Electrospun PVdF-based fibrous polymer electrolytes for lithium ion polymer batteries

This paper discusses the preparation of microporous fibrous membranes from PVdF solutions with different polymer contents, using the electrospinning technique. Electrospun PVdF-based fibrous membranes with average fiber diameters (AFD's) of 0.45-1.38 μm have an apparent porosity and a mean pore size (MPS) of 80-89% and 1.1-4.3 μm, respectively. They exhibited a high uptake of the electrolyte solution (320-350%) and a high ionic conductivity of above 1 × 10⁻³ s/cm at room temperature. Their ionic conductivity increased with the decrease in the AFD of the fibrous membrane due to its high electrolyte uptake. The interaction between the electrolyte molecules and the PVdF with a high crystalline content may have had a minor effect on the lithium ion transfer in the fibrous polymer electrolyte, unlike in a nanoporous gel polymer electrolyte. The fibrous polymer electrolyte that contained a 1 M LiPF₆-EC/DMC/DEC (1/1/1 by weight) solution showed a high electrochemical stability of above 5.0 V, which increased with the decrease in the AFD The interfacial resistance (R_i) between the polymer electrolyte and the lithium electrode slightly increased with the storage time, compared with the higher increase in the interfacial resistance of other gel polymer electrolytes. The prototype cell (MCMB/PVdF-based fibrous electrolyte/LiCoO₂) showed a very stable charge-discharge behavior with a slight capacity loss under constant current and voltage conditions at the C/2-rate of 20 and 60 °C.     

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.     

Dynamic Mechanical,DSC, and Electrical Investigations on Nano Al2O3 Filled PVA:NH4SCN:DMSO Polymer Composite Dried Gel Electrolytes

This paper reports the dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and ionic conductivity studies on nanosized Al₂O₃(aluminium oxide) filled PVA:NH₄SCN:DMSO polymer composite dried gel electrolytes prepared by the wet chemistry route. Better mechanical stability and thermal behavior are noticed in the composite system. Multiple relaxation peaks seen in tangent loss measurements (in DMA studies) have been suitably correlated. Enhancement in ionic conductivity has been noticed with an optimum value of 4.02 × 10^?3 Scm^?1 for 4 wt% nano Al₂O₃ filled composite electrolytes. Temperature dependence of ionic conductivity shows a combination of Arrhenius and VTF (Vogel-Tamman-Fulcher) behavior.     

Poly(vinylidenefluoride)-hexafluoropropylene gel electrolytes based on N-(2-hydroxyethyl)-N-methyl morpholinium ionic liquids

Poly(vinylidenefluoride)-hexafluoropropylene (PVdF(HFP))-ionic liquid gel electrolytes were prepared by using ionic liquids based on N-(2-hydroxyethyl)-N-methyl morpholinium tetrafluoroborate and N-(2-hydroxyethyl)-N-methyl morpholinium hexafluorophosphate. TGA and FT-IR analyses confirmed that the solvent, N,N-dimethylacetamide (DMAC), used for mixing the PVdF(HFP) polymer with the ionic liquid, was almost totally removed during the gelling and drying processes. SEM photographs were taken of the surface structure of the PVdF(HFP)-ionic liquid in order to evaluate the morphology of the film’s surface according to the mixing ratio, as well as the nature of the ionic liquid. The thermal behaviors of PVdF(HFP)-ionic liquid gels were observed to be similar to those of neat ionic liquids through a DSC analysis, and the compatibility between the polymer and the ionic liquid was investigated by an XRD analysis. The ionic conductivities of all the gels were 10⁻⁴–10⁻⁸S·cm⁻¹ in a temperature range of 20°C to 70°C.     

纳米复合在光聚合高分子固体电解质中的应用研究

将纳米级陶瓷粉末分散到含有高分子基体预聚物、高氯酸锂及光引发剂的光敏物质中 ,并通过紫外光辐射使其交联固化为导电薄膜锂聚合物电池用电解质材料 ,并对其成膜性、感光性能以及导电性能进行了研究 ;本文还介绍了近年来纳米复合材料在锂聚合物电池中的应用进展情况     

Ex-situ Raman spectroscopy to optimize the manufacturing process for a structural MWNT nanocomposite

The G and D doublet, an intrinsic Raman feature of multi-walled nanotubes (MWNTs), was monitored in an ex-situ fashion for all intermediate stages of a manufacturing process of a MWNT/polymer nanocomposite. The G peak position and D/G ratios were monitored to characterize the changes in load transfer and disorder, respectively, of the MWNTs. Differences in Raman characteristics desired during the manufacturing process for different structural applications are discussed. Techniques are presented that could optimize any manufacturing parameters for pressurized filtration and resin infusion using the G position and D/G integrated intensity ratio. Similar Raman control techniques could be applied to any intermediate phase of a manufacturing process to develop enhanced novel carbon nanotube composites for structural applications.     

