A preparation method of a carbon-coated synthetic sodium iron oxalate sulfate carbon composite material in situ

Abstract

The application discloses a preparation method of in-situ carbon-coated sodium iron oxalate sulfate composite material and application thereof, and first takes H2C2O4.2H2O, FeC2O4.2H2O, a sulfate and a sodium source as reaction raw materials, adds a surfactant and a carbon source, and prepares in-situ carbon-coated sodium iron oxalate sulfate nanocomposite material through accurate control of heating time of a hydrothermal reaction. The nanocomposite material exhibits excellent sodium storage performance when used as a sodium battery positive electrode, and the NaFe(C2O4)SO4@C nanocomposite material prepared by the application is uniform in morphology, fast in preparation and uniform in crystal grain size distribution.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and particularly relates to a preparation method of an in-situ carbon-coated sodium iron sulfate oxalate-coated carbon composite material and its application in sodium ion batteries. Background Art

[0002] Advancing the energy revolution requires the development of renewable energy. However, renewable energy sources such as wind and solar power are intermittent and unstable. There is an urgent need to build a new "new energy + energy storage" power system to achieve high-quality integration of renewable energy into the grid and stable output. Therefore, the development of energy storage technology is key. Lithium-ion batteries, due to their advantages such as high specific energy, have seen increasing application in both power batteries and energy storage in recent years, highlighting the shortage of lithium resources. my country is the world's largest importer, making lithium resource scarcity a potential bottleneck in the development of lithium-ion batteries in my country.

[0003] The structure and working principle of sodium-ion batteries are similar to those of lithium-ion batteries, but they have no resource restrictions, do not require copper current collectors, have high safety, good rate performance, good low-temperature performance, can achieve zero-point storage and transportation, are low-cost, and have high cost-effectiveness. They have shown broad application prospects in medium and low-speed electric vehicles and large-scale energy storage. At the same time, my country's National Development and Reform Commission and the Energy Bureau have also issued a series of relevant policies, listing sodium-ion batteries as one of the key research directions for new energy storage core technology equipment in the 14th Five-Year Plan, and proposing pilot demonstration requirements for new energy storage technologies.

[0004] Sodium-ion battery technology can be categorized by cathode type into three types: oxides, polyanions, and Prussian blue. Polyanion cathode materials offer advantages such as low cost, resource freedom, safety, non-toxicity, structural stability, abundant sodium ion channels, and excellent thermal stability. These materials are suitable for large-scale applications and are the preferred system for sodium-ion batteries with high stability, high specific power, and high safety. However, their inherent poor electrical conductivity limits the battery's specific capacity and rate performance, necessitating modification through methods such as carbon coating and doping. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide a preparation method for an in-situ carbon-coated sodium iron sulfate oxalate composite material with high safety, good conductivity, good rate performance and good cycle stability. The in-situ carbon-coated sodium iron sulfate oxalate composite material prepared by this method has relatively excellent sodium storage performance and can be used as a positive electrode material for high-performance sodium ion batteries.

[0006] The present invention adopts the following technical solution to solve the above technical problems, which is a preparation method of an in-situ carbon-coated modified synthetic sodium oxalate sulfate cathode material, characterized by the following specific steps:

[0007] Step S1, adding an appropriate amount of surfactant to the secondary water and stirring to form a clear and transparent solution, then adding an appropriate amount of carbon source and ultrasonically generating a uniform and stable dispersion, then weighing and mixing H2C2O4·2H2O, FeC2O4·2H2O, sulfuric acid and a sodium source according to a certain molar ratio and adding them to the dispersion, stirring at a speed of 200 to 500 rpm to form a uniform and stable solution, placing the mixture in a reactor and heating at 180 to 220° C. for 30 to 38 hours to obtain a composite material;

[0008] Step S2, filtering the synthesized composite material in glycerol at 60-80°C, washing to remove excess sodium source, surfactant and glycerol, and then drying the resulting reaction product to obtain a carbon-coated modified sodium ferric oxalate sulfate composite material; the in-situ carbon-coated modified sodium ferric oxalate sulfate nanocomposite material is specifically a NaFe(C2O4)SO4@C composite material.

