Porous carbon, preparation method thereof and battery

Abstract

The invention discloses porous carbon, a preparation method thereof and a battery, and belongs to the field of battery materials. The specific surface area of the porous carbon is greater than or equal to 2400m < 2 > / g, the pore volume ratio of micropores with the pore diameter smaller than or equal to 2nm is greater than or equal to 70%, and the large specific surface area and the pore diameter are distributed and concentrated on the micropores, so that the porous carbon keeps enough mechanical strength, sufficient pore space and channels can be provided, and subsequent uniform deposition of silicon is facilitated.

Description

Technical Field

[0001] The present application relates to the field of battery materials, and particularly to a porous carbon, a preparation method thereof, and a battery. Background Art

[0002] Due to its high specific surface area, good mechanical properties, adjustable pore structure, and excellent electrical conductivity, pitch-based porous carbon materials have been widely used in fields such as supercapacitors, anodes of lithium-ion batteries, and gas adsorption. With the rapid development of lithium-ion battery technology in the power battery, consumer battery, and energy storage markets, silicon-carbon anode materials have shown great application potential due to their high theoretical specific capacity. And porous carbon, as the skeleton material of silicon-carbon, its structure will directly affect the silicon deposition, thereby affecting the performance of the finally formed silicon-carbon anode material. Summary of the Invention

[0003] In view of this, the present application provides a porous carbon, a preparation method thereof, and a battery, aiming to provide a porous carbon with a large specific surface area suitable for silicon deposition.

[0004] The embodiment of the present application is implemented as follows. A porous carbon is provided, and the specific surface area of the porous carbon is greater than or equal to 2400 m 2 / g, and the pore volume ratio of micropores with a pore diameter less than or equal to 2 nm is ≥70%.

[0005] In some embodiments, the pore volume ratio of micropores with a pore diameter of 0.5 - 2 nm in the porous carbon is greater than 98%; and / or, the electrical conductivity of the porous carbon is 80 - 100 S / cm; and / or, the carbon source of the porous carbon includes pitch.

[0006] Correspondingly, the present application also provides a preparation method of a porous carbon, including: providing a pitch-based carbon source; performing vacuum pre-activation on the pitch-based carbon source in a vacuum atmosphere to obtain a pre-activated material;

[0007] Mixing the pre-activated material with an activator, and performing carbonization treatment on the mixture, wherein the temperature of the carbonization treatment is less than or equal to 700 °C.

[0008] In some embodiments, the vacuum degree of the vacuum atmosphere is 1*10 -1 ~1*10 -3 Pa; and / or, the activation temperature of the vacuum pre-activation is 400 - 650 °C; and / or, the activation time of the vacuum pre-activation is 1 - 6 h.

[0009] In some embodiments, the vacuum pre-activation is carried out by pre-activation at a gradient temperature, including a first heat preservation treatment and a second heat preservation treatment; wherein: the temperature of the first heat preservation treatment is 400 - 500 °C, and the temperature of the second heat preservation treatment is 550 - 650 °C; and / or, the time of the first heat preservation treatment is 0.5 - 3 h; and / or, the time of the second heat preservation treatment is 0.5 - 3 h; and / or, the absolute value of the temperature difference between the first heat preservation treatment and the second heat preservation treatment is greater than or equal to 100 °C.

[0010] In some embodiments, the vacuum pre-activation first rises to the temperature of the first heat preservation treatment at a first heating rate, and then rises to the temperature of the second heat preservation treatment at a second heating rate. Among them, the first heating rate is less than the second heating rate, the first heating rate is less than or equal to 5 °C / min, and the absolute value of the difference between the first heating rate and the second heating rate is greater than or equal to 3 °C / min.

[0011] In some embodiments, the vacuum pre-activation is carried out by gradient pressure control pre-activation, including a first vacuum stage and a second vacuum stage. Among them, the vacuum degree of the first vacuum stage is 1×10 -1 ~1×10 -2 Pa, the vacuum degree of the second vacuum stage is 1×10 -2 ~1×10 -3 , and the absolute value of the difference between the vacuum degree of the first vacuum stage and the vacuum degree of the second vacuum stage is greater than 0.

[0012] In some embodiments, the vacuum pre-activation is carried out by gradient temperature and gradient pressure control pre-activation, including: at a first vacuum degree, rising to the temperature of the first heat preservation treatment at a first heating rate, and carrying out the first heat preservation treatment; then evacuating to a second vacuum degree, rising to the temperature of the second heat preservation treatment at a second heating rate, and carrying out the second heat preservation treatment; wherein, the first vacuum degree is 1×10 -1 ~1×10 -2 Pa, the second vacuum degree is 1×10 -2 ~1×10 -3 Pa, and the absolute value of the difference between the first vacuum degree and the second vacuum degree is greater than 0; and / or, the temperature of the first heat preservation treatment is 400 - 500 °C, the temperature of the second heat preservation treatment is 550 - 650 °C, and the absolute value of the temperature difference between the first heat preservation treatment and the second heat preservation treatment is greater than or equal to 100 °C; and / or, the time of the first heat preservation treatment is 0.5 - 3 h; and / or, the time of the second heat preservation treatment is 0.5 - 3 h; and / or, the first heating rate is less than the second heating rate, the first heating rate is less than or equal to 5 °C / min, and the absolute value of the difference between the first heating rate and the second heating rate is greater than or equal to 3 °C / min.

[0013] In some embodiments, the heat preservation temperature of the carbonization treatment is 500-700 °C; and / or, the carbonization treatment is carried out in an inert atmosphere, wherein the inert atmosphere includes an atmosphere formed by one or more of nitrogen, helium, argon, neon and xenon; and / or, the heat preservation time of the carbonization treatment is 1-12 h.

