Poly Ethylene Oxide Electrolytes Research Articles

Preparation and Characterization of Hybrid Solid Electrolyte Consisted of Li Conductive Polyethylene Oxide and Inorganic Electrolyte Li7La3Zr2O12

All-solid-state lithium battery, which has higher energy density and safety than conventional lithium ion batteries are desired to stationary storage battery and electric vehicle battery. Solid polymer electrolyte (SPE) are one of candidate materials for all-solid-state lithium battery in term of high flexibility, compact, and the ability to prevent lithium dendrite formation.[1-2] Li7La3Zr2O12(LLZO) with garnet structure is most representive oxide-based inorganic electrolyte. and suitable stability for lithium metal anodes. Representive crystal structure of LLZO is reported cubic structure and tetragonal structure. Cubic LLZO shows relatively high ionic conductivity (10-4~10-3[S cm-1] ) at room temperature in oxide-based inorganic elctrolyte. Ionic conductivity of tetragonal phase is about 2 orders of magnitude lower than that for the cubic phase.[3-4] In this study, we prepared polyether-based polymer-LLZO composite electrolyte and measured temperature dependence of bulk ionic conductivity, interfacial resistance of Li/electrolyte and glass transition temperature (T g ) used by AC impedance method and differential scaning calorimetry (DSC). We investigated that the influence of LLZO additions for ionic conduction and thermal property by hybridization of LLZO and polyether-based solid polymer electrolyte. Experimental Preparation and characterization of hybrid solid electrolyte film Preparation of sample and cell preparation were examined in Ar-filled grovebox. LiTFSA was dissolved in polyether-based macromonomer solution ([Li] / [O] =0.1, amount of O was based on oxide unit from polyether). Tetragonal Li7La3Zr2O12 1.0wt% and 5.0wt%, DMPA (photoinitiator) and acetonitrile were added to the solution and stirred by stirrer. The solution was dried over 10h and obtained complete homogenerous solution. The solution was casted on glass plate and covered by two glass plate and 0.5mm teflon spacer. Hybrid solid electrolyte films were fabricated by radical photo polymerization under UV irradiation at 5 min. Characterization of hybrid solid electrolyte Ionic conductivity of hybrid solid electrolyte were measured by AC impedance method. Measurement samples were 12mm diameter disk. Frequence range is from 100kHz to 10mHz with a 500mV amplitude. Temperature range is -30 to 80 and all samples were thermally equilibrated at each temperature at least 1.5 h prior to the measurement. T g of hybrid solid electrolytes were measured by DSC measurement. The hybrid solid electrolyte films were cut into circle of 3mm diameter and enclosed into Al pans in the Ar-filled glovebox. The DSC measurements of hybrid solid electrolyte were conducted with the samples cooling to -100, followed by heating to 150 at cooling and heating rate of 10/min. The hybrid solid electrolyte films were cut into circle of 19mm diameter and then were sandwiched between Li metal nonblocking electrodes. These samples were enclosed into 2032 coin cell completely. Coin cells were settled in a constant temperature chamber at 60 over 100h to stabilize interface of Li/hybrid solid electrolyte. After that, temperature dependence of interfacial resistance of Li/hybrid solid electrolyte were mesured by AC impedance method under the same condition of ionic conductivity measurement. Results and discussion Fig.1 shows the temperature dependences of ionic conductivity for hybrid electrolyte. Ionic conductivity of the hybrid solid electrolyte showed larger values than that of LLZO free electrolyte. This tendency was remarkable in the case of low temperature. Fig. 2 shows DSC thermograms of hybrid solid electrolyte. T g of hybrid solid electrolyte were lower than LLZO free system. It is assumed that local segment motion of polymer were improved by interaction of between LLZO and matrix in polymer. Fig.3 shows temperature dependence of interfacial resistance of Li/hybrid solid electrolyte. Interfacial resistance of hybrid solid electrolyte composited 5.0wt% LLZO was lower than LLZO free system. It is assumed that solvation and desolvation reaction was promoted at Li/electrolyte interface by improving of local segment motion in matrix.