[0009] Furthermore, in the above technical solution, in step S1, the secondary water is 30 ml, the first stirring time is 10 to 30 min; the ultrasonic time is 1.5 to 3 h; and the second stirring time is 1.5 to 3 h;

[0010] Step S2, washing is performed by centrifugation and filtration in anhydrous ethanol, acetone and secondary water at least three times in sequence to wash away excess sodium source, surfactant and glycerol, and then the obtained reaction product is placed in a vacuum drying oven to dry the product quickly.

[0011] Furthermore, in the above technical solution, the sodium source is one or more of sodium sulfate, sodium carbonate, sodium acetate, sodium citrate and sodium edetate; the sulfate is one or more of potassium sulfate, sodium sulfate and sulfuric acid; and the surfactant is one or more of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate and polyvinylpyrrolidone.

[0012] Furthermore, in the above technical solution, the atomic molar ratio of the surfactant, H2C2O4·2H2O, FeC2O4·2H2O and the sodium source is (0.05-1):1:(2~4):(3~4).

[0013] Furthermore, in the above technical solution, the carbon source is one or more of carbon nanotubes, single-walled carbon nanotubes, graphene oxide, reduced graphene oxide, Ketjen black, and acetylene black.

[0014] The present invention provides the use of the carbon-coated sodium iron sulfate oxalate material prepared by the above method as a high-performance sodium ion battery positive electrode material.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0016] 1. Rationally adjust the ratio of carbon source to raw materials to achieve uniform carbon coating. Uniform carbon coating can 1) promote rapid electron migration and provide good conductivity, while also inhibiting volume expansion during cycling, thereby ensuring the structural stability of the composite material; 2) act as a nucleating agent during the hydrothermal process, reducing the particle size of the product; 3) enhance interparticle and surface electron conductivity, reducing the occurrence of battery polarization; and 4) adsorb and maintain the stability of the electrolyte.

[0017] 2. Use hexadecyltrimethylammonium bromide (CTAB) as a dispersant and surfactant to induce the synthesis of composite materials. CTAB is a cationic surfactant that exhibits positive charge when dissolved in water. Carbon nanotube particles are very small, have a large specific surface area, and have strong van der Waals forces between tubes, so entanglement often occurs. Adding CTAB can reduce the surface tension of carbon nanotubes. Carbon nanotubes also have a hydrophobic effect and are poorly dispersed in aqueous solutions. At this time, the positive charge on the surface of CTAB will form non-covalently functionalized carbon nanotubes with the carbon nanotubes with oxygen-rich functional groups, which can prevent or reduce the aggregation and mutual entanglement of carbon nanotubes, allowing the carbon nanotubes to be evenly dispersed in the solution.

[0018] 3. Ultrasonic-assisted dispersion of carbon nanotubes for 2 hours significantly enhances their stability. Ultrasonic waves generate "ultrasonic cavitation bubbles" that release a large amount of energy upon explosion, creating a localized high-temperature, high-pressure environment and high-impact microjets. This cavitation effect facilitates the formation of tiny particles, inhibiting their aggregation and growth, while also shearing the agglomeration of carbon nanotubes.

[0019] 4. Surfactants have a significant impact on the dispersion of carbon nanotubes. Excessive amounts of surfactant can actually reduce dispersion. Surfactants adsorb onto the carbon nanotubes, forming a saturated adsorption pattern on the surface. Excessive amounts do not reduce surface tension, but only increase the number of micelles. This increase in micelles can even compete for surfactant molecules on the surface, reducing the stability of the carbon nanotubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the SEM image of the NaFe(C2O4)SO4@C positive electrode active material prepared in Example 1.

[0021] Figure 2 XRD patterns of the prepared comparative example 1 NaFe(C2O4)SO4 and example 1 NaFe(C2O4)SO4@CNTs positive electrode active materials.

[0022] Figure 3 This is the rate comparison curve of sodium ion batteries using the prepared NaFe(C2O4)SO4 and NaFe(C2O4)SO4@CNTs as positive electrode active materials;

[0023] Figure 4 Comparative curves of long cycle times of sodium ion batteries using prepared NaFe(C2O4)SO4 and NaFe(C2O4)SO4@CNTs cathode active materials;

[0024] Figure 5 Comparison of the charge and discharge curves of the third cycle of sodium ion batteries using the prepared NaFe(C2O4)SO4 and NaFe(C2O4)SO4@C as positive electrode active materials. DETAILED DESCRIPTION

[0025] The above contents of the present invention are further described in detail below through examples, but this should not be understood as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above contents of the present invention fall within the scope of the present invention.

