A porous structure of nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material and a preparation method thereof

Abstract

The application discloses a porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material and a preparation method thereof. The porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material is prepared by taking polyimide as a matrix and nickel selenide-carbon nanotube microspheres as multi-component fillers, and has the properties of electrical conductivity, heat insulation, compression resistance and electromagnetic wave absorption.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic protection, and particularly relates to a porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material and a preparation method thereof. BACKGROUND

[0002] With the progress of science and technology, various electronic devices and communication systems play a vital role in people's daily life and social construction. However, due to the complexity of the actual application environment, the problems of electromagnetic wave (EMW) radiation and heat accumulation generated by these devices are increasingly prominent. Therefore, to reduce the harm of EMW to the human body and the environment, and to meet the application requirements in harsh environments, the development of integrated, multifunctional and high-performance EMW absorbing materials has become the focus of research.

[0003] Among the new generation of EMW absorbers, resin-based EMW absorbers have the characteristics of low density, high specific strength, good processing performance, and unique corrosion resistance, and are ideal materials for the aerospace industry. Polyimide (PI) is a kind of aromatic heterocyclic polymer containing imide groups. Its structure is derived from the polyamide acid generated by the melt polycondensation or solution polycondensation of aromatic diamine and aromatic dianhydride, and then it is formed by thermal or chemical imidization. Compared with traditional resin matrix materials, polyimide (PI) resin has high temperature thermal oxidation stability, reasonable dielectric properties, high radiation resistance, solvent resistance and high mechanical strength due to its special structure of five-membered heterocyclic ring. It is considered to be one of the most important dielectric materials that can be used in the fields of heat insulation, pressure resistance and high-efficiency EMW absorption function integration, and is widely used in the field of high-performance structure and function integrated materials. Enhancing the polymer matrix by functional powder is a common method for preparing functional materials. However, in order to fully exert the reinforcing effect of functional powder on the polymer matrix, three conditions need to be met: (1) the functional powder is uniformly dispersed in the matrix; (2) the functional powder itself has excellent mechanical properties; (3) the powder and the matrix have strong bonding force to realize effective transmission of external load. SUMMARY

[0004] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material and a preparation method thereof. The porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material with a porous foam structure is prepared by taking polyimide as a matrix and nickel selenide-carbon nanotube microspheres as a multi-component filler, which has conductivity, heat insulation, compression resistance and electromagnetic wave absorption performance.

[0005] In order to achieve the above technical purpose, the technical scheme adopted by the present application is as follows:

[0006] The application relates to a preparation method of a porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material.

[0007] (1) carbon nanotubes, a sugar, a nickel salt and selenium powder are dispersed in deionized water to obtain a mixed solution A; the mixed solution A is subjected to ultrasonic atomization and then is sent to a tubular furnace through an inert carrier gas for heating deposition to obtain nickel selenide-carbon nanotube microspheres;

[0008] (2) the nickel selenide-carbon nanotube microspheres are dispersed in deionized water to obtain a mixed solution B; polyamide acid and triethanolamine are dispersed in deionized water to obtain a mixed solution C; then the mixed solution B and the mixed solution C are uniformly mixed to obtain a mixed solution D; the mixed solution D is subjected to freeze drying to obtain nickel selenide-carbon nanotube microspheres / polyamide acid;

[0009] (3) the nickel selenide-carbon nanotube microspheres / polyamide acid are subjected to amidation to obtain the porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material.

[0010] Further, in the step (1), the mass ratio of the carbon nanotubes, the sugar, the nickel salt and the selenium powder is 2-6:1:1-4:1-3; the sugar is maltose, sucrose or glucose; the nickel salt is nickel nitrate, nickel sulfate or nickel chloride.

[0011] Further, in the step (1), the inert carrier gas is nitrogen, argon or helium; the temperature for the heating deposition is 500-700 DEG C.

[0012] Further, in the step (2), the dosages of the nickel selenide-carbon nanotube microspheres, the polyamide acid and the triethanolamine are 0.1-0.2 g:1-2 g:0.5-1 ml.

[0013] Further, in the step (2), the temperature for the freeze drying is-25--45 DEG C, and the time is 3-5 h.

