Carbon-silicon negative electrode material, preparation method thereof and battery

Abstract

The invention discloses a carbon-silicon negative electrode material, a preparation method thereof and a battery, and belongs to the technical field of carbon-silicon materials. The silicon content in the negative electrode material is 40-70wt%, the specific surface area is less than or equal to 3m < 2 > / g, the micropore volume is less than or equal to 0.001 m < 3 > / g, and the average grain size of silicon grains is less than or equal to 2nm; in a dQ / dV-V curve, h1 / h2 is greater than or equal to 1.5, and h1 and h2 are respectively lithium removal oxidation peak intensities corresponding to 0.28-0.32 V and 0.44-0.48 V. The preparation method comprises the following steps: carrying out surface passivation treatment on a precursor obtained by carrying out nanometer silicon vapor deposition on a carbon base material, and carrying out carbon coating in a rotary kiln, the method is simple, and the obtained negative electrode material has a double-layer coating structure, a relatively low specific surface area and relatively high mechanical strength, and is suitable for large-scale production. And the rapid volume expansion of the buffer silicon nanoparticles in the repeated lithiation / lithium removal process is facilitated, so that the negative electrode material has relatively high capacity and cycle performance.

Description

Technical Field

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

[0002] Although silicon has a high theoretical capacity, it will undergo a huge volume change (>300%) during charge and discharge processes. This change will cause the destruction of the material structure and particle pulverization, thereby leading to rapid attenuation of the electrode capacity and electrode failure.

[0003] To solve the above problems, taking advantage of the silicon material, an effective way is to prepare silicon-carbon materials by compounding it with carbon materials. On the one hand, carbon materials can increase the conductivity of silicon materials. On the other hand, the combination of silicon-carbon materials can keep the expansion of silicon materials within an allowable range. Generally speaking, the above method can make silicon-carbon materials exhibit high specific capacity while ensuring stability during the cycling process, and has broad commercial prospects.

[0004] The method of using porous carbon as a matrix and depositing silicon inside it can build a strong conductive network while providing enough expansion space for silicon particles, making the prepared silicon-carbon materials have a high capacity and good cycling performance. However, tiny pores do not contribute to the chemical vapor deposition of silane. Especially a large number of micropores below 1 nm will result in too high specific surface area of porous carbon, affecting the mechanical properties and mechanical parameters of the silicon-carbon negative electrode material.

[0005] In the preparation process of new silicon-carbon products, silicon deposition and carbon coating reactions are mainly carried out inside and on the surface of the pores of the porous carbon matrix through chemical vapor infiltration and chemical vapor deposition. However, currently, it is difficult for the carbon-silicon negative electrode materials obtained by this method to achieve both high capacity and excellent cycling performance.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide a carbon-silicon negative electrode material, a preparation method thereof, and a battery to solve or improve the above technical problems.

[0008] This application can be realized as follows:

[0009] In a first aspect, this application provides a carbon-silicon negative electrode material, in which the silicon content is 40 - 70 wt%; the specific surface area of the carbon-silicon negative electrode material ≤ 3m 2 / g, and the micropore pore volume ≤ 0.001m 3 / g, the average grain size of silicon grains ≤ 2 nm; in the first charge-discharge dQ / dV-V curve of the carbon-silicon negative electrode material, h1 / h2 ≥ 1.5, where h1 is the intensity of the de-lithiation oxidation peak corresponding to 0.28 V to 0.32 V, and h2 is the intensity of the de-lithiation oxidation peak corresponding to 0.44 V to 0.48 V.

[0010] In a second aspect, the present application provides a method for preparing a carbon-silicon negative electrode material as described in the foregoing embodiment, which includes the following steps: subjecting the precursor obtained by subjecting a carbon substrate to nano-silicon vapor deposition in a fluidized bed reactor to surface passivation treatment to obtain an intermediate material; subjecting the intermediate material to carbon coating in a rotary kiln; the temperature of the carbon coating is 500 - 650 °C.

[0011] In an alternative embodiment, the nano-silicon vapor deposition includes at least one of the following conditions:

[0012] Feature 1: The deposition temperature is 480 - 600 °C;

[0013] Feature 2: The deposition time is 4 - 9 h;

[0014] Feature 3: The pressure in the fluidized bed is 5 - 15 KPa;

[0015] Feature 4: The gas used for deposition is a first mixed gas containing a silicon source gas and an inert gas.

[0016] In an alternative embodiment, in the first mixed gas, the silicon source gas includes at least one of silane, disilane, and chlorosilane, preferably silane.

[0017] In an alternative embodiment, the flow rate of the silicon source gas is 1.5 - 5 L / min, and the flow rate of the inert gas is 10 - 18 L / min.

[0018] In an alternative embodiment, the carbon substrate is porous carbon, and the specific surface area of the porous carbon is 1500 - 3000 m 2 / g, and the pore volume is 0.5 - 2 cm 3 / g.

[0019] In an alternative embodiment, before performing the nano-silicon vapor deposition, it further includes replacing the oxygen-containing gas in the fluidized bed reactor with an inert gas.

[0020] In an alternative embodiment, the passivation treatment includes micro-oxidation treatment or carbon pre-coating treatment.

[0021] In an alternative embodiment, the micro-oxidation treatment includes: oxidizing the surface of the precursor with a second mixed gas of an oxygen-containing gas and a carrier gas.

[0022] In an alternative embodiment, in the second mixed gas, the oxygen-containing gas includes at least one of oxygen, carbon monoxide, carbon dioxide, ethanol gas, and isopropanol gas, and the carrier gas is an inert gas.

[0023] In an alternative embodiment, in the second mixed gas, the volume percentage of the oxygen-containing gas is 1-10%.

[0024] In an alternative embodiment, the flow rate of the second mixed gas is 1-50 L / min.

[0025] In an alternative embodiment, the temperature of the micro-oxidation treatment is 150-350 °C, and the time is 0.5-3.0 h.

[0026] In an alternative embodiment, the carbon pre-coating treatment includes: coating the surface of the precursor with a third mixed gas containing a carbon source gas and a carrier gas.

[0027] In an alternative embodiment, in the third mixed gas, the carbon source gas includes at least one of methane, ethane, propane, acetylene, ethylene, propylene, and toluene, and the carrier gas is an inert gas.

[0028] In an alternative embodiment, in the third mixed gas, the volume percentage of the carbon source gas is 10-20%.

[0029] In an alternative embodiment, the flow rate of the third mixed gas is 10-20 L / min.

[0030] In an alternative embodiment, the temperature of the carbon pre-coating treatment is 550-700 °C, and the time is 0.5-3.0 h.

