Preparation method of multi-stage ordered silicon-carbon negative electrode material

Abstract

The invention relates to a preparation method of a multi-stage ordered silicon-carbon negative electrode material, which comprises the following steps: (S1) carrying out chemical vapor deposition on porous carbon to obtain a silicon-carbon precursor I with the silicon content of 20-30wt%; (S2) carrying out heat treatment on the silicon-carbon precursor I by using a small molecule gas A and an organic lithium salt in sequence to obtain a silicon-carbon precursor II, the small molecule gas A being 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) carrying out heat treatment on the silicon-carbon precursor III by using a small molecule gas B and an organic lithium salt in sequence to obtain a silicon-carbon precursor IV, the small molecule gas B being at least one of water vapor and O2; and (S5) carrying out carbon coating on the silicon-carbon precursor IV to obtain the multi-stage ordered silicon-carbon negative electrode material. According to the preparation method disclosed by the invention, the pores of the porous carbon are efficiently utilized, and meanwhile, staged continuous and uniform distribution of silicon is realized.

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, thereby forming 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 relieve 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 the preparation of silicon-carbon composite materials by vapor deposition of silicon on porous carbon: 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, and silane molecules have a tetrahedral structure with a relatively large molecular size. When the pore size shrinks to less than the silane molecule, the silane molecule cannot enter, resulting in the remaining pore space being unable to be effectively utilized.

[0003] 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 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.

[0004] 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

[0005] In view of the problem that the pores of porous carbon cannot be efficiently utilized and uniform deposition of silicon cannot be achieved in the prior art, the present invention provides a method for preparing a multi-order ordered silicon-carbon anode material. By alternately depositing silane, heat-treating with different types of small-molecule gases and organic lithium salts on the porous carbon, agglomeration during the silane deposition process is effectively avoided, so that the pores of the porous carbon are efficiently utilized while achieving staged and continuous uniform distribution of silicon.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing a multi-order ordered silicon-carbon anode material, comprising the following steps: (S1) Chemically vapor-depositing porous carbon with silane gas to obtain a silicon-carbon precursor I with a silicon content of 20-30 wt%; (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 CO 2 , N 2 O, at least one of CO; (S3) Chemically vapor-depositing the silicon-carbon precursor II with silane gas to obtain a silicon-carbon precursor III; (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, O 2 ; (S5) Carbon-coating the silicon-carbon precursor IV with a gaseous carbon source to obtain a multi-order ordered silicon-carbon anode material.

[0007] 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 silicon deposition. And 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 SiO 2 ; At the same time, in the subsequent heat treatment, the lithium oxide generated by the decomposition of the organic lithium salt can continue to react with part of the SiO 2 to form lithium silicate, that is, part of the amorphous silicon on the surface layer in the ultramicropores reacts to form a SiO 2 / lithium silicate layer. SiO 2 / While playing an interface passivation role, the lithium silicate layer also has a lithium supplement function, enhancing the interface stability of the silicon-carbon anode material; that is, the heat treatment of the silicon-carbon precursor I with small molecule gas A and organic lithium salt effectively utilizes the originally unavailable space in the ultra-micropores after silicon deposition. At the same time, after step (S2), a part of the amorphous silicon on the surface layer in the micropores with a pore diameter larger than that of the ultra-micropores also reacts to form SiO 2 / The lithium silicate layer enhances the overall density of the silicon layer; due to the relatively large space of this part of the micropores, 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 a size where silane molecules cannot enter, and then heat treatment is carried out with small molecule gas B with a smaller molecular size and organic lithium salt to make the amorphous silicon on the surface layer of the second deposited silicon react to form SiO 2 / The 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 effectively utilizes various pore spaces of ultra-micropores and micropores, and forms a composite dense silicon layer with a staged uniform distribution in the pores of the porous carbon, that is, finally a multi-order ordered silicon-carbon anode material is formed, thereby enhancing the effective silicon content and interface stability of the silicon-carbon anode material.

[0008] 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 likely to agglomerate, 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.

[0009] Furthermore, 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%.

[0010] Furthermore, 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 of 450°C - 600°C, deposit for 2 h - 4 h, and the inert atmosphere is nitrogen and / or argon and / or helium.

[0011] Furthermore, in step (S2) and step (S4), the organic lithium 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.

[0012] 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.

