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

Abstract

The invention discloses a preparation method of a porous carbon material, which comprises the following steps: a, carbonizing a carbon material precursor to obtain a porous carbon crude product; b, adding the porous carbon crude product in the step a and a metal organic framework compound into water, stirring, filtering and drying to obtain a mixture; c, performing intermittent microwave heating activation treatment on the mixture in the step b to obtain an activated product; and d, carrying out acid pickling and water washing on the activated product in the step c, and drying to obtain the porous carbon material. According to the method, the metal organic framework compound is adopted as the activating agent, potential risks caused by the fact that acid and alkali serve as the activating agent can be avoided, meanwhile, the carbon precursor is activated through microwave intermittent heating, the activation efficiency of porous carbon is effectively improved, and energy consumption is reduced; the porous carbon material with high specific surface area, high micropore proportion, low mesopore and large pore volume is prepared.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of secondary batteries, and particularly relates to a porous carbon material and a preparation method thereof, further, the present application also relates to a silicon-carbon negative active material, a secondary battery and an electric device. BACKGROUND

[0002] With the development of society, the requirement for the energy density of lithium ion batteries is higher and higher, and it is urgent to develop electrode materials of lithium ion batteries with high energy density. The theoretical capacity of silicon negative electrode material can exceed 4000 mA h / g, however, the capacity utilization rate, rate performance and cycle life of silicon-based negative electrode are seriously limited due to the poor conductivity and high expansion rate of pure silicon negative electrode.

[0003] To overcome the above problems, the method of vapor deposition of nanosilicon in the pores of porous carbon has been widely studied, which can greatly improve the capacity and stability of silicon-carbon composite materials. At present, the preparation method of porous carbon is mainly through carbonization of carbon precursor and then activation by activator. However, the current physical activation is mainly through water vapor or carbon dioxide gas reaction, due to the involvement of surface adsorption process kinetics, there is a problem of poor activation depth; and chemical activation is realized by etching carbon atoms inside with KOH, NaOH and other activators, which has strong corrosive, irritating and unsafe problems.

[0004] Therefore, it is necessary to further study and improve the porous carbon material to safely and efficiently improve the capacity and cycle performance of the silicon-carbon negative active material. SUMMARY

[0005] The present application aims to at least solve one of the technical problems in the related art. To this end, the embodiments of the present application provide a porous carbon material and a preparation method thereof, which uses a metal organic framework compound as an activator, avoids the potential risks brought by acid-base activators, and uses intermittent microwave heating to activate the carbon precursor, effectively improving the activation efficiency of the porous carbon, reducing the energy consumption, and obtaining a porous carbon material with high specific surface area, high micropore ratio and low mesopore and macropore volume.

[0006] The present application provides a preparation method of a porous carbon material, which comprises the following steps:

[0007] a. carbonizing a carbon material precursor to obtain a porous carbon crude product;

[0008] b. adding the porous carbon crude product in step a and a metal organic framework compound into water, stirring, filtering and drying to obtain a mixture;

[0009] c. performing intermittent microwave heating activation treatment on the mixture in step b to obtain an activated product;

[0010] d. washing the activated product in step c with acid and water, and drying to obtain the porous carbon material.

[0011] The method for preparing the porous carbon material according to the embodiments of the present application has the following advantages and technical effects:

[0012] 1. In the method according to the embodiments of the present application, a metal organic framework compound is used as the activating agent. The metal organic framework compound is a new type of nanomaterial formed by the combination of metal ions and ligands, and has the characteristics of rich structure, rich metal sites, and uniform distribution of metal ions. The porous carbon crude product is immersed in the aqueous solution of the metal organic framework compound, so that the porous carbon crude product is fully infiltrated by the metal organic framework compound. Under the action of microwave heating, the nanometer metal particles generated by the pyrolysis of the metal organic framework compound serve as the activation center to etch the carbon of the porous carbon crude product. Since the metal particles generated by the decomposition of the metal organic framework compound are small, the size of the pores etched in the carbon matrix will also inherit the size of the metal particles, thereby generating small channels in the porous carbon crude product.

[0013] 2. In the method according to the embodiments of the present application, the intermittent heating activation treatment method is used. Through intermittent heating, the metal particles generated by the decomposition of the metal organic framework compound can be overheated, while the overall carbon matrix will not burn, so that the pores in the porous carbon crude product can be continuously created in a controllable manner, and a porous carbon material with rich micropores is prepared.

[0014] 3. In the method according to the embodiments of the present application, the carbon skeleton generated by the pyrolysis of the metal organic framework compound can effectively seal the large pores in the porous carbon crude product, thereby increasing the proportion of micropores in the porous carbon material and reducing the amount of mesopores and macropores.

[0015] 4. In the method according to the embodiments of the present application, microwave heating is used for activation treatment. Through the promotion of the intense internal molecular motion by microwaves, efficient activation is achieved. The operation is simple, the heating speed is fast, the reaction efficiency is high, the material agglomeration is reduced, and the energy consumption is effectively reduced.

