Structure Of PVDF Research Articles

Superior EMI shielding behavior of multi-layer structure of PVDF based laminated nanocomposite material by controlling the size and distribution of W-type hexaferrite magnetic nanofillers therein

Superior EMI shielding behavior of multi-layer structure of PVDF based laminated nanocomposite material by controlling the size and distribution of W-type hexaferrite magnetic nanofillers therein

High-sensitivity humidity sensor based on Poly(vinylidene fluoride)/Deep eutectic solvent composites

This study explores the incorporation of deep eutectic solvent (DES) into a poly (vinylidene fluoride) (PVDF) matrix to fabricate PVDF/DES composite thin films. Subsequently, electrodes were screen-printed onto the thin films to create PVDF/DES humidity sensors. The investigation delved into the crystalline structure of PVDF, the cross-sectional morphology and electrochemical property of PVDF/DES composite films, and the humidity sensing response of PVDF/DES humidity sensors. The study revealed that adding DES leads to the formation of porous composite films with electrical active phases and high electrical conductivity. The sensitivity of the PVDF/DES humidity sensor increases with the content of DES. This work provides a novel method for the fabrication of humidity sensors, holding significant potential in various applications such as respiratory monitoring.

Based on the strong oxidant AP adjustment strategy to obtain Al/AP@PVDF composite material with excellent energy release performance

In this paper, ammonium perchlorate (AP) as a strong oxidant has been added into Al/polyvinylidene difluoride (PVDF) nanothermites. Based on homogeneous structure of PVDF, shorter reaction contact between components can be obtained for more outstanding ignition and combustion performance. Water contact angle experiments were conducted to evaluate the hydrophobicity of the composite films, indicating that the suitability of composite material has enhanced under wet environment. According to TG-DSC results, the thermal decomposition of AP can improve the whole heat release process, which theoretically has excellent combustion performance advantages. Constant volume pressure tests were conducted to assess the energy release properties of the films compared with Al@PVDF films. Combustion performance in air was evaluated by employing optical sensors and a high-speed camera to measure factors such as the ignition delay time, light intensity and combustion flame propagation. After adding 15 % AP, the maximum pressure of Al/AP@PVDF film is 0.0960 Mpa, and that of Al@PVDF film is 0.0805 Mpa. The maximum pressure of the film is increased by nearly 19.25 %. Compared with Al@PVDF film, the ignition delay time of Al/AP@PVDF film is shortened by 45 ms, and the light intensity is increased by nearly 93.39 %. However, excessive AP content adversely impacted film formation efficiency, leading to the deterioration of various properties. Therefore, an optimal AP content of approximately 15 % in Al/AP@PVDF system was finally identified.

Design of PVDF hollow fiber membranes with stable crystalline and porous structure by solvent‐free method

AbstractOne of the critical principles of green chemistry and environmental sustainability is to avoid using harmful solvents in chemical processes. In this study, a novel solvent‐free method was employed to prepare poly (vinylidene fluoride) (PVDF) hollow fiber composite membranes with stable crystalline and porous structures. Utilizing the cold‐hot stretching method, the crystalline structure and orientation of PVDF were effectively redesigned, resulting in improved mechanical and penetration properties of the membrane. Additionally, an investigation into the internal crystalline structure of the PVDF hollow fiber membrane was conducted, focusing on crystalline changes induced by ion‐dipole interactions. Results indicated that the addition of neutral ion‐dipole functional particles (N‐P) promoted the conversion of α crystalline to β crystalline, leading to stable β crystalline and controllable pore sizes in the prepared PVDF hollow fiber membrane. Furthermore, the internal crystalline structure significantly contributed to enhancing the membrane's mechanical properties and penetration performance. Notably, a PVDF hollow fiber with high β crystalline content was achieved through 150% cold‐hot stretching and the addition of 20. wt% N‐P further enhanced the β‐crystalline content in the membrane. This study presents a promising approach for reducing solvent consumption and minimizing environmental impact in the field of environment‐friendly membrane fabrication.

