Sodium-ion battery positive electrode material coated with high-entropy oxide material as well as preparation method and application of sodium-ion battery positive electrode material

Abstract

The invention discloses a sodium ion battery positive electrode material coated with a high-entropy oxide material and a preparation method and application of the sodium ion battery positive electrode material, the preparation method comprises the following steps: taking nitrate of Co, Cu, Zn, Mn and Mg, dissolving and uniformly stirring to obtain a mixed solution containing metal salt; adding fuel or a mixture of the fuel and a combustion improver into the mixed solution, uniformly stirring, and adjusting the pH value to obtain sol; heating the sol, and removing the solvent in the sol to obtain gel; carrying out calcination or microwave heating on the gel to obtain a high-entropy oxide nano powder material; and mixing the layered cathode material of the sodium-ion battery with the high-entropy oxide nano-powder material, sintering in an air atmosphere, cooling to room temperature, grinding, and screening to obtain the lithium ion battery cathode material. According to the invention, the layered sodium ion battery positive electrode material is coated with the high-entropy oxide, so that the side reaction of the sodium ion layered oxide, moisture and electrolyte can be effectively avoided, and the stability of the structure can be kept.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for sodium-ion batteries, and particularly relates to a cathode material for sodium-ion batteries coated with a high-entropy oxide material, a preparation method thereof, and an application thereof. Background Art

[0002] Renewable energy sources, such as solar energy, wind energy, etc., all have the characteristics of intermittency and geographical limitations, which makes it difficult to directly integrate renewable energy into the power grid. Therefore, it is very important to develop suitable electrical energy storage technologies for peak shaving and valley filling. According to the energy density and conversion efficiency, secondary batteries are most suitable as electrical energy storage devices. Due to their high energy density and long cycle life, lithium-ion batteries have been successfully applied to portable electronic devices and electric vehicles. However, the continuously rising costs of lithium and cobalt make it difficult for lithium-ion batteries to meet the large-scale application of energy storage devices. Therefore, it is crucial to find a substitute for lithium-ion batteries that is inexpensive and resource-rich. Due to the abundant sodium resource reserves, sodium-ion batteries with low-cost advantages are considered ideal candidates to replace lithium-ion batteries and be applied to large-scale energy storage devices. However, the lack of suitable cathode materials severely restricts the practical application process of sodium-ion batteries. In the past decade, layered oxides have been considered a class of potential cathode materials for sodium-ion batteries due to their compact crystal structure, high energy density, and low cost.

[0003] However, due to scientific problems such as complex structural phase transitions and slow sodium-ion diffusion kinetics in layered oxide cathode materials, the practical application process of sodium-ion batteries is severely restricted. In recent years, with the in-depth understanding of layered oxide cathodes, some modification strategies, including surface coating, composition regulation, and structural design of layered cathode materials, have been further developed. Among them, surface coating is a relatively effective method. It can coat a physical protection layer on the material surface, which can inhibit volume changes during charge and discharge, and at the same time can also reduce the direct contact between the cathode material and the electrolyte, reducing interfacial side reactions. The coating material usually has a physical blocking effect on the coated cathode material, alleviating the reaction between the cathode material and the electrolyte or trace moisture in the environment, and improving the cycle life of the cathode. However, the stability of the coating material itself also needs to be taken seriously. The coating layer should have a certain rigidity and be difficult to react with the electrolyte or reaction products of the electrolyte (such as HF, etc.).

[0004] Therefore, reasonably using the surface coating strategy to modify layered oxide cathode materials, studying their internal modification methodology, and demonstrating the application potential of the modified cathode in a full battery are of great significance for realizing high-performance and practical sodium-ion batteries. Summary of the Invention

[0005] Objective of the Invention: To solve the problems existing in the prior art, the objective of the present invention is to provide a sodium-ion battery cathode material coated with a high-entropy oxide material, its preparation method and application. The present invention uses a high-entropy oxide to coat the layered oxide cathode material, which can improve its own strength and corrosion resistance, and thus can improve the stability of the entire cathode material system. Therefore, the present invention can solve the problems in the prior art such as difficult control of the coating amount and coating uniformity of the sodium-ion cathode material, single coating effect, poor capacity and cycling performance of the material, etc.

