A metal-covalent organic framework material and a preparation method thereof, and a lithium-air battery positive electrode sheet

Abstract

This invention provides a metal covalent organic framework material and its preparation method, as well as a positive electrode sheet for a lithium-air battery, belonging to the field of lithium-air battery technology. The metal covalent organic framework material represented by Formula I is a one-dimensional metal covalent organic framework material, avoiding the problem of insufficient utilization of active sites within a two-dimensional layered structure, thus improving the discharge specific capacity and cycle stability of the lithium-air battery. In Formula I, the electronegativity of the two nitrogen atoms in the two pyridine rings induces local positive charges at the M center, forming strong Lewis acid sites. Simultaneously, ligand-metal charge transfer enhances the conductivity and electron delocalization of the active sites in the metal covalent organic framework material, improving the discharge specific capacity of the lithium-air battery. Furthermore, the M atoms are anchored to the metal covalent organic framework material framework through coordination bonds, maintaining the active site density and structural integrity of the metal covalent organic framework material, thereby improving the cycle stability of the lithium-air battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-air battery technology, and in particular to a metal covalent organic framework material and its preparation method, and a positive electrode sheet for lithium-air batteries. Background Technology

[0002] Lithium-air batteries are a novel electrochemical energy storage device that uses metallic lithium as the negative electrode and oxygen from the air as the positive electrode active material. They possess ultra-high theoretical energy density, are suitable for high energy storage demands in extreme environments, and can be used in aerospace, deep-sea exploration, and other fields. The positive electrode of a lithium-air battery is the core reaction site for oxygen diffusion, oxygen reduction / oxygen evolution reactions, and the deposition and decomposition of discharge products. Its material composition directly determines the battery's charge-discharge efficiency, cycle life, and rate performance.

[0003] Covalent organic framework materials, due to their high specific surface area, provide ample active sites, offering sufficient space for oxygen diffusion, electrolyte wetting, and the deposition and decomposition of discharge products (Li2O2), demonstrating significant application potential in lithium-air battery cathodes. However, the covalent organic framework materials used in existing technologies are two-dimensional layered structures, whose internal active sites are covered and cannot be fully utilized. This results in lithium-air batteries with low discharge specific capacity and poor cycle stability when used as cathode materials. Summary of the Invention

[0004] The purpose of this invention is to provide a metal covalent organic framework material and its preparation method, as well as a lithium-air battery cathode. The lithium-air battery assembled from the cathode sheet made of the metal covalent organic framework material of this invention has high discharge specific capacity and good cycle stability.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A metal covalent organic framework material having the chemical structure shown in Formula I: Formula I, In Formula I, M is a transition metal.

[0006] Preferably, in Formula I, M is Ni or Co.

[0007] This invention also provides a method for preparing the metal covalent organic framework material described in the above technical solution, comprising the following steps: A metal covalent organic framework material was obtained by solvothermal reaction of 1,3,6,8-tetra-(p-aminophenyl)-pyrene, 2,2'-bipyridine-4,4'-dicarboxaldehyde, transition metal salt, protic acid catalyst and organic solvent.

[0008] Preferably, the molar ratio of 1,3,6,8-tetra-(p-aminophenyl)-pyrene to 2,2'-bipyridine-4,4'-dicarboxaldehyde is 1:(1.5~2.5).

[0009] Preferably, the molar ratio of 2,2'-bipyridine-4,4'-dicarboxaldehyde to the transition metal salt is 1:(1~2).

[0010] Preferably, the transition metal salt includes a cobalt salt or a nickel salt.

[0011] Preferably, the temperature of the solvothermal reaction is 100~200℃, and the time of the solvothermal reaction is 12~120h.

[0012] Preferably, the protic acid catalyst is an aqueous solution of acetic acid or an aqueous solution of trifluoroacetic acid.

[0013] Preferably, the concentration of acetic acid in the acetic acid aqueous solution and the concentration of trifluoroacetic acid in the trifluoroacetic acid aqueous solution can be independently 3-9 mol / L. -1 The volume ratio of the protic acid catalyst to the molar amount of 2,2'-bipyridine-4,4'-dicarboxaldehyde is (300~600) mL:1 mmol.

[0014] The present invention also provides a lithium-air battery positive electrode sheet, comprising a current collector and a positive electrode material coated on the surface of the current collector. The positive electrode material comprises an active material, a conductive agent, and a binder. The active material is a metal covalent organic framework material as described in the above technical solution or a metal covalent organic framework material prepared by the preparation method described in the above technical solution.

