Energy storage film and method of making

Abstract

The application relates to an energy storage film and a manufacturing method thereof, in particular to a high-temperature power storage energy storage film with a structure of fluorinated graphene (GF) sandwiched in aramid nanofiber (ANF) and a manufacturing method thereof.

Description

Technical Field

[0001] This invention relates to an energy storage membrane and its manufacturing method, specifically to a high-temperature energy storage membrane having a structure in which fluorinated graphene (GF) is sandwiched in aramid nanofibers (ANF) and its manufacturing method. Background Technology

[0002] With the rapid proliferation of portable electronic devices, lightweight and flexible energy storage devices with high energy, high power density, and fast charge / discharge cycles are essential in various technological fields such as wearable electronics, next-generation microelectronics, electric vehicles, and aerospace systems. Capacitors are one of the components used in advanced integrated electronics and power systems. Dielectric (electrostatic) capacitors can store electrical energy and, based on their high power density and low energy loss, can be rapidly charged / discharged by applying / removing an external electric field.

[0003] High dielectric constant (ε) r ) and breakdown strength (E b Both are necessary for achieving high energy density. Polymers, due to their excellent mechanical flexibility, high breakdown strength, ease of processing, extensibility, and low cost, have become a newly emerging dielectric material. However, most polymers have relatively low dielectric constants (ε). r (less than 10) and low polarizability, resulting in low energy storage density. To improve the ε of polymer materials... r It will have high ε r Ceramic or conductive nanomaterials are used as fillers in polymer matrices. However, the use of such fillers hinders an important property known as "low electrical loss".

[0004] Furthermore, current dielectric polymer nanocomposites are limited by relatively low operating temperatures (generally below 200°C), making them difficult to apply in practice. In particular, the heat generation issues under high electric fields and high temperatures necessitate the introduction of complex heat dissipation systems, which complicates the design and impacts the fuel efficiency of automobiles.

[0005] To improve the thermal stability of dielectric polymers, alumina (Al2O3), titanium dioxide (TiO2), and ceramic fillers such as boron nitride nanosheets (BNNS) have been introduced, but this has led to problems such as complex manufacturing processes, increased costs, and reduced flexibility. Summary of the Invention

[0006] The present invention is intended to solve the above problems and aims to provide an energy storage membrane and its manufacturing method, which has high-temperature energy storage characteristics (high energy density and charge / discharge efficiency), low cost, and excellent mass production capability.

[0007] According to one embodiment of the present invention, the energy storage membrane comprises: a first layer and a second layer comprising aramid nanofibers (ANF); and a first intermediate layer comprising graphene fluoride (GF) disposed between the first layer and the second layer.

[0008] According to an embodiment of the energy storage membrane of the present invention, the aramid nanofibers are cross-linked and bonded by a cross-linking agent.

[0009] According to an embodiment of the present invention, the energy storage membrane is characterized in that the fluorinated graphene is peeled from graphite fluoride and has a lateral size of 0.1 μm to 10 μm.

[0010] According to an embodiment of the present invention, the energy storage membrane is characterized by comprising 0.1 mg·mL⁻¹ -1 Up to 30 mg / mL -1 A GF suspension of fluorinated graphene at a certain concentration forms the first intermediate layer.

[0011] According to an embodiment of the energy storage membrane of the present invention, the aramid nanofibers have a diameter of 5nm-50nm.

[0012] According to an embodiment of the present invention, the energy storage membrane is characterized in that it further comprises: a third layer containing aramid nanofibers; and a second intermediate layer containing fluorinated graphene disposed between the second layer and the third layer.

[0013] A method for manufacturing an energy storage membrane according to an embodiment of the present invention includes: a step of preparing a suspension containing fluorinated graphene; a step of preparing an aramid nanofiber suspension; a step of coating the fluorinated graphene suspension onto an aramid nanofiber membrane prepared based on the aramid nanofiber suspension; and a step of forming the aramid nanofiber suspension on the fluorinated graphene and performing casting and drying.

[0014] A method for manufacturing an energy storage membrane according to an embodiment of the present invention is characterized in that the fluorinated graphene is peeled off from fluorinated graphite fluoride.

[0015] The exfoliation process for the fluorinated graphene is based on at least one of shear-induced fluidic reactor, tip sonication, and ball milling.

[0016] The aramid nanofiber suspension contains aramid nanofibers that are cross-linked based on a cross-linking agent.

[0017] The suspension containing fluorinated graphene contains 0.1 mg / mL -1 Up to 30 mg / mL -1 Concentration of fluorinated graphene.

[0018] The energy storage membranes according to different embodiments of the present invention have a sandwich structure, resulting in excellent high-temperature energy storage characteristics. Specifically, the energy storage membranes of the present invention effectively reduce leakage current density, thereby exhibiting large displacement, high energy density, and high charge / discharge efficiency, while maintaining excellent breakdown strength even at high temperatures.

[0019] The energy storage membrane of the present invention has excellent flexibility, thus making it suitable for flexible electronic devices.

