Porous carbon and silicon carbon negative electrode material and preparation method thereof

Abstract

The invention provides porous carbon, a silicon-carbon negative electrode material and a preparation method thereof, and the preparation method of the porous carbon comprises the following steps: providing a mixture comprising first resin, a flame retardant and a defoaming agent, dissolving the mixture in a first organic solvent, and carrying out spray drying to prepare a granular precursor, the flame retardant comprises at least one of decabromodiphenyl ethane, decabromodiphenyl ether, octabromodiphenyl ether, pentabromodiphenyl ether, tetrabromobisphenol A and hexabromocyclododecane, and at least one of decabromodiphenyl ether, octabromodiphenyl ether, pentabromodiphenyl ether, tetrabromobisphenol A and hexabromocyclododecane; carrying out carbonization treatment on the granular precursor to form a carbonization treatment product; and carrying out activating treatment on the carbonization treatment product to form the porous carbon.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and in particular to a porous carbon / silicon-carbon anode material and its preparation method. Background Technology

[0002] Silicon-carbon anodes are the current development direction of new energy systems and high-energy-density 3C consumer batteries. However, given the existing sources of raw materials and preparation processes, there are various problems in the production of low-cost biomass silicon-carbon and pitch-based silicon-carbon matrix materials.

[0003] Biomass carbon matrix materials are limited by the source of biomass. Even within the same species, different varieties, regions, and ages exhibit significant differences, making it difficult to produce porous carbon with completely consistent performance. Furthermore, the high ash content of biomass-based porous carbon necessitates thorough washing of the carbonization products after carbonization. However, with large quantities, this places high demands on equipment, which ordinary equipment often cannot meet. Moreover, biomass carbon matrix materials contain concentrated micropores with relatively large particle sizes, along with numerous large pores and voids, including information that is difficult to detect with nitrogen adsorption-desorption equipment. This results in low residual carbon yield in the formation of porous carbon.

[0004] When using silane as a raw material to deposit elemental silicon within the pores of porous carbon, the most prominent problem is the difficulty in controlling the deposition process. The deposited silicon nanoparticles are of varying sizes and the deposition is uneven, which significantly reduces the overall stress dispersion effect of the porous carbon matrix. It is difficult to buffer the particle expansion of silicon nanoparticles during lithium intercalation, causing the porous carbon matrix to expand outward as a whole, break through the carbon coating layer covering the surface of the porous carbon, and pulverize the porous carbon matrix, ultimately leading to the problem of biomass carbon matrix materials facing elimination.

[0005] Asphalt has a high sulfur content. During carbonization, a small portion of the sulfur can form sulfur-containing organic compounds and sulfur oxides, while the majority remains within the carbon material in various forms. This makes it easier for lithium ions to form lithium-sulfur-carbon compounds when entering the asphalt-based porous carbon matrix, reducing initial efficiency. Furthermore, asphalt's carbonization point is close to its glass transition temperature, resulting in numerous macropores in the prepared asphalt-based porous carbon matrix. These macropores persist during carbonization and affect the activation process. Additionally, due to the conditions under which asphalt is produced, its internal ash content remains high. These ash components, such as calcium sulfate and barium sulfate, are difficult to remove by acid washing. The presence of these inorganic salts indirectly reduces initial efficiency, increases DQ / DV voltage, affects lithium ion diffusion and shuttle movement within the carbon material, and impacts battery life and discharge rate.

[0006] Therefore, further research is needed on methods for forming porous carbon. Summary of the Invention

[0007] This application provides a method for preparing porous carbon, comprising: providing a mixture comprising a first resin, a flame retardant, and a defoamer; dissolving the mixture in a first organic solvent and spray-drying it to prepare a particulate precursor; wherein the flame retardant comprises at least one selected from decabromodiphenyl ethane, decabromodiphenyl ether, octabromodiphenyl ether, pentabromodiphenyl ether, tetrabromobisphenol A, and hexabromocyclododecane; carbonizing the particulate precursor to form a carbonized product; and activating the carbonized product to form the porous carbon.

[0008] In some embodiments of this application, the flame retardant has a mass percentage of 1% to 5% of the first resin.

[0009] In some embodiments of this application, the defoamer includes at least one of alcoholic organic compounds and etheric organic compounds, wherein the alcoholic organic compound includes polyoxyethylene alcohol and the etheric organic compound includes fatty alcohol polyether.

[0010] In some embodiments of this application, the defoamer has a mass percentage of 0.1‰ to 0.5‰ of the first resin.

[0011] In some embodiments of this application, the carbonization process includes: heating the ambient temperature to 300-1000°C in an inert atmosphere at a heating rate of 1-20°C / min, and the carbonization process lasting 0.5-10 hours.

[0012] In some embodiments of this application, the first resin includes at least one of epoxy resin, phenol-formaldehyde resin, m-diphenol-formaldehyde resin, cashew oil-modified phenolic resin, melamine-formaldehyde resin, urea-formaldehyde resin, furfuryl alcohol resin, polyurethane resin, and organosilicon resin.

[0013] In some embodiments of this application, the activation process includes: introducing an activation gas into a reaction chamber, the activation gas including at least one of water vapor, CO2, or air.

[0014] In some embodiments of this application, after forming the carbonization product, the process further includes: pulverizing the carbonization product to achieve a median particle size in the micrometer range.

