Porous carbon, preparation method thereof, negative electrode active material and application of negative electrode active material

Abstract

The invention provides porous carbon and a preparation method thereof, and a negative electrode active material and application thereof. The porous carbon has a brand new structural design, abundant pores and reasonable pore size distribution, and can be used for providing a negative electrode active material with relatively high capacity and relatively good long-cycle structure stability.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to porous carbon and its preparation method, anode active material and its application. Background Art

[0002] In order to meet the market demand for secondary batteries with high energy density, the industry has tried to use high-performance anode active materials such as silicon materials to replace the commonly used graphite materials. However, the volume change rate of silicon materials during the charge and discharge cycles of the battery can reach 300%, which will cause adverse consequences such as pulverization of silicon materials after multiple cycles, resulting in a decrease in battery capacity. To solve the above technical problems, the industry has chosen to nanometerize and amorphousize silicon materials. Among them, silicon materials pyrolyzed from silane gas are deposited in the pores of porous materials, which can achieve the nanometerization and amorphousization of silicon materials, and use the confinement effect of porous materials to inhibit the volume change of silicon materials during the cycle.

[0003] However, for the silicon-carbon anode active material prepared by the above method, silicon is easily deposited on the surface of the porous material, resulting in an increase in side reactions on the material surface, a decrease in the initial efficiency, a large lithium intercalation expansion, a low conductivity, and serious gas generation during the anode slurry preparation process; moreover, the distribution of silicon materials in the prepared silicon-carbon anode active material is uneven. During the charge and discharge cycles, the side reactions of the silicon-carbon anode active material increase, and the internal stress distribution is uneven, damaging the structural stability of the material; the silicon-carbon anode active material after silicon deposition is not resistant to pressure during the pole piece rolling process, the material compaction is low, and the stress distribution of the porous material is uneven after the particles are stressed, resulting in local stress concentration, particle breakage or microcracks. During the charge and discharge cycles, the material at the broken or microcracked places has high activity, resulting in an increase in the side reactions of the silicon-carbon anode active material. Summary of the Invention

[0004] In view of this, the embodiments of this application provide porous carbon and its preparation method, anode active material and its application. The porous carbon has a brand-new structural design, rich pores and a reasonable pore size distribution. The porous carbon can be used to provide an anode active material with a relatively high initial efficiency, a relatively high capacity, a relatively low expansion, a relatively high conductivity, a low gas generation rate during anode slurry preparation, a relatively high material compaction, and good long-cycle structural stability.

[0005] The first aspect of this application provides a kind of porous carbon, and the total pore volume of the porous carbon is 0.6 cm 3 / g - 1.2 cm 3 / g;

[0006] Based on the total pore volume of the porous carbon, the volume proportion of pores with a pore diameter < 2 nm is 70% - 95%, the volume proportion of pores with 2 nm ≤ pore diameter ≤ 10 nm is 2% - 12%, the volume proportion of pores with 10 nm < pore diameter ≤ 30 nm is 2% - 10%, the volume proportion of pores with 30 nm < pore diameter ≤ 50 nm is 1% - 8%, and the volume proportion of pores with a pore diameter > 50 nm is 0 - 4%.

[0007] The total pore volume of the above-mentioned porous carbon is relatively large, providing sufficient space for active nanoparticles. Moreover, the pore size distribution of the porous material is reasonable, with a large volume proportion of pores with a pore diameter less than 2 nm and a low content of pores with a pore diameter greater than 30 nm. As a result, the pore distribution inside the porous carbon is relatively uniform and shows a gradient distribution, which is conducive to the uniform deposition of active nanoparticles in the pore structure of the porous carbon, reducing the risk of active nanoparticles depositing on the surface of the porous carbon particles, reducing the degree of side reactions on the material surface and improving the initial efficiency of the material, increasing the powder conductivity of the material, reducing gas generation during the pulping process of the material, and also being conducive to improving the tap density of the material; and, the porous carbon with the above structure has a good threshold effect on active nanoparticles, can effectively inhibit their volume expansion during the cycle, and reduce the uneven distribution of internal stress in the material caused by the uneven distribution of active nanoparticles. Therefore, the above-mentioned porous material can be used to provide a negative electrode active material with a relatively high capacity and good long-cycle structural stability.

[0008] The second aspect of the embodiments of the present application provides a preparation method of porous carbon, including:

[0009] Activating the carbon matrix to obtain the porous carbon provided in the first aspect of the embodiments of the present application.

[0010] The above preparation method has simple steps, strong process controllability, high production efficiency, and can achieve large-scale industrial production.

[0011] The third aspect of the embodiments of the present application provides a negative electrode active material, including carbon-containing composite particles, where the carbon-containing composite particles include the porous carbon provided in the first aspect of the present application and nanoparticles located in the porous carbon, and the material of the nanoparticles includes at least one of silicon, germanium, and tin.

[0012] Since the porous carbon provided in the first aspect of the present application is used as the substrate, the nanoparticles are evenly distributed in the carbon-containing composite particles, and the particle size distribution of the nanoparticles is reasonable, without the situation of enrichment on the surface of the carbon-containing composite particles. Therefore, the problem of uneven stress distribution inside the carbon-containing composite particles caused by the difference in the swelling volume of the nanoparticles during the charge and discharge cycles can be effectively reduced, thereby improving the structural stability of the negative electrode active material during the charge and discharge cycles. Moreover, on the basis of ensuring the particle integrity of the carbon-containing composite particles, a high tap density can be achieved. At the same time, due to the high capacity of the nanoparticles and the certain confinement effect of the porous carbon on the nanoparticles, the above-mentioned negative electrode active material can be used as a negative electrode active material with a higher capacity, a lower expansion rate, and better long-cycle structural stability. In addition, there are no nanoparticles enriched on the surface of the above-mentioned negative electrode active material particles, the gas generation during the pulping process of the material is less, the side reactions on the particle surface are less, the initial efficiency of the material is high, and the conductivity of the material is high.

[0013] The fourth aspect of the embodiments of the present application provides a method for preparing a negative electrode active material, including: depositing nanoparticles in the porous carbon provided in the first aspect of the embodiments of the present application to form carbon-containing composite particles, thereby obtaining the negative electrode active material; the material of the nanoparticles includes at least one of silicon, germanium, and tin.

[0014] The above preparation method has strong process reliability and high production efficiency, and is suitable for large-scale industrial production.

[0015] The fifth aspect of the present application provides a negative electrode, including the negative electrode active material provided in the third aspect of the present application, or including the negative electrode active material prepared by the preparation method provided in the fourth aspect of the embodiments of the present application. Since the negative electrode active material provided by the present application is used as the active material, the negative electrode can be used to provide a battery with both a higher capacity, better cycling performance, and a lower expansion rate.

[0016] The sixth aspect of the present application provides an electrochemical energy storage device, including the negative electrode provided in the fifth aspect of the present application. Due to the negative electrode provided in the embodiments of the present application, the electrochemical energy storage device can achieve a higher capacity, better cycling performance, and a lower expansion rate.

