Silicon-carbon negative electrode material and preparation method thereof in low-temperature silicon-carbon deposition mode

Abstract

The invention relates to the technical field of battery negative electrode materials, in particular to a silicon-carbon negative electrode material and a preparation method of the silicon-carbon negative electrode material in a low-temperature silicon-carbon deposition mode. The method comprises the following steps: performing synchronous silicon-carbon deposition or step-by-step silicon-carbon deposition on carbon-based material particles in a fluidized bed at a relatively low temperature to form silicon-carbon intermediate phase particles, and further performing carbon coating to form the silicon-carbon negative electrode material. The low-temperature silicon-carbon deposition mode involved in the process can effectively control the stability of heat release of the chemical vapor deposition reaction in the aspect of operation and improve the uniformity of temperature field distribution in the reactor, so that the overall reaction rate is controllable, and parameters such as the particle size and the nano silicon content of the silicon-carbon negative electrode material are easy to regulate and control. When the preparation method provided by the scheme of the invention is adopted, on the basis of ensuring that the safety is effectively improved, the yield and the product quality of the silicon-carbon negative electrode material are obviously optimized, and the silicon-carbon negative electrode material shows excellent electrochemical performance.

Description

Technical Field

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

[0002] Lithium-ion batteries are the main energy storage solution for electric vehicles and portable electronic devices. The key to their performance lies in the electrochemical properties of positive and negative electrode materials. Traditional graphite negative electrode materials can no longer meet the requirements of higher energy density and long cycle life due to capacity limitations. Silicon-carbon composites, as a potential alternative material, have attracted much attention due to their high capacity, low cost and abundant resources.

[0003] However, the challenge of using silicon as a negative electrode material for lithium-ion batteries is that its volume expansion rate is as high as 300%, which causes the electrode material to expand and contract during the charge and discharge cycle, resulting in the breakage of electrode particles and the instability of the electrode structure, which seriously affects the cycle life and safety of the battery. To overcome this problem, researchers began to explore combining silicon with carbon to form a silicon-carbon composite material to improve its stability and electrochemical performance.

[0004] In the process of preparing silicon-carbon composite materials, there are mainly the following technical challenges:

[0005] High expansion problem of silicon: Silicon has a theoretical specific capacity of up to 4200mAh / g, which is much higher than traditional graphite (372mAh / g), but its volume expansion rate and mechanical brittleness limit its wide application as an electrode material. Therefore, effectively controlling the expansion of silicon is the key to preparing silicon-carbon negative electrode materials.

[0006] Combination of silicon and carbon: Silicon-carbon composites embed silicon particles in a carbon matrix, using the conductive properties and stability of carbon to inhibit silicon expansion and improve the conductivity and cycle stability of the electrode. Traditional methods usually involve chemical vapor deposition of silicon and subsequent carbon coating treatment.

[0007] Safety issues: Silicon source gas is flammable and explosive. Under high temperature operating conditions, silicon-carbon composite materials are prone to hot spot effects and dust explosion risks. Silane gas releases a large amount of heat at high temperatures, which may cause local temperature increases and trigger explosive reactions.

[0008] Complexity of the preparation process: Common problems in the preparation of traditional silicon-carbon composites include the difficulty in controlling reaction conditions, cumbersome post-reaction processing steps, and high energy consumption. Especially in the process of silicon deposition and carbon coating, precise control of temperature and atmosphere is crucial to the material structure and performance.

[0009] From the perspective of industrial-scale production, in the process of preparing silicon-carbon materials, the chemical vapor deposition method currently used by the mainstream market has great industrial prospects. However, when implementing silicon deposition and carbon coating operations, the reactions such as the decomposition of silicon source gas and carbon source gas have strong exothermic characteristics, and the continuous chemical vapor deposition reactions bring about unstable heat release and potential side reactions (such as carbon from the thermal decomposition of carbon source during carbon coating reacts with nano-silicon to generate silicon carbide and releases heat), which can easily have a negative impact on the uniformity of temperature distribution in the reactor. These difficult-to-control influencing factors, on the one hand, will challenge the safety of operations during the preparation of silicon-carbon materials, making the operating parameters of the silicon-carbon material preparation process more conservative, and the scale-up of the preparation will also be subject to corresponding restrictions; on the other hand, it will also cause the quality and yield of silicon-carbon negative electrode products to decline.

[0010] In view of this, the present invention is proposed. Summary of the invention

[0011] The object of the present invention is to provide a silicon-carbon negative electrode material and a preparation method thereof using a low-temperature silicon-carbon deposition method. The preparation method provided by the scheme of the present invention has a controllable reaction rate, the quality of the silicon-carbon intermediate phase particles is stable, and it is easy to control parameters such as particle size and nano-silicon content. The prepared silicon-carbon negative electrode material has the characteristics of high tap density and uniform nano-silicon distribution, and exhibits excellent electrochemical properties, including high specific capacity, stable cycle performance and low volume change rate.

