Silicon-carbon negative electrode material and preparation method therefor, negative electrode sheet, and secondary battery

Abstract

Disclosed in the present invention are a silicon-carbon negative electrode material and a preparation method therefor, a negative electrode sheet, and a secondary battery. The preparation method for the silicon-carbon negative electrode material comprises: using a carbon source (or a carbon source precursor) as a raw material for carbonization treatment to obtain a precursor, performing two activation treatments on the precursor to obtain porous carbon, and then using the porous carbon as a substrate to sequentially perform silicon deposition and carbon deposition so as to obtain the silicon-carbon negative electrode material. In the two activation treatments, the first activation treatment relates to using water vapor as an activator, and the second activation treatment relates to using carbon dioxide (or carbon monoxide) as an activator. By controlling different process parameters of the two activation treatments, two silicon-carbon negative electrode materials having different microscopic shapes are respectively prepared by accurately regulating and controlling a pore channel structure of a porous carbon substrate, and micropores having different pore sizes in the porous carbon substrate. The two silicon-carbon negative electrode materials both have high cycling stability, high capacity, and high initial coulombic efficiency, and can be applied to lithium-ion secondary batteries, sodium-ion secondary batteries, and the like.

Description

Silicon-carbon negative electrode material, negative electrode sheet, secondary battery and preparation method thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of secondary batteries, and particularly relates to a silicon-carbon negative electrode material, a negative electrode sheet, a secondary battery and a preparation method thereof. BACKGROUND

[0002] Silicon is currently the negative electrode material with the largest theoretical capacity, with a specific capacity as high as 4200 mAh / g, far higher than the theoretical capacity of graphite (the theoretical capacity of graphite negative electrode material is only 372 mAh / g), and has the advantages of low lithium intercalation potential and low cost, and is expected to replace graphite to become the next generation of lithium ion battery negative electrode material. However, during the electrochemical cycle process of silicon as a negative electrode material, the intercalation and deintercalation of lithium ions will cause the material to expand and shrink by more than 300%, and the mechanical force generated will cause the material to gradually pulverize, resulting in structural collapse, ultimately leading to the separation of the electrode active material and the current collector, losing electrical contact, and resulting in a significant reduction in battery cycle performance. In addition, due to this volume effect, silicon is difficult to form a stable solid electrolyte interface (SEI) film in the electrolyte. With the destruction of the electrode structure, new SEI films are continuously formed on the exposed silicon surface, exacerbating the corrosion and capacity decay of silicon.

[0003] Currently, the negative electrode industry focuses on the strategy of using chemical vapor deposition process to prepare silicon-carbon materials on a porous carbon substrate, which can provide high electrical conductivity and alleviate the severe volume expansion / contraction of silicon during lithium intercalation / deintercalation. However, the negative electrode material obtained by the existing silicon-carbon composite method has poor cycle performance, and the porous substrate has limited expansion restriction effect on nano-silicon particles.

[0004] A negative electrode material, a preparation method and application are disclosed in Chinese patent document CN 118431452 A, which includes a porous substrate, silicon elements distributed in the pores of the porous substrate, and carbon coated on the surface of the porous substrate. The preparation method includes first placing the porous substrate in an environment containing a silicon source gas for low-temperature adsorption, then performing high-temperature pyrolysis on the porous substrate adsorbed with the silicon source gas to obtain a porous substrate loaded with nano-silicon in the pore structure, and finally performing carbon coating. This scheme uses the method of adsorption followed by decomposition to adsorb silane gas to the inner wall of the substrate pore, and then uses the hydrogen gas released by the decomposition of silane gas to further provide a buffer space for nano-silicon particles; however, the buffer space provided by this method is formed by the decomposition of silane gas to release hydrogen gas, which cannot actively control the size of the reserved pores, cannot effectively control the structure of the reserved pores, and does not effectively alleviate the volume expansion of nano-silicon particles from the substrate.

[0005] Therefore, how to prepare from the perspective of the base, from the pore shape, structure, pore size distribution of the porous carbon, increase the adjustment of micropores, etc., is crucial for the effective adsorption of silane molecules and the relief of silicon volume expansion. SUMMARY

[0006] To solve the above problems, the application discloses a preparation method of a silicon-carbon negative electrode material, which uses a carbon source precursor as a raw material, and performs two activation treatments, and controls the specific process parameters in the two activation processes in different ranges to prepare a porous carbon base from different angles of the pore structure of the porous carbon base and the accurate control of micropores with different pore sizes in the porous carbon base, further prepares a silicon-carbon negative electrode material, and assembles a secondary battery to obtain a silicon-carbon negative electrode material with low expansion rate, high cycle stability, high capacity, and high initial efficiency.

[0007] To achieve the above object, the specific technical solutions of the application are as follows.

[0008] In a first aspect, the application provides a preparation method of a silicon-carbon negative electrode material, comprising:

[0009] S1: carbonizing a carbon source to obtain a precursor;

[0010] S2: activating the precursor in the presence of a first activator to obtain a first activation product;

[0011] S3: performing secondary activation treatment on the first activation product in the presence of a second activator to obtain a porous carbon;

[0012] S4: using the porous carbon prepared in step S3 as a base, sequentially performing silicon deposition and carbon deposition to obtain the silicon-carbon negative electrode material.

[0013] In an optional embodiment, in step S2, the first activator is selected from water vapor;

[0014] In an optional embodiment, in step S3, the second activator is selected from CO and / or CO2; optionally, CO2;

[0015] In a second aspect, the application further provides a preparation method of a silicon-carbon negative electrode material, comprising the following steps:

[0016] (S1) performing high-temperature carbonization treatment on a carbon source precursor, and then performing two activation treatments to obtain a porous carbon material;

[0017] The two activation treatments are primary activation with water vapor as an activator and secondary activation with carbon dioxide as an activator;

[0018] (S2) using the porous carbon material as a base, performing silicon deposition to obtain a porous carbon base loaded with nano-silicon particles;

[0019] (S3) performing carbon-coating treatment to obtain the silicon-carbon negative electrode material.

[0020] The preparation methods of the above-mentioned silicon-carbon negative electrode material are essentially the same, both of which use a carbon source (the carbon source and the carbon source precursor are the same substance, only the naming is different) as a raw material, perform twice activation treatment to prepare a porous carbon material, the first activation treatment uses steam as an activation agent, and the second activation treatment uses carbon dioxide (or carbon monoxide) as an activation agent. However, the two methods differ in that the specific process parameters for the twice activation treatment are not the same, and based on the above differences, the prepared porous carbon substrate is regulated from different angles.

[0021] In an optional embodiment, in step S1 or (S1):

[0022] The carbon source (or carbon source precursor) is selected from one or more of biomass, high molecular polymer, coal-based, petroleum-based;

[0023] Optionally, the biomass is selected from at least one of the following or a combination thereof: coconut shell, straw, rice husk, wood, bamboo, sugarcane residue, nut shell, etc.

[0024] Optionally, the high molecular polymer is selected from the common polymer categories in the art without special limitation, and specifically includes polyethylene, polyurethane, epoxy resin, phenolic resin, urea-formaldehyde resin, etc.

[0025] Optionally, the coal-based is selected from the common categories in the art, such as coal tar pitch, coal tar, etc.

[0026] Optionally, the petroleum-based is selected from the common categories in the art, such as petroleum coke, paraffin, etc.

[0027] In an optional embodiment, the temperature and time of the carbonization treatment are adaptively adjusted according to the type of the carbon source in the art.

[0028] Optionally, the temperature of the (high-temperature) carbonization treatment is 500-1500℃; more optionally, the temperature is 800-1500℃; or, more optionally, the temperature is 700-900℃.

[0029] Optionally, the time of the (high-temperature) carbonization treatment is 1-20h; or 6-12h.

[0030] Optionally, the heating rate of the (high-temperature) carbonization treatment is 1-20℃ / min, or 10-20℃ / min.

[0031] In the preparation method of the silicon-carbon negative electrode material provided in the above-mentioned first aspect:

[0032] In step S2

[0033] In an optional embodiment, the flow rate of the first activating agent is 1-20 kg / h; optionally, 1-10 kg / h.

[0034] In an optional embodiment, the temperature of the activation treatment is 500-1200 °C; optionally, 500-800 °C.

[0035] In an optional embodiment, the pressure of the activation treatment is 0.1-10 Kpa; optionally, 1-10 Kpa.

[0036] In an optional embodiment, the time of the activation treatment is 1-10 h.

[0037] Optionally, the mass ratio of the first activating agent to the precursor in the activation treatment in step S2 is 100:(1-20).

[0038] In an optional embodiment, the secondary activation treatment in step S3 comprises at least one of the following features (I)-(V):

[0039] (I) The temperature of the secondary activation treatment is 500-1200 °C; optionally, 650-1000 °C.

[0040] (II) The pressure of the secondary activation treatment is 0.1-10 Kpa; optionally, 1-8 Kpa.

[0041] (III) The time of the secondary activation treatment is 0.5-10 h.

[0042] (IV) The flow rate of the second activating agent is 1-20 kg / h; optionally, 1-10 kg / h.

[0043] (V) The secondary activation treatment is preceded by vacuum extraction.

[0044] Optionally, the mass ratio of the first activating product to the second activating agent in the secondary activation treatment in step S3 is 100:(0.1-10).

[0045] In the method for preparing the silicon-carbon negative electrode material provided in the second aspect above:

[0046] In an optional embodiment, in step (S1),

[0047] The mass ratio of the carbon source precursor to water vapor in the initial activation is (0.5-5.0):1; optionally, the mass ratio of the carbon source precursor to water vapor is (0.625-5.0):1; further optionally, the mass ratio of the carbon source precursor to water vapor is (1.875-5.0):1; more optionally, the mass ratio is 1.875:1.

[0048] In an optional embodiment, the flow rate of water vapor is 0.05-1 kg / h; optionally, the flow rate of water vapor is 0.25-1 kg / h.

[0049] Optionally, the temperature of the primary activation is 700-900℃.

[0050] Optionally, the heating rate is selected from 10-20℃ / min.

[0051] Optionally, the time of the primary activation is 6-12h.

[0052] In an optional embodiment, the mass ratio of the carbon source precursor to carbon dioxide in the re-activation is (0.3-5.0):1; optionally, the mass ratio of the carbon source precursor to carbon dioxide is (0.375-5.0):1; further optionally, the mass ratio of the carbon source precursor to carbon dioxide is (0.75-5.0):1; more optionally, the mass ratio is 1.875:1.

[0053] In an optional embodiment, the flow rate of carbon dioxide is 0.05-2 kg / h; optionally, the flow rate of carbon dioxide is 0.25-2 kg / h.

