Preparation method of soft-hard heterostructure porous carbon and application thereof in supercapacitor

Abstract

The application discloses a preparation method of soft-hard heterostructure porous carbon and application of the soft-hard heterostructure porous carbon in supercapacitors and belongs to the technical field of energy storage. The method comprises the following steps: biomass is put into a tubular furnace to prepare biomass pyrolysis carbon by pyrolysis, and the biomass pyrolysis carbon is used as a hard carbon precursor; PET is cut and washed, and plastic pyrolysis carbon is prepared by pyrolysis in the tubular furnace, and the plastic pyrolysis carbon is used as a soft carbon precursor; the soft and hard carbon precursors are mixed in a certain proportion and uniformly ground, and soft-hard heterostructure porous carbon material is prepared by a chemical co-activation method; through optimization of experimental conditions, the structure and properties of the soft-hard heterostructure porous carbon are regulated, the soft-hard heterostructure porous carbon is used as a high-quality loaded carbon electrode material, and the soft-hard heterostructure porous carbon is applied to supercapacitors. The graphitization degree and conductivity of the soft-hard heterostructure porous carbon are improved, defect engineering is effectively constructed through heteroatom self-doping, the interaction force between electrolyte ions and the electrode surface is increased, and the wettability of the electrode material is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of energy storage, and specifically discloses a preparation method of soft-hard heterogeneous structure porous carbon and application thereof in supercapacitors. BACKGROUND

[0002] Biomass-based porous carbon and PET plastic-derived porous carbon are ideal supercapacitor electrode materials due to their high carbon content and low cost. Biomass, as a thermosetting material, is an important precursor for preparing hard carbon materials after high-temperature carbonization. Hard carbon materials have high disorder degree and large interlayer distance, which is beneficial to ion intercalation and extraction. However, the low conductivity of hard carbon materials and the structural defects caused by the disordered structure result in unsatisfactory cycle performance of supercapacitors. PET is a condensation polymer of terephthalic acid and ethylene glycol, and is collectively referred to as thermoplastic polyester together with PBT. PET is an important source for preparing soft carbon materials after pyrolysis, cracking and other treatments. The interlayer arrangement of soft carbon is relatively ordered, and the degree of graphitization is high, which has excellent conductivity. However, the low interlayer spacing and limited adsorption sites of soft carbon limit ion transmission and thus reduce the electrochemical performance of the material. Therefore, both types of porous carbon materials have their advantages and disadvantages, and the synergistic effect between soft / hard carbon materials will compensate for their respective disadvantages and enhance the electrochemical performance of the composite material.

[0003] Most patent reports on plastics are used in automobile shells, biomedical engineering, building engineering materials, etc., and there is currently no patent report on using PET as a soft carbon precursor to prepare composite materials for energy storage. However, there have been reports on the use of plastics in the energy storage field, for example: Chinese patent document with publication number CN118744982A discloses a method for preparing carbon nanotubes from waste olefin plastics and waste carbon fibers, and its application in supercapacitors. And Chinese patent document with publication number CN118458765A discloses a method for preparing porous carbon from chlorinated plastics and its application. The above-mentioned prior art solutions all provide carbon materials derived from plastics for use in the energy storage field, providing an important reference for the high-value utilization of plastics, but the factors affecting their electrochemical performance are not elaborated in detail.

[0004] Laboratory studies usually use low mass loading electrodes, and the active material loading mass is usually 2-3 mg / cm 2 , which can exhibit good electrochemical performance. However, for commercial applications, the active material loading mass needs to be increased to 10 mg / cm 2, and can be used as the evaluation standard for its commercial application. There are related reports on patents for preparing high-quality supported electrode materials, for example: Chinese patent document with publication number CN108292608B discloses a supercapacitor electrode and a cell with high active mass loading. The electrode and the cell with high mass loading are prepared by increasing the specific surface area, pore structure and thickness of the material, but the influence of high mass loading structure on the electrochemical performance is not specifically described. With the increase of mass loading, the electrode thickens, the ion transport channel between the electrode active material and the electrolyte is lengthened, the utilization rate of the active material is reduced, which leads to the intensification of charge redistribution phenomenon, and the hindrance of the non-active materials such as the current collector and the binder will also lead to the decrease of the cycle stability, it is difficult to maintain excellent electrochemical performance in the case of thin electrode, and the decrease of the device performance is an inevitable phenomenon. Therefore, it is necessary to solve the related problems by adjusting the microstructure of the electrode material. SUMMARY

