Preparation and application of hydrophobically modified sodium electrically layered oxides

Abstract

This invention relates to the field of sodium-ion battery cathode materials technology, and discloses the preparation and application of hydrophobically modified sodium-ion battery layered oxides. The process includes preparing a layered oxide matrix by mixing sodium, iron, nickel, and manganese sources at high speed and then sintering at high temperature, followed by pulverizing and sieving to obtain the matrix; organic acid etching by dissolving an organic acid in an alcohol-based solvent to prepare an etching solution, adding it to the matrix, stirring in a water bath at 40-50°C, and filtering and washing to obtain etched layered oxides; and hydrophobic coating by dispersing the etched oxides into a suspension, mixing and stirring it with an alcohol-based solution of a low surface energy material, filtering, washing, and drying to obtain hydrophobically modified sodium-ion battery layered oxides. This invention solves the problems of insufficient hydrophobicity and low mechanical strength of existing hydrophobically modified materials by constructing micro / nano structures through organic acid etching and then coating them with low surface energy materials. It also reduces residual alkali on the material surface and improves air stability. Suitable for large-scale production, the resulting material, as a cathode material for sodium-ion batteries, can effectively improve the overall electrochemical performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode material technology, specifically to the preparation and application of a hydrophobically modified sodium-ion battery layered oxide. Background Technology

[0002] Sodium-ion batteries have become an important energy storage technology for large-scale electrochemical energy storage, low-speed electric vehicles, and backup power for communication base stations due to the abundance and wide distribution of sodium resources in the earth's crust, low production costs, and electrochemical working principle similar to that of lithium-ion batteries. Sodium-ion layered oxides are one of the most commercially promising cathode materials for sodium-ion batteries due to their high specific capacity, suitable charge and discharge voltage, and excellent compaction density.

[0003] The surface properties of sodium-ion battery layered oxide cathode materials directly affect the cycle stability, storage life, and safety of the battery. Their surfaces are prone to retaining alkaline substances and react with moisture and carbon dioxide in the air, leading to a decline in the material's electrochemical performance. To address this issue, existing technologies have developed hydrophobic modification schemes for sodium-ion battery layered oxides. These schemes involve first uniformly mixing sodium, iron, nickel, and manganese sources using physical methods such as ball milling, sand milling, or high-speed mixing, followed by solid-state sintering to prepare sodium-ion battery layered oxides. The oxides are then dispersed in a solvent, and a solution containing hydrophobic materials is added, stirred, and dried to obtain layered oxides coated with hydrophobic materials.

[0004] However, existing hydrophobic modification technologies still have two major drawbacks. First, the modified materials are not hydrophobic enough, with a contact angle with water typically less than 120°, which cannot effectively prevent moisture from contacting the material surface. Moisture in the air can still react with the material, leading to deterioration of material performance. Second, the bonding strength between the surface-coated hydrophobic layer and the oxide matrix is ​​low. The hydrophobic layer only adheres to the matrix surface through physical adsorption. During mechanical processing such as crushing, rolling, and coating in battery manufacturing, the hydrophobic layer is easily damaged and detached, rendering the hydrophobic modification ineffective. This, in turn, triggers side reactions between the electrolyte and the material surface, reducing the cycle life and stability of sodium-ion batteries.

[0005] Furthermore, existing hydrophobic modification schemes do not consider the effective treatment of residual alkali on the material surface. The presence of residual alkali not only exacerbates side reactions between the material and air and electrolyte, but also leads to abnormal viscosity of the battery slurry, affecting the quality of electrode preparation. To address the problems of the existing technology, there is an urgent need to develop a hydrophobic modification technology for sodium-ion layered oxides that combines high hydrophobicity and high bonding strength, while simultaneously achieving effective removal of residual alkali on the surface and improving the overall performance of the material. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing and applying hydrophobically modified sodium-ion layered oxides. This method solves the technical problems of insufficient hydrophobicity and low mechanical strength of the hydrophobic layer after hydrophobic modification, which are easily damaged. Simultaneously, it effectively reduces residual alkali on the material surface, improves the air stability and surface chemical properties of the sodium-ion layered oxide, and the resulting hydrophobically modified material, as a cathode material for sodium-ion batteries, can effectively improve the overall electrochemical performance of the battery. Furthermore, the present invention aims to provide a simple, mild, and readily available hydrophobically modified preparation method suitable for large-scale industrial production.

