A method for preparing carbon aerogel material used as silicon-carbon negative electrode

Abstract

The present invention discloses a method for preparing a carbon aerogel material used as a silicon-carbon negative electrode. The method uses phenolic resin as the main raw material and adjusts the pore structure distribution of the carbon aerogel through sol-gel, crushing, drying, grading, carbon activation, impurity removal, grinding and other steps to control the impurity content, ash content, moisture content and particle size distribution, so as to meet the requirements for the use of carbon aerogel in the field of silicon-carbon negative electrodes. The prepared carbon aerogel material has a specific surface area of ​​1000 to 3000 m 2 / g, pore volume is 0.3~2cm 3 / g, with an average pore size of 0.5-10nm and a micropore ratio of 30%-100%, making it a porous carbon matrix material for silicon-carbon anodes. The present invention uses phenolic resin, formaldehyde, potassium hydroxide, and other ingredients as its primary raw materials, resulting in low costs. The materials are graded prior to carbon activation, ensuring controllability and consistency during activation. Furthermore, the impurity removal process is simple, and the overall process is highly efficient, facilitating the large-scale production of carbon aerogel materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery material preparation, and in particular relates to a method for preparing a porous carbon matrix material for a silicon-carbon negative electrode. Background Art

[0002] Since their introduction in the 1970s, lithium-ion batteries have developed rapidly. With their high energy density and long cycle life, they have been widely used in portable electronic devices, vehicles, energy storage power stations, and other fields. In particular, in the field of new energy vehicles, the demand for lithium-ion batteries has been strong in recent years. With the growing demand for new energy vehicles with higher mileage and shorter charging times, higher requirements have been placed on the energy density of lithium batteries. Currently, among various lithium-ion battery anode materials, graphite anodes occupy the main market. However, the theoretical capacity of graphite is only 372mAh / g, which is difficult to meet the demand for higher energy density. Therefore, the development of new anode materials is necessary.

[0003] Inorganic silicon materials offer advantages such as high earth element abundance, excellent safety, and ease of industrialization. As lithium battery anode materials, their enormous theoretical specific capacity (4200 mAh / g) gives them a unique advantage in the preparation of high-performance anode materials. However, the significant volume change effect (>300%) during charge and discharge causes silicon materials to pulverize during cycling, leading to deterioration in battery performance. Furthermore, silicon is a common semiconductor material with poor electrical conductivity, which affects the cycling performance of silicon anode materials in lithium-ion batteries.

[0004] In recent years, in order to utilize the high specific capacity of silicon and suppress its volume expansion effect, scientific researchers have conducted a lot of research. Among them, the better technical route is to prepare silicon / carbon composite materials, while utilizing the high specific capacity of silicon and the good mechanical properties and conductivity of carbon materials.

[0005] Chinese patent CN110098380A discloses a method for preparing a silicon-based anode material for lithium-ion batteries. The method involves first etching the surface of a carbon material using physical or chemical methods to form multiple nano- to micron-sized pores on the carbon material surface. The resulting porous carbon material is then mixed with a certain proportion of nanosilicon and ball-milled to embed the nanosilicon within the pores of the carbon material. Finally, the milled material is carbon-coated to obtain a silicon-based anode material for lithium-ion batteries. This method uses commercial nanosilicon as a raw material, which is relatively expensive. Furthermore, the carbon material only forms a few pores on the surface, limiting the number of nanosilicon particles that can be embedded. These particles also struggle to evenly penetrate the pores of the carbon material, preventing the full performance of the silicon-carbon material. Clearly, carbon materials with high porosity and a well-distributed pore structure are essential for the performance of silicon-carbon anode materials. Carbon aerogels, with their excellent properties such as high porosity and adjustable pore structure, have great potential for application in the silicon-carbon anode field.