[0014] In some embodiments, the carbonization treatment includes a first heat preservation stage and a second heat preservation stage, wherein the temperature of the first heat preservation stage is 500-600 °C, the temperature of the second heat preservation stage is 600-700 °C, and the absolute value of the difference between the temperature of the first heat preservation stage and the temperature of the second heat preservation stage is greater than or equal to 50 °C; and / or, the pitch-based carbon source includes pitch, and the pitch includes one or more of natural pitch, coal tar pitch or petroleum pitch; and / or, the softening point of the pitch-based carbon source is 100-150 °C; and / or, the particle size D50 of the pitch-based carbon source is 5-10 μm; and / or, the activator includes one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, phosphoric acid, magnesium chloride and zinc chloride; and / or, the mass ratio of the pre-activated material to the activator is 1:0.2-1:1.5; and / or, the particle size D50 of the pre-activated material is 6-12 μm.

[0015] Correspondingly, the present application also provides a battery, the battery includes a negative electrode material, the negative electrode material includes porous carbon and silicon particles, and at least part of the silicon particles are distributed in the pores of the porous carbon; wherein, the porous carbon is the above-mentioned porous carbon, or is the porous carbon prepared by the above-mentioned preparation method.

[0016] The specific surface area of the porous carbon of the present application is greater than or equal to 2400 m 2 / g, and the pore volume ratio of micropores with a pore diameter less than or equal to 2 nm is ≥70%. The relatively large specific surface area and the pore size distribution concentrated in micropores enable the porous carbon to maintain sufficient mechanical strength, can provide sufficient pore space and channels, and facilitate the subsequent uniform deposition of silicon. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a schematic flow chart of an embodiment of a preparation method of a porous carbon provided by the present application;

[0019] Figures 2-4SEM images of the porous carbons of Examples 1-3;

[0020] Figures 5-7 SEM images of the porous carbons of Comparative Examples 1-3, respectively. Detailed implementation manners

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative efforts belong to the scope of protection of the present application. In addition, it should be understood that the specific implementation manners described herein are only for explaining and interpreting the present application, and are not used to limit the present application. In the present application, unless otherwise stated, the orientation words such as "upper" and "lower" specifically refer to the drawing directions in the drawings. Additionally, in the description of the present application, the term "including" means "including but not limited to".

[0022] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of what the range is. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0023] In the present application, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural.

[0024] In the present application, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one item (piece) below", or similar expressions refer to any combination of these items, including any combination of single item (piece) or plural items (pieces). For example, "at least one item (piece) of a, b, or c", or, "at least one item (piece) of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0025] This application provides a porous carbon, and the specific surface area of the porous carbon can be 2400 m 2 / g or more. Specifically, the specific surface area of the porous carbon can be 2400 - 2450 m 2 / g, 2450 - 2500 m 2 / g, 2500 - 2550 m 2 / g, 2550 - 2600 m 2 / g, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0026] Among them, the specific surface area is obtained by the nitrogen isothermal adsorption method. The nitrogen adsorption method is one of the most widely used methods for testing the pore size of porous carbon. This method is based on the Brunauer - Emmett - Teller (BET) theory. By analyzing the isothermal adsorption curve of nitrogen adsorbed by porous carbon at a certain temperature, parameters such as its specific surface area and pore volume can be obtained, and then the diameter distribution can be calculated.

[0027] The porous carbon of this application has a porous structure, specifically including micropores with a pore diameter less than 2 nm, may also include mesopores with a pore diameter of 2 - 50 nm, and may also include a small amount of macropores with a pore diameter greater than 50 nm. Among them, the micropores are mainly used for adsorbing small molecules such as gases or ions, while the mesopores are generally used to provide ion transport channels to reduce the diffusion resistance, and the macropores serve as macroscopic mass transfer channels to support rapid mass exchange.

[0028] In one embodiment, the pore volume ratio of the micropores with a pore diameter less than or equal to 2 nm ≥ 70%, specifically it can be 70% - 80%, 80% - 85%, 85% - 90%, 90% - 96%, 96% - 99.9%, etc. Of course, it can also be other values within the above range, which are not limited herein. Among them, the pore volume ratio of the micropores with a pore diameter less than or equal to 2 nm can be calculated by micropore models such as the DFT method. In a specific embodiment, the pore volume ratio of the micropores with a pore diameter of 0.5 - 2 nm is greater than 98%.

[0029] In this embodiment, the pore structure of the porous carbon is mainly a micropore structure with a pore diameter less than or equal to 2 nm, and the pore size distribution is concentrated in the micropores, which is beneficial to maintaining the body structure and its stability, has good compressive strength, and can provide more active sites for the deposition of nanosilicon.

[0030] In one embodiment, the conductivity of the porous carbon can be 80 - 100 S / cm, specifically it can be 80 - 90 S / cm, 90 - 100 S / cm, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0031] In one embodiment, the proportion of oxygen atoms in the porous carbon to the total number of atoms can be 3% - 8%, specifically it can be 3% - 4%, 4% - 6%, 6% - 8%, etc. Of course, it can also be other values within the above range, which are not limited herein. Among them, the percentage of oxygen atoms can be obtained by testing methods such as XPS (X-ray photoelectron spectroscopy).

[0032] The porous carbon of the present application has the specific surface area and pore size distribution within the above range, enabling the porous carbon to maintain sufficient mechanical strength, providing sufficient pore space and channels, and facilitating the subsequent uniform deposition of silicon. For the silicon deposition process, a larger specific surface area and a high proportion of micropores can help silicon better penetrate into the internal pores of the porous carbon, reducing surface deposition, thereby reducing the structural damage caused by the volume expansion of silicon in subsequent applications (such as battery cycling) and improving the cycling stability of the silicon-carbon material.

[0033] In one embodiment, the morphology of the porous carbon is an irregular block, and there are no obvious cracks or holes on the surface.

