A method for preparing silicon-carbon negative electrode material by regulating silicon deposition using solid fluidized medium

Abstract

The present invention, in the field of lithium-ion battery technology, relates to a method for preparing a silicon-carbon anode material using a solid fluidizing medium to regulate silicon deposition, comprising: (S1) mixing porous carbon with a modified high-silicon Y-type zeolite molecular sieve and placing the mixture in a fluidized bed for silicon deposition to obtain a precursor I; the high-silicon Y-type zeolite molecular sieve has a silicon-to-aluminum ratio of 20 to 30; the modified high-silicon Y-type zeolite molecular sieve is obtained by grafting and modifying the high-silicon Y-type zeolite molecular sieve with trimethylchlorosilane; (S2) carbon-coating the precursor I to obtain a precursor II; and (S3) removing the modified high-silicon Y-type zeolite molecular sieve from the precursor II to obtain a silicon-carbon anode material. The present invention introduces the modified high-silicon Y-type zeolite molecular sieve as a solid fluidizing medium during the porous carbon silicon deposition to restructure the fluidization system, effectively improving the uniformity of silicon deposition. As a result, the resulting silicon-carbon anode material has excellent cycling performance and pressure resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a method for preparing a silicon-carbon negative electrode material by utilizing a solid fluidized medium to regulate silicon deposition. Background Art

[0002] To adapt to the rapid development of the new energy market, the search and optimization of cathode and anode materials with higher energy density has become a mainstream research topic in the lithium-ion battery field. Among anode materials, commercially mature graphite materials have a low theoretical specific capacity (372 mAh / g), making them unable to meet the high energy density requirements of lithium-ion batteries. Compared to graphite, silicon-based materials offer higher theoretical specific capacity, are more abundant, and are less expensive. However, silicon-based materials experience significant volume expansion during lithium insertion and extraction, which can lead to pulverization of the electrode plates, damaging the electrode structure and causing rapid cycle life and capacity degradation. Furthermore, silicon-based materials exhibit poor electrical conductivity, hindering the commercial development of silicon-based anodes. To address the volume expansion and poor conductivity of silicon-based anode materials, the current mainstream technology utilizes chemical vapor deposition to deposit silicon into the pores of porous carbon, followed by surface carbon coating to produce silicon-carbon anode materials. The confinement effect of the porous carbon pores mitigates silicon volume expansion. Furthermore, the porous carbon framework and surface carbon coating, derived from hard carbon, significantly enhance the electrical conductivity and electronic conductance of the silicon-carbon material. However, this method of preparing silicon-carbon negative electrode materials still has some problems: 1) Micron-sized porous carbon is prone to agglomeration during silicon deposition, resulting in uneven fluidization, which makes it impossible for silicon to be effectively and evenly deposited inside the porous carbon, that is, the silicon deposition consistency is poor, which in turn leads to anisotropic volume expansion of the material, and ultimately leads to the cycle life of the silicon-carbon negative electrode material not being effectively improved; 2) The effective deposition rate of silicon is low, and it is difficult to balance the silane cracking rate and diffusion rate at a single temperature. Low temperature leads to insufficient cracking, while high temperature easily causes premature deposition in short diffusion paths, thereby blocking the pores. Summary of the Invention

[0003] In view of the problems of poor silicon deposition consistency and low effective deposition rate in the preparation of silicon-carbon negative electrode materials in the prior art, the present invention provides a method for preparing silicon-carbon negative electrode materials by using a solid fluidizing medium to regulate silicon deposition. When depositing silicon in a fluidized bed, a large-particle modified high-silicon Y-type zeolite molecular sieve (including conventional high-silicon Y-type zeolite molecular sieve or USY-type zeolite molecular sieve) is added as a solid fluidizing medium. The kinetic energy generated by the violent collision of the modified high-silicon Y-type zeolite molecular sieve is used to reconstruct the fluidization system, thereby improving the deposition uniformity and effective deposition rate of silicon, thereby obtaining a silicon-carbon negative electrode material with good cycle performance and compressive resistance.

