Effects of Anion Mobility on Electrochemical Behaviors of Lithium-Sulfur Batteries

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1 Effects of Anion Mobility on Electrochemical Behaviors of thium-sulfur Batteries Kee Sung Han*,#, Junzheng Chen,#, Ruiguo Cao,#, Nav Nidhi Rajput,,# Vijayakumar Murugesan,,#, li Shi,,# Huilin Pan,,# Ji-Guang Zhang*,#, Jun u,# Kristin A. Persson,,# and Karl T. Mueller*,# Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, United States Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States Energy and Environmental Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, Unites States Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, United States Department of Materials Science & Engineering, University of California, Berkeley, CA , United States # Joint Center for Energy Storage Research (JCESR), Lemont, IL 60439, United States Classical Molecular Dynamics Simulations Classical molecular dynamics (MD) simulations were conducted using GROMACS MD simulation package version for 0.25 M, 1M, and 3 M TFSI in / solvent mixture. 1 The initial configuration is minimized in two steps first using steepest descent employing a convergence criterion of 1000 kcal/mol*å, and then a conjugated-gradient energy minimization scheme employing a convergence criterion of 10 kcal/mol*å. The systems were equilibrated in the isothermal-isobaric ensemble (constant NPT) using the Berendsen barostat to maintain the pressure of 1 bar with a time constant of 2 ps for 2 ns. 2 All systems were then melted at 400 K for 2 ns and subsequently annealed from 400 to 298 K in three steps for 3 ns. Finally, the production runs of 20 ns were then obtained in the canonical ensemble (NVT) using an improved velocity-rescaling algorithm proposed by Parrinello et al. with a time constant of 0.1 ps at 298 K. The bonded and non-bonded parameters for and are taken from General Amber Force Field (GAFF), for TFSI - anions from Kelkar et al. and lithium from Sano et al. 3-4 The partial atomic charges for all molecules were derived by first optimizing the geometry using Becke s threeparameter exchange function combined with Lee-Yang-Parr correlation functional (B3LYP) at aug-ccpvdz theory level using the Gaussian 09 package 5 and then fitting the electrostatic potential surface using the RESP method. Other simulation details are very close to those contained in our previous publication. 6 Materials TFSI, TfO,, and (all in battery-grade purity) were ordered from BASF Battery Materials and used as received. FSI was obtained from Nippon Shokubai and used as received. Sulfur powder (purity 99.5%), N-methyl-2-pyrrolidone (NMP), and lithium nitrate (NO 3 ) were acquired from Sigma-Aldrich. S1

2 Multi-walled carbon nanotubes (MWCNTs, nm in diameter) were purchased from Cheap Tubes Inc. High-purity chips with dimensions of 15.6 mm diameter and 0.45 mm thickness were obtained from MTI Corporation. For viscosity measurements, FSI salt was obtained from Nippon Shokubai Co., Ltd. 1. Martínez, L.; Andrade, R.; Birgin, E. G.; Martínez, J. M., Packmol: A package for building initial configurations for molecular dynamics simulations. J. Computational chem. 2009, 30, Bussi, G.; Zykova-Timan, T.; Parrinello, M., Isothermal-isobaric molecular dynamics using stochastic velocity rescaling. J. Chem. Phys. 2009, 130, Takeuchi, M.; Kameda, Y.; Umebayashi, Y.; Ogawa, S.; Sonoda, T.; Ishiguro, S.-i.; Fujita, M.; Sano, M., Ion ion interactions of PF 6 and BF 4 in propylene carbonate solutions. J. Mol. q. 2009, 148, Kelkar, M. S.; Maginn, E. J., Effect of temperature and water content on the shear viscosity of the ionic liquid 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide as studied by atomistic simulations. J. Phys. Chem. B 2007, 111, Frisch, M.; Trucks, G.; Schlegel, H.; Scuseria, G.; Robb, M.; Cheeseman, J.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G., gaussian 09, Gaussian. Inc., Wallingford, CT 2009, Rajput, N. N.; Qu, X.; Sa, N.; Burrell, A. K.; Persson, K. A., The Coupling between Stability and Ion Pair Formation in Magnesium Electrolytes from First-Principles Quantum Mechanics and Classical Molecular Dynamics. J. Am. Chem. Soc. 2015, 137, S2

3 D (m 2 s -1 ) D (m 2 s -1 ) D (m 2 s -1 ) D (m 2 s -1 ) neat / (1:1 vol.) neat / (1:1 vol.) M FSI FSI M TfO TfO M FSI M 2 S 8 FSI 3 M FSI a FSI D a 1 M TfO M 2 S 8 TfO 3 M TfO b TfO /T (K -1 ) a neat / (1:1 vol.) neat / (1:1 vol.) M TFSI TFSI M TDI TDI c 1 M TFSI M 2 S 8 TFSI 3 M TFSI TFSI d 1 M TDI M 2 S 8 TDI D /T (K -1 ) Figure S1. Diffusion coefficients of each component for neat solvent (/; 1:1 vol.), 1 M salt dissolved in / with and without 0.12 M 2 S 8 and 3 M salt dissolved in / using supporting salt: a) FSI, b) TfO, c) TFSI and d) TDI. S3

4 FSI - TfO - TDI - TFSI - Figure S2. The size of solvent molecules and anions. The polar surface area (A) of and is 18.5 Å 2, which gives the radius of 2.43 Å (r = (A/π) 1/2 ). The polar surface area of and molecules obtained from the National Center for Biotechnology Information, and for and, respectively. S4