[0031] In an alternative embodiment, in the rotary kiln, the intermediate material is carbon-coated with a fourth mixed gas containing a carbon source gas and a carrier gas.

[0032] In an alternative embodiment, in the fourth mixed gas, the carbon source gas includes at least one of methane, ethane, propane, acetylene, ethylene, propylene, and toluene, and the carrier gas is an inert gas.

[0033] In an alternative embodiment, in the fourth mixed gas, the volume percentage of the carbon source gas is 20-70%.

[0034] In an alternative embodiment, the flow rate of the fourth mixed gas is 2-10 L / min.

[0035] In an alternative embodiment, the time of carbon coating is 0.5-5.0 h.

[0036] In an alternative embodiment, the pressure inside the rotary kiln is 5-50 Pa.

[0037] In a third aspect, the present application provides a battery, which includes the carbon-silicon anode material of the foregoing embodiments.

[0038] The beneficial effects of the present application include:

[0039] In the carbon-silicon anode material provided by the present application, the silicon content is 40-70 wt%; the specific surface area of the carbon-silicon anode material ≤ 3 m 2 / g, the micropore volume ≤ 0.001 m 3 / g, and the average particle size of the silicon grains ≤ 2 nm; in the first-cycle discharge dQ / dV-V curve of the carbon-silicon anode material, h1 / h2 ≥ 1.5, where h1 is the intensity of the lithium extraction oxidation peak corresponding to 0.28 V to 0.32 V, and h2 is the intensity of the lithium extraction oxidation peak corresponding to 0.44 V to 0.48 V. The carbon-silicon anode material with the above characteristics has high capacity and cycling performance.

[0040] The present application creatively uses a fluidized bed for silicon deposition and combines a rotary kiln for carbon coating, and the obtained silicon-carbon anode material has a double-layer coating structure, a relatively low specific surface area, and strong mechanical strength, which is beneficial to buffering the sharp volume expansion of silicon nanoparticles during repeated lithiation / delithiation processes, so that the silicon-carbon anode material has high capacity and cyclability. Specifically, on the one hand, a fluidized bed device is used in the silicon deposition stage to improve the silicon-loading capacity of porous carbon, and on the other hand, a rotary kiln is used in the carbon coating stage for carbon coating treatment to effectively reduce the specific surface area of the product and improve the product performance, thereby obtaining a product with high capacity and long cycle life. Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0042] Figure 1 SEM image of the carbon-silicon anode material prepared in Example 1;

[0043] Figure 2 SEM image of the carbon-silicon anode material prepared in Example 2;

[0044] Figure 3 SEM image of the anode material provided in Comparative Example 1;

[0045] Figure 4 SEM image of the anode material provided in Comparative Example 2;

[0046] Figure 5XRD pattern of the carbon-silicon anode material prepared in Example 1;

[0047] Figure 6 XRD pattern of the carbon-silicon anode material prepared in Comparative Example 1;

[0048] Figure 7 XRD pattern of the carbon-silicon anode material prepared in Comparative Example 6;

[0049] Figure 8 dQ / dV-V curve of the silicon-carbon material coin cell corresponding to Example 1;

[0050] Figure 9 dQ / dV-V curve of the silicon-carbon material coin cell corresponding to Example 2;

[0051] Figure 10 dQ / dV-V curve of the silicon-carbon material coin cell corresponding to Comparative Example 6. Detailed implementation manners

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0053] The carbon-silicon anode material provided in the present application, its preparation method, and the battery will be specifically described below.

[0054] After research, the inventors proposed that the reason why it is difficult for the carbon-silicon anode materials obtained by current conventional preparation methods to achieve both high capacity and excellent cycling performance may be as follows: When using a fluidized bed to prepare silicon-carbon materials, the silane deposition process cannot deposit into the micropores, resulting in the presence of microvoids (especially pores below 1 nm) in the product; moreover, during carbon coating in the fluidized bed, the carbon source gas has a short residence time and a low decomposition rate in the fluidized bed, resulting in poor carbon coating effect, and thus it is difficult for the prepared carbon-silicon materials to achieve both capacity and cycling performance.

[0055] Based on this, the present application creatively proposes a carbon-silicon anode material, which has a low specific surface area, high capacity, and excellent cycling performance.

[0056] As a reference, the silicon content in the above carbon-silicon anode material is 40-70 wt%; the specific surface area of the carbon-silicon anode material ≤ 3m 2 / g, and the micropore volume ≤ 0.001m 3 / g (A "micropore" refers to a pore with a pore diameter not exceeding 2 nm), the average particle size of the silicon grains ≤ 2 nm; in the first-cycle galvanostatic discharge dQ / dV-V curve of the carbon-silicon anode material, h1 / h2 ≥ 1.5, where h1 is the intensity of the de-lithiation oxidation peak corresponding to 0.28 V to 0.32 V, and h2 is the intensity of the de-lithiation oxidation peak corresponding to 0.44 V to 0.48 V.

[0057] The above carbon-silicon anode material has a relatively small specific surface area and no obvious silicon enrichment on the surface. The nano-silicon is evenly distributed in the porous carbon substrate and most of the nano-silicon accumulates in the pores of the porous carbon, which is beneficial to improving the capacity and cycle performance of the carbon-silicon anode material.

[0058] Correspondingly, the present application also provides a preparation method of the above carbon-silicon anode material, which includes the following steps: subjecting the precursor obtained by subjecting the carbon substrate to nano-silicon chemical vapor deposition in a fluidized bed reactor to surface passivation treatment to obtain an intermediate material; performing carbon coating on the intermediate material in a rotary kiln; the temperature of the carbon coating is 500 - 650 °C.

[0059] In the present application, the preparation of the precursor may include: subjecting the carbon substrate to nano-silicon chemical vapor deposition in a fluidized bed reactor.

[0060] As a reference, the above carbon substrate is porous carbon. The specific surface area of the porous carbon used can be 1500 - 3000 m 2 / g, and the pore volume is 0.5 - 2 cm 3 / g. Using porous carbon with this specific surface area and pore volume as the carbon substrate can deposit more nano-silicon in the pores of the porous carbon substrate.

[0061] In some embodiments, before performing nano-silicon chemical vapor deposition, it further includes replacing the oxygen-containing gas in the fluidized bed reactor with an inert gas to avoid the reaction of the silicon source gas with oxygen.

[0062] As a reference, the flow rate of the inert gas used in the replacement process can be 10 - 15 L / min, such as 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min or 15 L / min, etc., or any other arbitrary value within the range of 10 - 15 L / min. In some alternative ways, the flow rate of the inert gas used in the replacement process in the fluidized bed reactor can be 10 L / min. The replacement time can be 1 - 2 h, such as 1 h, 1.5 h or 2 h, etc. In specific operations, the replacement time and the flow rate of the inert gas can be adjusted accordingly according to the actual situation, and no further limitation is made here.

