Bipolar covalent organic framework and carbon nanotube composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a bipolar covalent organic framework and carbon nanotube composite material as well as a preparation method and application thereof. According to the bipolar organic covalent framework electrode, N, N, N ', N'-tetraphenylene-1, 4-phenylenediamine and phephthaldehydrate serve as construction units, in-situ growth is carried out on a carbon nano tube, and TATP-COF (at) CNT is synthesized through a solvothermal method. According to the method, n-type and p-type redox active sites are simultaneously integrated in a bipolar COF, and the obtained organic positive electrode effectively stores positive ions and negative ions during charging and discharging, so that the inherent advantages of two molecular types, including high capacity and high voltage of the battery, are utilized; and in-situ growth is carried out on the CNT, so that the accessibility of active sites and the charge transfer efficiency are ensured.

Description

Technical Field

[0001] This invention relates to the field of post-lithium-ion battery technology, and in particular to a bipolar covalent organic framework@carbon nanotube composite material, its preparation method, and its application. Background Technology

[0002] The growing demand for electrochemical energy storage has driven the development of post-lithium battery technologies that offer low cost, high safety, and high energy efficiency, with multivalent ion batteries showing great potential in terms of energy density and economic benefits. Firstly, compared to monovalent alkali metal ion batteries (such as lithium, sodium, and potassium), each ion in a multivalent ion battery can transfer two to three times more electrons, resulting in higher positive electrode capacity. Secondly, they are characterized by low cost and high safety.

[0003] Rechargeable calcium-ion batteries (CIBs) exhibit a low redox potential (-2.87 V vs. SHE), close to that of lithium (-3.04 V vs. SHE), and high volumetric and gravimetric capacities (2072 mAh mL). -1 and 1337 mAh g -1 ); and when carrying the same charge, Ca 2+ (1.12 Å) exhibits better performance than Mg 2+ A larger radius (0.72 Å) results in a lower charge density, thus making it more efficient than Mg. 2+ It is more easily desolvated and exhibits faster kinetics. Furthermore, calcium is the third most abundant metallic element in the Earth's crust (4.66 × 10⁻⁶). 4 (ppm), therefore, rechargeable Ca batteries are considered one of the most attractive candidates for post-lithium-ion battery technology.

[0004] To date, the reported organic CIBs cathode materials are very limited and suffer from the following problems: 1. Some inorganic cathode materials exhibit slow ion diffusion and are prone to structural collapse during charge-discharge cycles, resulting in poor cycle stability. Organic small molecules also suffer from easy dissolution, which cannot solve the cycle stability defect. 2. Most of the reported organic cathode materials for calcium-ion batteries are n-type or p-type materials. N-type materials have the disadvantage of low voltage, while p-type materials have the disadvantage of low capacity. 3. Covalent organic frameworks have poor conductivity and mostly exist in the form of agglomeration, leading to insufficient utilization of active sites. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a bipolar covalent organic framework@carbon nanotube composite material and its preparation method, which improves electronic conductivity and the utilization rate of active sites, thereby enhancing the specific capacity and cycle stability of calcium-ion batteries.

[0006] A bipolar covalent organic framework@carbon nanotube composite material includes carbon nanotubes and a bipolar covalent organic framework grown in situ thereon, wherein the bipolar covalent organic framework has the following structure: .

[0007] This invention provides a method for preparing the aforementioned bipolar covalent organic framework@carbon nanotube composite material, comprising the following steps: (1) After ultrasonic treatment of N,N,N',N'-tetraphenyl-1,4-phenylenediamine, p-phthalaldehyde, CNT and organic solvent, a catalyst was added and ultrasonically treated mixed solution A. (2) The mixed solution A obtained in step (1) is frozen-vacuumed-thawed three times, and then heated in an oven to obtain a solid. The solid is washed and dried to obtain a bipolar covalent organic framework TATP-COF@CNT.

