Carbon-silicon material, preparation method thereof and battery

Abstract

The invention discloses a carbon-silicon material, a preparation method thereof and a battery, and belongs to the technical field of negative electrode materials. The carbon-silicon material comprises silicon-carbon particles and a carbon coating layer coating the surfaces of the silicon-carbon particles, the silicon-carbon particles are porous carbon on which silicon is deposited; and the carbon coating layer is formed by adsorbing gaseous polycyclic aromatic hydrocarbon with the molecular weight of more than or equal to 1000 on the surfaces of the silicon carbon particles. The carbon coating layer is formed by gaseous polycyclic aromatic hydrocarbon and has relatively large molecular weight, so that the formed carbon coating layer has relatively few defects, the conductivity of the carbon coating layer is improved, the side reaction of the carbon-silicon material during lithiation reaction can be reduced, and the high-temperature storage and quick charge performance of a corresponding battery can be improved. The preparation method is simple and can be used for industrial production.

Description

Technical Field

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

[0002] Silicon-carbon composites are now considered the next generation of lithium battery negative electrode materials that are most likely to replace traditional graphite. However, due to the huge volume change of silicon particles during the lithium insertion and extraction process, the electrode structure collapses, the cycle life is rapidly reduced, and many other problems limit the widespread application of silicon-carbon composites. How to better alleviate the volume effect of silicon has become the focus of research and development and improvement of silicon-carbon materials.

[0003] In recent years, the composite structure design of porous carbon deposited nanosilicon has received widespread attention in the industry. This composite structure, with the help of the rich pore structure inside the porous carbon, not only solves the problem of silicon particle agglomeration and pulverization, but also the carbon matrix increases the stability of the electrode structure during silicon lithiation. However, in the preparation process of porous carbon deposited nanosilicon, due to the high activity of nanosilicon deposited inside or on the surface of porous carbon particles, it will undergo oxidation reaction when directly exposed to the air, releasing a large amount of heat and even causing spontaneous combustion, which poses a great safety hazard.

[0004] The existing technology is to perform inert treatment on the surface of silicon-carbon particles. Common methods include micro-oxidation method, carbon coating method, etc. However, the micro-oxidation method is difficult to control due to the trace introduction of oxygen elements, and it is very easy to cause safety accidents. In addition, too much oxygen elements will lead to low capacity and initial efficiency of the final product. At present, the commonly used inertization process on the market is still mainly based on the carbon coating method. However, as far as this method is concerned, if the crystallization and grain size of silicon particles are not properly controlled, it will also affect its cycle performance and rate performance.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The object of the present invention is to provide a carbon silicon material and a preparation method thereof and a battery to improve the above technical problems.

[0007] This application can be implemented as follows:

[0008] In a first aspect, the present application provides a carbon silicon material, which includes silicon carbon particles and a carbon coating layer coated on the surface of the silicon carbon particles;

[0009] Silicon carbon particles are porous carbon with silicon deposited;

[0010] The carbon coating layer is formed by the adsorption of gaseous condensed-ring aromatic hydrocarbons on the surface of silicon-carbon particles; the molecular weight of the gaseous condensed-ring aromatic hydrocarbons is ≥1000.

[0011] In an optional embodiment, the carbon silicon material has at least one of the following characteristics:

[0012] Feature 1: The D of the carbon-silicon material 50 = 4 - 8 μm;

[0013] Feature 2: The resistivity of the carbon-silicon material is 1 - 50 Ω·cm;

[0014] Feature 3: The specific surface area of the porous carbon in the carbon-silicon material is 1000 - 2000 m 2 / g.

[0015] In a second aspect, the present application provides a method for preparing a carbon-silicon material as described in the foregoing embodiment, including the following steps: preparing a carbon coating layer formed by a gaseous polycyclic aromatic hydrocarbon with a molecular weight ≥ 1000 on the surface of silicon-carbon particles.