[0004] A method for preparing a silicon-carbon negative electrode material by regulating silicon deposition using a solid fluidizing medium comprises the following steps:

[0005] (S1) mixing porous carbon with a modified high-silicon Y-type zeolite molecular sieve and placing the mixture in a fluidized bed for silicon deposition to obtain a precursor I; the high-silicon Y-type zeolite molecular sieve has a silicon-to-aluminum ratio of 20 to 30; and the modified high-silicon Y-type zeolite molecular sieve is obtained by grafting a high-silicon Y-type zeolite with trimethylchlorosilane;

[0006] (S2) introducing a gaseous carbon source to carbon-coat the precursor I to obtain the precursor II;

[0007] (S3) Removing the modified high-silicon Y-type zeolite molecular sieve from precursor II, a silicon-carbon negative electrode material is obtained in which silicon deposition is regulated by a solid fluidizing medium.

[0008] Y-type zeolite molecular sieves (including conventional Y-type zeolite or USY-type zeolite) have a unique pore structure (theoretical pore diameter 0.74 nm) and excellent thermal stability, and are commonly used in catalytic cracking or gas separation. The Si / Al ratio of Y-type zeolite significantly affects framework rigidity, acidic active sites, thermal stability, and hydrophobicity. As the Si / Al ratio increases, framework rigidity increases, acidic active sites decrease, and thermal stability and hydrophobicity improve. Generally, in catalytic cracking or gas separation applications, the Si / Al ratio of Y-type zeolite does not exceed 15. Through research, the inventors discovered that modifying large-particle, high-silica Y-type zeolite (Si / Al ratio 20-30) with trimethylchlorosilane to shrink its pores, and then using a specific proportion of this modified, large-particle, high-silica Y-type zeolite as a solid fluidizing medium during silicon deposition on porous carbon, can improve silicon deposition uniformity and effective deposition rate. The likely reason is that high-silicon Y-type zeolite with a silicon-aluminum ratio of 20-30 has good skeleton rigidity, thermal stability, and hydrophobicity. During fluidization in the fluidized bed, the modified high-silicon Y-type zeolite undergoes violent collisions, which transmit kinetic energy in the form of stress waves to smaller porous carbon agglomerates, shortening the disaggregation time of the agglomerated particles. This significantly inhibits the local agglomeration of porous carbon particles and promotes the transition of the fluidization state from agglomerated to dispersed state. In other words, the modified high-silicon Y-type zeolite can effectively regulate the fluidization of particles in the fluidized bed, thereby improving the uniformity and effective deposition rate of silicon deposition. Furthermore, the internal pores of the modified high-silicon Y-type zeolite are reduced and its hydrophobicity is enhanced, which prevents silane molecules from entering. Furthermore, there is a significant difference between the modified high-silicon Y-type zeolite and the porous carbon with rich pores. Therefore, silane gas is largely not deposited in the pores of the modified high-silicon Y-type zeolite, thus having no impact on the effective deposition rate of silicon. In addition, since the particle size of the modified high-silicon Y-type zeolite molecular sieve is quite different from that of the porous carbon, the silicon can be easily separated and recovered after the silicon deposition is completed, and can be recycled.

[0009] Preferably, the silicon-aluminum ratio of the high-silicon Y-type zeolite molecular sieve in step (S1) is 20-25. The silicon-aluminum ratio of the Y-type zeolite molecular sieve has a significant impact on the framework rigidity and thermal stability. If the silicon-aluminum ratio is too low, the framework rigidity is insufficient, the thermal stability is poor, the kinetic energy generated by collisions is insufficient, and the zeolite is easily broken, which is insufficient to promote the transition from agglomerated to dispersed fluidization state. A high silicon-aluminum ratio is usually achieved through deep dealumination (strong acid treatment, high-temperature hydrothermal treatment). However, if the silicon-aluminum ratio is too high, unrepaired framework vacancies (defects) may be left after aluminum removal. Some vacancies cannot be repaired by Si-OH condensation, resulting in localized framework collapse. In other words, a high silicon-aluminum ratio will reduce the framework rigidity. Therefore, the silicon-aluminum ratio of the Y-type zeolite molecular sieve should be controlled within the above range.

[0010] Furthermore, the grafting modification method described in step (S1) comprises: adding high-silicon Y-type zeolite and trimethylchlorosilane to an organic solvent and performing a reflux reaction under stirring. After the reaction, the mixture is filtered, washed, and dried to obtain a modified high-silicon Y-type zeolite. During the modification process, trimethylchlorosilane undergoes a grafting condensation reaction with hydroxyl groups on the surface of the Y-type zeolite. The resulting highly thermally stable trimethylsilyl groups form a physical barrier at the pore entrances of the zeolite, shrinking the pores and preventing silane molecules from entering the pores. Therefore, the effective deposition rate of silicon is not affected.

