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

Abstract

The application belongs to the technical field of batteries, and relates to a silicon-carbon negative electrode material, a preparation method thereof, a negative electrode sheet and a secondary battery, wherein the silicon-carbon negative electrode material comprises a porous carbon matrix and nano-silicon loaded on the porous carbon matrix, the porous carbon matrix contains F elements; the ultimate compaction density of the silicon-carbon negative electrode material is S g / cm 3 , the true density of the silicon-carbon negative electrode material is Z g / cm 3 , 2.3<=S*Z<=3.2, and the value range of S is 1.05-1.27. By loading nano-silicon on the F element-containing porous carbon matrix, the material resistance is enhanced, the ultimate compaction is higher than that of uncrosslinked material, and the true density of the material is also greater than that of conventional silicon-carbon. The ultimate compaction of the material is relatively large, the difference between the ultimate compaction and graphite is reduced, the structural stability is good, and the compatibility with electrolyte is improved. The resin carbon source and polyhydric alcohol fluoride are crosslinked, and the crosslinking degree of the carbon source is enhanced; the obtained porous carbon matrix has high hardness, high compression strength and high bending strength.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a silicon-carbon anode material and its preparation method, anode sheet and secondary battery. Background Technology

[0002] With the rapid development of new energy vehicles, higher requirements have been placed on the performance of on-board power batteries. Researching and developing power-type lithium-ion batteries with high-rate charge / discharge performance and high safety has become one of the main solutions for on-board power supplies.

[0003] Currently, the most commercially mature lithium-ion battery anode material is artificial graphite, with a reversible specific capacity of around 340mAh / g-360mAh / g. However, graphite materials suffer from poor structural stability and poor compatibility with electrolytes. Moreover, due to the anisotropic structural characteristics of graphite, the free diffusion of lithium ions in the graphite structure is restricted, thus affecting the rate performance of graphite anode materials. On the other hand, silicon-carbon materials have once again attracted attention in the field of power lithium-ion batteries due to their good rate performance and cycle performance.

[0004] However, existing technologies have fatal flaws. First, silicon-carbon materials have poor pressure resistance. The difference in ultimate compressibility between the two is too great. When silicon-carbon and graphite are blended, silicon-carbon is more prone to breakage, leading to a sharp deterioration in cell cycle life and cell expansion, and even causing cell cycle failure. Reducing the design compressibility significantly lowers the energy density of the cell, making it uncompetitive in practical applications. Second, silicon-carbon materials have poor intrinsic ionic conductivity, resulting in high material polarization. High polarization leads to low capacity utilization, resulting in low energy density of the cell. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a silicon-carbon anode material, its preparation method, an anode sheet, and a secondary battery. The silicon-carbon material is redesigned to increase its compaction density and improve its voltage resistance. Simultaneously, fluorine (F) atoms are introduced to generate fast lithium-ion conductors (LiF) during the formation of the SEI film, reducing material polarization. The generated LiF makes the SEI more stable and optimizes its composition and structure. This results in improved material capacity, initial efficiency, and long-cycle performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A silicon-carbon anode material includes a porous carbon matrix and nano-silicon supported on the porous carbon matrix, wherein the porous carbon matrix contains F element;

[0008] The limiting compaction density of the silicon-carbon anode material is S g / cm³. 3 The true density of the silicon-carbon anode material is Z g / cm³.3 2.3≤S*Z≤3.2, where S ranges from 1.05 to 1.27.

[0009] Preferably, the silicon-carbon anode material further includes a carbon coating layer covering at least a portion of the surface of the porous carbon matrix.

[0010] Preferably, the particle size Dv50 of the porous carbon matrix is ​​5-10 μm; and / or, the particle size of the nano-silicon is 6-10 nanometers; and / or, the mass of the nano-silicon is 46%-48% of the mass of the porous carbon matrix.

[0011] The present invention also provides a method for preparing the above-mentioned silicon-carbon anode material, comprising the following steps:

[0012] Step 1: Mix the resin-based carbon source with the polyol fluoride and heat in a constant temperature water bath to obtain the carbon source substrate;

[0013] Step 2: Carbonize, pore-form, and purify the carbon source substrate to obtain a porous carbon matrix;

[0014] Step 3: Introduce a silane mixed gas into the porous carbon matrix to perform vapor phase deposition of silicon, thereby obtaining nano-silicon-porous carbon material;

[0015] Step 4: Introduce a mixed gas containing a protective gas and an organic gas source into the nano-silicon-porous carbon material to perform chemical vapor deposition, thereby coating it with carbon to obtain a silicon-carbon anode material.

