A bipolar covalent organic framework material, preparation method and application and battery

Abstract

This invention belongs to the field of organic electrode material synthesis, and discloses a bipolar covalent organic framework material, its preparation method, application, and battery. The chemical structural formula of the bipolar covalent organic framework material is shown in formula (1). This invention can improve the specific capacity and electronic conductivity of the cathode material, and also solve the problem of dissolution of small organic molecules.

Description

A bipolar covalent organic framework material, its preparation method, applications, and batteries Technical Field

[0001] This invention belongs to the field of organic electrode material synthesis, and more specifically, relates to a bipolar covalent organic framework material, its preparation method, its application, and its battery. Background Technology

[0002] Lithium-ion batteries, as ideal energy storage devices for the future, have performance largely limited by their cathode materials. Traditional inorganic cathode materials generally suffer from unresolved problems such as limited capacity improvement, high energy consumption, and high cost, necessitating the development of novel electrode materials. In recent years, organic cathode materials have attracted much attention from researchers due to their abundant resources, renewability, high adjustability, and environmental friendliness.

[0003] Organic cathode systems can currently be categorized into three types: small organic molecule cathode materials, organic polymer cathode materials, and covalent organic framework cathode materials. Small organic molecule cathode materials can achieve reversible cycling and improve battery specific energy; however, their high solubility in organic electrolytes results in extremely poor actual capacity retention. Organic polymer cathode materials effectively improve the problem of easy solubility of small organic molecule cathode materials in electrolytes, but due to factors such as low doping levels and high ion transport resistance, their actual capacity differs significantly from their theoretical specific capacity. The inherent crystallinity and porosity of covalent organic frameworks allow them to exhibit better ion conductivity than typical organic polymer cathode materials while remaining insoluble in organic electrolytes. However, the linker units and rigid node units required for the synthesis of covalent organic frameworks often contain a large number of lithium-ion inactive sites. Therefore, designing as many active sites as possible while introducing the smallest possible inactive functional units is the fundamental way to further improve the specific capacity of covalent organic frameworks as cathode materials.

[0004] CN202211451031.X discloses the synthesis of a bipolar covalent organic framework material with porphyrin groups as rigid nodes and phenol units as linkers, which is applied to the field of aqueous photovoltaic proton batteries. However, its linker units have no redox activity in the working range of lithium-ion batteries. If used as a cathode material for lithium-ion batteries, its specific capacity and structural stability need to be further improved.

[0005] Therefore, there is an urgent need to propose a bipolar covalent organic framework material with a high proportion of active groups in both the connector and the rigid node unit, and its preparation method, so as to further improve the specific capacity of lithium-ion battery cathode materials. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a bipolar covalent organic framework material, its preparation method, and its applications. This invention can improve the specific capacity and electronic conductivity of cathode materials, and also solve the problem of dissolution of small organic molecules.

[0007] To achieve the above objectives, the first aspect of the present invention provides a bipolar covalent organic framework material, the chemical structural formula of which is shown in formula (1):

[0008]

[0009] Wherein, R is At least one of them.

[0010] A second aspect of this invention provides a method for preparing a bipolar covalent organic framework material, the method comprising the following steps:

[0011] S1: A monomer containing hydroxyl and aldehyde groups is dehydrated and condensed with 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin under the conditions of solvent, catalyst and inert gas atmosphere via Schiff base reaction. After the reaction is completed, the intermediate product is obtained by centrifugation, washing, Soxhlet extraction and vacuum drying.

[0012] S2: The intermediate product and an alkaline solvent are mixed and oxidized in an air atmosphere to oxidize the hydroxyl group of the intermediate product to a carbonyl group. After the reaction is completed, the bipolar covalent organic framework material is obtained by centrifugation, washing, Soxhlet extraction and vacuum drying.

[0013] According to the present invention, preferably, in step S1:

[0014] The hydroxyl and aldehyde-containing monomer is at least one of 2,5-dihydroxyterephthalaldehyde, 2,6-dialdehyde-1,5-dihydroxynaphthalene, and 4,4'-dihydroxy-3,3'-biphenyldialdehyde;

[0015] The solvent is solvent A and / or solvent B; solvent A is at least one selected from N,N-dimethylacetamide, 1,4-dioxane, and n-butanol; solvent B is mesitylene and / or o-dichlorobenzene;

[0016] The catalyst is at least one of acetic acid, trifluoroacetic acid, and scandium trifluoromethanesulfonate;

[0017] The Schiff base reaction was carried out at a temperature of 80–180 °C for a time of 72–144 h.

