Electrical and electrochemical studies on magnesium ion-based polymer gel electrolytes

The development of polymer gel electrolyte system with high ionic conductivity is the main objective of polymer research. Electrochemical devices based on lithium ion-conducting polymer electrolyte are not safe due to the explosive nature of lithium. An attempt has been made to synthesize magnesium ion-conducting polymeric gel electrolytes, poly (vinylidene fluoride-co-hexafluoropropylene)–propylene carbonate–magnesium perchlorate, PVdF(HFP)-PC–Mg(ClO₄)₂ using standard solution-cast techniques. The maximum room temperature ionic conductivity of the synthesized electrolyte system has been observed to be 5.0 × 10⁻³ S cm⁻¹, which is quite acceptable from a device fabrication point of view. The temperature-dependent conductivity and the dielectric behavior were also analyzed. The pattern of the temperature-dependent conductivity shows the Arrhenius behavior. The dielectric constant ε _r and dielectric loss ε _i increases with temperature in the low-frequency region but almost negligible in the high-frequency region. This behavior can be explained on the basis of electrode polarization effects. The real part M _r and imaginary part M _i versus frequency indicate that the systems are predominantly ionic conductors. Further, the synthesized electrolyte materials have been checked for its suitability in energy storage devices namely redox supercapacitor with conducting polymer polypyrrole as electrode materials, and finally, it was observed that it shows good capacitive behavior in low-frequency region. Preliminary studies show that the overall capacitance of 22 mF cm⁻² which is equivalent to a single electrode specific capacitance of 117 F gm⁻¹ was observed for the above said supercapacitors.     

Novel zinc ion conducting polymer gel electrolytes based on ionic liquids

We report novel zinc ion conducting polymer gel electrolytes (PGEs) based on non-volatile room temperature ionic liquids. The PGEs consist of an ionic liquid, with a zinc salt dissolved in it, blended with a polymer matrix, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). The resultant electrolyte membranes are freestanding, translucent, flexible and elastic, with excellent mechanical integrity and strength. They possess exceptional thermal stability, exhibit essentially no weight loss under dynamic vacuum or upon heating to 200 °C, and remain the same gel phase in wide temperature ranges, with ionic conductivities on the order of 10⁻³ S/cm at room temperature, 10⁻⁴ S/cm at −20 °C and 4–5 × 10⁻³ S/cm at 80 °C. Electrochemical tests show that zinc ions are mobile in the membranes and zinc metal is capable of dissolution into and deposition from the membranes. The membranes also exhibit wide electrochemical stability windows. The results of this study demonstrate the promise of developing PGEs based on ionic liquids for potential application in next-generation non-aqueous zinc battery systems.     

Investigations on electrochemical supercapacitors using polypyrrole redox electrodes and PMMA based gel electrolytes

Polypyrrole based solid state electrochemical redox supercapacitors have been fabricated using the polymeric gel electrolytes comprising of poly methyl methacrylate (PMMA)-propylene carbonate (PC)-ethylene carbonate (EC)-perchlorate salts of different cations [Li⁺, Na⁺ and (C₂H₅)₄N⁺ (TEA⁺)]. A comparative study has been carried out using linear sweep reversal voltammetry, complex impedance spectroscopy and constant current charge-discharge tests. The capacitance values of the cells have been observed to be in the range of 15.3-22.5 mF cm⁻² (equivalent to single electrode specific capacitance of 120-178 F g⁻¹ of polypyrrole). This corresponds to the values of energy density 16.7-24.7 Wh kg⁻¹ and power density 1.6-2.8 kW kg⁻¹ calculated for the working voltage of 1.0 V limited for polypyrrole based redox capacitors. Substantial improvements in the coulombic efficiency of the cells have been observed (close to 100%) due to the application of gel electrolytes showing flexible and liquid like behaviour. Further, the types and sizes of the cations in the gel electrolytes do not play any dominant role in the capacitive behaviour of the redox cells.     