[0016] Preferably, in step 1, the constant temperature water bath heating includes heating in a constant temperature water bath at 50-100℃ for 1-4 hours while stirring.

[0017] Preferably, the mass ratio of the polyol fluoride to the total mass of the polyol fluoride and the resin-based carbon source is 5%-30%.

[0018] Preferably, the mass ratio of the polyol fluoride to the total mass of the polyol fluoride and the resin-based carbon source is 10%-25%.

[0019] Preferably, the resin-based carbon source includes one or more of phenolic resin and epoxy resin.

[0020] Preferably, the polyol fluoride includes one or more of the following: fluorinated glycerol, fluorinated xylitol, fluorinated sorbitol, fluorinated ethylene glycol, fluorinated 1,2-propanediol, fluorinated 1,4-butanediol, fluorinated 1,6-hexanediol, fluorinated neopentyl glycol, fluorinated diethylene glycol, fluorinated dipropylene glycol, and fluorinated trimethylolpropane.

[0021] Preferably, in step 2, the carbonization includes carbonizing at 900-1200°C for 3-6 hours in an inert atmosphere; and / or, the pore-forming includes mixing the carbon matrix with a pore-forming agent and calcining at 850-1000°C for 1-2 hours; and / or, the purification includes acid washing, water washing until neutral, and then calcining at 500-600°C for 3-4 hours.

[0022] Further, the pore-forming agent is an alkaline pore-forming agent; preferably, the pore-forming agent includes at least one of sodium hydroxide and potassium hydroxide; preferably, the concentration of the pore-forming agent is 1-2 mol / L; preferably, the amount of the pore-forming agent added is 8%-15% of the mass of the carbon matrix.

[0023] Furthermore, the pore volume of the carbon source substrate treated with the pore-forming agent is 0.6-10 cm³. 3 / g, the pore structure is as follows: micropores account for 80%-90%, mesopores account for 5%-19%, and macropores account for 1%-5%. Among them, the pore size of micropores is ≤2nm, the pore size of mesopores is 2-50nm, and the pore size of macropores is ≥50nm.

[0024] Preferably, in step 3, the vapor deposition of silicon includes placing a porous carbon substrate in a reaction apparatus, introducing a first mixed gas containing a first protective gas and a silicon source gas, and performing vapor deposition of silicon on the porous carbon substrate; preferably, the conditions for vapor deposition of silicon are 350-450°C for 1-3 hours; preferably, the content of the first protective gas is 10%-30% of the volume of the first mixed gas; preferably, the silicon source gas includes silane gas; preferably, the first protective gas includes at least one of helium, nitrogen, argon and krypton.

[0025] Preferably, in step 4, the organic gas source includes at least one of acetylene, ethylene, and methane, and the protective gas includes at least one of nitrogen and argon; and / or, in step 4, the deposition temperature is 500-700℃, the deposition time is 1-3 hours, and the soft carbon deposition amount is 10%-15% of the mass of the silicon-carbon anode material.

[0026] A negative electrode sheet comprising the aforementioned silicon-carbon negative electrode material.

[0027] A secondary battery comprising the aforementioned negative electrode.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] By loading nano-silicon onto a porous carbon matrix containing sulfur (F), the compressive strength of the material is enhanced, resulting in a compressive strength ultimate density as high as 1.27 g / cm³. 3 It is higher than 1.0 g / cm³ of the uncrosslinked material. 3Furthermore, the true density of the material is 2.2-2.5 g / cm³. 3 It is greater than the 2.0 g / cm³ of conventional silicon-carbon. 3 This material exhibits a high ultimate compressibility, narrowing the compressibility difference with graphite compared to existing silicon-carbon materials, resulting in better structural stability and improved compatibility with electrolytes. Crosslinking resin-based carbon sources with polyol fluorides enhances the degree of crosslinking; the resulting porous carbon matrix possesses high hardness, compressive strength, and flexural strength. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] According to a first aspect of the present invention, the present invention provides a silicon-carbon anode material comprising a porous carbon matrix and nano-silicon supported on the porous carbon matrix, wherein the porous carbon matrix contains F element;