[0020] The energy storage membrane of this invention can be applied to various fields such as wearable electronic devices requiring harsh operating temperatures, next-generation microelectronics, electric vehicles, and aerospace systems. Attached Figure Description

[0021] Figure 1 (a) is a schematic diagram of the energy storage membrane manufacturing method of the present invention; (b) is a scanning electron microscope (SEM) image of the upper surface of the PANF membrane as the bottom layer; (c) is a SEM image of the upper surface of the PANF membrane coated with a GF membrane as the intermediate layer; (d) is a mapping image of the fluorine (F) element of the PANF membrane coated with the GF membrane by energy dispersive X-ray analysis (EDX); (e) is a cross-sectional SEM image of an AGA5 membrane with a GF layer inserted between two ANF layers; (f) is an EDX mapping image of the F element of the cross-section of the AGA5 membrane; and (g) is a digital photograph of the AGA5 membrane wound into a roll.

[0022] Figure 2 (a) Low-magnification transmission electron microscopy (TEM) image of GF; (b) High-magnification TEM image of GF, with the inserted image in (b) being the selected area electron diffraction (SAED) of the portion indicated by the box; (c) Statistical analysis results of 100 stripped GF films; (d) TEM image of ANF; (e) X-ray diffraction (XRD) patterns of GF, ANF, and AGA5 films; (f) Thermogravimetric analysis (TGA) results of GF, ANF, PANF, and AGA5 films.

[0023] Figure 3 (a) and (b) are in 10 3 Up to 10 6 The dielectric constant (ε) of PANF, AGA3, and AGA5 films measured at frequencies in the Hz range. r (c) and dielectric loss (tanδ); (d) are at 10 3 Measurement results of dielectric constant and dielectric loss based on temperature at Hz.

[0024] Figure 4 (a) Weibull curves of PANF and AGA films under different electric fields; (b) Breakdown strength (Eb) (symbol: solid rectangle) and shape parameter (β) (symbol: solid circle) of PANF and AGA films extracted from the Weibull curves; (c) Breakdown strength (Eb) of AGA5 film and PANF at different temperatures. b (d) are the E values ​​of a randomized polymer composite material (Random CPC) composed of fillers randomly dispersed at different temperatures and a sandwiched polymer composite material (Sdanwiched CPC) composed of fillers with a sandwich structure. b and ε r .

[0025] Figure 5 (a) is E b The maximum achievable electrical displacement (D) of PANF and AGAx films m ) and residual electric displacement (D r (a) is the comparison result; (b) is E b The maximum discharge energy density (Ua) of PANF and AGAx films d (c) and energy storage efficiency (η); (d) is the U of the AGA5 film under different electric fields and temperatures. d And η; (d) compares AGA5 films with high glass transition temperatures (T) under different electric fields at 200℃. g The U between polymers (PEI and PI) and polymer nanocomposite capacitors (Al2O3 / c-BCB and BNNS / c-BCB) d And a chart of η.

[0026] Figure 6 (a) is at 200 MV·m -1(a) Leakage current density of AGA5 film under different electric fields and temperatures; (b) Leakage current density of AGA5 film at high temperatures based on electric field variations; (c) Temperature-based critical electric field (E) of PANF and AGA5. t (d) is the activation energy (E) of the AGA5 film, calculated using the electric field function based on an Arrhenius-type relation. a (e) is the graph of PANF activation energy (E). a (The image is missing.) Detailed Implementation

[0027] The following describes different embodiments of this specification with reference to the accompanying drawings. It should be understood that the embodiments and the terminology therein are not intended to limit the technical features described in this specification to a particular implementation, but rather to include various modifications, equivalents, and / or substitutions of the embodiments.

[0028] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0029] The energy storage membrane according to different embodiments of the present invention has a structure in which fluorinated graphene (GF) is sandwiched between aramid nanofibers (ANF). Specifically, the energy storage membrane of the present invention comprises: a first layer and a second layer containing aramid nanofibers; and a first intermediate layer containing fluorinated graphene disposed between the first layer and the second layer.

[0030] Aramid nanofibers can be crosslinked using a crosslinking agent. For example, aramid nanofibers can be crosslinked using different crosslinking agents such as phosphonitrilic chloride trimer (PNCT), borate, polyethyleneimine, or phenylenediamine. Preferably, aramid nanofibers can be crosslinked using PNCT. This improves the thermal stability of the aramid nanofibers, allowing the energy storage membrane to operate even at 500°C.

[0031] Aramid nanofibers can have a maximum length of 10 μm and a diameter of 5 nm to 50 nm. Aramid nanofibers can exist in an interwoven form.

[0032] The first intermediate layer contains fluorinated graphene, characterized in that it is exfoliated from graphite fluoride. The average size of the fluorinated graphene can be 1.3 ± 0.4 μm, and the lateral size can range from 0.1 μm to 10 μm. Most fluorinated graphene can have a lateral size of 0.5–2 μm.

[0033] At this point, the first intermediate layer can consist of 0.1 mg·mL⁻¹ -1 Up to 30 mg / mL -1 It is formed by a GF suspension of fluorinated graphene at a certain concentration. This effectively suppresses dielectric loss, resulting in low leakage current and low energy loss.

[0034] Furthermore, the energy storage membrane of the present invention further includes: a third layer comprising aramid nanofibers; and a second intermediate layer comprising fluorinated graphene, disposed between the second and third layers. That is, the energy storage membrane may have a sandwich structure of a first layer / first intermediate layer / second layer / second intermediate layer / third layer. The embodiments are not limited thereto, and the number of intermediate layers disposed between the aramid nanofiber membranes may be different, thereby constituting multiple layer structures.