[0016] In an optional embodiment, the preparation of the carbon coating layer includes: preheating a first mixture of a carbon source and a first carrier gas and then depositing it on the surface of the silicon-carbon particles;

[0017] The preheating temperature of the first mixture is 800 - 1100 °C.

[0018] In an optional embodiment, the flow rate of the carbon source is 1 - 2.5 L / min, and the flow rate of the first carrier gas is 2.5 - 4 L / min.

[0019] In an optional embodiment, the carbon source includes gaseous hydrocarbon substances having 1 to 4 carbon atoms, and / or the first carrier gas includes an inert gas.

[0020] In an optional embodiment, before introducing the preheated first mixture, the temperature in the reactor where the silicon-carbon particles are located is 500 - 580 °C;

[0021] and / or the deposition time of the preheated first mixture on the silicon-carbon particles is 1 - 2 h.

[0022] In an optional embodiment, the preparation of the silicon-carbon particles includes: depositing and reacting a second mixture of a silicon source and a second carrier gas with porous carbon.

[0023] In an optional embodiment, the flow rate of the silicon source is 0.5 - 2 L / min, and the flow rate of the second carrier gas is 3 - 5 L / min.

[0024] In an optional embodiment, the silicon source includes silane, and / or the second carrier gas includes an inert gas.

[0025] In an optional embodiment, before introducing the second mixture, the temperature in the reactor where the porous carbon is located is 430 - 480 °C;

[0026] and / or the deposition reaction time of the second mixture with the porous carbon is 2 - 4 h.

[0027] In a third aspect, the present application provides a battery containing the carbon-silicon material of the foregoing embodiments.

[0028] In an alternative embodiment, the battery has at least one of the following characteristics:

[0029] Characteristic 1: The initial efficiency is ≥90.5%;

[0030] Characteristic 2: The charge specific capacity at 0.1C is ≥1890 mAh / g;

[0031] Characteristic 3: The discharge specific capacity at 0.1C is ≥2000 mAh / g;

[0032] Characteristic 4: The charge specific capacity at 1C is ≥1800 mAh / g;

[0033] Characteristic 5: The charge specific capacity at 3C is ≥1500 mAh / g;

[0034] Characteristic 6: The cycle retention rate after 50 cycles under the conditions of 25°C and 0.005 - 2V is ≥93.5%;

[0035] Characteristic 7: The capacity retention rate after being stored at 45°C for 7 days is ≥86.5%.

[0036] The beneficial effects of the present application include:

[0037] The carbon-silicon material provided by the present application has a carbon coating layer formed by gaseous polycyclic aromatic hydrocarbons with a molecular weight ≥1000. This coating layer has fewer defects, good electrical conductivity, can reduce side reactions during the lithiation reaction of the carbon-silicon material, and improve the electrochemical performance of the corresponding battery, such as high-temperature storage and fast charging performance, etc. Its preparation method is simple and can be industrially produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. 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, without creative efforts, other related drawings can also be obtained based on these drawings.

[0039] Figure 1 It is the SEM image of the carbon-silicon material prepared in Example 1 of the present application;

[0040] Figure 2 It is the SEM image of the carbon-silicon material prepared in Comparative Example 1 of the present application;

[0041] Figure 3 It is the SEM image of the carbon-silicon material prepared in Comparative Example 2 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] 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. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0043] The carbon-silicon material, its preparation method, and the battery provided by the present application will be specifically described below.

[0044] The present application provides a carbon-silicon material, which includes silicon-carbon particles and a carbon coating layer coated on the surface of the silicon-carbon particles.

[0045] Among them, the silicon-carbon particles are porous carbon deposited with silicon.

[0046] In some embodiments, the specific surface area of the porous carbon can be 1000-2000m 2 / g. Specifically, the specific surface area of the porous carbon can be measured by the static BET method.