[0063] In this application, the temperature of the nano-silicon chemical vapor deposition can be 480 - 600 °C, such as 480 °C, 490 °C, 500 °C, 510 °C, 520 °C, 530 °C, 540 °C, 550 °C, 560 °C, 570 °C or 600 °C, etc., or can also be any other value within the range of 480 - 600 °C. If the reaction temperature is lower than this range, the silane cracking is incomplete, thus reducing the conversion rate and utilization rate of silane. If the reaction temperature is higher than this range, the silane cracking rate is higher than the silane penetration rate into the porous carbon, causing the nano-silicon to deposit on the surface of the porous carbon.

[0064] The deposition time can be 4 - 9 h, such as 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h or 9 h, etc., or can also be any other value within the range of 4 - 9 h. If the deposition time is too short, too little nano-silicon is deposited in the porous carbon, affecting the capacity of the final product. If the deposition time is too long, too much nano-silicon on the porous carbon will affect the cycle performance of the product.

[0065] The pressure in the fluidized bed can be 5 - 15 KPa, such as 5 KPa, 6 KPa, 7 KPa, 8 KPa, 9 KPa, 10 KPa, 11 KPa, 12 KPa, 13 KPa, 14 KPa or 15 KPa, etc., or can also be any value or any interval range within 5 - 15 KPa. If the pressure in the fluidized bed is too low, it will affect the silane penetration rate in the porous carbon. If the pressure is too high, it will affect the service life of the equipment.

[0066] The gas used for deposition is the first mixed gas containing a silicon source gas and an inert gas. Among them, the silicon source gas can include at least one of silane, disilane and chlorosilane, and preferably silane. The inert gas can exemplarily but non-exclusively include at least one of nitrogen, argon and helium.

[0067] The flow rate of the silicon source gas can be 1.5 - 5 L / min, such as 1.5 L / min, 2 L / min, 2.5 L / min, 3 L / min, 3.5 L / min, 4 L / min, 4.5 L / min or 5 L / min, etc. The flow rate of the inert gas can be 10 - 18 L / min, such as 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min, 15 L / min, 16 L / min, 17 L / min or 18 L / min, etc.

[0068] The precursor prepared by the above method has a specific surface area of 20 - 100 m 2 / g, a micropore volume of 0.005 - 0.1 m 3 / g, a reversible specific capacity of 2050 - 2260 mAh / g, an initial efficiency of 88 - 94%, and a capacity retention rate after 500 cycles of 75 - 80%.

[0069] In this application, the passivation treatment may include micro-oxidation treatment or carbon pre-coating treatment.

[0070] Through the passivation treatment, the activity of the nanosilicon can be reduced to avoid its spontaneous combustion. Among them, when using micro-oxidation treatment for passivation, a SiO2 coating layer can be formed on the surface of the precursor; when using carbon pre-coating treatment, a carbon coating layer can be formed on the surface of the precursor.

[0071] For reference, the micro-oxidation treatment can be to oxidize the surface of the precursor with a second mixed gas of an oxygen-containing gas and a carrier gas.

[0072] In the second mixed gas, the oxygen-containing gas may include, for example, at least one of oxygen, carbon monoxide, carbon dioxide, ethanol gas, and isopropanol gas, and the carrier gas is an inert gas, such as at least one of nitrogen, argon, and helium.

[0073] In the second mixed gas, the volume percentage of the oxygen-containing gas is 1-10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc., and it can also be any other value within the range of 1-10%.

[0074] The flow rate of the second mixed gas can be 1-50 L / min, such as 1 L / min, 2 L / min, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, or 50 L / min, etc., and it can also be any other value within the range of 1-50 L / min.

[0075] The temperature of the micro-oxidation treatment can be 150-350 °C, such as 150 °C, 180 °C, 200 °C, 220 °C, 250 °C, 280 °C, 300 °C, 320 °C, or 350 °C, etc., and it can also be any other value within the range of 150-350 °C.

[0076] The time of the micro-oxidation treatment can be 0.5-3.0 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, etc., and it can also be any other value within the range of 0.5-3.0 h.

[0077] The carbon pre-coating treatment can be to coat the surface of the precursor with a third mixed gas of a carbon source gas and a carrier gas.

[0078] In the third mixed gas, the carbon source gas may include, for example, at least one of methane, ethane, propane, acetylene, ethylene, propylene, and toluene, and the carrier gas is an inert gas, such as at least one of nitrogen, argon, and helium.

[0079] In the third mixed gas, the volume percentage of the carbon source gas is 10-20%, such as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc., and can also be any other value within the range of 10-20%. If it is lower than this range, due to the low acetylene concentration, the deposition time will be prolonged, making the deposited nano-silicon more likely to crystallize and affecting the cycle performance. If it is higher than this range, due to the high acetylene concentration, the residence time of acetylene in the reactor will be reduced, affecting its conversion rate.

[0080] The flow rate of the third mixed gas can be 10-20 L / min, such as 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min, 15 L / min, 16 L / min, 17 L / min, 18 L / min, 19 L / min or 20 L / min, etc., and can also be any other value within the range of 10-20 L / min. If it is lower than this range, the fluidization effect will be poor due to the low mixed gas flow rate. If it is higher than this range, the residence time of acetylene in the reactor will be reduced, affecting its conversion rate.

[0081] The temperature of the carbon pre-coating treatment can be 550-700 °C, such as 550 °C, 600 °C, 610 °C, 620 °C, 630 °C, 640 °C, 650 °C, 660 °C, 670 °C, 680 °C, 690 °C or 700 °C, etc., and can also be any other value within the range of 550-700 °C. If it is lower than this range, the acetylene cracking will be affected due to the too low reaction temperature, affecting the coating effect. If it is higher than this range, the deposited nano-silicon will be more likely to crystallize due to the too high reaction temperature, and nano-silicon and carbon are likely to form SiC, affecting the electrochemical performance.

[0082] The time of the carbon pre-coating treatment can be 0.5-3.0 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc., and can also be any other value within the range of 0.5-3.0 h. If it is lower than this range, the acetylene cracking will be incomplete due to the too short time, affecting the coating effect. If it is higher than this range, the deposited nano-silicon will be more likely to crystallize due to the too long reaction time.

[0083] After obtaining the intermediate material, in a rotary kiln, the intermediate material is carbon-coated with a fourth mixed gas containing a carbon source gas and a carrier gas. Preferably, an inert gas is first used to displace the oxygen in the rotary kiln, and then the carbon coating is carried out.

