Preparation method of multi-ordered silicon-carbon anode material

Abstract

The present invention relates to a preparation method of a multi-ordered silicon-carbon anode material, comprising the following steps: (S1) performing chemical vapor deposition on porous carbon to obtain a silicon-carbon precursor I with a silicon content of 20-30 wt%; (S2) sequentially performing heat treatment on the silicon-carbon precursor I with a small molecule gas A and an organic lithium salt, to obtain a silicon-carbon precursor II, wherein the small molecule gas A is at least one of CO2, N2O, and CO; (S3) performing chemical vapor deposition on the silicon-carbon precursor II to obtain a silicon-carbon precursor III; (S4) sequentially performing heat treatment on the silicon-carbon precursor III with a small molecule gas B and an organic lithium salt, to obtain a silicon-carbon precursor IV, wherein the small molecule gas B is at least one of water vapor and O2; (S5) performing carbon coating on the silicon-carbon precursor IV to obtain a multi-ordered silicon-carbon anode material. The preparation method of the present invention realizes the efficient utilization of the pores of the porous carbon while achieving the staged, continuous, and uniform distribution of silicon.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a preparation method of a multi-order ordered silicon-carbon anode material. Background Art

[0002] Porous carbon materials have been widely used in lithium-ion batteries due to their high surface area, excellent electrical conductivity, and good chemical stability; silicon materials have also been widely used in fields such as batteries, electronic devices, and photovoltaic materials due to their excellent electron and ion conduction properties. Combining silicon with porous carbon to prepare silicon / carbon composite materials can combine the advantages of both and improve the comprehensive performance of the materials. The existing technology mainly deposits silicon on a porous carbon substrate through a chemical vapor deposition (CVD) process of silane to form a silicon-carbon composite material. This method can effectively improve the electrochemical performance of the silicon-carbon anode, such as cycle stability and capacity retention rate; at the same time, the porous carbon can alleviate the structural damage caused by the volume expansion of silicon during charge and discharge, and provide a framework support for the uniform distribution of silicon. However, there are still several problems to be solved urgently in preparing silicon-carbon composite materials by vapor deposition of silicon on porous carbon:

[0003] The pore utilization rate of porous carbon is not high: the deeper the pores of porous carbon, the longer the diffusion path of silane molecules and the greater the resistance. That is, the deeper the pores of porous carbon, the lower the silicon deposition efficiency, so that the deeper pores generally cannot be effectively utilized. In addition, at the initial stage of deposition, silane preferentially deposits at larger pores and short diffusion paths, resulting in further reduction of pores, that is, deposition causes pore shrinkage. Since silane molecules have a tetrahedral structure and their molecular size is relatively large, when the pore diameter shrinks to less than the silane molecule, the silane molecule cannot enter, resulting in the ineffective utilization of the remaining pore space.

[0004] The deposition uniformity of silicon is insufficient: in the traditional vapor deposition of silicon process, silane is prone to agglomeration during deposition, resulting in discontinuous distribution in porous carbon, which hinders the transport of electrons and ions. In addition, the pore structure inside the porous carbon material is usually not as developed as that on the outside, making it easier for silane molecules to deposit in the external macropore region, forming silicon aggregates or floating silicon. These non-uniform silicon depositions will lead to unstable growth of the SEI film and interface failure in subsequent electrochemical cycles, ultimately reducing the capacity retention rate and long-cycle performance of the battery. Non-uniform silicon deposition will also cause the structural stability of the silicon-carbon anode material to deteriorate, resulting in gas generation during the preparation of the anode slurry.

[0005] Therefore, how to efficiently utilize the pores of porous carbon and achieve uniform deposition of silicon is the key problem faced in the current preparation of silicon-carbon anode materials. Summary of the Invention

[0006] In view of the problem in the prior art that the pores of porous carbon cannot be efficiently utilized and the uniform deposition of silicon cannot be achieved, the present invention provides a preparation method of a multi-stage ordered silicon-carbon anode material. By alternately performing silane deposition, heat treatment with different types of small molecule gases and organic lithium salts on the porous carbon, the agglomeration during the silane deposition process is effectively avoided, so that the pores of the porous carbon are efficiently utilized while realizing the staged continuous and uniform distribution of silicon.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A preparation method of a multi-stage ordered silicon-carbon anode material, comprising the following steps:

[0009] (S1) Chemically vapor-depositing porous carbon with silane gas to obtain a silicon-carbon precursor I with a silicon content of 20-30 wt%;

[0010] (S2) Heat-treating the silicon-carbon precursor I with small molecule gas A and organic lithium salt in an inert atmosphere at 350-500 °C and 300-350 °C respectively to obtain a silicon-carbon precursor II, wherein the small molecule gas A is at least one of CO2, N2O, and CO;

[0011] (S3) Chemically vapor-depositing the silicon-carbon precursor II with silane gas to obtain a silicon-carbon precursor III;

[0012] (S4) Heat-treating the silicon-carbon precursor III with small molecule gas B and organic lithium salt in an inert atmosphere at 250-350 °C and 300-350 °C respectively to obtain a silicon-carbon precursor IV, wherein the small molecule gas B is at least one of water vapor and O2;

[0013] (S5) Carbon-coating the silicon-carbon precursor IV with a gaseous carbon source to obtain a multi-stage ordered silicon-carbon anode material.

[0014] In the present invention, the ultramicropores in the porous carbon become smaller after the silicon deposition in step (S1), and silane molecules can no longer enter to continue the silicon deposition. The small molecule gas A in step (S2) is a linear small molecule with a small molecular size. Therefore, the small molecule gas A can enter these ultramicropores after silicon deposition and react with the silicon on the surface layer to form SiO2 through an oxidation reaction. At the same time, during the subsequent heat treatment, the lithium oxide generated by the decomposition of the organic lithium salt can continue to react with part of the SiO2 to form lithium silicate, that is, part of the amorphous silicon on the surface layer in the ultramicropores reacts to form a SiO2 / lithium silicate layer. The SiO2 / lithium silicate layer not only plays an interface passivation role but also has a lithium supplement function, improving the interface stability of the silicon-carbon anode material. That is, the heat treatment of the silicon-carbon precursor I with the small molecule gas A and the organic lithium salt effectively utilizes the space that was originally unavailable in the ultramicropores after silicon deposition. At the same time, after step (S2), part of the amorphous silicon on the surface layer in the micropores with a pore diameter larger than that of the ultramicropores also reacts to form a SiO2 / lithium silicate layer, improving the overall denseness of the silicon layer. Since the space of this part of the micropores is relatively large, silicon can continue to be deposited, and a second silicon deposition is carried out in the next step (S3). After the second silicon deposition in step (S3), the micropores gradually shrink to the point where silane molecules can no longer enter, and then heat treatment is carried out with a small molecule gas B and an organic lithium salt with an even smaller molecular size, causing part of the amorphous silicon on the surface layer of the second-deposited silicon to react to form a SiO2 / lithium silicate layer, that is, a composite dense silicon layer is formed with a staged uniform distribution in the micropores. In summary, through the aforementioned alternating silicon deposition, heat treatment with different types of small molecule gases and organic lithium salts, the present invention efficiently utilizes various pore spaces of the ultramicropores and micropores, and forms a composite dense silicon layer with a staged uniform distribution within the pores of the porous carbon, that is, finally forms a multi-ordered silicon-carbon anode material, thereby improving the effective silicon content and interface stability of the silicon-carbon anode material.

[0015] In the present invention, it is very important to control the silicon content of the silicon-carbon precursor I formed in step (S1). If the silicon content is too high, the silicon particles are prone to agglomeration, resulting in an uneven and dense silicon layer, so that the subsequent steps (S2) and (S3) cannot function effectively, the pores cannot be effectively utilized, and ultimately the performance of the silicon-carbon anode material is affected.

[0016] Furthermore, in step (S1), the porous carbon has a particle size D50 of 3 - 10 μm, a specific surface area of 1600 - 2200 m² / g, a pore volume of 0.6 - 1.1 cm³ / g, an average pore diameter of 0.7 - 3 nm, and a microporosity of more than 70%.

[0017] Further, in step (S1), the silane gas is selected from at least one of silane, disilane, dichlorosilane, and chlorosilane, and the flow rate of the silane gas is 1-3 L / min; the conditions for chemical vapor deposition are: under an inert atmosphere at 450°C to 600°C, deposit for 2 h to 4 h, and the inert atmosphere is nitrogen and / or argon and / or helium.