[0017] The seventh aspect of the present application provides an electrical device, including the electrochemical device provided in the sixth aspect of the present application. Due to the electrochemical device provided in the embodiments of the present application, the electrical device has good market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the adsorption-desorption isotherm curve of the porous carbon of Example 1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The embodiments of the present application provide a porous carbon, and the total pore volume of the above-mentioned porous carbon is 0.6 cm3 / g - 1.2 cm 3 / g;

[0020] Based on the total pore volume of the porous carbon, the volume ratio of pores with a pore diameter < 2 nm is 70% - 95%, the volume ratio of pores with 2 nm ≤ pore diameter ≤ 10 nm is 2% - 12%, the volume ratio of pores with 0 nm < pore diameter ≤ 50 nm is 1% - 18%, and the volume ratio of pores with a pore diameter > 50 nm is 0 - 23%.

[0021] The inventors found through research that the properties of the silicon-carbon negative electrode active material largely depend on the porous material itself. In related technologies, the pore structure design of the porous material is poor, resulting in poor electrochemical performance of the silicon-carbon negative electrode active material. In this application, the total pore volume of the porous carbon is large, providing sufficient space to accommodate active material nanoparticles (such as silicon-containing particles). Moreover, the pore size distribution of the porous material is reasonable, with a large volume ratio of pores with a pore diameter less than 2 nm and a low content of pores with a pore diameter greater than 50 nm. As a result, the pore distribution inside the porous carbon is relatively uniform, facilitating the uniform deposition of active material nanoparticles, reducing the risk of active material nanoparticles depositing on the surface of the porous carbon particles, and reducing the pore size in the particles after the deposition of active material nanoparticles. This can reduce the gas generation during the pulping process of the finally obtained negative electrode active material and also improve the compaction density of the finally obtained negative electrode active material without damaging the particle integrity. At the same time, the above-mentioned porous carbon has a good threshold effect on active material nanoparticles, can effectively inhibit their volume expansion during the cycling process, and reduce the uneven internal stress distribution caused by the uneven distribution of active material nanoparticles, thereby reducing the fragmentation of the negative electrode active material due to uneven internal stress distribution during the charge-discharge cycling process. Therefore, the above-mentioned porous material can be used to provide a negative electrode active material with a relatively high capacity and good long-cycle structural stability.

[0022] In the embodiments of this application, the pore size distribution and total pore volume of the porous carbon are measured by the gas adsorption-desorption method. Specifically, the porous carbon is placed in a gas adsorption-desorption tester, and during the test, the degassing time ≥ 120 min and the degassing temperature ≥ 200 °C are maintained to obtain the adsorption-desorption curve of the porous carbon, and then data processing is carried out to obtain parameters such as the pore size distribution and total pore volume of the porous carbon.

[0023] Exemplarily, the volume fraction of pores with a pore diameter < 2 nm can be, but is not limited to, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, etc. If the volume fraction of pores with a pore diameter < 2 nm is too small, it will lead to an increase in the proportion of mesopores (pores with a pore diameter of 2 nm - 50 nm) and / or macropores (pores with a pore diameter > 50 nm), resulting in a wider pore size distribution in the porous carbon. At this time, when depositing active material nanoparticles (e.g., silicon-containing materials) again, it will lead to a wider particle size distribution of the active material nanoparticles in the obtained carbon-containing composite particles, and relatively serious uneven stress distribution will still occur during the charge and discharge cycling process, and the structural stability of the negative electrode active material still cannot be improved well, and finally the cycling performance of the battery is still poor. On the other hand, especially when depositing silane, the increase in the proportion of mesopores and macropores will lead to the main adsorption of silicon in multiple layers during the silane deposition process, and silicon-rich phenomena are likely to appear on the material surface. The silicon-rich problem will lead to low initial efficiency, serious gas generation, and reduced conductivity of the material; similarly, when the proportion of mesopores and macropores increases, during the rolling process of the material into a negative electrode sheet, under the condition of uniformly receiving external stress, the pore walls with larger sizes will be subject to stress concentration phenomena, resulting in larger strains in the pores with larger sizes and cracks, making the material easy to be crushed.

[0024] Exemplarily, the volume fraction of pores with a pore diameter of 2 nm ≤ pore diameter ≤ 10 nm can be, but is not limited to, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, etc. If the proportion of pores with the above pore diameters is too large, it will occupy the volume fraction of micropores (pores with a pore diameter less than 2 nm), resulting in a lower pore size concentration of the porous carbon; also, in the embodiments of the present application, the total pore volume of the porous carbon is certain. When the proportion of pores with larger pore diameters increases, it may lead to a decrease in the number of pores in the porous carbon, which is not conducive to the uniform deposition and distribution of subsequent active material nanoparticles in the porous carbon, resulting in a decrease in the structural uniformity of the final negative electrode active material.

[0025] Exemplarily, the volume fraction of pores with 10 nm < pore diameter ≤ 50 nm can be, but is not limited to, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, etc. If the volume fraction of pores with the above pore diameters is too large, it will not only cause the pore size distribution of the porous carbon to become wider, reduce the particle size and distribution uniformity of the active material nanoparticles in the final negative electrode active material, but also affect the structural stability of the negative electrode active material. In some embodiments of the present application, the volume fraction of pores with 10 nm < pore diameter ≤ 30 nm is 2% - 10%, and the volume fraction of pores with 30 nm < pore diameter ≤ 50 nm is 1% - 8%. In this way, it is more conducive to controlling the narrower pore size distribution of the porous carbon and improving the uniformity of the pore size distribution inside the porous carbon, so as to provide a negative electrode active material with better electrochemical performance. Exemplarily, the volume fraction of pores with 10 nm < pore diameter ≤ 30 nm can be, but is not limited to, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and the volume fraction of pores with 30 nm < pore diameter ≤ 50 nm can be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc.

[0026] Exemplarily, the volume fraction of pores with pore diameter > 50 nm can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, 21%, 22%, 23%, etc. The filling rate of macropores (pores with pore diameter > 50 nm) during the deposition of silicon-containing materials is low. After depositing active material nanoparticles, there will still be relatively large pores in the obtained negative electrode active material. These pores will become stress concentration points during the compaction process of the negative electrode active material, resulting in the cracking of the negative electrode active material. To avoid the above situation, the related art will choose to reduce the compaction density of the negative electrode active material, which is not conducive to its application. In some embodiments of the present application, based on the total pore volume of the porous carbon, the volume fraction of pores with pore diameter greater than 50 nm ≤ 4%. In some specific embodiments, the volume fraction of pores with pore diameter > 50 nm is 0, that is, the porous carbon does not contain macropores. In this way, the concentration of the pore size distribution of the porous carbon can be further improved, and the risk of relatively large pores in the finally obtained negative electrode active material can be further reduced. Thus, the compaction density of the negative electrode active material can be improved while ensuring the integrity of the particles of the negative electrode active material.

[0027] In some specific embodiments, the total pore volume of the porous carbon is 0.6 cm 3 / g - 1.2 cm 3 / g; Based on the total pore volume of the porous carbon, the volume fraction of pores with a pore diameter < 2 nm is 70% - 95%, the volume fraction of pores with 2 nm ≤ pore diameter ≤ 10 nm is 2% - 12%, the volume fraction of pores with 10 nm < pore diameter ≤ 30 nm is 2% - 10%, the volume fraction of pores with 30 nm < pore diameter ≤ 50 nm is 1% - 8%, and the volume fraction of pores with a pore diameter > 50 nm is 0 - 4%. Thus, the pore distribution of the porous carbon is more optimal, which is beneficial to improving the performance of the final anode active material.

