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Title: Elucidating the Solvation Structure and Dynamics of Lithium Polysulfides Resulting from Competitive Salt and Solvent Interactions

Abstract

Fundamental molecular level understanding of functional properties of liquid solutions provides an important basis for designing optimized electrolytes for numerous applica-tions. In particular, exhaustive knowledge of solvation structure, stability and transport properties is critical for developing stable electrolytes for fast charging and high energy density next-generation energy storage systems. Here we report the correlation between solubility, solvation structure and translational dynamics of a lithium salt (Li-TFSI) and polysulfides species using well-benchmarked classical molecular dynamics simulations combined with nuclear magnetic resonance (NMR). It is observed that the polysulfide chain length has a significant effect on the ion-ion and ion-solvent interaction as well as on the diffusion coefficient of the ionic species in solution. In particular, extensive cluster formation is observed in lower order poly-sulfides (Sx2-; x≤4), whereas the longer polysulfides (Sx2-; x>4) show high solubility and slow dynamics in the solu-tion. It is observed that optimal solvent/salt ratio is essen-tial to control the solubility and conductivity as the addi-tion of Li salt increases the solubility but decreases the mo-bility of the ionic species. This work provides a coupled theoretical and experimental study of bulk solvation struc-ture and transport properties of multi-component electro-lyte systems, yielding design metrics for developing optimal electrolytes withmore » improved stability and solubility.« less

Authors:
ORCiD logo; ORCiD logo; ; ; ; ; ; ORCiD logo; ORCiD logo;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1361977
Report Number(s):
PNNL-SA-125254
Journal ID: ISSN 0897-4756; 49376; KC0208010
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Chemistry of Materials; Journal Volume: 29; Journal Issue: 8
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Environmental Molecular Sciences Laboratory

