Ionic conductivity enhancement of the plasticized PMMA/LiClO4 polymer nanocomposite electrolyte containing clay

This work has demonstrated that the addition of an optimum content of dimethyldioctadecylammonium chloride (DDAC)-modified montmorillonite clay (Dclay) enhances the ionic conductivity of the plasticized poly(methyl methacrylate)-based electrolyte by nearly 40 times higher than the plain system. Specific interactions among silicate layer, carbonyl group (CO) and lithium cation have been investigated using Fourier-transform infrared (FTIR), solid-state NMR, alternating current impedance. The FTIR characterization confirms that both of the relative fractions of ‘complexed’ CO sites and ‘free’ anions increase with the increase of the Dclay content, indicating that strong interaction exists between the CO group and the lithium salt. In addition, the solid-state NMR demonstrates that the interaction between the PMMA and the clay mineral is insignificant. The addition of clay mineral promotes the dissociation of the lithium salt and thus, the specific interaction can be enhanced between the CO and the free lithium cation. However, the balanced attractive forces among silicate layers, CO groups, lithium cations and anions is critical to result in the higher ionic conductivity.     

Effect of modified montmorillonites on the ionic conductivity of (PEO)16LiClO4 electrolytes

Three kinds of modified montmorillonites were prepared by ion exchange method, and added into (PEO)₁₆LiClO₄ matrix to study the effect on the ionic conductivity of (PEO)₁₆LiClO₄ electrolytes. The structure of the modified montmorillonites and polymer composites were characterized by wide-angle X-ray diffraction. HP 4192A was used to measure the ionic conductivity of the polymer electrolytes. The results show that the addition of optimum content of 250-Li-mont enhances the ionic conductivity of the PEO based electrolyte by nearly 30 times more than the plain system and that is much higher than the other two modified montmorillonites. The difference of enhancement in conductivity caused by adding these three montmorillonites can be attributed to the difference in structure of the samples as characterized by wide-angle X-ray diffraction.     

Solid polymer electrolytes VIII: effect of LiClO4-doped level on the microstructure and ionic conductivity of a chemical-covalently polyether-siloxane hybrid electrolyte

A new hybrid polymer electrolyte system based on chemical-covalently polyether and siloxane phases is designed and prepared in the presence of lithium perchlorate (LiClO₄) which acted as both ionic source and the epoxide ring-opening catalyst. The effect of salt-doped level on the microstructure and ionic conductivity of these composite electrolytes were investigated by means of Fourier transform infra-red spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, a.c. impedance and multinuclear solid-state nuclear magnetic resonance measurements. DSC results indicate that the formation of transient cross-links between Li⁺ ions and the ether oxygens on complexation with LiClO₄ results in an increase in polyether segment T_g. However, the polyether segment T_g decreases at the highest salt concentration (5.0 mmol LiClO₄/g PEGDE), ascribing to the plasticizing effect. The behavior of ion transport is coupled with the segmental motions of polymer chains and also correlated with the interactions between ions and polymer host.     

Crystallinity, morphology, mechanical properties and conductivity study of in situ formed PVdF/LiClO4/TiO2 nanocomposite polymer electrolytes

Nanocomposite polymer electrolytes composed of poly(vinylidene fluoride) (PVdF), lithium perchlorate (LiClO₄) and TiO₂ nanoparticles were prepared by a solution-cast method. The nanosized ceramic filler, TiO₂, was synthesized in situ by a sol-gel process. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analysis revealed that the crystalline phase and crystallinity were slightly decreased with the addition of TiO₂ to the PVdF/LiClO₄ system. Scanning electron microscopy (SEM) micrographs showed that the PVdF/LiClO₄/TiO₂ solid polymer electrolyte (SPE) membranes had a porous structure to a certain extent, and that the pore size decreased with increasing TiO₂ content. The overfull nanoparticles tended to aggregate on the surface and inside the pores at TiO₂ content above 15 wt.% so that the porosity decreased. Regarding mechanical properties, the strength of the PVdF/LiClO₄/TiO₂ electrolytes decreased after the uptake of EC/PC solution. In contrast to the conductive behavior of wet PVdF/LiClO₄/TiO₂ membranes relative to the uptake of EC/PC solution, the conductive mechanism of the solid membranes, after the lithium ion of LiClO₄ had already been installed in the PVdF solid polymer network, was mainly influenced by the TiO₂ nanoparticles. At a TiO₂ content of 10 wt.%, the solid and wet PVdF/LiClO₄/TiO₂ systems had the maximum conductivity values of 7.1 × 10⁻⁴ and 1.8 × 10⁻³ S/cm, respectively.     

