Composite electrode with gradient distribution of multi-element nonmetal functional groups and preparation method and application of composite electrode

Abstract

The invention discloses a composite electrode with multi-element nonmetal functional groups in gradient distribution and a preparation method and application thereof. According to the preparation method, accurate distribution of different functional groups in a carbon fiber matrix from a surface layer to a shallow layer to a deep layer is realized through gradient design of a multi-element heteroatom functional group structure by virtue of non-metal atomic characteristics, meanwhile, a three-dimensional network gradient structure is constructed, a super-hydrophilic and progressive mass transfer function is obtained, and finally, synergistic improvement of stability and performance of the electrode is realized; the commercial application requirements of the vanadium battery are met.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a composite electrode with a gradient distribution of multi-component non-metallic functional groups, its preparation method, and its application. Background Technology

[0002] Vanadium redox flow batteries (also known as vanadium batteries) possess irreplaceable advantages in long-term energy storage due to their ultra-long cycle life, high safety, and flexible design. However, their high initial installation cost and low energy density are key issues limiting their widespread commercialization. Currently, improving vanadium battery performance to increase power density and energy density per unit area is one of the effective measures to reduce costs. Carbon-based porous electrodes, as the key site for electrochemical reactions in vanadium batteries, directly affect battery performance. However, the strong chemical inertness of carbon-based porous electrode fiber surfaces and the scarcity of inherent active sites result in poor electrocatalytic activity and electrolyte wettability. Furthermore, current electrode improvement technologies mainly address the issues of single non-metallic atoms and pore gradient distribution, failing to meet the demands for high electrical density, high power density, and high energy density.

[0003] In the prior art, Chinese invention patent CN117913289A describes a polyimide carbon-based gradient composite electrode for flow batteries and its preparation method. This method uses a high-concentration polyamic acid solution as a nitrogen source, allowing spontaneous deposition on the surface of a three-dimensional carbon fiber felt electrode to obtain a double-sided electrode structure with a gradient distribution along the thickness direction. One side exhibits high conductivity, and the other side exhibits high catalytic activity. Chinese invention patent CN106207201B describes a reduced graphene oxide / graphene foam composite material with a gradient distribution of oxygen-containing functional groups and its application in vanadium batteries. This method utilizes chemical... A graphene foam was obtained by chemical vapor deposition, combined with a graphene oxide aerogel preparation method, and then a metal gradient reduction was used to achieve a graphene oxide integrated composite electrode with high conductivity of the three-dimensional graphene network and a gradient distribution of oxygen-containing functional groups. Chinese invention patent CN106558704B describes a gradient electrode for flow batteries and its application. The electrode is made by stacking layers of low to high bulk density and forming a composite electrode with a gradient distribution of pores by longitudinal needle punching perpendicular to the electrode surface, thereby reducing the ohmic polarization, electrochemical polarization and concentration polarization of the flow battery.

[0004] However, in the aforementioned prior art, the performance of vanadium batteries is only 160 mA / cm². 2 Energy efficiency at current density is generally less than 78%, with some technologies achieving a maximum current density of 300 mA / cm². 2 Its energy efficiency is around 70%, which is insufficient to meet the requirements for high power density and energy density. Summary of the Invention

[0005] To address the problems of poor electrocatalytic activity and electrolyte wettability in existing carbon fiber-based electrodes, this invention relies on the characteristics of non-metallic atoms and achieves precise distribution of different functional groups in the carbon fiber matrix from the surface to the shallow to the deep layers through a gradient design of multi-component heteroatom functional groups. At the same time, a three-dimensional network gradient structure is constructed to obtain superhydrophilicity and progressive mass transfer functions, ultimately achieving a synergistic improvement in electrode stability and performance, meeting the needs of commercial applications of vanadium batteries.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The first aspect of this invention provides a method for preparing a composite electrode with a gradient distribution of multi-component non-metallic functional groups, comprising the following steps: S1. Pretreatment and pre-oxidation of carbon fiber matrix; S2. Gradient doping: Oxygen, nitrogen, and sulfur elements or compounds are introduced into the first carbon fiber matrix to obtain the surface layer; oxygen, nitrogen, sulfur, boron, and phosphorus elements or compounds are introduced into the second carbon fiber matrix to obtain the shallow layer; and oxygen, boron, and phosphorus elements or compounds are introduced into the third carbon fiber matrix to obtain the deep layer. S3. Electrode composite: The surface layer, shallow layer and deep layer can be composited in any order and then post-processed, with each of the surface layer, shallow layer and deep layer having a layer number greater than or equal to 1.

