Porous carbon as well as preparation method and application thereof

Abstract

The invention relates to the field of negative electrode materials, and discloses porous carbon and a preparation method and application thereof. The preparation method of the porous carbon comprises the following steps: mixing a carbonized material with a strong oxidant, carrying out chemical activation at a temperature lower than the decomposition temperature of the strong oxidant or a decomposition product thereof, and carrying out physical activation on the chemically activated material. According to the invention, the strong oxidant or the decomposition product thereof is slowly decomposed at low temperature, intercalation pore forming is carried out in the carbonized material, and oxidation reaction with the carbonized material is carried out, so that primary pores and oxidation active sites are formed on the surface of the carbonized material; primary pores are extruded to enhance the pore wall strength while physical activation pore forming is carried out, so that porous carbon which is rich in pore channel structure, concentrated on micropores and high in framework strength is formed, the pore volume and the micropore proportion of the porous carbon are increased, and the expansion of the silicon-carbon negative electrode is relieved. And no special treatment step exists between the two activation procedures, so that continuous operation can be realized, the dosage of chemicals and process energy consumption can be greatly reduced, and environment-friendly and energy-saving production is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of negative electrode materials, in particular to a porous carbon and a preparation method and application thereof. BACKGROUND

[0002] With the decreasing of fossil energy, electrochemical energy plays an increasingly important role in many fields such as power transportation, wind power and photovoltaic systems, power transmission and frequency modulation, energy storage, consumer electronics and electric tools due to its high efficiency and environmental protection. The improvement of energy density is the most concerned research direction of electrochemical energy technology.

[0003] Lithium ion battery is a representative of energy type electrochemical energy storage device, which has the typical advantage of high energy density. However, the index of mainstream negative electrode material graphite of lithium ion battery is close to the theoretical value, which limits the further improvement of its capacity. It is found that the theoretical specific capacity of silicon can reach 4200mAh / g, so the industry has gradually focused on silicon-based materials as the key of future negative electrode material development.

[0004] In recent years, the new type of silicon-carbon material using porous carbon to deposit nano-silicon has attracted widespread attention in the industry due to its excellent capacity and cycle performance. Accordingly, the development of porous carbon has also been increasingly valued in the industry. At present, there are mainly two ways to produce porous carbon: physical activation and chemical activation. The physical activation is to pass high-temperature gas into the carbon source to form pore structure by extruding the active sites of the carbon source with high-temperature gas. The disadvantage is that the activation energy consumption is high, the pore volume formed is low, and the silicon particle deposition space is small, resulting in low silicon-carbon negative electrode capacity. Chemical activation is to use activators (such as strong alkali) to etch the surface and interior of the carbon source to form pore structure. Although the activation efficiency is relatively high, a large amount of high-risk chemical reagents need to be consumed in the activation process, resulting in complex activation process, difficult process control, easy environmental pollution, high activation cost, and a large number of micropores formed by chemical activation, which are distributed in disorder, so that nano-silicon cannot be deposited in order, resulting in low pore utilization rate and a large number of closed pores in the material, which can easily collapse the pore structure of the silicon-carbon negative electrode in the charging and discharging process. Therefore, it is necessary to improve the preparation method of porous carbon to reduce the process energy consumption and obtain porous carbon with large pore volume and high micropore ratio, which can be used to alleviate the expansion of silicon-carbon negative electrode in the charging and discharging process. SUMMARY

[0005] The present application provides a preparation method of porous carbon, which aims to at least solve one of the above problems to some extent.

[0006] The present application also provides a low-expansion silicon-carbon material and its application.

[0007] In a first aspect, the present application provides a preparation method of porous carbon, comprising the following steps:

[0008] mixing the carbonized material with a strong oxidant and then performing chemical activation at a temperature lower than the decomposition temperature of the strong oxidant or its decomposition products;

[0009] performing physical activation on the material after chemical activation.

[0010] In an alternative embodiment, the mass ratio of the carbonized material to the strong oxidant is 10-20:1.

[0011] In an alternative embodiment, the temperature of the chemical activation is 60%-70% of the decomposition temperature of the strong oxidant or its decomposition products.

[0012] In an alternative embodiment, the time of the chemical activation is 1h-10h.

[0013] In an alternative embodiment, the strong oxidant is selected from at least one of sodium percarbonate, ammonium persulfate, and potassium permanganate.

[0014] In an alternative embodiment, the conditions of the physical activation include first passing in an inert protective gas and then heating to 650℃-950℃ at a programmed rate, and then passing in high-temperature water vapor.

[0015] In an alternative embodiment, the programmed heating rate is 5℃ / min-10℃ / min.

[0016] In an alternative embodiment, the passing-in speed of the high-temperature water vapor is 1L / min-5L / min.

[0017] In an alternative embodiment, the passing-in time of the high-temperature water vapor is 1h-5h.

[0018] In an alternative embodiment, the preparation method further includes sequentially performing acid washing, water washing, and heat treatment in an inert atmosphere on the material after physical activation.

[0019] In an alternative embodiment, the temperature of the heat treatment is 700℃-1100℃, and the time is 0.5h-5h.

[0020] In a second aspect, the present application provides a porous carbon prepared by the preparation method of the first aspect of the present application.

[0021] In an alternative embodiment, the porous carbon has a pore volume of 0.75cm 3 / g-0.95cm 3 / g, and the volume fraction of micropores is 72%-86%.

[0022] In a third aspect, the application further provides a silicon-carbon material, comprising nano-silicon and the porous carbon according to the second aspect of the application, wherein the nano-silicon is deposited in the pores and on the surface of the porous carbon.

[0023] In a fourth aspect, the application further provides a negative electrode sheet, comprising:

[0024] a negative current collector and a negative active material layer arranged on at least one side of the negative current collector, wherein the negative active material layer comprises the silicon-carbon material according to the third aspect of the application.

[0025] In a fifth aspect, the application further provides a secondary battery, comprising the negative electrode sheet according to the fourth aspect of the application.

[0026] In a sixth aspect, the application further provides an electric device, comprising the secondary battery according to the fifth aspect of the application.

