Silicon-carbon material, preparation method thereof, negative electrode material, negative electrode plate and battery

Abstract

The invention provides a silicon-carbon material and a preparation method thereof, a negative electrode material, a negative electrode plate and a battery, the silicon-carbon material comprises a plurality of primary particles, the plurality of primary particles are bonded by an amorphous carbon network structure to form secondary particles, the primary particles comprise porous carbon and nitrogen and phosphorus co-doped nano silicon deposited in the porous carbon holes, and the nitrogen and phosphorus co-doped nano silicon is bonded by an amorphous carbon network structure. At least part of the surface of the primary particles is provided with a first carbon coating layer. Therefore, the fast charging performance and the rate capability of the silicon-carbon material are improved.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and specifically, to silicon-carbon materials and their preparation methods, as well as anode materials, anode plates, and batteries. Background Art

[0002] Compared with traditional graphite anodes (the theoretical energy density is 372 mAh / g), silicon anodes have a higher theoretical energy density (4200 mAh / g). Therefore, silicon-based anodes are regarded as the next-generation anode materials most likely to replace traditional graphite. However, due to a series of problems inherent in silicon particles themselves, such as volume expansion effect and poor conductivity, the wide application of silicon-carbon composites is limited. In recent years, the composite structure design of a new type of silicon-carbon material (porous carbon-deposited nano-silicon) has received extensive attention. With the help of the rich pore structure inside the porous carbon, gaseous silicon sources are deposited into the pores of the porous carbon at a certain temperature, solving the problem of silicon particle agglomeration and pulverization. However, the problem of poor conductivity of silicon-based materials still exists at present, restricting their application in the fast-charging field. Therefore, the current silicon-carbon materials still need to be further improved. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to some extent.

[0004] In one aspect of the present invention, a silicon-carbon material is proposed, which includes a plurality of primary particles. The plurality of primary particles are bonded by an amorphous carbon network structure to form secondary particles. The primary particles include porous carbon and nitrogen-phosphorus co-doped nano-silicon deposited in the pores of the porous carbon. At least part of the surface of the primary particles has a first carbon coating layer. Thereby, the ionic conductivity and electronic conductivity of the silicon-carbon material are improved, and the fast-charging performance and rate performance of the silicon-carbon material are improved.

[0005] According to some embodiments of the present invention, based on the total mass of the silicon-carbon material, the mass ratio of nitrogen and phosphorus is 0.1%-1%. Thereby, the electronic conductivity of the silicon-based material is improved.

[0006] According to some embodiments of the present invention, the volume average particle size Dv50 of the porous carbon satisfies: 1 μm ≤ Dv50 ≤ 5 μm.

[0007] According to some embodiments of the present invention, at least one of the following conditions is satisfied: the silicon-carbon material further includes a conductive additive; at least part of the surface of the secondary particles has a second carbon coating layer. Thereby, the electronic conductivity of the silicon-carbon material is improved.

[0008] According to some embodiments of the present invention, the silicon-carbon material satisfies at least one of the following conditions: the powder resistivity of the silicon-carbon material is 0.1 Ω·cm - 1 Ω·cm; the cycle capacity retention rate of the silicon-carbon material after 50 cycles of constant current charge and discharge at 5C is greater than or equal to 85%.

[0009] According to some embodiments of the present invention, the silicon-carbon material satisfies at least one of the following conditions: based on the total mass of the silicon-carbon material, the mass proportion of the nano-silicon is 40% - 50%; based on the total mass of the silicon-carbon material, the mass proportion of the conductive additive is 1% - 5%; based on the total mass of the silicon-carbon material, the mass proportion of the amorphous carbon network structure is 1% - 5%. Thereby, the energy density and fast charging performance of the silicon-carbon material are improved.

[0010] According to some embodiments of the present invention, the volume average particle size Dv50 of the silicon-carbon material satisfies: 10 μm ≤ Dv50 ≤ 20 μm. Thereby, the uniformity of silicon deposition is improved.

[0011] In another aspect of the present invention, a method for preparing the aforementioned silicon-carbon material is proposed, including: placing porous carbon in a reactor, introducing a mixed gas of a silicon source gas, a phosphorus source gas, and a nitrogen source gas into the reactor, and performing a first heat treatment to obtain primary particles; introducing a first organic gas source into the reactor containing the primary particles, and performing a second heat treatment to form a first carbon coating layer on at least part of the surface of the primary particles; mixing the primary particles containing the first carbon coating layer with a binder solution, spray granulating to obtain secondary particles and performing a third heat treatment to obtain the silicon-carbon material. Thereby, the silicon-carbon material prepared by this method has excellent fast charging performance and rate performance.

[0012] According to some embodiments of the present invention, the primary particles containing the first carbon coating layer are mixed with a conductive additive and a binder solution.

[0013] According to some embodiments of the present invention, the third heat treatment includes: introducing a second organic gas source into the reactor to form a second carbon coating layer on at least part of the surface of the secondary particles.

[0014] According to some embodiments of the present invention, the method satisfies at least one of the following conditions: the temperature of the first heat treatment is 450°C - 550°C; the temperature of the second heat treatment is 550°C - 650°C; the temperature of the third heat treatment is 600°C - 900°C.

[0015] According to some embodiments of the present invention, the method satisfies at least one of the following conditions: the volume average particle size Dv50 of the porous carbon satisfies: 1 μm ≤ Dv50 ≤ 5 μm; the specific surface area of the porous carbon is greater than or equal to 1400m2 / g; the phosphorus source includes at least one of phosphorus pentoxide, triphenylphosphine, phytic acid, and phosphine; the nitrogen source includes at least one of melamine, polydopamine, urea, thiourea, and ammonia; the conductive additive includes at least one of graphene, carbon nanotubes, and Ketjen black; the binder includes at least one of glucose, sucrose, citric acid, phenolic resin, and asphalt; the first organic gas source and the second organic gas source each independently include at least one of methane, acetylene, propylene, and propane.

