Full-conjugated covalent organic framework compound, preparation method and application thereof, and lithium ion battery negative electrode

Abstract

The invention provides a fully-conjugated covalent organic framework compound, a preparation method and application thereof, and a lithium ion battery negative electrode, and belongs to the technical field of lithium ion batteries. The fully-conjugated covalent organic framework compound provided by the invention is formed by mutually connecting structural units as shown in a formula I and a formula II to form a multi-element annular skeleton structure with a high conjugation characteristic, so that the conductivity, chemical stability and thermal stability of COFs can be improved. The fully-conjugated covalent organic framework compound provided by the invention is used as an electrode material, the highly-conjugated structure is beneficial to charge transmission, and the multi-element annular structure avoids the situation that active sites cannot be fully utilized due to dense traditional COFs structures, so that the specific capacity and cycling stability of a battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a fully conjugated covalent organic framework compound, a preparation method and application thereof, and a lithium-ion battery negative electrode. Background Art

[0002] Lithium-ion batteries (LIBs) have attracted much attention as a high-performance energy storage device. However, the anode of traditional lithium-ion batteries has gradually reached its theoretical capacity limit. For example, the specific capacity of graphene-based anode materials has reached 700 mAh g -1 The specific capacity of the cobaltous oxide negative electrode material reached 700mAh·g -1 The specific capacity of the tin-based alloy negative electrode material has reached 800mAh g -1 , it is necessary to develop a new generation of lithium-ion battery negative electrode materials.

[0003] Covalent organic frameworks (COFs) are a class of organic porous crystalline materials composed of light elements (C, H, O, N) connected by covalent bonds. They have potential advantages in energy storage, but as electrode materials, their specific capacity can only reach 700-800 mAh g -1 Moreover, due to its dense two-dimensional layered structure, the active sites inside COFs cannot be fully utilized, resulting in poor battery cycle stability. Summary of the Invention

[0004] The present invention aims to provide a fully conjugated covalent organic framework compound, its preparation method and application, and a lithium-ion battery negative electrode. The fully conjugated covalent organic framework compound provided by the present invention can be used in a lithium-ion battery negative electrode to improve the battery's specific capacity and cycle stability.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a fully conjugated covalent organic framework compound, wherein the fully conjugated covalent organic framework compound is formed by interconnecting a two-connection-point structural unit as shown in Formula I and a four-connection-point structural unit as shown in Formula II; the connection point of each two-connection-point structural unit is connected to the connection point of the four-connection-point structural unit; and the connection point of each four-connection-point structural unit is connected to the connection point of the two-connection-point structural unit.

[0007]

[0008] In the formula II, R is one of the following structures:

[0009]

[0010] Preferably, the structural formula of the fully conjugated covalent organic framework compound is:

[0011]

[0012] Preferably, the structural formula of the fully conjugated covalent organic framework compound is:

[0013]

[0014] The present invention also provides a method for preparing the fully conjugated covalent organic framework compound described in the above technical solution, comprising: mixing a first monomer, a second monomer, an ammonium source and an organic solvent and then conducting a solvothermal reaction to obtain a fully conjugated covalent organic framework compound; the first monomer is pyrene-4,5,9,10-tetraketone, and the second monomer is 1,3,6,8-tetrakis(4-formaldehydephenyl)pyrene, tetrakis-(4-formyl-(1,1-biphenyl))ethylene, tetrakis-(4-formylphenyl)ethylene or 1,2,4,5-tetrakis(4-formylphenyl)benzene.

[0015] Preferably, the solvent thermal reaction is carried out in a vacuum environment, the reaction temperature is 100-200° C., and the reaction time is 24-120 h.

[0016] Preferably, the ammonium source is ammonium formate or ammonium acetate.

[0017] Preferably, the organic solvent is one or more of dioxane, mesitylene, n-butanol and o-dichlorobenzene.