[0011] Furthermore, the usage ratio of the Y-type zeolite molecular sieve, trimethylchlorosilane, and organic solvent is 100 g: (8-15) mL: (300-500) mL; and the organic solvent is at least one of toluene or xylene.

[0012] Furthermore, the reflux reaction conditions are 110-120° C. for 8-15 hours; the washing is ethanol washing until no chloride ions are detected in the filtrate; and the drying is 120-150° C. for 4-8 hours.

[0013] Furthermore, in step (S1), the ratio of the modified high-silicon Y-type zeolite molecular sieve particle size D50 to the porous carbon particle size D50 is 5 to 12:1, preferably 8 to 10:1. The particle size ratio of the modified high-silicon Y-type zeolite molecular sieve to the porous carbon affects the fluidization state. When the ratio is too low, the collision kinetic energy of the modified high-silicon Y-type zeolite molecular sieve as a solid fluidizing medium is insufficient, and the deagglomeration time of the porous carbon particle agglomerates is relatively long, which is insufficient to push the fluidization state from agglomerated to dispersed, thereby limiting the improvement in silicon deposition uniformity. When the ratio is too high, the difference in particle size between the two is too large, which easily forms a graded fluidization effect, resulting in channeling, which in turn reduces the uniformity of silicon deposition; and when the ratio is too high, the collision stress is too large, and when it exceeds its yield strength, it is easy to break, resulting in a high breakage rate of the modified high-silicon Y-type zeolite molecular sieve, which in turn affects its recycling. Therefore, the ratio of the modified high-silica Y-type zeolite molecular sieve particle size D50 to the porous carbon particle size D50 needs to be controlled within the above range.

[0014] Furthermore, in step (S1), the mass ratio of the porous carbon to the modified high-silica Y-type zeolite molecular sieve is 10:0.5-1.5, preferably 10:0.5-1. As a solid fluidizing medium, if the amount of the modified high-silica Y-type zeolite molecular sieve is too low, the collision energy generated is insufficient, and the effect on regulating the fluidization state is limited; if the amount of the modified high-silica Y-type zeolite molecular sieve is too high, it occupies a large space, extending the effective diffusion path of silane, thereby affecting deposition efficiency. Therefore, the mass ratio of the porous carbon to the modified high-silica Y-type zeolite molecular sieve must be controlled within the aforementioned range.

[0015] Furthermore, in step (S1), the particle size D50 of the porous carbon is 5-10 μm, and the specific surface area of ​​the porous carbon is 1500-2200 m 2 / g, pore volume 0.7~1.1 cm 3 / g, the average pore size is 1~2.5nm, and micropores account for 85~95%.

[0016] Furthermore, in step (S1), the silicon deposition conditions are as follows: under an inert gas atmosphere, silane gas is introduced at a temperature of 400-650°C for 5-10 hours. The inert gas is nitrogen and / or argon. The silane gas is selected from at least one of monosilane, disilane, trichlorosilane, dichlorodihydrosilane, and trichlorosilane. The ratio of porous carbon to silane gas is 1 kg:600-900 L, and the flow ratio of the inert gas to silane gas is 5-10:1. During the silicon deposition process, silane decomposes to produce amorphous silicon, which is deposited in the pores of the porous carbon, forming a silicon-carbon composite material. The modified high-silica Y-type zeolite molecular sieve, due to the grafting of trimethylchlorosilane, forms a physical barrier at the pore openings, thereby preventing the entry of silane molecules. Furthermore, there is a significant difference between the modified high-silica Y-type zeolite molecular sieve and the porous carbon with abundant pores, so silane gas is essentially prevented from depositing within the pores. Therefore, the precursor I is a mixture of the silicon-carbon composite material and the modified high-silicon Y-type zeolite molecular sieve.

