Covalent organic framework material as well as preparation method and application thereof

Abstract

The invention provides a covalent organic framework material as well as a preparation method and application thereof, and belongs to the technical field of electrochemical energy storage. The covalent organic framework material provided by the invention is a polymer as shown in a formula I, and two adjacent carbons of a cyclohexane group in the polymer are respectively connected with two ortho-nitrogen in tetraaminobenzene through carbon-nitrogen double bonds. The covalent organic framework material provided by the invention has a highly conjugated two-dimensional structure, so that the ratio of active sites is increased, the conductivity and stability of the material are improved, and the electrochemical performance is improved. A lithium ion half battery assembled by a lithium ion capacitor negative electrode prepared from the covalent organic framework material provided by the invention still has high specific capacity of 500mAh. G <-1 > after circulating for 1600 circles under the current density of 2A. G <-1 >, and has high specific capacity, excellent rate capability and good cycle performance.

Description

Technical Field

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

[0002] As a new type of electrochemical energy storage device, lithium-ion capacitors have huge market application value and competitive advantages. At present, the problems of lithium-ion capacitors are mainly concentrated in the capacity mismatch between the positive and negative electrodes and the imbalance of charge storage dynamics, which limits the further improvement of the power density and energy density of lithium-ion capacitors.

[0003] As a new type of organic porous material, covalent organic framework material has the advantages of low density, large specific surface area, high crystallinity, controllable pore size, good stability and high orientation, and is considered to be one of the excellent candidate materials for negative electrode materials of lithium ion capacitors. However, most covalent organic framework materials have low inherent conductivity and poor accessibility of redox sites, which cannot meet the needs of practical applications. The related study "A TP-COF covalent organic framework material prepared by microwave ultrasound and its preparation method and application" provides a lithium ion battery prepared by TP-COF covalent organic framework material. The lithium ion battery has the characteristics of high specific capacity, good cycle stability and good rate performance, but its performance is poor at 2A·g -1 The specific capacity can only reach 250 mAh g at a current density of -1 The number of cycles can only reach 120, and the specific capacity and cycle stability still need to be further improved. Summary of the invention

[0004] The purpose of the present invention is to provide a covalent organic framework material and its preparation method and application. The covalent organic framework material provided by the present invention has abundant C=N bond active sites, and as a negative electrode material for lithium ion capacitors, the lithium ion capacitors can have high specific capacity, excellent rate performance and good cycle performance.

[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 covalent organic framework material having a chemical structure as shown in Formula I:

[0007]

[0008] The present invention also provides a method for preparing the covalent organic framework material described in the above technical solution, comprising:

[0009] Cyclohexanone, tetraaminobenzene and an organic solvent are first mixed, then second mixed with an acid solution and subjected to a Schiff base reaction to obtain a covalent organic framework material.

[0010] Preferably, the mass ratio of cyclohexanone to tetraaminobenzene is 1:(1.3-1.7).

[0011] Preferably, the organic solvent comprises a first organic solvent and a second organic solvent;

[0012] The first organic solvent includes dioxane or o-dichlorobenzene;

[0013] The second organic solvent includes mesitylene or n-butanol.

[0014] Preferably, the volume ratio of the first organic solvent to the second organic solvent is 1:(0.8-1.2).

[0015] Preferably, the ratio of the mass of the cyclohexanone to the volume of the first organic solvent is (60-95) mg: (1-2) ml.

[0016] Preferably, the concentration of the acid solution is 3-12 mol / L; the acid solution includes acetic acid, sulfuric acid or p-toluenesulfonic acid.

[0017] Preferably, the ratio of the mass of cyclohexanone to the volume of the acid solution is (60-95) mg: (0.2-0.4) ml.

[0018] Preferably, the temperature of the Schiff base reaction is 120-180° C., and the time of the Schiff base reaction is 48-72 hours.