[0034] In one embodiment, the carbon source of the porous carbon includes asphalt. The porous carbon prepared using asphalt as the carbon source has a smooth surface and a high degree of compaction, which is beneficial to improving the energy density of the silicon-carbon material.

[0035] In other embodiments, the carbon source of the porous carbon includes asphalt and other carbon sources. The other carbon sources can include biomass carbon sources such as glucose, starch, coconut shell, etc. and / or resin-based carbon sources such as phenolic resin.

[0036] The conventional preparation methods of the porous carbon preparation method generally adopt high-temperature carbonization (>800 °C) combined with chemical / physical activation processes, which have significant technical bottlenecks: the high-temperature process causes excessive condensation of asphalt molecules, and the pore structure is prone to collapse; the strong corrosiveness of chemical activators (such as KOH) increases equipment loss and environmental protection costs; the control accuracy of physical activation (such as water vapor) for the pore structure is insufficient. In addition, the energy consumption cost of the high-temperature process is high, restricting the economy of large-scale production.

[0037] Based on this, the present application also provides a preparation method of porous carbon. Refer to Figure 1 , Figure 1 is a schematic flow chart of an embodiment of a preparation method of porous carbon provided by the present application, which specifically includes the following steps:

[0038] Step S11: Provide an asphalt-based carbon source;

[0039] Step S12: Perform vacuum pre-activation on the asphalt-based carbon source in a vacuum atmosphere to obtain a pre-activated material;

[0040] Step S13: Mix the pre-activated material with an activator and perform carbonization treatment on the mixture, wherein the temperature of the carbonization treatment is less than or equal to 700 °C.

[0041] In the preparation method of the present application, a vacuum pre-activation is used to form an open framework structure of the pitch, which can significantly improve the penetration uniformity of the activator. A relatively low activation treatment temperature can inhibit the excessive etching of the carbon framework, improve the micropore retention rate, and endow the porous carbon with a large specific surface area and a pore structure with a concentrated pore size distribution. This is beneficial for subsequent applications such as silicon deposition while ensuring the mechanical strength of the porous carbon. In other words, through the synergistic process of vacuum pre-activation and activator etching, on the basis of retaining the advantages of vacuum technology, the pore construction efficiency is further enhanced, the graphite lattice defects in the porous carbon are reduced, the conductivity and activation efficiency are improved, and the material properties are enhanced.

[0042] In step S11:

[0043] The pitch-based carbon source includes pitch, which can include one or more of natural pitch, coal tar pitch, or petroleum pitch. Among them, natural pitch, also known as asphalt or mineral pitch, is a conversion product of petroleum.

[0044] In one embodiment, the softening point of the pitch can be 100 - 150 °C, 150 - 200 °C, 200 - 250 °C, 250 - 280 °C, above 280 °C, etc. The present application does not particularly limit the softening point of the pitch.

[0045] In one embodiment, the pitch-based carbon source can be a mixed carbon source formed by pitch and other carbon sources. Among them, the other carbon sources can include one or more of biomass carbon sources and resin-based carbon sources; the biomass carbon sources include one or more of glucose, natural starch, modified starch, coconut shell, cellulose, lignin, etc., and the resin-based carbon sources include one or more of phenolic resin, polyacrylonitrile, polyimide, polyvinyl chloride, polyphenylene sulfide, etc. Specifically, the mass percentage of pitch in the pitch-based carbon source is greater than or equal to 80%, and can specifically be 80% - 85%, 85% - 90%, 90% - 95%, 95% - 100%. A mixed carbon source with a pitch proportion greater than or equal to 80% can further improve the pore structure, increase the specific surface area and porosity, and increase the proportion of micropores while ensuring that the porous carbon has a relatively high strength.

[0046] Specifically, the source of natural starch can be cereal foods such as corn, rice, and millet, tuber foods such as sweet potato, purple sweet potato, and potato, as well as cereal foods such as red bean and mung bean.

[0047] The modification method of modified starch can include one or more of physical modification, chemical modification, and enzymatic modification. It can be understood that the modified starch can be a modified starch obtained through one modification method, or a composite modified starch obtained through a composite treatment of two or more methods.

[0048] Specifically, physical modification includes modification of starch by physical means such as heat-moisture treatment, ball milling, microwave treatment, ultrasonic treatment, etc.

[0049] Chemical modification mainly refers to various modifications that carry out chemical reactions on the numerous alcohol hydroxyl groups in starch molecules, which can include one or more of esterified starch, etherified starch, crosslinked starch, and oxidized starch.

[0050] The esterified starch includes organic acid ester starch and inorganic acid ester starch. It can be understood that organic acid ester starch is obtained by esterifying the hydroxyl groups in starch, such as alkenyl succinic acid esterified starch, starch acetate, maleic acid esterified starch, succinic acid esterified starch, starch xanthate, starch amino acid methyl ester, starch sulfosuccinate, etc.; inorganic acid ester starch is obtained by esterifying the hydroxyl groups in starch with inorganic acids, such as starch sulfate, starch nitrate, starch selenate, starch phosphate, etc.

[0051] Etherified starch is a starch derivative in which the glycosidic bond or active hydroxyl group in starch is connected to an etherifying agent through an oxygen atom. Common ones include hydroxyalkyl starch, carboxymethyl starch, and cationic starch, etc. The etherifying agent can include one or more of ethylene oxide, propylene oxide, dimethyl sulfate, propylene chloride, ethyl chloride, methyl chloride, benzyl chloride, hydrocarbons containing part of bromine and iodine, organic amine compounds containing epoxy groups or halogenated hydrocarbon groups (such as tertiary amine alkyl, quaternary amine alkyl), monochloroacetic acid, etc.