Review on gel polymer electrolytes for lithium batteries

This paper reviews the state-of-art of polymer electrolytes in view of their electrochemical and physical properties for the applications in lithium batteries. This review mainly encompasses on five polymer hosts namely poly(ethylene oxide) (PEO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVdF) and poly(vinylidene fluoride-hexafluoro propylene) (PVdF-HFP) as electrolytes. Also the ionic conductivity, morphology, porosity and cycling behavior of PVdF-HFP membranes prepared by phase inversion technique with different non-solvents have been presented. The cycling behavior of LiMn₂O₄/polymer electrolyte (PE)/Li cells is also described.     

Research progress on gel polymer electrolytes for lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries have become a promising candidate for advanced energy storage system owing to low cost and high theoretical specific energy.In the last decade,in pursuit of Li-S batteries with enhanced safety and energy density,the investigation on the electrolytes has leaped form liquid organic electrolytes to solid polymer ones.However,such solid-state Li-S battery system is greatly limited by unfavorable ionic conductivity,poor interfacial contact and narrow electrochemical windows on account of the absence of any liquid components.To address these issues,gel polymer electrolytes(GPEs),the incorporation of liquid electrolytes into solid polymer matrixes,have been newly developed.Although the excellent ionic transport and low interfacial resistance provided by GPEs have prompted numerous researchers to make certain progress on high-performance Li-S coins,a comprehensive review on GPEs for Li-S batteries remains vacant.Herein,this review focuses on recent development and progress on GPEs in view of their physical and chemical properties for the applications in Li-S batteries.Studies on the components including solid hosts,liquid solutions and fillers of GPEs are systematically summarized with particular emphasis on the relationship between components and performance.Finally,current challenges and directional outlook for fabricating GPEs-based Li-S batteries with outstanding performance are outlined.     

Stabilities of flexible electrochemical capacitors based on polypyrrole/carbon fibers in different gel electrolytes

Flexible electrochemical capacitors(ECs) are vitally important as the emerging flexible electronics.We have prepared polypyrrole doped with counter ion of Cl-on carbon fibers(PPy-Cl/CFs) via the simple electrochemical deposition method.The flexible ECs based on PPy-Cl/CFs electrodes have been assembled by using H_3PO_4/poly(vinyl alcohol)(PVA),H_2SO_4/PVA,LiClO_4/PVA,KCl/PVA and Li Cl/PVA as gel electrolytes.The capacitive properties of ECs have been systematically evaluated with electrochemical methods.The results show that the cells with H_3PO_4/PVA electrolyte exhibit good cyclic stability(91.5% retention after 15000 cycles) although PPy-Cl/CFs has moderate specific capacitance in H_3PO_4/PVA(41.6 m F·cm~(-1) or 52.0 F·cm~(-3)).However,the ECs in other electrolytes have poor cyclic stability.Further electrochemical analysis reveals that the doping/dedoping processes of PPy-Cl/CFs are different in the five electrolytes,and X-ray photoelectron spectra demonstrate that the ratios of counter anions in PPy's oxidized states to those in reduced states are obviously different when PPy-Cl/CFs are kept in reduced or oxidized states in the five electrolytes.The results also illustrate why the capacitors using H_3PO_4/PVA as electrolyte exhibit good cyclic stability.Furthermore,a light emitting diode(LED) with a threshold voltage of 2.5 V can be lighted by three ECs connected in series.     

