A silicon-carbon negative electrode prepared by photolysis of silane and a preparation method thereof

Abstract

The present invention provides a silicon-carbon composite material prepared by photolysis of silane, the morphology is irregular, the surface is smooth, D50 is 6-10 μm, silicon particles are evenly distributed in the pore structure of porous carbon, Si content is 30-70wt%, wherein amorphous silicon accounts for ≥99.5wt%, and the silicon particles are silane process gas deposited in the pores of porous carbon in the presence of a photosensitizer. Deposition is carried out under low-temperature photolysis conditions, which can effectively avoid the formation of silicon carbide and the transformation of amorphous silicon to promote crystalline silicon. And the deposition of silicon is more uniform and stable, avoiding the agglomeration of silicon particles and deposition on the surface of porous carbon. By controlling the intensity, time and type of light, the decomposition rate of silane can be accurately controlled to form fine crystal nuclei, so that silicon can be evenly distributed on porous carbon to prevent silicon agglomeration, thereby improving battery performance.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-carbon negative electrode materials, and in particular to a silicon-carbon negative electrode prepared by photolysis of silane and a preparation method thereof. Background Art

[0002] Silicon-based negative electrode materials are considered to be ideal negative electrode materials for the next generation of lithium-ion batteries because of their high theoretical specific capacity (4200mAh / g). However, silicon-based negative electrode materials have serious volume expansion and contraction problems during the charge and discharge process, which can lead to the destruction of the electrode structure and the loss of electrical contact, thereby affecting the cycle performance of the battery. In order to solve this problem, a common method is to fill silicon in the pores of porous carbon to form a silicon-carbon composite material to buffer the volume change of silicon. Among them, silane cracking is a commonly used method, that is, silicon is deposited in the pores of porous carbon by high-temperature pyrolysis of silane. The existing mainstream technology is to use silane cracking in the pores of porous carbon, and then coating to obtain a silicon-carbon composite material. The main steps of this method include: first, introducing silane gas into a reactor containing porous carbon; then, the silane gas is cracked by heating, and the generated silicon is deposited in the pores of porous carbon; finally, the deposited silicon is coated by heat treatment to obtain a silicon-carbon composite material. For example, the technical solutions disclosed in CN116742002A, CN117673333A, and CN117650243A. By heat-treating the gaseous silicon source, silane is decomposed to deposit silicon. However, there are some problems in the preparation process of pyrolytic silane deposition: first, the temperature control of the pyrolysis process is difficult, which easily leads to the crystallization of silicon, causing the volume expansion of the material to be too large, thereby affecting its cycle performance. Secondly, the speed of the pyrolysis process is difficult to control, and the silane chain reaction and complex decomposition process lead to the agglomeration and uneven distribution of silicon on the porous carbon, which also affects the performance of the battery. In addition, the pyrolysis process has high equipment requirements, and the deposition efficiency of silane in porous carbon is not high, which easily leads to low silane utilization, which is also a problem that needs to be solved. Summary of the invention

[0003] In order to solve the defects of poor electrochemical performance and low silane utilization efficiency in the pyrolysis process of silicon-carbon composite negative electrode materials produced by pyrolysis of silane in the prior art, the present invention proposes a process for preparing silicon-carbon composite materials by photolysis of silane, and a silicon-carbon composite material obtained by the process. In order to solve the above technical problems, the present invention provides the following technical solutions:

[0004] A silicon-carbon composite material prepared by photolysis of silane, characterized in that the morphology is irregular, the surface is smooth, the D50 is 6-10μm, the silicon particles are evenly distributed in the pore structure of the porous carbon, the Si content is 45-55wt%, of which the amorphous silicon accounts for ≥99.5wt%, and the silicon particles are deposited in the pores of the porous carbon by silane process gas in the presence of a photosensitizer.

[0005] Furthermore, the silicon-carbon composite material is also carbon-coated, the thickness of the carbon coating layer is 5-20 nm, and the coating carbon content is 2-5 wt%.

[0006] The second object of the present invention is to provide a method for preparing the silicon-carbon composite material prepared by photolysis of silane, comprising the following steps:

[0007] The porous carbon material and the photosensitizer solution are placed in a reactor and mixed evenly, the solvent of the photosensitizer solution is evaporated, and the silane process gas is introduced, and the silane is photolyzed and evenly deposited in the pores of the porous carbon under light conditions.