[0016] 5. In the method according to the embodiments of the present application, no acid or base is used as the activating agent, which avoids the corrosion and potential risks brought by the acid and base, and is environmentally friendly and safe. The process is simple and easy to implement. The porous carbon material prepared by the method has a high proportion of micropores, a large specific surface area, and a low mesopore and macropore volume, and is suitable for use as a carbon substrate for preparing silicon-carbon negative active material by the vapor deposition method, so that the silicon-carbon negative active material prepared has excellent electrochemical performance.

[0017] In some embodiments, the carbon material precursor in step a includes at least one of a biomass precursor, a resin-based precursor, and a mineral-based carbon precursor.

[0018] Optionally, the biomass precursor comprises at least one of coconut shell, fruit shell; the resin-based precursor comprises phenolic resin; the mineral-based carbon precursor comprises at least one of petroleum coke, needle coke;

[0019] In some embodiments, in the step a, the carbonization temperature is 400-1000℃, and the carbonization time is no more than 10h.

[0020] In some embodiments, in the step a, the carbonization is carried out under inert gas protection, and the inert gas flow rate is 10-2000cm 3 / min.

[0021] In some embodiments, in the step b, the metal-organic framework compound comprises at least one of zinc-based metal-organic framework compound (such as ZIF-8, ZIF-L), nickel-based metal-organic framework compound (such as MOF-74), cobalt-based metal-organic framework compound (ZIF-67), iron-based metal-organic framework compound (such as MIL-101).

[0022] In some embodiments, the metal-organic framework compound is selected from at least one of zinc-based metal-organic framework compound or nickel-based metal-organic framework compound.

[0023] Optionally, the zinc-based metal-organic framework compound comprises at least one of ZIF-8 or ZIF-L.

[0024] Optionally, the nickel-based metal-organic framework compound comprises MOF-74.

[0025] In some embodiments, in the step b, the mass ratio of the metal-organic framework compound to the porous carbon crude product is 1:(1-100), optionally, the mass ratio is 1:(1-10), for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0026] In some embodiments, in the step b, the stirring time is no more than 12h.

[0027] In some embodiments, in the step b, the stirring is carried out under vacuum.

[0028] In some embodiments, in the step b, the intermittent microwave heating activation treatment comprises microwave pre-heating treatment and microwave heating-cooling cycle treatment, wherein one cycle is one microwave heating and one cooling;

[0029] Optionally, the microwave pre-heating treatment time is 5-30min;

[0030] Optionally, in each cycle, the ratio of the microwave heating time and the cooling time is 5:1-1:5.

[0031] Optionally, in each cycle, the microwave heating time is 1-3 min and the cooling time is 2-6 min.

[0032] Optionally, the intermittent microwave heating activation treatment comprises 10-30 cycles of treatment.

[0033] Optionally, the cooling mode comprises at least one of standing, passing in nitrogen, passing in water vapor, and disturbing the mixture, and optionally, the temperature of the nitrogen is 5-25℃.

[0034] Optionally, water vapor is passed in during the microwave heating process.

[0035] In some embodiments, in the step b, the microwave power is 1000-3000w; the microwave frequency is 2000-3000MHz; and the pressure of the microwave heating activation treatment is 0.1-10MPa.

[0036] In some embodiments, in the step c, the acid used in the pickling comprises at least one of hydrochloric acid or nitric acid, and optionally, the concentration of the acid is 0.5-10M.

[0037] The application also provides a porous carbon material prepared by the method for preparing a porous carbon material described above.

[0038] In some embodiments, the porous carbon material has a size of 5-8μm, a specific surface area of 1300-2400m 2 / g, a micropore volume of 0.3-0.9cm 3 / g, a micropore ratio of 50%-95%, and a total mesopore and macropore volume of not more than 0.25cm 3 / g. The micropore in the application refers to a pore structure with a pore size of ≤2nm, and the micropore ratio refers to the percentage of the micropore volume in the total pore volume.

[0039] The embodiment of the present application also provides a silicon-carbon negative electrode active material, which is prepared by a gas phase deposition method and takes a porous carbon material as a substrate, wherein the porous carbon material is the porous carbon material prepared by the preparation method of the above embodiment of the present application or the porous carbon material of the above embodiment of the present application. The silicon-carbon negative electrode active material of the embodiment of the present application takes the porous carbon material with high surface area, high micropore ratio and low mesopore and macropore volume as a substrate material, so that the silicon-carbon negative electrode active material not only has high initial reversible specific capacity, but also maintains high initial efficiency, has excellent negative electrode lithium storage capacity, and at the same time, the small pore size in the porous carbon material can play a confinement role in the deposition process, which not only reduces the size of the deposited particles and makes them less likely to be pulverized, but also inhibits the volume expansion of silicon in the reaction process, thereby prolonging the cycle life of the silicon-carbon negative electrode active material.

[0040] The embodiment of the present application also provides a secondary battery comprising the silicon-carbon negative electrode active material of the embodiment of the present application. The secondary battery of the embodiment of the present application has all the advantages brought by the silicon-carbon negative electrode active material of the embodiment of the present application, which will not be described here.