[0052] Crosslinked starch is a starch derivative formed by reacting a large number of hydroxyl groups on starch molecules with a crosslinking agent having two or more functional groups to form new chemical bonds (generating groups such as diether bonds and diester groups) and crosslinking the starch. Specifically, the crosslinking agent can include one or more of epichlorohydrin (ECH), phosphorus oxychloride, sodium trimetaphosphate (STMP), citric acid, malic acid, glutaraldehyde, sodium polyphosphate, isocyanate, etc. Common crosslinking methods include wet crosslinking, ultrasonic and microwave-assisted crosslinking, etc.

[0053] Oxidized starch refers to a modified starch obtained by reacting starch with an oxidizing agent. Among them, the oxidizing agent can include one or more of hydrogen peroxide, sodium hypochlorite, potassium permanganate, etc.

[0054] Enzyme-modified starch refers to modified starch obtained by treating starch with various enzymes, including cyclodextrin, maltodextrin, amylose, etc.

[0055] Composite modified starch can include one or more of crosslinked etherified starch, esterified etherified starch, esterified oxidized starch, oxidized etherified starch, etc.

[0056] In one embodiment, the particle size D50 of the asphalt-based carbon source is 5 to 10 μm, specifically, it can be 5 to 6 μm, 6 to 8 μm, 8 to 10 μm, etc. Of course, it can also be other values within the above range, which is not limited herein. When the particle size of the asphalt-based carbon source is within this range, it is beneficial to the full and uniform activation of the subsequent vacuum pre-activation treatment. The test method for the particle size D50, etc., can specifically refer to the laser diffraction method for particle size distribution in GB / T 19077-2016, and is measured by using a Malvern Mastersizer 2000E laser particle size analyzer made in the UK.

[0057] In some specific embodiments, the particle size range of the asphalt-based carbon source can be obtained by crushing the asphalt-based raw material with equipment such as a jet mill and a mechanical mill.

[0058] In one embodiment, the asphalt-based carbon source can be pretreated in a certain way. For example, the pretreatment can be to mix the asphalt-based carbon source with a solvent, and the mixing method can adopt a mixing method known in the art, such as a mixture of one or more of stirring, ultrasonic, ball milling, etc.

[0059] In the above embodiment, the solvent used can be selected to form a stable miscible system with the asphalt-based carbon source. In one specific embodiment, the solvent can include water. Specifically, the water can be one or more of tap water, deionized water, pure water, ultrapure water, distilled water, etc.

[0060] Among them, the mixing mass ratio of the asphalt-based carbon source to the solvent can be 1:1 to 1:4, specifically, it can be 1:1 to 1:2, 1:2 to 1:3, 1:3 to 1:4, etc. Of course, it can also be other values within the above range, which is not limited herein. The above mixing ratio is beneficial to the formation of a stable miscible system.

[0061] The step S12:

[0062] In one embodiment, the vacuum degree of the vacuum atmosphere can be between 1×10 -1 ~1×10 -3 Pa, specifically, it can be 1×10 -1 ~1×10 -2 、1×10 -2 ~1×10 -3 etc. Carrying out vacuum pre-activation in the above vacuum environment can regulate the pyrolysis kinetics of asphalt. The oxygen-containing functional groups in asphalt selectively decompose to generate CO / CO2 gas under vacuum, realizing physical pore formation without an external activator, and promoting the self-formation of nano-pores while inhibiting the generation of tar by-products, so that the asphalt forms an open framework structure. By regulating the volatilization path of volatile components through the vacuum environment, the penetration resistance after mixing with the subsequent activator can be reduced, and the directional construction of a micro-mesoporous hierarchical structure can be realized.

[0063] The activation temperature of the vacuum pre-activation can be 400 - 650 °C, specifically it can be 400 - 450 °C, 450 - 500 °C, 500 - 550 °C, 550 - 600 °C, 600 - 650 °C, etc. Of course, it can also be other values within the above range, which is not limited herein.

[0064] The activation time of the vacuum pre-activation can be 1 - 6 h, specifically it can be 1 - 2 h, 2 - 4 h, 4 - 6 h, etc. Of course, it can also be other values within the above range, which is not limited herein.

[0065] In some embodiments, the vacuum pre-activation is carried out with pre-activation at a gradient temperature, including a first heat preservation treatment and a second heat preservation treatment; wherein, the temperature of the first heat preservation treatment can be 400 - 500 °C and the time can be 0.5 - 3 h; the temperature of the second heat preservation treatment can be 550 - 650 °C and the time can be 0.5 - 3 h. In this embodiment, the first heat preservation treatment can slowly raise the temperature to induce the ordered arrangement of the mesophase, and then quickly raise the temperature to the second heat preservation treatment to fix the pore structure. Through the pre-activation treatment with a gradient temperature, a stable pore structure can be formed.

[0066] Furthermore, in some specific embodiments, the absolute value of the temperature difference between the first heat preservation treatment and the second heat preservation treatment is greater than or equal to 100 °C, so as to ensure a sufficient temperature gradient. It can be understood that the temperature of the first heat preservation treatment is lower than that of the second heat preservation treatment, and the absolute value of the temperature difference between the two is the absolute value of the temperature difference obtained by subtracting the temperature of the second heat preservation treatment from the temperature of the first heat preservation treatment, or the temperature difference obtained by subtracting the temperature of the first heat preservation treatment from the temperature of the second heat preservation treatment. The specific value of the temperature difference can be a value within the range of 100 - 250 °C, such as 100 °C, 150 °C, 200 °C, 250 °C, etc.

[0067] Furthermore, in some other specific embodiments, the temperature of the vacuum pre-activation first rises to the temperature of the first heat preservation treatment at a first heating rate, and then rises to the temperature of the second heat preservation treatment at a second heating rate, wherein, the first heating rate is less than the second heating rate, the first heating rate is less than or equal to 5 °C / min, and the absolute value of the difference between the first heating rate and the second heating rate is greater than or equal to 3 °C / min. Slowly heating at the first heating rate is beneficial to inducing the ordered arrangement of the mesophase, while quickly heating in the process of rising to the temperature of the second heat preservation treatment at the second heating rate is beneficial to fixing the pore structure.

