Conjugated organic framework compound, preparation method thereof and application of conjugated organic framework compound in lithium ion battery negative electrode material

Abstract

The invention belongs to the technical field of lithium ion batteries, and relates to a conjugated organic framework compound, a preparation method thereof and application of the conjugated organic framework compound in a lithium ion battery negative electrode material. As N atoms (C: N = 3: 1) are introduced, the intrinsic conductivity of the material is effectively improved, and electron transmission is promoted; meanwhile, the conjugated organic framework compound presents an ordered layered porous structure, and diffusion of lithium ions in the X-axis direction and the Y-axis direction is facilitated. Through the combined action of the characteristics, the gram capacity and the rate capability of the battery cell can be remarkably improved, and the requirements of modern electronic products on high-performance power supplies are met.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and relates to a conjugated organic framework compound and a preparation method thereof and application thereof in negative electrode materials of lithium ion batteries. Background Art

[0002] As a key energy source for today's portable electronic devices, electric vehicles, and energy storage systems, the performance of lithium-ion batteries is directly related to the user experience and market competitiveness of related products. In lithium-ion battery technology, the selection of negative electrode materials plays a vital role in the overall performance of the battery. Currently, common commercial lithium-ion negative electrode materials mainly include graphite materials, silicon-carbon composite materials, and lithium titanate. They each have unique physical and chemical properties, providing diverse choices for different application scenarios.

[0003] As a classic negative electrode material for lithium-ion batteries, graphite is favored for its low lithium insertion potential (close to the potential of metallic lithium), abundant lithium insertion sites, low preparation cost and abundant resources. These characteristics make graphite widely used in fast-moving consumer electronic products, such as mobile phones, computers and tablets, which greatly promotes the development of the consumer electronics industry. However, with the popularization of 5G networks and technological advances, digital products are not only increasing in number, but also becoming increasingly complex in functions, and the requirements for battery life are also increasing. In this context, the theoretical gram capacity of traditional graphite negative electrodes is only 372mAh / g, which is obviously difficult to meet the market demand for longer usage time and higher energy density.

[0004] To meet this challenge, researchers turned their attention to silicon-carbon composites with an ultra-high theoretical gram capacity of 4200mAh / g. This material can theoretically significantly increase the energy density of the battery, thereby extending the endurance of the device. However, silicon-carbon composites face the problem of volume expansion in practical applications, that is, during the charging and discharging process, the volume of the material increases significantly due to the alloying reaction between silicon and lithium. This volume change can cause damage to the electrode structure, reduce the cycle life of the battery, and may cause safety issues. Therefore, although silicon-carbon composites have great potential, the road to their commercialization is still full of obstacles.

[0005] In view of this, scientists are also exploring other alternatives, especially looking for carbon materials that are similar to graphite in structure but have higher gram capacity. This type of new carbon material is expected to combine the advantages of graphite while overcoming its capacity limitations and providing better electrochemical performance. In addition, as a negative electrode material, although lithium titanate has a theoretical gram capacity of only 175mAh / g, it has excellent fast charging capability and stability, and is suitable for application scenarios that require frequent and rapid charging and discharging.

[0006] Covalent organic framework compounds are a new type of two-dimensional layered porous materials with broad application prospects in energy storage, optoelectronics, adsorption and catalysis. Constructing conjugated organic framework compounds as lithium-ion batteries can improve the energy density and rate performance of batteries, but the synthesis of conjugated organic framework compounds has many steps, is time-consuming and expensive, which is a major obstacle to its commercialization.

[0007] A Chinese patent application document (CN112029107B) discloses a two-dimensional metal organic framework material (MOF) based on triazine ligands and its preparation method and application. The material is a Zn + The chelate with triazine organic ligand has the advantages of large specific surface area, regular structure and low cost. However, its synthesis method uses many raw materials and lengthy steps, which is not conducive to industrial application. More importantly, the triazine ring content of the material structure is too low, but the atomic ratio of N and C in the unit structure is only 0.55:1, which leads to certain limitations in electron transmission and ion diffusion capabilities, making it unsuitable for use as an electrode material for storing lithium ions. Summary of the invention

[0008] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and to propose a conjugated organic framework compound with relatively simple control conditions and simple preparation method, whose excellent electron transfer and ion diffusion can effectively improve the gram capacity and rate performance of the battery cell.

