A core-shell structured nanofiber and its application in preparing a high thermal conductivity composite material

Abstract

The present invention discloses a core-shell structured nanofiber and its application in the preparation of a highly thermally conductive composite material, belonging to the technical field of nanocomposite materials. In the present invention, an inorganic non-metallic BNNS is coated on the surface of a ceramic nanofiber to prepare a nanofiber with a core-shell structure, and then the core-shell structured nanofiber is compounded with a polymer to prepare a highly thermally conductive composite material. Using the core-shell structured nanofiber provided by the present invention as a filler for the polymer can effectively improve the thermal conductivity of the polymer. When the shell layer of the core-shell structure reaches a certain thickness, the thermal conductivity of the composite material reaches the maximum value. The preparation method of the core-shell structured nanofiber and the preparation method of the composite material in the present invention are simple, stable, and the parameters are easy to control. The nanocomposite material of the present invention has high thermal conductivity and good high-temperature energy storage performance, and can be used as a potential high-performance dielectric material in the thermal management application of high-power density electronic devices.

Description

Technical Field

[0001] The present invention relates to the technical field of nanocomposite materials, and particularly to a core-shell structure nanofiber and its application in the preparation of high thermal conductivity composite materials. Background Art

[0002] Dielectric thin film capacitors have become key devices in many fields, such as power grids, new energy vehicles, medical defibrillators, aerospace, and underground exploration, due to their advantages of high power density, fast charge and discharge, low density, high breakdown voltage, high flexibility, low loss, and long service life. Currently, the common commercial capacitor film is biaxially oriented polypropylene (BOPP) film. Due to its ultra-high breakdown strength (≈700 MV / m -1 ), a relatively high energy storage density (≈2 - 3 J / cm 3 ) is achieved. However, the defect of BOPP is that it cannot work in a high-temperature environment. When the operating temperature of the device exceeds 85°C, the breakdown strength of BOPP will decrease significantly, and its energy storage characteristics will also deteriorate. In addition, the maximum operating temperature of BOPP cannot exceed 105°C. However, since dielectric thin film capacitors are mostly used in high-power electrical energy storage devices, a large amount of heat is inevitably generated during the operation of the device. Therefore, strict requirements are imposed on dielectric thin film capacitors, that is, they should have excellent temperature stability and high-temperature energy storage performance even when working in a harsh high-temperature environment.

[0003] Generally speaking, if the fundamental problem of high-temperature energy storage of dielectric thin film capacitors is to be solved, it can be achieved by improving electrical insulation to suppress leakage current (i.e., regulating the bandgap to suppress the injection and transport of carriers to reduce conduction loss) or by increasing the glass transition temperature (T g)It is achieved by enhancing heat resistance. There are many strategies for regulating the bandgap. For example: (1) Adjust the bandgap of the polymer to enhance the ability to capture electrons and holes by lowering the lowest unoccupied molecular orbital (LUMO) and raising the highest occupied molecular orbital (HOMO); (2) Introduce inorganic nano-fillers with a wide bandgap to generate more local deep traps to limit the transport of charge carriers; (3) Composite inorganic fillers with a wide bandgap and graft-modified polymers to construct deeper charge carrier capture sites and enhance the resistance of charge carrier migration; (4) Dope a small amount of organic molecular semiconductors. Due to the strong electron affinity characteristics of molecular semiconductors, it can adsorb electrons in the interfacial region with the polymer to form deep traps and inhibit the accumulation of space charge. From the above research strategies, it can be seen that introducing charge carrier traps and adjusting the depth and density of charge carrier traps can effectively reduce the conductance loss, thereby improving the high-temperature resistance and service life of dielectric thin-film capacitors. In addition, charge carrier traps can be combined with special structures such as core-shell structures, heterostructures, multilayer structures, and crosslinked structures. And how to combine charge carrier traps with special structures such as core-shell structures, heterostructures, multilayer structures, and crosslinked structures to manufacture dielectric thin-film capacitors with excellent high-temperature energy storage characteristics is the focus of research by those skilled in the art. Summary of the Invention

[0004] The object of the present invention is to provide a core-shell structured nanofiber and its application in the preparation of a highly thermally conductive composite material to solve the problems existing in the above-mentioned prior art. The present invention prepares a nanofiber filler with a core-shell structure by coating inorganic non-metallic boron nitride nanosheets (BNNS) on the surface of one-dimensional (1D) ceramic nanofibers, and then composites the core-shell structured nanofiber filler with a polymer to obtain a highly thermally conductive composite material.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention: A core-shell structured nanofiber is composed of a ceramic nanofiber and a boron nitride nanosheet (BNNS) shell layer coated on the surface of the ceramic nanofiber; the ceramic nanofiber is one of barium calcium zirconate titanate (BZCT) nanofibers, barium titanate (BT) nanofibers, barium strontium titanate (BST) nanofibers, strontium titanate (SrTiO3) nanofibers, and calcium copper titanate (CCTO) nanofibers.

[0007] Further, the ceramic nanofiber is a one-dimensional ceramic nanofiber.

[0008] Further, the thickness of the boron nitride nanosheet shell layer of the core-shell structured nanofiber is 5-15 nm.

[0009] The second technical solution of the present invention: A method for preparing the above core-shell structured nanofibers, which chemically coats ceramic nanofibers with boron nitride nanosheets to obtain the core-shell structured nanofibers.

[0010] Further, the method of chemical coating is coaxial electrospinning.

[0011] Further, the coaxial electrospinning method includes the following steps: using a boron nitride nanosheet precursor solution as the shell and a ceramic nanofiber precursor solution as the core to perform coaxial electrospinning, drying the nanofibers obtained by coaxial electrospinning, and performing heat treatment to obtain the core-shell structured nanofibers.

