Ion-polymer Interactions Research Articles

Alginate Biopolymer Effect on the Electrodeposition of Manganese Dioxide on Electrodes for Supercapacitors

Electrolytic manganese dioxide (EMD) synthesized from different electrolytic baths with varying biopolymer additive concentrations has been investigated for application as an electrochemical supercapacitor. Alginic acid, also termed “alginate”, is a widely used biopolymer for various biological applications due to its physicochemical properties. Here, the EMD material synthesized with alginate crosslinking was introduced in the field of electrochemistry for supercapacitors. Different EMD and alginate composites were characterized to find the trade-off between the biopolymer content in the bath and the energy storage capability. Compared to the pristine EMD, the EMD composites at all of the alginate concentrations influenced both the physical and the electrochemical storage properties of the materials. The presence of alginate in the solution at higher concentrations altered the morphology from spindle-shaped to cactus-shaped with flutes. Rearranged morphology and enhanced particle size are attributed to the ability of the alginate to act as a template for binding the Mn2+ ions on the substrate in a relatively ordered and widely distributed manner. The EMD composite delivered 5 times higher capacitance (487 F g–1) than the pristine EMD at a current density of 1 mA cm–2 in a three-electrode system using a 2 M NaOH aqueous electrolyte. When the EMD composite was coupled with activated carbon, the asymmetric device exhibited 52 F g–1 capacitance at a current density of 2 mA cm–2 while giving excellent capacitance retention (94%) over 5000 cycles. The molecular dynamics simulation model supported the influence of alginate on ion–polymer interactions in the electrolytic bath. The simulations showed that the alginate provides a template for binding Mn2+ ions in a relatively ordered manner. It could assist the EMD/Alg composite growth in a more favorable condition for energy storage applications.

A new formulation for polymer fricke dosimeter and an innovative application of neural network to study dose profile from spin-echo NMR data

Dosimetric systems are used to evaluate absorbed dose and the induced effect caused by irradiation. The choice of dosimetric systems depends on their chemical and physical characteristics and in this study, the chemical Fricke dosimeter was prepared and experimentally tested with Poly(Ethylene Oxide) (PEO), a thermoplastic material. It was provided that the usage of PEO material, a cheap and clean polymer, instead of bovine gelatin, very commonly used in Fricke gel dosimeters, is a promising technological development in dosimetric systems. The improved accuracy of the dose estimation in these systems was demonstrated by comparing the results of ultraviolet–visible spectroscopy (UV-VIS) for the PEO-Fricke dosimeters and the Fricke made of bovine gel. Two sample sets of PEO-Fricke dosimeters were prepared, one set was irradiated with different absolute doses and the other set was prepared with different Fe (III) concentrations. The analyses were performed by using two different algorithms to treat Spin-Echo NMR data. The first methodology uses the single and bi-exponential functions to fit the decay data using the Nonlinear least square (NLLS) with the Levenberg-Marquardt algorithm, providing the relaxation time (T2) values as an average value. The second, more appropriate, consider the problem as a Fredholm integral equation to determine the T2 distribution functions by using Hopfield Neural Network (HNN). The results provide information about the ion-polymer interaction and spatial information of the dosimetric system.

Structural, Vibrational, Electrical, Electrochemical and Capacitive Investigations on Ionic Liquid Doped P (VDF-HFP) + NaSCN Based Polymer Electrolytes