[0018] Further, in steps (S2) and (S4), the organolithium salt is at least one of lithium acetate, lithium oxalate, lithium phenoxide, and lithium ethoxide; the inert atmosphere is nitrogen and / or argon and / or helium.

[0019] Further, in step (S2), the flow rate of the small molecule gas A is 0.5-2 L / min; the dosage of the organolithium salt is 5-10 wt% of the silicon-carbon precursor I.

[0020] Further, in step (S2), the heat treatment time is: heat treat the small molecule gas A for 1-2 h and heat treat the organolithium salt for 0.5-1 h.

[0021] Further, in step (S3), the flow rate of the silane gas is 2-5 L / min; the conditions for chemical vapor deposition are: under an inert atmosphere at 450°C to 600°C, deposit for 2 h to 5 h; control the flow rate of the silane gas and the deposition time so that the silicon content in the multi-stage ordered silicon-carbon anode material is 50-55 wt%. After the first silicon deposition, the pores in the porous carbon become smaller, and at this time, the resistance to secondary silicon deposition is greater. In order to achieve a suitable silicon content, it is more appropriate to control a larger silane flow rate and a longer deposition time at this time.

[0022] Further, in step (S4), the flow rate of the small molecule gas B is 1-3 L / min; the dosage of the organolithium salt is 8-12 wt% of the silicon-carbon precursor III.

[0023] Further, in step (S4), the heat treatment time is: heat treat the small molecule gas B for 1-2 h and heat treat the organolithium salt for 0.5-1 h.

[0024] Further, in step (S5), the gaseous carbon source is selected from at least one of methane, ethane, propane, butane, ethylene, propylene, butene, acetylene, and propyne. The flow rate of the gaseous carbon source is 1 - 3 L / min. The conditions for carbon coating are as follows: under an inert atmosphere at 400°C - 600°C, react for 3 h - 10 h; control the flow rate of the carbon-containing gas and the coating time so that the carbon content increment of the multi-ordered silicon-carbon anode material obtained in step (S5) relative to the silicon-carbon precursor IV in step (S4) is 0.8 - 3.5 wt%. That is, through the treatment of the foregoing steps, a dense and uniform silicon composite layer has been obtained in the pores of the porous carbon. In this step, only a relatively small number of carbon coating layers are required to obtain a silicon-carbon anode material with good performance. Therefore, the flow rate of the gaseous carbon source in this step is relatively low, and the reaction time is also relatively short.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1) By alternately depositing silane, heat-treating different types of small-molecule gases and organolithium salts on the porous carbon, the present invention effectively avoids agglomeration during the silane deposition process, enables the efficient utilization of the pores of the porous carbon while achieving the continuous and uniform distribution of silicon, thereby forming a multi-ordered composite dense silicon layer in the pores of the porous carbon. After carbon coating, a multi-ordered silicon-carbon anode material is finally formed, thereby improving the interfacial stability and effective silicon content of the material.

[0027] 2) The present invention only requires a relatively small number of carbon coating layers to obtain a silicon-carbon anode material with excellent performance. The relatively small number of carbon coating layers and the effective silicon content make the specific capacity of the material more advantageous. Description of the Drawings

[0028] Figure 1 It is a schematic structural diagram of the silicon-carbon precursor IV prepared in step (S4) in the embodiment;

[0029] Figure 2 It is an SEM image of the multi-ordered silicon-carbon anode material prepared in Example 1;

[0030] Figure 3 It is the first charge-discharge curve of the battery assembled with the multi-ordered silicon-carbon anode material prepared in Example 4 at a 0.1C rate. Detailed Embodiments

[0031] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0032] In the following embodiments, the experimental methods are all conventional methods unless otherwise specified; the reagents and materials can all be obtained from commercial channels unless otherwise specified.

[0033] The porous carbon was self-made, with a median particle size D50 of 6.9 μm, a pore volume of 0.88 cm 3 / g, an average pore diameter of 1.5 nm, the micropore proportion being 97.3%, and a specific surface area of 1950 m 2 / g.