[0027] The technical solution of the application has the following advantages:

[0028] 1. The preparation method of the porous carbon provided by the application first mixes the carbonized material with the strong oxidizing agent, and then performs chemical activation at a temperature lower than the decomposition temperature of the strong oxidizing agent or its decomposition product. The slow decomposition of the strong oxidizing agent or its decomposition product at low temperature continuously inserts and forms pores in the carbonized material and causes oxidation reaction with the carbonized material, thereby forming primary pores and oxidation active sites on the surface of the carbonized material. Then, the physical activation is performed to form pores and extrude the primary pores to enhance the strength of the pore walls, thereby forming the porous carbon with rich pore channel structure and high skeleton strength, which is concentrated in micropores, and further increasing the pore volume and micropore ratio of the porous carbon to relieve the expansion of the silicon-carbon negative electrode during the charging and discharging process.

[0029] Moreover, the preparation method of the application has no special treatment step between the two activation processes of chemical activation and physical activation, and can realize continuous operation. At the same time, the preparation method of the application uses the strong oxidizing agent or its decomposition product to oxidize the raw material, which not only significantly reduces the subsequent activation time, but also greatly reduces the chemical consumption, thereby reducing the process energy consumption and realizing environmentally friendly and energy-saving production.

[0030] 2. In the preparation method of the porous carbon provided by the application, the mass ratio of the carbonized material to the strong oxidizing agent is 10-20:1, which can ensure that the carbonized material can form rich pore channel structure and be concentrated in micropores after chemical activation, thereby improving the pore volume and micropore ratio of the porous carbon.

[0031] 3. In the preparation method of the porous carbon provided by the application, the temperature of chemical activation is 60%-70% of the decomposition temperature of the strong oxidizing agent or its decomposition product, and the time is 1h-10h. This condition can ensure the slow decomposition of the strong oxidizing agent or its decomposition product, thereby being more conducive to forming the porous carbon with rich pore channel structure, high micropore ratio and large pore volume.

[0032] 4. The preparation method of the porous carbon provided in the application, wherein the physical activation conditions comprise first passing in inert protective gas and heating in a programmed temperature rising manner to 650-950 DEG C, and then passing in high-temperature water vapor, so as to ensure sufficient oxidation of the carbonized material on the one hand, and prevent the material temperature from reaching the ignition point on the other hand, thereby being more conducive to forming the porous carbon with rich pore structure, high micropore ratio and large pore volume.

[0033] 5. The preparation method of the porous carbon provided in the application, further comprising sequentially performing acid pickling, water washing and heat treatment in an inert atmosphere on the material after physical activation, so that the heat treatment process can remove the residual oxygen-containing heteroatoms after activation and acid pickling, further improve the pore volume, and on the other hand, promote partial graphitization, increase the material strength, and relieve the expansion of the silicon-carbon negative electrode in the charging and discharging process.

[0034] 6. The porous carbon provided in the application, which has large pore volume and high micropore ratio, can be used as a skeleton structure for the production of silicon-carbon negative electrodes, can improve the silicon loading of the silicon-carbon negative electrode, reduce the expansion of the silicon-carbon negative electrode in the charging and discharging process of the secondary battery, and further improve the cycle life and initial efficiency of the secondary battery.

[0035] 7. The negative electrode sheet provided in the application, which adopts the porous carbon with large pore volume and high micropore ratio provided in the application, and thus has high silicon loading, can reduce the expansion of the silicon-carbon negative electrode in the charging and discharging process of the secondary battery, and further improve the cycle life and initial efficiency of the secondary battery.

[0036] 8. The secondary battery provided in the application, which adopts the negative electrode sheet provided in the application, and thus has the advantages of long cycle life and high initial efficiency. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description herein is for describing the specific embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having", and any variations thereof, are intended to cover a non-exclusive inclusion.

[0039] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all referring to a common embodiment, or an embodiment that is independent of other embodiments. One of ordinary skill in the art will readily recognize from the disclosure herein, that embodiments of the present application can be combined with embodiments of the other applications.

[0040] “Ranges” disclosed herein are defined, described and covered by the lower and upper limits of the range, given that the range is defined by selecting a lower limit and an upper limit, the selected lower limit and upper limit defining the boundaries of the particular range. Ranges defined by the lower and upper limits can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed, it is understood that ranges of 60-110 and 80-120 are also contemplated. Also, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4 and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise indicated, a numerical range“a-b” means a shorthand way of describing each and every intervening real number, between a and b, wherein a and b are both real numbers. For example, the numerical range“0-5” means that all real numbers between“0-5” have been listed herein, and“0-5” is merely a shorthand way of describing these numerical combinations. Also, when it is stated that a parameter is an integer > 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] In the description of the embodiments of the present application, the term“and / or” is merely used to describe associated objects, and can represent the following three meanings: A and / or B can represent that there are three cases, i.e., A exists alone, both A and B exist, and B exists alone. In addition, the character“ / ” in the present application generally represents an“or” relationship between the front and rear associated objects.

[0042] From the perspective of cost and application field requirements, the current production method of porous carbon is mainly physical activation, which has the disadvantages of high activation energy consumption, low pore volume, and small silicon particle deposition space, resulting in low silicon-carbon negative electrode specific capacity. Although chemical activation has relatively high activation efficiency, it also has the problem of high activation cost, and the utilization rate of the pores generated by chemical activation is low and there are many closed pores, so the pore structure of the silicon-carbon negative electrode prepared thereby is prone to collapse during the charging and discharging process.

[0043] In order to solve the problems in the related art, according to a first aspect of the present application, a method for preparing porous carbon is provided, comprising the following steps:

[0044] mixing the carbonized material with a strong oxidizing agent and then performing chemical activation at a temperature lower than the decomposition temperature of the strong oxidizing agent or its decomposition products;

[0045] performing physical activation on the material after chemical activation.

[0046] The method for preparing porous carbon provided in the present application first mixes carbonized material with a strong oxidizing agent and then performs chemical activation at a temperature lower than the decomposition temperature of the strong oxidizing agent or its decomposition products. The slow decomposition of the strong oxidizing agent or its decomposition products at low temperature continuously intercalates and creates pores in the carbonized material and causes oxidation reaction with the carbonized material, thereby forming primary pores and oxidation active sites on the surface of the carbonized material. Then, physical activation is performed to create pores and at the same time extrude the primary pores to enhance the strength of the pore walls, thereby forming porous carbon with rich pore channel structure and concentrated micropores and high skeleton strength. This further increases the pore volume and the proportion of micropores in the porous carbon and relieves the expansion of the silicon-carbon negative electrode during the charging and discharging process. Moreover, the preparation method of the present application has no special treatment steps between the two activation processes of chemical activation and physical activation, and can realize continuous operation. At the same time, the preparation method of the present application uses a strong oxidizing agent to oxidize the raw material, which not only significantly reduces the subsequent activation time, but also greatly reduces the chemical consumption, thereby reducing the process energy consumption and realizing environmentally friendly and energy-saving production.

