Preparation method of three-dimensional porous high-entropy oxide

Abstract

The invention relates to the technical field of oxide preparation, and discloses a three-dimensional porous high-entropy oxide preparation method, which comprises: dissolving a plurality of metal salts in deionized water according to an equal molar ratio; dropwise adding ammonia water into the metal salt mixed solution, and regulating the pH value of the solution to 4.8-8.2; carrying out homogenization treatment on the solution of which the pH value is regulated and controlled in a water bath of 50-60 DEG C; drying the stable precursor solution to obtain a precursor; calcining the precursor powder in an air atmosphere to form a three-dimensional porous structure; and grinding, cleaning and drying the high-entropy oxide material. The hydrolysis-polycondensation behavior of the precursor is accurately regulated and controlled through the pH value, a three-dimensional through pore channel structure is directly constructed without sacrificing a template, the process is simplified and environmentally friendly, systematic regulation and control of parameters such as pore channel morphology and specific surface area are achieved, and the prepared spinel type high-entropy oxide material has excellent ion diffusion efficiency and electrochemical performance and is suitable for industrial production. Higher specific capacity and cycling stability are shown in the field of lithium ion battery negative electrode materials.

Description

Technical Field

[0001] This invention relates to the field of oxide preparation technology, and more specifically, to a method for preparing three-dimensional porous high-entropy oxides. Background Technology

[0002] High-entropy oxides (HEOs), as an emerging multi-component functional material, have shown great potential in catalysis, energy storage, and other fields due to their unique lattice distortion effect, retarded diffusion characteristics, and synergistic advantages resulting from their high configurational entropy. Especially in applications such as lithium / sodium-ion battery electrodes and oxygen evolution reaction (OER) catalysts, their porous structural characteristics (e.g., specific surface area, porosity, pore size distribution) directly affect mass transfer efficiency and active site exposure, becoming key factors determining performance.

[0003] In existing technologies, the preparation of three-dimensional porous high-entropy oxides mainly relies on the following pathways, but significant limitations still exist:

[0004] In the application document with patent number CN116949487A: a nitrogen-doped carbon network (N-CN) is used as a sacrificial template, which requires multiple steps such as high-temperature carbonization and acid etching to remove the template. The process is cumbersome and easily introduces impurities (such as residual carbon).

[0005] In the application document with patent number CN115845868 B: polystyrene microspheres (PS) are used to construct ordered macropores, but template removal requires high-temperature calcination (>800℃), which leads to particle coarsening, increased risk of pore collapse, and a porosity of only 3-4%.

[0006] Although the template method can control macroscopic porosity, the process is complex, costly, and difficult to achieve precise control over the morphology and size of the pores.

[0007] The patent application with patent number CN112599749B describes a one-step solution combustion method to introduce metal particles, but it does not involve the active construction of three-dimensional pores. The resulting product is solid particles with limited specific surface area, leading to a low ion diffusion rate in the electrode material (e.g., a capacity of only 578 mAh·g after 300 cycles). -1 ).

[0008] The patent application with patent number CN115000387B describes a method for rapidly synthesizing TM-HEO / C composite materials using microwave heating on a carbon support. However, this method relies solely on the structure of the carbon support itself, making it impossible to actively control the pore characteristics of the oxides. This results in uneven pore size distribution in the product (requiring TEM verification) and limited rate performance (5 A·g). -1 Lower capacity 303mAh·g -1 ). Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a method for preparing three-dimensional porous high-entropy oxides, comprising the following steps:

[0010] Step 1: Dissolve multiple metal salts in deionized water in equimolar ratio to prepare a mixed metal salt solution;

[0011] Step 2: Add ammonia water dropwise to the metal salt mixture solution to adjust the pH value of the solution to the range of 4.8-8.2, and maintain the solution under magnetic stirring for 10 minutes to make the acidity and alkalinity of the solution uniform;

[0012] Step 3: Homogenize the pH-adjusted solution in a 50-60℃ water bath for 1 hour to form a stable precursor solution;

[0013] Step 4: Dry the stabilized precursor solution in an oven to obtain the precursor;

[0014] Step 5: Calcine the precursor powder in air atmosphere to form a high-entropy oxide material with a three-dimensional porous structure;

[0015] Step 6: Grind, clean and dry the high-entropy oxide material to obtain the final product.