[0013] Further, in step (S2), the heat treatment time is as follows: the small molecule gas A is heat-treated for 1 - 2 h, and the organolithium salt is heat-treated for 0.5 - 1 h.

[0014] Further, 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 2 h - 5 h; control the silane gas flow rate and deposition time so that the silicon content in the multi-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.

[0015] 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.

[0016] Further, in step (S4), the heat treatment time is as follows: the small molecule gas B is heat-treated for 1 - 2 h, and the organolithium salt is heat-treated for 0.5 - 1 h.

[0017] 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: in 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, after 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 carbon coating layer is 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.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) By subjecting porous carbon to alternating silane deposition, heat treatment with different types of small molecule gases and organolithium salts, the agglomeration during the silane deposition process is effectively avoided, enabling the efficient utilization of the pores of the porous carbon while achieving a continuous and uniform distribution of silicon. As a result, a multi-ordered composite dense silicon layer is formed within the pores of the porous carbon, and after carbon coating, a multi-ordered silicon-carbon negative electrode material is finally formed, thereby enhancing the interfacial stability and effective silicon content of the material.

[0019] 2) The present invention can obtain a silicon-carbon negative electrode material with excellent performance with only a small amount of carbon coating layer. The small amount of carbon coating layer and effective silicon content make the specific capacity of the material more advantageous. Brief Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of the silicon-carbon precursor IV prepared in step (S4) in the embodiment; Figure 2 It is an SEM image of the multi-ordered silicon-carbon negative electrode material prepared in Example 1; Figure 3 It is the first charge-discharge curve of the battery assembled with the multi-ordered silicon-carbon negative electrode material prepared in Example 4 at a rate of 0.1C. Detailed Embodiments

[0021] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0022] The experimental methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, can all be obtained from commercial channels.

[0023] 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, a micropore ratio of 97.3%, and a specific surface area of 1950 m 2 / g.

[0024] Example 1 (S1) Place 1 kg of porous carbon in a CVD furnace, introduce nitrogen at a flow rate of 5 L / min, and 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 for chemical vapor deposition for 3.5 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 the excess silane gas, and cool to room temperature to obtain the silicon-carbon precursor I; use the vario EL cube elemental analyzer of Elementar Company, Germany to test the silicon element content in the silicon-carbon precursor I to be 28.6 wt%; (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. Nitrogen is introduced at a flow rate of 2 L / min. After heating to 350 °C in a nitrogen environment, CO is introduced at a flow rate of 1 L / min. 2 Perform heat preservation treatment for 2 h; then stop introducing CO. 2 When the temperature drops to room temperature, place 50 g of lithium phenoxide into the aforementioned rotary kiln. Nitrogen is introduced at a flow rate of 2 L / min. After heating to 300 °C in a nitrogen environment, perform heat preservation for 1 h to obtain silicon-carbon precursor II; (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. Keep the nitrogen flow rate and introduce silane gas at a flow rate of 2.5 L / min for chemical vapor deposition for 4 h, and then cool to room temperature to obtain silicon-carbon precursor III; The silicon element content in silicon-carbon precursor III is tested by an elemental analyzer to be 52.9 wt%. (S4) Take 1 kg of the silicon-carbon precursor III prepared in step (S3) and place it in another rotary kiln. Nitrogen is introduced at a flow rate of 2 L / min. After heating to 250 °C in a nitrogen environment, steam is introduced at a flow rate of 2 L / min. Perform heat preservation treatment for 1 h; then stop introducing steam. When the temperature drops to room temperature, place 80 g of lithium phenoxide into the rotary kiln. Nitrogen is introduced at a flow rate of 2 L / min. After heating to 350 °C in a nitrogen environment, perform heat preservation for 0.5 h to obtain silicon-carbon precursor IV; (S5) Continue to heat the silicon-carbon precursor IV in the rotary kiln to 550 °C in a nitrogen environment. Ethylene gas is introduced at a flow rate of 1 L / min for coating treatment for 3 h to obtain a multi-ordered silicon-carbon anode material; The carbon content is tested by an elemental analyzer. Compared with silicon-carbon precursor IV, the carbon content increases by 1.1 wt%; The silicon element content in the multi-ordered silicon-carbon anode material is tested by an elemental analyzer to be 51.2 wt%.

[0025] The SEM image of the obtained multi-ordered silicon-carbon anode material is as Figure 2 shown.

[0026] Example 2 The rest is the same as in Example 1, except that: in step (S2), N 2 O is used to replace CO. 2 .