[0054] Optionally, the temperature of the re-activation is 900-1200℃.

[0055] Optionally, the heating rate is selected from 10-20℃ / min.

[0056] Optionally, the time of the re-activation is 6-12h.

[0057] In the above two preparation methods of silicon-carbon negative electrode materials, the process of silicon deposition and carbon deposition (or carbon coating) is the same, only the process parameters are slightly different.

[0058] In an optional embodiment, in step S4 or (S2), the silicon deposition is:

[0059] Specifically, the porous carbon material substrate is placed in a raw gas (or gas source) environment containing a silicon source gas for vapor deposition;

[0060] The gas source (or raw gas) used includes a silicon source gas, an inert atmosphere, and an optionally added second gas source;

[0061] Optionally, the silicon source gas is selected from the conventional types in the art, including one or more of monosilane, disilane, dichlorodisilane, and trichlorosilane;

[0062] The inert atmosphere serves as a carrier gas, and is optionally selected from argon, helium, and other inert gases;

[0063] In an optional embodiment, in step S4:

[0064] The proportion of the silicon source gas is 30-90 vol%; optionally, the proportion is 50-80 vol%;

[0065] The total flow rate of the gas source is 1-100 L / min; optionally, the total flow rate is 5-50 L / min;

[0066] The temperature for the silicon deposition is 400-1000 ℃, and the time is 1-50 h; optionally, the temperature for the silicon deposition is 400-600 ℃; more optionally, the temperature for the silicon deposition is 500 ℃;

[0067] The second gas source is selected from one or more of a carbon source gas, a nitrogen source gas, a sulfur source gas, and a phosphorus source gas;

[0068] Optionally, the carbon source gas is selected from an alkane gas with a cracking temperature in the range of the carbon deposition temperature, specifically common types such as ethylene and acetylene;

[0069] Optionally, the nitrogen source gas is selected from ammonia;

[0070] Optionally, the sulfur source gas is selected from one or more of hydrogen sulfide, sulfur dioxide, and sulfur hexafluoride;

[0071] Optionally, the phosphorus source gas is selected from one or more of phosphine, phosphorus chloride, and phosphorus fluoride;

[0072] The second gas source can be co-deposited after being blended with the silicon source gas, or can be alternately deposited with the silicon source gas.

[0073] Optionally, when co-deposition is performed, the proportion of the silicon source gas is 30-80 vol%, the proportion of the second gas source is 10-30 vol%, and the balance is an inert atmosphere; more optionally, the proportion of the silicon source gas is 50-80 vol%, the proportion of the second gas source is 15-25 vol%, and the balance is an inert atmosphere;

[0074] Optionally, when alternately deposition is performed, the proportion of the second gas source in the mixed gas composed of the second gas source and an inert atmosphere is 30-80 vol%; more optionally, the proportion of the second gas source is 40-70 vol%.

[0075] In the optional embodiment, in step (S2):

[0076] Optionally, the temperature for the silicon deposition is 400-600 ℃;

[0077] Optionally, the flow rate of the raw gas containing the silicon source gas is 1-30 L / h; further optionally, the flow rate is 10-30 L / h;

[0078] Optionally, the raw gas containing the silicon source gas further contains an inert gas, and the volume ratio of the inert gas is 0-30%;

[0079] Optionally, the silicon deposition is performed for 18-36 hours.

[0080] Optionally, the silicon deposition is performed after the temperature is raised to 400-600°C at a temperature raising rate of 10-20°C / min and then kept for 0.5-2 hours.

[0081] In the optional embodiment, in step S4 or (S3):

[0082] The carbon coating (carbon deposition) treatment is performed by placing the product after the silicon deposition in a raw gas (or gas source) environment containing a carbon source gas, and then performing vapor deposition.

[0083] The carbon deposition (carbon coating) is performed at a temperature of 300-1200°C for 2-20 hours.

[0084] Optionally, the temperature is 500-700°C.

[0085] The gas source used in the carbon deposition includes a carbon source gas and a carrier gas, and the volume ratio of the carbon source gas is 50-99 vol%; optionally, the volume ratio of the carbon source gas is 60-80 vol%.

[0086] Optionally, the carbon source gas is selected from alkanes with a cracking temperature in the range of the carbon deposition temperature.

[0087] Optionally, the carbon source gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes, and C2-C4 alkynes; optionally, the C1-C4 alkanes are selected from methane, ethane, propane, and butane; optionally, the C2-C4 alkenes are selected from ethylene, propylene, butylene, and 1,3-butadiene; and optionally, the C2-C4 alkynes are selected from acetylene, propyne, and butyne.

[0088] Optionally, the flow rate of the raw gas containing the carbon source gas is 1-20 L / h; further optionally, the flow rate is 5-15 L / h.

[0089] Optionally, the carrier gas is selected from argon, argon, nitrogen, and the like.

[0090] Optionally, the carbon coating (carbon deposition) treatment is performed after the temperature is raised to 500-700°C at a temperature raising rate of 10-20°C / min and then kept for 0.5-2 hours.

[0091] In the preparation method of the silicon-carbon negative electrode material provided in the first aspect, the porous carbon substrate with a dendritic-like pore structure is prepared through special secondary activation. The primary activation treatment uses water vapor as the activation agent to form uniform mesopores in the substrate, so that the average pore size of the pore structure is maintained at 3-20 nm. On the basis of the primary pore formation, the porous carbon substrate is used to adsorb carbon dioxide and / or carbon monoxide, which is used as a secondary pore-forming agent for secondary pore formation. Since the carbon-oxygen double bond exists in both of them, the pores are re-formed in the adsorbed pores, and micropores with a pore size of 0.4-2.0 nm are formed, thereby forming a dendritic-like pore channel. The primary activation pore formation enables the porous carbon substrate to have a good deposition channel, and the secondary activation pore formation can effectively form uniform micropores around the mesopores. These micropores can not only provide more space for the deposition of nanosilicon, but also (especially for the extremely small micropores with a size of less than 1 nm) provide additional buffer space for the expansion of nanosilicon particles in the subsequent assembly battery cycle process, and provide more pore structures for the transmission of lithium ions. In this way, the high reversible capacity and the charge-discharge efficiency are ensured, and the overall cycle stability of the silicon-carbon negative electrode material is further improved.

[0092] It has been found through experiments that if only the water vapor is used for the primary activation pore formation, or only the carbon dioxide and / or carbon monoxide is used for the primary activation pore formation, or the order of the two activation pore formations is changed, the negative electrode material with high capacity, high initial efficiency and excellent cycle stability cannot be prepared.

[0093] In a third aspect, the present application further provides a silicon-carbon negative electrode material prepared by the method provided in the first aspect, which comprises a porous carbon substrate, silicon elements distributed in the pore channels of the porous carbon substrate, and carbon coating the outer surfaces of the porous carbon substrate and the silicon elements.

[0094] The porous carbon substrate is prepared through two activation treatments, has a dendritic-like pore channel, and satisfies at least one of the following conditions a-f:

[0095] a. The volume fraction of micropores is 10-30%;

[0096] b. The volume fraction of mesopores is 60-90%;

[0097] c. The volume fraction of macropores is 0-10%;

[0098] d. The specific surface area is not less than 200 m 2 / g, and is optionally 200-4000 m 2 / g;

[0099] e. The pore volume is not less than 0.4 cm 3 / g, and is optionally 0.4-2.0 cm 3 / g;

[0100] f. The average particle size D50 is 1-20 μm.

[0101] In an optional embodiment, the average pore size D50 of the silicon-carbon negative electrode material is 6-9 μm.

[0102] And / or, the specific surface area of the silicon-carbon negative electrode material is less than 10 m 2 / g, optionally less than 5 m 2 / g.

[0103] And / or, the tap density of the silicon-carbon negative electrode material is 0.8-1.1 g / cm 3 .

[0104] In the preparation method of the silicon-carbon negative electrode material provided in the above second aspect, the porous carbon material is prepared by a special secondary activation method, the porous carbon material is mainly microporous, the proportion of micropores is as high as 95% or more, and micropores of different pore sizes are further divided into three categories and the proportions of each category; the composition of micropores in the prepared porous carbon material can be adjusted by adjusting the process parameters of the two activation treatments in the preparation method. By accurately adjusting the micropores of different pore sizes, the electrochemical performance of the secondary battery is accurately adjusted to prepare a negative electrode material with low expansion rate, high cycle stability, high capacity and high initial efficiency.

[0105] In a fourth aspect, the present application further provides a silicon-carbon negative electrode material prepared by the method provided in the above second aspect, taking a porous carbon material as a substrate, further comprising nano-silicon particles distributed in the pores of the porous carbon material, and a carbon coating layer on the outermost layer:

[0106] The porous carbon material:

[0107] The proportion of micropores in the total pore volume is ≥95%, and the micropores are pores with a pore size ≤2 nm;

[0108] The proportion of micropores with a pore size of 0-0.44 nm is denoted as X%, and 0.5≤X≤5.0;

[0109] The proportion of micropores with a pore size of 0.44-1.32 nm is denoted as Y%, and 65≤Y≤90;

[0110] The proportion of micropores with a pore size of 1.32-2 nm is denoted as Z%, and 5≤Z≤30;

[0111] And X+Y+Z=100.

[0112] In an optional embodiment, the average pore size of the porous carbon material is 1.5±0.3 nm.

[0113] And at least one of the following conditions is met:

[0114] (1) a specific surface area of 1500-2200 m 2 / g;

[0115] (2) a pore volume of 0.7-1.3 cm 3 / g;

[0116] (3) a particle size Dv50 of 7.0±1.0 μm.

[0117] In an optional embodiment, the porous carbon material satisfies at least one of the following conditions:

[0118] (1) 0.5≤X≤2.0; optionally, 0.5≤X≤1.5;

[0119] (2) 69≤Y≤90; optionally, 69≤Y≤80;

[0120] (3) 8≤Z≤30; optionally, 19≤Z≤30.

[0121] In an optional embodiment, the silicon-carbon negative electrode material satisfies at least one of the following conditions:

[0122] (a) a Dv50 of 7.0±1.0 μm;

[0123] (b) a specific surface area of 3±2 m 2 / g;

[0124] (c) a powder resistance of <10 Ω-cm at 20 MPa;

[0125] (d) a tap density of 0.9±0.05 g / cm 3 .

[0126] In a fifth aspect, the present application further provides a negative electrode sheet, comprising the two silicon-carbon negative electrode materials with different micro-morphologies prepared by the above two methods.

[0127] In a sixth aspect, the present application further provides a secondary battery, comprising the above negative electrode sheet. The secondary battery includes a lithium ion battery, a sodium ion battery, etc.