[0009] The purpose of the present invention can be achieved by the following technical solutions:

[0010] A method for preparing a conjugated organic framework compound, the method comprising the following steps:

[0011] S1, mixing 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine and ZnCl2, and then heat-treating them in a rare gas atmosphere to obtain a product;

[0012] S2, adding an organic solvent to the product for ball milling;

[0013] S3, then washing, and finally drying to obtain a conjugated organic framework compound.

[0014] In the above-mentioned method for preparing a conjugated organic framework compound, the molar ratio of 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine and ZnCl2 in step S1 is 1:1.5-2.0. The present invention firstly mixes 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine (monomer) and zinc chloride (ZnCl2) in a molar ratio of 1:1.5-2.0. In this step, ZnCl2 not only acts as a catalyst to promote the synthesis reaction of the triazine ring, but also acts as a solvent to ensure that the monomer can be completely dissolved and participate in the reaction. This dual role is crucial to the successful synthesis of the target COF material. If the proportion of ZnCl2 is too low, the monomer cannot be completely dissolved, which makes the polymerization reaction insufficient and ultimately reduces the yield; on the contrary, if the proportion of ZnCl2 is too high, the difficulty of subsequent product purification is increased, because the excess ZnCl2 requires more steps to remove, which increases the process complexity and cost.

[0015] In the above-mentioned method for preparing a conjugated organic framework compound, the heat treatment in step S1 is specifically carried out at 0.5-1.5°C min -1 The heating rate is raised to 350-450°C and then kept warm for 35-45h. The heating rate of the heat treatment of the present invention needs to be controlled between 0.5 and 1.5°C / min. A moderate heating rate helps to uniformly transform the internal structure of the material and avoids thermal stress caused by rapid heating that leads to material structural defects. High-temperature treatment within the range of 350-450°C is mainly based on the melting point of zinc chloride. When the temperature is lower than 350°C, zinc chloride cannot be fully dissolved, which means that its function as a solvent has not been fully exerted, thereby affecting the solubility and reactivity of the monomer, resulting in limited kinetics of the triazine ring synthesis reaction, and the triazine framework structure formed is incomplete, which in turn affects the purity of the product. On the contrary, if the temperature exceeds 450°C, it may cause the decomposition of the triazine ring that has been formed or unnecessary side reactions to occur, which will not only increase the risk of structural collapse, but also reduce the crystallinity of the product, affecting its electrochemical properties and other physical properties.

[0016] Preferably, the solvent in step S2 includes at least one of ethanol, propanol and ethylene glycol.

[0017] More preferably, the solvent in step S2 is anhydrous ethanol.

[0018] In the above-mentioned method for preparing a conjugated organic framework compound, the ball milling speed in step S2 is 200-300 r min -1 , time is 3-5h.

[0019] In the above-mentioned method for preparing a conjugated organic framework compound, step S3 washing is performed with hydrochloric acid solution and deionized water in sequence, wherein the concentration of the hydrochloric acid solution is 0.5-1.5 mol L-1 .

[0020] Preferably, step S3 needs to be continuously washed until the filtrate is tested by silver nitrate solution and no white precipitate is produced. The hydrochloric acid solution is used to wash away the zinc chloride on the surface and in the pores of the product.

[0021] In the above-mentioned method for preparing a conjugated organic framework compound, the drying treatment temperature in step S3 is 70-90° C. and the time is 5-10 hours.

[0022] The present invention also provides a conjugated organic framework compound, which is prepared by the above-mentioned preparation method.

[0023] The present invention also provides a method for preparing the above conjugated organic framework compound, which comprises the following steps: mixing the conjugated organic framework compound, conductive additive SP, conductive additive CNT, binder CMC and deionized water, then adding binder SBR and NMP and continuing to stir.

[0024] In the above-mentioned preparation method of a conjugated organic framework compound, the mass ratio of the conjugated organic framework compound material, the conductive agent SP, the binder SBR, the conductive additive CNT, the binder CMC, NMP, and deionized water is (95-98): (0.5-1.0): (0.01-0.05): (1.0-1.5): (1.5-2.0): 1.0: (95-105).

