Carbon aerogel with zif-8 as a skeleton and a preparation method and application thereof

Abstract

The application discloses a carbon aerogel with ZIF-8 as a skeleton and a preparation method and application thereof, and comprises the following steps: carrying out heating and stirring reaction on ZIF-8 and a polymer hydrogel, drying, and carbonizing, so as to obtain the carbon aerogel with ZIF-8 as the skeleton; wherein the ZIF-8 is carboxyl-modified ZIF-8; the preparation of the carboxyl-modified ZIF-8 comprises the following steps: reacting 2-methyl imidazole-4, 5-dicarboxylic acid with a cationic surfactant and a zinc salt under a pressurized condition. The carboxyl-modified ZIF-8 is compounded with a polymer containing an oxygen-containing hydrophilic functional group; in the compounding process, high temperature makes the -COOH and the oxygen-containing functional group better combined, and crosslinking action also exists between the polymers.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of porous carbon materials, in particular to a carbon aerogel with ZIF-8 as a skeleton and a preparation method and application thereof. BACKGROUND

[0002] Carbon materials are widely used in various fields due to their excellent mechanical properties, chemical properties and electrical conductivity. In recent years, with the progress and development of science and technology, people have higher and higher requirements for carbon materials, and long for the preparation of carbon materials with controllable structure and designed chemical properties. Although natural carbon materials have many advantages, they have some impurities and low controllability of structure, which limits their application. Therefore, people shift their attention to synthetic carbon materials. Among them, carbon aerogels have become the object of extensive research due to their adjustable structure, high porosity, large specific surface area and stable chemical structure.

[0003] For the preparation of carbon aerogels, biomass or organic materials are generally used as raw materials. However, the biomass materials on earth are not inexhaustible, and the pore structure of the carbon aerogels prepared from biomass materials varies greatly, which largely depends on the structure of the biomass itself.

[0004] Anjali et al. showed that the mechanical properties of carbon aerogels obtained by using biomass as a precursor are poor, and the preparation requires activation in an alkaline or acidic environment before treatment, which inevitably corrodes most of the carbon and destroys the inherent three-dimensional structure. In addition, using biomass as a raw material also has the disadvantage of poor batch stability. When using organic materials as raw materials, carbon aerogel materials with high pore volume and wide pore size distribution can be obtained, and the pore structure can also be adjusted through subsequent treatment (physical, chemical activation, calcination, etc.). However, this method has a complex synthesis route and requires additional activation post-processing.

[0005] Therefore, it is considered that the most optimal method is to extract polymers from biomass, obtain a three-dimensional network structure through chemical or physical cross-linking, and then dry and carbonize to obtain carbon aerogels, which has the advantages of high practicality, low cost, non-toxicity and environmental friendliness. However, the pore size distribution of carbon aerogels obtained by cross-linking and solidification of polymers is relatively dispersed. SUMMARY

[0006] In order to solve the above problems existing in the field, the present application aims to provide a carbon aerogel with ZIF-8 as a skeleton and a preparation method and application thereof. ZIF-8 is an organic metal structure with high metal density, and has the advantages of narrow pore size distribution, high specific surface area, etc.

[0007] According to an aspect of the present application, a preparation method of a carbon aerogel with ZIF-8 as a skeleton is provided, comprising:

[0008] The ZIF-8 is subjected to a heating stirring reaction, drying and carbonization with a polymer hydrogel to obtain a carbon aerogel with ZIF-8 as a skeleton.

[0009] In the formula, the ZIF-8 is a carboxyl-modified ZIF-8; and the preparation of the carboxyl-modified ZIF-8 comprises:

[0010] 2-methylimidazole-4,5-dicarboxylic acid is reacted with a cationic surfactant and a zinc salt under a pressurized condition.

[0011] According to some embodiments of the present application, the preparation of the carboxyl-modified ZIF-8 comprises:

[0012] The cationic surfactant is dissolved in deionized water, and NaOH is added to obtain a first solution;

[0013] 2-methylimidazole-4,5-dicarboxylic acid is added to the first solution to obtain a second solution;

[0014] Under the condition of severe stirring at 800-2000 rpm, a zinc salt is added to the second solution, and the stirring is continued to obtain a third solution;

[0015] The third solution is transferred to a high-pressure reaction kettle for reaction to obtain the carboxyl-modified ZIF-8.

