Ionic Conductivity Of Polyethylene Oxide Research Articles

Polymers for aluminium secondary batteries: Solubility, ionogel formation and chloroaluminate speciation

This work deals with the search of polymers apt for the preparation of solid-like chloroaluminate-based electrolytes. To accomplish this, the solubility and gelling ability of a large set of polymers in the deep eutectic solvent AlCl3:urea (uralumina) are studied, followed by the characterization of the electrochemical activity of the gels. The polymers are directly dissolved in urea:AlCl3 without auxiliary solvents following a fast and scalable gel preparation methodology previously reported for ultra-high molecular weight (UHMW) polyethylene oxide (PEO). The list of polymers studied includes diverse chemical structures, different thermal properties and different aggregation states at the mixing temperature of 70 °C, defined by the thermal stability of AlCl3:urea. To avoid a molecular weight influence on the ionogel rheological properties, polymers with molecular weight close to 100,000 g mol−1 have been chosen. The polymers considered include poly(ε-caprolactone) (PCL), poly(dimethyl siloxane) (PDMS), poly(vinyl pyrrolidone) (PVP), polyformal, thermoplastic polyurethanes, polymethacrylates, polyacetates and the elastomer SEBS. It was found that together with polyethylene oxide, only poly(ε-caprolactone) and poly(dimethyl siloxane) are soluble and produce gel electrolytes with AlCl3:urea. The solubility rules of polymers in chloroaluminates are discussed. The stripping/plating of Al and the ionic conductivity of PEO, PDMS and PCL ionogels are studied by cyclic voltammetry and impedance spectroscopy. PDMS proves to be as efficient as PEO to produce ionogels at low polymer concentration, that are also self-standing and electroactive, whereas a higher concentration of PCL is required to produce self-standing gels. The molecular structure of the ionogels and the modification of the chloroaluminate speciation is studied by vibrational spectroscopies, and supported by DFT calculations.

Promotion of Ionic Conductivity of PEO-Based Solid Electrolyte Using Ultrasonic Vibration.

All solid-state lithium-ion batteries based on polymer electrolytes have higher safety and energy density, but the low conductivity of lithium ion restricts its application. This study proposes a new method to promote the ionic conductivity of polyethylene oxide (PEO)-based solid electrolytes. In this method, the PEO-based solid electrolyte was first prepared by casting, and then power ultrasound was exerted on the electrolyte by a sandwich structure to modify the electrolyte structure. Through analysis of the performance and microstructure of the electrolyte, it was found that the ultrasonic treatment increased the ionic conductivity by 78%, improved tensile strength and plastic deformation ability, but did not affect the thermal stability and the chemical composition. The ultrasonic vibration, exerting high energy to the solid electrolyte through high-frequency vibration, broke PEO grains and melted them with the frictional heat at boundary. Due to the slight melting and fast solidifying produced by the pulsed ultrasonic treatment, the crystallization was suppressed. The crystallinity was thus reduced by 6.2%, which increased the migration channels of lithium ions and reduced the tortuosity effect. Furthermore, the ultrasonic vibration compressed the electrolyte to produce plastic flow of the material, which made the electrolyte structure more compact. The density of ethylene oxide (EO) units thus increased in the amorphous phase, providing multiple electron-donor coordination sites for the Li+. The hopping distance of the ion between donors decreased, which also facilitated the migration. In addition, the mechanical performance of the electrolyte membrane improved. This study provides a reference for the improvement of polymer based all-solid-state batteries.

Restricted lithium ion dynamics in PEO-based block copolymer electrolytes measured by high-field nuclear magnetic resonance relaxation.

The intrinsic ionic conductivity of polyethylene oxide (PEO)-based block copolymer electrolytes is often assumed to be identical to the conductivity of the PEO homopolymer. Here, we use high-field 7Li nuclear magnetic resonance (NMR) relaxation and pulsed-field-gradient (PFG) NMR diffusion measurements to probe lithium ion dynamics over nanosecond and millisecond time scales in PEO and polystyrene (PS)-b-PEO-b-PS electrolytes containing the lithium salt LiTFSI. Variable-temperature longitudinal (T1) and transverse (T2) 7Li NMR relaxation rates were acquired at three magnetic field strengths and quantitatively analyzed for the first time at such fields, enabling us to distinguish two characteristic time scales that describe fluctuations of the 7Li nuclear electric quadrupolar interaction. Fast lithium motions [up to O(ns)] are essentially identical between the two polymer electrolytes, including sub-nanosecond vibrations and local fluctuations of the coordination polyhedra between lithium and nearby oxygen atoms. However, lithium dynamics over longer time scales [O(10 ns) and greater] are slower in the block copolymer compared to the homopolymer, as manifested experimentally by their different transverse 7Li NMR relaxation rates. Restricted dynamics and altered thermodynamic behavior of PEO chains anchored near PS domains likely explain these results.