[0028] Exemplarily, the pore volume of the porous carbon can be but is not limited to 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 1.0 cm 3 / g, 1.2 cm 3 / g. If the pore volume of the porous carbon is too small, it cannot accommodate a sufficient amount of active material nanoparticles, which will result in too low a capacity of the final anode active material to meet the market demand for battery energy density, and may also cause the active material nanoparticles to be easily deposited on the surface of the porous carbon material; if the pore volume of the porous carbon is too large, it will weaken the confinement effect of the porous carbon on the active material nanoparticles and may also affect the thermodynamic stability of the anode active material. In some embodiments of the present application, the average pore diameter of the porous carbon is 0.8 - 2.6 nm. Exemplarily, the average pore diameter of the porous carbon can be but is not limited to 0.8 nm, 1.2 nm, 1.6 nm, 2.0 nm, 2.2 nm, 2.4 nm, 2.6 nm. Taking the above porous carbon used for depositing silane as an example for illustration: Controlling the average pore diameter of the porous carbon within the above range can make the proportion of micropores more appropriate, thus facilitating the diffusion of silane in the porous carbon; in addition, the proportion of mesopores and macropores in the porous carbon can be controlled within a suitable range to improve the deposition efficiency of silane in the porous carbon, thereby further reducing the risk of silicon-rich phenomenon caused by silicon deposition on the surface of the porous carbon particles.

[0029] In some embodiments of the present application, the above porous carbon is amorphous carbon. In some embodiments of the present application, the porous carbon may contain some heteroatoms, such as nitrogen atoms, oxygen atoms, etc., and the carbon content of the porous carbon is 50 wt.% - 60 wt.%.

[0030] In some embodiments of the present application, the specific surface area of the porous carbon is 1400 m 2 / g - 2400 m 2 / g. A suitable specific surface area is conducive to the subsequent deposition of active material nanoparticles, and the resulting negative electrode active material can also have a relatively suitable specific surface area accordingly, which is conducive to the deintercalation / insertion of active ions and can also fully reduce the risk of side reactions between the negative electrode active material and other substances during subsequent applications; for example, during the preparation of the negative electrode slurry, the side reaction between the negative electrode active material and the solvent; in the battery, the side reaction between the negative electrode active material and the electrolyte. Exemplarily, the specific surface area of the porous carbon can be but is not limited to 1400 m 2 / g, 1500 m 2 / g, 1600 m 2 / g, 1700 m 2 / g, 1800 m 2 / g, 1900 m 2 / g, 2000 m 2 / g, 2100 m 2 / g, 2200 m 2 / g, 2300 m 2 / g, 2400 m 2 / g, etc.

[0031] In some embodiments of the present application, the Dv50 of the porous carbon is 3 μm - 12 μm. Controlling the Dv50 of the porous carbon within the above range is conducive to controlling the particle size of the final negative electrode active material within a suitable range, enabling a relatively suitable deintercalation / insertion path of active ions in the negative electrode active material particles, and also facilitating the achievement of a relatively high tap density, thereby facilitating the obtaining of a battery with a high energy density. Exemplarily, the Dv50 of the porous carbon can be but is not limited to 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, etc. In the examples of the present application, a laser particle size analyzer can be used to measure the Dv50 of the porous carbon.

[0032] The examples of the present application also provide a preparation method of porous carbon, which can be used to prepare the aforementioned porous carbon, including:

[0033] Activating the carbon matrix to obtain the porous carbon provided in the examples of the present application; the total pore volume of the porous carbon is 0.6 cm 3 / g - 1.2 cm 3 / g; based on the total pore volume of the porous carbon, the volume fraction of pores with a pore diameter < 2 nm is 70% - 95%, the volume fraction of pores with 2 nm ≤ pore diameter ≤ 10 nm is 2% - 12%, the volume fraction of pores with 10 nm < pore diameter ≤ 50 nm is 1% - 18%, and the volume fraction of pores with a pore diameter > 50 nm is 0 - 23%.

[0034] The above preparation method has simple steps, strong process controllability, high production efficiency, and can achieve large-scale industrial production.

[0035] In some embodiments of the present application, the above activation treatment includes alkali activation treatment, steam activation treatment, and carbon dioxide activation treatment performed in sequence. The alkali activation treatment can effectively increase the specific surface area of the carbon matrix and is also conducive to removing impurities (such as oxides, etc.) in the carbon matrix. The steam activation treatment is conducive to obtaining mesopores in the carbon matrix, and the finally performed carbon dioxide activation treatment can prepare a microporous structure with developed and rich pores.

[0036] In some embodiments of the present application, the above alkali activation treatment includes mixing the carbon matrix with an alkali and reacting at 650°C - 850°C for 2h - 4h to obtain a first material. In this way, a suitable pore structure can be obtained, providing a basis for subsequent mesopore formation and micropore formation, and facilitating the final obtaining of porous carbon with a rich pore structure. Exemplarily, the reaction temperature during the alkali activation treatment can be but is not limited to 650°C, 675°C, 700°C, 725°C, 750°C, 775°C, 800°C, 825°C, 850°C, etc. Exemplarily, the reaction duration of the alkali activation treatment can be but is not limited to 2h, 2.5h, 3h, 3.5h, 4h, etc. In some specific embodiments, it further includes washing the material obtained after the alkali activation treatment to remove impurities generated during the alkali activation process. Specifically, it can be washed with water, and multiple washes (for example, 3 times) can be performed. Further, the above washing includes acid, hot water, and distilled water washing performed in sequence to remove the salts generated by the reaction.

[0037] In some specific embodiments of the present application, the above alkali includes but is not limited to potassium hydroxide, sodium hydroxide, and acids or salts, not limited to phosphoric acid, potassium chloride, aluminum chloride, zinc chloride, etc. It can be mixing a potassium hydroxide solution with the carbon matrix, or directly mixing potassium hydroxide solid with the carbon matrix for reaction. When using a potassium hydroxide solution, its concentration or pH value is not limited.

[0038] In some embodiments of the present application, the above steam activation treatment includes reacting the first material obtained after the above alkali activation in a steam environment at 500°C - 800°C for 2h - 4h to obtain a second material. A suitable activation temperature can enable the steam to uniformly diffuse within the first material particles, so that the entire first material particles can be uniformly activated, and then a mesoporous structure with uniform pore distribution and reasonable pore size distribution can be obtained. Exemplarily, the temperature of the above steam activation treatment can be, but is not limited to, 500°C, 525°C, 550°C, 575°C, 600°C, 625°C, 650°C, 675°C, 700°C, 725°C, 750°C, 775°C, 800°C, etc. Exemplarily, the duration of the above steam activation treatment can be, but is not limited to, 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0039] In some embodiments of the present application, the above carbon dioxide treatment includes placing the second material obtained after the above steam activation treatment in a carbon dioxide environment and reacting at 800°C - 1200°C for 2h - 4h. In this way, the specific surface area of the finally obtained porous carbon can be optimized, and at the same time, it is easy to obtain a microporous structure with reasonable pore size distribution, and a porous carbon material with a richer pore structure can be obtained. Exemplarily, the temperature of the above carbon dioxide treatment can be, but is not limited to, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, etc.

