Добірка наукової літератури з теми "Composite Polymet Electrolytes - Relaxation Dynamics"

Composite gel polymer electrolytes (GPEs) based on organo-modified montmorillonite clays have been prepared and investigated. The organo-clay was prepared by intercalation of CTAB molecules in the interlamellar space of sodium smectite clay (SWy) through a cation-exchange reaction. This was used as nanoadditive in polyacrylonitrile/polyethylene-oxide blend polymer, lithium trifluoromethanesulphonate (LiTr) as salt and a mixture of ethylene carbonate/propylene carbonate as plasticizer. GPEs were widely characterized by DSC, SEM, and DMA, while the ion transport properties were investigated by AC impedance spectroscopy and multinuclear NMR spectroscopy. In particular, 7Li and 19F self-diffusion coefficients were measured by the pulse field gradient (PFG) method, and the spin-lattice relaxation times (T1) by the inversion recovery sequence. A complete description of the ions dynamics in so complex systems was achieved, as well as the ion transport number and ionicity index were estimated, proving that the smectite clay surfaces are able to “solvatate” both lithium and triflate ions and to create a preferential pathway for ion conduction.

Following the COP26 Summit in November 2021, more than hundred countries pledged to reach zero-emission by 2070 at the latest and the major car manufacturers committed to selling only electric vehicles by 2040. Currently, lithium-ion batteries (LIBs) are among the most widely used storage systems because of their high energy and power densities and long lifespan.1 The early LIBs are composed of intercalation electrodes, electronically isolated by an ion-conducting organic liquid electrolyte. However, the use of liquid electrolytes presents some disadvantages – especially in regard to consumer safety – related to short-circuits and potential leakages of the flammable liquid solvent. Moreover, in the case of lithium metal batteries, the combination of a liquid electrolyte and a high-capacity lithium metal anode leads to the uncontrolled deposition of lithium during the reduction, forming dendrites between the electrodes. A promising way to avoid this instability and improve battery safety is to replace the liquid electrolyte with an ion-conducting solid electrolyte.2 Among them, solid polymer electrolytes (SPEs) represent one of the most attractive alternatives due to their capacity to effectively conduct ions and higher mechanical resistance than their liquid counterparts.3 An important criterion for selecting polymers for use in SPEs is their ability to dissolve lithium salts through polar functional groups. Salt dissolution results in the replacement of ion-ion interactions in the lithium salt, with ion-dipole interactions in the polymer. The transport mechanisms of these ion-conducting materials differ from those of liquid electrolytes. Cation transport in polymer involves two steps which are considered to be dissociated or not, depending on the model chosen (Arrhenius or Vogel-Fulcher-Tammann, respectively). The application of one of these models provides interesting information on the ionic mobility dynamics in SPEs and, in particular, on the interplay between ionic jumps and polymer chain mobility. In the Arrhenius model, ionic jumps occur between coordinating sites, without taking into account the influence of segmental relaxation. Conversely, the VTF equation implies a strong relationship between these parameters. According to previous studies, higher segmental motions in the amorphous phase of polymers mainly provide ionic transport, which explains the limited ionic conductivity of SPEs at ambient temperature (less than 10-5 S/cm). Another major limitation of SPEs is primarily related to their dual role as electrolyte and binder in composite electrodes, which requires contradictory requirements to be met. Indeed, SPEs must have both sufficient flexibility to allow good interfacial contact between the electrode components and sufficient rigidity to limit short circuits. Polymer blending has emerged as an economic and effective technique to develop new SPEs which may simultaneously combine properties of each polymer and control the intrinsic properties of the resulting blend by adjusting the formulation.4 Moreover, polymer blends can be obtained by a solvent-free processing method, which reduce SPE toxicity and production time (no solvent evaporation). However, polymer blending makes both the salt dissociation processes and the ionic transport more difficult to understand as both polymers can dissolve lithium salts with their polar functional groups. Each polymer has different ionic transport properties depending on its architecture and thermal properties. Currently, no systematic survey comparing the ability of polymers with various functional groups to dissolve lithium salts in blends has thus far been conducted. In this presentation, we will discuss the salt dissociation ability of polar functional groups in various polymer blend SPEs. These groups are limited to those that are most commonly present in SPEs : ether, nitrile, carbonate, ester, alcohol and amide.5 The blends presented have been obtained by extrusion, which allows the effect of solvents on salt/polymer interactions to be neglected. In this work, coupled FTIR, EDX and 7Li NMR analyses allow the interactions between LiTFSI and the polymer blends to be determined with a good degree of certainty. Our original study combines experimental and theoretical approaches to determine effects of polymers’ lithium salt solvating ability on polymer blend electrolyte properties and represents an advancement in understanding and optimizing polymer selection for SPEs, used in lithium-ion batteries. References Xie, W., Liu, X., He, R., Li, Y., Gao, X., Li, X., Peng, Z., Feng, S., Feng, X. and Yang, S. Journal of Energy Storage 2020, 32, 101837. Chen, R., Qu, W., Guo, X., Li, L. and Wu, F. Materials Horizons 2016, 3, 487-516. Gray, F. M. Solid polymer electrolytes, VCH New Tork 1991. Caradant, L., Lepage, D., Nicolle, P., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2020, 4943-4951. Caradant, L., Verdier, N., Foran, G., Lepage, D., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2021. Figure 1