[0041] The embodiment of the present application also provides an electric device comprising the secondary battery of the embodiment of the present application. The electric device of the embodiment of the present application has all the advantages brought by the secondary battery of the embodiment of the present application, which will not be described here. DETAILED DESCRIPTION

[0042] The embodiments of the present application are described in detail below, which are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0043] 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 the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "comprise" and "have" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusion.

[0044] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0045] Reference within this document to "an embodiment" 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 an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. It is expressly understood that any of the embodiments described herein can be combined with any of the other embodiments unless specifically noted otherwise.

[0046] "RANGES" disclosed herein are defined by a lower limit and an upper limit, and a given 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 in this manner 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 for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, 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" is intended to mean any range of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand for listing all of these numerical combinations. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to state that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] In the description of the embodiments of the application, the term "and / or" only means an association relationship of the associated objects, and means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone. In addition, the character " / " in this document generally means that the front and rear associated objects are in an "or" relationship.

[0048] In the description of the embodiments of the application, the term "a plurality of" means more than two (including two), and similarly, "a plurality of groups" means more than two groups (including two groups), and "a plurality of pieces" means more than two pieces (including two pieces).

[0049] In this application, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material, or characteristic is included in at least one embodiment or example of the present application. The illustrative representations in this specification are not necessarily drawn to the same embodiment or example. Moreover, the described specific features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Furthermore, the described specific features, structures, materials, or characteristics can be combined and / or sub-combined in different embodiments or examples, and in different ways, without contradiction.

[0050] The embodiment of the present application provides a preparation method of a porous carbon material, comprising the following steps:

[0051] a. performing carbonization treatment on a carbon material precursor to obtain a porous carbon crude product;

[0052] b. adding the porous carbon crude product in the step a and a metal organic framework compound into water, stirring, filtering and drying to obtain a mixture;

[0053] c. performing intermittent microwave heating activation treatment on the mixture in the step b to obtain an activation product;

[0054] d. performing acid washing and water washing on the activation product in the step c, and drying to obtain the porous carbon material.

[0055] The preparation method of the porous carbon material in the embodiment of the present application adopts a metal organic framework compound as an activation agent. The metal organic framework compound is a novel nanomaterial combined by metal ions and ligands, and has the characteristics of rich structure, rich metal sites and uniform distribution of metal ions. The porous carbon crude product is placed in the aqueous solution of the metal organic framework compound, so that the porous carbon crude product is fully infiltrated by the metal organic framework compound. Under the action of microwave heating, the nanometer metal particles generated by pyrolysis of the metal organic framework compound serve as activation centers to perform carbon etching on the porous carbon crude product. Since the metal particles generated after decomposition of the metal organic framework compound are small, the pore size etched in the carbon matrix will also inherit the size of the metal particles, so that small channels are generated in the porous carbon crude product.

[0056] The preparation method of the porous carbon material in the embodiment of the present application adopts an intermittent microwave heating activation treatment mode. Through intermittent heating, the metal particles generated by decomposition of the metal organic framework compound can be overheated, and the whole carbon matrix will not be combusted, so that pores can be continuously generated in the porous carbon crude product in a controllable manner, and the porous carbon material with rich micropores is prepared.

[0057] The preparation method of the porous carbon material in the embodiment of the present application, the metal organic framework compound can also generate a carbon skeleton after microwave pyrolysis, can effectively block the large pores in the porous carbon crude product, and can increase the micropore ratio of the porous carbon material and reduce the number of mesopores and macropores.

[0058] The preparation method of the porous carbon material in the embodiment of the present application adopts microwave heating for activation treatment, promotes the internal molecular movement through microwaves, thereby realizing efficient activation, and has the advantages of simple operation, fast heating speed, high reaction efficiency, reduced material agglomeration, and effectively reduced energy consumption.

[0059] The preparation method of the porous carbon material in the embodiment of the present application does not need to use an acid or a base as an activator, avoids the corrosion and potential risks caused by the acid or the base, is environmentally friendly and safe in production, has a simple and easy-to-operate process, and has the advantages that the prepared porous carbon material has a high micropore ratio and a large specific surface area, and has a low mesopore and macropore volume, is suitable for being used as a carbon substrate for preparing a silicon-carbon negative active material by a vapor deposition method, and makes the prepared silicon-carbon negative active material have excellent electrochemical performance.

[0060] The method in the embodiment of the present application is not particularly limited to a carbon material precursor, and a precursor with a high carbon content and capable of being carbonized to form a porous carbon can be applied to the method in the embodiment of the present application.

[0061] In some embodiments, in the step a, the carbon material precursor includes at least one of a biomass precursor, a resin-based precursor, and a mineral-based carbon precursor. The biomass precursor includes at least one of a coconut shell and a fruit shell. The resin-based precursor includes a phenolic resin. The mineral-based carbon precursor includes at least one of petroleum coke and needle coke.

[0062] In some embodiments, in the step a, the carbonization temperature is 400-1000 DEG C, and the carbonization time is not more than 10 h.

[0063] In some embodiments, in the step a, the carbonization is performed under the protection of an inert gas, and the flow rate of the inert gas is 10-2000 cm 3 / min.

[0064] In some embodiments, in the step a, the size of the prepared porous carbon crude product is 10-20 mu m, and the specific surface area is 10-300 m 2 / g.

