Nitrogen heterocyclic covalent organic framework material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electrochemical materials, and discloses a nitrogen heterocyclic covalent organic framework material, the chemical formula is (C42H18N12) n, and n is a positive integer greater than or equal to 4; the preparation method comprises the following steps: S1, in an inert atmosphere, adding a hexaaza-trinaphthalene-2, 3, 8, 9, 14, 15-hexa-halogen substitute, 2, 3, 6, 7, 10, 11-hexaamino triphenylene hexachloride, a deprotonation reagent, bis (1, 5-cyclooctadiene) rhodium tetrafluoroborate (I) and 1, 3-diisopropyl imidazole chloride into an organic solvent according to a molar ratio of 1: (1-1.5): (9-18): (0.02-0.12): (0.04-0.25), uniformly mixing, reacting for 1-7 days at the temperature of 50-150 DEG C, filtering, washing, and drying to obtain a target product. Naturally cooling to room temperature, filtering and collecting precipitate to obtain a crude product; s2, washing and drying the crude product in the S1 to prepare the azacyclo-covalent organic framework material; the material is applied to a negative electrode material and a positive electrode material of a lithium ion battery. According to the scheme, the problems that an existing covalent organic framework material is poor in rate capability and limited in application range are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical materials, and in particular to a nitrogen heterocyclic covalent organic framework material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in new energy vehicles, energy storage systems and various consumer electronic products due to their outstanding energy density advantages. For lithium-ion batteries, electrode materials are the key factors that determine the energy density, power density and cycle life of their energy storage devices. The electrode materials used in traditional lithium-ion batteries are mostly inorganic materials such as carbon materials or transition metal compounds. Among them, although carbon materials have certain characteristics, their actual capacity is low and it is difficult to meet the growing high-performance requirements; transition metal compounds are heavily dependent on scarce natural resources, which limits large-scale applications and keeps battery costs high. In view of the wider application needs of lithium-ion batteries in the future, it is urgently necessary to develop electrode materials with both high specific capacity and resource sustainability to push their energy density and power density to new heights.

[0003] Covalent organic frameworks (COFs) came into being. They are crystalline organic polymers connected by covalent bonds from widely available and abundant light elements such as C, H, N, O, B and S. The most notable feature of COFs is that they have regular doping of heteroelements and a unique porous structure. When used as electrode materials, they can provide ample active sites for lithium-ion storage, have high specific capacity and excellent rate performance, and show great potential in the preparation of lithium-ion batteries with both high energy density and high power density.

[0004] The technical solution with patent number CN112920405B discloses a thin layer covalent organic framework material connected by irreversible bonds and its preparation method and application. The preparation process is as follows: 2,3,6,7,10,11-hexabromotriphenylene, 2,3,6,7,10,11-hexaaminotriphenylene hexahydrochloride, a deprotonating agent, bis(1,5-cyclooctadiene) rhodium tetrafluoroborate (I) and N,N'-(isopropyl) imidazole chloride are weighed in a molar ratio of 1:(1-2):(7-14):(0.01-0.1):(0.02-0.2) and added to an organic solvent, mixed and reacted at 80-160°C for 3-15 days, and then solid-liquid separation was performed, and the solid phase was taken out and washed and dried to obtain the target material. All atoms in the prepared thin-layer covalent organic framework material are connected by irreversible piperazine rings, presenting a crystalline thin-layer COFs nanosheet form of orderly stacked single-layer COFs. This material has excellent chemical stability, good electrochemical lithium storage capacity and excellent cycle stability, providing a new direction for the development of negative electrode materials for lithium-ion batteries.

