Preparation process of graphene oxide-sodium ion positive electrode composite material

Abstract

This invention utilizes dopamine-modified three-dimensional graphene oxide to adsorb and chelate transition metal ions, followed by a hydrothermal reaction with sodium ferrocyanate. This process forms crystals within the three-dimensional network of graphene oxide, enabling in-situ coating of graphene oxide while reducing crystallization defects in Prussian blue-like materials, thereby minimizing hydration defects and improving battery performance.

Description

Technical Field

[0001] This application belongs to the field of battery cathode materials, and more particularly to the field of methods for preparing sodium ion cathode composite materials. Background Technology

[0002] The development of battery energy storage technology contributes to carbon neutrality. In recent years, battery energy storage technology has made significant progress. Currently, lithium-ion battery technology is mature, has a high market share, and boasts significant advantages in energy density. However, the limited availability of lithium-ion resources, reliance on imports, and high costs limit the long-term, large-scale promotion and application of lithium-ion energy storage batteries. Sodium, as a group metal element with lithium, has similar chemical properties. The abundance of sodium in the Earth's crust is 1000 times that of lithium. The abundant sodium ions in seawater provide an inexhaustible source for sodium-ion energy storage batteries, offering a significant low-cost advantage and making it a promising next-generation energy storage battery material for future widespread adoption.

[0003] In the research of sodium-ion batteries, more attention has been paid to layered metal oxides, polyanionic compounds, and Prussian blue analogs. Compared with layered metal oxides and polyanionic compounds, Prussian blue analogs, as sodium-ion electrode materials, have a three-dimensional open structure and large ion channels, which is conducive to the rapid insertion and extraction of sodium ions. Prussian blue analogs have high theoretical capacity and outstanding advantages in terms of high specific capacity and high energy density. In addition, the raw materials for preparing Prussian blue analogs are readily available, the process is simple and easy to prepare, the cost is low, and the environmental pollution is low. However, there are still many problems in the traditional rapid precipitation method for preparing Prussian blue analogs. For example, there are a large number of Fe(CN)6 vacancies occupied by coordinated water in the crystal framework. Vacancies and water can damage the performance of the battery. Furthermore, the large number of vacancy defects in Prussian blue analogs can easily lead to the destruction of the crystal structure during the insertion and extraction of Na+, thereby reducing the charge-discharge cycle stability of Prussian blue analogs.

[0004] Currently, several technologies focus on optimizing the doping of transition metal elements to improve the electrochemical performance of Prussian blue analogs. However, effectively reducing the defects of Prussian blue analogs and preparing Prussian blue sodium ion electrode materials with high crystallinity, resistance to collapse, and stable electrochemical performance, especially stable cycle performance, remains a subject of ongoing exploration. Meanwhile, the insufficient conductivity of Prussian blue analogs while reducing crystal defects has also attracted widespread interest. For example, the use of conductive additives such as graphite, carbon nanotubes, and graphene to modify Prussian blue analogs has significantly improved their conductivity and enhanced the long-cycle performance of batteries.