[0065] In some embodiments, the metal organic framework compound in step b comprises at least one of a zinc-based metal organic framework compound (such as ZIF-8, ZIF-L), a nickel-based metal organic framework compound (such as MOF-74), a cobalt-based metal organic framework compound (ZIF-67), and a iron-based metal organic framework compound (such as MIL-101). Optionally, the metal organic framework compound is selected from at least one of a zinc-based metal organic framework compound or a nickel-based metal organic framework compound; the zinc-based metal organic framework compound comprises at least one of ZIF-8 or ZIF-L; and the nickel-based metal organic framework compound comprises MOF-74. In the embodiments of the present application, the metal organic framework compound is used as an active agent, avoiding the corrosion and potential safety risks of acid-base active agents, and effectively realizing the etching of the carbon material under the action of microwaves by using the abundant metal sites, thereby obtaining a porous carbon material with a high micropore ratio.

[0066] In some embodiments, the mass ratio of the metal organic framework compound to the porous carbon crude product in step b is 1:(1-100), and optionally, the mass ratio is 1:(1-10), such as 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc. In the embodiments of the present application, the use of the metal organic framework compound with an appropriate ratio to the porous carbon crude product is beneficial to improving the micropore ratio of the porous carbon material, thereby improving the electrochemical performance of the silicon-carbon negative active material. If the amount of the metal organic framework compound added is too small, the etching of the carbon material is not sufficient, which is not conducive to improving the micropore ratio of the carbon material. If the amount of the metal organic framework compound added is too large, the material preparation cost is increased, and the carbon material derived from the metal organic framework compound will first fill the internal cavities during the activation process, resulting in poor activation effect.

[0067] In some embodiments, the stirring time in step b is not more than 12 h. In the embodiments of the present application, the stirring time of the metal organic framework compound and the porous carbon crude product is not particularly limited, as long as the metal organic framework compound can be fully infiltrated into the porous carbon crude product, which is beneficial to the etching of the carbon material by the nano-metal particles formed by microwave pyrolysis, and forms more microporous structures in the porous carbon material.

[0068] In some embodiments, the stirring in step b is performed under vacuum. In the embodiments of the present application, the stirring process is performed under vacuum, which is beneficial to the diffusion of the metal organic framework compound into the interior of the porous carbon crude product, the discharge of the gas in the solution of the porous carbon crude product, and the promotion of the contact between the metal organic framework compound activator and the porous carbon crude product.

[0069] In some embodiments, the intermittent microwave heating activation process in step b includes a microwave pre-heating process and a microwave heating-cooling cycle process, wherein one microwave heating and one cooling is one cycle.

[0070] Optionally, the microwave pre-heating process time is 5-30 min. In the embodiments of the present application, the microwave pre-heating process and the control of the pre-heating process time are beneficial to the pyrolysis of the metal organic framework compound to generate a carbon skeleton, effectively seal the large pores in the porous carbon crude product, increase the micropore ratio of the porous carbon material, and reduce the number of mesopores and macropores.

[0071] Optionally, in each microwave heating-cooling cycle, the ratio of microwave heating time to cooling time is 5:1-1:5, further, the microwave heating time is 1-3 min, and the cooling time is 2-6 min; the intermittent microwave heating activation process includes 10-30 microwave heating-cooling cycle processes. In the embodiments of the present application, the intermittent microwave activation process mode of alternating microwave heating and cooling cycles is adopted, and the appropriate microwave heating and cooling time and cycle period are controlled, which is beneficial to keeping the metal particles generated by the decomposition of the metal organic framework compound overheated without burning the whole carbon matrix, so that the metal particles can continuously pore-form inside the porous carbon crude product in a controllable manner, which is beneficial to the formation of micropores and increases the micropore amount in the porous carbon, effectively increasing the micropore ratio of the porous carbon material.

[0072] The cooling in the microwave heating-cooling cycle process in the embodiments of the present application refers to stopping the microwave heating. Optionally, during the process of stopping the microwave heating, the mixture can be cooled by standing, or cooled by introducing nitrogen with a temperature of 5-25℃, or cooled by introducing water vapor, or cooled by performing disturbance (such as rotation, tumbling, etc.) treatment on the mixture, further, two or more combinations of these methods can be used for cooling.

[0073] In some embodiments, water vapor is introduced during the microwave heating in step b. In the embodiments of the present application, when the microwave pre-heating process and the microwave heating in each microwave heating-cooling cycle are performed, the introduced water vapor not only can be used as a physical activator, but also can effectively improve the microwave energy absorption efficiency of the mixture, increase the heating speed of the mixture, increase the activation rate, and further reduce the energy consumption.

[0074] In some embodiments, in step b, the microwave power is 1000-3000 w; the microwave frequency is 2000-3000 MHz; and the pressure of the microwave heating activation process is 0.1-10 MPa.

[0075] In some embodiments, the acid used in the pickling in step c includes at least one of hydrochloric acid or nitric acid, and the concentration of the acid is 0.5-10M. In the embodiments of the present application, the activated material is subjected to pickling after the microwave activation treatment, so as to effectively remove the residual metal particles in the porous carbon material, thereby avoiding the adverse effects of the residual metal particles on the subsequent preparation of the silicon-carbon negative electrode active material.