[0026] Example 1

[0027] Preparation of NaFe(C2O4)SO4@C-1 cathode material

[0028] Step S1, adding an appropriate amount of polyvinyl pyrrolidone to 30 ml of secondary water and stirring for 15 minutes to generate a clear and transparent solution, then adding 2 wt% carbon nanotubes and ultrasonicating for 2 hours to generate a uniform and stable dispersion, then weighing and mixing H2C2O4·2H2O, FeC2O4·2H2O, and sodium sulfate in a molar ratio of 1:4:4 and adding the mixture to the dispersion, stirring at 350 rpm for 2 hours to form a uniform and stable solution, and then placing the mixture in a 100 ml reactor and heating at 180° C. for 30 hours to obtain a composite material;

[0029] Step S2, filtering the synthesized composite material in glycerol at 60° C., and then centrifugally filtering and washing in anhydrous ethanol, acetone and secondary water for at least three times to wash away excess sodium source, surfactant and glycerol, and then placing the resulting reaction product in a vacuum drying oven at 80° C. to quickly dry the product to obtain a carbon-coated modified sodium ferric oxalate sulfate composite material, wherein the in situ carbon-coated sodium ferric oxalate sulfate nanocomposite material is specifically a NaFe(C2O4)SO4@C composite material;

[0030] Example 2

[0031] Preparation of NaFe(C2O4)SO4@C-2 cathode material

[0032] Step S1, adding an appropriate amount of hexadecyltrimethylammonium bromide to 30 ml of secondary water and stirring for 15 minutes to generate a clear and transparent solution, then adding 4 wt% of graphene oxide and ultrasonicating for 2 hours to generate a uniform and stable dispersion, then weighing and mixing H2C2O4·2H2O, FeC2O4·2H2O and sodium sulfate in a molar ratio of 1:4:4 and adding the mixture to the dispersion, stirring at 350 rpm for 2 hours to form a uniform and stable solution, and then placing the mixture in a 100 ml reactor and heating at 200° C. for 36 hours to obtain a composite material;

[0033] Step S2, filtering the synthesized composite material in glycerol at 80° C., and then centrifugally filtering and washing in anhydrous ethanol, acetone and secondary water at least three times to wash away excess sodium source, surfactant and glycerol, and then placing the resulting reaction product in a vacuum drying oven at 80° C. to quickly dry the product to obtain a carbon-coated modified sodium iron oxalate sulfate composite material, wherein the in situ carbon-coated sodium iron oxalate sulfate nanocomposite material is specifically a NaFe(C2O4)SO4@C composite material;

[0034] Example 3

[0035] Preparation of NaFe(C2O4)SO4@C-3 cathode material

[0036] Step S1, adding an appropriate amount of sodium dodecylbenzenesulfonate to 30 ml of secondary water and stirring for 15 minutes to generate a clear and transparent solution, then adding 6 wt% of reduced graphene oxide and ultrasonicating for 2 hours to generate a uniform and stable dispersion, then weighing sodium acetate, H2C2O4·2H2O, FeC2O4·2H2O and sulfuric acid in a molar ratio of 8:1:4:4 and adding them to the dispersion, stirring at 350 rpm for 2 hours to form a uniform and stable solution, and then placing it in a 100 ml reactor and heating at 220° C. for 38 hours to obtain a composite material;

[0037] Step S2, filtering the synthesized composite material in glycerol at 80° C., and then centrifugally filtering and washing in anhydrous ethanol, acetone and secondary water at least three times to wash away excess sodium source, surfactant and glycerol, and then placing the resulting reaction product in a vacuum drying oven at 80° C. to quickly dry the product to obtain a carbon-coated modified sodium iron oxalate sulfate composite material, wherein the in situ carbon-coated sodium iron oxalate sulfate nanocomposite material is specifically a NaFe(C2O4)SO4@C composite material;

