Li+ transport in poly(ethylene oxide) based electrolytes: neutron scattering, dielectric spectroscopy, and molecular dynamics simulations.

The dynamics of Li(+) transport in polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imde mixtures are investigated by combining neutron spin-echo (NSE) and dielectric spectroscopy with molecular dynamics (MD) simulations. The results are summarized in a relaxation time map covering wide ranges of temperature and time. The temperature dependence of the dc conductivity and the dielectric α relaxation time is found to be identical, indicating a strong coupling between both. The relaxation times obtained from the NSE measurements at 0.05 Å(-1)<q<0.2 Å(-1) are of similar magnitude as the relaxation time of Li(+) predicted by MD simulation. Our results suggest that the characteristic live times of the ions within the oxygen cages are mainly determined by the α relaxation that corresponds to local segmental motions of polymers, to a much lesser extent by the main chain relaxation, and not at all by the β relaxation or other faster processes. It is the first time decisive experimental evidence for a microscopic picture of the Li ion transportation process is shown in which the PEO chain forms EO cages over several monomer units and the Li ion "jump" from cage to cage. The role of the backbone of the polymer is discussed and contributes signifcantly to the Li ion transportation process. Moreover, detailed characteristic length and time scales of the Li(+) transport process in this polymer electrolyte are identified and interpreted.

[1]  K. Shuler.  Advances in Chemical Physics: Stochastic Processes in Chemical Physics , 1969 .

[2]  Martin Goldstein,et al.  Viscous Liquids and the Glass Transition. II. Secondary Relaxations in Glasses of Rigid Molecules , 1970 .

[3]  G. Fulcher,et al.  ANALYSIS OF RECENT MEASUREMENTS OF THE VISCOSITY OF GLASSES , 1925 .

[4]  High-frequency dynamics of type B glass formers investigated by broadband dielectric spectroscopy , 2010, 1004.5145.

[5]  P. Lunkenheimer,et al.  Dielectric and conductivity relaxation in mixtures of glycerol with LiCl , 2008, The European physical journal. E, Soft matter.

[6]  Oleg Borodin,et al.  Mechanism of Ion Transport in Amorphous Poly(ethylene oxide)/LiTFSI from Molecular Dynamics Simulations , 2006 .

[7]  B. Scrosati,et al.  Nanocomposite polymer electrolytes for lithium batteries , 1998, Nature.

[8]  M. Armand,et al.  Issues and challenges facing rechargeable lithium batteries , 2001, Nature.

[9]  P. Bruce,et al.  Nanostructured materials for advanced energy conversion and storage devices , 2005, Nature materials.

[10]  Friedrich Kremer,et al.  Broadband dielectric spectroscopy , 2003 .

[11]  K. Shuler,et al.  Stochastic processes in chemical physics , 1969 .

[12]  Janna K. Maranas,et al.  Effect of LiClO4 on the Structure and Mobility of PEO-Based Solid Polymer Electrolytes , 2009 .

[13]  J. Colmenero,et al.  Single Chain Dynamic Structure Factor of Poly(ethylene oxide) in Dynamically Asymmetric Blends with Poly(methyl methacrylate). Neutron Scattering and Molecular Dynamics Simulations , 2012 .

[14]  Janna K. Maranas,et al.  Structure and mobility of PEO/LiClO4 solid polymer electrolytes , 2009 .

[15]  W. V. Gunsteren,et al.  Computer simulation of a polymer electrolyte: Lithium iodide in amorphous poly(ethylene oxide) , 1995 .

[16]  K. S. Nahm,et al.  Review on composite polymer electrolytes for lithium batteries , 2006 .

[17]  P. Bruce,et al.  Ionic conductivity in crystalline polymer electrolytes , 2001, Nature.

[18]  G. Tammann,et al.  Die Abhängigkeit der Viscosität von der Temperatur bie unterkühlten Flüssigkeiten , 1926 .

[19]  J. Goodenough.  Challenges for Rechargeable Li Batteries , 2010 .

[20]  Price,et al.  Structure of liquid PEO-LiTFSI electrolyte , 2000, Physical review letters.

[21]  J. Dygas,et al.  Conductivity and dielectric properties of polymer electrolytes PEO:LiN(CF3SO2)2 near glass transition , 2007 .

[22]  M. Armand,et al.  α-Relaxation in PEO-LiTFSI polymer electrolytes , 2002 .

[23]  A. Sokolov,et al.  Decoupling of ionic transport from segmental relaxation in polymer electrolytes. , 2012, Physical review letters.

[24]  M. Armand,et al.  Nuclear magnetic relaxation study of poly(ethylene oxide)–lithium salt based electrolytes , 1993 .

[25]  J. Colmenero,et al.  Study of the dynamics of poly(ethylene oxide) by combining molecular dynamic simulations and neutron scattering experiments. , 2009, The Journal of chemical physics.

[26]  David L. Price,et al.  Relaxation in polymer electrolytes on the nanosecond timescale , 2000, Nature.

[27]  J. Dygas,et al.  Influence of crystallization on dielectric properties of PEO:LiTFSI polymer electrolyte , 2006 .