[0012] Further, the conditions of the coaxial electrospinning include: the needle specifications are 15G / 22G, 16G / 22G, 17G / 22G or 18G / 22G, where 22G is the core layer with a diameter of 0.72 mm, and 15G, 16G, 17G, 18G are the shell layers with diameters of 1.8 mm, 1.64 mm, 1.49 mm, 1.27 mm respectively, the positive and negative electrospinning voltages are 15 kV, the electrospinning distance is 15 cm, the electrospinning speed of the ceramic nanofiber precursor solution is 0.3 mL / h, and the electrospinning speed of the boron nitride nanosheet precursor solution is 0.4 mL / h.

[0013] Further, the drying temperature is 50-90 °C and the time is 2-4 h; the heat treatment temperature is 700-950 °C and the time is 2-5 h.

[0014] Further, when the ceramic nanofiber is one-dimensional barium calcium zirconate titanate nanofiber (BZCT NFs), the coaxial electrospinning method includes the following steps: using a boron nitride nanosheet precursor solution as the shell and a one-dimensional barium calcium zirconate titanate nanofiber (BZCT NFs) precursor solution as the core to perform coaxial electrospinning, drying the nanofibers obtained by coaxial electrospinning, and performing heat treatment to obtain core-shell structured nanofibers BZCT NFs@BNNS.

[0015] Further, the preparation method of the one-dimensional barium calcium zirconate titanate nanofiber (BZCT NFs) precursor solution includes: dissolving a barium source and a calcium source in a mixed solvent, adding a zirconium source, a titanium source and polyvinylpyrrolidone (PVP) after forming a stable solution, and heating and stirring to obtain the one-dimensional BZCT NFs precursor solution; the mixed solvent is a mixed solvent of acetic acid (CH3COOH), acetylacetone (C5H8O2) and ethanol (CH3CH2OH); the temperature of the heating and stirring is 60 °C.

[0016] Further, the method for preparing the boron nitride nanosheet precursor solution includes: adding BNNS and PVP into a solvent, heating and stirring to obtain the BNNS precursor solution; the solvent is CH3CH2OH; the temperature of the heating and stirring is 60°C.

[0017] Further, by mass ratio, barium source: calcium source: CH3COOH: C5H8O2: CH3CH2OH: zirconium source: titanium source: PVP = 32:1:1:9:3:5:37:8, BNNS: PVP: CH3CH2OH = 2:1:2.

[0018] Technical solution three of the present invention: An application of the above core-shell structure nanofibers in the preparation of a highly thermally conductive composite material.

[0019] Technical solution four of the present invention: A highly thermally conductive composite material obtained by compounding the above core-shell structure nanofibers with a polymer; the polymer is one of polyacrylonitrile (PAN), polyimide (PI), poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), polyurethane (PU), and polyetherimide (PEI).

[0020] Further, by volume ratio, the compounding ratio of the core-shell structure nanofibers to the polymer is 1-4:10 (i.e., the dosage of the core-shell structure nanofibers is 10-40 vol% of the polymer).

[0021] Technical solution five of the present invention: A method for preparing the above highly thermally conductive composite material, in which the core-shell structure nanofibers and the polymer are compounded by a solution mixing method to obtain the highly thermally conductive composite material.

[0022] Further, the solution mixing method includes the following steps: dissolving the core-shell structure nanofibers and the polymer in a solvent to obtain a composite material solution; pouring the composite material solution into a mold, drying, and demolding to obtain the highly thermally conductive composite material.

[0023] Further, the solvent is N,N-dimethylformamide (DMF); the drying temperature is 60-90°C and the time is 9-14 h.

[0024] The present invention discloses the following technical effects:

[0025] The present invention prepares nanofibers with a core-shell structure by coating inorganic non-metallic BNNS on the surface of ceramic nanofibers, and then composites the core-shell structure nanofibers with a polymer to prepare a high thermal conductivity composite material. Introducing a BNNS shell layer with a relatively wide bandgap on the surface of the ceramic nanofibers can construct more carrier traps, and enhance the ability to capture electrons and holes by lowering the lowest unoccupied molecular orbital (LUMO) and raising the highest occupied molecular orbital (HOMO), effectively reducing charge injection and migration and suppressing the generation of leakage current, thereby improving the insulation and high-temperature energy storage characteristics of the composite material. In addition, the BNNS shell layer with high thermal conductivity can make the nanofiber filler more likely to form a thermal conduction path in the polymer matrix, playing a role in improving the thermal conductivity of the composite material. Using the core-shell structure nanofibers provided by the present invention as the filler of the polymer can effectively improve the thermal conductivity of the polymer. When the shell layer of the core-shell structure reaches a certain thickness, the thermal conductivity of the composite material reaches the maximum value.

[0026] The preparation method of the core-shell structure nanofibers of the present invention and the preparation method of the composite material are simple, stable, and the parameters are easy to control.

[0027] The nanocomposite material of the present invention has high thermal conductivity and good high-temperature energy storage performance, and can be used as a potential high-performance dielectric material in the thermal management application of high-power density electronic devices. Brief Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a schematic structural diagram of the core-shell structure nanofibers of the present invention;

[0030] Figure 2 It is a scanning transmission image of the BZCTNFs@BNNS core-shell structure nanofibers prepared in Example 2;

[0031] Figure 3 It is an XRD diagram of the BZCT NFs@BNNS core-shell structure nanofibers prepared in Examples 1 to 4 and the BZCT NFs prepared in Comparative Example 1;

[0032] Figure 4 It is an EDX diagram of the BZCTNFs prepared in Comparative Example 1. Detailed Embodiments

[0033] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terms used in the present invention are only for describing particular embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0036] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are merely exemplary.

[0037] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0038] The present invention provides a core-shell structured nanofiber, which is composed of a ceramic nanofiber and a boron nitride nanosheet (BNNS) shell layer coated on the surface of the ceramic nanofiber (the structural schematic diagram is as Figure 1 shown); the ceramic nanofiber is one of barium calcium zirconate titanate (BZCT) nanofiber, barium titanate (BT) nanofiber, barium strontium titanate (BST) nanofiber, strontium titanate (SrTiO3) nanofiber, and calcium copper titanate (CCTO) nanofiber.