[0034] Example 1

[0035] (S1) Place 1 kg of the porous carbon in a CVD furnace, introduce nitrogen at a flow rate of 5 L / min. After heating to 550 °C in a nitrogen environment, maintain the nitrogen flow rate and introduce silane gas at a flow rate of 2 L / min to carry out chemical vapor deposition for 3.5 h; after the silane deposition ends, stop introducing silane gas, continuously introduce nitrogen at a flow rate of 5 L / min to remove the excess silane gas, and cool to room temperature to obtain silicon-carbon precursor I; use the vario EL cube elemental analyzer of Elementar Company in Germany to test that the silicon element content in silicon-carbon precursor I is 28.6 wt%;

[0036] (S2) Take 1 kg of the silicon-carbon precursor I prepared in step (S1) and place it in a rotary kiln. The rotation speed of the rotary kiln is 20 rpm, introduce nitrogen at a flow rate of 2 L / min. After heating to 350 °C in a nitrogen environment, introduce CO2 at a flow rate of 1 L / min and carry out heat preservation treatment for 2 h; then stop introducing CO2. When the temperature drops to room temperature, place 50 g of lithium phenoxide into the aforementioned rotary kiln, introduce nitrogen at a flow rate of 2 L / min. After heating to 300 °C in a nitrogen environment, keep it warm for 1 h to obtain silicon-carbon precursor II;

[0037] (S3) Continue to heat the rotary kiln of silicon-carbon precursor II to 500 °C in a nitrogen environment, adjust the nitrogen flow rate to 5 L / min, maintain the nitrogen flow rate and introduce silane gas at a flow rate of 2.5 L / min to carry out chemical vapor deposition for 4 h, and cool to room temperature to obtain silicon-carbon precursor III; it is tested by an elemental analyzer that the silicon element content in silicon-carbon precursor III is 52.9 wt%;

[0038] (S4) Place 1 kg of the silicon-carbon precursor III prepared in step (S3) in another rotary kiln, introduce nitrogen at a flow rate of 2 L / min. After heating to 250 °C in a nitrogen environment, introduce water vapor at a flow rate of 2 L / min and carry out heat preservation treatment for 1 h; then stop introducing water vapor. When the temperature drops to room temperature, place 80 g of lithium phenoxide into the rotary kiln, introduce nitrogen at a flow rate of 2 L / min. After heating to 350 °C in a nitrogen environment, keep it warm for 0.5 h to obtain silicon-carbon precursor IV;

[0039] (S5) Continuously heat the silicon-carbon precursor IV in a rotary kiln to 550 °C in a nitrogen environment, and introduce ethylene gas at a flow rate of 1 L / min. Conduct the coating treatment for 3 h to obtain a multi-ordered silicon-carbon anode material. Test its carbon content with an elemental analyzer. Compared with the silicon-carbon precursor IV, the carbon content increases by 1.1 wt%. Test the silicon element content in the multi-ordered silicon-carbon anode material with an elemental analyzer, and the result is 51.2 wt%.

[0040] The SEM image of the prepared multi-ordered silicon-carbon anode material is as Figure 2 shown.

[0041] Example 2

[0042] The rest is the same as in Example 1, except that: in step (S2), N2O is used to replace CO2.

[0043] Example 3

[0044] The rest is the same as in Example 1, except that: in step (S3), O2 is used to replace water vapor.

[0045] Example 4

[0046] The rest is the same as in Example 1, except that: in step (S2), lithium oxalate is used to replace lithium phenoxide, and in step (S3), lithium ethoxide is used to replace lithium phenoxide.

[0047] Example 5

[0048] The rest is the same as in Example 1, except that: in step (S2), lithium oxalate is used to replace lithium phenoxide, and in step (S3), lithium acetate is used to replace lithium phenoxide.

[0049] Example 6

[0050] The rest is the same as in Example 1, except that: in step (S2), lithium acetate is used to replace lithium phenoxide, and in step (S3), lithium ethoxide is used to replace lithium phenoxide.