[0040] In other embodiments of the present application, the above activation treatment includes alkali activation treatment and mixed gas activation treatment, and the mixed gas includes steam and carbon dioxide.

[0041] In the embodiments of the present application, the above carbon matrix can be directly purchased or obtained by carbonizing a precursor material. In some specific embodiments, it further includes carbonizing the precursor material to obtain a carbon matrix, including:

[0042] In a protective atmosphere or a vacuum environment, the precursor material is carbonized at 500°C - 1500°C, and the carbonization duration is 2h - 8h. Exemplarily, the carbonization temperature can be, but is not limited to, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, etc. Exemplarily, the carbonization duration can be, but is not limited to, 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc.

[0043] The present application does not limit the type of precursor materials, which can be selected from any well-known precursor materials in the art. Exemplarily, the above-mentioned precursor materials include but are not limited to biomass precursors, polymer material precursors, or coke hard carbon, etc. Among them, the biomass precursors include but are not limited to coconut shells, moso bamboo, or starch, etc.; the polymer material precursors include resins, for example, phenolic resins, epoxy resins, etc.; the coke includes but is not limited to anthracite, coking coal, etc.

[0044] An embodiment of the present application provides a negative electrode active material, which includes carbon-containing composite particles. The carbon-containing composite particles include the aforementioned porous carbon provided by the embodiment of the present application and nanoparticles located in the porous carbon. The material of the nanoparticles contains at least one of silicon, germanium, and tin; the pore volume of the aforementioned porous carbon is 0.6 cm 3 / g - 1.2 cm 3 / g. Based on the total pore volume of the porous carbon, the volume ratio of pores with a pore diameter < 2 nm is 70% - 95%, the volume ratio of pores with 2 nm ≤ pore diameter ≤ 10 nm is 2% - 12%, the volume ratio of pores with 10 nm < pore diameter ≤ 50 nm is 1% - 18%, and the volume ratio of pores with a pore diameter > 50 nm is 0 - 23%.

[0045] Since the porous carbon provided by the embodiment of the present application is used as the substrate, the nanoparticles are uniformly distributed in the silicon-carbon particles, and the particle size distribution of the nanoparticles is reasonable. Therefore, the problem of uneven internal stress distribution of the carbon-containing composite particles caused by the difference in the expansion volume of the nanoparticles during the charge and discharge cycles can be effectively reduced, thereby improving the structural stability of the negative electrode active material during the charge and discharge cycles; the porous carbon has rich pores and a reasonable pore size distribution, and the material of the deposited nanoparticles is not easily enriched on the surface of the porous carbon particles. Moreover, on the basis of ensuring the particle integrity of the carbon-containing composite particles, a high tap density can be achieved; at the same time, based on the high capacity of the nanoparticles and the certain threshold effect of the porous carbon on the nanoparticles, the above-mentioned negative electrode active material can be used as a negative electrode active material with a higher capacity, a lower expansion rate, and better long-cycle structural stability.

[0046] In the embodiment of the present application, the negative electrode active material can be pretreated to remove the nanoparticles in the carbon-containing composite particles, and then the obtained porous carbon is subjected to gas adsorption and desorption tests. Among them, the pretreatment method is: dispersing the negative electrode active silicon-carbon material in a saturated NaOH solution, performing magnetic stirring at room temperature, with a stirring speed of 180 rpm and a stirring time of 6 h; then subjecting the magnetically stirred solution to microwave digestion, with a microwave power of 1000 W, a digestion temperature of 60 °C, and a digestion time of 6 h to completely react the silicon material, collecting the reacted material, and washing it three times with ultrapure water.

[0047] In some embodiments of the present application, the carbon-containing composite particles are silicon-carbon particles, and the material of the nanoparticles contains silicon. At this time, the material of the nanoparticles may be elemental silicon, or may be materials such as silicon oxides and silicon nitrides.

[0048] In the embodiments of the present application, the material of the nanoparticles may be crystalline or amorphous, and the present application does not limit this.

[0049] In some embodiments of the present application, in the silicon-carbon particles, the mass of silicon element in the silicon-carbon particles is: 40 w.t.% - 50 w.t.%. However, controlling the ratio of the two within the above range can enable the negative electrode active material to have a higher capacity, and exhibit a lower expansion rate and structural stability during the charge and discharge cycle. In the embodiments of the present application, the nitrogen content and oxygen content can be measured by a nitrogen-oxygen analyzer, the carbon content can be measured by a carbon-sulfur analyzer, and the silicon content = 1 - nitrogen content - oxygen content - carbon content method can be used to measure the silicon element content in the negative electrode active material.

[0050] In some embodiments of the present application, the mass ratio of carbon element in the negative electrode active material is 50% - 60%. Exemplarily, the mass ratio of carbon element in the negative electrode active material can be but is not limited to 50%, 52%, 54%, 56%, 58%, 60%, etc. In the embodiments of the present application, the carbon element content in the negative electrode active material can be measured by oxidizing the negative electrode active material with oxygen at high temperature in a combustion furnace, and the carbon is oxidized to produce carbon dioxide, and the carbon content is measured by a carbon-sulfur analyzer.

[0051] In some embodiments of the present application, the material of the nanoparticles in the silicon-carbon particles contains elemental silicon, and the thickness region extending 5 nm - 20 nm from the surface layer of the silicon-carbon particles to the center is a passivation region, and the passivation region includes silicon dioxide. In some specific embodiments, in the silicon-carbon particles, the nano-silicon-containing material in other regions except the passivation region is elemental silicon.

[0052] In some embodiments of the present application, the negative electrode active material further includes a coating layer provided on the surface of the carbon-containing composite particles, and the material of the coating layer includes conductive carbon and / or fast ion conductor material. The coating layer can effectively isolate the side reaction between the carbon-containing composite particles and the electrolyte or the solvent during the pulping process, thereby facilitating the capacity of the negative electrode active material; in addition, the coating layer has a certain inhibitory effect on the expansion of the carbon-containing composite particles, thereby further reducing the volume change rate during the charge and discharge cycle. In addition, the conductive carbon can improve the electronic conductivity of the negative electrode active material, and the fast ion conductor can improve the ionic conductivity of the negative electrode active material, both of which are beneficial to improving the rate performance of the negative electrode active material. In the embodiments of the present application, the coating layer can be a conductive carbon layer, a fast ion conductor material layer, or a composite layer of conductive carbon and fast ion conductor.

[0053] In some specific embodiments, the thickness of the coating layer is 10 nm - 50 nm. Controlling the thickness of the coating layer within the above range can control the length of the deintercalation / insertion path of the active ions within a suitable range, and can also sufficiently improve the electronic and / or ionic conductivity of the anode active material. Exemplarily, the thickness of the coating layer can be, but is not limited to, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, etc.

[0054] The embodiment of the present application also provides a preparation method of an anode active material, including:

[0055] S01. Depositing nanoparticles in the aforementioned porous carbon provided by the embodiment of the present application to obtain the anode active material provided by the embodiment of the present application; wherein, based on the total pore volume of the porous carbon, the volume ratio of pores with a pore diameter < 2 nm is 70% - 95%, the volume ratio of pores with 2 nm ≤ pore diameter ≤ 10 nm is 2% - 12%, the volume ratio of pores with 10 nm < pore diameter ≤ 50 nm is 1% - 18%, and the volume ratio of pores with a pore diameter > 50 nm is 0 - 23%.