[0005] The present application aims at the problems existing in the prior art, and provides a preparation method of soft-hard heterogeneous structure porous carbon. Biomass and PET plastic are used as hard carbon precursor and soft carbon precursor respectively to prepare soft-hard heterogeneous structure porous carbon through carbonization and chemical co-activation, and the soft-hard heterogeneous structure porous carbon is used as electrode material for supercapacitors. The electrode material prepared by the present application has a low oxygen functional group content, and is used as electrode material for high mass loading aqueous supercapacitors, which exhibits excellent electrochemical performance, especially slow leakage current, low self-discharge rate and high area capacitance.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] In a first aspect, a preparation method of soft-hard heterogeneous structure porous carbon is provided, comprising the following steps:

[0008] Step 1: Biomass raw materials are crushed and impurities are removed to obtain biomass powder; PET plastic is cut and washed and dried to obtain PET plastic fragments;

[0009] Step 2: The biomass powder and the PET plastic fragments prepared in step 1 are respectively placed in a tube furnace and pyrolyzed and carbonized in an inert atmosphere, the heating rate is 5℃ / min, the carbonization temperature is 600℃, and the carbonization time is 1h, to obtain biomass pyrolysis carbon CHC and plastic pyrolysis carbon PHC respectively;

[0010] Step 3: Biomass pyrolysis carbon CHC and plastic pyrolysis carbon PHC prepared in step 2 are mixed in different proportions, then mixed with NaOH in a mass ratio of 1:2.5, and then uniformly ground, activated in an inert atmosphere in a tube furnace at 750 DEG C for 1h, then taken out after cooling to room temperature, washed with deionized water until neutral, and then dried in an oven at 120 DEG C to obtain a soft and hard heterogeneous structure porous carbon.

[0011] Further, the biomass in step 1 includes one of chitosan, gelatin, rice husk, bamboo, and cotton.

[0012] Further, the PET plastic in step 1 is cut into pieces, then cleaned with anhydrous ethanol and deionized water by ultrasonic cleaning, and then dried at 50 DEG C.

[0013] According to an embodiment of the present application, the biomass pyrolysis carbon CHC and the plastic pyrolysis carbon PHC in step 3 are mixed in a mass ratio of 6:1.

[0014] According to an embodiment of the present application, the biomass pyrolysis carbon CHC and the plastic pyrolysis carbon PHC in step 3 are mixed in a mass ratio of 4:1.

[0015] According to an embodiment of the present application, the biomass pyrolysis carbon CHC and the plastic pyrolysis carbon PHC in step 3 are mixed in a mass ratio of 2:1.

[0016] According to a preferred embodiment of the present application, the biomass pyrolysis carbon CHC and the plastic pyrolysis carbon PHC in step 3 are mixed in a mass ratio of 1:1.

[0017] In a second aspect, the soft and hard heterogeneous structure porous carbon prepared by the above method is used as a high-quality 10-12mg / cm 2 The carbon electrode material is applied to a supercapacitor.

[0018] Preferably, the mass loading of the soft and hard heterogeneous structure porous carbon is 11.3mg / cm 2 .