[0014] Further, in the step (3), the amidation process is as follows: first, the temperature is raised to 120-150 DEG C and is kept for 0.5-1 h; then, the temperature is raised to 220-250 DEG C and is kept for 0.5-1 h; finally, the temperature is raised to 320-350 DEG C and is kept for 1-3 h.

[0015] The application further provides the nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material prepared by the above preparation method.

[0016] The present application grows carbon nanotubes on nickel selenide to form a microsphere structure of elongated carbon nanotubes interlaced with nickel selenide, which combines the wave-absorbing performance of nickel selenide / carbon nanotube microspheres and the wave-transmitting performance of PI, maximizes the electromagnetic wave loss capacity, and the high thermal stability and high glass transition temperature of PI help to stabilize the nickel selenide / carbon nanotube microspheres, prevent them from aggregating, and improve the dispersibility of the composite material. On the other hand, the carbon nanotubes are interlaced with nickel selenide and attached to the surface of the three-dimensional porous crosslinked network framework to form a multiple heterojunction structure, which provides an effective electron transport path and multiple interface polarization, is conducive to the multiple dissipation of electromagnetic waves, and significantly improves the electromagnetic wave absorbing capacity of the material. The magnetic nickel selenide increases the magnetic loss effects of the material, such as eddy current loss, natural resonance and exchange resonance, and the excellent electrical conductivity of the carbon nanotube endows the material with electric conduction loss and dielectric relaxation effect. Therefore, the material of the present application has both magnetic loss and dielectric loss characteristics, and combines the three-dimensional network porous foam structure of polyimide as a support framework for dielectric and magnetic loss materials to adjust the impedance matching, so that the material has a wide effective absorption frequency band and strong reflection loss performance at low thickness.

[0017] Firstly, the suitable electrical conductivity and porous structure enable the nickel selenide-carbon nanotube microsphere / polyimide composite material to have good impedance matching ability, which can reduce the reflection of incident electromagnetic waves and create opportunities for more electromagnetic waves to enter the material; secondly, the electromagnetic waves entering the porous structure will be trapped in the maximum propagation path constructed by nickel selenide-carbon nanotube microspheres and PI matrix for multiple reflections and scattering, so that the electromagnetic waves cannot escape from the limited space before being completely absorbed; thirdly, the nickel selenide-carbon nanotube microspheres form a non-uniform strong surface current under the action of alternating electromagnetic field, which is conducive to the movement, migration and jumping of free electrons on the heterogeneous structure interface of the nickel selenide-carbon nanotube microsphere / polyimide composite material, resulting in multiple polarization relaxation such as interface strong polarization and dipole polarization. Therefore, the porous structure of the present application and the nickel selenide-carbon nanotube microsphere multi-component conductive filler synergistically enhance the electromagnetic wave absorption, so that the nickel selenide-carbon nanotube microsphere / polyimide porous composite material has excellent EMW absorption effect.

[0018] The advantages of the present application are:

[0019] (1) The nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material of the present application can effectively adjust the dielectric performance to improve the impedance matching and attenuation ability, thereby enhancing the multifunctional EMW absorption performance of the PI composite material. The CNTs with three-dimensional tubular network structure and the NiSe2 with adjustable structure and high stability are randomly distributed in the PI matrix to form a complex conductive network, thereby forming a good rigid filler framework, which enhances the skeleton strength of the PI composite material and thus enhances the electromagnetic wave absorption performance of the PI composite material.

[0020] (2) The selenium nickel-carbon nanotube microsphere / polyimide composite wave-absorbing material of the present application has a porous structure, which not only prolongs the propagation path of electromagnetic waves, but also improves the uniform distribution of the conductive filler, builds a complete conductive network, enhances multiple reflection and scattering, and optimizes the electromagnetic wave absorption performance of PI.