[0012] The present invention is achieved in that:

[0013] In a first aspect, the present invention provides a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition, comprising: depositing silicon on carbon-based substrate particles in a fluidized bed to form silicon-carbon intermediate phase particles, and further subjecting the particles to carbon coating to prepare the silicon-carbon negative electrode material;

[0014] The specific steps are as follows:

[0015] S1. Low-temperature silicon-carbon deposition: introducing the carbon-based substrate particles into a fluidized bed, and performing chemical vapor deposition reaction by synchronous silicon-carbon deposition or step-by-step silicon-carbon deposition to form silicon-carbon intermediate phase particles;

[0016] S2, carbon coating: using a chemical vapor deposition method to carbon-coat the silicon-carbon mesophase particles obtained in S1 to form a silicon-carbon negative electrode material;

[0017] The reaction temperature in S1 is at least 50° C. lower than the reaction temperature in S2.

[0018] In an optional embodiment, the carbon-based material particles are selected from particles with a particle size D 50 No more than 20μm, specific surface area no less than 800m 2 / g porous carbon particles.

[0019] In an optional embodiment, the step of synchronous silicon-carbon deposition includes: mixing a silicon source, a carbon source and a diluent gas and simultaneously introducing them into a fluidized bed reactor for reaction, wherein the reaction temperature is 440 to 550° C. and the reaction time is 0.5 to 15 hours;

[0020] Preferably, before the simultaneous silicon-carbon deposition, a silicon source and a diluent gas are introduced to perform nano-silicon pre-deposition, and the reaction time is 0.05 to 5 hours.

[0021] In an optional embodiment, the step of stepwise silicon-carbon deposition comprises: introducing a silicon source and a diluent gas into a fluidized bed reactor at a temperature of 440 to 550° C., and performing nano-silicon deposition on the carbon-based substrate particles for 0.5 to 15 hours to form pre-deposited particles;

[0022] The introduction of the silicon source is stopped, and the carbon source and the diluent gas are introduced into the fluidized bed reactor, and the pre-deposited particles are subjected to carbon deposition at a temperature of 480 to 580° C. for 0.1 to 10 hours.

[0023] In an optional embodiment, the carbon coating temperature is 520-680°C and the reaction time is 0.2-60h;

[0024] Preferably, the carbon coating is carried out in another independent reactor. Preferably, the another independent reactor is selected from a rotary kiln reactor and a fluidized bed reactor.

[0025] In an optional embodiment, during low-temperature silicon-carbon deposition, the volume ratio of the silicon source to the diluent gas is not less than 1 / 80, and the volume ratio of the carbon source to the diluent gas is not less than 1 / 80;

[0026] When carbon coating, the volume ratio of carbon source to diluent gas is not less than 1 / 60;

[0027] Preferably, the volume ratio of the carbon source to the diluent gas for low-temperature silicon carbon deposition is smaller than the volume ratio of the carbon source to the diluent gas for carbon coating.

[0028] In an optional embodiment, the fluidized bed for low temperature silicon deposition has the following characteristics:

[0029] Feature 1: The filling height of the material in the fluidized bed is not less than 0.8 times the inner diameter of the fluidized bed; the superficial gas velocity entering the fluidized bed is not less than 0.001 m / s;

[0030] Feature 2: The local gas ejection velocity of the gas distributor in the fluidized bed is not less than 2 m / s; preferably, mechanical stirring is also included.

[0031] In an optional embodiment, the silicon source used in the low-temperature silicon-carbon deposition includes at least one of monosilane, disilane, trisilane, tetrafluorosilane, chlorosilane, polychlorosilane, isobutylsilane and hexamethyldisilane;

[0032] The carbon source used in low-temperature silicon-carbon deposition and carbon coating includes at least one of C1-C8 alkanes, C2-C8 alkynes, C2-C10 alkenes, C1-C5 alcohols and C6-C12 aromatic hydrocarbons;

[0033] The diluent gas used in low-temperature silicon-carbon deposition and carbon coating includes at least one of nitrogen, argon, helium, carbon dioxide, water vapor and hydrogen.

[0034] In a second aspect, the present invention provides a silicon-carbon negative electrode material, which is prepared by the method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition as described in the above embodiment;

[0035] Preferably, the tap density of the silicon-carbon negative electrode material is not less than 0.2 g / cm 3 , the mass percentage of silicon is not less than 4%; the tap density of silicon-carbon mesophase particles is not less than 0.22g / cm 3 , the silicon mass proportion is not less than 5%.

