Phase segregation phenomena in poly(ethylene oxide):LiN(CF3SO2)2 electrolyte studied by local Raman spectroscopy

Polymer electrolyte composed of poly(ethylene oxide) PEO with dissolved lithium bis (trifluoromethanesulfonyl)imide salt LiTFSI of molar ratio EO:Li 16:1 was prepared by casting from solution. The electrolyte has been investigated by microscope observation simultaneous with impedance spectroscopy, differential scanning calorimetry and local Raman spectroscopy. The presented results provide direct support for model of phase segregation which takes place in PEO:LiTFSI electrolytes. According to the model proposed in our earlier publications, crystallization of PEO or PEO:salt complexes causes rejection or drainage of salt from specific regions of electrolyte. Thus, a resulting semicrystalline electrolyte is divided into large domains of different composition. In the case of investigated PEO:LiTFSI 16:1 electrolyte, the results obtained by local Raman spectroscopy indicated, that in areas situated within large circular spherulites the concentration of salt is lower than in molten (amorphous) electrolyte. In areas situated outside of these spherulites, the concentration of salt was considerably higher than for amorphous electrolyte. This is in good agreement with the assumption that the circular spherulites have the crystalline skeleton of pure PEO, whereas the PEO₆:LiTFSI crystalline phase dominates in the areas between their borders.     

Investigations on the enhancement mechanism of inorganic filler on ionic conductivity of PEO-based composite polymer electrolyte: The case of molecular sieves

Polarized optical microscopy (POM) and differential scanning calorimeter (DSC) techniques are used to study the effect of ZSM-5 molecular sieves on the crystallization mechanism of poly(ethylene oxide) (PEO) in composite polymer electrolyte. POM results show that ZSM-5 has great influence on both the nucleation stage and the growth stage of PEO spherulites. ZSM-5 particles can act as the nucleus of PEO spherulites and thus increase the amount of PEO spherulites. POM and DSC results show that ZSM-5 can restrain the recrystallize tendency of PEO chains through Lewis acid-base interactions and hence decrease the growth speed of PEO spherulites. Room temperature ionic conductivity of PEO-LiClO₄-based polymer electrolyte can be enhanced by more than two magnitudes during long time storage with the addition of ZSM-5.     

Crystallization behavior of star-shaped poly(ethylene oxide) with cubic silsesquioxane (CSSQ) core

The crystallization behavior of well-defined star-shaped cubic silsesquioxane-poly(ethylene oxide) (CSSQ-PEO) and linear PEO were studied in terms of differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). It was found in DSC analysis that the glass transition temperature (T_g) and the crystallization temperature (T_c) of CSSQ-PEO are different from those of linear PEO. The presence of CSSQ in PEO reduced the overall crystallization growth rate. This effect can be ascribed to the reduction of the mobility of the PEO crystallites in the presence of CSSQ and the star structure of the polymer. The Ozawa method is qualitatively satisfactory for describing the nonisothermal crystallizations of linear PEO and CSSQ-PEO. The presence of CSSQ leads to the diffusion- and nucleation-controlled mechanisms in the crystallization process of CSSQ-PEO whilst only the nucleation-controlled mechanism was observed in the case of linear PEO. The apparent activation energy required for crystallization was calculated using the Kissinger method. The isothermal crystallization morphology of PEO and CSSQ-PEO were also examined by cross-polarizing optical microscopy (CPOM). The CPOM images indicated the spherulite growth is slower in CSSQ-PEO as compared to linear PEO. It was also investigated that more number of PEO spherulites in CSSQ-PEO were observed, which sizes are markedly smaller than the spherulites developed in linear PEO. Wide-angle X-ray scattering (WAXS) studies showed that the crystallization peaks for linear PEO and CSSQ-PEO appeared at different temperature revealing the crystallization process and crystal growth rate are different from each other. However, no significant distortion of the crystal structure of PEO was evaluated in the presence of CSSQ.     

