Polymer electrolytes based on poly(vinylidene fluoride-co-hexafluoropropylene) with crosslinked poly(ethylene glycol) for lithium batteries

The combination of a poly(ethylene glycol) (PEG) network and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) copolymer chains is one of the most efficient means for modifying PVDF-HFP gel electrolytes. Previous preparations tend to introduce contamination into the polymer gel electrolyte because of irradiation, high temperature or the initiator needed for crosslinking which might result in the electrochemical degradation. In order to overcome the above disadvantages, a new method has been developed to successfully prepare the semi-interpenetrating polymer networks of PVDF-HFP based electrolytes with crosslinked diepoxy polyethylene glycol (DIEPEG). In this process, impurities are avoided because of a moderate reaction temperature at 50 °C and poly(ethylenimine) (PEI) as the crosslinking agent. Microporous films with various compositions are prepared and characterized. Thermal, mechanical, swelling and electrochemical properties, as well as microstructures of the prepared polymer electrolytes have been investigated using thermogravimetric analysis, electrochemical impedance spectroscopy, linear sweep voltammetry, and scanning electron microscopy. The results show that the blend polymer electrolyte with PVDF-HFP/PEI + DIEPEG (60:40 w/w) has an ionic conductivity of 2.3 mS cm^? 1 at room temperature in the presence of 1 M LiPF₆ in EC and DMC (1:1 w/w). All the blend electrolytes are electrochemically stable up to 4.8 V versus Li/Li⁺. The results reveal that this new method may be very promising for improving PVDF-HFP based electrolytes.     

Mixed solid electrolytes based on poly(ethylene oxide)

Polymer solid electrolytes from a PEO-NaI system were mixed with Nasicon and Al₂O₃ powders. As a result an increase of ionic conductivity exceeding 10^–1 S/cm at room temperature was observed for both cases. This increase was due to a higher concentration of amorphous phase which resulted apparently from a higher nucleation rate during the solidification process. The samples were studied using impedance spectroscopy, X-ray diffraction, electron microscopy, NMR, and other techniques.     

Solvent-free double-layer capacitors with polymer electrolytes based on 1-ethyl-3-methyl- imidazolium triflate ionic liquid

A series of electrochemical capacitors based on carbon powders (specific surface areas 830 and 2600 m²/g) and polymer electrolytes were constructed and tested. Both polymer electrolytes as well as capacitor electrodes, in the form of thin foils, were prepared by a casting technique. All-plastic capacitors were coin-shaped, with a diameter of 12–18 mm and a mass of ∼100–500 mg, and were constructed by sandwiching the polymer electrolyte between two electrodes. An ionic liquid, 1-ethyl-3-methyl-imidazolium triflate, served both as a source of ions as well as a polymer plasticiser. In some cases, sulpholane was added to the system as an additional plasticiser. Poly(acrylonitrile), poly(vinylidenefluoride), and its copolymer with hexafluoropropylene, poly(ethylene oxide), poly(vinyl alcohol) as well as poly(methylmethacrylate) served as a polymer matrix. Polymer electrolytes showed conductivity up to 16 mS/cm. The performance of the capacitors was determined by cyclic voltammetry, impedance spectroscopy and galvanostatic charging/discharging. Specific capacity was up to 230 F/g, expressed versus the mass of the carbon material. PACS 82.47.Uv     

Magnesium ion-conductive poly(ethylene carbonate) electrolytes

Magnesium (Mg) electrolytes are presently under investigation for their promising performance capabilities in the next generation of batteries. The present work studies Mg-ion transport in polymers using different types of Mg salts. Polymer electrolytes comprising poly(ethylene carbonate) (PEC) with Mg salts (MgX₂; X?=?TFSI, ClO₄) were prepared by solution casting. The structural, thermal, and electrochemical properties of flexible self-standing membranes were studied as potential Mg electrolytes. The impedance results at 90 °C found the highest conductivities of 6.0?×?10^?6 S cm^?1 for PEC-Mg(TFSI)₂, and 5.2?×?10^?5 S cm^?1 for PEC-Mg(ClO₄)₂, at 40 mol%. FT-IR measurements revealed changes in the peak fraction from the region of carbonyl group, which explain the interaction with Mg ions. The glass transition temperature of the TFSI system decreased with increasing salt concentration due to the plasticizing effect of TFSI anions. Thermal gravimetric analysis revealed that the highest values of the 5% weight-loss temperature at 40 mol% are 174 °C for PEC-Mg(TFSI)₂ and 160 °C for PEC-Mg(ClO₄)₂. The electrochemical stability of PEC-Mg(TFSI)₂ at 40 mol% was up to 2.2 V. To confirm the redox reaction of Mg ions in PEC, CV measurement was carried out using symmetrical cells with quasi Mg electrodes. Cathodic and anodic current peaks were clearly observed, and the presence of these peaks indicates Mg-ion conduction in PEC.     

