Solid polymer electrolytes based on squaric acid structure

Poly(squarate)s (PPS-1 and PPS-2) were synthesized by the reaction of squaryl dichloride with hydroquinone for PPS-1 and with 2,5-diethoxy-1,4-bis(trimethylsilyloxy)benzene for PPS-2, and the ionic conductivities, thermal properties, and electrochemical and thermal properties of their polymer electrolytes with LiN(CF₃SO₂)₂ were investigated. The ionic conductivity increased with increasing the lithium salt concentration for the PPS-1–LiN(CF₃SO₂)₂ electrolyte, and the highest ionic conductivities of 8.60 × 10⁻⁵ S/cm at 100 °C and 9.57 × 10⁻⁸ S/cm at 30 °C were found at the [Li] to [O] ratio of 2:1. And also, the ionic conductivity for the PPS-1–LiN(CF₃SO₂)₂ electrolyte increased with an increase in the lithium salt concentration, reached a maximum value at the [Li] to [O] ratio of 1:2, and then decreased. The highest ionic conductivity was to be 1.04 × 10⁻⁵ S/cm at 100 °C and 1.71 × 10⁻⁸ S/cm at 30 °C, respectively. Both polymer electrolytes exhibited relatively better electrochemical and thermal stabilities. Addition of the PPS-1 as a plasticizer into the poly(ethylene oxide) (PEO)–LiN(CF₃SO₂)₂ electrolyte system suppressed the crystallization of PEO, and improved the ionic conductivity at room temperature. Invited paper dedicated to Professor W. Weppner on his 65th birthday.     

Electrical and structural properties of poly (ethylene oxide)/silver triflate polymer electrolyte system dispersed with MgO nanofillers

Solvent-free films of poly (ethylene oxide)–silver triflate (PEO–AgCF₃SO₃)/MgO-based nanocomposite polymer electrolytes (PEO)₅₀AgCF₃SO₃–x wt.% MgO (x = 1, 3, 5, 7, and 10) obtained using solution casting technique were found to exhibit an appreciably good complexation of MgO nanofiller within the polymer electrolyte system and non-Debye type of relaxation as revealed by Fourier transform infrared and complex impedance analyses. Optimized filler (5 wt.% MgO) when incorporated into the polymer electrolyte resulted in a maximum electrical conductivity of 2 × 10⁻⁶ S cm⁻¹ in conjunction with a silver ionic transference number (t _Ag+) of 0.23 at room temperature (298 K). Detailed structural, thermal, and surface morphological investigation indicated a slight reduction in the degree of crystallinity owing to the addition of MgO nanofiller.     

Ionic transport, thermal, XRD, and phase morphological studies on LiCF3SO3-based PVC–PVdF gel electrolytes

The plasticized polymer electrolyte composed of polyvinylchloride (PVC) and polyvinylidene fluoride (PVdF) as host polymer, the mixture of ethylene carbonate and propylene carbonate as plasticizer, and LiCF₃SO₃ as a salt was studied. The effect of the PVC-to-PVdF blend ratio with the fixed plasticizer and salt content on the ionic conduction was investigated. The electrolyte films reveal a phase-separated morphology due to immiscibility of the PVC with plasticizer. Among the three blend ratios studied, 3:7 PVC–PVdF blend ratio has shown enhanced ionic conductivity of 1.47 × 10⁻⁵ S cm⁻¹ at ambient temperature, i.e., the ionic conductivity decreased with increasing PVC-to-PVdF ratio and increased with increasing temperature. A temperature dependency on ionic conductivity obeys the Arrhenius behavior. The melting endotherms corresponding to vinylidene (VdF) crystalline phases are observed in thermal analysis. Thermal study reveals the different levels of uptake of plasticizer by VdF crystallites. The decrease in amorphousity with increase in PVC in X-ray diffraction studies and larger pore size appearance for higher content of PVC in scanning electron microscopy images support the ionic conductivity variations with increase in blend ratios.     