[0068] Specifically, the first heating rate can be 1-2 °C / min, 2-3 °C / min, 3-4 °C / min, 4-5 °C / min, etc. Of course, it can also be other values within the above range, which are not limited herein. The absolute value of the difference between the first heating rate and the second heating rate can be 3-4 °C / min, 4-5 °C / min, 4-5 °C / min, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0069] In some other embodiments, the vacuum pre-activation adopts gradient pressure-controlled pre-activation, including a first vacuum stage and a second vacuum stage. Among them, the vacuum degree of the first vacuum stage can be 1×10 -1 ~1×10 -2 Pa, and the vacuum degree of the second vacuum stage can be 1×10 -2 ~1×10 -3 . The vacuum degrees of the two vacuum stages are different, that is, the absolute value of the difference between the vacuum degree of the first vacuum stage and the vacuum degree of the second vacuum stage is greater than 0. Specifically, the vacuum degree of the first vacuum stage and the vacuum degree of the second vacuum stage can differ by one order of magnitude; or, the ratio of the vacuum degree of the first vacuum stage to the vacuum degree of the second vacuum stage is greater than or equal to 5, so as to achieve a better pressure gradient.

[0070] In some other embodiments, the vacuum pre-activation adopts gradient temperature and gradient pressure-controlled pre-activation, including: at the first vacuum degree, heating at the first heating rate to reach the temperature of the first heat preservation treatment, and performing the first heat preservation treatment; then evacuating to the second vacuum degree, heating at the second heating rate to reach the temperature of the second heat preservation treatment, and performing the second heat preservation treatment.

[0071] Among them, the first vacuum degree can be 1×10 -1 ~1×10 -2 Pa, the second vacuum degree can be 1×10 -2 ~1×10 -3 Pa, and the absolute value of the difference between the first vacuum degree and the second vacuum degree is greater than 0; specifically, the vacuum degree of the first vacuum stage and the vacuum degree of the second vacuum stage can differ by one order of magnitude; or, the ratio of the vacuum degree of the first vacuum stage to the vacuum degree of the second vacuum stage is greater than or equal to 5, so as to achieve a better pressure gradient.

[0072] Among them, the temperature of the first heat preservation treatment is 400-500 °C, the temperature of the second heat preservation treatment is 550-650 °C, and the absolute value of the temperature difference between the first heat preservation treatment and the second heat preservation treatment is greater than or equal to 100 °C. The specific value of the absolute value of the temperature difference can be a value within the range of 100-250 °C, such as 100 °C, 150 °C, 200 °C, 250 °C, etc.

[0073] Among them, the time of the first heat preservation treatment can be 0.5 to 3 h, and the time of the second heat preservation treatment can be 0.5 to 3 h.

[0074] Among them, the first heating rate is less than the second heating rate, the first heating rate is less than or equal to 5 °C / min, and the absolute value of the difference between the first heating rate and the second heating rate is greater than or equal to 3 °C / min. Specifically, the first heating rate can be 1 to 2 °C / min, 2 to 3 °C / min, 3 to 4 °C / min, 4 to 5 °C / min, etc. Of course, it can also be other values within the above range, which are not limited here. The absolute value of the difference between the first heating rate and the second heating rate can be 3 to 4 °C / min, 4 to 5 °C / min, 4 to 5 °C / min, etc. Of course, it can also be other values within the above range, which are not limited here.

[0075] In step S13:

[0076] Mix the pre-activated material with the activator and perform carbonization treatment on the mixture. Among them, the activator can include one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, phosphoric acid, magnesium chloride, zinc chloride, etc.

[0077] The mass ratio of the pre-activated material to the activator can be 1:0.2 to 1:1.5, specifically 1:0.3 to 1:1, 1:0.5 to 1:0.8, 1:0.5 to 1:1.5, 1:0.5 to 1:1.3, 1:0.8 to 1:1.3, etc. Of course, it can also be other values within the above range, which are not limited here. Compared with the usage amount of conventional chemical activators, in this embodiment, after vacuum pre-activation, the activator is added for activation, which can significantly reduce the usage amount of the activator, but still can ensure a good activation effect.

[0078] In one embodiment, the mixing method of the pre-activated material and the activator includes hand grinding with a mortar or high-speed mixing by a machine, etc. In a specific embodiment, the pre-activated material and the activator are mixed at a high speed, and the mixing speed can be 100 to 1000 rpm.

[0079] In one embodiment, before the mixing step, it also includes crushing the pre-activated material by means of air milling, mechanical milling, etc.

[0080] In one embodiment, the particle size distribution of the pre-activated material has a D50 of 6 - 20 μm and a D10 of greater than or equal to 2 μm. Specifically, the D50 can be 6 - 12 μm, 6 - 8 μm, 8 - 10 μm, 10 - 12 μm, etc., and the D10 can be 2 - 3 μm, 3 - 4 μm, 4 - 5 μm, 5 - 6 μm, 6 - 7 μm, etc. Of course, it can also be other values within the above ranges, which are not limited herein. When the particle size and particle size distribution of the pre-activated material are within this range, it can increase the contact area with the activator, improve the mixing uniformity, enhance the activation effect, and avoid over-activation caused by smaller particles and uneven activation caused by easy agglomeration.

[0081] In a specific embodiment, the D50 of the particle size of the pre-activated material is 6 - 12 μm, and the mass ratio of the pre-activated material to the activator can be 1:0.2 - 1:1.5. The pre-activated material within the above particle size range can achieve a good activation effect within the above dosage range of the activator, without over-activation (too high external specific surface area) or local over-etching. The prepared porous carbon has good mechanical strength, which is beneficial to the pore structure and surface structure for silicon deposition.