On nonaqueous electrochemical behavior of titanium and Ti compounds

In this study, we examined the electrochemical behavior of titanium and Ti⁴⁺ compounds in THF solutions. Tetra butyl ammonium chloride (TBACl) was used as supporting electrolyte in order to increase the ionic conductivity of the solutions. Electrodeposition of pure titanium could not be obtained. A variety of analytical techniques have been used in conjunction with electrochemical methods in order to analyze the reduction process of Ti⁴⁺. These included Raman and UV-vis spectroscopy, ICP and CHNS elemental analyses. Ti⁴⁺ is being reduced to Ti³⁺ in TiCl₄/THF/TBACl solutions.In addition we show that metallic titanium can be electrochemically dissolved from an organo-metallic electrolyte solution comprising EtAlCl₂ and LiCl in THF. The product is Ti⁴⁺. While LiCl is insoluble in THF it reacts with EtAlCl₂ to form ionic species. Hence, these solutions possessed reasonable ionic conductivity.We could not obtain electroactive Ti⁴⁺ with TiBr₄ or TiI₄ as starting materials, in similar solutions.     

Study of the interfacial stability of PVdF/HFP gel electrolytes with sub-micro- and nano-sized surface-modified silicas

The aim of the presented work was to perform a preliminary study of the physicochemical and interfacial properties of hybrid organic-inorganic gel electrolytes for Li-ion batteries based on the PVdF/HFP polymeric matrix and surface-modified silicas. Two types of silica fillers of different grain sizes (>500 nm and ∼100 nm) were used as additives. The silica particles were modified by two different functional groups, i.e. methacryloxy and vinyl ones. The gel electrolytes based on PVdF/HFP copolymer were prepared according to the so-called Bellcore two-step process. The motivation of the present work was to study more deeply those systems in terms of morphology by means of scanning electron microscopy techniques. Fillers modified with identical functional groups but differing fundamentally in the manufacturing processes were compared in terms of the impact on morphology and electrochemical performance of the resulting membranes. Interfacial properties were examined by means of impedance spectroscopy technique using Swagelok-type cells with two lithium electrodes.     

高分子固体电解质研究新进展

高分子固体电解质(SPE)是一类全新的电解质,具有质轻、易成膜、黏弹性好和稳定性好等许多无机电解质和有机溶剂电解质不可比拟的性能,近年来研究进展很快。介绍高分子固体电解质类型及其性能提高的途径。     

胶乳共混法制备聚合物/MMT纳米复合膜及其性能

降低涂料配方中的VOC含量,甚至完全消除VOC,达到零VOC,从而最大程度地降低涂料对环境的污染,是涂料行业当前面临的最大技术挑战．水基涂料是最为重要的环保涂料．在水性聚合物乳液涂料中,为保证涂膜具有较好的力学性能,必须使用玻璃化温度较高的聚合物树脂．涂料的配方中必须加入5％～20％左右的有机成膜剂,以促进成膜．如果要在配方中除去这部分有机成膜剂,聚合物的玻璃化转变温度必须降到0℃左右．     

Vibrational spectroscopic studies of cation effects in low molecular weight poly(propylene oxide) complexed with lithium, sodium and potassium thiocyanate

This paper presents the results of room temperature Raman scattering and infrared transmission investigations of an approximately 450 average molecular weight poly(propylene oxide), PPO, complexed with varying concentrations of lithium, sodium and potassium thiocyanate. The strength of interaction between the metal cation and the polymer is observed to increase in the order Li>Na>K. Spectral changes in the O---H stretching region show that the cations interact with the alcoholic oxygen atoms as well as the ether oxygen atoms. Frequency shifts in the C---H stretching region combined with the growth of splittings and structure in lower frequency bands suggest that increasing complexation is accompanied by changes in the polymer backbone dynamics and structure. The metal-oxygen stretching band is easily identified in the infrared transmission spectra. Finally, cation-dependent frequency shifts of the thiocyanate ion bands indicate the formation of contact ion pairs coordinated at the nitrogen end of the anion.     

Enhanced electrical and electrochemical properties of PMMA-clay nanocomposite gel polymer electrolytes

In the present work, effect of organically modified montmorillonite (MMT) clays on PMMA-based electrolytes has been investigated. The nanocomposites have been prepared by solution intercalation technique with varying clay loading from 0 to 5 wt.%. The formation of partially exfoliated nanocomposites has been confirmed by XRD and TEM analyses. The obtained nanocomposites were soaked with 1 M LiClO₄ in 1:1 (v/v) solution of propylene carbonate (PC) and diethyl carbonate (DEC) to get the required gel electrolytes. Surface morphology and structural conformation of the nanocomposite electrolytes have been examined by SEM and FTIR analyses, respectively. It has been observed that the ionic conductivity of the nanocomposite gel polymer electrolytes increases with the increase in clay loading and attains a maximum value of 1.3 × 10⁻³ S/cm at room temperature as revealed by ac impedance spectroscopy. Improvement of electrochemical and interfacial stabilities has also been observed in the gel electrolytes containing MMT fillers.     

聚合物基纳米复合材料的结构与性能

叙述了由插层复合法、溶胶-凝胶法和纳米微粒直接共混法制备的聚合物基纳米复合材料的结构和性能。     

Evidences of correlation between polymer particle size and Raman scattering

This work describes evidences of correlation between polymer particle size and Raman scattering and shows that it is possible to use Raman scattering to monitor the evolution of average particle size during emulsion polymerization reactions. The main focus is the estimation of the average polymer particle diameter from spectra collected in a short acquisition time and consequently low signal-to-noise ratio. Finally, a multivariate linear model, (Partial Least Square-PLS), is fitted from the reaction data and a good linearity between spectra and average polymer particle diameter is found. It is shown that despite varying monomer and polymer concentrations it is possible to monitor average particle sizes during emulsion polymerization reactions using Raman spectroscopy.