Ionic Conductivity Enhancement of Polyethylene Oxide-LiClO4Electrolyte by Adding Functionalized Multi-Walled Carbon Nanotubes

Polymer electrolytes are needed in many solid-state electronic and energy devices. But polymer electrolytes usually have a low ionic conductivity. This work reports the enhancement in the ionic conductivity of polyethylene oxide (PEO)-LiClO4 electrolyte by adding functionalized multiwalled carbon nanotubes (MWCNTs). MWCNTs are functionalized with carboxylic groups through oxidation with acids. They can be dispersed in acetonitrile solutions of PEO and LiClO4. The presence of functionalized MWCNTs can effectively enhance the ionic conductivity of the PEO-LiClO4 electrolyte, and the ionic conductivity enhancement depends on the loading of the functionalized MWCNTs. Enhancement by a factor of 3.3 was observed. The enhancement in the ionic conductivity is attributed to the functionalized MWCNT-induced decrease in the crystallinity of PEO and increase in the salt dissociation due to the Lewis acid–base interaction of the functionalized MWCNTs with PEO and LiClO4. The addition of functionalized MWCNTs can also effectively improve the mechanical properties of PEO films.

Effect of nanofillers on thermal and transport properties of potassium iodide–polyethylene oxide solid polymer electrolyte

In order to enhance the ionic conductivity of polyethylene oxide (PEO)–KI(80:20) based alkaline polymer electrolytes, nanosized inorganic filler ZnS has been incorporated into PEO–KI matrix and the corresponding nanocomposite polymer electrolytes are synthesized by the usual solution casting procedure. Atomic force microscope image of composite polymer electrolyte exhibits that the introduction of ZnS nanoparticles changes the surface morphology and aggregates them to form an arborization pattern. The prepared nanocomposite polymer electrolyte reveals an ionic conductivity of about 10 −4 S cm −1 for 5 wt% ZnS at room temperature.

Composite alkaline polymer electrolytes and its application to nickel–metal hydride batteries

In order to enhance the ionic conductivity of polyethylene oxide (PEO)-KOH based alkaline polymer electrolytes, three types of nano-powders, i.e., TiO 2, β-Al 2O 3 and SiO 2 were added to PEO-KOH complex, respectively, and the corresponding composite alkaline polymer electrolytes were prepared. The experimental results showed that the prepared polymer electrolytes exhibited higher ionic conductivities at room temperature, typically 10 −3 S cm −1 as measured by ac impedance method, and good electrochemical stability. The electrochemical stability window of ca. 1.6 V was determined by cyclic voltammetry with stainless steel blocking electrodes. The influence of the film composition such as KOH, H 2O and nano-additives on ion conductivity was investigated and explained. The temperature dependence of conductivity was also determined. In addition, polyvinyl alcohol (PVA)-sodium carboxymethyl cellulose (CMC)-KOH alkaline polymer electrolytes were obtained using solvent casting method. The properties of the polymer electrolytes were characterized by ac impedance, cyclic voltammetry and differential thermal analysis methods. The ionic conductivity of the prepared PVA-CMC-KOH-H 2O electrolytes can reach the order of 10 −2 S cm −1. The effect of CMC addition on the alkaline polymer electrolytes was also explained. The experimental results demonstrated that the PVA-CMC-KOH-H 2O polymer electrolyte could be used in Ni/MH battery.

Enhancement of Ionic Conductivity of PEO Based Polymer Electrolyte by the Addition of Nanosize Ceramic Powders

The ionic conductivity of polyethylene oxide (PEO) based solid polymer electrolytes (SPEs) has been improved by the addition of nanosize ceramic powders (TiO2 and AL2O3). The PEO based solid polymer electrolytes were prepared by the solution-casting method. Electrochemical measurement shows that the 10 wt% TiO2 PEO-LiClO4 polymer electrolyte has the best ionic conductivity (about 10(-4) S cm(-1) at 40-60 degrees C). The lithium transference number of the 10 wt% TiO2 PEO-LiClO4 polymer electrolyte was measured to be 0.47, which is much higher than that of bare PEO polymer electrolyte. Ac impedance testing shows that the interface resistance of ceramic-added PEO polymer electrolyte is stable. Linear sweep voltammetry measurement shows that the PEO polymer electrolytes are electrochemically stable in the voltage range of 2.0-5.0 V versus a Li/Li+ reference electrode.