Complex electrical impedance and dielectric spectroscopy were applied to study the dielectric relaxations and their thermal behavior in ion-conducting composites/complexes from polymer poly(ethylene oxide) (PEO) and E8 nematic liquid crystals (LCs), at the compositional ratio PEO:E8 = 70:30 wt%. Flexible thin films of PEO/E8 with a thickness of 150 μm were inspected, as well as such films from Na+ ion-conducting electrolyte PEO/E8/NaIO4 with the same PEO:E8 compositional ratio, but additionally containing 10 wt.% from the salt sodium metaperiodate (NaIO4) as a dopant of Na+ ions. The molecular dynamics, namely the dielectric relaxation of PEO/E8 and PEO/E8/NaIO4, were characterized through analyses of complex impedance and dielectric spectra measured in the frequency range of 1 Hz–1 MHz, under variation of temperature from below to above the glass-transition temperature of these composites. The relaxation and polarization of dipole formations in PEO/E8 and PEO/E8/NaIO4 were evidenced and compared in terms of both electrical impedance and dielectric response depending on temperature. The results obtained for molecular organization, molecular relaxation dynamics, and electric polarization in the studied ion-conducting polymer/LC composites/complexes can be helpful in the optimization of their structure and performance, and are attractive for applications in flexible organic electronics, energy storage devices, and mechatronics.

onic conductivity, dielectric and thermal properties of (PEO)12LiBF4 solid polymer electrolyte, dispersed with nanoporous Al2O3 have been studied. Out of seven different compositions studied, the (PEO)12LiBF4 polymer-salt complex showed the highest conductivity with σ25 oC = 8.27 × 10-6 S cm-1. Dispersion of different weight ratio of nano-porous alumina fillers to this electrolyte showed that the composite electrolyte composition with 15 wt. % Al2O3 gave the highest conductivity with σ25 oC = 6.05 × 10-5 S cm-1. The glass transition temperature, Tg decreased from -35.3 oC to -43.2 oC and the PEO crystallite melting temperature, Tm decreased from 64.5 oC to 58.8 oC due to the incorporation of 15 wt. % Al2O3 filler, suggesting that the interaction between the PEO backbone and the Al2O3 filler have affected the main chain dynamics of the host polymer. As the presence of the filler results in an increased conductivity mainly due to an increased amount of amorphous phase in the electrolyte above Tm, another mechanism, directly associated with the filler particles, appears to contribute to the observed conductivity enhancement. A possible mechanism for this could be the creation of additional hopping sites and favorable conducting pathways for migrating ionic species though Lewis acid-base type interactions between ionic species and O/OH sites on the filler grain surface. Results of the dielectric relaxation spectroscopy agree with the suggestion that the increased mobility is largely responsible for the obtained conductivity enhancement caused by the nano- porous filler.

NMR is the method of choice for molecular and ionic structures and dynamics investigations. The present review is devoted to solvation and mobilities in solid electrolytes, such as ion-exchange membranes and composite materials, based on cesium acid sulfates and phosphates. The applications of high-resolution NMR, solid-state NMR, NMR relaxation, and pulsed field gradient 1H, 7Li, 13C, 19F, 23Na, 31P, and 133Cs NMR techniques are discussed. The main attention is paid to the transport channel morphology, ionic hydration, charge group and mobile ion interaction, and translation ions and solvent mobilities in different spatial scales. Self-diffusion coefficients of protons and Li+, Na+, and Cs+ cations are compared with the ionic conductivity data. The microscopic ionic transfer mechanism is discussed.