[0016] Preferred: multiple metal salts including manganese acetate tetrahydrate, ferric nitrate nonahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and chromium nitrate nonahydrate.

[0017] Preferably, in step 2, the pH value of the solution is monitored in real time using a pH meter, and the pH value is precisely adjusted to 5.0±0.2 or 7.0±0.2.

[0018] Preferably, in step 3, the water bath temperature is 55±1℃.

[0019] Preferred option: In step 4, let it stand in an 80℃ oven for 10-12 hours.

[0020] Preferably, in step 5, the calcination conditions are to heat to 750°C in air at a heating rate of 2°C / min and hold for 2 hours.

[0021] Preferred method: In step 6, the cleaning method is to use anhydrous ethanol and deionized water to alternately centrifuge at a speed of 2000 rpm for 10 minutes each time, for a total of three cleanings; the drying conditions are to dry in a vacuum drying oven at 100°C for 12 hours.

[0022] Preferably, the total concentration of metal ions in the metal salt mixed solution is 0.1 mmol / L.

[0023] Preferred: The high-entropy oxide material has a spinel structure and a uniformly distributed three-dimensional porous sheet-like structure.

[0024] Application of a three-dimensional porous high-entropy oxide material prepared by the above method in lithium-ion battery anode materials.

[0025] The beneficial effects of this invention are as follows: the preparation method proposed in this invention can prepare high-entropy oxide materials with three-dimensional porous structures, with clear parameters for each step, consistent process, and strong repeatability.

[0026] By precisely controlling the amount of ammonia added (volume / concentration) and the target pH value, the precursor is guided to undergo directional hydrolysis and condensation, forming a self-assembled network of colloidal particles, directly constructing three-dimensional interconnected channels. This avoids the template removal step and grain growth caused by high temperatures, simplifying the process and improving structural stability.

[0027] The correlation design between ammonia water parameters and pH enables systematic control of pore morphology, specific surface area, porosity, and pore size (micro-mesoporous hierarchy), allowing for customized and optimized structures for different application scenarios (such as catalysis requiring large specific surface area and batteries requiring fast ion channels).

[0028] High porosity and interconnected pores enhance mass transfer efficiency, making it suitable for high current density batteries. The process requires no sophisticated equipment, and the raw materials are inexpensive and readily available, providing an economical pathway for the large-scale preparation of high-performance porous HEOs. Materials prepared using this method exhibit significant performance advantages in catalytic combustion and energy storage (lithium / sodium battery electrodes), driving the transition of high-entropy oxides from the laboratory to industrial applications. Attached Figure Description

[0029] Figure 1 These are the XRD patterns of HEO-pH2, HEO-pH3, HEO-pH5, HEO-pH7, and HEO-pH8 of the present invention;

[0030] Figure 2 The a1-a3, b1-b3, c1-c3, d1-d3, and e1-e3 images of HEO-pH2, HEO-pH3, HEO-pH5, HEO-pH7, and HEO-pH8 at different magnifications are SEM images of HEO-pH2, HEO-pH3, HEO-pH5, HEO-pH7, and HEO-pH8, respectively.

[0031] Figure 3 This is a rate test chart of HEO-pH2, HEO-pH3, HEO-pH5, HEO-pH7 and HEO-pH8 of the present invention;

[0032] Figure 4 This is a cyclic test diagram of HEO-pH2, HEO-pH3, HEO-pH5, HEO-pH7 and HEO-pH8 of the present invention. Detailed Implementation

[0033] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0034] Example 1

[0035] This embodiment proposes a method for preparing three-dimensional porous high-entropy oxides, including the following steps:

[0036] Step 1: Preparation of metal salt solution

[0037] Manganese acetate tetrahydrate, ferric nitrate nonahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and chromium nitrate nonahydrate were weighed in equimolar ratio and dissolved in 10 mL of deionized water. The solutions were then magnetically stirred at room temperature for 10 minutes to obtain a mixed nitrate solution with a metal ion concentration of 0.1 mmol / L and a pH of 2.