[0032] The limiting compaction density of this silicon-carbon anode material is S g / cm³. 3 The true density of silicon-carbon anode material is Z g / cm³. 3 2.3 ≤ S*Z ≤ 3.2, where S ranges from 1.05 to 1.27. Specifically, the limiting compaction density of this silicon-carbon anode material is 1.1 g / cm³. 3 1.12 g / cm 3 1.14 g / cm 3 1.15g / cm 3 1.18 g / cm 3 1.2g / cm 3 1.22g / cm 3 1.25g / cm 3 and 1.27 g / cm 3 wait.

[0033] In one embodiment of the present invention, the silicon-carbon anode material further includes a carbon coating layer covering at least a portion of the surface of the porous carbon matrix.

[0034] In one embodiment of the invention, the particle size Dv50 of the porous carbon matrix is ​​5-10 μm. For example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, etc.

[0035] According to a second aspect of the present invention, the present invention also provides a method for preparing the above-mentioned silicon-carbon anode material, comprising the following steps:

[0036] Step 1: Mix the resin-based carbon source with the polyol fluoride and heat in a constant temperature water bath to obtain the carbon source substrate;

[0037] Step 2: Carbonize, pore-form, and purify the carbon source substrate to obtain a porous carbon matrix;

[0038] Step 3: Introduce a silane mixed gas into the porous carbon matrix to perform vapor phase deposition of silicon, thereby obtaining nano-silicon-porous carbon material;

[0039] Step 4: Introduce a mixed gas containing a protective gas and an organic gas source into the nano-silicon-porous carbon material to perform chemical vapor deposition, thereby coating it with carbon to obtain a silicon-carbon anode material.

[0040] In one embodiment of the present invention, step 1, the constant temperature water bath heating includes heating in a constant temperature water bath at 50-100°C for 1-4 hours with stirring. The temperature of the constant temperature water bath can be, for example, 50°C, 60°C, 70°C, 75°C, 80°C, 90°C, or 100°C, etc. The heating time can also be 1 hour, 2 hours, 3 hours, or 4 hours, etc.

[0041] In one embodiment of the present invention, the mass ratio of the polyol fluoride to the total mass of the polyol fluoride and the resin-based carbon source is 5%-30%. More preferably, the mass ratio of the polyol fluoride to the total mass of the polyol fluoride and the resin-based carbon source is 10%-25%, for example, it can be 10%, 12%, 15%, 17%, or 20%, etc.

[0042] In one embodiment of the present invention, the resin-based carbon source includes one or more of phenolic resin and epoxy resin, and the polyol fluoride includes one or more of fluorinated glycerol, fluorinated xylitol, fluorinated sorbitol, fluorinated ethylene glycol, fluorinated 1,2-propanediol, fluorinated 1,4-butanediol, fluorinated 1,6-hexanediol, fluorinated neopentyl glycol, fluorinated diethylene glycol, fluorinated dipropylene glycol, and fluorinated trimethylolpropane. By crosslinking the polyol fluoride with the resin-based carbon source, the degree of crosslinking of the carbon source is enhanced, thereby increasing the compressive strength of the sintered material. The resulting material can achieve an ultimate compressive strength of 1.27 g / cm³. 3 The true density is 2.2-2.5 g / cm³. 3 .

[0043] In one embodiment of the present invention, step 2, the carbonization includes carbonization at 900-1200°C for 3-6 hours in an inert atmosphere. Too low a temperature results in ineffective carbonization, with too many heteroatoms, such as oxygen atoms, leading to low initial efficiency. Too high a carbonization temperature results in a porous carbon source structure with poor structural stability, leading to poor pressure resistance. Too short a time also results in ineffective carbonization, with too many heteroatoms, such as oxygen atoms, leading to low initial efficiency. Too long a time results in a porous carbon source structure with poor structural stability, leading to poor pressure resistance. Therefore, carbonization at a higher temperature and for a longer time reduces heteroatoms while enhancing the stability of the formed carbon structure, ensuring optimal overall structural stability and initial efficiency. Too high a temperature and too short a time result in a violent gasification reaction during carbonization, leading to a porous carbon matrix that is not pressure resistant. In this embodiment, an inert gas such as nitrogen atmosphere can be used to isolate the carbon source substrate from oxygen in the air.

