Porous graphene and method for preparing the same, and use of the conductive agent comprising the same

Abstract

The present application relates to the technical field of lithium ion batteries, and discloses porous graphene, a preparation method thereof, and application of a conductive agent containing the porous graphene; the preparation method of the porous graphene comprises the following steps: S1, dissolving a weak base in water to form an activation solution; S2, adding graphene into the activation solution to obtain a suspension; the suspension is subjected to heating pretreatment to obtain an activation product; and S3, the activation product is subjected to plasma treatment to obtain the porous graphene. Through the synergistic effect of weak base pretreatment and plasma etching pore treatment, the preparation of the porous graphene is realized in a mild environment of low alkali and low temperature. The method is simple, efficient, low in cost, green and environmentally friendly, low in energy consumption, easy to industrialize, and can prepare the porous graphene with different pore sizes and different pore amounts by changing the plasma radiation conditions.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to porous graphene, its preparation method, and the application of conductive agents containing it. Background Technology

[0002] Lithium-ion batteries are currently the most widely used energy storage devices. They are characterized by low cost, environmental friendliness, high specific energy, no memory effect, and light weight, making them a crucial component of power sources (medical equipment, entertainment devices, computers, communication equipment, electric vehicles, spacecraft, etc.). The positive electrode of lithium-ion batteries typically uses transition metal oxides as active materials, such as layered lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, or lithium iron phosphate, while the negative electrode often uses graphite, silicon-based materials, etc., as active materials.

[0003] Lithium iron phosphate (LFP) batteries play a vital role in power and energy storage due to their advantages such as high safety, long lifespan, low price, and environmental friendliness. However, LFP batteries also suffer from low conductivity (10⁻⁶ ppm). -9 -10 -10 S / cm) and low ion diffusion rate (10 -14 cm 2 The low specific capacity ( / s) of lithium-ion batteries limits their application. Therefore, conductive agents are added during battery manufacturing to create a continuous conductive network by utilizing the effective contact between conductive agents and filling the gaps in the active material. This improves the conductivity of the electrodes and enhances the electrical performance of lithium-ion batteries. Furthermore, the conductive agent needs to have good absorption and retention capabilities for the electrolyte, facilitating the transport and migration of lithium ions and reducing ohmic and electrochemical polarization of the electrodes.

[0004] Carbon-based conductive agents are commonly used in lithium-ion batteries due to their low cost and light weight. These agents mainly include conductive graphite, conductive carbon black, fibrous conductive agents, and graphene. Graphene, in particular, possesses the characteristics of being "extremely flexible, thin, and dense," exhibiting extremely high conductivity and a large contact area, far surpassing the performance of conductive graphite and conductive carbon black. However, its perfect two-dimensional planar sp2 structure, along with π–π stacking and van der Waals interactions, leads to graphene aggregation, posing a challenge to its dispersion. Furthermore, the dense planar structure of graphene hinders lithium-ion transport within the electrode, especially at high rates. Therefore, researchers have focused on preparing porous graphene. Various methods are used to create pores in graphene, and by adjusting the size and number of pores, the hindering effect of graphene on lithium-ion diffusion is minimized.

[0005] Traditional graphene activation and pore-forming techniques utilize strong acid and base reagents such as NaOH, KOH, HNO3, KMnO4, and concentrated H2SO4 for chemical activation and pore-forming. CN102070140A discloses a method that uses the reaction of strong base and carbon at high temperature to further chemically treat graphene powder obtained by heat treatment or microwave heat treatment, thereby rapidly and massively etching nanoscale micropores on the graphene surface, greatly increasing its specific surface area. However, the strong base reagent used in this invention is a prepared strong base aqueous solution with a concentration of 0.2-20 mol / L, which causes severe corrosion to equipment, has cumbersome operation steps, low production efficiency, and requires high activation temperature and time due to chemical reagent activation alone, resulting in high energy consumption and a significant increase in the cost of porous graphene. Furthermore, it generates a large amount of difficult-to-treat strong alkali and acid wastewater, increasing environmental pollution and treatment costs. Summary of the Invention

[0006] <Technical Problem Solved by the Invention>

[0007] This technology aims to address the problems of high energy consumption, high cost, and difficult post-processing caused by using strong alkalis and strong acids for hole formation in existing technologies.

[0008] <Technical Solution Adopted in This Invention>

[0009] To address the aforementioned technical problems, the present invention aims to provide porous graphene, its preparation method, and the application of conductive agents containing the same. The porous graphene provided by this invention features a mild, simple, and efficient process, making it easy to industrialize. The porous graphene obtained through this process, when used as a conductive agent, maintains high conductivity while providing a smooth and rapid channel for interlayer transport of electroactive materials, thereby enhancing the material's application potential in the lithium-ion battery field.