Comparing Two Electrochemical Approaches for Measuring Transference Numbers in Concentrated Electrolytes

We compare two experimental approaches for measuring the cation transference number in mixtures of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt: the well-established current-interrupt method proposed by Ma et al. [J. Electrochem. Soc., 142, 1859 (1995)], and a more recent method based on measuring the steady-state current proposed by Balsara and Newman [J. Electrochem. Soc., 162, A2720 (2015)]. In electrolytes comprised of high molecular weight PEO, the data from the two techniques agree, highlighting the equivalence of these two approaches. However, in lower molecular weight PEO electrolytes the values of the two approaches diverge at low salt concentrations. We posit this is because the approach of Ma et al. requires measurements that are sensitive to the nature of the interface between the electrolyte and the electrode. The transference numbers measured by the approach of Balsara and Newman for both low and high molecular weight samples vary from 0.7 to −0.8 and are within experimental error throughout the entire salt concentration window.

Electrochemical intercalation of fullerene and hydrofullerene with sodium

We herein report on the ability of fullerene C60 and hydrogenated fullerene C60Hx (x∼39) to operate as negative electrodes in novel Na-ion batteries. Building upon the known solubility of C60 in common organic electrolytes used in batteries, we developed a suitably optimized solid-state Na-(polyethylene oxide) electrolyte for this application. Electrochemical and structural properties of the fullerene electrodes were investigated through cyclic voltammetry, fixed-current charge/discharge of the electrodes, impedance spectroscopy and powder X-ray diffraction. Both C60 and hydrogenated C60 have been electrochemically intercalated with sodium. Specific capacities after the first cycle are 250 mAh g−1 and 230 mAh g−1 for C60 and C60Hx respectively. However, C60 electrode shows a strong irreversible character after the first discharge, probably due to the formation of stable polymeric NaxC60 phases, where Na+ ions diffusion is hindered. On the contrary, C60Hx displays better reversibility, suggesting that hydrogenation of the buckyball could be effective to preserve sufficiently large interstitial pathways for Na+ diffusion upon intercalation.

Towards improvement of the electrochemical properties of ionic liquid-containing polyethylene oxide-based electrolytes

We report an investigation on quaternary, polyethylene oxide (PEO)-based electrolytes as separators for lithium polymer batteries. The target is the development of Li+ conducting membranes, containing large fraction of the N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid, able to combine fast ion transport properties with improved electrochemical stability. The PEO electrolytes, prepared through a fully-dry solvent-free procedure, exhibited good aging resistance and conductivity values equal to 3.46×10−4 and 2.43×10−3Scm−1 at −20 and 20°C, respectively, combined with an anodic stability up to 4.5V (vs. Li°/Li+). These results represent the best performance, in terms of ion transport properties and electrochemical stability, reported till now for PEO electrolytes.

A Strategy to Make High Voltage LiCoO2 Compatible with Polyethylene Oxide Electrolyte in All-Solid-State Lithium Ion Batteries

Interface stability between cathode and electrolyte is closely related to the interface resistance and electrochemical performance of all-solid-state lithium ion batteries (LIBs). However, the significant interface issues between cathode and all-solid-state polymer electrolyte have been researched rarely. Here, we demonstrate that severe interface decomposition reactions occur continually and deteriorate the cycling life of high voltage LiCoO2/cellulose-supported poly(ethylene oxide) (PEO)-lithium difluoro(oxalato)borate (LiDFOB)/Li battery between 2.5 and 4.45 V vs. Li/Li+. To improve the interface stability between LiCoO2 and PEO-LiDFOB electrolyte, we modify the LiCoO2 surface by a thin layer of high ionic conducting and electrochemical oxidation resistant poly(ethyl cyanoacrylate) (PECA) through in-situ polymerization method. The PECA coating layer significantly suppresses the continuous decomposition of lithium difluoro(oxalato)borate (LiDFOB) salt in PEO electrolyte. As a result, the PECA-coated LiCoO2/PEO-LiDFOB/Li battery shows decreased interface resistance and enhanced cycling stability. This work will enlighten the understanding of interface stability and enrich the modification strategy between cathode and polymer electrolyte as well as boost the further development of all-solid-state LIBs.