[0018] The present invention also provides the use of the fully conjugated covalent organic framework compound described in the above technical solution or the fully conjugated covalent organic framework compound prepared by the preparation method described in the above technical solution in lithium ion batteries.

[0019] The present invention also provides a lithium-ion battery negative electrode, comprising a current collector and a negative electrode material coated on the surface of the current collector, wherein the negative electrode material comprises an active material, a conductive agent and a binder, and the active material is the fully conjugated covalent organic framework compound described in the above technical solution or the fully conjugated covalent organic framework compound prepared by the preparation method described in the above technical solution.

[0020] Preferably, the mass content of the fully conjugated covalent organic framework compound in the negative electrode material is 1 to 50%.

[0021] The present invention provides a fully conjugated covalent organic framework compound, which is formed by interconnecting a two-connection-point structural unit as shown in Formula I and a four-connection-point structural unit as shown in Formula II; the connection point of each two-connection-point structural unit is connected to the connection point of the four-connection-point structural unit; and the connection point of each four-connection-point structural unit is connected to the connection point of the two-connection-point structural unit.

[0022]

[0023] In the formula II, R is one of the following structures:

[0024]

[0025] The fully conjugated covalent organic framework compound provided by the present invention is composed of structural units represented by Formula I and Formula II connected to each other to form a multi-ring skeleton structure with highly conjugated properties, which can improve the conductivity, chemical stability and thermal stability of COFs.

[0026] The fully conjugated covalent organic framework compound provided by the present invention is used as an electrode material. Its highly conjugated structure facilitates charge transfer, and its polycyclic structure avoids the inadequate utilization of active sites caused by the dense structure of traditional COFs, thereby improving the specific capacity and cycle stability of the battery. The results of the examples show that after the fully conjugated covalent organic framework compound provided by the present invention is used as the negative electrode of a lithium-ion battery, the initial discharge specific capacity of the battery reaches 978.8 mAh g -1 , at a voltage of 0.01 to 3 V, the current density is 1 A·g -1 After 1800 cycles, the discharge capacity is 748.6 mAh g -1 , the capacity retention rate is as high as 76.4%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a SEM image of the fully conjugated covalent organic framework compound provided in Example 1 of the present invention, magnified 85,000 times;

[0028] Figure 2 This is a 35,000-fold magnified SEM image of the fully conjugated covalent organic framework compound provided in Example 1 of the present invention;

[0029] Figure 3 This is a 35,000-fold magnified SEM image of the fully conjugated covalent organic framework compound provided in Comparative Example 1 of the present invention;

[0030] Figure 4 This is a cycle performance diagram of the lithium-ion battery prepared in Application Example 1 of the present invention;

[0031] Figure 5 This is a cycle performance diagram of the lithium-ion battery prepared in Application Example 2 of the present invention;

[0032] Figure 6 This is a cycle performance diagram of the lithium-ion battery prepared in comparative application example 1 of the present invention. DETAILED DESCRIPTION

[0033] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0034] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses high-purity raw materials or raw materials with a purity commonly used in the field of lithium-ion batteries.

[0035] The present invention provides a fully conjugated covalent organic framework compound, wherein the fully conjugated covalent organic framework compound is formed by interconnecting a two-connection-point structural unit as shown in Formula I and a four-connection-point structural unit as shown in Formula II; the connection point of each two-connection-point structural unit is connected to the connection point of the four-connection-point structural unit; and the connection point of each four-connection-point structural unit is connected to the connection point of the two-connection-point structural unit.

[0036]

[0037] In the formula II, R is one of the following structures:

[0038]

[0039] In the present invention, the chemical structure of the fully conjugated covalent organic framework compound is preferably:

[0040]

[0041] The fully conjugated covalent organic framework compound provided by the present invention is composed of structural units represented by Formula I and Formula II connected to each other to form a multi-ring skeleton structure with highly conjugated properties, which can improve the conductivity, chemical stability and thermal stability of COFs.