[0056] The above preparation method has strong process controllability and high production efficiency, and is suitable for large-scale industrial production.

[0057] In some embodiments of the present application, the carbon-containing composite particles are silicon-carbon particles, the material of the nanoparticles contains silicon, and depositing the nanoparticles in the porous carbon includes:

[0058] Placing the porous carbon in a reaction chamber, introducing a silicon source, and depositing for 2 h - 6 h at 400°C - 600°C to obtain the anode active material. In the embodiment of the present application, the above reaction chamber can be, but is not limited to, a fluidized bed. Exemplarily, the deposition temperature can be, but is not limited to, 400°C, 450°C, 500°C, 550°C, 600°C, etc. Exemplarily, the deposition time can be, but is not limited to, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, etc. In some embodiments of the present application, the above silicon source is silane, and at this time, the deposited nano-silicon-containing material is silicon.

[0059] In some embodiments of the present application, the above silicon source includes silane, and the deposited nanoparticles contain silicon.

[0060] When the nanoparticles include elemental silicon, in order to avoid the sudden oxidation and exothermic combustion of elemental silicon caused by the newly prepared nanoparticles coming into contact with air, in some specific embodiments, it further includes step S02: performing oxidation passivation treatment on the deposited material; wherein, the passivation treatment includes exposing the deposited material to a dilute oxygen (an oxygen / nitrogen mixture with a volume content of 2%-4%) at a temperature of 200-500°C and keeping it warm for 2-4 hours to oxidize the elemental silicon nanoparticles on the surface layer of the silicon-carbon particles. Thus, for the silicon-carbon particles prepared in some embodiments of the present application, the thickness region extending 5nm-20nm from the surface layer of the silicon-carbon particles towards the center is the passivation region, and the nano-silicon-containing material in the passivation region includes silicon dioxide. In some specific embodiments, in the silicon-carbon particles, the nano-silicon-containing material in other regions except the passivation region is elemental silicon.

[0061] In some embodiments of the present application, it further includes: performing a coating treatment on the prepared carbon-containing composite particles. It can be depositing a carbon coating layer on the surface of the carbon-containing composite particles by means of chemical vapor deposition. In some specific embodiments, it can be introducing at least one of methane, ethylene, acetylene, and ethane and reacting at 500°C-800°C for 2-6 hours to obtain carbon-containing composite particles coated with a carbon coating layer.

[0062] In some other specific embodiments, a coating layer can also be formed on the surface of the carbon-containing composite particles by a solid-phase method. Specifically, the carbon-containing composite particles can be placed in a solid-phase mixing device (such as a ball mill) containing a conductive material and / or a fast ion conductor material, mixed, and a coating layer is formed on the surface of the carbon-containing composite particles.

[0063] In some embodiments of the present application, when the material of the deposited nanoparticles includes elemental silicon, it can be to first perform oxidation passivation treatment on the material obtained in step S01, and then perform a coating treatment on the silicon-carbon particles after the oxidation passivation treatment. At this time, the negative electrode active material includes silicon-carbon particles and a coating layer coated on the surface of the silicon-carbon particles, wherein the thickness region extending 5nm-20nm from the surface layer of the silicon-carbon particles towards the center is the passivation region, and the nano-silicon-containing material in the passivation region includes silicon dioxide. In some other specific embodiments, directly perform a coating treatment on the silicon-carbon particles obtained in step S01.

[0064] The embodiments of the present application also provide a negative electrode, including the negative electrode active material provided by the embodiments of the present application. Due to the use of the negative electrode active material provided by the embodiments of the present application, this negative electrode can be used to provide a battery with both a relatively high capacity, relatively excellent cycle performance, and a relatively low expansion rate.

[0065] In some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer includes the above-mentioned negative electrode active material and a binder. In some specific embodiments, a conductive agent is further included in the above-mentioned negative electrode material layer. In the embodiments of the present application, the above-mentioned negative electrode current collector can be any current collector known in the art suitable for the negative electrode. Exemplarily, the above-mentioned current collector can be, but is not limited to, aluminum foil, carbon-coated aluminum foil, etc.

[0066] In the embodiments of the present application, the above-mentioned binder can be any binder known in the art suitable for the negative electrode. Exemplarily, the above-mentioned binder includes, but is not limited to, styrene-butadiene rubber (SBR), etc.

[0067] In the embodiments of the present application, the above-mentioned conductive agent can be any conductive agent known in the art. Exemplarily, the conductive agent includes, but is not limited to, at least one of super p, acetylene black, graphene, and carbon nanotubes.

[0068] The embodiments of the present application further provide an electrochemical device, including the negative electrode provided by the embodiments of the present application. Due to the negative electrode provided by the embodiments of the present application, the electrochemical energy storage device can achieve a higher capacity, better cycle performance, and a lower expansion rate.

[0069] In some embodiments of the present application, the above-mentioned electrochemical device is a secondary battery. The above-mentioned secondary battery can be a lithium-ion battery or an alkali metal ion battery such as a sodium-ion battery. The above-mentioned secondary battery can be a liquid battery using a liquid electrolyte, a solid-state battery using a solid electrolyte, or a semi-solid battery.

[0070] In some embodiments of the present application, the above-mentioned secondary battery includes a positive electrode, a negative electrode, and an electrolyte and a separator provided between the positive electrode and the negative electrode.

[0071] In the embodiments of the present application, the above-mentioned positive electrode can be any positive electrode known in the art.

[0072] In some embodiments of the present application, the above-mentioned electrochemical device is a supercapacitor. In some specific embodiments, the supercapacitor includes a positive electrode, the above-mentioned negative electrode, and an electrolyte provided between the positive electrode and the negative electrode.

[0073] In the embodiments of the present application, the positive electrode in the supercapacitor can be any positive electrode known in the art, and the electrolyte can be any electrolyte known in the art, as long as they are mutually adapted.

[0074] The embodiments of the present application further provide an electrical device, including the electrochemical device provided. Due to the electrochemical device provided by the embodiments of the present application, the electrical device has a good market prospect.

[0075] In some embodiments of the present application, the above-mentioned electrical equipment includes, but is not limited to, vehicles, consumer electronic products, etc. Among them, the above-mentioned vehicles include, but are not limited to, new energy vehicles, power-assisted bicycles, etc.

[0076] The technical solution of the present application will be further described below with multiple embodiments.

[0077] Example 1

[0078] Preparation of porous carbon:

[0079] (1) Place the precursor material (specifically phenolic resin) in a vacuum tube furnace for vacuum high-temperature carbonization treatment. Among them, the carbonization temperature is 1000 °C and the duration is 5 h to obtain a carbon matrix.

[0080] (2) Uniformly mix the carbon matrix with KOH and perform alkali activation treatment at 750 °C for 2 h; wash the material obtained after alkali activation treatment with ultrapure water 3 times to obtain the first material.

[0081] (3) Perform steam activation on the above-mentioned first material at 700 °C for 2 h to obtain the second material.