Structural and ionic conductivity studies of solid polymer electrolytes based on poly (vinylchloride) and poly (methylmethacrylate) blends

Thin film of poly (vinylchloride) and poly (methylmethacrylate) blend polymer electrolytes plasticized with a combination of DBP and Li₂SO₄ salts have been prepared by solution casting technique. The prepared films were subjected to a.c. impedance measurements as a function of temperature ranging from 304–373 K. The maximum conductivity at 304 K was found to be 1.24 × 10⁻⁸ S·cm⁻¹ for PVC-PMMA-Li₂SO₄-DBP (7.5-17.5-5-70 mole-%). Temperature dependence studies on the ionic conductivity in the PVC-PMMA-Li₂SO₄-DBP system suggest that the ion conduction follows the Williams-Landel-Ferry (WLF) mechanism, which is further confirmed by Vogel-Tamman-Fulcher (VTF) plots. XRD, FTIR, SEM and thermal studies revealed complex formation in.     

Effect of ionic liquid on the properties of poly(vinylidene fluoride)-based gel polymer electrolytes

Poly(vinylidene fluoride)-based polymer electrolytes using ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide as the plasticizer were prepared by solution casting method. The effects of the solvent evaporation temperature (SET) and ionic liquid content (ILC) on the properties and structures of the polymer electrolytes were investigated by characterization of scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry, as well as mechanical and ionic conductivity test. It was confirmed that both SET and ILC had significant influence on the morphology, degree of crystallinity, mechanical properties, and ionic conductivity of the prepared polymer electrolytes. With ILC of 40 %, an excellent polymer electrolyte can be obtained at SET of 60 °C, which exhibited ionic conductivity up to ca. 10^?4 S/cm at room temperature, accompanied by excellent tensile strength of 22.8 MPa and elongation at break of 540 %.     

Polymer electrolytes based on ethylene oxide–epichlorohydrin copolymers

In this work we studied the ionic conductivity for three copolymers of the title co-monomers as a function of LiClO₄ content, temperature and ambient relative humidity. We also investigated the interactions between the salt and the co-monomer blocks in the copolymers and its effect on the morphology and thermal properties of the copolymer/salt complexes. Our data indicate that the Li⁺ ion predominantly interacts with the ethylene oxide repeating units of the copolymers. The copolymer with the highest ionic conductivity was obtained with an ethylene oxide/epichlorohydrin ratio of 84/16 containing 5.5% (w/w) of LiClO₄. It showed a conductivity of 4.1×10⁻⁵ S cm⁻¹ (30°C, humidity< 1 ppm) and 2.6×10⁻⁴ S cm⁻¹ at 84% relative humidity (24°C). The potential stability window of the copolymer/salt complex is 4.0 V, as measured by cyclic voltammetry. For comparison, we also prepared a blend of the corresponding homopolymers containing LiClO₄; it showed higher crystallinity and lower ionic conductivity.     

Small-angle neutron scattering studies on water soluble complexes of poly(ethylene glycol)-based cationic random copolymer and SDS

The interaction of cationic random copolymers of methoxy poly(ethylene glycol) monomethacrylate and (3-(methacryloylamino)propyl) trimethylammonium chloride with oppositely charged surfactant, sodium dodecyl sulphate, and the influence of surfactant association on the polymer conformation have been investigated by small-angle neutron scattering. SANS data showed a positive indication of the formation of RCPSDS complexes. Even though the complete structure of the polyion complexes could not be ascertained, the results obtained give us the information on the local structure in these polymer-surfactant systems. The data were analysed using the log-normal distribution of the polydispersed spherical aggregate model for the local structure in these complexes. For all the systems the median radius and the polydispersity were found to be in the range of 20 ± 2 Å and 0.6 ± 0.05, respectively.     