[0015] This invention provides a metal covalent organic framework material having a chemical structure as shown in Formula I: Formula I, where M is a transition metal. The metal covalent organic framework material represented by Formula I of this invention is a linear one-dimensional metal covalent organic framework material with abundant active sites, avoiding the problem of the active sites inside the two-dimensional layered structure being covered and not fully utilized, thus improving the discharge specific capacity and cycle stability of lithium-air batteries. In Formula I, M is a transition metal, which is connected to the two nitrogen atoms in the two pyridine rings through coordination bonds. The electronegativity of the N atom induces the generation of local positive charges at the center of M, forming Lewis acid sites. At the same time, the conductivity and electron delocalization of the active sites of the entire metal covalent organic framework material are improved through ligand-metal charge transfer, thereby improving the discharge specific capacity of lithium-air batteries. Moreover, the M atom is firmly anchored to the metal covalent organic framework material skeleton through strong MN coordination bonds, avoiding the migration and aggregation of metal active sites during the cycling process of lithium-air batteries, maintaining the density of active sites and the structural integrity of metal covalent organic framework materials, thereby improving the cycle stability of lithium-air batteries. The results of the examples show that the lithium-air battery assembled with the positive electrode made of the metal covalent organic framework material of the present invention can achieve a discharge specific capacity of 14223 mAh g. -1 At 200mA g -1 1000 mAh g -1 It can stably cycle 128 times. Attached Figure Description

[0016] Figure 1 This is a 100,000x magnified SEM image of the metal covalent organic framework material of Example 1 of the present invention; Figure 2 This is a 100,000x magnified SEM image of the metal covalent organic framework material of Example 2 of the present invention. Figure 3 This is a SEM image of the covalent organic framework material of Comparative Example 1 of this invention, magnified 100,000 times. Figure 4 The image shows the XRD pattern of the metal covalent organic framework material of Example 1 of this invention. Figure 5 The image shows the XRD pattern of the metal covalent organic framework material of Example 2 of this invention. Figure 6 The image shows the XRD pattern of the covalent organic framework material in Comparative Example 1 of this invention. Figure 7 This is a structural simulation diagram of the metal covalent organic framework material of Embodiment 1 of the present invention; Figure 8 This is a structural simulation diagram of the covalent organic framework material in Comparative Example 1 of the present invention; Figure 9 The graph shows the full discharge performance of the lithium-air battery prepared in Application Example 1 of this invention. Figure 10The graph shows the full discharge performance of the lithium-air battery prepared in Application Example 2 of this invention. Figure 11 The graph shows the full discharge performance of the lithium-air battery prepared in Comparative Application Example 1 of this invention. Figure 12 The graph shows the long-cycle performance of the lithium-air battery prepared in Application Example 1 of this invention. Figure 13 The graph shows the long-cycle performance of the lithium-air battery prepared in Application Example 2 of this invention. Figure 14 The graph shows the long-cycle performance of the lithium-air battery prepared in Comparative Application Example 1 of this invention. Detailed Implementation

[0017] This invention provides a metal covalent organic framework material having a chemical structure as shown in Formula I: Formula I, in which M is a transition metal.

[0018] In this invention, the chemical structure of the metal covalent organic framework material shown in Formula I is formed by interconnecting two-connection-point structural units as shown in Formula II and four-connection-point structural units as shown in Formula III; each connection point of each two-connection-point structural unit is connected to a connection point of a four-connection-point structural unit; each connection point of each four-connection-point structural unit is connected to a connection point of a two-connection-point structural unit; Formula II is... M is a transition metal, and M forms coordinate bonds with the nitrogen atoms in the two pyridines of the two-connection-point structural unit shown in Formula II; Formula III is In Formula I, the dashed line indicates that the orientation of the structure shown in Formula I extends horizontally along the plane of the paper. This invention, by defining the chemical structure of the metal-covalent organic framework material, obtains a linear one-dimensional metal-covalent organic framework material with abundant active sites. This avoids the problem of the active sites inside the two-dimensional layered structure being covered and not fully utilized, thus improving the discharge specific capacity and cycle stability of lithium-air batteries.