[0038] Example 4

[0039] Preparation of NaFe(C2O4)SO4@C-4 cathode material

[0040] Step S1, adding an appropriate amount of sodium lauryl sulfate to 30 ml of secondary water and stirring for 15 minutes to generate a clear and transparent solution, then adding an appropriate amount of acetylene black and sonicating for 2 hours to generate a uniform and stable dispersion, then weighing and mixing H2C2O4·2H2O, FeC2O4·2H2O, and sodium sulfate in a molar ratio of 1:4:4, and adding the mixture to the dispersion, stirring at 350 rpm for 2 hours to form a uniform and stable solution, placing the mixture in a 100 ml reactor and heating at 180° C. for 30 hours to obtain a composite material;

[0041] Step S2, filtering the synthesized composite material in glycerol at 60-80° C., then centrifugally filtering and washing in anhydrous ethanol, acetone, and secondary water for at least three times to remove excess sodium source, surfactant, and glycerol, and then placing the resulting reaction product in a vacuum drying oven at 80° C. to quickly dry the product to obtain a carbon-coated modified sodium iron oxalate sulfate composite material, wherein the in-situ carbon-coated sodium iron oxalate sulfate nanocomposite material is specifically a NaFe(C2O4)SO4@C composite material;

[0042] Comparative Example 1

[0043] Preparation of NaFe(C2O4)SO4 cathode material

[0044] Step S1, adding H2C2O4·2H2O, FeC2O4·2H2O, and sodium sulfate to 30 ml of secondary water in a molar ratio of 1:4:4, stirring at 350 rpm for 2 hours to form a uniform and stable solution, and then placing the solution in a 100 ml reactor and heating at 180-220° C. for 30-38 hours to obtain a composite material;

[0045] Step S2, filtering the synthesized composite material in glycerol at 60-80°C, and then centrifugally filtering and washing in anhydrous ethanol, acetone and secondary water at least three times to wash away excess sodium source and glycerol, and then placing the resulting reaction product in a vacuum drying oven at 80°C to dry the product quickly to obtain a carbon-coated modified sodium iron oxalate sulfate composite material. The in-situ carbon-coated sodium iron oxalate sulfate nanocomposite material is specifically a NaFe(C2O4)SO4 composite material.

[0046] Application Examples

[0047] The NaFe(C2O4)SO4@C cathode material prepared in Example 1 and the NaFe(C2O4)SO4 prepared in Comparative Example 1 were mixed with super P and a binder at a mass ratio of 70:20:10 to form a slurry, and the slurry was evenly coated on an aluminum mesh current collector to form a working electrode. Sodium metal was used as the counter electrode and a glass fiber microporous filter membrane was used as the diaphragm. 1 mol L -1NaPF6 (the solvent is 5% FEC of a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1) was used as the electrolyte, and button cells were assembled in a vacuum glove box with water and oxygen values ​​less than 0.1 ppm.

[0048] The assembled battery was tested on a charge and discharge tester with a charge and discharge range of 2.0 to 4.2 V. -1 , 10mA g -1 , 20mA g -1 、30mA g -1 , 50mA g -1 , 100mA g -1 , 150mA g -1 , 200mA g -1 , 5mA g -1 The rate performance of the assembled battery was tested at the charge and discharge rates of 50mA g -1 The cycle performance of the assembled battery was tested under the rate conditions of .