[0017] Furthermore, the silicon deposition is a staged process, where the temperature is first raised to 400°C to 500°C for a first silicon deposition for 2 to 5 hours, and then raised to 550°C to 650°C for a second silicon deposition for 2 to 4 hours. In the staged silicon deposition process, when deposition is performed at a lower first temperature, the silane gas diffusion rate into the pores is greater than the deposition growth rate, allowing the silane to diffuse more effectively and evenly into the pores of the porous carbon particles, allowing the silane molecules to be uniformly adsorbed within the porous carbon pores. Then, when deposition is performed at a higher second temperature, the silicon deposited at the first deposition temperature provides adsorption sites that induce more uniform adsorption and deposition of silane at the second deposition temperature. Furthermore, the higher deposition temperature results in a higher silane cracking rate, improving silane utilization.

[0018] The carbon coating process described in step (S2) is a technique well known to those skilled in the art and is not particularly limited. For example, the gaseous carbon source is selected from at least one of C1-4 alkanes, C2-4 alkenes, and C2-4 alkynes, such as methane, ethane, propane, acetylene, ethylene, or propylene. The carbon coating conditions are as follows: the ratio of Precursor I to the gaseous carbon source is 1 kg: 250-350 L, and the mixture is incubated at 500-700°C for 1-4 hours under an inert atmosphere. The carbon source gas decomposes to form a carbon coating layer, which coats the surface of the silicon-carbon composite material obtained in step (S1), forming a complete conductive network, thus forming the silicon-carbon anode material. However, the modified high-silicon Y-type zeolite molecular sieve, due to its small pores and large particle size, is unable to adsorb carbon source molecules and is essentially not coated with the carbon layer. Therefore, Precursor II is a mixture of the carbon-coated silicon-carbon anode material and the modified high-silicon Y-type zeolite molecular sieve.

[0019] Furthermore, in step (S3), the removal is performed by passing through a 600-800 mesh sieve. The modified high-silica Y-type zeolite molecular sieve after screening can be recycled (the crushing rate after screening must be less than 5%).

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention introduces a large-particle, trimethylchlorosilane-grafted, high-silicon Y-type zeolite molecular sieve as a solid fluidizing medium during silicon deposition on porous carbon to reconstruct the fluidizing system, thereby effectively improving the deposition uniformity and effective deposition rate of silicon.

[0022] 2. The modified high-silicon Y-type zeolite molecular sieve of the present invention can be recycled, and its breakage rate is still less than 5% after being recycled 10 times.

[0023] 3. The preferred segmented silicon deposition process of the present invention enables silane to be effectively and synchronously diffused and adsorbed into the porous carbon channels, thereby improving the effective deposition rate of silicon.

[0024] 4. The silicon-carbon negative electrode material prepared by the present invention has good cycle performance and pressure resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The cumulative pore volume-pore size distribution curves of the high-silicon Y-type zeolite molecular sieve B-60 before and after modification in Preparation Example 1 are shown;

[0026] Figure 2 This is a backscattered electron (BSE) image of the silicon-carbon negative electrode material prepared in Example 1;

[0027] Figure 3 This is a backscattered electron (BSE) image of the silicon-carbon negative electrode material prepared in Comparative Example 4;

[0028] Figure 4This is the XRD spectrum of the silicon-carbon negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to specific examples, but the present invention is not limited to the following examples.

[0030] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0031] The porous carbon was selected from Shanxi Fuji New Energy Materials Technology Co., Ltd., with a particle size D50 of 5.9 μm and a specific surface area of ​​1900 m 2 / g, pore volume is 0.81cm 3 / g, the average pore diameter is 1.9nm, and micropores account for 87.2%.

[0032] High-silicon Y-type zeolite molecular sieve, low-silicon Y-type zeolite molecular sieve, and X-type molecular sieve are all selected from Jiangxi Juli Qicheng New Environmental Protection Materials Co., Ltd. High-silicon Y-type zeolite molecular sieve has three silicon-aluminum ratios: 20.2, 24.8, and 29.2. Among them, the Y-type zeolite molecular sieve with a silicon-aluminum ratio of 24.8 has six particle size specifications, with particle sizes D50 of 19.2μm, 30.2μm, 47.5μm, 60.1μm, 71.8μm, and 90.5μm, respectively. The details are shown in the following table:

[0033] .

