Composite cathode material and preparation method thereof, lithium-air battery

Abstract

The present invention provides a preparation method of a composite positive electrode material, comprising the following steps: mixing an aqueous solution of a lignin salt and an anhydrous alcohol solution of polyacrylonitrile to prepare a first mixed solution; dispersing nano-silicon dioxide powder in the first mixed solution to obtain a second mixed solution, performing a programmed heating treatment to prepare a carbonized material; adding an etching solution to the carbonized material to prepare nitrogen-doped porous carbon; dispersing the nitrogen-doped porous carbon in deionized water or an organic alcohol to prepare a nitrogen-doped porous carbon solution; adding a mixed salt solution of an alloying element to the nitrogen-doped porous carbon solution to prepare a third mixed solution; adjusting the pH of the third mixed solution to make the solution alkaline, adding a reducing agent to perform a reduction reaction, collecting a precipitate by centrifugation, washing it to a neutral state, and calcining it under an inert atmosphere to prepare nitrogen-doped porous carbon loaded with Pd. x Fe y W z Nano-alloy composite cathode materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-air batteries, and particularly relates to a nitrogen-doped porous carbon loaded with Pd x Fe y W z A nano alloy composite positive electrode material and a preparation method thereof, as well as a lithium-air battery containing the composite positive electrode material. Background Art

[0002] In recent years, the development of pure electric vehicles has been accelerating, and lithium-ion batteries, as the power system of the new energy industry, have experienced rapid growth. Traditional lithium-ion batteries have limited capacity. Although their capacity is gradually increasing with technological advancements, they still struggle to meet consumer demand, hindering the further development of the new energy industry. Therefore, the development and application of new lithium battery systems is becoming increasingly necessary.

[0003] Lithium-air batteries (LIBAs) have attracted considerable attention due to their inherently unlimited oxygen supply and their compact size, which can rival gasoline in energy. However, the sluggish oxygen reduction reaction kinetics in LABs, which in turn affects overall battery performance, has become a major obstacle hindering their further development. Research has shown that adding a suitable oxygen reduction catalyst to the air electrode can accelerate the charge and mass transfer rates during the reaction, effectively improving electrochemical polarization and enhancing overall battery performance. Currently, a well-established catalyst is the precious metal platinum-on-carbon (Pt / C). However, Pt suffers from poor toxicity resistance and is expensive. Pd, with its similar electronic structure, electrochemical properties, and low cost, has been considered a potential alternative to Pt. However, pure Pd exhibits poor catalytic activity, far inferior to Pt / C, and the catalyst's inherent cycling stability is also poor, limiting its application. Therefore, further research is needed on existing technologies. Summary of the Invention

[0004] The purpose of the present invention is to provide a nitrogen-doped porous carbon loaded with Pd x Fe y W z The nano-alloy composite positive electrode material and its preparation method are intended to solve the problems of poor catalytic activity and poor self-cycling stability of Pd as an air electrode catalyst in lithium-air batteries.

[0005] Another object of the present invention is to provide a method for preparing a porous carbon containing nitrogen-doped Pd x Fe y W z Nano-alloy composite cathode materials for lithium-air batteries.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a composite positive electrode material, wherein the composite positive electrode material is nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloy, and the preparation method of the composite positive electrode material comprises the following steps:

[0008] Providing an aqueous solution of lignin salt and an anhydrous alcohol solution of polyacrylonitrile, and mixing the aqueous solution of lignin salt and the anhydrous alcohol solution of polyacrylonitrile to form a first mixed solution;

[0009] Providing nano-silica powder, dispersing the nano-silica powder in the first mixed solution to obtain a second mixed solution, and subjecting the second mixed solution to a programmed heat treatment to prepare a carbonized material; adding an etching solution to the carbonized material to etch away silicon dioxide in the carbonized material to prepare nitrogen-doped porous carbon; wherein the programmed heat treatment includes the steps of pre-oxidizing the obtained mixed sample and carbonizing the pre-oxidized sample;

[0010] The nitrogen-doped porous carbon is dispersed in deionized water or an organic alcohol to prepare a nitrogen-doped porous carbon solution; a salt solution of Pd salt, Fe salt and W salt is provided, and the salt solution of Pd salt, Fe salt and W salt is added to the nitrogen-doped porous carbon solution to prepare a third mixed solution; after adjusting the pH of the third mixed solution to make the solution alkaline, a reducing agent is added, and a reduction reaction is carried out under stirring, and the precipitate is collected by centrifugation and washed to neutrality, and calcined under an inert atmosphere to prepare nitrogen-doped porous carbon loaded with Pd. x Fe y W z A nano-alloy composite positive electrode material, wherein the ratio of x, y, and z is 1:(0.2-0.5):(0.2-0.5).

[0011] Preferably, in the step of mixing the aqueous solution of lignin salt and the anhydrous alcohol solution of polyacrylonitrile to prepare a first mixed solution, the aqueous solution of lignin salt and the anhydrous alcohol solution of polyacrylonitrile are mixed at a mass ratio of lignin salt to polyacrylonitrile of 10:(1-5).

[0012] Preferably, in the step of the programmed heating treatment, the method of the pre-oxidation treatment is: keeping the second mixed solution warm at a temperature of 180°C to 240°C for pre-oxidation; the method of the carbonization treatment is: keeping the sample after the pre-oxidation treatment warm at a temperature of 800°C to 1200°C in an inert atmosphere for carbonization.

[0013] Preferably, in the step of adding an etching solution to the carbonized material to etch away silicon dioxide in the carbonized material, the etching solution is an HF solution, or the etching solution is molten sodium hydroxide.

[0014] Preferably, in the step of adding the salt solution of Pd salt, Fe salt and W salt to the nitrogen-doped porous carbon solution, the nitrogen-doped porous carbon loaded with Pd is finally obtained. x Fe y W z In nano alloys, Pd x Fe y W z The weight percentage of the nano alloy is 10% to 40%, and the salt solution of the Pd salt, the Fe salt and the W salt is added to the nitrogen-doped porous carbon solution.

[0015] Preferably, in the step of adjusting the pH of the third mixed solution to make the solution alkaline, adding a reducing agent, and performing a reduction reaction under stirring conditions, sodium hydroxide solution is used to adjust the pH of the third mixed solution to 9-12, sodium borohydride is added as a reducing agent, and the reduction treatment is performed under stirring conditions.

[0016] Preferably, after adjusting the pH of the third mixed solution to make the solution alkaline, adding a reducing agent, and performing a reduction reaction under stirring conditions, urea is used to adjust the pH of the third mixed solution to 9~12, ethylene glycol is added as a reducing agent, and the reaction is stirred at a temperature of 70°C~90°C for reduction treatment.

[0017] Preferably, in the step of calcining under an inert atmosphere, the calcining is performed at a temperature of 300° C. to 500° C.

[0018] Preferably, the nano-silica is monodispersed nano-silica spheres, and the particle size of the nano-silica spheres is 150 nm to 250 nm.

[0019] Accordingly, a composite positive electrode material is provided, wherein the composite positive electrode material is nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloys, including Pd x Fe y W z The doping weight percentage of the nano alloy in the nitrogen-doped porous carbon is 10% to 40%, and the Pd x Fe y W z In nanoalloys, the ratio of x, y, and z is 1:(0.2-0.5):(0.2-0.5).

[0020] And, a lithium-air battery, the lithium-air battery contains a positive electrode active material, and the positive electrode active material is the composite positive electrode material described in the present invention, or the positive electrode active material is the composite positive electrode material prepared by the method described in the present invention.