[0019] The present invention also provides the use of the covalent organic framework material described in the above technical solution or the covalent organic framework material prepared by the preparation method described in the above technical solution in the negative electrode of a lithium ion capacitor.

[0020] The covalent organic framework material provided by the present invention is a polymer shown in Formula I, in which two adjacent carbon atoms of the cyclohexane group in the polymer are connected to two nitrogen atoms in the ortho position of tetraaminobenzene through carbon-nitrogen double bonds. The covalent organic framework material provided by the present invention has a highly conjugated two-dimensional structure, which not only increases the proportion of active sites, but also helps to improve the conductivity and stability of the material, thereby facilitating the improvement of electrochemical performance. The results of the embodiment show that the lithium ion half-cell assembled with the negative electrode of the lithium ion capacitor prepared by the covalent organic framework material provided by the present invention has a high conductivity at 2A·g -1 At a current density of 1.5 MW, it still has a capacity of 500 mAh g after 1600 cycles. -1 It has high specific capacity, excellent rate performance and good cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a SEM image of the covalent organic framework material in Example 1 of the present invention;

[0022] Figure 2 is the Raman spectrum of the covalent organic framework material in Example 1 of the present invention;

[0023] Figure 3 This is a rate performance diagram of a lithium ion half-cell assembled with the negative electrode of a lithium ion capacitor in Application Example 1 of the present invention;

[0024] Figure 4 The lithium ion half-cell assembled from the negative electrode of the lithium ion capacitor in Application Example 1 of the present invention is 2A·g -1 Cycling performance diagram at different current densities. DETAILED DESCRIPTION

[0025] The present invention provides a covalent organic framework material having a chemical structure as shown in Formula I:

[0026]

[0027] The covalent organic framework material provided by the present invention is a polymer shown in formula I, in which two adjacent carbons of a cyclohexane group in the polymer are connected to two adjacent nitrogens in tetraaminobenzene through carbon-nitrogen double bonds respectively.

[0028] The covalent organic framework material provided by the present invention has a highly conjugated two-dimensional structure, which not only increases the proportion of active sites, but also helps to improve the electrical conductivity and stability of the material, thereby facilitating the improvement of electrochemical performance.

[0029] The present invention also provides a method for preparing the covalent organic framework material described in the above technical solution, comprising:

[0030] Cyclohexanone, tetraaminobenzene and an organic solvent are first mixed, then second mixed with an acid solution and subjected to a Schiff base reaction to obtain a covalent organic framework material.

[0031] In the present invention, the mass ratio of cyclohexanone to tetraaminobenzene is preferably 1:(1.3-1.7), more preferably 1:1.5. The present invention can ensure a more complete Schiff base reaction by limiting the mass ratio of cyclohexanone to tetraaminobenzene to the above range.

[0032] In an embodiment of the present invention, the cyclohexanone is cyclohexanone octahydrate.

[0033] In the present invention, the organic solvent preferably includes a first organic solvent and a second organic solvent; the first organic solvent preferably includes dioxane or o-dichlorobenzene; and the second organic solvent preferably includes mesitylene or n-butanol.

[0034] As an embodiment of the present invention, the first organic solvent and the second organic solvent can be used in combination; when the first organic solvent is dioxane, the second organic solvent can be mesitylene; when the first organic solvent is o-dichlorobenzene, the second organic solvent can be n-butanol. In the present invention, the first organic solvent and the second organic solvent are used in combination to make the polarity of the first organic solvent and the second organic solvent compatible with the solubility of the monomer, thereby making the reaction more complete.

[0035] In the present invention, the volume ratio of the first organic solvent to the second organic solvent is preferably 1: (0.8-1.2), more preferably 1: 1. The present invention limits the volume ratio of the first organic solvent to the second organic solvent to the above range to better enable the subsequent reaction to proceed.

