Silicon-carbon negative electrode material, preparation method and application

Abstract

The present invention discloses a silicon-carbon anode material, a preparation method thereof, and an application thereof. The silicon-carbon anode material includes a porous carbon substrate, silicon elements distributed in the pores of the porous carbon substrate, and carbon coated on the outer surfaces of the porous carbon substrate and the silicon elements. The porous carbon substrate is prepared through two activation treatments, has dendritic pores, and satisfies at least one of the following a to f: a. The micropore volume ratio is 10 to 30%; b. The mesopore volume ratio is 60 to 90%; c. The macropore volume ratio is 0 to 10%; d. The specific surface area is not less than 200 m<supgt;2< / supgt> / g; e. The pore volume is not less than 0.4 cm<supgt;3 / g; f. The average particle size D50 is 1 to 20 μm. Through the activation treatment of the porous carbon substrate, the present invention can provide more buffer space for the volume expansion of nano-silicon particles from the perspective of substrate preparation, and significantly improve the cycle stability of the silicon-carbon anode material.

Description

Technical Field

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

[0002] Silicon is currently the negative electrode material with the largest theoretical capacity, with a specific capacity of up to 4200mAh / g, which is much higher than the theoretical capacity of graphite (the theoretical capacity of graphite-based negative electrode materials is only 372mAh / g). Silicon has the advantages of low lithium insertion potential and low cost, and is expected to replace graphite as the next generation of lithium-ion battery negative electrode material. However, during the electrochemical cycle of silicon as a negative electrode material, the insertion and extraction of lithium ions will cause the volume of the material to expand and contract by more than 300%. The mechanical force generated will gradually pulverize the material, causing structural collapse, and ultimately leading to the separation of the electrode active material from the current collector, loss of electrical contact, and greatly reduced battery cycle performance. In addition, due to this volume effect, it is difficult for silicon to form a stable solid electrolyte interface (SEI) film in the electrolyte. Along with the destruction of the electrode structure, a new SEI film is continuously formed on the exposed silicon surface, exacerbating the corrosion and capacity decay of silicon.

[0003] Due to the structural stability of carbon materials, the volume change during the charge and discharge process is relatively small, and it has good cycle stability. In addition, due to the similar chemical properties to silicon, silicon and carbon are often compounded to achieve the purpose of improving the volume expansion effect of silicon and improving its electrochemical stability. However, the negative electrode materials obtained by the existing silicon-carbon composite method have poor cycle performance, and the porous substrate has limited effect on limiting the expansion of nano-silicon particles.

[0004] A Chinese patent document with application publication number CN 118431452 A discloses a negative electrode material, preparation method and application, including 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 pyrolyzing the porous substrate adsorbed with the silicon source gas at high temperature to obtain a porous substrate loaded with nano-silicon in the pore structure, and finally coating with carbon. This scheme uses the method of first adsorption and then decomposition to adsorb silane gas to the inner wall of the substrate pores, and then uses the decomposition of silane to release hydrogen to further provide 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, and it is impossible to actively regulate the size of its reserved pores, and it is impossible to effectively control the structure of the reserved pores, and it does not solve the effective mitigation of the volume expansion of nano-silicon particles from the substrate.

[0005] Based on this, how to provide more buffer space for the volume expansion of nano-silicon particles from the perspective of substrate preparation remains to be solved. Summary of the invention

[0006] In view of the above problems, the present invention discloses a silicon-carbon negative electrode material, a preparation method and an application. By activating the porous carbon substrate, more buffer space can be provided for the volume expansion of nano-silicon particles from the perspective of substrate preparation, thereby significantly improving the cycle stability of the silicon-carbon negative electrode material.

[0007] To achieve the above purpose, the specific technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a silicon-carbon negative electrode material, comprising a porous carbon substrate, silicon elements distributed in the pores of the porous carbon substrate, and carbon coated on the outer surface of the porous carbon substrate and the silicon elements;

[0009] The porous carbon substrate is prepared after two activation treatments, has dendrite-like pores, and satisfies at least one of the following a to f:

[0010] a. The volume of micropores accounts for 10-30%;

[0011] b. The mesopore volume accounts for 60-90%;

[0012] c. The volume proportion of macropores is 0-10%;

[0013] d. Specific surface area not less than 200m 2 / g, optionally 200~4000m 2 / g;

[0014] e. Pore volume not less than 0.4cm 3 / g, optionally, 0.4 to 2.0 cm 3 / g;

[0015] f. The average particle size D50 is 1 to 20 μm.

[0016] In an optional embodiment, the average pore size D50 of the silicon-carbon negative electrode material is 6 to 9 μm;

[0017] And / or, the specific surface area of ​​the silicon-carbon negative electrode material is less than 10m 2 / g, optionally less than 5m 2 / g;

[0018] And / or, the tap density of the silicon-carbon negative electrode material is 0.8 to 1.1 g / cm 3 .

[0019] In a second aspect, the present invention further provides a method for preparing the aforementioned silicon-carbon negative electrode material, which specifically comprises:

[0020] S1: Carbonizing the carbon source to obtain a precursor;

[0021] S2: activating the precursor in the presence of a first activator to obtain a first activated product;

[0022] S3: subjecting the first activated product to a secondary activation treatment in the presence of a second activating agent to obtain porous carbon;

[0023] S4: Using the porous carbon prepared in step S3 as a substrate, sequentially performing silicon deposition and carbon deposition to obtain the silicon-carbon negative electrode material.