[0039] In the present invention, inorganic non-metallic BNNS is selected as the shell layer to coat the surface of ceramic nanofibers to form core-shell structure nanofiber fillers. Compared with the commonly used metal oxide coatings such as alumina (Al2O3) and titanium dioxide (TiO2), BNNS has a higher thermal conductivity and a wider bandgap. Introducing a relatively stable BNNS interface layer as a transition phase with independent properties not only improves the interfacial compatibility between the nanofiber fillers and the polymer matrix, but also introduces more local deep traps in the interfacial region between the nanofiber fillers and the polymer matrix to suppress the conduction loss caused by carrier injection and migration. The designed BNNS shell layer has a dielectric constant similar to that of the polymer matrix, which can not only relieve the local electric field distortion caused by charge aggregation due to the large difference in dielectric constant between the filler and the matrix, but also facilitate the formation of a heat conduction path to dissipate heat in time, ultimately synergistically improving the breakdown strength and thermal conductivity of the material.

[0040] Further, the ceramic nanofibers are preferably one of barium calcium zirconate titanate (BZCT) nanofibers, barium titanate (BT) nanofibers, and barium strontium titanate (BST) nanofibers, and more preferably barium calcium zirconate titanate (BZCT) nanofibers.

[0041] Further, the ceramic nanofibers are one-dimensional ceramic nanofibers.

[0042] Further, the thickness of the boron nitride nanosheet shell layer of the core-shell structure nanofibers is 5-15 nm; preferably 15 nm.

[0043] The present invention also provides a preparation method of the above-mentioned core-shell structure nanofibers, in which boron nitride nanosheets are used to chemically coat the ceramic nanofibers to obtain the core-shell structure nanofibers.

[0044] Further, the chemical coating method is the coaxial electrospinning method.

[0045] Further, the coaxial electrospinning method includes the following steps: using the boron nitride nanosheet precursor solution as the shell and the ceramic nanofiber precursor solution as the core to perform coaxial electrospinning, drying the nanofibers obtained by coaxial electrospinning, and performing heat treatment to obtain the core-shell structure nanofibers.

[0046] Further, the conditions for the coaxial electrospinning include: the needle specifications are 15G / 22G, 16G / 22G, 17G / 22G or 18G / 22G, where 22G is the core layer with a diameter of 0.72 mm, and 15G, 16G, 17G, 18G are the shell layers with diameters of 1.8 mm, 1.64 mm, 1.49 mm, and 1.27 mm respectively. The positive and negative electrospinning voltages are 15 kV, the electrospinning distance is 15 cm, the electrospinning speed of the ceramic nanofiber precursor solution is 0.3 mL / h, and the electrospinning speed of the boron nitride nanosheet precursor solution is 0.4 mL / h.

[0047] Further, the drying temperature is 50 - 90 °C and the time is 2 - 4 h; the heat treatment temperature is 700 - 950 °C and the time is 2 - 5 h.

[0048] Further, when the ceramic nanofiber is one-dimensional barium calcium zirconate titanate nanofiber (BZCT NFs), the coaxial electrospinning method includes the following steps: using the boron nitride nanosheet precursor solution as the shell and the one-dimensional barium calcium zirconate titanate nanofiber (BZCT NFs) precursor solution as the core for coaxial electrospinning, drying the nanofibers obtained by coaxial electrospinning, and performing heat treatment to obtain the core-shell structured nanofiber BZCT NFs@BNNS.

[0049] Further, the preparation method of the one-dimensional barium calcium zirconate titanate nanofiber (BZCT NFs) precursor solution includes: dissolving the barium source and calcium source in a mixed solvent, adding the zirconium source, titanium source, and polyvinylpyrrolidone (PVP) after forming a stable solution, and heating and stirring to obtain the one-dimensional BZCTNFs precursor solution; the mixed solvent is a mixed solvent of CH3COOH, C5H8O2, and CH3CH2OH; the temperature for heating and stirring is 60 °C.

[0050] Further, by mass ratio, barium source: calcium source: CH3COOH: C5H8O2: CH3CH2OH: zirconium source: titanium source: PVP = 32:1:1:9:3:5:37:8, BNNS: PVP: CH3CH2OH = 2:1:2.

[0051] Further, the barium source is Ba(OH)2·8H2O; the calcium source is Ca(OH)2; the zirconium source is (C5H8O2)4·Zr; the titanium source is C 16 H 36 O4Ti.

[0052] Further, the preparation method of the boron nitride nanosheet precursor solution includes: adding BNNS and PVP to a solvent, heating and stirring to obtain the BNNS precursor solution; the solvent is CH3CH2OH; the temperature for heating and stirring is 60 °C.

[0053] The present invention also provides an application of the above core-shell structured nanofibers in the preparation of high thermal conductivity composite materials.

[0054] The present invention also provides a high thermal conductivity composite material, which is obtained by compounding the above core-shell structured nanofibers with a polymer; the polymer is one of polyacrylonitrile (PAN), polyimide (PI), poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), polyurethane (PU), and polyetherimide (PEI).

[0055] Furthermore, the polymer is preferably polyacrylonitrile (PAN), and the ceramic nanofibers are preferably barium calcium zirconate titanate nanofibers (BZCT NFs); that is, the core-shell structured nanofibers are preferably BZCT NFs@BNNS core-shell structured nanofibers, and the high thermal conductivity composite material is preferably BZCT NFs@BNNS / PAN composite material.