[0006] Technical Solution: To achieve the above objective of the invention, the technical solutions adopted by the present invention are as follows:

[0007] In the first aspect, the present invention provides a preparation method of a sodium-ion battery cathode material coated with a high-entropy oxide material, comprising the following steps:

[0008] Step 1: Take nitrates of Co, Cu, Zn, Mn and Mg, dissolve them, and stir evenly to obtain a mixed solution containing metal salts;

[0009] Step 2: Take a fuel or a mixture of fuel and combustion improver, add it to the above mixed solution, stir evenly, and adjust the pH to obtain a sol;

[0010] Step 3: Heat the above sol to remove the solvent therein to obtain a gel;

[0011] Step 4: Calcinate or microwave-heat the above gel to obtain a high-entropy oxide nanopowder material;

[0012] Step 5: Mix the sodium-ion battery layered cathode material with the above high-entropy oxide nanopowder material and sinter it in an air atmosphere, cool it to room temperature, grind and screen it to obtain the sodium-ion battery cathode material coated with the high-entropy oxide material.

[0013] As a specific implementation, in Step 1, the nitrates are respectively Mg(NO3)2·6H2O, Co(NO3)2·6H2O, Cu(NO3)2·3H2O, Mn(NO3)2·4H2O and Zn(NO3)2·6H2O; for the nitrates of Co, Cu, Zn, Mn and Mg, the molar ratio of Co, Cu, Zn, Mn and Mg is 1:1:1:1:1; in the mixed solution, the concentration of the metal salt is 0.8 mol / L to 1.5 mol / L.

[0014] As a specific implementation, in Step 1, the solvent used for dissolution is distilled water or an ethanol aqueous solution, and in the ethanol aqueous solution, the volume fraction of ethanol is 20 to 80%.

[0015] As a specific implementation, in step two, the fuel is one or a mixture of several of citric acid, tartaric acid, and glucose, and the combustion aid is one or both of ammonium acetate and ammonium nitrate; the molar ratio of the fuel to the metal ions in the mixed solution is 1.8 - 2.5:1; the amount of the combustion aid is 1 - 3% of the mass of the fuel.

[0016] As a specific implementation, in step two, the pH is adjusted using ammonia water to a pH of 6 - 8.

[0017] As a specific implementation, in step three, the heating temperature is 80 - 200 °C.

[0018] As a specific implementation, in step four, the calcination temperature is 300 - 550 °C, and the time is 15 - 30 min; the input power of the microwave heating is 500 - 700 W, and the reaction time is 4 - 10 min.

[0019] As a specific implementation, in step five, the layered positive electrode material for the sodium-ion battery is NaNi A Fe B Mn C O2, where 0.2 ≤ A ≤ 0.5; 0.1 ≤ B ≤ 0.4, and C = 1 - A - B.

[0020] As a specific implementation, in step five, the sintering is carried out by heating at a heating rate of 2 - 4 °C / min to 600 °C - 800 °C and sintering for 5 - 7 h.

[0021] In the second aspect, the present invention provides a positive electrode material for a sodium-ion battery, and the positive electrode material for the sodium-ion battery is prepared by the above preparation method.

[0022] In the third aspect, the present invention provides the application of the positive electrode material for the sodium-ion battery in the preparation of a sodium-ion battery.

[0023] Beneficial effects: Compared with the prior art, in the present invention, the layered positive electrode material for the sodium-ion battery is coated with a high-entropy oxide. Due to the high-entropy effect and the sluggish diffusion effect, the high-entropy oxide material has good corrosion resistance and thermal stability, can effectively avoid side reactions between the sodium-layered oxide and moisture and the electrolyte, and can maintain the stability of the structure.