[0034] Preparation of modified high-silica Y-type zeolite molecular sieve

[0035] Preparation Example 1

[0036] High-silicon Y-type zeolite molecular sieve B-60 (silicon-aluminum ratio 24.8) and trimethylchlorosilane were added to toluene (the ratio of high-silicon Y-type zeolite molecular sieve, trimethylchlorosilane and toluene was 100g:12mL:400mL), and then refluxed at 110°C for 10 hours with a stirring speed of 300rpm. After the reaction was completed, it was cooled to room temperature, filtered, washed with anhydrous ethanol until no chloride ions were detected in the filtrate (detected with AgNO3 solution), and dried at 120°C for 5 hours to obtain modified high-silicon Y-type zeolite molecular sieve B-60.

[0037] According to GB / T 19587-2017 Gas Adsorption BET Method, a low-temperature nitrogen adsorption experiment was conducted on the high-silicon Y-type zeolite molecular sieve B-60 before and after modification to obtain the cumulative pore volume-pore size distribution curve, as shown in the figure. Figure 1 As shown. Figure 1 It can be seen that the pore volume of the modified high silicon Y-type zeolite molecular sieve B-60 is increased from 0.52 cm 3 / g is reduced to 0.22cm 3 / g, indicating that the pore size of high silicon Y-type zeolite molecular sieve B-60 is reduced after modification with trimethylchlorosilane.

[0038] Preparation Example 2

[0039] The rest is the same as Preparation Example 1, except that high-silicon Y-type zeolite molecular sieve A (silicon-aluminum ratio 20.2) is used instead of high-silicon Y-type zeolite molecular sieve B-60, and finally modified high-silicon Y-type zeolite molecular sieve A is obtained.

[0040] Preparation Example 3

[0041] The rest is the same as Preparation Example 1, except that high-silicon Y-type zeolite molecular sieve C (silicon-aluminum ratio 29.2) is used instead of high-silicon Y-type zeolite molecular sieve B-60, and finally modified high-silicon Y-type zeolite molecular sieve C is obtained.

[0042] Preparation Example 4

[0043] The rest is the same as Preparation Example 1, except that high-silicon Y-type zeolite molecular sieve B-30 is used instead of high-silicon Y-type zeolite molecular sieve B-60, and finally modified high-silicon Y-type zeolite molecular sieve B-30 is obtained.

[0044] Preparation Example 5

[0045] The rest is the same as Preparation Example 1, except that high-silicon Y-type zeolite molecular sieve B-47 is used instead of high-silicon Y-type zeolite molecular sieve B-60, and finally modified high-silicon Y-type zeolite molecular sieve B-47 is obtained.

[0046] Preparation Example 6

[0047] The rest is the same as Preparation Example 1, except that high-silicon Y-type zeolite molecular sieve B-71 is used instead of high-silicon Y-type zeolite molecular sieve B-60, and finally modified high-silicon Y-type zeolite molecular sieve B-71 is obtained.

[0048] Comparative Preparation Example 1

[0049] The rest is the same as Preparation Example 1, except that low-silicon Y-type zeolite molecular sieve is used instead of high-silicon Y-type zeolite molecular sieve B-60, and finally a modified low-silicon Y-type zeolite molecular sieve is obtained.

[0050] Comparative Preparation Example 2

[0051] The rest is the same as Preparation Example 1, except that: X-type zeolite molecular sieve is used instead of high-silicon Y-type zeolite molecular sieve B-60, and finally a modified X-type zeolite molecular sieve is obtained.

[0052] Example 1

[0053] (S1) 6 kg of porous carbon and 600 g of the modified high-silica Y-type zeolite molecular sieve B-60 prepared in Preparation Example 1 were mixed and placed in a fluidized bed. Nitrogen was introduced at a flow rate of 70 L / min, and the temperature was increased to 450°C at a heating rate of 5°C / min. After holding the temperature for 10 minutes, monosilane gas was introduced at a flow rate of 10 L / min and held at this temperature for 3 hours. Subsequently, the temperature was increased to 580°C at a heating rate of 5°C / min and held at this temperature for 4 hours to obtain Precursor I.

[0054] (S2) The mixture I is retained in the fluidized bed and the nitrogen flow rate is maintained constant. The temperature is increased to 650°C at a heating rate of 7°C / min, and ethylene is introduced at a flow rate of 10 L / min. The mixture is kept at this temperature for 4 h. After the temperature is maintained, the mixture is naturally cooled to room temperature to obtain precursor II.