[0036] The present invention has the following beneficial effects:

[0037] (1) The reaction temperature of the low-temperature silicon-carbon deposition of the present invention is lower than the subsequent carbon coating temperature. In terms of operation, it can effectively control the stability of heat release of the chemical vapor deposition reaction and improve the uniformity of the temperature field distribution in the reactor, thereby making the overall reaction rate controllable. The particle size, nano-silicon content and other parameters of the silicon-carbon negative electrode are easy to control, and the device scale is easy to scale up.

[0038] (2) When the preparation method of the present invention is adopted, silicon is chemically vapor deposited at a relatively low temperature, thereby avoiding the large amount of heat released by the thermalization of silane gas at high temperature under high temperature operating conditions, which may cause local temperature rise and then trigger an explosive reaction, and avoiding the hot spot effect and dust explosion risk of silicon-carbon composite materials in the reactor.

[0039] (3) The present invention can adopt a synchronous or step-by-step silicon-carbon deposition method to ensure the reliability and flexibility of the silicon-carbon combination, and utilize the conductive properties and stability of carbon to inhibit the expansion of silicon. On the basis of ensuring that safety is effectively improved, the yield and product quality of the silicon-carbon negative electrode are significantly optimized, showing excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0041] Figure 1 A schematic flow chart of a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition provided in an embodiment of the present invention;

[0042] Figure 2 A schematic diagram of an apparatus for a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition provided in an embodiment of the present invention;

[0043] Figure 3 The temperature change trend in the reactor when preparing the silicon-carbon negative electrode in Example 2 of the present invention and Comparative Example 4 is shown. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0045] In the first aspect, the present invention provides a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition. Figure 1 and Figure 2 , including: depositing silicon on carbon-based substrate particles in a fluidized bed to form silicon-carbon intermediate phase particles, and then further subjecting the particles to carbon coating to prepare silicon-carbon negative electrode materials;

[0046] The specific steps are as follows:

[0047] S1. Low temperature silicon carbon deposition:

[0048] The carbon-containing raw material is prepared into porous carbon particles with qualified particle size and specific surface area by existing physical, chemical or mechanical methods. The specific method or process is not described in detail in the present invention, as long as it meets the relevant particle size and specific surface area. Specifically, the carbon-based substrate particles are selected from the particle size D 50 No more than 20μm, specific surface area no less than 800m 2 / g porous carbon particles.

[0049] The carbon-based substrate particles meeting the requirements are placed in a well-designed fluidized bed reactor, and silicon source, carbon source and diluent gas are introduced to form silicon-carbon intermediate phase particles by synchronous silicon-carbon deposition or step-by-step silicon-carbon deposition.

[0050] Specifically, the step of synchronous silicon-carbon deposition includes: mixing a silicon source, a carbon source and a diluent gas and simultaneously introducing them into a fluidized bed reactor for reaction, wherein the reaction temperature is 440 to 550° C. and the reaction time is 0.5 to 15 hours.

[0051] For example, the reaction temperature is any value between 440-550°C, such as 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C and 550°C, and the reaction time is any value between 0.5-15h, such as 0.5h, 1h, 5h, 10h and 15h.

[0052] Preferably, before the simultaneous silicon-carbon deposition, a silicon source and a diluent gas are introduced to perform nano-silicon pre-deposition, and the reaction time is 0.05 to 5 hours, for example, any value between 0.05 hours, 1 hour, 2 hours, 3 hours, 4 hours and 5 hours.

[0053] The step of stepwise silicon-carbon deposition comprises: introducing silicon source and diluent gas into a fluidized bed reactor at a temperature of 440-550° C., and performing nano-silicon deposition on the carbon-based substrate particles for 0.5-15 hours to form pre-deposited particles.

[0054] For example, the reaction temperature is any value between 440-550°C, such as 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C and 550°C, and the reaction time is any value between 0.5-15h, such as 0.5h, 1h, 5h, 10h and 15h.

[0055] The introduction of the silicon source is stopped, and the carbon source and the diluent gas are introduced into the fluidized bed reactor, and the pre-deposited particles are subjected to carbon deposition at a temperature of 480 to 580° C. for 0.1 to 10 hours.

[0056] For example, the reaction temperature is any value between 480-580°C, such as 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C and 580°C, and the reaction time is any value between 0.1-10h, such as 0.1h, 0.5h, 1h, 5h and 10h.

[0057] Regardless of whether it is simultaneous silicon-carbon deposition or step-by-step silicon-carbon deposition, the volume ratio of the silicon source to the diluent gas is not less than 1 / 80, and the volume ratio of the carbon source to the diluent gas is not less than 1 / 80.

