Positive electrode material, method for producing the same, and sodium ion battery

Abstract

To provide a positive electrode material that can effectively improve storage stability and electrochemical performance in air.SOLUTION: A positive electrode material includes a Prussian blue substrate, and a first coating layer and a second coating layer sequentially coated on a surface of the Prussian blue substrate. A material forming the first coating layer includes a polymer of tannic acid. A material forming the second coating layer includes at least one of hexadecylamine, octadecylamine, octadecylphosphonic acid, N-phenyl-trifluoromethanesulfonimide, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and 1H,1H,2H,2H-perfluorodecanethiol. The positive electrode material of the present invention basically does not affect electrochemical performance, and can effectively solve the problem that a Prussian blue positive electrode material easily absorbs moisture, and thereby can effectively improve storage stability and electrochemical performance in air of the positive electrode material.SELECTED DRAWING: None

Description

Technical Field

[0001] This application claims the priority of a Chinese patent application with the application number 202311041962.7 filed on August 17, 2023, and incorporates all of its contents herein by reference.

[0002] Technical Field

[0003] The present invention relates to the technical field of sodium-ion batteries, and specifically, to a positive electrode material, a method for manufacturing the same, and a sodium-ion battery.

Background Art

[0004] Prussian blue (PB) is an important positive electrode material for sodium-ion batteries, and generally, Na x M a M’ b (CN)6·zH2O can be used, where 0 < x < 2, 0 < a < 1, 0 < b < 1, and z > 0, and M and M’ represent transition metals. The Prussian blue positive electrode material has advantages such as a high theoretical capacity, a large gap, adjustable chemical composition, and good structural stability, shows very excellent electrochemical performance, and at the same time, the material has advantages such as being inexpensive, non-toxic and harmless, easy to manufacture, and having a low energy consumption, and is a positive electrode material expected to be commercially applied in sodium-ion battery research.

[0005] In order to use Prussian blue as the cathode material of a sodium-ion battery, there are still problems to be solved. Since Prussian blue is usually manufactured by a simple chemical precipitation method, the material structure has pore defects and crystal water, where the crystal water is composed of adsorbed water, interstitial water and coordinated water. The crystal water in the structure may have a significant adverse impact on the electrode material and electrolyte, such as affecting the movement of sodium ions, causing side reactions with the electrolyte, or generating gases that affect the safety of the battery. Most of the adsorbed water and interstitial water in the material can be removed by high-temperature heat treatment. However, dehydrated Prussian blue has strong hygroscopicity because it can rapidly absorb water when exposed to air. In the manufacturing process of sodium-ion batteries, Prussian blue must go through processes such as pulping, coating, rolling, slicing, winding / layering, liquid injection, formation, and packaging. In these processes, most of the coating, rolling, slicing, and winding / layering are exposed to an air environment. Due to the hygroscopic properties of Prussian blue, the processing performance of the electrode sheet deteriorates, and the adsorbed moisture has a profound impact on its sodium storage performance and battery safety.

[0006] In view of this, the present invention is particularly proposed.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The first object of the present invention is to provide a cathode material that can suppress the hygroscopicity of the material on the basis of not affecting the electrochemical performance of Prussian blue, thereby effectively improving the storage stability and electrochemical performance of the cathode material in air.

[0008] The second object of the present invention is to provide a manufacturing method for the above-mentioned cathode material, and the manufacturing method has simple steps and is suitable for large-scale industrial production.

[0009] The third object of the present invention is to provide a sodium-ion battery including the above-mentioned cathode material and having excellent electrochemical performance.

Means for Solving the Problem

[0010] In order to achieve the above object of the present invention, the following technical solutions are particularly used. The present invention provides a positive electrode material including a Prussian blue matrix and a first coating layer and a second coating layer sequentially coated on the surface of the Prussian blue matrix. The material for forming the first coating layer contains a polymer of tannic acid. The material for forming the second coating layer contains at least one of hexadecylamine, octadecylamine, octadecylphosphonic acid, N-phenyltrifluoromethanesulfonimide, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and 1H,1H,2H,2H-perfluorodecane thiol.

[0011] The present invention further provides a method for manufacturing the above positive electrode material, and the manufacturing method includes: mixing tannic acid, formaldehyde, ammonium ions, a first solvent, and water to obtain a precursor solution containing tannic acid; performing a first reaction on a Prussian blue matrix and the precursor solution containing tannic acid to obtain PB@TA; performing a second reaction on the PB@TA, the material for forming the second coating layer, and a second solvent to obtain the positive electrode material. The present invention further provides a sodium ion battery including the above positive electrode material.