A bifunctional double-layer Fe3O4-Polyvinylidene fluoride(PVDF)/PVDF separator with enhanced thermal stability for Li-S batteries

Li-S batteries, utilizing sulfur as the active material, have garnered significant attention due to their impressive theoretical specific capacity of 1675 mA h g−1. However, the commercialization of these batteries faces challenges primarily stemming from the volume expansion of sulfur and the shuttling effect caused by soluble polysulfides. In this study, we present a novel solution through the development of a bifunctional double-layer Fe3O4-PVDF/PVDF separator via electrospinning. The mesh structure of PVDF facilitates rapid lithium ion transport and effectively accommodates the volume expansion of sulfur during discharge/charge, leveraging its high thermal stability and mechanical properties. The incorporation of Fe3O4 within the PVDF matrix serves to trap polysulfides, mitigating the shuttle effect. Experimental results demonstrate that Li-S batteries employing the Fe3O4-PVDF/PVDF separator exhibit an initial discharge capacity of 1052.7 mA h g−1 at a current density of 0.5 C, with a commendably low capacity decay rate of 0.08 % per cycle after 250 cycles. This innovative separator design showcases promising advancements in addressing critical issues hindering the commercial viability of Li-S batteries.

A cost-effective photothermal superhydrophobic coating with micro- and nano-graded structures for efficient solar energy harvesting

Solar collector coatings can solve the current energy shortage and environmental pollution by converting clean solar energy into thermal energy. However, once the coating is adhered to a liquid, the performance of the solar thermal conversion will be seriously affected. Here, a cost-effective photothermal superhydrophobic coating was designed by modulating the microstructure of a highly solar-absorbing material (MCN), followed by a simple spraying method combined with polyvinylidene fluoride resin (PVDF). The MCN in the coating provides excellent photothermal conversion performance, hence, the surface temperature of the coating can be rapidly increased to 97.5 °C at 1 kW/m2. In addition, the coating achieves a water contact angle (WCA) of 155.79° due to the combined micro-nano structure of MCN and PVDF coupled with the low surface energy of PVDF. More importantly, the coating possesses excellent mechanical properties and can be applied to different substrates. This cost-effective photothermal superhydrophobic coating has promising applications in outdoor environments such as insulated tents and waterproof insulation packaging.

Hydrogen Bonding-Assisted Complete Ferroelectric β-Phase Conversion in Poly(vinylidene fluoride) Thin Films: Exhibiting an Excellent Memory Window and Long Retention.

Organic nonvolatile memory with low power consumption is a critical research demand for next-generation memory applications. Ferroelectric switching characteristics of poly(vinylidene fluoride) (PVDF) thin films modified with a trace amount of hydrated Cu salt (CuCl2·2H2O) are explored in the present study. Herein, a Cu salt-mediated PVDF (Cu/PVDF) thin film with preferential edge-on β-crystallites is fabricated through the orientation-controlled spin coating (OCSC) technique. This work proposes a convenient and effective approach to produce edge-on-oriented electroactive PVDF thin films with a high degree of polar β-phase, so as to realize the favorable switching under low operating voltages. Herein, chemically modified PVDF is anticipated to form a complex intermediate, which attains its stability by undergoing favorable hydrogen bonding that reorients the C-C structure of PVDF to obtain the β-conformation. Such information is verified by X-ray photoelectron spectroscopy (XPS). Grazing incidence Fourier transform infrared (GI-FTIR) spectroscopy revealed that the Cu salt incorporated into the PVDF matrix favored the formation of the electroactive β-phase with edge-on crystallite lamellae. Consequently, the Cu/PVDF thin film demonstrates a good contrast between electric field-assisted written and erased data bits in the piezoresponse force microscopy (PFM) phase image. Furthermore, to obtain the ferroelectric memory window, a metal-ferroelectric-insulator-semiconductor (MFIS) diode with Cu/PVDF as a ferroelectric layer has been fabricated. The capacitance-voltage (C-V) characteristic of the MFIS diode exhibits a memory window of 12 V with a long-term retention behavior (∼longer than 7 days). In a nutshell, we tried to represent a clear understanding of the interfacial interactions of the Cu salt with PVDF, which favor the edge-on formation that results in the promising low-voltage ferroelectric switching and excellent retention response, where any additional electrical poling and/or external stretching is completely possible to be ruled out, thus offering a new prospect for the evolution of devices with long-lasting nonvolatile memories.