[0010] The details are as follows:

[0011] First, the present invention provides a method for preparing porous graphene, comprising the following steps:

[0012] S1 dissolves a weak base in water to form an activated solution;

[0013] S2 graphene is added to an activation solution to obtain a suspension; the suspension is pretreated by heating to obtain the activation product.

[0014] The S3 activation product was subjected to plasma treatment to obtain porous graphene.

[0015] Second, the present invention provides porous graphene obtained by the aforementioned preparation method.

[0016] Third, the present invention provides a positive electrode conductive agent for lithium-ion batteries, comprising porous graphene, active material, binder, and solvent as described above.

[0017] Fourth, the present invention provides a method for applying a conductive agent in the positive electrode of a lithium-ion battery, comprising the following steps:

[0018] Active materials, conductive agents, and binders are blended, ball-milled to obtain a slurry, the slurry is coated with aluminum foil, and assembled to obtain a button cell.

[0019] <Technical Mechanism Employed in This Invention>

[0020] Pretreatment of graphene with a weak base increases the number of active sites on the carbon layers. Then, oxygen plasma is generated by microwave irradiation of air, causing electron transitions and activating carbon atom reactions. Amorphous carbon is etched, thus producing porous graphene. The microwave Joule heating mechanism involves microwave-induced electron movement within the graphene, generating current in perfect graphene domains. This current encounters resistance heating at defects, causing thermal reactions in the oxygen-containing functional groups within the defect regions. The deoxygenation of sp3 carbon bonds produces sp2 carbon bonds, reducing the oxygen content of the porous graphene and maintaining its high electron mobility. The presence of these two reactions effectively reduces the problem of excessive oxygen-containing groups and decreased electron mobility in graphene caused by the alkali activation process while simultaneously creating pores on the graphene sheet.

[0021] <Beneficial effects achieved by the present invention>

[0022] By combining weak alkali pretreatment and plasma etching for pore formation, porous graphene was prepared under mild conditions of low alkali and low temperature. This method is simple, efficient, low-cost, environmentally friendly, energy-efficient, and easily industrialized. Furthermore, by changing the plasma radiation conditions, porous graphene with different pore sizes and quantities can be prepared. Besides its application as a conductive agent in lithium-ion batteries, the obtained porous graphene can also be used in various other fields, such as supercapacitor electrode materials, fuel cell catalysts, and various gas sensors, which is of great significance for expanding the industrial applications of porous graphene. Attached Figure Description

[0023] Figure 1 The images are scanning electron microscope (SEM) images of the porous graphene obtained in Example 3, a) is 5 μm, b) is 1 μm.

[0024] Figure 2 The images shown are transmission electron microscope (TEM) images of the porous graphene obtained in Example 3, where a) is 200 nm, b) is 100 nm, c) is 20 nm, and d) is 10 nm.

[0025] Figure 3 The graph shows the adsorption-desorption curves of the graphene derivatives obtained in Example 3 and Comparative Examples 2-3.

[0026] Figure 4 The graph shows the carbon, oxygen, and nitrogen content of the activated powder and porous graphene in Example 3.

[0027] Figure 5 The graph shows a comparison of the battery cycle performance and rate performance of Examples 3-4 and Comparative Examples 1-3. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0029] <Technical Solution>

[0030] A method for preparing porous graphene includes the following steps:

[0031] S1 dissolves a weak base in water to form an activated solution;

[0032] S2 graphene is added to an activation solution to obtain a suspension; the suspension is pretreated by heating to obtain the activation product.

[0033] The S3 activation product was subjected to plasma treatment to obtain porous graphene.

[0034] In some embodiments, the weak base includes at least one of NH3·H2O, (NH4)2CO3, or NH4HCO3; the pH of the activated solution formed by the weak base is between 7 and 8.5.

[0035] In some embodiments, the concentration of graphene in the suspension is 2-10 g / L; the particle size of graphene is 2-20 μm.

[0036] In some embodiments, the stirring speed during pretreatment is 20 rpm / min; the heating temperature is 70~100℃; and the heating time is 0.5~5h.

[0037] In some embodiments, the pretreatment drying method is vacuum drying, flash drying, or freeze drying.

[0038] In some embodiments, plasma treatment is performed by inductively coupled radio frequency discharge, plasma generation by electric field, or plasma generation by microwave radiation. Furthermore, microwave radiation technology is employed, utilizing microwave radiation of air to quickly and easily generate plasma for graphene etching. Simultaneously, the microwave Joule heating mechanism is used to reduce the oxygen content of the product and maintain its high electron mobility. Microwave radiation can be performed using a household or box furnace with a power of 800W~5KW, a microwave output density of 800W / g~1600W / g, and an output time of 1~5min. The container is one of an open beaker, a crucible, or a covered crucible.