[0047] In the present application, using porous carbon with a specific surface area of 1000-2000m 2 / g is beneficial to absorb sufficient active silicon particles, thereby showing the advantages of high capacity and low expansion during lithiation. If the specific surface area of the porous carbon is less than 1000m 2 / g, the area of the matrix affected by deposition is small, which is not conducive to giving full play to the advantages of the rich pore space of the porous carbon; if the specific surface area of the porous carbon is greater than 2000m 2 / g, there are still large pores on the surface of the finally formed carbon-silicon material that cannot be filled, and there are many defects, which is not conducive to the formation of a stable battery SEI film.

[0048] In the present application, the carbon coating layer is formed after gaseous polycyclic aromatic hydrocarbons are adsorbed on the surface of the silicon-carbon particles, and the molecular weight of the gaseous polycyclic aromatic hydrocarbons ≥1000.

[0049] By adsorbing gaseous polycyclic aromatic hydrocarbons with a relatively large molecular weight on the surface of the silicon-carbon particles to form a carbon coating layer, the formed carbon coating layer can have fewer defects, improve the conductivity of the carbon coating layer, and can reduce the side reactions during the lithiation reaction of the carbon-silicon material, improving the high-temperature storage and fast charging performance of the corresponding battery.

[0050] In some embodiments, the D 50 of the above carbon-silicon material is 4-8μm. The carbon-silicon material in this particle size range has good graphite compatibility, can give full play to the advantages of the porous structure of the carbon matrix, and is beneficial to slowing down the trap effect of the silicon negative electrode. In some embodiments, the resistivity of the above carbon-silicon material is 1-50Ω·cm, having good conductivity.

[0051] Continuing from the above, the carbon-silicon material provided by this application has good electrical conductivity, cycle performance, rate performance, etc.

[0052] Correspondingly, this application also provides a preparation method for the above carbon-silicon material, which may include the following steps: preparing a carbon coating layer formed by gaseous polycyclic aromatic hydrocarbons with a molecular weight ≥ 1000 on the surface of silicon-carbon particles.

[0053] For reference, the preparation of the carbon coating layer may include: preheating a first mixture of a carbon source and a first carrier gas and then depositing it on the surface of the silicon-carbon particles.

[0054] Among them, the carbon source includes gaseous hydrocarbon substances with 1 to 4 carbon atoms, such as methane, ethane, ethylene, or acetylene, etc. In some specific embodiments, acetylene is used as the carbon source.

[0055] The first carrier gas includes inert gases, for example, it may include nitrogen or argon, etc. In some specific embodiments, nitrogen is used as the first carrier gas.

[0056] During specific operations, the flow rate of the carbon source can be set to 1 - 2.5 L / min, such as 1 L / min, 1.5 L / min, 2 L / min, or 2.5 L / min, etc., or any other value within the range of 1 - 2.5 L / min. The flow rate of the first carrier gas can be set to 2.5 - 4 L / min, such as 2.5 L / min, 3 L / min, 3.5 L / min, or 4 L / min, etc., or any other value within the range of 2.5 - 4 L / min. Preferably, the volume of the carbon source is 5 - 60% of the first mixture.

[0057] In this application, during the preheating process, the carbon source first decomposes into carbon. When the generated carbon reaches a certain concentration, it will continue to generate gaseous polycyclic aromatic hydrocarbons during the preheating process. If the amount of the carbon source used is too small, it may not be possible to obtain gaseous polycyclic aromatic hydrocarbons, or it may obtain gaseous polycyclic aromatic hydrocarbons with a relatively small molecular weight. For gaseous polycyclic aromatic hydrocarbons with a relatively small molecular weight in the gas phase, it is easy to cause more defects in the subsequent formed carbon layer, resulting in poor electrical conductivity, and there are more side reactions during the lithiation reaction of the final product, leading to poor high-temperature storage and fast-charging performance of the battery. If the amount of the carbon source used is too large, it is easy to agglomerate and nucleate by itself to form particles, making it difficult to achieve the coating of the silicon-carbon particles.