[0128] Compared with the prior art, the present application has the following beneficial results:

[0129] The present application discloses a silicon-carbon negative electrode material, which takes a porous carbon material with a dendritic-like pore after secondary activation treatment as a substrate. The structural characteristics of the porous carbon material substrate prepared by a special activation process not only provide more space for the deposition of nano-silicon, but also provide additional buffer space for the expansion of nano-silicon particles in the subsequent battery assembly cycle process, and provide more pore structures for the transmission of lithium or sodium ions. While ensuring high reversible capacity and charge-discharge efficiency, the overall cycle stability of the silicon-carbon negative electrode material is further improved.

[0130] The application also discloses a silicon-carbon negative electrode material, which is also a porous carbon material after secondary activation treatment, and the porous carbon material focuses on adjustment of a pore structure, mainly micropores, and micropores account for 95% or above, and micropores of different pore sizes are further divided into three categories and the proportions of the three categories are clear; the electrochemical performance of the secondary battery is accurately controlled by accurately controlling micropores of different pore sizes, so that the negative electrode material with low expansion rate, high cycle stability, high capacity and high initial efficiency is prepared. BRIEF DESCRIPTION OF DRAWINGS

[0131] Figure 1 is a structural schematic diagram of a first activation product obtained after a primary activation treatment in Example 1;

[0132] Figure 2 is a structural schematic diagram of a porous carbon obtained after a secondary activation treatment in Example 1;

[0133] In the figure, 1 is a precursor substrate, 2 is a mesopore channel in the precursor substrate, and 3 is a micropore channel in the precursor substrate. DETAILED DESCRIPTION

[0134] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the application.

[0135] In the description of the application, it should be noted that the specific meanings of the above-mentioned terms in the application can be understood according to specific circumstances by those skilled in the art. The embodiments thereof will be described below according to the overall structure of the application. Unless otherwise specified, the raw materials in the embodiments of the application are purchased through commercial channels.

[0136] In a first aspect, the application provides a preparation method of a silicon-carbon negative electrode material, comprising:

[0137] S1: carbonizing a carbon source to obtain a precursor;

[0138] S2: activating the precursor in the presence of a first activator to obtain a first activation product;

[0139] S3: secondary activating the first activation product in the presence of a second activator to obtain a porous carbon;

[0140] S4: taking the porous carbon prepared in step S3 as a substrate, sequentially depositing silicon and carbon to obtain the silicon-carbon negative electrode material.

[0141] In an optional embodiment, in step S2, the first activating agent is selected from water vapor;

[0142] In an optional embodiment, in step S3, the second activating agent is selected from CO and / or CO2; optionally, CO2;

[0143] In a second aspect, the present application also provides a preparation method of a silicon-carbon negative electrode material, comprising the following steps:

[0144] (S1) performing high-temperature carbonization treatment on a carbon source precursor, and then performing twice activation treatment to obtain a porous carbon material;

[0145] The twice activation treatment is that the first activation treatment uses water vapor as the activating agent, and the second activation treatment uses carbon dioxide as the activating agent;

[0146] (S2) performing silicon deposition on the porous carbon material as a substrate to obtain a porous carbon substrate loaded with nano-silicon particles;

[0147] (S3) performing carbon coating treatment to obtain a silicon-carbon negative electrode material.

[0148] The preparation methods of the above silicon-carbon negative electrode materials are essentially the same, and all use a carbon source (the carbon source and the carbon source precursor are the same substance, only the names are different) as a raw material, perform twice activation treatment to obtain a porous carbon material, the first activation treatment uses water vapor as the activating agent, and the second activation treatment uses carbon dioxide (or carbon monoxide) as the activating agent. However, the two methods differ in that the specific process parameters for the twice activation treatment are not the same, and based on the above differences, the prepared porous carbon substrate is regulated from different angles.

[0149] In an optional embodiment, in step S1 or (S1):

[0150] The carbon source (or carbon source precursor) is selected from one or more of biomass, high molecular polymer, coal-based, and petroleum-based; all of the above substances contain abundant carbon elements, and after high-temperature carbonization, the carbon elements are converted into coke, which is used as a precursor for preparing a porous carbon in the next step.

[0151] In an optional embodiment, the biomass is selected from at least one of the following or a combination thereof: coconut shell, straw, rice husk, wood, bamboo, sugarcane residue, nut shell, etc.

[0152] In an optional embodiment, the high molecular polymer is selected from common polymer types in the art without special limitation, and is specifically polyethylene, polyurethane, epoxy resin, phenolic resin, urea-formaldehyde resin, etc.

[0153] In an optional embodiment, the coal-based is selected from common types in the art, such as coal pitch and coal tar, etc.

[0154] In optional embodiments, the petroleum-based is selected from the common types in the art, such as petroleum coke, paraffin, etc.

[0155] In optional embodiments, the carbonization treatment, in particular the temperature and time, is adapted according to the type of carbon source used.

[0156] In optional embodiments, the temperature of the (high-temperature) carbonization treatment is 500-1500℃; in particular, it can be 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, or any value within the above range; the carbonization treatment needs to provide a relatively high temperature to ensure complete carbonization of the carbon source; more optionally, the temperature is 800-1500℃; or, more optionally, the temperature is 700-900℃.

[0157] In optional embodiments, the time of the (high-temperature) carbonization treatment is 1-20h; in particular, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, or any value within the above range.

[0158] In optional embodiments, the heating rate of the (high-temperature) carbonization treatment is 1-20℃ / min, or 10-20℃ / min; in particular, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min, 20℃ / min, or any value within the above range.

[0159] In the method for preparing the silicon-carbon negative electrode material provided in the first aspect above:

[0160] In optional embodiments, in step S2, the activation treatment comprises at least one of the following features:

[0161] In optional embodiments, the first activation agent is selected from water vapor; it has been found through experiments that the use of water vapor as an activation agent can create uniform mesopores in the precursor.

[0162] The flow rate of the first activating agent is 1-20 kg / h; specifically, it can be 1 kg / h, 2 kg / h, 3 kg / h, 4 kg / h, 5 kg / h, 6 kg / h, 7 kg / h, 8 kg / h, 9 kg / h, 10 kg / h, 11 kg / h, 12 kg / h, 13 kg / h, 14 kg / h, 15 kg / h, 16 kg / h, 17 kg / h, 18 kg / h, 19 kg / h, 20 kg / h, or any value within the above range. Alternatively, it is 1-10 kg / h; more alternatively, it is 1-5 kg / h.

[0163] The activation treatment has a temperature of 500-1200℃; specifically, it can be 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, or any value within the above range; a too high activation treatment temperature results in too fast reaction speed, and the reaction degree is difficult to control; a too low activation treatment temperature results in poor activation effect; alternatively, the activation treatment temperature is 500-800℃.

[0164] The activation treatment has a pressure of 0.1-10 Kpa; specifically, it can be 0.1 Kpa, 1 Kpa, 2 Kpa, 3 Kpa, 4 Kpa, 5 Kpa, 6 Kpa, 7 Kpa, 8 Kpa, 9 Kpa, 10 Kpa, or any value within the above range; alternatively, the activation treatment pressure is 1-10 Kpa; more alternatively, the activation treatment pressure is 3-8 Kpa.

[0165] The activation treatment has a time of 1-10 h; specifically, it can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or any value within the above range; a too long activation treatment time results in too high activation degree, and the mechanical properties of the substrate become poor; a too short activation treatment time results in poor activation effect, and it is difficult to provide a good pore channel basis for secondary activation, affecting the secondary activation effect; alternatively, the activation treatment time is 3-8 h.

[0166] In a more alternative embodiment, the activation treatment has a temperature of 500-700℃, a pressure of 4-6 Kpa, and a time of 4-7 h.

[0167] Alternatively, the mass ratio of the first activating agent to the precursor in the activation treatment in step S2 is 100:(1-20); specifically, it can be 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, 100:16, 100:17, 100:18, 100:19, 100:20, or any ratio within the above range.

[0168] In optional embodiments, in step S3, the secondary activation treatment comprises at least one of the following features:

[0169] In optional embodiments, the second activation agent is selected from CO and / or CO2; it is found by experiments that using CO and / or CO2 as the activation agent for secondary pore formation, because both of them have carbon-oxygen double bonds, they can form micropores in the adsorbed pores and form dendritic-like channels; optionally, the second activation agent is selected from CO2.

[0170] The secondary activation treatment has a temperature of 500-1200°C; specifically, it can be 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, or any value within the above range; if the secondary activation treatment temperature is too high, the reaction speed is too fast, and the reaction degree is difficult to control; if it is too low, the activation effect is poor; optionally, the secondary activation treatment temperature is 650-1000°C.

[0171] The secondary activation treatment has a pressure of 0.1-10 KPa; specifically, it can be 0.1 KPa, 1 KPa, 2 KPa, 3 KPa, 4 KPa, 5 KPa, 6 KPa, 7 KPa, 8 KPa, 9 KPa, 10 KPa, or any value within the above range; optionally, the secondary activation treatment pressure is 1-8 KPa.

[0172] The secondary activation treatment has a time of 0.5-10 h; specifically, it can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or any value within the above range; if the secondary activation treatment time is too long, it will damage the pore structure of the substrate, resulting in poor mechanical properties of the substrate; if it is too short, the secondary pore formation effect is poor, and the pore structure change is not obvious; optionally, the secondary activation treatment time is 0.5-6 h.

[0173] In more optional embodiments, the secondary activation treatment has a temperature of 700-900°C, a pressure of 3-6 KPa, and a time of 0.5-4 h.

[0174] The secondary activation treatment has a flow rate of the second activation agent of 1-20 kg / h; specifically, it can be 1 kg / h, 2 kg / h, 3 kg / h, 4 kg / h, 5 kg / h, 6 kg / h, 7 kg / h, 8 kg / h, 9 kg / h, 10 kg / h, 11 kg / h, 12 kg / h, 13 kg / h, 14 kg / h, 15 kg / h, 16 kg / h, 17 kg / h, 18 kg / h, 19 kg / h, 20 kg / h, or any value within the above range; optionally, it is 1-10 kg / h; more optionally, it is 1-5 kg / h.

[0175] In an optional embodiment, the second activating agent is introduced after vacuumizing. By vacuumizing first and then introducing the second activating agent, the second activating agent is more likely to enter the interior of the mesopores formed in the first activation under the action of negative pressure, and the secondary poration is carried out in the interior of the mesopores, thereby providing additional buffer space for the expansion of the nano-silicon particles in the subsequent battery cycle process. This method is more controllable for the poration area, and can further improve the cycle stability of the secondary battery.