Nanocomposite polymer electrolyte comprising PEO/LiClO4 and solid super acid: effect of sulphated-zirconia on the crystallization kinetics of PEO

A novel PEO-based nanocomposite polymer electrolyte is prepared by using solid super acid sulphated-zirconia (, SZ) as the filler. Polarized optical microscopy (POM) and differential scanning calorimeter (DSC) results show that part of SZ particles may act as the nucleus of PEO spherulites and thus increase the amount of PEO spherulites. On the other hand, other SZ particles, which do not act as the nucleus, can restrain the recrystallization tendency of PEO chains through Lewis acid-base interaction and hence decrease the growth speed of PEO spherulites. As a result, the PEO component in PEO-LiClO₄-SZ can maintain a high amorphous state for a long time. The room temperature ionic conductivity of PEO-LiClO₄-SZ is relative high and stable compared with pristine PEO-LiClO₄, indicating that it is promising for all solid-state rechargeable lithium ion batteries.     

Miscibility and crystallization in crystalline/crystalline blends of poly(butylene succinate)/poly(ethylene oxide)

Miscibility and crystallization behavior have been investigated in blends of poly(butylene succinate) (PBSU) and poly(ethylene oxide) (PEO), both semicrystalline polymers, by differential scanning calorimetry and optical microscopy. Experimental results indicate that PBSU is miscible with PEO as shown by the existence of single composition dependent glass transition temperature over the entire composition range. In addition, the polymer-polymer interaction parameter, obtained from the melting depression of the high-T_m component PBSU using the Flory-Huggins equation, is composition dependent, and its value is always negative. This indicates that PBSU/PEO blends are thermodynamically miscible in the melt. The morphological study of the isothermal crystallization at 95 °C (where only PBSU crystallized) showed the similar crystallization behavior as in amorphous/crystalline blends. Much more attention has been paid to the crystallization and morphology of the low-T_m component PEO, which was studied through both one-step and two-step crystallization. It was found that the crystallization of PEO was affected clearly by the presence of the crystals of PBSU formed through different crystallization processes. The two components crystallized sequentially not simultaneously when the blends were quenched from the melt directly to 50 °C (one-step crystallization), and the PEO spherulites crystallized within the matrix of the crystals of the preexisted PBSU phase. Crystallization at 95 °C followed by quenching to 50 °C (two-step crystallization) also showed the similar crystallization behavior as in one-step crystallization. However, the radial growth rate of the PEO spherulites was reduced significantly in two-step crystallization than in one-step crystallization.     

Observation of the concentric diffractive banding on the spherulites of poly(ethylene oxide) by a dynamic method

The growth of poly(ethylene oxide) (PEO) spherulites was observed synchronously with a polarized optical microscope, which was equipped with a video detector, and so the whole growing process of the PEO spherulites was dynamically recorded as a movie. There was a series of concentric diffractive bands on the surface of the PEO spherulites; furthermore, the diffractive banding did not exist until at least two independent PEO spherulites came into contact with each other. However, the formation of the diffractive banding on the PEO spherulites was also related to the crystallization conditions. It was concluded qualitatively that the diffractive banding formed more easily at the crystallization temperature with a high degree of supercooling, and this was explained in kinetic terms. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2454–2458, 2005     

Synthesis,characterization, and electrochemical properties of poly(ethylene oxide)-based polyaniline electrolyte complex

The polymer electrolyte based poly(ethylene oxide) complexed with conducting polyaniline (PANI) has been prepared in different weight percentages. The complexation is confirmed by Fourier transform infrared spectroscopy (FTIR).The change in morphology is studied by using scanning electron microscopy. The DC conductivity measurements are carried out using Keithley digital multimeter. It is seen that DC conductivity shows exponential behavior for all PEO : PANI complexes. It is observed that among all the PEO : PANI complexes, 50 wt % of PEO in PANI shows highest conductivity. Electrochemical cell parameters for battery applications at room temperature also have been determined. The samples are fabricated for battery application in the configuration of Na:(PEO : PANI):(I₂ + C + sample), and their experimental data are measured using Wagner polarization technique. The cell parameters results in an open-circuit voltage of 0.4 V and a short-circuit current of 902 μA for PEO : PANI (50 : 50) composite. Hence, these composites can be better candidates for the polymer electrolyte studies. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of molar mass on the thermal properties,conductivity and intermolecular interaction of poly(ethylene oxide) solid polymer electrolytes