[0084] In some alternative ways, the flow rate of the inert gas used in the displacement process in the rotary kiln can be 5 L / min. The carbon coating of the intermediate material can be in the form of gas-phase coating, liquid-phase coating or solid-phase coating, etc. In some typical embodiments, gas-phase coating is used.

[0085] By carbon coating the intermediate material, the tiny pores in the product that are not filled during the silicon deposition and passivation processes can be sealed, thereby effectively reducing the specific surface area of the product.

[0086] It should be emphasized that in this application, a fluidized bed is creatively used for silicon deposition and a rotary kiln is used for carbon coating. The obtained silicon-carbon anode material has a double-layer coating structure, a relatively low specific surface area, and strong mechanical strength, which is beneficial for buffering the sharp volume expansion of silicon nanoparticles during repeated lithiation / delithiation processes, thereby enabling the silicon-carbon anode material to have a high capacity and good cycle performance. Specifically, the pressure in the fluidized bed is relatively high, which is conducive to the deposition of silane in the pores of porous carbon, and the prepared product can relatively reach a higher capacity. However, due to the short residence time of the carbon source gas in the fluidized bed and the low decomposition rate during the carbon coating stage, the carbon coating effect is not good. By combining the use of a rotary kiln for carbon coating treatment, by controlling the carbon source gas velocity, carbon source concentration, extending the residence time of carbon coating, and simultaneously controlling the gas pressure in the rotary kiln, the silicon deposition pores and the tiny pores without silicon deposition in the porous carbon can be better sealed to form a dense carbon coating layer. Therefore, the method provided in this application, on the one hand, uses a fluidized bed device in the silicon deposition stage to improve the silicon loading capacity of porous carbon, and on the other hand, uses a rotary kiln for carbon coating treatment in the carbon coating stage to effectively reduce the specific surface area of the product and improve the product performance, thereby obtaining a product with high capacity and long cycle life.

[0087] For reference, in the fourth mixed gas, the carbon source gas may include at least one of methane, ethane, propane, acetylene, ethylene, propylene, and toluene, and the carrier gas is an inert gas, such as at least one of nitrogen, argon, and helium.

[0088] In the fourth mixed gas, the volume percentage of the carbon source gas is 20-70%, such as 20%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 55%, 60%, or 70%, etc., and it can also be any other value within the range of 20-70%.

[0089] If the volume percentage of the carbon source gas in the fourth mixed gas is lower than 20%, due to the low concentration of acetylene, the deposition time of acetylene will be prolonged, making the deposited nano-silicon more likely to crystallize and affecting the cycle performance; if the volume percentage of the carbon source gas in the fourth mixed gas is higher than 70%, due to the high concentration of acetylene, the residence time of acetylene in the reactor will be reduced, affecting its conversion rate.

[0090] The flow rate of the fourth mixed gas can be 2-10 L / min, such as 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, or 10 L / min, etc., and it can also be any other value within the range of 2-10 L / min.

[0091] If the flow rate of the fourth mixed gas is lower than 2 L / min, an excessively long acetylene carbon coating time will cause the deposition of nanosilicon crystals; if the flow rate of the fourth mixed gas is higher than 10 L / min, the residence time of acetylene in the rotary kiln will be too short, which is not conducive to the full decomposition of acetylene in the rotary kiln.

[0092] The temperature of carbon coating can be 500 - 650 °C, such as 500 °C, 550 °C, 600 °C, 610 °C, 620 °C, 630 °C, 640 °C or 650 °C, etc., or any other arbitrary value within the range of 500 - 650 °C.

[0093] If the temperature of carbon coating is lower than 500 °C, it is not conducive to the complete decomposition of acetylene; if the temperature of carbon coating is higher than 650 °C, it will cause the deposition of nanosilicon crystals and the formation of SiC, thereby affecting the electrochemical performance of the product.

[0094] The time of carbon coating can be 0.5 - 5.0 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, etc., or any other arbitrary value within the range of 0.5 - 5.0 h.

[0095] If the time of carbon coating is shorter than 0.5 h, it is not conducive to the formation of a complete coating layer on the surface of the intermediate product due to the too short coating time; if the time of carbon coating is longer than 5 h, it is easy to overcoat the intermediate product, thus affecting the capacity of the final material.

[0096] The pressure in the rotary kiln can be 5 - 50 Pa, such as 5 Pa, 10 Pa, 15 Pa, 20 Pa, 25 Pa, 30 Pa, 35 Pa, 40 Pa, 45 Pa or 50 Pa, etc., or any arbitrary value or any interval range within 5 - 50 Pa.

[0097] If the pressure in the rotary kiln is lower than 5 Pa, it is easy to form a negative pressure in the furnace and introduce air due to the too low pressure, which is not conducive to the sealing of the rotary kiln; if the pressure in the rotary kiln is higher than 50 Pa, it is not conducive to the formation of a complete and continuous carbon coating layer on the surface of the intermediate material, and the specific surface area reduction effect is a little worse.

[0098] It should be noted that for the convenience of distinction, when the passivation treatment adopts the carbon pre - coating treatment method, the corresponding obtained carbon coating layer is defined as the first carbon coating layer, and the carbon coating layer obtained after the carbon coating of the intermediate material is defined as the second carbon coating layer.

[0099] In addition, the present application also provides a battery, which includes the above - mentioned carbon - silicon negative electrode material and can obtain good electrochemical performance.

[0100] The features and performance of the present invention will be further described in detail below in conjunction with the embodiments.

[0101] Example 1

[0102] This embodiment provides a carbon-silicon anode material, and its preparation method includes the following steps:

[0103] (1) Silane deposition: Place 1000 g of porous carbon (specific surface area is 2000 m 2 / g, pore volume is 0.9 cm 3 / g) raw materials in a fluidized bed reactor. First, introduce 10 L / min of nitrogen to displace the air in the fluidized bed reactor for 1 h. Heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 500 °C, introduce the first mixture of silane and nitrogen at a ratio of silane flow rate of 3.0 L / min and nitrogen flow rate of 15.0 L / min. The pressure in the fluidized bed is 8 - 12 KPa, and continue the deposition reaction for 6 h to obtain a precursor.

[0104] (2) Surface passivation treatment (carbon pre-coating treatment method): After the silicon deposition reaction ends, continue to heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 600 °C, start to introduce the third mixture of acetylene and nitrogen. The total gas flow rate is 17.0 L / min, and the volume percentage of acetylene in the third mixture is 12%. The coating time is 1 h. After the coating is completed, cool down and discharge to obtain an intermediate material with a first carbon coating layer.

