Polypropylene-based high-energy-storage-density nano composite material as well as preparation method and application thereof

Abstract

The invention discloses a polypropylene-based high-energy-storage-density nanocomposite and a preparation method and application thereof, and relates to the technical field of power capacitors. The preparation method of the polypropylene-based high-energy-storage-density nanocomposite material comprises the following steps: adding boron nitride nanosheets into a hydrogen peroxide solution, and fully stirring to obtain a first turbid liquid; adding barium titanate nanoparticles and the first turbid liquid into a high-pressure reaction kettle to react, so that the barium titanate nanoparticles are attached and combined on the boron nitride nanosheets to obtain a barium titanate / boron nitride nanomaterial; the barium titanate / boron nitride nanometer material and polypropylene are subjected to melt blending, the polypropylene-based high-energy-storage-density nanometer composite material is obtained, and the mass ratio of the barium titanate / boron nitride nanometer material is 2 wt%-4 wt%. Compared with a pure polypropylene material, the polypropylene-based high-energy-storage-density nano composite material prepared by the invention has higher breakdown field strength, and the energy storage density is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power capacitors, and in particular to a polypropylene-based high energy storage density nanocomposite material and a preparation method and application thereof. Background Art

[0002] As one of the core energy storage devices in the power system, power capacitors have significant advantages such as high power density and high withstand voltage. They are widely used in many fields such as pulse power systems, new energy power generation, high-voltage direct current transmission systems and electric vehicles. However, compared with other energy storage components such as batteries and supercapacitors, the energy storage density of power capacitors is relatively low, resulting in their large size, which greatly limits their application in more fields. Therefore, the development of dielectric materials with high energy storage density for the manufacture of the next generation of smaller and larger capacity power capacitors has become an urgent problem that needs to be solved.

[0003] Polypropylene is currently the most widely used dielectric material for power capacitors. It has the advantages of low dielectric loss, high withstand voltage, and good insulation performance. It is also easy to biaxially stretch and can be prepared into films on a large scale. However, although the electrical strength of biaxially oriented polypropylene film (BOPP) is as high as 700MV / m, its low dielectric constant (about 2.2) leads to a low energy storage density (about 1-2J / cm 3 ). Summary of the Invention

[0004] The invention provides a polypropylene-based high energy storage density nanocomposite material. The composite material has high breakdown field strength and high energy storage density and is suitable for power capacitors.

[0005] The polypropylene-based high energy storage density nanocomposite material provided by the present invention is prepared by melt blending polypropylene and barium titanate / boron nitride nanomaterials, wherein the mass proportion of the barium titanate / boron nitride nanomaterials is 2wt% to 4wt%; the barium titanate / boron nitride nanomaterials is formed by the attachment and bonding of barium titanate nanoparticles on boron nitride nanosheets.

[0006] Optionally, the mass proportion of the barium titanate / boron nitride nanomaterial is 3 wt%.

[0007] The preparation method of the polypropylene-based high energy storage density nanocomposite material provided by the present invention comprises the following steps:

[0008] Adding boron nitride nanosheets to a hydrogen peroxide solution and stirring thoroughly to obtain a first suspension;

[0009] adding the barium titanate nanoparticles and the first suspension into a high-pressure reactor for reaction, so that the barium titanate nanoparticles adhere to and bind to the boron nitride nanosheets, thereby obtaining a barium titanate / boron nitride nanomaterial;

[0010] The barium titanate / boron nitride nanomaterial is melt-blended with polypropylene to obtain the polypropylene-based high energy storage density nanocomposite material, wherein the mass proportion of the barium titanate / boron nitride nanomaterial is 2 wt % to 4 wt %.

[0011] Optionally, the barium titanate nanoparticles are prepared by the following steps:

[0012] Mixing barium hydroxide octahydrate, tetrabutyl titanate, surfactant PVP, and triethylene glycol in a preset ratio to obtain a first mixed solution;

[0013] adding sodium hydroxide to the first mixed solution, and diluting with deionized water when the pH is greater than 13 to obtain a second mixed solution;

[0014] The second mixed solution was heated and stirred at a constant temperature under reflux conditions in a condenser to obtain a light yellow sol;

[0015] The light yellow sol is sequentially centrifuged, washed and freeze-dried to obtain the barium titanate nanoparticles.

[0016] Optionally, the second mixed solution is heated and stirred at a constant temperature of 160° C. for 15 minutes.