[0055] (S3) Precursor II is passed through a 600-mesh sieve to remove the modified high-silicon Y-type zeolite molecular sieve B-60, and the undersize is collected to obtain a silicon-carbon negative electrode material in which silicon deposition is regulated by a solid fluidizing medium (the oversize is the modified high-silicon Y-type zeolite molecular sieve B-60, which is recorded as one use).

[0056] The backscattered electron (BSE) image of the prepared silicon-carbon negative electrode material is shown in the figure below. Figure 2 shown.

[0057] The particle size D50 of the modified high-silicon Y-type zeolite molecular sieve B-60 obtained by passing through a 600-mesh sieve was tested using a laser particle size analyzer. By comparing it with the original D50, its breakage rate was tested, and the measured breakage rate was 1.2%.

[0058] .

[0059] Example 2

[0060] The rest is the same as Example 1, except that in step (S1), the modified high-silica Y-type zeolite molecular sieve A prepared in Preparation Example 2 is used instead of the modified high-silica Y-type zeolite molecular sieve B-60.

[0061] Example 3

[0062] The rest is the same as Example 1, except that in step (S1), the modified high-silica Y-type zeolite C prepared in Preparation Example 3 is used instead of the modified high-silica Y-type zeolite B-60.

[0063] Example 4

[0064] The rest is the same as Example 1, except that: in step (S1), the modified high-silica Y-type zeolite molecular sieve B-30 prepared in Preparation Example 4 is used instead of the modified high-silica Y-type zeolite molecular sieve B-60; in step (S3), the sieve is 800 mesh.

[0065] Example 5

[0066] The rest is the same as Example 1, except that in step (S1), the modified high-silica Y-type zeolite molecular sieve B-47 prepared in Preparation Example 5 is used instead of the modified high-silica Y-type zeolite molecular sieve B-60.

[0067] Example 6

[0068] The rest is the same as Example 1, except that in step (S1), the modified high-silica Y-type zeolite molecular sieve B-71 prepared in Preparation Example 6 is used instead of the modified high-silica Y-type zeolite molecular sieve B-60.

[0069] Example 7

[0070] The rest is the same as Example 1, except that: in step (S1), the amount of modified high-silicon Y-type zeolite molecular sieve is 300 g.

[0071] Example 8

[0072] The rest is the same as Example 1, except that: in step (S1), the amount of modified high-silicon Y-type zeolite molecular sieve is 900 g.

[0073] Example 9

[0074] The rest is the same as Example 1, except that the silicon deposition process in step (S1) does not adopt a segmented method; specifically:

[0075] (S1) 6 kg of porous carbon and 600 g of modified high-silica Y-type zeolite molecular sieve B-60 were mixed and placed in a fluidized bed. Nitrogen was introduced at a flow rate of 70 L / min, and the temperature was increased to 500°C at a heating rate of 5°C / min. After holding the temperature for 10 min, monosilane gas was introduced at a flow rate of 10 L / min and held for 7 h to obtain precursor I;

[0076] (S2) Same as Example 1;

[0077] (S3) Same as Example 1.

[0078] Examples 10-11 are tests on the cyclic performance of modified high-silicon Y-type zeolite molecular sieves.

[0079] Example 10

[0080] The modified high-silica Y-type zeolite molecular sieve B-60 after passing through a 600-mesh sieve in Example 1 was recycled five times and its crushing rate was tested, with the other conditions being the same as in Example 1. The crushing rate after five cycles was 2.3%.

[0081] Example 11

[0082] The modified high-silica Y-type zeolite molecular sieve B-60, which passed the 600-mesh sieve after screening in Example 1, was recycled 10 times and its crushing rate was tested, while the other conditions were the same as in Example 1. The crushing rate after 10 cycles was 3.9%.

[0083] Comparative Example 1

[0084] The rest is the same as Example 1, except that in step (S1), the low-silicon Y-type zeolite molecular sieve prepared in Comparative Preparation Example 1 is used instead of the high-silicon Y-type zeolite molecular sieve B-60, and finally a modified low-silicon Y-type zeolite molecular sieve is obtained.

[0085] Comparative Example 2

[0086] The rest is the same as Example 1, except that in step (S1), the modified X-type molecular sieve prepared in Comparative Preparation Example 2 is used instead of the modified high-silicon Y-type zeolite molecular sieve B-60.

