High performance PEO-based polymer electrolytes and their application in rechargeable lithium polymer batteries

Solvent-free, lithium-ion-conducting, composite polymer electrolytes have been prepared by a double dispersion of an anion trapping compound, i.e., calyx(6)pyrrole, CP and a ceramic filler, i.e., super acid zirconia, S-ZrO₂ in a poly(ethylene oxide)-lithium bis(oxalate) borate, PEO–LiBOB matrix. The characterization, based on differential thermal analysis and electrochemical analysis, showed that while the addition of the S-ZrO₂ has scarce influence on the transport properties of the composite electrolyte, the unique combination of the anion-trapping compound, CP, with the large anion lithium salt, LiBOB, greatly enhances the value of the lithium transference number without depressing the overall ionic conductivity. These unique properties make polymer electrolytes, such as PEO₂₀LiBOB(CP)_0.125, of practical interest, as in fact confirmed by tests carried out on lithium battery prototypes.     

Broad band dielectric behaviour of plasticized PEO-based solid polymer electrolytes

The conductivity and dielectric response of poly(ethylene oxide) (PEO) based plasticized polymer electrolyte systems were studied in the broad frequency range from 5 Hz to 1.8 GHz and in the temperature range from 248 K to 353 K. Propylene carbonate (PC) and ethylene carbonate (EC) were used as conventional plasticizers while poly(perfluorinated ethylene methylene oxide) (M03) was used as a new type of plasticizer. PEO-LiN(CF₃SO₂)₂ plasticized with M03 shows high enough conductivity values to be used as electrolyte in rechargeable lithium polymer batteries. At high frequency a dielectric relaxation is observed for pure PEO as well as for the salt containing systems in the GHz region that is assumed to be due to segmental motion of the polymer chains. In the salt containing systems, this relaxation is shifted to lower frequencies relative to that of pure PEO, this is attributed to transient cross-linking. However, at lower frequencies another dielectric response peak was detected in all samples containing salts. The effect of the plasticizer on this relaxation is complex. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

A novel PEO-based blends solid polymer electrolytes doping liquid crystalline ionomers

A novel PEO-based blends solid polymer electrolytes doping liquid crystalline ionomers (LCI), PEO/PMMA/LiClO₄/LCI, and PEO/LiClO₄/LCI were prepared by solution casting technology. Scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) analysis proved that LCI uniformly dispersed into the solid electrolytes and restrained phase separation of PEO and PMMA. Differential scanning calorimetry (DSC) results showed that LCI decreases the crystallinity of blends solid polymer electrolytes. Thermogravimetric analysis (TGA) proved LCI not only improved thermal stability of PEO/PMMA/LiClO₄ blends but also prevent PEO/PMMA from phase separation. Infrared spectra results illustrated that there exists interaction among Li⁺ and O, and LCI that promotes the synergistic effects between PEO and PMMA. The EIS result revealed that the conductivity of the electrolytes increases with LiClO₄ concentration in PEO/PMMA blends, but it increases at first and reaches maximum value of 2.53?×?10^?4 S/cm at 1.0 % of LCI. The addition of 1.0 % LCI increases the conductivity of the electrolytes due to that LCl promoting compatibility and interaction of PEO and PMMA. Under the combined action of rigidity induced crystal unit, soft segment and the terminal ionic groups in LCI, PEO/PMMA interfacial interaction are improved, the reduction of crystallinity degree of PEO leads Li⁺ migration more freely.     

Dielectric behaviour of cellulose acetate-based polymer electrolytes

The present work deals with the findings on the dielectric behaviour of cellulose acetate (CA) and its complexes consisting of ammonium tetrafluoroborate (NH₄BF₄) and polyethylene glycol with a molecular weight of 600?g/mol (PEG₆₀₀) that were prepared using the solution casting method. The highest ?? obtained for CA-NH₄BF₄ film was 2.18?×?10^?7 S cm^?1 and enhanced to 1.41?×?10^?5 S cm^?1 with the addition of 30?wt.% PEG₆₀₀. The dielectric behaviours of the selected samples were analyzed using complex impedance Z*, complex admittance A*, complex permittivity ?*, and complex electric modulus M*-based frequency and temperature dependence in the range of 10?Hz?C1?MHz and 303?C363?K, respectively. The variation in dielectric permittivity (?? _r and ?? _i) as a function of frequency at different temperatures exhibits a dispersive behaviour at low frequencies and decays at higher frequencies. The variation in dielectric permittivity as a function of temperature at different frequencies is typical of polar dielectrics in which the orientation of dipoles is facilitated with the rising temperature, and thereby the permittivity is increased. Modulus analysis was also performed to understand the mechanism of electrical transport process, whereas relaxation time was determined from the variation in loss tangent with temperature at different frequencies.     