[0006] Regarding carbon aerogel preparation methods, Chinese patent CN1895770A discloses a "method for preparing carbon aerogel powder." This involves uniformly dispersing a resorcinol-formaldehyde solution containing a certain concentration and catalyst ratio in an oil phase under ultrasonication and low temperature. A gel polymerization reaction is then carried out under heating and ultrasonication. Organic aerogel powder is obtained through separation and cleaning, and then carbon activation is performed to obtain the carbon aerogel powder. This method uses resorcinol as a raw material, which is costly. The production process generates a large amount of organic oil that requires processing, resulting in a complex process that is not conducive to large-scale production.

[0007] In summary, whether a relatively simple process can be used to prepare high-purity carbon aerogel materials with a reasonable pore structure distribution is the key to improving the performance of silicon-carbon negative electrode materials. Summary of the Invention

[0008] The purpose of the present invention is to address the problems of the existing technology such as complex process, high production cost, low porosity, unreasonable pore structure distribution, poor product consistency, low purity and difficulty in large-scale production, and to provide a method for preparing carbon aerogel materials for silicon-carbon negative electrodes with a wide source of raw materials, simple production process, high product purity, and reasonable pore size and distribution.

[0009] To achieve the above-mentioned objectives, the present invention provides a method for preparing a carbon aerogel material for use as a silicon-carbon anode. The method uses phenolic resin as the main raw material and adjusts the pore structure distribution of the carbon aerogel through sol-gel, crushing, drying, classification, carbon activation, impurity removal, and grinding to meet the requirements for the use of carbon aerogel in the field of silicon-carbon anodes. The method specifically includes the following processes and steps:

[0010] 1) Sol-gel: Mix and dissolve a set amount of phenolic resin, formaldehyde solution, potassium hydroxide and pore-forming agent, and keep the mixture at a certain temperature T1 for a period of time to obtain a gel material;

[0011] In this step, the molar ratio of phenolic resin to formaldehyde is generally 1:1 to 3.5, preferably 1:1.5 to 2.5; the molar ratio of phenolic resin to potassium hydroxide is generally 10 to 200:1, preferably 40 to 80:1; the pore-forming agent is preferably hexadecyltrimethylammonium bromide, and the addition ratio of the pore-forming agent is generally 1 to 10% of the mass of the phenolic resin, preferably 1.5 to 4.0%;

[0012] In this step, the temperature T1 is 60-80° C., and the insulation time is 5-15 hours.

[0013] 2) Crushing: The gel material is crushed to obtain fine-particle gel material with a certain particle size distribution, and the D50 of the fine-particle gel material is controlled to be in the range of 100 to 600 μm, preferably 300 to 600 μm.

[0014] 3) Drying: The fine-grained gel material is placed in a drying device and dried at a certain temperature T2 for a period of time to obtain a dried material;

[0015] In this step, the temperature T2 is preferably 80-150° C., preferably 85-95° C., the drying time is 10-20 hours, and the moisture content of the dried material is controlled to be ≤1%.

[0016] 4) Classification: The dried material is classified by a classification device to obtain a classified material, and the particle size D50 of the classified material is controlled to be in the range of 300-500 μm, and (D90-D10) / D50≤1.5;

[0017] In this step, D50 is preferably in the range of 400 to 500 μm, and (D90-D10) / D50≤1.2 is preferred.

[0018] 5) Carbonization: Carbonize the graded material under a certain carbonization temperature, time and inert gas protection to obtain carbonized material. The carbonization temperature is controlled in the range of 600-1000℃;

[0019] The carbonization time in this step is 2 to 4 hours, and the carbonization temperature is preferably controlled in the range of 650 to 800° C.; the inert atmosphere is nitrogen, helium or argon, or a mixture of two or more thereof, with nitrogen having the lowest cost.

[0020] 6) Activation: Activate the carbonized material under a certain activation temperature, time and activator atmosphere to obtain an activated material. The activator is water vapor, carbon dioxide or a mixture of the two. The activation temperature is controlled in the range of 700-1000°C.

[0021] In this step, the activation time is controlled within the range of 6 to 15 hours, preferably 7 to 10 hours; and the activation temperature is preferably controlled within the range of 750 to 850°C.