[0042] The present invention also provides a method for preparing the fully conjugated covalent organic framework compound described in the above technical solution, comprising: mixing a first monomer, a second monomer, an ammonium source and an organic solvent and then conducting a solvothermal reaction to obtain a fully conjugated covalent organic framework compound; the first monomer is pyrene-4,5,9,10-tetraketone, and the second monomer is 1,3,6,8-tetrakis(4-formaldehydephenyl)pyrene, tetrakis-(4-formyl-(1,1-biphenyl))ethylene, tetrakis-(4-formylphenyl)ethylene or 1,2,4,5-tetrakis(4-formylphenyl)benzene.

[0043] In the present invention, the first monomer is pyrene-4,5,9,10-tetraketone, which has a fully conjugated molecular structure. In addition, the two adjacent ketone groups can react with the ammonium source and the aldehyde group of the second monomer to form an imidazole ring, thereby improving the stability of COFs.

[0044] In the present invention, the second monomer is 1,3,6,8-tetrakis(4-formaldehydephenyl)pyrene, tetrakis(4-formaldehyde-(1,1-biphenyl))ethylene, tetrakis(4-formaldehydephenyl)ethylene, or 1,2,4,5-tetrakis(4-formylphenyl)benzene. The above compounds contain four aldehyde groups with a centrosymmetric and fully conjugated structure, which can react with the ammonium source and the two ketone groups adjacent to the first monomer to form an imidazole ring, thereby improving the stability of COFs. The centrosymmetric and fully conjugated structure can enable COFs to form a regular multi-ring structure, improve the stability of COFs, and facilitate the exposure of active sites. When COFs are used as electrodes, they can improve the specific capacity and cycle stability of batteries.

[0045] In the present invention, the ammonium source is preferably ammonium formate or ammonium acetate. Ammonium formate or ammonium acetate can provide ammonium ions, which react with the two adjacent ketone groups of the first monomer and the one aldehyde group of the second monomer to form an imidazole ring. In addition, the use of ammonium formate or ammonium acetate provides mild reaction conditions and a stable system, which is conducive to further improving the reaction yield. As an embodiment of the present invention, the molar ratio of the ammonium source to the first monomer and the second monomer can be 12:2:1.

[0046] In the present invention, the organic solvent is preferably one or more of dioxane, mesitylene, n-butanol, and o-dichlorobenzene. In one embodiment, the organic solvent may be mesitylene and dioxane; the volume ratio of mesitylene to dioxane may be 1:1. The amount of the organic solvent used is not particularly limited, as long as the raw materials are uniformly mixed and the solvothermal reaction proceeds normally.

[0047] The present invention has no particular requirements for the specific method of mixing, as long as the raw materials can be mixed uniformly. As an embodiment of the present invention, the mixing can be carried out in a Pyrex tube, and the mixing is carried out by ultrasound, and the ultrasound time can be 15 minutes.

[0048] In the present invention, the solvent thermal reaction is preferably carried out in a vacuum environment; carrying out the solvent thermal reaction in a vacuum environment is beneficial to reducing impurities and side reactions, and further improving product purity and conversion rate.

[0049] As one embodiment of the present invention, the solvothermal reaction may further include a pretreatment. The pretreatment is preferably to place the Pyrex tube containing the uniformly mixed raw materials in liquid nitrogen for rapid freezing, evacuate for 10 minutes, then pass nitrogen into the Pyrex tube, and thaw the Pyrex tube in water. The freezing-evacuation-nitrogen passing-thaw cycle is repeated three times, and finally the Pyrex tube is frozen, evacuated, and sealed with a flame.

[0050] In the present invention, the temperature of the solvothermal reaction is preferably 100-200°C, more preferably 140-160°C; as an embodiment of the present invention, the temperature of the solvothermal reaction can be 120°C, 130°C, 150°C, 170°C, or 180°C. In the present invention, the time of the solvothermal reaction is preferably 24-120 hours, more preferably 72-96 hours; as an embodiment of the present invention, the time of the solvothermal reaction can be 36 hours, 48 ​​hours, 60 hours, 72 hours, 84 hours, 96 hours, or 120 hours. Solvothermal reaction parameters within the above ranges are conducive to the formation of COFs and further improve the reaction yield.

