PEO Systems Research Articles

Polyaspartate Polyurea-Based Solid Polymer Electrolyte with High Ionic Conductivity for the All-Solid-State Lithium-Ion Battery.

The existing in situ preparation methods of solid polymer electrolytes (SPEs) often require the use of a solvent, which would lead to a complicated process and potential safety hazards. Therefore, it is urgent to develop a solvent-free in situ method to produce SPEs with good processability and excellent compatibility. Herein, a series of polyaspartate polyurea-based SPEs (PAEPU-based SPEs) with abundant (PO)x(EO)y(PO)z segments and cross-linked structures were developed by systematically regulating the molar ratios of isophorone diisocyanate (IPDI) and isophorone diisocyanate trimer (tri-IPDI) in the polymer backbone and LiTFSI concentrations via an in situ polymerization method, which gave rise to good interfacial compatibility. Furthermore, the in situ-prepared PAEPU-SPE@D15 based on the IPDI/tri-IPDI molar ratio of 2:1 and 15 wt % LiTFSI exhibits an improved ionic conductivity of 6.80 × 10-5 S/cm at 30 °C and could reach 10-4 orders of magnitude when the temperature was above 40 °C. The Li|LiFePO4 battery based on PAEPU-SPE@D15 had a wide electrochemical stability window of 5.18 V, demonstrating a superior interface compatibility toward LiFePO4 and the lithium metal anode, exhibited a high discharge capacity of 145.7 mAh g-1 at the 100th cycle and a capacity retention of 96.8%, and retained a coulombic efficiency of above 98.0%. These results showed that the PAEPU-SPE@D15 system displayed a stable cycle performance, excellent rate performance, and high safety compared with PEO systems, indicating that the PAEPU-based SPE system may play a crucial role in the future.

Dielectric relaxation studies of poly(ethylene oxide) with the addition of salt or nanofiller

AbstractPoly(ethylene oxide) (PEO)–lithium perchlorate (LiClO4) serves as the classical model of polymer–salt systems with good polymer–salt molecular interaction at low salt concentration, whereas titanium dioxide (TiO2) without any surface treatment when added to PEO serves as a classical model of polymer–filler systems with weak polymer–filler molecular interaction. The correlation of molecular interactions of polymer–salt or polymer–filler with thermal properties of the systems, which govern the formation of morphologies of the systems, was attempted in a previous study. Hence, this work focuses on the correlation of morphologies and dielectric relaxation properties of PEO with the addition of LiClO4 or TiO2 investigated using polarized optical microscopy and electrochemical impedance spectroscopy over the frequency range from 50 Hz to 1 MHz at 25 °C. The effects of the addition of LiClO4 or TiO2 on the dynamics and relaxations of the polymer chain of PEO are discussed empirically following the fluctuation–dissipation effects from the common electrochemical terms and equivalent circuit model. The PEO–LiClO4 system seems to be one of the promising polymer electrolytes for application in lithium rechargeable batteries where the charged entities may arise from the interaction of salt with the ether oxygen of PEO in the amorphous region. Meanwhile, the PEO–TiO2 system may be analogous to a polar polymer with longitudinal dipoles along the PEO backbone, ethylene oxide monomers (from PEO) of which may represent the molecular dipole or charged entity. The findings show that the transport of charged entities in the PEO systems after the addition of LiClO4 or TiO2 is dominated by short‐range motion at room temperature. © 2022 Society of Industrial Chemistry.

DPD Study on the Interfacial Properties of PEO/PEO-PPO-PEO/PPO Ternary Blends: Effects of Pluronic Structure and Concentration.