[0017] Optionally, the boron nitride nanosheets are prepared by the following steps:

[0018] Dissolving hexagonal boron nitride in N,N-dimethylformamide solution and ultrasonically treating the solution to obtain a second suspension;

[0019] The second suspension is sequentially centrifuged, washed and freeze-dried to obtain the boron nitride nanosheets.

[0020] Optionally, in step S2, the reaction temperature is 180° C. and the reaction time is 6 hours.

[0021] Optionally, the rotation speed of melt blending the barium titanate / boron nitride nanomaterial and polypropylene is 30 r / min, and the time is 10-20 min.

[0022] The present invention also provides a dielectric film for use in power capacitors, which is prepared using the above-mentioned polypropylene-based high energy storage density nanocomposite material by the following steps:

[0023] placing a second polyimide film cut with holes on the first polyimide film, and filling the holes of the second polyimide film with the polypropylene-based high energy storage density nanocomposite material;

[0024] The third polyimide film is placed on the second polyimide film, and the three layers of polyimide film are subjected to heat pressing treatment to complete the packaging.

[0025] The present invention has the following beneficial effects:

[0026] The technical solution of the present invention uses hydrogen peroxide treatment to introduce strongly polar hydroxyl groups on the surface of boron nitride nanosheets. Barium titanate nanoparticles can be stably attached and bonded to the surface of the boron nitride nanosheets through conventional high-pressure reactor reaction treatment to form a barium titanate / boron nitride nanomaterial. By adding an appropriate amount of barium titanate / boron nitride nanomaterial to polypropylene for modification, the resulting polypropylene-based nanocomposite material has a higher breakdown field strength and significantly improved energy storage density than pure polypropylene materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 This is a process flow chart for preparing a polypropylene-based high energy storage density nanocomposite material according to an embodiment of the present invention;

[0029] Figure 2 TEM images of polypropylene-based high energy storage density nanocomposites prepared in some embodiments of the present invention;

[0030] Figure 3 Weibull distribution diagram of the dielectric films prepared according to some embodiments of the present invention in the DC breakdown characteristic test. DETAILED DESCRIPTION

[0031] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] The terms "first," "second," "third," "fourth," and the like (if any) in the specification and drawings of the present application are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or apparatus.

[0033] Maximum energy storage density of dielectric materials The external electric field E and the maximum electric displacement intensity The calculation method is as follows:

[0034]

[0035] For linear dielectrics, their energy storage density can be intuitively expressed as the following formula.

[0036]

[0037] Where, is the dielectric constant of vacuum, is the relative dielectric constant, E b is the breakdown field strength of the dielectric material.

[0038] In response to the disadvantage of low energy storage density of polypropylene materials in the prior art, an embodiment of the present invention provides a polypropylene-based high energy storage density nanocomposite material. The composite material is prepared by melt blending polypropylene and barium titanate / boron nitride nanomaterials, where the mass proportion of barium titanate / boron nitride nanomaterials is 2wt%~4wt%; the barium titanate / boron nitride nanomaterial is formed by barium titanate nanoparticles attached and bonded to boron nitride nanosheets.

[0039] Specifically, see Figure 1 The preparation method of the polypropylene-based high energy storage density nanocomposite material comprises the following steps:

[0040] S100: preparing barium titanate nanoparticles (barium titanate nanoparticles may be referred to as BT for short);

[0041] S200: preparing boron nitride nanosheets (boron nitride nanosheets can be abbreviated as BNNS);

[0042] S300: Preparation of barium titanate / boron nitride nanomaterials (barium titanate / boron nitride nanomaterials can be abbreviated as BT@BNNS);

[0043] S400: Preparation of polypropylene-based high energy storage density nanocomposites (abbreviated as BT@BNNS / PP).

[0044] The step S100 of preparing barium titanate nanoparticles specifically includes:

[0045] S101: The raw materials required for the reaction, barium hydroxide octahydrate (Ba(OH)2·8H2O), tetrabutyl titanate (Ti(OC4H9)4), surfactant PVP (C6H9NO) and solvent TEG (triethylene glycol, C6H 14 O4) adding the raw materials into the single-necked bottle of the reaction container in a preset ratio to obtain a first mixed solution; the ratio of the reaction raw materials can be set according to the target yield and actual process conditions.

[0046] S102: Sodium hydroxide solid (NaOH) is added to the single-necked bottle, and after the pH value of the first mixed solution is measured to satisfy pH>13, deionized water is added to dilute the solution to obtain a second mixed solution.