[0005] However, existing processing techniques for reducing crystal defects and improving conductivity are usually carried out separately. How to more effectively use the same processing technique to reduce crystal defects and improve conductivity, thereby significantly improving economic benefits, still requires continuous research and improvement. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a graphene oxide-sodium-ion battery composite material. Through extensive research on existing technologies, the aim is to provide a method that simultaneously solves the problems of structural defects and poor conductivity caused by water binding in crystals. By overcoming the shortcomings of the prior art, a Prussian blue analog sodium-ion battery cathode material with high specific capacity, excellent cycle stability, and superior rate performance is efficiently prepared. To achieve the above-mentioned problems, this invention specifically adopts the following technical solution: A preparation process for a graphene oxide-sodium ion cathode composite material includes the following steps: 1. Preparation of three-dimensional graphene oxide: Nano-graphene oxide is dissolved in deionized water and ultrasonically dispersed to obtain a nano-graphene oxide dispersion. The dispersion is placed in a hydrothermal reactor and subjected to hydrothermal reaction at 120-150℃ for 2-4 hours to obtain a three-dimensional graphene oxide precursor. The precursor is freeze-dried to obtain three-dimensional graphene oxide. II. Dopamine modification of three-dimensional graphene oxide: Three-dimensional graphene oxide is immersed in an aqueous solution of dopamine, ultrasonically dispersed for 4-6 hours, and then heated to 40-60℃ for 30-60 minutes to obtain a dopamine-modified three-dimensional graphene oxide dispersion. 3. Add the transition metal salt solution to the dopamine-modified graphene oxide dispersion prepared in step 2, and disperse it by ultrasonication to obtain a three-dimensional graphene oxide dispersion that chelates and adsorbs transition metal ions. IV. Dissolve polyvinylpyrrolidone and sodium ferrocyanide in deionized water, stir and disperse for 2-3 hours to obtain a mixed raw material solution of graphene oxide-transition metal salt-sodium ferrocyanide. 5. Stir the mixed raw material liquid obtained in step 4 for 20-40 minutes, then transfer it to a reaction vessel and hydrothermally react at 80-100℃ for 6-8 hours. After the reaction is completed, cool to room temperature, filter, wash and dry to obtain graphene oxide-sodium ion cathode composite material.

[0007] The transition metal salts are nickel salts and cobalt salts; the nickel salts are nickel nitrate and nickel acetate; the cobalt salts are cobalt nitrate and cobalt acetate. The molar ratio of the raw materials used—nano-graphene oxide, dopamine, transition metal salts, and sodium ferrocyanide—is 5-6:2-3:1:1-1.2.

[0008] In step one, the hydrothermal treatment temperature is 120℃. In step two, ultrasonic dispersion is performed for 5 hours, followed by heating to 40℃ for 40 minutes. In step three, ultrasonic dispersion is performed for 2-3 hours. In step four, stirring and dispersion is performed for 2 hours. In step five, stirring is continued for 30 minutes, and the reaction is carried out at 80℃ for 8 hours.

[0009] Compared with the prior art, the present invention has the following significant advantages and technical effects: This invention utilizes three-dimensional graphene oxide to in-situ coat and modify sodium ion cathode materials formed by hydrothermal processes of transition metal salts and sodium ferrocyanate, thereby improving the conductivity of Prussian blue electrode materials. Three-dimensional graphene oxide possesses excellent conductivity and adsorption properties. After impregnation with dopamine, in-situ chelation sites are formed on the graphene oxide surface through dopamine adsorption, allowing for binding with transition metal salt ions. Furthermore, the subsequent heating treatment after dopamine impregnation further promotes the local self-polymerization of dopamine on the surface of the three-dimensional graphene oxide, resulting in adhesion and bonding between dopamine and the graphene oxide surface. The chelation sites are more tightly bound to the surface of graphene oxide, forming in-situ chelation sites. The dopamine adhering to the graphene oxide surface has the function of chelating transition metal ions and adsorbing them within the three-dimensional graphene oxide for in-situ slow-release of these ions. Therefore, the three-dimensional graphene oxide not only provides a reaction site for Prussian blue-like materials, but its ability to adsorb and chelate transition metal ions also allows Prussian blue-like materials to slow down the reaction rate, reduce hydration defects, and improve crystallinity. Simultaneously, the adhesiveness of the dopamine bound to the surface of the three-dimensional graphene oxide facilitates the tight bonding between the crystals and the graphene oxide. Therefore, the process of this invention can achieve significant effects in reducing crystal defects and improving conductivity, cycle stability, and rate performance through a one-pot in-situ slow-release synthesis. Detailed Implementation