[0008] Further, in step (1), the mass ratio of N,N,N',N'-tetraphenyl-1,4-phenylenediamine to p-phthalaldehyde is 1:(1.76~3).

[0009] Furthermore, the organic solvent is n-butanol and o-dichlorobenzene, and the volume ratio of n-butanol to o-dichlorobenzene is 1:1.

[0010] Furthermore, the catalyst is acetic acid or p-toluenesulfonic acid.

[0011] Furthermore, the mass ratio of the catalyst to p-phthalaldehyde is 1-2:1.

[0012] Furthermore, the mass ratio of CNT to p-phthalaldehyde is 1:(4~8).

[0013] Furthermore, in step (2), the oven is heated to a temperature of 120~180℃ for a time of 72~120 h.

[0014] Furthermore, the washing specifically includes washing with N,N,-dimethylformamide and tetrahydrofuran in sequence.

[0015] Furthermore, the drying temperature is 80~100℃, and the drying time is 12~24 h.

[0016] This invention also provides the application of the aforementioned bipolar covalent organic framework@carbon nanotube composite material in the preparation of calcium-ion battery electrodes.

[0017] Furthermore, it is used in the preparation of the positive electrode for calcium-ion batteries, and its preparation method is as follows: The bipolar covalent organic framework@carbon nanotube composite material, conductive additives, and binders are ground and mixed, and a solvent is added for further mixing to obtain a block mixture. The mixture is then pressed into sheets using a roller mill and vacuum dried to obtain the positive electrode for a calcium-ion battery.

[0018] Furthermore, the mass ratio of the composite material, conductive additive, and adhesive is 6:3:1.

[0019] Furthermore, the conductive additive is one of Ketjen Black, acetylene black, or graphite conductive agent.

[0020] Furthermore, the adhesive is polyvinylidene fluoride and / or polytetrafluoroethylene, and the solvent is deionized water.

[0021] Furthermore, the tablet compression pressure is 1000–1400 psi.

[0022] Furthermore, the vacuum drying temperature is 60~80℃, and the drying time is 12~24 h.

[0023] Compared with the prior art, the beneficial effects of this invention are as follows: 1. This invention integrates both n-type and p-type redox active sites into bipolar COFs, resulting in an organic cathode that effectively stores cations and anions during charging and discharging, thereby utilizing the inherent advantages of both molecular types, including high battery capacity and high voltage; and in-situ growth on CNTs, forming a hierarchical core-shell heterostructure with CNTs, ensuring the accessibility of active sites, charge transfer efficiency, and rapid reaction kinetics.

[0024] 2. This invention uses N,N,N',N'-tetraphenyl-1,4-phenylenediamine, p-phthalaldehyde, and carbon nanotubes as main raw materials and is prepared by a solvothermal method. The synthesis method is simple and easy to operate, and it significantly improves the electrochemical performance of calcium-ion batteries. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation method of the TATP-COF@CNT composite material in Example 1; Figure 2 The images show the FTIR spectra of the TATP-COF@CNT composite material prepared in Example 1, and TA and TP. Figure 3 The N1s spectrum decomposition diagram of the X-ray photoelectron energy spectrum of TATP-COF@CNT composite material; Figure 4 SEM image of the TATP-COF@CNT composite material prepared in Example 1; Figure 5(a) shows the TATP prepared in Example 2. Cyclic CV curve images of COF@CNT batteries; Figure 5 (b) shows the TATP prepared in Comparative Example 2. Image of the cycle CV curve of a COF battery; Figure 5(c) shows the cycle CV curve of the NT-COF battery prepared in Comparative Example 4; Figure 6(a) shows the TATP prepared in Example 2. Impedance image of COF@CNT battery; Figure 6 (b) shows the TATP prepared in Comparative Example 2. Impedance image of COF battery; Figure 7(a) shows the TATP prepared in Example 2. Images showing the cycle performance of COF@CNT batteries at a current density of 0.1 A / g; Figure 7 (b) shows the TATP prepared in Comparative Example 2. Image showing the cycle performance of COF batteries at a current density of 0.1 A / g. Detailed Implementation