[0035] The energy storage membrane according to various embodiments of the present invention has a sandwich structure, resulting in excellent high-temperature energy storage characteristics. Specifically, the energy storage membrane of the present invention effectively reduces leakage current density, thereby exhibiting high energy density and charge / discharge efficiency, and maintaining excellent breakdown strength even at high temperatures.

[0036] The energy storage membrane of the present invention has excellent flexibility and can be applied to flexible electronic devices.

[0037] The energy storage membrane of this invention can be applied to a variety of fields, including wearable electronic devices requiring harsh operating temperatures, next-generation microelectronics, electric vehicles, and aerospace systems.

[0038] The method for manufacturing the energy storage membrane of the present invention will now be described.

[0039] Reference Figure 1 (a) According to various embodiments of the present invention, a method for manufacturing an energy storage membrane may include: a step of preparing a suspension containing fluorinated graphene; a step of preparing an aramid nanofiber suspension; a step of coating the fluorinated graphene suspension onto an aramid nanofiber membrane made from the aramid nanofiber suspension; and a step of forming the aramid nanofiber suspension on the fluorinated graphene and performing casting and drying.

[0040] In the step of preparing a suspension containing graphene fluoride (hereinafter referred to as "GF"), GF exfoliated from graphite fluoride can be prepared. The exfoliation process for fluorinated graphite can be based on at least one of a shear-induced fluidic reactor, tip sonication, and ball milling. For example, GF dispersed in N-methyl-2-pyrrolidone (5 mg·mL⁻¹) can be used. -1 After the fluorinated graphite is injected into the reactor, it is stripped at 2000 rpm for one hour. Afterwards, monolayers and / or a few layers of GF can be separated from the unstripped fluorinated graphite by centrifugation.

[0041] Suspensions containing fluorinated graphene can contain 0.1 mg / mL. -1 Up to 30 mg / mL -1 Concentration of GF.

[0042] Secondly, in the step of preparing the aramid nanofiber suspension, it can be prepared by stirring and homogenizing the mixture of aramid nanofibers and solvent. At this time, a cross-linking agent can be added to the aramid nanofibers to achieve cross-linking. For example, 5% by weight of phosphonitrilic chloride trimer (PNCT) can be added to the aramid nanofibers to produce aramid nanofibers (PANF) cross-linked by PNCT.

[0043] Subsequently, in the coating step, the fluorinated graphene suspension can be coated onto the aramid nanofiber membrane made based on the aramid nanofiber suspension. For example, coating can be performed by various methods such as ultrasonic spraying, pneumatic spraying, and casting. Specifically, the aramid nanofiber suspension can be cast onto a glass plate, and the GF suspension can be ultrasonically sprayed using an ultrasonic spraying machine with a nozzle diameter of 0.7 mm, a frequency of 130 kHz, and a power of 4.5 W.

[0044] Subsequently, an aramid nanofiber suspension is formed on the coated GF, and then cast and dried. At this time, it can be dried in air for 10 to 14 hours to obtain a sandwich structure PANF / GF / PANF membrane (hereinafter referred to as "AGA").

[0045] The energy storage membrane manufacturing method of the present invention can easily produce energy storage membranes at low cost, with excellent mass production capability.

[0046] The present invention will now be described in detail through specific embodiments.

[0047] However, the following embodiments are only for illustrating the present invention, and the present invention is not limited to the following embodiments.

[0048] Example 1 - Preparation of GF

[0049] The exfoliation process for fluorinated graphite (size: approximately 200μm-500μm) is carried out using a shear-induced fluidic reactor (also known as a Taylor-Couette (TC) reactor). The reactor consists of concentric inner and outer cylinders with an annular size of 500μm and an aspect ratio of Γ = L / d ~ 20. N-methyl-2-pyrrolidone (5 mg·mL⁻¹) is dispersed within the material. -1 Fluorinated graphite was injected into the reactor and then stripped at 2000 rpm for one hour. This indicates the formation of 10 4 s -1 The shear rate and stable TC flow were controlled. Homogeneous dispersions of monolayer and / or few-layer fluorinated graphene (GF) sheets were separated from unseparated fluorinated graphene by centrifugal separation. Centrifugal separation was initially performed at 5000g for 60 minutes, followed by 420g for 150 minutes.

[0050] Deionized water was added to the remaining GF suspension (the liquid portion remaining after centrifugation of the un-exfoliated GF) to disrupt the suspension and generate a precipitate. The precipitate was collected and freeze-dried for 24 hours to obtain GF powder. The drying yield of the exfoliated GF was measured using an electronic balance HS224S (Hansung Instrument Co., Ltd., South Korea).