Polyethylene oxide and ionic liquid-based solid polymer electrolyte for rechargeable magnesium batteries

Solid polymer electrolytes (SPEs) based on polyethylene oxide (PEO) complexed with magnesium triflate Mg(Tf)2 or Mg(CF3SO3)2) and incorporating the ionic liquid (IL) (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI)) were prepared by solution cast technique. The electrolyte was optimized and characterized using electrical conductivity, cationic transport number measurements, and cyclic voltammetry. The highest conductivity of the PEO/Mg(Tf)2, 15:1 (molar ratio), electrolyte at room temperature was 1.19 × 10−4 S cm−1 and this was increased to 3.66 × 10−4 S cm−1 with the addition of 10 wt.% ionic liquid. A significant increase in the Mg2+ ion transport number was observed with increasing content of the ionic liquid in the PEO-Mg(Tf)2 electrolyte. The maximum Mg2+ ion transport number obtained was 0.40 at the optimized electrolyte composition. A battery of the configuration Mg/ and [(PEO)15:Mg(Tf)2+10%IL]/TiO2-C was assembled and characterized. Preliminary studies showed that the discharge capacity of the battery was 45 mA h g−1.

A low-cost, high-energy polymer lithium-sulfur cell using a composite electrode and polyethylene oxide (PEO) electrolyte

Herein, we report a polymer cell using high-energy lithium metal anode, a composite sulfur-carbon cathode, and polyethylene oxide (PEO)-lithium trifluoromethan sulfonate (LiCF3SO3) electrolyte. The limited cost of raw materials as well as the very simple synthetic procedures, involving planetary ball milling (for S-C cathode) and solvent casting (for PEO-electrolyte), are expected to reflect into remarkable reduction of the economic impact of the proposed battery. Furthermore, the high energy of the Li-S cell and safety of the polymer configuration represent additional bonuses of the system. The S-C material, revealing a maximum capacity as high as 700 mAh g−1 in liquid electrolyte, is employed in a lithium-sulfur battery with the polymer configuration. The polymer cell delivers a capacity of 450 mAh g−1 at a voltage of about 2 V; hence, a theoretical energy density of 900 Wh kg−1 that may reflect into a high practical value, suitable for energy storage applications.

Influence of nanoparticle-ion and nanoparticle-polymer interactions on ion transport and viscoelastic properties of polymer electrolytes.

We use atomistic simulations to probe the ion conductivities and mechanical properties of polyethylene oxide electrolytes containing Al2O3nanoparticles. We specifically study the influence of repulsive polymer-nanoparticle and ion-nanoparticle interactions and compare the results with those reported for electrolytes containing the polymorph β-Al2O3nanoparticles. We observe that incorporating repulsive nanoparticle interactions generally results in increased ionic mobilities and decreased elastic moduli for the electrolyte. Our results indicate that both ion transport and mechanical properties are influenced by the polymer segmental dynamics in the interfacial zones of the nanoparticle in the ion-doped systems. Such effects were seen to be determined by an interplay between the nanoparticle-polymer,nanoparticle-ion, and ion-polymer interactions. In addition, such interactions were also observed to influence the number of dissociated ions and the resulting conductivities. Within the perspective of the influence of nanoparticles on the polymer relaxation times in ion-doped systems, our results in the context of viscoelastic properties were consistent with the ionic mobilities. Overall, our results serve to highlight some issues that confront the efforts to use nanoparticle dispersions to simultaneously enhance the conductivity and the mechanical strength of polymer electrolyte.

Simulation of synaptic short-term plasticity using Ba(CF3SO3)2-doped polyethylene oxide electrolyte film.

The simulation of synaptic plasticity using new materials is critical in the study of brain-inspired computing. Devices composed of Ba(CF3SO3)2-doped polyethylene oxide (PEO) electrolyte film were fabricated and with pulse responses found to resemble the synaptic short-term plasticity (STP) of both short-term depression (STD) and short-term facilitation (STF) synapses. The values of the charge and discharge peaks of the pulse responses did not vary with input number when the pulse frequency was sufficiently low(~1 Hz). However, when the frequency was increased, the charge and discharge peaks decreased and increased, respectively, in gradual trends and approached stable values with respect to the input number. These stable values varied with the input frequency, which resulted in the depressed and potentiated weight modifications of the charge and discharge peaks, respectively. These electrical properties simulated the high and low band-pass filtering effects of STD and STF, respectively. The simulations were consistent with biological results and the corresponding biological parameters were successfully extracted. The study verified the feasibility of using organic electrolytes to mimic STP.