[0018] The inert gas is argon and / or nitrogen.

[0019] In this invention, the chemical structural formula of the 2,6-dialdehyde-1,5-dihydroxynaphthalene is as follows:

[0020]

[0021] The chemical structural formula of the 4,4'-dihydroxy-3,3'-biphenyldicarboxaldehyde is as follows:

[0022]

[0023] According to the present invention, preferably, the molar ratio of 5,10,15,20-tetratetra(4-aminobenzene)-21H,23H-porphyrin and 2,5-dihydroxyterephthalaldehyde is 1:1.5 to 1:2.5.

[0024] The covalent organic framework material designed in this invention selects porphyrin groups as rigid nodes, which can be oxidized to a p-type structure as an anion binding site or reduced to an n-type structure as a lithium-ion binding site, providing two electrochemical activity capacities. Furthermore, by introducing linker units with a high proportion of active groups through hydroxyl oxidation, the specific capacity is further improved. Therefore, in this invention, the porphyrin rigid nodes in the bipolar covalent organic framework material have p-type electrochemical reaction sites (-N- groups) and n-type electrochemical reaction sites (-C=N-), while the phenyl linkers have n-type electrochemical reaction sites (-C=O- groups). This results in high theoretical capacity and a wide voltage range. The bipolar covalent organic framework not only has a simple preparation process and high yield but also exhibits good structural stability and excellent electrochemical performance, showing great promise for application in the lithium battery field.

[0025] According to the present invention, preferably, in step S2:

[0026] The alkaline solvent is triethylamine or pyridine;

[0027] The oxidation reaction is carried out at a temperature of 20–30°C for 8–10 hours.

[0028] In this invention, as a preferred embodiment, the method for preparing the bipolar covalent organic framework material includes:

[0029] 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin (TAPP) and 2,5-dihydroxyterephthalaldehyde (DCBH) were ultrasonically dispersed in a solvent, and then a catalyst was added to catalyze a Schiff base reaction for dehydration condensation under an inert gas atmosphere; or, 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin and 2,5-dihydroxyterephthalaldehyde were ultrasonically dispersed in a solvent and a catalyst, and then a Schiff base reaction was catalyzed under an inert gas atmosphere for dehydration condensation.

[0030] After the reaction was completed, the intermediate product DCBH-TAPP-COF was obtained by centrifugation, washing, Soxhlet extraction and vacuum drying.

[0031] The intermediate product was mixed with an alkaline solvent in an air atmosphere and subjected to an oxidation reaction to oxidize the hydroxyl groups in the intermediate product to carbonyl groups. After the reaction was completed, the bipolar covalent organic framework DCBQ-TAPP-COF with p-type electrochemical reaction sites -N- groups and n-type electrochemical reaction sites -C=N- and -C=O- groups was obtained by centrifugation, washing, Soxhlet extraction and vacuum drying.

[0032] The third aspect of this invention provides the application of the aforementioned bipolar covalent organic framework material as a cathode material in a battery.

[0033] A fourth aspect of the present invention provides a battery, wherein the positive electrode material of the battery comprises the aforementioned bipolar covalent organic framework material.

[0034] According to the present invention, preferably, the battery is a lithium battery or a sodium battery.

[0035] According to the present invention, preferably, the method for preparing the positive electrode material of the battery includes the following steps:

[0036] (1) The bipolar covalent organic framework material and the conductive agent are stirred and mixed evenly to obtain positive electrode powder;

[0037] (2) The positive electrode powder is mixed evenly with binder and organic solvent and then coated onto the positive electrode current collector. The mixture is then vacuum dried, pressed and cut to obtain the positive electrode material of the battery.

[0038] According to the present invention, preferably, the mass ratio of the bipolar covalent organic framework material to the conductive agent is 5:4 to 8:1.

[0039] The conductive agent is at least one of acetylene black, Ketjen black, and graphite conductive agent.

[0040] According to the present invention, preferably, the adhesive is polyvinylidene fluoride and / or polytetrafluoroethylene;

[0041] The mass ratio of the positive electrode powder to the binder is 8:2 to 9:1;

[0042] The positive current collector is aluminum foil and / or copper foil;

[0043] The vacuum drying temperature is 80–120°C, and the time is 10–18 hours.