[0044] In one embodiment of the present invention, the pore-forming process includes mixing a carbon matrix with a pore-forming agent and calcining at 850-1000°C for 1-2 hours; and / or, the purification process includes acid washing, water washing until neutral, and then calcining at 500-600°C for 3-4 hours. The pore-forming agent is an alkaline pore-forming agent; preferably, the pore-forming agent includes at least one of sodium hydroxide and potassium hydroxide; preferably, the concentration of the pore-forming agent is 1-2 mol / L; preferably, the amount of the pore-forming agent added is 8%-15% of the mass of the carbon matrix.

[0045] In one embodiment of the present invention, the pore volume of the carbon source substrate treated with the pore-forming agent is 0.6-10 cm³. 3 / g, the pore structure is as follows: micropores account for 80%-90%, mesopores account for 5%-19%, and macropores account for 1%-5%. Among them, the pore size of micropores is ≤2nm, the pore size of mesopores is 2-50nm, and the pore size of macropores is ≥50nm.

[0046] Insufficient concentration and amount of pore-forming agent, or too short etching time, results in uneven pore distribution, low porosity, and predominantly micropores. Excessive concentration and amount of alkali, or too long etching time, leads to predominantly mesopores, or even macropores, with a more porous structure and poor pressure resistance. Increasing pore volume increases the proportion of mesopores while decreasing the proportion of micropores.

[0047] Too short a purification time results in a high heteroatom content, while too long a time leads to poor stability of the porous carbon structure. Further purification of the carbon source substrate by high-temperature heating reduces the heteroatom content, especially oxygen atoms (<2%), thereby improving the material's initial efficiency in battery applications.

[0048] The particle size range Dv50 of the porous carbon matrix is ​​5-10μm. If it is too small, the yield is low and the cost increases. If it is too large, the diffusion resistance of lithium ions in the particles is large and the rate performance is poor. Also, if the particle size is too large, Dv100 is larger than the roller gap size of the coating machine, scratches may be generated during coating, resulting in low electrode yield.

[0049] In one embodiment of the present invention, the vapor deposition of silicon includes placing a porous carbon substrate in a reaction apparatus, introducing a first mixed gas containing a first protective gas and a silicon source gas, and performing vapor deposition of silicon on the porous carbon substrate; preferably, the conditions for vapor deposition of silicon are 350-450°C for 1-3 hours; preferably, the content of the first protective gas is 10%-30% of the volume of the first mixed gas; preferably, the silicon source gas includes silane gas; preferably, the first protective gas includes at least one of helium, nitrogen, argon and krypton.

[0050] If the deposition temperature is too low, silane will be difficult to reduce, resulting in low production capacity; if the deposition temperature is too high, nano-silicon will be transformed from amorphous silicon to crystalline silicon, resulting in anisotropic expansion and increasing the expansion rate of the material; and if the temperature is too high, chemically inert silicon carbide will be easily generated.

[0051] Deposition time can be 1 hour, 2 hours, or 3 hours, etc. If the time is too short, silicon cannot be completely deposited internally; if the time is too long, silicon tends to accumulate on the surface, increasing material expansion and shortening its lifespan. If the deposited nano-silicon particles are too small, there will be more silicon-carbon interfaces and more lithium-ion transfer interfaces, resulting in higher impedance and greater polarization of the material during use. If the nano-silicon particles are too large, the uniformity of lithium intercalation within the silicon will be poor, making it more prone to breakage and increased expansion.

[0052] In one embodiment of the present invention, a silane mixed gas is introduced into a porous carbon matrix and reduced to nano-silicon. The nano-silicon grows in the porous carbon matrix to obtain a nano-silicon-porous carbon material. The particle size of the nano-silicon is 6-10 nanometers, and the deposition amount of nano-silicon is 46%-48%. The particle size of the nano-silicon can be 6 nanometers, 7 nanometers, 8 nanometers, 9 nanometers, or 10 nanometers, etc., and the deposition amount of nano-silicon can be 46%, 47%, or 48%, etc. Too low a particle size results in low initial efficiency, low cathode specific capacity, and increased cell cost. Too high a particle size results in large material expansion, high stress during expansion, and severe damage to the porous carbon matrix. The material is also more prone to pulverization and failure.