[0036] As an embodiment of the present invention, the ratio of the mass of the cyclohexanone to the volume of the first organic solvent can be (60-95) mg: (1-2) ml, can also be (62-80) mg: (1.2-1.8) ml, can also be (62-70) mg: (1.3-1.5) ml. The present invention limits the ratio of the mass of the cyclohexanone to the volume of the first organic solvent to the above range to ensure that the cyclohexanone and tetraaminobenzene are fully dispersed in the solvent, which is more conducive to the reaction.

[0037] In the present invention, the first mixing is preferably ultrasonic dispersion; the ultrasonic dispersion time is preferably 10 to 20 minutes, more preferably 15 minutes. The present invention does not specifically limit the ultrasonic frequency of ultrasonic dispersion, and the ultrasonic dispersion frequency commonly used by those skilled in the art can be used. The present invention fully disperses the monomer in the organic solvent through ultrasonic dispersion, which is conducive to the subsequent Schiff base reaction and better obtains the covalent organic framework material.

[0038] In the present invention, the solvent of the acid solution is preferably water; the concentration of the acid solution is preferably 3-12 mol / L, more preferably 5-8 mol / L, and further preferably 6 mol / L; the acid solution preferably includes acetic acid, sulfuric acid or p-toluenesulfonic acid, more preferably acetic acid. The present invention limits the concentration and type of the acid solution to the above range to better catalyze the Schiff base reaction of cyclohexanone and tetraaminobenzene, thereby ensuring a more complete reaction.

[0039] In the present invention, the ratio of the mass of cyclohexanone to the volume of the acid solution is preferably (60-95) mg: (0.2-0.4) ml, more preferably (60-80) mg: (0.2-0.3) ml, and further preferably (60-65) mg: (0.2-0.25) ml. The present invention limits the ratio of the mass of cyclohexanone to the volume of the acid solution to the above range so that the acid can better catalyze the reaction.

[0040] In the present invention, the second mixing is preferably ultrasonic dispersion; the ultrasonic dispersion time is preferably 10 to 20 minutes, more preferably 15 minutes. The present invention does not specifically limit the ultrasonic frequency of ultrasonic dispersion, and the ultrasonic dispersion frequency commonly used by those skilled in the art can be used. The present invention can ensure that the raw materials are fully mixed through the ultrasonic dispersion of the second mixing, so that the subsequent Schiff base reaction can be more fully carried out.

[0041] In the present invention, the Schiff base reaction is preferably carried out under vacuum conditions.

[0042] As an embodiment of the present invention, the vacuum condition may be achieved by degassing the mixed liquid obtained by the second mixing and then flame sealing it.

[0043] As an embodiment of the present invention, the number of degassing treatments may be three times; the degassing treatment may be freezing, vacuumizing and thawing the mixed liquid in sequence; the freezing may be liquid nitrogen bath freezing; the temperature of the liquid nitrogen bath freezing may be 70-77K; the freezing time of the liquid nitrogen bath may be 3-5 minutes; the vacuumizing equipment may be a vacuum pump; the vacuumizing time may be 10-20 minutes; the thawing method may be hot water bath thawing; the hot water bath thawing temperature may be 20-35°C; the hot water bath thawing time may be 5-10 minutes.

[0044] The present invention has no special limitation on the flame sealing operation, and the flame sealing operation commonly used by those skilled in the art may be adopted.

[0045] After the flame sealing is completed, the sealed mixture is preferably heated in the present invention.

[0046] As an embodiment of the present invention, the heating temperature may be 20 to 50° C.; the heating time may be 30 to 60 minutes.