[0005] However, this material has obvious shortcomings. On the one hand, its rate performance is poor, which is particularly prominent in some scenarios with extremely high power requirements. For example, in the rapid acceleration of electric vehicles, emergency braking energy recovery, or some industrial equipment emergency power supply applications that require instantaneous high power output, due to its poor rate performance, it is difficult to charge and discharge quickly and efficiently, and it is difficult to meet the supply demand of instantaneous high current, resulting in limited equipment operation efficiency and even possible power shortage; on the other hand, at this stage, this material can only be used in the negative electrode of lithium-ion batteries. This limitation greatly restricts its application scope, making it difficult to play a role in a wider range of battery-related fields. Summary of the invention

[0006] The present invention aims to provide a nitrogen heterocyclic covalent organic framework material and a preparation method and application thereof, so as to solve the problems of poor rate performance and limited application range of existing covalent organic framework materials.

[0007] To achieve the above object, the present invention adopts the following technical scheme: a nitrogen heterocyclic covalent organic framework material, the chemical formula of which is (C 42 H 18 N 12 ) n , whose structural formula is:

[0008]

[0009] In the formula, n is a positive integer greater than or equal to 4.

[0010] The present invention also provides another technical solution, a method for preparing a nitrogen heterocyclic covalent organic framework material, comprising the following steps:

[0011] S1: Under an inert atmosphere, add hexaazatrinaphthyl-2,3,8,9,14,15-hexahalogen substituted product, 2,3,6,7,10,11-hexaaminotriphenylene hexahydrochloride, a deprotonating agent, bis(1,5-cyclooctadiene) rhodium tetrafluoroborate (I) and 1,3-diisopropylimidazole chloride in a molar ratio of 1:(1-1.5):(9-18):(0.02-0.12):(0.04-0.25) to an organic solvent, mix well, react at 50-150° C. for 1-7 days, cool naturally to room temperature, filter and collect the precipitate to obtain a crude product;

[0012] S2: Wash and dry the crude product in S1 to obtain a nitrogen heterocyclic covalent organic framework material.

[0013] Preferably, in S1, the structural formula of the hexaazatrinaphthyl-2,3,8,9,14,15-hexahalogen substituted product is:

[0014]

[0015] Wherein, X is any one of Br, Cl and F.

[0016] Preferably, in S1, the deprotonating agent is any one of a strong organic base and an inorganic base.

[0017] Preferably, the organic strong base is any one of lithium tert-butoxide, sodium tert-butoxide and potassium tert-butoxide; the inorganic base is any one of sodium carbonate, potassium carbonate and cesium carbonate.

[0018] Preferably, in S1, the inert atmosphere is any one of nitrogen and argon.

[0019] Preferably, in S1, the organic solvent is any one of ethylene glycol dimethyl ether, dimethyl sulfoxide, N-methylpyrrolidone and toluene.

[0020] Preferably, the washing process in S2 is: first, the crude product in S1 is preliminarily washed with N,N-dimethylformamide, deionized water and tetrahydrofuran in sequence; after the preliminarily washing, the wet product that has not been dried is deeply washed by Soxhlet extraction, and tetrahydrofuran and methanol are used as extraction solvents in sequence for deep washing.

[0021] Preferably, in S2, the drying temperature is 100-120°C and the drying time is 24-48h.

[0022] The present invention also provides another technical solution, which is the application of a nitrogen heterocyclic covalent organic framework material in negative electrode materials and positive electrode materials of lithium ion batteries.

[0023] The beneficial effects of this scheme are as follows: the nitrogen heterocyclic covalent organic framework material provided by this technical scheme is prepared by Buchwald-Hartwig aromatic amination reaction, an irreversible C-NH-C nitrogen heterocyclic ring and a large number of highly active C=N are introduced, and the triphenylene group and the hexaazatrinaphthalene group are connected by the irreversible C-NH-C nitrogen heterocyclic ring, which has the following advantages:

[0024] (1) The nitrogen heterocyclic covalent organic framework material provided by this technical solution innovatively introduces a large number of C=N and benzene ring structures. These structures serve as active sites for lithium ions, greatly increasing the density of redox active sites, thereby laying a solid foundation for a significant increase in the theoretical capacity of the battery. Experimental results show that at a current density of 0.1A / g, the specific capacity can reach 938mAh / g after 100 cycles.