Study on ionic conductivity and dielectric properties of PEO-based solid nanocomposite polymer electrolytes

The ionic conductivity and dielectric properties of the solid nanocomposite polymer electrolytes formed by dispersing a low particle-sized TiO₂ ceramic filler in a poly (ethylene oxide) (PEO)-AgNO₃ matrix are presented and discussed. The solid nanocomposite polymer electrolytes are prepared by hot press method. The optimum conducting solid polymer electrolyte of polymer PEO and salt AgNO₃ is used as host matrix and TiO₂ as filler. From the filler concentration-dependent conductivity study, the maximum ionic conductivity at room temperature is obtained for 10 wt% of TiO₂. The real part of impedance (Z′) and imaginary part of impedance (Z″) are analyzed using an LCR meter. The dielectric properties of the highest conducting solid polymer electrolyte are analyzed using dielectric permittivity (ε′), dielectric loss (ε″), loss tangent (tan δ), real part of the electric modulus (M′), and imaginary part of the electric modulus (M″). It is observed that the dielectric constant (ε′) increases sharply towards the lower frequencies due to the electrode polarization effect. The maxima of the loss tangent (tan δ) shift towards higher frequencies with increasing temperature. The peaks observed in the imaginary part of the electric modulus (M″) due to conductivity relaxation shows that the material is ionic conductor. The enhancement in ionic conductivity is observed when nanosized TiO₂ is added into the solid polymer electrolyte.     

Dielectric and conductivity relaxations in PVAc based polymer electrolytes

The polymer electrolytes composed of a blend of poly (vinyl acetate) (PVAc) and poly (methylmethacrylate) (PMMA) as a host polymer and LiClO₄ as a salt are prepared by a solution casting technique. The formation of blend polymer- salt complex has been confirmed by FT-IR spectral studies. The conductivity- temperature plots are found to follow an Arrhenius nature. Arrhenius plot shows the decrease in activation energy with the increase in salt concentration. The dielectric behaviour of the sample is analysed using dielectric permittivity (ε′), dielectric loss (ε″) and electric modulus (M″) of the samples. The impedance cole- cole plot shows the high frequency semi- circle is due to the bulk effect of the material and the depression in the semicircle shows the non-Debye nature of the material. The bulk conductivity is found to vary between 2.5×10⁻⁵ Scm⁻¹ to 1.7×10⁻³ Scm⁻¹ with the increase of salt concentration of blend polymer samples. The migration energy derived from the dissipation factor is almost equal to the activation energy calculated from conductivity. The modulus spectrum of the samples shows the non-Debye behaviour of the polymer electrolyte films. The low frequency dispersion of the dielectric constant implies the space charge effects arising from the electrodes. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Effect of silane-functionalized mesoporous silica SBA-15 on performance of PEO-based composite polymer electrolytes

Silane-functionalized mesoporous silica SBA-15 particles with ultra-high specific surface area and large pore size were used as fillers in PEO-based solid electrolytes. FT-IR results confirmed the silane functionalization of SBA-15. Ionic conductivity and lithium ion transference number of the composite polymer electrolytes were found to simultaneously reach a high value of 5 wt.% silane-functionalized SBA-15 introduced in the matrix. It may be due to the combination effects of the unique structure of SBA-15 (i.e., ultra-high specific surface area and large pore size), the particularly functionalized surface of SBA-15 to promote fast ion transfer, and the good dispersion and compatibility of silane-functionalized SBA-15 in the composite polymer electrolytes. The results suggest an alternative way to improve the performance of solid polymer electrolytes.     

Decoupling of ionic transport from segmental relaxation in polymer electrolytes

We present detailed studies of the relationship between ionic conductivity and segmental relaxation in polymer electrolytes. The analysis shows that the ionic conductivity can be decoupled from segmental dynamics and the strength of the decoupling correlates with the fragility but not with the glass transition temperature. These results call for a revision of the current picture of ionic transport in polymer electrolytes. We relate the observed decoupling phenomenon to frustration in packing of rigid polymers, where the loose local structure is also responsible for the increase in their fragility.     