Morphology and conductivity of electrolytes based on poly(ethylene oxide) - Eu(ClO4)3 films

Solid polymer electrolytes based on a poly(ethylene oxide), (PEO), host have been prepared using the solvent casting method and characterized by conductivity measurements and thermal analysis. The observed ionic conductivity of the novel system based on PEO and europium perchlorate was similar to that of other electrolytes based on the same polymer host with a different trivalent guest species [1]. The presence of the perchlorate anion widened the composition range of amorphous behaviour but limited the thermal stability of the electrolytes produced. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Upon a magnetic composite preparation based on magnetite and poly(succinimide)-b-poly(ethylene glycol) shell

Taking into account that magnetic particles with suitable surface characteristics have a high potential for the use in a lot of in vitro and in vivo applications, in the study is presented the in situ preparation of a core-shell magnetic composite based on the magnetite core and the shell composed from the poly(succinimide)-b-poly(ethylene glycol) copolymer. The average particle size of the synthesized magnetic microspheres is in the range of 6.5-8.8 μm with a magnetite content of around 11%. The saturation magnetization of the microspheres was found 26.8 emu/g, the magnetic microspheres being characterized by superparamagnetic properties. The particles have combined properties of high magnetic saturation and biocompatibility and interactive functions at the surface through the block copolymer shell. The surface of the magnetic particles has also the possibility for further functionalization or the attachment of various bioactive molecules after the hydrolysis of the succinimide cycle and the resulting carboxylic group.     

Characterization of poly(ethylene oxide) copper salt polymer electrolytes

The physico-chemical and electrochemical properties of a new class of polymer electrolytes formed by complexes of poly(ethylene oxide) and copper trifluorosulphonate salts have been investigated. The results suggest that these electrolytes are good copper ion conductors. Under particular conditions of concentration and temperature, and apparent electronic transport has also been evidenced.     

Covalent attachment of poly(ethylene glycol) on multi-walled carbon nanotubes

A new 'graft-onto' method to attach poly(ethylene glycol) (PEG) onto multi-walled carbon nanotubes (MWNTs) has been developed. The method is based on the coupling reaction of radicals formed at the chain end of PEG onto the surface of MWNTs. The polymeric radicals are generated by atom (halogen) transfer reaction between chloroacetyl-terminated PEG and transition metal catalysts. The method allows direct covalent attachment of PEG to pristine MWNTs without pretreatment that could alter their original structure. The resulting PEG-grafted MWNTs showed improved dispersion stability in isopropanol and methanol.     

Ionic conductivity of electrolytes based on star-branched poly(ethylene oxide) with high concentration of lithium salts

Electrolytes based on star-branched poly(ethylene oxide) with lithium bis(trifluoromethanesulfone)imide LiTFSI and lithium iodide salts were prepared by casting from solution. The electrical properties of electrolytes subjected to various heating and cooling runs were studied by impedance spectroscopy and impedance spectroscopy simultaneous with optical microscope observation. Differential scanning calorimetry was used for additional characterization. The results indicate that in electrolytes with high content of salt, values of ionic conductivity comparable to that of dilute electrolytes can be achieved. Moreover, electrolytes with high amount of salt seem to show weaker temperature dependence of conductivity. Promising results in terms of ionic conductivity were obtained for mixture of LiTFSI and lithium iodide. A few problems which may decrease the performance of studied system as a solid electrolyte were also identified, from which changes of physical properties of samples subjected to thermal cycles and aging seem to be the most important ones.     

Magnetic fluid poly(ethylene glycol) with moderate anticancer activity

Poly(ethylene glycol) (PEG)-containing magnetic fluids - magnetite (Fe₃O₄) stabilized by sodium oleate - were prepared. Magnetic measurements confirmed superparamagnetic behaviour at room temperature. The structure of that kind of magnetic fluid was characterized using different techniques, including electron microscopy, photon cross correlation spectroscopy and small-angle neutron scattering, while the adsorption of PEG on magnetic particles was analyzed by differential scanning calorimetry and Fourier transform infrared spectroscopy. From the in vitro toxicity tests it was found that a magnetic fluid containing PEG (MFPEG) partially inhibited the growth of cancerous B16 cells at the highest tested dose (2.1 mg/ml of Fe₃O₄ in MFPEG).     

The investigation of electrochemical properties and ionic motion of functionalized copolymer electrolytes based on polysiloxane

The effect of EO side chain functionalization on the transport and electrochemical properties of polysiloxane electrolytes has been examined in this report. First, a study of the electrochemical stability of the electrolytes by linear sweep voltammetry shows that the polymer electrolytes have a negligible effect on the electrolyte stability windows. In addition, the parameters of cation mobility in polysiloxane electrolytes, such as ionic transference numbers and diffusion coefficients, were increased by increasing the lengths of the EO side chain. However, cation mobility in polymer structures is quite different compared to liquid-based systems and is probably suppressed, resulting in their polymer structure. Therefore, Positron Annihilation Lifetime Spectroscopy (PALS) was used to study the relationship between orthopositronium (o-Ps) lifetime, free volume radius, free volume of micro voids and EO side chain affection at different temperatures. Finally, a battery application with LiCoO₂ and LiFePO₄/polymer electrolyte/lithium metal electrode was monitored for its potential use in the future.     

