Porous carbon and preparation method therefor, and negative electrode active material and use thereof

Abstract

A porous carbon and a preparation method therefor, and a negative electrode active material and the use thereof. The porous carbon has a pore volume of 0.6 cm3 / g-1.2 cm3 / g. Based on the total pore volume of the porous carbon, the volume proportion of pores with a pore diameter smaller than 2 nm is 70%-95%; the volume proportion of pores with a pore diameter greater than or equal to 2 nm but smaller than or equal to 10 nm is 2%-12%; the volume proportion of pores with a pore diameter greater than 10 nm but smaller than or equal to 50 nm is 1%-18%; and the volume proportion of pores with a pore diameter greater than 50 nm is 0-23%.

Description

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

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 29, 2023, with application number 202311865602.9 and application name “Porous carbon and its preparation method, negative electrode active material and its application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present disclosure relates to the field of battery technology, and in particular to porous carbon and a preparation method thereof, negative electrode active materials and applications thereof. Background Art

[0003] To meet the market demand for high-energy-density secondary batteries, the industry is attempting to replace commonly used graphite with high-performance negative electrode active materials, such as silicon. However, the volume change rate of silicon during the battery's charge-discharge cycle can reach 300%. Multiple cycles can lead to adverse consequences, such as silicon material pulverization, resulting in a decrease in battery capacity. To address these technical issues, the industry is opting to nano-scale and amorphize silicon materials. Silane gas cracks silicon material, depositing it within the pores of a porous material. This nano-scale and amorphous silicon material is achieved, utilizing the threshold-limiting effect of the porous material to suppress the volume change during cycling.

[0004] However, in the silicon-carbon negative electrode 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 and a decrease in the first efficiency, a large lithium insertion expansion, a low conductivity, and serious gas production during the negative electrode slurry preparation process; and the distribution of silicon material in the prepared silicon-carbon negative electrode active material is uneven, which causes an increase in side reactions of the silicon-carbon negative electrode active material during the charge and discharge cycle, and its internal stress is unevenly distributed, which damages the structural stability of the material; the silicon-carbon negative electrode active material after silicon deposition is not pressure-resistant and has low material compaction during the electrode rolling process. After the particles are subjected to force, the stress distribution of the porous material is uneven, local stress concentration will occur, and the particles will break or microcracks will occur. During the charge and discharge cycle, the material activity at the broken or microcracked locations is higher, which causes an increase in side reactions of the silicon-carbon negative electrode active material.

[0005] Summary of the Invention

[0006] In view of this, embodiments of the present disclosure provide porous carbon, a preparation method thereof, a negative electrode active material, and its application. The porous carbon has a novel structural design, rich pores, and a reasonable pore size distribution. The porous carbon can be used to provide a negative electrode active material with high initial efficiency, high capacity, low expansion, high conductivity, low negative electrode slurry gas production rate, high material compaction, and good long-cycle structural stability.

[0007] The present disclosure provides a porous carbon in a first aspect, wherein the total pore volume of the porous carbon is 0.6 cm3 / g-1.2cm 3 / g; based on the total pore volume of the porous carbon, the volume of pores with a pore diameter <2nm accounts for 70%-95%, the volume of pores with a pore diameter of 2nm≤≤10nm accounts for 2%-12%, the volume of pores with a pore diameter of 10nm<≤50nm accounts for 1%-18%, and the volume of pores with a pore diameter >50nm accounts for 0-23%.

[0008] In a possible embodiment, the volume proportion of pores with a diameter of 10 nm < pore diameter ≤ 30 nm is 2%-10%, and the volume proportion of pores with a diameter of 30 nm < pore diameter ≤ 50 nm is 1%-8%.

[0009] In a possible embodiment, based on the total pore volume of the porous carbon, the volume of pores with a pore diameter greater than 50 nm accounts for 0-4%.

[0010] In one possible embodiment, the specific surface area of ​​the porous carbon is 1400 m 2 / g-2400m 2 / g.

[0011] In a possible embodiment, the average pore diameter of the porous carbon is 0.8-2.6 nm.

[0012] In a possible embodiment, the porous carbon includes amorphous carbon.

[0013] The total pore volume of the above-mentioned porous carbon is large, and there is sufficient space to accommodate active nanoparticles. Moreover, the pore size distribution of the porous material is reasonable, the volume proportion of pores with a pore size less than 2nm is large, and the content of pores with a pore size greater than 30nm is low, so that the pore distribution inside the porous carbon is relatively uniform and presents a gradient distribution, which is conducive to the uniform deposition of active nanoparticles in the pore structure of the porous carbon, reduces the risk of active nanoparticles depositing on the surface of porous carbon particles, reduces the degree of side reactions on the surface of the material, improves the initial effect of the material, can improve the electrical conductivity of the material powder, can reduce the gas production of the material during the slurrying process, and is also conducive to improving the compaction density of the material; and, the porous carbon with the above-mentioned structure has a good threshold-limiting effect on the active nanoparticles, can effectively inhibit their volume expansion during the cycle, and reduce the uneven stress distribution inside 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 higher capacity and better long-cycle structural stability.

[0014] A second aspect of the present disclosure provides a method for preparing porous carbon, comprising:

[0015] The carbon matrix is ​​activated to obtain the porous carbon provided in the first aspect of the embodiment of the present disclosure.

[0016] In a possible embodiment, the activation treatment includes alkaline activation treatment, water vapor activation treatment, and carbon dioxide activation treatment performed in sequence; or the activation treatment includes alkaline activation treatment and mixed gas activation treatment, and the mixed gas includes water vapor and carbon dioxide.

[0017] In a possible embodiment, the alkali activation treatment, the steam activation treatment, and the carbon dioxide activation treatment performed sequentially include:

[0018] The carbon matrix is ​​mixed with a base, reacted at 650° C. to 850° C. for 2 h to 4 h, and washed to obtain a first material;

[0019] reacting the first material in a water vapor environment at 500° C.-800° C. for 2 h-4 h to obtain a second material;

[0020] The second material is reacted in a carbon dioxide atmosphere at 800° C.-1200° C. for 2 h-4 h to obtain the porous carbon.