[0047] As understood by those skilled in the art, the demand for nano-silicon particles by the silicon-carbon material is that the smaller the particle size is, the more advantageous it is. Therefore, the proportion of micropores in the porous carbon is high, and the pore channel structure can limit the growth of nano-silicon particles during silicon deposition and also limit the expansion of nano-silicon during the charging and discharging process. According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), pores with a pore size less than 2 nm are called micropores, pores with a pore size greater than 50 nm are called macropores, and pores with a pore size between 2 nm and 50 nm are called mesopores or called mesopores. The meaning of micropores in the present application is as described above.

[0048] The mechanisms of oxidation of different types of strong oxidizing agents are different. Some strong oxidizing agents can directly produce active oxygen through self-decomposition, and some strong oxidizing agents can produce active oxygen through secondary decomposition of the decomposition products formed by self-decomposition. Therefore, the decomposition temperature of the strong oxidizing agent or its decomposition product has a greater impact on the chemical activation effect. The present application found that chemical activation under the condition of 60%-70% of the decomposition temperature of the strong oxidizing agent or its decomposition product can ensure the slow decomposition of the strong oxidizing agent or its decomposition product, thereby being more conducive to the formation of porous carbon with abundant pore structure, high proportion of micropores, large pore volume, and high skeleton strength. If the chemical activation temperature is too high, the decomposition of the strong oxidizing agent or its decomposition product is too fast, causing the oxidation activation of the carbonized material to occur only in a local area, and the desired oxidation activation effect cannot be achieved. Conversely, if the chemical activation temperature is too low, the decomposition of the strong oxidizing agent or its decomposition product is incomplete, and the oxidation activation effect on the carbonized material is limited, and the desired activation effect cannot be achieved. In some embodiments, for example, sodium percarbonate is used as a strong oxidizing agent, and since its oxidizing property is mainly manifested by the decomposition of H2O2, H2O2 will decompose violently at a temperature higher than 100°C, resulting in loss of control. Therefore, when sodium percarbonate is used for chemical activation, the activation temperature can be controlled within 60°C, 65°C, 70°C, or within a range consisting of any of the above values. In some embodiments, for example, ammonium persulfate is used as a strong oxidizing agent, and the decomposition temperature of ammonium persulfate is 120°C. Therefore, the activation temperature can be controlled within 72°C, 75°C, 80°C, 84°C, or within a range consisting of any of the above values. In some embodiments, for example, potassium permanganate is used as a strong oxidizing agent, and its decomposition temperature is around 240°C. Therefore, the chemical activation temperature can be 145°C, 155°C, 165°C, or within a range consisting of any of the above values.

[0049] In an alternative embodiment, the chemical activation time is 1h-10h, thereby ensuring sufficient oxidation of the carbonized material. If the activation time is too long, a large amount of electrical energy will be consumed, resulting in energy waste. Conversely, if the activation time is too short, the decomposition of the strong oxidizing agent or its decomposition product is incomplete, and the oxidation activation effect on the carbonized material is limited. For example, the chemical activation time can be 1h, 3h, 5h, 7h, 9h, 10h, or within a range consisting of any of the above values.

[0050] In an alternative embodiment, the mass ratio of the carbonized material to the strong oxidizing agent is 10-20:1, which can ensure that the carbonized material forms a rich pore structure and focuses on micropores, thereby improving the pore volume and micropore ratio of the porous carbon. For example, the ratio can be 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, or within a range defined by any of the above values. The applicant has found that if the mass ratio of the carbonized material to the strong oxidizing agent is less than 10:1, the carbonized material will be oxidized to a high degree and will not form the pore structure required for subsequent physical activation, and the strength of the material skeleton will be reduced. Conversely, if the mass ratio of the carbonized material to the strong oxidizing agent is greater than 20:1, the oxidation and activation of the carbonized material will be limited, and the desired activation effect will not be achieved.

[0051] In an alternative embodiment, the conditions for physical activation include first passing an inert protective gas and heating to 650-950°C in a programmed temperature rise, and then passing high-temperature steam. For example, the temperature during the physical activation stage can be raised to 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or within a range defined by any of the above values, which can ensure sufficient oxidation of the carbonized material and prevent the material temperature from reaching the ignition point, thereby more favorably forming a porous carbon with a rich pore structure, a high micropore ratio, a large pore volume, and a high skeleton strength. The applicant has found that if the heating temperature during the physical activation stage is too high, the carbonized material will be activated to a high degree and the pore structure distribution will change, and the number of micropores will be greatly reduced. Conversely, if the heating temperature is too low, the activation degree will be low, and the pore structure required for the subsequent step will not be formed.

[0052] In an alternative embodiment, the inert protective gas is at least one selected from nitrogen, helium, neon, and argon. It can be understood that under the protection of the above-mentioned inert protective gas, the carbon material can be prevented from self-igniting at a high temperature.

[0053] In an alternative embodiment, the programmed temperature rise rate is 5-10°C / min. The applicant has found that a slower temperature rise rate can make the material temperature uniform, ensuring the effectiveness and uniformity of the activation process. If the temperature rise rate is too fast, there will be a temperature difference between the device display temperature and the actual temperature, making it difficult to ensure the effectiveness and uniformity of the activation process, and conversely, the experimental time will be greatly prolonged, causing energy waste. For example, the temperature rise rate during the physical activation stage can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or within a range defined by any of the above values.

[0054] In an alternative embodiment, the temperature of the high-temperature water vapor is 150°C to 400°C. For example, the temperature of the high-temperature water vapor can be 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, or within a range defined by any of the foregoing values.

[0055] In an alternative embodiment, the high-temperature water vapor is introduced at a rate of 1 L / min to 5 L / min. For example, the high-temperature water vapor can be introduced at a rate of 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, or within a range defined by any of the foregoing values. Applicant has found that a lower rate of introduction ensures that the pore formation proceeds normally. If the rate of introduction is too high, the pore formation rate will be too fast, and the micropores will expand rapidly into mesopores and macropores. Conversely, if the rate of introduction is too low, the pore formation efficiency will be reduced, and the activation time will be greatly extended, resulting in a waste of electrical energy.