[0021] (3) The present application uses ultrasonic atomization to prepare NiSe2 / CNTs microspheres in one step, and the liquid can be uniformly and quickly atomized into small particles, ensuring the uniformity and consistency of the material. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 XRD diffraction pattern of the NiSe2 / CNTs microspheres prepared in Example 1;

[0023] As Figure 1 shown, the diffraction peaks of pure NiSe2 appear obviously at 29.96°, 33.59°, 36.91°, 42.88°, 50.76°, 55.54° and 57.84°, corresponding to (200), (210), (211), (220), (311), (023) and (321) crystal planes (standard card PDF #65-1843), respectively, confirming the high phase purity of the NiSe2 sample; compared with pure NiSe2, the NiSe2 / CNTs microspheres have an additional peak at 26.54°, which is derived from the (002) crystal plane of CNTs (standard card PDF #26-1706), indicating the successful synthesis of NiSe2 / CNTs microspheres, while effectively maintaining the high purity of NiSe2.

[0024] Figure 2 SEM image of the NiSe2 / CNTs microspheres prepared in Example 1;

[0025] As Figure 2 shown, the microspherical NiSe2 / CNTs were successfully prepared after ultrasonic atomization, i.e. the elongated carbon nanotubes randomly intertwined and wrapped around the nickel selenide to form a spherical shape.

[0026] Figure 3 SEM image and wave-absorbing performance diagram of NIP prepared in Comparative Example 1;

[0027] As Figure 3 (a) shown, NIP forms a structure with small pores and high porosity; Figure 3 (b, c) are the three-dimensional and two-dimensional reflection loss (RL) diagrams of NIP, NIP only obtains a RL of -12.25 dB at a frequency band of 2.85 mm and 9.88 GHz min and an EAB of 0.71 GHz.

[0028] Figure 4SEM images and wave-absorbing performance of NICP-1 prepared in Example 1;

[0029] As shown in Figure 4 (a), the pore size of NICP-1 is obviously increased, which is due to the random distribution of CNTs with three-dimensional tubular network structure in the PI matrix, forming a dense conductive network, thus forming a good rigid filler framework, which makes the PI composite enhance the skeleton strength and limit the volume shrinkage in the thermal amide process; Figure 4 (b, c) are three-dimensional and two-dimensional reflection loss (RL) images of NICP-1, compared with NIP of Comparative Example 1, the RL of NICP-1 reaches -39.06 dB at 10.41 GHz and 1.62 mm, and the EAB increases to 1.98 GHz. min

[0030] Figure 5 SEM images and wave-absorbing performance of NICP-2 prepared in Example 2;

[0031] As shown in Figure 5 (a), the pore size of NICP-2 is also obviously increased compared with NIP; Figure 5 (b, c) are three-dimensional and two-dimensional reflection loss (RL) images of NICP-2, compared with NIP of Comparative Example 1, the RL of NICP-2 reaches -58.89 dB at 11.35 GHz and 1.57 mm, and the EAB increases to 3.23 GHz. min DETAILED DESCRIPTION

[0032] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0033] Example 1

[0034] A preparation method of a porous structure nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material, comprising the following steps:

[0035] (1) Disperse carbon nanotubes and sucrose in 60 ml of deionized water at a mass ratio of 2:1, then add nickel chloride and selenium powder at a mass ratio of 2:3, and stir magnetically at room temperature for 12 hours to obtain a mixed solution A; the mixed solution A is sent to an ultrasonic atomizer and transported to a tube furnace by an argon gas flow, and deposited at 500°C, and cooled to room temperature to obtain NiSe2 / CNTs microspheres;

[0036] ​​(2) 0.1 g of NiSe2 / CNTs was ultrasonically dispersed in 5 ml of deionized water for 1 h to obtain a mixed solution B; 1 g of PAA and 0.66 ml of TEA were dissolved in 13.52 ml of deionized water and stirred for 5 h to obtain a mixed solution C; then the mixed solution B was added to the mixed solution C and mixed uniformly to obtain a mixed solution D; the mixed solution D was freeze-dried at -45℃ for 5 h to obtain NiSe2 / CNTs / PAA;

[0037] (3) The NiSe2 / CNTs / PAA was first kept at 150℃ for 0.5 h, then kept at 250℃ for 0.5 h, and finally kept at 350℃ for 2 h for gradient temperature programmed amidation to obtain a nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material, denoted as NICP-1.