[0015] This application also provides a method for preparing a silicon-carbon anode material, comprising: using the above-mentioned porous carbon as a matrix, allowing silicon-containing gas to enter the pores of the porous carbon through diffusion adsorption and undergo a cracking reaction in the pores, and depositing elemental silicon on the pore walls of the pores.

[0016] In some embodiments of this application, the method further includes forming a carbon coating layer on the surface of the porous carbon.

[0017] In some embodiments of this application, the silicon-containing gas includes one or more of silane, silane, propane, dimethylsilane, hexamethyldisilane, dichlorosilane, trichlorosilane, silicon tetrachloride, and silicon tetrafluoride.

[0018] In some embodiments of this application, the temperature for depositing elemental silicon on the pore wall of the channel is 300–1000°C, and the time is 0.5–6 hours.

[0019] This application also provides a porous carbon, formed using any of the porous carbon preparation methods described in this application, comprising a carbon framework and channels located inside the carbon framework.

[0020] This application also provides a silicon-carbon anode material, comprising the aforementioned porous carbon and elemental silicon filling the channels.

[0021] In some embodiments of this application, the silicon-carbon anode material further includes a carbon coating layer covering the porous carbon surface.

[0022] Compared with the prior art, the preparation method of porous carbon and silicon-carbon anode materials in this application has the following advantages:

[0023] The method for preparing porous carbon and silicon-carbon anode materials disclosed in this application can improve the performance consistency of the formed porous carbon and significantly improve the strength, residual ratio, concentrated distribution of micropore regions, square root volume ratio, and vacancy ratio provided by mesopores of the porous carbon. It also improves the strength, yield, uniformity of elemental silicon deposited in the pores of the porous carbon, first-time efficiency, specific capacity, multiple-flush performance, low-temperature performance, and reduces floating silicon on the silicon-carbon surface, thereby increasing the production rate. It achieves the goal of improving quality and efficiency in an environmentally friendly and low-cost manner, ultimately reducing costs and increasing efficiency.

[0024] This application, by adding decabromodiphenyl ethane to phenolic resin, can further control the carbonization process, improve the residual carbon rate of the phenolic resin, increase the content of sp3 hybrid orbitals of carbon atoms, and increase the pore volume of the formed porous carbon mesopores. This allows the silicon particles in the porous carbon to expand into the carbon matrix during expansion, making the pore size distribution of the activated porous carbon more concentrated and controllable. This results in more uniform silane deposition during the subsequent formation of the carbon coating layer, ultimately improving the voltage resistance of the formed silicon-carbon anode material. The final performance in the battery is characterized by high density, low expansion coefficient, and long cycle life.

[0025] In this application, by adding an antifoaming agent to the thermosetting phenolic resin, the voids in the particulate precursor prepared by the spray drying process are reduced, the process time is reduced, the density and void concentration of the particulate precursor are enhanced, the process difficulty of the subsequent activation process is reduced, the uniformity of silane deposition during the subsequent formation of the carbon coating layer is improved, and the strength of the formed silicon-carbon anode material is increased.

[0026] This application uses a polyether-modified silicone defoamer. The polyether-modified silicone defoamer uses chemical modification technology to introduce polyether segments into the polysiloxane chain. After using the polyether-modified silicone defoamer, the mixture will exhibit a certain degree of self-emulsification characteristics. Specifically, the polysiloxane segments curl inward while the polyether segments stretch outward. This is caused by the difference in hydrophobicity and affinity of the siloxane segments and polyether segments to the foaming liquid.

[0027] By controlling the amount of defoamer added, the macropores in the particulate precursor can be effectively eliminated, the influence of the macropores in the particulate precursor on the macropores in the porous carbon can be effectively reduced, and the strength of the formed porous carbon can be enhanced. Detailed Implementation

[0028] The following description provides specific application scenarios and requirements for this application, intended to enable those skilled in the art to make and use the content of this application. Various partial modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but rather to the widest scope consistent with the claims.

[0029] This application provides a method for preparing porous carbon, comprising:

[0030] Step S1: Provide a mixture comprising a first resin, a flame retardant and a defoamer, dissolve the mixture in a first organic solvent, and prepare a granular precursor by spray drying;

[0031] Step S2: Carbonize the particulate precursor to form a carbonized product;

[0032] Step S3: Activate the carbonization product to form the porous carbon.

[0033] First, step S1 is performed: a mixture comprising a first resin, a flame retardant, and a defoamer is provided; the mixture is dissolved in a first organic solvent and prepared into a granular precursor by spray drying.

[0034] In some embodiments of this application, the first resin includes at least one selected from epoxy resin, phenol-formaldehyde resin, resorcinol-formaldehyde resin, cashew oil-modified phenolic resin, melamine-formaldehyde resin, urea-formaldehyde resin, furfuryl alcohol resin, polyurethane resin, and silicone resin. The following description uses a thermosetting phenolic resin as an example of the first resin being a thermosetting phenolic resin.

[0035] The flame retardant includes at least one of decabromodiphenyl ethane, decabromodiphenyl ether, octabromodiphenyl ether, pentabromodiphenyl ether, tetrabromobisphenol A, and hexabromocyclododecane. The flame retardant in the mixture has a mass percentage of 1% to 5% with respect to the first resin, for example, the flame retardant has a mass percentage of 2%, 3%, or 4% with respect to the first resin.