[0024] (1) The high-entropy effect and the sluggish diffusion effect of the high-entropy material contribute to further improving the cycle stability of the material;

[0025] (2) The "cocktail" effect of the high-entropy material can optimize the material composition, and through a large number of experiments, appropriate element selection is screened to improve the electronic conductivity of the material;

[0026] (3) The process used in the present invention is simple, the raw material cost is low, and it is suitable for large-scale production. Description of the Drawings

[0027] Figure 1 XRD patterns of the cathode material before and after coating with high-entropy oxide in Example 1.

[0028] Figure 2 SEM image of the cathode material coated with high-entropy oxide prepared in Example 1 magnified 15,000 times.

[0029] Figure 3 SEM image of the cathode material prepared in Comparative Example 1 magnified 15,000 times.

[0030] Figure 4 Discharge capacity curves of the sodium-ion batteries assembled with the cathode materials of Example 1 and Comparative Example 1 cycled 180 times at 25 °C and 1C. Detailed Description of the Invention

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0032] Example 1

[0033] (1) Preparation method of high-entropy oxide, the steps are as follows:

[0034] Weigh 12.85 g of Mg(NO3)2·6H2O, 14.55 g of Co(NO3)2·6H2O, 12.08 g of Cu(NO3)2·3H2O, 12.55 g of Mn(NO3)2·4H2O, and 14.87 g of Zn(NO3)2·6H2O and dissolve them in 62.5 mL of distilled water, stir evenly to obtain a mixed solution containing metal salts; then weigh 75.05 g of tartaric acid and 2.25 g of ammonium nitrate and add them to the above mixed solution, stir evenly and adjust the pH of the mixed solution to 6 with ammonia water to obtain a transparent sol; then place the above transparent sol in an oil bath at 150 °C and heat it to remove the solvent water to obtain a loose, foamy gel; finally, place the above gel in a muffle furnace at 300 °C and react for 30 min to obtain a rock salt-type crystal structure, and a spherical rock salt-type structure (CoCuZnMnMg)3O4 high-entropy oxide nanopowder material with an average particle size of 10 nm.

[0035] (2) Preparation method of the coated cathode material, the steps are as follows:

[0036] Mix the layered oxide cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 with the (CoCuZnMnMg)3O4 nanometer powder material to obtain a mixture. Place the mixture in an air atmosphere furnace with a flow rate of 3m 3 / h. Heat it up to 750°C at a heating rate of 3°C / min and sinter for 6h, then cool it to room temperature with the furnace, take it out, grind and screen it to obtain the sodium ion cathode material (CoCuZnMnMg)3O4@NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0037] (3) Preparation of sodium ion battery

[0038] The mass ratio of the positive electrode slurry is active material: PVDF: SuperP (conductive carbon black) = 8:1:1. Add NMP solvent, stir until PVDF is completely dissolved, adjust to an appropriate viscosity, and prepare the slurry. Use a homogenizer to mix the positive electrode slurry, 500r, 1 minute; 1800r, 4min; 500r 1 minute, homogenize twice. Coating the electrode sheet, transfer it to a blast drying oven and dry it at 120°C for 80min. Cut the positive electrode sheet into circular electrode sheets with a diameter of Φ14mm. Obtain the mass of the positive electrode active material of each electrode sheet through the mass difference. After weighing, dry the electrode sheet in a vacuum drying oven at 120°C, then transfer it to a glove box. The positive electrode uses a self-made electrode sheet; the negative electrode uses a sodium metal sheet; use glass fiber as the separator; the electrolyte composition is NaPF6 / EC / EMC / PC / VC / FEC / PS(13 / 5 / 49 / 30 / 1 / 1.5 / 0.5), using NaPF6 as the lithium salt; the solvent is a mixed solvent of EC / EMC / PC / VC / FEC / PS. Assemble a button cell in a glove box filled with high-purity argon.