[0021] In a possible embodiment, the carbon matrix is ​​obtained by carbonizing one or more of biomass, resin, and coal char, with a carbonization temperature of 500° C. to 1500° C. and a carbonization time of 2 h to 8 h.

[0022] The preparation method has simple steps, strong process controllability, high production efficiency, and can realize large-scale industrial production.

[0023] A third aspect of an embodiment of the present disclosure provides a negative electrode active material, comprising carbon-containing composite particles, wherein the carbon-containing composite particles include the porous carbon provided in the first aspect of the present disclosure and nanoparticles located in the porous carbon, wherein the material of the nanoparticles contains at least one of silicon, germanium, and tin.

[0024] In a possible embodiment, the carbon-containing composite particles are silicon-carbon particles, and the material of the nanoparticles includes silicon element; a region with a thickness of 5nm-20nm extending from the surface of the silicon-carbon particles to the center is a passivation zone, and the passivation zone includes silicon dioxide.

[0025] In a possible embodiment, the negative electrode active material further includes a coating layer disposed 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.

[0026] In a possible embodiment, the carbon-containing composite particles are silicon-carbon particles, and the material of the nanoparticles includes silicon; the silicon element accounts for 40wt.%-50wt.% of the mass of the silicon-carbon particles.

[0027] In a possible embodiment, the mass proportion of carbon element in the carbon-containing composite particles is 50wt.%-60wt.%.

[0028] Since the porous carbon provided by the first aspect of the present disclosure 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, and there is no 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 expansion volume of the nanoparticles during the charge and discharge cycle can be effectively reduced, thereby improving the structural stability of the negative electrode active material during the charge and discharge cycle; and, on the basis of ensuring the particle integrity of the carbon-containing composite particles, a higher compaction density can be achieved; at the same time, based on the high capacity of the nanoparticles and the fact that the porous carbon has a certain threshold limiting effect on the nanoparticles, the above-mentioned negative electrode active material can be used for negative electrode active materials with higher capacity, lower expansion rate, and better long-cycle structural stability. In addition, there is no enrichment of nanoparticles on the surface of the above-mentioned negative electrode active material particles, the material produces less gas during the pulping process, there are fewer side reactions on the particle surface, the material has a high first efficiency, and the material has high electrical conductivity.

[0029] The fourth aspect of the embodiments of the present disclosure provides a method for preparing a negative electrode active material, comprising: depositing nanoparticles in the porous carbon provided in the first aspect of the embodiments of the present disclosure to form carbon-containing composite particles to obtain a negative electrode active material; the material of the nanoparticles contains at least one of silicon, germanium, and tin.

[0030] In a possible embodiment, 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: placing the porous carbon in a reaction chamber, introducing a silicon source, and depositing at 400°C-600°C for 2h-6h to obtain a negative electrode active material.

[0031] In a possible embodiment, the silicon source includes silane, and the deposited nanoparticles contain silicon element.

[0032] In a possible embodiment, the preparation method further includes: performing an oxidation passivation treatment on the porous carbon on which the nanoparticles are deposited.

[0033] In a possible embodiment, the oxidative passivation treatment includes: exposing the porous carbon deposited with the nanoparticles to a gas with an oxygen volume content of 2%-4%, at a temperature of 200° C.-500° C., for a passivation treatment for 2 h-4 h.

[0034] The preparation method has strong process reliability and high production efficiency and is suitable for large-scale industrial production.

[0035] A fifth aspect of the present application provides an electrochemical device comprising a negative electrode. The negative electrode comprises the negative electrode active material provided in the third aspect of the present application, or comprises the negative electrode active material prepared by the preparation method provided in the fourth aspect of the present application. Due to the inclusion of the negative electrode provided in the embodiments of the present application, the electrochemical device can achieve high capacity, excellent cycle performance, and low expansion rate.

[0036] The sixth aspect of the present application provides an electrical device comprising the electrochemical device provided in the fifth aspect of the present application. Due to the electrochemical device provided in the embodiments of the present application, the electrical device has a good market prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG1 is an adsorption-desorption isotherm curve of the porous carbon according to Example 1 of the present disclosure.

[0038] FIG2 is a schematic structural diagram of a carbon-containing composite particle provided in an embodiment of the present disclosure.

[0039] FIG3 is a schematic structural diagram of an electrochemical device provided in an embodiment of the present disclosure.

[0040] FIG4 is a structural block diagram of an electric device provided by an embodiment of the present disclosure. DETAILED DESCRIPTION

[0041] The present disclosure provides a porous carbon having a total pore volume of 0.6 cm 3 / g-1.2cm 3 / g;

[0042] Based on the total pore volume of porous carbon, the volume of pores with a pore diameter <2nm accounts for 70%-95%, the volume of pores with a pore diameter of 2nm≤≤10nm accounts for 2%-12%, the volume of pores with a pore diameter of 10nm<≤50nm accounts for 1%-18%, and the volume of pores with a pore diameter >50nm accounts for 0-23%.

[0043] The inventors discovered through research that the properties of silicon-carbon anode active materials are largely determined by the porous material itself. In related art, the pore structure of the porous material is poorly designed, resulting in poor electrochemical performance of the silicon-carbon anode active material. The porous carbon disclosed herein has a large total pore volume, providing ample space for accommodating active material nanoparticles (e.g., silicon-containing particles). Furthermore, the pore size distribution of the porous material is reasonable, with a large volume fraction of pores with a pore size less than 2 nm and a low content of pores with a pore size greater than 50 nm. Consequently, the pore distribution within 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 deposition of the active material nanoparticles. This can reduce gas production during the slurrying process of the resulting negative electrode active material, and can also increase the compaction density of the final negative electrode active material without destroying the integrity of the particles. Furthermore, the porous carbon has a good threshold limiting effect on the active material nanoparticles, effectively inhibiting their volume expansion during the cycle, and reducing the uneven internal stress distribution of the material caused by the uneven distribution of the active material nanoparticles, thereby reducing the material fragmentation caused by the uneven internal stress distribution of the negative electrode active material during the charge and discharge cycle. Therefore, the porous material can be used to provide a negative electrode active material with a high capacity and good long-cycle structural stability.