[0082] (4) Perform carbon dioxide activation on the above-mentioned second material at 1000 °C for 2 h to obtain porous carbon.

[0083] Preparation of anode active material:

[0084] 1) Place the porous carbon in a fluidized bed, introduce silane gas, and deposit at 500 °C for 4 h.

[0085] 2) Still place the material obtained after the above deposition treatment in a fluidized bed, introduce lean oxygen with an oxygen volume content of 2-4% and perform oxidation passivation treatment at 500 °C for 2 h to obtain carbon-free coated silicon-carbon particles after oxygen passivation.

[0086] 3) Perform gas-phase coating on the above-mentioned silicon-carbon particles in a tube rotary furnace. The carbon source is acetylene, the coating temperature is 650 °C, and the coating time is 4 h to obtain the anode material. The thickness of the carbon coating layer obtained by gas-phase coating is 10 nm.

[0087] Example 2

[0088] The difference from Example 1 is only that in step (2), the temperature of the alkali activation treatment is 830 °C.

[0089] Example 3

[0090] The difference from Example 1 is only that in step (2), the temperature of the alkali activation treatment is 660 °C.

[0091] Example 4

[0092] The difference from Example 1 is only that in step (3), the temperature of steam activation is 780 °C.

[0093] Example 5

[0094] The difference from Example 1 is only that in step (3), the temperature of steam activation is 610 °C.

[0095] Example 6

[0096] The difference from Example 1 is only that in step (4), the temperature of carbon dioxide activation is 1180 °C.

[0097] Example 7

[0098] The difference from Example 1 is only that in step (4), the temperature of carbon dioxide activation is 900 °C.

[0099] Example 8

[0100] (1) Prepare porous carbon according to the method of Example 1; place the porous carbon in a fluidized bed, introduce silane gas, and deposit for 4 h at 500 °C to obtain silicon carbide particles coated with carbon-free;

[0101] (2) Still place the material obtained after the above deposition treatment in a fluidized bed, introduce a carbon source for gas-phase coating, where the carbon source is acetylene, the coating temperature is 650 °C, and the coating time is 4 h to obtain a negative electrode material, and the thickness of the carbon coating layer obtained by gas-phase coating is 10 nm.

[0102] Example 9

[0103] (1) Place the precursor material (specifically phenolic resin) in a vacuum tube furnace for vacuum high-temperature carbonization treatment, where the carbonization temperature is 1000 °C and the duration is 5 h to obtain a carbon matrix;

[0104] (2) Uniformly mix the carbon matrix with KOH, and carry out alkali activation treatment at 850 °C for 4 h; wash the material obtained after alkali activation treatment with ultrapure water for 3 times to obtain a first material;

[0105] (3) Carry out steam activation on the above first material at 550 °C for 2 h to obtain a second material;

[0106] (4) Carry out carbon dioxide activation on the above second material at 850 °C for 2 h to obtain porous carbon.

[0107] To highlight the beneficial effects of the embodiments of the present application, the following comparative examples are set.

[0108] Comparative Example 1

[0109] The difference from Example 1 is only that in step (2), the temperature of the alkali activation treatment is 900 °C.

[0110] Comparative Example 2

[0111] The difference from Example 1 is only that in step (2), the temperature of the alkali activation treatment is 600 °C.

[0112] Comparative Example 3

[0113] The difference from Example 1 is only that in step (3), the temperature of the steam activation is 860 °C.

[0114] Comparative Example 4

[0115] The difference from Example 1 is only that in step (3), the temperature of the steam activation is 450 °C.

[0116] Comparative Example 5

[0117] The difference from Example 1 is only that in step (4), the temperature of the carbon dioxide activation is 1300 °C.

[0118] Comparative Example 6

[0119] The difference from Example 1 is only that in step (4), the temperature of the carbon dioxide activation is 750 °C.

[0120] Comparative Example 7

[0121] The difference from Example 1 is that by adjusting the carbonization temperature and time of the precursor material, as well as the temperature and time of each step in the activation process, the parameters of the porous carbon are adjusted to those shown in Table 1.

[0122] Comparative Example 8

[0123] The difference from Example 1 is that by adjusting the carbonization temperature and time of the precursor material, as well as the temperature and time of each step in the activation process, the parameters of the porous carbon are adjusted to those shown in Table 1.

[0124] The porous carbons obtained in each of the examples and comparative examples were subjected to gas adsorption tests to obtain the total pore volume (pore volume), pore size distribution, average pore size, and specific surface area. The results are summarized in Table 1. Specifically, the total pore volume test was carried out according to the method of GB / T7702.20 - 2008 "Test Methods for Granular Activated Carbon from Coal - Determination of Pore Volume and Specific Surface Area", the pore size distribution and average pore size tests were carried out according to the method of GB / T 21650.3 - 2011 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion and Gas Adsorption", and the specific surface area test was carried out according to the method of GB / T 19587 - 2017 "Determination of Specific Surface Area of Solid Materials by Gas Adsorption BET Method". Among them, the analysis of pore volume, pore size distribution, and average pore size was carried out based on the BJH (Barrett - Joyner - Halenda) model, and the specific surface area analysis was carried out based on the BET (Brunauer - Emmett - Teller) model. Among them, Figure 1 is the adsorption - desorption isotherm curve measured for the porous carbon material of Example 1 under the above conditions.

[0125] Table 1

[0126]

[0127] Test of carbon content and silicon content:

[0128] The negative electrode active materials prepared in each of the above - mentioned examples and comparative examples were used to test the nitrogen content and oxygen content by a nitrogen - oxygen analyzer, and the carbon content was tested by a carbon - sulfur analyzer. The silicon content = 1 - nitrogen content - oxygen content - carbon content, that is, the content of silicon element in the negative electrode active material was obtained. Nitrogen element is a precursor impurity, and the nitrogen content is less than 0.1 w.t.%, so the nitrogen content can be basically ignored. Therefore, only the carbon, oxygen, and silicon contents are summarized in Table 2.

[0129] Table 2

[0130]

[0131]

[0132] Test of powder conductivity:

[0133] Take 2 g of the powder material of the negative electrode active materials prepared in each of the above - mentioned examples and comparative examples and place it in the fixture cavity of a powder resistance meter. The four - probe method was used for testing, the test pressure was 10 MPa, and the pressure - holding time was 20 s. The results are summarized in Table 3.

[0134] Test of gas generation of slurry:

[0135] The negative electrode active materials obtained in the above examples and comparative examples were mixed with a conductive agent (specifically acetylene black), a binder (specifically polyacrylic acid PAA), and a solvent (specifically water) at a mass ratio of 8:1:1:10 to obtain a slurry; 50 g of the slurry was sealed in an aluminum-plastic film bag with a size of 10*10 cm, and its volume was measured by the drainage method. The initial volume and the volume after being stored at 45 °C for 48 h were recorded, and then its volume was measured again by the drainage method (denoted as the final volume). The gas volume increase amount (ml / g) of the slurry = (final volume - initial volume) / mass of the negative electrode active material. The results are summarized in Table 3.