[0176] In an optional embodiment, the mass ratio of the first activation product to the second activating agent in the secondary activation treatment is 100:(0.1-10); specifically, it can be 100:0.1, 100:0.5, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, or any ratio within the above range.

[0177] In the preparation method of the silicon-carbon negative electrode material provided in the above second aspect:

[0178] In an optional embodiment, in step (S1),

[0179] The mass ratio of the carbon source precursor to the water vapor in the primary activation is (0.5-5.0):1; optionally, the mass ratio of the carbon source precursor to the water vapor is (0.625-5.0):1; further optionally, the mass ratio of the carbon source precursor to the water vapor is (1.875-5.0):1; more optionally, the mass ratio is 1.875:1.

[0180] In an optional embodiment, the flow rate of the water vapor is 0.05-1 kg / h; specifically, it can be 0.05 kg / h, 0.10 kg / h, 0.15 kg / h, 0.20 kg / h, 0.25 kg / h, 0.30 kg / h, 0.35 kg / h, 0.40 kg / h, 0.45 kg / h, 0.50 kg / h, 0.60 kg / h, 0.70 kg / h, 0.80 kg / h, 0.90 kg / h, 1.00 kg / h, or any value within the above range; optionally, the flow rate of the water vapor is 0.25-1 kg / h.

[0181] Optionally, the temperature in the primary activation is 700-900℃; specifically, it can be 700℃, 720℃, 750℃, 780℃, 800℃, 820℃, 850℃, 880℃, 900℃, or any value within the above range;

[0182] Optionally, the temperature rising rate is selected from 10-20℃ / min; specifically, it can be 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min, 20℃ / min or any value within the above range.

[0183] Optionally, the initial activation time is 6-12h; specifically, it can be 6h, 7h, 8h, 9h, 10h, 11h, 12h or any value within the above range.

[0184] In an optional embodiment, the mass ratio of carbon source precursor to carbon dioxide in the reactivation is (0.3-5.0):1; specifically, it can be 0.3:1, 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, 5.0:1 or any ratio within the above range; optionally, the mass ratio of carbon source precursor to carbon dioxide is (0.375-5.0):1; further optionally, the mass ratio of carbon source precursor to carbon dioxide is (0.75-5.0):1; more optionally, the mass ratio is 1.875:1.

[0185] In an optional embodiment, the flow rate of carbon dioxide is 0.05-2kg / h; specifically, it can be 0.05kg / h, 0.10kg / h, 0.15kg / h, 0.20kg / h, 0.25kg / h, 0.30kg / h, 0.35kg / h, 0.40kg / h, 0.45kg / h, 0.50kg / h, 0.80kg / h, 1.0kg / h, 1.5kg / h, 2.0kg / h or any value within the above range; optionally, the flow rate of carbon dioxide is 0.25-2kg / h.

[0186] In an optional embodiment, the temperature in the reactivation is 900-1200℃; specifically, it can be 900℃, 920℃, 950℃, 980℃, 1000℃, 1020℃, 1050℃, 1080℃, 1100℃, 1120℃, 1150℃, 1180℃, 1200℃ or any value within the above range.

[0187] In an optional embodiment, the temperature rising rate is selected from 10-20℃ / min; specifically, it can be 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min, 20℃ / min or any value within the above range.

[0188] In an optional embodiment, the reactivation is performed for 6-12 hours; specifically, it can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or any value within the above range.

[0189] In the above two preparation methods of the silicon-carbon negative electrode material, the process of silicon deposition and carbon deposition (or carbon coating) is the same, only the process parameters are slightly different.

[0190] In an optional embodiment, in step S4 or (S2), the silicon deposition is performed by:

[0191] Specifically, the porous carbon material substrate is placed in a raw gas (or gas source) environment containing a silicon source gas for vapor deposition.

[0192] The gas source (or raw gas) used includes a silicon source gas, an inert atmosphere, and an optional second gas source.

[0193] In an optional embodiment, the silicon source gas is selected from the conventional types in the art, including one or more of monosilane, disilane, dichlorodisilane, and trichlorosilane.

[0194] The inert atmosphere acts as a carrier gas, which can be added to improve the safety of vapor deposition. In an optional embodiment, it is selected from argon, helium, and other inert gases.

[0195] In an optional embodiment, in step S4:

[0196] The proportion of the silicon source gas is 30-90 vol%; specifically, it can be 30 vol%, 35 vol%, 40 vol%, 45 vol%, 50 vol%, 55 vol%, 60 vol%, 65 vol%, 70 vol%, 75 vol%, 80 vol%, 85 vol%, 90 vol%, or any value within the above range; optionally, the proportion is 50-80 vol%.

[0197] The total flow rate of the gas source is 1-100 L / min; specifically, it can be 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 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, 20 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min, 55 L / min, 60 L / min, 65 L / min, 70 L / min, 75 L / min, 80 L / min, 85 L / min, 90 L / min, 95 L / min, 100 L / min, or any value within the above range; optionally, the total flow rate of the gas source is 5-50 L / min; more optionally, the total flow rate of the gas source is 8-12 L / min.

[0198] In an optional embodiment, the temperature of the silicon deposition is 400-1000℃; specifically, it can be 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, or any value within the above range; a too high temperature of the silicon deposition will result in an excessively large size of the silicon crystalline domains, which is not conducive to the improvement of the cycle performance of the negative electrode material; optionally, the temperature of the silicon deposition is 400-600℃; more optionally, the temperature of the silicon deposition is 500℃.

[0199] In an optional embodiment, the time of the silicon deposition is 1-50 h; specifically, it can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h, 50 h, or any value within the above range. The time of the silicon deposition should be matched with the temperature of the silicon deposition; if the temperature of the silicon deposition is high, the deposition time is short; if the temperature of the silicon deposition is low, the deposition time is appropriately prolonged.

[0200] The addition of the second gas source can reduce the particle size of the silicon crystalline domains (i.e., nano-silicon particles), which is more conducive to the improvement of the cycle performance of the negative electrode material.

[0201] In an optional embodiment, the second gas source is selected from one or more of a carbon source gas, a nitrogen source gas, a sulfur source gas, and a phosphorus source gas.

[0202] In an optional embodiment, the carbon source gas is selected from an alkane gas with a cracking temperature within the carbon deposition temperature range, specifically, common types such as ethylene and acetylene.

[0203] In an optional embodiment, the nitrogen source gas is selected from ammonia.

[0204] In an optional embodiment, the sulfur source gas is selected from one or more of hydrogen sulfide, sulfur dioxide, sulfur hexafluoride.

[0205] In an optional embodiment, the phosphorus source gas is selected from one or more of phosphine, phosphorus chloride, phosphorus fluoride.

[0206] Optionally, the second gas source is selected from a carbon source gas and / or a nitrogen source gas; which is advantageous for further improving the electrical conductivity of the silicon-carbon negative electrode material and improving the rate performance of the negative electrode material.

[0207] In an optional embodiment, the second gas source can be co-deposited after being blended with the silicon source gas;

[0208] In an optional embodiment, during co-deposition, the proportion of the silicon source gas is 30-80 vol%; specifically, it can be 30 vol%, 35 vol%, 40 vol%, 45 vol%, 50 vol%, 55 vol%, 60 vol%, 65 vol%, 70 vol%, 75 vol%, 80 vol% or any value within the above range; optionally, the proportion of the silicon source gas is 50-80 vol%.

[0209] In an optional embodiment, during co-deposition, the proportion of the second gas source is 10-30 vol%; specifically, it can be 10 vol%, 15 vol%, 20 vol%, 25 vol%, 30 vol% or any value within the above range; optionally, the proportion of the second gas source is 15-25 vol%.

[0210] In an optional embodiment, during co-deposition, the balance is an inert atmosphere as a carrier gas.

[0211] In an optional embodiment, the second gas source can also be alternately deposited with the silicon source gas.

[0212] In an optional embodiment, during alternately deposition, in the mixed gas composed of the second gas source and an inert atmosphere, the proportion of the second gas source is 30-80 vol%; specifically, it can be 30 vol%, 35 vol%, 40 vol%, 45 vol%, 50 vol%, 55 vol%, 60 vol%, 65 vol%, 70 vol%, 75 vol%, 80 vol% or any value within the above range; optionally, the proportion of the second gas source is 40-70 vol%.

[0213] In an optional embodiment, in step (S2):

[0214] In an optional embodiment, the silicon deposition is performed at a temperature of 400-600°C; specifically, the temperature can be 400°C, 420°C, 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C, or any value within the range.

[0215] Optionally, the source gas containing the silicon source gas has a flow rate of 1-30 L / h; specifically, the flow rate can be 1 L / h, 3 L / h, 5 L / h, 8 L / h, 10 L / h, 12 L / h, 15 L / h, 18 L / h, 20 L / h, 22 L / h, 25 L / h, 28 L / h, 30 L / h, or any value within the range.

[0216] Optionally, the source gas containing the silicon source gas contains an inert gas, and the volume fraction of the inert gas is 0-30%; specifically, the volume fraction can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, or any value within the range.

[0217] Optionally, the silicon deposition is performed for 18-36 h; specifically, the time can be 18 h, 20 h, 24 h, 28 h, 32 h, 36 h, or any value within the range.

[0218] Optionally, the temperature is raised to 400-600°C at a rate of 10-20°C / min and then held for 0.5-2 h before the silicon deposition is performed.

[0219] In an optional embodiment, in step S4 or (S3):

[0220] The carbon coating (carbon deposition) treatment is performed by placing the product after the silicon deposition in a source gas (or gas source) environment containing a carbon source gas to perform vapor deposition.

[0221] In an optional embodiment, the carbon deposition (carbon coating) is performed at a temperature of 300-1200°C; specifically, the temperature can be 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, or any value within the range; a temperature that is too high can cause the particle size of the silicon crystal domains deposited in the previous step to increase, and a temperature that is too low can cause the conductivity of the carbon layer after deposition to decrease; optionally, the temperature is 500-700°C.

[0222] In an optional embodiment, the carbon deposition is performed for 2-20 h; specifically, the time can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, or any value within the range.

[0223] The carbon deposition uses a gas source including a carbon source gas and a carrier gas, and the carbon source gas accounts for 50-99 vol%; specifically, it can be 50 vol%, 55 vol%, 60 vol%, 65 vol%, 70 vol%, 75 vol%, 80 vol%, 85 vol%, 90 vol%, 95 vol%, 99 vol% or any value within the above range; optionally, the carbon source gas accounts for 60-80 vol%.

[0224] Optionally, the carbon source gas is selected from alkanes with a cracking temperature within the carbon deposition temperature range.