[0016] In another aspect of the present invention, a negative electrode material is provided, which includes the aforementioned silicon-carbon material. Thereby, the fast charging performance of the negative electrode material is improved.

[0017] In another aspect of the present invention, a negative electrode sheet is provided, which includes the aforementioned negative electrode material. Thereby, the fast charging ability of the battery is improved.

[0018] In another aspect of the present invention, a battery is provided, which includes the aforementioned negative electrode sheet. Thereby, the fast charging ability of the battery is improved. Description of the Drawings

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, wherein:

[0020] Figure 1 is a schematic structural diagram of a silicon-carbon material according to an embodiment of the present invention;

[0021] Figure 2 shows the dQ / dV curve of the silicon-carbon material in Example 1;

[0022] Figure 3 shows the dQ / dV curve of the silicon-carbon material in Example 2;

[0023] Figure 4 shows the dQ / dV curve of the silicon-carbon material in Example 3;

[0024] Figure 5 shows the dQ / dV curve of the silicon-carbon material in Example 4;

[0025] Figure 6 shows the dQ / dV curve of the silicon-carbon material in Example 5;

[0026] Figure 7 shows the dQ / dV curve of the silicon-carbon material in Example 6;

[0027] Figure 8 shows the dQ / dV curve of the silicon-carbon material in Comparative Example 1;

[0028] Figure 9Shows the dQ / dV curve of the silicon-carbon material in Comparative Example 2;

[0029] Figure 10 Shows the dQ / dV curve of the silicon-carbon material in Comparative Example 3. Specific Embodiments

[0030] The embodiments of the present invention will be described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention. For technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0031] In one aspect of the present invention, a silicon-carbon material is proposed. Referring to Figure 1 , the silicon-carbon material includes a plurality of primary particles, and the plurality of primary particles are bonded by an amorphous carbon network structure to form secondary particles. The primary particles include porous carbon and nitrogen-phosphorus co-doped nanosilicon deposited in the pores of the porous carbon. At least part of the surface of the primary particles has a first carbon coating layer. Thereby, the fast charging performance of the silicon-carbon material is improved.

[0032] The principle by which the present invention can achieve the above beneficial effects will be described in detail below:

[0033] Due to the poor electronic conductivity of silicon, the application of silicon-carbon materials in the high-rate and fast-charging fields is limited. In order to improve the conductivity of silicon materials, the present invention dopes nitrogen and phosphorus into nanosilicon. The nitrogen element and phosphorus element are doped into the lattice of silicon, replacing part of the position of silicon. Both nitrogen atoms and phosphorus atoms can form covalent bonds with silicon atoms, contributing free electrons, increasing the concentration of free electrons in the silicon-carbon material, thereby reducing the energy band gap of silicon and improving the conductivity of silicon. If nitrogen and phosphorus are doped on the porous carbon, it is impossible to dope nitrogen atoms and phosphorus atoms into the lattice of silicon, and it is impossible to reduce the energy band gap of silicon, and the improvement of the rate performance of the silicon-carbon material is limited. At the same time, in the silicon-carbon material proposed by the present invention, a plurality of primary particles are connected by an amorphous carbon network structure. During the transmission process of active ions, the amorphous carbon network structure can provide a fast channel for the transmission of active ions, realizing the rapid insertion and extraction of active ions, enabling the active ions to quickly reach the inside of the silicon particles, and further improving the fast charging performance of the silicon-carbon material. During the process of insertion and extraction of active ions, the amorphous carbon network structure can also relieve the volume expansion of the silicon-carbon material, avoid the collapse of the electrode structure, and improve the cycle life of the battery.

[0034] The active ions in the present invention include lithium ions.

[0035] According to some embodiments of the present invention, based on the total mass of the silicon-carbon material, the mass ratio of nitrogen and phosphorus is 0.1%-1%. For example, it can be 0.1%, 0.2%, 0.4%, 0.6%, 0.8% or 1%, etc., or it can be a range composed of any of the above values. Thus, nitrogen atoms and phosphorus atoms can contribute more free electrons, increase the concentration of free electrons in the silicon-carbon material, thereby reducing the energy band gap of silicon, improving the electrical conductivity of silicon, improving the electrical conductivity of the silicon-carbon material, and improving the fast charging performance of the silicon-carbon material.

[0036] In the present invention, an elemental analyzer is used to test the content of N element, and an inductively coupled plasma spectrometer is used to test the content of P element.

[0037] According to some embodiments of the present invention, the volume average particle size Dv50 of the porous carbon satisfies: 1μm ≤ Dv50 ≤ 5μm. For example, it can be 1μm, 2μm, 3μm, 4μm or 5μm, etc., or it can be a range composed of any of the above values. Thus, multiple porous carbons with small particle sizes (primary particles) are combined to form secondary particles, and multiple primary particles are connected through an amorphous carbon network structure. During the active ion transport process, the amorphous carbon network structure can provide a fast channel for the transport of active ions. At the same time, the porous carbon with small particle sizes can shorten the diffusion path of active ions, realize the rapid insertion and extraction of active ions, enable active ions to quickly reach the inside of silicon particles, and further improve the fast charging performance of the silicon-carbon material. During the process of insertion and extraction of active ions, the amorphous carbon network structure can also relieve the volume expansion of the silicon-carbon material, prevent the collapse of the electrode structure, and improve the cycle life of the battery.