[0038] In order to intuitively observe the heat preservation performance of the composite material, an infrared thermal imager was used to record the top surface temperature of the sample on the heating platform; a mechanical property test was performed by referring to the ASTM C1341-06 standard using an electronic universal testing machine; and a vector network analyzer was used to test the dielectric constant and wave-absorbing performance of the material in the frequency range of 8.2-12.4 GHz according to the ASTM D-5568 standard.

[0039] Test results show that the lowest top surface temperature of the NICP-1 wave-absorbing material is 45.2℃; the highest compressive strength and compressive modulus are 2107.93 Kpa and 2359.31 Kpa, respectively; the minimum reflection loss at 1.62 mm is -39.06 dB, and the effective absorption bandwidth is 1.98 GHz.

[0040] Example 2

[0041] A method for preparing a porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material, comprising the following steps:

[0042] (1) Carbon nanotubes and sucrose were dispersed in 60 ml of deionized water at a mass ratio of 4:1, and then nickel chloride and selenium powder were added at a mass ratio of 4:3, and after magnetic stirring at room temperature for 12 hours, a mixed solution A was obtained; the mixed solution A was sent to an ultrasonic atomizer and transported to a tube furnace by an argon gas flow, and deposited at 500℃, and then cooled to room temperature to obtain NiSe2 / CNTs microspheres;

[0043] (2) 0.1 g of NiSe2 / CNTs was ultrasonically dispersed in 5 ml of deionized water for 1 h to obtain a mixed solution B; 1 g of PAA and 0.66 ml of TEA were dissolved in 13.52 ml of deionized water and stirred for 5 h to obtain a mixed solution C; then the mixed solution B was added to the mixed solution C and mixed uniformly to obtain a mixed solution D; the mixed solution D was freeze-dried at -45℃ for 5 h to obtain NiSe2 / CNTs / PAA;

[0044] (3) The NiSe2 / CNTs / PAA is first kept at 150℃ for 0.5 h, then kept at 250℃ for 0.5 h, and finally kept at 350℃ for 2 h for gradient temperature programming amidation to obtain a nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material, denoted as NICP-2.

[0045] The lowest top surface temperature of the NICP-2 wave-absorbing material is 40.3℃; the highest compressive strength and compressive modulus are 2729.69 Kpa and 2912.12 Kpa, respectively; the minimum reflection loss at 1.57 mm is -58.89 dB, and the effective absorption bandwidth is 3.23 GHz.

[0046] Comparative Example 1

[0047] A preparation method of a nickel selenide / polyimide composite material, comprising the following steps:

[0048] (1) Nickel chloride, selenium powder and sucrose with a mass ratio of 4:3:1 are dispersed in 60 ml of deionized water, and after magnetic stirring at room temperature for 12 hours, a mixed solution A is obtained; the mixed solution A is sent to an ultrasonic atomizer and transported to a tube furnace by an argon gas flow, and deposited at 500℃, and cooled to room temperature to obtain NiSe2;

[0049] (2) 0.1 g of NiSe2 is ultrasonically dispersed in 5 ml of deionized water for 1 h to obtain a mixed solution B; 1 g of PAA and 0.66 ml of TEA are dissolved in 13.52 ml of deionized water, and stirred for 5 h to obtain a mixed solution C; then the mixed solution B is added to the mixed solution C, and mixed thoroughly to obtain a mixed solution D; the mixed solution D is freeze-dried at -45℃ for 5 h to obtain NiSe2 / PAA.

[0050] (3) The NiSe2 / PAA is first kept at 150℃ for 0.5 h, then kept at 250℃ for 0.5 h, and finally kept at 350℃ for 2 h for gradient temperature programming amidation to obtain a nickel selenide / polyimide composite wave-absorbing material, denoted as NIP.

[0051] The lowest top surface temperature of the NIP wave-absorbing material is 53.6℃; the highest compressive strength and compressive modulus are 1228.39 Kpa and 1526.61 Kpa, respectively; the minimum reflection loss at 2.85 mm is -12.25 dB, and the effective absorption bandwidth is 0.71 GHz.