[0082] In some embodiments, the heat preservation temperature of the carbonization treatment can be 500 - 700 °C, specifically 500 - 600 °C, 600 - 650 °C, 650 - 700 °C, etc. Of course, it can also be other values within the above ranges, which are not limited herein. The openness of the carbon skeleton has been optimized in the vacuum pre-activation stage. Performing low-temperature activation after mixing the activator in this step can inhibit the over-etching of the carbon skeleton by the activator, precisely control the pore size distribution, and increase the specific surface area and the proportion of micropores.

[0083] The carbonization treatment is carried out in an inert atmosphere, and the inert atmosphere includes an atmosphere formed by one or more of nitrogen, helium, argon, neon, and xenon.

[0084] The heat preservation time of the carbonization treatment can be 1 - 12 h, specifically 1 - 3 h, 3 - 5 h, 5 - 8 h, 8 - 10 h, 10 - 12 h, etc. Of course, it can also be other values within the above ranges, which are not limited herein.

[0085] In one embodiment, the carbonization treatment includes a first heat preservation section and a second heat preservation section. Among them, the temperature of the first heat preservation section can be 500 - 600 °C, and the time can be 0.5 - 6 h; the temperature of the second heat preservation section can be 600 - 700 °C, and the time can be 0.5 - 6 h. Further, the absolute value of the difference between the temperature of the first heat preservation section and the temperature of the second heat preservation section is greater than or equal to 50 °C, specifically 50 - 200 °C, such as 50 - 100 °C, 100 - 150 °C, 150 - 200 °C, etc. Of course, it can also be other values within the above ranges, which are not limited herein.

[0086] In the above embodiments, gradient temperature rise carbonization treatment is adopted. The gradient temperature rise can accurately control the dehydrogenation and polycondensation rate of asphalt molecular chains. In the low-temperature pre-carbonization stage (500 - 600 °C), slow temperature rise can promote the ordered arrangement of mesophase and form an open framework structure, reserving channels for the subsequent volatilization; while in the high-temperature shaping stage (600 - 700 °C), rapid temperature rise can fix the pore structure and avoid micropore collapse.

[0087] It can be understood that the carbonization treatment includes a heating stage and a heat preservation stage. In one embodiment, the heating rate in the heating stage can be 1 - 10 °C / min, specifically it can be 1 - 3 °C / min, 3 - 5 °C / min, 5 - 8 °C / min, 8 - 10 °C / min, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0088] In a specific embodiment, the carbonization treatment is specifically to transfer the mixture to a sagger and place it in a heating device to heat to the heat preservation temperature.

[0089] In one embodiment, after step S13, it further includes: cleaning the carbonized material obtained by the carbonization treatment to neutral (i.e., pH is 6 - 7) to completely remove the unreacted activator and its intermediate products, avoiding affecting the subsequent deposition.

[0090] Among them, the cleaning agent used for the cleaning treatment is one or more of water or acid solution. Among them, water can be tap water, deionized water, pure water, ultrapure water, etc. The acid solution can be a mixed acid solution formed by one or more of hydrochloric acid, nitric acid, hydrofluoric acid, and sulfuric acid aqueous solutions, and the mass concentration can be 2% - 60%. Specifically, the cleaning treatment can be one or more of soaking, rinsing, etc. And the cleaning treatment can be one or multiple times, which can be multiple times of water cleaning, multiple times of acid solution cleaning, or multiple times of combined water and acid solution cleaning. Drying can be carried out after the cleaning treatment, and drying can adopt known drying methods in the art, which are not specifically limited herein.

[0091] In some embodiments, after the carbonization treatment in step S13, it can further include a crushing step or processes such as screening and grading that can adjust the particle size distribution to adjust the particle size distribution and obtain porous carbon with a target particle size distribution.

[0092] This application also provides a silicon-carbon material. The silicon-carbon material includes porous carbon and nano-silicon. At least part of the nano-silicon is distributed in the pores of the porous carbon. Among them, the porous carbon and its preparation refer to the description above and will not be elaborated here. The silicon-carbon material can be used as an electrode in an electrochemical device and can be used as an electrode active material.

[0093] The present application also provides a method for preparing porous carbon, including: using the porous carbon as a carbon skeleton and placing it in a chemical vapor deposition furnace for silicon deposition treatment to obtain a corresponding silicon-carbon material; wherein, the porous carbon and its preparation are as described in the above text and will not be elaborated here.

[0094] In a specific embodiment, the method for preparing porous carbon specifically includes: putting the powder of the porous carbon provided by the present application into a feeding bin, and then sending the powder into the chemical vapor deposition furnace through positive pressure conveying. A silane / nitrogen mixed gas is introduced under high temperature conditions of 400-550 °C, so that silane pyrolyzes and deposits in the porous carbon. Subsequently, the temperature is raised to 550-700 °C, and an acetylene / nitrogen mixed gas is introduced, so that acetylene pyrolyzes and deposits on the surface of the silicon / carbon material. The entire deposition process takes about 8-12 h. After the reaction ends, screening and demagnetization are carried out to finally obtain the silicon-carbon negative electrode material.

[0095] The present application also provides an electrochemical device, the electrochemical device includes an electrode, and the electrode includes the silicon-carbon material. Specifically, the electrochemical device may include a battery, a capacitor, etc.

[0096] In a specific embodiment, the electrochemical device is a battery, and the negative electrode of the battery includes the silicon-carbon material.

[0097] The technical solutions and technical effects of the present application will be described in detail below through specific examples, comparative examples and experimental examples. The following examples are only partial examples of the present application and do not specifically limit the present application.

[0098] Example 1

[0099] Step 1. Raw material pretreatment:

[0100] Take petroleum pitch (softening point 200 °C), crush it to a particle size D50 = 5 μm, mix it with deionized water at a mass ratio of 1:3, ultrasonically disperse for 30 minutes, and dry in a hot air oven at 100 °C for 12 h.