[0007] To achieve the above-mentioned objective, this invention provides a method for preparing hydrophobically modified sodium-electric layered oxides, the specific preparation steps of which are as follows: S1. Weigh sodium source, iron source, nickel source and manganese source according to stoichiometric ratio, put each raw material into a high-speed mixer and mix at high speed. After mixing, put the powder into a box furnace for high-temperature solid-state sintering. After sintering, cool to room temperature with the furnace, mechanically crush the sintered product and sieve it to obtain a layered oxide matrix. S2. Select an organic acid as an etchant, dissolve the organic acid in an alcohol solvent to prepare a homogeneous etching solution, add the layered oxide matrix obtained in step S1 to the etching solution, heat and stir in a water bath at 40-50℃ for 2-4 hours, after etching is completed, perform solid-liquid separation on the mixed system, and wash the solid product multiple times with an alcohol solvent to remove the residual etchant on the surface, and obtain the etched layered oxide. S3. The etched layered oxide obtained in step S2 is dispersed in an alcohol-based solvent and stirred to form a uniform suspension. At the same time, a low surface energy material is dispersed in the alcohol-based solvent to form a low surface energy solution. The low surface energy solution is slowly added to the suspension and stirred for 0.5-2 hours to allow the low surface energy material to fully adhere to the surface of the etched oxide. Then, solid-liquid separation is performed, and the solid product is washed multiple times with an alcohol-based solvent. Finally, the washed product is dried to obtain a hydrophobically modified sodium-electric layered oxide.

[0008] Furthermore, the organic acid in step S2 is one of citric acid, malic acid, or tartaric acid, and the mass-volume concentration of the organic acid in the etching solution is 0.2-0.5 g / ml.

[0009] Furthermore, the alcohol solvent in steps S1, S2, and S3 is ethanol, specifically anhydrous ethanol or industrial-grade anhydrous ethanol.

[0010] Furthermore, the low surface energy substance in step S3 is a silane-based low surface energy reagent, preferably octadecyltrimethoxysilane.

[0011] Furthermore, in step S1, the sodium source is sodium carbonate, and the iron, nickel, and manganese sources are added in the form of nickel-iron-manganese hydroxide precursors. The molar ratio of the sodium source to the transition metal source is (1.00~1.05):1.

[0012] Furthermore, the high-speed mixing parameters in step S1 are: rotation speed 1000-2000 r / min, mixing time 10-30 min; the high-temperature sintering parameters are: heating rate 2-5℃ / min, sintering temperature 900-980℃, sintering time 12-16 h, and sintering atmosphere is air.

[0013] Furthermore, in step S1, the mechanically pulverized product is passed through a 200-300 mesh standard sieve; in steps S2 and S3, the solid-liquid separation method is centrifugation, with a centrifugation speed of 3000-5000 r / min and a centrifugation time of 5-10 min; the product is washed three times with an alcohol solvent.

[0014] Furthermore, the drying in step S3 is vacuum drying, with a drying temperature of 60-80℃ and a drying time of 8-12 hours, until the solid product reaches a constant weight.

[0015] The present invention also provides the application of the hydrophobically modified sodium-ion layered oxide obtained by the above preparation method in sodium-ion batteries. The hydrophobically modified sodium-ion layered oxide is used as the positive electrode active material of sodium-ion secondary batteries. It can be mixed with conductive agents and binders to prepare positive electrode slurry, and then coated, dried, rolled and cut to obtain sodium-ion battery positive electrode sheets.