[0024] The present invention prepares a porous carbon substrate with a dendrite-like pore structure by a special secondary activation method. The first activation treatment uses water vapor as an activator to form uniform mesopores in the substrate, so that the average pore size of the pore structure is maintained at 3 to 20 nm. On the basis of the first 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. Because there are carbon-oxygen double bonds between the two, pores are formed again in the adsorbed holes and micropores of 0.4 to 2.0 nm are formed, thereby forming a dendrite-like pore. The first activation pore formation enables the porous carbon substrate to have a good deposition channel, and the second activation pore formation can effectively create uniform micropores around the mesopores. This part of the micropores can provide more space for the deposition of nano-silicon, and can (especially the extremely micropores less than 1 nm) provide additional buffer space for the expansion of nano-silicon particles in the subsequent assembly battery cycle process, and provide more pore structures for the transmission of lithium ions, while ensuring high reversible capacity and charge and discharge efficiency, further improving the overall cycle stability of the silicon-carbon negative electrode material.

[0025] Experiments have found that if only one activation pore formation with water vapor is performed, or only one activation pore formation with carbon dioxide and / or carbon monoxide is performed, or if the order of the two activation pore formations is swapped, it is impossible to prepare a negative electrode material with high capacity, high initial efficiency and excellent cycle stability.

[0026] In an optional implementation, in step S1:

[0027] The carbon source is selected from one or more of biomass, high molecular polymer, coal-based, and petroleum-based;

[0028] Optionally, the biomass is selected from at least one of the following or a combination thereof: coconut shell, straw, rice husk, wood, bamboo, bagasse, nut shell, etc.;

[0029] Optionally, the high molecular polymer is selected from common polymer types in the art, without special restrictions, such as polyethylene, polyurethane, epoxy resin, phenolic resin, urea-formaldehyde resin, etc.;

[0030] Optionally, the coal base is selected from common types in the art, such as coal pitch, coal tar, etc.;

[0031] Optionally, the petroleum base is selected from common types in the art, such as petroleum coke, paraffin, etc.

[0032] In an optional embodiment, the specific temperature and time of the carbonization treatment are adaptively adjusted in the art according to the type of carbon source used.

[0033] Optionally, the temperature of the carbonization treatment is 500-1500°C; more preferably, the temperature is 800-1500°C.

[0034] Optionally, the carbonization treatment time is 1 to 20 hours;

[0035] Optionally, the heating rate of the carbonization treatment is 1 to 20° C. / min.

[0036] In an optional embodiment, in step S2, the activation treatment comprises at least one of the following features (1) to (5):

[0037] (1) The first activating agent is selected from water vapor;

[0038] (2) The flow rate of the first activator is 1 to 20 kg / h; optionally, 1 to 10 kg / h;

[0039] (3) The activation treatment is performed at a temperature of 500 to 1200° C.; optionally, 500 to 800° C.;

[0040] (4) The activation treatment pressure is 0.1 to 10 KPa; optionally, 1 to 10 KPa;

[0041] (5) The activation treatment lasts for 1 to 10 hours.

[0042] Optionally, in the activation treatment, the mass ratio of the first activator to the precursor is 100:(1-20).

[0043] In an optional embodiment, in step S3, the secondary activation treatment includes at least one of the following features (i) to (vi):

[0044] (i) The second activator is selected from CO and / or CO 2 ; Optionally, CO 2 ;

[0045] (ii) The secondary activation treatment is performed at a temperature of 500 to 1200° C.; optionally, 650 to 1000° C.;

[0046] (iii) The secondary activation treatment has a pressure of 0.1 to 10 KPa; optionally, 1 to 8 KPa;

[0047] (iv) the secondary activation treatment lasts for 0.5 to 10 hours;

[0048] (V) In the secondary activation treatment, the flow rate of the second activator is 1 to 20 kg / h; optionally, 1 to 10 kg / h;

[0049] (VI) Before introducing the second activator, vacuum is applied first.

[0050] Optionally, in the secondary activation treatment, the mass ratio of the first activation product to the second activating agent is 100:(0.1-10).

[0051] In an optional embodiment, in step S4, the silicon deposition:

[0052] The gas source used includes silicon source gas, inert atmosphere and a second gas source which can be added selectively;

[0053] Optionally, the silicon source gas is selected from conventional types in the art, including one or more of monosilane, disilane, dichlorosilane, and trichlorosilane;

[0054] The inert atmosphere is used as a carrier gas, and optionally, is selected from an inert gas such as argon and helium;

[0055] The silicon source gas accounts for 30 to 90 vol%; optionally, the silicon source gas accounts for 50 to 80 vol%;

[0056] The total flow rate of the gas source is 1 to 100 L / min; optionally, the total flow rate is 5 to 50 L / min;

[0057] The silicon deposition temperature is 400-1000°C for 1-50 hours; optionally, the silicon deposition temperature is 400-600°C; more optionally, the silicon deposition temperature is 500°C;

[0058] 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;

[0059] Optionally, the carbon source gas is selected from alkane gases whose cracking temperature is within the carbon deposition temperature range, such as common types such as ethylene and acetylene;

[0060] Optionally, the nitrogen source gas is selected from ammonia;

[0061] Optionally, the sulfur source gas is selected from one or more of hydrogen sulfide, sulfur dioxide, and sulfur hexafluoride;

[0062] Optionally, the phosphorus source gas is selected from one or more of phosphine, phosphorus chloride, and phosphorus fluoride;

[0063] The second source gas may be mixed with the silicon source gas for co-deposition, or may be alternately deposited with the silicon source gas.