Background: Solid polymer electrolyte (SPEs) films based on poly (vinylidene fluoride-co-hexafluoropropylene) P(VDF–HFP) and sodium thiocyanate (NaSCN) are prepared using the solution casting technique. Methods: Ionic liquid (IL; 1-ethyl-3-methyl-imidazolium tricyanomethanide ([EMIM] [TCM]) is incorporated into the prepared polymer-salt complex matrix to enhance its ionic conductivity further. Polarized optical microscopy (POM) shows a change in the surface morphology of IL doped polymer electrolyte films. The composite nature of polymer electrolyte films is confirmed using Fourier transform infrared (FT-IR) spectroscopy via studying ion-ion and ion-polymer interactions. The structural morphology of ionic liquid doped polymer electrolyte films (ILDPE) confirms the complexation between the ionic liquid ([EMIM][TCM]), salt (NaSCN) and polymer P(VDF-HFP). This is further confirmed using DSC and XRD measurements. The XRD structural analysis confirms that the intensity of crystalline peaks present in IL doped solid polymer electrolyte films decreases as compared to that of the pure polymer as well as polymer salt complex system. XRD clearly indicates the enhancement in its amorphous nature, which is necessary to increase the conductivity. Results: The incorporation of IL into polymer salt-complex matrix leads to changes in the melting of polymer electrolytes, confirmed by DSC thermograms. Polymer electrolyte films are also characterized using impedance spectroscopy (IS) to check their electrical properties. The highest ionic conductivity is found to be 7.80×10-4 S cm-1 for 6 wt% IL doped polymer electrolyte film. Conclusion: The Linear sweep voltammetry (LSV) analysis shows that the optimized polymer gel electrolyte is electrochemically stable up to 1.5 V. The calculated value of ionic transference number (tion) is found to be 0.985. A laboratory scale electrical double layer capacitor (EDLC) has been fabricated using this highly conducting polymer electrolyte film. The specific capacitance value is found to be 1.31 F g-1.

Computational insight into the structural properties and redox chemistry of poly (ethylene carbonate) as electrolytes for Lithium batteries

New electrolytes with high electrochemical stability and ionic conductivity are important in the development of lithium ion batteries. Polyethylene carbonate (PEC) is a very promising candidate. Herein, the DFT modeling approach is performed to investigate the coordination structure of Li+ ion in PEC, and the redox potentials of a set of polymer models to assess the effect of polymer monomer unit composition. [Li(PEC)] [Anion] (BF4−, PF6−, ClO4−, TFSI−) are also considered. It is highlighted that the coordination shell of Li+ ion is most likely fully occupied by four carbonyl oxygen atoms of PEC. Next, the carbonate group can lead to greater oxidation stability than ester, ketone and ether group, the length and configuration of alkyl chain affect the redox potential only slightly. Furthermore, the addition of electron-withdrawing groups (-F and -CF3) can increase the oxidation stability of PEC, while the -CN group substitution shows the opposite effect, due to the ring formation or bond breaking of intramolecular structure. All these findings provide important information for understanding the ion-polymer interactions and synthesizing the promising new electrolyte molecules for high-voltage batteries.

The Role of Polymer–Ion Interaction Strength on the Viscoelasticity and Conductivity of Solvent-Free Polymer Electrolytes

Metal–ligand coordinating polymers utilize labile bonds between polymer-bound ligands and free cations to delocalize and conduct mono and multivalent metal ions in the solid state. These interactio...

Effect of Structural Features on Ionic Conductivity and Dielectric Response of PVA Proton Conductor-Based Solid Polymer Electrolytes

In this study, the effect of structure on the ionic conductivity and dielectric response of polyvinyl alcohol solid polymer electrolyte films doped with ammonium nitrate (NH4NO3) was investigated. Structural studies show that the solid polymer electrolytes in a suitable salt ratio enhance the amorphous fraction of the host matrix and facilitate the fast movement of H-ions, resulting in the enhancement of electrical conductivity. The highest ionic conductivity at room temperature (5.17 × 10−5 S/cm) was achieved by incorporating 30 wt.% of NH4NO3, which shows the maximum ion dissociation in the host matrix due to ion–polymer interaction. The reduction in the ionic conductivity at higher salt concentrations (above 30 wt.%) is the consequence of a decrease in the carrier concentration and its movement, respectively, due to the formation of ion pairs and a reduction in the amorphous fraction of the system. A broad asymmetric peak of the imaginary part of the electrical modulus suggests a temperature-dependent non-Debye relaxation process for the present system.