[0076] The embodiments of the present application also provide a porous carbon material prepared by the method for preparing a porous carbon material described above.

[0077] In some embodiments, the porous carbon material has a size of 5-8μm, a specific surface area of 1300-2400m 2 / g, a micropore volume of 0.3-0.9cm 3 / g, a micropore ratio of 50%-95%, and a total mesopore and macropore volume of not more than 0.25cm 3 / g. The micropores in the embodiments of the present application refer to pore structures with a pore size of ≤2nm, and the micropore ratio refers to the percentage of the micropore volume in the total pore volume.

[0078] The embodiments of the present application also provide a silicon-carbon negative electrode active material prepared by a gas phase deposition method using a porous carbon material as a substrate, wherein the porous carbon material is the porous carbon material prepared by the method for preparing a porous carbon material described above or the porous carbon material described above.

[0079] In some embodiments, the porous carbon material is subjected to silicon deposition in a silane atmosphere and then subjected to carbon deposition in a methane and / or acetylene atmosphere, so as to prepare a silicon-carbon negative electrode active material.

[0080] The silicon-carbon negative electrode active material in the embodiments of the present application uses a porous carbon material with a high specific surface area, a high micropore ratio and a low mesopore and macropore volume as a substrate material, so that the silicon-carbon negative electrode active material not only has a high initial reversible specific capacity, but also maintains a high initial efficiency, and has excellent negative electrode lithium storage capacity. In addition, the porous carbon material has a small pore size inside, which can play a limiting role in the deposition process, so as to not only reduce the size of the deposited particles and prevent the particles from being easily pulverized, but also inhibit the volume expansion of silicon in the reaction process, thereby prolonging the cycle life of the silicon-carbon negative electrode active material.

[0081] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the present application.

[0082] Embodiment 1

[0083] I. Preparation of porous carbon material

[0084] 1. After drying the phenolic resin, the phenolic resin powder with a size of 10 μm is crushed as a carbon precursor raw material. The powder is heated to 600℃ at a heating rate of 5℃ / min in a nitrogen atmosphere, the gas flow rate is 200 cm 3 / min, and carbonization is performed for 1h to obtain a crude porous carbon product.

[0085] 2. Nanometer ZIF-8 (zinc-based metal organic framework compound) and the crude porous carbon product with a mass ratio of 1:5 are added to water, vacuum stirring and soaking are performed at 25℃ for 2h, and then filtration and drying are performed to obtain a mixture.

[0086] 3. The mixture is placed in a microwave heating device, water vapor is introduced at a flow rate of 200 cm 3 / min until the pressure in the reactor reaches 0.1 MPa, and then intermittent microwave heating and activation treatment is performed, the microwave power is 2000 W, the heating frequency is 2500 MHz, microwave preheating treatment is performed for 20 min, secondary carbonization is performed, and then microwave heating-cooling cycle treatment is performed, the microwave heating time is 2 min, then the microwave heating is stopped for cooling, the cooling time is 4 min, the water vapor is stopped during the cooling period, nitrogen gas at 25℃ is introduced, one cycle is 2 min of microwave heating + 4 min of cooling, and the cycle is repeated for 20 times to obtain an activated product.

[0087] 4. The activated product is washed with 1M hydrochloric acid for 3 times, then washed with deionized water until the solution is neutral, and then dried at 120℃ for 5h to obtain a porous carbon material.

[0088] II. Preparation of silicon-carbon negative electrode active material

[0089] 500 g of the porous carbon material prepared in this example was placed in a deposition reactor, 2 L / min of nitrogen was first introduced to continuously perform air replacement in the deposition reactor for 1 h, the deposition reactor was heated at a temperature increasing rate of 5 ℃ / min, when the temperature in the reactor rose to 450 ℃, the mixed gas of silane and nitrogen was introduced according to the ratio of 1 L / min of silane flow and 4 L / min of nitrogen flow, and the deposition reaction was continuously performed for 3 h; then the reactor was continuously heated at a temperature increasing rate of 5 ℃ / min, when the temperature in the reactor rose to 520 ℃, the flow rates of acetylene and nitrogen were adjusted, the flow rate of acetylene was 2 L / min, the flow rate of nitrogen was 3 L / min, the mixed gas was first mixed in a gas mixing tank, then preheated to 950 ℃ by a gas heater, and then introduced into the deposition reactor, and deposited for 1 h, and the deposition product was sieved to obtain a silicon-carbon negative electrode active material.

[0090] Example 2

[0091] The method was the same as that of Example 1, except that in step 2 of preparing the porous carbon material, the mass ratio of nano-ZIF-8 to the crude porous carbon was 1:1.

[0092] Example 3

[0093] The method was the same as that of Example 1, except that in step 2 of preparing the porous carbon material, the mass ratio of nano-ZIF-8 to the crude porous carbon was 1:10.

[0094] Example 4

[0095] The method was the same as that of Example 1, except that in step 2 of preparing the porous carbon material, the mass ratio of nano-ZIF-8 to the crude porous carbon was 1:100.