[0036] The following description uses decabromodiphenyl ethane as an example of a flame retardant. Decabromodiphenyl ethane can be well dispersed with thermosetting phenolic resins, and it is an environmentally friendly flame retardant that does not produce polybrominated dibenzodioxanes (PBDDs) and polybrominated dibenzofurans (PBDFs) during combustion, thus benefiting the environment.

[0037] Decabromodiphenyl ethane is a gas-phase flame retardant. When heated or burned, this flame retardant generates free radical inhibitors, thereby inhibiting free radical chain reactions and interrupting or stopping the free radical chain reactions that occur during the combustion of the polymer, thus achieving the purpose of flame retardant against the polymer produced during combustion. Furthermore, the gas-phase flame retardant generates fine particles during heating and combustion. These fine particles can promote the combination of free radicals generated during the combustion of the polymer, thereby terminating the combustion chain reaction. The gas-phase flame retardant can also release a large amount of inert gas upon thermal decomposition. This inert gas can dilute the flammable gas on the surface of the polymer, thereby preventing or interrupting the oxygen supply during the polymer combustion reaction. It can also lower the temperature of the flammable gas in the system, thus preventing the combustion reaction from continuing. When heated, the gas-phase flame retardant can also generate a high-density gas. This high-density gas can cover the surface of the polymer, hindering the contact between the flammable gas generated by the polymer decomposition and air and oxygen, thereby preventing combustion. For example, when the gas-phase flame retardant is heated, it decomposes to release free radicals (X·). These free radicals can react with the thermal decomposition products of the polymer to generate hydrogen halides (HX). HX can capture active free radicals in the combustion reaction, thereby slowing down or terminating combustion. The generated hydrogen halides can remain in the combustion zone for a relatively long time, having a dilution and covering effect, thus playing a good role in flame retardancy.

[0038] The defoamer includes alcohols and ethers such as polyoxyethylene alcohol and fatty alcohol polyether. The mass percentage of the defoamer to the first resin in the mixture is 0.1‰ to 0.5‰. For example, the mass percentage of the defoamer to the first resin in the mixture is 0.2‰, 0.3‰, 0.4‰, etc.

[0039] The defoamer can reduce the surface tension of the small droplets formed by spraying in the subsequent process of dissolving the mixture in a first organic solvent and preparing it into a granular precursor by spray drying, thereby reducing the voids in the granular precursor prepared by spray drying and increasing the powder density in the granular precursor.

[0040] In the absence of the aforementioned defoamer and flame retardant, if phenolic resin is directly spray-dried to prepare granular powder, the surface of the granular powder will dry preferentially, leading to preferential surface changes and solidification. The interior of the granular powder will subsequently solidify. However, the solid content of this subsequently solidified portion is insufficient to fill the internal areas of the granular powder, resulting in numerous voids within the granular powder. In other words, the porosity of the granular powder is related to the solid content, degree of drying, and ambient vacuum level of the phenolic resin material used during spraying.

[0041] In this embodiment, the addition of the defoamer can reduce the viscosity of the phenolic resin in the mixture and the tension in the droplets, which is beneficial for mass production and shortens the processing time and equipment usage cycle.

[0042] The mixture is added to a first organic solvent, and after being completely dissolved by stirring at a first temperature, it is spray-dried in a spray dryer to form a granular precursor. The granular precursor is a spherical powder with a median particle size ranging from 2 μm to 50 μm, such as 8 μm, 15 μm, 25 μm, 35 μm, and 45 μm.

[0043] In some embodiments of this application, the first organic solvent includes at least one of benzene, toluene, xylene, pentane, hexane, octane, cyclohexane, cyclohexanone, methylcyclohexanone, chlorobenzene, dichlorobenzene, dichloromethane, methanol, ethanol, isopropanol, diethyl ether, propylene oxide, methyl acetate, ethyl acetate, propyl acetate, acetone, methyl butyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, acetonitrile, and pyridine.

[0044] The drying method includes one of atmospheric pressure drying, vacuum drying, spray drying, and fluidized bed drying; the drying temperature is 50–300℃, and the drying time is 0.5–20 h.

[0045] Step S2: Carbonize the particulate precursor to form a carbonized product.

[0046] During the carbonization process, the resin molecules of the particulate precursor undergo a carbonization reaction and are transformed into porous carbon. The carbonization process includes the breaking of macromolecular C-C and CH bonds, the cleavage of oxygen- and nitrogen-containing functional groups, and then a series of complex physical and chemical processes such as cyclization and aromatization to transform into porous carbon. The porous carbon contains a certain amount of pores in its structure, which is beneficial for subsequent activation.

[0047] In some embodiments of this application, the carbonization process can be carried out under vacuum conditions or an inert atmosphere, wherein the inert atmosphere can be an inert atmosphere formed by at least one of nitrogen, argon, or helium; the carbonization equipment used in the carbonization process can be a box furnace, a vacuum furnace, a pusher kiln, or a rotary kiln. For example, the carbonization process includes: after introducing an inert atmosphere into the reaction chamber, heating at a rate of 1–20 °C / min, heating to 300–1000 °C, and holding at that temperature for 0.5–10 hours.