[0053] In one embodiment of the present invention, in step 4, the organic gas source includes at least one of acetylene, ethylene, and methane, and the protective gas includes at least one of nitrogen and argon; and / or, in step 4, the deposition temperature is 500-700°C, the deposition time is 1-3 hours, and the soft carbon deposition amount is 10%-15% of the mass of the silicon-carbon anode material. Too high a deposition temperature easily leads to the formation of chemically inert silicon carbide, while too low a deposition temperature makes it difficult for the organic gas source to be reduced. The same applies to too long or too short a deposition time. Too large a deposition amount results in low initial efficiency and increased lithium-ion diffusion resistance; too small a deposition amount results in a large specific surface area, leading to low initial efficiency, and a large contact area with water during homogenization easily generates gas. Reducing the gas flow rate slows down the rate at which the organic gas is reduced to carbon, allowing it to slowly deposit and block the pores in the porous carbon, enhancing the protection of silicon in the porous carbon and suppressing expansion during lithium intercalation. Finally, a silicon-based anode composite material with large pore volume, a high proportion of mesopores, and effective pore blocking is obtained.

[0054] According to a third aspect of the present invention, the present invention also provides a negative electrode sheet comprising the aforementioned silicon-carbon negative electrode material.

[0055] According to a fourth aspect of the present invention, the present invention also provides a secondary battery comprising the above-described negative electrode sheet.

[0056] The present invention will be further described below with reference to specific embodiments.

[0057] Example 1:

[0058] A method for preparing a silicon-carbon anode material is as follows:

[0059] Step 1: Phenolic resin crosslinking

[0060] Phenolic resin and fluorinated glycerol were mixed. The phenolic resin was a phenol-formaldehyde resin (purchased from Shaoguan Derui Chemical Industry Co., Ltd., CAS: 9003-35-4). The mixture was heated in a 50°C constant temperature water bath while stirring for 1 hour. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol was 5%, thus obtaining a carbon source substrate.

[0061] Step 2: Preparation of porous carbon substrate

[0062] Carbonization: First, the carbon source substrate in step 1 is carbonized. The carbonization conditions for the carbon source substrate are a carbonization temperature of 950℃ and a carbonization time of 3 hours. Nitrogen gas is introduced for high-temperature carbonization to isolate oxygen in the air and protect the carbon source substrate.

[0063] Activation and pore-forming: The above-mentioned carbon source substrate is mixed with the pore-forming agent and placed in a constant temperature device at 850℃ for etching reaction for 1 hour. After the reaction is complete, acid washing is performed, followed by water washing until neutral, drying, calcination at 500℃ for 4 hours, and pulverization to obtain a porous carbon matrix; the pore volume of the porous carbon matrix is ​​0.7 cm³. 3 / g, Dv50 is 8.5μm. In the pore distribution of the porous carbon matrix, micropores (pore size <2nm) account for 90%, mesopores (2-50nm) account for 5%, and macropores (pore size >50nm) account for 5%. The pore-forming agent is potassium hydroxide with a concentration of 0.6mol / L, and the amount of pore-forming agent added is 8% of the mass of the carbon source substrate.

[0064] Step 3, Silane deposition

[0065] The porous carbon matrix obtained in step 2 was placed in a rotary kiln, and a silane mixture consisting of a protective gas (nitrogen) and a silane gas (silane) was introduced for deposition, with the protective gas accounting for 15% of the volume. The rotary kiln used had a capacity of 50 kg, the deposition temperature was 400°C, the deposition time was 3 hours, and the silicon deposition amount was 48%, resulting in nano-silicon-porous carbon material.

[0066] Step 4, Carbon Packet

[0067] The product obtained in step 3 was placed in a rotary kiln / fluidized bed and chemical vapor deposition was carried out in a mixed atmosphere of protective gas nitrogen and organic gas source acetylene to coat the nano-silicon-porous carbon material with soft carbon. During this process, the deposition temperature was 600℃, the deposition time was 2 hours, and the amount of soft carbon deposited was 10% of the mass of the silicon-carbon anode material.