ABSTRACTPoly(p-phenylene terephthalamide) (PPTA) recognized as rigid-rod polymer is converted into polyanion by the reagent of sodium methylsulfinylcarbanion in dimethylsulfoxide (DMSO), which is dissolved in DMSO to form a dark red colored homogeneous solution. The electrolysis of PPTA polyanion in DMSO, which has also rigid-rod shape due to resonance effect, gives a PPTA gel swollen by DMSO on the anode. The gel is easily converted to a PPTA film. The structural change during the process was followed by the Xray diffraction. The PPTA film neutralized with acidic water and dried has the hydrogen-bonded sheet in crystal standing perpendicular to the film surface, whereas the same film annealed at temperatures above 300°C has the hydrogen-bonded sheet parallel to the film surface. The latter form is the stable structure. The orientational transition was energetically discussed by taking into the activation energy of the crystalline relaxation. A uniform and homogeneous film was prepared by using a coaxial rotating electrode cell. The modulus was 11 GPa and the strength was 150 MPa. The addition of polyacrylonitrile to the electrolytic solution as the frictionproviding polymer which was removed from the gel after electrolysis, provided the mechanical anisotropy, especially after annealing at 350°C: the modulus along the orientation direction was 14 GPa and the strength was 370 MPa.The PPTA film unannealed or annealed below 200°C in an unstable orientational tate was used as a matrix of electropolymerization of electroconductive polymers such as polypyrrole, polyaniline and polythiophene, resulting in the electroconductive composite film of PPTA with improved mechanical properties. The PPTA/polyyyrrole with p-toluenesulfonate as a dopant had the conductivity of 50 Scm−1, the modulus of 6.2 GPa and the strength of 140 MPa. The conductivity was stabilized as high as 150°C. The SEM observation and the analysis of dynamic viscoelasticity proved the composite film being composed of two-phase structure.A novel aramid, poly(p-phenylene[2,5-bis(4-carboxyphenyl)pyrazine]amide) (PPPA), was synthesized. PPPA is soluble in pure sulfuric acid to form liquid crystal. The X-ray diffraction pattern of the oriented PPPA film predicts that the conformation of the PPPA chain in crystal takes all-trans form, giving the good agreement of the fiber period with the calculated one. It is noticeable that PPPA is dissolved into DMSO with formation of polyanion by the reagent of sodium methylsulfinylcarbanion and the electrolysis of the solution is conducted, resulting in a PPPA film on the anode like PPTA. The aramid copolymer of PPTA forming a molecular coil was unable to be electrodeposited. Thus, it is believed that only the rigid-rod polyelectrolytes are capable of film formation by electrolysis.