[0047] S103: Under reflux conditions of a condenser, the single-necked bottle is placed in silicone oil preheated to 160° C., stirred and heated, and kept warm for 15 minutes to obtain a light yellow sol in which titanate particles are stably dispersed in the solvent.

[0048] S104: The obtained light yellow sol is taken out and placed in a high-speed centrifuge for centrifugation for 10 minutes.

[0049] S105: The solid obtained after centrifugation is washed with deionized water and anhydrous ethanol in sequence, with each washing time being 10 minutes. The washed solid is freeze-dried for 12 hours to obtain barium titanate nanoparticles.

[0050] The step S200 of preparing the boron nitride nanosheets specifically includes the following steps:

[0051] S201: Dissolve hexagonal boron nitride in N,N-dimethylformamide (DMF) solution at 30°C.

[0052] S202: placing the mixed solution obtained in step S201 into a reaction container beaker, and placing the beaker in an ultrasonic cell disruptor, and ultrasonically treating for 6 hours to obtain a boron nitride nanosheet suspension.

[0053] S203: The suspension obtained in step S202 is placed in a high-speed centrifuge and centrifuged for 10 minutes.

[0054] S204: The solid obtained after the centrifugation is washed with deionized water and anhydrous ethanol in sequence, with each washing time being 10 minutes. The washed solid is freeze-dried for 12 hours to obtain a single-layer or few-layer boron nitride nanosheet.

[0055] Step S300 of preparing BT@BNNS specifically includes:

[0056] S301: Add the boron nitride nanosheets prepared in step S200 to the hydrogen peroxide solution and stir thoroughly to obtain a first suspension. The purpose of this step is to hydroxylate the surface of the boron nitride nanosheets to generate BNNS-OH. The hydroxyl group, as a highly polar group, can make it easier for the barium titanate nanoparticles to combine with the boron nitride nanosheets.

[0057] S302, the barium titanate nanoparticles prepared in step S100 and the first suspension are added to a high-pressure reactor and reacted at 180°C for 6 hours; since the boron nitride nanosheets have been hydroxylated with hydrogen peroxide, they are more easily combined with the barium titanate nanoparticles. The high-temperature and high-pressure conditions provided by the high-pressure reactor allow the barium titanate nanoparticles to be stably attached to the surface of the boron nitride nanosheets to form BT@BNNS nanomaterials. The specific microstructure of the BT@BNNS nanomaterial is shown in FIG. Figure 2 shown.

[0058] S303, taking out the reaction solution obtained in step S302 and placing it in a high-speed centrifuge for centrifugation for 10 minutes.

[0059] S304, the solid obtained after centrifugation is washed with deionized water and anhydrous ethanol in sequence, each washing time is 10 minutes, and the washed solid is freeze-dried for 12 hours to obtain BT@BNNS nanomaterials.

[0060] Step S400 specifically includes:

[0061] S401: The BT@BNNS prepared in step S300 and the granular polypropylene are placed in a torque rheometer according to a preset mass ratio. The doping amount of BT@BNNS should not be too much, otherwise the insulation performance of the material will be deteriorated. In the embodiment of the present invention, the mass proportion of BT@BNNS is preferably 2wt% to 4wt%; in some specific embodiments, a BT@BNNS mass proportion of 3wt% can be selected.

[0062] S402: At 30 r / min, melt blending is performed for 10-20 min to obtain a composite matrix of polypropylene doped with BT@BNNS nanomaterials, which is the target product BT@BNNS / PP of the embodiment of the present invention. The temperature of melt blending can be adjusted according to the specific situation so that the polypropylene is fully melted and has good fluidity. For example, the melting point of polypropylene is generally between 164°C and 170°C, and the temperature of melt blending can be selected within the temperature range of 180°C to 240°C.

[0063] The BT@BNNS / PP material prepared in the embodiment of the present invention is suitable for power capacitors. Therefore, the embodiment of the present invention also uses the BT@BNNS / PP material to prepare a polypropylene-based composite material film for use as a dielectric film. The preparation of the dielectric film specifically includes the following steps:

[0064] S501: placing a second polyimide film cut with holes on the first polyimide film, and filling the holes of the second polyimide film with BT@BNNS / PP material. The shape and size of the holes can be selected according to actual needs.

[0065] S502: placing a third polyimide film on the second polyimide film, and performing a heat pressing process on the three layers of polyimide films to complete the packaging.

[0066] Based on the above embodiments, the present invention further proposes the following specific embodiments. It should be noted that the following specific embodiments are only illustrative and do not limit the scope of protection of this application in any form.