[0044] In the embodiments of the present disclosure, 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 the degassing time is maintained at ≥120 min and the degassing temperature is maintained at ≥200°C during the test to obtain the adsorption-desorption curve of the porous carbon, and then the data is processed to obtain parameters such as the pore size distribution and total pore volume of the porous carbon.

[0045] Illustratively, the volume fraction of pores with a pore size <2 nm may 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 proportion of pores with a pore size of <2nm is too small, the proportion of mesopores (pores with a pore size of 2nm-50nm) and / or macropores (pores with a pore size of >50nm) will increase, resulting in a wider pore size distribution in the porous carbon. At this time, depositing active material nanoparticles (for example, silicon-containing materials) will cause the particle size distribution of the active material nanoparticles in the obtained carbon-containing composite particles to become wider. During the charge and discharge cycle, serious stress unevenness will still occur, and the structural stability of the negative electrode active material will still not be improved well. Ultimately, the cycle 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 multi-layer adsorption of silicon in the silane deposition process, and silicon-rich phenomena will easily appear on the surface of the material. The silicon-rich problem will lead to low initial efficiency of the material, severe gas production and reduced conductivity. Similarly, when the proportion of mesopores and macropores increases, the material will be subjected to uniform external stress during the rolling process of the negative electrode sheet. The larger pore walls will be subjected to stress concentration, resulting in larger strains in the larger pores, cracks, and easy crushing of the material.

[0046] For example, the volume fraction of pores with a pore diameter of 2 nm ≤ ≤ 10 nm may be, but is not limited to, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, etc. If the pore fraction of the above pore diameter is too large, it will squeeze out the volume fraction of micropores (pores with a pore diameter less than 2 nm), resulting in a lower pore diameter concentration of the porous carbon; in addition, the total pore volume of the porous carbon in the embodiment of the present disclosure is constant. When the proportion of pores with large pore diameters increases, the number of pores in the porous carbon may decrease, 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.

[0047] For example, the volume proportion of pores with a pore size of 10 nm < pore size ≤ 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 proportion of pores with the above pore size is too large, it will not only cause the pore size distribution of the porous carbon to become wider, but also reduce the uniformity of the particle size and distribution of the active material nanoparticles in the final negative electrode active material, and affect the structural stability of the negative electrode active material. In some embodiments of the present disclosure, the volume proportion of pores with a pore size of 10 nm < pore size ≤ 30 nm is 2%-10%, and the volume proportion of pores with a pore size of 30 nm < pore size ≤ 50 nm is 1%-8%. This is more conducive to controlling the narrow pore size distribution of the porous carbon and improving the uniformity of the pore size distribution inside the porous carbon, thereby providing a negative electrode active material with better electrochemical performance. For example, the volume fraction of pores with a pore size of 10 nm < pore size ≤ 30 nm may be, but is not limited to, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, and the volume fraction of pores with a pore size of 30 nm < pore size ≤ 50 nm may be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%, etc.

[0048] Exemplarily, the volume fraction of pores with a pore diameter greater than 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 a pore diameter greater than 50 nm) is low when the silicon-containing material is deposited. After the active material nanoparticles are deposited, there will still be 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, causing the negative electrode active material to rupture. In order to avoid the above situation, the relevant technology 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 disclosure, based on the total pore volume of the porous carbon, the volume fraction of pores with a pore diameter greater than 50 nm is ≤4%. In some specific embodiments, the volume fraction of pores with a pore diameter greater than 50 nm is 0, that is, the porous carbon does not contain macropores. In this way, the pore size distribution concentration of the porous carbon can be further improved, and the risk of large pores in the final negative electrode active material can be reduced, thereby improving the compaction density of the negative electrode active material while ensuring the particle integrity of the negative electrode active material.

[0049] In some embodiments, the total pore volume of the porous carbon is 0.6 cm 3 / g-1.2cm 3 / g; based on the total pore volume of porous carbon, the volume of pores with a pore size <2nm accounts for 70%-95%, the volume of pores with a pore size of 2nm≤≤10nm accounts for 2%-12%, the volume of pores with a pore size of 10nm<≤30nm accounts for 2%-10%, the volume of pores with a pore size of 30nm<≤50nm accounts for 1%-8%, and the volume of pores with a pore size >50nm accounts for 0-4%. This improves the pore distribution of porous carbon, which is conducive to improving the performance of the final negative electrode active material.

[0050] For example, the pore volume of the porous carbon may be, but is not limited to, 0.6 cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g. If the pore volume of the porous carbon is too small and cannot accommodate a sufficient amount of active material nanoparticles, the capacity of the final negative electrode active material will be too low, which will not meet the market demand for battery energy density. It 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, the threshold limiting effect of the porous carbon on the active material nanoparticles will be weakened, and the thermodynamic stability of the negative electrode active material may also be affected. In some embodiments of the present disclosure, the average pore size of the porous carbon is 0.8-2.6nm. For example, the average pore size of the porous carbon can be, but is not limited to, 0.8nm, 1.2nm, 1.6nm, 2.0nm, 2.2nm, 2.4nm, and 2.6nm. Taking the above-mentioned porous carbon for the deposition of silane as an example: controlling the average pore size of the porous carbon within the above-mentioned range can make the proportion of micropores more appropriate, thereby 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, thereby improving the deposition efficiency of silane in the porous carbon, thereby further reducing the risk of silicon deposition on the surface of the porous carbon particles causing silicon-enriched phenomenon.

[0051] In some embodiments of the present disclosure, the porous carbon is amorphous carbon. In some embodiments of the present disclosure, 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.%.

[0052] In some embodiments of the present disclosure, the specific surface area of ​​the porous carbon is 1400 m 2 / g-2400m 2 / g. A suitable specific surface area is conducive to the subsequent deposition of active material nanoparticles, and the final negative electrode active material can also have a relatively suitable specific surface area, which is conducive to the deintercalation / embedding of active ions, and can also fully reduce the risk of side reactions between the negative electrode active material and other substances in the subsequent application process; for example, in the preparation of 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. For example, the specific surface area of ​​porous carbon can be, but is not limited to, 1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g, etc.

