Preparation method and application of boron-nitrogen co-doped gradient graphene-coated capacitor carbon type composite electrode material

Abstract

The application discloses a preparation method and application of a boron-nitrogen co-doped gradient graphene-coated capacitor carbon composite electrode material, and the boron-nitrogen doped graphene coating layer is formed on the capacitor carbon particles by controlling pyrolysis conditions, the graphene is graphene oxide, the boron-containing reducing agent is a reducing agent containing boron, and the nitrogen source is a nitrogen source, and a multi-stage pore structure of micropores-mesopores-macropores which is beneficial to the rapid transmission of ions is simultaneously constructed, so that the pore channel is avoided from being blocked due to coating, the specific capacity of the electrode is improved, the conductivity and the electrochemical activity are improved, and the interface wettability of the electrode and the electrolyte is optimized, the formed electrode material has the function of double inhibition of electrolyte side reactions, and is suitable for application in the fields of supercapacitors and the like.

Description

Technical Field

[0001] This invention relates to the field of materials technology, specifically to a method for preparing a capacitive carbon composite electrode material based on boron-nitrogen co-doped gradient graphene coating, and the application of the electrode material formed by this method in electrodes, electrocatalytic materials, or supercapacitors. Background Technology

[0002] As a high-efficiency energy storage device, the performance of supercapacitors hinges on their electrode materials, especially the carbon used for capacitors. However, while the oxygen-containing functional groups such as carboxyl (-COOH) and hydroxyl (-OH) on the surface of carbon capacitors provide pseudocapacitance to some extent, they are prone to electrochemical side reactions during charging and discharging, leading to problems such as electrolyte decomposition, gas generation, high self-discharge rate, and decreased cycle stability, thus limiting the development of supercapacitors.

[0003] Traditional high-temperature heat treatment (e.g., above 1000℃) can effectively remove some functional groups, but it is very easy to cause the microporous structure of the capacitive carbon to collapse, which greatly reduces the utilization of its huge specific surface area (usually up to 2000-3000 m² / g), thereby reducing the specific capacitance of the material, which needs to be improved. Summary of the Invention

[0004] To address at least one of the aforementioned technical deficiencies, the present invention provides the following technical solution:

[0005] This application discloses a method for preparing a capacitive carbon composite electrode material based on boron-nitrogen co-doped gradient graphene coating, characterized by the following steps:

[0006] Step 1: Add graphene oxide, boron-containing reducing agent and nitrogen source to solvent to form a uniform dispersion;

[0007] Step 2: Impregnate the pre-oxidized capacitor carbon in the dispersion obtained in Step 1, and dry it to obtain the precursor;

[0008] Step 3: Under an inert atmosphere, the precursor obtained in Step 2 is subjected to pyrolysis treatment to form a boron-nitrogen-doped graphene coating layer on the capacitor carbon particles. After cooling, the composite electrode material is obtained. The pyrolysis treatment includes three stages: the first stage: heating to 300-500℃ at a rate of 1-5℃ / min and holding for 0.5-2h; the second stage: heating to 600-900℃ at a rate of 3-8℃ / min and holding for 1-3h; the third stage: heating to 900-1100℃ at a rate of 5-10℃ / min and holding for 10-60min.

[0009] The key points of this scheme are: a three-stage pyrolysis process is designed with the participation of boron and nitrogen components. At a relatively mild temperature (first stage), the boron reducing agent and the nitrogen-assisted reducing agent preferentially attack the oxygen-containing functional groups (such as epoxy and carboxyl groups) on the surface of GO (graphene oxide), causing them to be removed. In the second stage, GO is reduced to rGO (reduced graphene oxide) and crystallization occurs. In the third stage, rGO spontaneously coats the surface of the capacitive carbon under capillary forces and π-π interactions, forming a dense, conductive and chemically stable boron and nitrogen-doped graphene coating layer. At the same time, this stage can repair defects in the carbon skeleton, further improve the graphitization degree and conductivity, and control the boron doping configuration.

[0010] The boron-nitrogen-doped graphene coating consists of an inner, middle, and outer layer. These three layers work together to provide gradient protection. The inner layer (strong bonding layer) utilizes hydroxyl-rich graphene oxide to form strong covalent bonds (COC) with the pre-oxidized capacitive carbon surface, ensuring a firm bond between the coating and the substrate. The middle layer (core functional layer) is composed of boron-doped graphene. During heat treatment, active species generated by the decomposition of the boron source (such as B2O2 vapor) react with carbon defect sites to form BC bonds, achieving boron doping into the carbon lattice. In this process, the reducing properties of boron effectively remove oxygen-containing functional groups from the carbon surface. The middle layer primarily provides excellent conductivity and physical shielding, while the generated rGO layer provides physical barrier, thus doubly suppressing electrolyte side reactions. The outer layer (interface optimization layer) introduces a boron-nitrogen co-doped carbon layer. Nitrogen atoms can provide additional electronegativity centers and pseudocapacitive activity, while boron atoms can provide hole carriers. The co-doping of the two will produce a synergistic effect, further improving the specific capacity of the electrode, enhancing conductivity and electrochemical activity, and optimizing the interfacial wettability between the electrode and the electrolyte.