[0025] (2) In the nitrogen heterocyclic covalent organic framework material provided by the present technical solution, due to the introduction of triphenylene groups and hexaazatrinaphthyl groups, the proportion of conjugated aromatic structures is greatly increased, and the rate performance of the material is improved, so that it can maintain a good charge and discharge efficiency even at a high current density. Even at a high current density of up to 5A / g, the material can still maintain a good charge and discharge efficiency, and can quickly restore a high specific capacity when returning to a low current density.

[0026] (3) The nitrogen heterocyclic covalent organic framework material provided by the present technical solution exhibits excellent tolerance in strong acids, strong bases and organic solvents, ensuring the long-term reliability of the material in harsh environments and reducing performance loss due to material dissolution or degradation.

[0027] (4) The nitrogen heterocyclic covalent organic framework material provided by this technical solution breaks through the limitation of the prior art that it is only applied to negative electrodes. It can be used as both negative electrode material and positive electrode material of lithium-ion batteries, greatly broadening its application field. This is of great significance for the development of new high-performance energy storage devices.

[0028] (5) This technical solution uses widely available and abundant light elements to construct nitrogen heterocyclic covalent organic framework materials, which reduces dependence on scarce natural resources, conforms to the concept of green chemistry, and is conducive to promoting the development of lithium-ion batteries in a more environmentally friendly direction. The synthesis process of the material uses the Buchwald-Hartwig aromatic amination reaction to ensure efficient and controllable C-NH-C bond formation, achieving effective resource utilization and environmentally friendly manufacturing processes.

[0029] (6) This technical solution ensures the purity and performance of the material by optimizing the washing process: using N,N-dimethylformamide for pre-washing can effectively wash away the unreacted raw materials, residual catalysts and small molecular products after the reaction, laying the foundation for the subsequent washing steps and reducing the potential impact of impurities on the material performance; using deionized water for pre-washing can specifically wash away the inorganic salt NaBr produced by the reaction, avoiding the residual inorganic salt from affecting the electrochemical properties of the material and ensuring the chemical purity of the material; using tetrahydrofuran for pre-washing can, on the one hand, wash away the high boiling point solvents (DMF and H2O) used in the previous washing, and on the other hand, further remove the small molecular products remaining after the reaction, further improving the purity of the material. Using Soxhlet extraction method for deep washing, using tetrahydrofuran for Soxhlet extraction washing for the second time can ensure that the impurities that are difficult to remove are thoroughly washed. Then washing with methanol can achieve the replacement of solvent molecules in the pores, which is convenient for subsequent drying treatment, ensuring the integrity and purity of the internal structure of the material, and thus ensuring the performance stability of the material in application.

[0030] In summary, the present invention connects the triphenylene group and the hexaazatrinaphthalene group through an irreversible C-NH-C nitrogen heterocycle through an innovative structural design, and combines an efficient synthesis method (such as Buchwald-Hartwig aromatic amination reaction), and cooperates with an optimized washing process, thereby successfully overcoming the problems existing in the prior art. The prepared nitrogen heterocyclic covalent organic framework material has excellent performance in electrochemical performance, stability, rate characteristics, environmental sustainability, and other aspects, and the purity and performance of the material are guaranteed by fine washing. This material is suitable for positive and negative electrode materials of high-performance lithium-ion batteries, injecting new vitality into the development of the lithium-ion battery field, and is expected to occupy an important position in future energy storage systems, providing innovative technical solutions for solving global energy storage problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the molecular structure of the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention;

[0032] Figure 2 This is a SEM image of the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention;

[0033] Figure 3 This is an infrared spectrum of the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention;

[0034] Figure 4 This is the XRD pattern of the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention;

[0035] Figure 5 This is a solid-state NMR carbon spectrum of the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention;

[0036] Figure 6 The infrared spectra of the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention after being immersed in 12 mol / L sodium hydroxide solution, 12 mol / L hydrochloric acid solution, diethyl carbonate, acetonitrile, and dichloromethane for 7 days respectively;