[0026] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0027] Example 1 23.63 mg of N,N,N',N'-tetraphenyl-1,4-phenylenediamine, 13.41 mg of p-phthalaldehyde, 3.33 mg of CNT, 1 mL of n-butanol, and 1 mL of o-dichlorobenzene were added to a glass pressure-resistant tube and sonicated for 30 min. Then, 0.2 mL of 3 mol / L acetic acid was added, and the mixture was sonicated for 5 min to obtain mixed solution A. Mixed solution A was subjected to a freeze-evacuation-thaw cycle three times, and then heated in an oven at 120–180 °C for 72–120 h to obtain a solid. This solid was washed sequentially with N,N'-dimethylformamide and tetrahydrofuran, and then dried in an oven at 80–100 °C for 12–24 h to obtain the bipolar covalent organic framework TATP. COF@CNT.

[0028] The preparation method of the bipolar covalent organic framework@carbon nanotube composite material of the present invention is as follows: Figure 1 As shown; Figure 2 The TATP prepared in this embodiment The infrared absorption spectra (FTIR) of COF@CNT composite materials and TA and TP show that the wavelengths are around 1617 cm⁻¹. -1 and 1313 cm -1There are two peaks, one at 1617 cm. -1 The peak at 1313 cm⁻¹ corresponds to -C=N⁻. -1 This corresponds to -CN-; Figure 3 The N1s spectrum decomposition diagram of the X-ray photoelectron spectroscopy of the TATP-COF@CNT composite material prepared in this embodiment shows that the measured binding energy has been corrected. The binding energy has two peaks at 399.8 eV and 398.8 eV. The peak at 398.8 eV corresponds to -CN-, and the peak at 399.8 eV corresponds to -C=N. ; Figure 4 The image shows a scanning electron microscope (SEM) image of the TATP-COF@CNT composite material prepared in this embodiment. It can be seen that the nanosheets are uniformly wrapped on the surface of the carbon nanotubes.

[0029] Example 2 In this embodiment, the bipolar covalent organic framework material prepared in Example 1 is used as the positive electrode material for a calcium-ion battery. The specific operation is as follows: Weigh 30 mg of the bipolar covalent organic framework / carbon nanotube composite material TATP-COF@CNT obtained in Example 1, mix it with 15 mg of Ketjen black, and grind it for 30 min to obtain a positive electrode powder. Mix the positive electrode powder with 5 mg of polytetrafluoroethylene, add deionized water, and grind to obtain a block. Press the block on a roller mill, place it in a vacuum oven at 110°C for 12 h, and heat it at a pressure of 1000~1400 psi. Cut it into square electrode sheets with a mass of 1~1.16 mg to obtain the positive electrode material of the calcium ion battery.

[0030] The assembly of the calcium-ion battery includes: Using the above-prepared calcium-ion battery positive electrode material as the positive electrode, activated carbon cloth as the negative electrode, glass fiber (GF / D) as the separator, and adding 120 μL of electrolyte (0.5 MCa (TFSI)2 dissolved in G4 (tetraethylene glycol dimethyl ether)), the battery was assembled in an argon-filled glove box and assembled into a button cell in a 2025 button cell casing.

[0031] Comparative Example 1 This comparative example provides a method for preparing a bipolar covalent organic framework material, the steps of which are the same as those in Example 1, except that CNTs are not added, and the resulting composite material is TATP-COF.

[0032] Comparative Example 2 This comparative example provides a method for preparing a positive electrode material for a calcium-ion battery. The positive electrode material for the calcium-ion battery is prepared using TATP-COF prepared in Comparative Example 1, and the calcium-ion battery is assembled. The specific process steps are the same as in Example 2.