[0039] Second, this invention provides porous graphene obtained by the aforementioned preparation method. The porous graphene material has a sheet diameter of 10 μm, an average pore size of 12 nm, and pore shapes selected from circular and elliptical shapes, with a specific surface area of ​​200 m². 2 With an electrical conductivity of approximately 9.25 × 10⁻⁶ g, it can reach 9.25 7 S·m -1 .

[0040] Third, the present invention provides a positive electrode conductive agent for lithium-ion batteries, comprising porous graphene, active material, binder, and solvent as described above.

[0041] In some embodiments, the active material is lithium iron phosphate, the conductive agent also includes carbon black, the binder is polyvinylidene fluoride, and the solvent is N-methylpyrrolidone.

[0042] Fourth, the present invention provides a method for applying the aforementioned conductive agent in the positive electrode of a lithium-ion battery, comprising the following steps:

[0043] Active materials, conductive agents, and binders are blended, ball-milled to obtain a slurry, the slurry is coated with aluminum foil, and assembled to obtain a button cell.

[0044] Here is a specific example of one implementation method, which can be elaborated upon here.

[0045] The active material, conductive agent, and binder were mixed evenly in a mass ratio of 8:1:1 and ball-milled at 300 rpm / min for 1 hour, then ball-milled at 600 rpm / min for 1 hour. The resulting slurry was coated onto aluminum foil, dried, and then punched into circular electrode sheets. The assembly was carried out in a glove box under a high-purity argon protective atmosphere. The button cell was assembled in the following order: positive electrode shell, electrode sheet, separator, electrolyte, lithium sheet, gasket, spring sheet, and negative electrode shell. The electrolyte was 1M LiPF6, and the solvent was EC:DEC:DMC = 1:1:1 (volume ratio). The CR2032 button cell was assembled and sealed by a press at a pressure between 5-6 MPa.

[0046] <Example>

[0047] Example 1

[0048] A method for preparing porous graphene includes the following steps:

[0049] S1. Prepare a solution of ammonium bicarbonate of a certain concentration using a volumetric flask, and take 100 mL as an activating agent.

[0050] S2 Add 0.5g of graphene powder with a sheet diameter of 10μm to the activator solution obtained in step S1, stir and mix to obtain a graphene suspension, keep it in a water bath at 70℃ for 0.5h with a stirring speed of 20rpm / min, filter while hot, dry to obtain a powdered activated product.

[0051] S3 Weigh 0.5g of the powder obtained in step S2, place it in a 50mL porcelain crucible, and treat it under 800W microwave radiation for 1min to obtain porous graphene.

[0052] The manufacturing process of button batteries:

[0053] Lithium iron phosphate, conductive carbon black, porous graphene obtained from S3, and polyvinylidene fluoride were mixed evenly in N-methylpyrrolidone solvent at a mass ratio of 8:0.8:0.2:1. The mixture was ball-milled at 300 rpm / min for 1 hour, and then at 600 rpm / min for 1 hour. The resulting slurry was coated onto aluminum foil, dried, and punched into circular electrode sheets. The assembly was carried out in a glove box under a high-purity argon protective atmosphere, and assembled into a button cell in the following order: positive electrode shell, electrode sheet, separator, electrolyte, lithium sheet, gasket, spring sheet, and negative electrode shell. The electrolyte was 1M LiPF6, and the solvent was EC:DEC:DMC = 1:1:1 (volume ratio). The CR2032 type button cell was assembled, sealed by a press at a pressure between 5-6 MPa, and its electrochemical performance was tested on a blue electrode.

[0054] Example 2

[0055] The difference between this embodiment and Embodiment 1 is that the graphene suspension is kept in a constant temperature water bath at 70°C for 1 hour.

[0056] Example 3

[0057] The difference between this embodiment and Embodiment 1 is that in step S2, the graphene suspension is kept at a constant temperature of 70°C for 2 hours in a water bath. The SEM and TEM images of the obtained porous graphene are shown below. Figure 1 and Figure 2 .

[0058] Example 4

[0059] The difference between this embodiment and embodiment 1 is that in step S2, the graphene suspension is kept in a constant temperature water bath at 70°C for 3 hours.

[0060] Example 5

[0061] The difference between this embodiment and embodiment 1 is that in step S2, the graphene suspension is kept in a constant temperature water bath at 70°C for 5 hours.

[0062] <Comparative Example>

[0063] Comparative Example 1

[0064] The electrode sheet was prepared according to the same method as the button cell preparation in Example 1. Porous graphene was not added to the conductive agent. Lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride were mixed evenly in the solvent N-methylpyrrolidone at a mass ratio of 8:1:1.

[0065] Comparative Example 2

[0066] The electrode sheet was prepared according to the same method as the button cell preparation in Example 1. Graphene, the raw material from step S2, was added to the conductive agent. Lithium iron phosphate, conductive carbon black, graphene, and polyvinylidene fluoride were mixed evenly in the solvent N-methylpyrrolidone at a mass ratio of 8:0.8:0.2:1.