[0038] Step 2: pH gradient adjustment

[0039] Place the solution obtained in step 1 on a magnetic stirrer and adjust the pH value of the solution dropwise with ammonia water. Monitor the pH value in real time with a pH meter and adjust it to four gradient values ​​of 3.0, 5.0, 7.0 and 8.0 respectively. After each pH gradient adjustment is completed, maintain magnetic stirring for 10 minutes to make the acidity and alkalinity of the solution uniform.

[0040] Step 3: Water bath homogenization treatment

[0041] The pH gradient solutions obtained in step 2 were transferred to a constant temperature water bath and stirred continuously at 55°C for 1 hour to eliminate local ion concentration gradients in the solution, thus obtaining four groups of stable precursor solution systems with different pH values.

[0042] Step 4: Preparation of precursor powder

[0043] The precursor solution obtained in step 3 was placed in an 80°C oven and left to stand for 11 hours to obtain a brown precursor.

[0044] Step 5: High-temperature calcination treatment

[0045] The precursor obtained in step 4 was transferred to a muffle furnace and heated to 750°C in air at a heating rate of 2°C / min. The temperature was maintained for 2 hours to obtain a fluffy black polycrystalline powder.

[0046] Step 6: Product post-processing

[0047] After the calcined product was ground and refined twice, it was washed three times by alternating centrifugation with anhydrous ethanol and deionized water (2000 rpm, 10 minutes / time) to remove surface adsorbed impurities. Finally, it was dried in a vacuum drying oven at 100℃ for 12 hours to obtain the target product, which was labeled as HEO-pH2, HEO-pH3, HEO-pH5, HEO-pH7 and HEO-pH8 according to the pH of the precursor solution.

[0048] Example 2

[0049] The difference between this embodiment and Embodiment 1 is that:

[0050] In step 2: the solution obtained in step 1 is placed on a magnetic stirrer, and the pH value of the solution is adjusted drop by drop using ammonia water. The pH value is monitored in real time with a pH meter and adjusted to four gradient values ​​of 2.8, 4.8, 6.8 and 7.8 respectively.

[0051] In step 3: Stir continuously at 54℃ for 1 hour to eliminate local ion concentration gradients in the solution.

[0052] In step 4: the precursor solution obtained in step 3 is placed in an 80°C oven and left to stand for 10 hours.

[0053] Example 3

[0054] The difference between this embodiment and Embodiment 1 is that:

[0055] In step 2: the solution obtained in step 1 is placed on a magnetic stirrer, and the pH value of the solution is adjusted dropwise with ammonia water. The pH value is monitored in real time with a pH meter and adjusted to four gradient values ​​of 3.2, 5.2, 7.2 and 8.2 respectively.

[0056] In step 3: Stir continuously at 56℃ for 1 hour to eliminate local ion concentration gradients in the solution.

[0057] In step 4: the precursor solution obtained in step 3 is placed in an 80°C oven and left to stand for 12 hours.

[0058] Example 4

[0059] This embodiment performs the following tests and analyses on the sample prepared in Example 1:

[0060] Phase analysis of a series of high-entropy oxide samples was performed using X-ray diffraction. The test parameters were set as follows: scan rate 10° min⁻¹, scan range 10–70°, tube current 25 mA, and voltage 35 kV.

[0061] like Figure 1As shown, the HEO series samples prepared by solution combustion all exhibit typical spinel structure characteristics, and their diffraction peaks perfectly match those of the standard card PDF#54-0964. In the spectrum, the five main diffraction peaks are located at 18.43°, 30.31°, 35.70°, 43.38°, 53.81°, 57.39°, and 63.02°, respectively, corresponding to the (111), (220), (311), (400), (422), (511), and (440) crystal planes. No impurity peaks appeared in the entire spectrum.

[0062] The microstructure and size of the materials were observed and analyzed using scanning electron microscopy (SEM). The instrument used was an SEM3100 with an accelerating voltage of 5 kV. Before testing, the powder underwent gold sputtering for 90 seconds at a current of 80 mA.