[0056] In an alternative embodiment, the high-temperature water vapor is introduced for a time period of 1 h to 5 h. For example, the high-temperature water vapor can be introduced for a time period of 1 h, 2 h, 3 h, 4 h, 5 h, or within a range defined by any of the foregoing values. Applicant has found that if the physical activation time is too long, the pore structure of the porous carbon will change, and the microporous pore structure required in the subsequent steps will not be formed. Conversely, if the physical activation time is too short, the degree of activation will be low, and the generated pore structure will be less.

[0057] In an alternative embodiment, the preparation method further comprises sequentially performing acid washing, water washing, and heat treatment in an inert atmosphere on the material after the physical activation. It can be understood that the acid washing can dissolve the metal impurities in the porous carbon, the water washing can remove the acid and the dissolved metal ions remaining from the acid washing process, and the heat treatment process can remove the oxygen-containing heteroatoms remaining after the activation and acid washing, to further increase the pore volume. In addition, the heat treatment process can also promote partial graphitization, increase the material strength, and alleviate the expansion of the silicon-carbon negative electrode during the charging and discharging process.

[0058] In an alternative embodiment, the temperature of the heat treatment is 700-1100℃, and the time is 0.5-5h. For example, the temperature of the heat treatment can be 700℃, 800℃, 900℃, 1000℃, 1100℃, or within a range defined by any of the above values; the time of the heat treatment can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 5h, or within a range defined by any of the above values. The applicant has found that if the temperature of the heat treatment is too high, the pore structure will collapse, the pore volume of the porous carbon will decrease, and the deposition space of the nano-silicon will become smaller, thereby affecting the capacity of the silicon-carbon negative electrode; on the contrary, if the temperature of the heat treatment is too low, the oxygen-containing functional groups on the surface of the porous carbon will remain, and oxidation will occur during the subsequent deposition of the nano-silicon, causing the nano-silicon particles to fall off; if the time of the heat treatment is too long, a large amount of electric energy will be consumed; on the contrary, the oxygen-containing functional groups on the surface of the porous carbon will remain, and oxidation will occur during the subsequent deposition of the nano-silicon, causing the nano-silicon particles to fall off.

[0059] In an alternative embodiment, the carbonized material is obtained by carbonizing a carbon source under an inert atmosphere and crushing it to 10-20μm, and the carbon source is selected from at least one of forestry biomass, agricultural and forestry residues, and organic polymers. It can be understood that forestry biomass refers to all organic matter formed by photosynthesis of green plants in forests, mainly including oil, starch, and fiber resources, and cutting, tending, processing residues and waste, etc., such as bamboo, wood, etc.; agricultural and forestry residues include agricultural residues and forestry three residues, agricultural residues include crop straw and agricultural product processing residues (such as peanut shells, rice husks, corn cobs, apricot shells, etc.), and forestry three residues mainly refer to cutting residues (such as branches, bark, leaves, roots, shrubs, etc.), processing residues (such as sawdust, shavings, etc.), and the like; organic polymers are a class of macromolecules formed by one or more molecules or molecular groups combined by covalent bonds to have multiple repeating monomer units, which can be natural products such as starch, fiber, etc., or can be obtained by synthetic methods, such as synthetic resins (phenolic resin), synthetic fibers, synthetic rubber, etc. The above-mentioned carbon sources can be applied to the present application, so that the preparation method of the present application has a wide application range and is not limited by raw materials, which is conducive to reducing production costs. As for the carbonization process, the present application uses the existing conventional carbonization process conditions, which are generally known by those skilled in the art, and therefore will not be described in detail.

[0060] According to a second aspect of the present application, a porous carbon is provided, which is prepared by the method of preparing a porous carbon according to the first aspect of the present application.

[0061] In an alternative embodiment, the pore volume of the porous carbon is 0.75-0.95cm 3 / g-0.95cm 3 / g, 0.90 cm3 / g, 0.95 cm3 / g, etc. or within a range formed by any of the above values; the volume percentage of micropores can be 72%, 75%, 78%, 80%, 83%, 86%, etc. or within a range formed by any of the above values. 3 / g, 0.80 cm 3 / g, 0.85 cm 3 / g, 0.90 cm 3 / g, 0.95 cm 3 / g, 0.95 cm

[0062] The porous carbon provided by the present application has a large pore volume and a high percentage of micropores, and can be used as a skeleton structure for deposition of silicon particles to produce a silicon-carbon negative electrode, thereby improving the silicon loading of the silicon-carbon negative electrode, reducing the expansion of the silicon-carbon negative electrode during the charging and discharging process of a secondary battery, and further improving the cycle life and initial efficiency of the secondary battery.

[0063] According to a third aspect of the present application, a silicon-carbon material is also provided, which comprises nanosilicon and the porous carbon according to the second aspect of the present application, and the nanosilicon is deposited in the pores and on the surface of the porous carbon.

[0064] Regarding the silicon deposition process, the present application uses existing conventional silicon deposition process conditions, which are generally known by those skilled in the art, and thus will not be described herein.

[0065] According to a fourth aspect of the present application, a negative electrode sheet is also provided, which comprises:

[0066] a negative current collector and a negative active material layer arranged on at least one side of the negative current collector, wherein the negative active material layer comprises the silicon-carbon material according to the third aspect of the present application.

[0067] The negative electrode sheet provided by the present application uses the porous carbon provided by the present application, which has a large pore volume and a high percentage of micropores, and thus has a high silicon loading, and can reduce the expansion of the electrode sheet during the charging and discharging process of a secondary battery, thereby improving the cycle life and initial efficiency of the secondary battery.

[0068] According to a fifth aspect of the present application, a secondary battery is also provided, which comprises the negative electrode sheet according to the fourth aspect of the present application. The secondary battery provided by the present application uses the negative electrode sheet provided by the present application, and thus has the advantages of long cycle life and high initial efficiency.

[0069] Generally, the secondary battery further includes a positive electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are inserted into and extracted from the positive electrode sheet and the negative electrode sheet, the electrolyte serves to conduct the ions between the positive electrode sheet and the negative electrode sheet, and the separator is disposed between the positive electrode sheet and the negative electrode sheet to prevent short circuiting between the positive electrode and the negative electrode, while allowing the ions to pass through.

[0070] The secondary battery of the present application is described below with reference to a lithium ion battery as an example.

[0071] [Negative electrode sheet]

[0072] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode active material layer is disposed on either one or both of the two surfaces of the negative electrode current collector.