Synthesis and electrochemical characterization of aPEO-based polymer electrolytes

In this paper, the preparation and purification of an amorphous polymer network, poly[oxymethylene-oligo(oxyethylene)], designated as aPEO, are described. The flexible CH₂CH₂O segments in this host polymer combine appropriate mechanical properties, over a critical temperature range from −20 to 60 °C, with labile salt-host interactions. The intensity of these interactions is sufficient to permit solubilisation of the guest salt in the host polymer while permitting adequate mobility of ionic guest species. We also report the preparation and characterisation of a novel polymer electrolyte based on this host polymer with lithium tetrafluoroborate, LiBF₄, as guest salt. Electrolyte samples are thermally stable up to approximately 250 °C and completely amorphous above room temperature. The electrolyte composition determines the glass transition temperature of electrolytes and was found to vary between −50.8 and −62.4 °C. The electrolyte composition that supports the maximum room temperature conductivity of this electrolyte system is n = 5 (2.10 × 10⁻⁵ S cm⁻¹ at 25 °C). The electrochemical stability domain of the sample with n = 5 spans about 5 V measured against a Li/Li⁺ reference. This new electrolyte system represents a promising alternative to LiCF₃SO₃ and LiClO₄-doped PEO analogues.     

Preparation and characterization of pva based solid polymer electrolytes for electrochemical cell applications

Solid polymer electrolyte films containing poly(vinyl alcohol) (PVA) and magnesium nitrate (Mg(NO3)2) were prepared by solution casting technique and characterized by using XRD, FTIR, DSC and AC impedance spectroscopic analysis. The amorphous nature of the polymer electrolyte films has been confirmed by XRD. The complex formation between PVA and Mg salt has been confirmed by FTIR. The glass transition temperature decreases with increasing the Mg salt concentration. The AC impedance studies are performed to evaluate the ionic conductivity of the polymer electrolyte films in the range of 303 383 K, and the temperature dependence seems to obey the Arrhenius behavior. Transport number measurements show that the charge transport is mainly due to ions. Electrochemical cell of configuration Mg/(PVA + Mg(NO3)2) (70:30)/(I2 + C + electrolyte) has been fabricated. The discharge characteristics of the cell were studied for a constant load of 100 kΩ.     

Thermal and electrochemical characteristics of plasticized polymer electrolytes based on poly(acrylonitrile-co-methyl methacrylate)

The thermal and electrochemical characteristics of plasticized polymer electrolytes composed of poly(acrylonitrile-co-methyl methacrylate) [P(AN-co-MMA)], a plasticizer [a mixture of ethylene carbonate and propylene carbonate], and LiCF₃SO₃ were investigated. The incorporation of a MMA unit into the matrix polymer was effective for an increase in the compatibility between the matrix polymer and the plasticizer. The comparative investigation of the interfacial resistance of the Li/polymer electrolyte/Li cell for the PAN-based and the P(AN-co-MMA)-based polymer electrolytes showed that the MMA unit could improve the stability of the polymer electrolyte toward the Li electrode, which is probably due to the enhanced adhesion of the polymer electrolyte to the Li electrode. Received: 14 July 1997 / Accepted: 14 May 1998     

Influence of plasticizer type on the properties of polymer electrolytes based on chitosan

Polymer electrolytes were obtained by the casting technique from a solution containing chitosan, hydrochloric acid, and plasticizer such as glycerol, ethylene glycol, and sorbitol. The transparent membranes with good ionic conductivity properties were characterized by impedance and UV-vis spectroscopies, thermal analysis (DSC), and X-ray diffraction. The best ionic conductivity values of 9.5 x 10(-4) S cm(-1) at room temperature and 2.5 x 10(-3) S cm(-1) at 80 degrees C were obtained for the sample containing 59 wt% of glycerol and an equimolar amount of HCl with respect to NH2 groups in chitosan. The temperature dependence of the ionic conductivity exhibits an Arrhenius behavior with activation energy of 16.6 kJ mol(-1). The thermal analysis indicates that both glass transition temperature (-87 degrees C) and crystallinity are low for this electrolyte. The samples with 13 wt% of LiCF3SO3 showed that the ionic conductivity values of 2.2 x 10(-5) S cm(-1) at room temperature and 4 x 10(-4) S cm(-1) at 80 degrees C are predominantly amorphous and showed a low glass transition temperature of about -73 degrees C.     

