Carbon material, preparation method thereof and application of carbon material in supercapacitor

Abstract

The invention relates to the field of electrochemistry, and particularly discloses a carbon material and a preparation method and application thereof in a supercapacitor, and the preparation method comprises the following steps: mixing biomass and graphite, then carrying out high-speed dry mixing with an activator to obtain mixed powder, then carrying out low-temperature pre-activation in inert gas, and then carrying out high-temperature activation to obtain the carbon material. And washing with water after pickling, filtering and drying to obtain the carbon material. The carbon material has relatively high compaction density and good conductivity, can be used as a super capacitor electrode active material to achieve better electrical properties by using a low-proportion conductive agent, does not need a multi-step activation synthesis step, and can greatly reduce the cost.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and particularly relates to a carbon material, a preparation method thereof, and an application in a supercapacitor. Background Art

[0002] A supercapacitor is a new type of energy storage device between traditional physical capacitors and secondary batteries. It has the advantages of high power density, fast charge and discharge, long cycle service life, and wide applicable temperature range. The electrode material of a supercapacitor is one of the main factors affecting its performance, mainly including three categories: carbon materials, metal oxides, and conductive polymers. Among them, activated carbon in carbon materials has been widely studied due to its advantages such as large specific surface area, adjustable pore structure, and stable chemical properties.

[0003] However, the current activated carbon materials used as supercapacitor electrode materials are mainly restricted by specific surface area and cost. Supercapacitors require electrode materials with a high specific surface area (>1000 m 2 / g) to achieve considerable electrochemical performance. This requires a high proportion of strong corrosive activators, which results in a low yield of the activated carbon electrode material and serious corrosion of equipment, not meeting the actual production requirements.

[0004] Chinese Patent Application CN1061855920A discloses a lignin porous carbon material, a preparation method thereof, and an application. This method uses alkali lignin in alkaline papermaking black liquor containing KOH as a carbon precursor, and obtains a porous carbon material with a high specific surface area through pretreatment, carbonization, and activation. However, the obtained lignin porous carbon is a severely agglomerated aggregate, and its preparation process requires secondary activation, with high energy consumption and being not conducive to industrial production. Chinese Patent Application CN 117263329 A discloses an electroadsorption desalination coconut shell-derived carbon electrode, a preparation method thereof, and an application. This method requires the use of NaOH as an activator, which can corrode equipment, and its electrolyte is an aqueous electrolyte, not meeting the actual application of commercial supercapacitors.

[0005] In addition, due to the large specific surface area and numerous micropores, most activated carbon materials have poor conductivity. When fabricating supercapacitor electrodes, conductive agents (such as acetylene black) need to be added additionally to reduce impedance, which reduces the specific content of active substances in the supercapacitor and thus reduces the performance of the supercapacitor. For example, in Chinese Patent CN 109485029B, a method for fabricating a supercapacitor electrode from an activated carbon material is introduced, which mentions that the component content of the working electrode is "lignin porous carbon nanosheets, acetylene black, and polytetrafluoroethylene emulsion (solid content 60 wt%) in a mass ratio of 8:1:1". Chinese Patent Application CN 116282016A introduces a method for improving the conductivity of activated carbon materials. By using the principles of metal-catalyzed graphitization and weak oxidation with a weak oxidant, single-layer or multi-layer graphite crystals are formed on the surface where the weak oxidant contacts the carbon, and by adjusting the pore size and pore volume using a gas-like weak oxidant, the conductivity and effective pore content of the activated carbon are improved. However, this method is relatively complex and requires reheating the already prepared activated carbon for treatment.

[0006] Therefore, there is an urgent need for a porous carbon material with a high specific surface area, high conductivity, and no other side effects on production. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the present invention provides a carbon material, its preparation method, and its application in supercapacitors. The carbon material has a high specific surface area and high conductivity, and does not require multiple activation synthesis steps, which can significantly reduce costs.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] On the one hand, the present invention provides a preparation method of a carbon material, including the following steps:

[0010] S1. Mix biomass and graphite to obtain a precursor mixture;

[0011] S2. Perform high-speed dry mixing of the precursor mixture and an activator, and fully mix to obtain a mixed powder;

[0012] S3. Perform low-temperature pre-activation of the mixed powder under an inert gas, then perform high-temperature activation. After the activation is completed, lower the temperature of the product to room temperature, wash it with acid, then wash, filter, and dry it with water to obtain the carbon material.

[0013] Preferably, the biomass described in step S1 includes agricultural biomass, forestry biomass, and fishery biomass.

[0014] Further preferably, the biomass includes at least one of coconut shell, walnut shell, rice husk, pine seed shell, corn straw, pepper straw, palm kernel shell, wheat straw, rice straw, cotton straw, soybean straw, broad bean straw, pea straw, peanut shell, sorghum straw, rice bran, banana peel, apple peel, orange peel, mango peel, radish leaves, wax gourd vine and corncob.