[0016] According to some embodiments of the present application, the reaction pressure is 0.1-8 MPa.

[0017] According to some embodiments of the present application, the cationic surfactant is selected from one or more of a quaternary amine salt surfactant and an amine salt surfactant.

[0018] The zinc salt is selected from one or more of zinc nitrate, zinc chloride, zinc sulfate and zinc acetate, and is preferably zinc nitrate.

[0019] According to some embodiments of the present application, the polymer is selected from a polymer containing a hydrophilic functional group.

[0020] According to some embodiments of the present application, the polymer containing a hydrophilic functional group is selected from hydroxyethyl cellulose, polyacrylic acid or guar gum.

[0021] According to some embodiments of the present application, the heating stirring reaction comprises:

[0022] The carboxyl-modified ZIF-8 is added to a solvent to obtain a uniform emulsion; and the emulsion is mixed with the polymer hydrogel for a stirring reaction.

[0023] Optionally, the stirring rate is 300-800 rpm.

[0024] Optionally, the solvent is a mixture of water and an organic solvent, wherein the organic solvent includes acetone, chloroform, chloroethane, and xylene.

[0025] According to some embodiments of this application, the drying method includes: supercritical CO2 drying and vacuum freeze drying.

[0026] According to some embodiments of this application, the carbonization process further includes purification;

[0027] The purification process includes: sonicating the ZIF-8-based carbon aerogel in 3-6 mol / L acid for 20-45 minutes;

[0028] Then soak in 0.05-3 mol / L acid for 2-6 hours and wash with water;

[0029] Optionally, the acid is selected from HCl and H2SO4.

[0030] According to another aspect of this application, a carbon aerogel with ZIF-8 as the backbone is also provided, wherein the D50 of the carbon aerogel is 1-3 μm;

[0031] The carbon aerogel comprises micropores and mesopores, with an average pore size of 1.8-2.4 nm and a specific surface area of ​​1000-2000 m². 2 / g; total pore volume is 0.20-0.99cm³ 3 / g;

[0032] The carbon aerogel has an ash content of <1% and a carbon content of >90%.

[0033] This application also provides a silicon-carbon composite anode material, comprising the aforementioned carbon aerogel with ZIF-8 as the framework and nano-silicon deposited within the pores of the carbon aerogel with ZIF-8 as the framework.

[0034] A negative electrode sheet comprising the aforementioned silicon-carbon composite negative electrode material.

[0035] A lithium-ion secondary battery, comprising the aforementioned negative electrode sheet.

[0036] An electrochemical device comprising the aforementioned lithium-ion secondary battery.

[0037] Compared with the prior art, this application has at least the following beneficial effects:

[0038] This application provides a method for preparing carbon aerogels with ZIF-8 as the backbone. The method involves compounding carboxyl-modified ZIF-8 with a polymer containing oxygen-containing hydrophilic functional groups. During the compounding process, high temperature allows for better bonding between the -COOH groups and the oxygen-containing functional groups, while also promoting cross-linking between the polymers. Furthermore, heating and stirring during the preparation process enhance the bonding between the polymer and the carboxyl-modified ZIF-8, as well as between the polymers themselves.

[0039] This application presents a carbon aerogel with a ZIF-8 framework. By adjusting the pressure, carboxyl-modified ZIF-8 particles of different sizes are obtained, thereby regulating the pore structure and resulting in a carbon aerogel material with high mechanical strength, dense and uniform pore structure, and large specific surface area. The average pore size of the carbon aerogel is only 1.8-2.4 nm, which allows elemental silicon particles to be uniformly distributed in the pore structure during silicon deposition, thereby inhibiting silicon nucleation growth, avoiding the formation of crystalline silicon, and improving battery capacity. Furthermore, the average pore size of the carbon aerogel is slightly larger than that of elemental silicon particles, providing a buffer space for silicon volume expansion, thus improving the initial coulombic efficiency and cycle stability of the battery. Attached Figure Description

[0040] Figure 1 This is a SEM image of the carboxyl-modified ZIF-8 from an example embodiment of this application.