[0064] Optionally, when co-deposition is performed, the silicon source gas accounts for 30-80 vol%, the second gas source accounts for 10-30 vol%, and the remainder is an inert atmosphere; more optionally, the silicon source gas accounts for 50-80 vol%, the second gas source accounts for 15-25 vol%, and the remainder is an inert atmosphere;

[0065] Optionally, when performing alternating deposition, in the mixed gas composed of the second gas source and the inert atmosphere, the proportion of the second gas source is 30 to 80 vol%; more preferably, the proportion of the second gas source is 40 to 70 vol%;

[0066] In an optional embodiment, in step S4:

[0067] The carbon deposition is carried out at a temperature of 300 to 1200° C. and for a time of 2 to 20 hours.

[0068] The gas source used for the carbon deposition includes a carbon source gas and a carrier gas, and the carbon source gas accounts for 50 to 99 vol%; optionally, the carbon source gas accounts for 60 to 80 vol%;

[0069] Optionally, the carbon source gas is selected from alkane gases whose cracking temperature is within the carbon deposition temperature range.

[0070] Optionally, the carrier gas is selected from gases such as argon, argon, and nitrogen.

[0071] In a third aspect, the present invention further provides a negative electrode plate, comprising the above-mentioned silicon-carbon negative electrode material or the silicon-carbon negative electrode material prepared by the above-mentioned method.

[0072] In a fourth aspect, the present invention further provides a secondary battery, comprising the above-mentioned negative electrode plate.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] The present invention discloses a silicon-carbon negative electrode material, which is prepared by using a porous carbon material having dendrite-like pores after secondary activation treatment as a substrate, and undergoing silicon deposition and carbon coating; 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 during the subsequent assembly of battery cycles, and provide more pore structures for the transmission of lithium ions, thereby further improving the overall cycle stability of the silicon-carbon negative electrode material while ensuring high reversible capacity and charge and discharge efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 It is a schematic structural diagram of the first activated product obtained after a single activation treatment of the present invention;

[0076] Figure 2 Schematic diagram of the structure of porous carbon obtained after secondary activation treatment of the present invention;

[0077] In the figure, 1-precursor substrate, 2-mesopore channels in the precursor substrate, 3-micropore channels in the precursor substrate. DETAILED DESCRIPTION

[0078] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0079] The embodiment of the present invention provides a silicon-carbon negative electrode material, comprising a porous carbon substrate, silicon elements distributed in the pores of the porous carbon substrate, and carbon coated on the outer surface of the porous carbon substrate and the silicon elements;

[0080] The porous carbon substrate is prepared after two activation treatments, has dendrite-like pores, and satisfies at least one of the following a to f:

[0081] a. The volume proportion of micropores 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%.

[0082] b. The mesopore volume accounts for 60 to 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 to 85 vol%.

[0083] c. The volume proportion of macropores is 0 to 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, it is 0 to 5 vol%.

[0084] The porous carbon matrix includes micropores, mesopores and macropores, wherein the micropores are pores with a pore diameter less than 2 nm, the mesopores are pores with a pore diameter of 2 to 50 nm, and the macropores are pores with a pore diameter greater than 50 nm.

[0085] In an optional embodiment of the present invention, the volume ratio of mesopores and micropores within the above range is disclosed to ensure that the silicon nanostructure has a sufficiently small size to prevent excessive stress during lithiation, while also ensuring that the pore size is large enough to enable deposition (e.g., by chemical vapor deposition) of high silicon levels within the pore structure of the porous carbon skeleton at an acceptable processing time. If the proportion of micropores is too high, silicon may block the pores when it is deposited by larger nano-silicon particles, especially when deposited at a higher deposition rate, resulting in excessive deposition of silicon on the surface of the external particles, and a significant decrease in substrate utilization; if the proportion of macropores is too high, silicon agglomerates in the pores, the volume expansion of nano-silicon is aggravated, and the limiting effect of the substrate on it is weakened, resulting in a decrease in the mechanical strength of the silicon-carbon negative electrode material and a weakened stability, which is not conducive to subsequent recycling.

[0086] d. Specific surface area not less than 200m 2 / g, optionally 200~4000m 2 / g; specifically, 200m 2 / g、300m 2 / g, 400m 2 / g、500m 2 / g, 600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g、1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g, 2000m 2 / g, 2500m 2 / g、3000m 2 / g、3500m 2 / g, 4000m 2 / g or any value within the above range.