[0105] (3) Post-treatment: Add the above intermediate material into a rotary kiln. First, introduce 5 L / min of nitrogen to displace the air in the rotary kiln for 1 h, and then heat the rotary kiln at a heating rate of 5 °C / min. When the temperature of the rotary kiln rises to 580 °C, start to introduce the fourth mixture of acetylene and nitrogen. The total gas flow rate is 3 L / min, and the volume percentage of acetylene in the fourth mixture is 30%. Control the pressure in the rotary kiln to be 10 - 20 Pa, and the coating time is 3 h. After the coating is completed, cool down and discharge.

[0106] Example 2

[0107] This embodiment provides a carbon-silicon anode material, and its preparation method includes the following steps:

[0108] (1) Silane deposition: Place 1000 g of porous carbon (specific surface area is 1800 m 2 / g, pore volume is 0.8 cm 3 / g) raw materials in a fluidized bed reactor. First, introduce 10 L / min of nitrogen to displace the air in the fluidized bed reactor for 1 h. Heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 500 °C, introduce the mixture of silane and nitrogen at a ratio of silane flow rate of 2.0 L / min and nitrogen flow rate of 12.0 L / min. The pressure in the fluidized bed is 6 - 10 KPa, and continue the deposition reaction for 6 h to obtain a precursor.

[0109] (2) Surface passivation treatment (micro-oxidation treatment method): After the silicon deposition reaction is completed, stop heating the fluidized bed and introduce nitrogen at a flow rate of 5 L / min to cool down the fluidized bed reactor. When the temperature in the reactor drops to 200 °C, start introducing the second mixed gas of carbon dioxide and nitrogen. The total flow rate of the mixed gas is 20 L / min, and the volume percentage of oxygen in the second mixed gas is 5%. The reaction time is 2 h. After the reaction, cool down and discharge the material to obtain the intermediate material.

[0110] (3) Post-treatment: Add the above intermediate material into a rotary kiln. First, introduce nitrogen at a flow rate of 5 L / min to displace the air in the rotary kiln for 1 h. Then, heat the rotary kiln at a heating rate of 5 °C / min. When the temperature of the rotary kiln rises to 580 °C, start introducing the fourth mixed gas of acetylene and nitrogen. The total gas flow rate is 2 L / min, and the volume percentage of acetylene in the fourth mixed gas is 30%. Control the pressure in the rotary kiln to be 5 - 15 Pa, and the coating time is 4 h. After the coating is completed, cool down and discharge the material.

[0111] Example 3

[0112] This example provides a carbon-silicon anode material, and its preparation method includes the following steps:

[0113] (1) Silane deposition: Place 1000 g of porous carbon (the same as in Example 1) raw material in a fluidized bed reactor. First, introduce nitrogen at a flow rate of 10 L / min to displace the air in the fluidized bed reactor for 1 h. Heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 480 °C, introduce the first mixed gas of silane and nitrogen at a ratio of silane flow rate of 2 L / min and nitrogen flow rate of 12 L / min. The pressure in the fluidized bed is 6 - 10 KPa, and continue the deposition reaction for 9 h to obtain the precursor.

[0114] (2) Surface passivation treatment (carbon pre-coating treatment method): After the silicon deposition reaction is completed, continue to heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 700 °C, start introducing the third mixed gas of methane and nitrogen. The total gas flow rate is 20.0 L / min, and the volume percentage of methane in the third mixed gas is 10%. The coating time is 0.5 h. After the coating is completed, cool down and discharge the material to obtain the intermediate material with the first carbon coating layer.

[0115] (3) Post-treatment: Add the above intermediate material into a rotary kiln. First, introduce nitrogen at a flow rate of 5 L / min to displace the air in the rotary kiln for 1 h. Then, heat the rotary kiln at a heating rate of 5 °C / min. When the temperature of the rotary kiln rises to 500 °C, start introducing a fourth mixed gas of propylene and nitrogen with a total gas flow rate of 5 L / min. The volume percentage of methane in the fourth mixed gas is 20%. Control the pressure in the rotary kiln to be 20 - 30 Pa, and the coating time is 5 h. After the coating is completed, cool down and discharge the material.

[0116] Example 4

[0117] This example provides a carbon-silicon negative electrode material, and its preparation method includes the following steps:

[0118] (1) Silane deposition: Place 1000 g of porous carbon (the same as in Example 1) raw material in a fluidized bed reactor. First, introduce nitrogen at a flow rate of 10 L / min to displace the air in the fluidized bed reactor for 1 h. Heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 600 °C, introduce a first mixed gas of silane and nitrogen at a ratio of a silane flow rate of 3 L / min and a nitrogen flow rate of 15.0 L / min. The pressure in the fluidized bed is 8 - 12 KPa, and continue the deposition reaction for 6 h to obtain a precursor.

[0119] (2) Surface passivation treatment (carbon pre-coating treatment method): After the silicon deposition reaction ends, continue to heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 550 °C, start introducing a third mixed gas of propylene and nitrogen with a total gas flow rate of 10 L / min. The volume percentage of propylene in the third mixed gas is 20%. The coating time is 3 h. After the coating is completed, cool down and discharge the material to obtain an intermediate material with a first carbon coating layer.

[0120] (3) Post-treatment: Add the above intermediate material into a rotary kiln. First, introduce nitrogen at a flow rate of 5 L / min to displace the air in the rotary kiln for 1 h. Then, heat the rotary kiln at a heating rate of 5 °C / min. When the temperature of the rotary kiln rises to 620 °C, start introducing a fourth mixed gas of methane and nitrogen with a total gas flow rate of 10 L / min. The volume percentage of propylene in the fourth mixed gas is 70%. Control the pressure in the rotary kiln to be 30 - 50 Pa, and the coating time is 0.5 h. After the coating is completed, cool down and discharge the material.

[0121] Example 5

[0122] This example provides a carbon-silicon negative electrode material, and its preparation method includes the following steps:

[0123] (1) Silane deposition: Place 1000 g of porous carbon (the same as in Example 2) raw material in a fluidized bed reactor. First, introduce nitrogen at a flow rate of 10 L / min to displace the air in the fluidized bed reactor for 1 h. Heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 480 °C, introduce the first mixture of silane and nitrogen according to the ratio of silane flow rate of 1.5 L / min and nitrogen flow rate of 10.0 L / min. The pressure in the fluidized bed is 5 - 8 KPa, and continuously carry out the deposition reaction for 8 h to obtain the precursor.

[0124] (2) Surface passivation treatment (micro-oxidation treatment method): After the silicon deposition reaction ends, stop heating the fluidized bed reactor, and introduce nitrogen at a flow rate of 5 L / min to cool down the fluidized bed reactor. When the temperature in the reactor drops to 150 °C, start introducing the second mixture of oxygen and nitrogen. The total flow rate of the mixture is 1 L / min, and the volume percentage of carbon monoxide in the second mixture is 1%. The reaction time is 3 h. After the reaction, cool down and discharge the material to obtain the intermediate material.