[0016] This invention provides a method for preparing and applying hydrophobically modified sodium-electric layered oxides, which has the following beneficial effects: By chemically etching sodium-ion layered oxides with organic acids, a uniform micro-nano composite structure is constructed on the material surface. The grooves in this micro-nano structure can effectively trap air and form a solid-liquid-gas three-phase composite contact interface on the material surface. This significantly reduces the contact area between water molecules and the material surface, effectively blocks water from penetrating into the material interior, and significantly improves the hydrophobicity of the material, solving the problem of insufficient hydrophobicity in existing technologies. This invention coats the surface of a micro / nano structure with a low surface energy material. The low surface energy material can weaken the van der Waals forces between water molecules and the surface of a solid material, making it difficult for water molecules to adhere, spread and penetrate the material surface. This forms a synergistic hydrophobic effect with the micro / nano structure, further enhancing the superhydrophobic properties of the material. At the same time, it effectively reduces the degree of contact reaction between the material surface and moisture and carbon dioxide in the air, improving the air stability of the material. The micro-nano structure on the oxide surface can increase the contact area and bonding sites with low surface energy materials, allowing the low surface energy materials to be embedded in the micro-nano grooves. This effectively enhances the bonding force between the layered oxide matrix and the low surface energy hydrophobic layer, allowing the hydrophobic layer to form a stable physical-chemical bond with the matrix. This prevents the hydrophobic layer from being damaged or falling off during subsequent mechanical processing such as crushing, rolling, and coating, ensuring the durability of the hydrophobic modification effect. During the organic acid etching process of this invention, the organic acid can undergo an acid-base neutralization reaction with the residual alkali on the surface of the sodium-ion layered oxide, thereby effectively reducing the residual alkali on the material surface, improving the surface chemical properties of the sodium-ion layered oxide, reducing the decomposition effect of residual alkali on the battery electrolyte, reducing the probability of side reactions between the electrolyte and the material surface, and thus improving the cycle stability and safety of sodium-ion batteries. The preparation process of this invention is simple, and the organic acids, alcohol solvents, and low surface energy substances used are all commonly used chemical raw materials that are readily available and inexpensive. The reaction conditions are mild and easy to control, requiring no complex special equipment. Each process step is a mature industrial operation, suitable for large-scale industrial production, and has good industrial application prospects. The resulting hydrophobically modified sodium-ion battery layered oxide, as a cathode material, has the characteristics of high hydrophobicity, high air stability, and low surface residual alkali, which can effectively improve the cycle life, storage life, and safety of the battery, while not adversely affecting the electrochemical performance of the material itself, and can meet the needs of large-scale preparation of sodium-ion batteries. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the process of this invention; Figure 2 This is a charge / discharge curve. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] Example 1 This embodiment provides a method for preparing hydrophobically modified sodium-electric layered oxides, the specific steps of which are as follows (e.g. Figure 1 (as shown) S1. Weigh sodium carbonate and nickel-iron-manganese hydroxide precursor (Ni:Fe:Mn molar ratio 0.33:0.33:0.33) according to the stoichiometric ratio Na:Ni:Fe:Mn=1.02:0.33:0.33:0.33. Place the above raw materials in a high-speed mixer and mix at 1500 r / min for 20 min. Place the resulting powder in a box furnace and heat it to 950℃ at a heating rate of 3℃ / min. Sinter it in air atmosphere for 14 h. After sintering, cool it to room temperature with the furnace. Mechanically pulverize the sintered powder and pass it through a 200-mesh standard sieve to obtain a layered oxide matrix, denoted as NFM. S2. Dissolve 30g of citric acid in 100ml of anhydrous ethanol to prepare an etching solution with a mass-volume concentration of 0.3g / ml. Add 20g of NFM to the etching solution and stir for 2h under constant temperature conditions in a water bath at 40℃. After etching, centrifuge at 4000r / min for 8min to separate the solid and liquid phases. Wash the solid product after centrifugation with anhydrous ethanol 3 times to remove residual citric acid on the surface and obtain the etched layered oxide, denoted as C-NFM. S3. Disperse 150g of C-NFM in anhydrous ethanol and stir to form a uniform suspension. Simultaneously, disperse 10g of octadecyltrimethoxysilane in anhydrous ethanol to form a low surface energy solution. Slowly add the low surface energy solution to the suspension and continue stirring for 1 hour to allow octadecyltrimethoxysilane to fully adhere to the C-NFM surface. Then, centrifuge at 4000r / min for 8 minutes to separate the solid and liquid phases. Wash the solid product three times with anhydrous ethanol. Finally, place the product in a vacuum drying oven and vacuum dry at 70℃ for 10 hours to constant weight to obtain a hydrophobically modified sodium-electric layered oxide, denoted as C-NFM-C.

[0020] Comparative Example 1 This comparative example provides a method for hydrophobic modification of sodium-electric layered oxides without organic acid etching. The specific steps are as follows: S1. Weigh sodium carbonate and nickel-iron-manganese hydroxide precursor (Ni:Fe:Mn molar ratio 0.33:0.33:0.33) according to the stoichiometric ratio Na:Ni:Fe:Mn=1.02:0.33:0.33. Place the above raw materials in a high-speed mixer and mix at 1500 r / min for 20 min. Place the resulting powder in a box furnace and heat it to 950℃ at a heating rate of 3℃ / min. Sinter it in air atmosphere for 14 h. After sintering, cool it to room temperature with the furnace. Mechanically pulverize the sintered powder and pass it through a 200-mesh standard sieve to obtain layered oxide matrix NFM. S2. Disperse 150g NFM in anhydrous ethanol to form a suspension. Disperse 10g octadecyltrimethoxysilane in anhydrous ethanol to form a low surface energy solution. Add the low surface energy solution to the suspension. Stir for 1 hour and centrifuge at 4000 r / min for 8 minutes. Wash the filtered product three times with anhydrous ethanol. Dry under vacuum at 70°C for 10 hours to constant weight to obtain a hydrophobically modified layered oxide, denoted as NFM-C.