[0225] Optionally, the carbon source gas is selected from one or more of C1-C4 alkanes, C2-C4 alkenes and C2-C4 alkynes; optionally, the C1-C4 alkanes are selected from methane, ethane, propane and butane; optionally, the C2-C4 alkenes are selected from ethylene, propylene, butylene and 1,3-butadiene; optionally, the C2-C4 alkynes are selected from acetylene, propyne and butyne.

[0226] Optionally, the raw gas containing the carbon source gas has a flow rate of 1-20 L / h; specifically, it can be 1 L / h, 2 L / h, 5 L / h, 8 L / h, 10 L / h, 12 L / h, 15 L / h, 18 L / h, 20 L / h or any value within the above range; further optionally, the flow rate is 5-15 L / h.

[0227] Optionally, the carrier gas is selected from argon, argon, nitrogen and the like.

[0228] Optionally, the temperature is first raised to 500-700°C at a temperature raising rate of 10-20°C / min and then held for 0.5-2 h before the carbon coating (carbon deposition) treatment.

[0229] In the preparation method of the silicon-carbon negative electrode material provided in the first aspect, the porous carbon substrate with a dendritic-like pore structure is prepared through special secondary activation. The primary activation treatment uses water vapor as an activation agent to create uniform mesopores in the substrate, so that the average pore size of the pore structure is maintained at 3-20 nm. On the basis of the primary pore creation, the porous carbon substrate is used to adsorb carbon dioxide and / or carbon monoxide, which is used as a secondary pore creator for secondary pore creation. Since the carbon-oxygen double bond exists in both of them, the pores are created again in the adsorbed pores and micropores with a size of 0.4-2.0 nm are created, so as to form a dendritic-like pore channel. The primary activation pore creation enables the porous carbon substrate to have a good deposition channel, and the secondary activation pore creation can effectively create uniform micropores around the mesopores. The micropores can not only provide more space for the deposition of nanosilicon, but also (especially for the extremely small micropores with a size of less than 1 nm) provide additional buffer space for the expansion of nanosilicon particles in the subsequent assembly battery cycle process and provide more pore structures for the transmission of lithium ions. In this way, the high reversible capacity and the charge-discharge efficiency are ensured, and the overall cycle stability of the silicon-carbon negative electrode material is further improved.

[0230] It has been found through experiments that, if only the water vapor is used for the primary activation pore creation, or only the carbon dioxide and / or carbon monoxide is used for the primary activation pore creation, or the order of the two activation pore creations is changed, the negative electrode material with high capacity, high initial efficiency and excellent cycle stability cannot be prepared.

[0231] In a third aspect, the present application further provides a silicon-carbon negative electrode material prepared by the method provided in the first aspect, which comprises a porous carbon substrate, silicon elements distributed in the pore channels of the porous carbon substrate, and carbon coating the outer surfaces of the porous carbon substrate and the silicon elements.

[0232] The porous carbon substrate is prepared through two activation treatments and has a dendritic-like pore channel and satisfies at least one of the following a-f:

[0233] a. The micropore volume ratio is 10-30%; specifically, it can be 10 vol%, 15 vol%, 20 vol%, 25 vol%, 30 vol% or any value within the above range; optionally, it is 15-25 vol%.

[0234] b. The mesopore volume ratio is 60-90%; specifically, it can be 60 vol%, 65 vol%, 70 vol%, 75 vol%, 80 vol%, 85 vol%, 90 vol% or any value within the above range; optionally, it is 70-85 vol%.

[0235] c. The macropore volume ratio is 0-10%, specifically, it can be 0 vol%, 1 vol%, 2 vol%, 3 vol%, 4 vol%, 5 vol%, 6 vol%, 7 vol%, 8 vol%, 9 vol%, 10 vol% or any value within the above range; optionally, 0-5 vol%.

[0236] The porous carbon matrix comprises micropores, mesopores and macropores, wherein the micropores are pores with a pore size of less than 2 nm, the mesopores are pores with a pore size of 2-50 nm, and the macropores are pores with a pore size of greater than 50 nm.

[0237] In the alternative embodiment of the present application, the mesopore and micropore volume ratios within the above range ensure that the silicon nanostructure has a small enough size to prevent excessive stress during lithiation, while also ensuring that the pore size is large enough to enable the deposition (for example, by chemical vapor deposition) of a high level of silicon within the pore structure of the porous carbon skeleton within an acceptable processing time. If the micropore ratio is too high, the silicon can be blocked by the larger nanosilicon particles when it is deposited, especially at a high deposition rate, thereby causing excessive deposition of silicon on the surface of the external particles, and a significant decrease in substrate utilization; if the macropore ratio is too high, the silicon agglomerates within the pores, the volume expansion of the nanosilicon is intensified, the substrate's limiting effect is weakened, resulting in a decrease in the mechanical strength and stability of the silicon-carbon negative electrode material, which is not conducive to subsequent recycling.

[0238] d. The specific surface area is not less than 200 m 2 / g, optionally 200-4000 m 2 / g; specifically, it can be 200 m 2 / g, 300 m 2 / g, 400 m 2 / g, 500 m 2 / g, 600 m 2 / g, 700 m 2 / g, 800 m 2 / g, 900 m 2 / g, 1000 m 2 / g, 1100 m 2 / g, 1200 m 2 / g, 1300 m 2 / g, 1400 m 2 / g, 1500 m 2 / g, 1600 m 2 / g, 1700 m 2 / g, 1800 m 2 / g, 1900 m 2 / g, 2000 m 2 / g, 2500 m 2 / g, 3000 m 2 / g, 3500 m 2 / g, 4000 m 2 / g, or any value within the above range.

[0239] e. a pore volume of no less than 0.4 cm 3 / g, optionally 0.4-2.0 cm 3 / g; specifically, 0.4 cm 3 / g, 0.5 cm 3 / g, 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g, 1.1 cm 3 / g, 1.2 cm 3 / g, 1.3 cm 3 / g, 1.4 cm 3 / g, 1.5 cm 3 / g, 1.6 cm 3 / g, 1.7 cm 3 / g, 1.8 cm 3 / g, 1.9 cm 3 / g, 2.0 cm 3 / g, or any value within the above range.

[0240] f. an average particle size D50 of 1-20 μm; specifically, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any value within the above range. Optionally, 2-5 μm.

[0241] In an optional embodiment, the average pore size D50 of the silicon-carbon negative electrode material is 6-9 μm; specifically, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or any value within the above range. If the particle size of the negative electrode material is too large, the path for lithium to be deintercalated at the center position increases, and the difficulty of lithium deintercalation increases; optionally, 6.5-7.5 μm.

[0242] and / or, the specific surface area of the silicon-carbon negative electrode material is less than 10 m 2 / g, specifically, 9 m 2 / g, 8 m 2 / g, 7 m 2 / g, 6 m 2 / g, 5 m2 / g, 4m 2 / g, 3m 2 / g, 2m 2 / g, 1m 2 / g or less than 10m 2 / g. The specific surface area increase can increase the number of active sites for lithium deintercalation, which is beneficial for lithium deintercalation, but too large specific surface area is not conducive to improving the cycle performance of the negative electrode material; and optionally less than 5m 2 / g;

[0243] And / or, the tap density of the silicon-carbon negative electrode material is 0.8-1.1g / cm 3 , specifically 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 or any value within the above range. Increasing the tap density is beneficial to increasing the energy density of the material, but too high tap density will reduce the pore structure and increase the difficulty of lithium deintercalation; and optionally 0.85-1.0g / cm 3 .

[0244] In the preparation method of the silicon-carbon negative electrode material provided in the above second aspect, the porous carbon material is prepared by a special secondary activation method, the porous carbon material is mainly microporous, the proportion of micropores is as high as 95% or more, and micropores of different pore sizes are further divided into three categories and the proportion of each category; by adjusting the process parameters of the two activation treatments in the preparation method, the composition of micropores in the prepared porous carbon material can be adjusted. By accurately adjusting the micropores of different pore sizes, the electrochemical performance of the secondary battery is accurately adjusted to prepare a negative electrode material with low expansion rate, high cycle stability, high capacity and high initial efficiency.

[0245] In a fourth aspect, the present application also provides a silicon-carbon negative electrode material prepared by the method provided in the above second aspect, taking the porous carbon material as the substrate, further comprising nano-silicon particles distributed in the pores of the porous carbon material, and a carbon coating layer on the outermost layer:

[0246] The porous carbon material:

[0247] The proportion of micropores in the total pore volume is ≥95%, and the micropores are pores with a pore size ≤2nm;

[0248] Wherein, the proportion of micropores with a pore size of 0-0.44nm is X%, and 0.5≤X≤5.0; specifically 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 or any value within the above range;

[0249] The ratio of micropores with a pore size of 0.44-1.32 nm is denoted as Y%, 65≤Y≤90; specifically, it can be 65, 66, 67, 68, 69, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, or any value within the above range;

[0250] The ratio of micropores with a pore size of 1.32-2 nm is denoted as Z%, 5≤Z≤30; specifically, it can be 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, or any value within the above range;

[0251] And X+Y+Z=100.

[0252] In an optional embodiment, the average pore size of the porous carbon material is 1.5±0.3 nm; specifically, it can be 1.2 nm, 1.25 nm, 1.3 nm, 1.35 nm, 1.4 nm, 1.45 nm, 1.5 nm, 1.55 nm, 1.6 nm, 1.65 nm, 1.7 nm, 1.75 nm, 1.8 nm, or any value within the above range; optionally, the average pore size is 1.4-1.7 nm.

[0253] And at least one of the following conditions is met:

[0254] (1) The specific surface area is 1500-2200 m 2 / g; specifically, it can be 1500 m 2 / g, 1550 m 2 / g, 1600 m 2 / g, 1650 m 2 / g, 1700 m 2 / g, 1750 m 2 / g, 1800 m 2 / g, 1850 m 2 / g, 1900 m 2 / g, 1950 m 2 / g, 2000 m 2 / g, 2050 m 2 / g, 2100 m 2 / g, 2150 m 2 / g, 2200 m 2 / g, or any value within the above range;

[0255] (2) The pore volume is 0.7-1.3 cm 3 / g; specifically, it can be 0.7 cm 3 / g, 0.75 cm 3 / g, 0.8 cm 3 / g, 0.85 cm 3 / g, 0.9 cm 3 / g, 0.95 cm 3 / g, 1.0 cm 3 / g, 1.05 cm 3 / g, 1.1 cm 3 / g, 1.15 cm 3 / g, 1.2 cm 3 / g, 1.25 cm 3 / g, 1.3 cm 3 / g, or any value within the above range.