A novel PEO-based composite polymer electrolyte with NaAlOSiO molecular sieves powders

Ion-conducting thin film polymer electrolytes based on poly(ethylene oxide) (PEO) complexes with NaAlOSiO molecular sieves powders has been prepared by solution casting technique. X-ray diffraction, scanning electron microscopy, differential scanning calorimeter, and alternating current impedance techniques are employed to investigate the effect of NaAlOSiO molecular sieves on the crystallization mechanism of PEO in composite polymer electrolyte. The experimental results show that NaAlOSiO powders have great influence on the growth stage of PEO spherulites. PEO crystallization decrease and the amorphous region that the lithium-ion transport is expanded by adding appropriate NaAlOSiO, which leads to drastic enhancement in the ionic conductivity of the (PEO)₁₆LiClO₄ electrolyte. The ionic conductivity of (PEO)₁₆LiClO₄-12 wt.% NaAlOSiO achieves (2.370 ± 0.082) × 10⁻⁴ S · cm⁻¹ at room temperature (18 °C). Without NaAlOSiO, the ionic conductivity has only (8.382 ± 0.927) × 10⁻⁶ S · cm⁻¹, enhancing 2 orders of magnitude. Compared with inorganic oxide as filler, the addition of NaAlOSiO molecular sieves powders can disperse homogeneously in the electrolyte matrix without forming any crystal phase and the growth stage of PEO spherulites can be hindered more effectively.     

Studies on PEO-based sodium ion conducting composite polymer films

A sodium ion conducting composite polymer electrolyte (CPE) prepared by solution-caste technique by dispersion of an electrochemically inert ceramic filler (SnO₂) in the PEO–salt complex matrix is reported. The effect of filler concentration on morphological, electrical, electrochemical, and mechanical stability of the CPE films has been investigated and analyzed. Composite nature of the films has been confirmed from X-ray diffraction and scanning electron microscopy patterns. Room temperature d.c. conductivity observed as a function of filler concentration indicates an enhancement (maximum) at 1–2 wt% filler concentration followed by another maximum at ∼10 wt% SnO₂. This two-maxima feature of electrical conductivity as a function of filler concentration remains unaltered in the CPE films even at 100 °C (i.e., after crystalline melting), suggesting an active role of the filler particles in governing electrical transport. Substantial enhancement in the voltage stability and mechanical properties of the CPE films has been noticed on filler dispersion. The composite polymer films have been observed to be predominantly ionic in nature with t _ion ∼ 0.99 for 1–2 wt% SnO₂. However, this value gets lowered on increasing addition of SnO₂ with t _ion ∼ 0.90 for 25 wt% SnO₂. A calculation of ionic and electronic conductivity for 25 wt% of SnO₂ film works out to be ∼2.34 × 10⁻⁶ and 2.6 × 10⁻⁷ S/cm, respectively.     

Photovoltaic activity in a ZnSe/PEO–chitosan blend electrolyte junction

Thin films of ZnSe and PEO–chitosan blend polymer doped with NH₄I and iodine crystals were prepared to form the two sides of a semiconductor electrolyte junction. ZnSe was electrodeposited on indium tin oxide (ITO) conducting glass. The polymer is a blend of 50 wt% chitosan and 50 wt% polyethylene oxide. The polymer blend was complexed with ammonium iodide (NH₄I), and some iodine crystals were added to the polymer–NH₄I solution to provide the I⁻/I³⁻redox couple. The room temperature ionic conductivity of the polymer electrolyte is 4.32 × 10⁻⁶ S/cm. The polymer film was sandwiched between the ZnSe semiconductor and an ITO glass to form a ZnSe/polymer electrolyte/ITO photovoltaic cell. The open circuit voltage (V _oc) of the fabricated cells ranges between 200 to 400 mV and the short circuit current between 7 to 10 μA.     

