Microporous carbon as well as preparation method and application thereof

Abstract

The invention relates to microporous carbon as well as a preparation method and application thereof. The microporous carbon consists of intercommunicated micropores and locally ordered pore walls. Biomass is used as a precursor, and the microporous carbon with high specific surface area, high micropore proportion and high electron conductivity is obtained by combining oxidizing atmosphere pre-carbonization, chemical activation and transient high-temperature treatment. The specific surface area of the obtained microporous carbon is greater than 1800m < 2 > / g, the average pore size is less than 2nm, the total pore volume is 0.8-1.1 cm < 3 > / g, and the micropore proportion is greater than or equal to 90%. The microporous carbon is prepared by adopting cheap raw materials and a simple method, the energy consumption is low, the cost is low, the period is short, and large-scale production is facilitated.

Description

Technical Field

[0001] The invention relates to the field of novel energy storage materials, in particular to microporous carbon and a preparation method and application thereof. Background Art

[0002] In order to achieve the "dual carbon" goal, the development of electric vehicles is the only way, but in order to overcome mileage anxiety, it is necessary to develop high-energy-density lithium-ion batteries. Using silicon-based anodes instead of traditional graphite anodes is an effective way to increase battery energy density, but silicon-based anodes face the problems of low first storage efficiency and short cycle life. At present, the use of porous carbon to deposit nanosilicon and prepare new silicon-carbon anodes is one of the most promising means. However, porous carbon faces problems such as high preparation cost and difficulty in modulating pore size, and the electrical conductivity of porous carbon is poor, resulting in high polarization and poor rate performance of silicon-carbon anodes. Therefore, an effective solution is needed. Summary of the invention

[0003] The purpose of the present invention is to provide a microporous carbon and a preparation method and application thereof to solve the problems raised in the above background technology.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A microporous carbon is composed of interconnected micropores and locally ordered pore walls.

[0006] The technical solution adopted by the present invention is: using low-cost and sustainable biomass as a precursor, through acid washing, pre-carbonization, high-temperature activation, and transient Joule heat reaction, a microporous carbon material with interconnected micropores and locally ordered pore walls is obtained.

[0007] As a further solution of the present invention: the microporous carbon has a specific surface area greater than 1800 m2 / g, an average pore diameter less than 2 nm, and a total pore volume of 0.8 to 1.1 cm 3 / g, of which micropores account for ≥90%.

[0008] The present invention also discloses a method for preparing the microporous carbon, the steps of which are as follows:

[0009] 1) Pretreatment of biomass;

[0010] 2) pre-carbonizing the pretreated biomass to obtain biochar;

[0011] 3) Mixing the above-mentioned biochar, catalyst and activator and performing high-temperature activation;

[0012] 4) The activated product is subjected to transient Joule heat reaction and post-treatment to obtain the microporous carbon.

[0013] As a further solution of the present invention: in step 1), the biomass is selected from at least one of coconut shell, wood, bamboo, fruit core, straw, and sugars, and the sugars are selected from glucose, fructose, polysaccharides or starch.

[0014] As a further solution of the present invention: the biomass needs to be pre-treated by crushing, acid washing, etc. before carbonization. The crushing generally refers to breaking the biomass into small particles ranging from millimeter to centimeter. The acid washing can be carried out by hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid. After acid washing, impurity elements can be effectively removed.

[0015] As a further solution of the present invention: in step 2), the pre-carbonization temperature is 400-600°C, the pre-carbonization time is 1-4 hours, and the pre-carbonization atmosphere is air or oxygen. Through pre-carbonization, a cross-linked structure can be formed, which promotes the formation of interconnected micropores.

[0016] As a further embodiment of the present invention: in step 3), the activator is selected from KOH, K 2 CO 3 , H 3 PO 4 、ZnCl 2 , KH 2 PO 4 At least one of the above, the activation temperature is 800-1000°C, the activation time is 1-3 hours, the activation atmosphere is an inert gas, and preferably, the weight ratio of the activator to the pre-carbonized biomass charcoal is 1-10:1. Through activation, a porous structure dominated by micropores is formed. The so-called micropores refer to pores with a pore size of less than 2 nanometers. Experiments have found that when the pore size is micropores, it is conducive to the deposition of nano-silicon, and when the pore size becomes smaller, it is conducive to the deposition of amorphous nano-silicon, thereby improving the cycle life and first storage effect of the silicon-carbon negative electrode.

[0017] As a further embodiment of the present invention: the catalyst is a transition metal oxide selected from NiO, FeO, Fe 2 0 3 , Fe 3 O 4 , CoO, Co 3 O 4 At least one of the above, preferably, the weight ratio of the catalyst to the pre-carbonized biomass carbon is 0.1 to 1: 1. During the high temperature activation process, the transition metal oxide is reduced to metal, which acts as a catalyst to promote the ordering of the carbon layer and form a locally ordered pore wall structure.

[0018] As a further solution of the present invention: in step 4), the transient Joule heat reaction temperature is 1500-2000°C, and the reaction time is 5-60 seconds. After the transient Joule heat reaction, the pore structure of the microporous carbon can be reorganized, further promoting the formation of microporous carbon and the construction of a partially ordered pore wall structure.

[0019] As a further solution of the present invention: the post-treatment includes pickling, drying and crushing.

[0020] It should be noted that the above steps are interdependent. Under the synergistic effect of the above steps, a porous carbon with interconnected micropores as the main component can be obtained, and the pore walls present a locally ordered structure. Any deviation from the above conditions will not result in the above structure.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention uses cheap and sustainable biomass as raw materials and prepares microporous carbon by a simple method, which has low energy consumption, low cost, short cycle, and is conducive to large-scale production.