[0256] (3) the particle size Dv50 is 7.0 ± 1.0 μm; specifically, it can be 6.0 μm, 6.2 μm, 6.5 μm, 6.7 μm, 6.9 μm, 7.0 μm, 7.2 μm, 7.5 μm, 7.7 μm, 8.0 μm, or any value within the above range; optionally, the particle size Dv50 is 6.9-7.2 μm.

[0257] In an optional embodiment, the porous carbon material satisfies at least one of the following conditions:

[0258] (1) 0.5 ≤ X ≤ 2.0; optionally, 0.5 ≤ X ≤ 1.5;

[0259] (2) 69 ≤ Y ≤ 90; optionally, 69 ≤ Y ≤ 80;

[0260] (3) 8 ≤ Z ≤ 30; optionally, 19 ≤ Z ≤ 30.

[0261] In an optional embodiment, the silicon-carbon negative electrode material satisfies at least one of the following conditions:

[0262] (a) the Dv50 is 7.0 ± 1.0 μm; specifically, it can be 6.0 μm, 6.2 μm, 6.5 μm, 6.7 μm, 6.9 μm, 7.0 μm, 7.2 μm, 7.5 μm, 7.7 μm, 8.0 μm, or any value within the above range;

[0263] (b) the specific surface area is 3 ± 2 m 2 / g; specifically, it can be 1 m 2 / g, 1.2 m 2 / g, 1.5 m 2 / g, 1.8 m 2 / g, 2 m 2 / g, 2.2 m 2 / g, 2.5 m 2 / g, 2.8 m 2 / g, 3 m 2 / g, 3.5 m 2 / g, 4 m2 / g, 4.5 m 2 / g, 5 m 2 / g or any value within the above range;

[0264] (c) a powder resistance < 10 Ω-cm at 20 MPa; specifically, it can be 0.01 Ω-cm, 0.05 Ω-cm, 0.1 Ω-cm, 0.5 Ω-cm, 1 Ω-cm, 2 Ω-cm, 3 Ω-cm, 4 Ω-cm, 5 Ω-cm, 6 Ω-cm, 7 Ω-cm, 8 Ω-cm, 9 Ω-cm, 9.5 Ω-cm, 9.9 Ω-cm or any value within the above range;

[0265] (d) a tap density of 0.9 ± 0.05 g / cm 3 ; specifically, it can be 0.85 g / cm 3 , 0.86 g / cm 3 , 0.87 g / cm 3 , 0.88 g / cm 3 , 0.89 g / cm 3 , 0.90 g / cm 3 , 0.91 g / cm 3 , 0.92 g / cm 3 , 0.93 g / cm 3 , 0.94 g / cm 3 , 0.95 g / cm 3 or any value within the above range.

[0266] In a fifth aspect, the present application further provides a negative electrode sheet, which comprises two kinds of silicon-carbon negative electrode materials with different micro-morphologies prepared by the above two methods.

[0267] In a sixth aspect, the present application further provides a secondary battery, which comprises the above negative electrode sheet. The secondary battery includes lithium ion batteries, sodium ion batteries, etc.

[0268] Example 1

[0269] S1: 500 g of epoxy resin was placed in a carbonization furnace, the temperature of the carbonization furnace was adjusted to 1200℃, and a carbonization product was obtained after 3h of carbonization treatment, and the precursor was obtained after grading and dispersing;

[0270] S2: the precursor obtained in step (1) was placed in an activation furnace, the temperature of the activation furnace was adjusted to 600℃, the pressure was 5KPa, water vapor was introduced at a flow rate of 1 kg / h, and the activation treatment was carried out for 5h;

[0271] The performance data of the first activated product prepared in this step are shown in Table 1 below, wherein the pore volume, average pore size and specific surface area are obtained by the test of the MAC 3020.

[0272] S3: After the activation treatment is completed, the temperature of the activation furnace is adjusted to 800°C, vacuum is first extracted, and then carbon dioxide is introduced at a flow rate of 2 kg / h until the pressure reaches 4 KPa, and secondary activation treatment is performed for 1 h to obtain the porous carbon material;

[0273] Through testing, the performance data of the porous carbon material prepared in this step are shown in Table 1 below, wherein the pore volume, average pore size, and specific surface area are obtained by the Micromeritics 3020 test.

[0274] Through pore size distribution testing, the micropore volume ratio of the porous carbon material prepared in this step is 19.7%, the mesopore volume ratio is 78.1%, and the macropore volume ratio is 2.2%.

[0275] S4: The porous carbon material is placed in a CVD furnace, the temperature in the furnace is adjusted to 500°C, and a mixed gas composed of silane and argon at a volume ratio of 60:40 is introduced at a flow rate of 10 L / min for gas deposition, and the deposition is performed for 10 h;

[0276] S5: After the deposition is completed, a mixed gas of acetylene and nitrogen at a volume ratio of 70:30 is introduced at a flow rate of 5 L / min for carbon coating treatment, the treatment time is 2 h, and after the coating is completed, the final silicon-carbon negative electrode material is obtained after being dispersed, sieved, and magnetically removed.

[0277] The performance data of the silicon-carbon negative electrode material prepared in this embodiment are shown in Table 2 below.

[0278] Comparative Example 1

[0279] The preparation process is basically the same as that of Example 1, except that only the activation treatment of step S2 is performed, and the secondary activation treatment of step S3 is not performed.

[0280] Comparative Example 2

[0281] The preparation process is basically the same as that of Comparative Example 1, except that the activation treatment time of step S2 is extended to 6 h.

[0282] Through testing, the micropore volume ratio of the porous carbon material prepared in this comparative example is 6.4%, the mesopore volume ratio is 77.7%, and the macropore volume ratio is 15.9%.

[0283] Comparative Example 3

[0284] The preparation process is basically the same as that of Example 1, except that the order of steps S2 and S3 is changed, i.e., carbon dioxide activation is performed first, the activation treatment parameters are exactly the same as in Example 1, and then water vapor activation is performed, the activation treatment parameters are also exactly the same as in Example 1.

[0285] The micropore volume ratio of the porous carbon material prepared in the present comparative example is 5.9%, the mesopore volume ratio is 74.7%, and the macropore volume ratio is 19.4%.

[0286] Comparative Example 4

[0287] The preparation process is basically the same as that of Example 1, except that the activation treatment of step S2 is not performed, and the secondary activation treatment of step S3 is directly performed for 5h.

[0288] Comparative Example 5

[0289] The preparation process is basically the same as that of Comparative Example 4, except that the secondary activation treatment time is extended to 6h.

[0290] The micropore volume ratio of the porous carbon material prepared in the present comparative example is 42.4%, the mesopore volume ratio is 53.4%, and the macropore volume ratio is 4.2%.

[0291] Example 2

[0292] The preparation process is basically the same as that of Example 1, except that the activation time of step S2 is adjusted to 8h.

[0293] Example 3

[0294] The preparation process is basically the same as that of Example 1, except that the activation time of step S2 is adjusted to 3h.

[0295] Example 4

[0296] The preparation process is basically the same as that of Example 1, except that in step S3:

[0297] After the activation treatment of step S2 is completed, the activation furnace temperature is adjusted to 800℃, the pressure is 4KPa, and carbon dioxide is introduced at a flow rate of 2kg / h for secondary activation treatment for 1h, but without the prior vacuum treatment.

[0298] Comparative Example 6

[0299] The preparation process is basically the same as that of Example 4, and the prior vacuum treatment is also not performed, except that the pressure of the activation furnace is replaced by 10Kpa during the secondary activation treatment.

[0300] Comparative Example 7

[0301] The preparation process is basically the same as that of Example 4, and the prior vacuum treatment is also not performed, except that the secondary activation treatment is performed under normal pressure.

[0302] Example 5

[0303] The preparation process is basically the same as that of Example 1, except that the carbon dioxide in step S3 is replaced by an equal volume flow of carbon monoxide.

[0304] Example 6

[0305] The preparation process is basically the same as that of Example 1, except that:

[0306] The carbon source in step S1 is replaced by 500g of low-temperature pitch, and the carbonization temperature is replaced by 850℃;

[0307] The silane vapor deposition time in step S4 is adjusted to 5h.

[0308] Example 7

[0309] The preparation process is basically the same as that of Example 1, except that:

[0310] The carbon source in step S1 is replaced by 500g of coconut shell powder, the carbonization temperature is replaced by 1300℃, and the carbonization time is replaced by 5h;

[0311] The silane vapor deposition time in step S4 is adjusted to 15h.

[0312] Example 8

[0313] The preparation process is basically the same as that of Example 1, except that in step S4, a mixed gas of silane, acetylene and argon with a volume ratio of 7:2:1 is passed at a flow rate of 10L / min.

[0314] Example 9

[0315] The preparation process is basically the same as that of Example 1, except that in step S4, silane (volume ratio of silane to argon is 8:2) and ammonia (volume ratio of ammonia to argon is 1:1) are alternately passed at a flow rate of 5L / min, each for 1h, for a total of 5 times.

[0316] Table 1

[0317] Table 2

[0318] Performance test:

[0319] The products prepared according to each of the examples and each of the comparative examples are used as negative electrode materials to assemble batteries.

[0320] (1) Preparation of the positive electrode sheet: the positive electrode active material lithium nickel cobalt manganese oxide (NCM811), the conductive agent Super P, the carbon nanotube, the binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:0.5:1.5 and N-methyl pyrrolidone (NMP) were uniformly mixed to prepare a positive electrode slurry (solid content of 70 wt%), which was coated on the positive and negative sides of the current collector aluminum foil, dried at 100°C, cold-pressed at 4 MPa at room temperature, then edge cut, sheet cutting, striping, and tab welding to prepare the positive electrode sheet.

[0321] (2) Preparation of the negative electrode sheet: under a nitrogen protective atmosphere, the solvent N-methyl pyrrolidone (NMP) and the binder PVDF were stirred and uniformly mixed, then the conductive agent Super P was added and stirred and uniformly mixed, and then the product prepared in each example and each comparative example was added as the negative electrode active material and stirred and uniformly mixed to prepare a negative electrode slurry (solid content of 50 wt%).

[0322] The above negative electrode slurry was coated on the positive and negative sides of the current collector copper foil, dried at 100°C, cold-pressed at 4 MPa at room temperature, then edge cut, sheet cutting, striping, and tab welding to prepare the negative electrode sheet.