[0048] In this embodiment, the well-dispersed polyether-modified silicone defoamer undergoes pyrolysis during the carbonization treatment of the particulate precursor, producing uniformly dispersed silicon atoms. Since the carbon content in the polyether-modified silicone defoamer is lower than that in phenolic resin, tiny voids resembling a core-shell structure are easily generated around the silicon atoms, which then attach to the carbon wall in the form of Si-H bonds, forming amorphous hard carbon bonded by CH bonds and silicon atoms containing Si-H bonds. The amorphous hard carbon bonded by CH bonds is easily activated, and the Si-H bonds readily adsorb silane molecules, making them easier to deposit. This can reduce the gas consumption of the CO2 activation method and improve the silane pyrolysis efficiency.

[0049] In this embodiment, the flame retardant decabromodiphenyl ethane can slow down the carbonization process of the first resin, such as phenolic resin, preventing bubbles generated by excessively rapid carbonization of the phenolic resin from remaining in the particulate precursor. The flame retardant decabromodiphenyl ethane can also increase the residual carbon rate of the first resin, such as phenolic resin, during the carbonization process, increasing the yield of the particulate precursor in forming the porous carbon and reducing the manufacturing cost of the porous carbon. Furthermore, the flame retardant decabromodiphenyl ethane can also improve the matrix strength of the porous carbon formed using the first resin. The addition of the flame retardant is beneficial for the carbonization products of the phenolic resin to shift towards SP3, reducing the amount of SP2 formed. In addition, since the bromine content of decabromodiphenyl ethane is as high as 82.3%, such a high bromine content in the early stages of carbonization of the particulate precursor causes the closed pores in the porous carbon to transform into open pores, thereby reducing the generation of closed pores in the porous carbon and facilitating the manufacture of mesopores, thus forming porous carbon with micropores as the main component and mesopores as the secondary component.

[0050] This application, by adding decabromodiphenyl ethane to phenolic resin, can further control the carbonization process, improve the residual carbon rate of the phenolic resin, increase the content of sp3 hybrid orbitals of carbon atoms, and increase the pore volume of the formed porous carbon mesopores. This allows the silicon particles in the porous carbon to expand into the carbon matrix during expansion, making the pore size distribution of the activated porous carbon more concentrated and controllable. This results in more uniform silane deposition during the subsequent formation of the carbon coating layer, ultimately improving the voltage resistance of the formed silicon-carbon anode material. The final performance in the battery is characterized by high density, low expansion coefficient, and long cycle life.

[0051] This application uses thermosetting phenolic resin to prepare the particulate precursor. Compared with thermoplastic phenolic resin, thermosetting phenolic resin has better compatibility with decabromodiphenyl ethane and is easier to mix evenly. This allows the thermosetting phenolic resin to be completely dispersed at relatively low temperatures using dispersants such as alcohol. Furthermore, thermosetting phenolic resin has better flame retardant properties, with a higher oxygen index, higher ignition point, higher glass transition, and higher char residue. This makes it easier to form amorphous glassy carbon during the carbonization process. Amorphous glassy carbon is a typical hard carbon, and if the particulate precursor has high density, the surface of the formed glassy carbon has a metallic luster.

[0052] When thermosetting phenolic resin and decabromodiphenyl ethane are mixed with spherical phenolic resin to form a spherical particulate precursor, hydrogen bromide gas can escape from the surrounding porous carbon during the subsequent carbonization process. This reduces the adhesion of the spherical phenolic resin during the carbonization process, keeping the carbon particles in a loose state. It also reduces the damage to the spherical shape of the particulate precursor caused by the pulverizing airflow during the carbonization process, which is beneficial for maintaining the spherical shape of the porous carbon formed after the activation process.

[0053] Secondly, since the bromine content in the flame retardant exceeds 80% by mass, the porosity distribution and the number of mesopores in the porous carbon can be controlled by controlling the flame retardant content. These mesopores can disperse stress in the silicon-carbon anode material, reduce the expansion of the silicon-carbon anode material before and after lithium intercalation, and ensure good overall pressure resistance of the silicon-carbon anode material, compensating for the deficiency that the activation process can only generate micropores in the porous carbon.

[0054] Furthermore, after carbonizing the particulate precursor to form a carbonized product, the carbonized product retains the shape of the particulate precursor. The carbonization process requires only a low pulverizing airflow to pulverize the agglomerated carbonized product into powder. This not only shortens processing time but also allows for uniform stress release from the inside to the outside of the particulate precursor during carbonization, preventing external cracking and facilitating the formation of open pores, thus reducing the activation time required for the activation process. The technical solution of this application also improves the uniformity of the activation process. For example, during the adsorption-desorption process of nitrogen in the porous carbon channels, it can exhibit an H4-type hysteresis loop shape, and the micropore distribution is more concentrated, resulting in micropores concentrated at around 1 nm, leading to more uniform deposition of elemental silicon in the porous carbon channels.

[0055] Furthermore, since hydrogen halides are continuously generated in the particle precursor during the carbonization process, and hydrogen halides have a protective and isolating effect, the internal and external temperatures of the particle precursor are more consistent and the internal and external structural compositions are more similar during the carbonization process. This avoids the structural inconsistencies caused by uneven heating of the internal and external parts of the particle precursor, thereby avoiding the defect of poor internal and external compatibility of the silicon-carbon anode material.

[0056] In this embodiment of the application, after forming the carbonization product, the process further includes: pulverizing the carbonization product. The pulverization method, for example, employs air jet milling to pulverize the carbonization product into particles with a median particle size D50 ranging from 2 μm to 50 μm, such as 5 μm, 10 μm, 20 μm, 30 μm, and 40 μm.

[0057] Step S3: Activate the carbonization product to form the porous carbon.