[0125] (3) Post-treatment: Add the above intermediate material into a rotary kiln. First, introduce nitrogen at a flow rate of 5 L / min to displace the air in the rotary kiln for 1 h, and then heat the rotary kiln at a heating rate of 5 °C / min. When the temperature of the rotary kiln rises to 600 °C, start introducing the fourth mixture of toluene and nitrogen. The total gas flow rate is 5 L / min, and the volume percentage of toluene in the fourth mixture is 35%. Control the pressure in the rotary kiln to be 20 - 30 Pa, and the coating time is 4 h. After the coating ends, cool down and discharge the material.

[0126] Example 6

[0127] This example provides a carbon-silicon anode material, and its preparation method includes the following steps:

[0128] (1) Silane deposition: Place 1000 g of porous carbon (the same as in Example 2) raw material in a fluidized bed reactor. First, introduce nitrogen at a flow rate of 10 L / min to displace the air in the fluidized bed reactor for 1 h. Heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 600 °C, introduce the first mixture of silane and nitrogen according to the ratio of silane flow rate of 3 L / min and nitrogen flow rate of 15.0 L / min. The pressure in the fluidized bed is 8 - 12 KPa, and continuously carry out the deposition reaction for 4 h to obtain the precursor.

[0129] (2) Surface passivation treatment (micro-oxidation treatment method): After the silicon deposition reaction is completed, stop heating the fluidized bed and introduce nitrogen at a flow rate of 5 L / min to cool down the fluidized bed reactor. When the temperature in the reactor drops to 350 °C, start introducing the second mixed gas of carbon monoxide and nitrogen. The total flow rate of the mixed gas is 50 L / min, and the volume percentage of carbon monoxide gas in the second mixed gas is 10%. The reaction time is 0.5 h. After the reaction, cool down and discharge the material to obtain the intermediate material.

[0130] (3) Post-treatment: Add the above intermediate material into a rotary kiln. First, introduce nitrogen at a flow rate of 5 L / min to displace the air in the rotary kiln for 1 h. Then, heat the rotary kiln at a heating rate of 5 °C / min. When the temperature of the rotary kiln rises to 650 °C, start introducing the fourth mixed gas of ethane and nitrogen. The total gas flow rate is 10 L / min, and the volume percentage of ethane in the fourth mixed gas is 45%. Control the pressure in the rotary kiln to be 30 - 50 Pa, and the coating time is 2 h. After the coating is completed, cool down and discharge the material.

[0131] Example 7

[0132] This example provides a carbon-silicon negative electrode material, and its preparation method includes the following steps:

[0133] (1) Silane deposition: Place 1000 g of porous carbon (specific surface area is 3000 m 2 / g, pore volume is 2 cm 3 / g) raw material in a fluidized bed reactor. First, introduce nitrogen at a flow rate of 10 L / min to displace the air in the fluidized bed reactor for 1 h. Heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 500 °C, introduce the first mixed gas of disilane and nitrogen according to the ratio of silane flow rate of 5.0 L / min and nitrogen flow rate of 18.0 L / min. The pressure in the fluidized bed is 10 - 15 KPa, and continue the deposition reaction for 8 h to obtain the precursor.

[0134] (2) Surface passivation treatment (carbon pre-coating treatment method): After the silicon deposition reaction is completed, continue to heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 600 °C, start introducing the third mixed gas of acetylene and nitrogen. The total gas flow rate is 17.0 L / min, and the volume percentage of acetylene in the third mixed gas is 12%. The coating time is 2 h. After the coating is completed, cool down and discharge the material to obtain the intermediate material with the first carbon coating layer.

[0135] (3) Post-treatment: Add the above intermediate material into a rotary kiln. First, introduce nitrogen at a flow rate of 5 L / min to displace the air in the rotary kiln for 1 h. Then, heat the rotary kiln at a heating rate of 5 °C / min. When the temperature of the rotary kiln rises to 600 °C, start introducing the fourth mixed gas of acetylene and nitrogen with a total gas flow rate of 3 L / min, and the volume percentage of acetylene in the fourth mixed gas is 30%. Control the pressure in the rotary kiln to be 10 - 20 Pa, and the coating time is 4 h. After the coating is completed, cool down and discharge the material.

[0136] Example 8

[0137] This example provides a carbon-silicon anode material, and its preparation method includes the following steps:

[0138] (1) Silane deposition: Place 1000 g of porous carbon (specific surface area is 1500 m 2 / g, pore volume is 0.5 cm 3 / g) raw materials in a fluidized bed reactor. First, introduce nitrogen at a flow rate of 10 L / min to displace the air in the fluidized bed reactor for 1 h. Heat the fluidized bed reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 500 °C, introduce the mixed gas of disilane and nitrogen according to the ratio of the silane flow rate of 1.5 L / min and the nitrogen flow rate of 12.0 L / min. The pressure in the fluidized bed is 6 - 10 KPa, and continuously carry out the deposition reaction for 6 h to obtain a precursor.

[0139] (2) Surface passivation treatment (micro-oxidation treatment method): After the silicon deposition reaction is completed, stop heating the fluidized bed and introduce nitrogen at a flow rate of 5 L / min to cool down the fluidized bed reactor. When the temperature in the reactor drops to 200 °C, start introducing the second mixed gas of oxygen and nitrogen with a total gas flow rate of 20 L / min, and the volume percentage of oxygen in the second mixed gas is 5%. The reaction time is 1.5 h. After completion, cool down and discharge the material to obtain an intermediate material.

[0140] (3) Post-treatment: Add the above intermediate material into a rotary kiln. First, introduce nitrogen at a flow rate of 5 L / min to displace the air in the rotary kiln for 1 h. Then, heat the rotary kiln at a heating rate of 5 °C / min. When the temperature of the rotary kiln rises to 500 °C, start introducing the fourth mixed gas of acetylene and nitrogen with a total gas flow rate of 2 L / min, and the volume percentage of acetylene in the fourth mixed gas is 30%. Control the pressure in the rotary kiln to be 5 - 15 Pa, and the coating time is 3 h. After the coating is completed, cool down and discharge the material.

[0141] Comparative Example 1

[0142] The difference between this comparative example and Example 1 is that the intermediate material is not post-treated, that is, this comparative example is the intermediate material in Example 1.

[0143] Comparative Example 2

[0144] The difference between this comparative example and Example 2 is that the intermediate material was not post-treated, that is, this comparative example is the intermediate material in Example 2.