The sample preparation pathway of solid polymer electrolytes (SPEs ) influences their thermal properties, which in turn governs the ionic conductivity of the materials especially for systems consisting of a crystallizable constituent. Majority of poly(ethylene oxide) (PEO)‐based SPEs with molar masses of PEO well above 10⁴ g mol^?1 (where PEO is crystallizable and should reach an asymptote in thermal behaviour) display molar mass dependence of the thermal properties and ionic conductivities in non‐equilibrium conditions, as reported in the literature. In this study, PEO of different viscosity‐molar masses (M _η = 3 × 10⁵, 6 × 10⁵, 1 × 10⁶, 4 × 10⁶ g mol^?1) and LiClO₄ salt (0 to 16.7 wt%) were used. The SPEs were thermally treated under inert atmosphere above the melting temperature of PEO and then cooled down for subsequent isothermal crystallization for sufficient experimental time to develop morphology close to equilibrium conditions. The thermal properties (e.g. glass transition temperature, melting temperature, crystallinity) according to differential scanning calorimetry and the ionic conductivity obtained from impedance spectroscopy at room temperature (σ _DC ～ 10^?6 S cm^?1) demonstrate insignificant variation with respect to the molar mass of PEO at constant salt concentration. These findings are in agreement with the PEO crystalline structures using X‐ray diffraction and ion ? dipole interaction by Fourier transform infrared results. © 2017 Society of Chemical Industry     

Ionic conductivity in polyethylene-b-poly(ethylene oxide)/lithium perchlorate solid polymer electrolytes

The ionic conductivity and phase arrangement of solid polymeric electrolytes based on the block copolymer polyethylene-b-poly(ethylene oxide) (PE-b-PEO) and LiClO₄ have been investigated. One set of electrolytes was prepared from copolymers with 75% of PEO units and another set was based on a blend of copolymer with 50% PEO units and homopolymers. The differential scanning calorimetry (DSC) results, for electrolytes based on the copolymer with 75% of PEO units, were dominated by the PEO phase. The PEO block crystallinity dropped and the glass transition increased with salt addition due to the coordination of the cation by PEO oxygen. The conductivity for copolymers 75% PEO-based electrolyte with 15 wt% of salt was higher than 10⁻⁵ S/cm at room temperature and reached to 10⁻³ S/cm at 100 °C on a heating measurement. The blend of PE-b-PEO (50% PEO)/PEO/PE showed a complex thermal behavior with decoupled melting of the blocks and the homopolymers. Upon salt addition the endotherms associated with PEO domains disappeared and the PE crystals remained untouched. The conductivity results were limited at 100 °C to values close to 10⁻⁴ S/cm and at room temperature values close to 3 × 10⁻⁶ S/cm were obtained for the 15 wt% salt electrolyte. Raman study showed that the ionic association of the highly concentrated blend electrolytes at room temperature is not significant. Therefore, the lower values of conductivity in the case of the blend with 50% PEO can be assigned to the higher content of PE domains leading to a morphology with lower connectivity for ionic conduction both in the crystalline and melted state of the PE domains.     

Eutectic‐forming binary system of poly(ethylene oxide) and p‐hydroxybenzaldehyde

The binary system consisting of poly(ethylene oxide) (PEO) and p‐hydroxybenzaldehyde (PHD) was characterized with the aid of differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy and Fourier‐transform infrared spectroscopy. The phase diagram created from thermal analysis data provides clear evidence for the presence of a eutectic at 35.5 °C and PHD weight fraction of 42%. Microscopy studies show that, for the mixtures with a PHD weight fraction below 42%, the resulting morphology of the crystallized sample is coarse spherulitic texture. In the case of eutectic composition, the crystallization of the binary melt produces degenerated homogenous spherulites. For the hypoeutectic PEO–PHD mixtures, the PHD crystals become large and thick with decreasing the PEO fraction. Moreover, the infrared measurements indicate that hydrogen bonding in the PEO–PHD binary system has an important effect on the PEO helical conformation. With increase of the amount of PHD component, the PEO helical conformation in the PEO–PHD mixtures changes from the 7₂ helix to the 10₃ helix. Further increase of the PHD content leads to the destruction of the PEO helical conformation. Copyright © 2003 Society of Chemical Industry     