[0008] Compared with traditional pyrolytic silane, the rate of photolysis is relatively slow, and finer crystal nuclei can be formed during the decomposition process, preventing excessive growth and agglomeration of silicon particles. Due to this relatively slow decomposition rate, the deposited silane is also more uniform. By controlling the time of light exposure, the decomposition of silane can be precisely controlled to avoid excessive deposition of silane and exposure on the outer surface of porous carbon. At the same time, adding appropriate photosensitizers can effectively promote the decomposition of silane and improve the utilization rate of silane.

[0009] Furthermore, the specific surface area of ​​the porous carbon is 1500-2500m 2 / g, pore volume is 0.6-1.5cm 3 / g.

[0010] Further, the silane process gas is a silane containing a C1-4 alkyl group, specifically selected from at least one of monosilane, disilane, trisilane, and butadisilane; the photosensitizer is selected from at least one of aromatic diazonium salts (such as diazonium chloride, diazonium sulfate), aromatic ketones, styrene, and alkyl acrylates;

[0011] Furthermore, the aromatic ketone is selected from at least one of aromatic ketones, acetophenone, benzophenone, and dichloroacetophenone; and the aromatic diazonium salt is selected from at least one of benzene diazonium chloride and benzene diazonium sulfate.

[0012] Preferably, the photosensitizer is a compound of aromatic ketones and aromatic diazonium salts in a mass ratio of 1-3:1-3. The inventors have found that the above-mentioned compounded photosensitizer can make the electrochemical properties of the product obtained by photolysis of silane more excellent. The possible reason is that the two photosensitizers work together to cooperate. Since each photosensitizer has differences in the degree of absorption of photons, sensitization time and response time, the use of mixed photosensitizers can improve the utilization rate of light source energy and the decomposition efficiency of silane.

[0013] Furthermore, the solvent of the photosensitizer solution is selected from low boiling point solvents such as methanol, ethanol, acetone, etc.; the photosensitizer concentration in the photosensitizer solution is 1-5wt%; the solvent of the photosensitizer solution is evaporated cleanly, and it is heated to 30-50°C under vacuum conditions in the dark, and the vacuum conditions are 0.01-0.1MPa.

[0014] Furthermore, the usage ratio of porous carbon, silane process gas, and photosensitizer is 1kg:800-1200L:10-50g.

[0015] Furthermore, the illumination conditions are a light wavelength of 300-600nm and a light intensity of 100-500mW / cm 2 .

[0016] Furthermore, the gas flow rate of silane and the mass ratio of porous carbon are 1.5-3 L / min / kg, and the deposition time is 10-16 h.

[0017] Furthermore, the illumination condition is that during the illumination deposition time, the light intensity is from 100 mW / cm 2 Up to 500mW / cm 2 Gradually increase; the light intensity can be increased linearly, that is, the light intensity increases linearly during the deposition time; it can also be increased in stages, for example, 100-200mW / cm 2 Light 2-16h, 300-400mW / cm 2 Light 2-16h, 450-500mW / cm 2 Irradiation for 1-16 hours. Gradually increase the light intensity. First, under the action of lower light intensity, silane slowly decomposes in the pores of porous carbon to form a large number of fine crystal nuclei. These crystal nuclei are adsorbed in the pores of porous carbon under the action of high specific surface area, effectively avoiding silicon agglomeration and deposition on the surface of porous carbon, so that amorphous silicon is deposited more evenly. The photosensitizer can absorb photons, transfer energy, and improve the utilization rate of silane. Then gradually increase the light intensity to speed up the decomposition efficiency of silane. However, if a stronger light intensity is used at the beginning, the silane deposition will be uneven, affecting the electrochemical performance of the silicon-carbon composite negative electrode material.

[0018] Furthermore, the preparation method of the silicon-carbon composite material also includes a carbon coating process: the silicon-carbon composite material obtained by photolysis of silane is transferred into a rotary kiln, a carbon-containing process gas is introduced, and carbon coating is performed under the protection of an inert atmosphere and a high temperature of 450-650°C.

[0019] Furthermore, the carbon-containing process gas is selected from at least one of C1-4 alkanes (methane, ethane, propane, butane), C2-4 olefins (ethylene, propylene, butene, 1,3-butadiene), and C2-4 alkynes (acetylene, propyne, butyne). The inert gas is nitrogen and / or argon.

[0020] Further, the ratio of carbon-containing process gas to porous carbon is 10-20 L:10 kg, the gas flow rate and the porous carbon mass are 1-3 L / min:1 kg, the heating rate to 450-650° C. is 1-20° C. / min, preferably 5-10° C. / min. The carbon coating time is 3-10 h, such as 3 h, 6 h, 10 h.