[0087] Comparative Example 3

[0088] The rest is the same as Example 1, except that high silicon Y-type zeolite molecular sieve B-60 is used in step (S1) instead of modified high silicon Y-type zeolite molecular sieve B-60, that is, the Y-type zeolite molecular sieve is directly used as the solid fluidizing medium without modification.

[0089] Comparative Example 4

[0090] Without using modified high-silicon Y-type zeolite molecular sieve as a solid fluidizing medium, a conventional silicon deposition process is performed, specifically:

[0091] (S1) 6 kg of porous carbon was placed in a fluidized bed, nitrogen was introduced at a flow rate of 70 L / min, and the temperature was increased to 450°C at a heating rate of 5°C / min. After holding the temperature for 10 minutes, monosilane gas was introduced at a flow rate of 10 L / min and held at this temperature for 3 hours. Subsequently, the temperature was increased to 580°C at a heating rate of 5°C / min and held at this temperature for 4 hours to obtain a silicon-carbon composite material.

[0092] (S2) The silicon-carbon composite material is retained in the fluidized bed and the nitrogen flow rate is kept constant. The temperature is raised to 650°C at a heating rate of 7°C / min, and ethylene is added at a flow rate of 10 L / min. The temperature is kept at this temperature for 4 hours. After the temperature is kept at this temperature, the temperature is naturally lowered to room temperature to obtain a silicon-carbon negative electrode material.

[0093] The backscattered electron (BSE) image of the prepared silicon-carbon negative electrode material is shown in the figure below. Figure 3 shown.

[0094] Testing and Analysis

[0095] 1) Surface morphology and structure analysis

[0096] The backscattered electron (BSE) image of the silicon-carbon negative electrode material prepared in Example 1 is as follows: Figure 2 As shown, the backscattered electron (BSE) image of the silicon-carbon negative electrode material prepared in Comparative Example 4 is as follows Figure 3 shown. Figure 2 There are fewer dark particles in the middle. Dark particles represent that no silicon is deposited on the porous carbon or less silicon is deposited. The fewer dark particles, the better the uniformity of silicon deposition. Figure 3 There are obviously more dark particles.

[0097] The XRD spectrum of the silicon-carbon negative electrode material prepared in Example 1 is as follows: Figure 4 As shown, Figure 4 Only silicon characteristic peaks appear at 27° and 47°, and there are no other impurity characteristic peaks, indicating that the use of modified high-silicon Y-type zeolite molecular sieve as a solid fluidizing medium in the silicon deposition process of porous carbon has no effect on the structure of the silicon-carbon negative electrode material.

[0098] 2) Electrochemical performance test

[0099] The electrochemical performance of the silicon-carbon negative electrode materials obtained in the above examples and comparative examples was tested:

[0100] (a) Pole sheet preparation: A slurry was prepared by mixing the silicon-carbon anode material, a conductive agent (Super-P), and a polyacrylic acid (PAA) binder in a mass ratio of 8:1:1. The mixture was stirred and then coated onto a copper foil current collector. After drying at room temperature, the slurry was placed in a vacuum oven at 60°C for 12 hours to obtain a pole sheet.

[0101] (b) Battery assembly: The electrode sheets obtained above were cut into pieces with a diameter of 10 mm and an active material loading of 1.4 mg / cm 2 A lithium metal sheet was used as the counter electrode, 1 mol / L LiPF6 (the solvent was a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, with 5% volume of fluoroethylene carbonate added) was used as the electrolyte, and a polypropylene microporous membrane was used to assemble 2032-type button cells in an argon atmosphere glove box. 50 μL of electrolyte was added to each cell.

[0102] (c) Battery Testing: Charge and discharge cutoff voltages were set at 1.5V and 0.005V, respectively, followed by charge and discharge cycling at a rate of 0.1C. To test the voltage resistance, the prepared electrode was rolled at a pressure of 10 tons before being subjected to electrical performance testing. The electrochemical performance of the first cycle was compared with that of an unrolled electrode. The test results are shown in Table 1.

[0103] Table 1 Electrochemical performance test

[0104] .