Investigation of the optimum vibration energy harvesting performance of electrospun PVDF/BaTiO3 nanogenerator

The piezoelectric vibration energy harvesting performance of an electrospun poly(vinylidene fluoride) (PVDF)/Barium Titanate (BaTiO3) nanocomposite piezo polymer nanogenerator was investigated in this study. To obtain the highest piezoelectric output value, electrospinning was performed using four distinct solvent volume ratios of Acetone/Dimethylformamide (DMF) of 0:10, 2:8, 4:6, and 6:4 and three different PVDF weight percent polymer concentrations of 10, 15, and 20. Additionally, three distinct BaTiO3 addition weight percents of 5, 10, and 15 were investigated. The optimal concentration of PVDF (15 wt.%) was combined with a 6:4 volume ratio of Acetone/DMF to form a nanocomposite piezo polymer nanogenerator. The morphology and crystalline structure of PVDF and PVDF/BaTiO3 were analyzed using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques. Nanocomposite piezo polymer nanogenerator was manufactured to harvest energy from vibration. A cantilever beam was developed without a tip mass type system for piezoelectric energy harvesting tests. The highest piezoelectric power output was obtained as 0.243 μW (15 wt.% PVDF and 5 wt.% BaTiO₃), Acetone/DMF (6:4 vol./vol.)) under 10 MΩ at the 15.7 Hz resonance frequency. The morphology of electrospun nanofibers has a significant impact on the piezoelectric performance of a nanocomposite piezo polymer nanogenerator at high-amplitude vibration.

Porous AgNWs/Poly(vinylidene fluoride) Composite-Based Flexible Piezoresistive Sensor with High Sensitivity and Wide Pressure Ranges.

Flexible piezoresistive sensors are highly desirable for tactile sensing and wearable electronics. However, the reported flexible piezoresistive sensors have the inherent trade-off effect between high sensitivity and wide pressure ranges. Herein, we report a flexible piezoresistive sensor with a three-dimensional (3D) porous microstructured sensing layer composed of silver nanowires (AgNWs) and a poly(vinylidene fluoride) (PVDF) matrix, exhibiting high sensitivity and wide pressure ranges. Benefiting from the conductive networks of AgNWs and the 3D porous structure of PVDF, the porous AgNWs/PVDF composite (PAPC)-based flexible piezoresistive sensor exhibits high sensitivities of 0.014 and 0.009 kPa-1 in the wide pressure ranges of 0-30 and 30-100 kPa, respectively. In addition, the fabricated sensor also shows a fast response time of 64 ms, a low detection limit of 25 Pa, and long-term durability over 10,000 continuous cycles. The PAPC-based flexible piezoresistive sensor can accurately monitor various human physiological activities (ranging from subtle deformations to vigorous body movements) by quantitatively measuring the tactile sensation on human skin. This work indicates that the proposed sensor can be potentially applicable to mobile healthcare monitoring devices as well as next-generation wearable electronics.

Electric poling-assisted additive manufacturing technique for piezoelectric active poly(vinylidene fluoride) films: Towards fully three-dimensional printed functional materials