[0087] e. Pore volume not less than 0.4cm 3 / g, optionally 0.4 to 2.0 cm 3 / g; specifically, it can be 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 / g, 1.6cm 3 / g, 1.7cm 3 / g, 1.8cm 3 / g, 1.9cm 3 / g, 2.0cm 3 / g or any value within the above range.

[0088] f. The average particle size D50 is 1 to 20 μm; specifically, it can be 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, it is 2 to 5 μm.

[0089] In an optional embodiment, the average pore size D50 of the silicon-carbon negative electrode material is 6 to 9 μm; specifically, it can be 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 deintercalation at the center will increase, and the difficulty of lithium deintercalation will increase; optionally, it is 6.5 to 7.5 μm.

[0090] In an optional embodiment, the specific surface area of ​​the silicon-carbon negative electrode material is less than 10 m 2 / g, specifically 9m 2 / g, 8m 2 / g, 7m 2 / g, 6m 2 / g, 5m 2 / g, 4m 2 / g, 3m 2 / g, 2m 2 / g, 1m 2 / g or less than 10m 2 Any value within the range of 500 μm / g. The increase in specific surface area can increase the number of active sites for lithium insertion and extraction, which is beneficial to lithium insertion and extraction. However, too large a specific surface area is not conducive to the improvement of the cycle performance of the negative electrode material; it can be less than 5 m 2 / g.

[0091] In an optional embodiment, the tap density of the silicon-carbon negative electrode material is 0.8 to 1.1 g / cm 3 , specifically 0.8 g / 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 improving the energy density of the material, but too high a tap density will reduce the pore structure and increase the difficulty of lithium insertion and extraction; it can be optionally 0.85-1.0 g / cm 3 .

[0092] An embodiment of the present invention provides a method for preparing the silicon-carbon negative electrode material according to any one of the aforementioned embodiments, specifically comprising:

[0093] S1: Carbonizing the carbon source to obtain a precursor;

[0094] S2: activating the precursor in the presence of a first activator to obtain a first activated product;

[0095] S3: subjecting the first activated product to a secondary activation treatment in the presence of a second activating agent to obtain porous carbon;

[0096] S4: Using the porous carbon prepared in step S3 as a substrate, sequentially performing silicon deposition and carbon deposition to obtain the silicon-carbon negative electrode material.

[0097] The present invention prepares a porous carbon substrate with a dendrite-like pore structure by a special secondary activation method. The first activation treatment uses water vapor as an activator to form uniform mesopores in the substrate, so that the average pore size of the pore structure is maintained at 3 to 20 nm. On the basis of the first 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. Because there are carbon-oxygen double bonds between the two, pores are formed again in the adsorbed holes and micropores of 0.4 to 2.0 nm are formed, thereby forming a dendrite-like pore. The first activation pore formation enables the porous carbon substrate to have a good deposition channel, and the second activation pore formation can effectively create uniform micropores around the mesopores. This part of the micropores can provide more space for the deposition of nano-silicon, and can (especially the extremely micropores less than 1 nm) provide additional buffer space for the expansion of nano-silicon particles in the subsequent assembly battery cycle process, and provide more pore structures for the transmission of lithium ions, while ensuring high reversible capacity and charge and discharge efficiency, further improving the overall cycle stability of the silicon-carbon negative electrode material.

[0098] In an optional implementation, in step S1:

[0099] The carbon source is selected from one or more of biomass, high molecular polymer, coal-based, and petroleum-based; all of the above substances are rich in carbon elements. After high-temperature carbonization, the carbon elements are converted into coke, which is used as a precursor for the next step of preparing porous carbon.

[0100] 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, bagasse, nut shell, etc.;

[0101] In an optional embodiment, the high molecular polymer is selected from common polymer types in the art without special restrictions, such as polyethylene, polyurethane, epoxy resin, phenolic resin, urea-formaldehyde resin, etc.;

[0102] In an optional embodiment, the coal base is selected from common types in the art, such as coal pitch, coal tar, etc.;

[0103] In an optional embodiment, the petroleum base is selected from common types in the art, such as petroleum coke, paraffin, and the like.

[0104] In an optional embodiment, the specific temperature and time of the carbonization treatment are adaptively adjusted in the art according to the type of carbon source used.

[0105] In an optional embodiment, the temperature of the carbonization treatment is 500-1500°C; specifically, it can be 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C 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, optionally, the temperature is 800-1500°C.

[0106] In an optional embodiment, the carbonization treatment time is 1 to 20 hours; 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 or any value within the above range.

[0107] In an optional embodiment, the heating rate of the carbonization treatment is 1 to 20°C / min; specifically, it can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min, 20°C / min or any value within the above range.

[0108] In an optional embodiment, in step S2, the activation treatment comprises at least one of the following features:

[0109] In an optional embodiment, the first activator is selected from water vapor. Experiments have found that using water vapor as an activator can create uniform mesopores in the precursor.

[0110] In an optional embodiment, the flow rate of the first activator is 1 to 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 to 10 kg / h; more optionally, it is 1 to 5 kg / h.

[0111] In an optional embodiment, the activation treatment temperature is 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 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 activation treatment temperature is 500-800°C;

[0112] In an optional embodiment, the activation treatment pressure is 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 activation treatment pressure is 1-10 Kpa; more optionally, the activation treatment pressure is 3-8 Kpa.