[0051] The present invention has no particular limitation on the heating device for the solvothermal reaction, as long as it can provide a stable heat source for the solvothermal reaction. In an embodiment of the present invention, the heating device for the solvothermal reaction is a blast oven.

[0052] After the solvothermal reaction is completed, the present invention preferably performs post-processing on the obtained product. As one embodiment of the present invention, the post-processing may include solid-liquid separation, washing, purification and drying performed sequentially; the solid-liquid separation may be performed by suction filtration; the washing may be performed by washing with N-methylpyrrolidone (DMF) and anhydrous ethanol in sequence; the purification may be Soxhlet purification using tetrahydrofuran (THF), the temperature of the Soxhlet purification may be 100-150°C, and the purification time may be 24-72 hours; the drying may be vacuum drying, and the drying temperature may be 100°C.

[0053] The preparation method provided by the present invention has mild conditions, is easy to control, has high conversion efficiency, and is conducive to industrial production.

[0054] The present invention also provides the use of the fully conjugated covalent organic framework compound described in the above technical solution or the fully conjugated covalent organic framework compound prepared by the preparation method described in the above technical solution in lithium ion batteries.

[0055] The present invention also provides a lithium-ion battery negative electrode, comprising a current collector and a negative electrode material coated on the surface of the current collector, wherein the negative electrode material comprises an active material, a conductive agent and a binder, and the active material is the fully conjugated covalent organic framework compound described in the above technical solution or the fully conjugated covalent organic framework compound prepared by the preparation method described in the above technical solution.

[0056] In the present invention, the mass content of the fully conjugated covalent organic framework compound in the negative electrode material is preferably 1-50%, more preferably 20-30%. As one embodiment of the present invention, the mass content of the fully conjugated covalent organic framework compound in the negative electrode material can be 5%, 10%, 15%, 20%, 25%, 30%, 40%, or 50%. A mass content of the fully conjugated covalent organic framework compound as the active material of the negative electrode material within the above range is conducive to fully exerting its function and further improving the electrochemical performance of the electrode.

[0057] As an embodiment of the present invention, the conductive agent may be acetylene black, the binder may be polyvinylidene fluoride (PVDF), and the current collector may be a carbon-coated copper foil current collector; the mass ratio of the active material, the conductive agent, and the binder may be 5:4:1.

[0058] In an embodiment of the present invention, the preparation method of the lithium ion battery negative electrode can be: the active material, the conductive agent and the binder are mixed and added to N-methylpyrrolidone (NMP), the mixture is shaken and mixed to obtain a slurry, the slurry is evenly coated on the current collector, and then vacuum dried at 110°C for 12 hours to obtain the lithium ion battery negative electrode.

[0059] The lithium-ion battery negative electrode provided by the present invention uses a fully conjugated covalent organic framework compound as the electrode material. The highly conjugated structure is conducive to the transmission of charges, and the multi-ring structure avoids the inability to fully utilize the active sites caused by the dense structure of traditional COFs, thereby improving the battery's specific capacity and cycle stability.

[0060] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] Example 1

[0062] A fully conjugated covalent organic framework compound with the following structural formula:

[0063] Denoted as TFPPy-PyTO-COF.

[0064] The preparation method is as follows:

[0065] Add 29.7 mg (0.048 mmol) of 1,3,6,8-tetrakis(4-formylphenyl)pyrene, 25.2 mg (0.096 mmol) of pyrene-4,5,9,10-tetraone, 44.4 mg (0.576 mmol) of ammonium acetate, and 2 mL of a mixed solvent of mesitylene and dioxane (volume ratio 1:1) into a 10 mL Pyrex tube and mix thoroughly by ultrasonication for 15 min.