Using the method of dissipative particle dynamics (DPD) simulations, we investigated the interfacial properties of PEO/PEO-PPO-PEO/PPO ternary blends composed of the Pluronics L64(EO13PO30EO13), F68(EO76PO29EO76), F88(EO104PO39EO104), or F127(EO106PO70EO106) triblock copolymers. Our simulations show that: (i) The interfacial tensions () of the ternary blends obey the relationship < < < , which indicates that triblock copolymer F68 is most effective in reducing the interfacial tension, compared to L64, F88, and F127; (ii) For the blends of PEO/L64/PPO and the F64 copolymer concentration ranging from ccp = 0.2 to 0.4, the interface exhibits a saturation state, which results in the aggregation and micelle formation of F64 copolymers added to the blends, and a lowered efficiency of the L64 copolymers as a compatibilizer, thus, the interfacial tension decreases slightly; (iii) For the blends of PEO/F68/PPO, elevating the Pluronic copolymer concentration can promote Pluronic copolymer enrichment at the interfaces without forming the micelles, which reduces the interfacial tension significantly. The interfacial properties of the blends contained the PEO-PPO-PEO triblock copolymer compatibilizers are, thus, controlled by the triblock copolymer structure and the concentration. This work provides important insights into the use of the PEO-PPO-PEO triblock copolymer as compatibilizers in the PEO and PPO homopolymer blend systems.

Interaction of PEO with LiI/NaI: a density functional approach

The first-principles study of alkali halides dispersed in polyethylene chains is performed, the dispersion of salts modifies the bond lengths of atoms, bending of polymer chains is occurred, and Li/Na cations are found to be attracted towards oxygen anions; it causes to the reduction in crystallinity. Charge density analysis exhibits partially ionic and covalent bonds between C and O atoms of all PEO systems, and ionic bonds between Li and O and between Na and O atoms. There is sp hybridization in all polymer systems; the forbidden energy gap reduces gradually by increasing dispersed salt molecules and is smaller in PEO10–4NaI. The formation of the concentration of Na cations is higher than Li cations in polymer salts. The stability of PEO10–4LiI is larger and that of PEO5–LiI is smaller, and the bond breaking energy is higher in PEO10–4NaI and lower in PEO10–2NaI.

Effects of nanoparticle addition to poly(ε-caprolactone) electrolytes: Crystallinity, conductivity and ambient temperature battery cycling

It has previously been shown that nanoparticle additives can, in a simple way, significantly improve the ionic conductivity in solid polymer electrolyte systems with the semi-crystalline poly(ethylene oxide) (PEO) as a host material. It has been suggested that the improved ionic conductivity is a result of reduced degree of crystallinity and additional conductivity mechanisms occurring in the material. In this work, this principle is applied to another semi-crystalline polymer host: poly(ε-caprolactone) (PCL). This is a polymer with comparable properties (Tg, Tm, etc.) as PEO, and constitute a promising material for use in solid polymer electrolytes for lithium ion batteries. 15 wt% of the respective nanoparticles TiO2, Al2O3 and h-BN have been added to the PCL-LiTFSI solid polymer electrolyte in an attempt to increase the conductivity and achieve stable room temperature cyclability. The crystallinity, ionic conductivity and electrochemical properties were investigated by differential scanning calorimetry, electrochemical impedance spectroscopy and galvanostatic cycling of cells. The results showed that with an addition of 15 wt% Al2O3, the degree of crystallinity is reduced to 6–7% and the ionic conductivity increased to 6–7 × 10−6 S cm−1 at room temperature, allowing successful cycling of cells at 30 °C, while h-BN did not contribute to similar improvements. The effect of nanoparticles, however, differ significantly from previous observations in PEO systems, which could be explained by different surface-polymer interactions or the degree of ordering in the amorphous phases of the materials.

Studies of the synergistic effects of crosslink density and crosslink inhomogeneity on crosslinked PEO membranes for CO2-selective separations

Crosslinked poly(ethylene oxide) (PEO) membranes are attractive for performing CO2 separations. However, the effects of crosslink density on CO2 separation performance vary widely among reported crosslinked PEO systems, while crosslink inhomogeneity, the uneven distribution of crosslinks in the network, has been largely unexplored. This work reports on a series of PEO-based, model crosslinked membranes with systematically varied crosslink density and crosslink inhomogeneity. Crosslink density was controlled via end-crosslinking commercial Jeffamine® polyetheramines of specific molecular weight of 148, 600, 900, or 2000g/mol with an epoxy terminated PEO; the distribution of crosslinks was controlled by the timed addition of PEO diamine oligomers of differing molecular weight. Three distinct series of networks were produced in increasing crosslink inhomogeneity levels: unimodal, bimodal, and clustered. It was found that while decreasing crosslink density is a prominent factor in increasing CO2 permeability, further improvements in overall CO2 separation performance were realized by adjusting crosslink inhomogeneity. In particular, both the bimodal and clustered films outperformed respective unimodal films in CO2 permeability and CO2/H2 selectivity, suggesting the important role of crosslink inhomogeneity in dictating gas transport properties. These crosslinked PEO films approach or surpass the most recent Robeson upper bounds for pure gas CO2/H2 and CO2/N2 separations, making them attractive membranes for H2 purification and carbon capture.