[0021] Compared with other prior arts, the present invention has the following characteristics:

[0022] 1. In the preparation process of the present invention, since silicon exists in the form of photolytic amorphous state, the volume expansion rate is lower, and the deposition is carried out under low temperature conditions, it can effectively avoid the formation of silicon carbide and the transformation of amorphous silicon to crystalline silicon. In addition, the deposition of silicon is more uniform and stable, avoiding the agglomeration of silicon particles and the phenomenon of deposition on the surface of porous carbon. In general, compared with the process of pyrolytic silane deposition, the photolytic silane deposition process of the present invention has a lower proportion of crystalline silicon, a smaller silicon particle size, a higher probability of silicon deposition in porous carbon, and a more uniform distribution of silicon.

[0023] 2. The process of the present invention uses light to decompose silane to deposit silicon on porous carbon: by controlling the intensity, time and type of light, the decomposition rate of silane can be accurately controlled to form fine crystal nuclei, so that silicon can be evenly distributed on the porous carbon to prevent silicon agglomeration, thereby improving battery performance.

[0024] 3. By adding a small amount of photosensitizer, the efficiency of photolysis and the utilization rate of silane can be improved, the waste of silane can be reduced, and the production efficiency can be improved.

[0025] 4. During the photolysis process, the light intensity is highly controllable and easier to control than the thermal decomposition temperature, which can optimize the temperature and speed of the photolysis process: by precisely controlling the selection of photosensitizers in the photolysis process and coordinating with the light intensity, the crystallization of silicon can be effectively prevented, allowing silicon to be evenly distributed on the porous carbon, thereby improving battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1This is the XRD pattern of the product obtained in Example 1;

[0027] Figure 2 This is the SEM image of the product obtained in Example 1;

[0028] Figure 3 Thermogravimetric curve of the sample obtained in Example 1;

[0029] Figure 4 This is the first charge and discharge curve of the product obtained in Example 1. DETAILED DESCRIPTION

[0030] The present invention is described below by means of specific embodiments, but the present invention is not limited thereto.

[0031] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0032] Example 1

[0033] (S1) preparing a porous carbon material having a pore size of 1.5 nm and a specific surface area of ​​1900 m 2 / g, pore volume is 0.85cm 3 / g. More than 3kg of porous carbon material was placed in a 50L reactor with an operating pressure of 1atm and a temperature of room temperature. 50g of acetophenone was dissolved in 1kg of ethanol to prepare a photosensitizer solution. The photosensitizer and porous carbon were mixed evenly under stirring conditions, vacuumed to 0.1Mpa, and heated to 40°C to completely volatilize the ethanol to obtain a porous carbon and photosensitizer mixture;

[0034] (S2) Monosilane was continuously introduced at a gas flow rate of 3 L / min. After no other gas was present in the container, the light source was turned on. The wavelength of the light source was 365 nm and the light intensity was 100 mW / cm 2 A total of 2800 L of monosilane was introduced, and the illumination time was 8 h; then the illumination intensity was increased to 300 mW / cm 2 ; Continue to illuminate for 4 hours; increase the light intensity to 400mW / cm 2 , continue to illuminate for 2 hours; finally increase the light intensity to 500mW / cm 2 , continue to illuminate for 1.55 hours to ensure that silane is completely decomposed. Under the action of light, silane slowly decomposes in the pores of porous carbon to form a large number of tiny crystal nuclei. These crystal nuclei are implanted in the pores of porous carbon, effectively avoiding the agglomeration of silicon and making the deposition more uniform. The photosensitizer can absorb photons, transfer energy, and improve the utilization rate of silane.

[0035] (S3) The silicon-carbon composite material obtained in step (S2) is transferred into a rotary kiln, and acetylene is introduced as a process gas at a flow rate of 3 L / min. A total of 1600 L of acetylene is introduced. The speed of the rotary kiln is 50 r / min, and the temperature is increased to 450°C at a heating rate of 5°C / min. The temperature is kept at this temperature for 10 hours to complete the carbon coating.

[0036] Figure 1 This is the XRD diagram of the product obtained in Example 1. It is clearly observed that the curve is a diffuse amorphous state, and no crystalline Si and other peaks are detected, indicating that the silicon in the sample exists in an amorphous form and the sample has high purity characteristics. Figure 2 This is the SEM picture of the product obtained in Example 1, which has an irregular shape, a particle size distribution of 6-10 μm, a smooth surface, and a particle size that is basically consistent with the porous carbon material before deposition, which indicates that silicon is basically deposited inside the porous carbon. Figure 3 This is the thermogravimetric curve of the sample obtained in Example 1, and its silicon content is 53.35wt%.