[0056] BZCT NFs have a high dielectric constant (8000 - 16000), a high spontaneous polarization (59.25 μC / cm), a low dielectric loss (≤0.005), excellent ferroelectric properties, and insulating properties. Compared with other polymers, PAN contains strong polar groups that can improve the overall polarizability of the composite material and better improve the energy storage density. In addition, PAN also contains a large number of acrylonitrile groups (-C≡N-), and these groups endow PAN with excellent mechanical properties and heat resistance. Coating a layer of BNNS shell with high thermal conductivity and wide bandgap (≈5.9 eV) on the surface of BZCT NFs has the following advantages. First, introducing a BNNS shell with a relatively wide bandgap can construct more carrier traps and enhance the ability to capture electrons and holes by reducing the lowest unoccupied molecular orbital (LUMO) and increasing the highest occupied molecular orbital (HOMO), effectively reducing charge injection and migration, inhibiting the generation of leakage current, and thus improving the insulation and high-temperature energy storage characteristics of the composite material. Second, the BNNS shell with high thermal conductivity can make the nanofiber fillers more easily form a thermal conduction path in the polymer matrix, playing a role in improving the thermal conductivity of the composite material. Finally, the dielectric constant of the BNNS shell (≈2.9) is close to that of PAN (≈3.0), which can improve the dispersion of the fillers and their compatibility with the polymer matrix. The synergistic cooperation among the BZCT NFs core, the BNNS shell, and the PAN matrix constitutes a composite material with excellent thermal conductivity and excellent high-temperature dielectric energy storage performance.

[0057] Furthermore, by volume ratio, the compounding ratio of the core-shell structured nanofibers to the polymer is 1 - 4:10 (that is, the dosage of the core-shell structured nanofibers is 10 - 40 vol% of the polymer).

[0058] The present invention also provides a method for preparing the above-mentioned high thermal conductivity composite material, which composites the core-shell structure nanofibers and the polymer by a solution mixing method to obtain the high thermal conductivity composite material.

[0059] Further, the solution mixing method includes the following steps: dissolving the core-shell structure nanofibers and the polymer in a solvent to obtain a composite material solution; pouring the composite material solution into a mold, drying, and demolding to obtain the high thermal conductivity composite material.

[0060] Further, the solvent is N,N-dimethylformamide (DMF); the drying temperature is 60-90 °C, and the time is 9-14 h.

[0061] Further preferably, after dissolving the core-shell structure nanofibers and the polymer in the solvent, it also includes an operation of stirring for 12-24 h and then performing ultrasonic dispersion treatment for 4-8 h. The present invention performs long-term stirring and ultrasonic dispersion treatment, which is more conducive to making the composite material solution mix evenly.

[0062] The core-shell structure nanofibers and the high thermal conductivity composite material provided by the present invention will be further described in detail below with reference to specific embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0063] All raw materials used in the following examples and comparative examples are ordinary commercially available products.

[0064] Example 1

[0065] (1) Preparation of core-shell structure nanofibers (BZCTNFs@BNNS)

[0066] Dissolve Ba(OH)2·8H2O and Ca(OH)2 in a mixed solvent of CH3COOH, C5H8O2 and CH3CH2OH. After forming a stable solution, add (C5H8O2)4·Zr, C 16 H 36 O4Ti and PVP (by mass ratio, Ba(OH)2·8H2O: Ca(OH)2: CH3COOH: C5H8O2: CH3CH2OH: (C5H8O2)4·Zr: C 16 H 36O4Ti:PVP = 32:1:1:9:3:5:37:8), and heated and stirred in a water bath at 60 °C until a stable solution was formed to obtain a one-dimensional BZCT NFs precursor solution; BNNS and PVP were added to a CH3CH2OH solvent (by mass ratio, BNNS:PVP:CH3CH2OH = 2:1:2), and heated and stirred in a water bath at 60 °C until a stable solution was formed to obtain a BNNS precursor solution; then, using the BNNS precursor solution as the shell and the one-dimensional BZCT NFs precursor solution as the core, coaxial electrospinning was carried out under the conditions that the coaxial spinning needle size was 15G / 22G, the positive and negative voltages were 15 kV, the spinning distance was 15 cm, and the spinning speeds of the one-dimensional BZCT NFs precursor solution and the BNNS precursor solution were 0.3 mL / h and 0.4 mL / h, respectively. The nanofibers obtained by coaxial electrospinning were transferred to an oven and dried at 50 °C for 2 h, and then transferred to a muffle furnace for heat treatment at 700 °C for 2 h. After naturally cooling to room temperature, BZCT NFs@BNNS core-shell structured nanofibers were obtained. After testing, the thickness of the BNNS shell layer of the BZCT NFs@BNNS core-shell structured nanofibers prepared in this example was uniform, about 20 nm.

[0067] (2) Preparation of BZCT NFs@BNNS / PAN composite material

[0068] Weigh BZCT NFs@BNNS core-shell structured nanofibers and PAN according to a volume ratio of 2:10 (i.e., the dosage of BZCT NFs@BNNS core-shell structured nanofibers is 20 vol% of PAN). PAN was added to a DMF solvent and completely dissolved, and then BZCT NFs@BNNS core-shell structured nanofibers were added. Magnetic stirring was carried out for 12 h, and then ultrasonic dispersion treatment was carried out for 7 h to obtain a composite material solution; the composite material solution was poured into a clean petri dish with a smooth inner wall and dried in a vacuum drying oven at 70 °C for 12 h to obtain a composite film. The composite film was taken out of the petri dish by demolding with ice water, and then the composite film was rinsed with deionized water and left to dry at room temperature to obtain a BZCT NFs@BNNS / PAN composite material.