(Oxalato)borate: The key ingredient for polyethylene oxide based composite electrolyte to achieve ultra-stable performance of high voltage solid-state LiNi0.8Co0.1Mn0.1O2/lithium metal battery

Searching novel polyethylene oxide (PEO) based composite electrolyte that can be compatible with high voltage cathodes (> 4 V) at room temperature is a long-standing challenge, but essential to achieve high-energy-density for solid-state lithium (Li) metal batteries. Herein, we develop an advanced dual-salts reinforced PEO/garnet solid-state composite electrolyte (SCE) with high ionic conductivity of 9 × 10 −4 S cm −1 and an electrochemical stability window up to ~ 4.7 V, where the lithium bis(oxalate)borate (LiBOB) is used as additive with LiClO 4 . The dual-salts reinforced SCE can achieve excellent room temperature cycling performance of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)/Li metal batteries. The multiplied polymer-ion interactions and formation of Li‒B‒O/C‒O species originated from the (oxalato)borate group of LiBOB effectively promotes the electrochemical stability of the PEO based composite electrolyte and its wetting properties with electrodes. Unwanted non-conductive decomposition products, such as Li 2 O and Li 2 CO 3 , and NCM particles cracking during cycling are successfully suppressed. The NCM811 solid-state cells using the optimized dual-salts composite electrolyte delivers high specific capacity of 190 mA h g −1 and exhibit stable cycling performance for more than 200 cycles at 25 °C. Stable charge–discharge performance of 4 V NCM solid-state battery are realized via addition of LiBOB salts to conventional single salt plasticized PEO solid-state composite electrolyte. Polymer electrolyte decomposition and active materials cracking at high voltage are suppressed by multiplied polymer-ion interactions and formation of stable C‒O/Li‒B‒O containing solid electrolyte interphase, leading to strikingly improvement in capacity retention. • A fast ion conducting dual-salts polyethylene oxide (PEO) based solid-state composite electrolyte (SCE) is developed. • Electrochemical stability of the SCE is greatly enhanced via addition of lithium bis(oxalate)borate (LiBOB) salt. • Adding LiBOB salt to the PEO-based SCE enables stable cycling of high voltage solid-state LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)/Li battery.

Holistically Engineered Polymer-Polymer and Polymer-Ion Interactions in Biocompatible Polyvinyl Alcohol Blends for High-Performance Triboelectric Devices in Self-Powered Wearable Cardiovascular Monitorings.

The capability of sensor systems to efficiently scavenge their operational power from stray, weak environmental energies through sustainable pathways could enable viable schemes for self-powered health diagnostics and therapeutics. Triboelectric nanogenerators (TENG) can effectively transform the otherwise wasted environmental, mechanical energy into electrical power. Recent advances in TENGs have resulted in a significant boost in output performance. However, obstacles hindering the development of efficient triboelectric devices based on biocompatible materials continue to prevail. Being one of the most widely used polymers for biomedical applications, polyvinyl alcohol (PVA) presents exciting opportunities for biocompatible, wearable TENGs. Here, the holistic engineering and systematic characterization of the impact of molecular and ionic fillers on PVA blends' triboelectric performance is presented for the first time. Triboelectric devices built with optimized PVA-gelatin composite films exhibit stable and robust triboelectricity outputs. Such wearable devices can detect the imperceptible skin deformation induced by the human pulse and capture the cardiovascular information encoded in the pulse signals with high fidelity. The gained fundamental understanding and demonstrated capabilities enable the rational design and holistic engineering of novel materials for more capable biocompatible triboelectric devices that can continuously monitor vital physiological signals for self-powered health diagnostics and therapeutics.