[0022] 7) Impurity removal: The activated material is passed through a magnetic separation device to remove iron impurities and obtain pure material;

[0023] In this step, the selected magnetic separation equipment is preferably a dry magnetic separation equipment, such as using Chinese patent ZL201610978391.3 "A dry iron removal device for hollow glass microspheres", and controlling the magnetic field strength of the magnetic separation equipment to make the iron content of the pure material ≤100ppm.

[0024] 8) Grinding: The pure material is further ground to obtain a specific surface area of ​​1000 to 3000 m 2 / g, pore volume is 0.3~2cm 3 / g, an average pore diameter of 0.5 to 10 nm, and micropores smaller than 2 nanometers accounting for 30% to 100% of the carbon aerogel material product.

[0025] In step 8), the grinding operation is performed using a vibration grinder or a high-speed centrifugal grinder with a frequency of 20 to 45 Hz, preferably 30 to 40 Hz; the particle size distribution D50 of the finished carbon aerogel material is 2 to 15 μm.

[0026] Experimental studies have shown that by controlling the process parameters of each step, carbon aerogel material products with the following product properties can be obtained:

[0027] ①Specific surface area is 1000~3000m 2 / g, pore volume is 0.3~2cm 3 / g, the average pore size is 0.5-10nm, and the proportion of micropores is 30%-100%;

[0028] ②Specific surface area is 1100~2400m 2 / g, pore volume is 0.4~1.5cm 3 / g, the average pore size is 1.5-3nm, and the proportion of micropores is 60%-100%;

[0029] ③Specific surface area is 1150~1350m 2 / g, pore volume is 0.45~0.60cm 3 / g, the average pore size is 1.5-2.5nm, and the proportion of micropores is 80%-100%;

[0030] ④Specific surface area is 1350~1550m 2 / g, pore volume is 0.55~0.70cm 3 / g, the average pore size is 1.5-2.5nm, and the proportion of micropores is 80%-100%;

[0031] ⑤Specific surface area is 1550~1750m 2 / g, pore volume is 0.65~0.80cm 3 / g, the average pore size is 1.5-2.5nm, and the proportion of micropores is 80%-100%;

[0032] ⑥Specific surface area is 1750~1950m 2 / g, pore volume is 0.75~0.90cm 3 / g, the average pore size is 1.5-2.5nm, and the proportion of micropores is 80%-100%;

[0033] ⑦Specific surface area is 1950~2150m 2 / g, pore volume of 0.85~1.00cm 3 / g, the average pore size is 1.5-2.5nm, and the proportion of micropores is 80%-100%;

[0034] ⑧Specific surface area is 2150~2350m 2 / g, pore volume is 0.95~1.10cm 3 / g, the average pore size is 1.5-2.5nm, and the proportion of micropores is 80%-100%.

[0035] Micropores here refer to pores smaller than 2 nanometers.

[0036] Compared with the prior art, the preparation method of a carbon aerogel material used as a silicon-carbon negative electrode of the present invention has the following advantages:

[0037] (1) The present invention uses phenolic resin, formaldehyde, potassium hydroxide and the like as main raw materials, which have a wide source of raw materials, low cost, relatively simple preparation process and high production efficiency, and is suitable for use in large-scale industrial production.

[0038] (2) The raw materials used in the present invention are of high purity and low impurity content. During the production process, the effect of removing metal impurities such as iron can be achieved only by using magnetic separation equipment. Compared with the traditional process for preparing porous carbon, there is no need to pickle or wash the product to remove metal impurities, and no oxygen-containing functional groups are introduced on the surface of the product, so there is no need for subsequent high-temperature heat treatment to remove the oxygen-containing functional groups.

[0039] (3) The present invention performs carbon activation after classifying the dried material. The control of particle size is beneficial to improving the uniformity of heat and mass transfer of the particles during high temperature processes, and is particularly beneficial to controlling the contact between the particles and the activator during the activation process, thereby improving the activation uniformity of the carbon aerogel material product and ensuring the consistency of the product.