Effects of poly(ethylene glycol) on electrical conductivity of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) film

A series of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) composite thin films with prescribed concentrations of poly(ethylene glycol) were prepared. The PEDOT–PSS pristine film and PEDOT–PSS/PEG films were studied using four-probe method, photoelectron spectroscopy and atomic force microscopy. The electrical conductivity of PEDOT–PSS/PEG hybrid films was found to be enhanced compared to the PEDOT–PSS pristine film, depending on the PEG concentration and molecular weight. XPS analysis and AFM results showed that PEG induces the phase separation between the PEDOT–PSS conducting particles and the excessive PSSNa shell. Simultaneously PEG may form hydrogen bond with sulfonic groups of PSSH, and hence weaken the electrostatic interactions between PEDOT cationic chains and PSS anionic chains. These resulted in the creation of a better conduction pathway among PEDOT–PSS particles, attributed to the improvement of conductivity.     

A phosphate additive for poly(ethylene oxide)-based gel polymer electrolytes

The influence of an organophosphosphate additive on poly(ethylene oxide) lithium bis(trifluoromethylsulfonyl)imide-based gel polymer electrolytes for secondary lithium battery applications is described. Tris(2-(2-methoxyethoxy)ethyl)phosphate, is compared to the well known gel-battery component, propylene carbonate, through a study of complex impedance analysis, differential scanning calorimetry, and limiting oxygen index combustion analysis. The conductivities of the gels at low concentrations of tris(2-(2-methoxyethoxy)ethyl)phosphate (1.9–4.2 mol%) are higher to those of propylene carbonate-based systems with the same concentration. Despite micro-phase separation at high concentrations of tris(2-(2-methoxyethoxy)ethyl)phosphate (7.0–14.9 mol%), the conductivities remain comparable to systems that use propylene carbonate. The addition of tris(2-(2-methoxyethoxy)ethyl)phosphate to poly(ethylene oxide) gives increased fire retardance, while the addition of propylene carbonate to poly(ethylene oxide) results in increased flammability.     

Solid polymer electrolytes based on poly(lithium carboxylate) salts

The ionic conductivity, lithium ion transference number, electrochemical stability, and thermal property of solid polymer electrolytes composed of poly(ethylene oxide) (PEO) and poly(lithium carboxylate)s, (poly(lithium acrylate) (Poly(Li-A)) or poly(lithium fumarate) (Poly(Li-F)), with and without BF₃·OEt₂ were investigated. The ionic conductivities of all solid polymer electrolytes were enhanced by one to two orders of magnitude with addition of BF₃·OEt₂ because the dissociation of lithium ion and carboxylate anion was promoted by the complexation with BF₃. The lithium ion transference number in the solid polymer electrolytes based on poly(lithium carboxylate)s showed relatively high values of 0.41–0.70, due to the suppression of the transport of counter anion by the use of a polymeric anion. The solid polymer electrolytes with addition of BF₃·OEt₂ showed good electrochemical stability.     

Experimental investigations on poly(ethylene oxide) based sodium ion conducting composite polymer electrolytes dispersed with SnO2

New Na⁺ ion conducting composite polymer electrolytes comprising of polyethylene oxide (PEO)-NaClO₄ and PEO-NaI complexes dispersed with SnO₂ are reported. The results of the studies based on optical microscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infra-red (FTIR) spectroscopy, impedance analysis and mechanical testing are presented and discussed. The electrical conductivity of ≈5·10⁻⁵ S·cm⁻¹ at 40 °C was achieved for the dispersion of ≈10 wt.% of SnO₂ in both systems. The composition dependence of the conductivity has been well correlated with the variation in glass transition temperature and degree of crystallinity. A substantial enhancement in the mechanical properties of the composite films was observed at the cost of slight decrease in the conductivity at higher concentration of SnO₂. The temperature dependence of the conductivity follows apparently the Arrhenius type thermally activated process below and above the melting temperature of PEO. The conductivity of the materials has been found to be strongly humidity dependent. The materials are shown to be ionic with t_ion>0.9. The electrochemical stability of the materials has been observed to be up to ≈3.2 V for (PEO)₂₅NaClO₄+x% SnO₂ and is limited to ≈1.9 V for (PEO)₂₅NaI+x% SnO₂.