The development of science and technology simplifies the fabrication of functional materials and devices. Polymeric piezoelectric materials have attracted interest for actuation, sensing, energy harvesting, and storage applications due to their capability to sustain larger strains than ceramic piezoelectric materials. In this work, a novel electric poling-assisted additive manufacturing (EPAM) technology that integrates a fused deposition modeling (FDM) three-dimensional (3D) printer with a corona electric poling setup is demonstrated to directly print piezoelectric active materials with improved piezoelectric characteristics. The developed EPAM technology overcomes two main shortcomings of the conventional manufacturing methods for poly(vinylidene fluoride) (PVdF) materials: (1) their shapes are constrained to planar or fiber-like geometries, and (2) the need for additional electric poling as a post-processing treatment. Compared with the contact poling method, the EPAM method eliminates the need to apply electrodes for poling. The EPAM process can accomplish stretching and poling simultaneously which are necessary conditions for the polarization. During the EPAM process, stretching the molten PVdF rod rearranges the amorphous strands in the film plane, and the applied electric field aligns dipoles towards the same direction. The EPAM process can print free-form PVdF structures and induce the formation of β -phase, which is primarily responsible for the piezoelectric response. The Fourier-transform infrared spectroscopy (FTIR) results indicate the β -phase content increased from 15.38% to 17.14% corresponding to unpoled printed and EPAM printed samples, respectively. PVdF force sensors were successfully printed, and the piezoelectric activity (pC/N) was calculated based on the piezoelectric output voltage. The piezoelectric activity has a positive correlation with the piezoelectric coefficient that is explained in detail in section 3.2. The results demonstrate that the average piezoelectric activity of EPAM printed PVdF films was 47.76 pC/N, or about five times higher than unpoled 3D printed films, at 9.0 pC/N. The piezoelectric activity of unpoled 3D printed PVdF films indicates that 3D printing in the absence of an electric field does not result in dipole alignment. The 3D printed samples show an anisotropic mechanical behavior, and the bonding surface strength is sensitive to the printing speed. The maximum Young’s modulus (534.63 MPa) occurred at 3 mm/s and 0° infill, and the highest ultimate tensile strength (UTS) (25.35 MPa) was achieved at 20 mm/s, and 90° infill. Both the Young’s modulus and UTS from the EPAM printed samples are lower than unpoled samples. A fully 3D printed device was demonstrated to identify the position and magnitude of forces and results were visualized via structure-embedded integrated Light emitting diodes (LEDs). Overall, with the advantage of mechanical structural design flexibility and ease of printing of piezoelectric materials, the developed EPAM technology opens a new avenue to simplify device design and fabrication methodologies along with low-cost implementations.

A portable colorimetric device based on PVDF indicator gel for formaldehyde detection in food and wood products

A novel indicator gel for formaldehyde detection is described. The poly(vinylidene fluoride) polymer (PVDF) gel was used in a portable colorimetric sensor to screen for formaldehyde in food and wood products. The gel presented excellent entrapment properties based on the porous structure of PVDF. Color changes from orange to brown, green, and blue could be observed with the naked eye. Images of colorimetric products were captured using the digital camera in a mobile phone. Our sensor produced two linear ranges in the calibration curves: from 0.0 to 100 mg/L and 100 to 6000 mg/L. The limit of detection was 0.47 mg/L. Reproducibility was good. The PVDF indicator gel was stable for up to 70, and 28 days storage at 4 and 25 °C, respectively. The proposed sensor provided good accuracy with recoveries of 96.10–102.03 % for formaldehyde in real samples. The determination of formaldehyde in real samples agreed well with the reference spectrophotometric method at the 95 % confidence level. The proposed integrated colorimetric sensor provides a compact, inexpensive, portable, and semi-quantitative method of determining formaldehyde on-site.

Freestanding 3D piezoelectric PVDF sensors via electroprinting

Polyvinylidene fluoride, PVDF is a soft piezoelectric material with potential applications in robotic sensors and actuators, wearable electronics, and energy harvesting. The sensitivity of piezoelectric PVDF is attributed primarily to the β-crystalline phase with oriented dipoles. 3D electroprinting process is a promising technique to achieve 3D PVDF-based piezoelectric devices because the combined mechanical stretching and electric field-assisted poling can improve the electroactive crystalline phases in PVDF. In this work, we show that the incorporation of an anti-solvent in the PVDF solution was instrumental in obtaining an optimum solution viscosity and solvent evaporation rate to achieve mechanically stable layer-by-layer printing. Two major process parameters further influencing the resolution of the printed structure were nozzle-to-collector distance and extrusion pressure. Freestanding 3D PVDF structures with an average individual layer height as small as 30 µm and continuous prints for multiple 3D designs have been achieved. FTIR and XRD spectra show an improvement in the electroactive β and γ phases in the electroprinted PVDF compared to the dominant α phase of PVDF powder. Furthermore, the 3D PVDF structures display sensitivity to various load profiles at varying frequencies with the piezoelectric voltage coefficient (g33) range between 1.72E-4 and 4.08E-4 V.m/N.