Effects of MnO<Subscript>2</Subscript> nano-particles on the conductivity of PMMA-PEO-LiClO<Subscript>4</Subscript>-EC polymer electrolytes

Li-ion rechargeable batteries based on polymer electrolytes are of great interest for solid state electrochemical devices nowadays. Many studies have been carried out to improve the ionic conductivity of polymer electrolytes, which include polymer blending, incorporating plasticizers and filler additives in the electrolyte systems. This paper describes the effects of incorporating nano-sized MnO₂ filler on the ionic conductivity enhancement of a plasticized polymer blend PMMA–PEO–LiClO₄–EC electrolyte system. The maximum conductivity achieved is within the range of 10⁻³ S cm⁻¹ by optimizing the composition of the polymers, salts, plasticizer, and filler. The temperature dependence of the polymer conductivity obeys the VTF relationship. DSC and XRD studies are carried out to clarify the complex formation between the polymers, salts, and plasticizer.     

Solvent-free nanocomposite proton-conducting membranes composed of cesium salt of phosphotungstic acid doped PVDF–CTFE/PEO blend

In this research, novel nanocomposite membranes were prepared using polymer blend of polyethylene oxide (PEO) and polyvinylidene fluoride–chloro tetrafluoro ethylene (PVDF–CTFE) copolymer with cesium salt of phosphotungstic acid (Cs_2.5H_0.5PWO₄₀) as proton conductor. Nanocomposite membranes were prepared by solvent-free procedure. The DSC studies show a decrease in crystalinity of polymer matrix with increasing PEO to PVDF–CTFE proportional ratio and the filler. The TGA studies show that membranes are stable up to 180 °C. The TGA also indicates that addition of cesium salt of phosphotungstic acid increases the thermal stability of membranes. The SEMs exhibit that membranes are non-porous and the additive components are homogenously dispersed. Conductivity tests for membranes were carried out in the range of 25–100 °C in dry and hydrated states. Results show that by increasing the temperature, membranes conductivities are increased. In dry state, except at the temperature of 45 °C, membranes which have the highest crystalinity, have the highest conductivity. The alteration of the conductivity in the range of temperatures in dry condition may be attributed to segmental motion of polymer which resulted in proton hopping from one site to another or increasing free volume for proton motion. In fully hydrated state, dynamic equilibrium between different proton moieties determines the mode of proton conductivity which can be described by Grothuss mechanism. In the presence of water molecule, the free proton may be formed. The conductivity for the membrane in hydrated state with the blend ratio of PVDF:PEO = 95:5 w/w and 10% addition of cesium salt of phosphotungstic acid at the temperature of 90 °C is 1.05 × 10⁻⁴ S cm⁻¹.     

Impedance and FTIR studies on plasticized PMMA–LiN(CF<Subscript>3</Subscript>SO<Subscript>2</Subscript>)<Subscript>2</Subscript> nanocomposite polymer electrolytes

Plasticized polymer electrolytes composed of poly(methyl methacrylate) (PMMA) as the host polymer and lithium bis(trifluoromethanesulfonyl)imide LiN(CF₃SO₂)₂ as a salt were prepared by solution casting technique at different ratios. The ionic conductivity varied slightly and exhibited a maximum value of 3.65 × 10⁻⁵ S cm⁻¹ at 85% PMMA and 15% LiN(CF₃SO₂)₂. The complexation effect of salt was investigated using FTIR. It showed some simple overlapping and shift in peaks between PMMA and LiN(CF₃SO₂)₂ salt in the polymer electrolyte. Ethylene carbonate (EC) and propylene carbonate (PC) were added to the PMMA–LiN(CF₃SO₂)₂ polymer electrolyte as plasticizer to enhance the conductivity. The highest conductivities obtained were 1.28 × 10⁻⁴ S cm⁻¹ and 2.00 × 10⁻⁴ S cm⁻¹ for EC and PC mixture system, respectively. In addition, to improve the handling of films, 1% to 5% fumed silica was added to the PMMA–LiN(CF₃SO₂)₂–EC–PC solid polymer electrolyte which showed a maximum value at 6.11 × 10⁻⁵ S cm⁻¹ for 2% SiO₂.     