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The conjugated organic framework compound of the present invention has a theoretical specific capacity far higher than that of the traditional graphite negative electrode, which can not only improve the energy density of the battery, that is, store more electrical energy under the same volume or weight, but also improve the rate performance of the battery, so that the battery can be quickly charged and discharged at high current density without obvious loss of capacity.

[0027] 2. The present invention synthesizes the conjugated organic framework compound by the molten salt method, which is simpler than other synthesis routes and has relatively simple control conditions (mainly temperature and inert gas protection). In addition, the final product is in powder form, which is easy to transport and handle, thereby reducing manufacturing costs and simplifying the production process.

[0028] 3. The present invention effectively improves the intrinsic conductivity of the material and promotes electron transmission by introducing N atoms (C:N=3:1); at the same time, the conjugated organic framework compound presents an ordered layered porous structure, which is conducive to the diffusion of lithium ions along the X-axis and Y-axis. These characteristics work together to significantly improve the gram capacity and rate performance of the battery cell, meeting the needs of modern electronic products for high-performance power supplies.

[0029] 4. Compared with traditional silicon-carbon composite materials, the conjugated organic framework compound of the present invention avoids the problem of poor cycle life caused by volume expansion. By flexibly changing the repeating units to adjust its topological structure, it can maintain stable electrochemical performance while ensuring high gram capacity, which is crucial for long-term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a TEM image of the microstructure of the conjugated organic framework compound prepared in Example 1.

[0031] Figure 2 The figure is a comparison of the discharge specific capacities of lithium-ion batteries prepared using the conjugated organic framework compound of Example 1 at different rates.

[0032] Figure 3 The cycle performance (1.0A g -1 ). DETAILED DESCRIPTION

[0033] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0034] Embodiment 1:

[0035] S1. In a glove box filled with Ar gas, 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine (C 24 H 12 N6) and ZnCl2 were fully mixed in a molar ratio of 1:1.5, and the mixture was quickly transferred to a tube furnace and heated at 1 °C min -1 The temperature was raised to 400°C at a heating rate and then kept at this temperature for 40 hours, during which the tube furnace must be kept in a N2 atmosphere, to obtain product A.

[0036] S2. Transfer the cooled product A to a ball mill at room temperature and pressure, add ethanol (C2H5OH) to two-thirds of the ball mill volume, and grind at 250 r min -1 The mixture was ball milled at a speed of 4 h to obtain powder B.

[0037] S3, 1g powder B was mixed with 100ml 1mol L -1 The product was washed with hydrochloric acid solution and deionized water for 12 h, and finally dried in vacuum at 80 °C for 8 h to obtain a conjugated organic framework compound.

[0038] Figure 1 This is a TEM image of the microscopic morphology of the conjugated organic framework compound prepared in Example 1. As can be seen from the image, the material has a two-dimensional sheet structure with uniform micropores on its surface.

[0039] Figure 2 The discharge capacity comparison of lithium-ion batteries prepared using the conjugated organic framework compound in Example 1 at different rates. As can be seen from the figure, the material has excellent specific capacity and rate performance. The specific capacity is close to 1350 mAh g at a current density of 0.1C. -1 , when returning from 10C to 0.1C, the specific capacity recovered to the original value, indicating that the structure was stable and not destroyed.

[0040] Figure 3 The cycle performance (1.0A g -1 ). As can be seen from the figure, the material has excellent cycle performance, and the capacity hardly decays after 500 cycles, indicating that the material framework structure is stable.

[0041] Embodiment 2:

[0042] S1. In a glove box filled with Ar gas, 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine (C 24 H 12 N6) and ZnCl2 were mixed in a molar ratio of 1:1, and the mixture was quickly transferred to a tube furnace and heated at 1 °C min -1 The temperature was raised to 350°C at a heating rate and then kept at that temperature for 40 hours. During this period, the tube furnace must be kept in a N2 atmosphere to obtain product A.

[0043] S2. Transfer the cooled product A to a ball mill at room temperature and pressure, add ethanol (C2H5OH) to two-thirds of the ball mill volume, and grind at 250 r min -1 The mixture was ball milled at a speed of 4 h to obtain powder B.