[0019] Through the above technical solutions, the present application can bring the following beneficial effects:

[0020] 1. PET is a high-molecular-weight polymer formed by the esterification and polycondensation reaction of terephthalic acid and ethylene glycol. The presence of ester bonds gives PET good thermal stability, with a melting point of approximately 260℃. During high-temperature carbonization, PET undergoes molecular chain breakage and isomerization, transforming large organic molecules into smaller molecules such as gases and liquids (oils) and coke, forming PET pyrolysis char (PHC). Biomass contains active groups such as amino and hydroxyl groups. Under carbonization conditions of 600℃ for 1 hour, some C, H, O, and N escape in gaseous form, relatively reducing heteroatoms and generating biomass pyrolysis char (CHC). The soft-hard heterostructure porous carbon prepared by chemical co-activation of CHC and PHC has a higher heteroatom content, a larger specific surface area, and a rich microporous structure. Introducing PHC into CHC increases the mechanical properties of the soft-hard heterostructure porous carbon, which is beneficial for improving the cycle stability of electrochemical energy storage devices.

[0021] 2. Compared to PET-derived soft carbon and biomass-derived hard carbon, the soft-hard heterostructure porous carbon prepared in this invention, through the synergistic effect between short-range disordered hard carbon and long-range ordered soft carbon, increases the specific surface area of ​​the composite material. Its abundant pore structure provides more adsorption sites for ion storage. Simultaneously, the conductivity, graphitization degree, and mechanical stability of the soft-hard heterostructure porous carbon material are all improved, which is beneficial for enhancing the electrochemical performance of supercapacitors.

[0022] A further beneficial effect is that porous carbon with a soft-hard heterostructure is used as an electrode material in supercapacitors, with a mass loading of 11.3 mg / cm³. 2 It exhibits excellent electrochemical performance: at a current density of 0.1 A / g, the areal capacitance is 3.72 F / cm². 2 The specific capacitance is 329.57 F / g, the voltage retention rate is 78.29%, and the open-circuit voltage decay rate is 21.85 mV / h; after 10,000 constant current charge-discharge cycles at a current density of 1 A / g, the capacitance retention rate is 94.14%. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 Leakage current versus constant voltage charging time curves for porous carbon with different soft and hard heterostructures.

[0025] Figure 2The rate performance comparison chart of the soft and hard heterogeneous structure porous carbon of different samples.

[0026] Figure 3 The constant current charge and discharge comparison chart of the soft and hard heterogeneous structure porous carbon of different samples.

[0027] Figure 4 The area capacitance comparison chart of the soft and hard heterogeneous structure porous carbon of different samples.

[0028] Figure 5 The impedance comparison chart of the soft and hard heterogeneous structure porous carbon of different samples.

[0029] Figure 6 The cycle stability comparison chart of the soft and hard heterogeneous structure porous carbon of different samples.

[0030] Figure 7 The energy density and power density relationship chart of the soft and hard heterogeneous structure porous carbon of different samples.

[0031] Figure 8 The SEM chart of the CP-HPC-4 soft and hard heterogeneous structure porous carbon;

[0032] Figure 9 The preparation method flow chart of the soft and hard heterogeneous structure porous carbon. DETAILED DESCRIPTION

[0033] The biomass is put into a tube furnace for pyrolysis to prepare biomass pyrolysis carbon, which is used as a hard carbon precursor; the waste plastic PET is cut and washed, and is pyrolyzed in a tube furnace to prepare plastic pyrolysis carbon, which is used as a soft carbon precursor; the soft and hard carbon precursors are mixed in a set ratio and uniformly ground, and a soft and hard heterogeneous structure porous carbon material is prepared by a chemical co-activation method; through optimization of experimental conditions, the structure and properties of the soft and hard heterogeneous structure porous carbon are regulated, and the soft and hard heterogeneous structure porous carbon is used as a high-quality load (10-12mg / cm 2 ) carbon electrode material and is applied to supercapacitors.

[0034] In order to more clearly show the present application, the present application will be further described below in combination with preferred embodiments, and those skilled in the art should understand that the specific description below is illustrative rather than limiting, and should not limit the protection scope of the present application. In order to avoid obscuring the essence of the present application, well-known methods and processes are not described in detail.