Solid polymer electrochemical capacitors using heteropoly acid electrolytes

An electrochemical capacitor utilizing a polyvinyl alcohol (PVA) and H₄SiW₁₂O₄₀ (SiWA) solid polymer electrolyte was developed. The electrolyte was deposited via precursor solution coating followed by thermal pressing and exhibited an ionic conductivity of 0.01 S/cm. The electrolyte has also shown good stability and cycle life. The performance of the solid polymer electrolyte-based capacitor was characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and was compared to a similar capacitor with an aqueous electrolyte.     

Polyacrylamide-methanesulfonic acid gel polymer electrolytes for tin-air battery

The present work describes the synthesis and characterization of gel polymer electrolytes containing methanesulfonic acid (MSA) with Polyacrylamide (PAAm). The PAAm–MSA gel electrolytes were prepared with different concentrations of MSA. Addition of 0.5 M of MSA into the electrolyte increased the ionic conductivity of PAAm from 1.35 × 10^?3 to 1.56 × 10^?2 S cm^?1. The maximum ionic conductivity of 7.0 × 10^?1 S cm^?1 was obtained with 3 M MSA at room temperature. The chemical interaction between PAAm and MSA was studied by Fourier transformed infra-red. The performance as a polymer electrolyte was evaluated from the cell discharge and open circuit potential measurements of a tin-air cell. The tin-air cell supported relatively high current, up to 12 mA cm^?2 with a maximum power density of 5 mW cm^?2. The open-circuit potential of the cell was 1.27 V for 24 h.     

Solid asymmetric electrochemical capacitors using proton-conducting polymer electrolytes

Solid asymmetric electrochemical capacitors (EC) using polyvinyl alcohol (PVA)–heteropoly acid (HPA) electrolytes and RuO₂–graphite electrodes were developed. The devices were about 0.2 mm thick and had a working voltage window of 0–1.5 V, 50% wider than that of any proton-conducting symmetric EC. Pseudocapacitance from HPA contributes to the total capacitance of the asymmetric EC within a certain potential window. The PVA–HPA polymers have been proven to function both as electrolyte and as pseudocapacitive electrode material in EC cells.     

Highly concentrated polycarbonate‐based solid polymer electrolytes having extraordinary electrochemical stability

Solid polymer electrolytes (SPEs) are compounds of great interest as safe and flexible alternative ionics materials, particularly suitable for energy storage devices. We study an unusual dependence on the salt concentration of the ionic conductivity in an SPE system based on poly(ethylene carbonate) (PEC). Dielectric relaxation spectroscopy reveals that the ionic conductivity of PEC/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte continues to increase with increasing salt concentration because the segmental motion of the polymer chains is enhanced by the plasticizing effect of the imide anion. Fourier transfer‐infrared (FTIR) spectroscopy suggests that this unusual phenomenon arises because of a relatively loose coordination structure having moderately aggregated ions, in contrast to polyether‐based systems. Comparative FTIR study against PEC/lithium perchlorate (LiClO₄) electrolytes suggests that weak ionic interaction between Li and TFSI ions is also important. Highly concentrated electrolytes with both reasonable conductivity and high lithium transference number (t₊) can be obtained in the PEC/LiTFSI system as a result of the unusual salt concentration dependence of the conductivity and the ionic solvation structure. The resulting concentrated PEC/LiTFSI electrolytes have extraordinary oxidation stability and prevent any Al corrosion reaction in a cyclic voltammetry. These are inherent effects of the highly concentrated salt. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2442–2447     

Study of the role of ceramic filler in composite gel electrolytes based on microporous polymer membranes

The presented contribution aims at reconsidering the role of filler in affecting the ionic transport in composite gel electrolytes for Li-ion cells based on microporous polymer membranes. The gels have been prepared by swelling thin PVdF/HFP membranes either with conventional liquid electrolyte or with pure propylene carbonate solvent. The membranes contained dispersed submicron-size modified silica filler added in a wide range of weight ratios. The effect of filler content on the kinetics of liquid phase absorption and evaporation from the composite membranes, as well as on the conductivity of the corresponding gel electrolytes, has been studied and discussed in terms of the “colloidal” and “soggy sand” electrolyte concepts. It has been found that conductivity increase of composite gels is not directly correlated with the liquid electrolyte uptake. On this basis it is concluded that important part of ionic transport in this type of composite gel polymer electrolytes is realized on the filler grain boundaries, through overlapping space charge layers of the silica grains.     

