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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

SolutionNMR spectra of varying concentrations of Li+ + Sx2– in the electrolyte,1 M LiTFSI in DOL/DME. In (a) a 1:4 Li:S starting ratio was employed,while in (b) the ratio was 1:3 Li:S. (c) The chemical shift displaysa linear dependence on the concentration in each case. A lower Li:Sratio causes a smaller signal shift to higher frequencies.
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fig3: SolutionNMR spectra of varying concentrations of Li+ + Sx2– in the electrolyte,1 M LiTFSI in DOL/DME. In (a) a 1:4 Li:S starting ratio was employed,while in (b) the ratio was 1:3 Li:S. (c) The chemical shift displaysa linear dependence on the concentration in each case. A lower Li:Sratio causes a smaller signal shift to higher frequencies.

Mentions: Instead, we utilize 7Li NMR to explorethe nature ofintermediates and products formed during Li–S discharge. Sincethe solution products are key reaction intermediates during discharge,we first explore the sensitivity of 7Li NMR to changesin Li+ and Sx2– concentrations. During cell operation, an increase in dissolvedLi+ concentration must coincide with an increase in Sx2– concentration. To simulatethis effect, Li+ and Sx2– are titrated into the electrolyte solution at a ratioof 1:3 and 1:4 (Figure 3). The titration experimentsindicate that the resonance frequency varies significantly with theion concentration (Li+ and Sx2–) but only mildly with the length of the S chain.


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)

SolutionNMR spectra of varying concentrations of Li+ + Sx2– in the electrolyte,1 M LiTFSI in DOL/DME. In (a) a 1:4 Li:S starting ratio was employed,while in (b) the ratio was 1:3 Li:S. (c) The chemical shift displaysa linear dependence on the concentration in each case. A lower Li:Sratio causes a smaller signal shift to higher frequencies.
© Copyright Policy
Related In: Results  -  Collection

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

fig3: SolutionNMR spectra of varying concentrations of Li+ + Sx2– in the electrolyte,1 M LiTFSI in DOL/DME. In (a) a 1:4 Li:S starting ratio was employed,while in (b) the ratio was 1:3 Li:S. (c) The chemical shift displaysa linear dependence on the concentration in each case. A lower Li:Sratio causes a smaller signal shift to higher frequencies.
Mentions: Instead, we utilize 7Li NMR to explorethe nature ofintermediates and products formed during Li–S discharge. Sincethe solution products are key reaction intermediates during discharge,we first explore the sensitivity of 7Li NMR to changesin Li+ and Sx2– concentrations. During cell operation, an increase in dissolvedLi+ concentration must coincide with an increase in Sx2– concentration. To simulatethis effect, Li+ and Sx2– are titrated into the electrolyte solution at a ratioof 1:3 and 1:4 (Figure 3). The titration experimentsindicate that the resonance frequency varies significantly with theion concentration (Li+ and Sx2–) but only mildly with the length of the S chain.

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