PVdF-HFP/P123 hybrid with mesopores: a new matrix for high-conducting, low-leakage porous polymer electrolyte

Highly conducting porous polymer electrolytes comprised of poly(vinylidene-fluoride-co-hexafluoropropylene) (PVdF-HFP), polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide (P123), ethylene carbonate (EC), propylene carbonate (PC), and LiClO₄ were fabricated. The PVdF-HFP/P123 hybrid polymer membranes were made with a phase inverse method and the electrolyte solution uptake was carried out in glove box to avoid the moisture contamination. It was found that when a small amount of polymer surfactant (P123) was blended into the PVdF-HFP, mesopores with well-defined sizes were formed. Impedance spectroscopy showed that the room temperature conductivity of (PVdF-HFP)/P123 polymer electrolytes increased as the content of P123 increased up to 4×10⁻³ S/cm. Nitrogen adsorption isotherms, electrolyte solution uptake, porosity measurements, and SEM micrographs showed that the enhanced conductivity was due to increase the pore volume, pore density, and electrolyte uptake. The highest conduction was found when the weight ratio of P123 to PVdF-HFP was 70%, when big channels were formed in the hybrid polymer membrane. Furthermore, blending P123 in PVDF-HFP reduced the pore size of polymer membrane, therefore, the solution leakage was also reduced. These polymer electrolytes were stable up to 4.5 V (vs Li/Li⁺) and the performance of the model lithium ion battery made by sandwiching the polymer electrolyte between a LiCoO₂ anode and a MCMB cathode, showed great promise for the use of these polymer electrolytes in lithium ion batteries.     

Solid polymer electrolytes V: microstructure and ionic conductivity of epoxide-crosslinked polyether networks doped with LiClO4

A crosslinked polyether network was prepared from poly(ethylene glycol) diglycidyl ether (PEGDE) cured with poly(propylene oxide) polyamine. Significant interactions between ions and polymer host have been observed for the crosslinked polyether network in the presence of LiClO₄ by means of FT-IR, DSC, TGA, and ⁷Li MAS solid-state NMR. Thermal stability and ionic conductivity of these complexes were also investigated by TGA and AC impedance measurements. The results of FT-IR, DSC, TGA and ⁷Li MAS solid-state NMR measurements indicate the formation of different types of complexes through the interaction of ions with different coordination sites of polymer electrolyte networks. The dependence of ionic conductivity was investigated as a function of temperature, LiClO₄ concentration and the molecular weight of polyether curing agents. It is observed that the behavior of ion transport follows the empirical Vogel-Tamman-Fulcher (VTF) type relationship for all the samples, implying the diffusion of charge carrier is assisted by the segmental motions of polymer chains. Moreover, the conductivity is also correlated with the interactions between ions and polymer host, and the maximum ionic conductivity occurs at the LiClO₄ concentration of [O]/[Li⁺]=15.     

Ionic conductivities of solid polymer electrolyte/salt systems for lithium secondary battery

We establish a new ionic conductivity model based on the Nernst-Einstein equation in which the diffusion coefficient is derived from modified double lattice-nonrandom-Pitzer-Debye-Hückel (MDL-NR-PDH) model. The proposed model takes into account the mobility of the salt and the motion of the polymer host simultaneously by expressing the effective chemical potential as the sum of chemical potentials of the salt and the polymer. To describe the segmental motion of the polymer chain, which is the well-known conduction mechanism for solid polymer electrolyte (SPE) systems, the effective co-ordinated unit parameter is introduced. The obtained co-ordinated unit parameter for each state is used to describe the behavior of the ionic conductivities of the given systems. Good agreement is obtained upon comparison with experimental data of various PEO and salt systems in the interested ranges.     