[0021] The preparation method of the composite positive electrode material provided by the present invention first adopts the template removal method to prepare nitrogen-doped porous carbon to obtain nitrogen-doped porous carbon with uniform and orderly pore dispersion; then adopts the chemical reduction method to simply and quickly synthesize Pd x Fe y W z The ternary alloy is loaded in the pore structure of nitrogen-doped porous carbon, and finally a composite cathode material with strong stability and good catalytic activity is obtained - nitrogen-doped porous carbon loaded Pd x Fe y W z Nano alloy (Pd x Fe y W z -N / C). Specifically, the preparation method of the composite positive electrode material has the following advantages:

[0022] First, the silica template method can be used to prepare porous materials with uniform pore size, high repeatability, rich specific surface area and porosity. On the one hand, the nitrogen-doped porous carbon prepared by the silica template method has rich specific surface area and can be used as a catalyst for Pd x Fe y W z Ternary alloy nucleation provides more sites, which is beneficial for Pd x Fe y W z Uniform dispersion of ternary alloy, increasing Pd x Fe y W z The exposed surface of the ternary alloy creates more catalytic active sites and improves the catalytic effect. At the same time, since the pores of the nitrogen-doped porous carbon are relatively independent, it can prevent the alloy from migrating and agglomerating, or even falling off, during the cycle, thereby enhancing the stability of the alloy. On the other hand, the method provided by the present invention can uniformly dope the N element into the C element. The doped N element affects the spin density and charge of the surrounding C atoms, thereby increasing the conductivity of the carbon material and promoting more active sites. In addition, the three-dimensional porous structure of the nitrogen-doped porous carbon obtained in this way is conducive to the transmission of oxygen, an active substance. In summary, the nitrogen-doped porous carbon (N / C) prepared by the present invention is a good catalyst carrier.

[0023] Secondly, Pd was synthesized simply and quickly by chemical reduction. x Fe y W zThe ternary alloy is loaded in the pore structure of nitrogen-doped porous carbon under mild conditions, and the prepared Pd x Fe y W z The ternary alloy has very good dispersion, uniform shape and uniform particle size, mainly concentrated between 5-10nm. Compared with traditional commercial Pd / C, the chemical reduction method can quickly achieve the co-doping of transition metal elements Fe and W, thereby changing the electronic structure of Pd. Fe, W and Pd produce a synergistic effect, which improves the nitrogen-doped porous carbon loading of Pd. x Fe y W z The nanoalloy exhibits excellent catalytic activity and stability as a positive electrode active material in lithium-air batteries. Furthermore, nitrogen doping increases the conductivity of the carbon support, while the porous structure facilitates oxygen transport and the large surface area facilitates alloy dispersion. Consequently, through multi-layered synergistic effects, the present invention not only reduces the amount of precious metal Pd used but also demonstrates enhanced oxygen reduction catalytic activity and stability in three-electrode cyclic voltammetry and lithium-air battery capacity-limited cycling tests.

[0024] Again, the preparation method of the composite cathode material provided by the present invention uses water as the main solvent when preparing nitrogen-doped porous carbon by removing the template; Pd is synthesized simply and quickly by chemical reduction. x Fe y W z When the ternary alloy is loaded onto nitrogen-doped porous carbon, the process can be performed in a water solvent at room temperature without the use of any surfactants, thus minimizing environmental pollution. Fe and W are abundant resources and widely used in industry, offering high conductivity and environmentally friendly properties. Therefore, the method for preparing the composite cathode material provided by the present invention aligns with the concept of "green chemistry."

[0025] In addition, the preparation method of the composite positive electrode material provided by the present invention has a simple process, is easy to operate, has a low cost, and can achieve large-scale production.

[0026] The composite positive electrode material provided by the present invention is nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloy.

[0027] First, nitrogen-doped porous carbon is used as a carrier. The nitrogen-doped porous carbon is uniformly doped with N elements in the C elements. The doped N elements affect the spin density and charge of the surrounding C atoms, thereby increasing the conductivity of the carbon material and generating more active sites. At the same time, the nitrogen-doped porous carbon has a rich specific surface area and can be used as a carrier for Pd x Fe y W z Ternary alloy nucleation provides more sites, which is beneficial for Pdx Fe y W z Uniform dispersion of ternary alloy, increasing Pd x Fe y W z The exposed surface of the ternary alloy creates more catalytically active sites, improving the catalytic effect. The relatively independent pores of the nitrogen-doped porous carbon provided by the present invention prevent the alloy from migrating, agglomerating, or even falling off during cycling, thereby enhancing the alloy's stability. The three-dimensional porous structure facilitates the transport of oxygen, the active substance.

[0028] Secondly, Fe and W co-doping produce a synergistic effect with Pd, which improves the loading of Pd on nitrogen-doped porous carbon. x Fe y W z The nanoalloy exhibits excellent catalytic activity and stability as a positive electrode active material for lithium-air batteries. Furthermore, nitrogen doping increases the conductivity of the carbon support, while the porous structure facilitates oxygen transport and the large surface area facilitates alloy dispersion. Consequently, the composite positive electrode material of the present invention exhibits enhanced oxygen reduction catalytic activity and stability in three-electrode cyclic voltammetry tests and limited-capacity cycling tests for lithium-air batteries, driven by multi-layered synergistic effects.

[0029] The nitrogen-doped porous carbon is loaded with Pd x Fe y W z Nano-alloys are used as positive electrode active materials for lithium-air batteries. They have the advantages of good stability and good electrochemical properties, and are expected to provide a new positive electrode material for the future commercialization of lithium-air batteries.

[0030] The lithium-air battery provided by the present invention is a Pd-doped porous carbon x Fe y W z Nano-alloys, as the positive electrode active material of lithium-air batteries, give lithium-air batteries the advantages of good stability and good electrochemical performance.

[0031] The preparation method of the synthetic nitrogen-doped porous carbon of the present invention fully utilizes the lignin-based derivatives, a by-product of papermaking, achieves waste utilization, and conforms to the concept of "green chemistry". BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The nitrogen-doped porous carbon supported PdFe provided in Example 4 of the present invention 0.2 W 0.2 Field emission scanning electron microscope (SEM) image of nano-alloy;

[0033] Figure 2 The nitrogen-doped porous carbon supported PdFe provided in Example 4 of the present invention0.2 W 0.2 XRD pattern of nanoalloy;

[0034] Figure 3 The nitrogen-doped porous carbon supported PdFe provided in Example 4 of the present invention 0.2 W 0.2 Cyclic voltammetry of the nanoalloy in a 0.1M KOH solution saturated with oxygen using a three-electrode electrochemical workstation;

[0035] Figure 4 The nitrogen-doped porous carbon supported PdFe provided in Example 4 of the present invention 0.2 W 0.2 Cycling curve of lithium-air battery prepared with nano-alloy as positive electrode active material. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0038] The present invention provides a method for preparing a composite positive electrode material, wherein the composite positive electrode material is nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloy, and the preparation method of the composite positive electrode material comprises the following steps:

[0039] S01 provides an aqueous solution of lignin salt and an anhydrous alcohol solution of polyacrylonitrile, the aqueous solution of lignin salt and the anhydrous alcohol solution of polyacrylonitrile are mixed to form a first mixed solution;

[0040] S02. Providing nano-silica powder, dispersing the nano-silica powder in the first mixed solution to obtain a second mixed solution, and subjecting the second mixed solution to a program heat treatment to prepare a carbonized material; adding an etching solution to the carbonized material to etch away the silicon dioxide in the carbonized material to prepare nitrogen-doped porous carbon; wherein the program heat treatment includes the steps of pre-oxidizing the obtained mixed sample and carbonizing the pre-oxidized sample;

[0041] S03. The nitrogen-doped porous carbon is dispersed in deionized water or an organic alcohol to prepare a nitrogen-doped porous carbon solution; a salt solution of Pd salt, Fe salt and W salt is provided, and the salt solution of Pd salt, Fe salt and W salt is added to the nitrogen-doped porous carbon solution to prepare a third mixed solution; after adjusting the pH of the third mixed solution to make the solution alkaline, a reducing agent is added, and a reduction reaction is carried out under stirring, the precipitate is collected by centrifugation and washed to neutrality, and calcined under an inert atmosphere to prepare nitrogen-doped porous carbon loaded with Pd. x Fe y W z A nano-alloy composite positive electrode material, wherein the ratio of x, y, and z is 1:(0.2-0.5):(0.2-0.5).