[0101] Step 2. Vacuum pre-activation:

[0102] Place the dried asphalt powder in a vacuum tube furnace, evacuate to 10 -1 Pa, heat up at a rate of 2 °C / min to 450 °C, and keep the temperature for 1 h; after the heat preservation ends, evacuate to 10 -3 Pa, heat up at a rate of 5 °C / min to 600 °C, and keep the temperature for 2 hours.

[0103] Step 3: KOH activation:

[0104] Mix the pre-activated asphalt product with KOH at a ratio of 1:0.8, place it in an inert atmosphere furnace, heat it to 500 °C at a rate of 2 °C / min and hold for 1 hour, then continue to heat it to 600 °C at a rate of 2 °C / min and hold for 1 hour. After cooling, wash it with deionized water until neutral, and dry it in a hot oven at 100 °C for 24 hours.

[0105] Mix the pre-activated asphalt with KOH at a mass ratio of 1:0.8, grind for 1 h, and place it in an inert atmosphere furnace; heat it to 600 °C at a rate of 2 °C / min and hold for 2 hours. After cooling, wash it with deionized water until neutral, and dry it in a hot oven at 100 °C for 24 hours.

[0106] Example 2:

[0107] Similar to Example 1, the difference is that in Step 2, the dried asphalt powder is placed in a vacuum tube furnace, evacuated to 10 -2 Pa, heated to 450 °C at a rate of 2 °C / min and held for 1 hour; continue to heat to 600 °C at a rate of 5 °C / min and hold for 2 hours, and naturally cool to room temperature to obtain vacuum pre-activated asphalt.

[0108] Example 3:

[0109] Similar to Example 1, the difference is that in Step 3, the pre-activated asphalt is mixed with KOH at a mass ratio of 1:0.8, ground for 1 h, and placed in an inert atmosphere furnace; heated to 600 °C at a rate of 2 °C / min and held for 2 hours. After cooling, wash it with deionized water until neutral, and dry it in a hot oven at 100 °C for 24 hours.

[0110] Example 4:

[0111] Similar to Example 1, the difference is that in Step 2, the dried asphalt powder is placed in a vacuum tube furnace, evacuated to 10 -1 Pa, heated to 600 °C at a rate of 2 °C / min and held for 1 h. After the holding ends, evacuate to 10 -3 Pa and hold for 2 h.

[0112] Example 5:

[0113] Similar to Example 1, the difference is that in Step 2, the dried asphalt powder is placed in a vacuum tube furnace, evacuated to 10 -1 Pa, heated to 400 °C at a rate of 2 °C / min and held for 1 h; after the holding ends, evacuate to 10 -3 Pa, heated to 600 °C at a rate of 5 °C / min, and the holding time is 2 hours.

[0114] Example 6:

[0115] Similar to Example 1, the difference is that in Step 2, the dried asphalt powder is placed in a vacuum tube furnace, evacuated to 10 -1 Pa, heated at a rate of 2 °C / min to 450 °C, and held for 1 h; after the holding is completed, evacuated to 10 -3 Pa, heated at a rate of 5 °C / min to 550 °C, and held for 2 hours.

[0116] Example 7:

[0117] Similar to Example 3, the difference is that in Step 3, heated to 400 °C at a rate of 2 °C / min and held for 1 hour, then continued to heat to 600 °C at a rate of 2 °C / min and held for 1 hour.

[0118] Example 8:

[0119] Similar to Example 3, the difference is that in Step 3, heated to 500 °C at a rate of 2 °C / min and held for 1 hour, then continued to heat to 700 °C at a rate of 2 °C / min and held for 1 hour.

[0120] Comparative Example 1:

[0121] Mix petroleum asphalt (softening point 200 °C) and KOH in a mass ratio of 1:2, heat to 800 °C at a rate of 3 °C / min in an N2 atmosphere, and hold for 2 hours; after cooling, wash with deionized water until neutral, and dry in a hot oven at 100 °C for 24 hours.

[0122] Comparative Example 2:

[0123] Similar to Example 1, the difference is that the vacuum pre-activation step of Step 2 is not carried out, and the KOH activation step of Step 3 is directly carried out.

[0124] Comparative Example 3:

[0125] Mix asphalt and nano-MgO template in a ratio of 1:2, carbonize at 600 °C in N2 for 3 hours; etch the template with 5% HF solution, wash and dry to obtain.

[0126] [Testing]

[0127] Figures 2-4 SEM images of the porous carbon of Examples 1-3, Figures 5-7 are SEM images of the porous carbon of Comparative Examples 1-3 respectively. It can be seen from Figures 2-4 that the porous carbon prepared in Examples 1 to 3 has a good morphology, and almost no obvious pores can be observed on the surface; while Figures 5-7 a large number of obvious irregular pores and cracks exist on the surface of the porous carbon prepared in Comparative Examples 1-3, and the morphology is not good.

[0128] During the preparation processes of various embodiments and comparative examples, as well as the relevant tests on the porous carbons prepared from various embodiments and comparative examples, the test methods are as follows, and the test results are shown in Table 1.

[0129] The nitrogen adsorption test is used to obtain the nitrogen adsorption isotherm. From the nitrogen adsorption isotherm and the BET method, the specific surface area is obtained, and the pore volume ratio of micropores with a pore diameter less than or equal to 2 nm calculated by the DFT method is obtained.

[0130] Table 1:

[0131]

[0132] As can be seen from Table 1:

[0133] Compared with Comparative Examples 1-3, the porous carbons of Embodiments 1-8 have a relatively high specific surface area and a high micropore ratio. Specifically, the specific surface areas of Embodiments 1-8 can exceed 2400 m 2 / g, reaching 2500 m 2 / g and above, and the pore volume ratio of micropores with a pore diameter less than or equal to 2 nm can reach a high ratio of 99.70%. Moreover, the preparation method of the porous carbon provided in this application can significantly reduce the usage amount of the activator compared with the conventional chemical activation method in Comparative Example 1, but still can achieve a good activation effect.