[0058] Regardless of whether it is simultaneous silicon-carbon deposition or step-by-step silicon-carbon deposition, the above-mentioned silicon source includes at least one of monosilane, disilane, trisilane, tetrafluorosilane, chlorosilane, polychlorosilane, isobutylsilane and hexamethyldisilane; the carbon source includes at least one of C1-C8 alkanes, C2-C8 alkynes, C2-C10 olefins, C1-C5 alcohols and C6-C12 aromatic hydrocarbons; and the diluent gas includes at least one of nitrogen, argon, helium, carbon dioxide, water vapor and hydrogen.

[0059] The fluidized bed for the above-mentioned low-temperature silicon-carbon deposition includes a reactor shell and a gas distributor; optionally, it also includes a stirring device, a cyclone separator and / or a heat exchange tube bundle; and when a stirring device is used, a mechanical stirring method is preferred.

[0060] At the same time, the filling height of the material in the fluidized bed is not less than 0.8 times the inner diameter of the fluidized bed; the superficial gas velocity entering the fluidized bed is not less than 0.001m / s; and the local gas ejection velocity of the gas distributor in the fluidized bed is not less than 2m / s.

[0061] The embodiments of the present invention use a fluidized bed to effectively control the reaction temperature and atmosphere, reducing the risk of dust explosions that may be caused during silicon deposition and carbon coating. Through mild silicon deposition conditions and precise gas flow control, the probability of hot spots in the reaction is reduced, thereby improving operational safety. At the same time, uniform stirring and gas distribution optimization in the fluidized bed reactor help ensure that the silicon and carbon sources are evenly mixed and fully contacted, thereby forming silicon-carbon mesophase particles with good crystallization and uniform distribution. This uniformity improves the electrochemical stability and cycle life of the material.

[0062] The tap density of the silicon-carbon mesophase particles formed by the low-temperature silicon-carbon deposition is not less than 0.22 g / cm 3 , the silicon mass proportion is not less than 5%.

[0063] S2, carbon coating;

[0064] After the low-temperature silicon-carbon deposition is completed, carbon coating is performed. The carbon coating can be performed in another independent reactor. Preferably, the other independent reactor is selected from a rotary kiln reactor and a fluidized bed reactor.

[0065] The temperature of low-temperature silicon-carbon deposition is at least 50°C lower than the temperature of carbon coating. The temperature of low-temperature silicon-carbon deposition is 50°C, 60°C, 70°C, 80°C, 90°C, 100°C lower than the temperature of carbon coating, etc., preferably at least 80°C lower.

[0066] The embodiment of the present invention uses relatively low temperature conditions to complete silicon deposition and carbon coating, which reduces energy consumption. At the same time, the fluidized bed reactor structure also helps to reduce the emission of reaction waste gas, meeting the requirements of energy conservation and environmental protection.

[0067] The temperature of carbon coating is 520-680°C, and the reaction time is 0.2-60h; for example, the temperature is 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C and 680°C, etc., and the reaction time is 0.2h, 0.5h, 5h, 10h, 20h, 30h, 40h, 50h and 60h, etc., any value between 0.2-60h.

[0068] Furthermore, during carbon coating, the volume ratio of the carbon source to the diluent gas is not less than 1 / 60; the volume ratio of the carbon source to the diluent gas in low-temperature silicon-carbon deposition is smaller than the volume ratio of the carbon source to the diluent gas in carbon coating.

[0069] The carbon source used for carbon coating includes at least one of C1-C8 alkanes, C2-C8 alkynes, C2-C10 olefins, C1-C5 alcohols and C6-C12 aromatic hydrocarbons; the diluent gas used includes at least one of nitrogen, argon, helium, carbon dioxide, water vapor and hydrogen.

[0070] In a second aspect, the present invention provides a silicon-carbon negative electrode material, which is prepared by the method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition as described in the above embodiment, wherein the tap density of the silicon-carbon negative electrode material is not less than 0.2 g / cm 3 , the silicon mass proportion is not less than 4%.

[0071] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0072] Example 1

[0073] The embodiment of the present invention provides a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition, comprising:

[0074] S1. Low temperature silicon carbon deposition:

[0075] A phenolic resin with a particle size of no more than 80 μm is used as a carbon-containing raw material. The raw material is placed in a fluidized bed reactor, the reactor is heated to 600°C, and a mixed gas of water vapor and nitrogen is introduced for activation reaction. The reaction time is controlled to be 6 hours. After that, the reactor is cooled to room temperature, and the reaction material is ground and sieved to obtain a particle size of less than 10 μm and a specific surface area of ​​more than 1600 m 2 / g porous carbon particles.

[0076] The porous carbon particles are placed in a fluidized bed reactor, the reactor is heated to 500°C, silicon source gas SiH4 and diluent gas nitrogen are introduced, the volume ratio of the silicon source is 1 / 40, the silicon deposition reaction time is 8 hours, and pre-deposition particles are formed. The gas is switched to carbon source gas C2H2 and diluent gas nitrogen, the volume ratio of the carbon source is 1 / 60, the carbon deposition reaction time is controlled to 3 hours, and the carbon source air intake is closed.