[0068] Example 2:

[0069] The only difference from Example 1 is that in step 1, the mixture is heated in a 50°C constant temperature water bath while stirring for 1 hour. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 10%. Steps 2, 3, and 4 are the same as in Example 1.

[0070] Example 3:

[0071] The only difference from Example 1 is that in step 1, the mixture is heated in a 50°C constant temperature water bath while stirring for 1 hour. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 15%. Steps 2, 3, and 4 are the same as in Example 1.

[0072] Example 4:

[0073] The only difference from Example 1 is that in step 1, the mixture is heated in a 50°C constant temperature water bath with stirring for 2 hours. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 10%. Steps 2, 3, and 4 are the same as in Example 1.

[0074] Example 5:

[0075] The only difference from Example 1 is that in step 1, the mixture is heated in a 75°C constant temperature water bath with stirring for 2 hours. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 10%. Steps 2, 3, and 4 are the same as in Example 1.

[0076] Example 6:

[0077] The only difference from Example 1 is that in step 1, the mixture is heated in a 100°C constant temperature water bath with stirring for 2 hours. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 10%. Steps 2, 3, and 4 are the same as in Example 1.

[0078] Example 7:

[0079] The only difference from Example 1 is that in step 1, the mixture is heated in a 50°C constant temperature water bath while stirring for 3 hours. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 10%. Steps 2, 3, and 4 are the same as in Example 1.

[0080] Example 8:

[0081] The only difference from Example 1 is that the phenolic resin is replaced with an equal amount of bisphenol A type epoxy resin (purchased from Langfang Rongkun Environmental Protection Technology Co., Ltd., model: epoxy resin E128), and the rest is the same as Example 1.

[0082] Example 9:

[0083] The only difference from Example 1 is that fluorinated glycerol is replaced with an equal amount of fluorinated ethylene glycol, otherwise it is the same as Example 1.

[0084] Example 10:

[0085] The only difference from Example 1 is that fluorinated glycerol is replaced with an equal amount of fluorinated xylitol, otherwise it is the same as Example 1.

[0086] Example 11:

[0087] The only difference from Example 1 is that in step 1, the mixture is heated in a 50°C constant temperature water bath while stirring for 1 hour. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 20%. Steps 2, 3, and 4 are the same as in Example 1.

[0088] Example 12:

[0089] The only difference from Example 1 is that in step 1, the mixture is heated in a 50°C constant temperature water bath while stirring for 1 hour. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 25%. Steps 2, 3, and 4 are the same as in Example 1.

[0090] Example 13:

[0091] The only difference from Example 1 is that in step 1, the mixture is heated in a 50°C constant temperature water bath while stirring for 1 hour. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 30%. Steps 2, 3, and 4 are the same as in Example 1.

[0092] Comparative Example 1:

[0093] The only difference from Example 1 is that: no polyol fluoride was added in Comparative Example 1, but the same phenolic resin as in Example 1 was used to prepare the porous carbon substrate. Otherwise, it was the same as Example 1.

[0094] Comparative Example 2:

[0095] The only difference from Example 1 is that in step 1, the mixture is heated in a 50°C constant temperature water bath while stirring for 1 hour. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 2%. Steps 2, 3, and 4 are the same as in Example 1.

[0096] Comparative Example 3:

[0097] The only difference from Example 1 is that in step 1, the mixture is heated in a 50°C constant temperature water bath while stirring for 1 hour. The mass ratio of fluorinated glycerol to the total mass of phenolic resin and fluorinated glycerol is 35%. Steps 2, 3, and 4 are the same as in Example 1.

[0098] The negative electrode materials of the above embodiments and comparative examples are further applied to the preparation of lithium-ion batteries. The specific preparation methods include:

[0099] S1. Preparation of the positive electrode sheet: Lithium cobalt oxide (positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) are mixed in a mass ratio of 97:1.5:1.5. N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry is uniformly coated onto one surface of an 8 μm thick aluminum foil. The aluminum foil is dried at 125°C for 1 hour to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. After cold pressing, cutting, and slitting, the sheet is dried under vacuum at 125°C for 2 hours to obtain a positive electrode with dimensions of 65 mm × 860 mm.