[0047] As an embodiment of the present invention, the Schiff base reaction can be carried out in an oven; the temperature of the Schiff base reaction can be 120-180°C, 130-160°C, or 150°C; the time of the Schiff base reaction can be 48-72h, 54-66h, or 60h. In the present invention, the temperature of the Schiff base reaction will affect the structure of the material. A temperature below 120°C will result in incomplete reaction and incomplete material structure. A temperature above 180°C will result in too fast reaction speed, poor crystallinity, and incomplete material structure. The time of the Schiff base reaction will affect the structure of the material. A too short reaction time will result in insufficient reaction and incomplete material structure. A too long time will result in low reaction efficiency. The present invention limits the temperature and time of the Schiff base reaction to the above range to ensure that the obtained polymer has the structure shown in Formula I, and the polymer has a suitable molecular weight, so as to ensure that the lithium ion half-battery assembled with the negative electrode of the lithium ion capacitor prepared by the polymer has a high specific capacity, excellent rate performance, and good cycle performance.

[0048] After the Schiff base reaction is completed, the present invention preferably sequentially washes, purifies and dries the product of the Schiff base reaction to obtain a covalent organic framework material.

[0049] As an embodiment of the present invention, the washing liquids used in the washing can be N,N-dimethylformamide and ethanol in sequence; the number of washings can be independently 3 to 6 times.

[0050] As an embodiment of the present invention, the purification can be Soxhlet purification; the solvent used for the Soxhlet purification can be tetrahydrofuran; the temperature of the Soxhlet purification can be 110-150°C, or 120-140°C; or 130°C; the time of the Soxhlet purification can be 24-48h, or 24-26h.

[0051] As an embodiment of the present invention, the drying can be vacuum drying; the temperature of the vacuum drying can be 80-120°C; it can also be 90-100°C; the time of the vacuum drying can be 12-18h, or 12-14h; the vacuum degree of the vacuum drying can be 0.01-0.05mmHg. The present invention has no special limitation on the equipment for the vacuum drying, and vacuum drying equipment well known in the art can be used. In an embodiment of the present invention, the equipment for the vacuum drying is a vacuum drying oven.

[0052] The present invention also provides the use of the covalent organic framework material described in the above technical solution or the covalent organic framework material prepared by the preparation method described in the above technical solution in the negative electrode of a lithium ion capacitor.

[0053] In the present invention, the method for preparing the negative electrode of the lithium ion capacitor preferably includes:

[0054] mixing a covalent organic framework material, a conductive agent, a binder and a solvent to obtain a slurry;

[0055] The slurry is coated on a carbon-coated copper foil and then dried to obtain a negative electrode for a lithium ion capacitor.

[0056] In the present invention, the covalent organic framework material, the conductive agent, the binder and the solvent are preferably mixed to obtain a slurry.

[0057] The present invention has no special limitation on the types of the conductive agent, binder and solvent, and the conductive agent, binder and solvent commonly used by those skilled in the art can be used. In the application example of the present invention, the conductive agent is acetylene black, the binder is polytetrafluoroethylene, and the solvent is N-methylpyrrolidone (NMP).

[0058] In the present invention, the mass ratio of the covalent organic framework material, the conductive agent and the binder is preferably (5-7):(2-4):1, and more preferably 5:4:1.

[0059] The present invention has no particular limitation on the amount of the solvent added, and the solvent can be added as needed.

[0060] After obtaining the slurry, the present invention preferably applies the slurry to a carbon-coated copper foil and then dries it to obtain a negative electrode for a lithium ion capacitor.

[0061] The present invention has no special limitation on the coating method, and any coating method commonly used by those skilled in the art may be used.

[0062] As an embodiment of the present invention, the coating amount of the slurry on the carbon-coated copper foil can be 0.5-1.0 mg / cm 2 .

[0063] The present invention has no particular limitation on the drying temperature and time. The solvent in the slurry can be removed by using the drying temperature and time commonly used by those skilled in the art.

[0064] As an embodiment of the present invention, the loading amount of the covalent organic framework material on the negative electrode of the lithium ion capacitor can be 0.5 to 0.8 mg / cm 2 .

[0065] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part 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 creative work are within the scope of protection of the present invention.