PEO + NaSCN and ionic liquid based polymer electrolyte for supercapacitor

In this study, initially ion conducting solid polymer electrolyte films (SPEs) based on polyethylene oxide (PEO) and sodium thiocyanate (NaSCN) have been prepared using the standard solution cast technique. For further enhancement in the ionic conductivity value of optimized film, an ionic liquid (IL; 1-ethyl-3-methyl-imidazolium tricyanomethanide) ([EMIM][TCM]) has been incorporated in different weight ratios into the optimized polymer-salt complex matrix. The prepared SPEs are free-standing, flexible and exhibit good thermal and mechanical stabilities. Polarized optical microscopy (POM) shows a change in the surface morphology of IL doped polymer electrolyte films. The composition nature of polymer electrolyte films was confirmed using fourier transform infrared spectroscopy (FT-IR) via studying ion-ion and ion-polymer interactions. The FTIR studies confirm that complexation occurs between polymer-salt and polymer-salt-ionic liquid interactions. Polymer electrolyte films have been also characterized using X-Ray Diffraction (XRD). The structural analysis confirms that the intensity of crystalline peaks existing in solid polymer electrolyte films decreases after doping IL which enhances its amorphous nature. The thermal stability of different prepared electrolyte films has been investigated using thermogravinometric analysis (TGA). Ionic liquid doped polymer electrolyte films show more stable behavior than polymer host PEO and polymer-salt complex at high temperatures. IL doped polymer electrolyte film shows reduction in the degradation process with a residue mass of 29% at 400 °C. Polymer electrolyte films were also characterized using impedance spectroscopy (IS) to check their electrical properties. The maximum ionic conductivity is found to be 8.44 × 10−5 S cm−1 for 4 wt% IL doped solid polymer electrolyte film and the calculated value of ionic transference number (tion) for optimized electrolyte film is 0.98. Using this maximum ion-conducting polymer electrolyte film, we have developed a electrical double layer capacitor (EDLC). The calculated value of the specific capacitance of prepared EDLC is 1.07 Fg−1.

Ion Conductivity and Correlations in Model Salt-Doped Polymers: Effects of Interaction Strength and Concentration

Correlated anion and cation motion can significantly reduce the overall ion conductivity in electrolytes versus the ideal conductivity calculated based on the diffusion constants alone. Using coarse-grained molecular dynamics simulations, we calculate conductivity and the degree of uncorrelated ion motion in salt-doped homopolymers and block copolymers as a function of concentration and interaction strengths. Calculating conductivity from ion mobility under an applied electric field increases accuracy versus the typical use of fluctuation dissipation relationships in equilibrium simulations. In typical electrolytes, correlation in cation-anion motion is often expected to be reduced at low ion concentrations. However, for these polymer electrolytes with strong ion-polymer and ion-ion interactions, we find correlations are increased at lower concentrations when other variables are held constant. We show this phenomenon is related to the slower ion cluster relaxation rate at low concentrations rather than the static spatial state of ion aggregation or the fraction of free ions.

The Role of Backbone Polarity on Aggregation and Conduction of Ions in Polymer Electrolytes.

The usual understanding in polymer electrolyte design is that an increase in the polymer dielectric constant results in reduced ion aggregation and therefore increased ionic conductivity. We demonstrate here that in a class of polymers with extensive metal-ligand coordination and tunable dielectric properties, the extent of ionic aggregation is delinked from the ionic conductivity. The polymer systems considered here comprise ether, butadiene, and siloxane backbones with grafted imidazole side-chains, with dissolved Li+, Cu2+, or Zn2+ salts. The nature of ion aggregation is probed using a combination of X-ray scattering, electron paramagnetic resonance (in the case where the metal cation is Cu2+), and polymer field theory-based simulations. Polymers with less polar backbones (butadiene and siloxane) show stronger ion aggregation in X-ray scattering compared to those with the more polar ether backbone. The Tg-normalized ionic conductivities were however unaffected by the extent of aggregation. The results are explained on the basis of simulations which indicate that polymer backbone polarity does impact the microstructure and the extent of ion aggregation but does not impact percolation, leading to similar ionic conductivity regardless of the extent of ion aggregation. The results emphasize the ability to design for low polymer Tg through backbone modulation, separately from controlling ion-polymer interaction dynamics through ligand choice.