[0042] The preparation method of the composite positive electrode material provided by the embodiment of the present invention first adopts the template removal method to prepare nitrogen-doped porous carbon to obtain nitrogen-doped porous carbon with uniform and orderly pores; then adopts the chemical reduction method to simply and quickly synthesize Pd x Fe y W z The ternary alloy is loaded in the pore structure of nitrogen-doped porous carbon, and finally a composite cathode material with strong stability and good catalytic activity is obtained - nitrogen-doped porous carbon loaded Pd x Fe y W z Nano alloy (Pd x Fe y W z -N / C). Specifically, the preparation method of the composite positive electrode material has the following advantages:

[0043] First, the silica template method can be used to prepare porous materials with uniform pore size, high repeatability, rich specific surface area and porosity. On the one hand, the nitrogen-doped porous carbon prepared by the silica template method has rich specific surface area and can be used as a catalyst for Pd x Fe y W z Ternary alloy nucleation provides more sites, which is beneficial for Pd x Fe y W zUniform dispersion of ternary alloy, increasing Pd x Fe y W z The exposed surface of the ternary alloy creates more catalytic active sites and improves the catalytic effect. At the same time, since the pores of the nitrogen-doped porous carbon are relatively independent, it can prevent the alloy from migrating and agglomerating, or even falling off, during the cycle, thereby enhancing the stability of the alloy. On the other hand, the method provided in the embodiment of the present invention can uniformly dope the N element into the C element. The doped N element affects the spin density and charge of the surrounding C atoms, thereby increasing the conductivity of the carbon material and promoting more active sites. In addition, the three-dimensional porous structure of the nitrogen-doped porous carbon obtained in this way is conducive to the transmission of oxygen, an active substance. In summary, the nitrogen-doped porous carbon (N / C) prepared by the present invention is a good catalyst carrier.

[0044] Secondly, Pd was synthesized simply and quickly by chemical reduction. x Fe y W z The ternary alloy is loaded in the pore structure of nitrogen-doped porous carbon under mild conditions, and the prepared Pd x Fe y W z The ternary alloy has very good dispersion, uniform shape and uniform particle size, mainly concentrated between 5-10nm. Compared with traditional commercial Pd / C, the chemical reduction method can quickly achieve the co-doping of transition metal elements Fe and W, thereby changing the electronic structure of Pd. Fe, W and Pd produce a synergistic effect, which improves the nitrogen-doped porous carbon loading of Pd. x Fe y W z The catalytic activity and stability of the nanoalloy as a positive electrode active material for lithium-air batteries. Furthermore, nitrogen doping can increase the conductivity of the carbon support, while the porous structure facilitates oxygen transport and the large specific surface area facilitates alloy dispersion. Therefore, through multi-layered synergistic effects, the embodiments of the present invention not only reduce the amount of precious metal Pd used but also demonstrate higher oxygen reduction catalytic activity and stability in three-electrode cyclic voltammetry tests and lithium-air battery capacity-limited cycling tests.

[0045] Again, in the preparation method of the composite cathode material provided by the embodiment of the present invention, the main solvent for preparing nitrogen-doped porous carbon by removing the template is water; the chemical reduction method is used to simply and quickly synthesize Pd x Fe y W zWhen the ternary alloy is loaded onto nitrogen-doped porous carbon, the process can be performed in a water solvent at room temperature without the use of any surfactants, thus minimizing environmental pollution. Fe and W are abundant resources and widely used in industry, offering high conductivity and environmentally friendly properties. Therefore, the method for preparing the composite cathode material provided by the present invention aligns with the concept of "green chemistry."

[0046] In addition, the method for preparing the composite positive electrode material provided by the embodiment of the present invention has a simple process, is easy to operate, has a low cost, and can be produced on a large scale.

[0047] Specifically, in the above step S01, the aqueous solution of the lignin salt and the anhydrous alcohol solution of the polyacrylonitrile are mixed and processed to form a first mixed solution, that is, a lignin / polyacrylonitrile precursor is obtained. The lignin salt provides a carbon source for the nitrogen-doped porous carbon obtained in the following step, and the polyacrylonitrile provides a nitrogen source for the nitrogen-doped porous carbon obtained in the following step. Compared with directly using carbon as a catalyst carrier, nitrogen-doped porous carbon introduces nitrogen into the carbon material. On the one hand, the doped N element affects the spin density and charge of the surrounding C atoms, thereby increasing the conductivity of the carbon material and generating more active sites. The nitrogen-doped porous carbon thus obtained serves as an auxiliary disperser for Pd x Fe y W z Nano alloy carrier can improve the nitrogen-doped porous carbon loaded with Pd x Fe y W z Catalytic activity and stability of nanoalloys.

[0048] In some embodiments, the lignin salt is sodium lignosulfonate, but is not limited thereto. In specific embodiments, the lignin salt is derived from papermaking wastewater lignin as a precursor. Using papermaking wastewater lignin as a raw material for synthesizing nitrogen-doped porous carbon fully utilizes lignin-based derivatives, a byproduct of papermaking, achieving waste recycling and aligning with the concept of "green chemistry."

[0049] In an embodiment of the present invention, the aqueous solution of the lignin salt is prepared by dissolving the lignin salt in water. In some embodiments, the solid content of the aqueous solution of the lignin salt is 10% to 20%. Within this range, the aqueous solution of the lignin salt has a suitable viscosity after mixing with the anhydrous alcohol solution of polyacrylonitrile, which is conducive to the sufficient dispersion and infiltration of the nano-silica powder. In specific preferred embodiments, the solid content of the aqueous solution of the lignin salt can be 12%, 13%, 15%, 16%, 18%, etc.

[0050] In an embodiment of the present invention, the polyacrylonitrile is used as a nitrogen source precursor, which is low in cost. Preferably, the molecular weight of the polyacrylonitrile is 80,000 to 15,000. Specifically, the polyacrylonitrile purchased by Aladdin can be selected, but is not limited thereto. The anhydrous alcohol solution of the polyacrylonitrile is achieved by dissolving and dispersing the polyacrylonitrile powder in an organic alcohol solution, and the organic alcohol is a liquid alcohol at room temperature. In some embodiments, the organic alcohol used to dissolve and disperse the polyacrylonitrile powder is anhydrous ethanol or anhydrous propyl alcohol.

[0051] In some embodiments, the solids content of the anhydrous alcohol solution of polyacrylonitrile is 10% to 20%. Within this range, the anhydrous alcohol solution of polyacrylonitrile and the aqueous solution of lignin salt have an appropriate viscosity upon mixing, which facilitates sufficient dispersion and infiltration of the nano-silica powder. In specific preferred embodiments, the solids content of the anhydrous alcohol solution of polyacrylonitrile can be 12%, 13%, 15%, 16%, 18%, etc.

[0052] Based on the above embodiments, in some embodiments, the solid content of the aqueous solution of the lignin salt is 10% to 20%, specifically 10%, 12%, 13%, 15%, 16%, 18%, and 20%, and the solid content of the anhydrous alcohol solution of the polyacrylonitrile is 10% to 20%, specifically 10%, 12%, 13%, 15%, 16%, 18%, and 20%. The first mixed solution thus formed has a suitable viscosity, which can promote the uniform dispersion of the nano-silica powder, and then obtain nitrogen-doped porous carbon with uniform and orderly pore dispersion through subsequent pre-oxidation and carbonization treatment. In a specific preferred embodiment, the lignin salt is sodium lignin sulfonate, the solid content of the aqueous solution of the lignin salt is 15%, and the solid content of the anhydrous alcohol solution of the polyacrylonitrile is 15%. At this time, the obtained first mixed solution is used to disperse the nano-silica powder, which has the best dispersion effect. Further preferably, the lignin salt is selected from papermaking waste liquid lignin, which is compounded with the equally cheap polyacrylonitrile to prepare lignin / polyacrylonitrile nitrogen-doped porous carbon, which is not only low in cost but also has excellent effect in loading and dispersing the nano-alloy catalyst.

[0053] In the embodiment of the present invention, preferably, the aqueous solution of the lignin salt and the anhydrous alcohol solution of the polyacrylonitrile are mixed to prepare the first mixed solution, and the aqueous solution of the lignin salt and the anhydrous alcohol solution of the polyacrylonitrile are mixed at a mass ratio of lignin salt to polyacrylonitrile of 10: (1-5). If the content of the polyacrylonitrile in the first mixed solution is too low, the nitrogen doping content in the obtained nitrogen-doped porous carbon is too low, the number of nitrogen atoms is small, the effect on the carbon atoms is relatively small, and the active sites generated are reduced, therefore, it is not conducive to significantly improving the catalytic effect. If the content of the polyacrylonitrile in the first mixed solution is too high, the carbon content is reduced, which will affect the obtained nitrogen-doped porous carbon loaded with Pd x Fe y W z Conductivity of nanoalloys, which in turn affects the loading of Pd on nitrogen-doped porous carbon x Fe y W z Electrochemical performance of lithium-air batteries with nanoalloys as cathode active materials.