Study of a new polymer electrolyte poly(ethylene oxide): NaClO3 with several plasticizers for battery application

Sodium ion conducting thin film polymer electrolytes based on poly(ethylene oxide) (PEO) complexed with NaClO₃ were prepared by a solution‐casting method. Characterization by XRD, IR spectroscopy and AC conductivity has been carried out on these thin film electrolytes to analyse their properties. The conductivity studies show that the conductivity value of PEO:NaClO₃ complex increases with the increase in salt concentrations. Increase in conductivity was found in the electrolyte system by the addition of low molecular weight polymer poly(ethylene glycol) (PEG) and the organic solvents dimethylformamide (DMF) and propylene carbonate (PC). Using these electrolyte systems, cell parameters were measured from the discharge study with the application of load 100 kΩ at room temperature with common cell configuration Na|electrolyte|C:I₂:electrolyte. The open circuit voltage (OCV) ranges from 2.81 to 3.23 V and the short circuit current (SCC) ranges from 340 to 1180 µA. © 2001 Society of Chemical Industry     

Influence of crystalline complexes on electrical properties of PEO:LiTFSI electrolyte

Polymer electrolytes of poly(ethylene oxide) matrix with lithium imide salt LiN(CF₃SO₂)₂ were prepared by casting from solution. Thin films with compositions corresponding to molar ratios 6:1, 3:1 and 2:1 EO:Li were investigated by impedance spectroscopy, impedance spectroscopy simultaneous with polarizing microscope observation, X-ray diffraction and differential scanning calorimetry. The presence of PEO:LiTFSI stoichiometric complexes was found to significantly decrease conductivity at temperature of crystallization, which indicates that those complexes should be regarded as poorly conductive. Changes of properties of amorphous phase related to crystallization were also observed. Crystallization induced phase segregation, which in some cases caused considerable shift of the glass transition temperature of amorphous phase remaining in a semicrystalline system. For PEO:LiTFSI electrolyte with molar ratio of 3:1 EO:Li this effect was found to be responsible for enhancement of conductivity of semicrystalline sample in respect to the amorphous one, which was observed at low temperatures. Phase separation involving precipitation of LiTFSI salt was also found to be a likely explanation for significant enhancement of conductivity for PEO:LiTFSI 2:1 electrolyte subjected to rapid cooling below the glass transition temperature.     

Study of poly(organic palygorskite-methyl methacrylate)/poly(ethylene oxide) blended gel polymer electrolyte for lithium-ion batteries

In this study, the composite polymer was prepared by blending poly(ethylene oxide) (PEO) and POPM (the copolymer of methyl methacrylate [MMA] and organically modified palygorskite), and then the composite polymer based membrane was obtained by phase-inversion method. The scanning electron microscopy results showed that the composite polymer membrane has a three-dimensional network structure. X-ray diffraction results indicated that the crystalline region of PEO is disappeared when introduction of a certain amount of the PEO. Meanwhile, the elongation of composite polymer membrane increased when increasing PEO concentration, but the value of tensile strength of PEO-POPM membrane decreased. When the mass fraction of PEO was 24%, the porosity and maximum value of ionic conductivity of the composite polymer membrane were 54% and 2.41 mS/cm, respectively. The electrochemical stability window of Li/gel composite polymer electrolyte/stainless steel batteries was close to 5.3 V (vs. Li⁺/Li), and the battery of Li/gel composite polymer electrolyte/LiFePO₄ showed good cycling performance and the discharge capacity of the battery were between 169.8 and 155 mAh/g. Meanwhile, the Coulombic efficiency of the battery maintained over 95% during the 80 cycles.     