[0058] The activation treatment can be physical activation, which can yield porous carbon with a higher specific surface area. Physical activation refers to gas activation, which uses water vapor, flue gas (a mixture of water vapor, CO2, N2, etc.), CO2, or air as the activation gas, and activates the carbonized product at a high temperature of 800-1000℃. During physical activation, the oxidizing activation gas erodes the surface of the carbonized product at high temperature, causing the previously blocked pores in the carbonized product to reopen and further expand. The structure of the carbonized product generates new pores due to selective oxidation, while tar and uncarbonized materials are also removed, ultimately yielding a porous carbon product. Physical activation typically uses gas as the activation gas, the process is relatively simple, and the generated waste gas is mainly CO2 and water vapor, resulting in less environmental pollution.

[0059] The activation gas in the activation treatment described in this application embodiment includes at least one of water vapor, carbon dioxide, or a mixture of water vapor and carbon dioxide; the activation temperature is 600–1000°C, and the activation time is 0.5–12 h. The activation treatment forms a rich pore structure in the porous carbon. During the activation process, the activation gas reacts with the porous carbon, consuming some carbon atoms in the continuous reaction, thus leaving pores at those locations. Through the selective reaction of the active sites in the porous carbon with the activation gas, porous carbon microspheres with a multi-level (including microspheres and mesopores) pore structure are formed. The framework structure is stable and does not easily react with the activation gas, thus maintaining its original structure well.

[0060] Furthermore, during the activation process, activating gases such as CO2 are adsorbed in the open pores, resulting in a higher porosity of the micropores. This facilitates the uniform deposition of silanes when elemental silicon is subsequently deposited in the channels of the porous carbon. In addition, the increased porosity of the micropores in the porous carbon can alleviate the expansion problem of silicon-carbon anode materials before and after lithium intercalation, which is of great significance for the industry system of soft-pack batteries that is mainly based on winding.

[0061] This application also provides a method for preparing a silicon-carbon anode material, comprising: using any of the porous carbons described in the embodiments of this application as a matrix, allowing silicon-containing gas to diffuse and adsorb into the pores of the porous carbon and undergo a cracking reaction within the pores, and depositing elemental silicon on the pore walls of the pores.

[0062] In some embodiments of this application, the silicon-containing gas includes one or more of silane, disilane, propane, dimethylsilane, hexamethyldisilane, dichlorosilane, trichlorosilane, silicon tetrachloride, and silicon tetrafluoride. In some embodiments of this application, the porous carbon is used as a matrix and fed into a fluidized bed or CVD furnace. A silicon-containing gas, silane, is introduced and diffuses into the pores. Silicon is then deposited on the pore walls of the porous carbon through high-temperature pyrolysis to obtain a silicon-carbon anode material. In the embodiments of this application, the flow rate of the silicon-containing gas ranges from 0.1 to 50 L·kg⁻¹. -1 min -1 For example, 3L·kg -1 min -1 10L·kg -1 min -1 20L·kg -1 min -1 30L·kg -1 min -1 and 40L·kg -1 min -1The permeation time is 1h to 36h, for example, 8h, 12h, 20h, and 30h. The temperature for depositing elemental silicon on the pore wall of the channel is 300 to 1000℃, for example, 500℃ or 800℃, and the time is 3 to 13h, for example, 5h, 8h, and 10h.

[0063] In some embodiments of this application, a step of carbon coating is further included to form a carbon coating layer on the porous carbon surface of elemental silicon deposited within the channels. The method for forming the carbon coating layer includes gas-phase coating and liquid-phase coating, with gas-phase coating being preferred. The gas-phase coating method includes: subjecting a carbon-containing gas to high-temperature pyrolysis, thereby forming the carbon coating layer on the porous carbon surface of elemental silicon deposited within the channels. The carbon-containing gas includes one or more of methane, ethane, propane, acetylene, propyne, butyne, and ethylene. For example, one or more of methane, ethylene, and acetylene are introduced into a reactor, and high-temperature pyrolysis forms a uniform carbon coating layer on the entire surface of the silicon-carbon anode material. The temperature for forming the carbon coating layer is 300–1000°C, and the coating time is 0.5–6 hours.

[0064] This application also provides a porous carbon, formed using any of the porous carbon preparation methods described in this application, comprising a carbon framework and channels located inside the carbon framework.

[0065] This application also provides a silicon-carbon anode material, comprising the aforementioned porous carbon and elemental silicon filling the channels.

[0066] In some embodiments of this application, the silicon-carbon anode material further includes a carbon coating layer covering the porous carbon surface.

[0067] In this embodiment, the method for determining the char residue rate is as follows: Weigh a certain weight of the cured phenolic resin sample (W1) and place it in a crucible (W0) with a constant weight. Cover the crucible and place it in a resistance furnace that has been heated to 800°C. After the temperature is raised back to 800°C and held at that temperature for a certain period of time, remove the sample and place it in a desiccator. After cooling to room temperature, weigh the sample (W2). Perform three parallel determinations and take the arithmetic mean. Char residue rate = 1 - (W1 + W0 - W2) / W1.