[0145] Comparative Example 3

[0146] The difference between this comparative example and Example 1 is that the post-treatment process was still carried out in a fluidized bed, and the corresponding process conditions included: in the fluidized bed, a carbon pre-coating treatment stage was carried out, and the coating time was extended from 1 h to 2 h to keep the acetylene feeding amount the same as that in Example 1.

[0147] Comparative Example 4

[0148] The difference between this comparative example and Example 1 is that the carbon coating temperature during the post-treatment process was 480 °C.

[0149] Comparative Example 5

[0150] The difference between this comparative example and Example 1 is that the carbon coating temperature during the post-treatment process was 750 °C.

[0151] Comparative Example 6

[0152] The difference between this comparative example and Example 1 is that both the nano-silicon chemical vapor deposition and the post-treatment process were carried out in a rotary kiln, and the process was the same as that in Example 1.

[0153] ①. The morphologies of the anode materials provided in Examples 1-2 and Comparative Examples 1-2 were observed using a ULTRA 55 thermal field emission scanning electron microscope from ZEISS, Germany, and the results are as Figures 1 to 4 shown.

[0154] It can be seen from Figures 1 to 4 the SEM pictures of Example 1 and Example 2 that after the carbon coating post-treatment, a dense and complete carbon layer has wrapped the surface of the material, and obvious pores or hole structures cannot be observed on the surface of the material. In Comparative Examples 1 and 2, due to the lack of carbon coating post-treatment or the lack of carbon coating treatment in the rotary kiln, obvious pores or void structures can still be observed in the SEM pictures, indicating that the carbon coating post-treatment in the rotary kiln has an obvious improvement effect on the surface pores of the material.

[0155] ②. BET specific surface area and pore volume test of the silicon-carbon material: It was carried out using a 3H-2000PS2 type static volumetric method specific surface area and pore size analyzer produced by Beijing Beishide Company. According to the nitrogen adsorption and desorption curves, the BET (Brunauer-Emmett-Teller) specific surface area calculation method was used to calculate the specific value of the material specific surface area. The pore volume of the silicon-carbon material can be calculated by the amount of vapor adsorbed at different relative pressures through the adsorption isotherm.

[0156] ③ The X-ray diffractometer used for X-ray diffraction is the German (BRUKER D8 ADVANCE) X-ray diffractometer. The calculation of the grain size is based on the full width at half maximum (FWHM) of the diffraction peak of Si(110) in the X-ray diffraction measurement and is determined according to the Scherrer equation (1). XRD can be carried out in the 2θ range of 10 - 90° using CuKα rays (for example, the wavelength of the light source: 1.5406 Å).

[0157] Equation (1): D[nm] = K·λ / (β·cosθ); where D is the silicon grain size, K = 0.9, λ = 0.154 μm, β is the half width (FWHM) in radian, and θ is the peak position in degrees.

[0158] The XRD results of the materials obtained in Example 1, Comparative Example 1, and Comparative Example 6 Figure 5 、 Figure 6 and Figure 7 were compared. From the perspective of the silicon grain size corresponding to silicon crystallization at 28.4°, although the sample of Example 1 had undergone secondary high-temperature carbon coating treatment, due to the control of the post-treatment process of carbon coating in the rotary kiln, the silicon grain size of the final material did not increase significantly compared to the intermediate material obtained in Comparative Example 1. In Comparative Example 6, both the gas-phase deposition and post-treatment processes of nano-silicon were carried out in the rotary kiln, resulting in a significant increase in the silicon grain size.

[0159] ④ The silicon content in the material was analyzed by ICP emission spectroscopy. The content of Si element in the material was tested using an inductively coupled plasma spectrometer (ICP) of model 7500ce produced by Agilent Corporation of the United States.

[0160] ⑤ The following method was used to test the electrochemical performance of the anode materials provided in Examples 1 - 8 and Comparative Examples 1 - 6:

[0161] Prepare a working electrode slurry by mixing a negative electrode material, sodium carboxymethyl cellulose (CMC), conductive carbon black (SP), and styrene-butadiene rubber (SBR) in a mass ratio of 94.5:1.5:1.5:2.5 in sequence. Coat the above slurry on a copper foil current collector, dry it in vacuum to obtain a negative electrode sheet; then assemble a button cell with a lithium sheet, an electrolyte prepared by mixing a ternary mixed solvent of 1 mol / L LiPF6 in a ratio of EC:DMC:EMC = 1:1:1 (v / v), a Celgard 2400 separator, and a casing in a glove box filled with argon. Among them, the diameter of the electrode sheet is 14 mm, the diameter of the lithium sheet is 16 mm, the diameter of the separator is 19 mm, the size of the battery case (positive electrode case and negative electrode case) is 20 mm, and the separator is 12 μm thick. Place the assembled button cell in the mold groove of a hydraulic sealing machine (purchased from Shenzhen Kejing Zhida Technology Co., Ltd.), lock it, apply a pressure > 500 kg / cm 2 , then unlock it and take out the sealed button cell.

[0162] The charge and discharge tests of the button cell are carried out on a LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd., and the charge and discharge voltage is limited to 0.05 V to 2 V; the cycle performance test is carried out under normal temperature conditions with a constant current charge and discharge at 0.1 C.

[0163] Use the above button cell as an experimental example to carry out charge and discharge cycles at a rate of 0.1 C at 25 °C, record the capacity (Q)-voltage (V) curve of the first cycle, and obtain the dQ / dV-V curve by differentiating it. Figure 8 , Figure 9 and Figure 10 are the dQ / dV-V curve graphs of the button cells of the silicon-carbon materials according to Example 1, Example 2, and Comparative Example 6. The relative peak intensity h1 of the de-lithiation oxidation peak near 0.3 V (such as 0.28 V to 0.32 V) and the relative peak intensity h2 of the de-lithiation oxidation peak near 0.46 V (such as 0.44 V to 0.48 V) can be used to judge the silicon-rich problem on the surface of the silicon-carbon material. The higher the h1 / h2 peak intensity ratio, the less silicon-rich on the surface.

[0164] Further data results are shown in Table 1.

[0165] Table 1 Test results of silicon-carbon materials

[0166]

[0167]

[0168] As can be seen from Table 1, the carbon-silicon negative electrode material provided by the embodiments of the present application has better comprehensive performance than the comparative examples.

[0169] It can be seen from the comparison between Example 1 and Comparative Example 1, and between Example 2 and Comparative Example 2 that post-treatment to form a carbon coating layer on the surface of the intermediate material can significantly improve the specific surface area of the final product, which is conducive to enhancing the capacity and cycle stability of the material.