[0019] In this invention, M in Formula I is a transition metal. In one embodiment, M can be Co or Ni. The transition metal in this invention is connected to the two nitrogen atoms in the two pyridine rings via coordination bonds. The electronegativity of the N atoms induces a local positive charge at the center of M, forming Lewis acid sites. Simultaneously, ligand-metal charge transfer enhances the conductivity and electron delocalization of the active sites in the entire metal-covalent organic framework material, thereby increasing the discharge specific capacity of the lithium-air battery. Furthermore, the M atoms are firmly anchored to the metal-covalent organic framework material skeleton through strong MN coordination bonds, preventing the migration and aggregation of metal active sites during cycling, maintaining the density of active sites and the structural integrity of the metal-covalent organic framework material, thus improving the cycle stability of the lithium-air battery.

[0020] This invention forms a linear one-dimensional metal covalent organic framework material with abundant active sites by connecting two connection point structural units as shown in Formula II and four connection point structural units as shown in Formula III. This avoids the problem that the active sites inside the two-dimensional layered structure are covered and cannot be fully utilized, thereby improving the discharge specific capacity and cycle stability of lithium-air batteries.

[0021] This invention also provides a method for preparing the metal covalent organic framework material described in the above technical solution, comprising the following steps: A metal covalent organic framework material was obtained by solvothermal reaction of 1,3,6,8-tetra-(p-aminophenyl)-pyrene, 2,2'-bipyridine-4,4'-dicarboxaldehyde, transition metal salt, protic acid catalyst and organic solvent.

[0022] In this invention, 1,3,6,8-tetra-(p-aminophenyl)-pyrene and 2,2'-bipyridine-4,4'-dicarboxaldehyde are used as monomers for the metal covalent organic framework material. The carbon-oxygen bond in 2,2'-bipyridine-4,4'-dicarboxaldehyde after metal coordination has an angle of 120° with the carbon-carbon bond connecting the pyridine. Taking advantage of its property that it cannot be flipped during the reaction, it reacts with 1,3,6,8-tetra-(p-aminophenyl)-pyrene and extends in a single direction after reaction, thereby obtaining a one-dimensional metal covalent organic framework material.

[0023] In one embodiment of the present invention, the molar ratio of 1,3,6,8-tetra-(p-aminophenyl)-pyrene to 2,2'-bipyridine-4,4'-dicarboxaldehyde can be 1:(1.5~2.5) or 1:(1.8~2.1). The present invention, by limiting the molar ratio of 1,3,6,8-tetra-(p-aminophenyl)-pyrene to 2,2'-bipyridine-4,4'-dicarboxaldehyde, ensures precise matching of the reaction sites of the aldehyde group and the amino group, avoids unreacted end groups, and forms a highly cross-linked, defect-free rigid framework; it also ensures maximum crystallinity, porosity, and specific surface area of ​​the metal covalent organic framework material, providing sufficient space for oxygen diffusion and Li2O2 deposition.

[0024] In one embodiment of the present invention, the transition metal salt can be a cobalt salt or a nickel salt; the cobalt salt can be cobalt acetate, cobalt chloride, or cobalt nitrate; the nickel salt can be nickel acetate, nickel chloride, or nickel nitrate. The present invention, by limiting the type of transition metal salt, ensures sufficient connection with the two nitrogen atoms in the two pyridine rings through coordination bonds. The electronegativity of the N atom induces a local positive charge at the M center, forming a Lewis acid site. Simultaneously, ligand-metal charge transfer enhances the conductivity and electron delocalization of the active sites of the entire metal covalent organic framework material, thereby improving the discharge specific capacity of the lithium-air battery.

[0025] In one embodiment of the present invention, the molar ratio of 2,2'-bipyridine-4,4'-dicarboxaldehyde to the transition metal salt can be 1:(1~2), 1:(1.2~1.8), or 1:(1.4~1.6). By limiting the molar ratio of 2,2'-bipyridine-4,4'-dicarboxaldehyde to the transition metal salt, the present invention ensures sufficient coordination between the metal ions in the transition metal salt and the nitrogen in 2,2'-bipyridine-4,4'-dicarboxaldehyde, further ensuring that the angle between the carbon-oxygen bond in 2,2'-bipyridine-4,4'-dicarboxaldehyde and the carbon-carbon bond connecting the pyridine is 120°, thus fully generating a one-dimensional metal-covalent organic framework material.