[0008] A second aspect of the present invention provides another method for preparing a composite electrode with a gradient distribution of multi-component non-metallic functional groups, comprising the following steps: Step 1. Pretreatment and pre-oxidation of the carbon fiber matrix; Step 2. Gradient doping: Introduce elements or compounds of oxygen, nitrogen, and sulfur into the first carbon fiber matrix to obtain the surface layer; introduce elements or compounds of oxygen, boron, and phosphorus into the third carbon fiber matrix to obtain the deep layer; Step 3. Electrode composite: The surface layer and deep layer are composited and post-processed, with each layer having at least one layer; the contact points of the surface layer and deep layer naturally transition to form a shallow layer.

[0009] In some preferred embodiments, the carbon fiber matrix includes one or more of carbon felt, carbon cloth, and graphite felt.

[0010] In some preferred embodiments, the pretreatment method is as follows: the carbon fiber matrix is ​​cut into the required size, and then repeatedly washed and dried with organic solvent and deionized water before proceeding to the next step.

[0011] Preferably, the present invention does not impose special limitations on the organic solvent used in the pretreatment, and the solvent can be selected from conventional organic solvents in the art, including but not limited to ethanol and acetone.

[0012] In some preferred embodiments, the pre-oxidation method includes one or more of chemical oxidation, electrochemical oxidation, gas-phase oxidation, and liquid-phase oxidation.

[0013] Preferably, the pre-oxidation method includes anodizing, plasma treatment, ozone treatment, hot air treatment, Joule heat treatment, or immersion treatment in a strong oxidizing solution (one or more of concentrated sulfuric acid, concentrated nitric acid, or potassium permanganate solution).

[0014] After the pretreated carbon fiber matrix is ​​pre-oxidized using the above method, oxygen-containing functional groups can be formed on the surface of the carbon fiber matrix, which significantly improves its hydrophilicity.

[0015] In some preferred embodiments, the preparation method of the surface layer includes: loading elements or compounds of oxygen, nitrogen, and sulfur onto a first carbon fiber matrix, controlling the reaction temperature at 20-900°C under a protective atmosphere, and holding the temperature for 0.05-3 hours to form a surface layer with a heteroatom content of 0.05-25 at%.

[0016] In some preferred embodiments, the preparation method of the deep layer includes: loading elements or compounds of oxygen, boron, and phosphorus onto a third carbon fiber matrix, controlling the reaction temperature at 400-1800℃ under a protective atmosphere, and holding the temperature for 0.05-12h to form a deep layer with a heteroatom content of 0.05-25 at%.

[0017] In some preferred embodiments, the method for preparing the shallow layer includes: introducing elements or compounds of oxygen, nitrogen, sulfur, boron, and phosphorus onto a second carbon fiber matrix, controlling the reaction temperature at 100-1800℃ under a protective atmosphere, and holding the temperature for 0.05-8h to form a shallow layer with a heteroatom content of 0.05-25 at%.

[0018] The oxygen element or compound described in this invention includes, but is not limited to, hydrogen peroxide, oxygen, air, ozone, carbon dioxide, water vapor, potassium permanganate, perchloric acid, nitric acid, sulfuric acid, citric acid, oxalic acid, etc., forming an effective doping gas, or element, or compound in powder, solution, suspension, sol-gel state, or other forms.

[0019] The nitrogen element or compound described in this invention includes, but is not limited to, ammonia, ammonia water, melamine, urea, dicyandiamide, ammonium carbamate, ammonium bicarbonate, polyimide, ammonium hydrogen phosphate, guanidine carbonate, guanidine phosphonate, adipamide, etc., forming an effective doping gas, or element, or compound in powder, solution, suspension, sol-gel state, etc.

[0020] The sulfur element or compound described in this invention includes, but is not limited to, sodium thiosulfate, carbon disulfide, thioacetic acid, thymol blue, thiourea, sodium sulfide, ammonium sulfate, benzothiophene, diphenyl disulfide, sulfone, etc., forming an effective doping gas, or element, or compound in powder, solution, suspension, sol-gel state, etc.