[0051] Example 2 - Preparation of aramid nanofiber (ANF) suspension

[0052] 1.5 g of potassium hydroxide (KOH, purity: 85%, Alfa Aesar (USA)) was dissolved in 500 mL of a solvent mixture of dimethyl sulfoxide (DMSO, purity: 99.7%, Alfa Aesar (USA)) and water (25:1, v / v). Then, 1 g of aramid nanofibers (TWARON OA-06, Teijin Aramid (Japan)) was added to the prepared solution. The mixture was magnetically stirred at 400 rpm at 30°C for 4 hours to dissolve ANF, thus forming a 2 mg / mL solution.-1 A dark red solution was obtained. To initiate the precipitation of the polymer chains, 100 mL of deionized water and distilled water were added to 100 mL of ANF solution in a beaker with continuous stirring. The mixture was then vigorously homogenized at 8000 rpm for five minutes to guide the contact between the macromolecules forming the colloidal suspension of ANF. The colloidal suspension was then vacuum filtered, and the filtrate (exfoliated ANF) was washed with deionized distilled water to remove DMSO solvent adsorbed on the fiber surface and residual KOH. For further use, 0.5 mg / mL was added under gentle stirring. -1 The concentration will redisperse the generated moistened ANF in distilled water.

[0053] Example 3 - Fabrication of a sandwich-structured membrane

[0054] A solution of 0.5 mg / mL of ANF containing 5% by weight of phosphonitrilic chloride trimer (PNCT) (Alfa Aesar (USA)) as a crosslinking agent to impart flame retardancy. -1 The ANF solution was cast onto a glass plate to a thickness of approximately 30 μm. At this point, the ANF solution was cast onto the release agent layer. Afterward, it was dried at 50°C for 12 hours to obtain an ANF film (hereinafter referred to as 'PANF') crosslinked by free-standing PNCT. The film was then dried at 150°C at a depth of 5 × 5 cm. 2 On the area, a supersonic sprayer (NS130K50, Sonaer Inc., USA) with a nozzle diameter of 0.7 mm, a frequency of 130 kHz, and a power of 4.5 W was used to spray a certain concentration (1 to 7 mg·mL) onto the prepared ANF film for 20 seconds. -1 The GF suspension was peeled off. As the GF coating dried, the ANF suspension layer was cast onto the dried GF-coated ANF film located on a glass plate. Finally, after air drying for 12 hours, a sandwich structure PANF / GF / PANF film (hereinafter referred to as "AGA") was obtained.

[0055] Experiment 1 - Confirmation of Morphology and Thermal Stability

[0056] Below, the AGA membrane will be denoted as AGAx, where x is the concentration of GF in the GF solution used when preparing the GF membrane (intermediate layer) interlayer. Figure 1 (b) is a SEM image of the upper surface of the lower PANF film. (Refer to...) Figure 1 As shown in (b), the upper surface of the lower PANF membrane is rough, and fiber fragments are exposed from the membrane surface outward.

[0057] Figure 1 (c) is a SEM image of the upper surface of the PANF film coated with the intermediate GF film. (Refer to...) Figure 1 As shown in (c), the upper surface of the intermediate GF film is very smooth.

[0058] Figure 1 (d) is for Figure 1 EDX mapping image of fluorine (F) in a PANF film coated with a GF film in (c). (See reference...) Figure 1 From (d), we can see that the F element is uniformly distributed, which suggests that the PANF surface is completely and uniformly covered by GF.

[0059] Figure 1 Image (e) is a cross-sectional SEM image of an AGA5 film with a GF layer inserted between two ANF layers. (Refer to...) Figure 1 (e) confirms the sandwich structure of the AGA5 membrane. Furthermore, the total thickness of the AGA5 membrane is 11 μm. Using a higher concentration of GF solution results in a thicker GF sandwich layer within the AGA membrane.

[0060] Figure 1 (f) is for Figure 1 EDX mapping image of the F element in the AGA5 film in (e). (See reference...) Figure 1 The (f) indicates a high distribution of F element in the membrane interlayer.

[0061] in addition, Figure 1 Image (g) is a digital photograph of an AGA5 film wound into a roll. (See reference) Figure 1 The (g) result confirms that the AGA5 membrane exhibits excellent flexibility.

[0062] Taylor-Couette (TC) flow has proven to be an effective technique for stripping 2D materials to produce high-concentration solutions at high production rates. In this invention, this technique was applied to stripping graphite fluoride, confirming a higher yield of approximately 46% compared to ball milling or supersonic processing techniques. The morphology and properties of the generated GF and ANF are described in [the following section]. Figure 2 As shown in the image. Figure 2 (a) is a low-magnification TEM image of GF; (b) is a high-magnification TEM image of GF. The image inserted in (b) is the SAED (Selected Area Electron Diffraction) of the portion indicated by the red box. (See reference...) Figure 2In (a), the low-magnification TEM image reveals that GF is a transparent 2D nanosheet shape with a lateral dimension greater than 1 μm. The arrows indicate the folded edges that demonstrate the flexibility of GF. (See reference...) Figure 2 (b) It can be confirmed by high-magnification TEM images that sp 2 A continuous and irregular pattern on the GF basal plane caused by the transfer of fluorine structure from (C=C) to sp3(CF). (See reference...) Figure 2 The inserted image (b) confirms that SAED is latticeless, thus indicating that GF is an amorphous phase.

[0063] Figure 2 (c) shows the statistical analysis results of 100 stripped GFs. (Refer to...) Figure 2 As shown in (c), the average size of GF is 1.3 ± 0.4 μm, and most of the transverse dimensions of GF are between 0.5 and 2 μm.