[0100] S2. Preparation of the negative electrode sheet: The negative electrode material, CMC, PAA, and CNT are mixed in a mass ratio of negative electrode material:CMC:PAA:CNT = 80:9:10:1. Deionized water is added, and the mixture is stirred evenly under vacuum to obtain a negative electrode slurry with a solid content of 60 wt%. The negative electrode slurry is uniformly coated onto one surface of a 6 μm thick copper foil, and the copper foil is dried at 120°C to obtain a negative electrode with a single-sided coating of negative electrode material. The above steps are repeated on the other surface of the aluminum foil to obtain a negative electrode with a double-sided coating of negative electrode material. After cold pressing, cutting, and slitting, the negative electrode is dried under vacuum at 120°C for 2 hours to obtain a negative electrode with a size of 69 mm × 868 mm.

[0101] S3. Electrolyte preparation: In an argon-atmospheric glove box with a water content of <10ppm, EC, PC, and DMC are mixed in a mass ratio of 3:2:4 to obtain an organic solvent. Then, lithium hexafluorophosphate is added to the organic solvent to obtain the electrolyte. The concentration of the lithium salt is 1 mol / L.

[0102] S4. Assembly of the lithium-ion battery: Stack the positive electrode, separator (PE), and negative electrode prepared above in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Wind the electrodes together to obtain the electrode assembly. Assemble the electrode assembly into a button cell.

[0103] Performance testing includes ultimate compaction, true density, capacity, first-efficiency and cycle performance.

[0104] The test methods and conditions are as follows: (1) The ultimate compaction is the compaction of the electrode under a pressure of 60T; (2) The true density is determined by the gas volume method, which uses Archimedes' principle to calculate the true volume of the sample by measuring the change in gas volume after the sample is placed in the test chamber; (3) The capacity and first-effect test steps are: discharge to 0.05V at 0.1C and rest for 5 minutes, discharge to 0.05V at 0.01C and rest for 5 minutes, charge to 1.5V at 0.1C and rest for 5 minutes; (4) Cyclic capacity retention: charge to 4.53V at 1C constant current and constant voltage, cutoff rate of 0.05C and rest for 5 minutes; discharge to 3.0V at 1C constant current and rest for 5 minutes. Cycle 800 times.

[0105] The specific test results are shown in Table 1.

[0106] Table 1:

[0107]

[0108]

[0109] According to the test results in Table 1, the silicon-carbon anode material provided in this embodiment of the invention not only contains F element, but also has a limiting compaction density of S g / cm³. 3 The true density is Z g / cm³ 3 It satisfies 2.3≤S*Z≤3.2, and the value of S is in the range of 1.05-1.27, and has good electrochemical performance. Compared with comparative examples 1-3, its capacity, first-time efficiency and capacity retention are all higher.

[0110] After cross-linking the polyol fluoride of the present invention with a resin-based carbon source, a silicon-carbon anode material with suitable ultimate compaction density and true density can be obtained. The ultimate compaction density is much greater than that of the silicon-carbon material obtained without cross-linking with polyol fluoride. Moreover, its capacity and first efficiency are relatively improved, and the capacity retention rate is also improved.

[0111] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A silicon-carbon anode material, characterized in that: It includes a porous carbon matrix and nano-silicon supported on the porous carbon matrix, wherein the porous carbon matrix contains F element, and the porous carbon matrix is ​​obtained by crosslinking a resin-based carbon source with a polyol fluoride; The limiting compaction density of the silicon-carbon anode material is Sg / cm³. 3 The true density of the silicon-carbon anode material is Z g / cm³. 3 2.3≤S*Z≤3.2, where S ranges from 1.05 to 1.

27.

2. The silicon-carbon anode material according to claim 1, characterized in that: The silicon-carbon anode material further includes a carbon coating layer covering at least a portion of the surface of the porous carbon matrix.

3. The silicon-carbon anode material according to claim 1, characterized in that: The particle size Dv50 of the porous carbon matrix is ​​5-10 μm; And / or, the particle size of the nano-silicon is 6-10 nanometers; And / or, the mass of the nano-silicon is 46%-48% of the mass of the porous carbon matrix.