Ionic transport behavior in poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) and LiClO4 complex

The effect of LiClO₄ on the ionic transport behavior in poly(ethylene oxide)₂₀-poly(propylene oxide)₇₀-poly(ethylene oxide)₂₀ (P123) polymer electrolyte was studied. Its conductivity reaches maximum as molar ratio between ether O atoms and lithium ions [n(O)/n(Li)] equals 8. The results show that LiClO₄ could interact with P123 well and has impacts on polymer organization and chain dynamics. As LiClO₄ concentration decreases, the glass transition temperature (T_g) decreases and the free ion percentage increases. The tendency of conductivity with LiClO₄ concentration is the result of competing effects between polymer chain mobility and free charge carrier concentration.     

Ionic conductivity of a novel solid polymer electrolyte

A novel kind of solid polymer electrolyte, the solvation unit of which is O?CNHR, has been studied. The effects of host polymer structure, ion species, salt concentration, and plasticizers on ionic conductivity are discussed in detail. The solvability of host polymers is a very important factor that affects the ionic conductivity of electrolytes and is fully decided by the structure of solvation units and their density in polymer chain. The latter two rest with monomers structure and copolymerization ratio. Effects of alkali metal salts and divalent metal salts on ionic conductivity are different because of their different leading factor of cation radius. Salt concentration dependence of ionic conductivity appears as a double‐peak shape when alkali metal salts are added because of the total contribution of two kinds of ionic conductance modes, and appears as similar shapes when divalent metal salts are added. Different influences of plasticizers on ionic conductivity result from their different action ways. Ethylene glycol acts well because of its effective action from three different modes. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2176–2184, 2001     

Thermal, electrical and mechanical properties of plasticized polymer electrolytes based on PEO/P(VDF-HFP) blends

The polymer electrolytes composed of a blend of poly(ethylene oxide) (PEO) and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) as a host polymer, mixture of ethylene carbonate (EC) and propylene carbonate (PC) as a plasticizer, and LiClO₄ as a salt were prepared by a solution casting technique. SEM micrographs show that P(VDF-HFP) is very compatible with PEO. The ionic conductivity of the electrolytes increases with increasing plasticizer content, while the mechanical properties become obviously worse. By addition of a certain content of PEO in P(VDF-HFP) matrix, a good compromise between high ionic conductivity and mechanical stability can be obtained.     

Synthesis and peculiarities of electric properties of Li1.3Zr1.4Ti0.3Al0.3(PO4)3 solid electrolyte ceramics

The solid electrolyte Li_1.3Zr_1.4Ti_0.3Al_0.3(PO₄)₃ compound was synthesized by a solid-state reaction. The ceramic samples were sintered 1, 2 and 3 h and studied by X-ray and complex impedance spectroscopy in the frequency range from 10⁶ to 1.2 × 10⁹ Hz in temperature range from 300 to 600 K. The investigated compound at room temperature belongs to rhombohedral symmetry (s.g. ) with six formula units in the lattice. Two regions of relaxation dispersion were found. The dispersions are related to the fast Li⁺ ion transport in the grain and grain boundaries of ceramics. Varying of the sintering time affects the density of the ceramics, the values of total conductivity and its activation energy. The values of grain conductivity, its activation energy, and relaxation frequency in grain, dielectric permittivity and dielectric losses are independent from sintering duration of the ceramics. The value of activation energy of grain conductivity and activation energy of relaxation frequency is the same. That can be attributed to the fact that the temperature dependence of the grain conductivity is caused only by the mobility of Li⁺ ions, while a number of charge carriers remains constant with temperature.     