[0052] Comparative Example 2

[0053] A preparation method of a porous nickel selenide-carbon nanotube / polyimide composite wave-absorbing material, comprising the following steps:

[0054] Step 1: CNTs were dispersed into 10 ml deionized water, and ultrasonic treatment was performed for 1 h to prepare a CNTs dispersion solution (5 mg / ml).

[0055] Step 2: 1 mmol NiCl2·6H2O, 180 mg Se and 3 g KOH were added to the CNTs dispersion solution, and magnetic stirring was performed for 30 min to dissolve uniformly.

[0056] Step 3: The mixed solution was subjected to hydrothermal reaction at 150℃ for 12 h, and after the reaction was naturally cooled, the hydrothermal product was centrifuged at 8000 rpm / min for 5 min, and then removed with anhydrous ethanol.

[0057] Step 4: Finally, the product was washed in ionized water for 3 times alternately, and vacuum dried at 70℃ for 24 h to obtain a NiSe2 / CNTs composite material.

[0058] Step 5: 1 g PAA and 0.66 ml TEA were dissolved in 13.52 ml deionized water, and stirred for 5 h to form a uniform solution.

[0059] Step 6: After 0.1 g NiSe2 / CNTs were ultrasonically dispersed in 5 ml deionized water for 1 h, the uniform solution was added and stirred for 5 h, and the obtained mixed solution was frozen at -50℃ for 5 h, and then freeze-dried for 48 h to obtain NiSe2 / CNTs / PAA.

[0060] Step 7: The product obtained in step 6 was subjected to a gradient temperature programmed amidation at 150℃ / 0.5 h, 250℃ / 0.5 h and 350℃ / 2 h, respectively, and after the heating was completed, the obtained nickel selenide / carbon nanotube / polyimide porous composite material was named as NICP-3.

[0061] It was tested that the prepared NICP-3 wave absorbing material had a minimum top surface temperature of 50.4℃; the maximum compressive strength and compressive modulus were 1545.96 Kpa and 1737.62 Kpa, respectively; the minimum reflection loss at 1.60 mm was -17.89 dB, and the effective absorption bandwidth was 0.93 GHz.

[0062] Comparative Example 3

[0063] A preparation method of a porous structure nickel selenide-carbon microsphere / polyimide composite wave absorbing material, comprising the following steps:

[0064] Step 1: Mesocarbon microbeads (MCMB) were dispersed into 10 ml deionized water, and ultrasonic treatment was performed for 1 h to prepare a MCMB dispersion solution (5 mg / ml).

[0065] Step 2: 1 mmol of NiCl2·6H2O, 180 mg of Se and 3 g of KOH were added to the CNTs dispersion solution, and magnetic stirring was performed for 30 min to make them uniformly dissolved.

[0066] Step 3: The mixed solution was hydrothermally reacted at 150℃ for 12 h, and after the reaction was naturally cooled, the hydrothermal product was centrifuged at 8000 rpm / min for 5 min, and then removed with anhydrous ethanol.

[0067] Step 4: Finally, the product was washed in ionized water for 3 times alternately, and vacuum dried at 70℃ for 24 h to obtain the NiSe2 / MCMB composite material.

[0068] Step 5: 1 g of PAA and 0.66 ml of TEA were dissolved in 13.52 ml of deionized water, and stirred for 5 h to form a uniform solution.

[0069] Step 6: After 0.1 g of NiSe2 / MCMB was ultrasonically dispersed in 5 ml of deionized water for 1 h, the uniform solution was added and stirred for 5 h, and the obtained mixed solution was frozen at -50℃ for 5 h, and then freeze-dried for 48 h to obtain NiSe2 / MCMB / PAA.

[0070] Step 7: The product obtained in step 6 was subjected to a gradient temperature program amidation at 150℃ / 0.5 h, 250℃ / 0.5 h and 350℃ / 2 h respectively, and after the heating was completed, the obtained nickel selenide-carbon microsphere / polyimide porous composite material was named as NICP-4.