[0021] Comparative Example 2 This comparative example provides a method for preparing sodium-electric layered oxides without etching and hydrophobic modification. The specific steps are as follows: S1. Weigh sodium carbonate and nickel-iron-manganese hydroxide precursor (Ni:Fe:Mn molar ratio 0.33:0.33:0.33) according to the stoichiometric ratio Na:Ni:Fe:Mn=1.02:0.33:0.33. Place the above raw materials in a high-speed mixer and mix at 1500 r / min for 20 min. Place the resulting powder in a box furnace and heat it to 950℃ at a heating rate of 3℃ / min. Sinter it in air atmosphere for 14 h. After sintering, cool it to room temperature with the furnace. Mechanically pulverize the sintered powder and pass it through a 200-mesh standard sieve to obtain a layered oxide matrix, denoted as NFM.

[0022] Comparison of Implementation Results The C-NFM-C prepared in Example 1 was used to construct a micro / nano structure through organic acid etching and then coated with a low surface energy material. Its surface hydrophobicity (as shown in Table 1) was significantly improved compared to the NFM-C prepared in Comparative Example 1. Furthermore, the C-NFM-C had a lower surface residual alkali content and better air stability (as shown in Table 2). The three materials were used as positive electrode active materials for sodium-ion batteries, respectively. They were mixed with conductive agents and binders to prepare positive electrode sheets and assembled into coin cells. The battery assembled with C-NFM-C showed significantly better cycle performance than the batteries assembled with NFM-C and NFM (as shown in Table 3), proving that the hydrophobic modification process of the present invention can effectively improve the application performance of materials.

[0023] Table 1 Contact Angle Measurement Record ; Table 2 Record of surface residual alkali changes ; Table 3 Cyclic Capacity Retention Rate ; The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a hydrophobically modified sodium-electric layered oxide, characterized in that, Includes the following steps: S1. Weigh sodium source, iron source, nickel source and manganese source according to stoichiometric ratio, mix the raw materials at high speed and then perform high-temperature solid-state sintering. After sintering, cool to room temperature, mechanically crush the sintered product and sieve it to obtain a layered oxide matrix. S2. Select an organic acid as an etching agent, dissolve the organic acid in an alcohol solvent to prepare an etching solution, add the layered oxide matrix obtained in step S1 to the etching solution, heat and stir in a water bath at 40-50℃ for 2-4 hours, after which solid and liquid are separated, and the solid product is washed multiple times with an alcohol solvent to obtain the etched layered oxide. S3. Disperse the etched layered oxide obtained in step S2 in an alcohol-based solvent to form a uniform suspension. At the same time, disperse the low surface energy material in the alcohol-based solvent to form a low surface energy solution. Add the low surface energy solution to the above suspension and stir for 0.5-2 hours. Then, separate the solid and liquid phases. Wash the solid product multiple times with an alcohol-based solvent. Finally, dry the washed product to obtain the hydrophobically modified sodium-electric layered oxide.

2. The method for preparing the hydrophobically modified sodium-electric layered oxide according to claim 1, characterized in that, The organic acid in step S2 is one of citric acid, malic acid or tartaric acid, and the mass-volume concentration of the organic acid in the etching solution is 0.2-0.5 g / ml.

3. The method for preparing the hydrophobically modified sodium-electric layered oxide according to claim 1, characterized in that, The alcohol solvent in steps S1, S2, and S3 is anhydrous ethanol, and the low surface energy substance in step S3 is one of hexadecyltrimethoxysilane, tridecafluorooctyltriethoxysilane, octyltriethoxysilane, and isooctyltriethoxysilane.

4. The method for preparing the hydrophobically modified sodium-electric layered oxide according to claim 1, characterized in that, In step S1, the sodium source is sodium carbonate, and the iron, nickel, and manganese sources are added in the form of nickel-iron-manganese hydroxide precursors. The molar ratio of sodium source to transition metal source is (1.00~1.05):

1.

5. The application of a hydrophobically modified sodium-ion layered oxide obtained by the preparation method according to any one of claims 1 to 4 in a sodium-ion battery, characterized in that, The hydrophobically modified sodium-ion layered oxide is used as the positive electrode active material of sodium-ion secondary batteries. It is mixed with conductive agents and binders to prepare a positive electrode slurry, which is then coated, dried, rolled, and cut to obtain a sodium-ion battery positive electrode sheet.

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