[0044] The tablet compression pressure is 1000–1400 psi.

[0045] In this invention, the organic solvent is N-methylpyrrolidone (NMP).

[0046] In this invention, as a preferred embodiment, the battery is a lithium battery, and the assembly of the lithium battery includes: assembling the above-obtained positive electrode material (preferably a circular electrode sheet with a diameter of 12 mm after cutting) and the lithium negative electrode in a standardized manner in the battery casing, adding electrolyte and a separator between the positive and negative electrodes and encapsulating them.

[0047] The electrolyte is at least one selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium bis(difluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The encapsulation is performed using methods known in the art.

[0048] The beneficial effects of the technical solution of this invention are as follows: This invention selects a bipolar porphyrin group as a rigid node, and simultaneously introduces a linker unit with a high proportion of active groups, resulting in a bipolar covalent organic framework with multiple redox active sites containing nitrogen and carbonyl groups. Utilizing the excellent one-dimensional channels of the covalent organic framework, not only is the accessibility of active sites achieved, but the ion conduction efficiency is also greatly improved. This invention can both improve the specific capacity and electronic conductivity of cathode materials, and also solve the problem of dissolution of small organic molecules, showing great application prospects in the field of lithium batteries. Specifically:

[0049] (1) The covalent organic framework material with bipolar electrochemical active sites prepared in this invention improves the specific capacity of the material by introducing linker units with a high proportion of active groups. Simultaneously, it can be used as a cathode material for lithium-ion batteries, wherein the p-type electrochemical active site -N- can provide a large amount of 3.3V vs. Li-. + The effective reversible capacity of Li is above / Li, and the n-type electrochemical active sites -C=N- and -C=O- provide a large amount of 3.0V vs. Li. + Reversible capacity within / Li. By designing multiple redox active sites, a reversible ion storage process with a wide voltage range and high specific capacity was achieved.

[0050] (2) The bipolar covalent organic framework material prepared by the present invention improves the electronic conductivity of the material through the large conjugated structure of the porphyrin group. At the same time, the π channels between the 2D planar structure layers also help the conduction of electrons in the lattice, which greatly improves the poor conductivity of the organic electrode.

[0051] (3) The bipolar covalent organic framework material prepared by the present invention has a high specific surface area and abundant open one-dimensional mesoporous channels. This structural feature provides ion transport channels, fully exposes reactive sites, and facilitates full wetting of electrolyte, thus realizing rapid ion transport and full utilization of active sites.

[0052] (4) The bipolar covalent organic framework material of the present invention exhibits good electrochemical performance in electrochemical performance testing: the material using the bipolar covalent organic framework material of the present invention as the positive electrode shows good electrochemical performance at 1.0–4.0 V vs. Li + / Li contains reversible redox pairs within a wide voltage range; at a current density of 0.1 A / g, the initial specific capacity of the bipolar covalent organic framework material of the present invention can reach a high 173 mAh / g, and it retains more than 10% after 200 cycles; these excellent electrochemical properties make the bipolar covalent organic framework material of the present invention promising for development in the field of lithium batteries.

[0053] (5) The bipolar covalent organic framework material and electrode material of the present invention have simple processing operation, do not require complex system equipment, have high feasibility, and can achieve large-scale production.

[0054] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0055] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0056] Figure 1 illustrates the chemical reaction process of a method for preparing a bipolar covalent organic framework material provided in Example 1 of the present invention (“days” refers to the number of days; “solvent” refers to the solvent, “catalyst” to the catalyst, “air” to the air, and “Et3N” to the triethylamine).

[0057] Figure 2 shows the infrared absorption spectra (“Intensity”, “Wavenumber”) of the DCBQ-TAPP-COF prepared in Example 1 of the present invention and the DCBH and TAPP used therein.

[0058] Figure 3 shows the N1s spectral decomposition diagrams of the X-ray photoelectron spectroscopy of DCBQ-TAPP-COF and DCBH-TAPP-COF prepared in Example 1 of the present invention ("pyrrolic N", "Intensity", "Binding energy").

[0059] Figure 4 shows a scanning electron microscope (SEM) image of the DCBQ-TAPP-COF prepared in Example 2 of the present invention (Figure 4(a) and Figure 4(b) are at different magnifications).