[0039] Example 2

[0040] Weigh 12.85 g of Mg(NO3)2·6H2O, 14.55 g of Co(NO3)2·6H2O, 12.08 g of Cu(NO3)2·3H2O, 12.55 g of Mn(NO3)2·4H2O, and 14.87 g of Zn(NO3)2·6H2O and dissolve them in a solvent composed of 45 mL of distilled water and 10 mL of ethanol. Stir evenly to obtain a mixed solution containing metal salts; then weigh 86.45 g of citric acid and add it to the above mixed solution. After stirring evenly, adjust the pH of the mixed solution to 7 with ammonia water to obtain a transparent sol; then place the above transparent sol in a water bath at 90 °C to heat and remove the solvent water to obtain a loose, foamy gel; finally, place the above gel in a muffle furnace at 500 °C and react for 20 min to obtain a spherical rock salt-type structured (CoCuZnMnMg)3O4 high-entropy oxide nanopowder material with an average particle size of 25 nm. The remaining steps are the same as those in Example 1.

[0041] Example 3

[0042] Weigh 12.85 g of Mg(NO3)2·6H2O, 14.55 g of Co(NO3)2·6H2O, 12.08 g of Cu(NO3)2·3H2O, 12.55 g of Mn(NO3)2·4H2O, and 14.87 g of Zn(NO3)2·6H2O and dissolve them in 45 mL of distilled water. Stir evenly to obtain a mixed solution containing metal salts; then weigh 43.22 g of citric acid, 72.06 g of glucose, and 1.2 g of ammonium acetate and add them to the above mixed solution. After stirring evenly, adjust the pH of the mixed solution to 8 with ammonia water to obtain a transparent sol; then place the above transparent sol in an oil bath at 200 °C to heat and remove the solvent water to obtain a loose, foamy gel; finally, place the above gel in a microwave oven with a power of 600 W and react for 5 min to obtain a spherical rock salt-type structured (CoCuZnMnMg)3O4 high-entropy oxide nanopowder material with an average particle size of 55 nm. The remaining steps are the same as those in Example 1.

[0043] Comparative Example 1

[0044] A preparation method of a sodium ion cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is basically the same as the steps (2) and (3) in the examples, except that (CoCuZnMnMg)3O4 coating modification is not carried out.

[0045] Example 4 Material Morphology and Property Detection

[0046] I. Sample Characterization and Testing

[0047] X-Ray Diffraction (XRD) technology is a commonly used testing method for studying the crystal phase and structure of crystals or the microscopic structure of certain amorphous materials. In this experiment, a German Bruker D8 Advance intelligent X-ray diffractometer was used, with a radiation source of CuKα, a scanning range of 10~80°, and a scanning rate of 2° / min, to test the crystal structure of the prepared NFM.

[0048] A Scanning Electron Microscope (SEM) uses a highly focused electron beam to scan the surface of the sample to be measured, and the physical signals obtained are the result of the interaction between the electron beam and the sample. The SEM device processes these physical signals to reflect the microscopic morphological characteristics of the material. The instrument used in this article is an ionization dual-beam electron microscope produced by TESCAN BRNO in the Czech Republic to obtain surface information of the sample.

[0049] The XRD detection results are as Figure 1 shown. The background of the spectrum is flat and the peak shape is sharp, indicating that the material has a high degree of crystallinity. The positions of the remaining diffraction peaks correspond exactly to the characteristic diffraction peaks of the standard card, indicating that the obtained material can be attributed to the layered O3 rhombohedral structure.

[0050] The SEM detection results are as Figure 2 、 Figure 3 shown. The sample is composed of flaky particles with an average size of about 2 μm. These particles are agglomerated by small particles with sufficient surface area, indicating that the two samples have good catalytic reaction activity for the oxygen reduction with surface activity as the point. And there are no obvious morphological differences in the particle shape and size of the coated sample.

[0051] II. Performance Detection Electrochemical Performance Detection

[0052] A Hubei Lanbo BT-2018R multi-channel charge-discharge test system was used for constant current charge-discharge and cycle performance tests. Here, 1C = 120 mA / g was defined, and the charge-discharge voltage range was 2.0~4.0 V.