[0136] Table 3

[0137] Case Powder conductivity (S / cm) Gas production of slurry in 48h (mL / g) Example 1 0.318 0.07 Example 2 0.161 0.22 Example 3 0.184 0.25 Example 4 0.159 0.47 Example 5 0.378 0.38 Example 6 0.296 0.11 Example 7 0.253 0.24 Example 8 0.367 0.93 Example 9 0.226 0.21 Comparative Example 1 0.002 1.83 Comparative Example 2 0.026 1.58 Comparative Example 3 0.047 1.73 Comparative Example 4 0.034 1.55 Comparative Example 5 0.117 0.98 Comparative Example 6 0.094 0.69 Comparative Example 7 0.118 0.68 Comparative Example 8 0.175 0.58

[0138] Powder particle pressure resistance test:

[0139] 5 g of the carbon-free coated silicon-carbon particle samples prepared after silicon deposition in each of the examples and comparative examples were respectively taken for pressure compaction tests. The test pressures were 10 MPa, 30 MPa, 60 MPa, and 90 MPa, and the pressure holding time was 5 min. The samples after the pressure tests were collected for specific surface area tests (the specific surface area test was carried out according to the method of GB / T 19587-2017 "Determination of Specific Surface Area of Solid Substances by Gas Adsorption BET Method"). The specific surface area data of each example and comparative example after different test pressures are summarized in Table 4.

[0140] Compare the change of specific surface area with the increase of pressure. The greater the change in specific surface area, the lower the compaction of the material particles and the less pressure-resistant they are. The increased specific surface area is caused by the pores exposed after the material is crushed.

[0141] Table 4

[0142] Case 0 MPa (not pressed) 10 MPa 30 MPa 60 MPa 90 MPa Example 1 <![CDATA[8.9m 2 / g]]> <![CDATA[9.5m 2 / g]]> <![CDATA[10.8m 2 / g]]> <![CDATA[12.7m 2 / g]]> <![CDATA[26.9m 2 / g <!-- 12 -->]]> Example 2 <![CDATA[9.2m 2 / g]]> <![CDATA[12.7m 2 / g]]> <![CDATA[17.3m 2 / g]]> <![CDATA[25.1m 2 / g]]> <![CDATA[62.7m 2 / g]]> Example 3 <![CDATA[8.6m 2 / g]]> <![CDATA[11.3m 2 / g]]> <![CDATA[14.8m 2 / g]]> <![CDATA[20.8m 2 / g]]> <![CDATA[47.8m 2 / g]]> Example 4 <![CDATA[8.7m 2 / g]]> <![CDATA[11.3m 2 / g]]> <![CDATA[15.8m 2 / g]]> <![CDATA[19.4m 2 / g]]> <![CDATA[43.8m 2 / g]]> Example 5 <![CDATA[9.3m 2 / g]]> <![CDATA[12.5m 2 / g]]> <![CDATA[16.7m 2 / g]]> <![CDATA[23.4m 2 / g]]> <![CDATA[49.3m 2 / g]]> Example 6 <![CDATA[8.8m 2 / g]]> <![CDATA[11.1m 2 / g]]> <![CDATA[13.4m 2 / g]]> <![CDATA[16.7m 2 / g]]> <![CDATA[35.8m 2 / g]]> Example 7 <![CDATA[8.9m 2 / g]]> <![CDATA[11.7m 2 / g]]> <![CDATA[14.9m 2 / g]]> <![CDATA[18.3m 2 / g]]> <![CDATA[41.8m 2 / g]]> Example 8 <![CDATA[9.2m 2 / g]]> <![CDATA[10.7m 2 / g]]> <![CDATA[12.8m 2 / g]]> <![CDATA[15.1m 2 / g]]> <![CDATA[30.5m 2 / g]]> Example 9 <![CDATA[9.1m 2 / g]]> <![CDATA[15.3m 2 / g]]> <![CDATA[21.2m 2 / g]]> <![CDATA[27.7m 2 / g]]> <![CDATA[59.4m 2 / g]]> Comparative Example 1 <![CDATA[8.5m 2 / g]]> <![CDATA[15.3m 2 / g]]> <![CDATA[28.3m 2 / g]]> <![CDATA[58.3m 2 / g]]> <![CDATA[125.8m 2 / g]]> Comparative Example 2 <![CDATA[9.0m 2 / g]]> <![CDATA[15.2m 2 / g]]> <![CDATA[26.8m 2 / g]]> <![CDATA[52.3m 2 / g]]> <![CDATA[112.4m 2 / g]]> Comparative Example 3 <![CDATA[9.2m 2 / g]]> <![CDATA[16.1m 2 / g]]> <![CDATA[24.7m 2 / g]]> <![CDATA[49.7m 2 / g]]> <![CDATA[116.8m 2 / g]]> Comparative Example 4 <![CDATA[9.1m 2 / g]]> <![CDATA[16.8m 2 / g]]> <![CDATA[26.3m 2 / g]]> <![CDATA[54.7m 2 / g]]> <![CDATA[124.5m 2 / g]]> Comparative Example 5 <![CDATA[8.5m 2 / g]]> <![CDATA[13.8m 2 / g]]> <![CDATA[22.6m 2 / g]]> <![CDATA[38.9m 2 / g]]> <![CDATA[82.4m 2 / g]]> Comparative Example 6 <![CDATA[8.7m 2 / g]]> <![CDATA[15.8m 2 / g]]> <![CDATA[25.3m 2 / g]]> <![CDATA[53.8m 2 / g]]> <![CDATA[127.4m 2 / g]]> Comparative Example 7 <![CDATA[8.9m 2 / g]]> <![CDATA[17.7m 2 / g]]> <![CDATA[26.8m 2 / g]]> <![CDATA[47.2m 2 / g]]> <![CDATA[86.3m 2 / g]]> Comparative Example 8 <![CDATA[9.0m 2 / g]]> <![CDATA[12.8m 2 / g]]> <![CDATA[19.5m 2 / g]]> <![CDATA[35.2m 2 / g]]> <![CDATA[68.4m 2 / g]]>

[0143] Electrochemical performance test:

[0144] ① The negative electrode active materials obtained in the above examples and comparative examples were mixed with a conductive agent (specifically acetylene black) and a binder (specifically polyacrylic acid PAA) at a mass ratio of 8:1:1 and added to a solvent (specifically water). After mixing evenly, it was coated on a copper foil, dried, rolled, and slit to obtain the negative electrodes of each example and comparative example.

[0145] ②Using a lithium metal sheet as the counter electrode and a polyethylene / polypropylene composite membrane as the separator, stack the counter electrode, the separator, and the working electrode, and inject the electrolyte to prepare a button cell. Among them, the electrolyte is a lithium salt solution with a concentration of 1 mol / L (specifically lithium hexafluorophosphate LiPF6), and the solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) with a mass ratio of 23:25:24:28:15. Here, EC refers to ethylene carbonate, EMC refers to ethyl methyl carbonate, DMC refers to dimethyl carbonate, DEC refers to diethyl carbonate, and FEC refers to fluoroethylene carbonate.

[0146] ③First Coulomb efficiency test: Constant current discharge the button cells of each example and comparative example at 0.01C to 0.005V at 25 ± 2°C, then charge at 0.1C constant current to 1.5V, record the first discharge capacity and the first charge capacity of the battery, and the first Coulomb efficiency = first constant current charge capacity / first constant current discharge capacity. The results are summarized in Table 5.