[0323] (3) Assembly of the lithium ion battery

[0324] The prepared positive electrode sheet, the separator, and the negative electrode sheet were sequentially stacked with the separator between the positive and negative electrode sheets, and the bare cell was obtained by winding. The bare cell was placed in an aluminum plastic shell package, and dried at 100°C to a moisture content of less than 100 ppm under a relative vacuum pressure of -0.95×10 5 Pa. The electrolyte was injected into the dried bare cell, wherein the electrolyte was composed of ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) (EC:EMC:DEC volume ratio = 1:1:1) and LiPF6 (1.0 M), and the soft-packaged liquid lithium ion battery was obtained by packaging, standing, formation (0.02C constant current charging for 2h, 0.1C constant current charging for 2h), shaping, capacity testing (sub-packaging), and so on.

[0325] During battery assembly, five batteries were prepared for each test, and five sets of data were tested, and the average value of the five sets of data was taken as the final performance.

[0326] The battery cycle performance was tested on a newwei device, specifically:

[0327] Firstly, discharge at 0.1C to 0.005V, then discharge at 0.08C to 0.001V, discharge at 0.05C to 0.001V, discharge at 0.02C to 0.001V at 25℃, and then stand for 10min; secondly, charge at 0.1C to 1.5V, stand for 10min, record the charge-discharge capacity after the first cycle, and calculate the first coulombic efficiency; cycle for 600 times according to the above method, record the charge-discharge capacity after 600 times, and calculate the capacity retention rate after 600 times, the tap density is measured by a tap density instrument, and the specific test / calculated results are shown in Table 3 below:

[0328] Table 3

[0329] As can be seen from the data of Example 1 and Comparative Examples 1-2 in Table 3, for Comparative Examples 1 and 2, only the first activation is performed or the first activation time is prolonged to be the same as that of Example 1, at this time, the pore structure is poor, there is not much pore volume, and the average pore diameter is relatively large, and the accommodation and restriction of the substrate to the nano-silicon particles are both weak; therefore, the cycle stability of the assembled secondary battery is significantly reduced.

[0330] As can be seen from the data of Example 1 and Comparative Example 3 in Table 3, when the order of the first activation and the second activation is reversed, Comparative Example 3 first forms small pores on the precursor, and water vapor is adsorbed on the small pores during the second activation, the pore diameter is expanded horizontally and vertically, the average pore diameter is increased, but the pore volume changes is not obvious, therefore, the nano-silicon particle agglomeration obtained during subsequent silicon deposition is obvious, and the cycle stability of the assembled secondary battery is poor.

[0331] As can be seen from the data of Example 1 and Comparative Examples 4 and 5 in Table 3, Comparative Examples 4-5 only perform the second activation, that is, only use carbon dioxide as the activation gas, the average pore diameter of the obtained pore structure is small, only a small amount of nano-silicon particles enter the substrate, and most of the nano-silicon particles cover the surface of the substrate, which is not of test value.

[0332] From the data of Example 1, 4 and Comparative Examples 6, 7 in Table 3, it can be seen that when the specific operation adopted in the secondary activation is different, there is no obvious difference in the conventional parameters (including pore volume, specific surface area, average pore size) of the porous carbon obtained after secondary activation, but when the porous carbon prepared by different processes is used as a substrate for the deposition of silicon and carbon to prepare a silicon-carbon negative electrode material, and the lithium ion battery is assembled and electrochemical performance test is carried out, obvious differences are shown. The result is that the battery electrochemical performance of Example 1 which adopts vacuumizing and then introducing carbon dioxide to a lower pressure is the best; the battery electrochemical performance of Example 4 and Comparative Example 6 which does not vacuumize and directly uses low pressure for secondary activation is the second, and the battery performance decreases slightly as the pressure increases; the battery electrochemical performance of Comparative Example 7 which does not vacuumize and uses atmospheric pressure for secondary activation is the worst, which is significantly worse than that of Example 1. Based on this conclusion, it can be more favorably proved that the vacuumizing in the secondary activation and the size of the pressure adopted should have more influence on the modification of the micro-pore structure of the porous carbon material.

[0333] Example 10

[0334] (S1) 7.5 kg of phenolic resin was placed in a carbonization furnace, the oxygen content in the carbonization furnace was controlled to be lower than 20 ppm under nitrogen atmosphere, then the temperature was raised to 800 ℃ at a heating rate of 15 ℃ / min and kept for 7 h; after the end of the heat preservation, water vapor was introduced at a flow rate of 0.5 kg / h for primary activation for 8 h; then nitrogen was introduced, the temperature was raised to 1100 ℃ at a heating rate of 15 ℃ / min, and then carbon dioxide was introduced at a flow rate of 0.5 kg / h for secondary activation for 8 h; after the material was cooled, it was taken out, and after acid washing, pressure filtration and drying, the porous carbon was obtained.

[0335] (S2) The porous carbon obtained in step (S1) was placed in a rotary furnace, the oxygen content in the rotary furnace was controlled to be lower than 20 ppm under nitrogen atmosphere, then the temperature was raised to 500 ℃ at a heating rate of 15 ℃ / min and kept for 1.5 h; then under the atmosphere of silane gas, the silane gas flow rate was 20 L / h, and the heat preservation time was 24 h.

[0336] (S3) Nitrogen was introduced into the rotary furnace again, the temperature was raised to 600 ℃ at a heating rate of 15 ℃ / min and kept for 1.5 h; finally, acetylene gas was introduced, the acetylene gas flow rate was 10 L / h, and the heat preservation time was 8 h, after the material was cooled, it was taken out, and the silicon-carbon negative electrode material was obtained.

[0337] Example 11

[0338] The preparation process is basically the same as that of Example 10, the only difference is that the flow rate of carbon dioxide in step (S1) is replaced by 0.25 kg / h, and the secondary activation time is replaced by 6 h.

[0339] Example 12

[0340] The preparation process is substantially the same as that of Example 10, except that the flow rate of water vapor in step (S1) is replaced by 1 kg / h, and the initial activation time is replaced by 10 h; the flow rate of carbon dioxide is replaced by 0.25 kg / h, and the reactivation time is replaced by 6 h.

[0341] Example 13

[0342] The preparation process is substantially the same as that of Example 10, except that the flow rate of water vapor in step (S1) is replaced by 0.25 kg / h, and the initial activation time is replaced by 6 h; the flow rate of carbon dioxide is replaced by 1 kg / h, and the reactivation time is replaced by 10 h.

[0343] Example 14

[0344] The preparation process is substantially the same as that of Example 10, except that the flow rate of water vapor in step (S1) is replaced by 1 kg / h, and the initial activation time is replaced by 10 h; the flow rate of carbon dioxide is replaced by 0.25 kg / h, and the reactivation time is replaced by 6 h.

[0345] Example 15

[0346] The preparation process is substantially the same as that of Example 10, except that the flow rate of water vapor in step (S1) is replaced by 0.25 kg / h, and the initial activation time is replaced by 6 h.

[0347] Example 16

[0348] The preparation process is substantially the same as that of Example 10, except that the flow rate of water vapor in step (S1) is replaced by 1 kg / h, and the initial activation time is replaced by 12 h.

[0349] Comparative Example 8

[0350] The preparation process is substantially the same as that of Example 10, except that only water vapor is used for initial activation in step (S1), i.e., no reactivation of carbon dioxide is performed.

[0351] Comparative Example 9

[0352] The preparation process is substantially the same as that of Example 10, except that the flow rate of carbon dioxide in step (S1) is replaced by 4 kg / h, and the reactivation time is replaced by 16 h.

[0353] The mass ratio of phenolic resin to carbon dioxide is calculated to be 0.12:1.

[0354] Comparative Example 10

[0355] The preparation process is basically the same as that of Example 10, except that the flow rate of water vapor in step (S1) is replaced by 1.5 kg / h, and the initial activation time is replaced by 12 h; the flow rate of carbon dioxide is replaced by 1 kg / h, and the secondary activation time is replaced by 10 h.

[0356] The mass ratio of phenolic resin to water vapor is calculated to be 0.42:1;

[0357] The mass ratio of phenolic resin to carbon dioxide is 0.75:1.

[0358] Comparative Example 11

[0359] The preparation process is basically the same as that of Example 10, except that the flow rate of water vapor in step (S1) is replaced by 1.5 kg / h, and the initial activation time is replaced by 16 h; the flow rate of carbon dioxide is replaced by 0.25 kg / h, and the secondary activation time is replaced by 6 h.

[0360] The mass ratio of phenolic resin to water vapor is calculated to be 0.31:1;

[0361] The mass ratio of phenolic resin to carbon dioxide is 5:1.

[0362] Comparative Example 12

[0363] The preparation process is basically the same as that of Example 10, except that the flow rate of water vapor in step (S1) is replaced by 0.02 kg / h, and the initial activation time is replaced by 4 h.

[0364] The mass ratio of phenolic resin to water vapor is calculated to be 93.75:1.

[0365] Comparative Example 13

[0366] The preparation process is basically the same as that of Example 10, except that only water vapor is used for initial activation in step (S1), and the flow rate of water vapor is replaced by 4 kg / h, and the initial activation time is replaced by 24 h, and no secondary activation of carbon dioxide is performed.

[0367] Comparative Example 14

[0368] The preparation process is basically the same as that of Example 10, except that only water vapor is used for initial activation in step (S1), and the flow rate of water vapor is replaced by 6 kg / h, and the initial activation time is replaced by 32 h, and no secondary activation of carbon dioxide is performed.

[0369] The specific surface area and pore size distribution parameters of the porous carbon prepared in Examples 10-16 and Comparative Examples 9-14 were tested by using a JW-BK300C surface instrument and a pore size analyzer, and the particle size was tested by using a Malvern 3000 laser particle size analyzer, and the results are shown in Table 4.

[0370] Table 4

[0371] Application Example

[0372] The silicon-carbon negative electrode material prepared in each of Examples 10-16 and Comparative Examples 9-14 was subjected to electrochemical performance testing, and the results are shown in Table 5.

[0373] The silicon-carbon negative electrode material was mixed with carboxymethyl cellulose (CMC), acrylonitrile (LA133), single-walled carbon nanotubes (SWCNT), and carbon black (SP) in a mass ratio of 90:3.5:3.5:0.2:2.8 to form a slurry, which was uniformly coated on a copper foil and dried to form a negative electrode sheet. The thickness of the electrode sheet was measured, and the electrode sheet was assembled into a button cell with a negative electrode shell, an electrolyte, a separator, a lithium sheet, a foam nickel, and a positive electrode shell in an argon atmosphere glove box.

[0374] The 15 groups of batteries described above were tested by a blue cell test system. At 25℃, first discharged at 0.05C to 0.005V, and then discharged at 0.02C to 0.001V after 10 minutes of standing; then charged at 0.1C to 1.5V after 10 minutes of standing, and the first charge capacity was recorded, and the first coulombic efficiency was calculated; then the button cell was disassembled in an argon atmosphere glove box, and the thickness of the negative electrode sheet was measured after drying, and the expansion rate was calculated.