4. A method for preparing a silicon-carbon anode material, characterized in that: Includes the following steps: Step 1: Mix the resin-based carbon source with the polyol fluoride and heat in a constant temperature water bath to obtain the carbon source substrate; Step 2: Carbonize, pore-form, and purify the carbon source substrate to obtain a porous carbon matrix; Step 3: Introduce a silane mixed gas into the porous carbon matrix to perform vapor phase deposition of silicon, thereby obtaining nano-silicon-porous carbon material; Step 4: Introduce a mixed gas containing a protective gas and an organic gas source into the nano-silicon-porous carbon material to perform chemical vapor deposition, thereby coating it with carbon to obtain a silicon-carbon anode material.

5. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that: In step 1, the constant temperature water bath heating includes heating in a constant temperature water bath at 50-100℃ for 1-4 hours while stirring; And / or, the mass ratio of the polyol fluoride to the total mass of the polyol fluoride and the resin carbon source is 5%-30%; And / or, the resin-based carbon source includes one or more of phenolic resin and epoxy resin; And / or, the polyol fluoride includes one or more of fluorinated glycerol, fluorinated xylitol, fluorinated sorbitol, fluorinated ethylene glycol, fluorinated 1,2-propanediol, fluorinated 1,4-butanediol, fluorinated 1,6-hexanediol, fluorinated neopentyl glycol, fluorinated diethylene glycol, fluorinated dipropylene glycol, and fluorinated trimethylolpropane.

6. The method for preparing silicon-carbon anode material according to claim 4, characterized in that: The mass ratio of the polyol fluoride to the total mass of the polyol fluoride and the resin carbon source is 10%-25%.

7. The method for preparing silicon-carbon anode material according to claim 4, characterized in that: In step 2, the carbonization includes carbonization at 900-1200°C for 3-6 hours in an inert atmosphere; And / or, the pore-forming process includes mixing a carbon matrix with a pore-forming agent and calcining at 850-1000°C for 1-2 hours; And / or, the purification includes acid washing, water washing until neutral, and then calcination at 500-600°C for 3-4 hours.

8. The method for preparing silicon-carbon anode material according to claim 7, characterized in that: The pore-forming agent is an alkaline pore-forming agent.

9. The method for preparing the silicon-carbon anode material according to claim 7, characterized in that: The pore-forming agent includes at least one of sodium hydroxide and potassium hydroxide.

10. The method for preparing the silicon-carbon anode material according to claim 7, characterized in that: The concentration of the pore-forming agent is 1-2 mol / L.

11. The method for preparing silicon-carbon anode material according to claim 7, characterized in that: The amount of the pore-forming agent added is 8%-15% of the carbon matrix mass.

12. The method for preparing silicon-carbon anode material according to claim 7, characterized in that: The pore volume of the carbon source substrate treated with the pore-forming agent is 0.6-10 cm³. 3 / g, the pore distribution structure is as follows: micropores account for 80%-90%, mesopores account for 5%-19%, and macropores account for 1%-5%. Among them, the pore size of micropores is ≤2nm, the pore size of mesopores is 2-50nm, and the pore size of macropores is ≥50nm.

13. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that: In step 3, the vapor deposition of silicon includes placing a porous carbon substrate in a reaction apparatus, introducing a first mixed gas containing a first protective gas and a silicon source gas, and performing vapor deposition of silicon on the porous carbon substrate.

14. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that: The conditions for the vapor-phase silicon deposition are 350-450℃ for 1-3 hours.

15. The method for preparing the silicon-carbon anode material according to claim 13, characterized in that: The content of the first protective gas is 10%-30% of the volume of the first mixed gas.

16. The method for preparing silicon-carbon anode material according to claim 13, characterized in that: The silicon source gas includes silane gas.

17. The method for preparing silicon-carbon anode material according to claim 13, characterized in that: The first protective gas includes at least one of helium, nitrogen, argon and krypton.

18. A negative electrode sheet, characterized in that, This includes silicon-carbon anode materials as described in any one of claims 1-3 or silicon-carbon anode materials prepared according to any one of claims 4-17.

19. A secondary battery, characterized in that, Includes the negative electrode as described in claim 18.