Influences of gamma-ray irradiation on PVDF membrane behavior: An experimental study based on simulation and numerical analysis

This study aims to explore the effects of gamma rays on various properties of poly(1,1-difluoroethylene) (PVDF) membranes under different irradiation conditions. The effects of 60Co γ-ray irradiation on the hydrophilicity, permeability, and mechanical performances of the PVDF membranes were discussed. Results showed that the size of the radiation dose rate had almost no effect on the performance of the membranes, as determined by the total radiation dose. The fracture and collapse of the PVDF structure under anaerobic conditions were obviously lower than those under aerobic conditions. Advanced characterization methods confirmed that the initial impact of gamma rays on the PVDF membranes occurred between 50 and 200 kGy. When the total dose exceeded 200 kGy, structural collapse and chain scission caused by the oxidative degradation mechanism became widespread, thereby leading to the relaxation of the PVDF network and the decline in properties. This study provides valuable information for the application of PVDF membranes to radioactive wastewater and clarifies the mechanism of membrane irradiation degradation to help prolong the service life of membranes. In addition, low total irradiation dose can embellish polymers and thus provide a feasible method for modifying and grafting polymer membranes in the future.

Phase Transitions in Poly(vinylidene fluoride)/Polymethylene-Based Diblock Copolymers and Blends.

The crystallization and morphology of two linear diblock copolymers based on polymethylene (PM) and poly(vinylidene fluoride) (PVDF) with compositions PM23-b-PVDF77 and PM38-b-PVDF62 (where the subscripts indicate the relative compositions in wt%) were compared with blends of neat components with identical compositions. The samples were studied by SAXS (Small Angle X-ray Scattering), WAXS (Wide Angle X-ray Scattering), PLOM (Polarized Light Optical Microscopy), TEM (Transmission Electron Microscopy), DSC (Differential Scanning Calorimetry), BDS (broadband dielectric spectroscopy), and FTIR (Fourier Transform Infrared Spectroscopy). The results showed that the blends are immiscible, while the diblock copolymers are miscible in the melt state (or very weakly segregated). The PVDF component crystallization was studied in detail. It was found that the polymorphic structure of PVDF was a strong function of its environment. The number of polymorphs and their amount depended on whether it was on its own as a homopolymer, as a block component in the diblock copolymers or as an immiscible phase in the blends. The cooling rate in non-isothermal crystallization or the crystallization temperature in isothermal tests also induced different polymorphic compositions in the PVDF crystals. As a result, we were able to produce samples with exclusive ferroelectric phases at specific preparation conditions, while others with mixtures of paraelectric and ferroelectric phases.

Interfacial Nanostructuring of Poly(vinylidene fluoride) Homopolymer with Predominant Ferroelectric Phases.

Facile preparation of poly(vinylidene fluoride) (PVDF) homopolymer nanoparticles (NPs) with monodispersed size distribution and predominant ferroelectric phases was done in an interfacial nonsolvent (water/methanol)-solvent (dimethylformamide (DMF))-polymer (PVDF) ternary system using two interfacial nanoassembly methods. First, a fluidic liquid-liquid interface consisting of two miscible solvents was created by introducing nonsolvent (water) under the PVDF solution. After the interface was created, the interface moved up to the DMF phase direction; PVDF NPs were produced through nonsolvent-induced phase separation. As the water content decreased in the nonsolvent by mixing with methanol, PVDF structures changed from nanoparticles with 252 nm average diameter (PVDF NP-1) to a porous membrane through membrane-wrapped NPs. The phenomena were found to be related to the mutual affinity of solvent, nonsolvent, and PVDF. When an additional external force was introduced to the water-DMF-PVDF system through magnetic stirring (reprecipitation method), smaller PVDF NPs with 61.4 nm diameter were obtained (PVDF NP-2). Both the as-prepared PVDF NPs were demonstrated with the predominant ferroelectric (electroactive (EA)) phase up to 97-98% among crystalline phases, which is apparently the highest value ever reported for PVDF homopolymer NPs. It is noteworthy that PVDF NP-2 showed a higher β phase ratio than that of PVDF NP-1, as proved using Fourier transform infrared (FT-IR) spectroscopy. Also, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements revealed that PVDF NP-1 exhibited higher crystallinity and that PVDF NP-2 underwent a well-separated two-step phase transition under heating. Results suggest that controlling interface formation with DMF and water plays a crucial role in manipulating ferroelectric PVDF nanostructures in terms of crystallinity and the ferroelectric β phase-to-γ phase ratio.