[0375] The 15 groups of batteries described above were tested by a blue cell test system in the above manner, and after 500 cycles, the charge and discharge capacities after 500 cycles were recorded, and the capacity retention rate after 500 cycles was calculated.

[0376] Table 5

[0377] As can be seen from Table 5, the secondary batteries assembled from the negative electrode materials prepared in each of the examples of the application all have a low expansion rate, and have a high first efficiency and a high capacity retention rate. Among them, the secondary battery assembled from the negative electrode material prepared in Example 1 has the best comprehensive electrical performance.

[0378] As can be seen from Example 10 and Comparative Example 9 in Table 5, the first efficiency and cycle stability of the secondary battery assembled from Comparative Example 1 are too low, and the expansion rate is too high. This may be due to the fact that the porous carbon prepared without reactivating the carbon dioxide gas has a too low X value, and the proportion of pores available for lithium ion transmission is too low, resulting in a too low first efficiency and a reduced space for relieving volume changes, which is not conducive to relieving volume expansion, leading to a decrease in cycle stability and a too high expansion rate.

[0379] As can be seen from the comparison between Example 10 and Comparative Example 10 in Table 5, the secondary battery assembled from Comparative Example 10 has obvious cycle degradation and high expansion rate; this is probably because the amount of carbon dioxide used in the reactivation is too high, resulting in a high X value in the prepared porous carbon, a high proportion of invalid pores (pores that silane molecules cannot enter), and easy deposition of silicon on the surface of the porous carbon, which is prone to silicon floating.

[0380] As can be seen from the comparison between Example 10 and Comparative Example 11 in Table 5, the secondary battery assembled from Comparative Example 11 has obvious cycle degradation and high expansion rate; this is probably because the amount of activator used in the primary activation and the secondary activation is too high, resulting in a low Y value in the prepared porous carbon, a high proportion of X value and Z value, and easy occurrence of silicon floating.

[0381] As can be seen from the comparison between Example 10 and Comparative Example 12 in Table 5, the secondary battery assembled from Comparative Example 12 has obvious cycle degradation and high expansion rate; this is probably because the amount of activator used in the primary activation is too high and the amount of activator used in the secondary activation is too low, resulting in a high Z value in the prepared porous carbon, a large average pore size, a low proportion of effective pores (pores that can accommodate 2-3 silane molecules, i.e., pores represented by the Y value) for limiting nano-silicon particles, and easy occurrence of silicon floating.

[0382] As can be seen from the comparison between Example 10 and Comparative Example 13 in Table 5, the secondary battery assembled from Comparative Example 13 has obvious degradation in the initial efficiency and cycle; this is probably because the amount of activator used in the primary activation is too low, resulting in a low Z value in the prepared porous carbon, and a small average pore size that is not conducive to the transmission of lithium ions.

[0383] As can be seen from the comparison between Example 10 and Comparative Examples 14 and 15 in Table 4, the secondary batteries assembled from Comparative Examples 14 and 15 have obvious degradation in the initial efficiency and cycle, and high expansion rate; this is probably because no carbon dioxide reactivation is performed, and the amount of activator used in the primary activation is too low, resulting in a high average pore size (greater than the total size of 2-3 silane molecules) in the prepared porous carbon, which is greater than 5 nm, and easy occurrence of homogeneous nucleation and growth of silicon, i.e., easy occurrence of silicon floating.

[0384] The above discloses preferred embodiments, but the scope of protection of the present application is not limited thereto, and those skilled in the art can easily understand the spirit of the present application from the above embodiments and make different inferences and changes, as long as they do not deviate from the spirit of the present application.

Claims

1. A method for preparing a silicon-carbon negative electrode material, characterized by, The method comprises the following steps: S1: carbonizing a carbon source to obtain a precursor; S2: activating the precursor in the presence of a first activating agent to obtain a first activated product; S3: secondarily activating the first activated product in the presence of a second activating agent to obtain a porous carbon; S4: depositing silicon and carbon on the porous carbon prepared in step S3 to obtain the silicon-carbon negative electrode material.

2. The method of claim 1, wherein the silicon-carbon negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. In step S1: The carbon source is selected from one or more of biomass, high molecular polymer, coal-based, and petroleum-based; The carbonization treatment is performed at a temperature of 500-1500°C for 1-20 h at a heating rate of 1-20°C / min.

3. The method of claim 1, wherein the silicon-carbon negative electrode material is prepared by a process comprising: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. In step S2, the activation treatment comprises at least one of the following features (1)-(4): (1) The first activating agent is selected from water vapor; (2) The flow rate of the first activating agent is 1-20 kg / h; (3) The activation treatment is performed at a temperature of 500-1200°C; (4) The activation treatment is performed for 1-10 h.

4. The method of claim 1, wherein the silicon-carbon negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. In step S3, the secondary activation treatment comprises at least one of the following features (1)-(6): (1) The second activating agent is selected from CO and / or CO2; (2) The secondary activation treatment is performed at a temperature of 500-1200°C; (3) The secondary activation treatment is performed at a pressure of 0.1-10 KPa; (4) The secondary activation treatment is performed for 0.5-10 h; (5) The flow rate of the second activating agent is 1-20 kg / h; (6) Vacuum is applied before the second activating agent is introduced.

5. The method of claim 1, wherein the silicon-carbon negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. In step S4: The silicon deposition: The gas source comprises a silicon source gas, an inert atmosphere, and an optional second gas source; the proportion of the silicon source gas is 30-90 vol%; The total flow rate of the gas source is 1-100 L / min; The silicon deposition is performed at a temperature of 400-1000°C for 1-50 h; The second gas source is selected from one or more of a carbon source gas, a nitrogen source gas, a sulfur source gas, and a phosphorus source gas; The second gas source can be co-deposited with the silicon source gas or alternatively deposited with the silicon source gas; The carbon deposition is performed at a temperature of 300-1200°C for 2-20 h; The carbon deposition gas source comprises a carbon source gas and a carrier gas, and the proportion of the carbon source gas is 50-99 vol%; The carbon source gas is selected from an alkane gas with a cracking temperature within the carbon deposition temperature range.

6. A silicon-carbon negative electrode material prepared by the method of any one of claims 1-5, comprising a porous carbon substrate, silicon elements distributed in the pores of the porous carbon substrate, and carbon coating the outer surfaces of the porous carbon substrate and the silicon elements, characterized in that: The porous carbon substrate is prepared by two activation treatments, has a dendritic-like pore structure, and satisfies at least one of the following a-f: a. The proportion of micropore volume is 10-30%; b. The proportion of mesopore volume is 60-90%; c. The proportion of macropore volume is 0-10%; d. a specific surface area of not less than 200 m 2 / g, optionally 200 to 4000 m 2 / g; e. a pore volume of not less than 0.4 cm3 / g 3 / g, optionally 0.4 to 2.0 cm3 / g 3 / g; f. The average particle size D50 is 1-20 μm.

7. The silicon-carbon negative electrode material of claim 6, characterized in that: The average pore size D50 of the silicon-carbon negative electrode material is 6-9 μm. and / or the silicon-carbon negative electrode material has a specific surface area of less than 10 m 2 / g, optionally less than 5 m 2 / g; And / or, the tap density of the silicon-carbon negative electrode material is 0.8-1.1 g / cm 3 .

8. A method for preparing a silicon-carbon negative electrode material, characterized by, The method comprises the following steps: (S1) performing high-temperature carbonization treatment on a carbon source precursor, and then performing two activation treatments to obtain a porous carbon material; The two activation treatments are: the first activation uses water vapor as the activation agent, and the second activation uses carbon dioxide as the activation agent; (S2) performing silicon deposition on the porous carbon material as a substrate to obtain a porous carbon substrate loaded with nano-silicon particles; (S3) performing carbon coating treatment to obtain a silicon-carbon negative electrode material.

9. The method for preparing a silicon-carbon negative electrode material according to claim 8, characterized in that: In step (S1): The carbon source precursor is selected from a high-molecular carbon source and / or a biomass carbon source; The high-temperature carbonization treatment is performed at a temperature of 700-900 ℃; In the first activation, the mass ratio of the carbon source precursor to water vapor is (0.5-5.0):1; The flow rate of water vapor is 0.05-1 kg / h, and the activation temperature is 700-900 ℃; In the second activation, the mass ratio of the carbon source precursor to carbon dioxide is (0.3-5.0):1; The flow rate of carbon dioxide is 0.05-2 kg / h, and the activation temperature is 900-1200 ℃; In step (S2): The silicon deposition is performed at a temperature of 400-600 ℃; In step (S3): The carbon coating treatment is performed at a temperature of 500-700 ℃.

10. A silicon-carbon negative electrode material prepared by the method according to claim 8 or 9, wherein the porous carbon material is used as a substrate, and further comprises nano-silicon particles distributed in the pores of the porous carbon material, and an outermost carbon coating layer, characterized in that: The porous carbon material: The proportion of micropores (pore size ≤2 nm) in the total pore volume is ≥95%; Among them, the proportion of micropores with a pore size of 0-0.44 nm is denoted as X%, and 0.5≤X≤5.0; The proportion of micropores with a pore size of 0.44-1.32 nm is denoted as Y%, and 65≤Y≤90; The proportion of micropores with a pore size of 1.32-2 nm is denoted as Z%, and 5≤Z≤30; And X+Y+Z=100.

11. The silicon-carbon anode material prepared according to the method of claim 10, characterized in that, The average pore size of the porous carbon material is 1.5±0.3 nm; And at least one of the following conditions is satisfied: (1) a specific surface area of 1500 to 2200 m2 / g 2 / g; (2) the pore volume is 0.7-1.3 cm3 / g 3 / g; (3) The particle size Dv50 is 7.0±1.0 μm.

12. The silicon-carbon anode material prepared according to the method of claim 10, characterized in that, The porous carbon material satisfies at least one of the following conditions: (1)0.5≤X≤2.0； (2)69≤Y≤90； (3)8≤Z≤30。 13. The silicon-carbon anode material prepared according to the method of claim 10, characterized in that, The silicon-carbon negative electrode material satisfies at least one of the following conditions: (a) Dv50 is 7.0±1.0 μm; (b) a specific surface area of 3 ± 2 m 2 / g; (c) The powder resistance is <10 Ω-cm at 20 MPa; (d) a tapped density of 0.9 ± 0.05 g / cm 3 .

14. A negative electrode sheet characterized by comprising: The silicon-carbon negative electrode material as claimed in any one of claims 6, 7, 10-13.

15. A secondary battery characterized by comprising: The negative electrode sheet as claimed in claim 14.

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