[0038] In the present invention, Dv50 refers to the particle size corresponding to when the cumulative volume distribution percentage reaches 50%. For example, Dv50 can be measured with a laser particle size analyzer (such as Malvern Master Size 3000) with reference to Standard GB / T 19077-2016.

[0039] According to some embodiments of the present invention, referring to Figure 1 , the silicon-carbon material further includes a conductive additive. Thus, the electrical conductivity of the silicon-carbon material is improved.

[0040] According to some embodiments of the present invention, referring to Figure 1 , at least part of the surface of the secondary particle has a second carbon coating layer. Thus, the second carbon coating layer can limit the volume expansion of silicon while improving the electrical conductivity of the silicon-carbon material.

[0041] According to some embodiments of the present invention, the powder resistivity of the silicon-carbon material is 0.1 Ω·cm - 1 Ω·cm. For example, it can be 0.1 Ω·cm, 0.2 Ω·cm, 0.4 Ω·cm, 0.6 Ω·cm, 0.8 Ω·cm, 1 Ω·cm, etc., or it can be a range composed of any of the above values. Thereby, the conductivity of the silicon-carbon material is improved.

[0042] In the present invention, the powder resistance of the silicon-carbon composite material is measured using a powder resistivity measuring instrument with reference to GB / T 24521-2018. The silicon-carbon composite material is added into the sample cylinder, tamped and leveled the upper surface of the sample, then placed it in the testing machine, applied a pressure of 4 Mpa, and measured the height of the sample. Adjust the regulated power supply to make the current passing through the sample be 500 mA ± 0.1 mA, and measure the voltage drop of the sample. Finally, calculate the powder resistivity of the sample according to Ohm's law.

[0043] According to some embodiments of the present invention, the cycling capacity retention rate of the silicon-carbon material after 50 cycles of constant current charge and discharge at 5C is greater than or equal to 85%.

[0044] In the present invention, the testing method of the cycling capacity retention rate is to charge and discharge the coin cell at a rate of 5C at 25°C, and calculate the charge capacity retention rate after 50 cycles.

[0045] According to some embodiments of the present invention, based on the total mass of the silicon-carbon material, the mass proportion of the nano-silicon can be 40% - 50%. For example, it can be 40%, 42%, 44%, 46%, 48% or 50%, etc., or it can be a range composed of any of the above values. Thereby, the energy density of the silicon-carbon material is improved.

[0046] In the present invention, the testing method of the nano-silicon content is to analyze the silicon content in the material using ICP-MS after microwave digestion, and use an inductively coupled plasma mass spectrometer of model ICP-MS 7500CE produced by Agilent Company of the United States to test the Si element content in the material.

[0047] According to some embodiments of the present invention, based on the total mass of the silicon-carbon material, the mass proportion of the conductive additive is 1% - 5%. For example, it can be 1%, 2%, 3%, 4% or 5%, etc., or it can be a range composed of any of the above values. Thereby, the conductivity of the silicon-carbon material is improved.

[0048] According to some embodiments of the present invention, based on the total mass of the silicon-carbon material, the mass proportion of the amorphous carbon network structure is 1%-5%. For example, it can be 1%, 2%, 3%, 4% or 5%, etc., or it can be a range composed of any of the above values. Thus, a fast channel is provided for the transport of active ions, enabling the rapid insertion and extraction of active ions. At the same time, the volume expansion of the silicon-carbon material is alleviated, the collapse of the electrode structure is avoided, and the cycle life of the battery is improved.

[0049] According to some embodiments of the present invention, the volume average particle size Dv50 of the silicon-carbon material satisfies: 10μm ≤ Dv50 ≤ 20μm. For example, it can be 10μm, 12μm, 14μm, 16μm, 18μm or 20μm, etc., or it can be a range composed of any of the above values. Thus, the uniformity of silicon deposition is improved, and the energy density of the silicon-carbon material is increased.

[0050] In another aspect of the present invention, a method for preparing the aforementioned silicon-carbon material is proposed, including: placing porous carbon in a reactor, introducing a mixed gas of a silicon source gas, a phosphorus source gas, and a nitrogen source gas into the reactor, and performing a first heat treatment to obtain primary particles; introducing a first organic gas source into the reactor containing the primary particles, and performing a second heat treatment to form a first carbon coating layer on at least part of the surface of the primary particles; mixing the primary particles containing the first carbon coating layer with a binder solution, spray granulating to obtain secondary particles and performing a third heat treatment to obtain the silicon-carbon material. Thus, for the silicon-carbon material prepared by this method, through the nitrogen and phosphorus doping of nano-silicon, the nitrogen element and the phosphorus element are doped into the silicon lattice, which can replace part of the silicon positions. Both nitrogen atoms and phosphorus atoms can form covalent bonds with silicon atoms, contributing free electrons, thereby increasing the concentration of free electrons in the silicon-carbon material, reducing the energy band gap of silicon, and further improving the conductivity of silicon. At the same time, multiple primary particles are connected by an amorphous carbon network structure. During the transport process of active ions, the amorphous carbon network structure can provide a fast channel for the transport of active ions, enabling the rapid insertion and extraction of active ions, allowing active ions to quickly reach the inside of silicon particles, and further improving the fast charging performance of the silicon-carbon material. During the process of insertion and extraction of active ions, the amorphous carbon network structure can also alleviate the volume expansion of the silicon-carbon material, avoid the collapse of the electrode structure, and improve the cycle life of the battery.

[0051] The following details each step of this method:

[0052] S100: Prepare primary particles

[0053] In this step, porous carbon is placed in a reactor, and a mixed gas of a silicon source gas, a phosphorus source gas, and a nitrogen source gas is introduced into the reactor, and a first heat treatment is performed to obtain primary particles.