[0051] Example 7

[0052] (S1) Place 1 kg of porous carbon in a CVD furnace, introduce nitrogen at a flow rate of 5 L / min, heat it to 500 °C in a nitrogen environment, then maintain the nitrogen flow rate and introduce silane gas at a flow rate of 1.5 L / min for chemical vapor deposition for 3 h. After the silane deposition is completed, stop introducing silane gas, continuously introduce nitrogen at a flow rate of 5 L / min to remove the excess silane gas, and cool it to room temperature to obtain the silicon-carbon precursor I. Test the silicon element content in the silicon-carbon precursor I with a vario EL cube elemental analyzer from Elementar, Germany, and the result is 21.3 wt%.

[0053] (S2) Take 1 kg of the silicon-carbon precursor I obtained in step (S1) and place it in a rotary kiln. The rotation speed of the rotary kiln is 20 rpm. Nitrogen is introduced at a flow rate of 2 L / min. After heating to 500 °C in a nitrogen environment, CO2 is introduced at a flow rate of 1 L / min and heat preservation treatment is carried out for 1 h; then the introduction of CO2 is stopped. When the temperature drops to room temperature, 100 g of lithium phenoxide is placed into the aforementioned rotary kiln. Nitrogen is introduced at a flow rate of 2 L / min. After heating to 350 °C in a nitrogen environment, heat preservation is carried out for 0.5 h to obtain the silicon-carbon precursor II;

[0054] (S3) Continue to heat the rotary kiln of the silicon-carbon precursor II to 550 °C in a nitrogen environment, adjust the nitrogen flow rate to 5 L / min, keep the nitrogen flow rate and introduce silane gas at a flow rate of 3.5 L / min for chemical vapor deposition for 5 h, and then cool to room temperature to obtain the silicon-carbon precursor III. The silicon content of the silicon-carbon precursor III is tested by an elemental analyzer to be 54.2 wt%;

[0055] (S4) Take 1 kg of the silicon-carbon precursor III obtained in step (S3) and place it in another rotary kiln. Nitrogen is introduced at a flow rate of 2 L / min. After heating to 350 °C in a nitrogen environment, water vapor is introduced at a flow rate of 2 L / min and heat preservation treatment is carried out for 1 h; then the introduction of water vapor is stopped. When the temperature drops to room temperature, 120 g of lithium phenoxide is placed into the rotary kiln. Nitrogen is introduced at a flow rate of 2 L / min. After heating to 300 °C in a nitrogen environment, heat preservation is carried out for 1 h to obtain the silicon-carbon precursor IV;

[0056] (S5) Continue to heat the silicon-carbon precursor IV in the rotary kiln to 550 °C in a nitrogen environment, and introduce ethylene gas at a flow rate of 1 L / min for coating treatment for 3 h to obtain a multi-stage ordered silicon-carbon anode material; its carbon content is tested by an elemental analyzer. Compared with the silicon-carbon precursor IV, the carbon content increases by 1.3 wt%; the silicon element content in the multi-stage ordered silicon-carbon anode material is tested by an elemental analyzer to be 52.4 wt%.

[0057] Comparative Example 1

[0058] Compared with Example 1, Comparative Example 1 does not go through stepwise silicon deposition and heat treatment of stepwise small molecule gases and organic lithium salts, but only goes through one-step silicon deposition and one-step heat treatment of small molecule gases and organic lithium salts to make the silicon content of the silicon-carbon anode material close to that of Example 1. The specific steps are as follows:

[0059] (S1) Place 1 kg of porous carbon in a CVD furnace, introduce nitrogen at a flow rate of 5 L / min. After heating to 550 °C in a nitrogen environment, maintain the nitrogen flow rate and introduce silane gas at a flow rate of 2.5 L / min for chemical vapor deposition for 7 h. After the silane deposition is completed, stop introducing silane gas, continue to introduce nitrogen at a flow rate of 5 L / min to remove excess silane gas, and cool to room temperature to obtain silicon-carbon precursor I. The silicon element content in silicon-carbon precursor I is tested to be 52.4 wt% by an elemental analyzer;

[0060] (S2) Place 1 kg of silicon-carbon precursor I prepared in step (S1) in a rotary kiln, introduce nitrogen at a flow rate of 2 L / min. After heating to 250 °C in a nitrogen environment, introduce CO2 at a flow rate of 2 L / min and hold for 1 h. Then stop introducing CO2. When the temperature drops to room temperature, place 80 g of lithium phenoxide in the rotary kiln, introduce nitrogen at a flow rate of 2 L / min. After heating to 350 °C in a nitrogen environment, hold for 0.5 h to obtain silicon-carbon precursor II;