[0021] The boron element or compound described in this invention includes, but is not limited to, boron oxide, boron nitride, boric acid, borax, potassium tetraborate, triethyl borate, triphenylborane, etc., which form effective doping gases, or elements, or compounds in powder, solution, suspension, sol-gel, or other forms.

[0022] The phosphorus element or compound described in this invention includes, but is not limited to, phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, triethyl phosphate, triphenyl phosphate, phosphine, red phosphorus, phytic acid, triphenylphosphine, hydroxyethylidene diphosphonic acid, etc., forming an effective doping gas, or one or more of the elements or compounds in the form of powder, solution, suspension, sol-gel, etc.

[0023] In some preferred embodiments, the composite method includes one or more of physical-mechanical bonding, chemical bonding, and thermal bonding.

[0024] In some preferred embodiments, the post-processing method is to keep the composite electrode at 30-500°C for 0.5-24 hours under a protective atmosphere.

[0025] A third aspect of the present invention provides a composite electrode with a gradient distribution of multi-component non-metallic functional groups, obtained by the above-described preparation method.

[0026] The fourth aspect of this invention provides an application of a composite electrode with a gradient distribution of multi-component non-metallic functional groups, applied to an all-vanadium redox flow battery.

[0027] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: (1) Based on the current market demand for electrode performance, this invention constructs electrode structures with different properties in the surface layer, shallow transition layer and deep layer in sequence to achieve layered synergistic effect of "high activity at the surface interface - high efficiency transition in the shallow layer - high transport in the deep layer". Different functional layers are firmly bonded through bonding, needle punching and welding processes to strengthen the three-dimensional network gradient structure of the electrode and realize the superhydrophilic properties and progressive transport function of the electrode to meet the needs of flow battery system.

[0028] (2) This invention precisely controls the electrode structure and interlayer function by gradient layering of electrode structure and gradient of non-metallic active atom content, constructs an efficient transport layer and a stable system of stepped structure, realizes synergistic effect of electrode structure and function, and simultaneously improves the interlayer bonding strength and overall synergy, effectively solving the problem of difficulty in balancing electrode activity and stability.

[0029] (3) There are a variety of carbon fiber matrices to choose from, and the pre-oxidation and doping methods are compatible and adaptable. The composite process can be combined as needed according to the application scenario. The raw materials are cheap and readily available, the process flow is simple, the reaction conditions are mild and easy to control, which is conducive to industrial scale-up production. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the electrode prepared in Example 1 of this patent; Figure 2 This is a schematic diagram of the structure of the electrode prepared in Example 2 of this patent; Figure 3 SEM image of the surface high catalytic surface of the composite electrode with functional group gradient distribution prepared in Example 1 of this patent; Figure 4 SEM image of the surface high catalytic surface of the composite electrode with functional group gradient distribution prepared in Example 1 of this patent; Figure 5 This is a SEM image of the high catalytic surface of the polyimide carbon-based gradient composite electrode in Comparative Example 1. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1 This embodiment provides a composite electrode with a gradient distribution of multi-component non-metallic functional groups. The preparation method includes the following steps: S1. Pretreatment and pre-oxidation of carbon fiber matrix; Graphite felt was selected as the carbon fiber matrix and cut into 30mm×30mm×1mm sizes. It was then ultrasonically cleaned with acetone, ethanol, and ultrapure water for 30 minutes each, and dried in an oven at 105℃ for 12 hours. The carbon fiber matrix was then pre-oxidized at 550℃ for 2 hours in air.