[0069] Example 2

[0070] (1) Preparation of core-shell structured nanofibers (BZCT NFs@BNNS)

[0071] Dissolve Ba(OH)2·8H2O and Ca(OH)2 in a mixed solvent of CH3COOH, C5H8O2 and CH3CH2OH. After forming a stable solution, add (C5H8O2)4·Zr, C 16 H 36O4Ti and PVP (by mass ratio, Ba(OH)2·8H2O: Ca(OH)2: CH3COOH: C5H8O2: CH3CH2OH: (C5H8O2)4·Zr: C 16 H 36 O4Ti: PVP = 32: 1: 1: 9: 3: 5: 37: 8), heat and stir in a water bath at 60 °C until a stable solution is formed to obtain a one-dimensional BZCT NFs precursor solution; add BNNS and PVP to the CH3CH2OH solvent (by mass ratio, BNNS: PVP: CH3CH2OH = 2: 1: 2), heat and stir in a water bath at 60 °C until a stable solution is formed to obtain a BNNS precursor solution; then, using the BNNS precursor solution as the shell and the one-dimensional BZCT NFs precursor solution as the core, perform coaxial electrospinning under the conditions that the coaxial spinning needle size is 16G / 22G, the positive and negative voltages are 15 kV, the spinning distance is 15 cm, and the spinning speeds of the one-dimensional BZCT NFs precursor solution and the BNNS precursor solution are 0.3 mL / h and 0.4 mL / h respectively. Transfer the nanofibers obtained by coaxial electrospinning to an oven and dry at 90 °C for 4 h, and then transfer them to a muffle furnace for heat treatment at 950 °C for 4 h. After natural cooling to room temperature, BZCTNFs@BNNS core-shell structured nanofibers are obtained. After testing, the thickness of the BNNS shell layer of the BZCT NFs@BNNS core-shell structured nanofibers prepared in this example is uniform, about 15 nm.

[0072] (2) Preparation of BZCTNFs@BNNS / PAN composite material

[0073] Weigh the BZCT NFs@BNNS core-shell structured nanofibers and PAN according to a volume ratio of 2:10 (i.e., the dosage of the BZCT NFs@BNNS core-shell structured nanofibers is 20 vol% of PAN). Add PAN to the DMF solvent and dissolve it completely, then add the BZCTNFs@BNNS core-shell structured nanofibers, stir magnetically for 20 h, and then perform ultrasonic dispersion treatment for 6 h to obtain a composite material solution; pour the composite material solution into a clean petri dish with a smooth inner wall, place it in a vacuum drying oven and dry at 60 °C for 14 h to obtain a composite membrane. Take out the composite membrane from the petri dish by demolding with ice water, then rinse the composite membrane with deionized water, and let it stand to dry at room temperature to obtain the BZCT NFs@BNNS / PAN composite material.

[0074] Example 3

[0075] (1) Preparation of core-shell structured nanofibers (BZCTNFs@BNNS)

[0076] Dissolve Ba(OH)2·8H2O and Ca(OH)2 in a mixed solvent of CH3COOH, C5H8O2 and CH3CH2OH. After forming a stable solution, add (C5H8O2)4·Zr, C 16 H 36 O4Ti and PVP (by mass ratio, Ba(OH)2·8H2O:Ca(OH)2:CH3COOH:C5H8O2:CH3CH2OH:(C5H8O2)4·Zr:C 16 H 36 O4Ti:PVP = 32:1:1:9:3:5:37:8). Heat and stir in a water bath at 60 °C until a stable solution is formed to obtain a one-dimensional BZCT NFs precursor solution; add BNNS and PVP to the CH3CH2OH solvent (by mass ratio, BNNS:PVP:CH3CH2OH = 2:1:2). Heat and stir in a water bath at 60 °C until a stable solution is formed to obtain a BNNS precursor solution; then use the BNNS precursor solution as the shell and the one-dimensional BZCT NFs precursor solution as the core. Under the conditions of a coaxial electrospinning needle size of 17G / 22G, a positive and negative voltage of 15 kV, a spinning distance of 15 cm, and spinning speeds of 0.3 mL / h and 0.4 mL / h for the one-dimensional BZCTNFs precursor solution and the BNNS precursor solution respectively, perform coaxial electrospinning. Transfer the nanofibers obtained by coaxial electrospinning to an oven and dry at 60 °C for 3 h, and then transfer them to a muffle furnace for heat treatment at 850 °C for 3 h. After natural cooling to room temperature, obtain BZCTNFs@BNNS core-shell structured nanofibers. After testing, the thickness of the BNNS shell layer of the BZCT NFs@BNNS core-shell structured nanofibers prepared in this example is uniform, about 10 nm.

[0077] (2) Preparation of BZCTNFs@BNNS / PAN composite material

[0078] Weigh the BZCT NFs@BNNS core-shell structured nanofibers and PAN according to a volume ratio of 2:10 (i.e., the dosage of the BZCT NFs@BNNS core-shell structured nanofibers is 20 vol% of PAN). Add PAN to the DMF solvent and dissolve it completely. Then add the BZCTNFs@BNNS core-shell structured nanofibers, stir magnetically for 18 h, and then perform ultrasonic dispersion treatment for 8 h to obtain a composite material solution; pour the composite material solution into a clean petri dish with a smooth inner wall, place it in a vacuum drying oven and dry at 90 °C for 9 h to obtain a composite film. Take out the composite film from the petri dish by demolding with ice water, then rinse the composite film with deionized water, and leave it to dry at room temperature to obtain the BZCT NFs@BNNS / PAN composite material.