[0040] (4) By adjusting the process parameters, silicon-carbon negative electrode carbon aerogel material products with different specific surface areas, pore volumes, average pore sizes, and micropore ratios can be prepared, which have strong market adaptability. DETAILED DESCRIPTION

[0041] To illustrate the present invention, a method for preparing a carbon aerogel material for a silicon-carbon negative electrode according to the present invention is further described in detail below with reference to the accompanying drawings and examples, but this is not intended to limit the present invention.

[0042] Example 1

[0043] The present invention provides a method for preparing a carbon aerogel material used as a silicon-carbon negative electrode, comprising the following steps:

[0044] (1) Sol-gel: A certain amount of phenolic resin, formaldehyde aqueous solution, potassium hydroxide and pore-forming agent are mixed and dissolved, wherein the molar ratio of the phenolic resin to formaldehyde is 1:2; the molar ratio of the phenolic resin to potassium hydroxide is 50:1; the pore-forming agent is hexadecyltrimethylammonium bromide, and the addition ratio is 2% of the mass of the phenolic resin; and the mixture is kept warm at 65°C for 10 hours to obtain a gel material.

[0045] (2) Crushing: Crushing the gel material to obtain a crushed gel material with a particle size distribution D50 of 400 μm.

[0046] (3) Drying: The crushed gel material is placed in a drying device and dried at 90°C for 15 hours to obtain a dried material.

[0047] (4) Classification: The dried material is subjected to classification treatment by a classification device to obtain a classified material. The particle size distribution D50 of the classified material is 400 μm, and (D90-D10) / D50≤1.2.

[0048] (5) Carbonization: Carbonize the graded material at 700°C for 3 h with nitrogen as the protective gas to obtain carbonized material.

[0049] (6) Activation: At 800°C, the activation time is 8 hours, and carbon dioxide is used as an activating agent to activate the carbonized material to obtain an activated material.

[0050] (7) Impurity removal: The activated material is passed through a magnetic separation device to remove iron impurities and obtain impurity-free material.

[0051] (8) Grinding: The impurity-removed material is further crushed at a grinding frequency of 35 Hz to obtain a finished carbon aerogel material with a particle size distribution that meets the requirements.

[0052] Examples 2-6

[0053] The steps for preparing the carbon aerogel material for use as a silicon-carbon negative electrode in Example 2-4 are the same as those in Example 1, except that the activation temperature and time in step (6) activation are different from those in Example 1. The steps for preparing the carbon aerogel material for use as a silicon-carbon negative electrode in Example 5-6 are the same as those in Example 1, except that the addition ratio of the pore-forming agent in the sol-gel in step (1) and the activation temperature and time in step (6) activation are different from those in Example 1. The technical parameters used in Examples 2-6 are shown in Table 1.

[0054] Table 1 Technical parameters of carbon aerogel materials for preparing silicon-carbon negative electrodes in Examples 2-6

[0055]

[0056] Performance Testing

[0057] The carbon aerogel materials prepared in the present invention were subjected to performance testing. The specific surface area, pore volume, average particle size, and micropore ratio were measured using a static specific surface area and pore size analyzer. The ash content was measured using a muffle furnace, the pH value was measured using a pH meter, the moisture content was measured using a moisture meter, the particle size distribution was measured using a particle size analyzer, and the impurity iron content was measured using an ICP device. The performance test results of the carbon aerogel materials prepared in Examples 1-6 are shown in Table 2.

[0058] Table 2 Performance data of carbon aerogel materials prepared in Examples 1-6

[0059]

[0060]

[0061] As can be seen from Table 2, Examples 1-4 can conveniently control the specific surface area and pore volume of the carbon aerogel material by changing the activation temperature and time; Examples 4-6 also have good control effects on the specific surface area and pore volume by changing the addition of pore-forming agent and slightly adjusting the activation time.