[0041] Figure 2 This is a schematic diagram of the structure of carboxyl-modified ZIF-8 in an example embodiment of this application.

[0042] Figure 3 SEM image of carbon aerogel with ZIF-8 as the backbone, which is an example embodiment of this application. Detailed Implementation

[0043] The technical solution of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] It should be particularly noted that similar substitutions and modifications made to this application are obvious to those skilled in the art, and they are all considered to be included in this application. Those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this application to implement and apply the technology of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0045] Unless otherwise specified, this application is conducted under standard conditions or conditions recommended by the manufacturer. The raw materials or excipients used, as well as the reagents or instruments used, whose manufacturers are not specified, are all conventional products that can be obtained commercially.

[0046] The following is a detailed description of this application.

[0047] Carbon aerogel materials can be considered as those obtained from carbon-containing materials through subsequent processing. Natural carbon materials exhibit uneven pore structure and poor batch-to-batch stability. Furthermore, the preparation of carbon aerogels from organic materials requires sophisticated processes. Currently, carbon aerogels, with their uniform pore structure and simple preparation process, are attracting significant attention.

[0048] ZIF-8, as an organometallic structure, has a high metal density and advantages such as narrow pore distribution and high specific surface area. Based on this, this application provides a method for preparing carbon aerogels using ZIF-8 as a framework composite polymer.

[0049] However, due to the large size of ZIF-8, controlling its size is very difficult. This application obtained ZIF-8 particles of different sizes by changing the pressure. Furthermore, to better facilitate the composite formation of ZIF-8 with the polymer, this application introduced -COOH into ZIF-8 to functionalize it. This carboxyl-modified ZIF-8 has a relatively regular rhombic dodecahedral structure, as shown in the schematic diagram below. Figure 2 As shown; SEM image of carboxyl-modified ZIF-8, as shown. Figure 1 As shown, its morphology is clear and uniform. Subsequently, carbon aerogels were prepared by composite polymers with carboxyl-modified ZIF-8 of different particle sizes as a framework, and then prepared by high-temperature carbonization using supercritical CO2 drying. The carbon aerogels prepared in this application have the advantages of controllable particle size and uniform morphology, such as... Figure 3 As shown. Furthermore, this application has advantages such as simple synthesis steps, and the pore structure can be controlled by adjusting the structure of ZIF-8, thus improving the problems existing in existing carbon aerogels.

[0050] The method for preparing ZIF-8-based carbon aerogels in this application is as follows:

[0051] Synthesis of carboxyl-modified ZIF-8: A cationic surfactant was dissolved in deionized water at a certain temperature, followed by the addition of NaOH until completely dissolved, wherein the molar ratio of surfactant:NaOH:water was 1:(20-40):(0.1-2). Then, 2-methylimidazole-4,5-dicarboxylic acid was added until completely dissolved. Finally, a zinc source was added under vigorous stirring, with a molar ratio of zinc source to 2-methylimidazole-4,5-dicarboxylic acid of 1:(2-5). After stirring for 30 min, the mixture was transferred to a high-pressure reactor and reacted at 0.1-8 MPa for 24 h to obtain carboxyl-modified ZIF-8 particles of different sizes.

[0052] The sample was then collected by vacuum filtration. After collection, the sample was first washed with alkaline solution and deionized water, then washed three times with ethanol at 80°C, and finally vacuum dried for 8-24 hours.

[0053] The cationic surfactant includes, but is not limited to, one or more of quaternary ammonium salts and amine salts. The stirring rate is 300-600 rpm, and the vigorous stirring rate is 800-2000 rpm.

[0054] Synthetic polymer hydrogel: Under normal temperature conditions, 1-10g of polymer powder is dissolved in 10-1000mL of deionized water, and a polymer hydrogel with a mass concentration of 1-10% is formed by stirring at room temperature.

[0055] The stirring speed is 300-500 rpm. The polymer includes, but is not limited to, polymers rich in hydrophilic functional groups such as sodium carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, and guar gum.