[0053] In some embodiments of the present disclosure, the Dv50 of the porous carbon is 3μm-12μm. 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, which can make the deintercalation / embedding path of the active ions in the negative electrode active material particles more suitable, and it is also easy to achieve a higher compaction density, thereby easily obtaining a battery with a high energy density. Exemplarily, the Dv50 of the porous carbon can be, but is not limited to, 3.0μm, 3.5μm, 4.0μm, 4.5μm, 5.0μm, 5.5μm, 6.0μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm, 10.0μm, 10.5μm, 11.0μm, 11.5μm, 12.0μm, etc. In the embodiment of the present disclosure, the Dv50 of the porous carbon can be tested using a laser particle size analyzer.

[0054] The present disclosure also provides a method for preparing porous carbon, which can be used to prepare the aforementioned porous carbon, comprising:

[0055] The carbon matrix is ​​activated to obtain the porous carbon provided in the embodiment of the present disclosure; the total pore volume of the porous carbon is 0.6 cm 3 / g-1.2cm 3 / g; based on the total pore volume of the porous carbon, the volume of pores with a pore diameter <2nm accounts for 70%-95%, the volume of pores with a pore diameter of 2nm≤≤10nm accounts for 2%-12%, the volume of pores with a pore diameter of 10nm<≤50nm accounts for 1%-18%, and the volume of pores with a pore diameter >50nm accounts for 0-23%.

[0056] The preparation method has simple steps, strong process controllability, high production efficiency, and can realize large-scale industrial production.

[0057] In some embodiments of the present disclosure, the activation treatment includes an alkali activation treatment, a water vapor activation treatment, and a carbon dioxide activation treatment performed sequentially. The alkali activation treatment can effectively increase the specific surface area of ​​the carbon matrix and is also beneficial for removing impurities (e.g., oxides, etc.) in the carbon matrix. The water vapor activation treatment is beneficial for obtaining mesopores in the carbon matrix, while the final carbon dioxide activation treatment can produce a microporous structure with rich pores.

[0058] In some embodiments of the present disclosure, the above-mentioned alkali activation treatment includes mixing the carbon matrix with an alkali, reacting it at 650°C-850°C for 2h-4h to obtain a first material. In this way, a suitable pore structure can be obtained, which provides a basis for subsequent mesopore pore formation and micropore pore formation, and is conducive to finally obtaining a porous carbon with 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 time of the alkali activation treatment can be, but is not limited to, 2h, 2.5h, 3h, 3.5h, 4h, etc. In some specific embodiments, the material obtained after the alkali activation treatment is further washed to remove impurities generated during the alkali activation process. Specifically, it can be washed with water, and multiple washings (for example, 3 times) can be performed. Further, the above-mentioned washing includes washing with acid, hot water, and distilled water in sequence to remove salts generated by the reaction.

[0059] In some specific embodiments of the present disclosure, the base includes, but is not limited to, potassium hydroxide, sodium hydroxide, and acids or salts, including, but not limited to, phosphoric acid, potassium chloride, aluminum chloride, and zinc chloride. A potassium hydroxide solution may be mixed with the carbon substrate, or solid potassium hydroxide may be directly mixed with the carbon substrate for reaction. When a potassium hydroxide solution is used, its concentration or pH value is not limited.

[0060] In some embodiments of the present disclosure, the steam activation treatment includes reacting the first material obtained after the alkali activation in a steam environment at 500°C-800°C for 2h-4h to obtain a second material. The appropriate activation temperature can make the water vapor diffuse evenly within the first material particles, so that the entire first material particles can be evenly activated, thereby obtaining a mesoporous structure with uniform pore distribution and reasonable pore size distribution. Exemplarily, the temperature of the 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 steam activation treatment can be, but is not limited to, 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0061] In some embodiments of the present disclosure, the carbon dioxide treatment includes placing the second material obtained after the 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 porous carbon obtained can be optimized, and it is easy to obtain a microporous structure with a reasonable pore size distribution, thereby obtaining a porous carbon material with a richer pore structure. For example, the temperature of the 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.

[0062] In some other embodiments of the present disclosure, the activation treatment includes alkali activation treatment and mixed gas activation treatment, and the mixed gas includes water vapor and carbon dioxide.

[0063] In the embodiments of the present disclosure, the carbon matrix can be purchased directly or obtained by carbonizing a precursor material. In some specific embodiments, the precursor material is carbonized to obtain the carbon matrix, including:

[0064] In a protective atmosphere or vacuum environment, the precursor material is carbonized at 500° C. to 1500° C. for 2 to 8 hours. For example, the carbonization temperature may 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. For example, the carbonization time may be, but is not limited to, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc.

[0065] The present disclosure does not limit the type of precursor material; it can be selected from any known precursor material in the art. For example, the precursor materials include, but are not limited to, biomass precursors, polymer precursors, or coal char hard carbon. Biomass precursors include, but are not limited to, coconut shells, bamboo, or starch; polymer precursors include resins such as phenolic resins and epoxy resins; and coal char includes, but is not limited to, anthracite and coking coal.

[0066] The present disclosure provides a negative electrode active material, including carbon-containing composite particles. Please refer to Figure 2, which is a schematic structural diagram of a carbon-containing composite particle provided by the present disclosure. The carbon-containing composite particle includes the porous carbon provided by the present disclosure 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 porous carbon is 0.6 cm 3 / g-1.2cm 3 / g, based on the total pore volume of the porous carbon, the volume of pores with a pore diameter <2nm accounts for 70%-95%, the volume of pores with a pore diameter of 2nm≤≤10nm accounts for 2%-12%, the volume of pores with a pore diameter of 10nm<≤50nm accounts for 1%-18%, and the volume of pores with a pore diameter >50nm accounts for 0-23%.