[0054] In the above step S02, nano-silica powder is provided as a template for the three-dimensional porous structure in nitrogen-doped porous carbon. Preferably, the nano-silica is a monodisperse nano-silica sphere. On the one hand, the monodisperse nano-silica sphere not only has good dispersibility, but is also conducive to being evenly dispersed in the urea / polyacrylonitrile precursor solution, i.e., the first mixed solution, and then through subsequent carbonization and etching, a nitrogen-doped porous carbon with uniform and orderly pore dispersion is obtained. On the other hand, using spherical nano-silica as a template is conducive to obtaining a honeycomb pore structure, increasing the void specific surface area, and helping to improve the dispersibility and stability of the alloy catalyst, thereby improving the catalytic activity and stability. Further preferably, the particle size of the nano-silica sphere is 150nm~250nm. Nano-silica spheres in this particle size range can regulate the pore size and obtain a honeycomb pore structure of corresponding size, which is conducive to Pd x Fe y W z Dispersion of nanoalloys.

[0055] In some embodiments, the monodisperse nano-silica spheres are prepared by the following method:

[0056] The composite was prepared by combining traditional sol-gel and homogeneous precipitation method in alkaline aqueous solution with tetraethyl orthosilicate as silicon source and hexadecyltrimethylammonium bromide as template.

[0057] The nano-silica powder is dispersed in the first mixed solution, and the mixture is allowed to stand to allow both to be fully immersed, thereby obtaining a second mixed solution. In some embodiments, the first mixed solution is slowly added to a container containing the nano-silica powder to promote full wetting and uniform dispersion of the nano-silica powder. Preferably, in the step of dispersing the nano-silica powder in the first mixed solution, the nano-silica powder is dispersed in the first mixed solution in a ratio of 1:(1-10) of the total weight of lignin salts and polyacrylonitrile to the weight of the nano-silica powder. If the total weight content of lignin salts and polyacrylonitrile is too little, the carbon wall will be too thin and the pore structure will easily collapse; if the total weight content of lignin salts and polyacrylonitrile is too much, the carbon wall will be too thick, resulting in a reduction in pore volume and specific surface area, which is not conducive to the dispersion of the alloy. Specifically preferably, in the step of dispersing the nano-silica powder in the first mixed solution, the nano-silica powder is dispersed in the first mixed solution according to the weight ratio of the total weight of lignin salt and polyacrylonitrile to the weight of the nano-silica powder of 1:5, 1:6, or 1:8.

[0058] Furthermore, the second mixed solution is subjected to a heat treatment to carbonize the lignin and polyvinyl nitrile therein to form a carbonized material. In an embodiment of the present invention, the heat treatment of the second mixed solution is achieved by a programmed heating process. Specifically, the programmed heating process includes the steps of pre-oxidizing the obtained mixed sample and carbonizing the pre-oxidized sample.

[0059] In an embodiment of the present invention, the mixed sample is first pre-oxidized to remove the solvent in the liquid solution. The chain structure is gradually transformed into a relatively stable and heat-resistant trapezoidal structure through pre-oxidation, and the liquid mixture is solidified, so that it can withstand high-temperature carbonization in the later stage, thereby improving the carbon yield. In some embodiments, in the step of the program heating treatment, the method of the pre-oxidation treatment is: the second mixed solution is kept warm for pre-oxidation at a temperature of 180°C to 240°C. Within this temperature range, the solvent in the second mixed solution evaporates, and at the same time, the cyclization reaction of the second mixed solution begins during the initial low-temperature pre-oxidation. As the temperature increases, the cross-linking and cyclization rapidly increase. When the temperature reaches 240°C, the maximum cyclization temperature is reached, and a heat-resistant trapezoidal structure is formed. In addition, it can avoid the carbon in the sample directly generating carbon dioxide gas due to excessively high temperature, thereby changing the carbon content in the sample and avoiding the introduction of other impurities. The pre-oxidation time is 4 hours to 10 hours. Further preferably, the method of the pre-oxidation treatment is: first, the second mixed solution is kept warm for the first pre-oxidation at a temperature of 180°C to 200°C; then, the second pre-oxidation is carried out at a temperature of 220°C to 240°C. The segmented pre-oxidation can fully oxidize the substance, and the precursor gradually undergoes oxidation, dehydrogenation and cross-linking cyclization reactions. The viscosity of the precursor gradually increases, and finally becomes a solid and loses fluidity. On the basis of the above embodiment, in the step of the pre-oxidation treatment, the temperature is raised to the pre-oxidation treatment temperature at a heating rate of 3~8°C / min, and then the pre-oxidation treatment is carried out, thereby avoiding the oxidation of the first mixed solution caused by excessive heating speed, and its dehydrogenation and cross-linking cyclization are not thorough, which affects the carbon yield in the later stage. In a specific preferred embodiment, in the step of the program heating treatment, the method of the pre-oxidation treatment is: first, the temperature is raised to 180°C at a heating rate of 5°C / min, and the temperature is kept for 4 hours for the first pre-oxidation treatment; then, the temperature is raised to 240°C at a heating rate of 5°C / min, and the temperature is kept for 4 hours for the second pre-oxidation treatment.

[0060] After the pre-oxidation treatment is completed, the obtained solid sample is placed in a sealed heating device for carbonization treatment. The sealed heating device can be a tubular furnace. In some embodiments, in the step of the program heating treatment, the method of the carbonization treatment is: the sample after the pre-oxidation treatment is kept warm under an inert atmosphere at a temperature of 800°C to 1200°C for carbonization to obtain a black powder. Carrying out carbonization treatment under these conditions can improve the crystallinity of carbon, promote the graphitization of carbon, thereby improving the conductivity of the material, and then the obtained nitrogen-doped porous carbon is loaded with Pd x Fe y W zWhen nanoalloys are used as lithium-air batteries, their electrochemical performance can be improved. Wherein, the inert atmosphere includes but is not limited to a nitrogen atmosphere. On the basis of the above embodiment, in the step of carbonization treatment, the temperature is raised to the carbonization treatment temperature at a heating rate of 3~8°C / min, and then the carbonization treatment is carried out, thereby avoiding the further uneven cross-linking and cyclization caused by excessive heating speed, affecting the rearrangement of carbon atoms, and ultimately affecting the orientation and stability of the carbon material. In a specific preferred embodiment, in the step of programmed heating treatment, the method of carbonization treatment is: first, the temperature is raised to 800℃~1200℃ at a heating rate of 5℃ / min, and the carbonization treatment is carried out by keeping the temperature for 4 hours.

[0061] Furthermore, an etching solution is added to the obtained carbonized material to etch away the silicon dioxide in the carbonized material to prepare nitrogen-doped porous carbon. The porous sites in the nitrogen-doped porous carbon are the sites occupied by the original nano-silicon dioxide. The dispersibility, appearance, and particle size of nano-silicon dioxide directly affect the dispersibility and orderliness of the porous structure in the nitrogen-doped porous carbon, as well as the pore size and shape of the porous structure, and ultimately affect the Pd x Fe y W z Supporting effect of nanocomposites in nitrogen-doped porous carbon.

[0062] In some embodiments, in the step of adding an etching solution to the carbonized material and etching away the silicon dioxide in the carbonized material, the etching solution is an HF solution. In some embodiments, in the step of adding an etching solution to the carbonized material and etching away the silicon dioxide in the carbonized material, the etching solution is molten sodium hydroxide. Through the etching action of the HF solution and the molten sodium hydroxide, the nano-silicon dioxide can be removed without affecting other components of the carbonized material, and corresponding pores are formed at the sites where the nano-silicon dioxide is located, ultimately obtaining nitrogen-doped porous carbon with a three-dimensional porous structure.

[0063] In step S03, the nitrogen-doped porous carbon is dispersed in deionized water or an organic alcohol to prepare a nitrogen-doped porous carbon solution. Deionized water or an organic alcohol, as a solvent, not only has good dispersibility for the nitrogen-doped porous carbon, but also for Pd salts, Fe salts, and W salts. The organic alcohol is preferably a liquid at room temperature (5°C to 40°C), more preferably ethanol or propanol. In a preferred embodiment, the solvent for dispersing the nitrogen-doped porous carbon is deionized water, which is inexpensive and environmentally friendly.