[0010] Example 1: A preparation process of a graphene oxide-sodium ion cathode composite material, comprising the following steps: 1. Preparation of three-dimensional graphene oxide: 0.05 mol of nano-graphene oxide was dissolved in deionized water and ultrasonically dispersed to obtain a nano-graphene oxide dispersion. The dispersion was placed in a hydrothermal reactor and subjected to hydrothermal reaction at 120°C for 2 hours to obtain a three-dimensional graphene oxide precursor. The precursor was freeze-dried to obtain three-dimensional graphene oxide. II. Dopamine modification of three-dimensional graphene oxide: Three-dimensional graphene oxide was immersed in an aqueous solution containing 0.02 mol of dopamine, ultrasonically dispersed for 5 hours, and then heated to 40℃ for 40 min to obtain a dopamine-modified three-dimensional graphene oxide dispersion. 3. Add a solution containing 0.01 mol of nickel nitrate to the dopamine-modified graphene oxide dispersion prepared in step 2, and ultrasonically disperse for 3 hours to obtain a three-dimensional graphene oxide dispersion that chelates and adsorbs transition metal ions. IV. Polyvinylpyrrolidone and 0.01 mol sodium ferrocyanide were dissolved in deionized water and stirred and dispersed for 2 hours to obtain a mixed raw material solution of graphene oxide-transition metal salt-sodium ferrocyanide. 5. Stir the mixed raw material liquid prepared in step 4 for 20 minutes, then transfer it to a reaction vessel and hydrothermally react at 80°C for 8 hours. After the reaction is completed, cool it to room temperature, filter, wash and dry it to obtain the graphene oxide-sodium ion cathode composite material.

[0011] Example 2: A preparation process for a graphene oxide-sodium ion cathode composite material includes the following steps: 1. Preparation of three-dimensional graphene oxide: 0.05 mol of nano-graphene oxide was dissolved in deionized water and ultrasonically dispersed to obtain a nano-graphene oxide dispersion. The dispersion was placed in a hydrothermal reactor and subjected to hydrothermal reaction at 120°C for 2 hours to obtain a three-dimensional graphene oxide precursor. The precursor was freeze-dried to obtain three-dimensional graphene oxide. II. Dopamine modification of three-dimensional graphene oxide: Three-dimensional graphene oxide was immersed in an aqueous solution containing 0.023 mol of dopamine, ultrasonically dispersed for 5 hours, and then heated to 40℃ for 40 min to obtain a dopamine-modified three-dimensional graphene oxide dispersion. 3. Add a solution containing 0.01 mol of nickel nitrate to the dopamine-modified graphene oxide dispersion prepared in step 2, and ultrasonically disperse for 3 hours to obtain a three-dimensional graphene oxide dispersion that chelates and adsorbs transition metal ions. IV. Polyvinylpyrrolidone and 0.01 mol sodium ferrocyanide were dissolved in deionized water and stirred and dispersed for 2 hours to obtain a mixed raw material solution of graphene oxide-transition metal salt-sodium ferrocyanide. 5. Stir the mixed raw material liquid obtained in step 4 for 20 minutes, then transfer it to a reaction vessel and hydrothermally react at 100°C for 6 hours. After the reaction is completed, cool it to room temperature, filter, wash and dry it to obtain the graphene oxide-sodium ion cathode composite material.

[0012] Example 3: A preparation process for a graphene oxide-sodium ion cathode composite material includes the following steps: 1. Preparation of three-dimensional graphene oxide: 0.05 mol of nano-graphene oxide was dissolved in deionized water and ultrasonically dispersed to obtain a nano-graphene oxide dispersion. The dispersion was placed in a hydrothermal reactor and subjected to hydrothermal reaction at 120°C for 2 hours to obtain a three-dimensional graphene oxide precursor. The precursor was freeze-dried to obtain three-dimensional graphene oxide. II. Dopamine modification of three-dimensional graphene oxide: Three-dimensional graphene oxide was immersed in an aqueous solution containing 0.03 mol of dopamine, ultrasonically dispersed for 4 hours, and then heated to 50℃ for 35 min to obtain a dopamine-modified three-dimensional graphene oxide dispersion. 3. Add a solution containing 0.01 mol of nickel nitrate to the dopamine-modified graphene oxide dispersion prepared in step 2, and ultrasonically disperse for 3 hours to obtain a three-dimensional graphene oxide dispersion that chelates and adsorbs transition metal ions. IV. Polyvinylpyrrolidone and 0.01 mol of sodium ferrocyanide were dissolved in deionized water and stirred and dispersed for 2 hours to obtain a mixed raw material solution of graphene oxide-transition metal salt-sodium ferrocyanide. 5. Stir the mixed raw material liquid obtained in step 4 for 20 minutes, then transfer it to a reaction vessel and hydrothermally react at 90°C for 6 hours. After the reaction is completed, cool it to room temperature, filter, wash and dry it to obtain the graphene oxide-sodium ion cathode composite material.