[0079] Example 4

[0080] (1) Preparation of core-shell structured nanofibers (BZCTNFs@BNNS)

[0081] Dissolve Ba(OH)2·8H2O and Ca(OH)2 in a mixed solvent of CH3COOH, C5H8O2 and CH3CH2OH. After forming a stable solution, add (C5H8O2)4·Zr, C 16 H 36 O4Ti and PVP (by mass ratio, Ba(OH)2·8H2O:Ca(OH)2:CH3COOH:C5H8O2:CH3CH2OH:(C5H8O2)4·Zr:C 16 H 36 O4Ti:PVP = 32:1:1:9:3:5:37:8). Heat and stir in a water bath at 60 °C until a stable solution is formed to obtain a one-dimensional BZCT NFs precursor solution; add BNNS and PVP to the CH3CH2OH solvent (by mass ratio, BNNS:PVP:CH3CH2OH = 2:1:2). Heat and stir in a water bath at 60 °C until a stable solution is formed to obtain a BNNS precursor solution; then use the BNNS precursor solution as the shell and the one-dimensional BZCT NFs precursor solution as the core. Under the conditions that the coaxial spinning needle size is 18G / 22G, the positive and negative voltages are 15 kV, the spinning distance is 15 cm, and the spinning speeds of the one-dimensional BZCTNFs precursor solution and the BNNS precursor solution are 0.3 mL / h and 0.4 mL / h respectively, perform coaxial electrospinning. Transfer the nanofibers obtained by coaxial electrospinning to an oven and dry at 70 °C for 3 h, and then transfer them to a muffle furnace for heat treatment at 800 °C for 4 h. After natural cooling to room temperature, obtain BZCTNFs@BNNS core-shell structured nanofibers. After testing, the thickness of the BNNS shell layer of the BZCT NFs@BNNS core-shell structured nanofibers prepared in this example is uniform, about 5 nm.

[0082] (2) Preparation of BZCTNFs@BNNS / PAN composite materials

[0083] Weigh BZCT NFs@BNNS core-shell structured nanofibers and PAN at a volume ratio of 2:10 (i.e., the dosage of BZCT NFs@BNNS core-shell structured nanofibers is 20 vol% of PAN). Add PAN to the DMF solvent and dissolve it completely. Then add BZCT NFs@BNNS core-shell structured nanofibers, stir magnetically for 24 h, and then perform ultrasonic dispersion treatment for 4 h to obtain a composite material solution. Pour the composite material solution into a clean petri dish with a smooth inner wall, place it in a vacuum drying oven, and dry it at 75 °C for 10 h to obtain a composite membrane. Take out the composite membrane from the petri dish by demolding with ice water, then rinse the composite membrane with deionized water, and leave it to dry at room temperature to obtain the BZCT NFs@BNNS / PAN composite material.

[0084] Comparative Example 1

[0085] (1) Preparation of BZCT NFs

[0086] Dissolve Ba(OH)2·8H2O and Ca(OH)2 in a mixed solvent of CH3COOH, C5H8O2, and CH3CH2OH. After forming a stable solution, add (C5H8O2)4·Zr, C 16 H 36 O4Ti and PVP (by mass ratio, Ba(OH)2·8H2O:Ca(OH)2:CH3COOH:C5H8O2:CH3CH2OH:(C5H8O2)4·Zr:C 16 H 36 O4Ti:PVP = 32:1:1:9:3:5:37:8). Heat and stir in a water bath at 60 °C until a stable solution is formed to obtain a one-dimensional BZCT NFs precursor solution. Then, under the conditions of a spinning needle gauge of 22G (needle inner diameter of 0.72 mm), a positive and negative voltage of 15 kV, a spinning distance of 15 cm, and a spinning speed of the one-dimensional BZCT NFs precursor solution of 0.3 mL / h, perform electrospinning. Transfer the electrospun nanofibers to an oven and dry them at 50 °C for 2 h, and then transfer them to a muffle furnace for heat treatment at 700 °C for 2 h. After natural cooling to room temperature, obtain one-dimensional (1D) BZCT NFs.

[0087] (2) Preparation of BZCT NFs / PAN composite material

[0088] Weigh BZCT NFs and PAN at a volume ratio of 2:10 (i.e., the dosage of BZCT NFs is 20 vol% of PAN). Add PAN to the DMF solvent and dissolve it completely. Then add BZCT NFs, stir magnetically for 12 h, and then perform ultrasonic dispersion treatment for 7 h to obtain a composite material solution. Pour the composite material solution into a clean petri dish with a smooth inner wall, place it in a vacuum drying oven and dry it at 70 °C for 12 h to obtain a composite film. Take out the composite film from the petri dish by demoulding with ice water, then rinse the composite film with deionized water, and leave it to dry naturally at room temperature to obtain the BZCT NFs / PAN composite material. The difference between this comparative example and Example 1 is that BZCT NFs with an equal volume dosage are used instead of the BZCTNFs@BNNS core-shell structure nanofibers.

[0089] Comparative Example 2

[0090] (1) Preparation of BZCTNFs@AlN

[0091] Dissolve Ba(OH)2·8H2O and Ca(OH)2 in a mixed solvent of CH3COOH, C5H8O2 and CH3CH2OH. After forming a stable solution, add (C5H8O2)4·Zr, C 16 H 36 O4Ti and PVP (by mass ratio, Ba(OH)2·8H2O:Ca(OH)2:CH3COOH:C5H8O2:CH3CH2OH:(C5H8O2)4·Zr:C 16 H 36 O4Ti:PVP = 32:1:1:9:3:5:37:8). Heat and stir in a water bath at 60 °C until a stable solution is formed to obtain a one-dimensional BZCT NFs precursor solution. Add aluminum nitride (AlN) and PVP to the CH3CH2OH solvent (by mass ratio, AlN:PVP:CH3CH2OH = 2:1:2), heat and stir in a water bath at 60 °C until a stable solution is formed to obtain an AlN precursor solution. Then, using the AlN precursor solution as the shell and the one-dimensional BZCT NFs precursor solution as the core, perform coaxial electrospinning under the conditions that the coaxial spinning needle specification is 15G / 22G, the positive and negative voltages are 15 kV, the spinning distance is 15 cm, and the spinning speeds of the one-dimensional BZCTNFs precursor solution and the AlN precursor solution are 0.3 mL / h and 0.4 mL / h respectively. Transfer the nanofibers obtained by coaxial electrospinning to an oven and dry them at 50 °C for 2 h, and then transfer them to a muffle furnace for heat treatment at 700 °C for 2 h. After natural cooling to room temperature, obtain one-dimensional (1D) BZCT NFs@AlN.