[0060] Figure 5 shows the nitrogen adsorption-desorption curves (Figure 5(a)) and pore size distribution data (Figure 5(b)) of the DCBQ-TAPP-COF and DCBH-TAPP-COF prepared in Example 2 of the present invention (“Adsorption”, “Desorption”, “N2uptake”, “Relative pressure”, “dV / dW”, “Pore width”).

[0061] Figure 6 shows the cyclic voltammetry (CV) curves of the lithium batteries obtained in Examples 1-2 and Comparative Example 1 (Figure 6(a) is the CV curve of Example 1; Figure 6(b) is the CV curve of Comparative Example 1; Figure 6(c) is the CV curve of Example 2; "Current" current, "Voltage" voltage, "1st", "2nd", and "3rd" are respectively 1 cycle, 2 cycles, and 3 cycles).

[0062] Figure 7 shows the impedance diagrams obtained by AC impedance (EIS) testing of the lithium batteries obtained in Example 1 and Comparative Example 1 (Figure 7(a) is the impedance diagram of Example 1; Figure 7(b) is the impedance diagram of Comparative Example 1; the horizontal axis is the real part of the impedance; the vertical axis is the imaginary part of the impedance, and “0th”, “1st”, “2nd”, “5th”, and “10th” are respectively 0 cycles, 1 cycle, 2 cycles, 5 cycles, and 10 cycles).

[0063] Figure 8 shows the constant current cycling performance of the lithium batteries obtained from Examples 1-2 and Comparative Example 1 after cycling stability testing (Figure 8(a) is the performance graph of Example 1 and Comparative Example 1, DCBQ-TAPP-COF in Figure 8(a) represents the lithium battery of Example 1, and DCBH-TAPP-COF represents the lithium battery of Comparative Example 1; Figure 8(b) is the performance graph of Example 2; “charge” refers to charging, “Discharge” refers to discharging, “Specific Capacity” refers to specific capacity, “Cycle number” refers to the number of cycles, and “Coulombic efficiency” refers to coulombic efficiency).

[0064] Figure 9 shows the X-ray diffraction (XRD) pattern and theoretical simulation spectrum (“Experimental”, “Tetragonal”, “AA Eclipsed”, “Intensity”, and “2θ degree”) of the DCBQ-TAPP-COF prepared in Example 1 of the present invention. Detailed Implementation

[0065] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0066] Example 1

[0067] This embodiment provides a method for preparing a bipolar covalent organic framework material, the method comprising the following steps:

[0068] S1: 0.2 mmol of 2,5-dihydroxyterephthalaldehyde (DCBH), 0.1 mmol of 5,10,15,20-tetra(4-aminobenzene)-21H,23H-porphyrin (TAPP), and solvent (2.5 ml n-butanol + 2.5 ml o-dichlorobenzene) were added to a glass pressure-resistant tube and ultrasonically dispersed for 10 min. Then, 0.5 ml of 6 mol acetic acid was added to the glass pressure-resistant tube. The gas in the glass pressure-resistant tube was then replaced with argon gas and ultrasonicated for 5 min. The glass pressure-resistant tube was then placed in an oven at 120 °C for 72 h. After the reaction was completed, the solid was collected by vacuum filtration and transferred to a centrifuge tube. The solid was washed five times each with N,N-dimethylformamide and tetrahydrofuran, and then subjected to Soxhlet extraction and vacuum drying to obtain the purple intermediate product DCBH-TAPP-COF.

[0069] S2: Place the dried DCBH-TAPP-COF powder in a round-necked flask, add sufficient triethylamine solution, and introduce air into the round-necked flask. Stir for 8 hours at room temperature and in an air atmosphere. After the reaction is complete, collect and filter the solid obtained and transfer it to a centrifuge tube. Wash the solid five times each with N,N-dimethylformamide and tetrahydrofuran, and then perform Soxhlet extraction and vacuum drying to obtain the purple final product DCBH-TAPP-COF (bipolar covalent organic framework material), as shown in formula (2).

[0070]

[0071] This embodiment also provides a lithium battery:

[0072] The method for preparing the positive electrode material of the lithium battery includes the following steps:

[0073] (1) Weigh 50mg of the bipolar covalent organic framework material obtained in this embodiment, mix it with 30mg of conductive carbon black (i.e., super P) and grind it for 1h to obtain positive electrode powder. Since the porous structure of COF is easy to absorb water and moisture, put the ground positive electrode powder into a vacuum oven at 100℃ to dry it.