[0063] Depend on Figure 2 It can be seen that the HEO series samples exhibit good overall dispersion uniformity. With increasing pH, the powder transforms from irregular primary particle agglomeration into a three-dimensional plate-like structure. When the solution pH is 5, the powder presents a porous plate-like structure formed by the self-assembly of primary particles. When the solution pH rises to 7, the size of the primary particles increases significantly, leading to an increase in the stacking density between particles. This causes the pores of the three-dimensional plate-like structure to be filled, ultimately resulting in the collapse and disappearance of the porous structure. When pH = 8, the enhanced surface charge repulsion of the particles leads to the reappearance of the porous structure, but the pore density is lower than that of HEO-pH5. The porous material significantly increases the specific surface area of ​​the electrode material. A larger contact area means more active sites can participate in electrochemical reactions. At the same time, the pores in the porous structure form interconnected channels, facilitating the diffusion of ions within the electrode material, and the porous structure of the material contributes to the uniform distribution of the electrolyte within the electrode.

[0064] The cycle and rate tests of coin cells were conducted using a Xinwei battery testing system (CT-4008Tn-5V50mA-164), with a test voltage range of 0.01V to 3V. A constant current was used to charge and discharge the electrodes under test, with the current density and number of cycles set, and the change in reversible capacity with the number of cycles recorded. For rate testing, discharge rates were set to 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C.

[0065] Example 5

[0066] This embodiment investigates the effect of different pH values ​​on the electrochemical performance of HEO batteries. Rate cycling performance tests were conducted on the batteries (0.1C charge at different discharge rates, e.g., ...). Figure 3As shown in the figure, the voltage range is 0.1–3V, and the current density at 0.1C is 100 mA / g. As can be seen from the figure, the specific discharge capacity of the battery decreases with increasing discharge rate, but recovers when the battery returns to 0.1C. At a discharge rate of 3C, the specific discharge capacities of HEO-pH2, HEO-pH3, HEO-pH5, HEO-pH7, and HEO-pH8 are 15.4 mA / g, 420.8 mA / g, 481.2 mA / g, 478.0 mA / g, and 252.0 mA / g, respectively. The rate performance of the battery significantly improves with increasing precursor solution pH, thanks to the effective liquid absorption and volume buffering characteristics of the three-dimensional porous structure during charge and discharge.

[0067] Figure 4 The cycling test graphs for HEO-pH2, HEO-pH3, HEO-pH5, HEO-pH7, and HEO-pH8 show a significant decrease in discharge specific capacity during the first 10 weeks, followed by a plateau between weeks 10 and 50. Overall, HEO-pH5 and HEO-pH8 exhibit better discharge specific capacity than HEO-pH7 within 50 weeks, while HEO-pH2 and pH3 show poorer performance. The capacity retention rates of HEO-pH2, HEO-pH3, HEO-pH5, HEO-pH7, and HEO-pH8 after 50 weeks are 41.0%, 37.6%, 68.1%, 67.0%, and 72.6%, respectively.

[0068] As the solution pH increases, the microstructure of the HEO powder gradually evolves from an initial irregular primary particle agglomerate (pH = 2-3) to a three-dimensional lamellar porous structure (pH = 7-8). This morphological transformation may be related to changes in the complexation state of metal ions in the precursor solution. The three-dimensional porous structure significantly improves the specific surface area and electrolyte wettability of the material, providing continuous channels for ion diffusion, thereby enabling the HEO electrode to exhibit higher specific capacity and cycle stability in rate performance testing.

[0069] Spinel-type high-entropy oxides (HEOs) are potential candidates for high-performance lithium-ion battery anode materials due to their high structural stability and multiple active sites. In this study, spinel-type HEOs with different pH values ​​(2–8) were successfully prepared via solution combustion, and the correlation between their phase composition, morphology, and electrochemical performance was systematically analyzed.

[0070] The main conclusions are as follows:

[0071] A pH gradient control combined with a low-temperature water bath homogenization process effectively suppressed the segregation of metal ions in the precursor solution. XRD confirmed that the product was a single spinel phase. SEM showed that the material formed a uniform porous sheet-like structure at pH=5, while at pH=8, although the pore density decreased, excessive particle stacking was suppressed through surface charge repulsion, forming stable open channels. HEO-pH5 and HEO-pH8 had initial capacities of 1036.8 mAh / g and 782.0 mAh / g, respectively, at 0.1C rate. After 50 cycles, the capacity retention was significantly better than the low pH sample (HEO-pH2 only 41.0%), which was attributed to the enhanced electrolyte wettability and ion diffusion efficiency of the porous structure. Furthermore, the three-dimensional porous structure synergistically improved the rate performance and cycling stability of the material by providing continuous ion transport channels and buffering volume expansion stress.