[0092] (2) Preparation of BZCTNFs@AlN / PAN composite material

[0093] Weigh BZCT NFs@AlN and PAN at a volume ratio of 2:10 (i.e., the dosage of BZCT NFs@AlN is 20 vol% of PAN). Add PAN to the DMF solvent and dissolve it completely. Subsequently, add BZCT NFs@AlN and stir magnetically for 12 h, then perform ultrasonic dispersion treatment for 7 h to obtain a composite material solution. Pour the composite material solution into a clean petri dish with a smooth inner wall, place it in a vacuum drying oven and dry it at 70 °C for 12 h to obtain a composite film. Remove the composite film from the petri dish by demoulding with ice water, then rinse the composite film with deionized water and leave it to dry at room temperature to obtain the BZCT NFs@AlN / PAN composite material. The difference between this comparative example and Example 1 is that BZCT NFs@AlN with an equal volume dosage is used to replace the BZCT NFs@BNNS core-shell structure nanofibers.

[0094] Comparative Example 3

[0095] Preparation of carbon nanotube / PAN composite material

[0096] The preparation method is the same as that of Comparative Example 1, except that carbon nanotubes with an equal volume dosage are used to replace BZCT NFs.

[0097] Comparative Example 4

[0098] (1) Preparation of C (carbon nanofiber)@BNNS nanofibers

[0099] Dissolve PAN in the DMF solvent (by mass ratio, PAN:DMF = 1:5), mix by magnetic stirring until a stable solution is formed to obtain a one-dimensional carbon nanofiber precursor solution; add BNNS and PAN to the DMF solvent (by mass ratio, BNNS:PAN:DMF = 2:1:2), mix by magnetic stirring until a stable solution is formed to obtain a BNNS precursor solution; then use the BNNS precursor solution as the shell and the one-dimensional carbon nanofiber precursor solution as the core, and perform coaxial electrospinning under the conditions that the coaxial spinning needle has a specification of 15G / 22G, the positive and negative voltages are 15 kV, the spinning distance is 15 cm, and the spinning speeds of the one-dimensional carbon nanofiber precursor solution and the BNNS precursor solution are 0.3 mL / h and 0.4 mL / h respectively. Subsequently, pre-oxidize the electrospun nanofibers at 260 °C for 40 min. Finally, carbonize the pre-oxidized body in an argon atmosphere at 950 °C for 2 h to prepare C@BNNS nanofibers.

[0100] (2) Preparation of C@BNNS / PAN composite material

[0101] Weigh C@BNNS and PAN according to a volume ratio of 2:10 (i.e., the dosage of C@BNNS is 20 vol% of PAN). Add PAN to the DMF solvent and dissolve it completely. Then add C@BNNS and stir magnetically for 12 h, and then perform ultrasonic dispersion treatment for 7 h to obtain a composite material solution. Pour the composite material solution into a clean petri dish with a smooth inner wall, place it in a vacuum drying oven and dry it at 70 °C for 12 h to obtain a composite film. Take out the composite film from the petri dish by demoulding with ice water, then rinse the composite film with deionized water, and leave it to dry at room temperature to obtain the C@BNNS / PAN composite material. The difference between this comparative example and Example 1 is that C@BNNS with an equal volume dosage is used to replace the BZCT NFs@BNNS core-shell structure nanofibers.

[0102] Comparative Example 5

[0103] (1) The preparation of the core-shell structure nanofibers (BZCTNFs@BNNS) is the same as that in Example 1.

[0104] (2) Preparation of the BZCTNFs@BNNS / PVDF composite material

[0105] Weigh the BZCT NFs@BNNS core-shell structure nanofibers and PVDF (polyvinylidene fluoride) according to a volume ratio of 2:10. Add PVDF to the DMF solvent and dissolve it completely. Then add the BZCT NFs@BNNS core-shell structure nanofibers, stir magnetically for 12 h, and then perform ultrasonic dispersion treatment for 7 h to obtain a composite material solution. Pour the composite material solution into a clean petri dish with a smooth inner wall, place it in a vacuum drying oven and dry it at 70 °C for 12 h to obtain a composite film. Take out the composite film from the petri dish by demoulding with ice water, then rinse the composite film with deionized water, and leave it to dry at room temperature to obtain the BZCT NFs@BNNS / PVDF composite material. The difference between this comparative example and Example 1 is that PVDF with an equal volume dosage is used to replace PAN.

[0106] Test Example 1

[0107] Take the BZCT NFs@BNNS core-shell structure nanofibers prepared in Example 2 for scanning transmission. Its scanning transmission image is as Figure 2 shown, Figure 2 which proves the formation of the core-shell structure nanofibers. As Figure 2 can be seen, the thickness of the BNNS shell layer is uniform, about 15 nm.

[0108] Test Example 2

[0109] Take the BZCT NFs@BNNS core-shell structure nanofibers prepared in Examples 1 to 4 and the BZCTNFs prepared in Comparative Example 1 for XRD testing. Their XRD patterns are as Figure 3As shown (Example 1 corresponds to Instance 1, Example 2 corresponds to Instance 1, Example 3 corresponds to Instance 3, Example 4 corresponds to Instance 4), from Figure 3 it can be seen that characteristic diffraction peaks belonging to BZCT NFs are detected at 2θ of 22.30°, 31.75°, 39.08°, 45.52°, 51.22°, 56.42°, 66.29°, 75.37°, 79.67°, and 88.17°, and they belong to the perovskite structure. The corresponding diffraction crystal planes are (100), (110), (111), (200), (210), (211), (220), (310), (311), and (322) respectively. In addition, EDX elemental analysis tests were also carried out on the BZCT NFs prepared in Comparative Example 1, and its EDX pattern is as Figure 4 shown. From Figure 4 it can be seen that the chemical formula of BZCT NFs is 0.5Ba(Zr 0.2 Ti 0.8 )O3 - 0.5(Ba 0.7 Ca 0.3 )TiO3.