[0026] In one embodiment of the present invention, the protic acid catalyst can be an aqueous solution of acetic acid or an aqueous solution of trifluoroacetic acid; the concentration of acetic acid in the aqueous solution of acetic acid and the concentration of trifluoroacetic acid in the aqueous solution of trifluoroacetic acid can be independently 3~9 mol L. -1 It can also be used independently as 5~8 mol L. -1 The present invention employs a protic acid catalyst to accelerate the solvation reaction rate of 1,3,6,8-tetra-(p-aminophenyl)-pyrene with 2,2'-bipyridine-4,4'-dicarboxaldehyde; and adjusts the reaction system to an acidic environment to prevent the hydrolysis and precipitation of transition metal salts, which is conducive to the formation of stable coordination bonds between transition metal ions and nitrogen atoms in 2,2'-bipyridine-4,4'-dicarboxaldehyde, ensuring the uniform dispersion of active sites.

[0027] In one embodiment of the present invention, the volume ratio of the protic acid catalyst to the molar ratio of 2,2'-bipyridine-4,4'-dicarboxaldehyde can be (300~600) mL:1 mmol, (350~550) mL:1 mmol, or (400~500) mL:1 mmol. The present invention further improves the solvation reaction rate of 1,3,6,8-tetra-(p-aminophenyl)-pyrene with 2,2'-bipyridine-4,4'-dicarboxaldehyde by limiting the ratio of the protic acid catalyst to 2,2'-bipyridine-4,4'-dicarboxaldehyde, ensuring that the transition metal ions form stable coordination bonds with the nitrogen atoms in 2,2'-bipyridine-4,4'-dicarboxaldehyde, and improving the uniform dispersion of active sites.

[0028] In one embodiment of the present invention, the organic solvent may be one or more of o-dichlorobenzene, n-butanol, mesitylene, and dioxane. In an embodiment of the present invention, the organic solvent may be mesitylene and dioxane; the volume ratio of mesitylene to dioxane may be 1:1. The present invention does not have a particular limitation on the amount of organic solvent added; the amount of organic solvent added is well known in the art to fully dissolve 1,3,6,8-tetra-(p-aminophenyl)-pyrene, 2,2'-bipyridine-4,4'-dicarboxaldehyde, transition metal salt, and protic acid catalyst.

[0029] In one embodiment of the present invention, the mixing of 1,3,6,8-tetra-(p-aminophenyl)-pyrene, 2,2'-bipyridine-4,4'-dicarboxaldehyde, transition metal salt, protonic acid catalyst, and organic solvent can be performed by first mixing 1,3,6,8-tetra-(p-aminophenyl)-pyrene, 2,2'-bipyridine-4,4'-dicarboxaldehyde, transition metal salt, and organic solvent, followed by adding the protonic acid catalyst for a second mixing. The first and second mixing can be performed under ultrasonic conditions, and the ultrasonic time for each mixing can be independently 5-25 minutes. In another embodiment of the present invention, the mixing can be performed in a Pyrex tube. After mixing, the Pyrex tube can be sequentially frozen, degassed, thawed, and sealed. The present invention does not impose any particular limitations on the freezing-degasting-thawing and sealing processes; any freezing-degasting-thawing and sealing methods well-known in the art can be used to ensure a vacuum environment in the Pyrex tube.

[0030] In this invention, during the solvothermal reaction, the amino group in 1,3,6,8-tetra-(p-aminophenyl)-pyrene forms a carbon-nitrogen double bond with the aldehyde group in 2,2'-bipyridine-4,4'-dicarboxaldehyde, and the metal ion in the transition metal salt coordinates with the nitrogen on the pyridine in 2,2'-bipyridine-4,4'-dicarboxaldehyde to form a coordinate bond. As one embodiment of this invention, the temperature of the solvothermal reaction can be 100~200℃, 120~180℃, or 140~160℃. As another embodiment of this invention, the time of the solvothermal reaction can be 12~120h, 24~100h, or 50~70h. This invention ensures a more complete preparation of metal covalent organic framework materials by limiting the temperature and time of the solvothermal reaction, using 1,3,6,8-tetra-(p-aminophenyl)-pyrene, 2,2'-bipyridine-4,4'-dicarboxaldehyde, and transition metal salts under the catalysis of a protic acid catalyst. As one embodiment of this invention, the solvothermal reaction can be carried out under vacuum conditions.