[0035] Example 1

[0036] The embodiment provides a preparation method of biomass-based porous carbon, including:

[0037] The chitosan powder is placed in a tube furnace filled with a nitrogen atmosphere (the chitosan itself has a certain heteroatomic content, so no additional doping is required), and heated to 600℃ at a heating rate of 5℃ / min, maintained for 1h, ground to room temperature, to obtain biomass pyrolysis carbon CHC; the obtained CHC is uniformly ground with NaOH at a mass ratio of 1:2.5, placed in a tube furnace filled with nitrogen, heated to 450℃ at a heating rate of 5℃ / min, maintained for 30min, and then heated to 750℃ for 1h, cooled to room temperature, washed with deionized water until neutral, then soaked in a 1mol / L HCl solution for 1h, washed with deionized water until neutral, placed in an oven at 120℃ for drying and grinding, to obtain biomass-based porous carbon CHPC.

[0038] Example 2

[0039] The present embodiment proposes a method for preparing plastic-derived porous carbon, comprising:

[0040] The raw material PET plastic is cut into pieces, ultrasonically cleaned with anhydrous ethanol and deionized water, and dried in an oven at 50℃ to obtain PET pieces; the obtained PET pieces are placed in a tube furnace filled with a nitrogen atmosphere, heated to 600℃ at a heating rate of 5℃ / min, maintained for 1h, ground to room temperature, to obtain plastic pyrolysis carbon PHC; the obtained PHC is uniformly ground with NaOH at a mass ratio of 1:2.5, placed in a tube furnace filled with nitrogen, heated to 450℃ at a heating rate of 5℃ / min, maintained for 30min, and then heated to 750℃ for 1h, cooled to room temperature, washed with deionized water until neutral, then soaked in a 1mol / L HCl solution for 1h, washed with deionized water until neutral, placed in an oven at 120℃ for drying and grinding, to obtain plastic-derived porous carbon PHPC.

[0041] Example 3

[0042] The present embodiment proposes a method for preparing soft-hard heterogeneous structure porous carbon, comprising:

[0043] The biomass pyrolysis carbon CHC in Example 1 and the plastic pyrolysis carbon PHC in Example 2 are mixed at a mass ratio of 6:1, and uniformly ground to obtain a pyrolysis carbon mixture; the obtained pyrolysis carbon mixture is uniformly ground with NaOH at a mass ratio of 1:2.5, placed in a tube furnace filled with nitrogen, heated to 450℃ at a heating rate of 5℃ / min, maintained for 30min, and then heated to 750℃ for 1h, cooled to room temperature, washed with deionized water until neutral, then soaked in a 1mol / L HCl solution for 1h, washed with deionized water until neutral, placed in an oven at 120℃ for drying and grinding, to obtain soft-hard heterogeneous structure porous carbon CP-HPC-6.

[0044] Example 4

[0045] The biomass pyrolysis carbon CHC in Example 1 and the plastic pyrolysis carbon PHC in Example 2 were mixed in a mass ratio of 4:1, and other conditions were consistent with Example 3, to obtain the soft and hard heterogeneous structure porous carbon CP-HPC-4.

[0046] Example 5

[0047] The biomass pyrolysis carbon CHC in Example 1 and the plastic pyrolysis carbon PHC in Example 2 were mixed in a mass ratio of 2:1, and other conditions were consistent with Example 3, to obtain the soft and hard heterogeneous structure porous carbon CP-HPC-2.

[0048] Example 6

[0049] The biomass pyrolysis carbon CHC in Example 1 and the plastic pyrolysis carbon PHC in Example 2 were mixed in a mass ratio of 1:1, and other conditions were consistent with Example 3, to obtain the soft and hard heterogeneous structure porous carbon CP-HPC-1.