[0037] (S4) Under the protection of nitrogen, the sample was naturally cooled and collected to obtain the silicon-carbon negative electrode material, which was sieved in a 300-mesh vibrating screen with a vibration frequency of 3600 times / min. The fine powder was collected, and polyacrylic acid (PAA), super P, and silicon-carbon composite materials were used in a mass ratio of 1:1:8, and deionized water was used as a solvent. The slurry was evenly ground and coated on the copper foil, and then transferred to a vacuum oven for drying at 80°C for 12 hours. After that, it was cut into 12mm pole pieces under the action of a punching machine and transferred to a glove box filled with argon, oxygen and water content less than 0.01ppm. A 16mm metal lithium sheet was used as the counter electrode, and 1MLiPF 6 Dissolved in EC:EDC:EMC with a volume ratio of 1:1:1, add 5% FEC as electrolyte, Celgard2600, cut into 18mm as separator, assembled into CR2032 button battery. The battery test system is Blue Electric CT2001A, the range is 0.001-1.5V, and the current density is 200mA / g. The first discharge / charge capacity of the tested material is: 2276 / 2073mA h / g, the first coulomb efficiency is: 91.11%, such as Figure 4 The above are the specific operation steps of this embodiment, which can effectively solve the problems of uneven distribution of silane caused by cracking of silane in the CVD process, the insufficiency of easy conversion of amorphous silicon into crystalline silicon, too fast pyrolysis rate, and difficulty in controlling silane decomposition, resulting in silicon deposition on the surface of porous carbon.

[0038] Example 2

[0039] Other conditions and operations are the same as those in Example 1, except that in step (S1), the photosensitizer is changed to diazonium chloride.

[0040] Example 3

[0041] Other conditions and operations are the same as those in Example 1, except that in step (S1), the illumination condition is changed to 150 mW / cm 2 The illumination time was 5 h; then the illumination intensity was increased to 300 mW / cm 2 ; Continue illumination for 5 hours; increase the light intensity to 500mW / cm 2 , continue illumination for 5.55h.

[0042] Example 4

[0043] Other conditions and operations are the same as those in Example 1, except that in step (S1), the illumination condition is changed to 300 mW / cm 2 The illumination was continued for 15.55 h.

[0044] Example 5

[0045] Other conditions and operations are the same as those in Example 1, except that in step (S1), the illumination condition is changed from 100 mW / cm 2 According to 28.57mW / cm 2 / h to increase the light intensity, gradually increasing the light intensity to 500mW / cm 2 , continuous illumination for 15.55h, that is, linearly increase the light intensity from 100mW / cm 2 Up to 500mW / cm 2 .

[0046] Example 6

[0047] Other conditions and operations are the same as those in Example 1, except that in step (S1), the wavelength of the ultraviolet light is adjusted to 245 nm.

[0048] Example 7

[0049] Other conditions and operations are the same as those in Example 1, except that in step (S1), the wavelength of the ultraviolet light is adjusted to 302 nm.

[0050] Example 8

[0051] Other conditions were the same as those in Example 1, except that the photosensitizer was changed from 50 g of acetophenone to 25 g of acetophenone and 25 g of diazonium chloride.

[0052] Example 9

[0053] The other conditions were the same as those in Example 1, except that the photosensitizer was changed from 50 g of acetophenone to 37.5 g of acetophenone and 12.5 g of diazonium chloride.

[0054] Example 10

[0055] The other conditions were the same as those in Example 5, except that the photosensitizer was changed from 50 g of acetophenone to 37.5 g of acetophenone and 12.5 g of diazonium sulfate.

[0056] Comparative Example 1

[0057] Other conditions and operations are the same as those in Example 1, except that step (S1) is changed to: prepare a porous carbon material having a pore size of 1.5 nm and a specific surface area of ​​1900 m 2 / g, pore volume is 0.85cm 3 / g. 3kg of porous carbon material was placed in a 50L reactor with an operating pressure of 1atm and a temperature of room temperature. Step 2: Introduce silane gas into the reactor (according to the mass ratio of porous carbon to silicon of 1:1, 1L of silane theoretically produces 1.14g of silicon), the flow rate of silane was 3L / min, and ensure that there was no other gas in the container. At 500℃ and 1atm pressure, 2800L of monosilane was continuously introduced for thermal decomposition deposition of silane, and the deposition time was 15.55h.

[0058] The batteries assembled with the silicon-carbon composite negative electrode materials obtained in the above examples and comparative examples were subjected to electrochemical performance tests, and the results are shown in Table 1 below:

[0059] The silane utilization rate is obtained by calculating the amount of silane introduced and the silicon content of the final product.