[0068] Example 1

[0069] Preparation of porous carbon:

[0070] An ether-based defoamer was added to thermoplastic phenolic resin powder, with a solid content ratio of phenolic resin to defoamer of 1:0.3‰. Decabromodiphenyl ethane was also added, with a solid content ratio of 1:2 to the phenolic resin, forming a mixture. Anhydrous ethanol was added to the mixture, with a solid content ratio of 1:1 to the phenolic resin. The mixture was stirred at 600 r / min for 1 hour under vacuum at 45°C, and then transferred to a spray dryer. After a test spray drying in the spray dryer until the particle size was approximately 8 μm, the mixture was transferred to a rotary kiln for carbonization. The temperature was increased to 650°C at 2°C / min and held for 2 hours. The rotary kiln speed was set to 6 r / min, and the carbonization rate was 1 L·kg⁻¹. - 1 min -1 Nitrogen gas was introduced for protection, and the resulting exhaust gas was treated with a potassium hydroxide alkaline solution to obtain carbonized products. The carbonized products were then processed using an air jet mill to reduce the particle size (D50) to approximately 8 μm. The milled carbonized products were then activated by introducing CO2 gas at a flow rate of 2 L / kg. -1 min -1 The temperature was increased to 700℃ at a rate of 5℃ / min for 3 hours to carry out the activation reaction, forming porous carbon.

[0071] Preparation of silicon-carbon anode materials:

[0072] The prepared porous carbon was transferred into a fluidized bed, and silane deposition was carried out by introducing alkane gas at 600°C with a gas flow rate of 3 L·kg⁻¹. -1 min -1 The gas flow time was 12 hours, during which silicon was deposited on the pore walls of the porous carbon. Then, 1 L / kg acetylene gas was introduced into a rotary furnace. -1 min -1 Carbon coating is carried out at 500℃ for 6 hours to form a carbon coating layer on the porous carbon surface, thus obtaining the finished silicon-carbon anode material.

[0073] Examples 2-9

[0074] Compared to Example 1, Examples 2 through 9 only changed the ratio of defoamer and flame retardant content, while other parameters remained unchanged. The first resin was a thermosetting phenolic resin, the defoamer was a polyether-modified silicone defoamer, the flame retardant was decabromodiphenyl ethane, and the first organic solvent was anhydrous ethanol. The carbonization process was carried out in a rotary furnace at 6 r / min and 1 L·kg⁻¹. -1 min -1 Nitrogen gas was introduced, and the temperature was increased to 650℃ at a rate of 2℃ / min, and held for 2 hours. The activation gas used in the activation treatment was CO2, with a gas flow rate of 2 L·kg⁻¹. -1 min -1The temperature was increased to the required experimental temperature of 700℃ at a rate of 5℃ / min for activation reaction, which lasted for 3 hours. Silane was used as the silicon source in the elemental silicon deposition process, and the deposition process used was 3 L·kg⁻¹. - 1 min -1 The deposition was carried out at 600℃ for 12 hours. Acetylene was used in the carbon coating formation stage, with an intake rate of 1 L / kg. - 1 min -1 A carbon coating layer is formed by deposition at 500℃ for 6 hours.

[0075] The silicon-carbon anode materials formed in Examples 1 to 9 were used to prepare coin cells, and their electrochemical performance was tested. The true density measurement method in Examples 1 to 9 used an ULTRA1000 true density meter, the particle size measurement used a Masterizer-2000 laser particle size analyzer, the BET test (specific surface area test) and whole-pore test used a Micron ASAP2020, and the battery capacity testing system used a Xinwei CT-4008Q-5V6A. The first-cycle efficiency was determined by dividing the discharge capacity of the coin cell in the first cycle by the charging capacity. The fast-charge capacity retention rate was determined by dividing the discharge capacity of the coin cell by its 0.1C discharge capacity. The capacity retention rate was determined by dividing the discharge capacity of the coin cell after cycling by its first-cycle discharge capacity.

[0076] Table 1 below shows the process parameters for the corresponding process steps in Examples 1 and 2-9, as well as the porous carbon content (%) and BET (m) of the formed porous carbon. 2 / g), wherein the porous carbon percentage is the ratio of the weight of the formed porous carbon to the weight of the particulate precursor. The residual carbon percentage (%) is the ratio of the weight of the carbonized product formed after carbonization treatment to the weight of the particulate precursor, and the true density is the true density of the formed carbonized product.

[0077] Table 1

[0078]

[0079]

[0080] As can be seen from Examples 1 to 5, with the increase of defoamer content, the residual carbon rate of the particulate precursor after carbonization did not change significantly; however, the true density after carbonization showed an upward trend. This is mainly because the defoamer eliminated the macropores in the particulate precursor, resulting in a slight increase in true density. Additionally, with the increase of defoamer content, the porous carbon rate of the activated porous carbon showed a downward trend. This is mainly because the defoamer has a lower carbon content, and the carbonization process leaves trace voids, making the surrounding carbon structure more disordered, which is conducive to CO2 gas adsorption during activation, making activation easier. This is accompanied by a slight decrease in porous carbon rate and a slight increase in specific surface area. Furthermore, the main reason for the increase in elemental silicon deposition rate is that the Si-H bonds broken in the defoamer are more effective at adsorbing silane molecules onto the porous carbon surface during silane cracking. The micropores generated by the defoamer cracking also have stronger capillary action, which is more conducive to gas adsorption, thus increasing the silane cracking rate. Furthermore, because the silicon atoms in the defoamer are more uniformly dispersed, their gripping effect also makes the silicon nanoparticles more uniformly dispersed, which is more conducive to uniform deposition inside the activated carbon. This increases the initial efficiency from 86% to 87.3%. With the increase of defoamer content, the increase of residual Si-H bonds makes silanes easier to deposit, but also leads to uneven deposition of some silanes. This results in a trend of first increasing and then decreasing in cycle retention rate, and a trend of first decreasing and then increasing in expansion amount. As can be seen from the examples, the optimal amount of defoamer added is 1.5%.