[0064] Figure 2 (d) is the TEM image of ANF. (Refer to...) Figure 2 From (d), it can be seen that ANF has a uniform appearance, a maximum length of 10 μm, a diameter of 10 nm to 20 nm, and exists in a tangled state.

[0065] Figure 2 (e) shows the X-ray diffraction (XRD) patterns of the GF, ANF, and AGA5 films. This confirms the crystal structure. (See reference...) Figure 2 (e) can be confirmed by XRD of ANF with two typical peaks centered at 2θ = 20.3° and 26.8°, corresponding to the (110) and (004) crystal planes of poly(p-phenylenetephthalamide) (PPTA). The XRD pattern of the sandwich AGA5 film shows all the peak characteristics of ANF and GF.

[0066] Figure 2 (f) shows the thermogravimetric analysis (TGA) results for the GF, ANF, PANF, and AGA5 films. This confirms their thermal stability. (Refer to...) Figure 2(f) GF exhibits excellent thermal stability, meaning that GF shows no mass loss (no thermal degradation) up to a maximum of 400°C, with a mass loss of less than 5% in the temperature range of 400-550°C. Violent thermal decomposition of GF begins at approximately 600°C, reaching a mass loss of approximately 83% at 800°C. Furthermore, the ANF film begins to degrade at approximately 100°C, with a mass loss reaching 8% by weight at 500°C. This mass loss is due to the decomposition of thermally unstable oxygen-containing groups (carboxyl and hydroxyl groups) on the ANF surface. To improve the thermal stability of ANF, 5% by weight of phosphonitrilic chloride trimer (PNCT) was added to the ANF film, creating ANF (PANF) crosslinked via PNCT. The PANF and AGA5 films exhibited excellent thermal stability, decomposing only 3% by weight of their mass at 500°C, thus confirming that the dielectric film can operate even at 500°C.

[0067] Experiment Example 2 - Confirming Dielectric Properties

[0068] Figure 3 (a) and (b) are in 10 3 Up to 10 6 The dielectric constant (ε) of PANF, AGA3, and AGA5 films measured at frequencies in the Hz range. r And dielectric loss (tanδ). ε of all AGAx films r Both ε and tanδ gradually decrease with increasing frequency. This is because when the applied electric field frequency exceeds the relaxation frequency, the contribution of the polar group mobility to the dielectric constant is weak. The ε of the PANF film... r In 10 3 The Hz is approximately 15.3. After that, at 10... 4 The ε-coefficient of dielectric constant (ε) decreases sharply to 7.1 Hz, but remains stable above 6 at higher frequencies. The AGAx film exhibits the same trend as the PANF film, indicating that the inherent chain structure and dielectric properties of the PANF film do not undergo significant changes in the AGA film. At the same frequency, compared to the PANF film, incorporating GF nanosheets into the AGA film reduces ε. r Value. For example, a GF concentration of 5 mg / mL is of interest. -1 ε of AGA5 membrane r In 10 3 The frequency is 12.8 Hz, which is about 16% lower than that of pristinePANF film at the same frequency. This is due to the relatively low dielectric constant of GF (i.e., ≈3).

[0069] Reference Figure 3 From (b) and (d), it can be seen that, especially at low frequencies, the dielectric loss of the AGA film is lower than that of the PANF film. For example, at 10 3 The dielectric loss of the PANF film is 0.11 Hz, while that of the AGA5 film is 0.046 Hz. In particular, the AGA film exhibits lower dielectric loss than both high-dielectric polymers and nanocomposites. This indicates that the sandwiched GF layer effectively suppresses dielectric loss caused by low conductivity and contributes to the low leakage current and energy loss of the AGA film.

[0070] To confirm the effect of temperature on the dielectric properties of PANF and AGA films, at 10 3 The dielectric constant and dielectric loss were measured at frequencies ranging from 30°C to 250°C. The results are referenced in [reference needed]. Figure 3 In (c) and (d), compared to room temperature, both the dielectric constant and dielectric loss showed a change of less than 5% at 250℃, indicating that both PANF and AGA films have very stable dielectric properties at high temperatures.

[0071] Experimental Example 3 - Confirmation of Breakdown Strength Characteristics

[0072] Breakdown strength (Eb) is important for high energy density dielectric materials. This is because as the electric field strength increases, the discharge energy density of the material also increases; a high breakdown strength allows for the application of Eb. <E b The breakdown strength of the AGA film is analyzed using the following Webull distribution function.

[0073] Equation (1)

[0074]

[0075] Where P(E) is the cumulative breakdown probability, E is the experimental result of the breakdown strength, and E0 is the cumulative breakdown probability. b At a cumulative breakdown probability of 63.2%, the breakdown strength characteristics of the material, β (shape parameter), represent the standard of reliability against failure. A high β value indicates high reliability and low scattering. The Weibull distribution as a function of the electric field and the Ep of PANF and AGA films... b The values ​​of β and the fitted values ​​are in Figure 4 As shown in (a) and (b), the E of all AGA membranes is known. b The Eb of the PANF membrane was significantly increased with increasing GF content. The Eb of the PANF membrane was approximately 321 MV·m. -1 The AGA3 membrane gradually increased to 488 MV·m -1The AGA membrane was slightly increased to 502 MV·m. -1 Compared to PANF membranes, this represents an increase of over 150%. The E of the AGA7 membrane... b The value is approximately 507 MV·m -1 The E b The value is approximately higher than that of the AGA5 membrane. b Value. The optimal concentration of the GF solution used for preparing the insulating film was confirmed to be 5 mg / mL. -1 To ensure high breakdown strength and flexibility of the insulating film. The low breakdown strength of PANF film is due to its uncompressed structure; the arrangement of 1DANF may contain air gaps, due to the low breakdown strength (3MV·m) of air. -1 This reduces the breakdown strength of the PANF film.