[0015] Further preferably, the biomass is coconut shell or walnut shell.

[0016] Preferably, the graphite in step S1 includes natural graphite, synthetic graphite or graphite that has been used but still maintains a lamellar structure.

[0017] Further preferably, the graphite includes at least one of highly oriented pyrolytic graphite, flake graphite, cryptocrystalline graphite and granite-type graphite.

[0018] Preferably, the activator in step S2 includes at least one of potassium carbonate, potassium bicarbonate, potassium oxalate, potassium acetate, potassium dihydrogen phosphate, potassium sodium tartrate, potassium citrate and potassium metaaluminate.

[0019] Further preferably, the activator includes at least one of potassium carbonate, potassium bicarbonate, potassium oxalate, potassium acetate and potassium dihydrogen phosphate.

[0020] Most preferably, the activator is potassium carbonate.

[0021] Preferably, the particle sizes of the biomass and graphite in step S1 are 1 - 500 μm; the particle size of the activator in step S2 is 1 - 500 μm.

[0022] Preferably, the mass of the graphite in step S1 is 2% - 10% of the precursor mixture.

[0023] Further preferably, the mass of the graphite in step S1 is 5% - 10% of the precursor mixture.

[0024] Most preferably, the mass of the graphite in step S1 is 5% of the precursor mixture.

[0025] Preferably, the mass ratio of the biomass and graphite in step S1 is 1:X, where X is greater than 0 and less than or equal to 1.

[0026] Preferably, the mass ratio of the precursor mixture and the activator in step S2 is 1:Y, where Y is greater than or equal to 0.1.

[0027] Preferably, the conditions for low-temperature pre-activation in step S3 are: temperature 400 - 600 °C, time 1 - 2 h.

[0028] Further preferably, the conditions for the low-temperature pre-activation in step S3 are: temperature 400°C, time 1 h.

[0029] Preferably, the conditions for the high-temperature activation in step S3 are: temperature 700 - 900°C, time 1 - 3 h.

[0030] Further preferably, the conditions for the high-temperature activation in step S3 are: temperature 800°C, time 2 h.

[0031] Preferably, the conditions for the pickling in step S3 are: acid solution concentration 0.5 - 2 mol / L, pickling time 10 min - 4 h.

[0032] The present invention also provides a carbon material prepared by the above preparation method.

[0033] Preferably, the carbon material contains a multi-layer graphene structure.

[0034] The multi-layer graphene structure can provide a certain number of micropores and improve the conductivity of the carbon material at the same time.

[0035] On the other hand, the present invention also provides an application of the carbon material prepared by the above preparation method or the above carbon material in the preparation of a supercapacitor.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The porous carbon material of the present invention has a high tap density and good electrical conductivity. As an active material for a supercapacitor electrode, a lower proportion of conductive agent can be used to achieve better electrical properties; the present invention synthesizes a porous carbon material with a high specific surface area and high conductivity by a one-step method, without multiple activation synthesis steps, which can greatly reduce costs and has no side effects. Description of the Drawings

[0038] Figure 1 It is the SEM image of the carbon material of Example 1;

[0039] Figure 2 It is the TEM image of the carbon material of Example 1, where the white dotted box indicates the multi-layer graphene sheet structure, and it can be observed that there are about 5 - 7 layers of graphene;

[0040] Figure 3 It is the typical pore distribution diagram of the carbon material of Example 1;

[0041] Figure 4 It is the graph of the specific surface area of the carbon material of Example 1 changing with the graphite content;

[0042] Figure 5 It is the graph of the tapped density of the carbon material of Example 1 changing with the graphite content;

[0043] Figure 6 It is a charge-discharge comparison diagram of the supercapacitor battery made of the active carbon material in Example 1 and the commercial one. Specific Embodiments

[0044] The present invention will be described below through specific embodiments to make the technical solutions of the present invention easier to understand and master. However, the present invention is not limited thereto. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0045] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. Unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" as used herein include both singular and plural referents. Numerical ranges expressed by endpoints include all values and fractions within the corresponding ranges, as well as the expressed endpoints.

[0046] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. The experimental methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, can all be obtained from commercial channels.

[0047] Sources of experimental raw materials:

[0048] YP-50 activated carbon was purchased from Kuraray Co., Ltd. in Japan; commercial activated carbon was purchased from Yuanli Co., Ltd., with the model DR-90; artificial granulated graphite was purchased from BETRAY Co., Ltd., with the model EH.