[0073] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0074] In some embodiments, the negative electrode active material layer does not exclude other negative electrode active materials other than the silicon-carbon material described in the third aspect of the present application. For example, the other negative electrode active material can be a negative electrode active material known in the art for use in a lithium ion battery. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a tin-based material, and lithium titanate, etc. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy.

[0075] In some embodiments, the negative electrode active material layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0076] In some embodiments, the negative electrode active material layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In some embodiments, the negative active material layer can also optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

[0078] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, and the like, the negative electrode sheet can be obtained.

[0079] [Positive electrode sheet]

[0080] The positive electrode sheet includes a positive electrode current collector and a positive active material layer disposed on at least one surface of the positive electrode current collector.

[0081] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive active material layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0082] The positive active material layer includes a positive active material, which can be selected from materials capable of absorbing and releasing lithium. The specific type of the positive active material in the present application is not particularly limited and can be selected as needed. As an example, the positive active material can include, but is not limited to, lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), iron pyrophosphate (Li2FeP2O7), lithium cobaltate (LiCoO2), spinel lithium manganate (LiMn2O4), spinel lithium nickel manganate (LiNi 0.5 Mn 1.5 O4), layered lithium manganate (LiMnO2), lithium nickelate (LiNiO2), lithium niobate (LiNbO2), lithium ferrate (LiFeO2), lithium magnesiumate (LiMgO2), lithium calciumate (LiCaO2), lithium copperate (LiCuO2), lithium zincate (LiZnO2), lithium molybdate (LiMoO2), lithium tantalate (LiTaO2), lithium tungstate (LiWO2), lithium nickel cobalt aluminum oxide (LiNi x Co y Al 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example, LiNi 0.8 Co 0.15 Al 0.05 O2), lithium nickel cobalt manganese oxide (LiNi x Co y Mn 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example, LiNi 1 / 3 Co1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.), lithium-rich materials (e.g., lithium-rich nickel cobalt manganese oxide), manganese oxide (MnO2), vanadium oxide, sulfur oxide, silicate oxide, and each modified compound thereof. These materials can be used alone or in combination with two or more.

[0083] The modified compound of each of the above positive electrode active materials can be a modification by doping, a modification by surface coating, or a modification by doping and coating at the same time.

[0084] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0085] In some embodiments, the positive electrode active material layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0086] In some embodiments, the positive electrode active material layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the positive electrode tab can be prepared by dispersing the above components for preparing the positive electrode tab, e.g., the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and subjecting to a drying, cold-pressing, or the like process to obtain the positive electrode tab.

[0088] [Electrolyte]

[0089] The electrolyte functions to conduct ions between the positive electrode and the negative electrode. The type of electrolyte is not particularly limited in the present application and can be selected as desired. For example, the electrolyte can be liquid, gel, or solid.

[0090] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0091] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0092] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0093] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive that improves certain properties of the battery, such as an additive that improves overcharge performance of the battery, an additive that improves high or low temperature performance of the battery, etc.

[0094] In some embodiments, the electrolyte employs a solid-state electrolyte, which can be any of various lithium ion solid-state electrolytes commonly used in the art. Lithium ion solid-state electrolytes are exemplified herein, including but not limited to:

[0095] LISICON type: such as γ-Li3PO4, etc.

[0096] NASICON type: such as Li (1+x1) Q x M (2-x1) (PO4)3, 0≤x1<1, Q includes at least one of Al, Cr, Ba, Fe, Sc, In, Lu, Y, La;

[0097] Garnet type: such as Li (7-x2) La3Zr (2-x2) M x2 O 12and 0 < x2< 1, M includes at least one of Sb, Nb, Ta, Te, and W;

[0098] LIPON type: Li3PO4N, for example x3 PO y1 N z1 ; 0 < x3< 1, 0 < y1< 1, 0 < z1< 1;

[0099] Perovskite type: Li3BO3, for example x 4Q (2 / 3-x4) MO3, and 0.04 < x4< 0.17, Q includes at least one of La, Sr, Ba, and Nd, and M includes at least one of Al, Ti, and Ge;

[0100] Anti-Perovskite type: Li3OCl, for example;

[0101] Thio-LiSICON type: Li (3+x5) My2A (1-y2) Q (4-z2) T z2 , where -1 < x5< 2, 0 < y2< 1, 0 < z2< 2, M includes at least one of B, Al, In, Si, Ge, Sn, Ti, W, and Mo, A includes at least one of P, As, Sb, and Bi, Q includes at least one of S and Se, and T includes at least one of F, Cl, Br, and I;

[0102] Sulfide solid electrolyte, including: Thiophosphate type: Li3PS4, Argyrodite type: Li6PS5Cl, Halide type: Li3InCl6, Hydride type: 0.7Li(CB9H 10 )-0.3Li(CB 11 H 12 ) at least one; for example (10+x6) M (1+y3) A (2-y3) Q (12-z3) H z3Type: wherein -2 < x6 < 2, 0≤y3≤2, 0≤z3≤2, M includes at least one of B, Al, In, Si, Ge, Sn, Ti, W, Mo; A includes at least one of P, As, Sb, Bi, Q includes at least one of S, Se, H includes at least one of F, Cl, Br, I: (100-x7)Li2S-x7M-y4Q Type: wherein 20≤x7≤30, 0≤y4≤50, M includes at least one of B2S3, Al2S3, In2S3, SiS2, GeS2, SnS2, P2S5, As2S3, Sb2S5, Bi2S3, WS2, MoS2, Q includes at least one of B2O3, Al2O3, In2O3, SiO2, GeO2, SnO2, P2O5, Sb2O5, Bi2O3, WO2, WO3, MoO2, MoO3, Fe2O3, ZnO, MgO, CuO, CaO, LiN, Li2O, LiF, LiCl, LiBr, LiI; Argyrodite Type: Li (6+x8) M y5 A (1-y5) Q (5-z5) T (1+z5) wherein -1≤x8≤1, 0≤y5≤1, -1<z5≤1, M includes at least one of B, Al, In, Si, Ge, Sn, Ti, W, Mo, A includes at least one of P, As, Sb, Bi, Q includes at least one of S, Se, T includes at least one of F, Cl, Br, I; Halide Type: Li3MJ or Li2Sc 2 / 3 J; M includes at least one of Y, Er, In, Sc, Ga, J includes at least one of F, Cl, Br, I.