Quaternary Polyethylene Oxide Electrolytes Containing Ionic Liquid for Lithium Polymer Battery

Herein we report a comparative study of quaternary polymer electrolyte membranes, comprising polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonyl)imide, LiTFSI(salt), SiO2-filler and N-methyl-N-butyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr1,4TFSI) ionic liquid. The membranes are developed in view of an efficient application in polymeric lithium battery. The study shows improvement of the ionic conductivity and the stability of the lithium interphase by increasing the Pyr1,4TFSI content up to 20% wt, as revealed by Arrhenius conductivity plots, electrochemical impedance spectroscopy as well as by cyclic test in symmetrical lithium cell. This trend is directly reflected in enhanced behavior of lithium polymer cell using LiFePO4, in terms of delivered capacity. Furthermore, the measurement indicated that setting up a proper amount of added IL is a key requirement for an optimal behavior of the electrolyte in battery.

Preparation and characterization of hot-pressed Li+ ion conducting PEO composite electrolytes

Preparation and characterization of hot-pressed Li+ ion conducting Polyethylene oxide (PEO) composite electrolytes are discussed in this paper. Lithium trifluoromethanesulfonate with linear formula CF3SO3Li is selected as Li+ ion source for polymer composite electrolyte processing. Polyethylene oxide as matrix for polymer electrolyte is selected, because of its cation solvatation and salt complexes formation partibility. Nano-sized fillers such as carbon nanotube (CNT) and graphene (GR) are introduced to polymeric composite to improve PEO electrolyte mechanical properties. The composites were prepared from PEO, CF3SO3LP CNT and GR by solution casting and by hot-pressing method. Influence of CF3SO3LP CNT and GR concentrations on the electrical, thermal and mechanical properties of PEO composite is investigated and discussed. The additives addition to the PEO matrix improves the electrical, thermal and mechanical properties of the composite. The crystallinity of the PEO decreases.

Strange discharge current transients in polyethylene oxide

The polarization and the depolarization current after application of a voltage step are investigated in the solid electrolyte polyethylene oxide. For low applied fields the current density follows a Kohlrausch behavior, i.e. j α fα, in the long time range during the polarization and the depolarization process respectively. By using sufficiently high applied fields charge injection sets in and the current during the polarization process is nearly constant at long times. It turns out that the transient depolarization current in this case shows a pronounced unforeseen maximum. The time to the maximum as well as the height of the current peak depend on the field applied before, the polarization time, the temperature, the LiClO4 doping, the electrode material, and the sample length. Simulations carried out using a discrete three-dimensional hopping model reveal qualitatively comparable results. It is concluded that the injection and later extraction of excess electrons according to Lindmayer's theorem is responsible for the appearance of the current maximum.

Polyethylene oxide electrolyte added by silane-functionalized TiO2 filler for lithium battery

Titanium dioxide ceramic functionalized with silane organic group is used here to improve polyethylene oxide electrolyte properties. The results demonstrate the effective role of the silane coating in enhancing the polymer–ceramic interactions and, consequently, the polymer electrolyte properties for application in lithium polymer battery. The ceramic added electrolyte shows conductivity higher than 10−4Scm−1 above 65°C and a transference number approaching 0.5. The electrolyte membrane is then selected as the polymer separator in a lithium cell using LiFePO4 electrode, characterized by enhanced behavior in terms of capacity, cycling stability and efficiency.

Effects of ionic liquids on cation dynamics in amorphous polyethylene oxide electrolytes

We perform extensive molecular dynamics simulations of a poly(ethylene oxide)-based polymer electrolyte material containing lithium bis(trifluoromethanesulfonyl)imide salt for a wide temperature regime above and below the experimental crystallization temperature with and without N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid (IL). The impact of the IL-concentration on the cation dynamics is studied. The increase of the cation mobility upon addition of IL is significant but temperature-independent. This can be related to distinct variations of the underlying transport properties as expressed within the previously introduced transport model of polymer electrolytes. Even for the largest IL concentration the transport model perfectly predicts the non-trivial time-dependence of the cationic mean square displacement for all temperatures. Finally, we compare our numerical and theoretical findings with the results of recent nuclear magnetic resonance experiments. In this way we can exclusively relate the strong experimentally observed dependence of the low-temperature Li-diffusivity on the IL concentration to the impact of IL on crystallization.