Electrochemical study of P(VDF-HFP)/PMMA blended polymer electrolyte with high-temperature stability for polymer lithium secondary batteries

In the present study, a kind of solid polymer electrolyte (SPE) based on poly(vinylidene difluoride-co-hexafluoropropylene)/poly(methyl methacrylate) blends was prepared by a casting method to solve the safety problem of lithium secondary batteries. Owing to being plasticized with a room temperature ionic liquid, N-butyl-N′-methyl-imidiazolium hexafluorophosphate, the obtained SPE shows a thermal decomposition temperature over 300°C and an ionic conductivity close to 10⁻³ S cm⁻¹. The SPE-3 sample, in which the weight of two polymers is equivalent, possesses an ionic conductivity of 0.45 × 10⁻³ S cm⁻¹ at 25°C and presents an electrochemical window of 4.43 V. The ionic conductivity of the SPE-3 is as high as 1.73 × 10⁻³ S cm⁻¹ at 75°C approaching to that of liquid electrolyte. The electrochemical performances of the Li/LiFePO₄ cells confirmed its feasibility in lithium secondary batteries.     

Dielectric spectra of LiTFSI-doped chitosan/PEO blends

Solid-polymer-blend electrolyte consisting of chitosan and polyethylene oxide (PEO) in a 1:1 weight ratio and doped with lithium trifluoromethanesulfonimide (LiTFSI) salt was prepared by solution cast technique. The highest conducting film with conductivity value of 1.40 × 10^-6 S cm⁻¹ at room temperature consists of 30 wt% LiTFSI. The temperature dependence for the highest conducting film obeyed Arrhenius relationship. From loss tangent–frequency plots at different temperatures, the frequency f _max at which the plot is a maximum was obtained. From this, ln f _max vs 10³/T was plotted. The activation energy value obtained from the log σ vs 10³/T plot and ln f _max vs 10³/T plot is about the same, suggesting that the processes of conductivity and relaxation for the charge carriers are the same. This paper was presented at the International Conference on Solid State Science and Technology 2006, Kuala Terengganu, Malaysia, Sept. 4–6, 2006.     

Effect of ethylene carbonate plasticizer and TiO<Subscript>2</Subscript> nanoparticles on 49% poly(methyl methacrylate) grafted natural rubber-based polymer electrolyte

The effect of plasticizer and TiO₂ nanoparticles on the conductivity, chemical interaction and surface morphology of polymer electrolyte of MG49–EC–LiClO₄–TiO₂ has been investigated. The electrolyte films were successfully prepared by solution casting technique. The ceramic filler, TiO₂, was synthesized in situ by sol-gel process and was added into the MG49–EC–LiClO₄ electrolyte system. Alternating current electrochemical impedance spectroscopy was employed to investigate the ionic conductivity of the electrolyte films at 25 °C, and the analysis showed that the addition of TiO₂ filler and ethylene carbonate (EC) plasticizer has increased the ionic conductivity of the electrolyte up to its optimum level. The highest conductivity of 1.1 × 10⁻³ Scm⁻¹ was obtained at 30 wt.% of EC. Fourier transform infrared spectroscopy measurement was employed to study the interactions between lithium ions and oxygen atoms that occurred at carbonyl (C=O) and ether (C-O-C) groups. The scanning electron microscopy micrograph shows that the electrolyte with 30 wt.% EC posses the smoothest surface for which the highest conductivity was obtained.     

Transport properties of hexanoyl chitosan-based gel electrolyte

Films of hexanoyl chitosan-based polymer electrolyte were prepared by the technique of solution casting. The effect of plasticizer on the transport properties of hexanoyl chitosan:lithium trifluoromethanesulfonate (LiCF₃SO₃) electrolytes have been investigated. The plasticizer used was ethylene carbonate (EC). The highest room temperature conductivity achieved in the EC-plasticized hexanoyl chitosan-based electrolytes is 2.75×10⁻⁵ S cm⁻¹. The Rice and Roth model was used to explain the variations in the dc conductivity observed. The exponent, s, in Jonscher’s universal power law equation σ(ω)=σ _dc+Aω ^s , was analyzed as a function of temperature for the sample containing 30 wt% of EC. The analysis suggests that the conduction mechanism follows that proposed by the overlapping large polaron tunneling model.     