[0076] In addition, the significantly improved breakdown strength of the AGA film is due to the GF having a strength of 1000 MV·m. -1 The AGA5 film exhibits excellent breakdown strength, and the GF layer sandwiched within it acts as an insulating wall, effectively resisting current transfer through the ANF matrix. Furthermore, variations in shape parameters show a trend very similar to those observed in breakdown strength. Specifically, the AGA5 film achieved a maximum β value of 13.7, nearly 30% higher than that of the PANF film, demonstrating the superior dielectric reliability of the AGA5 film.

[0077] Reference Figure 4 (c) The AGA5 film exhibits excellent temperature-dependent stability. As the temperature increases from 30°C to 300°C, the Et of the AGA5 film... b From 502MV·m -1 Change to 426MV·m -1 The E of the PANF film decreased by approximately 17%. As the temperature increased from 30°C to 300°C, the E of the PANF film... b It decreased by approximately 37%, which translates to 196 MV·m -1 AGA membrane's high E b The stability is attributed to the excellent thermal stability of PANF and GF.

[0078] Figure 4 (d) refers to a storage polymer composite material composed of randomly dispersed fillers at different temperatures (Random CPC) and a storage polymer composite material composed of sandwiched fillers (Sdanwiched CPC), as well as the E of AGA5. b and ε r . Specifically, Figure 4 The materials in (d) [1] to [7] are shown in Table 1 below.

[0079] Table 1

[0080]

[0081]

[0082] Reference Figure 4 (d) confirmed that at 200℃, the ε of AGA5 r The value is 12.7, and the Eb value is 478 MV·m⁻¹. This AGA5, compared to the ε in Random CPC, r The BNNS / c-BCB composite material with a strength of 3.1 and an Eb of ~410MV·m-1[5] is superior, and this AGA5 is also superior to the ε in the sandwiched CPC. r The Al2O3 / PI composite material with a strength of 3.1 and an Eb of ~410MV·m-1[3] is superior.

[0083] Experiment 4 - Confirming Dielectric Displacement and Energy Storage Characteristics

[0084] The dielectric displacement-electric field (DE) loops of PANF and AGA films were measured using a ferroelectrics workstation under different electric fields and temperatures. The discharge energy density (Ud), stored energy density (Us), and energy storage efficiency (η) were calculated using the following equations (2) to (4) from the DE hysteresis loop obtained during the charge-discharge cycle of the AGA film.

[0085] The discharge energy density (Ud) is calculated using the following equation (2).

[0086] Equation (2)

[0087]

[0088] Among them, D m In a given charging cycle (0-E) m Within the range of ), the maximum achievable electrical displacement of the AGA film. m It is the maximum applicable electric field strength. E m Can be used with 0.8E b (Retaining 20% ​​of dielectric strength) is equally applicable, D r It is the charge density remaining in the membrane after the discharge cycle is completed.

[0089] Stored energy density (U s The calculation is performed using equation (3).

[0090] Equation (3)

[0091]

[0092] The charge / discharge efficiency (η) is calculated using equation (4).

[0093] Equation (4)

[0094]

[0095] (D m -D r The effective electric displacement (D) reflects the material's high electric field polarization capability. The maximum achievable electric displacement (D) is... m The higher the residual electric displacement (D), the greater the residual electric displacement (D). r The lower the value, the higher the effective electric displacement (D) can be achieved. m -D r (D) m -D r The high value of ) is used to obtain the maximum discharge energy density (U d The required energy storage efficiency (η) is as follows.

[0096] AGA film at the maximum applicable electric field strength E b This displacement is extracted from the dielectric displacement-electric field (DE) loop and... Figure 5 As shown in (a). D of the PANF membrane m Only 0.051 C·m -2 AGA3 has a concentration of 0.073 C·m. -2 This resulted in a significant increase, ultimately leading to a 49% increase in C·m compared to the PANF membrane. -2 D m Higher E can be achieved based on AGA films with thicker GF layers. b This is improved. Furthermore, the ANF-GF and GF-ANF present in the AGA sandwich structure, acting as mesoscopic interfaces, can generate strong interfacial polarization. More importantly, a thicker GF layer in the sandwich film provides greater (D... m -D r ) value. For example, AGA5's (D m -D r The value is 0.068 C·m -2 This is compared to the AGA1 membrane (0.051 C·m). -2 It is 70% higher, thus enabling high energy density performance and easy depolarization when the applied electric field is removed.

