Electrospining: Polyvinylidene fluoride-co-hexafluoropropylene-based membrane with high ferroelectric properties was prepared by electrospinning and multilayer composite technology

Background

Dielectric materials with ultrahigh energy storage density are in great demand for applications in mobile communications, biomedical devices, self-powered electronics, renewable energy, power distribution, and waste energy harvesting. These systems store energy in batteries and fuel cells, but higher energy efficiency can be achieved using supercapacitors due to their faster response. Compared to electrochemical energy storage devices (batteries and fuel cells), ferroelectric microelectronic capacitors generally have higher power density due to their high charge and discharge rates.

The main point of this paper

Polymorphic crystallinity of PVDF:

PVDF is a polymorphic crystalline polymer with different crystal phases, including α-phase, β-phase and γ-phase. Among them, the β-phase has attracted much attention due to its electroactivity and high polarizability

Under different processing conditions, PVDF can form different crystal phases, and the use of additives can promote the transformation of some α-crystalline phases to β-crystalline phases and increase the crystallinity of PVDF membranes

Preparation of ferroelectric PVDF nanofibers:

Ferroelectric PVDF nanofibers can be prepared by electrospinning process, in which the use of ionic liquid as additive can stabilize the spinning process and increase the proportion of ferroelectric β phase

In addition, the formation of nanofibers can be optimized by adjusting the parameters in the electrospinning process, such as solution concentration, voltage and ambient humidity

Preparation of PVDF-co-HFP film:

PVDF-co-HFP copolymer has good piezoelectricity, mechanical properties and electrical breakdown strength, and can be used to prepare nanofibers by electrospinning process

By alternately laminating PVDF-co-HFP nanofiber membranes with PMMA films, a multilayer polymer structure can be prepared to minimize dielectric loss and maximize electrical breakdown strength

Applications of ferroelectric multilayer laminated films:

Ferroelectric multilayer laminated films are expected to be used in efficient, lightweight, economical, and durable pulse power devices due to their lightweight and high energy density

The multilayer structure can lead to charge accumulation at the interface, resulting in interfacial polarization and capacitance effects, thereby improving energy density

Optimization of ferroelectric domain structure:

The optimized ferroelectric domain structure requires that the axial direction of the crystal orientation in the nanofibers is consistent with the planar direction of the laminate to achieve high discharge energy density

By adjusting the morphological aspect ratio of the film, the voltage required to achieve a high electric field can be reduced, thereby optimizing polarization and energy density

Multilayer all-polymer laminates: ultrahigh energy storage and discharge via electrospinning of PVDF-co-HFP nanofibers and PMMA films

Advantages of ferroelectric polymers:

Ferroelectric polymers, especially polyvinylidene fluoride (PVDF) and its copolymers, are becoming increasingly important in modern electronics due to their relatively low cost, light weight and lower carbon footprint of production and maintenance compared to ceramics, especially in applications requiring huge pulsed power transmission

Electrospinning PVDF nanofibers:

Electrospinning PVDF nanofibers has been shown to produce highly polarized polymorphs, but dielectrics involving these alone often suffer from leakage current issues

Preparation of PMMA/PVDF-co-HFP multilayer composites:

Multilayer all-polymer laminates are assembled by alternating stacking of polymethyl methacrylate (PMMA) films and electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP) films. PVDF-co-HFP nanofibrous membranes were electrospun with an ionic liquid (1-allyl-3-methylimidazolium chloride (AMIM)) to eliminate leakage current and maximize discharge energy density

Effects of crystallography, microstructure, and interface on energy storage performance:

The effects of crystallography, microstructure, and interface of PMMA/PVDF-co-HFP multilayer composites on energy storage performance were discussed. These factors have a significant impact on the energy storage capacity of the material

Strategies to eliminate leakage current:

By adding an ionic liquid (AMIM) during the electrospinning process of PVDF-co-HFP nanofibrous membranes, leakage current can be effectively eliminated, thereby improving the energy storage performance of the material

Summarize

Here, we have demonstrated that electrospinning PVFHA with an ionic liquid (AMIM) additive produces nanofibers with a higher ferroelectric crystalline β-phase content. XRD and SEM test results show that the nanofibers can still maintain the β-phase content and produce a certain preferred orientation under hot pressing at 160°C. The hot pressed nanofibers were added to 3-layer and 7-layer PMMA:PVFHA laminates to produce multilayer polymer laminate film structures. When the pressure reached 160°C, the laminates retained their fibrous structure. However, when pressed at 160°C, a uniform layered structure dominated in the laminate and the fibrous structure was lost. This was confirmed by EDS, and the elemental map of the layered structure showed that the distinct layers were retained at 160°C, while they were lost at higher pressure temperatures. XRD and WAXS data showed that the β-phase crystalline structure of both 3-layer and 7-layer composites remained unchanged at a pressing temperature of 140°C. At pressing temperatures of 140°C and 160°C, the 3-ply laminates showed a preferential orientation of the nanofibers; however, this orientation was lost in the 7-ply laminates at both pressing temperatures. Thus, the 3-ply laminates showed a higher content of β-phase crystals at pressing temperatures up to 160°C compared to the 7-ply laminates and maintained the fibrous nanofiber structure.