[0170] From the comparison between Example 1, Example 2 and Comparative Example 6, it can be seen that for the dQ / dV-V curves of Example 1 and Example 2, the peak intensity ratio of h1 / h2 > 1.5, and the peak shape at about 0.46V is flat without obvious peaks. For Comparative Example 6, the peak intensity of h1 / h2 < 1.5, and the peak shape at about 0.46V is sharp. This shows that the silicon-carbon anode material prepared by the combination of fluidized bed and rotary kiln has a high silicon content and no obvious silicon enrichment on the surface. The nano-silicon is evenly distributed in the porous carbon substrate and most of the nano-silicon accumulates in the pores of the porous carbon. While the sample prepared only by the rotary kiln has a low silicon content and the nano-silicon is enriched on the surface of the porous carbon substrate, ultimately affecting the product capacity and cycle performance.

[0171] It can be seen from Example 1 and Comparative Examples 3-6 that if the equipment or conditions used in the post-treatment are improper, the performance of the carbon-silicon anode material will deteriorate. For the product preparation process of Comparative Example 3, only the fluidized bed equipment is used without the secondary coating of the rotary kiln, which will result in a relatively large specific surface area of the product. For the product preparation process of Comparative Example 6, only the rotary kiln equipment is used, which will result in a low silicon content of the product, thus reducing the capacity and the h1 / h2 being less than 1.5, and the surface silicon enrichment will affect the battery cycle performance. For Comparative Example 4, due to the too low carbon coating temperature in the post-treatment, the carbon source cracking is incomplete, affecting the final specific surface area and electrochemical performance of the product. For Comparative Example 5, due to the too high carbon coating temperature in the post-treatment, the nano-silicon reacts with the carbon material to form SiC, resulting in a very obvious decline in the electrochemical performance.

[0172] In summary, in this application, the fluidized bed silicon deposition product is coated in a rotary kiln by optimizing the product process. On the one hand, the fluidized bed equipment is used in the silicon deposition stage to improve the silicon loading capacity of the porous carbon. On the other hand, the rotary kiln is used for carbon coating treatment. By controlling the process conditions, the silicon deposition pores and the tiny pores without silicon deposition in the porous carbon can be better sealed, so as to form a dense carbon coating layer on the surface of the silicon-carbon material, thereby reducing the specific surface area of the product, improving the product performance, and obtaining an excellent product with high capacity and long cycle life.

[0173] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A carbon-silicon anode material, characterized in that, The silicon content in the carbon-silicon negative electrode material is 40-70 wt%; the specific surface area of the carbon-silicon negative electrode material is ≤ 3 m 2 / g, the micropore volume is ≤ 0.001 m 3 / g, and the average grain size of silicon grains is ≤ 2 nm; in the dQ / dV-V curve of the first charge-discharge cycle of the carbon-silicon negative electrode material, h1 / h2 ≥ 1.5, where h1 is the intensity of the de-lithiation oxidation peak corresponding to 0.28 V to 0.32 V, and h2 is the intensity of the de-lithiation oxidation peak corresponding to 0.44 V to 0.48 V.

2. A method for preparing the carbon-silicon negative electrode material according to claim 1, characterized in that, It includes the following steps: subjecting the precursor obtained by nano-silicon chemical vapor deposition of a carbon-based substrate in a fluidized bed reactor to surface passivation treatment to obtain an intermediate material; subjecting the intermediate material to carbon coating in a rotary kiln; the temperature of carbon coating is 500 - 650 °C.

3. The preparation method according to claim 2, characterized in that, The nano-silicon chemical vapor deposition includes at least one of the following conditions: Feature 1: The deposition temperature is 480 - 600 °C; Feature 2: The deposition time is 4 - 9 h; Feature 3: The pressure in the fluidized bed is 5 - 15 KPa; Feature 4: The gas used for deposition is a first mixed gas containing a silicon source gas and an inert gas; Preferably, in the first mixed gas, the silicon source gas includes at least one of silane, disilane, and chlorosilane, and more preferably is silane; Preferably, the flow rate of the silicon source gas is 1.5 - 5 L / min, and the flow rate of the inert gas is 10 - 18 L / min.

4. The preparation method according to claim 3, characterized in that, The carbon substrate is porous carbon, and the specific surface area of the porous carbon is 1500 - 3000 m 2 / g, and the pore volume is 0.5 - 2 cm 3 / g.

5. The preparation method according to claim 3, characterized in that, Before performing nano-silicon chemical vapor deposition, it also includes replacing the oxygen-containing gas in the fluidized bed reactor with an inert gas.

6. The preparation method according to any one of claims 3-5, characterized in that, The passivation treatment includes micro-oxidation treatment or carbon pre-coating treatment.

7. The preparation method according to claim 6, characterized in that, The micro-oxidation treatment includes: oxidizing the surface of the precursor with a second mixed gas of an oxygen-containing gas and a carrier gas; Preferably, in the second mixed gas, the oxygen-containing gas includes at least one of oxygen, carbon monoxide, carbon dioxide, ethanol gas, and isopropanol gas, and the carrier gas is an inert gas; Preferably, in the second mixed gas, the volume percentage of the oxygen-containing gas is 1 - 10%; Preferably, the flow rate of the second mixed gas is 1 - 50 L / min; Preferably, the temperature of the micro-oxidation treatment is 150 - 350 °C, and the time is 0.5 - 3.0 h.

8. The preparation method according to claim 6, wherein The carbon pre-coating treatment includes: coating the surface of the precursor with a third mixed gas of a carbon source gas and a carrier gas; Preferably, in the third mixed gas, the carbon source gas includes at least one of methane, ethane, propane, acetylene, ethylene, propylene, and toluene, and the carrier gas is an inert gas; Preferably, in the third mixed gas, the volume percentage of the carbon source gas is 10 - 20%; Preferably, the flow rate of the third mixed gas is 10 - 20 L / min; Preferably, the temperature of the carbon pre-coating treatment is 550 - 700 °C, and the time is 0.5 - 3.0 h.

9. The preparation method according to claim 2, wherein In the rotary kiln, the intermediate material is carbon-coated with a fourth mixed gas of a carbon source gas and a carrier gas; Preferably, in the fourth mixed gas, the carbon source gas includes at least one of methane, ethane, propane, acetylene, ethylene, propylene, and toluene, and the carrier gas is an inert gas; Preferably, in the fourth mixed gas, the volume percentage of the carbon source gas is 20 - 70%; Preferably, the flow rate of the fourth mixed gas is 2 - 10 L / min; Preferably, the time of carbon coating is 0.5 - 5.0 h; Preferably, the pressure in the rotary kiln is 5 - 50 Pa.

10. A battery, characterized in that, It includes the carbon-silicon negative electrode material described in claim 1.

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