[0074] (2) 80 mg of dried positive electrode powder was mixed with 20 mg of polyvinylidene fluoride (PVDF) and 100 μl of N-methylpyrrolidone (NMP) in a sealed weighing bottle and stirred for 8 h to obtain a slurry. The slurry was coated onto aluminum foil using a 100 μm scraper and then heated in a vacuum oven at 110 °C for 12 h. The pressing pressure was 1000–1400 psi, and the slurry was cut into circular electrode sheets with a diameter of 12 mm to obtain the positive electrode material of the lithium battery.

[0075] The assembly of the lithium battery includes:

[0076] Using the positive electrode material of the lithium battery prepared above as the positive electrode, the lithium metal sheet as the negative electrode, the polypropylene microporous membrane (Celgard 2400) as the separator, and adding 50 μl of electrolyte (1M LiPF6 dissolved in EC (ethylene carbonate) / DMC (dimethyl carbonate) = 1:1 (v / v)), the battery was assembled in an argon-filled glove box and assembled into a button cell in a 2025 button cell casing.

[0077] Figure 2 shows the Fourier Transform Infrared (FTIR) spectra of DCBQ-TAPP-COF (bipolar covalent organic framework material), DCBH, and TAPP prepared in this embodiment. As can be seen from Figure 2, the wavelengths at 1666 cm⁻¹... -1 and 1615cm -1 There are two peaks, one at 1666cm. -1The peak at 1615 cm⁻¹ corresponds to the -C=O- group of benzoquinone. -1 The -C=N- is formed by the Schiff base reaction of 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin and 2,5-dihydroxy-terephthalaldehyde.

[0078] Figure 3 shows the N1s spectral decomposition diagrams of the X-ray photoelectron spectroscopy of DCBQ-TAPP-COF and DCBH-TAPP-COF prepared in this embodiment. As can be seen from Figure 3, the measured binding energies have been corrected. There are two peaks at 400.6 eV and 399.2 eV. The peak at 400.6 eV corresponds to porphyrin nitrogen, and the peak at 399.2 eV corresponds to the -C=N- formed by the Schiff base reaction of 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin and 2,5-dihydroxyterephthalaldehyde.

[0079] Example 2

[0080] This embodiment provides a method for preparing a bipolar covalent organic framework material. The difference between this embodiment and Embodiment 1 is that:

[0081] S1: 0.2 mmol of 2,5-dihydroxyterephthalaldehyde (DCBH), 0.1 mmol of 5,10,15,20-tetra(4-aminobenzene)-21H,23H-porphyrin (TAPP), solvent (2.5 ml n-butanol + 2.5 ml o-dichlorobenzene), and 0.5 ml 6 mol acetic acid were added to a glass pressure-resistant tube and ultrasonically dispersed for 10 min. Then, the gas in the glass pressure-resistant tube was replaced with argon gas and ultrasonicated for another 5 min. The glass pressure-resistant tube was then placed in an oven at 120 °C for 72 h. After the reaction was completed, the solid was collected by vacuum filtration and transferred to a centrifuge tube. The solid was washed five times each with N,N-dimethylformamide and tetrahydrofuran, and then subjected to Soxhlet extraction and vacuum drying to obtain the purple intermediate product DCBH-TAPP-COF.

[0082] Step S2 is the same as in Example 1.

[0083] This embodiment provides a lithium battery:

[0084] The difference between the preparation method of the positive electrode material of the lithium battery and that of Example 1 is as follows:

[0085] Step (1) Weigh 60 mg of the bipolar covalent organic framework material obtained in this embodiment;

[0086] Step (2) Mix 90 mg of dried positive electrode powder with 10 mg of polyvinylidene fluoride (PVDF) and 100 μl of N-methylpyrrolidone (NMP) in a sealed weighing bottle for 8 h.

[0087] The assembly of the lithium battery is the same as in Example 1.

[0088] Figure 4 shows a scanning electron microscope (SEM) image of the DCBQ-TAPP-COF (bipolar covalent organic framework material) prepared in this embodiment. As can be seen from Figure 4, the DCBQ-TAPP-COF material prepared in this embodiment is loose and porous, and its shape is mostly sheet-like, thus increasing the contact area between the reactants and the material and accelerating the transfer of electrons.

