low-energycompoundsin the series LixS1–x. The distributions of CQ values for each Li atom in 28 stoichiometries found by AIRSS areshown as histogram plots with the height of the line indicating thenumber of atoms exhibiting that CQ.

Mentions: Despite the very low probabilitythat intermediate solid lithiumpolysulfide structures will form, it is interesting to explore thestructural trends in phases closest to the hull (Figure 1). The quadrupolar coupling constants, CQ, of the 7Li nuclei in the lowest energy structuresin a number of stoichiometries, were calculated and plotted (Figure 2). The magnitude of the CQ is dictated by the symmetry and distortion of the local bondingenvironment and changes in these values are one measure of structuraltrends. All the calculated 7Li CQ values are nonzero throughout the series save for Li2S (Figure 2), which exhibits a CQ value of 0 MHz owing to the tetrahedral bonding environmentof Li in the fluorite structure.


Ab initio structure search and in situ 7Li NMR studies of discharge products in the Li-S battery system.

See KA, Leskes M, Griffin JM, Britto S, Matthews PD, Emly A, Van der Ven A, Wright DS, Morris AJ, Grey CP, Seshadri R - J. Am. Chem. Soc. (2014)

Calculated quadrupolar coupling constants, CQ, for the 7Li nuclei of the low-energycompoundsin the series LixS1–x. The distributions of CQ values for each Li atom in 28 stoichiometries found by AIRSS areshown as histogram plots with the height of the line indicating thenumber of atoms exhibiting that CQ.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4353022&req=5

fig2: Calculated quadrupolar coupling constants, CQ, for the 7Li nuclei of the low-energycompoundsin the series LixS1–x. The distributions of CQ values for each Li atom in 28 stoichiometries found by AIRSS areshown as histogram plots with the height of the line indicating thenumber of atoms exhibiting that CQ.
Mentions: Despite the very low probabilitythat intermediate solid lithiumpolysulfide structures will form, it is interesting to explore thestructural trends in phases closest to the hull (Figure 1). The quadrupolar coupling constants, CQ, of the 7Li nuclei in the lowest energy structuresin a number of stoichiometries, were calculated and plotted (Figure 2). The magnitude of the CQ is dictated by the symmetry and distortion of the local bondingenvironment and changes in these values are one measure of structuraltrends. All the calculated 7Li CQ values are nonzero throughout the series save for Li2S (Figure 2), which exhibits a CQ value of 0 MHz owing to the tetrahedral bonding environmentof Li in the fluorite structure.

Bottom Line: We suggest that during the first discharge plateau, S is reduced to soluble polysulfide species concurrently with the formation of a solid component (Li2S) which forms near the beginning of the first plateau, in the cell configuration studied here.The NMR data suggest that the second plateau is defined by the reduction of the residual soluble species to solid product (Li2S).A ternary diagram is presented to rationalize the phases observed with NMR during the discharge pathway and provide thermodynamic underpinnings for the shape of the discharge profile as a function of cell composition.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry and Materials Research Laboratory and ∥Materials Department, University of California, Santa Barbara (UCSB) , Santa Barbara, California 93106, United States.

ABSTRACT
The high theoretical gravimetric capacity of the Li-S battery system makes it an attractive candidate for numerous energy storage applications. In practice, cell performance is plagued by low practical capacity and poor cycling. In an effort to explore the mechanism of the discharge with the goal of better understanding performance, we examine the Li-S phase diagram using computational techniques and complement this with an in situ (7)Li NMR study of the cell during discharge. Both the computational and experimental studies are consistent with the suggestion that the only solid product formed in the cell is Li2S, formed soon after cell discharge is initiated. In situ NMR spectroscopy also allows the direct observation of soluble Li(+)-species during cell discharge; species that are known to be highly detrimental to capacity retention. We suggest that during the first discharge plateau, S is reduced to soluble polysulfide species concurrently with the formation of a solid component (Li2S) which forms near the beginning of the first plateau, in the cell configuration studied here. The NMR data suggest that the second plateau is defined by the reduction of the residual soluble species to solid product (Li2S). A ternary diagram is presented to rationalize the phases observed with NMR during the discharge pathway and provide thermodynamic underpinnings for the shape of the discharge profile as a function of cell composition.

No MeSH data available.


Related in: MedlinePlus