[0023] 2. The porous carbon prepared by the present invention has the advantages of high specific surface area, high proportion of micropores, interconnected micropores, high total pore volume, high electronic conductivity, etc., and is suitable for use as a carrier of nano-silicon in silicon-carbon negative electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a pore size distribution diagram of the microporous carbon prepared in Example 1 of the present invention;

[0025] Figure 2 This is a transmission electron microscope (TEM) photograph of the microporous carbon prepared in Example 1 of the present invention;

[0026] Figure 3 The pore size distribution diagram of the microporous carbon prepared in Comparative Example 1;

[0027] Figure 4 This is the TEM photo of the microporous carbon prepared in Comparative Example 1. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Example 1

[0030] In an embodiment of the present invention, a method for preparing microporous carbon is to grind 10 grams of bamboo into powder with a particle size of about 1 mm, firstly pass through 20% HN0 3 The dried product was placed in a tube furnace and pre-carbonized at 500°C for 2 hours in an air atmosphere to obtain a pre-carbonized material. 2 0 3 The carbonized carbon was mixed with the pre-carbonized material in a weight ratio of 2:0.1:1, placed in a tube furnace, introduced with Ar gas, kept at 850°C for 2 hours, and then acid-washed and dried to obtain activated carbon. The activated carbon was subjected to transient Joule heat treatment at a temperature of 1600°C for 30 seconds to obtain microporous carbon. The obtained microporous carbon was analyzed and the specific surface area was 1918m 2 / g, pore volume 0.91cm 3 / g, of which micropores account for 90.5% and the average pore size is 1.69nm. Figure 1 TEM analysis shows that the pore wall presents a local ordered structure. Figure 2 .

[0031] Example 2

[0032] In an embodiment of the present invention, a method for preparing microporous carbon is to grind 10 grams of fir wood into powder with a particle size of about 1 mm, and then 3 The dried product was placed in a tube furnace and calcined at 450°C in air for 3 hours to obtain a pre-carbonized material. 2 CO 3 , Fe 3 O 4 It was mixed evenly with the pre-carbonized material in a weight ratio of 1.5:0.2:1, placed in a tubular furnace, introduced with Ar gas, kept at 800°C for 3 hours, and then acid-washed and dried to obtain activated carbon. The activated carbon was subjected to transient Joule heat treatment at a temperature of 1550°C for 40 seconds to obtain microporous carbon. The obtained microporous carbon was analyzed to have a specific surface area of ​​1945m2 / g and a pore volume of 0.93cm3 / g, of which micropores accounted for 91.1% and the average pore size was 1.71nm. TEM analysis showed that the pore wall showed a local ordered structure.

[0033] Comparative Example 1

[0034] The preparation of microporous carbon was the same as in Example 1, except that it was not subjected to transient Joule heat treatment. The specific surface area of ​​the obtained microporous carbon was 1690 m 2 / g, pore volume 0.74cm 3 / g, micropores account for 81.5%, and mesopores are present. Figure 3 , the pore wall presents a disordered structure, see Figure 4.

[0035] Comparative Example 2

[0036] The preparation of microporous carbon was the same as in Example 1, except that the transient Joule heat treatment time was 80 seconds, and the specific surface area of ​​the obtained microporous carbon was 1590 m 2 / g, micropores account for 77.3%, and the pore wall presents a disordered structure.

[0037] Comparative Example 3

[0038] The preparation of microporous carbon was the same as in Example 1, except that no catalyst was added. The specific surface area of ​​the obtained microporous carbon was 1634 m 2 / g, micropores account for 82.2%, and the pore wall presents a disordered structure.

[0039] Comparative Example 4

[0040] The preparation of microporous carbon was the same as in Example 1, except that the activation temperature was 700°C and the specific surface area of ​​the obtained microporous carbon was 1378 m 2 / g, and the proportion of micropores is 67.3%.

[0041] Comparative Example 5

[0042] The preparation of microporous carbon was the same as in Example 1, except that the activation time was 0.5 h, and the specific surface area of ​​the obtained microporous carbon was 1611 m 2 / g, and micropores account for 70.5%.

[0043] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A microporous carbon, characterized in that: The microporous carbon is composed of interconnected micropores and locally ordered pore walls, and the specific surface area of ​​the microporous carbon is greater than 1800 m 2 / g, the average pore diameter is less than 2nm, and the total pore volume is 0.8~1.1cm 3 / g, of which micropores account for ≥90%.

2. The method for preparing microporous carbon according to claim 1, characterized in that: Here are the steps: 1) Pretreatment of biomass; 2) pre-carbonizing the pretreated biomass to obtain biochar; 3) Mixing the above-mentioned biochar, catalyst and activator and performing high-temperature activation; 4) The activated product is subjected to transient Joule heat reaction and post-treatment to obtain the microporous carbon.

3. The method for preparing microporous carbon according to claim 2, characterized in that: In step 1), the biomass is selected from at least one of coconut shells, wood, bamboo, fruit cores, straw, and sugars.

4. The method for preparing microporous carbon according to claim 2, characterized in that: In step 2), the pre-carbonization temperature is 400-600° C., and the pre-carbonization time is 1-4 hours; The pre-carbonization atmosphere is air or oxygen.

5. The method for preparing microporous carbon according to claim 2, characterized in that: In step 3), the catalyst is selected from transition metal oxides, and the activator is selected from at least one of KOH, K2CO3, H3PO4, ZnCl2, and KH2PO4; the activation temperature is 800-1000°C, the activation time is 1-3 hours, and the activation atmosphere is an inert gas.

6. The method for preparing microporous carbon according to claim 2, characterized in that: In step 4), the transient Joule heat reaction temperature is 1500-2000° C., and the reaction time is 5-60 seconds.

7. Use of the microporous carbon according to claim 1 in a silicon-carbon negative electrode of a lithium-ion battery.

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