[0049] Example 1

[0050] A precursor mixture was obtained by mixing coconut shell and artificial granulated graphite in a mass ratio of 0.95:0.05. The precursor mixture was dry-mixed with potassium carbonate at a mass ratio of 1:2 at high speed to obtain a well-mixed powder mixture. Then, the powder mixture was pre-activated at a low temperature under nitrogen. The pre-activation temperature was 400 °C and the time was 1 h. Then, high-temperature activation was carried out. The high-temperature activation temperature was 800 °C and the high-temperature activation time was 2 h. After the activation was completed, the temperature of the product was lowered to room temperature, and it was soaked in 1 mol / L acid solution for 10 min for pickling, and then washed with water and filtered. The pH of the obtained filtrate was > 6.0. Then, it was dried to obtain the carbon material described above.

[0051] Figure 1It is the SEM image of the carbon material. It can be seen that multilayer graphene begins to exfoliate from the graphite surface. Both graphite and multilayer graphene can improve the conductivity of the carbon material; the porous carbon has no obvious structure. Figure 2 It is the TEM image of the carbon material, showing a multilayer graphene structure, which can further improve the conductivity of the material.

[0052] Example 2

[0053] Mix coconut shell and artificial granulated graphite in a mass ratio of 0.9:0.1 to obtain a precursor mixture. Perform high-speed dry mixing of the precursor mixture and potassium carbonate in a mass ratio of 1:2 to obtain a well-mixed powder mixture. Then, pre-activate the powder mixture under nitrogen at a pre-activation temperature of 500 °C for 1 h, followed by high-temperature activation at a high-temperature activation temperature of 900 °C for 1 h. After the activation is completed, cool the product temperature to room temperature, soak it in 1 mol / L acid solution for 10 min for pickling, then wash with water and filter. The pH of the obtained filtrate is > 6.0, and then dry to obtain the carbon material described above.

[0054] Example 3

[0055] Mix walnut shell and artificial granulated graphite in a mass ratio of 0.95:0.05 to obtain a precursor mixture. Perform high-speed dry mixing of the precursor mixture and potassium carbonate in a mass ratio of 1:2 to obtain a well-mixed powder mixture. Then, pre-activate the powder mixture under nitrogen at a pre-activation temperature of 600 °C for 1 h, followed by high-temperature activation at a high-temperature activation temperature of 700 °C for 3 h. After the activation is completed, cool the product temperature to room temperature, soak it in 1 mol / L acid solution for 10 min for pickling, then wash with water and filter. The pH of the obtained filtrate is > 6.0, and then dry to obtain the carbon material described above.

[0056] Example 4

[0057] Compared with Example 1, the only difference is that the mass ratio of coconut shell to artificial granulated graphite is 0.98:0.02, and the other steps are the same as those in Example 1.

[0058] Comparative Example 1

[0059] Compared with Example 1, the only difference is that the mass ratio of coconut shell to artificial granulated graphite is 0.99:0.01, and the other steps are the same as those in Example 1.

[0060] Comparative Example 2

[0061] Compared with Example 1, the only difference is that the mass ratio of coconut shell to artificial granulated graphite is 0.7:0.3, and the other steps are the same as those in Example 1.

[0062] Comparative Example 3

[0063] Compared with Example 1, the only difference is that the mass ratio of coconut shell to artificial granulated graphite is 0.5:0.5, and other steps are the same as those in Example 1.

[0064] Effect Example

[0065] 1. Comparison of conductivity and capacitance of electrodes

[0066] Test method: The carbon materials of Examples 1-4 and Comparative Examples 1-3 were respectively crushed and sieved to obtain powders with a particle size of <20um. About 0.5g of carbon material powder was put into a circular mold, and its conductivity was measured by a powder resistivity meter. YP-50 activated carbon and commercial activated carbon were respectively crushed and sieved to obtain powders with a particle size of <20um. About 0.5g of activated carbon powder was respectively put into a circular mold, and its conductivity was measured by a powder resistivity meter.

[0067] The carbon material powder and the activated carbon powder were respectively mixed with modified PTFE at a mass ratio of 96:4 at high speed, ground and repeatedly roll-pressed to obtain a dry electrode film with a thickness of 150um. After the electrode was compounded with carbon-coated aluminum foil, a sheet electrode was made, and a battery was made with a cellulose separator and a 1M TEABF4 / ACN solution. The fabricated battery was charged and discharged in the voltage range of 0-2.5V at a current density of 0.1A / g to measure the specific capacitance of the supercapacitor.

[0068] Test results: As shown in Table 1 below.

[0069] Table 1 Comparison table of conductivity and specific capacitance of dry electrodes made of carbon materials and activated carbon with different graphite precursor ratios

[0070]

[0071]

[0072] According to the results in Table 1, it can be seen that compared with commercial activated carbon materials, the conductivity of the materials after adding graphite increases significantly, and its conductivity increases with the increase of graphite content. However, the specific capacitance of the battery made of activated carbon added with graphite reaches the peak when the graphite content is 5%, and then its specific capacitance decreases rapidly, which may be mainly due to the rapid decrease of its specific surface area. Compared with commercial activated carbon, the supercapacitor specific capacitance of the materials with a graphite content of 2%-10% is better.