The increasing demand for miniaturized portable electrical energy sources has led towards intensive research on developing efficient electrochemical energy storage/conversion devices. Based on the capability of delivering continuous energy for a longer period of time or quick charge-discharge capabilities, these devices can be divided into energy and current sourcing devices. Among these devices, batteries show intermediate power density along with energy density. At present in most of the commercially available devices, liquid organic carbonate electrolytes having conductivity values close to 10􀀀3 Scm􀀀1 are being used. Although liquid electrolyte shows a high conductivity value, they possess a serious safety concern. Therefore, prior importance is given to developing a polymer electrolyte with comparable ionic conductivity at ambient temperature. Polymer electrolyte has the prospect to improve various key properties of lithium based batteries when used as the electrolyte. These properties include design flexibility, safety, cyclability, energy and power density etc. However, polymer electrolytes are having a serious drawback of low ionic conductivity limiting its potential application. Therefore primary interest is given in the preparation of polymer electrolytes with high ionic conductivity at room temperature. Achievement of the desired level of ambient temperature ionic conductivity (_ 10􀀀3 Scm􀀀1) is still an open problem. Literature suggests that to improve the ionic conductivity of polymer electrolytes several strategies such as plasticization, copolymerization, fabrication of composite/nano-composite etc. have been studied extensively. These techniques mainly concentrate on increasing the amorphous content of polymer electrolytes in order to favour ion mobility to increase the ionic conductivity. In this regard, optimization of ionic conductivity of polymer electrolytes is carried out in the present investigation for composite polymer electrolytes and gel polymer electrolytes. In addition to the process of optimization, prior importance is also given on the understanding the ion conduction mechanism in these two class of polymer electrolytes. In this study three different series of polymer composite electrolytes are prepared using polyethylene oxide as the host polymer, lithium triflate as salt and nanocrystalline zirconia, titania and organo-modified hydrophobic montmorillonite clay as fillers. In addition to this a series of gel polymer electrolyte is also prepared by blending polymer host and 1 molar lithium triflate electrolyte solution consisting of a mixture of ethylene carbonate and diethyl carbonate as solvent. Phase formation of the filler materials, composite nature of polymer composite electrolytes and blended polymer host matrix prepared for gel polymer electrolytes are studied using X-ray diffraction technique. Surface morphology of all these materials is studied using FE-SEM. Polymer salt interactions are investigated using FTIR. Ionic conductivity is measured over a wide range of temperature for getting proper idea about its temperature dependent behaviour. In all these electrolytes, we have achieved room temperature ionic conductivity up to the order of 10􀀀5 S cm􀀀1. This is nearly two order higher in magnitude than conventional polymer-salt complexes at room temperature. Though we are successful in increasing the ionic conductivity by almost two orders in magnitude at room temperature, there exist a huge scope for further improvement in terms of the magnitude of the ionic conductivity. For this reason, a proper understanding of ion conduction mechanism is necessary. Ionic transport mechanism is probed using broadband dielectric spectroscopy over a wide range of frequency and temperature. Relaxation dynamics at different length and time scale is analyzed using broadband dielectric spectroscopy in order to get a proper idea about the ion conduction processes taking place at the microscopic level. The physical parameters that aids in increasing the ionic conductivity of these materials are also studied with observations made from broadband dielectric spectroscopy. An in-depth step by step analysis of the data obtained from electrical characterizations are carried out. The temperature-dependent ionic conductivity for polymer composite electrolytes are found to follow VTF behaviour, indicating there exist coupling between ionic conductivity and polymer segmental motion. Segmental relaxation time also follow similar behaviour. To explain and investigate the coupled nature of ion conduction mechanism, ion diffusivity analysis is carried out by employing Trukhan model. The outcome of these analysis also supports the coupled nature of ion conduction process. Empirical laws like Jonscher power law, double power law and different models like RFEBM, Ngai coupling model, MIGRATION model are used to describe the frequency and temperature dependent ionic conductivity of polymer electrolytes. Havriliak -Negami expression is used to analyze the relaxation phenomenon present in polymer electrolytes. Study of ion conduction mechanism in polymer nanocomposite electrolyte suggest ionic conduction and segmental relaxation are coupled physical process. In the case of polymer gel electrolytes, polymer host does not play any significant role in ionic conduction but only provide the mechanical stability to the absorbed liquid electrolytes. Proper understanding of ion conduction mechanism will help us for preparing good quality polymer electrolytes with high room temperature ionic conductivity, excellent mechanical, thermal and electrochemical stability. By achieving the aforementioned desired properties, the solid polymer electrolytes can replace the organic carbonate liquid based electrolytes commonly used in most of the portable energy storage/conversion devices.

With low driving voltage (<5V) and the ability to be operated in aqueous environments, ionic polymer-metal composite (IPMC) materials are quickly gaining attention for use in underwater applications. There are, however, drawbacks to IPMCs, including the “back relaxation” effect. Specifically, when subjected to a DC input (or an excessively slow dynamic input), the IPMC actuator will slowly relax back toward its original position. There is debate over the physical mechanism of back relaxation, although one prevalent theory describes an initial current, caused by the electrostatic forces of the charging electrodes, which drives water molecules across the ion-exchange membrane and deforms the IPMC. Once the electrodes are fully charged, however, the dominant element of the motion is the osmotic pressure, driving the water molecules back to equilibrium, thus causing back relaxation. A new method to mitigate back relaxation is proposed, taking advantage of controlled activation of patterned (sectored) electrodes on the IPMC. Whereas previous approaches to correct back relaxation rested on an increase of input voltage which can lead to electrolysis, subsequently damaging the material, this method involves only proper control of isolated electrodes to compensate for the back relaxation and does not require sensor feedback. An electromechanical model of the actuator is used to guide the design of these input signals, and the feasibility of using electrode patterning to mitigate back relaxation is demonstrated. Without reaching electrolysis, an IPMC is able to maintain its position for approximately 30 seconds. Compared to a simple step response, the rate of relaxation is reduced by 94% and the maximum error is reduced by 64%.