[0064] In the embodiment of the present invention, Pd salt, Fe salt and W salt are selected as precursors to prepare Pd x Fe y W zNano alloy. By doping with Fe and W, not only can the cost of the original pure palladium catalyst be reduced, but the obtained Pd x Fe y W z Nanoalloys have good oxygen reduction catalytic activity and stability. When loaded on nitrogen-doped porous carbon and used as the positive electrode active material of lithium-air batteries, they can solve the problems of high cost of precious metals in existing oxygen reduction catalysts, poor catalytic activity and the cyclic stability of the catalyst itself.

[0065] Specifically, Pd x Fe y W z The preparation method of the nanoalloy includes: providing a salt solution of Pd salt, Fe salt and W salt. The selection of Pd salt, Fe salt and W salt is not strictly limited, and commonly used Pd salt, Fe salt and W salt can be used. In some specific embodiments, the Pd salt is palladium chloride; in some embodiments, the Fe salt is ferric chloride; in some embodiments, the W salt is ammonium tungstate. In some embodiments, the Pd salt is palladium chloride, the Fe salt is ferric chloride or ferric sulfate, and the W salt is ammonium tungstate. Preferably, the concentration of the Pd salt is 5~7 mg / ml, specifically 5 mg / ml, 6 mg / ml, 7 mg / ml; the concentration of the Fe salt is 5~7 mg / ml, specifically 5 mg / ml, 6 mg / ml, 7 mg / ml; the concentration of the W salt is 5~7 mg / ml, specifically 5 mg / ml, 6 mg / ml, 7 mg / ml.

[0066] Further, the salt solution of the Pd salt, Fe salt and W salt is added to the nitrogen-doped porous carbon solution to prepare a third mixed solution. Specifically preferably, the salt solutions of Pd salt, Fe salt and W salt are added to the nitrogen-doped porous carbon solution respectively, whereby the metal salt added first can be evenly dispersed and occupy the void sites. After adding other metal salts, they are evenly arranged under the guidance of the metal salt added first, and finally a uniformly dispersed metal salt is obtained. In a specific embodiment, Pd salt is added first, and then Fe salt and W salt are added. The order of adding Fe salt and W salt is not strictly limited. On the basis of the above embodiment, the salt solution of Pd salt, Fe salt and W salt is slowly added such as being added dropwise to the nitrogen-doped porous carbon solution to promote the metal salt to enter the pore structure of the nitrogen-doped porous carbon and be evenly dispersed. Further, after adding each metal salt, stirring treatment is carried out so that Pd salt, Fe salt and W salt are evenly dispersed and combined with each other, and the preferred stirring time is 2 hours to 5 hours, more preferably 3 hours.

[0067] In a preferred embodiment, the salt solution of Pd salt, Fe salt and W salt is added to the nitrogen-doped porous carbon solution, and the nitrogen-doped porous carbon loaded with Pd is finally obtained. xFe y W z In nano alloys, Pd x Fe y W z The weight percentage of the nano alloy is 10% to 40%, and the salt solution of the Pd salt, Fe salt and W salt is added to the nitrogen-doped porous carbon solution. x Fe y W z The nano alloy is within the above range, and the obtained nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloys have good redox catalytic effects. x Fe y W z If the weight percentage of nano alloy exceeds 40%, Pd x Fe y W z Nano alloys are not conducive to the desorption of oxygen, which slows down the redox reaction and reduces the catalytic effect. More preferably, the nitrogen-doped porous carbon loaded with Pd x Fe y W z In nano alloys, Pd x Fe y W z The weight percentage of the nano alloy is 20%, and the salt solution of the Pd salt, the Fe salt and the W salt is added to the nitrogen-doped porous carbon solution.

[0068] After adjusting the pH of the third mixed solution to make the solution alkaline, a reducing agent is added to cause the Pd salt, Fe salt and W salt to undergo a reduction reaction at room temperature to generate Pd x Fe y W z Preferably, the pH of the third mixed solution is adjusted to 9-12, so that the Pd salt, Fe salt and W salt are reduced to generate Pd x Fe y W z The nano alloy provides suitable alkaline conditions. The reduction reaction is preferably carried out under stirring conditions, and the stirring reaction time is 20 to 48 hours.

[0069] In some embodiments, after adjusting the pH of the third mixed solution to make the solution alkaline, a reducing agent is added, and in the step of performing a reduction reaction under stirring, a sodium hydroxide solution is used to adjust the pH of the third mixed solution to 9-12, sodium borohydride is added as a reducing agent, and the reduction treatment is performed under stirring. This method can reduce Pd salt, Fe salt and W salt to Pd x Fey W z Nano alloy. Preferably, the concentration of the sodium hydroxide solution is 0.5~1.5mol L -1 , more preferably 1.0 mol L -1 .

[0070] In some embodiments, after adjusting the pH of the third mixed solution to make the solution alkaline, a reducing agent is added, and in the step of performing a reduction reaction under stirring, urea is used to adjust the pH of the third mixed solution to 8-10, ethylene glycol is added as a reducing agent, and the reduction treatment is performed by stirring the reaction at a temperature of 70°C to 90°C. This method can reduce Pd salt, Fe salt and W salt to Pd x Fe y W z Nano alloy.

[0071] In the above embodiment, the reducing agent is added to the third mixed solution at a molar ratio of the reducing agent to the total molar amount of the metal of (4-6):1. More preferably, the reducing agent is added to the third mixed solution at a molar ratio of the reducing agent to the total molar amount of the metal of 5:1.

[0072] The sample obtained by the reduction reaction was centrifuged, the precipitate was collected, washed to neutrality, and then vacuum dried. Further, the sample was calcined under an inert atmosphere to prepare nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloy composite positive electrode material. Preferably, in the step of calcining in an inert atmosphere, the calcining is carried out at a temperature of 300°C to 500°C. By the above calcining, the Pd x Fe y W z The crystallinity of nano alloys can improve the Pd x Fe y W z The stability of the nano alloy. The calcination time is preferably 2 to 5 hours, more preferably 3 hours. The inert atmosphere includes but is not limited to a nitrogen atmosphere.

[0073] In the embodiment of the present invention, the Pd x Fe y W z In the nano alloy, the ratio of x, y, and z is 1: (0.2-0.5): (0.2-0.5). The content of Pd, Fe, and W is controlled within the above range, and the resulting alloy element has a good redox catalytic effect. Specifically, the Pd x Fe y W z Nano alloy can be PdFe0.2 W 0.2 Nano alloy, PdFe 0.5 W 0.5 Nano alloy, PdFe 0.2 W 0.3 Nano alloy, PdFe 0.3 W 0.2 Nano alloy, PdFe 0.2 W 0.2 Nano alloy, PdFe 0.3 W 0.3 Nano alloy, PdFe 0.5 W 0.2 Nano alloy, PdFe 0.2 W 0.5 Nano alloys, but not limited to them.

[0074] Accordingly, the embodiment of the present invention provides a composite cathode material, wherein the composite cathode material is nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloys, including Pd x Fe y W z The doping weight percentage of the nano alloy in the nitrogen-doped porous carbon is 10% to 40%, and the Pd x Fe y W z In nanoalloys, the ratio of x, y, and z is 1:(0.2-0.5):(0.2-0.5).

[0075] The composite positive electrode material provided by the embodiment of the present invention is nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloy.

[0076] First, nitrogen-doped porous carbon is used as a carrier. The nitrogen-doped porous carbon is uniformly doped with N elements in the C elements. The doped N elements affect the spin density and charge of the surrounding C atoms, thereby increasing the conductivity of the carbon material and generating more active sites. At the same time, the nitrogen-doped porous carbon has a rich specific surface area and can be used as a carrier for Pd x Fe y W z Ternary alloy nucleation provides more sites, which is beneficial for Pd x Fe y W z Uniform dispersion of ternary alloy, increasing Pd x Fe y W zThe exposed surface of the ternary alloy creates more catalytically active sites, improving the catalytic effect. The relatively independent pores of the nitrogen-doped porous carbon provided by the present invention prevent the alloy from migrating, agglomerating, or even falling off during cycling, thereby enhancing the alloy's stability. The three-dimensional porous structure facilitates the transport of oxygen, the active substance.