[0066] Example 1

[0067] A covalent organic framework material having a chemical structure as shown in Formula I:

[0068]

[0069] The preparation method of the covalent organic framework material:

[0070] 1.5 ml of dioxane and 1.5 ml of mesitylene were added to a Pyrex tube, followed by the addition of cyclohexane (cyclohexane octahydrate, 62.44 mg, 0.2 mmol) and tetraaminobenzene (85.20 mg, 0.3 mmol), and ultrasonic dispersion was performed for 20 min. Then, acetic acid solution (0.2 ml, 6 mol / L) was added and ultrasonic dispersion was performed for 15 min. Then, the Pyrex tube was frozen in a liquid nitrogen bath (the freezing temperature was 77 K), vacuumed for 15 min, and then thawed in a hot water bath (25° C.), and repeated three times. After freezing-vacuuming-thawing in a hot water bath, the tube was flame-sealed under vacuum conditions. The thawed Pyrex tube was placed in an oven at 120°C for 72 hours to perform a Schiff base reaction. After the reaction was completed, the tube was cooled and the product was collected by filtration. After washing with N,N-dimethylformamide (washed three times, 10 mL each time) and ethanol (washed three times, 10 mL each time), tetrahydrofuran was used as a solvent, and the product was purified in a Soxhlet extractor at 110°C for 24 hours. The obtained product was vacuum dried at 80°C for 12 hours to obtain a covalent organic framework material, which was recorded as TAB-COF-1.

[0071] The mass ratio of cyclohexanone to tetraaminobenzene is 1:1.36;

[0072] The volume ratio of the first organic solvent (dioxane) to the second organic solvent (mesitylene) is 1:1;

[0073] The ratio of the mass of the cyclohexanone to the volume of the first organic solvent (dioxane) is 62.44 mg:1.5 ml;

[0074] The ratio of the mass of the cyclohexanone to the volume of the acetic acid solution is 62.44 mg:0.2 ml.

[0075] Example 2

[0076] The only difference between Example 2 and Example 1 is that the Schiff base reaction temperature is 150° C., and the other steps are the same as Example 1. The obtained covalent organic framework material is recorded as TAB-COF-2.

[0077] Example 3

[0078] The only difference between Example 3 and Example 1 is that the first organic solvent is o-dichlorobenzene and the second organic solvent is n-butanol. The other steps are the same as Example 1. The obtained covalent organic framework material is recorded as TAB-COF-3.

[0079] The covalent organic framework material in Example 1 was observed using a scanning electron microscope, and the obtained SEM image is as follows: Figure 1 As shown, from Figure 1 It can be seen that the covalent organic framework material in Example 1 exhibits a wrinkled layered morphology, which is conducive to the infiltration of the electrolyte and the exposure of the active sites.

[0080] The covalent organic framework in Example 1 was subjected to Raman testing using a laser Raman spectrometer (LabRAM HR Evolution). The obtained Raman spectrum is as follows: Figure 2 As shown in the figure, it can be seen that the Raman spectra of the covalent organic framework material in Example 1 are at 1361 and 1514 cm -1 There are two peaks at , which are attributed to the D band and G band of TAB-COF-1; from the Raman spectrum, the ID / IG value is 0.92, indicating that TAB-COF-1 has a graphene-like two-dimensional structure.

[0081] Application Example 1

[0082] The application method of the covalent organic framework material in Example 1 in the negative electrode of a lithium ion capacitor:

[0083] The covalent organic framework material in Example 1 was dispersed in an NMP solution with acetylene black and polytetrafluoroethylene in a mass ratio of 5:4:1, ground into a slurry and uniformly coated on a carbon-coated copper foil, then dried at 110°C in a vacuum environment for 12 hours, and cut into discs with a diameter of 12 mm using a cutting machine to obtain a lithium ion capacitor negative electrode, which was recorded as TAB-COF-E-1; the loading of the covalent organic framework material in the lithium ion capacitor negative electrode was 0.6 mg / cm 2 .