[0077] This step adopts step-by-step silicon-carbon deposition, and the material particles obtained in the fluidized bed reactor are silicon-carbon mesophase particles.

[0078] S2, Carbon coating:

[0079] The temperature of the fluidized bed reactor was raised to 600°C, and carbon source C2H2 and nitrogen were introduced with a volume ratio of 1 / 25. The carbon coating reaction time was controlled to be 6 hours. The carbon source air intake was closed, the heating was stopped, the reactor was cooled to room temperature, the carbon coating treatment was completed, and the silicon-carbon negative electrode material was removed from the reactor.

[0080] Detection:

[0081] The silicon-carbon negative electrode material prepared in this example was used as the positive electrode and the lithium sheet was used as the negative electrode to assemble into a button-type battery half-cell, and the relevant electrochemical properties were tested at 25°C.

[0082] After testing, the tap density of the silicon-carbon negative electrode material prepared in this embodiment is 0.94 g / cm 3 The first discharge specific capacity is 661 mAh / g, the first cycle efficiency is 89.2%, and the capacity retention rate after 100 cycles is 84.5%.

[0083] Example 2

[0084] The embodiment of the present invention provides a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition, comprising:

[0085] S1. Low temperature silicon carbon deposition:

[0086] The same porous carbon particles as in Example 1 were placed in a fluidized bed reactor, and the reactor was heated to 500°C. Silicon source gas SiH4, carbon source gas C2H2 and nitrogen were introduced at the same time. The volume ratio of the silicon source was 1 / 20, and the volume ratio of the carbon source was 1 / 50. The silicon deposition reaction time was controlled to be 4.5 hours, and the silicon source and carbon source gas intake were closed.

[0087] This step uses synchronous silicon-carbon deposition, and the material particles obtained in the fluidized bed reactor are silicon-carbon mesophase particles.

[0088] S2, Carbon coating:

[0089] The temperature of the fluidized bed reactor was raised to 580°C, and carbon source gas C3H8 and nitrogen were introduced with a volume ratio of 1 / 25. The carbon coating reaction time was controlled to be 2 hours. The carbon source gas intake was closed, the heating was stopped, the reactor was cooled to room temperature, the carbon coating treatment was completed, and the silicon-carbon negative electrode material was taken out from the reactor.

[0090] Detection:

[0091] A button cell half-cell was formed according to the method of Example 1, and the relevant electrochemical properties were tested at 25°C.

[0092] After testing, the tap density of the silicon-carbon negative electrode material prepared in this embodiment is 0.95g / cm 3 The first discharge specific capacity is 817 mAh / g, the first cycle efficiency is 83.6%, and the capacity retention rate after 100 cycles is 87.3%.

[0093] Example 3

[0094] The embodiment of the present invention provides a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition, comprising:

[0095] S1. Low temperature silicon carbon deposition:

[0096] The specific surface area of ​​the purchased 2 / g porous carbon coarse particles are ball-milled and sieved to obtain porous carbon particles with a particle size of no more than 10 μm.

[0097] The porous carbon particles are placed in a fluidized bed reactor, and the reactor is heated to 550°C. Silicon source gas SiH4 and nitrogen are introduced at the same time, with a silicon source volume ratio of 1 / 40, for nano-silicon pre-deposition, and the reaction time is controlled to be 0.5h; the reactor temperature is further adjusted to 500°C, and silicon source gas SiH4, carbon source gas C2H2 and nitrogen are introduced at the same time, with a silicon source volume ratio of 1 / 80 and a carbon source volume ratio of 1 / 80, and the silicon deposition reaction time is controlled to be 3h, and the silicon source and carbon source air intakes are closed.

[0098] This step adopts step-by-step silicon-carbon deposition and performs nano-silicon pre-deposition. The material particles obtained in the fluidized bed reactor are silicon-carbon mesophase particles.

[0099] S2, Carbon coating:

[0100] The temperature of the fluidized bed reactor was raised to 680°C, and carbon source gas C3H8 and nitrogen were introduced with a volume ratio of 1 / 60. The carbon coating reaction time was controlled to be 2 hours. The carbon source gas intake was closed, the heating was stopped, the reactor was cooled to room temperature, the carbon coating treatment was completed, and the silicon-carbon negative electrode material was taken out from the reactor.

[0101] Detection:

[0102] A button cell half-cell was formed according to the method of Example 1, and the relevant electrochemical properties were tested at 25°C.

[0103] After testing, the tap density of the silicon-carbon negative electrode material prepared in this embodiment is 0.93 g / cm 3 The first discharge specific capacity is 744mAh / g, the first cycle efficiency is 81.8%, and the capacity retention rate after 100 cycles is 80.3%.