[0050] Example 7

[0051] The optimal mixing ratio of biomass pyrolysis carbon CHC and plastic pyrolysis carbon PHC is 4:1 in mass ratio. On this basis, the soft and hard heterogeneous structure porous carbon CP-HPC-4 prepared therefrom is applied in supercapacitors as a high-quality loading electrode material. The mass loading of the electrode material is improved to the commercial level, and good electrochemical performance is maintained.

[0052] Through N2 adsorption test, the specific surface area of the optimal sample CP-HPC-4 is 2710m 2 / g, the proportions of micropores and mesopores are 79.35% and 20.65% respectively. The high specific surface area can provide abundant active sites for the adsorption of charge ions, the proportion of micropores is conducive to ion storage, and the mesopores are conducive to the rapid transfer of charge ions. The cooperation between micropores and mesopores exhibits the efficient mass transfer advantage of CP-HPC-4. According to the resistivity of four-probe powder resistivity test, the resistivities of CHPC, PHPC and CP-HPC-4 are 0.31Ω / cm, 0.19Ω / cm and 0.25Ω / cm respectively ， The introduction of soft carbon enhances the conductivity of the soft and hard heterogeneous structure porous carbon. The present application effectively constructs defect engineering through heteroatom self-doping, increases the interaction force between electrolyte ions and the electrode surface, and improves the wettability of the electrode material. The fine adjustment of the above microstructure effectively reduces the leakage current and self-discharge problem of the supercapacitor, and improves the cycle stability of the electrochemical energy storage device.

[0053] Table 1 and Table 2 show the electrochemical performance of the samples of Examples 1-6. Table 3 and Table 4 show the electrochemical performance of the sample of Example 7 at different mass loadings. Figure 1 Time curves of the leakage current of different samples of soft-hard heterostructure porous carbon and constant voltage charging are shown. Figure 2 A comparison chart of the rate performance of different samples of soft-hard heterostructure porous carbon is shown. Figure 3 A comparison chart of the constant current charging and discharging of different samples of soft-hard heterostructure porous carbon is shown. Figure 4 A comparison chart of the area capacitance of different samples of soft-hard heterostructure porous carbon is shown. Figure 5 A comparison chart of the impedance of different samples of soft-hard heterostructure porous carbon is shown. Figure 6 A comparison chart of the cycle stability of different samples of soft-hard heterostructure porous carbon is shown. Figure 7 A graph of the energy density and power density of different samples of soft-hard heterostructure porous carbon is shown. Figure 8 A SEM image of CP-HPC-4 soft-hard heterostructure porous carbon is shown. Figure 9 A flow chart of the preparation method of soft-hard heterostructure porous carbon is shown.

[0054] Table 1

[0055]

[0056] Table 2

[0057]

[0058] Table 3

[0059]

[0060]

[0061] Table 4

[0062]

[0063] Note: All electrochemical tests were tested in a two-electrode system in a KOH aqueous electrolyte with a molar concentration of 6 mol / L.

[0064] According to Table 1 and Table 2, compared with biomass hard carbon and plastic-derived soft carbon, the leakage current and self-discharge phenomenon of soft-hard heterostructure porous carbon CP-HPC-X are reduced. X is the ratio of CHC to PHC, X = 6, 4, 2, 1; with the introduction of soft carbon, the cycle stability and rate performance of the heterostructure porous carbon are also improved.

[0065] According to Table 3 and Table 4, compared with the low mass loading electrode, the optimal sample CP-HPC-4 has weakened leakage current, reduced open circuit voltage decay rate and improved cycle stability after being made into high mass loading electrode. The soft-hard heterogeneous structure porous carbon applied to supercapacitors as electrode material shows good electrochemical performance.

[0066] The biomass of the application is not limited to chitosan, and one of gelatin, rice husk, bamboo, cotton and the like can also be used.

[0067] In addition to PET plastic, the raw material of the plastic pyrolysis carbon can also use one of polyethylene PE, polypropylene PP, polystyrene PS and polyester.