[0056] To obtain the carboxyl-modified ZIF-8 complex hydrogel: Dissolve 0.5-5 g of carboxyl-modified ZIF-8 in a mixed solution of 15-150 mL of deionized water and acetone, and sonicate for 15-80 min to obtain a homogeneous emulsion. At 25-60℃, mix the carboxyl-modified ZIF-8 emulsion with 1-10% of the polymer hydrogel at a volume ratio of 1:(10-500), and stir for 2-6 h to form the carboxyl-modified ZIF-8 complex hydrogel.

[0057] The stirring speed is 300-800 rpm. The mixed solution includes, but is not limited to, organic solvents with properties similar to acetone, such as chloroform, chloroethane, xylene, etc.

[0058] To obtain carboxyl-modified ZIF-8 composite aerogel: The carboxyl-modified ZIF-8 composite polymer hydrogel was supercritically dried with CO2 at 40-60℃ and 7-20MPa for 24-94h to obtain the carboxyl-modified ZIF-8 composite aerogel.

[0059] Alternatively, the drying method can be replaced by vacuum freeze drying at -35 to -60°C.

[0060] Obtaining carboxyl-modified ZIF-8 composite carbon aerogel: Place the carboxyl-modified ZIF-8 composite aerogel in a furnace, introduce nitrogen or argon gas or a mixture of both, and heat from 25℃ to 800-1200℃ at a heating rate of 2-10℃ / min, then hold at that temperature for 3-6 hours. Subsequently, cool to 400-600℃ at a rate of 2-10℃ / min, then turn off the furnace power and allow it to cool naturally to room temperature.

[0061] Purification of carboxyl-modified ZIF-8 composite carbon aerogel: The prepared carbon aerogel was sonicated in 3-6 mol / L acid for 20-45 minutes, then soaked in 0.05-3 mol / L acid for 2-6 hours, and then washed 2-3 times with deionized water. The acid could be HCl, H2SO4, etc.

[0062] The carboxyl-modified ZIF-8 particles of this application have a rhombic dodecahedral structure. The carboxyl-modified ZIF-8 coated with polymer is subjected to high-temperature carbonization treatment to generate carboxyl-modified ZIF-8 derived carbon materials, which ultimately form a carbon aerogel material with micro-mesopores and relatively uniform pore size.

[0063] In this process, the polymer is coated on the surface of ZIF-8. Since ZIF-8 itself has micropores and there are also pores between ZIF-8 particles, after high-temperature carbonization, ZIF-8 undergoes cracking, causing structural collapse. The micropores of ZIF-8 expand to form mesopores; the pores between particles are filled by the surface polymer, forming smaller mesopores; and the high-temperature carbonization and decomposition of the polymer produces pores, forming larger mesopores or macropores, etc.

[0064] The carboxyl-modified ZIF-8 has a particle size of 100-600 nm, optionally 100-200 nm, 200-300 nm, 300-400 nm, 400-500 nm, or 500-600 nm; preferably 200-300 nm, 300-400 nm, or 400-500 nm; it mainly has a microporous structure with micropores of 0.5-1.6 nm, optionally 0.5-0.8 nm, 0.8-1.0 nm, 1.0-1.2 nm, 1.2-1.4 nm, or 1.4-1.6 nm; and a specific surface area of ​​1500-2500 m². 2 / g, optionally 1500-2000m 2 / g、2000-2500m 2 / g.

[0065] The carbon aerogel particles have a particle size D50 of 1-3 μm, optionally 1.0-1.5 nm, 1.5-2.0 nm, 2.0-2.5 nm, or 2.5-3 nm;

[0066] The carbon aerogel comprises micropores and mesopores, with an average pore size of 1.8-2.4 nm, optionally 1.8-1.9 nm, 1.9-2.0 nm, 2.0-2.1 nm, 2.1-2.2 nm, 2.2-2.3 nm, or 2.3-2.4 nm; and a specific surface area of ​​1000-2000 m². 2 / g, optionally 1000-1500m 2 / g, 1500-2000m 2 / g; preferably 1500-1800m 2 / g; the total pore volume determined by the BJH method is 0.20-0.99 cm³. 3 / g, optionally 0.2-0.3cm 3 / g, 0.3-0.4cm 3 / g, 0.4-0.5cm 3 / g, 0.5-0.6cm 3 / g, 0.6-0.7cm 3 / g, 0.7-0.8cm 3 / g, 0.8-0.9cm 3 / g, 0.9-0.99cm 3 / g.