[0147] ④First swelling rate test: Before assembling the button cell, use a micrometer to measure the original thickness of the negative electrode sheets of each example and comparative example. Assemble the button cell according to the above parameters and charge it to 100% SOC (state of charge). Disassemble the button cell, take out the negative electrode sheet, clean it with dichloromethane (DCM), dry it, and measure its thickness again. The first swelling rate = [(thickness of the negative electrode sheet at 100% SOC - thickness of the copper foil) - (original thickness of the negative electrode sheet - thickness of the copper foil)] / (original thickness of the negative electrode sheet - thickness of the copper foil) × 100%. The results are summarized in Table 5.

[0148] ⑤Stack and assemble the negative electrodes of each example and comparative example with a ternary positive electrode or a lithium iron phosphate positive electrode to form a soft pack battery. The soft pack batteries are subjected to charge and discharge cycle tests at 25 ± 2°C respectively. Specifically: charge at 0.33C constant current to 3.8V, then charge at constant voltage until the cut-off current is 0.05C; rest for 10 minutes; discharge at 0.33C constant current to 2.0V, which is one cycle. Repeat this step, and test the capacity and capacity retention rate of the battery after 100 cycles. The results are summarized in Table 5.

[0149] Table 5

[0150]

[0151] Combining the data in Tables 1 to 5, it can be found that using the porous carbon provided in the examples of the present application as the matrix and further depositing silane, the obtained negative electrode active material can achieve a relatively high tap density while having a relatively low powder resistivity, a relatively low swelling rate, a relatively high first discharge capacity, and excellent cycle performance.

[0152] The above are exemplary embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present application.

Claims

1. A porous carbon, characterized in that, The pore volume of the porous carbon is 0.6 cm 3 / g - 1.2 cm 3 / g; Based on the total pore volume of the porous carbon, the volume fraction of pores with a pore diameter < 2 nm is 70% - 95%, the volume fraction of pores with 2 nm ≤ pore diameter ≤ 10 nm is 2% - 12%, the volume fraction of pores with 10 nm < pore diameter ≤ 50 nm is 1% - 18%, and the volume fraction of pores with a pore diameter > 50 nm is 0 - 23%.

2. The porous carbon according to claim 1, wherein The volume fraction of pores with 10 nm < pore diameter ≤ 30 nm is 2% - 10%, and the volume fraction of pores with 30 nm < pore diameter ≤ 50 nm is 1% - 8%.

3. The porous carbon according to claim 1 or 2, characterized in that, Based on the total pore volume of the porous carbon, the volume fraction of pores with a pore diameter > 50 nm is 0 - 4%.

4. The porous carbon according to any one of claims 1-3, characterized in that, The specific surface area of the porous carbon is 1400 m 2 / g - 2400 m 2 / g.

5. The porous carbon according to any one of claims 1-4, characterized in that, The average pore diameter of the porous carbon is 0.8 - 2.6 nm.

6. The porous carbon according to any one of claims 1-5, characterized in that, The porous carbon includes amorphous carbon.

7. A method for preparing the porous carbon according to any one of claims 1-6, characterized in that, Comprising: The porous carbon is obtained by activating a carbon matrix.

8. The preparation method according to claim 7, characterized in that, The activation treatment includes sequentially performing alkali activation treatment, steam activation treatment, and carbon dioxide activation treatment; or The activation treatment includes alkali activation treatment and mixed gas activation treatment, and the mixed gas includes steam and carbon dioxide.

9. The preparation method according to claim 8, wherein, The sequentially performed alkali activation treatment, steam activation treatment, and carbon dioxide activation treatment include: Mix the carbon matrix with an alkali, react at 650°C - 850°C for 2 h - 4 h, wash, and obtain a first material; React the first material in a steam environment at 500°C - 800°C for 2 h - 4 h to obtain a second material; React the second material in a carbon dioxide atmosphere at 800°C - 1200°C for 2 h - 4 h to obtain the porous carbon.

10. The preparation method according to any one of claims 7-9, characterized in that, The carbon matrix is obtained by carbonizing one or more of biomass, resin, and coal tar, the carbonization temperature is 500°C - 1500°C, and the carbonization duration is 2 h - 8 h.

11. A negative electrode active material, characterized in that, Comprising carbon-containing composite particles, the carbon-containing composite particles include the porous carbon according to any one of claims 1 - 6 and nanoparticles located in the porous carbon, and the material of the nanoparticles contains at least one of silicon, germanium, and tin.

12. The negative electrode active material according to claim 11, wherein The carbon-containing composite particles are silicon-carbon particles, and the material of the nanoparticles contains silicon; the thickness region extending 5 nm - 20 nm from the surface layer of the silicon-carbon particles to the center is a passivation region, and the passivation region includes silicon dioxide.

13. The negative electrode active material according to claim 11 or 12, characterized in that, The negative electrode active material further includes a coating layer provided on the surface of the carbon-containing composite particles, and the material of the coating layer includes conductive carbon and / or fast ion conductor material; Preferably, the thickness of the coating layer is 10 nm - 50 nm.

14. The negative electrode active material according to any one of claims 11-13, characterized in that, The carbon-containing composite particles are silicon-carbon particles, and the material of the nanoparticles contains silicon; the mass of silicon element in the silicon-carbon particles is: 40 w.t.% - 50 w.t.%.

15. The negative electrode active material according to any one of claims 11-14, characterized in that, The mass fraction of carbon element in the carbon-containing composite particles is 50 w.t.% - 60 w.t.%.

16. A method for preparing a negative electrode active material, characterized in that, Comprising: Deposit nanoparticles in the porous carbon according to any one of claims 1 - 6 to form carbon-containing composite particles, and obtain a negative electrode active material; the material of the nanoparticles contains at least one of silicon, germanium, and tin.

17. The method for preparing the negative electrode active material according to claim 16, wherein, The carbon-containing composite particles are silicon-carbon particles, the material of the nanoparticles contains silicon, and depositing the nanoparticles in the porous carbon comprises: placing the porous carbon in a reaction chamber, introducing a silicon source, and depositing at 400° C.-600° C. for 2 h-6 h to obtain a negative electrode active material.

18. The preparation method of the negative electrode active material according to claim 17, characterized in that, The silicon source includes silane, and the deposited nanoparticles contain silicon element.

19. The method for preparing the negative electrode active material according to claim 17 or 18, characterized in that, The preparation method further comprises: performing an oxidation passivation treatment on the porous carbon on which the nanoparticles are deposited.

20. The preparation method of the negative electrode active material according to claim 19, characterized in that, The oxidation passivation treatment comprises: exposing the porous carbon deposited with the nanoparticles to a gas with an oxygen volume content of 2%-4% at 200° C.-500° C. for a passivation treatment for 2h-4h.

21. A negative electrode, characterized in that, The negative electrode comprises the negative electrode active material according to any one of claims 11 to 15 or the negative electrode active material prepared by the method for preparing the negative electrode active material according to any one of claims 16 to 20.

22. An electrochemical device, characterized in that, The electrochemical device comprises the negative electrode as claimed in claim 21.

23. An electrical device, characterized in that, The electrical equipment comprises the electrochemical device as claimed in claim 22.

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