[0067] Example

[0068] In this embodiment, a polypropylene-based high energy storage density nanocomposite material and a dielectric film were prepared.

[0069] The polypropylene-based high energy storage density nanocomposite material comprises 3 wt% of BT@BNNS material and 97 wt% of polyethylene and is prepared by the following steps:

[0070] Preparation of barium titanate nanoparticles:

[0071] 1.56 g of barium hydroxide octahydrate (Ba(OH)2·8H2O), 1.7 mL of tetrabutyl titanate (Ti(OC4H9)4), 0.5 g of surfactant PVP (C6H9NO) and 4.3 mL of solvent TEG (C6H 14 O4) is added to the single-necked bottle of the reaction vessel;

[0072] Add 10g of sodium hydroxide solid to the reaction vessel, and add 100ml of deionized water after measuring the pH value of the mixed solution to meet pH>13;

[0073] Under reflux conditions of the condenser, the single-necked bottle was placed in silicone oil preheated to 160°C, stirred and heated, and kept warm for 15 minutes to obtain a light yellow sol;

[0074] The obtained light yellow sol was taken out and then centrifuged in a high-speed centrifuge for 10 min;

[0075] The solid obtained after centrifugation is washed with deionized water and anhydrous ethanol in sequence, with each washing time being 10 minutes. The washed solid is freeze-dried for 12 hours to obtain barium titanate nanoparticles.

[0076] Preparation of boron nitride nanosheets:

[0077] 5 g of hexagonal boron nitride was dissolved in 300 mL of N,N-dimethylformamide (DMF) solution at 30°C; the resulting solution was placed in a reaction vessel beaker, and the beaker was placed in an ultrasonic cell disruptor and ultrasonicated for 6 hours to obtain a boron nitride nanosheet suspension;

[0078] The boron nitride nanosheet suspension was taken out and then centrifuged in a high-speed centrifuge for 10 minutes;

[0079] The solid obtained after centrifugation was washed with deionized water and anhydrous ethanol in sequence, with each washing time of 10 min;

[0080] The washed solid is placed in a vacuum freeze drying chamber and freeze-dried for 12 hours to obtain single-layer or few-layer boron nitride nanosheets (BNNS).

[0081] Preparation of BT@BNNS materials:

[0082] 1 g of boron nitride nanosheets was added to 100 ml of hydrogen peroxide solution and stirred thoroughly to obtain a first suspension.

[0083] The prepared barium titanate nanoparticles and the first suspension were added into a high-pressure reactor and reacted at 180° C. for 6 h.

[0084] The reaction solution was taken out and placed in a high-speed centrifuge for centrifugation for 10 minutes.

[0085] The solid obtained after centrifugation was washed with deionized water and anhydrous ethanol in sequence, with each washing time being 10 min. The washed solid was freeze-dried for 12 h to obtain BT@BNNS nanomaterials.

[0086] Preparation of BT@BNNS / PP material:

[0087] The BT@BNNS and polypropylene pellets prepared above were placed in a torque rheometer at a mass ratio of 3%:97%;

[0088] The BNNS-OH / PP material was prepared by melt blending BT@BNNS and polypropylene pellets at 30 r / min for 10-20 min.

[0089] Preparation of dielectric films:

[0090] Use a paper cutter to cut a 10 cm × 10 cm square hole on a 100 μm thick polyimide film.

[0091] A polyimide film B with a thickness of 100 μm is placed on the bottom of the polyimide film A. After 0.3 g of the composite material is placed in the square hole of the polyimide film A, a polyimide film C with a thickness of 100 μm is placed on top of the polyimide film A for packaging.

[0092] The encapsulated polyimide films A, B, and C were placed on two square iron plates and subjected to hot pressing treatment using a flat-plate rheometer to obtain a dielectric film containing BT@BNNS / PP material. The hot pressing temperature of the flat-plate rheometer was set to 190°C, the pressure was set to 15 MPa, the processing time was set to 10 minutes, the number of exhaust times was set to 15 times, and the exhaust time for each time was set to 10 seconds.

[0093] Comparative Example

[0094] The difference between this comparative example and the above embodiment is that the BT@BNNS / PP material in the dielectric film is replaced with pure polypropylene material.

[0095] The DC breakdown characteristics test results of the dielectric films prepared in the examples and comparative examples are shown in FIG. Figure 3 As shown, it can be seen that the DC breakdown field strength of the dielectric film doped with 3% BT@BNNS nanoparticles is significantly higher than that of the pure polypropylene film. Therefore, according to the energy storage density calculation method of linear dielectrics, the polypropylene-based nanocomposite material prepared in the embodiment of the present invention has a significantly improved energy storage density compared with pure polypropylene material.