[0054] According to some embodiments of the present invention, the volume average particle size Dv50 of the porous carbon satisfies: 1 μm ≤ Dv50 ≤ 5 μm. For example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc., or it can be a range composed of any of the above values. Thus, using porous carbon with a small particle size for granulation to form secondary particles can shorten the transport path of active ions and improve the ionic conductivity of the silicon-carbon material.

[0055] According to some embodiments of the present invention, the specific surface area of the porous carbon is greater than or equal to 1400 m 2 / g. For example, it can be 1400 m 2 / g, 1600 m 2 / g, 1800 m 2 / g, or 2000 m 2 / g, etc., or it can be a range composed of any of the above values.

[0056] In the present invention, the specific surface area of the porous carbon is tested using a static specific surface area analyzer.

[0057] According to some embodiments of the present invention, the porous carbon is placed in a tubular reactor, the phosphorus source and the nitrogen source are placed in the gasification chamber, and the gas mixture of the gasified phosphorus source, nitrogen source, and silicon source is introduced into the tubular reactor.

[0058] As an example, the phosphorus source includes at least one of phosphorus pentoxide, triphenylphosphine, phytic acid, and phosphine. When the phosphorus source is phosphine, the hydrogen generated by the decomposition of phosphine can inhibit the decomposition rate of the silicon source gas, enable more silicon to be deposited in the pores of the porous carbon, and reduce the degree of silicon coating on the surface of the silicon-carbon material.

[0059] As an example, the nitrogen source includes at least one of melamine, polydopamine, urea, thiourea, and ammonia.

[0060] As an example, the silicon source includes but is not limited to at least one of silane and chlorosilane. Thus, the source of the silicon source gas is wide, which can meet various designs for preparing the silicon-carbon material.

[0061] As an example, the porous carbon includes but is not limited to at least one of biomass carbon, resin carbon, and porous graphite. Thus, the source of the porous carbon is wide, which can meet various designs for preparing the silicon-carbon material.

[0062] According to some embodiments of the present invention, the temperature of the first heat treatment can be 400°C - 500°C. For example, it can be 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, etc., or it can be a range composed of any of the above values.

[0063] S200: Form a first carbon coating layer on at least part of the surface of the primary particles

[0064] In this step, a first organic gas source is introduced into the reactor containing the primary particles for a second heat treatment to form a first carbon coating layer on at least a part of the surface of the primary particles. Thereby, the conductivity of the silicon-carbon material is improved.

[0065] According to some embodiments of the present invention, the temperature of the second heat treatment can be 550°C - 650°C. For example, it can be 550°C, 570°C, 590°C, 610°C, 630°C or 650°C, etc., or can be a range composed of any of the above values.

[0066] As an example, the first organic gas source includes at least one of methane, acetylene, propylene, and propane.

[0067] S300: Prepare secondary particles

[0068] In this step, the primary particles containing the first carbon coating layer are mixed with a binder solution, spray granulated, and the secondary particles are obtained and subjected to a third heat treatment to obtain the silicon-carbon material.

[0069] According to some embodiments of the present invention, the temperature of the third heat treatment can be 600°C - 900°C. For example, it can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 900°C, etc., or can be a range composed of any of the above values.

[0070] According to some embodiments of the present invention, this step may further include mixing the primary particles containing the first carbon coating layer with a conductive additive and a binder solution, spray granulating, and obtaining secondary particles and performing a third heat treatment to obtain the silicon-carbon material. Thereby, the conductivity of the silicon-carbon material is improved.

[0071] As an example, the binder may include at least one of glucose, sucrose, citric acid, phenolic resin, and pitch. The above types of binders are carbonized after the third heat treatment to form an amorphous carbon network structure. Thereby, the amorphous carbon network structure can provide a fast channel for the transport of active ions, realize the rapid insertion and extraction of active ions, and at the same time, relieve the volume expansion of the silicon-carbon material, avoid the collapse of the electrode structure, and improve the cycle life of the battery.

[0072] As an example, the solvent for dissolving the primary particles and the binder includes at least one of ethanol, isopropanol, and N-methylpyrrolidone (NMP).

[0073] According to some embodiments of the present invention, the third heat treatment includes: introducing a second organic gas source into the reactor to form a second carbon coating layer on at least a part of the surface of the secondary particles. Thus, the second carbon coating layer can improve the conductivity of the silicon-carbon material while restricting the volume expansion of silicon.

[0074] As an example, the conductive additive may include at least one of graphene, carbon nanotubes, and Ketjen black.

[0075] As an example, the second organic gas source includes at least one of methane, acetylene, propylene, and propane.

[0076] In yet another aspect of the present invention, a negative electrode material is proposed, including the aforementioned silicon-carbon material. Thus, the fast charging performance of the negative electrode material is improved.

[0077] In yet another aspect of the present invention, a negative electrode plate is proposed, including the aforementioned negative electrode material. Thus, the fast charging performance of the negative electrode material is improved.

[0078] In yet another aspect of the present invention, a battery is proposed, including the aforementioned negative electrode plate. Thus, the fast charging performance of the battery is improved.

[0079] The solution of the present invention will be described below through specific examples. It should be noted that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples in terms of specific technology or conditions, they shall be carried out according to the technology or conditions described in the literature in the field or according to the product specifications. For those reagents or instruments not specified in terms of the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0080] Example 1

[0081] Add 500 g of porous carbon raw material with a particle size Dv50 = 3 μm into a fluidized bed reactor, and introduce nitrogen at a flow rate of 20 L / min for replacement and purging. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 8 °C / min. After the reactor temperature rises to 520 °C, introduce silane gas at a flow rate of 1.5 L / min, hydrogen at a flow rate of 10 L / min, phosphine gas at a flow rate of 0.01 L / min, and ammonia gas at a flow rate of 0.01 L / min, and react for 270 min. After the reaction is completed, heat the reactor to 600 °C at a heating rate of 4 °C / min, introduce acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 10 L / min, and continue the deposition reaction for 160 min. After the reaction is completed, cool down in a nitrogen atmosphere at a flow rate of 10 L / min. When the reactor temperature drops to 50 °C, discharge the material to obtain an intermediate product P1.