[0096] Example 5

[0097] The method was the same as that of Example 1, except that in step 3 of preparing the porous carbon material, the microwave heating-cooling cycle treatment was different, the microwave heating time was 1 min, then the microwave heating was stopped for cooling, the cooling time was 2 min, the water vapor was stopped during the cooling period, and 25 ℃ nitrogen was introduced, one cycle was microwave heating for 1 min + cooling for 2 min, and the cycle was repeated for 40 times.

[0098] Example 6

[0099] The method was the same as that of Example 1, except that in step 3 of preparing the porous carbon material, the microwave heating-cooling cycle treatment was different, the microwave heating time was 3 min, then the microwave heating was stopped for cooling, the cooling time was 6 min, the water vapor was stopped during the cooling period, and 25 ℃ nitrogen was introduced, one cycle was microwave heating for 3 min + cooling for 6 min, and the cycle was repeated for 13 times.

[0100] Example 7

[0101] The method is the same as that of Example 1, except that the number of periodic cycles of microwave heating + cooling in step 3 of preparing the porous carbon material is 15 times.

[0102] Example 8

[0103] The method is the same as that of Example 1, except that the number of periodic cycles of microwave heating + cooling in step 3 of preparing the porous carbon material is 25 times.

[0104] Example 9

[0105] The method is the same as that of Example 1, except that the microwave pre-heating treatment time in step 3 of preparing the porous carbon material is 15 min.

[0106] Example 10

[0107] The method is the same as that of Example 1, except that the microwave pre-heating treatment time in step 3 of preparing the porous carbon material is 30 min.

[0108] Example 11

[0109] The method is the same as that of Example 1, except that the metal organic framework used in step 2 of preparing the porous carbon material is a nickel-based metal organic framework compound MOF-74.

[0110] Example 12

[0111] The method is the same as that of Example 1, except that the metal organic framework used in step 2 of preparing the porous carbon material is a cobalt-based metal organic framework compound ZIF-67.

[0112] Example 13

[0113] The method is the same as that of Example 1, except that the metal organic framework used in step 2 of preparing the porous carbon material is an iron-based metal organic framework compound MIL-101.

[0114] Example 14

[0115] The method is the same as that of Example 1, except that no vacuum stirring is performed in step 2 of preparing the porous carbon material, and instead the nano-ZIF-8 and the porous carbon crude product are stirred and infiltrated under normal pressure for 2 h.

[0116] Comparative Example 1

[0117] The method is the same as that of Example 1, except that steps 2 and 3 of preparing the porous carbon material are different, KOH is used as the activating agent, and no microwave heating activation treatment is performed, and the details are as follows:

[0118] The crude porous carbon was placed in a 5M KOH solution, vacuum stirring and infiltrating at room temperature for 2h, then filtered, and dried at 120℃ for 4h to obtain the mixed alkali material.

[0119] The mixed alkali material was placed in a reactor, and water vapor was introduced at a flow rate of 200cm 3 / min until the pressure in the reactor reached 0.1MPa, then the temperature was raised to 800℃ at a rate of 5℃ / min and maintained for 2h to obtain the activated product.

[0120] Comparative Example 2

[0121] The method was the same as that of Example 1, except that the step 3 of preparing the porous carbon material was different, and instead of microwave heating activation treatment, a box furnace was used for heating activation treatment, as follows:

[0122] The mixed material was placed in a box furnace, and water vapor was introduced at a flow rate of 200cm 3 / min until the pressure in the reactor reached 0.1MPa, then the temperature was raised to 800℃ at a rate of 5℃ / min and maintained for 2h.

[0123] Comparative Example 3

[0124] The method was the same as that of Example 1, except that the step 3 of preparing the porous carbon material was different, and instead of microwave heating activation treatment, a continuous microwave heating activation treatment was used, as follows:

[0125] The mixed material was placed in a microwave heater, and water vapor was introduced at a flow rate of 200cm 3 / min until the pressure in the reactor reached 0.1MPa, then microwave heating was performed, with a microwave power of 2000W, a heating frequency of 2500MHz, and a microwave heating treatment time of 60min to obtain the activated product.

[0126] Comparative Example 4

[0127] The method was the same as that of Example 1, except that the step 2 of preparing the porous carbon material was different, and KOH was used as the activation agent, as follows:

[0128] The crude porous carbon was placed in a 5M KOH solution, vacuum stirring and infiltrating at room temperature for 2h, then filtered, and dried at 120℃ for 4h to obtain the mixed alkali material.

[0129] Comparative Example 5

[0130] Commercially available porous carbon was selected as the carbon material substrate for silicon deposition, and the method for preparing the silicon-carbon negative electrode active material was the same as that of Example 1.

[0131] The porous carbon materials and silicon-carbon negative electrode active materials prepared in Examples 1-14 and Comparative Examples 1-5 were subjected to performance testing.

[0132] 1. The specific surface area and pore size of the porous carbon materials prepared in Examples 1-14 and Comparative Examples 1-5 were tested, and the test results are shown in Table 1.