[0027] Example 3 The rest is the same as in Example 1, except that: in step (S3), O 2 is used to replace steam.

[0028] Example 4 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.

[0029] Example 5 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.

[0030] Example 6 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.

[0031] Example 7 (S1) Place 1 kg of porous carbon in a CVD furnace, introduce nitrogen at a flow rate of 5 L / min. After heating to 500 °C in a nitrogen environment, 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, 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; use a vario EL cube elemental analyzer from Elementar, Germany to test the silicon element content in silicon-carbon precursor I, which is 21.3 wt%. (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 500 °C in a nitrogen environment, introduce CO 2 , and perform heat preservation treatment for 1 h; then stop introducing CO 2 , when the temperature drops to room temperature, place 100 g of lithium phenoxide into the aforementioned rotary kiln, introduce nitrogen at a flow rate of 2 L / min, and after heating to 350 °C in a nitrogen environment, perform heat preservation for 0.5 h to obtain silicon-carbon precursor II. (S3) Continue to heat the rotary kiln of silicon-carbon precursor II to 550 °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 3.5 L / min for chemical vapor deposition for 5 h, and cool to room temperature to obtain silicon-carbon precursor III. The silicon content of silicon-carbon precursor III is tested by an elemental analyzer to be 54.2 wt%. (S4) Place 1 kg of the silicon-carbon precursor III obtained in step (S3) in another rotary kiln, introduce nitrogen at a flow rate of 2 L / min, heat it to 350 °C under a nitrogen atmosphere, then introduce steam at a flow rate of 2 L / min, and keep it warm for 1 h; then stop introducing steam. When the temperature drops to room temperature, place 120 g of lithium phenoxide into the rotary kiln, introduce nitrogen at a flow rate of 2 L / min, heat it to 300 °C under a nitrogen atmosphere and keep it warm for 1 h to obtain the silicon-carbon precursor IV; (S5) Continuously heat the silicon-carbon precursor IV in the rotary kiln to 550 °C under a nitrogen atmosphere, and introduce ethylene gas at a flow rate of 1 L / min to carry out a coating treatment for 3 h to obtain a multi-stage 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 1.3 wt%; test the silicon element content in the multi-stage ordered silicon-carbon anode material with an elemental analyzer, which is 52.4 wt%.

[0032] Comparative Example 1 Compared with Example 1, in Comparative Example 1, without undergoing stepwise silicon deposition and heat treatment of stepwise small molecule gases and organic lithium salts, only one-step silicon deposition and one-step heat treatment of small molecule gases and organic lithium salts are carried out to make the silicon content of the silicon-carbon anode material close to that of Example 1. The specific steps are as follows: (S1) Place 1 kg of porous carbon in a CVD furnace, introduce nitrogen at a flow rate of 5 L / min, heat it to 550 °C under a nitrogen atmosphere, keep the nitrogen flow rate and introduce silane gas at a flow rate of 2.5 L / min to carry out chemical vapor deposition for 7 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 it to room temperature to obtain the silicon-carbon precursor I; test the silicon element content in the silicon-carbon precursor I with an elemental analyzer, which is 52.4 wt%; (S2) Place 1 kg of the silicon-carbon precursor I obtained in step (S1) in a rotary kiln, introduce nitrogen at a flow rate of 2 L / min, heat it to 250 °C under a nitrogen atmosphere, and then introduce CO 2 and keep it warm for 1 h; then stop introducing CO 2 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, heat it to 350 °C under a nitrogen atmosphere and keep it warm for 0.5 h to obtain the silicon-carbon precursor II; (S3) Continuously heat the silicon-carbon precursor II in the rotary kiln to 550 °C under a nitrogen atmosphere, and introduce ethylene gas at a flow rate of 1 L / min to carry out a coating treatment for 3 h to obtain a multi-stage ordered silicon-carbon anode material; test its carbon content with an elemental analyzer. Compared with the silicon-carbon precursor II, the carbon content increases by 0.9 wt%; test the silicon element content in the multi-stage ordered silicon-carbon anode material with an elemental analyzer, which is 50.9 wt%.