Stretching Ion Conducting Polymer Electrolytes: In-Situ Correlation of Mechanical, Ionic Transport, and Optical Properties

In this work we perform mechanical stretching tests while monitoring optical and ionic transport properties of ion-intercalated semi-crystalline polyethylene-oxide (PEO) electrolytes in-situ. Utilizing ionic liquid (EMIBF4) – PEO electrolytes, we demonstrate a correlation between the degree of crystallinity, which depends on the ion concentration, and the Young's modulus, ultimate tensile strength, and yield stress. Upon stretching solid-state PEO electrolytes, we observe an anisotropic increase in ionic conductivity that we correlate to the optical polarized Raman spectroscopic and microscopic signatures of polymer domain alignment - especially notable in the plastic regime. In-situ Raman spectroscopic studies indicate mechanically-induced ionic transport effects originate from chemical and structural rearrangement of polymer chains, and are independent of the ion species utilized. To emphasize this, we demonstrate the ideas of this study to be similarly transferrable to LiPF6 and LiI/I2 intercalated PEO solid-state electrolytes which exhibit similar mechanical-ionic transport response as ionic liquids. This study lays the groundwork for studying the mechanochemistry of solid-state electrolytes, with relevance toward specific electrolyte configurations employed in supercapacitors, lithium ion batteries, and dye sensitized solar cells.

Ion Transport and Switching Speed in Redox-Gated 3-Terminal Organic Memory Devices

The dynamics of redox gated organic memory devices based on dynamic doping of polythiophene were examined in detail in order to improve “write” and “erase” speed and determine ultimate performance. A 3-terminal geometry similar to a field effect transistor provided a source/gate circuit which reversibly oxidized a polythiophene polymer to cause a large increase in conductance between the source and drain electrodes. The devices were cycled for >1000 complete R/W/R/E cycles, and operated at relatively low voltage compared to commercial “flash” memory. The “write” and “erase” speeds were improved by a factor of >100 by using a spin-coated electrolyte layer and by small increases in device temperature. The influence of charging current and polaron propagation on response time were determined to be minor, with the rate limiting process being identified as the rate of conducting polaron generation. The main factor determining the W/E time was the mobility of ions in the polyethylene oxide electrolyte layer, which resulted in resistance losses during the application of the S-G “write” pulse. Response time was strongly dependent on the atmosphere, with water or acetonitrile vapor significantly increasing the rate of polaron generation. The results are important for design of molecular memory devices based on dynamic doping, and indicate likely avenues for further performance improvements.

Monte Carlo simulation of ionic conductivity in polyethylene oxide

Abstract A Monte Carlo (MC) model to incorporate the effect of Al2O3 with different particle sizes in enhancing the ionic conductivity of composite polymer electrolytes consisting of polyethylene oxide (PEO), lithium trifluoromethanesulfonate (LiCF3SO3), and ethylene carbonate (EC), is proposed. The simulated ionic conductivity in our MC model is validated by the results of electrochemical impedance spectroscopy, which determined the room temperature ionic conductivity of various composite electrolyte samples differing from the size of the Al2O3 prepared via the solution cast method. With the simulated current density and recurrence relation, cation transference numbers, t+si of composite polymer electrolytes were derived using the steady-state current method proposed by Bruce et al. Addition of Al2O3 (≤10 μm) in micron size greatly enhances the ionic conductivity to a magnitude of two orders, i.e., from 2.9025×10-7 S/cm to 2.970×10-5 S/cm and doubles the cation transference number from 0.230 to 0.465. However, the addition of Al2O3 (<50 nm) in nano size decreases both the ionic conductivity and the cation transference number. The smaller size of Al2O3 in the nano range is responsible for the congestion on the conducting pathways that traps some of the Li+ in PEO electrolytes.