Effect of Mg(CF3SO3)2 concentration on structural and electrochemical properties of ionic liquid incorporated polymer electrolyte membranes

In the present study, a magnesium ion conducting polymer electrolyte membrane system based on polyethylene oxide (PEO) containing magnesium triflate Mg(CF3SO3)2 salt and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) ionic liquid is prepared using standard solution casting technique. X-ray diffraction and differential scanning calorimetry studies reveal change in crystalline character with variation in Mg(CF3SO3)2 concentration within PEMs. Fourier transform infrared spectroscopy technique reflects ion-polymer interactions within the prepared polymer electrolyte system. Dielectric and modulus properties of prepared electrolyte membranes show significant changes in dielectric constant and relaxation behavior respectively on varying Mg(CF3SO3)2 concentration. The optimized polymer electrolyte membrane with 6 wt% of magnesium triflate salt shows maximum ionic conductivity of ~ 9.4 × 10−5 S cm−1 at room temperature. The ionic conductivity variation with temperature shows Arrhenius behavior for PEMs. The Mg2+ conduction within the PEMs is established using CV study and electrochemical stability window of ~ 4.0 V is determined using linear sweep voltammetry. The PEMs are dominantly ionic conducting with Mg2+ transport number ~ 0.22 for the optimized PEM.

Investigation on enhancement of electrical, dielectric and ion transport properties of nanoclay-based blend polymer nanocomposites

An intercalated blend polymer nanocomposite (PNC) films based on blend (PEO–PVC), LiPF6 as salt and modified montmorillonite (MMMT) as nanoclay are prepared via solution cast method. The impact of the nanoclay on the morphology, structure, polymer–polymer, polymer–ion interactions, ionic conductivity, voltage stability window, glass transition temperature, dielectric permittivity, and ac conductivity has been explored. The structural analysis evidenced the formation of blended and intercalated polymer nanocomposites. The FTIR analysis confirmed the interaction between polymer–ion-nanoclay, and polymer intercalation is evidenced by the out-of-the-plane mode [Si–O mode] of MMMT. An increase in the fraction of free anions with clay addition is confirmed. The highest ionic conductivity of about ~ 8.2 × 10−5 S cm−1 (at RT) and 1.01 × 10−3 S cm−1 (at 100 °C) is exhibited by 5 wt% MMMT based PNC. A strong correlation is observed between the glass transition temperature, crystallinity, melting temperature (Tm), ionic conductivity, relaxation time, and dielectric strength. The dielectric data have been fitted and enhanced dielectric strength and lowering of the relaxation time ($$ \tau_{{\varepsilon^{\prime} }} \;{\text{and}}\;\tau_{\text{m}} $$) with clay addition evidences the faster segmental motion of polymer chain. The intercalated PNC shows thermal stability up to ~ 300 °C, high ion transference number (~ 1), and broad voltage stability window of ~ 5 V. An absolute agreement between ion mobility (μ), diffusion coefficient (D), and ionic conductivity is observed. An ion transport mechanism has been proposed on the basis of experimental results. Therefore, the proposed PNC can be adopted as electrolyte cum separator for energy storage devices.

Effects of Natural Clay on Ionic Conductivity, Crystallinity and Thermal Properties of PEO-LiCF<sub>3</sub>SO<sub>3</sub>-Natural Clay as Solid Polymer Electrolyte Nanocomposites

The polymer nanocomposites of PEO-LiCF3SO3 based solid polymer electrolyte were prepared using two kinds of natural clays, which are halloysite nanotube (HNT) and montmorillonite (MMT) nanoparticle. Different contents (0, 1, 5 and 10wt %) of halloysite nanotube (HNT) and montmorillonite (MMT) nanoparticle were explored. Solid polymer electrolyte nanocomposite film was prepared by solution casting method. The ionic conductivity, crystallinity and thermal properties of solid polymer electrolyte membranes were studied by impedance spectroscopy, X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. It was found that HNT provided higher ionic conductivity for solid polymer electrolyte nanocomposite than what MMT did. The highest ionic conductivity at room temperature was found at 5% HNT as 2.068 x 10-5 S.cm-1. The ion-polymer interactions between PEO-LiCF3SO3 and natural clay nanoparticle were investigated by using Fourier transform infrared (FTIR) spectra. The PEO-LiCF3SO3-5%HNT showed good oxidative stability than PEO-LiCF3SO3 composite.