[0081] As can be seen from Examples 6 to 9, with the addition of flame retardant, the residual carbon rate of the particulate precursor increased significantly, and the true density after carbonization also improved. This is mainly because the release of bromine in the flame retardant makes the formed porous carbon more inclined to form open pores. The pore distribution after carbonization is different from that of conventional phenolic resin carbonization, which makes the capillary action in the pores stronger and the utilization rate of the pores to provide capillary action higher, thereby avoiding the pore closure. This characteristic also makes CO2 activation easier. It can be seen that when the amount of flame retardant added is 4%, the specific surface area tends to decrease. This is because with the increase of bromine fumes, the generated mesopores tend to merge to form macropores, which reduces the specific surface area of ​​the carbon material, and the first efficiency, specific capacity, and cycle retention rate all show adverse changes. The main reason for this is that with the fusion of numerous mesopores, the overall strength of the material decreases. Although it helps the carbon composition to change from SP2 to SP3, because the pore composition of the carbon material changes and affects the deposition of silane, the overall cell performance shows a trend of first increasing and then decreasing. As can be seen from the data in the examples, the optimal amount of flame retardant added is 3%.

[0082] Table 2 shows the performance test data of the formed porous carbon and silicon-carbon anode materials. Among them, the ratio of mesopores providing vacancy (%) is the percentage of the total volume of mesopores in the porous carbon to the total volume of the porous carbon. The elemental silicon deposition rate is the percentage of the weight of elemental silicon deposited in the channels of the porous carbon to the weight of the particulate precursor. The weight of elemental silicon after deposition / particulate precursor is the percentage of the weight of elemental silicon after deposition in the channels of the porous carbon to the weight of the particulate precursor. The weight of carbon coating layer after formation / particulate precursor is the weight ratio of the silicon-carbon anode material formed after the carbon coating layer is applied to the surface of the porous carbon to the weight of the particulate precursor.

[0083] The 0.1C 0.8V specific capacity was measured at 25℃ using a Xinwei CT-4008Q-5V6 testing system. First, a CR2450 button cell was assembled. Then, a constant voltage discharge method was used, discharging to 0.000V at 0.1V / h, followed by charging to 0.8V at 0.1V / h. The 0.1C current of the charging capacity was recorded. A new CR2450 button cell was reassembled, and a constant current charge-discharge test was performed, recording the 0.1C current of the charging capacity. After discharging to 0V, it was charged to 0.8V to obtain the capacity. The specific capacity at 0.1C 0.8V = capacity / mass of active material in the electrode. The mass of active material in the electrode = mass of silicon-carbon anode material + mass of graphite. The 0.2C 0.8V specific capacity was measured at 25℃ using a Xinwei CT-4008Q-5V6 testing system. First, a CR2450 button cell was assembled. Then, a constant voltage discharge method was used, discharging to 0.000V at 0.1V / h, followed by charging to 0.8V at 0.1V / h. The 0.2C current for the charging capacity was recorded. A new CR2450 button cell was reassembled, and a constant current charge-discharge test was performed, discharging to 0V and then charging to 0.8V to obtain the capacity. The specific capacity at 0.2C 0.8V = capacity / mass of active material in the electrode. The mass of active material in the electrode = mass of silicon-carbon anode material + mass of graphite. These two data points show that the amount of flame retardant added not only changes the porous carbon structure but also affects the first-efficiency and rate performance of the silicon-carbon anode material. Appropriate flame retardant addition can effectively improve the rate capability, first-efficiency performance, and reduce some of the expansion.

[0084] The first-cycle lithium insertion expansion (%) is (thickness of electrode after saturated lithium insertion - thickness of copper foil) / (thickness of electrode without lithium insertion - thickness of copper foil) - 1. The 10-cycle retention rate is obtained by cycling the battery at a current of 0.2C, with the battery cutoff voltage of 0-1.5V and the charge / discharge cutoff current of 0.1mAh. Then, the charging capacity of the battery in the 10th cycle is compared with the charging capacity in the first cycle.

[0085] As shown in Table 2, with the addition of flame retardants, the mesoporous ratio in the silicon-carbon anode material tends to increase, and the amount of silicon deposited also increases. This indicates that the reasonable addition of gas-phase flame retardants can develop micropores while also promoting mesoporous development. The increase in mesopores in porous carbon affects micropores and thus the deposition of silicon atoms in the channels of the porous carbon. The enhanced initial efficiency of the silicon-carbon anode material may be due to the complete opening of micropores in the porous carbon. The opening of micropores makes the deposition of silicon atoms in the channels of the porous carbon more uniform, thereby inhibiting the formation of silicon crystals and reducing ion diffusion resistance. In addition, the specific capacity and rate capability are also improved to a certain extent, which is also related to the more uniform deposition of silicon in the porous carbon, allowing silicon particles to develop towards sub-nanometer size. The expansion amount is affected by both the amount of silicon deposited and the pore structure. Its overall pattern is that it first increases and then decreases. The decrease in the latter part is mainly due to the higher amount of mesopores. The increase in expansion amount in the initial stage may be due to the lower proportion of mesopore volume and the increase in silicon deposition. Furthermore, the initial efficiency also shows that the increase in mesopores did not reduce the initial efficiency. This indicates that the strength of the porous carbon particles is sufficient at this compaction density. Otherwise, the initial efficiency should have decreased under the condition of increased mesopore volume. The main reason may be that the flame retardant increased the proportion of SP3 hybrid forms in the silicon-carbon anode material. The stress release effect of isotropic carbon materials is more obvious than that of anisotropic graphitized carbon materials, which can significantly improve the strength of single particles. At the same time, in conjunction with the development of pores, it can also optimize the shortcomings of low initial efficiency and poor rate capability of traditional hard carbon materials. Ultimately, it achieves a balance between the high strength of hard carbon materials and the high rate capability and high initial efficiency of graphitized materials, while reducing the production cost of porous carbon and improving the yield of porous carbon, thus achieving a win-win situation.