[0113] In an optional embodiment, the activation treatment time is 1 to 10 hours; specifically, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h or any value within the above range; if the activation treatment time is too long, the degree of activation is too high and the mechanical properties of the substrate deteriorate; if the activation time is too short, the activation effect is poor and a good pore foundation cannot be provided for the secondary activation, thus affecting the secondary activation effect; optionally, the activation treatment time is 3 to 8 hours.

[0114] In a more optional embodiment, the activation treatment is carried out at a temperature of 500-700° C., a pressure of 4-6 KPa, and a time of 4-7 hours.

[0115] In an optional embodiment, the mass ratio of the first activator to the precursor 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.

[0116] In an optional embodiment, in step S3, the secondary activation treatment includes at least one of the following features:

[0117] In an optional embodiment, the second activator is selected from CO and / or CO 2 ; It has been found through experiments that the use of CO and / or CO 2 As an activator, it is used for secondary pore formation. Because of the presence of carbon-oxygen double bonds between them, pores are formed again in the adsorbed pores and micropores are formed, thereby forming a dendritic channel; optionally, the second activator is selected from CO 2 .

[0118] In an optional embodiment, the secondary activation treatment is carried out at 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 rate 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.

[0119] In an optional embodiment, the secondary activation treatment has a pressure of 0.1 to 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 to 8 Kpa.

[0120] In an optional embodiment, the secondary activation treatment time is 0.5 to 10 hours; specifically, it can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h or any value within the above range; if the secondary activation treatment time is too long, the pore structure of the substrate will be destroyed, resulting in deterioration of the mechanical properties of the substrate, while if it is too short, the secondary pore-making effect will be poor and the pore structure will not change significantly; optionally, the secondary activation treatment time is 0.5 to 6 hours.

[0121] In a more optional embodiment, the secondary activation treatment is carried out at a temperature of 700-900° C., a pressure of 3-6 KPa, and a time of 0.5-4 h.

[0122] In an optional embodiment, in the secondary activation treatment, the flow rate of the second activator 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; optionally, it is 1-10 kg / h; more optionally, it is 1-5 kg / h.

[0123] In an optional embodiment, vacuum is first applied before the second activator is introduced. By applying vacuum first and then introducing the second activator, the second activator can more easily enter the mesopores formed by the primary activation under the action of negative pressure, and perform secondary pore formation inside the mesopores, thereby providing additional buffer space for the expansion of the nano-silicon particles during the subsequent battery cycle, and further improving the cycle stability of the secondary battery.

[0124] In an optional embodiment, in the secondary activation treatment, the mass ratio of the first activation product to the second activating agent 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.

[0125] In an optional embodiment, in step S4, the silicon deposition:

[0126] The gas source used includes silicon source gas, inert atmosphere and a second gas source which can be added selectively;

[0127] In an optional embodiment, the silicon source gas is selected from conventional types in the art, including one or more of monosilane, disilane, dichlorosilane, and trichlorosilane.

[0128] The inert atmosphere is used as a carrier gas, and its addition can help improve the safety of vapor deposition. In an optional embodiment, the inert atmosphere is selected from common inert gases such as argon and helium.

[0129] In an optional embodiment, the silicon source gas accounts for 30 to 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 to 80 vol%.

[0130] In an optional embodiment, the total flow rate of the gas source is 1 to 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, 30L / min, 35L / min, 40L / min, 45L / min, 50L / min, 55L / min, 60L / min, 65L / min, 70L / min, 75L / min, 80L / min, 85L / min, 90L / min, 95L / min, 100L / min or any value within the above range; optionally, the total flow rate of the gas source is 5-50L / min; more optionally, the total flow rate of the gas source is 8-12L / min.

[0131] In an optional embodiment, the temperature of silicon deposition is 400-1000°C; specifically, it can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C or any value within the above range; too high a temperature of silicon deposition will cause the size of silicon domains to increase excessively, which is not conducive to improving the cycle performance of negative electrode materials; optionally, the temperature of silicon deposition is 400-600°C; more optionally, the temperature of silicon deposition is 500°C.

[0132] In an optional embodiment, the silicon deposition time is 1 to 50 hours; specifically, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, 50 hours or any value within the above range. The silicon deposition time must match the silicon deposition temperature. If the silicon deposition temperature is high, the deposition time is short; if the silicon deposition temperature is low, the deposition time is appropriately extended.

[0133] The addition of the second gas source can reduce the particle size of the silicon crystal domains (ie, nano-silicon particles), which is more conducive to improving the cycle performance of the negative electrode material.

[0134] 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.

[0135] In an optional embodiment, the carbon source gas is selected from alkane gases whose cracking temperature is within the carbon deposition temperature range, such as common types such as ethylene and acetylene.

[0136] In an optional embodiment, the nitrogen source gas is selected from ammonia.

[0137] In an optional embodiment, the sulfur source gas is selected from one or more of hydrogen sulfide, sulfur dioxide, and sulfur hexafluoride.

[0138] In an optional embodiment, the phosphorus source gas is selected from one or more of phosphine, phosphorus chloride, and phosphorus fluoride.