Dielectric relaxation spectroscopy during isothermal curing of semi-interpenetrating polymer networks

Dielectric relaxation spectroscopy measurements have been performed during isothermal curing of semi-interpenetrating polymer networks (semi-IPNs) and the related pure networks at frequencies between 3 kHz and 3 MHz and curing temperatures between 313 and 393 K. The pure networks consist of diglycidyl ether of bisphenol A (DGEBA) cross-linked with diaminodiphenylmethane (DDM) and the semi-IPNs contain in addition 10 or 20 wt% of polysulfone PSn) as the linear component. Temperature dependent dielectric measurements have been performed on the fully cured samples in the temperature range from 130 to 550 K for the same frequencies. For the pure networks, the imaginary part of the complex permittivity ?″ shows a decrease with curing time t _cure followed by a peak. For the semi-IPNs this peak is much broader for all cases and can be resolved into two maxima for several curing conditions. The decrease in ?″ is connected to the decrease in the dc-conductivity due to gelation, whereas the peak is related to the relaxation of dipoles. The existence of two maxima in the time dependence of ?″ is an indication for two different relaxations in a phase separated structure. This is supported by temperature dependent measurements on the fully cured samples. The characteristic relaxation times ι, which are extracted from the maxima of ?″(t _cure) for different frequencies f using the relation ωτ = 1(ω = 2πf), increase during curing by several orders of magnitude for both the pure networks and the semi-IPNs. In order to extract the characteristic times for gelation t _g and the times t ₀ where the dc-conductivity σ_dc approaches a singularity, σ_dc was fitted by a power law, σ_dc = σ₀[(t _g - t)/t _g]^p, and an exponential function, σ_dc = A exp [B/(t - t _o)], respectively. In the error limits of the experiments both procedures lead to similar results. The t _g and t _o values are in good agreement with those measured mechanically and no significant differences between pure networks and semi-IPNs cured at the same temperature were found.     

Structural relaxation and anharmonicity in polymer electrolytes: Effect of the thermal history

Summary The effects of the storage at room temperature of PEO-KSCN polymer electrolytes have been studied by differential scanning calorimetry (DSC) and dynamical mechanical analysis. It has been revealed that, over the explored time interval, the annealing causes small variations in the anharmonic and relaxation properties of the samples, which are to be ascribed to changes in the relative amount of the phases building up the structure. The elastic and anelastic characteristics show a well-defined dependence on the degree of crystallinity of the polymer, which grows slightly with increasing annealing time. The application of a simplified version of a quasi-harmonic model and of the Kolrausch-Williams-Watts stretched exponential function permits to describe the temperature behaviour of the elastic modulusE′ and to obtain an anharmonicity parameter characterizing the polymeric system. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Effects of various LiPF<Subscript>6</Subscript> salt concentrations on PEO-based solid polymer electrolytes

In this research, various weight percents of LiPF₆ are incorporated into PEO-based polymer electrolyte system. Thin film electrolytes are prepared via solution casting technique and characterized by FTIR, XRD and DSC analyses in order to study their complex behaviour. The amorphicity of the electrolytes are measured by DC impedance. The results reveal that the conductivity increases with increasing temperature when the salt concentration increases to 20 wt.%. The conductivity for 20 wt.% of salt remains similar to the conductivity of 15 wt.% of salt at 318 K. Impedance studies show that the conductivity increases with increasing LiPF₆ concentration, whereas XRD studies reveal that the phase changes from crystalline to amorphous when LiPF₆ concentration increases. DSC studies indicate a decrease in T _m with increasing LiPF₆ concentration. Finally, the complexation process is examined using FTIR.     

Nanocomposite polymer electrolytes

The present effort reviews the state-of-the-art trends in respect of composite polymer electrolytes (CPEs) which are nowadays revolutionizing the modern approach towards energy storage and power supply gadgets. This evaluation mainly encompasses a series of systems based on polymer hosts such as poly(ethylene oxide) (PEO), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), poly(vinylidene fluoride) (PVDF), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), and polyvinylchloride (PVC) developed and analyzed so far apart from certain nanofiller incorporated composite polymer electrolytes being used in conjunction with well-suited electrodes owing to their practical significance in several advanced types of power sources including hybrid electric vehicles. The emerging nanoscale techniques have by now led the market to appreciate the application potential of nanostructured inorganic and organic materials so as to realize enhanced efficiencies of batteries thereby providing one of the most promising energy storage devices as well.     

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.     

Dielectric spectroscopy and confirmation of ion conduction mechanism in direct melt compounded hot-press polymer nanocomposite electrolytes

Solid-type polymer nanocomposite electrolyte (PNCE) comprising poly(ethylene oxide) (PEO), lithium perchlorate (LiClO₄) and montmorillonite (MMT) nano-platelets were synthesized by direct melt compounded hot-press technique at 70 °C under 3 tons of pressure. The spectra of complex dielectric function, electric modulus and alternating current (ac) electrical conductivity, and complex impedance plane plots of these materials were investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. The variation of electrode polarization and ionic conduction relaxation times with MMT concentration up to 20 wt.% confirms their strong correlation with direct current ionic conductivity. The predominance of exfoliated MMT structures in PEO matrix and their effect on cation conduction mechanism and ion pairing were discussed by considering a supramolecular transient cross-linked structure. The normalized ac conductivity as a function of scaled frequency of these PNCE materials obey the universal time–concentration superposition behaviour alike the disordered solid ionic conductors.     