[0082] After discharging, the intermediate product P1 is stirred and mixed evenly with 1000 g of graphene slurry with a solid content of 2%, 100 g of glucose, 100 g of citric acid, and 3.4 L of isopropanol to obtain a slurry with a solid content of 25%. The above slurry is processed using a spray drying device, with the inlet air temperature set at 160 °C, the exhaust air temperature set at 80 °C, and the atomizing disk rotation speed set at 50 Hz to obtain the secondary particle powder intermediate product P2.

[0083] The above secondary particle intermediate product P2 is loaded into a rotary kiln, and nitrogen is used to displace the kiln furnace. When the oxygen content in the rotary kiln drops to 500 ppm, the reactor is heated at a heating rate of 5 °C / min. When the reactor temperature rises to 700 °C, 1 L / min of acetylene and 2 L / min of nitrogen are introduced, and the deposition reaction is continued for 240 min. After cooling and discharging, silicon-carbon material 1 is obtained.

[0084] Example 2

[0085] 500 g of porous carbon raw material with a particle size Dv50 = 1 um is added to a fluidized bed reactor, and 20 L / min of nitrogen is introduced for displacement and purging. When the oxygen content drops to 500 ppm, the reactor is heated at a heating rate of 8 °C / min. After the reactor temperature rises to 480 °C, 1.5 L / min of silane gas, 10 L / min of hydrogen gas, 0.02 L / min of phosphine gas, and 0.02 L / min of ammonia gas are introduced, and the reaction is carried out for 270 min. After the reaction ends, the reactor is heated at a heating rate of 4 °C / min to 600 °C, 1 L / min of acetylene and 10 L / min of nitrogen are introduced, and the deposition reaction is continued for 160 min. After the reaction ends, it is cooled in an atmosphere of 10 L / min of nitrogen. When the reactor drops to 50 °C, it is discharged to obtain the intermediate product P1.

[0086] After discharging, the intermediate product P1 is stirred and mixed evenly with 20 g of Ketjen black, 100 g of glucose, 100 g of citric acid, and 4.6 L of isopropanol to obtain a slurry with a solid content of 25%. The above slurry is processed using a spray drying device, with the inlet air temperature set at 160 °C, the exhaust air temperature set at 80 °C, and the atomizing disk rotation speed set at 50 Hz to obtain the secondary particle powder intermediate product P2.

[0087] The above secondary particle intermediate product P2 is loaded into a rotary kiln, and nitrogen is used to displace the kiln furnace. When the oxygen content in the rotary kiln drops to 500 ppm, the reactor is heated at a heating rate of 5 °C / min. When the reactor temperature rises to 700 °C, 1 L / min of acetylene and 2 L / min of nitrogen are introduced, and the deposition reaction is continued for 240 min. After cooling and discharging, silicon-carbon material 2 is obtained.

[0088] Example 3

[0089] 500 g of porous carbon raw material with a particle size Dv50 = 2 μm was added into a fluidized bed reactor, and nitrogen was introduced at a flow rate of 20 L / min for replacement and purging. When the oxygen content decreased to 500 ppm, the reactor was heated at a heating rate of 8 °C / min. After the reactor temperature reached 500 °C, silane gas with a flow rate of 1.5 L / min, hydrogen with a flow rate of 10 L / min, phosphine gas with a flow rate of 0.04 L / min, and ammonia gas with a flow rate of 0.04 L / min were introduced, and the reaction was carried out for 270 min. After the reaction ended, the reactor was heated to 600 °C at a heating rate of 4 °C / min, 1 L / min of acetylene and 10 L / min of nitrogen were introduced, and the continuous deposition reaction was carried out for 160 min. After the reaction ended, it was cooled in a nitrogen atmosphere with a flow rate of 10 L / min. When the reactor temperature dropped to 50 °C, the product was discharged to obtain intermediate P1.

[0090] After discharging, intermediate P1 was stirred and mixed evenly with 40 g of carbon nanotubes, 100 g of glucose, 100 g of citric acid, and 4.6 L of isopropanol to obtain a slurry with a solid content of 25%. The above slurry was processed by a spray drying device, with the inlet air temperature set at 160 °C, the outlet air temperature set at 80 °C, and the atomizing disk rotation speed set at 50 Hz to obtain secondary particle powder intermediate P2.

[0091] The above secondary particle intermediate P2 was loaded into a rotary kiln, and the kiln was replaced with nitrogen. When the oxygen content in the rotary kiln decreased to 500 ppm, the reactor was heated at a heating rate of 5 °C / min. When the reactor temperature reached 700 °C, 1 L / min of acetylene and 2 L / min of nitrogen were introduced, and the continuous deposition reaction was carried out for 240 min. After cooling and discharging, silicon-carbon material 3 was obtained.