Compositional effect of PVdF-PEMA blend gel polymer electrolytes for lithium polymer batteries

Owing to their improved mechanical properties and good polymer miscibility, the blend gel polymer electrolytes of poly (vinylidene fluoride) (PVdF)-poly(ethyl methacrylate) (PEMA) have been prepared using solvent casting technique and characterized for their electrochemical performances. The electrolyte shows a maximum ionic conductivity of 1.5 × 10⁻⁴ S cm⁻¹ at 301 K for the 90:10 blend ratio of PVdF:PEMA system with good transport property. The ionic conductivity is enhanced, in accompany with improved microstructural homogeneity, at low PEMA contents, while the decreased conductivity at high contents has been attributed to increasing crystalline PEMA domains. With the optimum PVdF:PEMA ratio, the complex system was found to facile reasonable ionic transference number and exhibit superior interfacial stability with Li electrode.     

Semi-interpenetrated polymer networks based on modified cellulose and starch as gel polymer electrolytes for high performance lithium ion batteries

Cellulose - Poly(ethylene oxide) (PEO) is one of the most famous polymer electrolytes; however, its low conductivity and capacity have prevented its commercial applications. This study utilizes...     

Amphiphilic polymer gel electrolytes. II. Influence of the ethylene oxide side‐chain length on the gel properties

Amphiphilic polymers consisting of copolymethacrylates carrying about 26 wt % ethylene oxide [(EO)_n] side chains of different lengths were used as matrices in gel electrolytes. The gel electrolytes were composed of 30 wt % copolymer and 70 wt % 1 M LiPF₆ in a mixture of ethylene carbonate and γ‐butyrolactone (2/1 w/w). The coordination of lithium ions by the (EO)_n side chains in competition with the solvent was studied by Raman spectroscopy. A significantly stronger lithium coordination was observed when the gel electrolyte was based on a copolymer carrying (EO)₉ units in comparison with copolymers having (EO)₁, (EO)₂, and (EO)₄ units. Despite the observed stronger lithium coordination by (EO)₉ units in the gel, the ion conductivity was not significantly lower with respect to the gels based on the other copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1519–1524, 2001     

Proton conducting polymer blend electrolytes based on MC: FTIR,ion transport and electrochemical studies

In this work, the free-standing plasticized solid polymer electrolyte films were made utilizing methylcellulose (MC) and dextran (DN) doped with ammonium fluoride (NH₄F) and plasticized with glycerol by a typical solution casting approach. Based on the characterizations, MC-DN-NH₄F electrolyte has been shown to improve the structural, electrical, and electrochemical properties resulting from the dispersion of glycerol plasticizer. The electrochemical impedance spectroscopy (EIS) measurement for the highest inclusion of plasticizer revealed a conductivity of 2.25 × 10^-3 S/cm. The electrical equivalent circuit (EEC) model has established the circuit elements for each electrolyte. The variation trend of dielectric constant and DC conductivity was matched and confirmed by the EIS data. The fourier transform infrared (FTIR) analysis displayed credible confirmation of polymers-ion-plasticizer interactions. The dielectric study is extra highlighted the conductivity behavior. The dielectric constant and loss (ε′ and ε″) quantities were reported to be high at low frequencies. On the other hand, the irregular shape of the imaginary part of modulus (M“) spectra denotes the non-Debye behaviors of relaxation. The ion transference number (t_ion) value for the maximum plasticized system is 0.944, where the ions are the primary components for the charge transfer process. Stability of the highest conducting sample is determined to be 1.6 V, using linear sweep voltammetry (LSV).