[0104] Example 4

[0105] The embodiment of the present invention provides a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition, comprising:

[0106] S1. Low temperature silicon carbon deposition:

[0107] The same porous carbon particles as those in Example 1 are placed in a fluidized bed reactor, and the reactor is heated to 480°C. Silicon source gas SiH4 and diluent gas nitrogen are introduced, and the volume ratio of the silicon source is 1 / 20. The silicon deposition reaction time is 4 hours to form pre-deposited particles. The reaction temperature is kept unchanged and the gas is switched to carbon source gas C2H2 and diluent gas nitrogen, and the volume ratio of the carbon source is 1 / 30. The carbon deposition reaction time is controlled to be 3 hours, and the carbon source air intake is closed. At this time, the silicon deposition step is completed. The silicon deposition method adopted is step-by-step silicon-carbon deposition. The material particles obtained in the fluidized bed reactor are silicon-carbon intermediate phase particles.

[0108] S2, Carbon coating:

[0109] Heat the reactor to 570°C, introduce carbon source C2H2 and nitrogen, control the carbon coating reaction time to 3 hours, turn off the carbon source gas supply, stop heating, cool the reactor to room temperature, complete the carbon coating treatment, and remove the silicon-carbon negative electrode material from the reactor.

[0110] A button cell half-cell was formed according to the method of Example 1, and the relevant electrochemical properties were tested at 25°C.

[0111] After testing, the tap density of the silicon-carbon negative electrode material prepared in this embodiment is 0.98g / cm 3 The first discharge specific capacity is 792mAh / g, the first cycle efficiency is 80.4%, and the capacity retention rate after 100 cycles is 82.6%.

[0112] Example 5

[0113] An embodiment of the present invention provides a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition. Compared with the preparation method provided in Example 1, S1 is the same, and the only difference is that when S2 is subjected to carbon coating treatment, the reactor form is changed from a fluidized bed to a rotary kiln. Specifically, the carbon coating time is 60 hours, and the carbon coating temperature is 550°C. Other uniform methods are the same as Example 1.

[0114] After testing, the tap density of the silicon-carbon negative electrode material prepared in this embodiment is 0.97g / cm 3 The first discharge specific capacity is 801mAh / g, the first cycle efficiency is 79.1%, and the capacity retention rate after 100 cycles is 80.6%.

[0115] Example 6

[0116] An embodiment of the present invention provides a method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition. Compared with the preparation method provided in Example 2, S2 is the same, the only difference is that the conditions of S1 are different. Specifically, the reactor temperature of S1 is 450°C, the silicon deposition time is 10 hours, and the rest is the same as Example 2.

[0117] After testing, the tap density of the silicon-carbon negative electrode material prepared in this embodiment is 0.92 g / cm 3 The first discharge specific capacity is 612mAh / g, the first cycle efficiency is 74.9%, and the capacity retention rate after 100 cycles is 79.3%.

[0118] Comparative Example 1

[0119] This comparative example provides a method for preparing a silicon-carbon negative electrode material. Compared with the preparation method provided in Example 1, the operation of S2 is the same, and the only difference is S1. The specific content of S1 in this comparative example is:

[0120] The same porous carbon particles as in Example 1 were placed in a fluidized bed reactor, and the reactor was heated to 500°C. Silicon source gas SiH4 and diluent gas nitrogen were introduced, with a volume ratio of the silicon source of 1 / 90. The silicon deposition reaction time was 12 hours to form pre-deposited particles. The gas was switched to carbon source gas C2H2 and diluent gas nitrogen, with a volume ratio of the carbon source of 1 / 80. The carbon deposition reaction time was controlled to be 10 hours, and the carbon source air intake was closed.

[0121] This step adopts step-by-step silicon-carbon deposition, and the material particles obtained in the fluidized bed reactor are silicon-carbon mesophase particles.

[0122] After testing, the tap density of the silicon-carbon negative electrode material prepared in this comparative example is 0.86 g / cm 3 The first discharge specific capacity is 578mAh / g, the first cycle efficiency is 69.8%, and the capacity retention rate after 100 cycles is 70.2%.

[0123] Compared with Example 1, the volume ratio of silicon source to diluent gas in Comparative Example 1 is lower than 1 / 80, and the tap density, first discharge specific capacity, first cycle efficiency and capacity retention rate after 100 cycles of the obtained silicon-carbon negative electrode material are significantly reduced.

[0124] Comparative Example 2

[0125] This comparative example provides a method for preparing a silicon-carbon negative electrode material. Compared with the preparation method provided in Example 2, the operation and method of S2 remain unchanged, and the only difference is that the reactor of S1 is replaced by a rotary kiln from a fluidized bed, and the rest is the same as Example 2.