[0061] (S3) Continue to heat silicon-carbon precursor II to 550 °C in a nitrogen environment in the rotary kiln, and introduce ethylene gas at a flow rate of 1 L / min for coating treatment for 3 h to obtain a multi-ordered silicon-carbon anode material. Test its carbon content by an elemental analyzer. Compared with silicon-carbon precursor II, the carbon content increases by 0.9 wt%. The silicon element content in the multi-ordered silicon-carbon anode material is tested to be 50.9 wt% by an elemental analyzer.

[0062] Comparative Example 2

[0063] Compared with Example 1, without the heat treatment of small molecule gas B and organic lithium salt, the silicon content of the silicon-carbon anode material is close to that of Example 1. The specific steps are as follows:

[0064] (S1): The same as (S1) of Example 1;

[0065] (S2): The same as (S2) of Example 1;

[0066] (S3): (S3) of Example 1 to obtain silicon-carbon precursor III;

[0067] (S4): Continue to heat silicon-carbon precursor III to 550 °C in a nitrogen environment in the rotary kiln, and introduce ethylene gas at a flow rate of 1 L / min for coating treatment for 3 h to obtain a multi-ordered silicon-carbon anode material. Test its carbon content by an elemental analyzer. Compared with silicon-carbon precursor III, the carbon content increases by 1.2 wt%. The silicon element content in the multi-ordered silicon-carbon anode material is tested to be 51.7 wt% by an elemental analyzer.

[0068] Comparative Example 3

[0069] The rest is the same as in Example 1, except that: in step (S2), small molecule gas B is used, and in step (S4), small molecule gas A is used. Specifically, in step (S2), water vapor is used to replace CO2, and in step (S4), CO2 is used to replace water vapor.

[0070] Testing and Analysis

[0071] 1) Element content test of silicon-carbon anode material: According to GB / T 38823-2020, a vario EL cube elemental analyzer from Elementar, Germany is used to test the silicon element content in the silicon-carbon anode material, and an HCS-801 infrared carbon-sulfur analyzer is used to test the carbon element content in the silicon-carbon anode material.

[0072] 2) Electrochemical performance test

[0073] Gas generation test: Put 5 g of the silicon-carbon anode material prepared in the example or comparative example into a mixed solution composed of 0.76 g of ethanol and 7.5 g of deionized water, stir evenly and transfer it to an aluminum-plastic bag, seal it under vacuum, and use a solid density meter to test the initial slurry density value, denoted as ρ0; place it in a water bath at 45 °C for 7 days, and test the density value again, denoted as ρ1; the gas generation amount = , where m is the mass of the slurry. The more the gas generation amount, the worse the interfacial stability of the material.

[0074] Charge and discharge test: Apply the silicon-carbon anode materials prepared in the examples and comparative examples to the negative electrode of a lithium-ion battery, assemble them into a lithium-ion coin-type half-cell, and test their electrochemical performance. The specific steps are as follows: Mix the prepared silicon-carbon anode material, conductive carbon black, and polyacrylonitrile-based binder LA133 glue in a mass ratio of 91:3:6 to form a slurry (the solid content of LA133 glue is 5%), evenly coat the slurry on a copper foil current collector, and make a negative electrode plate after vacuum drying at 80 °C for 12 h; the counter electrode is a lithium metal sheet, the separator is Celgard 2400, and the electrolyte is a 1 mol / L LiPF6 solution (the solvent is prepared according to the volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:1:1), and assemble it into a coin-type battery in a glove box with an argon atmosphere. Charge and discharge test the above-assembled battery on a LAND battery tester, the voltage range is 0.01 V to 1.5 V, and the current density is 0.1 C (1 C = 2000 mAh / g).

[0075] The first charge and discharge curve of the battery assembled with the multi-stage ordered silicon-carbon anode material prepared in Example 4 at a 0.1 C rate is shown in Figure 3.

[0076] The gas generation test and charge and discharge results are shown in Table 1.