[0031] After the solvothermal reaction is completed, the product of the solvothermal reaction is sequentially subjected to solid-liquid separation, washing, purification, and drying to obtain a metal covalent organic framework material. As one embodiment of the invention, the solid-liquid separation can be performed by vacuum filtration; the washing can be performed sequentially using dichloromethane and anhydrous ethanol; the purification can be performed by Soxhlet extraction; the solvent for Soxhlet extraction can be tetrahydrofuran; the temperature for Soxhlet extraction can be 100-150°C; the extraction time can be 24-72 hours; and the drying can be vacuum drying, with a temperature of 80-120°C and a drying time of 12-24 hours.

[0032] This invention involves a solvothermal reaction of 1,3,6,8-tetra-(p-aminophenyl)-pyrene, 2,2'-bipyridine-4,4'-dicarboxaldehyde, and a transition metal salt under the catalysis of a protic acid catalyst. This reaction allows the amino group in 1,3,6,8-tetra-(p-aminophenyl)-pyrene to form a unidirectional covalent carbon-nitrogen double bond with the aldehyde group in 2,2'-bipyridine-4,4'-dicarboxaldehyde. Furthermore, it promotes the coordination of the metal ion in the transition metal salt with the nitrogen on the pyridine in 2,2'-bipyridine-4,4'-dicarboxaldehyde to form a coordinate bond. This further ensures that the carbon-nitrogen double bond formed between the amino group in 1,3,6,8-tetra-(p-aminophenyl)-pyrene and the aldehyde group in 2,2'-bipyridine-4,4'-dicarboxaldehyde is covalently linked in a unidirectional direction, thereby obtaining a one-dimensional metal covalent organic framework material.

[0033] The present invention also provides a lithium-air battery positive electrode sheet, comprising a current collector and a positive electrode material coated on the surface of the current collector. The positive electrode material comprises an active material, a conductive agent, and a binder. The active material is a metal covalent organic framework material as described in the above technical solution or a metal covalent organic framework material prepared by the preparation method described in the above technical solution.

[0034] In one embodiment of the present invention, the current collector can be carbon paper, the conductive agent can be acetylene black, and the binder can be vinylidene fluoride. In another embodiment of the present invention, the mass ratio of the active material, conductive agent, and binder can be (8~4.5):(1~4.5):1. The present invention does not impose any particular limitation on the preparation method of the lithium-air battery positive electrode sheet; any lithium-air battery positive electrode sheet prepared using a method well-known in the art can be used to obtain the desired lithium-air battery positive electrode sheet.

[0035] The lithium-air battery assembled with the lithium-air battery positive electrode provided by this invention has high discharge specific capacity and good cycle stability.

[0036] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0037] Example 1 A metal covalent organic framework compound has the following structural formula: It is denoted as Py-Ni COF.

[0038] The preparation method is as follows: 2,2'-bipyridine-4,4'-dicarboxaldehyde (0.4 mmol), 1,3,6,8-tetra-(p-aminophenyl)-pyrene (0.2 mmol), nickel acetate (0.4 mmol), mesitylene (1.5 mL), and dioxane (1.5 mL) were placed in a Pyrex tube and ultrasonically dispersed for 10 minutes. Add 0.2 mL of 6 mol / L acetic acid aqueous solution and sonicate for 5 min. Place the Pyrex tube containing the mixture in liquid nitrogen to freeze, connect a vacuum pump and evacuate for 15 min, then introduce nitrogen and thaw. Repeat the freezing-degassing-thawing step 3 times. Seal the Pyrex tube with a flame under vacuum. After thawing, place the sealed Pyrex tube in a forced-air drying oven and keep it at 120℃ for 72 h. After natural cooling, take out the solid product from the Pyrex tube, wash the product with dichloromethane and anhydrous ethanol respectively, and perform Soxhlet extraction with tetrahydrofuran at 110℃ for 24 h. Place the Soxhlet extracted product in a vacuum drying oven and vacuum dry at 100℃ for 24 h to finally obtain orange-red metal covalent organic framework compound powder Py-Ni. COF; the molar ratio of 1,3,6,8-tetra-(p-aminophenyl)-pyrene to 2,2'-bipyridine-4,4'-dicarboxaldehyde is 1:2; the molar ratio of 2,2'-bipyridine-4,4'-dicarboxaldehyde to nickel acetate is 1:1; the volume ratio of the acetic acid aqueous solution to the molar ratio of 2,2'-bipyridine-4,4'-dicarboxaldehyde can be 1 mL: 2 mmol; the volume ratio of mesitylene to dioxane is 1:1.