[0067] After purification, the carbon aerogel contained less than 1% ash and more than 90% carbon.

[0068] The carboxyl-modified ZIF-8 composite carbon aerogel of this application involves mixing carboxyl-modified ZIF-8 with a polymer to prepare a hydrogel. During this process, the polymer, containing oxygen-containing hydrophilic functional groups, crosslinks with the -COOH groups on the ZIF-8 surface. Furthermore, the polymer itself also interacts with these functional groups, resulting in a granular structure where the polymer encapsulates the carboxyl-modified ZIF-8 framework. Subsequent drying and carbonization yields a carbon aerogel material with high mechanical strength, a dense and uniform pore structure, a large specific surface area, and a relatively uniform distribution of micropores and mesopores.

[0069] This application improves the particle size of ZIF-8 by adjusting the pressure; the higher the pressure, the smaller the synthesized particles. ZIF-8, as a metal framework structure, can be modified by carbonizing carboxyl groups of different particle sizes to obtain pore structures with slightly different pore sizes.

[0070] In the preparation of ZIF-8, this application incorporates a quaternary ammonium salt cationic surfactant. Upon addition, the surfactant first fully coordinates with the carboxyl group in 2-methylimidazolium dicarboxylic acid, further ensuring the Zn content during the reaction. 2+ It can only react with methylimidazole. After the synthesis process, the quaternary ammonium salt cationic surfactant is removed by washing with ethanol, exposing the -COOH group and thus obtaining the functionalized ZIF-8.

[0071] The -COOH group in the carboxyl-modified ZIF-8 of this application can undergo a cross-linking reaction with polymers rich in hydrophilic functional groups such as oxygen groups, resulting in a more ordered arrangement. Moisture in the sample is removed using a specific drying method without damaging its structure, and carbon aerogel is obtained through high-temperature carbonization. The average pore size of the carbon aerogel is only 1.8-2.4 nm, allowing elemental silicon particles to be uniformly distributed within the pore structure during silicon deposition, thereby inhibiting silicon nucleation growth, preventing the formation of crystalline silicon, and improving battery capacity. Furthermore, the average pore size of the carbon aerogel is slightly larger than that of elemental silicon particles, providing a buffer space for silicon volume expansion, thus improving the initial coulombic efficiency and cycle stability of the battery.

[0072] Example 1

[0073] 2g of benzalkonium chloride was dissolved in 80mL of deionized water at a certain temperature. Then, 6.5g of NaOH was added until completely dissolved, followed by the addition of 0.5g of 2-methylimidazolium-4,5-dicarboxylic acid until completely dissolved. Under vigorous stirring, 0.4g of Zn(NO3)2·6H2O was added, and the mixture was stirred for 30 minutes to obtain a mixed solution. This solution was transferred to a high-pressure reactor and reacted at atmospheric pressure for 24 hours to obtain carboxyl-modified ZIF-8 particles of approximately 500nm. The sample was collected by vacuum filtration, washed with deionized water, and then washed three times with ethanol at 80℃. Finally, the sample was vacuum dried for 12 hours to obtain carboxyl-modified ZIF-8.

[0074] Dissolve 6g of guar gum powder in 100mL of deionized water and stir at room temperature to form a guar gum hydrogel with a mass concentration of 6%.

[0075] Dissolve 4.5g of carboxyl-modified ZIF-8 powder in a mixed solution of 150mL deionized water and acetone, and sonicate for 60min to obtain a homogeneous emulsion.

[0076] At room temperature, carboxyl-modified ZIF-8 emulsion and 6% guar gum hydrogel were mixed at a volume ratio of 1:50 and stirred at 40°C for 2 hours to form a carboxyl-modified ZIF-8 composite hydrogel.

[0077] The carboxyl-modified ZIF-8 composite was dried using supercritical CO2 for 24 h at 50 °C and 7 MPa pressure to obtain a carboxyl-modified ZIF-8 composite aerogel material.