[0097] Figure 5 (b) shows the maximum U values ​​of different AGA films at room temperature. dThe calculation results for η and the maximum U of the AGA membrane. d The concentration increases significantly with the thickness of the GF layer in the middle, reaching a maximum of 16.7 J·com for AGA5. -3 This represents an increase of approximately 156% compared to PANF films, and is 10 times higher than that of commercially available dielectric biaxial polypropylene (BOPP) polymers. The maximum UAGA value increases with increasing thickness of the sandwich-type GF layer. d The main reason for this increase is high D m And the enhanced E b U d It is approximately proportional to the square of the electric field. As U... d The maximum η was effectively increased with increasing thickness of the GF layer sandwiched within the AGA film. In particular, the AGA5 film exhibited a higher η value (86%) than the PANF film (73.4%). This improved η can likely be attributed to the low D-strain design for minimum energy loss. r The cause, namely, D r From 0.011 C·m of PANF film -2 - Reduced to 0.008 C·m of the AGA5 membrane. -2 D r Related to the mutual contribution between ferroelectric loss and conduction loss, a thick GF layer can minimize conduction loss in high electric fields, thereby suppressing D. r This also increases η. More importantly, undischarged energy is converted into ohmic heat, ultimately leading to deterioration of discharge behavior and increased conduction and ferroelectric losses at high temperatures. The presence of the GF layer can effectively dissipate the heat generated by the inherently high thermal conductivity of ANF and GF, thereby improving efficiency.

[0098] Besides the energy storage characteristics of dielectric capacitors, the stability of energy storage density and efficiency under high applied electric fields and high temperatures is a very important factor in practical applications. Figure 5 (c) shows the U at different temperatures (30℃~250℃) calculated based on the DE heterolytic hysteresis loop. d And the electric field dependence of η. In general, when an electric field is applied, the U of the AGA5 film... d Both and η show a decreasing trend with increasing temperature. At 400 MV·m -1 Under an electric field, for a temperature change from 30°C to 250°C, U d From 13.6 J·cm- 3 Reduced to 10.2 J·cm -3 η decreased from 92% to 76%.

[0099] Figure 5(d) represents the U values ​​of AGA5 films and polymers (PEI and PI) with high Tg and polymer nanocomposite capacitors (Al2O3 / c-BCB and BNNS / c-BCB) under different electric fields at 200℃. d And a chart comparing η. (See reference) Figure 5 From (d), it can be seen that the high-temperature energy storage characteristics of the AGA5 film are significantly superior to those of dielectric polymers and polymer nanocomposite capacitors with high Tg. For example, at E = 200 MV·m -1 At this point, the storage density of AGA5 is 3.1 J·cm³. -3 The efficiency (η) is 94.8, which is 8 times and 2.5 times higher than that of PEI, respectively. Furthermore, the efficiency of BOPP capacitors commonly used in electric vehicles is around 400 MV·m⁻¹. 1 The electric field and temperature of 140°C are reduced to approximately 70%. Therefore, the AGA5 film of this invention can replace commonly used BOPP energy storage films, eliminating the need for complex heat dissipation plate systems used in power inverters. Furthermore, randomly dispersed BNNS and the Al2O3 nanosheet-based BCB composite are two commercially viable polymer nanocomposites for high-temperature (200°C) energy storage. However, referring to… Figure 5 As can be seen from (d), the high-temperature energy storage characteristics of the AGA5 film of the present invention are significantly superior to those of this nanocomposite. In particular, the AGA5 film can withstand high temperatures of 200°C and 400 MV·m⁻¹. -1 11.6 J·cm -3 U d This is compared to BNNS / c-BCB (2.1 J·cm⁻¹). -3 ) and Al2O3 / c-BCB (2.4 J·cm -3 The concentration was approximately five times higher. Furthermore, the AGA5 membrane performed better at 200℃ and 400 MV·m. -1 It still exhibits an η of 88% under an electric field, which is higher than that of Al2O3 / c-BCB (80%) and BNNS / c-BCB nanocomposite (78%).

[0100] Experimental Example 5 - Confirmation of Leakage Current Density and Activation Energy Characteristics

[0101] The loss mechanism of dielectric energy storage materials operating under high electric fields and high temperatures has been shown to be mainly controlled by conductivity. Figure 6 (a) is in an electric field of 200 MV·m -1 The leakage current density of the AGA5 film at different temperatures, based on the measurement time; Figure 6(b) shows the leakage current density of the AGA5 film at different temperatures based on the electric field strength. Furthermore, although not shown in the figure, under high electric fields, the leakage current density of the PANF film increases sharply with increasing temperature. That is, as the temperature rises from 30°C to 250°C, at a current density of 200 MV·m⁻¹... 1 Below, the leakage current density of the PANF film decreased from 9.43 × 10⁻⁶. -11 It rose to 9.07×10 -6 A / cm 2 Furthermore, the introduction of the GF layer effectively hinders conductivity, thereby significantly reducing the current (I) of the AGA6 film under high electric fields and high temperatures. That is, referring to... Figure 6 (a) shows that as the temperature rises from 30°C to 250°C, at 200 MV·m -1 Below, the leakage current density of the AGA5 film is 1.38 × 10⁻⁶. -12 Increased to 3.24 × 10 -7 A / cm 2 .