[0058] In this application, the preheating temperature of the first mixture is 800 - 1100 °C, for example, it can be 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, or 1100 °C, etc., or any other value within the range of 800 - 1100 °C.

[0059] A large amount of thermal decomposition occurs in the carbon source at the above preheating temperature, rapidly generating gaseous polycyclic aromatic hydrocarbon compounds with relatively large molecular weights (molecular weight > 1000). Subsequently, the preheated mixed gas is introduced into a deposition reactor (which can be a fluidized bed, a rotary kiln, or other types of deposition reaction equipment). The gaseous polycyclic aromatic hydrocarbons are adsorbed on the surface of the silicon-carbon particles in the reactor. When the adsorption layer reaches the critical size, they coagulate and nucleate to form a solid carbon coating layer.

[0060] Before introducing the preheated first mixed gas, the temperature in the reactor where the silicon-carbon particles are located is 500 - 580 °C, such as 500 °C, 510 °C, 520 °C, 530 °C, 540 °C, 550 °C, 560 °C, 570 °C, or 580 °C, etc., and it can also be any other value within the range of 500 - 580 °C.

[0061] It should be noted that by controlling the temperature in the reactor before introducing the first mixed gas within the above range in this application, a more appropriate carbon deposition reaction temperature can be ensured, which is conducive to controlling the crystallization of silicon particles and the excessive growth of grain size in the carbon-silicon composite material. If the deposition temperature is relatively high, the silicon particles inside the carbon-silicon composite material will transform from amorphous to crystalline, and as the reaction temperature increases, the silicon grain size becomes larger. When the silicon grain size exceeds 10 nm, the volume effect of the carbon-silicon composite material during the cycling process is obvious, and the cycling structure stability deteriorates significantly, resulting in a shorter battery life. However, if the first mixed gas without high-temperature preheating is directly introduced at a relatively low deposition temperature (such as 500 - 700 °C), the gas phase generated by the carbon source cracking will have a relatively small molecular weight, the formed carbon layer will have more defects and poor conductivity, and there will be more side reactions during the lithiation reaction of the final product, resulting in poor high-temperature storage and fast charging performance of the battery.

[0062] In some embodiments, the deposition time of the preheated first mixed gas on the silicon-carbon particles can be 1 - 2 h, such as 1 h, 1.5 h, or 2 h, etc. In addition, the deposition time can also be appropriately adjusted according to the actual situation.

[0063] In this application, the preparation of the silicon-carbon particles can include: carrying out a deposition reaction between a second mixed gas of a silicon source and a second carrier gas and porous carbon.

[0064] Among them, the silicon source includes silane. The second carrier gas includes an inert gas, for example, it can include nitrogen or argon, etc. In some specific embodiments, nitrogen is used as the second carrier gas.

[0065] During specific operations, the flow rate of the silicon source can be set to 0.5 - 2 L / min, such as 0.5 L / min, 1 L / min, 1.5 L / min, or 2 L / min, etc., or any other arbitrary value within the range of 0.5 - 2 L / min. The flow rate of the second carrier gas can be set to 3 - 5 L / min, such as 3 L / min, 3.5 L / min, 4 L / min, 4.5 L / min, or 5 L / min, etc., or any other arbitrary value within the range of 3 - 5 L / min.

[0066] Before introducing the second mixed gas, the temperature in the reactor where the porous carbon is located can be 430 - 480 °C, such as 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, or 480 °C, etc. Before introducing the second mixed gas, the air in the reactor can be replaced with an inert gas first to make the environment in the reactor oxygen-free.

[0067] The time for the deposition reaction of the second mixed gas with the porous carbon can be 2 - 4 h, such as 2 h, 2.5 h, 3 h, 3.5 h, or 4 h, etc.

[0068] It should be noted that other steps and conditions in the preparation process of the carbon-silicon material not described in detail in this application can refer to the relevant existing technologies and will not be elaborated here.

[0069] In addition, this application also provides a battery, the negative electrode material of which is the above-mentioned carbon-silicon material. This battery has good cycle performance and rate performance.