Bi-continuous phases structured nanocomposite polymer electrolytes: Facile preparation and electrochemical properties

Abstract In this paper, inspired by the cubic bi-continuous gyroid structure self-assembled by block copolymers, we start with the application of a novel and more facile approach, compared to the tedious synthetic procedures of block copolymers, to prepare the bi-continuous phases structured nanocomposite electrolytes. The bi-continuous phase structure is composed of a hard phase of the electrospun poly vinylidene fluoride (PVDF) non-woven scaffold providing the mechanical support for the electrolyte membranes and another soft phase built up then by the infiltration of polyethylene oxide (PEO) electrolyte into the PVDF scaffold membrane to be the ionic conducting phase. Therefore, the nanocomposite polymer electrolytes of the bi-continuous phase structure are prepared with addition of the different amounts of TiO 2 nanoparticles into the PEO electrolyte (containing LiClO 4 ). The nanocomposite electrolyte membranes have systematically been characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), X-ray diffraction (XRD), and tensile test. The tensile results indicate that the infiltration of PEO phase into the PVDF scaffold can greatly improve the elongation of the electrolyte membrane at break, but the tensile strength of the electrolyte membrane is substantially dependent on the electrospun PVDF scaffold. The ionic conductivity measurements show that addition of TiO 2 nanoparticles with an appropriate amount of ca . 10 wt% enhances the ionic conductivity of the nanocomposite electrolytes to 7.60 × 10 −5 S cm −1 at 60 °C, compared to 8.33 × 10 −6 S cm −1 at 60 °C of the PEO–LiClO 4 electrolyte. The effect of TiO 2 nanoparticles on the enhancement of Li + ion conductivity has been investigated by attenuated total reflectance-Fourier transform infrared spectra (ATR-FTIR), and the results show that a competitive interaction between TiO 2 nanoparticles and Li + ions weakens to some extent the existing complexing action of ether-O…Li + , allowing Li + ions faster transfer. However, we have found by high-resolution transmission electron microscopy (HRTEM) that the real dispersion state of TiO 2 nanoparticles in the nanocomposite electrolytes is in the form of large aggregates instead of the individual primary nanoparticles, which would tremendously depress the surface effect of the individual nanoparticles and greatly impact on the enhancement of the ionic conductivity.

The influence of interface polarization on the determination of lithium transference numbers of salt in polyethylene oxide electrolytes

Lithium transference numbers, salt diffusion coefficients and effective lithium conductivities are investigated with the steady state polarization method for poly(ethylene oxide) (PEO) based polymer electrolytes containing lithium bis(oxalato)borate (LiBOB) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). We compare the commonly used evaluation technique with our approach. Here, the focus is laid on the potential relaxation of the polarized sample which delivers information about the salt diffusion and the potential distribution in symmetric Li/electrolyte/Li cell. The new approach circumvents the well-known initial current issue and thus increases the reliability of the experiment. The temperature dependence of the lithium transference numbers and the importance of data acquisition time are also discussed. The highest lithium transference numbers are 0.19 for P(EO)60·LiTFSI at 90 °C.

Carbon nanotube and graphite oxide surfaces modified with polyethylene oxide for dye-sensitized solar cells

In this study, the photovoltaic properties of the dye sensitized solar cells (DSSCs) were enhanced by the incorporation of the polyethylene oxide (PEO) intercalated graphite oxides sheets (GO-P) or PEO surface grafted carbon nanotubes (CNT-P) into the PEO gel electrolytes. The PEO modified carbon materials were served as the extended electron transfer materials, and the catalysts for the electrochemical reduction of I3−. The ionic conductivity of PEO gel electrolyte was not significantly influenced by the incorporation of GO-P or CNT-P. Because of the high catalytic activities, the incorporation of GO-P or CNT-P into the gel electrolyte is favorable for decreasing the charge transfer and recombination resistances. Therefore, better PV performance was observed for the DSSCs based on the GO-P/PEO or CNT-P/PEO electrolytes as compared to the PEO electrolyte based DSSCs. The photoelectric conversion efficiencies of DSSCs were respectively enhanced by 19 % and 32 % via the incorporations of GO-P and CNT-P.