[0011] In addition, during the composite process, GO and reducing agent molecules (including boron reducing agent and nitrogen source) can act as soft templates. By controlling the composition ratio of the precursor and the pyrolysis conditions, a multi-level pore structure of micropore-mesopore-macropore that is conducive to rapid ion transport can be constructed, avoiding pore blockage due to coating.

[0012] This invention controls the reaction process by programmed temperature rise, avoiding structural damage caused by violent reduction, thereby minimizing the loss of specific surface area (<4%), and maximizing the selective and efficient removal of functional groups on the surface of capacitive carbon while effectively maintaining the carbon skeleton structure.

[0013] Furthermore, the capacitor carbon is pre-oxidized using nitric acid oxidation, and the oxygen content on the surface of the pre-oxidized capacitor carbon accounts for 3-10% of its total mass.

[0014] Furthermore, the mass ratio of graphene oxide, boron-containing reducing agent, and nitrogen source is 1:0.1-5:0.2-8; the mass ratio of graphene oxide to capacitor carbon is 1:10-50.

[0015] Furthermore, the boron-containing reducing agent is at least one of sodium borohydride, boron oxide, or boric acid; the nitrogen source is at least one of urea, melamine, or ammonia.

[0016] The second aspect of this invention discloses the application of the composite electrode material prepared by the above-described method in electrodes, electrocatalytic materials, or supercapacitors.

[0017] Examples of applications of this composite electrode material include its use in the large-scale production of high-performance supercapacitor electrode materials, its use in lithium-sulfur battery cathode materials, and its use in electrocatalytic materials.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] This invention enables the formation of a boron-nitrogen-doped graphene coating layer on capacitive carbon particles by controlling pyrolysis conditions, incorporating graphene oxide, a boron-containing reducing agent, and a nitrogen source. Simultaneously, a multi-level pore structure facilitating rapid ion transport—micropore-mesopore-macropore—is constructed, preventing pore blockage due to coating. This coating layer enhances the electrode's specific capacitance, conductivity, and electrochemical activity, and optimizes the interfacial wettability between the electrode and the electrolyte. The resulting electrode material exhibits dual suppression of electrolyte side reactions, making it suitable for applications in supercapacitors and other fields. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments.

[0021] Example 1

[0022] A method for preparing a capacitive carbon composite electrode material based on boron-nitrogen co-doped gradient graphene coating includes the following steps:

[0023] Step 1: Add graphene oxide, boron-containing reducing agent and nitrogen source to solvent to form a uniform dispersion;

[0024] 5g of graphene oxide (Changzhou Sixth Element Materials Technology Co., Ltd., model SE2430), 10g of sodium borohydride and 15g of urea were dispersed in 2000mL of water-ethanol mixed solvent (volume ratio 1:1) and ultrasonically treated for 30min to form the desired dispersion.

[0025] Step 2: Impregnate the pre-oxidized capacitor carbon in the dispersion obtained in Step 1, and dry it to obtain the precursor;

[0026] 100g of coconut shell capacitor carbon (specific surface area 1800m² / g, Suzhou Yituolian International Trade Co., Ltd., 8-12 mesh, CAS No. 7440-44-0) was added to 1000mL of 68wt% nitric acid solution and refluxed at 90℃ for 6h. After cooling, it was filtered, washed until neutral, and dried at 120℃ for 12h to obtain pre-oxidized capacitor carbon (oxygen content accounts for 5.2% of its total mass).

[0027] 50g of pre-oxidized capacitor carbon was impregnated in the prepared dispersion, stirred for 6 hours, and dried at 80℃ to obtain the precursor.

[0028] Step 3: The precursor is pyrolyzed under an inert atmosphere to form a boron-nitrogen-doped graphene coating layer on the capacitor carbon particles.

[0029] The dried precursor was placed in a tube furnace and subjected to programmed heating under argon protection: in the first stage, the temperature was increased to 400℃ at 2℃ / min and held for 1 hour; in the second stage, the temperature was increased to 800℃ at 5℃ / min and held for 2 hours; in the third stage, the temperature was increased to 1000℃ at 8℃ / min and annealed for 10 minutes. After natural cooling, the composite electrode material was obtained.