[0067] Comparative Example 3

[0068] The electrode sheet is prepared according to the method in Example 1, skipping step S3. In the preparation of the button cell, the conductive agent is conductive carbon black and the activated powder in step S2. Lithium iron phosphate, conductive carbon black, graphene activated powder, and polyvinylidene fluoride are mixed evenly in the solvent N-methylpyrrolidone at a mass ratio of 8:0.8:0.2:1.

[0069] <Experimental Example>

[0070] The electrochemical performance of the coin cells obtained in Examples 1-5 and Comparative Examples 1-3 was tested on the Blue Battery Testing System. The charge and discharge voltage range was 2.0V to 3.8V. The first three cycles of testing were activated at a charging current of 0.1C, and then cycled at a charge and discharge current of 1C.

[0071] Figure 3 The graph shows the adsorption-desorption curves of the graphene derivatives obtained in Example 3 and Comparative Examples 2-3.

[0072] Figure 4 The graph shows the carbon, oxygen, and nitrogen content of the activated powder and porous graphene in Example 3.

[0073] Figure 5 The graph shows a comparison of the battery cycle performance and rate performance of Examples 3-4 and Comparative Examples 1-3.

[0074] Table 1 shows the electrochemical performance of lithium iron phosphate batteries using different conductive agent materials in each embodiment and comparative example.

[0075] Table 1. Cycle performance test results of lithium iron phosphate batteries in each embodiment and comparative example:

[0076]

[0077] From the data in Table 1 and Figure 1 It can be seen that the discharge capacity, first-charge efficiency, and cycle performance of the porous graphene conductive agent materials prepared in Examples 1-5 of the present invention are significantly better than those in Comparative Examples 1-3. When pores are formed in the graphene, the capacity of the lithium iron phosphate battery is greatly improved, and the first charge-discharge efficiency exceeds 100%. The main reasons are: porous graphene has a high specific surface area and the effect of its internal pore structure. The presence of the pore structure provides channels and additional capacity for lithium-ion transport. The porous graphene obtained after microwave treatment has fewer oxygen-containing functional groups, maintaining the original high conductivity of graphene, enhancing the conductivity with conductive materials and current collectors, and enhancing electronic conductivity.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing porous graphene, characterized in that, Includes the following steps: S1 dissolves a weak base in water to form an activated solution; the weak base includes at least one of NH3·H2O, (NH4)2CO3, or NH4HCO3; S2 graphene is added to an activation solution to obtain a suspension; the suspension is pretreated by heating to obtain the activation product. The heating temperature is 70~100℃, and the heating time is 1~3 hours; S3 activation products are treated with oxygen plasma to obtain porous graphene.

2. The method for preparing porous graphene according to claim 1, characterized in that, In S2, the graphene includes at least one of features (1) to (2): (1) The concentration of graphene in the suspension is 2-10 g / L; (2) The particle size of graphene is 2~20μm.

3. The method for preparing porous graphene according to claim 1, characterized in that, In S2, the preprocessing includes at least one of features (1) to (2): (1) The stirring speed is 20 rpm / min; (2) Drying is performed by vacuum drying, flash drying, or freeze drying.

4. The method for preparing porous graphene according to any one of claims 1 to 3, characterized in that, In S3, oxygen plasma processing is achieved through inductively coupled radio frequency discharge, electric field-generated oxygen plasma, or microwave radiation-generated oxygen plasma.

5. The method for preparing porous graphene according to claim 4, characterized in that, In S3, the microwave radiation includes at least one of features (1) to (4): (1) Microwave power is 800W-5KW; (2) Microwave output density: 800W / g-1600W / g; (3) The microwave output time is 1-5 min; (4) Microwave containers are open beakers, crucibles, or covered crucibles.

6. The method for preparing porous graphene according to any one of claims 1 to 3, characterized in that, In S1, the pH of the activated solution formed by the weak base is between 7 and 8.

5.

7. Porous graphene obtained by the preparation method according to any one of claims 1 to 6.

8. A conductive agent for the positive electrode of a lithium-ion battery, characterized in that, It includes the porous graphene, active material, binder, and solvent as described in claim 7.

9. The lithium-ion battery positive electrode conductive agent according to claim 8, characterized in that, The active material is lithium iron phosphate, the conductive agent also includes carbon black, the binder is polyvinylidene fluoride, and the solvent is N-methylpyrrolidone.

10. A method for applying the positive electrode conductive agent of a lithium-ion battery as described in claim 9, characterized in that, Includes the following steps: Active materials, conductive agents, and binders are blended, ball-milled to obtain a slurry, the slurry is coated with aluminum foil, and assembled to obtain a button cell.

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