[0049] The prepared NaFe(C2O4)SO4@C and NaFe(C2O4)SO4 cathode active materials were characterized by X-ray diffraction patterns. Figure 2 Figure 2 is the XRD spectrum of the prepared NaFe(C2O4)SO4@C and NaFe(C2O4)SO4 positive electrode active materials. It can be seen from the figure that NaFe(C2O4)SO4@C and NaFe(C2O4)SO4 positive electrode active materials have been successfully prepared and are pure phases. By comparison, it can be obtained that the (002) crystal plane of the material after coating preferentially grows, which can prove the successful recombination of carbon elements. Figure 1 The prepared NaFe ( Scanning electron microscopy (SEM) image of the C2O4)SO4@C cathode active material shows that the composite material is a spherical polycrystalline aggregate with a particle size of 30 to 50 nm; Figure 3 The rate comparison curve of the prepared NaFe(C2O4)SO4@C and NaFe(C2O4)SO4 positive electrode active materials is shown in the figure. It can be seen that the NaFe(C2O4)SO4@C has a high conductivity at 5mA g -1 , 10mA g -1 , 20mA g -1 、30mA g -1 , 50mA g -1 , 100mAg -1 , 150mA g -1 , 200mA g -1 The specific capacity under current is 143.5mAh g -1 、123.1mAh g -1、106.8mAh g -1 、99.2mAh g -1 、89.9mAh g -1 、81.7mAh g -1 , 77.72mAh g -1 , 70.5mAh g -1 , the discharge capacity of the comparative materials is 101.0 mAh g -1 、80.1mAh g -1 、66.4mAh g -1 , 46.6mAh g -1 、33.8mAh g -1 , 27.2mAh g -1 , 18.2mAh g -1 , 13.2mAh g -1 ,Comparison between the two shows that the electrical conductivity of the material is greatly improved after carbon coating, and the internal skeleton of the material is stable and has abundant sodium ion diffusion channels; Figure 4 The long cycle comparison curves of NaFe(C2O4)SO4@C and NaFe(C2O4)SO4 positive electrode active materials are shown in the figure. It can be seen that at 50mA g -1 After 170 cycles, the specific capacity is 92.6 mAh g -1 The coulombic efficiency is 100%, the capacity retention rate is 94.2%, and the specific capacity of the comparative material NaFe(C2O4)SO4 is 34.56mA g after 54 cycles. -1 The capacity retention rate is 88.9%, indicating that the NaFe(C2O4)SO4@C composite material prepared after carbon coating exhibits good rate performance and cycle stability when used as a positive electrode material for sodium ion batteries compared with the reference material NaFe(C2O4)SO4. Figure 5 Comparison of the charge and discharge curves of NaFe(C2O4)SO4 and NaKFe(C2O4)SO4 positive electrode active materials. The comparison shows that the in situ carbon-coated material has higher operating voltage and specific capacity and smaller polarization effect.

[0050] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an in-situ carbon-coated modified sodium oxalate sulfate cathode material, characterized in that The specific steps are: Step S1, adding an appropriate amount of surfactant to the secondary water and stirring to form a clear and transparent solution, then adding an appropriate amount of carbon source and ultrasonically generating a uniform and stable dispersion, then weighing and mixing H2C2O4·2H2O, FeC2O4·2H2O, sulfate or sulfuric acid, and a sodium source according to a certain molar ratio and adding them to the dispersion, stirring at a speed of 200 to 500 rpm to form a uniform and stable solution, placing the mixture in a reactor and heating it at 180 to 220°C for 30 to 38 hours to obtain a composite material; Step S2: Filter the synthesized composite material in glycerol at 60-80° C., wash to remove excess sodium source, surfactant, and glycerol, and then dry the resulting reaction product to obtain a carbon-coated modified sodium ferric oxalate sulfate composite material; the in-situ carbon-coated modified sodium ferric oxalate sulfate nanocomposite material is specifically a NaFe(C2O4)SO4@C composite material.

2. The preparation method according to claim 1, wherein: Step S1: the secondary water volume is 30 ml, the first stirring time is 10 to 30 min, the ultrasonic time is 1.5 to 3 h, and the second stirring time is 1.5 to 3 h; Step S2, washing is performed by centrifugation and filtration in anhydrous ethanol, acetone and secondary water at least three times in sequence to wash away excess sodium source, surfactant and glycerol, and then the obtained reaction product is placed in a vacuum drying oven to dry the product quickly.

3. The preparation method according to claim 1, wherein: The sodium source is one or more of sodium sulfate, sodium carbonate, sodium acetate, sodium citrate and sodium edetate; the sulfate is one or both of potassium sulfate and sodium sulfate; and the surfactant is one or more of cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, sodium lauryl sulfate and polyvinylpyrrolidone.

4. The preparation method according to claim 1, wherein: The atomic molar ratio of the surfactant, H2C2O4·2H2O, FeC2O4·2H2O and the sodium source is (0.05-1):1:(2-4):(3-4).

5. The preparation method according to claim 1, wherein: The carbon source is one or more of carbon nanotubes, graphene oxide, reduced graphene oxide, Ketjen black, and acetylene black.

6. The preparation method according to claim 5, wherein: The carbon nanotubes are single-walled carbon nanotubes.

7. Use of the carbon-coated sodium iron sulfate oxalate material prepared by the method according to any one of claims 1 to 6 as a high-performance positive electrode material for sodium ion batteries.

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