[0126] After testing, the tap density of the silicon-carbon negative electrode material prepared in this comparative example is 0.88 g / cm 3 The first discharge specific capacity is 496 mAh / g, the first cycle efficiency is 65.4%, and the capacity retention rate after 100 cycles is 73.7%.

[0127] Compared with Example 2, this comparative example only changes the fluidized bed into a rotary kiln. The tap density, first discharge specific capacity, first cycle efficiency and capacity retention rate after 100 cycles of the obtained silicon-carbon negative electrode material are significantly reduced, indicating that the use of a fluidized bed reactor has a great influence on the performance of the silicon-carbon negative electrode material in the embodiment of the present invention.

[0128] Comparative Example 3

[0129] This comparative example provides a method for preparing a silicon-carbon negative electrode material. Compared with the preparation method provided in Example 3, the only difference is that the reaction temperature for nano-silicon deposition in S1 is 620°C, the reaction temperature for carbon coating treatment in S2 is 700°C, and the rest is the same as Example 3.

[0130] After testing, the tap density of the silicon-carbon negative electrode material prepared in this comparative example is 0.87 g / cm 3 The first discharge specific capacity is 533mAh / g, the first cycle efficiency is 71.3%, and the capacity retention rate after 100 cycles is 66.7%.

[0131] Compared with Example 3, the temperature of nano-silicon deposition and the temperature of carbon coating in this comparative example are not within the range specified in the embodiments of the present invention, which leads to a significant decrease in the tap density, first discharge specific capacity, first cycle efficiency and capacity retention rate after 100 cycles of the obtained silicon-carbon negative electrode material, indicating that the silicon-carbon deposition temperature and the carbon coating temperature have a great influence on the performance of the silicon-carbon negative electrode material in the embodiments of the present invention.

[0132] Comparative Example 4

[0133] This comparative example provides a method for preparing a silicon-carbon negative electrode material. Compared with the preparation method provided in Example 2, the operation and method of S2 remain unchanged, and the only difference is that the silicon-carbon deposition temperature of S1 is 520°C, the carbon coating temperature of S2 is 550°C, and the other uniformities are the same as Example 2. In the actual operation process, when the carbon coating of S2 is performed, it is monitored that the temperature fluctuation in the reactor of this comparative example is significantly larger. Compared with Example 2, the stability of the reactor temperature control is obviously not as good as the corresponding situation in Example 2 where the set temperature of S1 is 80°C lower than the set temperature of S2, such as Figure 3 Therefore, the use of low-temperature silicon-carbon deposition can effectively bring about uniform control of the flow field in the reactor, so that the uniformity of heat transfer is guaranteed, which can not only effectively improve product quality, but also reduce the hot spots between particle materials, the risk of local accumulation of gas in the reactor and dust explosion, and improve the safety of operation.

[0134] After testing, the tap density of the silicon-carbon negative electrode material prepared in this comparative example is 0.96 g / cm 3 The first discharge specific capacity is 677mAh / g, the first cycle efficiency is 73.8%, and the capacity retention rate after 100 cycles is 81.2%.

[0135] Compared with Example 2, the temperature difference between the silicon-carbon deposition temperature and the carbon coating temperature is 30°C in this comparative example, and the tap density of the obtained silicon-carbon negative electrode material does not change much, but the first discharge specific capacity, the first cycle efficiency and the capacity retention rate after 100 cycles are significantly reduced, indicating that the temperature difference between the silicon-carbon deposition temperature and the carbon coating temperature has a great influence on the performance of the silicon-carbon negative electrode material in the embodiment of the present invention.

[0136] Comparative Example 5

[0137] This comparative example provides a method for preparing a silicon-carbon negative electrode material. Compared with the preparation method provided in Example 2, the operations of S1 and S2 are the same as those of Example 2, except that the particle size D of the carbon-based material particles formed in S1 is 50 The surface area is 15 μm and the specific surface area is 720 m 2 / g.

[0138] After testing, the tap density of the silicon-carbon negative electrode material prepared in this comparative example is 0.86 g / cm 3 The first discharge specific capacity is 491 mAh / g, the first cycle efficiency is 67.6%, and the capacity retention rate after 100 cycles is 69.2%.

[0139] Compared with Example 2, in this comparative example, after the particle size of the selected carbon-based material becomes larger and the surface area becomes smaller, the first discharge specific capacity, the first cycle efficiency and the capacity retention rate after 100 cycles are greatly reduced, and the tap density is also reduced. Therefore, the electrochemical properties are significantly deteriorated.