[0133] The testing process is as follows:

[0134] Sample preparation: Place the solid sample in the degassing station of the ASAP2460 multi-station fully automated microporous adsorption instrument and dry it at 120℃ for 12 hours to remove moisture and other volatile substances.

[0135] Sample degassing: Transfer the sample to the detection area and select nitrogen for adsorption isotherm measurement.

[0136] Data processing: Select a carbon material model, and use NLDFT to fit the model to calculate the specific surface area, pore size distribution, and proportion.

[0137] Table 1

[0138]

[0139] As shown in Table 1, the porous carbon materials prepared in this application have a large specific surface area and a high proportion of micropores, while having a low mesopore volume. Compared with Comparative Example 1, which uses KOH as an activator, Example 1 uses a metal-organic framework compound as an activator. Although the porous carbon material obtained by activation with the metal-organic framework compound has a smaller specific surface area than Comparative Example 1, it has a higher proportion of micropores and lower mesopore and macropore volumes, exhibiting a more uniform pore size, which is beneficial for use as a template in the synthesis of silicon-carbon composite materials. This is mainly because the metal-organic framework compound in Example 1 also generates a carbon skeleton after microwave pyrolysis, which can effectively seal the macropores in the crude porous carbon. In an instantaneous heating environment, metal nanoparticles can etch the surrounding carbon in a water vapor environment. By adjusting the heating time to control the pore size, a porous carbon material with a high proportion of micropores and low mesopore and macropore volumes can be obtained.

[0140] 2. The porous carbon materials prepared in Examples 1-14 and Comparative Examples 1-5 were tested for metal residue. The test results are shown in Table 2.

[0141] The metal content was determined using atomic absorption spectrometry.

[0142] Sample digestion: The sample is placed in a muffle furnace for calcination, where the metallic elements are converted into inorganic salts. Then, the ash is dissolved in hydrochloric acid to prepare a dilute acid solution for atomic absorption spectrometry.

[0143] Test: Pour the blank solution (water), 50.0 ug / L main standard solution, and sample solution into a cleaned and rinsed sample cup. Place the sample cup in the autosampler position set in the method and sample information. Perform a blank test on the graphite tube once to eliminate the influence of graphite tube residue on the determination. Analyze the standard solution and sample automatically using the instrument. Finally, obtain the metal content data.

[0144] Table 2

[0145]

[0146] Although the method in this application uses a metal-organic framework compound as an activator, the subsequent acid washing treatment effectively removes metal impurities, avoiding the negative effects of introducing foreign metals into the porous carbon material. The porous carbon material prepared in this application has a metal impurity content of no more than 20 ppm after acid washing, which meets the requirements for use.

[0147] 3. The silicon-carbon anode active materials prepared in Examples 1-14 and Comparative Examples 1-5 were tested using coin cells. The test results are shown in Tables 3 and 4.

[0148] The button cell battery testing procedure is as follows:

[0149] Negative electrode preparation: Conductive agent, binder, and silicon-carbon negative electrode active material are placed in a container at a mass ratio of 1:1:8, deionized water is added, and the mixture is stirred to prepare the required slurry. The negative electrode slurry is coated onto a copper foil current collector using a coating device, and then dried to obtain the negative electrode sheet.

[0150] Electrolyte preparation: Prepare a mixed solvent of 4-fluoro-1,3-dioxolane-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:2:7, and dissolve the electrolyte salt lithium hexafluorophosphate at a ratio of 1.2 mol / kg.

[0151] The electrode sheets were cut into suitable shapes and assembled into button cells together with lithium sheets, separators, and electrolytes in an argon-filled glove box. The performance of the button cells was then tested in a button cell test cabinet with a test voltage window of 0-2V.

[0152] For the initial charge-discharge characteristics, based on a current density of 100 mA / g, the initial efficiency is calculated as: initial delithiation capacity / initial lithium insertion capacity × 100%.

[0153] Cyclic performance test: Capacity retention rate after 50 cycles at 0.5C current.

[0154] Table 3

[0155]

[0156] As shown in Table 3, the silicon-carbon anode active material prepared by vapor deposition using the porous carbon material obtained in the embodiments of this application exhibits excellent lithium storage performance. Due to the large specific surface area, high micropore ratio, and low mesopore volume of the porous carbon material, the silicon-carbon anode active material not only has a high initial reversible capacity but also maintains a high initial efficiency. Among them, the silicon-carbon anode active material prepared in Example 1 exhibits the best anode lithium storage capacity. Although the silicon-carbon anode active material prepared in Comparative Example 1 has a high specific surface area and micropore ratio, its mesopore volume is high, and the absolute number of mesopores is excessive, resulting in a greater amount of large silicon particles deposited, thus leading to a significant decrease in performance compared to Example 1.