[0070] In some embodiments, the initial efficiency of this battery ≥ 90.5%; in some embodiments, the 0.1C charge specific capacity of this battery ≥ 1890 mAh / g; in some embodiments, the 0.1C discharge specific capacity of this battery ≥ 2000 mAh / g; in some embodiments, the 1C charge specific capacity of this battery ≥ 1800 mAh / g; in some embodiments, the 3C charge specific capacity of this battery ≥ 1500 mAh / g; in some embodiments, the cycle retention rate of this battery after 50 cycles under the conditions of 25 °C and 0.005 - 2 V ≥ 93.5%; in some embodiments, the capacity retention rate of this battery after being stored at 45 °C for 7 days ≥ 86.5%.

[0071] The features and properties of the present invention will be further described in detail below in conjunction with the embodiments.

[0072] Example 1

[0073] This example provides a carbon-silicon material, and its preparation method includes:

[0074] S1: Prepare silicon-carbon particles.

[0075] Place 500 g of porous carbon raw material (specific surface area: 1500 m 2 / g) in a fluidized bed reactor. First, introduce nitrogen at a flow rate of 2 L / min to continuously displace the air in the reactor for 1 h. Heat the reactor at a heating rate of 5 °C / min. When the temperature in the reactor reaches 450 °C, introduce a second mixture of silane and nitrogen at a ratio of silane flow rate of 1.0 L / min and nitrogen flow rate of 4.0 L / min, and continuously carry out the deposition reaction for 3 h to obtain silicon-carbon particles deposited with silicon.

[0076] S2: Perform carbon coating on the surface of the silicon-carbon particles.

[0077] Continue to heat the reactor in S1 at a heating rate of 5 °C / min. When the temperature in the reactor reaches 520 °C, introduce a first mixture of acetylene and nitrogen preheated to 950 °C and deposit for 1 h to obtain a carbon-silicon material. Among them, the acetylene flow rate is 2.0 L / min and the nitrogen flow rate is 3.0 L / min (acetylene and nitrogen are first mixed in a gas mixing tank to obtain the first mixture, and then preheated to 950 °C by a gas heater).

[0078] The SEM image of this carbon-silicon material is as Figure 1 shown, and it can be seen from Figure 1 that the coated carbon layer on the particle surface has the characteristics of a continuous and regular two-dimensional layered structure, indicating that after being preheated by the preheater, the carbon layer structure generated after the deposition of the carbon source gas is more ideal and has fewer defects.

[0079] Example 2

[0080] The difference between this example and Example 1 is that:

[0081] S2: Continue to heat the reactor in S1 at a heating rate of 5 °C / min. When the temperature in the reactor reaches 520 °C, introduce a first mixture of acetylene and nitrogen preheated to 850 °C and deposit for 2 h to obtain a carbon-silicon material. Among them, the acetylene flow rate is 1.0 L / min and the nitrogen flow rate is 4.0 L / min (acetylene and nitrogen are first mixed in a gas mixing tank to obtain the first mixture, and then preheated to 850 °C by a gas heater).

[0082] Example 3

[0083] The difference between this example and Example 1 is that:

[0084] S2: Continue to heat the reactor in S1 at a heating rate of 5 °C / min. When the temperature in the reactor rises to 500 °C, introduce a first mixed gas composed of acetylene and nitrogen preheated to 1050 °C, and deposit for 1 h to obtain a carbon-silicon material. Among them, the acetylene flow rate is 2.5 L / min, and the nitrogen flow rate is 2.5 L / min (acetylene and nitrogen are first mixed in a gas mixing tank to obtain the first mixed gas, and then preheated to 1050 °C by a gas heater).

[0085] Example 4

[0086] This example provides a carbon-silicon material, and its preparation method includes:

[0087] S1: Prepare silicon-carbon particles.