Solid polymeric electrolyte of PVC–ENR–LiClO<Subscript>4</Subscript>

The ionic conductivity of PVC–ENR–LiClO₄ (PVC, polyvinyl chloride; ENR, epoxidized natural rubber) as a function of LiClO₄ concentration, ENR concentration, temperature, and radiation dose of electron beam cross-linking has been studied. The electrolyte samples were prepared by solution casting technique. Their ionic conductivities were measured using the impedance spectroscopy technique. It was observed that the relationship between the concentration of salt, as well as temperature, and conductivity were linear. The electrolyte conductivity increases with ENR concentration. This relationship was discussed using the number of charge carrier theory. The conductivity–temperature behaviour of the electrolyte is Arrhenian. The conductivity also varies with the radiation dose of the electron beam cross-linking. The highest room temperature conductivity of the electrolyte of 8.5 × 10⁻⁷ S/cm was obtained at 30% by weight of LiClO₄. The activation energy, E _a and pre-exponential factor, σ _o, are 1.4 × 10⁻² eV and 1.5 × 10⁻¹¹ S/cm, respectively.     

Ionic conductivity studies of chitosan-based polymer electrolytes doped with adipic acid

Chitosan acetate–adipic acid film polymer electrolytes have been prepared by the solution cast technique. The highest conductivity is 1.4 × 10⁻⁹ S cm⁻¹ for 35 wt.% of adipic acid at room temperature. The sample with highest conductivity has the lowest activation energy. Calculations using the Rice and Roth model provide number of mobile ions, η. The conductivity is dependent on the diffusion coefficient and mobility.     

Effects of gamma radiation treatment and plasticizer on alkaline solid polymer electrolytes

Alkaline solid polymer electrolyte films have been prepared by the solvent-casting method. Gamma radiation treatment and propylene carbonate plastisizer were used to improve the ionic conductivity of the electrolytes at ambient temperature. The structure of the irradiated electrolytes changes from semi-crystalline to amorphous, indicating that the crosslinking of the polymer has been achieved at a dose of 200 kGy. The ionic conductivity at room temperature of PVA/KOH blend increases from 10⁻⁷ to 10⁻³ Scm⁻¹ after the PVA crosslinking and when the plasticizer concentration was increased from 20 to 30%. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

The effects of ceramic fillers on the PMMA-based polymer electrolyte systems

The effects of ceramics fillers on the polymethylmethacrylate (PMMA)-based solid polymer electrolytes have been studied using ac impedance spectroscopy and infrared spectroscopy. The polymer film samples were prepared using solution cast technique, tetrahydrofuran (THF) used as a solvent, and ethylene carbonate (EC) has been used as plasticizer. Lithium triflate salt (LiCF₃SO₃) has been incorporated into the polymer electrolyte systems. Two types of ceramic fillers, i.e., SiO₂ and Al₂O₃, were then implemented into the polymer electrolyte systems. The solutions were stirred for several hours before it is poured into petri dishes for drying under ambient air. After the film has formed, it was transferred into desiccator for further drying before the test. From the observation done by impedance spectroscopy, the room temperature conductivity for the highest conducting film from the (PMMA–EC–LiCF₃SO₃) system is 1.36 × 10⁻⁵ S cm⁻¹. On addition of the SiO₂ filler and Al₂O₃ filler, the conductivity are expected to increase in the order of ∼10⁻⁴ S cm⁻¹. Infrared spectroscopy indicates complexation between the polymer and the plasticizer, the polymer and the salts, the plasticizer and the salts, and the polymer and the fillers. The interactions have been observed in the C=O band, C–O–C band, and the O–CH₃ band. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7-9, 2006.     