[0066] The Pyrex tube containing the mixed material was placed in liquid nitrogen for rapid freezing and connected to a vacuum pump for 10 minutes. Nitrogen was then introduced into the Pyrex tube and the tube was placed in water for thawing. This freezing-vacuuming-nitrogen-thawing cycle was repeated three times. Finally, after freezing and vacuuming, the Pyrex tube was sealed with a flame, allowed to thaw to room temperature, and then placed in a forced air oven for reaction at 150°C for 120 hours.

[0067] After the reaction is completed, the mixture is cooled to room temperature, filtered, and the precipitate is collected. The precipitate is washed with DMF and anhydrous ethanol in sequence, and Soxhlet purification is performed with THF at 150°C for 24 hours. Then, the mixture is vacuum-dried at 100°C to obtain a dark yellow powder, which is a fully conjugated covalent organic framework compound.

[0068] The micromorphology of the product was observed using a scanning electron microscope to obtain an SEM image, such as Figure 1 、 2 As shown. Figure 1 、 2 It can be seen that TFPPy-PyTO-COF is mainly a rod-shaped morphology formed by stacking thin layer structures. This structure usually has a large specific surface area, and the surface of the thin layer structure may expose more active sites. At the same time, the thin layer structure is conducive to improving the conductivity of electrons and ions in the material, which is conducive to the redox reaction.

[0069] Example 2

[0070] A fully conjugated covalent organic framework compound with the following structural formula:

[0071]

[0072] Denoted as TFPBi-PyTO-COF.

[0073] The preparation method was the same as that of Example 1, except that 35.9 mg, 0.048 mmol of tetrakis-(4-formyl-(1,1-biphenyl))ethylene was used instead of 1,3,6,8-tetrakis(4-formylphenyl)pyrene.

[0074] Comparative Example 1

[0075] A fully conjugated covalent organic framework compound with the following structural formula:

[0076] Denoted as TFPBe-PyTO-COF. The preparation method was the same as that in Example 1, except that 23.7 mg, 0.048 mmol of 1,2,4,5-tetrakis(4-formylphenyl)benzene was used instead of 1,3,6,8-tetrakis(4-formylphenyl)pyrene.

[0077] The micromorphology of the product was observed using a scanning electron microscope to obtain an SEM image, such as Figure 3 As shown. Figure 3 It can be seen that TFPBe-PyTO-COF is mainly a uniform spherical structure. The spherical structure usually reduces the specific surface area and limits the exposure of redox active sites, resulting in lower electrochemical activity. The spherical particles have fewer particle contact points, resulting in a slower charge transfer rate, and are not as good as thin layer structures in charge conduction.

[0078] Application Examples 1-2, Comparative Application Example 1

[0079] The fully conjugated covalent organic framework compounds provided in Examples 1-2 and Comparative Example 1 were applied as active materials to the negative electrode of a lithium-ion battery, and the battery was assembled. The preparation method is as follows:

[0080] The negative electrode active material, acetylene black, and PVDF were mixed in a 5:4:1 (mass ratio) solution and added to NMP. After thorough shaking and mixing, the slurry was evenly coated on a carbon-coated copper foil current collector and vacuum-dried at 110°C for 12 hours. After drying, the slurry was removed and cut into 12mm diameter negative electrode sheets using a cutting machine.

[0081] The weighed electrode was placed in an argon glove box with water and oxygen content less than 0.01 ppm. Metal lithium was used as the counter electrode, polypropylene diaphragm was used as the battery diaphragm, and 1M LiPF6 (EC / EMC, 3:7, v / v) was selected as the electrolyte to assemble into a CR2032 button battery.