[0037] Figure 7 A cycle performance diagram of a button cell assembled from the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention at a current density of 0.1 A / g;

[0038] Figure 8 The cyclic voltammetry curve of the button cell assembled with the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention as the negative electrode after activation;

[0039] Fig. 9 This is a rate performance diagram of a button cell assembled from the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention after activation;

[0040] Fig.10 This is a long cycle performance diagram of a button cell assembled from the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention at a current density of 5 A / g;

[0041] Fig.11 Cyclic voltammetry curves of button cells assembled with the nitrogen heterocyclic covalent organic framework material prepared in Example 1 of the present invention as the positive electrode at different scan rates;

[0042] Fig.12 This is a rate performance diagram of a button-type battery assembled from a thin layer of covalent organic framework material connected by irreversible bonds prepared in Comparative Example 1 of the present invention after activation. DETAILED DESCRIPTION

[0043] The following is further described in detail through specific implementation methods:

[0044] Example 1

[0045] A nitrogen heterocyclic covalent organic framework material, the chemical formula is (C 42 H 18 N 12 ) n , whose structural formula is:

[0046]

[0047] In the formula, n is a positive integer greater than or equal to 4.

[0048] A method for preparing a nitrogen heterocyclic covalent organic framework material comprises the following steps:

[0049] S1: Under an inert atmosphere, add hexaazatrinaphthyl-2,3,8,9,14,15-hexahalogen substituted product, 2,3,6,7,10,11-hexaaminotriphenylene hexahydrochloride, a deprotonating agent, bis(1,5-cyclooctadiene) rhodium tetrafluoroborate (I) and 1,3-diisopropylimidazole chloride in a molar ratio of 1:(1-1.5):(9-18):(0.02-0.12):(0.04-0.25) to an organic solvent, mix well, react at 50-150° C. for 1-7 days, cool naturally to room temperature, filter and collect the precipitate to obtain a crude product;

[0050] Wherein, the hexaazatrinaphthyl-2,3,8,9,14,15-hexahalogen substituted product is any one of 2,3,8,9,14,15-hexabromohexaazanaphthalene, 2,3,8,9,14,15-hexachlorohexaazanaphthalene, and 2,3,8,9,14,15-hexafluorohexaazanaphthalene;

[0051] The structural formula of hexaazatrinaphthalene-2,3,8,9,14,15-hexahalogen substituted is:

[0052]

[0053] Wherein, X is any one of Br, Cl and F;

[0054] The structural formula of 2,3,6,7,10,11-hexaminotriphenylene hexahydrochloride is:

[0055]

[0056] The deprotonating agent is any one of an organic strong base and an inorganic base; wherein the organic strong base is any one of lithium tert-butoxide, sodium tert-butoxide and potassium tert-butoxide; and the inorganic base is any one of sodium carbonate, potassium carbonate and cesium carbonate;

[0057] The organic solvent is any one of ethylene glycol dimethyl ether, dimethyl sulfoxide, N-methylpyrrolidone and toluene;

[0058] The inert gas is any one of nitrogen and argon;

[0059] In this embodiment, in a glove box with an argon atmosphere, 2,3,8,9,14,15-hexabromohexaazonaphthalene (abbreviated as HATN-Br6), 2,3,6,7,10,11-hexaaminotriphenylene hexahydrochloride (abbreviated as HATP-6HCl), sodium tert-butoxide, bis(1,5-cyclooctadiene) tetrafluoroborate rhodium (I) and 1,3-diisopropylimidazole chloride were added to a thick-walled pressure-resistant reaction tube containing ethylene glycol dimethyl ether in a molar ratio of 1:1:15:0.05:0.1, wherein the amount of ethylene glycol dimethyl ether was 8 mL. Subsequently, a sealing operation was performed, and the reaction tube was removed from the glove box. After ultrasonic dispersion for 30 minutes, the reaction tube was placed in an oven at 120° C. and reacted for 3 days. After the reaction system was naturally cooled to room temperature, the precipitate was collected by filtration to obtain a crude product.