[0067] Since the porous carbon provided in the embodiment of the present disclosure is used as the substrate, the nanoparticles are evenly distributed in the silicon-carbon particles, and the particle size distribution of the nanoparticles is reasonable. Therefore, the problem of uneven stress distribution inside the carbon-containing composite particles caused by the difference in the expansion volume of the nanoparticles during the charge and discharge cycle can be effectively reduced, thereby improving the structural stability of the negative electrode active material during the charge and discharge cycle; the porous carbon has rich pores and a reasonable pore size distribution, and the material of the nanoparticles is not easily enriched on the surface of the porous carbon particles after deposition, and a higher compaction density can be achieved on the basis of ensuring the particle integrity of the carbon-containing composite particles; at the same time, based on the high capacity of the nanoparticles and the fact that the porous carbon has a certain threshold limiting effect on the nanoparticles, the above-mentioned negative electrode active material can be used for negative electrode active materials with higher capacity, lower expansion rate and better long-cycle structural stability.

[0068] In the disclosed embodiments, the negative electrode active material can be pretreated to remove nanoparticles from the carbon-containing composite particles, and the resulting porous carbon can then be subjected to gas adsorption and desorption testing. The pretreatment method is as follows: the negative electrode active silicon-carbon material is dispersed in a saturated NaOH solution and subjected to magnetic stirring at room temperature at a stirring speed of 180 rpm for 6 hours; the magnetically stirred solution is then subjected to microwave digestion at a microwave power of 1000 W, a digestion temperature of 60°C, and a digestion time of 6 hours to allow the silicon material to react completely. The reacted material is then collected and rinsed three times with ultrapure water.

[0069] In some embodiments of the present disclosure, the carbon-containing composite particles are silicon-carbon particles, and the nanoparticles are made of silicon. In this case, the nanoparticles may be made of silicon alone, silicon oxide, silicon nitride, or other materials.

[0070] In the embodiments of the present disclosure, the material of the nanoparticles can be crystalline or amorphous, and the present disclosure does not limit this.

[0071] In some embodiments of the present disclosure, the silicon content of the silicon-carbon particles is 40-50% by weight. However, controlling the ratio of the two within the above range can result in a higher capacity of the negative electrode active material and lower expansion rate and structural stability during charge and discharge cycles. In the embodiments of the present disclosure, the nitrogen and oxygen contents can be measured using a nitrogen-oxygen meter, the carbon content can be measured using a carbon-sulfur meter, and the silicon content in the negative electrode active material can be measured using the method of silicon content = 1 - nitrogen content - oxygen content - carbon content.

[0072] In some embodiments of the present disclosure, the mass proportion of carbon in the negative electrode active material is 50%-60%. For example, the mass proportion of carbon 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 disclosure, the carbon 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 to produce carbon dioxide after carbon oxidation, and then measuring the carbon content using a carbon-sulfur analyzer.

[0073] In some embodiments of the present disclosure, the nanoparticles in the silicon-carbon particles are made of elemental silicon. A passivation zone extending from the surface of the silicon-carbon particle toward the center with a thickness of 5 nm to 20 nm is defined as the passivation zone, which comprises silicon dioxide. In some specific embodiments, the nano-silicon-containing material in regions other than the passivation zone is made of elemental silicon.

[0074] In some embodiments of the present disclosure, the negative electrode active material also 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 reactions between the carbon-containing composite particles and the electrolyte or the solvent in the pulping process, thereby facilitating the utilization of 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 thereof 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 embodiment of the present disclosure, the coating layer can be a conductive carbon layer, a fast ion conductor material layer, or a composite layer of conductive carbon and a fast ion conductor.

[0075] In some specific embodiments, the thickness of the coating layer is 10 nm to 50 nm. By controlling the thickness of the coating layer within the above range, the length of the active ion extraction / intercalation path can be controlled within a suitable range, and the electronic and / or ionic conductivity of the negative electrode active material can be more fully improved. For example, 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.

[0076] The present disclosure also provides a method for preparing a negative electrode active material, comprising:

[0077] S01. Nanoparticles are deposited in the aforementioned porous carbon provided in the embodiment of the present disclosure to obtain the negative electrode active material provided in the embodiment of the present disclosure; wherein, based on the total pore volume of the porous carbon, the volume of pores with a pore diameter <2 nm accounts for 70%-95%, the volume of pores with a pore diameter of 2 nm ≤ ≤ 10 nm accounts for 2%-12%, the volume of pores with a pore diameter of 10 nm < ≤ 50 nm accounts for 1%-18%, and the volume of pores with a pore diameter > 50 nm accounts for 0-23%.

[0078] The preparation method has strong process controllability and high production efficiency, and is suitable for large-scale industrial production.

[0079] In some embodiments of the present disclosure, the carbon-containing composite particles are silicon-carbon particles, the material of the nanoparticles comprises silicon, and depositing the nanoparticles in the porous carbon comprises:

[0080] Porous carbon is placed in a reaction chamber, a silicon source is introduced, and the negative electrode active material is obtained by deposition at 400°C-600°C for 2h-6h. In the embodiment of the present disclosure, the reaction chamber may be, but is not limited to, a fluidized bed. For example, the deposition temperature may be, but is not limited to, 400°C, 450°C, 500°C, 550°C, 600°C, etc. For example, the deposition time may be, but is not limited to, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, etc. In some embodiments of the present disclosure, the silicon source is silane. In this case, the deposited nano-silicon-containing material is a silicon element.

[0081] In some embodiments of the present disclosure, the silicon source includes silane, and the deposited nanoparticles contain silicon element.

[0082] When the nanoparticles include silicon, in order to avoid the oxidation and exothermic combustion of silicon caused by the sudden contact of the newly prepared nanoparticles with air, some specific embodiments further include step S02: performing an oxidative passivation treatment on the deposited material; wherein the passivation treatment includes exposing the deposited material to a thin oxygen (oxygen / nitrogen mixture with a volume content of 2%-4%) at a temperature of 200-500°C for 2h-4h to oxidize the nano-silicon particles on the surface of the silicon-carbon particles. In this way, in some embodiments of the present disclosure, the silicon-carbon particles prepared have a thickness of 5nm-20nm extending from the surface of the silicon-carbon particles to the center thereof as a passivation zone, and the nano-silicon-containing material in the passivation zone includes silicon dioxide. In some specific embodiments, in the silicon-carbon particles, the nano-silicon-containing material in other regions except the passivation zone is silicon.