[0103] When the above-mentioned sulfide solid electrolyte is a sulfide type solid electrolyte, it includes but is not limited to: argyrodite electrolyte; Li2S-P2S5, Li2S-SiS2, Li2S-GeS and Li2S-B2S3, etc. binary sulfide type solid system, Li2S-Me-P2S5 ternary system, wherein Me is selected from Si, Ge, Sn or Al, etc.

[0104] Specifically, the above-mentioned sulfide electrolyte is selected from at least one of Li2S-P2S5, Li2S-SiS2, Li2S-GeS, Li2S-B2S3 and Li2S-Me-P2S5.

[0105] [Separation membrane]

[0106] The kind of the separation membrane is not particularly limited in the present application, and any known porous structure separation membrane with good chemical stability and mechanical stability can be selected.

[0107] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0108] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film in the secondary battery can be made into an electrode assembly through a roll-pressing process or a stacking process.

[0109] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0110] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0111] The shape of the secondary battery according to the present application is not particularly limited, and can be cylindrical, square, or any other shape.

[0112] According to a sixth aspect of the present application, a power consuming device is also provided, which includes the secondary battery according to the fifth aspect of the present application. The power consuming device provided by the present application has the advantages of long cycle life and high initial efficiency, because it uses the secondary battery provided by the present application.

[0113] In some embodiments, the power consuming device can also include a battery module or a battery pack assembled from the secondary battery. The secondary battery, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include, but is not limited to, a mobile device (such as a mobile phone, a notebook computer, or the like), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, or the like), an electric train, a ship or a satellite, an energy storage system, or the like.

[0114] As the power consuming device, the secondary battery, the battery module, or the battery pack can be selected according to the requirements of the power consuming device. As an example of the power consuming device, a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, or the like, in order to meet the requirements of high power and high energy density of the secondary battery for the power consuming device, a battery pack or a battery module can be used.

[0115] As another example, the power consuming device can be a mobile phone, a tablet computer, a notebook computer, etc. The device generally requires thinning, and a secondary battery can be used as a power source.

[0116] The application will be further described in conjunction with specific embodiments, which should not be construed as limiting the scope of the application.

[0117] Embodiment 1

[0118] The preparation method of the porous carbon provided in the embodiment includes the following steps:

[0119] (1) After drying apricot shells at 110°C for 3h, the apricot shells were placed in a box furnace, high-purity argon was continuously introduced, the temperature was raised to 700°C and maintained for 2h, and then the apricot shells were cooled, crushed to 20μm, and apricot shell carbonized material was obtained.

[0120] (2) The apricot shell carbonized material and sodium percarbonate were mixed in an efficient mixing modifier at a mass ratio of 15:1 until complete dispersion, and the obtained mixture was transferred to a rotary kiln, the rotation speed was set to 5Hz, and the temperature was raised to 70°C and maintained for 1h.

[0121] (3) High-purity nitrogen was introduced into the rotary kiln and the temperature was raised to 900°C at a rate of 10°C / min, and then 250°C high-temperature water vapor was introduced into the rotary kiln at a flow rate of 5L / min, and the heating was stopped after 2h.

[0122] (4) After cooling under high-purity nitrogen atmosphere, the activated material was soaked in 35wt% hydrochloric acid aqueous solution for 2h, then washed with deionized water, dried, and then heat treated at 850°C under high-purity nitrogen atmosphere for 2h to obtain the porous carbon material.

[0123] Embodiment 2

[0124] Different from embodiment 1, the mass ratio of apricot shell carbonized material and sodium percarbonate in step (2) was 20:1.

[0125] Embodiment 3

[0126] Different from embodiment 1, the mass ratio of apricot shell carbonized material and sodium percarbonate in step (2) was 10:1.

[0127] Embodiment 4

[0128] Different from embodiment 1, the mass ratio of apricot shell carbonized material and sodium percarbonate in step (2) was 8:1.

[0129] Embodiment 5

[0130] Different from embodiment 1, the mass ratio of apricot shell carbonized material and sodium percarbonate in step (2) was 22:1.

[0131] Embodiment 6

[0132] Different from example 1, the heating temperature in step (2) is 50℃.

[0133] Example 7

[0134] Different from example 1, the heating temperature in step (2) is 90℃.

[0135] Example 8

[0136] Different from example 1, in step (2), ammonium persulfate is used instead of sodium carbonate and heated to 72℃ for 5h.

[0137] Example 9

[0138] Different from example 1, in step (2), potassium permanganate is used instead of sodium carbonate and heated to 155℃ for 10h.

[0139] Example 10

[0140] Different from example 1, in step (3), the flow rate of high-temperature steam is 3L / min.

[0141] Example 11

[0142] Different from example 1, in step (3), the flow rate of high-temperature steam is 7L / min.

[0143] Example 12

[0144] Different from example 1, in step (4), the heat treatment temperature is 700℃ and the time is 5h.

[0145] Example 13

[0146] Different from example 1, in step (4), the heat treatment temperature is 1100℃ and the time is 0.5h.

[0147] Example 14

[0148] Different from example 1, in step (4), the heat treatment process is omitted.

[0149] Example 15

[0150] The preparation method of the porous carbon provided in the embodiment comprises the following steps:

[0151] (1) After drying the thermosetting phenolic resin at 110℃ for 1h, it is placed in a box furnace, continuously passed with high-purity argon, heated to 900℃ for 2h, cooled, and crushed to 10μm to obtain resin carbonized material.

[0152] (2) The resin carbonization material and ammonium persulfate were mixed in a mass ratio of 12:1 in a high-efficiency mixing modifier machine until completely dispersed, and the obtained mixture was placed in a rotary kiln, the rotation speed was set to 5 Hz, and heating was performed to 80°C for 7 h.

[0153] (3) High-purity nitrogen was introduced into the rotary furnace, and the temperature was increased to 850°C at a rate of 5°C / min, then 300°C high-temperature water vapor was introduced at a flow rate of 1 L / min, and heating was stopped after 5 h of maintenance.

[0154] (4) After the activated material was cooled in a high-purity nitrogen atmosphere, it was soaked in a 35% wt aqueous hydrochloric acid solution for 1 h, washed with deionized water, dried, and then heat-treated at 950°C in a high-purity nitrogen atmosphere for 1 h to obtain a porous carbon material.

[0155] Example 16

[0156] The preparation method of the porous carbon provided in this example includes the following steps:

[0157] (1) The bamboo was dried at 110°C for 5 h, then placed in a box furnace, continuously introduced with high-purity argon, heated to 900°C for 2 h, cooled, and pulverized to 15 μm to obtain a bamboo carbonization material.