[0068] In summary, the application provides a soft-hard heterogeneous structure porous carbon preparation method and its application in supercapacitors, which provides an innovative scheme for high-value utilization of plastic waste and biomass waste. Through the synergistic effect of soft and hard carbon, the specific surface area of the soft-hard heterogeneous structure porous carbon is improved, the graphitization degree and mechanical stability of the material are enhanced, the leakage current and self-discharge phenomenon of the supercapacitor are inhibited, and the electrochemical performance of the high mass loading supercapacitor is enhanced.

[0069] Obviously, the above description of the embodiments is only used to help understand the method of the application and its core idea, but for those skilled in the art, various changes, modifications and replacements can be made to the embodiments without departing from the spirit and principles of the application described in the claims, and these improvements and modifications also fall within the protection scope of the claims of the application.

Claims

1. A method for producing a soft-hard heterostructure porous carbon, characterized by, The method comprises the following steps: Step 1: crushing a biomass raw material, removing impurities, and obtaining a biomass powder; cutting PET plastic, and cleaning and drying the PET plastic to obtain PET plastic pieces; Step 2: placing the biomass powder and the PET plastic pieces prepared in step 1 in a tube furnace respectively, pyrolyzing and carbonizing in an inert atmosphere, a temperature rising rate being 5 ℃ / min, a carbonization temperature being 600 ℃, and a carbonization time being 1 h, to obtain biomass pyrolysis carbon CHC and plastic pyrolysis carbon PHC respectively; Step 3: mixing the biomass pyrolysis carbon CHC and the plastic pyrolysis carbon PHC prepared in step 2 according to different proportions, mixing with NaOH according to a mass ratio of carbon to alkali of 1:2.5, grinding thoroughly and uniformly, raising the temperature to 450 ℃ at a temperature rising rate of 5 ℃ / min and keeping for 30 min, continuously raising the temperature to 750 ℃ and keeping for 1 h, lowering to room temperature, washing with deionized water until neutral, adding a 1 mol / L HCl solution for immersion for 1 h, washing with deionized water until neutral, placing in an oven for drying at 120 ℃ and grinding, to obtain a soft-hard heterogeneous structure porous carbon.

2. The method for producing a soft-hard heterostructure porous carbon according to claim 1, wherein The biomass in step 1 comprises one of chitosan, gelatin, rice husk, bamboo and cotton.

3. The method for preparing porous carbon with a soft-hard heterostructure according to claim 1, characterized in that, After the PET plastic is cut in step 1, the PET plastic is cleaned with anhydrous ethanol and deionized water by ultrasonic cleaning, and dried at 50 ℃.

4. The method of claim 1, wherein the soft-hard heterostructure porous carbon is prepared by the steps of: In step 3, the biomass pyrolysis carbon CHC and the plastic pyrolysis carbon PHC are mixed according to a mass ratio of 6:

1.

5. The method of claim 1, wherein the soft-hard heterostructure porous carbon is prepared by the steps of: In step 3, the biomass pyrolysis carbon CHC and the plastic pyrolysis carbon PHC are mixed according to a mass ratio of 4:

1.

6. The method of claim 1, wherein the soft-hard heterostructure porous carbon is prepared by the steps of: In step 3, the biomass pyrolysis carbon CHC and the plastic pyrolysis carbon PHC are mixed according to a mass ratio of 2:

1.

7. The method for preparing porous carbon with a soft-hard heterostructure according to claim 1, characterized in that, In step 3, the biomass pyrolysis carbon CHC and the plastic pyrolysis carbon PHC are mixed according to a mass ratio of 1:

1.

8. The soft-hard heterostructure porous carbon prepared by the method of any one of claims 1-7 as high quality support of 10-12 mg / cm 2 Carbon electrode materials are applied in supercapacitors.

9. The soft-hard heterostructure porous carbon prepared by the method of any one of claims 1-7 has a mass loading of 11.3 mg / cm 2 .

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