[0096] In summary, the embodiments of the present invention utilize hydrogen peroxide treatment to introduce strongly polar hydroxyl groups onto the surface of boron nitride nanosheets. Barium titanate nanoparticles can be stably attached and bonded to the surface of boron nitride nanosheets simply through conventional high-pressure reactor reaction treatment to form a barium titanate / boron nitride nanomaterial. By adding an appropriate amount of barium titanate / boron nitride nanomaterial to polypropylene for modification, the resulting polypropylene-based nanocomposite material has a higher breakdown field strength and significantly improved energy storage density than pure polypropylene material.

[0097] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a polypropylene-based high energy storage density nanocomposite material, characterized in that: The following steps are involved: Adding boron nitride nanosheets to a hydrogen peroxide solution and stirring thoroughly to obtain a first suspension; adding the barium titanate nanoparticles and the first suspension into a high-pressure reactor for reaction, so that the barium titanate nanoparticles adhere to and bind to the boron nitride nanosheets, thereby obtaining a barium titanate / boron nitride nanomaterial; The barium titanate / boron nitride nanomaterial is melt-blended with polypropylene to obtain the polypropylene-based high energy storage density nanocomposite material, wherein the mass proportion of the barium titanate / boron nitride nanomaterial is 2 wt % to 4 wt %.

2. The method for preparing a polypropylene-based high energy storage density nanocomposite material according to claim 1, wherein: The barium titanate nanoparticles are prepared by the following steps: Mixing barium hydroxide octahydrate, tetrabutyl titanate, surfactant PVP, and triethylene glycol in a preset ratio to obtain a first mixed solution; adding sodium hydroxide to the first mixed solution, and diluting with deionized water when the pH is greater than 13 to obtain a second mixed solution; The second mixed solution was heated and stirred at a constant temperature under reflux conditions in a condenser to obtain a light yellow sol; The light yellow sol is sequentially centrifuged, washed and freeze-dried to obtain the barium titanate nanoparticles.

3. The method for preparing the polypropylene-based high energy storage density nanocomposite material according to claim 2, characterized in that: The second mixed solution was heated and stirred at a constant temperature of 160° C. for 15 minutes.

4. The method for preparing the polypropylene-based high energy storage density nanocomposite material according to claim 1, characterized in that: The boron nitride nanosheets are prepared by the following steps: Dissolving hexagonal boron nitride in N,N-dimethylformamide solution and ultrasonically treating the solution to obtain a second suspension; The second suspension is sequentially centrifuged, washed and freeze-dried to obtain the boron nitride nanosheets.

5. The method for preparing the polypropylene-based high energy storage density nanocomposite material according to claim 1, characterized in that: In step S2, the reaction temperature is 180° C. and the reaction time is 6 hours.

6. The method for preparing the polypropylene-based high energy storage density nanocomposite material according to claim 1, characterized in that: The barium titanate / boron nitride nanomaterial and polypropylene are melt-blended at a rotation speed of 30 r / min for 10-20 min.

7. A polypropylene-based high energy storage density nanocomposite material, characterized in that: It is prepared by melt blending polypropylene and barium titanate / boron nitride nanomaterials, wherein the mass proportion of the barium titanate / boron nitride nanomaterials is 2wt%~4wt%; the barium titanate / boron nitride nanomaterials are formed by the attachment and bonding of barium titanate nanoparticles on boron nitride nanosheets.

8. The polypropylene-based high energy storage density nanocomposite material according to claim 7, characterized in that: The mass proportion of the barium titanate / boron nitride nanomaterial is 3 wt %.

9. Use of the polypropylene-based high energy storage density nanocomposite material prepared by the preparation method according to any one of claims 1 to 6, or the polypropylene-based high energy storage density nanocomposite material according to claim 7 or 8 in the field of power capacitors.

10. A dielectric film for use in power capacitors, comprising a polypropylene-based nanocomposite material with high energy storage density prepared by the preparation method according to any one of claims 1 to 6, or a polypropylene-based nanocomposite material with high energy storage density according to claim 7 or 8, characterized in that: Prepared by the following steps: placing a second polyimide film cut with holes on the first polyimide film, and filling the holes of the second polyimide film with the polypropylene-based high energy storage density nanocomposite material; The third polyimide film is placed on the second polyimide film, and the three layers of polyimide film are subjected to heat pressing treatment to complete the packaging.

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