[0092] Example 4

[0093] 500 g of porous carbon raw material with a particle size Dv50 = 5 μm was added into a fluidized bed reactor, and nitrogen was introduced at a flow rate of 20 L / min for replacement and purging. When the oxygen content decreased to 500 ppm, the reactor was heated at a heating rate of 8 °C / min. After the reactor temperature reached 520 °C, silane gas with a flow rate of 1.5 L / min, nitrogen with a flow rate of 10 L / min, phosphine gas with a flow rate of 0.06 L / min, and ammonia gas with a flow rate of 0.06 L / min were introduced, and the reaction was carried out for 270 min. After the reaction ended, the reactor was heated to 600 °C at a heating rate of 4 °C / min, 1 L / min of acetylene and 10 L / min of nitrogen were introduced, and the continuous deposition reaction was carried out for 160 min. After the reaction ended, it was cooled in a nitrogen atmosphere with a flow rate of 10 L / min. When the reactor temperature dropped to 50 °C, the product was discharged to obtain intermediate P1.

[0094] After discharging, the intermediate product P1 is stirred and mixed evenly with 50 g of Ketjen black, 100 g of glucose, 100 g of citric acid, and 4.6 L of isopropanol to obtain a slurry with a solid content of 25%. The above slurry is processed using a spray drying device, with the inlet air temperature set at 160 °C, the exhaust air temperature set at 80 °C, and the atomizing disk rotation speed set at 50 Hz, to obtain the secondary particle powder intermediate product P2.

[0095] The above secondary particle intermediate product P2 is loaded into a rotary kiln, and nitrogen is used to displace the kiln furnace. When the oxygen content in the rotary kiln is reduced to 500 ppm, the reactor is heated at a heating rate of 5 °C / min. When the reactor temperature rises to 700 °C, 1 L / min of acetylene and 2 L / min of nitrogen are introduced, and the deposition reaction is continued for 240 min. After cooling and discharging, silicon-carbon material 4 is obtained.

[0096] Example 5

[0097] 500 g of porous carbon raw materials with a particle size Dv50 = 2 μm are added to a fluidized bed reactor, and 20 L / min of nitrogen is introduced for displacement and purging. When the oxygen content is reduced to 500 ppm, the reactor is heated at a heating rate of 8 °C / min. After the reactor temperature rises to 520 °C, 1.5 L / min of silane gas, 10 L / min of nitrogen, 0.08 L / min of phosphine gas, and 0.08 L / min of ammonia gas are introduced, and the reaction is carried out for 270 min. After the reaction ends, the reactor is heated at a heating rate of 4 °C / min to 600 °C, 1 L / min of acetylene and 10 L / min of nitrogen are introduced, and the deposition reaction is continued for 160 min. After the reaction ends, it is cooled in an atmosphere of 10 L / min of nitrogen. When the reactor temperature drops to 50 °C, it is discharged to obtain the intermediate product P1.

[0098] After discharging, the intermediate product P1 is stirred and mixed evenly with 10 g of carbon nanotubes, 100 g of glucose, 100 g of citric acid, and 4.6 L of isopropanol to obtain a slurry with a solid content of 25%. The above slurry is processed using a spray drying device, with the inlet air temperature set at 160 °C, the exhaust air temperature set at 80 °C, and the atomizing disk rotation speed set at 50 Hz, to obtain the secondary particle powder intermediate product P2.

[0099] The above secondary particle intermediate product P2 is loaded into a rotary kiln, and nitrogen is used to displace the kiln furnace. When the oxygen content in the rotary kiln is reduced to 500 ppm, the reactor is heated at a heating rate of 5 °C / min. When the reactor temperature rises to 700 °C, 1 L / min of acetylene and 2 L / min of nitrogen are introduced, and the deposition reaction is continued for 240 min. After cooling and discharging, silicon-carbon material 5 is obtained.

[0100] Example 6

[0101] Add 500 g of porous carbon raw material with a particle size Dv50 = 2 μm into a fluidized bed reactor, and introduce nitrogen at a flow rate of 20 L / min for replacement and purging. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 8 °C / min. After the reactor temperature rises to 520 °C, introduce silane gas at a flow rate of 1.5 L / min, hydrogen at a flow rate of 10 L / min, phosphine gas at a flow rate of 0.1 L / min, and ammonia gas at a flow rate of 0.1 L / min, and react for 270 min. After the reaction is completed, heat the reactor to 600 °C at a heating rate of 4 °C / min, introduce 1 L / min of acetylene and 10 L / min of nitrogen, and continue the deposition reaction for 160 min. After the reaction is completed, cool down in a nitrogen atmosphere at a flow rate of 10 L / min. When the reactor temperature drops to 50 °C, discharge the material to obtain the intermediate product P1.

[0102] After discharging, mix the intermediate product P1 evenly with 100 g of glucose, 100 g of citric acid, and 3.6 L of ethanol to obtain a slurry with a solid content of 25%. Use spray drying equipment to process the above slurry, set the inlet air temperature at 160 °C, the outlet air temperature at 80 °C, and the rotation speed of the atomizing disk at 50 Hz to obtain the intermediate product P2 of the secondary particle powder.

[0103] Load the above intermediate product P2 of the secondary particles into a rotary kiln, use nitrogen to replace the kiln, and when the oxygen content in the rotary kiln is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min. When the reactor temperature rises to 900 °C, introduce 1 L / min of acetylene and 2 L / min of nitrogen, and continue the deposition reaction for 240 min. Cool down and discharge to obtain the silicon-carbon material 6.

[0104] Comparative Example 1

[0105] Mix 1 kg of coconut shell particles evenly with 5 g of phytic acid and 5 g of urea, place them in a carbonization kiln for carbonization treatment, set the carbonization temperature at 900 °C, and carbonize for 4 h to prepare a nitrogen and phosphorus co-doped coconut shell carbon material. Then put the coconut shell carbon into a fluidized bed reactor, introduce 1 L / min of water vapor and 2 L / min of N2, and activate for 2 h to obtain nitrogen and phosphorus co-doped porous carbon particles with a specific surface area of 1500 m 2 / g.