[0088] Place 500 g of porous carbon raw material (specific surface area is 1000 m 2 / g) in a fluidized bed reactor. First, introduce 2 L / min of nitrogen to continuously displace the air in the reactor for 1 h. Heat the reactor at a heating rate of 5 °C / min. When the temperature in the reactor rises to 430 °C, introduce a second mixed gas of silane and nitrogen at a ratio of silane flow rate of 0.5 L / min and nitrogen flow rate of 3.0 L / min, and continuously carry out the deposition reaction for 2 h to obtain silicon-carbon particles deposited with silicon.

[0089] S2: Perform carbon coating on the surface of the silicon-carbon particles.

[0090] Continue to heat the reactor in S1 at a heating rate of 5 °C / min. When the temperature in the reactor rises to 500 °C, introduce a first mixed gas composed of acetylene and nitrogen preheated to 800 °C, and deposit for 2 h to obtain a carbon-silicon material. Among them, the acetylene flow rate is 1.0 L / min, and the nitrogen flow rate is 2.5 L / min (acetylene and nitrogen are first mixed in a gas mixing tank to obtain the first mixed gas, and then preheated to 800 °C by a gas heater).

[0091] Example 5

[0092] This example provides a carbon-silicon material, and its preparation method includes:

[0093] S1: Prepare silicon-carbon particles.

[0094] Place 500 g of porous carbon raw material (specific surface area is 2000 m 2 / g) is placed in a fluidized bed reactor. First, nitrogen is introduced at a rate of 2 L / min to continuously displace the air in the reactor for 1 h. The reactor is heated at a heating rate of 5 °C / min. When the temperature in the reactor rises to 480 °C, a second mixture of silane and nitrogen is introduced at a ratio of a silane flow rate of 2.0 L / min and a nitrogen flow rate of 5.0 L / min, and the deposition reaction is continuously carried out for 4 h to obtain silicon-carbon particles deposited with silicon.

[0095] S2: Perform carbon coating on the surface of the silicon-carbon particles.

[0096] Continue to heat the reactor in S1 at a heating rate of 5 °C / min. When the temperature in the reactor rises to 580 °C, a first mixture of acetylene and nitrogen preheated to 1100 °C is introduced and deposited for 1.5 h to obtain a carbon-silicon material. Among them, the acetylene flow rate is 2.5 L / min and the nitrogen flow rate is 4.0 L / min (acetylene and nitrogen are first mixed in a gas mixing tank to obtain the first mixture, and then preheated to 1100 °C by a gas heater).

[0097] Comparative Example 1

[0098] The difference between this comparative example and Example 1 is:

[0099] S2: Continue to heat the reactor in S1 at a heating rate of 5 °C / min. When the temperature in the reactor rises to 650 °C, a first mixture of acetylene and nitrogen is introduced and deposited for 1 h to obtain a carbon-silicon material. Among them, the acetylene flow rate is 2 L / min and the nitrogen flow rate is 3 L / min.

[0100] The SEM image of this carbon-silicon material is as Figure 2 shown, and it can be seen from Figure 2 that there is no obvious layered structure found in the carbon coating layer on the particle surface, and it still shows an amorphous characteristic, indicating that when there is no preheater preheating, the carbon layer formed after the deposition of the carbon source gas is non-continuous and has many defects.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is:

[0103] S2: Continue to heat the reactor in S1 at a heating rate of 5 °C / min. When the temperature in the reactor rises to 950 °C, a first mixture of acetylene and nitrogen is introduced and deposited for 1 h to obtain a carbon-silicon material. Among them, the acetylene flow rate is 2 L / min and the nitrogen flow rate is 3 L / min.

[0104] The SEM image of this carbon-silicon material is as Figure 3 shown, and it can be seen from Figure 3It can be seen that there is a partial two-dimensional layered structure on the surface of the particles, but overall observation shows discontinuity. Further magnification reveals the formation of crystalline silicon inside, which affects the cycling and storage performance of the material.