[0084] Application Example 2

[0085] The difference between Application Example 2 and Application Example 1 is that the covalent organic framework material in Example 2 is used to replace the covalent organic framework material in Example 1, and the rest is the same as Application Example 1.

[0086] Application Example 3

[0087] The difference between Application Example 3 and Application Example 1 is that the covalent organic framework material in Example 3 is used to replace the covalent organic framework material in Example 1, and the rest is the same as Application Example 1.

[0088] Test Case

[0089] A CR-2032 button cell was assembled using a metallic lithium sheet as the counter electrode, a polypropylene (PP) separator, and a 1M LiPF6 (EC / DEC / DMC, 1:1:1, v / v / v) electrolyte. The entire assembly process was carried out in an argon-filled glove box. The assembled lithium-ion half-cell was placed on a Land CT2001A battery testing system for electrochemical performance testing at a temperature of 25°C and a voltage range of 0.01V to 3V.

[0090] The rate performance diagram of the lithium-ion half-cell assembled with the negative electrode of the lithium-ion capacitor in Application Example 1 is as follows: Figure 3 As shown, from Figure 3 It can be seen that at 0.1A·g -1 The discharge capacity is 980 mAh g -1 As the current density increases, the discharge capacity gradually decreases. When the current density returns to 0.1A·g -1 , the discharge specific capacity returns to the initial level.

[0091] The lithium-ion half-cell assembled from the negative electrode of the lithium-ion capacitor in Application Example 1 is 2A·g -1 Long cycle charge and discharge test was carried out under current density, and the cycle performance diagram is shown in Figure 4 As shown, from Figure 4 It can be seen that at 2A·g -1 At the current density, the discharge capacity is 500mAh g after 1600 cycles. -1 , which shows that the lithium ion half-cell assembled with the negative electrode of the lithium ion capacitor in Application Example 1 has excellent lithium ion storage capacity, high specific capacity and good cycle stability.

[0092] The lithium ion half-cell assembled from the negative electrode of the lithium ion capacitor prepared by the covalent organic framework material provided by the present invention has a high conductivity at 2A·g -1 At a current density of 1.5 MW, it still has a capacity of 500 mAh g after 1600 cycles. -1 It has high specific capacity, excellent rate performance and good cycle performance.

[0093] 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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A covalent organic framework material having a chemical structure as shown in Formula I:

2. The method for preparing the covalent organic framework material according to claim 1, comprising: Cyclohexanone, tetraaminobenzene and an organic solvent are first mixed, then second mixed with an acid solution and subjected to a Schiff base reaction to obtain a covalent organic framework material.

3. The preparation method according to claim 2, characterized in that: The mass ratio of cyclohexanone to tetraaminobenzene is 1:(1.3-1.7).

4. The preparation method according to claim 2, characterized in that: The organic solvent comprises a first organic solvent and a second organic solvent; The first organic solvent includes dioxane or o-dichlorobenzene; The second organic solvent includes mesitylene or n-butanol.

5. The preparation method according to claim 4, characterized in that: The volume ratio of the first organic solvent to the second organic solvent is 1:(0.8-1.2).

6. The preparation method according to claim 5, characterized in that: The ratio of the mass of the cyclohexanone to the volume of the first organic solvent is (60-95) mg: (1-2) ml.

7. The preparation method according to claim 2, characterized in that: The concentration of the acid solution is 3-12 mol / L; the acid solution includes acetic acid, sulfuric acid or p-toluenesulfonic acid.

8. The preparation method according to claim 7, characterized in that: The ratio of the mass of the cyclohexanone to the volume of the acid solution is (60-95) mg: (0.2-0.4) ml.

9. The preparation method according to claim 2, characterized in that: The temperature of the Schiff base reaction is 120-180° C., and the time of the Schiff base reaction is 48-72 hours.

10. Use of the covalent organic framework material according to claim 1 or the covalent organic framework material prepared by the preparation method according to any one of claims 2 to 9 in the negative electrode of a lithium ion capacitor.

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