[0060] Table 1 Performance test of silicon-carbon composite negative electrode materials

[0061]

[0062]

Claims

1. A method for preparing a silicon-carbon composite material prepared by photolysis of silane, characterized in that: The following steps are involved: The porous carbon material and the photosensitizer solution are placed in a reactor, mixed evenly, the solvent of the photosensitizer solution is evaporated, and the silane process gas is introduced, and the silane is photolyzed and evenly deposited in the pores of the porous carbon under light conditions; The silane process gas is silane containing a C1-4 alkyl group; the photosensitizer is selected from at least one of aromatic diazonium salts and aromatic ketones; the photosensitizer concentration in the photosensitizer solution is 1-5 wt%; the usage ratio of porous carbon, silane process gas, and photosensitizer is 1 kg: 800-1200 L: 10-50 g; The illumination conditions are a wavelength of 300-600 nm and an intensity of 100-500 mW / cm²; The silicon-carbon composite material has an irregular shape, a smooth surface, a D50 of 6-10 μm, silicon particles are evenly distributed in the pore structure of the porous carbon, and a Si content of 30-70 wt%, of which amorphous silicon accounts for ≥99.5 wt%.

2. The preparation method according to claim 1, characterized in that: The Si content is 40-55 wt%.

3. The preparation method according to claim 1, characterized in that: The silicon-carbon composite material is further carbon-coated, the carbon coating layer has a thickness of 1-30 nm and a carbon content of 0.5-6 wt%.

4. The preparation method according to claim 3, characterized in that: The thickness of the carbon coating layer is 5-20 nm and the carbon content is 2-5wt%.

5. The preparation method according to claim 1, characterized in that: The porous carbon has a specific surface area of ​​1500-2500 m² / g and a pore volume of 0.6-1.5 cm 3 / g.

6. The preparation method according to claim 1, characterized in that: The silane process gas is selected from at least one of monosilane, disilane, trisilane and butadisilane; the aromatic ketone is selected from at least one of aromatic ketones, acetophenone, benzophenone and dichloroacetophenone; the aromatic diazonium salt is selected from at least one of diazonium chloride and diazonium sulfate.

7. The preparation method according to claim 1, characterized in that: The solvent of the photosensitizer solution is selected from methanol, ethanol and acetone. The solvent of the photosensitizer solution is evaporated cleanly, and heated at 30-50° C. under vacuum conditions in the dark, and the vacuum conditions are 0.01-0.1 MPa.

8. The preparation method according to claim 1, characterized in that: The gas flow rate of silane and the mass ratio of porous carbon are 1.5-3 L / min / kg, and the deposition time is 10-16 h.

9. The preparation method according to claim 8, characterized in that: The illumination condition is that the light intensity is gradually increased from 100 mW / cm² to 500 mW / cm² during the illumination deposition time; the light intensity increase is a linear increase, that is, during the deposition time, the degree of light intensity increase increases linearly; or the light intensity is increased in stages.

10. The preparation method according to claim 9, characterized in that: The light intensity is increased in stages. The light conditions are 100-200 mW / cm² for 2-16 h, 300-400 mW / cm² for 2-16 h, and 450-500 mW / cm² for 1-16 h.

11. The preparation method according to claim 3, characterized in that: The method for preparing the silicon-carbon composite material also includes a carbon coating process: the silicon-carbon composite material obtained by photolysis of silane is transferred into a rotary kiln, a carbon-containing process gas is introduced, and carbon coating is performed under the protection of an inert atmosphere and a high temperature of 450-650°C.

12. The preparation method according to claim 11, characterized in that: The carbon-containing process gas is selected from at least one of C1-4 alkanes, C2-4 alkenes, and C2-4 alkynes; and the inert gas is nitrogen and / or argon.

13. The preparation method according to claim 12, characterized in that: The C1-4 alkane is selected from methane, ethane, propane, butane; the C2-4 olefin is selected from ethylene, propylene, butene, 1,3-butadiene; the C2-4 alkyne is selected from acetylene, propyne, butyne.

14. The preparation method according to claim 12, characterized in that: The ratio of carbon-containing process gas to porous carbon is 10-20 L:10 kg, the gas flow rate and porous carbon mass are 1-3 L / min:1 kg; the heating rate to 450-650 °C is 1-20 °C / min; and the carbon coating time is 3-10 h.

15. The preparation method according to claim 14, characterized in that: The heating rate to 450-650°C is 5-10°C / min.

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