[0105] Comparative Example 3

[0106] The difference between this comparative example and Example 1 is that in S2, the preheating temperature of the first mixed gas is 600 °C.

[0107] Comparative Example 4

[0108] The difference between this comparative example and Example 1 is that in S2, the preheating temperature of the first mixed gas is 1200 °C.

[0109] Comparative Example 5

[0110] The difference between this comparative example and Example 1 is that in S2, the temperature in the reactor is raised to 600 °C.

[0111] Test Example

[0112] ①. Measure the particle size and resistivity of the carbon-silicon materials prepared in Examples 1-5 and Comparative Examples 1-5.

[0113] Among them, the particle size is measured according to the particle size test method described in the national standard GB / T 19077-2016, and the resistivity is measured according to the test method of the resistivity of particulate powder described in the national standard GB / T 30835-2014.

[0114] The measurement results are shown in Table 1.

[0115] Table 1 Measurement Results

[0116] Group <![CDATA[D 50 (μm)]]> Resistivity Ω·cm Example 1 5.5 14.2 Example 2 5.1 23.8 Example 3 6.0 35.8 Example 4 7.9 41.7 Example 5 4.3 18.6 Comparative Example 1 5.3 193.6 Comparative Example 2 5.8 57.2 Comparative Example 3 5.2 2151.9 Comparative Example 4 5.7 65.8 Comparative Example 5 5.6 114.3

[0117] ②. Assemble the carbon-silicon materials prepared in Examples 1-5 and Comparative Examples 1-5 into batteries in the following manner, and test the electrochemical performance of the obtained batteries. The results are shown in Table 2.

[0118] Assembly method: The battery manufacturing method is as follows. Mix the silicon-carbon negative electrode material: carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR): conductive carbon black (SP) in a mass ratio of 80:4:6:10, add deionized water to make a slurry, uniformly coat it on the copper foil, and vacuum dry it at 120 °C for 24 hours to obtain a battery electrode sheet. Then, use a lithium sheet as the counter electrode and use 1.1 mol / L of LiPF 6, An electrolyte prepared by mixing ethylene carbonate (EC): vinylene carbonate (VC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) in a mass ratio of 1:1:1:1 was used. A polypropylene microporous film was used as the separator, and a CR2032 coin-type half-cell was assembled in a vacuum glove box. The cell was tested under the working conditions of discharging at a constant current of 0.05C to 5mV, discharging at a constant current of 0.05mA to 5mV, and charging at a constant current of 0.05C to 2.0V.

[0119] Table 2 Test Results

[0120]

[0121] As can be seen from Table 2, Comparative Example 1 is a deposition process without using the preheating method. Under this process condition, the initial efficiency of the material is low, the rate performance is poor, and the storage capacity retention rate is low. The reason may be that there are many defects in the carbon layer formed after the first mixed gas is not preheated, resulting in poor conductivity.

[0122] Moreover, it should be further noted that compared with the characteristics of the carbon coating layer formed by the low-temperature deposition of acetylene, the molecular weight of the gas-phase polycyclic aromatic hydrocarbons formed by the decomposition of acetylene at high temperature is larger, the internal defects of the molecules are smaller, the carbon plane of the deposited carbon coating layer is more continuous, and the in-plane defects are less, showing higher conductivity. At the same time, due to the smaller defects during the lithiation reaction, the degree of side reactions is reduced. At low temperatures, the molecular weight of the gaseous hydrocarbons formed by the decomposition of acetylene is smaller, and there are more five-membered ring and seven-membered ring structures. After deposition into carbon, the carbon layer plane structure is discontinuous and disordered, with many defects, which affects the rapid migration of lithium ions and electrons. At the same time, during the cycling process, the defect positions continuously cause irreversible lithium consumption, resulting in a decline in cycling and storage performance.

[0123] Comparative Example 2 is a direct high-temperature carbon deposition process. Under this process condition, the material is significantly worse than Example 1 in terms of cycle stability and storage performance.