[0044] S3, 1g powder B was mixed with 100ml 1mol L -1 The product was washed with hydrochloric acid solution and deionized water for 12 h, and finally dried in vacuum at 80 °C for 8 h to obtain a conjugated organic framework compound.

[0045] Embodiment 3:

[0046] S1. In a glove box filled with Ar gas, 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine (C 24 H 12 N6) and ZnCl2 were fully mixed in a molar ratio of 1:2, and the mixture was quickly transferred to a tube furnace and heated at 1 °C min -1 The temperature was raised to 450°C at a heating rate and then kept at this temperature for 40 hours. During this period, the tube furnace must be kept in a N2 atmosphere to obtain product A.

[0047] S2. Transfer the cooled product A to a ball mill at room temperature and pressure, add ethanol (C2H5OH) to two-thirds of the ball mill volume, and grind at 250 r min -1 The mixture was ball milled at a speed of 4 h to obtain powder B.

[0048] S3, 1g powder B was mixed with 100ml 1mol L -1 The product was washed with hydrochloric acid solution and deionized water for 12 h, and finally dried in vacuum at 80 °C for 8 h to obtain a conjugated organic framework compound.

[0049] Embodiment 4:

[0050] The only difference from Example 1 is that in step S1, 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine (C 24 H 12 The molar ratio of N6) and ZnCl2 is 1:0.1.

[0051] Embodiment 5:

[0052] The only difference from Example 1 is that in step S1, 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine (C 24 H 12 The molar ratio of N6) and ZnCl2 is 1:3.0.

[0053] Comparative Example 1:

[0054] The only difference from Example 1 is that ZnCl2 is replaced by NaCl in step S1.

[0055] Comparative Example 2:

[0056] The only difference from Example 1 is that the heat treatment in step S1 is not performed in a N2 atmosphere, that is, the tube furnace is kept in air during the process.

[0057] Comparative Example 3:

[0058] The only difference from Example 1 is that step S3 does not perform washing with a hydrochloric acid solution.

[0059] The conjugated organic framework compound materials prepared in Examples 1-5 and Comparative Examples 1-3, the conductive additive SP, the conductive additive CNT, the binder CMC and the solvent deionized water were mixed evenly, and stirred at high speed for 2 to 5 hours at a revolution speed of 25 rmin. -1 、Rotation speed 2000r min -1 After adding appropriate amount of SBR glue and NMP, stir at low speed for 2 to 5 hours, with the revolution speed of 25 r min -1 、Rotation speed 2000r min -1Among them, conjugated organic framework compound material: conductive agent SP: binder SBR: conductive additive CNT: binder CMC: solvent NMP: solvent deionized water = 96.28: 0.7: 0.02: 1.30: 1.70: 1.0: 100. The slurry obtained after stirring is carried out to the next lithium battery preparation process.

[0060] Preparation of lithium-ion batteries:

[0061] S1. Prepare the electrode by wet coating. The slurry is evenly coated on the copper foil and then a circular electrode with a diameter of about 14 mm is cut. The electrode is welded to the positive electrode shell of a 2016 button battery and placed in an oven at 80 ° C for 12 h under vacuum. The material loading is 1.0 mg cm -2 .

[0062] S2. Assemble button cells in a glove box filled with high-purity argon. Place the negative electrode shell welded with stainless steel mesh, metal lithium sheet and diaphragm in order. Moisten the parts with electrolyte and buckle the positive electrode shell welded with electrodes to the negative electrode shell. After sealing, the battery is left at room temperature and pressure for 12 hours before testing. The diaphragm used in this application is Celgand 2300 polypropylene diaphragm; the electrolyte is EC / EMC (1:1 vol%) solution of LiPF6, and the dosage is 0.4 ml.