[0071] It was tested that the prepared NICP-4 wave absorbing material had a lowest top surface temperature of 51.7℃, had poor heat preservation performance, had a highest compressive strength and compressive modulus of 1503.34 Kpa and 1692.75 Kpa respectively, had a minimum reflection loss of -18.21 dB at 1.58 mm, and had an effective absorption bandwidth of 0.98 GHz.

[0072] Comparative Example 4

[0073] A preparation method of a porous structure nickel selenide-carbon black microsphere / polyimide composite wave absorbing material, comprising the following steps:

[0074] Step 1: Carbon black (CB) and sucrose were dispersed in 60 ml of deionized water at a mass ratio of 4:1, and then nickel chloride and selenium powder were added at a mass ratio of 4:3.

[0075] Step 2: After the mixed solution obtained in step 1 was magnetically stirred at room temperature for 12 hours, it was sent to an ultrasonic atomizer for atomization.

[0076] Step 3: Then transported into a tube furnace under argon flow, deposited at 500℃, after cooling to room temperature, NiSe2 / CB microspheres were obtained.

[0077] Step 4: 1g PAA and 0.66 ml TEA were dissolved in 13.52 ml deionized water, stirred for 5h to form a uniform solution.

[0078] Step 5: After ultrasonic dispersion of 0.1g NiSe2 / CB obtained in step 3 in 5ml deionized water for 1h, the uniform solution obtained in step 4 was added and stirred for 5h, the obtained mixed solution was frozen at-45℃ for 5h, then freeze-dried for 48h to obtain NiSe2 / CB / PAA.

[0079] Step 6: The product obtained in step 5 was subjected to a gradient temperature program amidation at 150℃ / 0.5h, 250℃ / 0.5h and 350℃ / 2h respectively, after heating, the obtained nickel selenide-carbon black microspheres / polyimide porous composite material was named NICP-5.

[0080] Tested, the prepared NICP-5 wave absorbing material has the lowest top surface temperature of 52.8℃, poor heat preservation performance; the highest compressive strength and compressive modulus are 1483.67Kpa and 1547.39Kpa respectively; the minimum reflection loss at 1.85mm is-16.97dB, and the effective absorption bandwidth is 0.86GHz.

Claims

1. A method for preparing a porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material, characterized in that, The preparation method comprises the following steps: (1) dispersing carbon nanotubes, sugar, nickel salt and selenium powder in deionized water to obtain a mixed solution A; the mixed solution A is atomized by ultrasonic and then sent to a tubular furnace by inert carrier gas for heating deposition to obtain nickel selenide-carbon nanotube microspheres; (2) dispersing the nickel selenide-carbon nanotube microspheres in deionized water to obtain a mixed solution B; dispersing polyamide acid and triethanolamine in deionized water to obtain a mixed solution C; then mixing the mixed solution B and the mixed solution C to obtain a mixed solution D; freeze-drying the mixed solution D to obtain nickel selenide-carbon nanotube microspheres / polyamide acid; (3) amidating the nickel selenide-carbon nanotube microspheres / polyamide acid to obtain porous nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material.

2. The production method according to claim 1, characterized by, In step (1), the mass ratio of the carbon nanotubes, the sugar, the nickel salt and the selenium powder is 2-6:1:1-4:1-3; the sugar is maltose, sucrose or glucose; the nickel salt is nickel nitrate, nickel sulfate or nickel chloride.

3. The preparation method according to claim 1, characterized in that, In step (1), the inert carrier gas is nitrogen, argon or helium; the temperature for heating deposition is 500-700℃.

4. The method of claim 1, wherein, In step (2), the amount of the nickel selenide-carbon nanotube microspheres, the polyamide acid and the triethanolamine is 0.1-0.2 g:1-2 g:0.5-1 ml.

5. The preparation method according to claim 1, characterized in that, In step (2), the temperature for freeze-drying is-25--45℃, and the time is 3-5 h.

6. The method of claim 1, wherein, In step (3), the amidation process is: first, heating to 120-150℃ for 0.5-1 h, then heating to 220-250℃ for 0.5-1 h, and finally heating to 320-350℃ for 1-3 h.

7. The nickel selenide-carbon nanotube microsphere / polyimide composite wave-absorbing material prepared by the preparation method of any one of claims 1-6.

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