[0039] Example 2 A metal covalent organic framework compound has the following structural formula: It is denoted as Py-Co COF.

[0040] The preparation method is the same as in Example 1, except that cobalt acetate (0.4 mmol) is used instead of nickel acetate (0.4 mmol) to obtain metal covalent organic framework compound powder Py-Co COF.

[0041] Comparative Example 1 A covalent organic framework compound has the following structural formula: The difference between this comparative example and Example 1 is that the addition of nickel acetate is omitted, while the rest is the same as in Example 1, and a covalent organic framework compound, denoted as Py-COF, is prepared.

[0042] Application Example 1 A slurry was formed by mixing 200 μL of N-methylpyrrolidone solvent, the metal covalent organic framework prepared in Example 1, conductive carbon black, and vinylidene fluoride. The slurry was coated onto carbon paper with a diameter of 12 mm and then vacuum dried at 110 °C for 12 h to obtain a lithium-air battery positive electrode sheet.

[0043] Application Example 2 A slurry was formed by mixing 200 μL of N-methylpyrrolidone solvent, the metal covalent organic framework prepared in Example 2, conductive carbon black, and vinylidene fluoride. The slurry was coated onto carbon paper with a diameter of 12 mm and then vacuum dried at 110 °C for 12 h to obtain a lithium-air battery positive electrode sheet.

[0044] Comparative Application Example 1 A slurry was formed by mixing 200 μL of N-methylpyrrolidone solvent, the metal covalent organic framework prepared in Comparative Example 1, conductive carbon black, and vinylidene fluoride. The slurry was coated onto carbon paper with a diameter of 12 mm and then vacuum dried at 110 °C for 12 h to obtain the positive electrode sheet for a lithium-air battery.

[0045] The morphology of the metal covalent organic framework materials prepared in Examples 1-2 and the covalent organic framework material prepared in Comparative Example 1 was characterized using scanning electron microscopy. The results are as follows: Figures 1-3 As shown. Figure 1 The image shows the morphology of the metal covalent organic framework material in Example 1, which consists of clusters of petal-shaped particles with a particle size of 3 micrometers. Figure 2 The morphology of the metal covalent organic framework material in Example 2 is shown as a cluster of nanorods with a particle size of 5 micrometers. Figure 3 The morphology of the covalent organic framework material in Comparative Example 1 is shown, consisting of irregular particles with a particle size of 1-2 micrometers.

[0046] The phases of the metal covalent organic framework materials prepared in Examples 1-2 and the covalent organic framework material prepared in Comparative Example 1 were characterized using X-ray diffraction, and the results are as follows: Figures 4-6 As shown. By combining crystal structure modeling with structural refinement, it can be seen that... Figure 4The metal covalent organic framework material prepared in Example 1 shows multiple strong peaks, with 2 θ The peaks appearing at 7.55°, 8.95°, 11.76°, 14.9°, 16.02°, and 24.06° are respectively attributed to (110), (200), and (3). 0), (220), (4) 0) and (3) 1) Crystal planes demonstrate that the material possesses good crystallinity, and its weighted residual variance factor and residual variance factor are 3.45% and 2.71%, respectively, proving that the crystal structure of the metal covalent organic framework material prepared in Example 1 is consistent with the crystal structure of the established model, such as... Figure 7 As shown, this is a one-dimensional metal-covalent organic framework structure; composed of Figure 5 It can be seen that the metal covalent organic framework material prepared in Example 2 has obvious peaks, good crystallinity, and its structure is similar to that in Example 1, being a one-dimensional metal covalent organic framework structure; Figure 6 It can be seen that the covalent organic framework material prepared in Comparative Example 1 shows that in 2 θ Strong peaks appear at 3.55° and 7.16°, which are attributed to (010) and (2) respectively. 0) Crystal plane, 2 θ The peak near 24.15° belongs to the stacking of the (001) crystal plane, indicating that it has good crystallinity and is significantly different from that of Examples 1-2. Its weighted residual variance factor and residual variance factor are 3.17% and 2.49%, respectively, proving that the crystal structure of the covalent organic framework material prepared in Comparative Example 1 is consistent with the crystal structure of the established model. Figure 8 As shown, this is a two-dimensional covalent organic framework structure.