5 Figure S3. DFT Optimized configurations for the -3 and -4 solvates (-purple, O-red, C-gray) (ball-and-stick and spacefill images shown). thium solvate structures were analyzed using density functional theory (DFT)-based calculations with the ADF-2014 package. All of the calculations were done at the PBE theory level with dispersion correction (D3) using the TZP (all-electron valence triple zeta with polarization function) Slater-type basis set without any geometrical constraints2. To capture the solvent ensemble effect, COSMO (an implicit solvent model3) was employed with dielectric constants (ε) of 7.2. Initially, the + cation solvates with either or solvent molecules alone were analyzed separately. For the global energy minimum structures, the + cation were solvated by either three molecules or four molecules. The bonding energy difference between the solvated + cation and isolated + cation and pure solvent molecules reveals that the solvated + cation (~298 kj mol-1) is more than twice as energetically favorable as the solvation by four solvent molecules (~128 kj mol-1). This indicates that for the / mixture, the + cation are likely to be preferentially solvated by the molecules rather than the molecules. S5

6 a TDI 1 M salt 1 M salt M 2 S 8 b TFSI TFSI - (2) (1) c 4 M FSI FSI - TFSI FSI 3 M FSI FSI TfO TfO - 4 M TfO TfO neat / ( 17 O) (ppm) neat / ( 17 O) (ppm) 3 M TfO ( 17 O) (ppm) Figure S4. 17 O NMR spectra obtained from a) 1 M salt dissolved in / (1:1 vol.) electrolytes with and without 0.12 M 2 S 8, b) from 3 M salt dissolved in / electrolytes, which show the largely down-field shifted peak, (2) and the suppression of the intensities of 17 O peaks (ca. 150 ppm) from TfO - and TFSI - anions and c) from 4 M salt dissolved in / electrolytes, which showed (1) resonances shifted to down field and merged to (2) peaks. S6

7 ( 17 O) (ppm) Anion Volume (Å 3 ) Intensity (%) Anion Volume (Å 3 ) ( 17 O) Anion Volume Intensity Anion Volume a b TfO - FSI - TFSI - Aions TfO - FSI - TFSI - Anions 100 Figure S5. a) δ( 17 O) and b) peak intensity of (2), in Figure S4, relative to the total peak intensity for 3 M salt concentration electrolytes are plotted with the anion volume. S7

8 D (m 2 /s) -1 (mpa -1 s -1 ) D (10-7 cm 2 /s) -1 (mpa s -1 ) 10-9 (a) TFSI G3 HFE -1 (b) anion FSI 1-TfO 1-TFSI 3-TfO 3-TFSI 3-FSI Samples x (G3/TFSI) 0.00 Figure S6. Comparisons of diffusion coefficient and the inverse of viscosity (η -1 ): (a) D and η -1 at 30 C for the electrolytes studied in this work and (b) D HFE and η -1 for the TFSI dissolved in G3/HFE (the data obtained from H. Moon, et al., J. Phys. Chem. C 2015, 119, ). The diffusion of hydrofluoroether (D HFE ) is inversely proportional to the viscosity of the solutions because the interactions of HFE molecules with other components of the electrolyte are relatively weaker. For the electrolytes studied in this work it is difficult to estimate the interactions of to other components of electrolyte by the comparisons of D and η -1 due to a larger deviation in viscosity values. But we confirmed that the diffusion coefficients of these electrolytes are globally proportional to the inverse of viscosity (η -1 ) as predicted by the Stokes-Einstein relation of diffusion. S8

9 g(r) (arb. unit) g(r) (arb. unit) g(r) (arb. unit) 25 (a) 20 -_0.25 M -_1 M -_3M 25 (b) 20 -_0.25 M -_1M -_3 M r (Å) r (Å) (c) TFSI_0.25 M -TFSI_1 M -TFSI_3 M r (Å) Figure S7. The radial distribution functions (RDF) of (a) + -, (b) + - and (c) + -TFSI in 0.25, 1 and 3 M TFSI dissolved in / (1:1 vol.) dissolved in / (1:1 vol.). S9

10 Figure S8. Specific capacity retention plot for -S cells fabricated with 1 M (a) and 3 M (b) salt dissolved in / (1:1 vol.) electrolytes. S10

11 SC (mah g -1 ) SC (mah g -1 ) at 33th cycle at 100th cycle a D /D at 33th cycle at 100th cycle b D /D Figure S9. Specific capacity, SC at 33 th and 100 th cycles in -S batteries fabricated with the electrolytes composed of 1 M or 3 M salt (FSI, TfO, TFSI or TDI) dissolved in / (1:1 vol) plotted as a function of a) D /D and D /D. S11

12 M salt 1 M salt M 2 S 8 3 M salt 2.4 r s, /r FSI - TfO - TFSI - TDI - anions Figure S10. The calculated r s, /r for 1 M salt dissolved in / (1:1 vol.) electrolytes with and without 0.12 M 2 S 8 and for 3 M salt dissolved in / electrolytes are plotted along with a kind of anions. S12

Solvation Structure and Dynamics of Lithium Polysulfides

Supplemental Information Solvation Structure and Dynamics of Lithium Polysulfides Nav Nidhi Rajput 1,5 *, Vijayakumar Murugesan 2,5, Yongwoo Shin 1, Kee Sung Han 2,5, Kah Chun Lau 3,4, Junzheng Chen 2,