[0124] In addition, the overall electrochemical performance of the batteries obtained in Comparative Examples 3-5 is also worse than that of Example 1.

[0125] In summary, the carbon-silicon material provided by this application has a carbon coating layer formed by gaseous polycyclic aromatic hydrocarbons with a molecular weight ≥ 1000, which can reduce the side reactions during the lithiation reaction of the carbon-silicon material and improve the electrochemical performance of the corresponding batteries, such as high-temperature storage and fast charging performance. Its preparation method is simple and can be industrially produced.

[0126] 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 changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A carbon-silicon material, characterized in that the carbon-silicon material comprises silicon-carbon particles and a carbon coating layer coated on the surface of the silicon-carbon particles; the silicon-carbon particles are porous carbon deposited with silicon; the carbon coating layer is formed after gaseous polycyclic aromatic hydrocarbons are adsorbed on the surface of the silicon-carbon particles; the molecular weight of the gaseous polycyclic aromatic hydrocarbons ≥ 1000.

2. The carbon-silicon material according to claim 1, characterized in that the carbon-silicon material has at least one of the following characteristics: Feature 1: The D of the carbon-silicon material 50 = 4 - 8 μm; Characteristic two: the resistivity of the carbon-silicon material is 1-50 Ω·cm; Feature Three: The specific surface area of the porous carbon in the carbon-silicon material is 1000 - 2000 m 2 / g.

3. A preparation method of the carbon-silicon material according to claim 1 or 2, characterized in that it comprises the following steps: Preparing a carbon coating layer formed by gaseous polycyclic aromatic hydrocarbons with a molecular weight ≥ 1000 on the surface of the silicon-carbon particles.

4. The preparation method according to claim 3, characterized in that the preparation of the carbon coating layer includes: preheating a first mixed gas of a carbon source and a first carrier gas and then depositing it on the surface of the silicon-carbon particles; the preheating temperature of the first mixed gas is 800-1100 °C.

5. The preparation method according to claim 4, characterized in that the flow rate of the carbon source is 1-2.5 L / min, and the flow rate of the first carrier gas is 2.5-4 L / min; Preferably, the carbon source includes gaseous hydrocarbon substances having 1 to 4 carbon atoms, and / or the first carrier gas includes an inert gas.

6. The preparation method according to claim 4, characterized in that before introducing the preheated first mixed gas, the temperature in the reactor where the silicon-carbon particles are located is 500-580 °C; and / or the deposition time of the preheated first mixed gas on the silicon-carbon particles is 1-2 h.

7. The preparation method according to any one of claims 3-6, characterized in that the preparation of the silicon-carbon particles includes: depositing and reacting a second mixed gas of a silicon source and a second carrier gas with porous carbon.

8. The preparation method according to claim 7, characterized in that the flow rate of the silicon source is 0.5-2 L / min, and the flow rate of the second carrier gas is 3-5 L / min; Preferably, the silicon source includes silane, and / or the second carrier gas includes an inert gas.

9. The preparation method according to claim 7, characterized in that before introducing the second mixed gas, the temperature in the reactor where the porous carbon is located is 430-480 °C; and / or the deposition reaction time of the second mixed gas and the porous carbon is 2-4 h.

10. A battery, characterized in that the battery contains the carbon-silicon material according to claim 1 or 2; Preferably, the battery has at least one of the following characteristics: Characteristic one: the initial efficiency ≥ 90.5%; Characteristic two: the 0.1C charge specific capacity ≥ 1890 mAh / g; Characteristic three: the 0.1C discharge specific capacity ≥ 2000 mAh / g; Characteristic four: the 1C charge specific capacity ≥ 1800 mAh / g; Characteristic five: the 3C charge specific capacity ≥ 1500 mAh / g; Characteristic six: the cycle retention rate after 50 cycles under the conditions of 25 °C and 0.005-2 V ≥ 93.5%; Feature Seven: The capacity retention rate after being stored for 7 days at 45°C is ≥ 86.5%.

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