Cluster formation during aging of colloid-polymer dispersions

We report the dynamics of aqueous dispersions of the disk-shaped colloidal clay laponite® with poly(ethylene oxide) (PEO) chains of moderate molecular weight, explored via angle-dependent dynamic light scattering (DLS) and rheology. The PEO chains adsorb onto the laponite® surfaces, causing interesting dynamic behavior, including transitions from arrested states to liquid states as the concentration and molecular weight of PEO is increased. This re-entrant behavior has been attributed to formation of particle clusters induced free PEO chains. Our DLS results are consistent with a slow diffusive dynamic process, suggesting the formation of large particle clusters, in samples at aging times <75 days. By contrast to behavior observed in laponite® dispersions with a non-adsorbing polymer, poly(acrylic acid) (PAA), diffusion coefficients of these clusters in the laponite®-PEO systems continue to decrease with aging time until samples reach an arrested state.

Studying the effects of elongational properties on atomization of weakly viscoelastic solutions using Rayleigh Ohnesorge Jetting Extensional Rheometry (ROJER)

The extensional rheological properties of dilute polymer solutions play a dominant role in many commercial processes such as air-assisted atomization. This is a high deformation rate process important in application of diverse materials such as paints, fertilizer sprays and delivery of airborne drugs. Dilute polymeric solutions which have identical values of high shear-rate viscosity (HSV) often exhibit different values of Sauter Mean Diameter (SMD) in their spray size distributions as a result of differing extensional rheological properties. We explore the atomization of a series of model Poly(ethylene oxide) (PEO) solutions dissolved in water/glycerol mixtures. Each solution is sprayed with an air-assisted spray gun under similar conditions and imaged with a commercial spray measurement system. The values of HSV for PEO solutions are close to the solvent viscosity and matched to those of typical ink or paint samples. The surface tensions of the fluids are also tuned to be very similar, however both the SMD and the droplet size distribution change considerably. For the highest molecular weight PEO systems, interconnected beads-on-string structures are observed at different positions of the spray fan. Capillary Break-up Extensional Rheometry (CaBER) can be used to measure the extensional properties of the more viscous solutions, but the well-known limitations of this approach include inertially-induced asymmetries, gravitational sagging and the very short filament lifetimes of low viscosity samples all of which constrain the range of relaxation times that can be probed. Consequently we also explore the use of Rayleigh Ohnesorge Jet Elongational Rheometry (ROJER) to probe the extensional response of these viscoelastic solutions at realistic timescales and deformation rates. A cylindrical liquid jet is excited by a piezo-actuator at a known frequency as it exits a micromachined nozzle, and stroboscopic imaging provides high temporal and spatial resolution in the break-up process. Analyzing the evolution in the jet diameter before break-up enables meaningful measurement of relaxation times down to values as small as 60μs, and these values can be directly correlated with the differences in the final spray size distributions and the mean diameters. We outline a simple model for the fluid dynamics of the thinning filaments close to breakup that accurately describes the variation of the average droplet diameter as a function of the elongational relaxation time measured for each fluid.

Synthesis and Properties of High Strength Thin Film Composites of Poly(ethylene Oxide) and PEO-PMMA Blend with Cetylpyridinium Chloride Modified Clay

Ion-conducting thin film composites of polymer electrolytes were prepared by mixing high MW poly(ethylene oxide) (PEO), poly(methyl methacrylate) (PMMA) as a polymer matrix, cetylpyridinium chloride (CPC) modified MMT as filler, and different content of LiClO4by using solution cast method. The crystallinity, ionic conductivity (σ), and mechanical properties of the composite electrolytes and blend composites were evaluated by using XRD, AC impedance, and UTM studies, respectively. The modification of clay by CPC showed enhancement in thed-spacing. The loading of clay has effect on crystallinity of PEO systems. Blend composites showed better mechanical properties. Young’s modulus and elongation at break values showed increase with salt and clay incorporation in pure PEO. The optimum composition composite of PEO with 3.5 wt% of salt and 3.3 wt% of CPMMT exhibited better performance.