[0157] Table 4

[0158] 0.5C 50 cycle capacity retention / % Example 1 97％ Example 2 90％ Example 3 91％ Example 4 92％ Example 5 93％ Example 6 89％ Example 7 88％ Example 8 91％ Example 9 92％ Example 10 96％ Example 11 95％ Example 12 95％ Example 13 95％ Example 14 86％ Comparative Example 1 94％ Comparative Example 2 85％ Comparative Example 3 86％ Comparative Example 4 90％ Comparative Example 5 92％

[0159] As shown in Table 4, silicon-carbon anode active materials prepared by vapor deposition using porous carbon with a high micropore content exhibit high capacity retention, especially the silicon-carbon anode active material prepared in Example 1, which can achieve a capacity retention of up to 97%. This is mainly because the small pore size inside the porous carbon material can play a confinement role during the deposition process, not only reducing the size of the deposited particles and making them less prone to pulverization, but also suppressing the volume expansion of silicon during the reaction, thereby extending the cycle life of the anode material.

[0160] The method of this application embodiment does not require the use of acids or bases as activators. By using metal-organic framework compounds as activators and combining them with intermittent microwave heating activation treatment, porous carbon materials with high specific surface area, high micropore ratio, low mesopore and macropore volume are prepared. Moreover, the method of this application embodiment has the advantages of rapid preparation and being green and pollution-free. The silicon-carbon anode active material prepared by vapor deposition on the substrate of the porous carbon material of this application embodiment has excellent lithium storage capacity and cycle life, and has great application potential in the field of energy storage.

[0161] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing porous carbon materials, characterized in that, Includes the following steps: a. Carbonize the carbon material precursor to obtain porous crude carbon; b. Add the porous carbon crude product and metal-organic framework compound from step a to water, stir, filter, and dry to obtain a mixture; c. The mixture in step b is subjected to intermittent microwave heating activation treatment to obtain the activated product; d. The activated product from step c is acid-washed and water-washed, and then dried to obtain a porous carbon material.

2. The method for preparing porous carbon materials according to claim 1, characterized in that, In step a, the carbon material precursor includes at least one of biomass precursor, resin-based precursor, and mineral carbon precursor; optionally, the biomass precursor includes at least one of coconut shell and fruit shell; the resin-based precursor includes phenolic resin; and the mineral carbon precursor includes at least one of petroleum coke and needle coke. And / or, the carbonization temperature is 400-1000℃, and the carbonization time does not exceed 10h; And / or, the carbonization is carried out under the protection of an inert gas at a flow rate of 10-2000 cm⁻¹. 3 / min.

3. The method for preparing porous carbon materials according to claim 1, characterized in that, In step b, the metal-organic framework compound includes at least one of zinc-based metal-organic framework compounds, nickel-based metal-organic framework compounds, cobalt-based metal-organic framework compounds, and iron-based metal-organic framework compounds.

4. The method for preparing porous carbon materials according to claim 3, characterized in that, The metal-organic framework compound is selected from at least one of zinc-based metal-organic framework compounds or nickel-based metal-organic framework compounds; Optionally, the zinc-based metal-organic framework compound includes at least one of ZIF-8 or ZIF-L; Optionally, the nickel-based metal-organic framework compound includes MOF-74.

5. The method for preparing porous carbon materials according to claim 1, characterized in that, In step b, the mass ratio of the metal-organic framework compound to the porous carbon crude product is 1:(1-100); And / or, the stirring time does not exceed 12 hours; And / or, the stirring is carried out under vacuum.

6. The method for preparing porous carbon materials according to claim 1, characterized in that, In step b, the intermittent microwave heating activation treatment includes microwave preheating treatment and microwave heating-cooling cycle treatment, wherein one microwave heating and one cooling constitute one cycle; Optionally, the microwave preheating treatment time is 5-30 minutes; Optionally, in each cycle, the ratio of microwave heating time to cooling time is 5:1 to 1:5; Optionally, in each cycle, the microwave heating time is 1-3 minutes and the cooling time is 2-6 minutes; Optionally, the intermittent microwave heating activation treatment includes 10-30 cycle treatments; Optionally, the cooling method includes at least one of standing, introducing nitrogen, introducing water vapor, and disturbing the mixture; optionally, the nitrogen temperature is 5-25°C. Optionally, water vapor is introduced during the microwave heating process.

7. The method for preparing porous carbon materials according to claim 1, characterized in that, In step b, the microwave power is 1000-3000W; And / or, the microwave frequency is 2000-3000MHz; And / or, the pressure of the microwave heating activation treatment is 0.1-10 MPa.

8. The method for preparing porous carbon materials according to claim 1, characterized in that, In step c, the acid used in the pickling includes at least one of hydrochloric acid or nitric acid, and optionally, the concentration of the acid is 0.5-10M.

9. A porous carbon material, characterized in that, It is prepared by any one of claims 1-8.

10. The porous carbon material according to claim 9, characterized in that, The porous carbon material has a size of 5-8 μm and a specific surface area of ​​1300-2400 m². 2 / g, micropore volume is 0.3-0.9cm 3 / g, micropores account for 50%-95%, and the combined pore volume of mesopores and macropores does not exceed 0.25cm³. 3 / g.

11. A silicon-carbon anode active material, characterized in that, The silicon-carbon anode active material is prepared by vapor deposition using a porous carbon material as a substrate. The porous carbon material is the porous carbon material prepared by the method described in any one of claims 1-8 or the porous carbon material described in any one of claims 9-10.

12. A secondary battery, characterized in that, Includes the silicon-carbon anode active material as described in claim 11.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 12.

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