Fabrication of Piezoelectric PVDF/PAR Composites Using a Sheath-Core Fiber Method.

We report the preparation of sheath-core type fibers made from poly(vinylidene fluoride) (PVDF) and polyarylate (PAR) using melt conjugate spinning to fabricate piezolectric composites. The morphology of this sheath-core fiber was determined through scanning electron microscopy. Subsequently, by the compression molding of the PVDF/PAR sheath-core fiber assembly, we fabricated PVDF/PAR composites exhibiting piezoelectric properties. For enhancing the piezoelectric properties, we increased the concentration of PVDF β-crystalline phase in the PVDF/PAR composite through poling post-treatments. The resulting crystal structure of PVDF was confirmed through infrared spectroscopy and X-ray diffraction. A universal testing machine was employed to measure the tensile properties of the PVDF/PAR composites. Finally, through a hydrothermal growing method, ZnO was coated on the composite surface to enhance the piezoelectric properties, which were subsequently optimized by varying the hydrothermal growing conditions.

Enhancement of EMI shielding effectiveness of flexible Co2U-type hexaferrite (Ba4Co2Fe36O60)-poly(vinylidene fluoride) heterostructure composite materials: An improved radar absorbing material to combat against electromagnetic pollution

In this report, for the first time, Co2U-type hexaferrite (Ba4Co2Fe36O60) nanomaterials have been considered along with their conjugation with a poly(vinylidene fluoride) (PVDF) matrix for the fabrication of heterostructure composite materials with superior electromagnetic interference shielding effectiveness (SE) that can produce better attenuation of microwave radiation. The high value of magnetizations of ∼7.21 and 10.63 emu/g is significant for the improvement of the shielding effectiveness due to absorption (SEA) of the composite materials. The unique combination of magnetic and dielectric responses of these Co2U-type hexaferrite nanomaterials helps to get significantly high total shielding effectiveness (SET) in their PVDF composite states within the frequency range of 8–18 GHz. A very high value of SET of approximately −83 dB at 14.2 GHz with >99.999 999% of attenuation of incident radiation has been observed for the Co2U-type hexaferrite–PVDF composite materials. The β-phase modified PVDF structure also plays the most important role to generate induced polarization inside the structure of composite materials. Also, this PVDF matrix provides the application friendly laminated structure of Co2U-type hexaferrite–PVDF composite materials. Structural, morphological, and chemical studies reveal the presence of the polycrystalline phase of Co2U-type hexaferrite and β-phase crystallization of polar PVDF in the multi-phase Co2U-type hexaferrite–PVDF composite materials. This study has helped us to understand the importance of magnetic Co2U-type hexaferrite nanomaterials for the fabrication of lightweight, large area, flexible, and thickness-controlled radar absorbing materials to combat against electromagnetic pollution.