[0110] Test Example 3

[0111] The BZCT NFs@BNNS / PAN composites prepared in Examples 1 to 4 and the composites prepared in Comparative Examples 1 to 5 were taken for thermal conductivity tests (thermal conductivity at 25°C), and pure PAN was used as a blank control. The results are shown in Table 1:

[0112] Table 1

[0113]

[0114] As can be seen from Table 1, the thermal conductivity of the BZCT NFs@BNNS(20nm) / PAN composite material in Example 1 is 3.14 W / (m·K), which is about 55.10% higher than that of BZCT NFs / PAN (1.41) in Comparative Example 1; the thermal conductivity of the BZCT NFs@BNNS(15nm) / PAN composite material in Example 2 is 3.36 W / (m·K), which is about 58.04% higher than that of BZCT NFs / PAN (1.41) in Comparative Example 1; the thermal conductivity of the BZCT NFs@BNNS(10nm) / PAN composite material in Example 3 is 3.07 W / (m·K), which is about 54.07% higher than that of BZCT NFs / PAN (1.41) in Comparative Example 1; the thermal conductivity of the BZCT NFs@BNNS(5nm) / PAN composite material in Example 4 is 1.93 W / (m·K), which is about 26.94% higher than that of BZCT NFs / PAN (1.41) in Comparative Example 1. The thermal conductivity of the BZCT NFs@BNNS / PAN composite materials prepared in Examples 1 to 4 is significantly improved compared to the PAN matrix and BZCT NFs / PAN in Comparative Example 1. In addition, the thermal conductivity of the BZCT NFs@BNNS / PAN composite material prepared in Example 1 is also significantly improved compared to Comparative Examples 2 to 4 with BZCT NFs@AlN, carbon nanotubes and other substances as fillers, and Comparative Example 5 with PVDF as the polymer substrate, indicating that the improvement effect of the BZCT NFs@BNNS core-shell structure nanofibers of the present invention as fillers on the various properties of PAN is significantly higher than that of the uncoated BZCT NFs, BZCT NFs@AlN and carbon nanotubes and other fillers, and the high thermal conductivity of the composite material is achieved by the synergistic cooperation between the BZCT NFs inner core, the BNNS shell layer and the PAN matrix.

[0115] Test Example 4

[0116] The BZCT NFs@BNNS / PAN composite material prepared in Example 1 and the BZCT NFs / PAN composite material prepared in Comparative Example 1 were taken for the test of energy storage density. After testing, the energy storage densities of BZCT NFs / PAN and BZCT@BNNS / PAN at room temperature (25°C) are 2.51 J / cm 3 and 12.23 J / cm 3 , respectively, indicating that the introduction of the BNNS shell layer significantly improves the energy storage characteristics of the composite material.

[0117] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the spirit of the present invention's design, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A high thermal conductivity composite material, characterized in that: The composite material is obtained by combining core-shell structure nanofibers and polymers; the core-shell structure nanofibers are composed of barium calcium zirconate titanate nanofibers and boron nitride nanosheet shells coated on the surface of the barium calcium zirconate titanate nanofibers; the polymer is polyacrylonitrile; the preparation method of the high thermal conductivity composite material comprises the following steps: (1) Preparation of core-shell nanofibers BZCTNFs@BNNS: Ba(OH)2·8H2O and Ca(OH)2 were dissolved in a mixed solvent of CH3COOH, C5H8O2 and CH3CH2OH to form a stable solution, and then (C5H8O2)4·Zr, C 16 H 36 O4Ti and PVP, by mass ratio, Ba (OH)2·8H2O:Ca(OH)2:CH3COOH:C5H8O2:CH3CH2OH:(C5H8O2)4·Zr:C 16 H 36 O4Ti:PVP=32:1:1:9:3:5:37:8, heated in a water bath at 60℃ with stirring until a stable solution is formed to obtain a one-dimensional BZCT NFs precursor solution; BNNS and PVP are added to a CH3CH2OH solvent, and the mass ratio is BNNS:PVP:CH3CH2OH=2:1:2, heated in a water bath at 60℃ with stirring until a stable solution is formed to obtain a BNNS precursor solution; then, the BNNS precursor solution is used as the shell and the one-dimensional BZCT NFs precursor solution is used as the core. The coaxial spinning needle has a specification of 16G / 22G, a positive and negative voltage of 15kV, a spinning distance of 15cm, and a one-dimensional BZCT The NFs precursor solution and the BNNS precursor solution were coaxially electrospun at spinning speeds of 0.3 mL / h and 0.4 mL / h, respectively. The nanofibers obtained by coaxial electrospinning were transferred to an oven for drying at 90° C. for 4 h, and then transferred to a muffle furnace for heat treatment at 950° C. for 4 h. After naturally cooling to room temperature, BZCTNFs@BNNS core-shell structured nanofibers were obtained. The thickness of the BNNS shell layer of the BZCTNFs@BNNS core-shell structured nanofibers was 15 nm. (2) Preparation of BZCTNFs@BNNS / PAN composites: BZCT NFs@BNNS core-shell structure nanofibers and PAN were weighed at a volume ratio of 2:10, PAN was added to DMF solvent to completely dissolve, and then BZCT NFs@BNNS core-shell structure nanofibers were added, magnetic stirring was performed for 20 hours, and then ultrasonic dispersion treatment was performed for 6 hours to obtain a composite material solution; the composite material solution was poured into a culture dish with a smooth and clean inner wall, and placed in a vacuum drying oven for drying at 60°C for 14 hours to obtain a composite film, and the composite film was removed from the culture dish by demolding with ice water, and then the composite film was rinsed with deionized water, and allowed to stand at room temperature to dry to obtain a BZCT NFs@BNNS / PAN composite material, which is the high thermal conductivity composite material.

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