Ionic conduction in P(VDF-HFP)/PVDF-(PC + DEC)-LiClO4 polymer gel electrolytes

Gel polymer electrolytes composed of poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride) polymer, PC+DEC as plasticizer and LiClO₄ as salt have been synthesized by solvent casting technique with varying the plasticizer-salt concentration ratio systematically. Complex impedance spectroscopy has been carried out to investigate ionic conduction in P(VDF-HFP)-(PC+DEC)-LiClO₄ and PVDF-(PC+DEC)-LiClO₄ electrolyte systems. Transport number measurements have been made by Wagner’s polarization technique. With all other parameters same, P(VDF-HFP) electrolytes exhibit higher ionic conductivity and transport number as compared to PVDF based electrolytes which could be attributed to higher degree of amorphicity in the P(VDF-HFP) system. XRD and FTIR studies have been conducted to investigate the structural and complexation in the polymer gel electrolytes. Microstructural studies by SEM exhibit higher amorphicity and solvent retention capability for P(VDF-HFP)-(PC+DEC)-LiClO₄ system than those of PVDF-(PC+DEC)-LiClO₄ system.     

Hybrid inorganic-organic polymer electrolytes: synthesis, FT-Raman studies and conductivity of {Zr[(CH2CH2O)8.7]ρ/(LiClO4)z}n network complexes

This paper describes the synthesis and characterization of three-dimensional hybrid inorganic-organic networks prepared by a polycondensation reaction between Zr(O(CH₂)₃CH₃)₄ and polyethylene glycol 400 (PEG400). Eleven hybrid networks doped with varying concentrations of LiClO₄ salt were prepared. On the basis of analytical data and FT-Raman studies it was concluded that these polymer electrolytes consist of inorganic-organic networks with zirconium atoms bonded together by PEG400 bridges. These polymers are transparent with a solid rubber consistency and are very stable under inert atmosphere. Scanning electron microscopy revealed a smooth glassy surface. X-ray fluorescence microanalysis with energy dispersive spectroscopy demonstrated that all the constituent elements are homogeneously distributed in the materials. Thermogravimetric measurements revealed that these materials are thermally stable up to 262 °C. Differential Scanning Calorimetry measurements indicated that the glass transition temperature T_g of these inorganic-organic hybrids varies from −43 to −15 °C with increasing LiClO₄ concentration. FT-Raman investigations revealed the TGT (T=trans, G=gauche) conformation of polyether chains and allowed characterization of the types of ion-ion and ion-polymer host interactions in the bulk materials. The conductivity of the materials at different temperatures was determined by impedance spectroscopy over the 20 Hz-1 MHz frequency range. Results indicated that the materials conduct ionically and that their ionic conductivity is strongly influenced by the segmental motion of the polymer network and the type of ionic species distributed in the bulk material. Finally, it is to be highlighted that the hybrid network with a n_Li/n_O molar ratio of 0.0223 shows a conductivity of ca. 1×10⁻⁵ S cm⁻¹ at 40 °C.     

Suppression of crystallization in a plastic crystal electrolyte (SN/LiClO4) by a polymeric additive (polyethylene oxide) for battery applications

A basic problem with many promising solid electrolyte materials for battery applications is that crystallization in these materials at room temperature makes ionic mobilities plummet, thus compromising battery function. In the present work, we consider the use of a polymer additive (polyethylene oxide, PEO) to inhibit the crystallization of a promising battery electrolyte material, the organic crystal forming molecule succinonitrile (SN) mixed with a salt (LiClO₄). While SN spherulite formation still occurs at low PEO concentrations, the SN spherulites become progressively irregular and smaller with an increasing PEO concentration until a ‘critical’ PEO concentration (20% molar fraction PEO) is reached where SN crystallization is no longer observable by optical microscopy at room temperature. Increasing the PEO concentration further to 70% (molar fraction PEO) leads to a high PEO concentration regime where PEO spherulites become readily apparent by optical microscopy. Additional diffraction and thermodynamic measurements establish the predominantly amorphous nature of our electrolyte-polymer mixtures at intermediate PEO concentrations (20-60% molar fraction PEO) and electrical conductivity measurements confirm that these complex mixtures exhibit the phenomenology of glass-forming liquids. Importantly, the intermediate PEO concentration electrolyte-polymer mixtures retain a relatively high conductivity at room temperature in comparison to the semicrystalline materials that are obtained at low and high PEO concentrations. We have thus demonstrated an effective strategy for creating highly conductive and stable conductive polymer-electrolyte materials at room temperature that are promising for battery applications.     