[0089] Nitrogen adsorption-desorption tests were conducted on DCBQ-TAPP-COF and DCBH-TAPP-COF from Example 2 at 77K. The results are shown in Figure 5. As can be seen from Figure 5, the specific surface area of ​​the DCBQ-TAPP-COF synthesized in this invention is 576 m². 2 The COF material of the present invention has a large specific surface area and large mesoporous channels, which facilitates ion transport and exposure of active sites. The pore size is mostly distributed within 2 nm.

[0090] Comparative Example 1

[0091] This comparative example provides a lithium battery, which differs from Example 1 only in that:

[0092] In the method for preparing the positive electrode material of the lithium battery, the intermediate product DCBH-TAPP-COF obtained in step S1 of Example 1 is used to replace "DCBQ-TAPP-COF of Example 1" in order to prepare the positive electrode material of the lithium battery and assemble the lithium battery.

[0093] Test Example 1: Cyclic Voltmeter (CV) Test

[0094] This test example demonstrates cyclic voltammetry (CV) testing of the lithium batteries obtained in the above embodiments and comparative examples. The cyclic voltammetry (CV) curves are in the range of 1.0–4.0 V vs. Li. + The tests were conducted within the voltage range of / Li, with a sweep rate of 0.1mV / s.

[0095] Figure 6(a) shows the cyclic CV curve of DCBQ-TAPP-COF in Example 1, from which we can conclude: 2.7V / 1.6V vs. Li + The pair of redox peaks corresponding to / Li includes the lithium insertion-delithiation process of benzoquinone -C=O- and porphyrin ring -C=N-, which is an n-type electrochemical process. 3.5V / 2.3V vs. Li + The pair of redox peaks corresponding to / Li represents the capacity contribution from the dual-ion mechanism provided by the -N-oxidized anion on the porphyrin ring, which is a p-type electrochemical process. This is consistent with the expected activity characteristics based on theoretical design.

[0096] Figure 6(b) shows the cyclic CV curve of DCBH-TAPP-COF in Comparative Example 1, from which we can conclude: 2.7V / 1.6V vs. Li + The pair of redox peaks corresponding to / Li represents the lithium insertion-delithiation process at the -C=N- ring of the porphyrin ring, which is an n-type electrochemical process. It is clear from this that the redox peak area of ​​Comparative Example 1 is significantly smaller than that of Example 1, indicating that Example 1 provides a significantly higher capacity at this potential than Comparative Example 1. 3.5V / 2.3V vs. Li + The pair of redox peaks corresponding to / Li represents the capacity contribution from the dual-ion mechanism provided by the -N-oxidized anion on the porphyrin ring, which is a p-type electrochemical process.

[0097] Figure 6(c) shows the cyclic CV curve of DCBQ-TAPP-COF in Example 2. It can be concluded that Example 2 and Example 1 have similar redox couples, but the polarization degree of the CV curve of Example 2 is greater than that of the CV curve of Example 1.

[0098] Test Example 2: Electro-acoustic Impedance (EIS) Test

[0099] This test example performs AC impedance (EIS) tests on the lithium batteries obtained in the above embodiments and comparative examples, with the frequency set to 0.1Hz-1 MHz.

[0100] As shown in Figure 7(a), the impedance of the DCBQ-TAPP-COF in Example 1 is relatively low, indicating that the battery assembled from this electrode material has a good wetting effect in the electrolyte and that the material has a porous structure with good ion diffusion performance, thus resulting in a low overall internal resistance of the battery. This is beneficial to improving the overall battery performance.

[0101] As shown in Figure 7(b), the impedance of DCBH-TAPP-COF in Comparative Example 1 is significantly increased compared to that in Example 1, indicating that the oxidized material improves the interfacial transport resistance to a certain extent.

[0102] Test Example 3 Cyclic Stability Test

[0103] This test example uses the Newway testing system to perform cycle stability tests on the lithium batteries obtained in the above embodiments and comparative examples. The voltage test range is 1.0–4.0V vs. Li. + / Li, the current density is 0.1A / g.