[0033] Comparative Example 3 This comparative example provides a method for preparing a bipolar covalent organic framework material, including the following steps: (1) Add 40 mg of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine (TTTA), 45.4 mg of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), 1 mL of mesitylene, 1 mL of 1-methyl-2-pyrrolidone and 0.01 mL of isoquinoline to a glass pressure-resistant tube and sonicate for 30 min to obtain mixed solution A; (2) The mixed solution A obtained in step (1) is subjected to freezing-vacuuming-thawing, and the cycle is repeated three times. It is then placed in an oven at 180~200℃ and heated for 96~120 h to obtain a solid. The solid is washed with acetone, N,N,-dimethylformamide, tetrahydrofuran and anhydrous ethanol in sequence, and dried in an oven at 80~100℃ for 12~24 h to obtain the bipolar covalent organic framework NT-COF.

[0034] Comparative Example 4 This comparative example provides a method for preparing a positive electrode material for a calcium-ion battery. The steps are the same as in Example 2, except that the NT-COF prepared in Comparative Example 3 is used instead of TATP-COF@CNT to prepare the positive electrode material for the calcium-ion battery and to assemble the calcium-ion battery.

[0035] Performance testing: Cyclic voltammetry (CV) tests were performed on the calcium-ion batteries obtained in Example 2 and Comparative Example 2. The CV curves were tested in the voltage range of -2.5V to 1.5V vs. ACC, and the scan rate was 0.5 mV / s.

[0036] Figure 5(a) shows the TATP of Example 2. The cyclic CV curves of COF@CNT show that a pair of redox peaks corresponding to the voltage range of -2.5V to -0.5V vs. ACC include... C = N calcium intercalation The decalcification process is an n-type electrochemical process; the pair of redox peaks corresponding to -0.5V~1.5V vs. ACC are... CN The capacity contribution provided by the oxidative anion intercalation mechanism is a p-type electrochemical process, which is consistent with the expected activity characteristics based on theoretical design.

[0037] Figure 5(b) shows the TATP of Comparative Example 2. From the cyclic CV curve of COF, we can derive a pair of redox peaks corresponding to the voltage range of -2.5V to -0.5V vs. ACC, including... C = N calcium intercalation The decalcification process is an n-type electrochemical process; the pair of redox peaks corresponding to -0.5V~1.5V vs. ACC are... CN The capacity contribution provided by the oxidative anion intercalation mechanism under the dual-ion mechanism is a p-type electrochemical process. It can be seen that the redox peak area of ​​Comparative Example 2 is significantly smaller than that of Example 2, indicating that the capacity provided by Example 2 at this potential is significantly greater than that of Comparative Example 2.

[0038] Figure 5(c) shows the cyclic CV curve of NT-COF in Comparative Example 4. It can be seen that there is only one pair of redox peaks in the voltage range of -2.5V to 1V vs. ACC, which corresponds to the calcium insertion-decalcification process of -C=O-, which is an n-type electrochemical process. The working voltage window of this comparative example is significantly narrower than that of Example 2. Example 2 has a higher working voltage than Comparative Example 4.

[0039] Based on the two comparative examples above, it can be concluded that the n-type mainly provides high capacity, the p-type provides high voltage, and this embodiment 2 combines the advantages of both n-type and p-type, providing both high capacity and high voltage.

[0040] The calcium-ion batteries obtained in Example 2 and Comparative Example 2 were subjected to electrochemical impedance spectroscopy (EIS) testing at a frequency of 0.1 Hz. 1 MHz.

[0041] The results are shown in Figure 6(a), TATP in Example 2 The relatively low impedance of COF@CNT indicates that the battery assembled from this composite CNT electrode material has fast ion / electron transport, resulting in a low overall internal resistance and thus improving overall battery performance; while as shown in Figure 6(b), the TATP of Comparative Example 2... The impedance of COF is significantly increased compared to that of Example 2, indicating that the composite CNT material improves the interfacial transport resistance to some extent.