[0060] S2: Wash the crude product in S1 and vacuum dry it to obtain a nitrogen heterocyclic covalent organic framework material; the washing process is: first use N, N-dimethylformamide, deionized water, and tetrahydrofuran to perform preliminary washing on the crude product in S1, and after preliminary washing, use Soxhlet extraction to perform deep washing on the wet product that has not been dried, and use tetrahydrofuran and methanol as extraction solvents to perform deep washing; place the washed product in a vacuum drying oven, dry it at 100-120°C for 24-48h, and obtain a reddish brown solid product PIPHATN COF, i.e., a nitrogen heterocyclic covalent organic framework material. In this embodiment, the drying temperature is 120°C and the drying time is 24h.

[0061] The invention discloses an application of a nitrogen heterocyclic covalent organic framework material, which is used in negative electrode materials and positive electrode materials of lithium-ion batteries.

[0062] Figure 1 The molecular structure diagram of the nitrogen heterocyclic covalent organic framework material prepared in Example 1 is as follows: Figure 1 It can be seen that the nitrogen heterocyclic covalent organic framework material is a two-dimensional COF material obtained by connecting triphenylene and hexaazatrinaphthalene through C-NH-C nitrogen heterocyclic ring and expanding in the two-dimensional direction.

[0063] The nitrogen heterocyclic covalent organic framework material prepared in Example 1 was photographed and observed using a scanning electron microscope. The results are as follows: Figure 2 As shown, the nitrogen heterocyclic covalent organic framework material is a strip structure composed of small flakes stacked together, which is conducive to the rapid transmission of lithium ions and improves the rate performance.

[0064] The nitrogen heterocyclic covalent organic framework material prepared in Example 1 was detected and analyzed using infrared spectroscopy detection technology. Figure 3 It can be seen that there is no 600cm -1 The C-Br peak near 1514 cm -1 and 838cm -1 The in-plane bending vibration mode and out-of-plane bending vibration mode of the NH bond in the piperazine linker are shown at 3332 cm -1 The stretching vibration mode of the NH bond is shown at 1089cm -1 The CN asymmetric stretching vibration mode of the piperazine bond is exhibited at the reaction site. The above experimental results fully illustrate the transformation from reactants to products.

[0065] The nitrogen heterocyclic covalent organic framework material prepared in Example 1 was tested and analyzed using X-ray diffraction technology. Figure 4 It can be seen that the nitrogen heterocyclic covalent organic framework material exhibits diffraction peaks at 8.9°, 24.5° and 42°, corresponding to the two-dimensional stacked (100), (001) and (110) crystal planes, respectively, proving that the nitrogen heterocyclic covalent organic framework material has been successfully synthesized.

[0066] The nitrogen heterocyclic covalent organic framework material prepared in Example 1 was detected and analyzed by solid nuclear magnetic carbon spectroscopy technology. Figure 5 It can be seen that the chemical shifts of different types of carbons connecting triphenylene and hexaazine by C-NH-C indicate that the nitrogen heterocyclic covalent organic framework material was successfully synthesized.

[0067] The nitrogen heterocyclic covalent organic framework material prepared in Example 1 was immersed in 12 mol / L sodium hydroxide solution, 12 mol / L hydrochloric acid solution, diethyl carbonate, acetonitrile, and dichloromethane for 7 days, filtered and washed with water and methanol, dried in vacuum at 120°C, and then analyzed by infrared spectroscopy. Figure 6 It can be seen that there is no change in the infrared spectrum, indicating that the C=N and C-NH-C inside it still exist, indicating that it has good stability in strong acids, strong bases and organic solvents.