Claims

1. A method for preparing a carbon aerogel material used as a silicon-carbon negative electrode, characterized in that The following process is used: 1) Sol-Gel: A set amount of phenolic resin, formaldehyde solution, potassium hydroxide and a pore-forming agent are mixed and dissolved, and then kept warm at a certain temperature T1 for a period of time to obtain a gel material; the molar ratio of phenolic resin to formaldehyde is 1:1 to 3.5, the molar ratio of phenolic resin to potassium hydroxide is 10 to 200:1, and the pore-forming agent is hexadecyltrimethylammonium bromide, and the addition ratio of the pore-forming agent is 1 to 10% of the mass of the phenolic resin; the temperature T1 is 60 to 80° C., and the holding time is 5 to 15 hours; 2) Crushing: crushing the gel material to obtain fine-grained gel material with a certain particle size distribution, and controlling the D50 of the fine-grained gel material in the range of 100 to 600 μm; 3) Drying: The fine-grained gel material is placed in a drying device and dried at a certain temperature T2 for a period of time to obtain a dried material; the temperature T2 is 80-150° C., the drying time is 10-20 hours, and the moisture content of the dried material is ≤1%; 4) Classification: The dried material is classified by a classification device to obtain a classified material, and the particle size D50 of the classified material is controlled to be in the range of 300-500 μm, and (D90-D10) / D50≤1.5; 5) Carbonization: Carbonize the graded material under a certain carbonization temperature, time and inert gas protection to obtain carbonized material. The carbonization temperature is controlled in the range of 600-1000℃; 6) Activation: Activate the carbonized material under a certain activation temperature, time and activator atmosphere to obtain an activated material. The activator is water vapor, carbon dioxide or a mixture of the two. The activation temperature is controlled in the range of 700-1000°C. 7) Impurity removal: The activated material is passed through a magnetic separation device to remove iron impurities and obtain pure material; 8) Grinding: The pure material is further ground to obtain a specific surface area of ​​1000 to 3000 m 2 / g, pore volume is 0.3~2cm 3 / g, an average pore diameter of 0.5 to 10 nm, and micropores smaller than 2 nanometers accounting for 30% to 100% of the carbon aerogel material product.

2. The method for preparing a carbon aerogel material for a silicon-carbon negative electrode according to claim 1, wherein: In step 5), the carbonization time is 2 to 4 hours, and the inert atmosphere is nitrogen, helium or argon; in step 6), the activation time is 6 to 15 hours.

3. The method for preparing a carbon aerogel material for a silicon-carbon negative electrode according to claim 2, wherein: In step 7), the magnetic field strength of the magnetic separation equipment is controlled so that the iron content of the pure material is ≤100ppm.

4. The method for preparing a carbon aerogel material for a silicon-carbon negative electrode according to claim 3, wherein: In step 8), the grinding operation is performed using a vibration grinder or a high-speed centrifugal grinder with a frequency of 20 to 45 Hz; the particle size distribution D50 of the finished carbon aerogel material is 2 to 15 μm.

5. The method for preparing a carbon aerogel material for a silicon-carbon negative electrode according to claim 4, wherein: By controlling the process parameters of each step, the specific surface area is 1150~1350m 2 / g, pore volume is 0.45~0.60cm 3 / g, an average pore diameter of 1.5 to 2.5 nm, and micropores smaller than 2 nanometers accounting for 80% to 100% of the carbon aerogel material finished product.

6. The method for preparing a carbon aerogel material for a silicon-carbon negative electrode according to claim 4, wherein: By controlling the process parameters of each step, the specific surface area is 1750~1950m 2 / g, pore volume is 0.75~0.90cm 3 / g, the average pore size is 1.5-2.5nm, and the proportion of micropores smaller than 2 nanometers is 80%-100%.

7. The method for preparing a carbon aerogel material for a silicon-carbon negative electrode according to claim 4, wherein: By controlling the process parameters of each step, the specific surface area is 2150~2350m 2 / g, pore volume is 0.95~1.10cm 3 / g, the average pore size is 1.5-2.5nm, and the proportion of micropores smaller than 2 nanometers is 80%-100%.

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