[0042] The calcium-ion batteries obtained in Example 2 and Comparative Example 2 were subjected to cycle stability tests using the Blue Electric test system. The voltage test range was -2.5~1.5V vs. ACC, and the current density was 0.1 A / g.

[0043] The results are shown in Figure 7(a), TATP of Example 1 COF@CNT was cycled 100 times at a current density of 0.1 A / g, with an initial capacity of 129.6 mAh / g and a capacity retention of over 10%, indicating that the TATP synthesized in this invention... COF@CNT materials provide a core-shell structure design to achieve high-performance calcium-ion batteries with organic electrodes that utilize highly efficient electroactive sites; while as shown in Figure 7(b), Comparative Example 2's TATP COF was cycled 100 times at a current density of 0.1 A / g, with an initial capacity of 94.9 mAh / g and a capacity retention of less than 10%, indicating that the TATP without CNT complexation was effective. COF materials have a low specific capacity.

[0044] For any points not covered above, existing technologies shall apply.

[0045] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A bipolar covalent organic framework@carbon nanotube composite material, characterized in that, It includes carbon nanotubes and a bipolar covalent organic framework grown in situ thereon, the bipolar covalent organic framework having the following structure: 。 2. A method for preparing a bipolar covalently coupled framework@carbon nanotube composite material according to claim 1, characterized in that, It includes the following steps: (1) Sonicate N,N,N',N'-tetraphenyl-1,4-phenylenediamine, p-phthalaldehyde, CNT and organic solvent, and then add catalyst and sonicate to obtain mixed solution A; (2) The mixed solution A obtained in step (1) is frozen-vacuumed-thawed three times, and then heated in an oven to obtain a solid. The solid is washed and dried to obtain a bipolar covalent organic framework TATP-COF@CNT.

3. The preparation method according to claim 2, characterized in that, In step (1): The mass ratio of N,N,N',N'-tetraphenyl-1,4-phenylenediamine to p-phthalaldehyde is 1:(1.76~3). The organic solvent is n-butanol and o-dichlorobenzene, and the volume ratio of n-butanol to o-dichlorobenzene is 1:1; The catalyst is acetic acid or p-toluenesulfonic acid; The mass ratio of the catalyst to p-phthalaldehyde is 1-2:

1.

4. The preparation method according to claim 2, characterized in that, The mass ratio of CNT to p-phthalaldehyde is 1:(4~8).

5. The preparation method according to claim 2, characterized in that, In step (2): The oven is heated at a temperature of 120~180℃ for 72~120 h. The washing process specifically includes washing with N,N,-dimethylformamide and tetrahydrofuran in sequence. The drying temperature is 80~100℃, and the drying time is 12~24 h.

6. The application of the bipolar covalent organic framework@carbon nanotube composite material according to claim 1 in the preparation of calcium-ion battery electrodes.

7. An application according to claim 6, characterized in that, The calcium-ion battery electrode is the positive electrode of a calcium-ion battery, and its preparation method is as follows: The bipolar covalent organic framework@carbon nanotube composite material, conductive additives, and binders are ground and mixed, and a solvent is added for further mixing to obtain a block mixture. The mixture is then pressed into sheets using a roller mill and vacuum dried to obtain the positive electrode for a calcium-ion battery.

8. The application according to claim 7, characterized in that, The mass ratio of the polar covalent organic framework@carbon nanotube composite material, the conductive additive, and the binder is 6:3:1; the conductive additive is one of Ketjen Black, acetylene black, or graphite conductive agent.

9. The application according to claim 7, characterized in that, The adhesive is polyvinylidene fluoride and / or polytetrafluoroethylene, and the solvent is deionized water.

10. The application according to claim 7, characterized in that, The tableting pressure is 1000-1400 psi; the vacuum drying temperature is 60-80℃, and the drying time is 12-24 h.

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