[0068] The nitrogen heterocyclic covalent organic framework material prepared in Example 1 was kept at 450° C. for 2 h in a nitrogen atmosphere to remove residual impurity molecules in the pores, and then assembled into a button battery, and its performance was tested. The assembly process is as follows: the nitrogen heterocyclic covalent organic framework material prepared in Example 1, conductive carbon black and PVDF binder were added to N-methylpyrrolidone solution in a weight ratio of 6:3:1 and fully mixed to prepare a uniform slurry, which was then coated on a copper foil to prepare a working electrode; a lithium metal sheet was used as a counter electrode, and 1 mol / L lithium hexafluorophosphate ethylene carbonate / dimethyl carbonate / methylethyl carbonate (volume ratio 1:1:1) + 1% vinylene carbonate solution was used as an electrolyte to assemble the button battery, and after standing for 12 hours, its performance was tested, and the test voltage range was 0.01-3V (V vs Li / Li + ).

[0069] Under the condition of current density of 0.1A / g, the button cell assembled from the nitrogen heterocyclic covalent organic framework material prepared in Example 1 was activated, and the cycle performance diagram was measured. Figure 7 It can be seen that in the cycle with a current density of 0.1A / g, the specific capacity increased in the early stage. After 100 cycles of the electrode, the specific capacity increased to 938mAh / g. The phenomenon of gradual increase in specific capacity indicates that the electrode needs an activation process before achieving its maximum specific capacity.

[0070] The button cell assembled from the nitrogen heterocyclic covalent organic framework material prepared in Example 1 was subjected to cyclic voltammetry tests at different scan rates. Figure 8 It can be seen that the cyclic voltammetry curve has a pair of redox peaks near 1V, and the peaks at this position are attributed to the C=N group in the structure, indicating that C=N participates in the storage of lithium ions as an active site.

[0071] The button cell assembled from the nitrogen heterocyclic covalent organic framework material prepared in Example 1 was tested for rate performance at different current densities; Fig. 9It can be seen that the GCD test at different current densities was carried out to test the specific capacity of the PIPHATN COF electrode, thereby measuring its rate performance and cycle stability. When the current density was 0.1A / g, 0.2A / g, 0.5A / g, 1A / g, 2A / g, and 5A / g, the electrode showed a reversible specific capacity of 710, 644, 545, 464, 378, and 275mAh / g, respectively; as the test progressed, when the current density was restored from a high current density of 5A / g to a low current density of 0.1A / g, the specific capacity of the COF electrode could quickly recover to a high specific capacity of 788mAh / g, indicating that it has good reversibility.

[0072] A 5A / g high current cycle test was performed on the button cell assembled from the nitrogen heterocyclic covalent organic framework material prepared in Example 1. Fig.10 It can be seen that after 2600 cycles, there is still a high capacity retention rate, indicating that it has good cycle stability.

[0073] The button cell was prepared by using the nitrogen heterocyclic covalent organic framework material prepared in Example 1 as the positive electrode. The assembly process was as follows: the nitrogen heterocyclic covalent organic framework material prepared in Example 1, conductive carbon black and PVDF binder were added to an N-methylpyrrolidone solution in a weight ratio of 6:3:1, and mixed thoroughly to prepare a uniform slurry, which was then coated on a copper foil to prepare a positive electrode; a lithium metal sheet was used as the negative electrode, and 1 mol / L lithium hexafluorophosphate ethylene carbonate / dimethyl carbonate / methyl ethyl carbonate (volume ratio 1:1:1) + 1% vinylene carbonate solution was used as the electrolyte to assemble the button cell. After standing for 12 hours, its performance was tested. The test voltage range was 1-4V, and it could withstand a voltage of 4V, so it could be used as the positive electrode of a lithium ion battery, indicating that it can be used as an excellent positive electrode material for a lithium battery.

[0074] Comparative Example 1

[0075] A thin layer of covalent organic framework material connected by irreversible bonds disclosed in the technical solution of patent number CN112920405B is used as a comparison.