Dielectric relaxation in Ih ice

Relaxation processes in Ih ice are studied in the temperature interval 77–27G°K and frequency band 5 Hz–500 kHz. A new maximum in thermally stimulated currents was found at 97°K, clarifying the nature of the relaxing defects. The parameters of the peaks of the thermally stimulated currents at 97, 127, 139, and 158°K are determined, and the concentrations of L defects and oriented H₂O dipoles are evaluated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 72–76, October, 1986.     

Dielectric relaxation and dc conductivity on the PVOH-CF3COONH4 polymer system

In the present paper, the ionic conductivity and the dielectric relaxation properties on the poly(vinyl alcohol)-CF₃COONH₄ polymer system have been investigated by means of impedance spectroscopy measurements over wide ranges of frequencies and temperatures. The electrolyte samples were prepared by solution casting technique. The temperature dependence of the sample’s conductivity was modeled by Arrhenius and Vogel-Tammann-Fulcher (VTF) equations. The highest conductivity of the electrolyte of 3.41×10^− 3 (Ωcm)^− 1 was obtained at 423 K. For these polymer system two relaxation processes are revealed in the frequency range and temperature interval of the measurements. One is the glass transition relaxation (α-relaxation) of the amorphous region at about 353 K and the other is the relaxation associated with the crystalline region at about 423 K. Dielectric relaxation has been studied using the complex electric modulus formalism. It has been observed that the conductivity relaxation in this polymer system is highly non-exponential. From the electric modulus formalism, it is concluded that the electrical relaxation mechanism is independent of temperature for the two relaxation processes, but is dependent on composition.     

Dielectric properties and fluctuating relaxation processes of poly(methyl methacrylate) based polymeric nanocomposite electrolytes

Solid polymer nanocomposite electrolytes (SPNEs) consisted of poly(methyl methacrylate) (PMMA) and lithium perchlorate (LiClO₄) of molar ratio C=O:Li⁺=4:1 with varying concentration of montmorillonite (MMT) clay as nanofiller have been prepared by classical solution casting and high intensity ultrasonic assisted solution casting methods. The dielectric/electrical dispersion behaviour of these electrolytes was studied by dielectric relaxation spectroscopy at ambient temperature. The dielectric loss tangent and electric modulus spectra have been analyzed for relaxation processes corresponding to the side groups rotation and the segmental motion of PMMA chain, which confirm their fluctuating behaviour with the sample preparation methods and also with change of MMT concentration. The feasibility of these relaxation fluctuations has been explained using a transient complex structural model based on Lewis acid–base interactions. The low permittivity and moderate dc ionic conductivity at ambient temperature suggest the suitability of these electrolytes in fabrication of ion conducting electrochromic devices and lithium ion batteries. The amorphous behaviour and the exfoliated/intercalated MMT structures of these nanocomposite electrolytes were confirmed by X-ray diffraction measurements.     

Effects of plasticizer and nanofiller on the dielectric dispersion and relaxation behaviour of polymer blend based solid polymer electrolytes

Solid polymer electrolytes consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend (50:50 wt/wt%) with lithium triflate (LiCF₃SO₃) as a dopant ionic salt at stoichiometric ratio [EO + (CO)]:Li⁺ = 9:1, poly(ethylene glycol) (PEG) as plasticizer (10 wt%) and montmorillonite (MMT) clay as nanofiller (3 wt%) have been prepared by solution cast followed by melt–pressing method. The X–ray diffraction study infers that the (PEO–PMMA)–LiCF₃SO₃ electrolyte is predominantly amorphous, but (PEO–PMMA)–LiCF₃SO₃–10 wt% PEG electrolyte has some PEO crystalline cluster, whereas (PEO–PMMA)–LiCF₃SO₃–10 wt% PEG–3 wt% MMT electrolyte is an amorphous with intercalated and exfoliated MMT structures. The complex dielectric function, ac electrical conductivity, electric modulus and impedance spectra of these electrolytes have been investigated over the frequency range 20 Hz to 1 MHz. These spectra have been analysed in terms of the contribution of electrode polarization phenomenon in the low frequency region and the dynamics of cations coordinated polymer chain segments in the high frequency region, and also their variation on the addition of PEG and MMT in the electrolytes. The temperature dependent dc ionic conductivity, dielectric relaxation time and dielectric strength of the plasticized nanocomposite electrolyte obey the Arrhenius behaviour. The mechanism of ions transportation and the dependence of ionic conductivity on the segmental motion of polymer chain, dielectric strength, and amorphicity of these electrolytes have been explored. The room temperature ionic conductivity values of the electrolytes are found ∼10⁻⁵ S cm⁻¹, confirming their use in preparation of all-solid-state ion conducting devices.