[0158] (2) The bamboo carbonization material and potassium permanganate were mixed in a mass ratio of 15:1 in a high-efficiency mixing modifier machine until completely dispersed, and the obtained mixture was transferred to a rotary kiln, the rotation speed was set to 5 Hz, and heating was performed to 165°C for 3 h.

[0159] (3) High-purity nitrogen was introduced into the rotary furnace, and the temperature was increased to 950°C at a rate of 7.5°C / min, then 300°C high-temperature water vapor was introduced at a flow rate of 2 L / min, and heating was stopped after 3 h of maintenance.

[0160] (4) After the activated material was cooled in a high-purity nitrogen atmosphere, it was soaked in a 35% wt aqueous hydrochloric acid solution for 1 h, washed with deionized water, dried, and then heat-treated at 1150°C in a high-purity nitrogen atmosphere for 1 h to obtain a porous carbon material.

[0161] Example 17

[0162] The preparation method of the porous carbon provided in this example includes the following steps:

[0163] (1) The starch was dried at 110°C for 1 h, then placed in a box furnace, continuously introduced with high-purity argon, heated to 900°C for 2 h, cooled, and pulverized to 20 μm to obtain a starch carbonization material.

[0164] (2) The starch carbonized material and sodium percarbonate were mixed in a high-efficiency mixing modifier at a mass ratio of 18:1 until completely dispersed, and the obtained mixture was placed in a rotary kiln, the rotation speed was set to 5 Hz, and heated to 70°C for 6 h.

[0165] (3) High-purity nitrogen was introduced into the rotary kiln, and the temperature was increased to 800°C at a rate of 6°C / min, then 300°C high-temperature water vapor was introduced at a flow rate of 5 L / min, maintained for 1 h, and then heating was stopped.

[0166] (4) After cooling in a high-purity nitrogen atmosphere, the activated material was soaked in a 35% wt aqueous hydrochloric acid solution for 1 h, washed with deionized water, dried, and then heat treated at 650°C in a high-purity nitrogen atmosphere for 1 h to obtain the porous carbon material.

[0167] Comparative Example 1

[0168] Unlike Example 1, sodium percarbonate was not used in step (2), i.e.:

[0169] The apricot shell carbonized material was directly placed in a rotary kiln and high-purity nitrogen was introduced, the temperature was increased to 650°C at a rate of 10°C / min, then 250°C high-temperature water vapor was introduced into the rotary kiln at a flow rate of 3 L / min, maintained for 2 h, and then heating was stopped; after cooling in a high-purity nitrogen atmosphere, the activated material was soaked in a 35% wt aqueous hydrochloric acid solution for 2 h, then washed with deionized water, dried, and then heat treated at 850°C in a high-purity nitrogen atmosphere for 2 h to obtain the porous carbon material.

[0170] Comparative Example 2

[0171] Unlike Example 1, step (3) was omitted, i.e.:

[0172] The apricot shell carbonized material and sodium percarbonate were mixed in a high-efficiency mixing modifier at a mass ratio of 15:1 until completely dispersed, and the obtained mixture was transferred to a rotary kiln, the rotation speed was set to 5 Hz, and heated to 70°C for 1 h; after cooling in a high-purity nitrogen atmosphere, the activated material was soaked in a 35% wt aqueous hydrochloric acid solution for 2 h, then washed with deionized water, dried, and then heat treated at 850°C in a high-purity nitrogen atmosphere for 2 h to obtain the porous carbon material.

[0173] Test Example

[0174] 1. BET and pore volume test of porous carbon

[0175] A certain amount of porous carbon material powder was taken in a sample tube, vacuum degassing at 110°C for 12h. The adsorption amount of nitrogen gas of the porous carbon material under different pressures was tested by ASAP2460 physical adsorption analyzer to obtain the adsorption and desorption isotherm curves of the porous carbon material. The pore size distribution curve of micropore was fitted by DFT model, and the specific surface area and pore volume of the porous carbon material were calculated. The results are shown in Table 1.

[0176] Table 1 Porous carbon structure

[0177]

[0178]

[0179] 2. Preparation of silicon-carbon negative electrode

[0180] The preparation of silicon-carbon material was carried out in a fluidized bed: first, 2L / min of argon was introduced into the fluidized bed reactor to continuously replace air for 1h until the oxygen concentration was reduced to below 500ppm, and the reactor was heated at a rate of 10°C / min, when the temperature in the reactor rose to 500°C, 1Kg of porous carbon material was introduced into the reactor. The mixed gas of silane and argon was introduced from the bottom of the reactor at a ratio of 1.0L / min of silane and 2.0L / min of argon, and the deposition reaction was continued for 6h, then the silane was stopped and the fluidized bed reactor was continued to be heated, when the temperature in the reactor rose to 600°C, the mixed gas of acetylene and argon was introduced, both of which were 2.0L / min, and the reaction was continued for 2h, then the acetylene was stopped and the heating was stopped, and the reactor was cooled to room temperature in argon atmosphere, and the product was discharged.

[0181] The silicon-carbon material, conductive agent acetylene black, binder CMC and binder SBR were mixed at a mass ratio of 85:9:3:3, deionized water was added and uniformly mixed to prepare a slurry, which was uniformly coated on a copper foil current collector, vacuum dried for 24h, and roll pressed to obtain a silicon-carbon negative electrode sheet.

[0182] 3. Electrochemical test

[0183] 1) Lithium ion battery preparation:

[0184] The silicon-carbon negative electrode material, conductive agent acetylene black, binder CMC and binder SBR were mixed at a mass ratio of 85:10:3:2, deionized water was added and uniformly mixed to prepare a slurry, which was uniformly coated on a copper foil current collector, vacuum dried for 24h, and roll pressed to obtain a battery negative electrode sheet. Lithium sheet was used as the counter electrode, 1mol / L LiPF6(solvent was a mixture of EC and EMC at a volume ratio of 1:1) was used as the electrolyte, and PP microporous membrane was used as the separator, and a button cell was assembled in an argon-filled glove box.

[0185] 2) Battery test:

[0186] The test was performed on a blue CT2001A battery test system, the charge and discharge current density was 0.1C, the test temperature was 25±1℃, the cut-off voltage was between 0.005V-2V, the capacity was tested, and the first discharge efficiency was calculated according to the formula: first discharge efficiency = 0.1C discharge capacity of the first circle / 0.1C charge capacity, and the measured value was the average value of 3-5 button cells.