[0086] Table 2

[0087]

[0088]

[0089] Finally, it should be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments of this application. Other modified embodiments are also within the scope of this application. Therefore, the embodiments disclosed herein are merely examples and not limitations. Those skilled in the art can implement the applications in this application by adopting alternative configurations based on the embodiments in this application. Therefore, the embodiments of this application are not limited to those embodiments precisely described in the application.

Claims

1. A method for producing a porous carbon, characterized by, The method comprises: providing a mixture comprising a first resin, a flame retardant, and a defoaming agent, dissolving the mixture in a first organic solvent, and preparing a granular precursor by spray drying, wherein the flame retardant comprises at least one of decabromodiphenyl ethane, decabromodiphenyl ether, octabromodiphenyl ether, pentabromodiphenyl ether, tetrabromobisphenol A, hexabromocyclododecane, decabromodiphenyl ether, octabromodiphenyl ether, pentabromodiphenyl ether, tetrabromobisphenol A, and hexabromocyclododecane; subjecting the granular precursor to a carbonization treatment to form a carbonization treatment product; subjecting the carbonization treatment product to an activation treatment to form the porous carbon.

2. The method for producing porous carbon according to claim 1, wherein The mass percentage of the flame retardant to the first resin is 1% to 5%.

3. The method for producing porous carbon according to claim 1, wherein The defoaming agent comprises at least one of an alcohol organic compound and an ether organic compound, wherein the alcohol organic compound comprises polyoxyethylene alcohol, and the ether organic compound comprises a fatty alcohol polyether.

4. The method for producing porous carbon according to claim 1, wherein The mass percentage of the defoaming agent to the first resin is 0.1‰ to 0.5‰.

5. The method of claim 1, wherein the porous carbon is prepared by a method comprising: mixing a carbon source and a polymer to form a mixture; and heating the mixture to form the porous carbon. The carbonization treatment comprises: in an inert atmosphere, increasing the ambient temperature to 300 to 1000℃ at a rate of 1 to 20℃ / min, and performing the carbonization treatment for 0.5 to 10h.

6. The method of claim 1, wherein the porous carbon is prepared by a method comprising: The first resin comprises at least one of an epoxy resin, a phenol formaldehyde resin, a m-phenol formaldehyde resin, a cashew oil modified phenol formaldehyde resin, a melamine formaldehyde resin, a urea formaldehyde resin, a furfuryl alcohol resin, a polyurethane resin, and a silicone resin.

7. The method of claim 1, wherein the porous carbon is prepared by a method comprising: mixing a carbon source and a polymer to form a mixture; and heating the mixture to form the porous carbon. The activation treatment comprises: introducing an activation gas into a reaction chamber, wherein the activation gas comprises at least one of water vapor, CO2, or air.

8. The method of claim 1, wherein the porous carbon is prepared by a method comprising: After forming the carbonization treatment product, the method further comprises: crushing the carbonization treatment product to make the median particle size of the carbonization treatment product reach a micron level.

9. A method for preparing a silicon-carbon negative electrode material, characterized by, The method comprises: using the porous carbon of any one of claims 1 to 8 as a substrate, allowing a silicon-containing gas to diffuse and adsorb into the pores of the porous carbon and undergo a cracking reaction in the pores, and depositing elemental silicon on the pore walls of the pores.

10. The method of claim 9, wherein the silicon-carbon negative electrode material is prepared by a process comprising: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. The method further comprises: forming a carbon coating layer on the surface of the porous carbon.

11. The method of claim 9, wherein the silicon-carbon negative electrode material is prepared by a process comprising: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. The silicon-containing gas comprises one or more of monosilane, disilane, trisilane, dimethylsilane, hexamethyldisilane, dichlorosilane, trichlorosilane, silicon tetrachloride, and silicon tetrafluoride.

12. The method of claim 11, wherein the silicon-carbon negative electrode material is prepared by a process comprising: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the silicon-carbon negative electrode material. The temperature for depositing the elemental silicon on the pore walls of the pores is 300 to 1000℃, and the time is 0.5 to 6h.

13. A porous carbon formed by any one of claims 1 to 8, comprising a carbon skeleton and pores inside the carbon skeleton.

14. A silicon-carbon negative electrode material, comprising the porous carbon of claim 13 and elemental silicon filled in the pores.

15. The silicon-carbon negative electrode material of claim 14, wherein, The method further comprises: forming a carbon coating layer on the surface of the porous carbon.

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