Conduction mechanism in polymeric membranes based on PEO or PVdF-HFP and containing a piperidinium ionic liquid

Two types of polymer electrolyte membranes were prepared using poly(ethylene oxide) (PEO) and poly(vinylidene difluoride-co-hexafluoropropylene) (PVdF-HFP), with different amounts of the ionic liquid N-methyl-N-propylpiperidinium bis(trifluoromethane-sulfonyl)imide ([PP13][TFSI]) added. The results from differential scanning calorimetry and conductivity measurements show that in the case of PVdF-HFP membranes the glass transition temperature Tg decreases and the room temperature ionic conductivity increases with increasing content of the ionic liquid (up to 60 wt.%). However, in the case of PEO based membranes Tg is less significantly affected and the room temperature ionic conductivity increases only up to 30 wt.% of ionic liquid, beyond which a steady value of about 5⋅10−5 S/cm is reached. The results from Raman spectroscopy show that the characteristic vibrational mode of the TFSI anion at ∼742 cm−1 is weakly affected in the membranes prepared from PVdF-HFP, whereas for those based on PEO it has a clearer composition dependence. These results suggest ion-ion and ion-polymer interactions of different nature, which together with the different nanomorphologies adopted by PEO and PVdF-HFP, as revealed by X-ray scattering, give rise to different composition dependences of the macroscopically measured ionic conductivity.

Molecular dynamics simulation of polymer-coupled ion transport in the crystalline polymer electrolyte poly(ethylene oxide)3:NaI

While solid polymer electrolytes (SPEs) possess a combination of the requisite properties to merit their use in all-solid-state rechargeable batteries, their low ionic conductivity (σ) at room temperature limits their widespread use in advanced commercial applications. To overcome this limitation, it is necessary to understand the crucial molecular factors that govern the energetics and transport of ions in SPEs. In this Article, all-atom molecular dynamics (MD) and adaptive biasing force (ABF) simulations are used to characterize the mechanism and energetics of polymer-coupled ion transport and to probe the nature of interactions of polymers and ions in a crystalline SPE (PEO3:NaI). In particular, the free energy profiles associated with the cation transport along the polymer helix, the activation energy for hopping of a cation between adjacent energetically favourable coordination sites, and crucial factors determining the features of the free energy profiles are examined. The calculated free energy profiles exhibit well-defined minima (correspond to favourable cation coordination sites) separated by relatively high energy barriers (12–14 kcal/mol) indicating that ion hopping is the likely mechanism of cation transport in PEO3:NaI crystals. The influence of the conformational flexibility of the polymer on the energetics of cation transport is also examined. The dissection of interaction of the cations provides insights into the interplay of ion-ion, ion-polymer, and polymer-polymer interactions in determining the activation barrier for cation transport in the crystalline PEO3:NaI.

Effect of Polymer Polarity on Ion Transport: A Competition between Ion Aggregation and Polymer Segmental Dynamics.

In this work, we use computer simulations to demonstrate that there may be limits to which polymer polarity alone can be used to influence the ionic conductivity of salt-doped polymer electrolytes. Specifically, we use coarse-grained molecular dynamics simulations to probe the effect of the polarity of the polymer electrolyte upon ion mobilities and conductivities of dissolved salts. At low polymer polarities, increasing the polymer dielectric constant reduces ionic aggregation and the resultant correlated ionic motion, and increases the ionic conductivity. At higher polymer polarities, polymer-polymer and polymer-ion interactions slows polymer segmental dynamics, leading to a reduction in the conductivity of the electrolyte. As a consequence, ionic conductivity achieves an optimum at an intermediate polymer polarity.