[0083] Some embodiments of the present disclosure further include: coating the prepared carbon-containing composite particles. This may involve vapor deposition to form a carbon coating on the surface of the carbon-containing composite particles. In some specific embodiments, at least one of methane, ethylene, acetylene, and ethane may be introduced and reacted at 500°C to 800°C for 2 to 6 hours to obtain carbon-containing composite particles coated with the carbon coating.

[0084] In other specific embodiments, a solid-phase method can be used to form a coating layer on the surface of the carbon-containing composite particles. Specifically, the carbon-containing composite particles can be placed in a solid-phase mixing device (e.g., a ball mill) containing a conductive material and / or a fast ion conductor material, and mixed to form a coating layer on the surface of the carbon-containing composite particles.

[0085] In some embodiments of the present disclosure, when the material of the deposited nanoparticles includes silicon, the material obtained in step S01 may be first subjected to an oxidative passivation treatment, and then the silicon-carbon particles after the oxidative passivation treatment may be coated. In this case, the negative electrode active material includes silicon-carbon particles and a coating layer coated on the surface of the silicon-carbon particles, wherein the region extending from the surface of the silicon-carbon particles toward the center with a thickness of 5nm-20nm is the passivation zone, and the nano-silicon-containing material in the passivation zone includes silicon dioxide. In other specific embodiments, the coating treatment is directly performed on the silicon-carbon particles obtained in step S01.

[0086] The present disclosure also provides a negative electrode 20 comprising the negative electrode active material provided in the present disclosure. Due to the use of the negative electrode active material provided in the present disclosure, the negative electrode 20 can be used to provide a battery with higher capacity, better cycle performance, and lower expansion rate.

[0087] In some embodiments of the present disclosure, the negative electrode 20 includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes the aforementioned negative electrode active material and a binder. In some specific embodiments, the negative electrode material layer further includes a conductive agent. In the embodiments of the present disclosure, the negative electrode current collector can be any current collector known in the art as being suitable for the negative electrode 20. For example, the current collector can be, but is not limited to, aluminum foil, carbon-coated aluminum foil, or the like.

[0088] In the embodiment of the present disclosure, the binder may be any binder known in the art and applicable to the negative electrode 20. For example, the binder includes but is not limited to styrene-butadiene rubber (SBR).

[0089] In the embodiments of the present disclosure, the conductive agent may be any conductive agent known in the art. For example, the conductive agent includes but is not limited to at least one of super P, acetylene black, graphene, and carbon nanotubes.

[0090] The present disclosure also provides an electrochemical device 10, including a negative electrode 20 according to the present disclosure. See Figure 3, which is a schematic diagram of the structure of an electrochemical device according to the present disclosure. Due to the negative electrode 20 according to the present disclosure, the electrochemical device 10 can achieve high capacity, excellent cycle performance, and low expansion rate.

[0091] In some embodiments of the present disclosure, the electrochemical device 10 is a secondary battery. The secondary battery may be a lithium-ion battery or an alkali metal ion battery such as a sodium-ion battery. The secondary battery may be a liquid battery using a liquid electrolyte, a solid-state battery using a solid electrolyte, or a semi-solid-state battery.

[0092] In some embodiments of the present disclosure, the secondary battery includes a positive electrode, a negative electrode 20 , and an electrolyte and a separator disposed between the positive electrode and the negative electrode 20 .

[0093] In the embodiments of the present disclosure, the positive electrode can be any positive electrode known in the art.

[0094] In some embodiments of the present disclosure, the electrochemical device 10 is a supercapacitor. In some specific embodiments, the supercapacitor includes a positive electrode, the negative electrode 20 , and an electrolyte disposed between the positive electrode and the negative electrode 20 .

[0095] In the embodiments of the present disclosure, 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, and they can be compatible with each other.

[0096] The present disclosure also provides an electrical device 1 including an electrochemical device 10. Referring to Figure 4 , which is a block diagram of the structure of an electrical device according to the present disclosure, the electrical device 1 has a promising market prospect due to the electrochemical device 10 provided in the present disclosure.

[0097] In some embodiments of the present disclosure, the electrical equipment 1 includes but is not limited to vehicles, consumer electronic products, etc. Among them, the vehicles include but are not limited to new energy vehicles, power-assisted bicycles, etc.

[0098] The technical solution of the present disclosure is further illustrated below with multiple embodiments.

[0099] Example 1

[0100] Preparation of porous carbon:

[0101] (1) placing the precursor material (specifically phenolic resin) in a vacuum tube furnace for vacuum high-temperature carbonization treatment, wherein the carbonization temperature is 1000° C. and the duration is 5 h to obtain a carbon matrix;

[0102] (2) uniformly mixing the carbon matrix with KOH, and performing an alkali activation treatment at 750° C. for 2 h; washing the material obtained after the alkali activation treatment with ultrapure water for 3 times to obtain a first material;

[0103] (3) activating the first material with steam at 700° C. for 2 h to obtain a second material;

[0104] (4) Activating the second material with carbon dioxide at 1000° C. for 2 h to obtain porous carbon.

[0105] Preparation of negative electrode active material:

[0106] 1) The porous carbon was placed in a fluidized bed, silane gas was introduced, and the deposition was carried out at 500°C for 4 hours;

[0107] 2) The material obtained after the above deposition treatment is still placed in a fluidized bed, and a dilute oxygen with an oxygen volume content of 2-4% is introduced at 500° C. for oxidative passivation treatment for 2 hours to obtain oxygen-passivated carbon-free coated silicon-carbon particles;

[0108] 3) The silicon-carbon particles were vapor-coated in a tubular rotary furnace with acetylene as the carbon source, the coating temperature being 650° C., and the coating time being 4 h to obtain a negative electrode material. The thickness of the carbon coating layer obtained by vapor-coating was 10 nm.

[0109] Example 2

[0110] The only difference from Example 1 is that in step (2), the temperature of the alkali activation treatment is 830°C.