Low temperature mechanical behaviour of PVDF: cryogenic pre-treatment, quasi-static, cyclic and dynamic experimental testing and modelling

PVDF has historically drawn the interest of the scientific community because of its mechanical response to external stimuli. Recently, novel 3D printing techniques have been proposed to manufacture responsive PVDF components, leading to the reconsideration of this polymer in many applications (i.e., sensor-actuator or energy harvesting systems). During manufacturing and/or service conditions, PVDF structures can be subjected to large deformations that, eventually, can involve low temperature loading (e.g., piezoelectric sensors for aircrafts). In this work, a deep mechanical characterisation of PVDF specimens is carried out under low temperature conditions. To this end, we first evaluate potential effects of cryogenic pre-treatment going beyond the glass transition temperature of the polymer. Then, mechanical tests are conducted at different loading conditions and a wide range of testing temperatures from room to temperatures below glass transition: quasi-static compression tests, cyclic loading tests, and high strain rate tests. The complete set of experiments is analysed together to identify slow and fast relaxation mechanisms within the polymeric structure and motivate a new constitutive model. Finally, taking the experimental observations as formulation's basis, a thermodynamically consistent constitutive model is developed for finite deformations. This model describes the mechanical behaviour of PVDF as the combination of slow and fast response and accounts for strain rate dependency, temperature sensitivity, hysteresis and thermal evolution during the deformation process. The results from this work provide a full study of the mechanical behaviour of PVDF at low temperature, considering effects of both pre-treatment and testing temperature, and a new modelling tool to predict its response under a wide range of room-to-low temperature loading conditions.

Effect of Electrode Fabrication Process on the Crystallinity of PVDF Binder and Electrochemical Performance of Electrode

In lithium ion battery in fabrication of electrode with good mechanical performance, active materials and conductive agent have to be mixed with specific polymer as binder to binding the other components together. As an effective binder, the polymer should meet some requirements for battery performance and production, such as excellent adhesion to current collector, suitable cohesion to active material and conductive agent, good electrochemical stability over a wide voltage window, high lithium ion conductivity, and so on. Because the binder may coat on the surface of active material particles, the binder layer should have high ionic conductivity and lithium ion can pass through the binder. Poly (vinylidene fluoride) (PVDF) is the mostly common used binder in lithium ion battery production. The amorphous phase in PVdF is a good matrix for polar molecules, and lithium ions can pass through a thin layer of swollen PVdF[1]. PVDF is a semi-crystalline polymer with a repeating unit of –CH2-CF2-. The spatial arrangement of the CH2 and CF2 groups along the polymer chains can contribute to the unique properties of PVDF from its crystalline phase. But it is seldom researched that the effect of crystalline structure of PVDF on the electrochemical performance in lithium ion battery. In our recent study, we found that the impedance of electrode is dependent on the drying temperature of coated slurry[2]. In this research we investigated the relationship of process conditions with crystalline phases of PVDF binder in the electrode and the dependence of the electrochemical performance of the electrode on the process conditions.[1]. K. Tsunemi , H. Ohno , E. Tsuchida , Electrochimica Acta , 28 (6) , 591 (1983) .[2]. Y. Fu, X. Song, G. Liu, V. Battaglia, 236th ECS Meeting ,353, Oct. 13-17, 2019, Atlanta, GA. Figure 1

Pre‐thermal treatment in binary solvent systems promoting β crystalline phase of electrospun poly(vinylidene fluoride) nanofibers

AbstractPoly(vinylidene fluoride) (PVDF) nanofibers were fabricated via electrospinning with an investigation of various ratios of binary solvents at different temperatures. The amount of acetone influenced the morphology. Scanning electron microscopy showed a PVDF membrane composed of smooth and unblemished fibers without beads and dark spots with small diameters of 201 ± 54 nm at a dimethylformamide‐to‐acetone ratio of 4:6. The temperature of pre‐thermal treatment from room temperature to 120 °C was investigated to promote the β crystalline phase in electrospun PVDF nanofibers. The result was characterized using Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD). PVDF solution prepared at 80 °C was used to increase the β crystalline phase of the electrospun PVDF nanofibers due to the transformation of α to β phase occurring during the spinning process and also bead‐free PVDF nanofibers were obtained. Differential scanning calorimetry revealed crystallization behavior corresponding with that determined using FTIR spectroscopy and XRD. Therefore, the solvent proportion and pretreatment temperature were observed to affect ultrafine nanofiber and crystalline structure of PVDF, respectively. © 2020 Society of Chemical Industry