[0105] As can be seen from Table 1, the prepared silicon-carbon negative electrode material has good cycle performance and pressure resistance when used in lithium-ion batteries. The capacity retention rate of 200 cycles at 0.1C is more than 90%, and the capacity loss rate at 10t is no more than 5%. In the preferred embodiment, the capacity retention rate of 200 cycles at 0.1C is more than 95%, and the capacity loss rate at 10t is no more than 2%. Figure 1 and Figure 2 The comparison shows that the present invention introduces large-particle, trimethylchlorosilane-grafted high-silicon Y-type zeolite molecular sieve as a solid fluidizing medium to reconstruct the fluidizing system during silicon deposition on porous carbon, which effectively improves the deposition uniformity and effective deposition rate of silicon, thereby achieving good electrochemical properties and voltage resistance of silicon-carbon negative electrode materials.

Claims

1. A method for preparing a silicon-carbon negative electrode material by controlling silicon deposition using a solid fluidizing medium, characterized in that: The following steps are involved: (S1) mixing porous carbon with a modified high-silicon Y-type zeolite molecular sieve and placing the mixture in a fluidized bed for silicon deposition to obtain a precursor I; the high-silicon Y-type zeolite molecular sieve has a silicon-to-aluminum ratio of 20 to 30; and the modified high-silicon Y-type zeolite molecular sieve is obtained by grafting a high-silicon Y-type zeolite with trimethylchlorosilane; (S2) introducing a gaseous carbon source to carbon-coat the precursor I to obtain the precursor II; (S3) Removing the modified high-silicon Y-type zeolite molecular sieve in the precursor II to obtain a silicon-carbon negative electrode material in which silicon deposition is regulated by a solid fluidizing medium.

2. The preparation method according to claim 1, characterized in that The silicon-aluminum ratio of the high-silicon Y-type zeolite molecular sieve in step (S1) is 20-25.

3. The preparation method according to claim 1, characterized in that The grafting modification method in step (S1) is as follows: adding high-silicon Y-type zeolite molecular sieve and trimethylchlorosilane into an organic solvent and performing reflux reaction under stirring; filtering, washing and drying after the reaction is completed to obtain a modified high-silicon Y-type zeolite molecular sieve.

4. The preparation method according to claim 3, characterized in that The amount ratio of the Y-type zeolite molecular sieve, trimethylchlorosilane, and organic solvent is 100g: (8-15) mL: (300-500) mL; the organic solvent is at least one of toluene or xylene; and / or The reflux reaction conditions are 110-120° C. for 8-15 hours; the washing is ethanol washing until no chloride ions are detected in the filtrate; and the drying is 120-150° C. for 4-8 hours.

5. The preparation method according to claim 1, characterized in that In step (S1), the ratio of the modified high-silica Y-type zeolite molecular sieve particle size D50 to the porous carbon particle size D50 is 5-12:

1.

6. The preparation method according to claim 5, characterized in that The ratio of the modified high-silica Y-type zeolite molecular sieve particle size D50 to the porous carbon particle size D50 is 8-10:

1.

7. The preparation method according to claim 1, characterized in that In step (S1), the mass ratio of the porous carbon to the modified high-silica Y-type zeolite molecular sieve is 10:0.5-1.

5.

8. The preparation method according to claim 7, characterized in that The mass ratio of the porous carbon to the modified high-silica Y-type zeolite molecular sieve is 10:0.5-1.

9. The preparation method according to claim 1, characterized in that In step (S1), the particle size D50 of the porous carbon is 5-10 μm, and the specific surface area of ​​the porous carbon is 1500-2200 m 2 / g, pore volume 0.7~1.1 cm 3 / g, with an average pore size of 1-2.5 nm and micropores accounting for 85-95%; and / or The silicon deposition conditions are as follows: under inert gas protection, silane gas is introduced at 400-650° C. and maintained for 5-10 hours, wherein the inert gas is nitrogen and / or argon, the silane gas is selected from at least one of monosilane, disilane, trichlorosilane, dichlorodihydrosilane, and trichlorosilane, the ratio of porous carbon to silane gas is 1 kg:600-900 L, and the flow ratio of the inert gas to silane gas is 5-10:

1.

10. The preparation method according to claim 9, characterized in that The silicon deposition is a staged silicon deposition, that is, the temperature is first raised to 400° C. to 500° C. for a first silicon deposition for 2 to 5 hours, and then the temperature is raised to 550° C. to 650° C. for a second silicon deposition for 2 to 4 hours.

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