[0030] By mass, the composite electrode material has an oxygen content of 0.8%, a specific surface area retention of 97.5%, an electrical conductivity of 125 S / cm, a boron doping amount of 1.2 at, a nitrogen doping amount of 3.5 at, a specific capacitance of 185 F / g at a current density of 1 A / g, a capacity retention of 96.5% after 3000 cycles, and a self-discharge rate of 18% after 72 hours.

[0031] Example 2

[0032] The difference from Example 1 is that the material composition in this example is: 5g graphene oxide, 25g sodium borohydride, 40g urea, and 125g pre-oxidized capacitor carbon.

[0033] The performance of the prepared composite electrode material is as follows: by mass, the nitrogen doping amount is increased to 6.9 at, the boron doping amount is 3.2 at, the specific capacitance is 188 F / g, but the conductivity is 148 S / cm, and the rate performance (capacity retention) is only 65%, which is significantly reduced.

[0034] Example 3

[0035] The difference from Example 1 is that the material composition in this example is: 5g graphene oxide, 5g sodium borohydride, 8g urea, and 125g pre-oxidized capacitor carbon. Other processes and parameters are the same.

[0036] The properties of the prepared composite electrode material are as follows: by mass, the nitrogen doping amount is reduced to 1.8 at and the boron doping amount is 0.5 at. The specific capacitance is 158 F / g, but the conductivity is only 75 S / cm, and the rate performance is 88%.

[0037] Example 4

[0038] The difference from Example 1 is that the material composition in this example is: sodium borohydride 2.5g and urea 1.0g. All other processes and parameters are the same.

[0039] The composite electrode material prepared in this example exhibits the following properties by mass: boron doping increased to 2.8 at and nitrogen doping to 2.2 at. It has a conductivity of 142 S / cm and a specific capacitance of 192 F / g, but its cycling stability is slightly reduced (94.2% retention after 3000 cycles).

[0040] Example 5

[0041] The difference from Example 1 is that the material composition in this example is: 3.0g of urea and 0.8g of sodium borohydride. All other processes and parameters remain the same.

[0042] The composite electrode material prepared in this example exhibits the following performance characteristics: by mass, nitrogen doping is increased to 5.8 at and boron doping is 0.9 at. The specific capacitance is 205 F / g, but the conductivity is 98 S / cm, resulting in a slight decrease in rate performance.

[0043] Example 6

[0044] The difference from Example 1 is that 2.0g of boric acid is used instead of sodium borohydride. All other procedures and parameters remain the same.

[0045] The composite electrode material prepared in this example has the following properties by mass: boron doping amount of 1.0 at and nitrogen doping amount of 3.2 at. The composite electrode material has a more uniform coating layer and improved cycle stability (97.2% retention after 3000 cycles), but the conductivity is 105 S / cm.

[0046] Example 7

[0047] The difference from Example 1 is that 2.0g of melamine is used instead of urea. All other procedures and parameters remain the same.

[0048] The composite electrode material prepared in this example exhibits the following properties by mass: nitrogen doping content of 4.2 at and boron doping content of 1.1 at. The material has a higher specific surface area (specific surface area retention of 98.2%) and a specific capacitance of 195 F / g.

[0049] Example 8

[0050] The difference from Example 1 is that during the pyrolysis treatment, the temperature is first increased to 400°C at 2°C / min and held for 2 hours; then the temperature is increased to 700°C at 5°C / min and held for 3 hours, omitting the high-temperature annealing step. All other processes and parameters remain the same.

[0051] The composite electrode material prepared in this example exhibits the following properties by mass: boron doping of 0.8 at and nitrogen doping of 2.8 at. It has a conductivity of 85 S / cm, but the preparation energy consumption is reduced by 30%.

[0052] Example 9

[0053] The difference from Example 1 is that the capacitor carbon in Example 1 is replaced with E01 type capacitor carbon from Hainan Xingguang Activated Carbon Co., Ltd. All other processes and parameters remain the same.

[0054] The composite electrode material prepared in this example exhibits excellent flexibility, with a conductivity of 115 S / cm and a specific capacitance of 178 F / g.

[0055] Example 10

[0056] The difference from Example 1 is that during the pyrolysis treatment, the third-stage annealing temperature is 1100℃, and the annealing time is extended to 30 minutes. All other processes and parameters remain the same.

[0057] The composite electrode material prepared in this example exhibits the following properties: increased conductivity to 155 S / cm, significantly improved graphitization, and excellent rate performance, but with a slight loss in specific surface area (retention rate of 95.8%).

[0058] Comparative Example 1

[0059] The difference from Example 1 is that there is no boron source or nitrogen source. All other processes and parameters are the same.