[0111] Example 3

[0112] The only difference from Example 1 is that in step (2), the temperature of the alkali activation treatment is 660°C.

[0113] Example 4

[0114] The only difference from Example 1 is that in step (3), the temperature of water vapor activation is 780°C.

[0115] Example 5

[0116] The only difference from Example 1 is that in step (3), the temperature of water vapor activation is 610°C.

[0117] Example 6

[0118] The only difference from Example 1 is that in step (4), the temperature for carbon dioxide activation is 1180°C.

[0119] Example 7

[0120] The only difference from Example 1 is that in step (4), the temperature for carbon dioxide activation is 900°C.

[0121] Example 8

[0122] 1) Preparing porous carbon according to the method of Example 1; placing the porous carbon in a fluidized bed, introducing silane gas, and depositing at 500° C. for 4 h to obtain carbon-free silicon-carbon particles;

[0123] 2) The material obtained after the above deposition treatment is still placed in a fluidized bed, and a carbon source is introduced for vapor coating, wherein the carbon source is acetylene, the coating temperature is 650°C, and the coating time is 4 hours to obtain a negative electrode material. The thickness of the carbon coating layer obtained by vapor coating is 10 nm.

[0124] Example 9

[0125] (1) placing the precursor material (specifically phenolic resin) in a vacuum tube furnace for vacuum high-temperature carbonization treatment, wherein the carbonization temperature is 1000° C. and the duration is 5 h to obtain a carbon matrix;

[0126] (2) uniformly mixing the carbon matrix with KOH, and performing an alkali activation treatment at 850° C. for 4 hours; washing the material obtained after the alkali activation treatment with ultrapure water for 3 times to obtain a first material;

[0127] (3) activating the first material with steam at 550° C. for 2 h to obtain a second material;

[0128] (4) Activating the second material with carbon dioxide at 850° C. for 2 h to obtain porous carbon.

[0129] In order to highlight the beneficial effects of the embodiments of the present disclosure, the following comparative examples are provided.

[0130] Comparative Example 1

[0131] The only difference from Example 1 is that in step (2), the temperature of the alkali activation treatment is 900°C.

[0132] Comparative Example 2

[0133] The only difference from Example 1 is that in step (2), the temperature of the alkali activation treatment is 600°C.

[0134] Comparative Example 3

[0135] The only difference from Example 1 is that in step (3), the temperature of water vapor activation is 860°C.

[0136] Comparative Example 4

[0137] The only difference from Example 1 is that in step (3), the temperature of water vapor activation is 450°C.

[0138] Comparative Example 5

[0139] The only difference from Example 1 is that in step (4), the temperature for carbon dioxide activation is 1300°C.

[0140] Comparative Example 6

[0141] The only difference from Example 1 is that in step (4), the temperature for carbon dioxide activation is 750°C.

[0142] Comparative Example 7

[0143] The difference from Example 1 is that the parameters of the porous carbon are adjusted to those shown in Table 1 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.

[0144] Comparative Example 8

[0145] The difference from Example 1 is that the parameters of the porous carbon are adjusted to those shown in Table 1 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.

[0146] The porous carbon obtained in each embodiment and comparative example was subjected to gas adsorption testing to obtain the total pore volume (pore volume), pore size distribution, average pore size, and specific surface area per unit mass of the porous carbon. The results are summarized in Table 1. Specifically, the total pore volume test was performed using the method of GB / T 7702.20-2008 "Test method for granular activated carbon from coal - Determination of pore volume and specific surface area", the pore size distribution and average pore size test were performed using 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 performed using the method of GB / T 19587-2017 "Determination of specific surface area of ​​solid materials by gas adsorption BET method". The pore volume, pore size distribution, and average pore size analysis were performed according to the BJH (Barrett-Joyner-Halenda) model, and the specific surface area analysis was performed according to the BET (Brunauer-Emmett-Teller) model. 1 is an adsorption-desorption isotherm curve of the porous carbon material of Example 1 measured under the above conditions.

[0147] Table 1

[0148] Carbon content and silicon content test:

[0149] The negative electrode active materials prepared in the above examples and comparative examples were tested for nitrogen and oxygen content using a nitrogen-oxygen analyzer, and for carbon content using a carbon-sulfur analyzer. The silicon content in the negative electrode active materials is calculated as follows: silicon content = 1 - nitrogen content - oxygen content - carbon content. Nitrogen is a precursor impurity, and the nitrogen content is less than 0.1 wt %, which is essentially negligible. Therefore, only the carbon, oxygen, and silicon contents are summarized in Table 2.

[0150] Table 2

[0151] Powder conductivity test:

[0152] 2 g of the negative electrode active material prepared in the above examples and comparative examples was placed in the fixture cavity of a powder resistance meter and tested using a four-probe method with a test pressure of 10 MPa and a holding time of 20 s. The results are summarized in Table 3.

[0153] Slurry gas production test:

[0154] The negative electrode active materials prepared in the above embodiments and comparative examples were mixed with a conductive agent (specifically acetylene black), a binder (specifically polyacrylic acid PAA) and a solvent (specifically water) in 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 tested by the water displacement method. The initial volume and the volume after storage at 45°C for 48 h were recorded, and the volume was measured again by the water displacement method (recorded as the final volume). The increase in the gas production volume of the slurry (ml / g) = (final volume-initial volume) / mass of the negative electrode active material. The results are summarized in Table 3.

[0155] Table 3

[0156] Powder particle pressure resistance test:

[0157] 5 g of each carbon-free coated silicon-carbon particle sample obtained after silicon deposition in each embodiment and comparative example was subjected to pressure compaction testing at test pressures of 10 MPa, 30 MPa, 60 MPa, and 90 MPa, respectively, with a holding time of 5 min. The samples after the pressure test were collected for specific surface area testing (the specific surface area test was performed using the BET method for determination of the specific surface area of ​​solid substances by gas adsorption in accordance with GB / T 19587-2017). The specific surface area data for each embodiment and comparative example after different test pressures are summarized in Table 4.

[0158] Compare the changes in specific surface area as pressure increases. 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 pores exposed after the material is crushed.