[0063] Table 1: Performance test results of lithium ion batteries prepared in Examples 1-5 and Comparative Examples 1-3

[0064] Example <![CDATA[0.1C Specific capacity (mAh g -1 )]]> <![CDATA[5C specific capacity (mAh g -1 )]]> Example 1 1350 750 Example 2 1100 550 Example 3 1200 600 Example 4 150 10 Example 5 1000 400 Comparative Example 1 10 0 Comparative Example 2 / / Comparative Example 3 / /

[0065] From the above results, it can be seen that for Example 4, only 0.1 zinc chloride can only allow a small part of the monomers to polymerize, but the high temperature will destroy the remaining monomers, so most of the powder is fragmented compounds without lithium storage activity. For Example 5, zinc chloride should be more rather than less as a catalyst and solvent. More zinc chloride will only consume more hydrochloric acid in the subsequent washing process. In Comparative Example 1, the melting point of NaCl is as high as 800 degrees, and it cannot play the role of solvent and pore formation. In Comparative Example 2, zinc chloride has strong hygroscopicity in the air, and zinc chloride hydrate and zinc hydroxide generated after deliquescence cannot play a role. In Comparative Example 3, the residual zinc chloride reacts with the electrolyte, such as EC and DEC, to generate organic chlorine compounds or solid precipitates, resulting in the battery failing to perform.

[0066] In summary, the present invention effectively improves the intrinsic conductivity of the material and promotes electron transmission by introducing N atoms (C:N=3:1); at the same time, the conjugated organic framework compound presents an ordered layered porous structure, which is conducive to the diffusion of lithium ions along the X-axis and Y-axis directions. These characteristics work together to significantly improve the gram capacity and rate performance of the battery cell, meeting the needs of modern electronic products for high-performance power supplies.

[0067] The parts of the embodiments herein that are not exhaustive of the midpoint values ​​of the technical scope claimed for protection by the present invention and the new technical solutions formed by equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also within the scope claimed for protection by the present invention; at the same time, in all the listed or unlisted embodiments of the scheme of the present invention, each parameter in the same embodiment merely represents an example of its technical solution (i.e., a feasible solution), and there is no strict coordination and limitation relationship between the parameters, wherein the parameters can be replaced with each other without violating the axioms and the claims of the present invention, unless otherwise stated.

[0068] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above technical means, but also include technical schemes composed of any combination of the above technical features. The above is a specific implementation 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, and these improvements and modifications are also regarded as the protection scope of the present invention.

[0069] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for preparing a conjugated organic framework compound, characterized in that: The method comprises the following steps: S1, mixing 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine and ZnCl2, and then heat-treating them in a rare gas atmosphere to obtain a product; S2, adding an organic solvent to the product for ball milling; S3, then washing, and finally drying to obtain a conjugated organic framework compound.

2. The method for preparing a conjugated organic framework compound according to claim 1, characterized in that: In step S1, the molar ratio of 2,4,6-tris(4-cyanophenyl)-1,3,5-triazine to ZnCl2 is 1:1.5-2.

0.

3. The method for preparing a conjugated organic framework compound according to claim 1, characterized in that: The heat treatment in step S1 is specifically carried out at 0.5-1.5°C min -1 The temperature is raised to 350-450℃ at a heating rate and then kept at this temperature for 35-45h.

4. The method for preparing a conjugated organic framework compound according to claim 1, characterized in that: Step S2 ball milling speed is 200-300 r min -1 , time is 3-5h.

5. The method for preparing a conjugated organic framework compound according to claim 1, characterized in that: Step S3 washing: washing with hydrochloric acid solution and deionized water in sequence, wherein the concentration of the hydrochloric acid solution is 0.5-1.5 molL -1 .

6. The method for preparing a conjugated organic framework compound according to claim 1, characterized in that: The drying treatment temperature in step S3 is 70-90°C and the time is 5-10h.

7. A conjugated organic framework compound, characterized in that: The conjugated organic framework compound is prepared by the preparation method according to claim 1.

8. A negative electrode material for a lithium ion battery, characterized in that: The negative electrode material of the lithium-ion battery comprises the conjugated organic framework compound according to claim 7.

9. A method for preparing a negative electrode material for a lithium ion battery as claimed in claim 8, characterized in that: The method comprises the following steps: mixing and stirring a conjugated organic framework compound, a conductive additive SP, a conductive additive CNT, a binder CMC and deionized water, and then adding a binder SBR and NMP and continuing to stir.

10. The method for preparing a negative electrode material for a lithium ion battery according to claim 9, characterized in that: The mass ratio of conjugated organic framework compound material, conductive agent SP, binder SBR, conductive additive CNT, binder CMC, NMP and deionized water is (95-98): (0.5-1.0): (0.01-0.05): (1.0-1.5): (1.5-2.0): 1.0: (95-105).

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