[0134] For the silicon deposition process, the porous carbon with a high specific surface area and a high micropore ratio can help silicon better penetrate into the internal pores of the porous carbon, reduce surface deposition, and thus reduce the structural damage caused by the volume expansion of silicon in subsequent applications (such as battery cycling), and improve the cycle stability of the silicon-carbon material.

[0135] The above has introduced in detail a porous carbon, its preparation method, and a battery provided by the embodiments of the present application. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A porous carbon, characterized in that The specific surface area of ​​the porous carbon is greater than or equal to 2400 m 2 / g, the pore volume of micropores with a pore diameter of less than or equal to 2nm accounts for ≥70%.

2. The porous carbon according to claim 1, characterized in that The pore volume of micropores with a pore diameter of 0.5 to 2 nm in the porous carbon accounts for more than 98%; and / or, The electrical conductivity of the porous carbon is 80-100 S / cm; and / or, The carbon source of the porous carbon includes pitch.

3. A method for preparing porous carbon, characterized in that: include: providing a pitch-based carbon source; performing vacuum preactivation on the asphalt-based carbon source under a vacuum atmosphere to obtain a preactivated material; The preactivated material is mixed with an activator, and the mixture is carbonized, wherein the temperature of the carbonization treatment is less than or equal to 700°C.

4. The preparation method according to claim 3, characterized in that: The vacuum degree of the vacuum atmosphere is 1*10 -1 ~1*10 -3 Pa; and / or, The activation temperature of the vacuum pre-activation is 400-650° C.; and / or, The activation time of the vacuum pre-activation is 1 to 6 hours.

5. The preparation method according to claim 3, characterized in that: The vacuum pre-activation adopts pre-activation at a gradient temperature, including a first heat preservation treatment and a second heat preservation treatment; wherein: The temperature of the first heat preservation treatment is 400-500° C., and the temperature of the second heat preservation treatment is 550-650° C.; and / or, The first heat preservation treatment lasts for 0.5 to 3 hours; and / or, The second heat preservation treatment time is 0.5 to 3 hours; and / or, An absolute value of a temperature difference between the first heat preservation treatment and the second heat preservation treatment is greater than or equal to 100° C.

6. The preparation method according to claim 3 or 4, characterized in that: The vacuum pre-activation adopts gradient pressure control pre-activation, including a first vacuum section and a second vacuum section, wherein the vacuum degree of the first vacuum section is 1*10 -1 ~1*10 -2 Pa, the vacuum degree of the second vacuum section is 1*10 -2 ~1*10 -3 Pa, the absolute value of the difference between the vacuum degree of the first vacuum section and the vacuum degree of the second vacuum section is greater than 0.

7. The preparation method according to claim 3, characterized in that: The vacuum pre-activation adopts gradient temperature and gradient pressure control pre-activation, including: Under a first vacuum degree, heating at a first heating rate to reach a temperature for a first heat preservation treatment, and performing a first heat preservation treatment; then evacuating to a second vacuum degree, heating at a second heating rate to reach a temperature for a second heat preservation treatment, and performing a second heat preservation treatment; Wherein, the first vacuum degree is 1*10 -1 ~1*10 -2 Pa, the second vacuum degree is 1*10 -2 ~1*10 -3 Pa, the absolute value of the difference between the first vacuum degree and the second vacuum degree is greater than 0; and / or, The temperature of the first heat preservation treatment is 400-500° C., the temperature of the second heat preservation treatment is 550-650° C., and the absolute value of the temperature difference between the first heat preservation treatment and the second heat preservation treatment is greater than or equal to 100° C.; and / or, The first heat preservation treatment lasts for 0.5 to 3 hours; and / or, The second heat preservation treatment time is 0.5 to 3 hours; and / or, The first heating rate is less than the second heating rate, the first heating rate is less than or equal to 5°C / min, and the absolute value of the difference between the first heating rate and the second heating rate is greater than or equal to 3°C / min.

8. The preparation method according to claim 3, characterized in that: The heat preservation temperature of the carbonization treatment is 500-700° C.; and / or, The carbonization treatment is carried out under an inert atmosphere, wherein the inert atmosphere includes an atmosphere formed by one or more of nitrogen, helium, argon, neon and xenon; and / or, The heat preservation time of the carbonization treatment is 1 to 12 hours.

9. The preparation method according to claim 8, characterized in that: The carbonization treatment includes a first heat preservation section and a second heat preservation section, wherein the temperature of the first heat preservation section is 500-600°C, the temperature of the second heat preservation section is 600-700°C, and the absolute value of the difference between the temperature of the first heat preservation section and the temperature of the second heat preservation section is greater than or equal to 50°C; and / or, The asphalt-based carbon source includes asphalt, and the asphalt includes one or more of natural asphalt, coal tar asphalt or petroleum asphalt; and / or, The softening point of the pitch-based carbon source is 100-150° C.; and / or, The particle size D50 of the pitch-based carbon source is 5 to 10 μm; and / or, The activator comprises one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, phosphoric acid, magnesium chloride and zinc chloride; and / or, The mass ratio of the pre-activated material to the activator is 1:0.2 to 1:1.5; and / or, The particle size D50 of the preactivated material is 6 to 12 μm.

10. A battery, characterized in that: The battery includes a negative electrode material, which includes porous carbon and silicon particles, and at least part of the silicon particles are distributed in the pores of the porous carbon; wherein the porous carbon is the porous carbon described in any one of claims 1 to 2, or is the porous carbon prepared by the preparation method described in any one of claims 3 to 9.

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