[0140] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. 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 method for preparing a silicon-carbon negative electrode material by low-temperature silicon-carbon deposition, characterized in that: include: The carbon-based substrate particles are subjected to silicon deposition in a fluidized bed to form silicon-carbon intermediate phase particles, which are then further subjected to carbon coating to prepare silicon-carbon negative electrode materials; The specific steps are as follows: S1. Low-temperature silicon-carbon deposition: introducing the carbon-based substrate particles into a fluidized bed, and performing chemical vapor deposition reaction by synchronous silicon-carbon deposition or step-by-step silicon-carbon deposition to form silicon-carbon intermediate phase particles; S2, carbon coating: using a chemical vapor deposition method to carbon-coat the silicon-carbon mesophase particles obtained in S1 to form a silicon-carbon negative electrode material; The reaction temperature in S1 is at least 50° C. lower than the reaction temperature in S2.

2. The method for preparing silicon-carbon negative electrode material by low-temperature silicon-carbon deposition according to claim 1, characterized in that: The carbon-based material particles are selected from the group consisting of particles having a particle size D 50 No more than 20μm, specific surface area no less than 800m 2 / g porous carbon particles.

3. The method for preparing silicon-carbon negative electrode material by low-temperature silicon-carbon deposition according to claim 1, characterized in that: The step of synchronous silicon-carbon deposition includes: mixing a silicon source, a carbon source and a diluent gas and simultaneously introducing them into a fluidized bed reactor for reaction, wherein the reaction temperature is 440 to 550° C. and the reaction time is 0.5 to 15 hours; Preferably, before the simultaneous silicon-carbon deposition, a silicon source and a diluent gas are introduced to perform nano-silicon pre-deposition, and the reaction time is 0.05 to 5 hours.

4. The method for preparing silicon-carbon negative electrode material by low-temperature silicon-carbon deposition according to claim 1, characterized in that: The step of stepwise silicon-carbon deposition comprises: introducing a silicon source and a diluent gas into a fluidized bed reactor at a temperature of 440 to 550° C., and performing nano-silicon deposition on the carbon-based substrate particles for 0.5 to 15 hours to form pre-deposited particles; The introduction of the silicon source is stopped, and the carbon source and the diluent gas are introduced into the fluidized bed reactor, and the pre-deposited particles are subjected to carbon deposition at a temperature of 480 to 580° C. for 0.1 to 10 hours.

5. The method for preparing silicon-carbon negative electrode material by low-temperature silicon-carbon deposition according to claim 1, characterized in that: The temperature of carbon coating is 520-680°C, and the reaction time is 0.2-60h; Preferably, the carbon coating is carried out in another independent reactor. Preferably, the another independent reactor is selected from a rotary kiln reactor and a fluidized bed reactor.

6. The method for preparing silicon-carbon negative electrode material by low-temperature silicon-carbon deposition according to claim 1, characterized in that: During low-temperature silicon-carbon deposition, the volume ratio of the silicon source to the diluent gas is not less than 1 / 80, and the volume ratio of the carbon source to the diluent gas is not less than 1 / 80; When carbon coating, the volume ratio of carbon source to diluent gas is not less than 1 / 60; Preferably, the volume ratio of the carbon source to the diluent gas for low-temperature silicon carbon deposition is smaller than the volume ratio of the carbon source to the diluent gas for carbon coating.

7. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The fluidized bed for low temperature silicon deposition has the following characteristics: Feature 1: The filling height of the material in the fluidized bed is not less than 0.8 times the inner diameter of the fluidized bed; the superficial gas velocity entering the fluidized bed is not less than 0.001 m / s; Feature 2: The local gas ejection velocity of the gas distributor in the fluidized bed is not less than 2m / s.

8. The method for preparing the silicon-carbon negative electrode material according to claim 1, characterized in that: The silicon source used in the low-temperature silicon-carbon deposition includes at least one of monosilane, disilane, trisilane, tetrafluorosilane, chlorosilane, polychlorosilane, isobutylsilane and hexamethyldisilane; The carbon source used in low-temperature silicon-carbon deposition and carbon coating includes at least one of C1-C8 alkanes, C2-C8 alkynes, C2-C10 alkenes, C1-C5 alcohols and C6-C12 aromatic hydrocarbons; The diluent gas used in low-temperature silicon-carbon deposition and carbon coating includes at least one of nitrogen, argon, helium, carbon dioxide, water vapor and hydrogen.

9. A silicon-carbon negative electrode material, characterized in that: The silicon-carbon negative electrode material is prepared by the method for preparing the silicon-carbon negative electrode material by low-temperature silicon-carbon deposition as described in any one of claims 1 to 8.

10. The silicon-carbon negative electrode material according to claim 9, characterized in that: The tap density of silicon-carbon negative electrode material is not less than 0.2g / cm 3 , the mass percentage of silicon is not less than 4%; the tap density of silicon-carbon mesophase particles is not less than 0.22g / cm 3 , the silicon mass proportion is not less than 5%.

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