Citation Formats

Rajput, Nav Nidhi, Murugesan, Vijayakumar, Shin, Yongwoo, Han, Kee Sung, Lau, Kah Chun, Chen, Junzheng, Liu, Jun, Curtiss, Larry A., Mueller, Karl T., and Persson, Kristin A. Elucidating the Solvation Structure and Dynamics of Lithium Polysulfides Resulting from Competitive Salt and Solvent Interactions. United States: N. p., 2017. Web. doi:10.1021/acs.chemmater.7b00068.
Rajput, Nav Nidhi, Murugesan, Vijayakumar, Shin, Yongwoo, Han, Kee Sung, Lau, Kah Chun, Chen, Junzheng, Liu, Jun, Curtiss, Larry A., Mueller, Karl T., & Persson, Kristin A. Elucidating the Solvation Structure and Dynamics of Lithium Polysulfides Resulting from Competitive Salt and Solvent Interactions. United States. doi:10.1021/acs.chemmater.7b00068.
Rajput, Nav Nidhi, Murugesan, Vijayakumar, Shin, Yongwoo, Han, Kee Sung, Lau, Kah Chun, Chen, Junzheng, Liu, Jun, Curtiss, Larry A., Mueller, Karl T., and Persson, Kristin A. Mon . "Elucidating the Solvation Structure and Dynamics of Lithium Polysulfides Resulting from Competitive Salt and Solvent Interactions". United States. doi:10.1021/acs.chemmater.7b00068.
@article{osti_1361977,
title = {Elucidating the Solvation Structure and Dynamics of Lithium Polysulfides Resulting from Competitive Salt and Solvent Interactions},
author = {Rajput, Nav Nidhi and Murugesan, Vijayakumar and Shin, Yongwoo and Han, Kee Sung and Lau, Kah Chun and Chen, Junzheng and Liu, Jun and Curtiss, Larry A. and Mueller, Karl T. and Persson, Kristin A.},
abstractNote = {Fundamental molecular level understanding of functional properties of liquid solutions provides an important basis for designing optimized electrolytes for numerous applica-tions. In particular, exhaustive knowledge of solvation structure, stability and transport properties is critical for developing stable electrolytes for fast charging and high energy density next-generation energy storage systems. Here we report the correlation between solubility, solvation structure and translational dynamics of a lithium salt (Li-TFSI) and polysulfides species using well-benchmarked classical molecular dynamics simulations combined with nuclear magnetic resonance (NMR). It is observed that the polysulfide chain length has a significant effect on the ion-ion and ion-solvent interaction as well as on the diffusion coefficient of the ionic species in solution. In particular, extensive cluster formation is observed in lower order poly-sulfides (Sx2-; x≤4), whereas the longer polysulfides (Sx2-; x>4) show high solubility and slow dynamics in the solu-tion. It is observed that optimal solvent/salt ratio is essen-tial to control the solubility and conductivity as the addi-tion of Li salt increases the solubility but decreases the mo-bility of the ionic species. This work provides a coupled theoretical and experimental study of bulk solvation struc-ture and transport properties of multi-component electro-lyte systems, yielding design metrics for developing optimal electrolytes with improved stability and solubility.},
doi = {10.1021/acs.chemmater.7b00068},
journal = {Chemistry of Materials},
number = 8,
volume = 29,
place = {United States},
year = {Mon Apr 10 00:00:00 EDT 2017},
month = {Mon Apr 10 00:00:00 EDT 2017}
}
  • Designing optimal electrolytes is key to enhancing the performance of energy storage devices,especially relating to cycle life, efficiency, and stability.1 Specifically, for future beyond-Li ion energy storage, there is still ample room for electrolyte improvements. Among the candidates for higher gravimetric energy storage, the Li-S battery is considered quite promising, owing to its theoretical specific energy density (2600 Wh/kg) and specific capacity (1675 mAh/g) and significantly lower cost as compared to state-of-art lithium-ion batteries.
  • A short linear peptide in solution may populate several stable states (denoted here microstates) in thermodynamic equilibrium. Elucidating its dynamic 3D structure by multidimensional nuclear magnetic resonance (NMR) is complex, since the experimentally measured nuclear Overhauser effect intensities (NOEs) represents averages. In previous papers we have developed a new theoretical methodology over the individual contributions based on statistical mechanical considerations for analyzing NMR data from flexible molecules and applied it to Leu-enkephalin(H-Tyr-Gly-Gly-Phe-Leu-OH) using the potential energy function ECEPP. Here we apply this methodology to the same molecule described by the ECEPP energy and a solvation free energy term for watermore » developed by Wesson and Eisenberg. This term is a summation over products of the solvent-accessible surface area of each atom and its solvation parameter. Since water is the most important solvent in biological systems, investigating the properties of this model is an imperative step in the development of our methodology. Thus, the energy barriers of the solvation model are expected to be lower than those of ECEPP alone; hence it is crucial to verify that the MC microstates of the former model are thermodynamically stable and structurally distinctive (i.e., they do not overlap). Criteria for these purposes, proposed in paper 2, are further developed her and applied to the MC microstates. 36 refs., 5 figs., 8 tabs.« less
  • The composition of the lithium cation (Li+) solvation shell in mixed linear and cyclic carbonate-based electrolytes has been re-examined using Born–Oppenheimer molecular dynamics (BOMD) as a function of salt concentration with ethylene carbonate:dimethyl carbonate (EC:DMC)-LiPF6 as a model system. A slight coordination preference for EC over DMC to a Li+ was found at low salt concentrations, while a slightly higher preference for DMC over EC was found at high salt concentrations. Analysis of the relative binding energies of the (EC)n(DMC)m-Li+ and (EC)n(DMC)m-LiPF6 solvates in the gas-phase and for an implicit solvent (as a function of the solvent dielectric constant) indicatedmore » that the DMC-containing Li+ solvates were stabilized relative to (EC4)-Li+ and (EC)3-LiPF6 by immersing them in the implicit solvent. Such stabilization was more pronounced in the implicit solvents with a high dielectric constant. Results from previous Raman and IR experiments were reanalyzed and reconciled by correcting them for changes of the Raman activities, IR intensities and band shifts for the solvents which occur upon Li+ coordination. After these correction factors were applied to the results of BOMD simulations, the composition of the Li+ solvation shell from the BOMD simulations was found to agree well with the solvation numbers extracted from Raman experiments. Finally, the mechanism of the Li+ diffusion in the (EC:DMC)LiPF6 mixed solvent electrolyte was studied using the BOMD simulations.« less
  • The composition of the lithium cation (Li +) solvation shell in mixed linear and cyclic carbonate-based electrolytes has been re-examined using Born–Oppenheimer molecular dynamics and Li +(EC) n(DMC) mcluster calculations.
  • The composition of the lithium cation (Li +) solvation shell in mixed linear and cyclic carbonate-based electrolytes has been re-examined using Born–Oppenheimer molecular dynamics and Li +(EC) n(DMC) mcluster calculations.