Controlling Electrochemical Properties with the LCST Phase Behavior of Homopolymers in Ionic Liquids

In recent years, remarkable progress in the development of batteries, supercapacitors and Li-ion technology has led to devices that deliver new records in power and energy density. The thermal instability in batteries, particularly lithium ion, creates a major roadblock to implementing these devices into large scale systems to support emerging, intermittent energy sources such as wind and solar. Efforts to mitigate safety issues such as flammability, reactivity, and thermal runaway typically involve the implementation of low conductivity solid-state materials or irreversible safety devices, which prove problematic for efficient, large-scale energy systems. Before high performance devices can be applied to large format energy storage applications, thermal safety must be improved. “Smart materials” or stimuli-responsive materials are those with properties responding in a desired manner to an external stimulus or environmental change. While several classes of responsive materials exist, soft materials, particularly synthetic polymers, represent an opportunity to design systems with unique functionality to achieve a wide variety of chemical and physical properties. Here we present two systems utilizing thermally-responsive polymers capable of reducing lithium conductivity or lithium charge transfer ability in non-aqueous electrolytes with increasing temperature. These proposed systems would create self-limiting lithium reactions within a battery should the temperature increase beyond a target, thus inhibiting thermal runaway. Li-ion systems utilizing polymer gel electrolytes are commercially available and ionic liquids (IL) have gained attention as potential replacements for traditional electrolytes (low volatility, non-flammability, high conductivity, and a wide potential window). Poly(ethylene oxide) (PEO) gels have long been combined with lithium salts to create polymeric electrolytes, which while safe, possess diminished conductivity. These PEO systems have recently been combined with ILs to boost performance while retaining the safety and mechanical stability of conventional polymer gel electrolytes. In our first proposed system, we combine current research efforts utilizing polymer gel electrolytes and ILs, both of which provide improved thermal stability, while making use of the recently discovered lower critical solution temperature (LCST) between PEO and certain ILs, to modulate electrolyte conductivity with temperature [1,2]. We design the polymer electrolyte to decrease conductivity during a phase transition at elevated temperatures. As the temperature cools, the initial conductivity is reversibly restored as the electrolyte returns to its initial state. Additionally, we show how the PEO/IL composition and the addition of lithium salts affect both the magnitude of change in conductivity and the LCST in these thermally-responsive polymer electrolyte systems. In our second proposed system, we utilize similar LCST phase behavior in IL systems by modifying electrode surfaces with responsive polymer brushes consisting of poly(methacrylates) [3-5]. Electrode surfaces were modified using the grafting from approach so that the polymer collapses on the surface of the electrode during a phase transition at elevated temperatures. In this collapsed form, the electrode surface is coated with an electrically and ionically insulating layer that prevents double layer formation in supercapacitors and charge transfer (or redox behavior) in Faradaic systems. As in the previous system, the initial electrochemical activity is reversibly restored as the temperature cools and the responsive brushes return to their solvated state. The experiments performed to date show tremendous promise for controlling battery or supercapacitor operation using temperature. Further development of responsive electrolytes and electrode surfaces will lead to numerous opportunities associated with thermal safety and “smart” electrochemical systems.H.-N. Lee and T. P. Lodge, J. Phys. Chem. Lett., 1, 1962 (2010).H.-N. Lee, N. Newell, Z. Bai and T. P. Lodge, Macromolecules, 45, 3627 (2012).T. Ueki and M. Watanabe, Langmuir, 23, 988 (2006).K. Kodama et al., Langmuir, 25, 3820 (2009).H.-N. Lee and T. P. Lodge, J. Phys. Chem. B, 115, 1971 (2011).