Novel composite polymer electrolyte comprising poly(ethylene oxide) and triblock copolymer/mesostructured silica hybrid used for lithium polymer battery

Ordered mesoporous materials, due to its potential applications in catalysis, separation technologies, and nano-science have attracted much attention in the past few years. In this work, a novel PEO-based composite polymer electrolyte by using organic-inorganic hybrid EO₂₀PO₇₀EO₂₀ @ mesoporous silica (P123 @ SBA-15) as the filler has been developed. The interactions between P123 @ SBA-15 hybrid and PEO chains are studied by X-ray diffraction (XRD), differential scanning calorimeter (DSC), and FT-IR techniques. The effects of P123 @ SBA-15 on the electrochemical properties of the PEO-based electrolyte, such as ionic conductivity, lithium ion transference number are studied by electrochemical ac impedance spectroscopy and steady-state current method. The experiment results show that P123 @ SBA-15 can enhance the ionic conductivity and increase the lithium ion transference number of PEO-based electrolyte, which are induced by the special topology structure of P123 in P123 @ SBA-15 hybrid, at the same time. The excellent lithium transport properties and broad electrochemical stability window suggesting that PEO-LiClO₄/P123 @ SBA-15 composite polymer electrolyte can be used as candidate electrolyte materials for lithium polymer batteries.     

Improved photovoltage and performance by aminosilane-modified PEO/P(VDF-HFP) composite polymer electrolyte dye-sensitized solar cells

A PEO/P(VDF-HFP) composite polymer electrolyte was modified by different amounts of NH₂-end functional silane (3-amonopropyltriethoxysilane, APTS). Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were carried out to examine the configuration changes of the polymer electrolyte. The newly formed Si-O-Si network and interactions influenced the ionic conductivity of the APTS-modified polymer electrolyte and also enhanced the connection of the polymer electrolyte with the electrodes of the dye sensitized solar cells (DSSCs). The cyclic voltammograms and electrochemical impedance measurements indicated that the APTS deprotonated the TiO₂ photoanode surface and negatively changed the Fermi energy level and the conduction band edge to the vacuum level. This effectively reduced the interface recombination in the DSSC and improved the open circuit voltage. With moderate APTS content (0.1 M) modification, the DSSC exhibited a 58 mV improvement of photovoltage and an improved performance of 5.08% compared with 3.74% of the original DSSC.     

添加TiO2的聚合物电解质膜PVDF-HFP的性能研究

通过添加不同质量分数的TiO2纳米粒子制备多孔聚合物电解质膜PVDF-HFP,制备的聚合物电解质膜通过红外,交流阻抗,线性伏安扫描、首次充放电测试等方法进行了性能测试。添加TiO2纳米填料后,降低了聚合物链的结晶度和极性,当填料的质量分数为8%时,表现出较好的电化学性能,吸液率为184%,孔隙率为93%,室温电导率达到2.05×10-3 S/cm,电化学稳定窗口为4.7V,能满足要求。     

Influence of metal coordination on conductivity behavior in poly(butadiene-acrylonitrile)-CoCl2 system