Optical microscopy study on the crystallization in PEO-salt polymer electrolytes

The ionic conductivity of polyethylene oxide (PEO)-salt electrolytes is complicated due to the coexistence of crystalline and amorphous phase and, furthermore, due to the slow phase equilibration processes. In the present study, thermal, optical and electrical data have been measured with similar experimental conditions to compare the effect of slow crystallization kinetics. The differential scanning calorimetry (DSC) data and optical micrographs show that the onset of crystalline to amorphous transition occurs from far below the melting peak temperature, more seriously for higher salt content. The pre-melting, hence, varying degree of crystallinity, further complicates the ionic conductivity. The primary crystallization, corresponding to radial growth of spherulites, occurs very fast, within a few minutes except just within the vicinity of the melting point. However, the spherulitic texture once impinged is gradually perfected for a long time. It corresponds to a secondary crystallization, by thickening slowly through a development of subsidiary lamellae. In the case of higher salt content (e.g., PEO 10LiClO 4), a non-volume filling pattern of spherulites appears and the isolated spherulitic aggregates grow very slowly over 10 days.

Thermal history effects on the ionic conductivity of PEO-salt electrolytes

The ionic conductivity of polyethylene oxide (PEO)-based electrolytes has been known to be greatly enhanced by filling with nano ceramic particles, though it is strongly dependent on thermal treatment schedule and decreases slowly for long aging. The unstableness of the conductivity was attributed to the change of crystallization kinetics caused by some kind of interactions among polymer chains and incorporated ceramic particles. In this paper, ceramic-free PEO n LiClO 4 polymer electrolytes were studied by measuring ionic conductivity and optical micrographs. We show that the unstableness of the ionic conductivity is inherent in the semicrystalline state of ceramic-free PEO-salt electrolytes and the conductivity below melting temperature can be variant by almost two orders of magnitude according to thermal treatment and storage time, although it may be changed by introducing ceramic particles. The melting temperature T m increases with storage time due to the stiffening of spherulites, and the increment of T m is more pronounced for higher salt ratio. All these are primarily concerned with the two-phase nature and the slow re-crystallization kinetics of PEO.

Conductivity relaxation in the PEO–salt polymer electrolytes

The ionic conductivity of polyethylene oxide (PEO)-based electrolytes is complicated due to the coexistence of crystalline and amorphous phase below melting point of PEO complexes. The two-phase characteristics are greatly dependent upon thermal history, exhibiting variety of spherulitic morphology and crystallinity. Further complicacy comes from slow crystallization kinetics of the spherulites. We found that the ionic conductivity of PEO n LiClO 4 polymer electrolytes under isothermal conditions, after quenching from high-temperature phase, drops significantly for roughly first 10 h and then decreases very slowly thereafter. The conductivity relaxation observed can be assigned to be a consequence of the slow recrystallization kinetics of PEO. It corresponds to a gradual, slow secondary crystallization of PEO and PEO–salt complexes corresponding to thickening of spherulitic aggregates, possibly through a development of subsidiary lamellae which fill in the space between the dominant lamellae crystals. Hence, large inconsistencies in the conductivity values reported in many papers, varying more than three orders of magnitude, are rather obvious, originated from non-equilibrium nature and slow recrystallization kinetics of semicrystalline state.

Optical modulation of ionic conductivity of PEO and azobenzene-based electrolytes

By mixing short polyethyleneoxide (PEO) chains end-grafted with azobenzene groups with long PEO chains together with a lithium salt, we obtained ionically conducting films whose conductivity can be modulated by UV light up to 90% of its dark value on a wide temperature range. From electrical (impedance spectroscopy) and structure measurements (SAXS), we can conclude that this behavior is essentially resulting from a localized process of freeing of charge carriers via the conformational change of the azobenzene molecules. This article mainly compares the results obtained with two different photosensitive derivatives.

Nonlinear Effects on the Ionic Conductivity of Polyethylene Oxide)/Uthium Perchlorate Complexes Caused by the Blending of Polyvinyl Acetate)

Abstract Poly(ethylene oxide) (PEO)/LiClO4/poly(vinyl acetate) (PVAc) and PEO/LiClO4/poly(vinyl pyrrolidone) (PVP) complexes were prepared with various weight ratios of PVAc and PVP to PEO. The conductivity (σ) of the PEO/LiClO4 complex was increased in a nonlinear fashion by the presence of up to 60 wt% PVAc. PEO/LiClO4/PVAc complexes with weight percents of PVAc greater than 60 had σ's less than that of PEO/LiClO4. The σ of PEO/LiClO4 was decreased by the presence of any PVP.