[0076] The thin-layer covalent organic framework material connected by irreversible bonds obtained from the patent was assembled into button batteries, and its rate performance was tested. The experimental data showed that when the current density was set to 0.1A / g, 0.2A / g, 0.5A / g, 1A / g, 2A / g, and 5A / g, the corresponding specific capacities of the material were 1696, 1511, 1159, 851, 579, and 329mAh / g, respectively (note in particular that the above experimental data are directly derived from patent CN112920405B).

[0077] By comparison Fig. 9 and Fig.12It can be seen that the rate performance of nitrogen heterocyclic covalent organic framework materials is significantly better than that of thin-layer covalent organic framework materials connected by irreversible bonds.

[0078] Further exploration of the application scope of the two shows that nitrogen heterocyclic covalent organic framework materials have unique advantages. They can be adapted to the positive electrode materials of lithium-ion batteries, and can also meet the needs of negative electrode materials. In sharp contrast, thin-layer covalent organic framework materials connected by irreversible bonds are only limited to the application field of negative electrode materials of lithium-ion batteries, and their application range is relatively narrow.

[0079] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A nitrogen heterocyclic covalent organic framework material, characterized in that: The chemical formula is (C 42 H 18 N 12 ) n , whose structural formula is: In the formula, n is a positive integer greater than or equal to 4.

2. A method for preparing a nitrogen heterocyclic covalent organic framework material, characterized in that: The following steps are involved: S1: Under an inert atmosphere, add hexaazatrinaphthyl-2,3,8,9,14,15-hexahalogen substituted product, 2,3,6,7,10,11-hexaaminotriphenylene hexahydrochloride, a deprotonating agent, bis(1,5-cyclooctadiene) rhodium tetrafluoroborate (I) and 1,3-diisopropylimidazole chloride in a molar ratio of 1:(1-1.5):(9-18):(0.02-0.12):(0.04-0.25) to an organic solvent, mix well, react at 50-150° C. for 1-7 days, cool naturally to room temperature, filter and collect the precipitate to obtain a crude product; S2: Wash and dry the crude product in S1 to obtain a nitrogen heterocyclic covalent organic framework material.

3. The method for preparing a nitrogen heterocyclic covalent organic framework material according to claim 2, characterized in that: In S1, the structural formula of hexaazatrinaphthalene-2,3,8,9,14,15-hexahalogen substituted product is: Wherein, X is any one of Br, Cl and F.

4. The method for preparing a nitrogen heterocyclic covalent organic framework material according to claim 3, characterized in that: In S1, the deprotonating agent is any one of an organic strong base and an inorganic base.

5. The method for preparing a nitrogen heterocyclic covalent organic framework material according to claim 4, characterized in that: The organic strong base is any one of lithium tert-butoxide, sodium tert-butoxide and potassium tert-butoxide; the inorganic base is any one of sodium carbonate, potassium carbonate and cesium carbonate.

6. The method for preparing a nitrogen heterocyclic covalent organic framework material according to claim 5, characterized in that: In S1, the inert atmosphere is any one of nitrogen and argon.

7. The method for preparing a nitrogen heterocyclic covalent organic framework material according to claim 6, characterized in that: In S1, the organic solvent is any one of ethylene glycol dimethyl ether, dimethyl sulfoxide, N-methylpyrrolidone and toluene.

8. The method for preparing a nitrogen heterocyclic covalent organic framework material according to claim 7, characterized in that: The washing process in S2 is: first use N,N-dimethylformamide, deionized water, and tetrahydrofuran in sequence to perform preliminary washing on the crude product in S1. After the preliminary washing, the wet product that has not been dried is deeply washed by Soxhlet extraction, and tetrahydrofuran and methanol are used as extraction solvents in turn for deep washing.

9. The method for preparing a nitrogen heterocyclic covalent organic framework material according to claim 8, characterized in that: In S2, the drying temperature is 100-120°C and the drying time is 24-48h.

10. An application of a nitrogen heterocyclic covalent organic framework material, characterized in that: Used in negative electrode materials and positive electrode materials of lithium-ion batteries.

Images