[0072] The technical effects of this invention are as follows:

[0073] No template sacrifice required: Completely eliminates the reliance on template sacrifice in existing methods (as described in patent CN 116949487 A), thereby avoiding the template removal step and reducing the risk of impurity residue.

[0074] Process simplification: The preparation process has been optimized, making operation simpler, reducing cumbersome steps (such as template treatment or high-temperature combustion), and improving efficiency and product purity.

[0075] Active control of three-dimensional porous structure: It can precisely control the generated three-dimensional porous structure, solve the problems of low specific surface area and slow ion diffusion caused by the solution combustion method in the cited patent CN112599749B, thereby improving the material performance.

[0076] pH control mechanism: The pH of the precursor solution is precisely controlled within the range of 5±0.2 to 7±0.2 (i.e., pH range 4.8–7.2) by adding ammonia dropwise, which serves as the core control parameter.

[0077] Directed pore structure design: By using pH value to regulate hydrolysis-condensation behavior (i.e., the hydrolysis and condensation reaction process of precursor molecules), the directional design of pore structure (such as pore size, distribution and connectivity) can be achieved, thereby optimizing the specific surface area and ion diffusion path of the material.

[0078] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for preparing three-dimensional porous high-entropy oxides, characterized in that, Includes the following steps: Step 1: Dissolve multiple metal salts in deionized water in equimolar ratio to prepare a mixed metal salt solution; Step 2: Add ammonia water dropwise to the metal salt mixture solution to adjust the pH value of the solution to the range of 4.8-8.2, and maintain the solution under magnetic stirring for 10 minutes to make the acidity and alkalinity of the solution uniform; Step 3: Homogenize the pH-adjusted solution in a 50-60℃ water bath for 1 hour to form a stable precursor solution; Step 4: Dry the stabilized precursor solution in an oven to obtain the precursor; Step 5: Calcine the precursor powder in air atmosphere to form a high-entropy oxide material with a three-dimensional porous structure; Step 6: Grind, clean and dry the high-entropy oxide material to obtain the final product.

2. The method for preparing a three-dimensional porous high-entropy oxide according to claim 1, characterized in that, Various metal salts include manganese acetate tetrahydrate, ferric nitrate nonahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and chromium nitrate nonahydrate.

3. The method for preparing a three-dimensional porous high-entropy oxide according to claim 1, characterized in that, In step 2, the pH value of the solution is monitored in real time using a pH meter, and the pH value is precisely adjusted to 5.0±0.2 or 7.0±0.

2.

4. The method for preparing a three-dimensional porous high-entropy oxide according to claim 1, characterized in that, In step 3, the water bath temperature is 55±1℃.

5. The method for preparing a three-dimensional porous high-entropy oxide according to claim 1, characterized in that, In step 4, let it stand in an 80℃ oven for 10-12 hours.

6. The method for preparing a three-dimensional porous high-entropy oxide according to claim 1, characterized in that, In step 5, the calcination conditions are as follows: heating to 750°C in air at a heating rate of 2°C / min and holding for 2 hours.

7. The method for preparing a three-dimensional porous high-entropy oxide according to claim 1, characterized in that, In step 6, the cleaning method is to use anhydrous ethanol and deionized water to alternately centrifuge at a speed of 2000 rpm for 10 minutes each time, for a total of three cleanings; the drying conditions are to dry in a vacuum drying oven at 100℃ for 12 hours.

8. The method for preparing a three-dimensional porous high-entropy oxide according to claim 1, characterized in that, The total concentration of metal ions in the mixed metal salt solution is 0.1 mmol / L.

9. The method for preparing a three-dimensional porous high-entropy oxide according to claim 1, characterized in that, High-entropy oxide materials have a spinel structure and a uniformly distributed three-dimensional porous sheet-like structure.

10. The application of a three-dimensional porous high-entropy oxide material prepared by the preparation method according to any one of claims 1-9 in lithium-ion battery anode materials.

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