Molecular dynamics study of linear and comb-like polyelectrolytes in aqueous solution: effect of Ca2+ ions

All-atom molecular dynamics simulations were employed to provide microscopic mechanism for the salt tolerance of polyelectrolytes dispersants. The conformational variation of polyelectrolytes and interactions between COO− groups and counterions/water molecules were also studied via radius of gyration and pair correlations functions. Sodium polyacrylate (NaPA) and sodium salts of poly(acrylic acid)–poly(ethylene oxide) (NaPA–PEO) were selected as the representative linear and comb-like polyelectrolyte, respectively. The results show that Ca2+ ions interact with COO− groups much stronger than Na+ ions and can bring ion-bridging interaction between intermolecular COO− groups in the NaPA systems. While in the NaPA–PEO systems, the introduced PEO side chains can prevent backbone chains from ion-bridging interactions and weaken the conformational changes. The present results can help in selecting and designing new-type efficient polyelectrolyte dispersants with good salt tolerance.

Effect of particle polydispersity on the structure and dynamics of complex formation between small particles and large polymer

The effect of particle polydispersity on the structure and dynamics of small silica particle–large polymer chain mixtures at low polymer concentration has been investigated. Two types of silica particles were used as model systems, having similar mean size, specific surface area and surface properties but differing substantially in size polydispersity. Mixtures of PEO with the polydisperse silica particles showed strong shear-thickening upon shaking, while mixtures of the same composition with the monodisperse silica did not. Fluorescence correlation spectroscopy revealed that larger flocs were formed in the polydisperse particle–PEO systems. Particle polydispersity was identified as the major factor accounting for these differences and a plausible mechanism was proposed based on the spatial distribution of the silica particles within the complexes. This work suggests that the rheological behavior of colloid–polymer mixtures can be dramatically modified by a simple change in particle polydispersity, rather than more involved surface modifications or the use of additives.

A Molecular Dynamics study of the influence of side-chain length and spacing on lithium mobility in non-crystalline LiPF 6·PEO x; x = 10 and 30

Molecular Dynamics (MD) simulation techniques have been used to investigate systematically how the length and spacing of poly(ethylene oxide) (PEO) side-chains along a PEO backbone influence ion mobility for two different salt concentrations. This is of fundamental relevance to the design of new polymer electrolytes for battery applications. The salt used has been LiPF 6 in concentrations corresponding to Li:EO ratios of 1:30 and 1:10. The MD box contained PEO backbones of 89–343 EO units to which 3, 6, 7, 8, 9 and 15 EO unit side-chains were added. The selected spacings along the backbone between the PEO side-chains attachment points were 5, 10, 15, 20 and 50 EO units. The backbone and all side-chains were methoxy end-capped, and the simulations were all made at 293 K. Ion mobilities have been estimated from the variation of mean-square-displacement with time, and have been analysed in relation to chain dynamics, cross-linking and ion pairing. Comparisons are also made with the results of simulated PEO systems without side-chains and/or without salt. It is found that, at a higher concentration, many short side-chains give the highest ion mobility, while the mobility is highest for side-chain lengths of 7–9 EO units at the lower concentration.

NMR studies of equilibriums in electrolytes: Ionic pairing in glymes

In this article, the formation constants of ionic pairs in salt-low molecular weight analogs of PEO (glyme, diglyme, triglyme) systems are estimated using NMR spectroscopy. The results from 7Li, 11B and 19F NMR titration are compared and the role of the nuclei studied is discussed. It is shown that even in the solvents of very similar coordination (in terms of the donor and acceptor number values) and dielectric properties, the ionic pair formation constant depends on solvent used. The role of the solvent is discussed in terms of effects related to ion agglomerate formation, non-covalent interactions between ions and liquid matrix as well as the number of interacting centers present in the molecules of the solvent. The discrepancies between the results obtained using various nuclei NMR as well as discrepancies between ion pair formation constant calculated for different experimental regimes are also analyzed.

Evidence for re-entrant behavior in laponite–PEO systems

We observe evidence of re-entrant behavior in dispersions of a discotic clay, laponite, with added polymer. Under basic conditions, neat laponite forms a disordered colloidal glass. Rheologically, this phase behaves as a viscoelastic solid, and dynamic light scattering shows evidence of non-ergodic behavior. Addition of low molecular weight poly(ethylene oxide) (PEO) melts the glass, resulting in a low-viscosity liquid with fast dynamics. We believe this is due to a depletion force caused by excess PEO chains in solution. A viscoelastic solid is re-formed with the addition of high molecular weight PEO, which we believe to be caused by polymer chains bridging between laponite particles. The physics in our system is quite different from the hard sphere/nonadsorbing polymer systems for which re-entrant glass transitions have been reported in the literature; however, we believe there may be similarities between these phenomena. To our knowledge, this is the first evidence of a type of re-entrant behavior in anisotropic colloids.