The metal complex formation and the electrical properties of amorphous solid polymer electrolytes, based on poly(butadiene-acrylonitrile) copolymer (PBAN) and CoCl₂, have been studied over the homogeneity region of the system limited by the CoCl₂ concentration of 1.89 mol kg⁻¹. It has been found that ionic conductivity is carried out by the unipolar anion transfer at lower CoCl₂ concentrations (up to 0.10 mol kg⁻¹). As the CoCl₂ concentration increases, electronic conductivity appears in addition to ionic conductivity, and the former becomes dominant, starting from 0.38 mol kg⁻¹. It has been shown that the nature of charge carriers is determined by the composition of metal complexes formed by CoCl₂ and the macromolecular solvent PBAN. At lower concentrations, the [Co₂L₂Cl₄]⁰ dimers are the predominant species (L being macromolecule side groups CN), and their dissociation is followed by the formation of mobile Cl⁻ anions and immobile binuclear [Co₂Cl₃]⁺ complexes. As CoCl₂ concentration increases, polynuclear [Co_nL₂Cl_2n]⁰ (n > 2) complexes appear (L being CN and CC groups of PBAN). Specific features of chemical bonds in π-complexes of transition metals result in the appearance of electronic charge carriers. The abrupt increase in conductivity observed at the highest CoCl₂ concentration is connected with the formation of a percolation network of polynuclear [Co_nL₂Cl_2n]⁰ complexes.     

Isothermal crystallization kinetics and effect of crystallinity on the optical properties of nanosized CeO2 powder

The isothermal crystallization kinetics and effect of crystallinity on the optical properties of cerium dioxide (CeO₂) nanopowders synthesized using a coprecipitation route at 293 K and pH 9 were investigated using X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and ultraviolet–visible absorption spectrophotometry. The activation energy of CeO₂ crystallization from dried cerium dioxide precursor powders by isothermal method of 64.1±3.24 kJ/mol was obtained. The average value of the growth morphology parameter (n) is 1.94, meaning that two-dimensional growth with plate-like morphology was the primary mechanism of CeO₂ crystallization from cerium dioxide precursor powders. The indirect band gap energy (E_i) of CeO₂ decreased from 3.03 eV to 2.83 eV when the crystallinity increased from 18% to 82%, and the direct band gap energy (E_d) of CeO₂ also decreased from 3.76 eV to 3.64 eV.     

Effect of ethylene carbonate on properties of PVP-CsAlO2-LiClO4 solid polymer electrolytes

ABSTRACT

Solid polymer electrolytes (SPEs) have been widely studied due to its extensive applications in high energy rechargeable batteries, supercapacitors, fuel cells, photoelectrochemical and electrochromic displays. Herein, SPEs based on polyvinyl pyrrolidone (PVP) doped with cesium aluminate (CsAlO₂) nanoparticles (NPs), lithium perchlorate (LiClO₄) as an electrolyte and varying amounts viz., 2, 4, 6 and 8 wt.% of ethylene carbonate (EC) as plasticizer have been fabricated by solution intercalation technique. The structural features of PVP-CsAlO₂-LiClO₄-EC SPEs have been studied by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The morphology of PVP-CsAlO₂-LiClO₄-EC SPEs has been examined by scanning electron microscopy (SEM). The thermal properties of the SPEs were characterized by the thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC) techniques. The TGA and DSC results revealed that a significant reduction in thermal stability and glass transition temperature (T_g) of PVP with an increase in EC content in SPE films. The optoelectrical properties of PVP-CsAlO₂-LiClO₄-EC SPE films have been evaluated using UV–visible spectroscopy. The band gap energy (E_g) was found to decrease with an increase in EC content, exhibiting a minimum of 4.23 eV for PVP-8 wt.% CsAlO₂-15 wt.% LiClO₄-8 wt.% EC. This could be ascribed to the formation of localized states and increased degree of disorder in the PVP-CsAlO₂-LiClO₄ SPE films. The integrated plasticizers increase the values of refractive index (RI), optical conductivity, and dielectric constants of PVP-CsAlO₂-LiClO₄ SPE films. The AC conductivity of the SPEs has been evaluated at room temperature using digital LCR meter in the frequency range 100 Hz – 5 MHz. The conductivity strongly depends on CsAlO₂ NPs and EC plasticizer content in SPEs.