Optical microscopy and conductivity of poly(ethylene oxide) complexed with KI salt

The optical microscopy, crystallinity and ion conductivity of PEO complexed with potassium iodide (KI) salt are present. The spherulite structure derived from polarized optical microscopy (POM) suggested the ion induces different spherulite structures from that without salt. The size of the spherulites decreases with increasing salt concentration and is completely destroyed with KI salt content of 20 wt% (O-K ratio 15:1). This result concurs with the X-ray diffraction and DSC studies, that PEO crystallinity is reduced upon addition of KI salt. Upon elevating the temperature, the POM micrographs elucidate degradation of the spherulite structure when smaller crystallites begin to melt before the melting temperature of SPE, and become completely opaque above PEO melting temperature (T_m). The pseudo-activation energy derived from variable temperature conductivity measurements of about 0.24 eV is similar to that of PEO-lithium salt systems and suggested the identical PEO segmental motion governs the fundamental ion movement. Stable PEO-K complex (T_m from 135 to 155 °C) is formed after annealing at 120 °C for 12 h. However, the conductivity is about one order smaller compared to lithium salt due to the shorter hopping distance of the heavier potassium ion.     

Synthesis, characterization and device application of hot-pressed solid polymer electrolytes:(1 − x) PEO:x NaHCO3

Synthesis and io n transport characterization of hot-pressed solid polymer electrolyte (SPE) membranes:(1 ? x) poly (ethylene oxide) (PEO):x NaHCO₃, where 0 < x < 50 wt.%, have been reported. SPE films have been synthesized using a hot-press technique in place of the traditional solution-cast method. A conductivity enhancement of the two orders of magnitude was achieved in SPE film:70PEO:30NaHCO₃ and this composition has been referred to as optimum conducting composition (OCC). Materials characterization was done with the help of XRD, SEM, FTIR, DSC and TGA techniques. The ion transport behavior in SPE membranes has been discussed on the basis of experimental measurements on their ionic conductivity (σ), ionic mobility (μ) and some other important parameters. A solid-state polymer battery was fabricated using SPE OCC at room temperature, as a device application.     

Nano-assembly of intertwining lamellae of opposite bending senses in poly(ethylene oxide) co-crystallizing with poly(p-vinyl phenol)

Strongly interacting amorphous poly(p-vinyl phenol) (PVPh) was added into semi-crystalline poly(ethylene oxide) (PEO) at 20 wt.% to generate dendritic lamellae of alternating birefringence colors, which intertwine roughly in the radial directions as periodic stripes. Optical and atomic-force microscopy analyses are performed on revealing lamellae assembly in highly dendritic PEO spherulites by crystallizing PEO/PVPh (80/20) at crystallization temperature (T _c ) equals to 45 °C. The lamellae of two opposite colors in the same PEO spherulite quadrant are exactly of same geometry (of elongated plates, each being 0.2 μm in width and 2–5 μm in length), but they fan out +/?45^o, respectively, as they grow away from the radial direction. The opposite colored-lamellae are radiating out in radial directions, interweaving each other to display alternating colors in radial alignment. However, such alternating colors can also be similarly seen in ring-banded spherulites in many polymers. The results presented in this study have demonstrated that the lamellae of alternating birefringent colors cannot only be seen in banded spherulites, but also in spherulites with radial dendrites.     

增塑剂PC掺杂（PEO）_8-LiClO_4-SiO_2电解质体系的性能研究

以增塑剂碳酸丙烯酯（PC）作为掺杂物,混于（PEO）8-LiClO4-SiO2固体电解质体系中。得到厚度约为350μm性能良好的聚合物电解质薄膜,利用交流阻抗法测定聚合物电解质的电导率,通过XRD对聚合物电解质薄膜的物相结构进行分析研究。结果表明掺杂后（PEO）8-LiClO4-SiO2-PC固体电解质的室温电导率较（PEO）8-LiClO4-SiO2体系有了进一步提高,在PC质量分数为40%时最高,达到3.083×10-6 S.cm-1;电导率与温度关系遵循Arrhenius方程。温度的升高有利于电导率的提升,在80℃时体系的离子电导率为1.180×10-5 S.cm-1。XRD分析表明,加入PC后PEO的结晶度进一步减小,体系不定形相增加,有利于离子电导率的提高。     

Crystallization and melting of PEO:LiTFSI polymer electrolytes investigated simultaneously by impedance spectroscopy and polarizing microscopy