[0077] Secondly, Fe and W co-doping produce a synergistic effect with Pd, which improves the loading of Pd on nitrogen-doped porous carbon. x Fe y W z The catalytic activity and stability of the nanoalloy as a positive electrode active material for lithium-air batteries. Furthermore, nitrogen doping can increase the conductivity of the carbon support, while the porous structure facilitates oxygen transport and the large specific surface area facilitates alloy dispersion. Therefore, under the synergistic effects of multiple levels, the composite positive electrode material of the present invention exhibits higher oxygen reduction catalytic activity and catalytic stability in three-electrode cyclic voltammetry tests and lithium-air battery capacity-limited cycling tests.

[0078] In the embodiment of the present invention, the nitrogen-doped porous carbon is loaded with Pd x Fe y W z Nano-alloys are used as positive electrode active materials for lithium-air batteries. They have the advantages of good stability and good electrochemical properties, and are expected to provide a new positive electrode material for the future commercialization of lithium-air batteries.

[0079] Preferably, the weight percentage of N in the nitrogen-doped porous carbon is 1% to 5%, based on the total weight of the nitrogen-doped porous carbon being 100%. If the N content is too low, the effect on promoting active sites is not obvious; if the N content is too high, the carbon content is reduced, which will affect the Pd loading of the obtained nitrogen-doped porous carbon. x Fe y W z Conductivity of nanoalloys, which in turn affects the loading of Pd on nitrogen-doped porous carbon x Fe y W z The electrochemical properties of lithium-air batteries with nano-alloys as positive electrode active materials. In addition, the N content is directly related to the carbonization temperature and carbonization time. If the carbonization temperature is too high or the carbonization time is too long, the final N content will be reduced.

[0080] The nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloy, preferably, the diameter of the porous structure is 150nm~250nm, and the porous structure is preferably honeycomb porous.

[0081] The nitrogen-doped porous carbon loaded with Pd in ​​the embodiment of the present invention xFe y W z Nano alloys can be prepared by the above method.

[0082] In addition, an embodiment of the present invention further provides a lithium-air battery, which contains a positive electrode active material, and the positive electrode active material is the composite positive electrode material described in the present invention, or the positive electrode active material is the composite positive electrode material prepared by the method described in the present invention.

[0083] The lithium-air battery provided by the embodiment of the present invention is a lithium-air battery in which nitrogen-doped porous carbon is loaded with Pd x Fe y W z Nano-alloys, as the positive electrode active material of lithium-air batteries, give lithium-air batteries the advantages of good stability and good electrochemical performance.

[0084] The composite positive electrode material is as described above, and will not be described again here to save space.

[0085] Specifically, the composite positive electrode material is mixed with a binder and then deposited on a positive electrode current collector to form a positive electrode sheet. The binder includes but is not limited to polyvinylidene fluoride, preferably, Pd is loaded on a nitrogen-doped porous carbon. x Fe y W z The nano alloy and polyvinylidene fluoride are mixed in a ratio of 9: (0.8-1.2), dispersed in a solvent, and further deposited on the positive electrode current collector. More preferably, the nitrogen-doped porous carbon is loaded with Pd x Fe y W z The nano alloy and polyvinylidene fluoride are mixed in a ratio of 9:1, dispersed in a solvent, and further deposited on the positive electrode current collector. The solvent includes but is not limited to anhydrous ethanol. The positive electrode current collector can be a conventional lithium-air battery positive electrode current collector, more preferably carbon paper / foam nickel / foam copper. x Fe y W z The nano-alloy is loaded on nitrogen-doped porous carbon and deposited, for example, by spraying on the surface of carbon paper / nickel foam / copper foam as a cathode material for lithium-air batteries, which has the advantages of good oxidation catalytic activity and stability.

[0086] Further preferably, based on the total weight of the positive electrode sheet being 100%, the nitrogen-doped porous carbon loaded with Pd x Fe y W z The weight of the nanoalloy is 0.2-1 mg cm -2 , more preferably 0.4 mg cm -2 .

[0087] The following describes the details in conjunction with specific embodiments.

[0088] Example 1

[0089] A method for preparing a composite positive electrode material comprises the following steps:

[0090] (1) Using tetraethyl orthosilicate as the silicon source and hexadecyltrimethylammonium bromide as the template, SiO2 spheres with a particle size of 150-200 nm were prepared in an alkaline aqueous solution by combining the traditional sol-gel method with homogeneous precipitation.

[0091] (2) Sodium lignin sulfonate was dissolved in water and stirred to form a uniform solution A with a solid content of 20%. Polyacrylonitrile powder was dissolved and dispersed in anhydrous ethanol and stirred to form a uniform solution B with a solid content of 20%. Solutions A and B were mixed in a volume ratio of 10:1 to form a mixed solution C.

[0092] (3) Preparation of nitrogen-doped porous carbon N / C. Take an appropriate amount of SiO2 from step (1) and put it into a 50 mL corundum boat. Then take an appropriate amount of solution C from step (2) and slowly drip it into the SiO2 powder. Let it stand to allow both to be fully impregnated. Then, pre-oxidize the mixed sample in air at 180 °C and 220 °C for 4 h respectively. The solid obtained by pre-oxidation is heated to 800 °C at a heating rate of 3 °C / min in a tube furnace under N2 atmosphere and carbonized for 4 h to obtain black powder. Finally, the template is etched with HF solution to prepare nitrogen-doped porous carbon (N / C).

[0093] (4) PdFe 0.5 W 0.2 Nanoalloys were loaded on nitrogen-doped porous carbon surfaces. 20 mg of nitrogen-doped porous carbon support (N / C) was weighed and ultrasonically dispersed in 200 mL of deionized water for 30 min to obtain solution D. Then, according to the designed alloy loading [alloy loading = alloy mass / (the sum of alloy mass and N / C mass)] of 30 wt%, and the predetermined Pd, Fe, and W molar ratio of 1:0.5:0.2, pre-prepared palladium chloride, ferric chloride, and ammonium tungstate salt solutions were slowly added dropwise to the mixed solution D under stirring. Stirring was continued for 3 h until fully mixed to obtain mixed solution E. Then, 1 mol L -1 Adjust the pH value to 11 with sodium hydroxide aqueous solution, then drop the prepared sodium borohydride aqueous solution (sodium borohydride to metal molar ratio is 5:2) and stir at room temperature for 48 hours. 0.5 W 0.2The mixed solution of nano-ternary metal alloy was centrifuged, washed and precipitated to neutrality, then vacuum dried, and finally heated to 300℃ in a nitrogen inert gas atmosphere at a heating rate of 3℃ / min for 3h to obtain nitrogen-doped porous carbon loaded with PdFe 0.5 W 0.2 Nano alloy.

[0094] Example 2

[0095] A method for preparing a composite positive electrode material comprises the following steps:

[0096] (1) Using tetraethyl orthosilicate as the silicon source and hexadecyltrimethylammonium bromide as the template, SiO2 spheres with a particle size of 150-200 nm were prepared in an alkaline aqueous solution by combining the traditional sol-gel method with homogeneous precipitation.

[0097] (2) Sodium lignin sulfonate was dissolved in water and stirred to form a uniform solution A with a solid content of 10%. Polyacrylonitrile powder was dissolved and dispersed in anhydrous ethanol and stirred to form a uniform solution B with a solid content of 10%. Solutions A and B were mixed in a volume ratio of 10:2 to form a mixed solution C.

[0098] (3) Preparation of nitrogen-doped porous carbon N / C. Take an appropriate amount of SiO2 from step (1) and put it into a 50ML corundum boat. Then take an appropriate amount of solution C from step (2) and slowly drip it into the SiO2 powder. Let it stand to allow both to be fully impregnated. Then, pre-oxidize the mixed sample in air at 200℃ and 240℃ for 4 h respectively. The solid obtained by pre-oxidation is heated to 1000℃ at a heating rate of 8℃ / min in a tube furnace under N2 atmosphere and then carbonized for 4 h to obtain black powder. Finally, the template is etched with HF solution to prepare nitrogen-doped porous carbon (N / C).