[0013] Comparative Example 1: A preparation process for a graphene oxide-sodium ion cathode composite material includes the following steps: 1. Preparation of three-dimensional graphene oxide: 0.05 mol of nano-graphene oxide was dissolved in deionized water and ultrasonically dispersed to obtain a nano-graphene oxide dispersion. The dispersion was placed in a hydrothermal reactor and subjected to hydrothermal reaction at 120°C for 3 hours to obtain a three-dimensional graphene oxide precursor. The precursor was freeze-dried to obtain three-dimensional graphene oxide. II. Aqueous solution of three-dimensional graphene oxide: Three-dimensional graphene oxide is dissolved in deionized water and ultrasonically dispersed to obtain a three-dimensional graphene oxide dispersion. 3. Add a solution containing 0.01 mol nickel nitrate to the three-dimensional graphene oxide dispersion prepared in step 2, and ultrasonically disperse for 3 hours to obtain a three-dimensional graphene oxide dispersion adsorbed with transition metal ions. IV. Polyvinylpyrrolidone and 0.01 mol of sodium ferrocyanide were dissolved in deionized water and stirred and dispersed for 2 hours to obtain a mixed raw material solution of graphene oxide-transition metal salt-sodium ferrocyanide. 5. Stir the mixed raw material liquid prepared in step 4 for 20 minutes, then transfer it to a reaction vessel and hydrothermally react at 80°C for 8 hours. After the reaction is completed, cool it to room temperature, filter, wash and dry it to obtain the graphene oxide-sodium ion cathode composite material.

[0014] Comparative Example 2: A preparation process for a graphene oxide-sodium ion cathode composite material includes the following steps: 1. Preparation of three-dimensional graphene oxide: 0.05 mol of nano-graphene oxide was dissolved in deionized water and ultrasonically dispersed to obtain a nano-graphene oxide dispersion. The dispersion was placed in a hydrothermal reactor and subjected to hydrothermal reaction at 120°C for 3 hours to obtain a three-dimensional graphene oxide precursor. The precursor was freeze-dried to obtain three-dimensional graphene oxide. 2. Three-dimensional graphene oxide was immersed in an aqueous solution containing 0.02 mol citric acid, ultrasonically dispersed for 5 hours, and then heated to 40℃ for 40 min to obtain a citric acid modified three-dimensional graphene oxide dispersion. 3. Add a solution containing 0.01 mol of nickel nitrate to the citric acid modified graphene oxide dispersion prepared in step 2, and ultrasonically disperse for 3 hours to obtain a three-dimensional graphene oxide dispersion that chelates and adsorbs transition metal ions. IV. Polyvinylpyrrolidone and 0.01 mol of sodium ferrocyanide were dissolved in deionized water and stirred for 2 hours to obtain graphene oxide. transition metal salts Sodium ferrocyanide mixed feed solution; 5. Stir the mixed raw material liquid prepared in step 4 for 20 minutes, then transfer it to a reaction vessel and hydrothermally react at 80°C for 8 hours. After the reaction is completed, cool it to room temperature, filter, wash and dry it to obtain the graphene oxide-sodium ion cathode composite material.

[0015] Table 1. Electrochemical performance tests of the full cells prepared by the graphene oxide-sodium ion cathode composite materials in Examples 1-3 and Comparative Examples 1-2.