[0102] Reference Figure 6 From (b), it can be seen that at 100℃, as the electric field decreases from 50 MV·m -1 Increased to 200 MV·m -1 The current of the AGA5 film is 2.34 × 10⁻⁶. -12 A / cm 2 Increased to 3.03×10 -11 A / cm 2 At 250℃, it is 3.30×10 -7 A / cm 2 This increases by approximately 1000 times. The excellent resistance of the AGA5 film effectively reduces dielectric loss under high electric fields and high temperatures, resulting in the observed increase in η in the AGA film, thus indicating that the AGA5 film has excellent capacitance performance.

[0103] As is well known, the critical electric field (E) represents the electric field deviation applicable to the slope I. t ) and activation energy of the conduction mechanism (E) a They have a mutual relationship.

[0104] Figure 6 (c) represents the critical electric field (E) of PANF and AGA5 films based on temperature. t A graph showing the jump distance (α) and the hopping distance. (See also...) Figure 6 (c) In the temperature range of 100℃~250℃, the E of the AGA5 film... t It exhibits higher E than PANF film tFurthermore, both show a gradual decrease with increasing temperature. For example, the Ea of the AGA5 film... t It reaches as high as 163.2 MV·m at 100℃. -1 This is approximately 77% higher than that of PANF film. Furthermore, it decreases to 96.3 MV·m at 250°C. -1 At the same applicable temperature, the efficiency was 36% higher than that of the PANF film. This indicates that at high temperatures, the PANF film has a lower activation energy (E0) compared to the AGA5 film. a ).

[0105] Reference Figure 6 (c) Within the temperature range of 100℃ to 250℃, the jump distance (α) of the AGA5 film is consistently smaller than that of the PANF film. Specifically, as the temperature increases from 100℃ to 250℃, the jump distance (α) of the PANF film increases from 1.0825nm to 1.3951nm, while that of the AGA5 film increases from 0.7953nm to 1.2502nm.

[0106] Figure 6 (d) and (e) are the activation energies (E) of the AGA5 and PANF films, respectively, calculated based on the Arrhenius relation using the electric field function. a E a This can be determined by the Arrhenius relation. (See reference...) Figure 6 (d) and (e) show that the AGA5 membrane exhibits higher E compared to the PANF membrane. a Specifically, at 200 MV·m -1 E of AGA5 film under electric field a It is approximately 1.042 eV, while the E of PANF is... a It is 0.836 eV. A shorter jump distance (α) and a larger activation energy (E) a This allows for a deeper average trap depth for charge carriers, resulting in reduced I and dielectric loss, thus significantly improving the U of AGA5. d and η.

[0107] The features, structures, effects, etc., described in the above embodiments are included in at least one embodiment of the present invention, and are not limited to only one embodiment. Furthermore, those skilled in the art can combine or modify the features, structures, effects, etc., illustrated in the embodiments with other embodiments and implement them accordingly. Therefore, content related to such combinations and modifications should be interpreted as falling within the protection scope of the present invention.

[0108] Furthermore, although the specification focuses on embodiments, these are merely illustrative and do not limit the invention. Those skilled in the art will understand that various modifications and applications, not shown, can be made without departing from the essential characteristics of these embodiments. For example, the structural elements specifically shown in the embodiments can be modified and implemented. Moreover, differences related to such modifications and applications should be understood as falling within the scope of the invention as defined in the claims.

Claims

1. An energy storage film, comprising: a first layer and a second layer, the first layer and the second layer comprising aramid nanofibers; a first intermediate layer comprising fluorinated graphene and disposed between the first layer and the second layer, wherein the energy storage film is a freestanding structure, and wherein the aramid nanofibers are cross-linked by a cross-linking agent.

2. The energy storage film of claim 1, wherein: the fluorinated graphene is exfoliated from graphite fluoride, and the lateral dimension of the fluorinated graphene is 0.1 pm to 10 pm.

3. The energy storage film of claim 1, wherein: GF suspensions formed from graphene fluoride comprising a concentration of 0.1 mg mL -1 to 30 mg mL -1 concentrations form the first intermediate layer.

4. The energy storage film of claim 1, wherein: the aramid nanofibers have a diameter of 5 nm to 50 nm.

5. The energy storage film of claim 1, wherein, further comprising: a third layer comprising aramid nanofibers; and a second intermediate layer comprising fluorinated graphene and disposed between the second layer and the third layer.

6. A method of making an energy storage film, comprising: preparing a suspension comprising fluorinated graphene; preparing a suspension of aramid nanofibers; coating the suspension of fluorinated graphene as a second layer on an aramid nanofiber film made based on the suspension of aramid nanofibers, wherein the aramid nanofiber film is a first layer; and casting a suspension of aramid nanofibers as a third layer on the fluorinated graphene and drying the energy storage film, the energy storage film being a freestanding energy storage film, wherein the suspension of aramid nanofibers comprises aramid nanofibers cross-linked by a cross-linking agent.

7. The method of making an energy storage film of claim 6, wherein: the fluorinated graphene is exfoliated from graphite fluoride.

8. The method of making an energy storage film of claim 7, wherein: the exfoliation process of the fluorinated graphene is performed by at least any one of shear-induced fluid reactor, tip sonication, and ball milling.

9. The method of making an energy storage film of claim 6, wherein: ​ ​ The suspension comprising fluorinated graphene comprises 0.1 mg mL -1 to 30 mg mL -1 of fluorinated graphene at a concentration of 0.1 mg mL

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