[0060] The composite electrode material prepared in this example exhibits the following properties: conductivity of 65 S / cm, specific capacitance of 152 F / g, capacity retention of only 82% after 3000 cycles, and self-discharge rate of 35% after 72 hours, indicating that boron / nitrogen doping is crucial for performance improvement.

[0061] Comparative Example 2

[0062] The difference from Example 1 is that there is no nitrogen source. All other procedures and parameters are the same.

[0063] The composite electrode material prepared in this example exhibits the following performance characteristics: boron doping amount of 1.5 at%, but specific capacitance of 165 F / g and decreased cycle stability (retention rate of 89%), indicating that nitrogen doping plays an important role in pseudocapacitance contribution and stability.

[0064] Comparative Example 3

[0065] The difference from Example 1 is that there is no boron source. All other processes and parameters are the same.

[0066] The composite electrode material prepared in this example has the following properties: nitrogen doping amount of 4.2 at%, but electrical conductivity of 78 S / cm, indicating poor rate performance, which shows that boron doping plays a key role in improving conductivity.

[0067] Comparative Example 4

[0068] The difference from Example 1 is that the material components in Example 1 were directly mixed and mechanically stirred, and then pyrolyzed at high temperature (960°C, 2h).

[0069] The composite electrode material prepared in this example exhibits the following characteristics: uneven coating, low boron / nitrogen doping levels (0.3 at% and 1.2 at% respectively), electrical conductivity of 52 S / cm, and specific capacitance of 138 F / g, resulting in a significant decrease in performance.

[0070] Comparative Example 5

[0071] The difference from Example 1 is as follows: During the pyrolysis treatment: the temperature is increased to 400℃ at a rate of 10℃ / min and held for 1 hour; the temperature is increased to 800℃ at a rate of 15℃ / min and held for 2 hours; the temperature is increased to 1000℃ at a rate of 20℃ / min and annealed for 10 minutes. Other processes and parameters are the same.

[0072] The performance of the composite electrode material prepared in this example is as follows: due to excessively rapid heating, the molecular reaction is insufficient, resulting in defects in the material structure. The obtained material has a boron doping amount of 0.9 at%, a nitrogen doping amount of 2.8 at%, an electrical conductivity of 98 S / cm, a specific capacitance of 168 F / g, and a capacity retention rate of 88.5% after 3000 cycles.

[0073] Comparative Example 6

[0074] The difference from Example 1 is as follows: During the pyrolysis treatment: the temperature is increased to 400℃ at a rate of 0.5℃ / min and held for 1 hour; the temperature is increased to 800℃ at a rate of 2℃ / min and held for 2 hours; the temperature is increased to 1000℃ at a rate of 3℃ / min and annealed for 10 minutes. Other processes and parameters are the same.

[0075] The performance of the composite electrode material prepared in this example is as follows: the boron doping content is 1.3 at%, the nitrogen doping content is 3.6 at%, the conductivity is 128 S / cm, the specific capacitance is 188 F / g, and the capacity retention rate is 96.8% after 3000 cycles. The slow heating significantly prolongs the process cycle and increases energy consumption, but has limited effect on performance improvement.

[0076] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a capacitive carbon composite electrode material based on boron-nitrogen co-doped gradient graphene coating, characterized in that, Includes the following steps: Step 1: Add graphene oxide, boron-containing reducing agent and nitrogen source to solvent to form a uniform dispersion; Step 2: The pre-oxidized capacitor carbon is immersed in the dispersion obtained in Step 1, and dried to obtain the precursor; the capacitor carbon is pre-oxidized by nitric acid oxidation, and the oxygen content on the surface of the pre-oxidized capacitor carbon accounts for 3-10% of its total mass; Step 3: Under an inert atmosphere, the precursor obtained in Step 2 is subjected to pyrolysis treatment to form a boron-nitrogen-doped graphene coating layer on the capacitor carbon particles. After cooling, the composite electrode material is obtained. The pyrolysis treatment includes three stages: the first stage: heating to 300-500℃ at a rate of 1-5℃ / min and holding for 0.5-2h; the second stage: heating to 600-900℃ at a rate of 3-8℃ / min and holding for 1-3h; the third stage: heating to 900-1100℃ at a rate of 5-10℃ / min and holding for 10-60min. The mass ratio of graphene oxide, boron-containing reducing agent, and nitrogen source is 1:0.1-5:0.2-8; the mass ratio of graphene oxide to capacitor carbon is 1:10-50. The boron-containing reducing agent is at least one of sodium borohydride, boron oxide, or boric acid; the nitrogen source is at least one of urea, melamine, or ammonia.

2. The application of the composite electrode material formed by the preparation method of claim 1 in supercapacitors.