[0078] The carboxyl-modified ZIF-8 composite aerogel material was placed in a furnace under an argon atmosphere and heated from 25°C to 800°C at a rate of 2.5°C / min, and held at that temperature for 3 hours. It was then cooled to 400°C at a rate of 2.5°C / min, and allowed to cool naturally to room temperature. The sample was then sonicated in 3 mol / L HCl for 20 minutes, then immersed in 2 mol / L HCl for 4 hours. After washing with deionized water until neutral, it was dried in a vacuum drying oven at 70°C for 24 hours to obtain a carbon aerogel material with ZIF-8 as the framework.

[0079] Example 2

[0080] The carbon aerogel with ZIF-8 as the backbone of this application was prepared, the only difference from that in Example 1 was that guar gum was replaced with sodium carboxymethyl cellulose.

[0081] Example 3

[0082] The carbon aerogel with ZIF-8 as the backbone of this application was prepared, and the only difference from that in Example 1 was that the pressure of the high-pressure reactor was increased to 2 MPa to obtain carboxyl-modified ZIF-8 particles of about 350 nm.

[0083] Example 4

[0084] The carbon aerogel with ZIF-8 as the backbone of this application was prepared, and the only difference from that in Example 1 was that the pressure of the high-pressure reactor was increased to 5 MPa to obtain carboxyl-modified ZIF-8 particles of about 200 nm.

[0085] Comparative Example 1

[0086] The difference compared to Example 1 is that 2-methylimidazole is used as the raw material.

[0087] Comparative Example 2

[0088] The difference compared to Example 1 is that cationic surfactants are not used in the raw materials.

[0089] Comparative Example 3

[0090] The difference compared to Example 1 is that the pressure in the high-pressure reactor is 0.01 MPa.

[0091] Comparative Example 4

[0092] The difference compared to Example 1 is that the pressure in the high-pressure reactor is 10 MPa.

[0093] Experimental Example

[0094] The carbon aerogel properties of the test examples and comparative examples are shown in Table 1.

[0095] Table 1. Properties of ZIF-8 and carbon aerogel in each embodiment and comparative example

[0096]

[0097] As shown in the table above, the carboxyl-modified ZIF-8 particles prepared in this application are uniform in size. Furthermore, the particle size can be controlled by adjusting the pressure during the reaction process. When the pressure is in the range of 0.1-8 MPa, ZIF-8 particles with a particle size distribution of 100-600 nm can be prepared. Porous carbon aerogels were prepared using these ZIF-8 particles as composite polymers. These carbon aerogels exhibit uniform pore distribution and good specific surface area and pore volume. The D of the carbon aerogel... 50 The carbon aerogel has a pore size of 1-3 μm, and includes both micropores and mesopores, with an average pore size of 1.8-2.4 nm and a specific surface area of ​​1000-2000 m². 2 / g, with a total pore volume of 0.20-0.99cm³. 3 / g. This facilitates the uniform distribution of elemental silicon particles within the pore structure during silicon deposition, thereby suppressing silicon nucleation growth, preventing the formation of crystalline silicon, and improving battery capacity. Furthermore, the average pore size of the carbon aerogel is slightly larger than that of elemental silicon particles, providing a buffer space for silicon volume expansion, thus improving the battery's initial coulombic efficiency and cycle stability.

[0098] As shown in Comparative Example 1, the carbon aerogel prepared using ZIF-8 without carboxyl groups as the backbone has a small pore volume and specific surface area, with a pore volume of only 0.30 cm³. 3 / g, with a specific surface area of ​​only 900m² 2 / g. The small pore volume of carbon aerogel prevents silicon from depositing into the pores, resulting in low battery capacity and poor rate performance.

[0099] As shown in Comparative Example 3, when the pressure is too low and less than 0.1 MPa, the particle size of ZIF-8 particles is relatively large, reaching 720 nm. The carbon aerogel D prepared using these ZIF-8 particles... 50 The particle size is up to 3.3 μm, and the pore volume of the carbon aerogel is 0.80 cm³. 3 / g, but the pore size reaches 4.00nm, and the specific surface area is only 800m². 2 / g.