[0099] (4) PdFe 0.2 W 0.5 Nanoalloys were loaded on the surface of nitrogen-doped porous carbon. 20 mg of nitrogen-doped porous carbon support (N / C) was weighed and ultrasonically dispersed in 200 mL of deionized water for 30 min to obtain solution D. Then, according to the designed alloy loading of 40 wt% and the predetermined Pd, Fe, and W molar ratio of 1:0.2:0.5, the pre-prepared palladium chloride, ferric chloride, and ammonium tungstate salt solutions were slowly added dropwise to the mixed solution D under stirring. Stirring was continued for 2 h until fully mixed to obtain mixed solution E. Then, 1 mol L -1 Adjust the pH value to 10 with sodium hydroxide solution, then drop the prepared sodium borohydride solution (sodium borohydride to metal molar ratio is 5:1) and stir at room temperature for 24 hours. 0.2 W 0.5The mixed solution of nano-ternary metal alloy was centrifuged, washed and precipitated to neutrality, then vacuum dried, and finally heated to 400℃ in a nitrogen inert gas atmosphere at a heating rate of 8℃ / min for 3h to obtain nitrogen-doped porous carbon loaded with PdFe 0.2 W 0.5 Nano alloy.

[0100] Example 3

[0101] A method for preparing a composite positive electrode material comprises the following steps:

[0102] (1) Using tetraethyl orthosilicate as the silicon source and hexadecyltrimethylammonium bromide as the template, SiO2 spheres with a particle size of 150-200 nm were prepared in an alkaline aqueous solution by combining the traditional sol-gel method with homogeneous precipitation.

[0103] (2) Sodium lignin sulfonate was dissolved in water and stirred to form a uniform solution A with a solid content of 15%. Polyacrylonitrile powder was dissolved and dispersed in anhydrous ethanol and stirred to form a uniform solution B with a solid content of 15%. Solutions A and B were mixed in a volume ratio of 10:3 to form a mixed solution C.

[0104] (3) Preparation of nitrogen-doped porous carbon N / C. Take an appropriate amount of SiO2 from step (1) and put it into a 50 mL corundum boat. Then take an appropriate amount of solution C from step (2) and slowly drip it into the SiO2 powder. Let it stand to allow both to be fully impregnated. Then, pre-oxidize the mixed sample in air at 180 °C and 200 °C for 4 h respectively. The solid obtained by pre-oxidation is heated to 1200 °C at a heating rate of 5 °C / min in a tube furnace under N2 atmosphere and carbonized for 4 h to obtain black powder. Finally, the template is etched with HF solution to prepare nitrogen-doped porous carbon (N / C).

[0105] (4) PdFe 0.5 W 0.2 Nanoalloys were loaded on the surface of nitrogen-doped porous carbon. 20 mg of nitrogen-doped porous carbon support (N / C) was weighed and ultrasonically dispersed in 200 mL of deionized water for 30 min to obtain solution D. Then, according to the designed alloy loading of 20 wt% and the predetermined Pd, Fe, and W molar ratio of 1:0.5:0.2, the pre-prepared palladium chloride, ferric chloride, and ammonium tungstate salt solutions were slowly added dropwise to the mixed solution D under stirring. Stirring was continued for 5 h until fully mixed to obtain mixed solution E. Then, 1 mol L -1 Adjust the pH value to 9 with sodium hydroxide solution, then drop the prepared sodium borohydride solution (sodium borohydride to metal molar ratio is 5:1) and stir at room temperature for 36 hours. 0.5 W 0.2The mixed solution of nano-ternary metal alloy was centrifuged, washed and precipitated to neutrality, then vacuum dried, and finally heated to 500℃ at a heating rate of 5℃ / min in a nitrogen inert gas atmosphere and calcined for 3h to obtain nitrogen-doped porous carbon loaded with PdFe 0.5 W 0.2 Nano alloy.

[0106] Example 4

[0107] A method for preparing a composite positive electrode material comprises the following steps:

[0108] (1) Using tetraethyl orthosilicate as the silicon source and hexadecyltrimethylammonium bromide as the template, SiO2 spheres with a particle size of 150-200 nm were prepared in an alkaline aqueous solution by combining the traditional sol-gel method with homogeneous precipitation.

[0109] (2) Sodium lignin sulfonate was dissolved in water and stirred to form a uniform solution A with a solid content of 15%. Polyacrylonitrile powder was dissolved and dispersed in anhydrous ethanol and stirred to form a uniform solution B with a solid content of 15%. Solutions A and B were mixed in a volume ratio of 10:5 to form a mixed solution C.

[0110] (3) Preparation of nitrogen-doped porous carbon N / C. Take an appropriate amount of SiO2 from step (1) and put it into a 50 mL corundum boat. Then take an appropriate amount of solution C from step (2) and slowly drip it into the SiO2 powder. Let it stand to allow both to be fully impregnated. Then, pre-oxidize the mixed sample in air at 190 °C and 220 °C for 4 h respectively. The solid obtained by pre-oxidation is heated to 800 °C at a heating rate of 5 °C / min in a tube furnace under N2 atmosphere and carbonized for 4 h to obtain black powder. Finally, the template is etched with HF solution to prepare nitrogen-doped porous carbon (N / C).

[0111] (4) PdFe 0.2 W 0.2 Nanoalloys were loaded on the surface of nitrogen-doped porous carbon. 20 mg of nitrogen-doped porous carbon support (N / C) was weighed and ultrasonically dispersed in 200 mL of deionized water for 30 min to obtain solution D. Then, according to the designed alloy loading of 30 wt% and the predetermined Pd, Fe, and W molar ratio of 1:0.2:0.2, the pre-prepared palladium chloride, ferric chloride, and ammonium tungstate salt solutions were slowly added dropwise to the mixed solution D under stirring. Stirring was continued for 3 h until fully mixed to obtain mixed solution E. Then, 1 mol L -1 Adjust the pH value of sodium hydroxide solution to 9, then drop the prepared sodium borohydride solution (sodium borohydride to metal molar ratio is 5:1) and stir at room temperature for 20 hours. 0.2 W 0.2The mixed solution of nano-ternary metal alloy was centrifuged, washed and precipitated to neutrality, then vacuum dried, and finally heated to 400℃ in a nitrogen inert gas atmosphere at a heating rate of 5℃ / min for 3h to obtain nitrogen-doped porous carbon loaded with PdFe 0.2 W 0.2 Nano alloy.

[0112] Nitrogen-doped porous carbon loaded with PdFe prepared in Example 4 0.2 W 0.2 Field emission scanning electron microscope (SEM) images of nano alloys are shown in Figure 2. Figure 1 As shown in the figure, nitrogen-doped porous carbon loaded with PdFe 0.2 W 0.2 The nano alloy has a large number of regular pores, which look like honeycombs. The pores are independent of each other, which can prevent the catalyst from falling off and agglomerating during the reaction. In addition, the little bright white particles are PdFe 0.2 W 0.2 Nano alloy, it can be seen that it is successfully loaded onto the surface of honeycomb carbon. After loading the alloy, the original structure of honeycomb carbon is not destroyed, indicating that honeycomb carbon has good structural stability. It is worth mentioning that nitrogen-doped porous carbon loaded with PdFe 0.2 W 0.2 The nano alloy has a high degree of alloy dispersion, no agglomeration, and is uniform in size, with particle sizes below 10 nm.

[0113] Nitrogen-doped porous carbon loaded with PdFe prepared in Example 4 0.2 W 0.2 The XRD pattern of nano alloy is as follows Figure 2 As shown (porous carbon loaded with Pd was used as a control), Figure 2 Pd- / C and PdFe 0.2 W 0.2 There are obvious diffraction peaks, corresponding to the (111), (200), (220), and (311) crystal planes of Pd, and no other impurity peaks are found in the entire XRD pattern; and PdFe 0.2 W 0.2 Compared with that of Pd- / C, the XRD characteristic peaks of Pd- / C shift to higher angles as a whole. This is because the addition of Fe and W changes the Pd crystal structure, resulting in the contraction of the palladium lattice, indicating that Pd forms an alloy with Fe and W.