[0016]

[0017] Table 2. Water content of the graphene oxide-sodium ion cathode composite materials prepared in Examples 1-3 and Comparative Examples 1-2.

[0018]

[0019] The difference between Examples 1-3 and Comparative Examples 1-2 is that Comparative Example 1 did not use dopamine as a modifier, while Comparative Example 2 used a commonly used citric acid complexing agent. A comparison of Examples 1-3 and Comparative Example 1 shows that modifying three-dimensional graphene oxide with dopamine significantly improves conductivity and reduces crystal defects, thereby enhancing capacity and cycling performance. A comparison of Examples 1-3 and Comparative Example 2 illustrates that when citric acid cannot interact with three-dimensional graphene, failing to utilize the formation of Prussian blue analogue composites with in-situ graphene coating to reduce moisture defects and improve conductivity can easily lead to a decrease in electrochemical performance, such as a reduction in capacity.

Claims

1. A preparation process for a graphene oxide-sodium ion cathode composite material, characterized in that, Includes the following steps: I. Preparation of three-dimensional graphene oxide: Nano-graphene oxide is dissolved in deionized water and ultrasonically dispersed to obtain a nano-graphene oxide dispersion. The dispersion is placed in a hydrothermal reactor and subjected to hydrothermal reaction at 120-150℃ for 2-4 hours to obtain a three-dimensional graphene oxide precursor. The precursor is freeze-dried to obtain three-dimensional graphene oxide. II. Dopamine modification of three-dimensional graphene oxide: Three-dimensional graphene oxide is immersed in an aqueous solution of dopamine, ultrasonically dispersed for 4-6 hours, and then heated to 40-60℃ for 30-60 minutes to obtain a dopamine-modified three-dimensional graphene oxide dispersion.

3. Add the transition metal salt solution to the dopamine-modified graphene oxide dispersion prepared in step 2, and disperse it by ultrasonication to obtain a three-dimensional graphene oxide dispersion that chelates and adsorbs transition metal ions. IV. Dissolve polyvinylpyrrolidone and sodium ferrocyanide in deionized water, stir and disperse for 2-3 hours to obtain a mixed raw material solution of graphene oxide-transition metal salt-sodium ferrocyanide.

5. Stir the mixed raw material liquid prepared in step 4 for 20-40 minutes, then transfer it to a reaction vessel and hydrothermally react at 80-100℃ for 6-8 hours. After the reaction is completed, cool to room temperature, filter, wash and dry to obtain graphene oxide-sodium ion cathode composite material. The molar ratio of nano-graphene oxide, dopamine, transition metal salt, and sodium ferrocyanide is 5-6:2-3:1:1-1.

2. In-situ coating modification of sodium-ion cathode materials formed by hydrothermal processes of transition metal salts and sodium ferrocyanide using three-dimensional graphene oxide was carried out.

2. The preparation process of the graphene oxide-sodium ion cathode composite material according to claim 1, characterized in that, The transition metal salt is a nickel salt or a cobalt salt; the nickel salt is nickel nitrate or nickel acetate; the cobalt salt is cobalt nitrate or cobalt acetate.

3. The preparation process of the graphene oxide-sodium ion cathode composite material according to claim 1, characterized in that, The temperature of the hydrothermal treatment in step one is 120℃.

4. The preparation process of the graphene oxide-sodium ion cathode composite material according to claim 1, characterized in that, In step two, ultrasonic dispersion is performed for 5 hours, followed by heating to 40°C for 40 minutes.

5. The preparation process of the graphene oxide-sodium ion cathode composite material according to claim 1, characterized in that, The ultrasonic dispersion time in step three is 2-3 hours.

6. The preparation process of the graphene oxide-sodium ion cathode composite material according to claim 1, characterized in that, In step four, the mixture is stirred and dispersed for 2 hours; in step five, the mixture is stirred continuously for 30 minutes and reacted at 80°C for 8 hours.

7. The graphene oxide-sodium ion cathode composite material prepared by the preparation process according to any one of claims 1-6.

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