[0047] The positive electrodes of the lithium-air batteries in Application Examples 1-2 and Comparative Application Example 1 were placed in an argon glove box with water and oxygen contents both less than 0.01 ppm. A lithium metal sheet was used as the negative electrode, a glass fiber membrane as the separator, and TEGDME containing 1 M LiTFSI as the electrolyte. A coin cell lithium-air battery was assembled using a CR2032 type coin cell battery case with holes on the positive electrode side. The assembled coin cell lithium-air battery was then placed in a sealed battery test chamber. The battery test chamber was connected to a vacuum pump to extract the internal air and then introduce sufficient oxygen.

[0048] Discharge tests were conducted on coin-type lithium-air batteries prepared using the LAND battery testing system, corresponding to test cases 1-2 and comparative application example 1. The test current density was 200 mA g. -1 The cutoff voltage is 2V (vs. Li + / Li), the result is as follows Figures 9-11 As shown. By Figures 9-11It can be seen that the full discharge specific capacity of the lithium-air batteries prepared in Application Examples 1-2 and Comparative Application Example 1 is 14223 mAh g, respectively. -1 11255 mAh g -1 and 3487 mAh g -1 Therefore, it can be seen that the lithium-air batteries prepared by Example 1 to 2 of this invention have a higher full-discharge specific capacity.

[0049] Long-cycle testing was conducted on coin-type lithium-air batteries prepared using the LAND battery testing system, corresponding to test cases 1-2 and comparative application example 1. The test current density was 200 mA g. -1 The specific capacity is limited to 1000 mAh g. -1 The result is as follows Figures 12-14 As shown. By Figures 12-14 It can be seen that the coin-type lithium-air batteries prepared in Application Examples 1-2 and Comparative Application Example 1 can be cycled 128 times, 103 times and 52 times respectively; thus, it can be seen that the lithium-air batteries prepared in Application Examples 1-2 of the present invention have better long-cycle performance.

[0050] In summary, lithium-air batteries assembled from the positive electrode sheet made of the metal covalent organic framework material of this invention have high discharge specific capacity and good cycle stability.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A metal covalent organic framework material having the chemical structure shown in Formula I: Equation I, In Formula I, M is a transition metal.

2. The metal covalent organic framework material according to claim 1, characterized in that, In Formula I, M is Ni or Co.

3. A method for preparing the metal covalent organic framework material according to claim 1 or 2, comprising the following steps: A metal covalent organic framework material was obtained by solvothermal reaction of 1,3,6,8-tetra-(p-aminophenyl)-pyrene, 2,2'-bipyridine-4,4'-dicarboxaldehyde, transition metal salt, protic acid catalyst and organic solvent.

4. The preparation method according to claim 3, characterized in that, The molar ratio of 1,3,6,8-tetra-(p-aminophenyl)-pyrene to 2,2'-bipyridine-4,4'-dicarboxaldehyde is 1:(1.5~2.5).

5. The preparation method according to claim 3, characterized in that, The molar ratio of 2,2'-bipyridine-4,4'-dicarboxaldehyde to the transition metal salt is 1:(1~2).

6. The preparation method according to claim 3, characterized in that, The transition metal salts include cobalt salts or nickel salts.

7. The preparation method according to claim 3, characterized in that, The temperature of the solvothermal reaction is 100~200℃, and the time of the solvothermal reaction is 12~120h.

8. The preparation method according to claim 3, characterized in that, The protic acid catalyst is an aqueous solution of acetic acid or an aqueous solution of trifluoroacetic acid.

9. The preparation method according to claim 8, characterized in that, The concentrations of acetic acid in the acetic acid aqueous solution and trifluoroacetic acid in the trifluoroacetic acid aqueous solution can be independently 3-9 mol / L. -1 The volume ratio of the protic acid catalyst to the molar amount of 2,2'-bipyridine-4,4'-dicarboxaldehyde is (300~600) mL:1 mmol.

10. A lithium-air battery positive electrode sheet, comprising a current collector and a positive electrode material coated on the surface of the current collector, wherein the positive electrode material comprises an active material, a conductive agent, and a binder, characterized in that, The active material is the metal covalent organic framework material according to claim 1 or 2, or the metal covalent organic framework material prepared by the preparation method according to any one of claims 3 to 9.

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