[0139] Optionally, the second gas source is selected from a carbon source gas and / or a nitrogen source gas; this is beneficial to further improve the conductivity of the silicon-carbon negative electrode material and improve the rate performance of the negative electrode material.

[0140] In an optional embodiment, the second gas source may be mixed with a silicon source gas for co-deposition;

[0141] In an optional embodiment, during co-deposition, the proportion of 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 silicon source gas is 50-80 vol%.

[0142] In an optional embodiment, during co-deposition, the second gas source accounts for 10 to 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 second gas source accounts for 15 to 25 vol%.

[0143] In an alternative embodiment, during co-deposition, the balance is an inert atmosphere as a carrier gas.

[0144] In an optional embodiment, the second source gas may also be deposited alternately with the silicon source gas.

[0145] In an optional embodiment, during alternating deposition, in the mixed gas consisting of the second gas source and the 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%.

[0146] In an optional embodiment, in step S4, the carbon deposition temperature is 300-1200°C; specifically, it 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 above range; if the carbon deposition temperature is too high, the particle size of the silicon domains deposited in the previous step will increase, and if the temperature is too low, the conductivity of the deposited carbon layer will deteriorate.

[0147] In an optional embodiment, in step S4, the carbon deposition time is 2 to 20 hours; specifically, it can be 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.

[0148] In an optional embodiment, the gas source used for the carbon deposition includes a carbon source gas and a carrier gas, and the carbon source gas accounts for 50 to 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 to 80 vol%.

[0149] In an optional embodiment, in step S4, the carbon source gas is selected from an alkane gas having a cracking temperature within the carbon deposition temperature range.

[0150] In an optional embodiment, in step S4, the carrier gas is selected from argon, argon, nitrogen and other gases.

[0151] An embodiment of the present invention provides a negative electrode plate, comprising the silicon-carbon negative electrode material as described in any one of the aforementioned embodiments and the silicon-carbon negative electrode material prepared by the preparation method as described in any one of the aforementioned embodiments.

[0152] An embodiment of the present invention provides a secondary battery, comprising the negative electrode plate as described in the above embodiment, and the secondary battery has excellent cycle stability and both high reversible specific capacity and first coulombic efficiency.

[0153] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0154] Example 1

[0155] S1: 500g of epoxy resin is placed in a carbonization furnace, the temperature of the carbonization furnace is adjusted to 1200°C, and a carbonized product is obtained after carbonization treatment for 3 hours, and a precursor is obtained after graded dispersion;

[0156] S2: placing the precursor obtained in step (1) in an activation furnace, adjusting the temperature of the activation furnace to 600°C and the pressure to 5 KPa, introducing water vapor at a flow rate of 1 kg / h, and performing activation treatment for 5 hours;

[0157] After testing, the performance data of the first activated product prepared in this step are listed in the following Table 1, wherein the pore volume, average pore diameter and specific surface area are obtained by Micromeritics 3020 test.

[0158] S3: After the activation treatment is completed, the temperature of the activation furnace is adjusted to 800°C, vacuum is first drawn, and then carbon dioxide is introduced at a flow rate of 2kg / h until the pressure reaches 4KPa, and a secondary activation treatment is performed for 1h to obtain a porous carbon material;

[0159] After testing, the performance data of the porous carbon material prepared in this step are listed in the following Table 1, wherein the pore volume, average pore diameter and specific surface area are obtained by Micromeritics 3020 test.

[0160] According to the pore size distribution test, in the pores of the porous carbon material prepared in this step, the volume of micropores accounts for 19.7%, the volume of mesopores accounts for 78.1%, and the volume of macropores accounts for 2.2%.

[0161] S4: placing the porous carbon material in a CVD furnace, adjusting the temperature in the furnace to 500°C, introducing a mixed gas consisting of monosilane and argon in a volume ratio of 60:40 at a flow rate of 10 L / min for vapor deposition for 10 h;

[0162] S5: After the deposition is completed, a mixed gas of acetylene and nitrogen with a volume ratio of 70:30 is introduced at a flow rate of 5L / min for carbon coating. The treatment time is 2h. After the coating is completed, the final silicon-carbon negative electrode material is obtained after dispersion, screening, demagnetization and other treatments.

[0163] The performance data of the silicon-carbon negative electrode material prepared in this example are listed in Table 2 below.

[0164] Comparative Example 1

[0165] 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.

[0166] Comparative Example 2

[0167] 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 hours.

[0168] According to the test, in the pores of the porous carbon material prepared in this comparative example, the volume of micropores accounted for 6.4%, the volume of mesopores accounted for 77.7%, and the volume of macropores accounted for 15.9%.

[0169] Comparative Example 3

[0170] The preparation process is basically the same as that in Example 1, except that the order of steps S2 and S3 is swapped, that is, carbon dioxide activation is performed first, and the parameters of the activation treatment are exactly the same as those in Example 1, and then water vapor activation is performed, and the parameters of the activation treatment are also exactly the same as those in Example 1.

[0171] According to the test, in the pores of the porous carbon material prepared in this comparative example, the volume of micropores accounted for 5.9%, the volume of mesopores accounted for 74.7%, and the volume of macropores accounted for 19.4%.

[0172] Comparative Example 4

[0173] 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 for 5 hours is directly performed.