[0187] The nominal specific capacity was 130mAh / g, the test voltage was 2V-4V, the first circle was 0.1C charge and discharge, and then the cycle was connected, the cycle was 0.1C charge and discharge, and the cycle number was 50.

[0188] The capacity retention rate = the discharge capacity after cycling under the condition of 0.1C charge and discharge / 0.1C first circle discharge capacity.

[0189] The electrode expansion rate = (the thickness of the electrode after 50 weeks of cycling-the thickness of the electrode before assembly) / the thickness of the electrode before assembly*100%

[0190] The above test results are shown in Table 2.

[0191] Table 2 Performance of lithium ion battery

[0192]

[0193] From the above test results, it can be seen that the lithium ion battery prepared by using the porous carbon provided by the application as raw material shows high first efficiency, reversible capacity and cycle stability, which shows that the use of the dual activation action of strong oxidizing agent and high temperature steam can significantly improve the pore volume and micropore ratio of the porous carbon, improve the skeleton strength of the porous carbon, and thus be beneficial to improving the battery performance.

[0194] Compared with examples 1-3, the amount of strong oxidizing agent in example 4 is larger, although it can increase the pore volume and micropore ratio of the porous carbon, but it will affect the skeleton strength, and thus is not conducive to relieving the expansion of the silicon-carbon negative electrode; the amount of strong oxidizing agent in example 5 is less, and the chemical activation temperature in example 6 is lower, both of which are difficult to significantly improve the total pore volume of the porous carbon, and thus affect the cycle performance of the battery; the chemical activation temperature in example 7 is higher, which leads to a higher degree of activation of the porous carbon, so that the micropore ratio is small, which is also not conducive to relieving the expansion of the silicon-carbon negative electrode. Therefore, it can be seen that the chemical activation of the appropriate amount of strong oxidizing agent at the appropriate temperature is more conducive to improving the pore volume and micropore volume ratio of the porous carbon, and also can improve the skeleton strength of the porous carbon, so as to significantly relieve the expansion of the silicon-carbon negative electrode and improve the battery performance.

[0195] Compared with Example 1, Comparative Example 1 is not chemically activated, so that the micropore content in the porous carbon is less, and Comparative Example 2 is not physically activated, so that the total pore volume of the porous carbon is small, and the application of the two kinds of porous carbon to the silicon-carbon negative electrode is not conducive to relieving the expansion of the electrode plate.

[0196] 4. Process economy evaluation

[0197] The preparation of 1000 g of the porous carbon material in Example 1 of the present application requires the consumption of raw materials and strong oxidants, nitrogen, high-temperature steam, hydrochloric acid and other chemicals, which is equivalent to 4.8 yuan in RMB, and the consumption of electric energy is equivalent to 2.1 yuan in RMB, and the total is 6.9 yuan.

[0198] The preparation of 1000 g of the porous carbon material with a structure similar to that of Example 1 of the present application (measured by micropore volume) using the KOH chemical activation process requires the consumption of raw materials and KOH, hydrochloric acid and other chemicals, which is equivalent to 10.08 yuan in RMB, and the consumption of electric energy is equivalent to 1.9 yuan in RMB, and the total is 11.98 yuan.

[0199] The preparation of 1000 g of the porous carbon material with a structure similar to that of Example 1 of the present application (measured by micropore volume) using the water vapor physical activation process requires the consumption of raw materials and water vapor, hydrochloric acid and other chemicals, which is equivalent to 4.96 yuan in RMB, and the consumption of electric energy is equivalent to 4.2 yuan in RMB, and the total is 9.16 yuan.

[0200] It can be seen that, compared with the pure chemical or physical activation process, the preparation of the same or similar amount of porous carbon material with the same or similar structure using the method of the present application requires less chemicals and lower energy consumption. This shows that the method provided by the present application can obtain porous carbon with large pore volume and low expansion while reducing process energy consumption, and solves the problem of high energy consumption of the existing process.

[0201] Obviously, the above examples are merely examples for the purpose of clear illustration, and are not limitations on the embodiments. Based on the above description, other different forms of changes or variations can also be made by those of ordinary skill in the art. Here, it is not necessary and impossible to exhaust all embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for producing a porous carbon, characterized by, The method comprises the following steps: mixing the carbonized material with a strong oxidant and then performing chemical activation at a temperature lower than the decomposition temperature of the strong oxidant or its decomposition products; performing physical activation on the material after chemical activation.

2. The method for producing porous carbon according to claim 1, wherein The mass ratio of the carbonized material to the strong oxidant is 10-20:1; and / or, the temperature for chemical activation is 60%-70% of the decomposition temperature of the strong oxidant or its decomposition products; and / or, the time for chemical activation is 1h-10h; and / or, the strong oxidant is at least one selected from sodium percarbonate, ammonium persulfate and potassium permanganate.

3. The method for producing porous carbon according to claim 1, wherein The conditions for physical activation include first passing in inert protective gas and then heating to 650℃-950℃ at a programmed rate, and then passing in high-temperature water vapor.

4. The method for producing porous carbon according to claim 3, characterized by, The programmed heating rate is 5℃ / min-10℃ / min; and / or, the passing-in speed of the high-temperature water vapor is 1L / min-5L / min; and / or, the passing-in time of the high-temperature water vapor is 1h-5h.

5. The method for producing porous carbon according to any one of claims 1 to 4, characterized by, The preparation method further comprises sequentially performing acid washing, water washing and heat treatment in an inert atmosphere on the material after physical activation.

6. The method for producing porous carbon according to claim 5, wherein The temperature for heat treatment is 700℃-1100℃ and the time is 0.5h-5h.

7. A porous carbon, characterized by, The porous carbon is prepared by the method of any one of claims 1-6.

8. The porous carbon according to claim 7, characterized in that, The porous carbon has a pore volume of 0.75 cm 3 / g-0.95 cm 3 / g, and the volume fraction of micropores is 72%-86%.

9. A silicon-carbon material comprising nano-silicon and the porous carbon of claim 7 or 8, wherein the nano-silicon is deposited in the pores and on the surface of the porous carbon.

10. A negative electrode sheet characterized by comprising: The method comprises: a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises the silicon-carbon material of claim 9.

11. A secondary battery characterized by comprising: The negative electrode sheet comprises the negative electrode sheet of claim 10.

12. An electrical device, characterized by The secondary battery comprises the secondary battery of claim 11. The secondary battery comprises the secondary battery of claim 11.

Images