[0053] The discharge capacity curves of the sodium-ion batteries assembled with the NFM cathode material before and after coating NFM were cycled 180 times at 25°C and 1C conditions. The results are as Figure 4As described, the uncoated NFM material has an initial discharge specific capacity of 114.7 mAh / g and a capacity retention rate of 87.7% after 180 cycles. In Example 1, the coated NFM has an initial discharge specific capacity of 118.27 mAh / g compared to the uncoated NFM material, with better cycle life. After 180 cycles, the capacity retention rate is approximately 86.9%. This material has good rate performance and certain cycle stability, and the entire preparation process is simple with inexpensive and easily available raw materials.

[0054] The embodiments of the present invention have been described in detail above in conjunction with specific embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

Claims

1. A method for preparing a sodium ion battery positive electrode material coated with a high entropy oxide material, characterized in that: The following steps are involved: Step 1, taking nitrates of Co, Cu, Zn, Mn and Mg, dissolving them, and stirring them evenly to obtain a mixed solution containing metal salts; Step 2, taking a fuel or a mixture of a fuel and a combustion improver, adding it to the above mixed solution, stirring it evenly, adjusting the pH, and obtaining a sol; Step 3, heating the sol to remove the solvent therein to obtain a gel; Step 4, calcining or microwave heating the gel to obtain a high entropy oxide nanopowder material; Step 5: Mix the sodium ion battery layered positive electrode material with the above-mentioned high entropy oxide nanopowder material and sinter them in an air atmosphere, cool them to room temperature, grind and sieve them to obtain the sodium ion battery positive electrode material coated with the high entropy oxide material.

2. The method for preparing a sodium ion battery positive electrode material coated with a high entropy oxide material according to claim 1, characterized in that: In step one, the nitrates are Mg(NO3)2·6H2O, Co(NO3)2·6H2O, Cu(NO3)2·3H2O, Mn(NO3)2·4H2O and Zn(NO3)2·6H2O respectively; the nitrates of Co, Cu, Zn, Mn and Mg, wherein the molar ratio of Co, Cu, Zn, Mn and Mg is 1:1:1:1:1; in the mixed solution, the concentration of the metal salt is 0.8 mol / L to 1.5 mol / L.

3. The method for preparing a sodium ion battery positive electrode material coated with a high entropy oxide material according to claim 1, characterized in that: In step 1, the solvent used for dissolving is distilled water or ethanol aqueous solution, and the volume fraction of ethanol in the ethanol aqueous solution is 20-80%.

4. The method for preparing a sodium ion battery positive electrode material coated with a high entropy oxide material according to claim 1, characterized in that: In step 2, the fuel is a mixture of one or more of citric acid, tartaric acid and glucose, and the combustion improver is one or two of ammonium acetate and ammonium nitrate; the molar ratio of the fuel to the metal ions in the mixed solution is 1.8-2.5:1; the amount of the combustion improver is 1-3% of the fuel mass; and the pH is adjusted by ammonia water to adjust the pH to 6-8.

5. The method for preparing a sodium ion battery positive electrode material coated with a high entropy oxide material according to claim 1, characterized in that: In step three, the heating temperature is 80-200°C.

6. The method for preparing a sodium ion battery positive electrode material coated with a high entropy oxide material according to claim 1, characterized in that: In step 4, the calcination temperature is 300-550° C., and the time is 15-30 min; the input power of the microwave heating is 500-700 W, and the reaction time is 4-10 min.

7. The method for preparing a sodium ion battery positive electrode material coated with a high entropy oxide material according to claim 1, characterized in that: In step 5, the sodium ion battery layered positive electrode material is NaNi A Fe B Mn C O2, where 0.2≤A≤0.5; 0.1≤B≤0.4, C=1-AB.

8. The method for preparing a sodium ion battery positive electrode material coated with a high entropy oxide material according to claim 1, characterized in that: In step five, the sintering is carried out by heating the temperature to 600°C-800°C at a heating rate of 2-4°C / min and sintering for 5-7h.

9. A sodium ion battery positive electrode material, characterized in that: The sodium ion battery positive electrode material is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the sodium ion battery positive electrode material according to claim 9 in the preparation of sodium ion batteries.

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