Li+Transport in Poly(Ethylene Oxide) Based Electrolytes: Neutron Scattering, Dielectric Spectroscopy, and Molecular Dynamics Simulations

Abstract

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.

Molecular diffusion and dc conductivity perfectly correlated with molecular rotational dynamics in a plastic crystalline electrolyte

“…In condensed phases other than ideal ionic solutions, the validity of the Walden rule was only reported in some disordered systems such as glass-forming supercooled liquids or polymers. 3 There is, however, a class of ordered solids in which molecular dynamics are extremely important, namely plastic crystals. Plastic crystals are molecular solids which display long-range translational order and dynamic orientational disorder.…”

Synergetic effect of TiO2 nano filler additives on conductivity and dielectric properties of PEO/PVP nanocomposite electrolytes for electrochemical cell applications

“…Polyethylene oxide (PEO) based polymer electrolytes have been employed extensively for battery applications since Armand et al have demonstrated the feasibility of using PEO as a potential ion conductive electrolyte [17]. PEO is one of the widely investigated host polymers used for synthesizing SPEs to employ in alkali metal ion-conducting batteries due to its high electrochemical stability, good solvation, complexation and ion dissociation abilities [18][19][20][21][22][23][24][25]. Several researchers have reported about various sodium salt complexes of PEO based polymer electrolytes for sodium ion battery applications [26,27].…”

Dynamics of Water Associated with Lithium Ions Distributed in Polyethylene Oxide

“…2(d)-(f). The trapped Li + in fact shows the Li + caged by the PEO due to the strong interaction between Li + and the oxygen atoms of PEO [24,70,71]. The segmental motion of PEO, which is determined by the solvent viscosity and temperature, promotes a longer residing time for the caged configuration [24].…”

“…The energy of neutrons and large incoherent scattering cross section of hydrogen made quasielastic neutron scattering a powerful tool for accessing dynamics of water in sub ps to ns time scales. By having similar length and time scales, atomistic MD simulation is a complimentary tool to neutron scattering to obtain experimentally inaccessible information such as atom positions and dynamics [24,35,36]. Here, we use quasielastic neutron scattering (QENS) and MD simulations to study a PEO/water mixture (wt% = 50%) with and without lithium salts (LiCl) (Molar ratio EO:Li + = 10:1).…”

“…For example, the forward rate of proton hopping in Nafion is known to be determined by the orientational dynamics of water near the polymer [21]. In solid polymer electrolyte batteries [22][23][24] based on poly (ethylene oxide) (PEO) and lithium, it has been reported that hydrating PEO increases the conductivity by as much as 1000 times that of the typical binary mixture of PEO/lithium salts [25,26]. Such enhancement was attributed to water absorption, which increases the mobility of PEO chains producing more free mobile ions by reducing the coordination between PEO and cations [26,27].…”