[0106] Add 500 g of the above-mentioned porous carbon raw material with a particle size Dv50 = 3 μm into a fluidized bed reactor, and introduce nitrogen at a flow rate of 20 L / min for displacement and purging. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 8 °C / min. After the reactor temperature rises to 520 °C, introduce silane gas at a flow rate of 1.5 L / min and nitrogen at a flow rate of 10 L / min for reaction for 270 min. After the reaction is completed, heat the reactor to 600 °C at a heating rate of 4 °C / min, introduce acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 10 L / min, and continue the deposition reaction for 160 min. After the reaction is completed, cool down in a nitrogen atmosphere with a flow rate of 10 L / min. When the reactor temperature drops to 50 °C, discharge the material to obtain a composite material of silicon-nitrogen-phosphorus-doped porous carbon.

[0107] Comparative Example 2

[0108] Add 500 g of porous carbon raw material with a particle size Dv50 = 3 μm into a fluidized bed reactor, and introduce nitrogen at a flow rate of 20 L / min for displacement and purging. When the oxygen content is reduced to 500 ppm, heat the reactor at a heating rate of 8 °C / min. After the reactor temperature rises to 520 °C, introduce silane gas at a flow rate of 1.5 L / min and nitrogen at a flow rate of 10 L / min for reaction for 270 min. After the reaction is completed, heat the reactor to 600 °C at a heating rate of 4 °C / min, introduce acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 10 L / min, and continue the deposition reaction for 160 min. After the reaction is completed, cool down in a nitrogen atmosphere with a flow rate of 10 L / min. When the reactor temperature drops to 50 °C, discharge the material to obtain intermediate product P1.

[0109] After discharging, stir and mix the intermediate product P1 evenly with 1000 g of graphene slurry with a solid content of 2%, 100 g of glucose, 100 g of citric acid, and 3.4 L of isopropanol to obtain a slurry with a solid content of 25%. Use a spray drying device to process the above slurry, set the inlet air temperature at 160 °C, the outlet air temperature at 80 °C, and the atomizing disk rotation speed at 50 Hz to obtain secondary particle powder intermediate product P2.

[0110] Load the above secondary particle intermediate product P2 into a rotary kiln, use nitrogen to displace the kiln, and when the oxygen content in the rotary kiln is reduced to 500 ppm, heat the reactor at a heating rate of 5 °C / min. When the reactor temperature rises to 700 °C, introduce acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 2 L / min, and continue the deposition reaction for 240 min. Cool down and discharge the material to obtain a silicon-carbon composite material.

[0111] Comparative Example 3

[0112] 500 g of porous carbon raw material with a particle size Dv50 = 7 μm was added into a fluidized bed reactor, and nitrogen was introduced at a flow rate of 20 L / min for replacement and purging. When the oxygen content decreased to 500 ppm, the reactor was heated at a heating rate of 8 °C / min. After the reactor temperature reached 520 °C, silane gas was introduced at a flow rate of 1.5 L / min and nitrogen at a flow rate of 10 L / min, and the reaction was carried out for 270 min. After the reaction, the reactor was heated to 600 °C at a heating rate of 4 °C / min, and acetylene at a flow rate of 1 L / min and nitrogen at a flow rate of 10 L / min were introduced, and the continuous deposition reaction was carried out for 160 min. After the reaction, it was cooled down in a nitrogen atmosphere at a flow rate of 10 L / min. When the reactor temperature dropped to 50 °C, the product was discharged to obtain the silicon-carbon composite material.

[0113] Performance testing methods

[0114] 1. Resistivity testing method

[0115] The powder resistance of the silicon-carbon composite material was measured using a powder resistivity measuring instrument with reference to GB / T 24521-2018. The silicon-carbon composite material was added into the sample cylinder, vibrated and compacted to make the upper surface of the sample flat, and then placed in the testing machine. A pressure of 4 Mpa was applied, and the height of the sample was measured. The regulated power supply was adjusted to make the current passing through the sample 500 mA ± 0.1 mA, and the voltage drop of the sample was measured. Finally, the powder resistivity of the sample was calculated according to Ohm's law. The test results of Comparative Examples 1-3 and Examples 1-6 are shown in Table 1.

[0116] 2. Electrochemical performance testing method

[0117] The above-mentioned coin cells were charged and discharged cyclically at a rate of 0.1C at 25 °C, and the initial discharge specific capacity and charge specific capacity were recorded, and the first Coulomb efficiency was calculated. The above-mentioned coin cells were charged and discharged cyclically at a rate of 5C at 25 °C, and the charge capacity retention rate after 50 cycles was calculated. The test results of Comparative Examples 1-3 and Examples 1-6 are shown in Table 1.

[0118] 3. dQ / dV test

[0119] The dQ / dV curve was plotted through the 0.1C first-cycle charge-discharge curve of the coin cell. The peak height in the range of 0.25 V - 0.3 V in the curve was denoted as h1, and the peak height in the region of 0.4 V - 0.5 V in the curve was denoted as h2. The value of Y = h2 / h1 was calculated to characterize the silicon-rich situation on the surface of the sample. The test spectra of Comparative Examples 1-3 and Examples 1-6 are shown in the appendix Figures 2 - 10 .

[0120] Table 1

[0121]

[0122]

[0123] Conclusion: As can be seen from the comparison between Examples 1-6 and Comparative Example 1, compared with doping nitrogen and phosphorus elements in carbon materials, by doping nitrogen and phosphorus in nanosilicon and adding a conductive additive during the granulation process in the present invention, the resistivity of the battery can be significantly reduced, indicating that the silicon-carbon material proposed in the present invention has excellent conductivity.