[0077] Table 1 Performance Test

[0078] 。

[0079] It can be seen from Table 1 that, compared with the comparative example, when the silicon content is close, the stepwise ordered silicon-carbon anode material prepared in the embodiment of the present invention has excellent cycle capacity retention rate and high discharge specific capacity. At the same time, even when the carbon coating amount is small, its stability in water is good, and the gas generation amount at 45°C for 7 days is less than 0.5 ml / g.

[0080] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or change without departing from the present invention shall be included within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a multi-stage ordered silicon-carbon anode material, characterized in that, It includes the following steps: (S1) Carry out chemical vapor deposition on porous carbon using silane gas to obtain silicon-carbon precursor I with a silicon content of 20-30 wt%; (S2) Heat-treat silicon-carbon precursor I with small molecule gas A and organolithium salt successively at 350-500 °C and 300-350 °C respectively in an inert atmosphere to obtain silicon-carbon precursor II, where the small molecule gas A is at least one of CO2, N2O, and CO; (S3) Carry out chemical vapor deposition on silicon-carbon precursor II using silane gas to obtain silicon-carbon precursor III; (S4) Heat-treat silicon-carbon precursor III with small molecule gas B and organolithium salt successively at 250-350 °C and 300-350 °C respectively in an inert atmosphere to obtain silicon-carbon precursor IV, where the small molecule gas B is at least one of water vapor and O2; (S5) Carry out carbon coating on silicon-carbon precursor IV using a gaseous carbon source to obtain a multi-order ordered silicon-carbon anode material.

2. The preparation method according to claim 1, wherein, In step (S1), the particle size D50 of the porous carbon is 3-10 μm, the specific surface area is 1600-2200 m² / g, the pore volume is 0.6-1.1 cm³ / g, the average pore diameter is 0.7-3 nm, and the microporosity is more than 70%.

3. The preparation method according to claim 1, wherein, In step (S1), the silane gas is selected from at least one of silane, disilane, dichlorosilane, and chlorosilane, and the flow rate of the silane gas is 1-3 L / min; the conditions for chemical vapor deposition are: in an inert atmosphere at 450 °C - 600 °C, deposit for 2h - 4h, and the inert atmosphere is nitrogen and / or argon and / or helium.

4. The preparation method according to claim 1, wherein In steps (S2) and (S4), the organolithium salt is at least one of lithium acetate, lithium oxalate, lithium phenoxide, and lithium ethoxide; the inert atmosphere is nitrogen and / or argon and / or helium.

5. The preparation method according to claim 1, wherein In step (S2), the flow rate of the small molecule gas A is 0.5-2 L / min; the dosage of the organolithium salt is 5-10 wt% of silicon-carbon precursor I.

6. The preparation method according to claim 1, characterized in that, In step (S2), the heat treatment time is: 1-2 h for heat treatment with small molecule gas A and 0.5-1 h for heat treatment with organolithium salt.

7. The preparation method according to claim 1, characterized in that, In step (S3), the flow rate of the silane gas is 2-5 L / min; the conditions for chemical vapor deposition are: in an inert atmosphere at 450 °C - 600 °C, deposit for 2h - 5h; control the flow rate of the silane gas and the deposition time so that the silicon content of the multi-order ordered silicon-carbon anode material is 50-55 wt%.

8. The preparation method according to claim 1, characterized in that, In step (S4), the flow rate of the small molecule gas B is 1-3 L / min; the dosage of the organolithium salt is 8-12 wt% of silicon-carbon precursor III.

9. The preparation method according to claim 1, characterized in that, In step (S4), the heat treatment time is: 1-2 h for heat treatment with small molecule gas B and 0.5-1 h for heat treatment with organolithium salt.

10. The preparation method according to claim 1, characterized in that, In step (S5), the gaseous carbon source is selected from at least one of methane, ethane, propane, butane, ethylene, propylene, butene, acetylene, and propyne. The flow rate of the gaseous carbon source is 1 to 3 L / min. The conditions for carbon coating are as follows: in an inert atmosphere at 400°C to 600°C, react for 3 h to 10 h; control the flow rate of the carbon-containing gas and the coating time so that the increment of the carbon content of the multi-ordered silicon-carbon anode material obtained in step (S5) relative to the silicon-carbon precursor IV in step (S4) is 0.8 to 3.5 wt%.

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