[0100] As shown in Comparative Example 4, when the pressure is too high and exceeds 8 MPa, the particle size of the prepared ZIF-8 particles is only 50 nm. The carbon aerogel D prepared using these ZIF-8 particles... 50 The particle size is only 0.9 μm, but the carbon aerogel has a pore size of 2.60 nm and a pore volume of 1.50 cm³. 3 / g, and the specific surface area also reached 2300m². 2 / g. Excessively large pores or pore volume can cause deposited silicon to easily dissolve during charging and discharging, resulting in reduced battery capacity, shortened cycle life, and deteriorated rate performance.

[0101] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for preparing carbon aerogel with ZIF-8 as the framework, characterized in that, include: Carboxyl-modified ZIF-8 was heated and stirred with polymer hydrogel, then dried and carbonized to obtain carbon aerogel with ZIF-8 as the backbone. The method for preparing the carboxyl-modified ZIF-8 includes: The cationic surfactant was dissolved in deionized water, and NaOH was added to obtain the first solution; Add 2-methylimidazole-4,5-dicarboxylic acid to the first solution to obtain the second solution; Add zinc salt to the second solution while stirring at 800-2000 rpm, and continue stirring to obtain the third solution; The third solution was transferred to a high-pressure reactor for reaction to obtain the carboxyl-modified ZIF-8. The reaction pressure in the high-pressure reactor is 0.1-8 MPa.

2. The preparation method according to claim 1, characterized in that, The cationic surfactant is selected from one or more of quaternary ammonium salt surfactants and amine salt surfactants; The zinc salt is selected from one or more of zinc nitrate, zinc chloride, zinc sulfate, and zinc acetate.

3. The preparation method according to claim 2, characterized in that, The zinc salt is zinc nitrate.

4. The preparation method according to claim 1, characterized in that, The polymer hydrogel is prepared by dissolving a polymer in water and stirring the mixture. The polymer is selected from polymers containing hydrophilic functional groups.

5. The preparation method according to claim 4, characterized in that, The polymer containing hydrophilic functional groups is selected from hydroxyethyl cellulose, polyacrylic acid, or guar gum.

6. The preparation method according to claim 1, characterized in that, The heating and stirring reaction includes: The carboxyl-modified ZIF-8 was added to a solvent to obtain a homogeneous emulsion; the emulsion was then mixed with the polymer hydrogel and stirred to react.

7. The preparation method according to claim 6, characterized in that, The stirring speed is 300-800 rpm.

8. The preparation method according to claim 6, characterized in that, The solvent is a mixture of water and an organic solvent, including acetone, chloroform, chloroethane, or xylene.

9. The preparation method according to claim 1, characterized in that, The drying process includes: supercritical CO2 drying or vacuum freeze drying.

10. The preparation method according to claim 1, characterized in that, The carbonization process also includes purification; The purification process includes: sonicating the carbon aerogel in 3-6 mol / L acid for 20-45 minutes, then soaking it in 0.05-3 mol / L acid for 2-6 hours and washing it with water.

11. The preparation method according to claim 10, characterized in that, The acid is selected from HCl or H2SO4.

12. A carbon aerogel with ZIF-8 as its framework, characterized in that, The carbon aerogel's D 50 1-3μm; The carbon aerogel includes micropores and mesopores, and the average pore size of the carbon aerogel is 1.8-2.4 nm; The specific surface area of ​​the carbon aerogel is 1000-2000 m². 2 / g, total pore volume is 0.20-0.99cm³ 3 / g; The carbon aerogel has an ash content of <1% and a carbon content of >90%.

13. A silicon-carbon composite anode material, characterized in that, The carbon aerogel with ZIF-8 as its framework prepared by any of the preparation methods described in claims 1-11 or the carbon aerogel with ZIF-8 as its framework described in claim 12, as well as nano-silicon deposited in the pores of the carbon aerogel with ZIF-8 as its framework.

14. A negative electrode sheet, characterized in that, Including the silicon-carbon composite anode material as described in claim 13.

15. A lithium-ion secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 14.

16. An electrochemical device, characterized in that, Including the lithium-ion secondary battery as described in claim 15.

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