Simultaneous impedance measurements and optical observations of polymer electrolytes were conducted in an automated experimental setup that combined an impedance dielectric analyzer, a polarizing microscope with a heating stage and a digital camera. The polymer film was placed between glasses with ITO conductive layers, forming a transparent cell mounted in a custom designed holder that preserved argon atmosphere.Films of high molecular weight poly(ethylene oxide) with dissolved lithium bis(trifluoromethanesulfone) imide(LiTFSI) of two compositions: 50:1 and 6:1 (EO:Li molar ratio) were investigated in transparent cells above room temperature and in cells with gold electrodes in temperature range between −60 and 90 °C. Various heating and cooling runs enabled observation of the crystallization and melting.The results indicate that the decrease of conductivity observed in impedance spectra during crystallization is related to the closing of amorphous conductivity pathways by growing spherulites. In the dilute system, composition 50:1 EO:Li, amorphous areas were still visible in the film after the growth of spherulites ceased. In the film of composition 6:1, corresponding to the polymer-salt complex, densification of the structure and interfacial phenomena caused a large drop of conductivity at the late stage of crystallization. In the dense structure of crystallized P(EO)₆:LiN(CF₃SO₂)₂ film no amorphous areas were visible. Differences in the structure have a reflection in the relative change of conductivity caused by crystallization, which decreased six times for the 50:1 composition and 500 times for the 6:1 composition.     

Preparation and application of poly(ethylene oxide)-based all solid-state electrolyte with a walnut-like SiO2 as nano-fillers

Poly(ethylene oxide) (PEO) is one of the most promising candidates in polymer solid-state electrolyte. However, the polymer matrix has a high degree of crystallinity and thus manifests low conductivity, which restricts its application in all solid-state lithium-ion battery. Herein, a new composite polymer electrolyte (PLWLS), which is comprised of PEO, LiClO₄, and the independently synthetized walnut-like SiO₂ (WLS) as nano-fillers, is designed and prepared by the tape-casting way. The optimum mass fraction of walnut-like SiO₂ is determined by physical and electrochemical characterization. The result shows that the PLWLS-15 with 15 wt % walnut-like SiO₂ nanoparticles has a crystallinity of 13.7%. Similarly, the maximum tensile strength is improved greatly. The assembled all-solid-state lithium-ion battery with LiFePO₄/PLWLS-15/Li exhibits a higher discharge capacity of 167 mAh g⁻¹ at 0.1 C (1C = 170 mAh g⁻¹) and 143 mAh g⁻¹ at 0.5 C in first cycle, lower voltage polarization and better cycle performance. Therefore, adding nanoparticle into PEO-based solid-state electrolyte could effectively promote the mechanical property and electrochemical performance, and thus provide a possibility of application for PLWLS-15 in next generation all solid-state lithium battery. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48810.     

Synthesis of high molecular weight polyoxyethylene with a quaternary catalyst and study of its conductive blends with poly(2‐vinyl pyridine)

High molecular weight polyoxyethylene (PEO) was synthesized by using a quaternary catalyst composed of triisobutyl aluminum, phosphoric acid, water, and N,N‐dimethylaniline (DMA). Optimum synthesis conditions and some properties of the product were studied. This catalyst showed high activity and the molecular weight of the polyoxyethylene obtained can approach one million. The activity of polymerization mainly depends upon the composition of catalyst. The optimum composition is as follows: i‐Bu₃Al:H₃PO₄:H₂O:DMA = 1 : 0.17 : 0.17 : 0.10–0.15 (molar ratio).The active centers of the catalyst was thus proposed. The high molecular weight PEO synthesized by this catalyst was blended with poly(2‐vinyl pyridine) (PVP) and then doped with LiClO₄ and TCNQ to obtain a conductive elastomeric material. Ionic, electronic, and mixed (ionic–electronic) conductivities of blends were investigated. At a Li/EO molar ratio of 0.1 and a TCNQ/VP molar ratio of 0.5, the mixed conductivity of the blend of PEO/PVP/LiCIO₄/TCNQ is higher than the sum of ionic conductivity of PEO/PVP/LiCIO₄ and electronic conductivity of PEO/PVP/TCNQ, when the weight ratio of PEO to PVP is 6/4 or 5/5. It can reach 4 × 10^?6 S/cm at room temperature. Differential scanning calorimetry, thermal gravimetric analysis, and the appearance of the blend showed that both TCNQ and LiClO₄ can complex with PEO and PVP, thus enhancing the compatibility between PEO and PVP. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007