[0159] Table 4

[0160] Electrochemical performance test:

[0161] ① The negative electrode active material prepared in the above embodiments and comparative examples, a conductive agent (specifically acetylene black), and a binder (specifically polyacrylic acid PAA) were added to a solvent (specifically water) in a mass ratio of 8:1:1, mixed evenly, and then coated on a copper foil. After drying, rolling, and slitting, the negative electrodes of the embodiments and comparative examples were obtained.

[0162] ② Using a metallic lithium sheet as a counter electrode and a polyethylene / polypropylene composite film as a diaphragm, the counter electrode, diaphragm, and counter electrode are stacked, and an electrolyte is injected to prepare a button battery. The electrolyte is a lithium salt (specifically lithium hexafluorophosphate LiPF6) solution with a concentration of 1 mol / L, and the solvent is a mass ratio of EC:EMC:DMC:DEC:FEC of 23:25:24:28:15. The above-mentioned 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 fluoroacetone.

[0163] ③ First coulombic efficiency test: The button cells of each embodiment and comparative example were discharged at a constant current of 0.01C to 0.005V at 25±2°C, and then charged to 1.5V at a constant current of 0.1C. The first discharge capacity and the first charge capacity of the battery were recorded. First coulombic efficiency = first constant current charge capacity / first constant current discharge capacity. The results are summarized in Table 5.

[0164] ④ Initial expansion rate test: Before assembling button batteries, the original thickness of the negative electrode sheet of each embodiment and comparative example was measured with a micrometer. Button batteries were assembled according to the aforementioned parameters and charged to 100% SOC (state of charge). The button batteries were disassembled, the negative electrode sheet was removed, cleaned with dichloromethane (DCM), dried, and its thickness was measured again. Initial expansion rate = [(negative electrode sheet thickness at 100% SOC - copper foil thickness) - (original thickness of negative electrode sheet - copper foil thickness)] / (original thickness of negative electrode sheet - copper foil thickness) × 100%. The results are summarized in Table 5.

[0165] ⑤ The negative electrodes of each embodiment and comparative example were assembled with a ternary positive electrode or a lithium iron positive electrode laminate to form a soft-pack battery. The soft-pack battery was subjected to a charge-discharge cycle test at 25±2°C. Specifically, the battery was charged at a constant current of 0.33C to 3.8V, then charged at a constant voltage of 0.05C to cut off; left for 10 minutes; and discharged at a constant current of 0.33C to 2.0V. This cycle was repeated. The battery capacity and capacity retention after 100 cycles were tested. The results are summarized in Table 5.

[0166] Table 5

[0167] Combining the data in Tables 1 to 5, it can be found that the porous carbon provided in the embodiments of the present disclosure is used as a matrix and silane is further deposited to obtain a negative electrode active material that can achieve a higher compaction density while also having lower powder resistivity, lower expansion rate, higher first discharge capacity and better cycle performance.

[0168] The above is an exemplary embodiment of the present disclosure. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present disclosure. These improvements and modifications are also considered to be within the scope of protection of the present disclosure.

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 of pores with a pore diameter <2 nm accounts for 70%-95%, the volume of pores with a pore diameter of 2 nm ≤ pore diameter ≤ 10 nm accounts for 2%-12%, the volume of pores with a pore diameter of 10 nm < pore diameter ≤ 50 nm accounts for 1%-18%, and the volume of pores with a pore diameter > 50 nm accounts for 0-23%.

2. The porous carbon according to claim 1, characterized in that, The volume proportion of pores with a pore diameter of 10 nm < ≤ 30 nm is 2%-10%, and the volume proportion of pores with a pore diameter of 30 nm < ≤ 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 of pores with a pore diameter of more than 50 nm accounts for 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 size 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 a porous carbon according to any one of claims 1-6, characterized in that, include: The carbon matrix is ​​activated to obtain the porous carbon.

8. The preparation method according to claim 7, characterized in that, The activation treatment comprises an alkali activation treatment, a water vapor activation treatment and a carbon dioxide activation treatment performed in sequence; or The activation treatment includes alkali activation treatment and mixed gas activation treatment, and the mixed gas includes water vapor and carbon dioxide.

9. The preparation method according to claim 8, characterized in that, The alkali activation treatment, the steam activation treatment, and the carbon dioxide activation treatment performed in sequence include: The carbon matrix is ​​mixed with a base, reacted at 650° C. to 850° C. for 2 h to 4 h, and washed to obtain a first material; The first material is reacted in a water vapor environment at 500° C.-800° C. for 2 h-4 h to obtain a second material; The second material is reacted 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 char, the carbonization temperature is 500° C.-1500° C., and the carbonization time is 2 h-8 h.

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

12. The negative electrode active material according to claim 11, characterized in that, The carbon-containing composite particles are silicon-carbon particles, and the material of the nanoparticles contains silicon alone; a region with a thickness of 5nm-20nm extending from the surface 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 comprises a coating layer disposed on the surface of the carbon-containing composite particles, wherein the material of the coating layer comprises conductive carbon and / or a fast ion conductor material; The coating layer has a thickness of 10 nm to 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 silicon element accounts for 40wt.%-50wt.% of the mass of the silicon-carbon particles.

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

16. A method for preparing a negative electrode active material, characterized in that, include: Nanoparticles are deposited in the porous carbon according to any one of claims 1 to 6 to form carbon-containing composite particles to obtain negative electrode active materials; the material of the nanoparticles comprises 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, and the material of the nanoparticles contains silicon. Depositing the nanoparticles in the porous carbon includes: 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 negative electrode active material.

18. The method for preparing the negative electrode active material according to claim 17, wherein, The silicon source includes silane, and the deposited nanoparticles contain elemental silicon.

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

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

21. An electrochemical device (10), characterized in that, The electrochemical device (10) includes a negative electrode (20), and the negative electrode (20) includes the negative electrode active material according to any one of claims 11 - 15 or the negative electrode active material prepared by the preparation method of the negative electrode active material according to any one of claims 16 - 20.

22. An electrical device (1), characterized in that, The electrical equipment (1) includes the electrochemical device (10) according to claim 21.

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