[0174] Comparative Example 5

[0175] The preparation process is basically the same as that of Comparative Example 4, except that the time of the secondary activation treatment is extended to 6 hours.

[0176] According to the test, in the pores of the porous carbon material prepared in this comparative example, the volume of micropores accounted for 42.4%, the volume of mesopores accounted for 53.4%, and the volume of macropores accounted for 4.2%.

[0177] Example 2

[0178] The preparation process is basically the same as that of Example 1, except that the activation time of step S2 is adjusted to 8 h.

[0179] Example 3

[0180] The preparation process is basically the same as that of Example 1, except that the activation time of step S2 is adjusted to 3 h.

[0181] Example 4

[0182] The preparation process is basically the same as that of Example 1, except that in step S3:

[0183] After the activation treatment in step S2 is completed, the temperature of the activation furnace is adjusted to 800° C. and the pressure is adjusted to 4 KPa, and carbon dioxide is introduced at a flow rate of 2 kg / h for secondary activation treatment for 1 hour.

[0184] Example 5

[0185] The preparation process is substantially the same as that of Example 1, except that the carbon dioxide in step S3 is replaced by carbon monoxide of equal volume flow rate.

[0186] Example 6

[0187] The preparation process is basically the same as that of Example 1, except that:

[0188] The carbon source in step S1 was replaced with 500 g of low-temperature asphalt, and the carbonization temperature was replaced with 850°C;

[0189] The silane vapor deposition time in step S4 was adjusted to 5 h.

[0190] Example 7

[0191] The preparation process is basically the same as that of Example 1, except that:

[0192] The carbon source in step S1 was replaced with 500 g of coconut shell powder, the carbonization temperature was replaced with 1300 °C, and the carbonization time was replaced with 5 h;

[0193] The silane gas deposition time in step S4 is adjusted to 15 h.

[0194] Example 8

[0195] The preparation process is substantially the same as that of Example 1, except that in step S4, a mixed gas of monosilane, acetylene and argon in a volume ratio of 7:2:1 is introduced at a flow rate of 10 L / min.

[0196] Example 9

[0197] The preparation process is basically the same as that in Example 1, except that in step S4, monosilane (the volume ratio of monosilane to argon is 8:2) and ammonia (the volume ratio of ammonia to argon is 1:1) are alternately introduced at a flow rate of 5 L / min, each deposition is for 1 hour, and the alternation is 5 times in total.

[0198] Table 1

[0199]

[0200] Table 2

[0201]

[0202]

[0203] Performance Test:

[0204] Batteries were assembled using the products prepared in each embodiment and each comparative example as negative electrode materials.

[0205] (1) Preparation of positive electrode sheets: The positive electrode active material lithium nickel cobalt manganese oxide (NCM811), the conductive agent SuperP, carbon nanotubes, the binder polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) were mixed in a mass ratio of 97:1:0.5:1.5 to form a positive electrode slurry (solid content of 70 wt%), which was coated on both sides of the current collector aluminum foil, dried at 100°C, and cold pressed at 4 MPa at room temperature, and then trimmed, cut, and slit, and the tabs were welded to form positive electrode sheets.

[0206] (2) Preparation of negative electrode sheets: Under a nitrogen protective atmosphere, the solvent N-methylpyrrolidone (NMP) and the binder PVDF were stirred and mixed, and then the conductive agent SuperP was added and stirred and mixed. Then, the products prepared in each embodiment and each comparative example were added as negative electrode active materials and stirred and mixed thoroughly to prepare a negative electrode slurry (solid content of 50wt%).

[0207] The negative electrode slurry is coated on both sides of the current collector copper foil, dried at 100°C, cold pressed at 4MPa at room temperature, and then trimmed, cut, stripped, and the tabs are welded to make negative electrode sheets.

[0208] (3) Assembly of lithium-ion batteries

[0209] Using PE porous polymer film as separator, the prepared positive electrode sheet, separator and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets, and wound to obtain a bare battery cell; the bare battery cell is placed in an aluminum-plastic shell package and placed under a relative vacuum pressure of -0.95×10 5 Pa, dried at 100 ° C to a moisture content of less than 100 ppm. The electrolyte is injected into the dried bare battery, wherein the electrolyte consists of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) (EC:EMC:DEC volume ratio = 1:1:1) and LiPF6 (1.0M), and is packaged, left to stand, formed (0.02C constant current charging for 2h, 0.1C constant current charging for 2h), shaped, and capacity tested (capacity division) to make a soft-pack liquid lithium-ion battery.

[0210] When assembling the battery, five batteries are prepared for each test, and a total of five sets of data are tested. The final performance is the average value of the five sets of data.

[0211] The battery cycle performance is tested on the Xinwei equipment, specifically:

[0212] At 25°C, first 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, and let stand for 10 minutes; then charge at 0.1C to 1.5V, let stand for 10 minutes, record the charge and discharge capacity after the first cycle, and calculate the first coulomb efficiency; cycle 600 times in the above manner, record the charge and discharge capacity after 600 times, and calculate the capacity retention rate after 600 cycles. The tap density is measured by a tap density meter. The specific test / calculation results are shown in Table 3 below:

[0213] Table 3

[0214]

[0215] By comparing the data of Example 1 and Comparative Examples 1 to 2 in Table 3, it can be seen that in Comparative Examples 1 and 2, only the first activation is performed or the first activation time is extended, which is the same as Example 1. At this time, the pore structure is poor, does not have much pore volume, and the average pore size is relatively large. The substrate has weak accommodation and restriction effects on nano-silicon particles; therefore, the cycle stability of the assembled secondary battery is significantly reduced.