[0082] The batteries prepared in Examples 1 and 2 and Comparative Example 1 were subjected to long cycle tests using the LAND battery testing system. The test voltage range was 0.01 to 3 V, and the current density was 1 A·g -1 , the results are as follows Figure 4 、 Figure 5 、 Figure 6 As shown. Figure 4 It can be seen that the initial discharge capacity of the battery prepared in Application Example 1 is 979.8 mAh g -1 After 1800 stable cycles, the discharge capacity is 748.6 mAh g -1 , the capacity retention rate is as high as 76.4%. Figure 5 It can be seen that the initial discharge capacity of the battery prepared in Application Example 2 is 889.4 mAh g -1 After 1800 stable cycles, the discharge capacity is 665.8 mAh g -1 , the capacity retention rate is as high as 74.9%.

[0083] from Figure 6 It can be seen that the initial discharge capacity of the battery prepared in Comparative Application Example 1 is 254.7 mAh g -1 After 1276 cycles, the capacity retention rate is only 39.8% (discharge capacity is 101.3 mAh g -1 ).

[0084] Through the electrochemical performance tests of Application Example 1 and Comparative Application Example 1, it can be seen that due to the introduction of pyrene units, TFPPy-PyTO-COF exhibits a higher degree of conjugation than TFPBe-PyTO-COF. The structure with a higher degree of conjugation not only further enhances the stability of the material but also helps to improve the conductivity of the covalent organic framework, thereby giving it better electrochemical performance.

[0085] It can be seen from the above examples and comparative examples that the fully conjugated covalent organic framework compound provided by the present invention can be used as an active material to significantly improve the discharge capacity and cycle stability of lithium-ion batteries.

[0086] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A fully conjugated covalent organic framework compound, characterized in that: The fully conjugated covalent organic framework compound is formed by interconnecting a two-connection-point structural unit as shown in Formula I and a four-connection-point structural unit as shown in Formula II; the connection point of each two-connection-point structural unit is connected to the connection point of the four-connection-point structural unit; and the connection point of each four-connection-point structural unit is connected to the connection point of the two-connection-point structural unit; In the formula II, R is one of the following structures:

2. The fully conjugated covalent organic framework compound according to claim 1, characterized in that The structural formula of the fully conjugated covalent organic framework compound is:

3. The fully conjugated covalent organic framework compound according to claim 1, characterized in that The structural formula of the fully conjugated covalent organic framework compound is:

4. A method for preparing the fully conjugated covalent organic framework compound according to any one of claims 1 to 3, comprising: A first monomer, a second monomer, an ammonium source and an organic solvent are mixed and then subjected to a solvothermal reaction to obtain a fully conjugated covalent organic framework compound; the first monomer is pyrene-4,5,9,10-tetraketone, and the second monomer is 1,3,6,8-tetrakis(4-formaldehydephenyl)pyrene, tetrakis-(4-formyl-(1,1-biphenyl))ethylene, tetrakis-(4-formylphenyl)ethylene or 1,2,4,5-tetrakis(4-formylphenyl)benzene.

5. The preparation method according to claim 4, characterized in that The solvent thermal reaction is carried out in a vacuum environment, the reaction temperature is 100-200° C., and the reaction time is 24-120 hours.

6. The preparation method according to claim 4, characterized in that The ammonium source is ammonium formate or ammonium acetate.

7. The preparation method according to claim 4, characterized in that The organic solvent is one or more of dioxane, mesitylene, n-butanol and o-dichlorobenzene.

8. Use of the fully conjugated covalent organic framework compound according to any one of claims 1 to 3 or the fully conjugated covalent organic framework compound prepared by the preparation method according to any one of claims 4 to 7 in lithium-ion batteries.

9. A lithium ion battery negative electrode, characterized in that It comprises a current collector and a negative electrode material coated on the surface of the current collector, wherein the negative electrode material comprises an active material, a conductive agent and a binder, and the active material is a fully conjugated covalent organic framework compound as described in any one of claims 1 to 3 or a fully conjugated covalent organic framework compound prepared by the preparation method as described in any one of claims 4 to 7.

10. The lithium-ion battery negative electrode according to claim 9, characterized in that The mass content of the fully conjugated covalent organic framework compound in the negative electrode material is 1 to 50%.

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