[0124] As can be seen from the comparison between Examples 1-6 and Comparative Example 1, compared with doping nitrogen and phosphorus elements in carbon materials, by doping nitrogen and phosphorus in nanosilicon in the present invention, the charging capacity, initial efficiency and 5C cycle capacity retention rate of the battery can be significantly improved, indicating that the silicon-carbon material proposed in the present invention has excellent fast charging ability.

[0125] As can be seen from the comparison between Examples 1-6 and Comparative Example 1, compared with doping nitrogen and phosphorus elements in carbon materials, by doping nitrogen and phosphorus in nanosilicon in the present invention, the Y value can be significantly reduced, indicating that for the silicon-carbon material proposed in the present invention, nanosilicon is mainly deposited in the pores of porous carbon.

[0126] As can be seen from the comparison between Examples 1-6 and Comparative Example 2, compared with the silicon-carbon material without nitrogen and phosphorus doping, by doping nitrogen and phosphorus on nanosilicon in the present invention, the charging capacity of the battery can be increased, and the initial efficiency and cycle capacity retention rate of the battery can be improved.

[0127] As can be seen from the comparison between Examples 1-6 and Comparative Example 3, compared with using large-particle-size porous carbon for silicon deposition, by using small-particle-size porous carbon for granulation in the present invention, the transmission path of active ions can be shortened, the rapid insertion and extraction of active ions can be realized, and the active ions can quickly reach the inside of silicon particles, thereby improving the fast charging performance of the silicon-carbon material.

[0128] As can be seen from the comparison between Examples 1-5 and Example 6, adding a conductive additive to the silicon-carbon material can further reduce the powder resistivity of the silicon-carbon material and improve the conductivity of the silicon-carbon material.

[0129] In the description of this specification, the descriptions with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0130] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A silicon carbide material, characterized in that, It includes a plurality of primary particles, and the plurality of primary particles are bonded by an amorphous carbon network structure to form secondary particles. The primary particles include porous carbon and nitrogen-phosphorus co-doped nanosilicon deposited in the pores of the porous carbon, and at least part of the surface of the primary particles has a first carbon coating layer.

2. The silicon carbide material according to claim 1, characterized in that, Based on the total mass of the silicon-carbon material, the mass ratios of nitrogen and phosphorus are 0.1%-1%.

3. The silicon carbide material according to claim 1 or 2, characterized in that, The volume average particle size Dv50 of the porous carbon satisfies: 1μm ≤ Dv50 ≤ 5μm.

4. The silicon-carbon material according to claim 3, characterized in that, At least one of the following conditions is satisfied: The silicon-carbon material further includes a conductive additive; At least part of the surface of the secondary particles has a second carbon coating layer.

5. The silicon-carbon material according to claim 4, wherein At least one of the following conditions is satisfied: The powder resistivity of the silicon-carbon material is 0.1Ω·cm - 1Ω·cm; The cycle capacity retention rate of the silicon-carbon material at 5C constant current charge and discharge for 50 cycles is greater than or equal to 85%.

6. The silicon-carbon material according to claim 5, characterized in that, At least one of the following conditions is satisfied: Based on the total mass of the silicon-carbon material, the mass ratio of the nanosilicon is 40%-50%; Based on the total mass of the silicon-carbon material, the mass ratio of the conductive additive is 1%-5%; Based on the total mass of the silicon-carbon material, the mass ratio of the amorphous carbon network structure is 1%-5%.

7. The silicon carbide material according to claim 6, wherein The volume average particle size Dv50 of the silicon-carbon material satisfies: 10μm ≤ Dv50 ≤ 20μm.

8. A method for preparing the silicon-carbon material according to any one of claims 1-7, characterized in that, It includes: Placing the porous carbon in a reactor, introducing a mixed gas of a silicon source gas, a phosphorus source gas, and a nitrogen source gas into the reactor, and performing a first heat treatment to obtain primary particles; Introducing a first organic gas source into the reactor containing the primary particles, and performing a second heat treatment to form a first carbon coating layer on at least part of the surface of the primary particles; Mixing the primary particles with the first carbon coating layer with a binder solution, spray granulating to obtain secondary particles and performing a third heat treatment to obtain the silicon-carbon material.

9. The method according to claim 8, characterized in that, Mixing the primary particles with the first carbon coating layer with a conductive additive and a binder solution.

10. The method according to claim 9, wherein The third heat treatment includes: introducing a second organic gas source into the reactor to form a second carbon coating layer on at least part of the surface of the secondary particles.

11. The method according to claim 10, characterized in that, At least one of the following conditions is satisfied: The temperature of the first heat treatment is 450°C - 550°C; The temperature of the second heat treatment is 550°C - 650°C; The temperature of the third heat treatment is 600°C - 900°C.

12. The method according to claim 11, characterized in that, At least one of the following conditions is satisfied: The volume average particle size Dv50 of the porous carbon satisfies: 1μm ≤ Dv50 ≤ 5μm; The specific surface area of the porous carbon is greater than or equal to 1400 m 2 / g; The phosphorus source includes at least one of phosphorus pentoxide, triphenylphosphine, phytic acid, and phosphine; The nitrogen source includes at least one of melamine, polydopamine, urea, thiourea, and ammonia; The conductive additive includes at least one of graphene, carbon nanotubes, and Ketjen black; The binder includes at least one of glucose, sucrose, citric acid, phenolic resin, and pitch; The first organic gas source and the second organic gas source each independently include at least one of methane, acetylene, propylene, and propane.

13. A negative electrode material, characterized in that, It includes the silicon-carbon material according to any one of claims 1-7.

14. A negative electrode sheet, characterized in that, It includes the negative electrode material according to claim 13.

15. A battery, characterized in that, Including the negative electrode tab described in claim 14.

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