[0216] From the data of Example 1 and Comparative Example 3 in Comparative Table 3, it can be seen that when the order of the primary activation and the secondary activation is reversed, small pores are first formed on the precursor in Comparative Example 3, and during the secondary activation, water vapor is adsorbed on the small pores, expanding the pore diameter laterally and vertically, and the average pore diameter increases, but the pore volume does not change significantly. Therefore, the nano-silicon particles obtained during the subsequent silicon deposition are obviously agglomerated, and the cycle stability of the assembled secondary battery deteriorates.

[0217] By comparing the data of Example 1 and Comparative Examples 4 and 5 in Table 3, it can be seen that Comparative Examples 4 and 5 only undergo a second activation, i.e., only carbon dioxide is used as the activation gas, and the average pore size of the obtained pore structure is small, only a small amount of nano-silicon particles enter the substrate, and most of the nano-silicon covers the surface of the substrate, which has no testing value.

[0218] The above-mentioned embodiments are preferred embodiments, but the protection scope of the present invention is not limited thereto. A person skilled in the art can easily understand the spirit of the present invention based on the above-mentioned embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A silicon-carbon negative electrode material, comprising a porous carbon substrate, silicon elements distributed in the pores of the porous carbon substrate, and carbon coated on the outer surface of the porous carbon substrate and the silicon elements, characterized in that: The porous carbon substrate is prepared after two activation treatments, has dendritic pores, and satisfies at least one of the following a to f: a. The volume proportion of micropores is 10~30%; b. The volume proportion of mesopores is 60~90%; c. The volume proportion of macropores is 0~10%; d. Specific surface area not less than 200m 2 / g; e. Pore volume not less than 0.4cm 3 / g; f. Average particle size D50 is 1~20μm; The method for preparing the silicon-carbon negative electrode material comprises: S1: Carbonizing the carbon source to obtain a precursor; S2: activating the precursor in the presence of a first activator to obtain a first activated product; The first activator is selected from water vapor; S3: subjecting the first activated product to a secondary activation treatment in the presence of a second activating agent to obtain porous carbon; The second activator is selected from CO and / or CO2; The secondary activation treatment has a pressure of 0.1~10Kpa; Before introducing the second activator, vacuum is first applied; S4: Using the porous carbon prepared in step S3 as a substrate, sequentially performing silicon deposition and carbon deposition to obtain the silicon-carbon negative electrode material.

2. The silicon-carbon negative electrode material according to claim 1, characterized in that: The average pore size D50 of the silicon-carbon negative electrode material is 6-9 μm; And / or, the specific surface area of ​​the silicon-carbon negative electrode material is less than 10m 2 / g; And / or, the tap density of the silicon-carbon negative electrode material is 0.8-1.1 g / cm 3 .

3. The silicon-carbon negative electrode material according to claim 1, characterized in that: 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 carried out at a temperature of 500-1500°C, for a time of 1-20 hours, and at a heating rate of 1-20°C / min.

4. The silicon-carbon negative electrode material according to claim 1, characterized in that: In step S2, the activation treatment includes at least one of the following features (1) to (4): (1) The flow rate of the first activator is 1-20 kg / h; (2) The activation treatment is carried out at a temperature of 500-1200°C; (3) The activation treatment has a pressure of 0.1~10Kpa; (4) The activation treatment lasts for 1 to 10 hours.

5. The silicon-carbon negative electrode material according to claim 1, characterized in that: In step S3, the secondary activation treatment includes at least one of the following features (i) to (iii): (i) The secondary activation treatment is carried out at a temperature of 500-1200°C; (ii) the secondary activation treatment lasts for 0.5 to 10 hours; (iii) In the secondary activation treatment, the flow rate of the second activating agent is 1-20 kg / h.

6. The silicon-carbon negative electrode material according to claim 1, characterized in that: In step S4, the silicon deposition: The gas source used includes silicon source gas, inert atmosphere and a second gas source that can be added selectively; the silicon source gas accounts for 30-90 vol%; The total flow rate of the gas source is 1~100L / min; The silicon deposition temperature is 400-1000°C and the time is 1-50h; 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 source gas is mixed with the silicon source gas for co-deposition, or is alternately deposited with the silicon source gas.

7. The silicon-carbon negative electrode material according to claim 1, characterized in that: In step S4: The carbon deposition temperature is 300-1200°C and the time is 2-20h; The gas source used in the carbon deposition includes a carbon source gas and a carrier gas, and the carbon source gas accounts for 50-99 vol%; The carbon source gas is selected from alkane gases whose cracking temperature is within the carbon deposition temperature range.

8. A negative electrode plate, characterized in that: Comprising the silicon-carbon negative electrode material as described in any one of claims 1 to 7.

9. A secondary battery, characterized in that: Comprising the negative electrode sheet as described in claim 8.

Images