Molecular thermodynamics approach for phase behaviors of solid polymer electrolytes/salt system in lithium secondary battery on the nonrandom mixing effect: Applicability of the group-contribution method

A new group-contribution model based on the lattice model is developed to interpret phase behaviors of solid polymer electrolyte/salt systems on the nonrandom mixing effect. The model includes the combinatorial energy contribution that is responsible for the revised Flory–Huggins entropy of mixing, the van der Waals energy contribution from dispersion, and the polar force and the specific energy contribution from hydrogen bonding. Lattice model gives a starting point for a theoretical description of thermodynamic properties of polymer solution systems. The proposed model in this study improves the configurational energy of mixing and correlates energy of mixing term including the effect of nonrandom mixing on the configurational thermodynamic properties of a binary mixture with experimental data. Our results show that good agreement is obtained upon comparison with experimental data of various PEO and salt systems in the interested ranges.

Application of UNIFAC–vdW–FV model to water–PEO systems

The recently introduced UNIFAC–vdW–FV model has been extended to account for the molecular weight effect in water–PEO systems, one of the most important polymer systems. New groups have been defined and new interaction parameters have been regressed. The UNIFAC–vdW–FV model is able to predict the significant end-group effect in these low molecular weight water–PEO systems.

Ionic conductivities of solid polymer electrolyte/salt systems: Group-contribution method

We establish a new group-contribution model based on the Nernst–Einstein equation in which the diffusion coefficient is derived from the modified double-lattice (MDL) model and the Debye–Hückel (DH) theory. The model includes the combinatorial energy contribution that is responsible for the revised Flory–Huggins entropy of mixing, the van der Waals energy contribution from dispersion, and the polar force and the specific energy contribution from hydrogen bonding. The Nernst–Einstein equation takes into account the mobility of the salt and the motion of the polymer host. To describe the segmental motion of the polymer chain, which is the well known conduction mechanism for solid polymer electrolyte (SPE) systems, the effective co-ordinated unit parameter is introduced. Our results show that good agreement is obtained upon comparison with experimental data of various PEO and salt systems in the interested ranges.

Ionic conductivities of solid polymer electrolyte/salt systems for lithium secondary battery

We establish a new ionic conductivity model based on the Nernst–Einstein equation in which the diffusion coefficient is derived from modified double lattice-nonrandom-Pitzer–Debye–Hückel (MDL-NR-PDH) model. The proposed model takes into account the mobility of the salt and the motion of the polymer host simultaneously by expressing the effective chemical potential as the sum of chemical potentials of the salt and the polymer. To describe the segmental motion of the polymer chain, which is the well-known conduction mechanism for solid polymer electrolyte (SPE) systems, the effective co-ordinated unit parameter is introduced. The obtained co-ordinated unit parameter for each state is used to describe the behavior of the ionic conductivities of the given systems. Good agreement is obtained upon comparison with experimental data of various PEO and salt systems in the interested ranges.

Micellar properties of zwitterionic surfactant - alkoxyethanol mixed micelles

The micelle formation process for a zwitterionic surfactant, N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (ZW3-12), has been investigated in a series of mixed solvents consisting of different concentrations of ethoxylated alcohols and polymers. The critical micelle concentrations (cmc values) of the aggregates were determined by fluorescence spectroscopy, and the surfactant aggregation numbers were obtained from luminescence probing experiments. The cmc values for ZW3-12 changed very little in the presence of increasing amounts of poly(ethyleneoxide) (PEO) in the mixed solvent. In the case of the ethoxylated alcohol – ZW3-12 systems, the cmc values and aggregation numbers decreased systematically with increasing alcohol concentration. However, the cmc values of the mixed micelles showed little dependence on the number of ethylene oxide (EO) groups at constant alcohol concentration. These results are compared with the well-studied sodium dodecylsulfate – ethoxylated alcohol, and dodecyltrimethylammonium bromide – ethoxylated alcohol mixed micellar systems and to SDS–PEO systems and are discussed in terms of the contribution of the EO groups to the hydrophobic interactions. Key words: zwitterionic surfactant, alcohols, mixed micelles, luminescence probing.