Structural and ionic conductivity studies on P(ECH-EO):γ-BL:LiClO<Subscript>4</Subscript> plasticized polymer electrolyte

The plasticized polymer electrolyte consisting of poly(epichlorohydrin-ethyleneoxide) [P(ECH-EO)], lithium perchlorate (LiClO₄) and γ-butyrolactone (γ-BL) have been prepared by simple solution casting technique. The polymer–salt–plasticizer complex has been confirmed by XRD analysis. The ionic conductivity studies have been carried out using AC impedance technique. The effect of plasticizer (γ-BL) on ionic conductivity has been discussed with respect to different temperatures. The maximum value of ionic conductivity is found to be 1.3 × 10⁻⁴ Scm⁻¹ for 70P(ECH-EO):15γ-BL:15LiClO₄ at 303 K. The temperature dependence of the plasticized polymer electrolyte follows the Vogel–Tamman–Fulcher formalism. The activation energy is found to decrease with the increase in plasticizer.     

Investigation of dibutyl phthalate as plasticizer on poly(methyl methacrylate)–lithium tetraborate based polymer electrolytes

Polymer electrolyte membranes, comprising of poly(methyl methacrylate) (PMMA), lithium tetraborate (Li₂B₄O₇) as salt and dibutyl phthalate (DBP) as plasticizer were prepared using a solution casting method. The incorporation of DBP enhanced the ionic conductivity of the polymer electrolyte. The polymer electrolyte containing 70 wt.% of poly(methyl methacrylate)–lithium tetraborate and 30 wt.% of DBP presents the highest ionic conductivity of 1.58 × 10⁻⁷ S/cm. The temperature dependence of ionic conductivity study showed that these polymer electrolytes obey Vogel–Tamman–Fulcher (VTF) type behaviour. Thermogravimetric analysis (TGA) was employed to analyse the thermal stability of the polymer electrolytes. Fourier transform infrared (FTIR) studies confirmed the complexation between poly(methyl methacrylate), lithium tetraborate and DBP.     

Impedance spectroscopy studies of poly (methyl methacrylate)-lithium salts polymer electrolyte systems

In the present work, five systems of samples have been prepared by the solution casting technique. These are the plasticized poly(methyl methacrylate) (PMMA-EC) system, the LiCF₃SO₃ salted-poly(methyl methacrylate) (PMMA-LiCF₃SO₃) system, the LiBF₄ salted-poly(methyl methacrylate) (PMMA-LiBF₄) system, the LiCF₃SO₃ salted-poly(methyl methacrylate) containing a fixed amount of plasticizer ([PMMA-EC]-LiCF₃SO₃) system, and the LiBF₄ salted-poly(methyl methacrylate) containing a fixed amount of plasticizer ([PMMA-EC]-LiBF₄) system. The conductivities of the films from each system are characterized by impedance spectroscopy. The room temperature conductivity in the pure PMMA sample and (PMMA-EC) system is 8.57 × 10⁻¹³ and 2.71 × 10⁻¹¹ S cm⁻¹, respectively. The room conductivity for the highest conducting sample in the (PMMA-LiCF₃SO₃), (PMMA-LiBF₄), ([PMMA-EC]-LiCF₃SO₃), and ([PMMA-EC]-LiBF₄) systems is 3.97 × 10⁻⁶, 3.66 × 10⁻⁷, 3.40 × 10⁻⁵, and 4.07 × 10⁻⁷ S cm⁻¹, respectively. The increase in conductivity is due to the increase in number of mobile ions, and decrease in conductivity is attributed to ion association. The increase and decrease in the number of ions can be implied from the dielectric constant, ɛ_r-frequency plots. The conductivity–temperature studies are carried out in the temperature range between 303 and 373 K. The results show that the conductivity is increased when the temperature is increased and obeys Arrhenius rule. The plots of loss tangent against temperature at a fixed frequency have showed a peak at 333 K for the ([PMMA-EC]-LiBF₄) system and a peak at 363 K for the ([PMM-EC]-LiCF₃SO₃) system. This peak could be attributed to β-relaxation, as the measurements were not carried out up to glass transition temperature, T _g. It may be inferred that the plasticizer EC has dissociated more LiCF₃SO₃ than LiBF₄ and shifted the loss tangent peak to a higher temperature. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006