[0114] Nitrogen-doped porous carbon loaded with PdFe prepared in Example 4 0.2 W 0.2 Cyclic voltammetry of the nanoalloy in a 0.1M KOH solution containing saturated oxygen (scan rates of 50 mV s-1 )like Figure 3 As shown (porous carbon loaded with Pd was used as a control), Figure 3 Visible PdFe 0.2 W 0.2 The onset potential, half-wave potential and limiting current density of –N / C are all positively shifted compared to Pd- / C, so it can be judged that PdFe 0.2 W 0.2 –N / C has better oxygen reduction catalytic ability than Pd- / C.

[0115] Nitrogen-doped porous carbon loaded with PdFe prepared in Example 4 0.2 W 0.2 The lithium-air battery prepared by nano alloy has a constant current of 300 mAh g -1 , with a constant specific capacity of 500 mAh g -1 The charge and discharge protection range is 5.0 V-2.0 V. The cycle test results are as follows Figure 4 As shown (porous carbon loaded with Pd was used as a control), Figure 4 It can be seen that under the condition of limiting the charge and discharge capacity of lithium-air batteries, the cycle performance of PdFe 0.2 W 0.2 –N / C has a smaller overpotential and a longer cycle time within a limited voltage range, which is far superior to the cycling performance of commercial Pd / C.

[0116] Example 5

[0117] A method for preparing a composite positive electrode material comprises the following steps:

[0118] (1) Using tetraethyl orthosilicate as the silicon source and hexadecyltrimethylammonium bromide as the template, SiO2 spheres with a particle size of 150-200 nm were prepared in an alkaline aqueous solution by combining the traditional sol-gel method with homogeneous precipitation.

[0119] (2) Sodium lignin sulfonate was dissolved in water and stirred to form a uniform solution A with a solid content of 15%. Polyacrylonitrile powder was dissolved and dispersed in anhydrous ethanol and stirred to form a uniform solution B with a solid content of 15%. Solutions A and B were mixed in a volume ratio of 10:4 to form a mixed solution C.

[0120] (3) Preparation of nitrogen-doped porous carbon N / C. Take an appropriate amount of SiO2 from step (1) and put it into a 50 mL corundum boat. Then take an appropriate amount of solution C from step (2) and slowly drip it into the SiO2 powder. Let it stand to allow both to be fully impregnated. Then, pre-oxidize the mixed sample in air at 180 °C and 240 °C for 4 h respectively. The solid obtained by pre-oxidation is heated to 1000 °C at a heating rate of 5 °C / min in a tube furnace under N2 atmosphere and then carbonized for 4 h to obtain a black powder. Finally, the template is etched with a molten NaOH solution to prepare nitrogen-doped porous carbon (N / C).

[0121] (4) PdFe 0.5 W 0.5 Nanoalloys are loaded on the surface of nitrogen-doped porous carbon. Weigh 20 mg of nitrogen co-doped honeycomb carbon support (N / C) and disperse it in 50 mL of urea solution to form a mixed solution D. According to the predetermined alloy loading of 40 wt%, and the predetermined Pd, Fe, W molar ratio of 1:0.5:0.5, the pre-configured palladium chloride, ferric chloride, and ammonium tungstate salt solutions are slowly dripped into the mixed solution D respectively under stirring, and continue stirring for 3 hours. After being fully mixed, a mixed solution E is obtained, and the mixed solution E is transferred into a three-necked flask, a condensation reflux device is built, and the temperature is raised to 80 ° C and kept warm in an oil bath for 1 hour. After cooling to room temperature, 50 mL of ethylene glycol is added, and the solution is heated to 120 ° C and kept warm for 12 hours under stirring. After the reaction is completed, the mixture containing PdFe 0.2 W 0.2 The mixed solution of nano-ternary metal alloy was centrifuged, washed and precipitated to neutrality, then vacuum dried, and finally heated to 400℃ in a nitrogen inert gas atmosphere at a heating rate of 5℃ / min for 3h to obtain nitrogen-doped porous carbon loaded with PdFe 0.5 W 0.5 Nano alloy.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a composite positive electrode material, characterized in that: The composite positive electrode material is nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloy, and the preparation method of the composite positive electrode material comprises the following steps: Providing an aqueous solution of a lignin salt and an anhydrous alcohol solution of polyacrylonitrile, mixing the aqueous solution of the lignin salt and the anhydrous alcohol solution of the polyacrylonitrile to form a first mixed solution; wherein the lignin salt is selected from papermaking waste liquid lignin as a precursor; Nano-silica powder is provided, and the nano-silica powder is dispersed in a first mixed solution to obtain a second mixed solution. The second mixed solution is subjected to a program heat treatment to prepare a carbonized material; an etching solution is added to the carbonized material to etch away the silicon dioxide in the carbonized material to prepare nitrogen-doped porous carbon; wherein the program heat treatment includes the steps of pre-oxidizing the obtained mixed sample and carbonizing the pre-oxidized sample; the pre-oxidation method is: pre-oxidizing the second mixed solution at a temperature of 180°C to 240°C; the carbonization method is: carbonizing the pre-oxidized sample at a temperature of 800°C to 1200°C under an inert atmosphere; wherein the nano-silica is monodispersed nano-silica spheres, and the particle size of the nano-silica spheres is 150nm to 250nm; The nitrogen-doped porous carbon is dispersed in deionized water or an organic alcohol to prepare a nitrogen-doped porous carbon solution; a salt solution of Pd salt, Fe salt and W salt is provided, and the salt solution of Pd salt, Fe salt and W salt is added to the nitrogen-doped porous carbon solution to prepare a third mixed solution; after adjusting the pH of the third mixed solution to make the solution alkaline, a reducing agent is added, and a reduction reaction is carried out under stirring, and the precipitate is collected by centrifugation and washed to neutrality, and calcined under an inert atmosphere to prepare nitrogen-doped porous carbon loaded with Pd. x Fe y W z A nano-alloy composite positive electrode material, wherein the ratio of x, y, and z is 1:(0.2-0.5):(0.2-0.5).

2. The method for preparing a composite positive electrode material according to claim 1, wherein: In the step of mixing the aqueous solution of lignin salt and the anhydrous alcohol solution of polyacrylonitrile to prepare a first mixed solution, the aqueous solution of lignin salt and the anhydrous alcohol solution of polyacrylonitrile are mixed according to a mass ratio of lignin salt to polyacrylonitrile of 10:(1-5).

3. The method for preparing a composite positive electrode material according to claim 1, wherein: In the step of adding an etching solution to the carbonized material to etch away silicon dioxide in the carbonized material, the etching solution is an HF solution, or the etching solution is molten sodium hydroxide.

4. The method for preparing a composite cathode material according to claim 1, wherein: In the step of adding the salt solution of Pd salt, Fe salt and W salt into the nitrogen-doped porous carbon solution, the nitrogen-doped porous carbon loaded with Pd x Fe y W z In nano alloys, Pd x Fe y W z The weight percentage of the nano alloy is 10% to 40%, and the salt solution of the Pd salt, the Fe salt and the W salt is added to the nitrogen-doped porous carbon solution.

5. The method for preparing a composite positive electrode material according to any one of claims 1 to 4, wherein: After adjusting the pH of the third mixed solution to make the solution alkaline, adding a reducing agent, and performing a reduction reaction under stirring conditions, in the step of adjusting the pH of the third mixed solution to 9-12 using sodium hydroxide solution, adding sodium borohydride as a reducing agent, and performing the reduction treatment under stirring conditions; or The pH of the third mixed solution is adjusted to 9-12 by using urea, ethylene glycol is added as a reducing agent, and the mixture is stirred and reacted at a temperature of 70° C.-90° C. to perform reduction treatment.

6. The method for preparing a composite cathode material according to any one of claims 1 to 4, wherein: In the step of calcining under an inert atmosphere, the calcining is performed at a temperature of 300° C. to 500° C.

7. A composite positive electrode material prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The composite positive electrode material is nitrogen-doped porous carbon loaded with Pd x Fe y W z Nano alloys, including Pd x Fe y W z The doping weight percentage of the nano alloy in the nitrogen-doped porous carbon is 10% to 40%, and the Pd x Fe y W z In nanoalloys, the ratio of x, y, and z is 1:(0.2-0.5):(0.2-0.5).

8. A lithium-air battery, characterized in that: The lithium-air battery contains a positive electrode active material, and the positive electrode active material is the composite positive electrode material according to claim 7, or the positive electrode active material is a composite positive electrode material prepared by the method according to any one of claims 1 to 6.

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