[0073] 2. Detection of specific surface area of carbon materials

[0074] Test method: The BET specific surface area of the carbon material of Example 1 was measured by the nitrogen adsorption method as Figure 4 shown.

[0075] According to Figure 4It can be seen that the specific surface area of the carbon material changes with the proportion of graphite. It decreases slowly before 5% and rapidly after 5%.

[0076] 3. Detection of the Compaction Density of the Carbon Material

[0077] Test method: The carbon material of Example 1 was crushed and sieved to obtain a powder with a particle size of <20 μm. Approximately 0.5 g of the material powder was placed into a circular mold, and its compaction density was measured using a powder compaction density meter.

[0078] According to Figure 5 It can be seen that the compaction density of the carbon material increases with the increase in the proportion of graphite.

[0079] 4. Comparison of the Charge-Discharge Performance of the Supercapacitors Prepared from the Carbon Material

[0080] Test method: The carbon material of Example 1 and the commercial YP-50 activated carbon material were respectively mixed with modified PTFE at a mass ratio of 96:4 at high speed, ground, and repeatedly roll-pressed to obtain a dry electrode film with a thickness of 150 μm. After the electrode was compounded with carbon-coated aluminum foil, a sheet electrode was made, and a battery was made together with a cellulose separator and a 1 M TEABF4 / ACN solution. The voltage change of the fabricated battery was measured during charge and discharge at a current density of 0.1 A / g in the voltage range of 0 - 2.5 V. The results are as Figure 6 shown.

[0081] According to Figure 6 It can be seen that during the charge-discharge experiment at the same current density, the charge-discharge time of the carbon material of Example 1 is longer than that of the YP-50 activated carbon, proving that it can store more charges, and the capacity of the carbon material of Example 1 is significantly better than that of the commercial YP-50 activated carbon material. The instantaneous voltage drop of the carbon material of Example 1 during the discharge stage is less than that of the commercial YP-50, proving that its internal resistance is less than that of the commercial YP-50 material.

[0082] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the protection scope of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A preparation method of a carbon material, characterized in that: It includes the following steps: S1. Mix biomass and graphite to obtain a precursor mixture; S2. Carry out high-speed dry mixing of the precursor mixture and an activator, and fully mix to obtain a mixed powder; S3. Carry out low-temperature pre-activation of the mixed powder under an inert gas, then carry out high-temperature activation. After the activation is completed, cool the product temperature to room temperature, wash with acid, then wash with water, filter, and dry to obtain a carbon material.

2. The preparation method according to claim 1, characterized in that: The biomass described in step S1 includes agricultural biomass, forestry biomass, and fishery biomass.

3. The preparation method according to claim 2, wherein: The biomass includes at least one of coconut shell, walnut shell, rice husk, pine nut shell, corn straw, pepper straw, palm kernel shell, wheat straw, rice straw, cotton straw, soybean straw, broad bean straw, pea straw, peanut shell, sorghum straw, rice bran, banana peel, apple peel, orange peel, mango peel, radish leaves, wax gourd vine, and corn cob.

4. The preparation method according to claim 3, characterized in that: The biomass is coconut shell or walnut shell.

5. The preparation method according to claim 1, characterized in that: The graphite described in step S1 includes natural graphite, synthetic graphite, or graphite that has been used but still maintains a lamellar structure.

6. The preparation method according to claim 1, characterized in that: The activator described in step S2 includes at least one of potassium carbonate, potassium bicarbonate, potassium oxalate, potassium acetate, potassium dihydrogen phosphate, sodium potassium tartrate, potassium citrate, and potassium metaaluminate.

7. The preparation method according to claim 6, characterized in that: The activator includes at least one of potassium carbonate, potassium bicarbonate, potassium oxalate, potassium acetate, and potassium dihydrogen phosphate.

8. The preparation method according to claim 7, characterized in that: The activator is potassium carbonate.

9. The preparation method according to claim 1, characterized in that: The mass of the graphite described in step S1 is 2%-10% of the precursor mixture.

10. The preparation method according to claim 1, characterized in that: The conditions for the low-temperature pre-activation described in step S3 are: temperature 400-600 °C, time 1-2 h.

11. According to the preparation method described in claim 1, wherein: The conditions for the high-temperature activation described in step S3 are: temperature 700-900 °C, time 1-3 h.

12. A carbon material prepared by the preparation method according to any one of claims 1-11.

13. The carbon material according to claim 12, characterized in that: The carbon material contains a multi-layer graphene structure, and the multi-layer graphene has micropores.

14. Application of the carbon material prepared by the preparation method according to any one of claims 1-11 or the carbon material according to any one of claims 12-13 in the preparation of a supercapacitor.

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