[0033] S2. Gradient doping: O2 and NH3 gases (volume ratio 6:1) were successively introduced into the first carbon fiber matrix, the temperature was controlled at 300℃, the gas flow rate was 100mL / min, and the temperature was maintained for 2h. Then, it was immersed in 0.5mol / L thiourea solution, dried, and then heated to 600℃ at 10℃ / min and maintained at N2 atmosphere for 3h to obtain the surface layer. The second carbon fiber matrix was immersed in 50 mL of a mixed solution of 0.1 mol / L dicyandiamide and 0.2 mol / L thiourea for 3 h, then dried at 80 °C. Under N2 atmosphere in a tube furnace, the temperature was increased to 600 °C at 10 °C / min and held for 3 h. Subsequently, it was immersed in 50 mL of a mixed solution of 0.1 mol / L boric acid and 0.2 mol / L phosphoric acid. After the functional layer was fully impregnated, the electrode was dried. After drying, the atmosphere was changed to Ar and the temperature was increased to 1000 °C at 10 °C / min and held for 3 h to obtain a shallow layer. The third carbon fiber matrix was immersed in 50 mL of a mixed solution of 1 mol / L boric acid and 2 mol / L phosphoric acid, dried, and then rapidly heated to 1000 °C at 10 °C / min under an Ar atmosphere and held for 3 h to obtain the deep layer. S3. Electrode composite: One surface layer, one shallow layer, and one deep layer are stacked sequentially using a needle-punching method with a needle density of 100 needles / cm² and a depth of 3mm. After composite, the electrode is obtained by holding it at 400℃ for 1.5h in a N2 atmosphere and then cooling it.

[0034] The structural domains of Example 1 are as follows Figure 1 As shown, it should be noted that Figure 1 The structure of Example 1 is only listed here, and is not limited to the implementation of the present invention. The technical solution of the present invention also includes a variety of implementations with different numbers of layers and different arrangements.

[0035] Example 2 This embodiment provides a composite electrode with a gradient distribution of multi-component non-metallic functional groups. The preparation method includes the following steps: S1. The pretreatment and pre-oxidation of the carbon fiber matrix are the same as in Example 1, except that the size of the carbon fiber matrix is ​​30mm×30mm×1.5mm; S2. Gradient doping: 3g of urea and 3g of thiourea powder were spread on the first carbon fiber matrix, and the temperature was controlled at 300℃. The surface layer was obtained by keeping it at this temperature for 2 hours under N2 atmosphere. The third carbon fiber matrix was immersed in 50 mL of a mixed solution of 1 mol / L borax and 2 mol / L diammonium hydrogen phosphate, dried, and then rapidly heated to 1000℃ at 10℃ / min under an Ar atmosphere and held for 3 h to obtain the deep layer. S3. Electrode composite: One surface layer and one deep layer are stacked sequentially using a needle punching method with a needle density of 100 needles / cm² and a depth of 3mm. After composite, the electrode is obtained by holding it at 400℃ for 1.5h in a N2 atmosphere and then cooling it.

[0036] Comparative Example 1 This comparative example refers to the technical solution of Example 1 in Chinese Patent CN117913289A, "Polyimide Carbon-based Gradient Composite Electrode for Flow Batteries and its Preparation Method Thereof," as follows: The pretreated carbon fiber felt was placed in a tube furnace and heated to 500°C at 8°C / min under an air atmosphere. After holding at that temperature for 3 hours, it was cooled to room temperature and removed. Prepare a certain concentration of 1,4 The phenylenediamine solution was stirred in an ice-water bath until it was completely dissolved. Then, pyromellitic dianhydride was added in several portions until it was completely dissolved, resulting in a 110 mg / mL polyamic acid solution.

[0037] Take 250 mg of graphene oxide and add it to the above polyamic acid solution, then ultrasonically disperse for 0.7 h; The oxidized carbon fiber felt was immersed in the above-mentioned mixed slurry and ultrasonically treated for 0.5 hours before being removed. The A-side up and B-side down were placed in a vacuum oven and kept at 50°C for 10 hours to allow for complete spontaneous settling. Then, the polyimide was sequentially kept at 95°C for 0.5 hours, 135°C for 0.25 hours, and 220°C for 0.33 hours to completely cure it. The material was then removed after cooling to room temperature.

[0038] Take the above graphene oxide polyimide Carbon fiber felt is carbonized at high temperature by heating to 400℃ at a rate of 6℃ / min and holding for 1 hour in an N2 atmosphere, then heating to 550℃ and holding for 1 hour. After cooling to room temperature, it is taken out and transferred to a muffle furnace, where it is heated to 450℃ at a rate of 8℃ / min and held for 2 hours in an Air atmosphere. After cooling to room temperature, it is taken out to obtain a polyimide carbon-based gradient composite electrode.