[0104] As shown in Figure 8(a), the DCBQ-TAPP-COF of Example 1 was cycled 200 times at a current density of 0.1 A / g, with an initial capacity of 173 mAh / g and a capacity retention rate of more than 10%, indicating that the DCBQ-TAPP-COF material designed and synthesized by the present invention has certain cycling stability.

[0105] As shown in Figure 8(a), the DCBH-TAPP-COF of Comparative Example 1 was cycled for 200 cycles at a current density of 0.1 A / g, and the initial capacity was 48.3 mAh / g, with a capacity retention rate of less than 10%. This indicates that the unoxidized DCBH-TAPP-COF material has a low specific capacity and poor capacity retention rate.

[0106] As shown in Figure 8(b), the DCBQ-TAPP-COF of Example 2 retained less than 10% of its capacity after 200 cycles at a current density of 0.1 A / g. The cycling stability of Example 2 was worse than that of Example 1 because: the porphyrin-based COF material is porous and bulky, and there is less binder, resulting in poor adhesion between the active material, the electrode, and the current collector, thus causing greater polarization and poorer cycling performance.

[0107] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. The application of bipolar covalent organic framework materials as cathode materials in batteries, characterized in that, The chemical structural formula of the bipolar covalent organic framework material is shown in formula (1): Equation (1); where -R- is 、 and At least one of them.

2. The application according to claim 1, wherein, The preparation method of the bipolar covalent organic framework material includes the following steps: S1: A monomer containing hydroxyl and aldehyde groups is dehydrated and condensed with 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin under the conditions of solvent, catalyst and inert gas atmosphere via Schiff base reaction. After the reaction, the intermediate product is obtained by centrifugation, washing, Soxhlet extraction and vacuum drying; S2: The intermediate product and an alkaline solvent are mixed under the condition of air atmosphere and subjected to oxidation reaction to oxidize the hydroxyl group of the intermediate product to carbonyl group. After the reaction, the bipolar covalent organic framework material is obtained by centrifugation, washing, Soxhlet extraction and vacuum drying.

3. The application according to claim 2, wherein, In step S1: the hydroxyl and aldehyde monomer is at least one of 2,5-dihydroxyterephthalaldehyde, 2,6-dialdehyde-1,5-dihydroxynaphthalene, and 4,4'-dihydroxy-3,3'-biphenyldicarboxaldehyde; the solvent is solvent A and / or solvent B; solvent A is at least one of N,N-dimethylacetamide, 1,4-dioxane, and n-butanol; solvent B is mesitylene and / or o-dichlorobenzene; the catalyst is at least one of acetic acid, trifluoroacetic acid, and scandium trifluoromethanesulfonate; the Schiff base reaction is carried out at a temperature of 80~180℃ for a time of 72~144 h; and the inert gas is argon and / or nitrogen.

4. The application according to claim 3, wherein, The molar ratio of 5,10,15,20-tetra(4-aminobenzene)-21H,23H-porphyrin and 2,5-dihydroxyterephthalaldehyde is 1:1.5 to 1:2.

5.

5. The application according to claim 2, wherein, In step S2: the alkaline solvent is triethylamine or pyridine; the oxidation reaction is carried out at a temperature of 20-30°C for 8-10 hours.

6. A battery, characterized in that, The positive electrode material of the battery includes the aforementioned bipolar covalent organic framework material.

7. The battery according to claim 6, wherein, The battery is a lithium battery or a sodium battery; the preparation method of the positive electrode material of the battery includes the following steps: (1) stirring and mixing the bipolar covalent organic framework material with a conductive agent to obtain a positive electrode powder; (2) stirring and mixing the positive electrode powder with a binder and an organic solvent to obtain a positive electrode powder, and then coating it onto a positive electrode current collector, and then drying it under vacuum, pressing it into sheets and cutting it into sheets in sequence to obtain the positive electrode material of the battery.

8. The battery according to claim 7, wherein, The mass ratio of the bipolar covalent organic framework material to the conductive agent is 5:4 to 8:1; the conductive agent is at least one of acetylene black, Ketjen black, and graphite conductive agent.

9. The battery according to claim 7, wherein, The binder is polyvinylidene fluoride and / or polytetrafluoroethylene; the mass ratio of the positive electrode powder to the binder is 8:2 to 9:1; the positive electrode current collector is aluminum foil and / or copper foil; the vacuum drying temperature is 80 to 120°C and the time is 10 to 18 hours; the pressing pressure is 1000 to 1400 psi.

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