Ionic effects on polymers

In the conventional theories, ions are usually treated as point charges, and their influences on the properties of polymers are mainly controlled by the ionic strength effect. However, many important phenomena in polymer systems cannot be understood by merely considering the ionic strength effect. This requires us to consider the ionic effects on polymers beyond the influence of ionic strength. Herein, we will discuss the specific ion effect, the ionic hydrogen bond effect, the ionic hydrophilicity/hydrophobicity effect, and the multivalent ion effect in polymer systems. The specific ion effect exists in various charged and neutral polymer systems, and can be observed in different types of solvent systems. The ionic hydrophilicity/hydrophobicity effect can be used to modulate many important properties of strong polyelectrolyte brushes including hydration, wettability, and adhesion. The ionic hydrophilicity/hydrophobicity effect can be applied to tune not only the properties of the surface-grafted polyelectrolytes, but also the properties of the polyelectrolyte solutions and hydrogels. The multivalent ion effect can be used to control the properties of polyelectrolyte brushes and polymer hydrogels through the electrostatic crosslinking interactions. The ionic effects on polymers demonstrated here would widen and deepen our understanding of the interactions between ions and polymers, forming a basis for tuning the polymer properties with ions, and can be further expanded to other types of important ion-polymer interactions.

Study of time-ageing effect on the ionic conduction and structural dynamics in solid polymer electrolytes by dielectric relaxation spectroscopy

This research work demonstrates the effect of time-ageing on the dielectric and electrical properties, and also the structural dynamics of solid polymer electrolyte (SPE) and nanocomposite solid polymer electrolyte (NSPE) films over a period of one-year. The SPE and NSPE films based on polymer blend matrix of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) (50/50 wt%) with lithium triflate (LiCF3SO3) as dopant ionic salt (22 wt%) and montmorillonite (MMT) clay (3 wt%) as inorganic nanofiller have been prepared by solution-cast method followed by melt-pressing technique. These films are characterized by employing scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dielectric relaxation spectroscopy (DRS) and electrochemical analysis (ECA) techniques. The influence of MMT filler on the polymer-ion interactions was confirmed from comparative analysis of the structural and electrochemical properties of the SPE and NSPE films. The XRD and DRS measurements on these films were repeated at various time intervals over one-year duration in order to explore the time-ageing effect on the structural properties, dielectric parameters, and ionic conduction mechanisms in the electrolyte samples. The XRD study reveals the irregular variation of PEO crystalline phase in these films and also the intercalated/exfoliated MMT phases in the NSPE film with time-ageing. The ionic conductivity of the SPE and NSPE films increases by about one order of magnitude over the time-ageing period of 2 to 3 months of these films, whereas it drops by more than one order of magnitude at the one-year ageing in comparison to that of the freshly prepared films measured on day first. It is found that the ionic conductivity of these materials has a correlation with the relaxation time of polymers cooperative chain segmental motion which validates the fact that the ions transport in the solid ion-dipolar complexes occurs through hopping mechanism coupled with polymers structural dynamics not only for the freshly prepared electrolyte films but also for the films with time-ageing. Further, these electrolyte films have good electrochemical stability, better reversibility and cyclability, and the ion transference number close to unity.

Globally Suppressed Dynamics in Ion-Doped Polymers.

We investigate how ion-polymer complexation suppresses molecular motion in conventional polymer electrolytes using molecular dynamics (MD) simulations of lithium hexafluorophosphate in poly(ethylene oxide) and a modified Rouse model. The employed model utilizes an inhomogeneous friction distribution to describe ion-polymer interactions and provides an effective way to examine how ion-polymer interactions affect polymer motion. By characterizing the subdiffusive Li+ transport and polymer relaxation times at several salt concentrations, we observe that increases in local friction due to ion-polymer complexation are significantly smaller than previously assumed. We find that a Rouse-based model that only considers local increases in friction cannot simultaneously capture the magnitude of increased polymer relaxation times and the apparent power-law exponent for Li+ subdiffusion observed in MD simulations. This incompatibility is reconciled by augmenting the modified Rouse model with a term that increases the global friction with the square of the salt concentration; this significantly improves the agreement between the model and MD, indicating the importance of ion-ion interactions and distributions on ion/polymer mobility.