[0039] Special note: In this patent, the relevant content of Comparative Example 1 is only cited from the content of patent CN117913289A. As a composite electrode product with better performance among current patents, this patent is only used to compare the relevant performance parameters of the product. It is particularly emphasized that it is only used for comparison and does not involve commercial application.

[0040] Performance testing The products of the embodiments and comparative examples of the present invention were subjected to the following tests, and the results are shown in Table 1.

[0041] Table 1

[0042] Note: As described in Example 1 of Comparative Example 1, the specific surface area of ​​the flow battery electrode prepared in this example, as tested, is: A surface 4.17m². 2 g -1 Side B, 5.82m 2 g -1 Converted to a total test, it is approximately 5 m 2 / g, which is the data in Table 1.

[0043] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a composite electrode with a gradient distribution of multi-component non-metallic functional groups, characterized in that, Includes the following steps: S1. Pretreatment and pre-oxidation of carbon fiber matrix; S2. Gradient doping: Oxygen, nitrogen, and sulfur elements or compounds are introduced into the first carbon fiber matrix to obtain the surface layer; oxygen, nitrogen, sulfur, boron, and phosphorus elements or compounds are introduced into the second carbon fiber matrix to obtain the shallow layer; and oxygen, boron, and phosphorus elements or compounds are introduced into the third carbon fiber matrix to obtain the deep layer. S3. Electrode composite: The surface layer, shallow layer and deep layer can be composited in any order and then post-processed, with each of the surface layer, shallow layer and deep layer having a layer number greater than or equal to 1.

2. A method for preparing a composite electrode with a gradient distribution of multi-component non-metallic functional groups, characterized in that, Includes the following steps: Step 1. Pretreatment and pre-oxidation of the carbon fiber matrix; Step 2. Gradient doping: Introduce elements or compounds of oxygen, nitrogen, and sulfur into the first carbon fiber matrix to obtain the surface layer; introduce elements or compounds of oxygen, boron, and phosphorus into the third carbon fiber matrix to obtain the deep layer; Step 3. Electrode composite: Composite the surface layer and the deep layer and then perform post-processing. The number of layers in both the surface layer and the deep layer is greater than or equal to 1. The contact points between the surface and deep layers naturally transition to form the shallow layer.

3. The preparation method according to claim 1 or 2, characterized in that, The pre-oxidation method includes one or more of chemical oxidation, electrochemical oxidation, gas-phase oxidation, and liquid-phase oxidation.

4. The preparation method according to claim 1 or 2, characterized in that, The preparation method of the surface layer includes: loading oxygen, nitrogen, sulfur or compounds onto a first carbon fiber matrix, controlling the reaction temperature at 20-900℃ under a protective atmosphere, and holding the temperature for 0.05-3h to form a surface layer with a heteroatom content of 0.05-25at%.

5. The preparation method according to claim 1 or 2, characterized in that, The method for preparing the deep layer includes: loading oxygen, boron, phosphorus or their compounds onto a third carbon fiber matrix, controlling the reaction temperature at 400-1800℃ under a protective atmosphere, and holding the temperature for 0.05-12h to form a deep layer with a heteroatom content of 0.05-25 at%.

6. The preparation method according to claim 1, characterized in that, The method for preparing the shallow layer includes: introducing elements or compounds of oxygen, nitrogen, sulfur, boron, and phosphorus onto a second carbon fiber matrix, controlling the reaction temperature at 100-1800℃ under a protective atmosphere, and holding the temperature for 0.05-8h to form a shallow layer with a heteroatom content of 0.05-25 at%.

7. The preparation method according to claim 1 or 2, characterized in that, The composite method includes one or more of physical-mechanical bonding, chemical bonding, and thermal bonding.

8. The preparation method according to claim 1 or 2, characterized in that, The post-processing method is as follows: the composite electrode is kept at 30-500℃ for 0.5-24h under a protective atmosphere.

9. A composite electrode with a gradient distribution of multi-component non-metallic functional groups, characterized in that, The preparation method according to any one of claims 3-8 is obtained.

10. An application of a composite electrode with a gradient distribution of multi-component non-metallic functional groups according to claim 9, characterized in that, It is used in vanadium redox flow batteries.

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