[0033] Comparative Example 2 Compared with Example 1, without the heat treatment of small molecule gas B and organolithium salt, the silicon content of the silicon-carbon anode material is close to that of Example 1. The specific steps are as follows: (S1): The same as (S1) in Example 1; (S2): The same as (S2) in Example 1; (S3): (S3) in Example 1 to obtain silicon-carbon precursor III; (S4): Heat the silicon-carbon precursor III in a rotary kiln under a nitrogen atmosphere to 550 °C, and introduce ethylene gas at a flow rate of 1 L / min to carry out coating treatment for 3 h to obtain a multi-ordered silicon-carbon anode material; the carbon content is tested by an elemental analyzer. Compared with the 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 by an elemental analyzer to be 51.7 wt%.

[0034] Comparative Example 3 The rest is the same as 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 CO 2 , and in step (S4), CO 2 is used to replace water vapor.

[0035] Testing and Analysis 1) Element content test of silicon-carbon anode material: According to GB / T 38823-2020, the silicon element content in the silicon-carbon anode material is tested by a vario EL cube elemental analyzer of Elementar Company in Germany, and the carbon element content in the silicon-carbon anode material is tested by an HCS-801 infrared carbon-sulfur analyzer.

[0036] 2) Electrochemical performance test 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 ρ 0 ; Place it in a water bath at 45 °C for 7 days, and test the density value again, denoted as ρ 1 ; Gas generation volume = , where m is the mass of the slurry. The more gas generation indicates the worse the interfacial stability of the material.

[0037] Charge and discharge test: The silicon-carbon anode materials prepared in the examples and comparative examples were applied to the anode of a lithium-ion battery, assembled into a lithium-ion coin-type half-cell, and their electrochemical performance was tested. The specific steps were as follows: The prepared silicon-carbon anode material, conductive carbon black, and polyacrylonitrile-based binder LA133 glue were mixed in a mass ratio of 91:3:6 to form a slurry (where the solid content of LA133 glue was 5%). The slurry was evenly coated on a copper foil current collector and vacuum dried at 80 °C for 12 h to make a negative electrode sheet; the counter electrode was a lithium metal sheet, the separator was Celgard 2400, and the electrolyte was 1 mol / L LiPF 6 solution (where the solvent was prepared according to the volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:1:1), and a coin-type battery was assembled in a glove box under an argon atmosphere. The above-assembled battery was subjected to charge and discharge tests on a LAND battery tester, and the voltage range was 0.01 V to 1.5 V, and the current density was 0.1 C (1 C = 2000 mAh / g).

[0038] 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 rate of 0.1 C is shown in Figure 3.

[0039] The gas generation test and charge and discharge results are shown in Table 1.

[0040] Table 1 Performance test 。

[0041] As can be seen from Table 1, compared with the comparative example, when the silicon content was close, the hierarchical ordered silicon-carbon anode material prepared in the examples of the present invention had excellent cycle capacity retention and a relatively high discharge specific capacity. At the same time, even with a relatively small amount of carbon coating, its stability in water was good, and the gas generation amount at 45 °C for 7 days was less than 0.5 ml / g.

[0042] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification without departing from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a multi-order ordered silicon-carbon negative electrode material, characterized in that: The following steps are involved: (S1) chemically vapor depositing porous carbon using silane gas to obtain a silicon-carbon precursor I having a silicon content of 20 to 30 wt %; (S2) heat treating the silicon-carbon precursor I in an inert atmosphere at 350-500° C. and 300-350° C. respectively using 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) using silane gas to perform chemical vapor deposition on the silicon-carbon precursor II to obtain a silicon-carbon precursor III; (S4) heat treating the silicon-carbon precursor III with a small molecule gas B and an 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; (S5) Carbon coating the silicon-carbon precursor IV using a gas-phase carbon source to obtain a multi-ordered silicon-carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that: 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 size is 0.7-3 nm, and the microporosity is greater than 70%.

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

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

5. The preparation method according to claim 1, characterized in that: In step (S2), the flow rate of the small molecule gas A is 0.5-2 L / min; the amount of the organic lithium salt is 5-10 wt % of the silicon-carbon precursor I.

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

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

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 amount of the organic lithium salt is 8-12 wt% of the silicon-carbon precursor III.

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

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, and the flow rate of the gaseous carbon source is 1-3 L / min. The carbon coating conditions are: reacting for 3h-10h under an inert atmosphere at 400°C-600°C; controlling the carbon-containing gas flow rate and coating time so that the carbon content increment of the multi-order ordered silicon-carbon negative electrode material obtained in step (S5) relative to the silicon-carbon precursor IV in step (S4) is 0.8-3.5wt%.

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