Effects of the Invention

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows. 1. The positive electrode material provided by the present invention can effectively solve the problem that the Prussian blue positive electrode material is prone to moisture absorption on the basis of not affecting the electrochemical performance by double coating the Prussian blue matrix, thereby effectively improving the storage stability and electrochemical performance of the positive electrode material in the air. 2. The manufacturing method of the positive electrode material provided by the present invention can uniformly coat two coating layers on the surface of the Prussian blue matrix, so it can effectively suppress the hygroscopicity of the material and the steps are simple. 3. Since the positive electrode material of the present invention is used in a sodium ion battery, based on ensuring that the sodium ion battery has excellent cycle performance and rate performance, the storage performance under high humidity environment can be improved.

[0013] Brief Description of the Accompanying Drawings To more clearly explain the specific embodiments of the present invention or the technical solutions of the prior art, the accompanying drawings that need to be used in the following descriptions of specific embodiments or the prior art will be briefly described. Of course, the accompanying drawings described below are some embodiments of the present invention, and those skilled in the art can conceive of other accompanying drawings based on these accompanying drawings without creative effort.

Brief Description of the Drawings

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Modes for Carrying Out the Invention

[0015] Hereinafter, in conjunction with the accompanying drawings and specific embodiments, the technical solution means of the present invention will be clearly and completely described. However, those skilled in the art will understand that the embodiments described below are only part of the embodiments of the present invention, not all embodiments, and are only used for explaining the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention. When specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. When the manufacturer is not specified for the reagents or equipment used, they are all conventional products that can be purchased on the market.

[0016] In a first aspect, some embodiments of the present invention provide a positive electrode material including a Prussian blue matrix and a first coating layer and a second coating layer sequentially coated on the surface of the Prussian blue matrix. The material forming the first coating layer includes a polymer of tannic acid. The material forming the second coating layer includes at least one of hexadecylamine, octadecylamine, octadecylphosphonic acid, N-phenyltrifluoromethanesulfonimide, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and 1H,1H,2H,2H-perfluorodecane thiol.

[0017] In the positive electrode material of the present invention, a polymer of tannic acid uniformly and completely covers the surface of the Prussian blue matrix to form a first coating layer, that is, a tannic acid polymer layer, and a second coating layer is coated on the surface of the first coating layer and connected to the first coating layer by a chemical bond.

[0018] In the positive electrode material of the present invention, by doubly coating the surface of the Prussian blue matrix, the surface of the Prussian blue matrix is changed from hydrophilic to hydrophobic. According to research, the positive electrode material provided by the present invention has little weight loss under the conditions of 150-250 °C after being left for 7 days under the conditions of normal temperature, normal pressure, and high humidity. Therefore, the positive electrode material provided by the present invention can well suppress hygroscopicity under the environment of normal temperature, normal pressure, and high humidity. Based on the fact that it does not affect the electrochemical performance, the problem that the Prussian blue positive electrode material is prone to moisture absorption can be effectively solved. Thereby, it can be seen that the positive electrode material can be well stored in the air and can have excellent electrochemical performance.

[0019] In the positive electrode material of the present invention, the Prussian blue matrix is used as an active substance, the first coating layer provides a bonding group for the second coating layer, the second coating layer forms a hydrophobic coating layer, and through the mutual cooperation of the three, the Prussian blue-based positive electrode material has excellent electrochemical performance and at the same time has good environmental storage performance.

[0020] In a preferred embodiment, the chemical formula of the Prussian blue matrix is Na x M a M’ b (CN)6·zH2O, where M and M’ are each independently selected from at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < x < 2, 0 < a < 1, 0 < b < 1, and z > 0. M and M’ may be the same or different.

[0021] In a preferred embodiment, the Prussian blue matrix is Na x Fe a [Fe b (CN)6]·zH2O, Na x Mn a [Fe b(CN)6]·zH2O, Na x Ni a [Fe b (CN)6]·zH2O and Na x Co a [Fe b contains at least one of (CN)6]·zH2O.

[0022] In a preferred embodiment, the particle size of the positive electrode material is 200 - 300 nm, typically but not limited to, for example, the particle size of the positive electrode material is 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm or a range value consisting of any two of these values.

[0023] In a preferred embodiment, the thickness of the first coating layer is 3 - 4 nm, typically but not limited to, for example, the thickness of the first coating layer may be 3 nm, 3.5 nm, 4 nm or a range value consisting of any two of these values.

[0024] In a preferred embodiment, the thickness of the second coating layer is 1 - 2 nm, typically but not limited to, for example, the thickness of the second coating layer may be 1 nm, 1.5 nm, 2 nm or a range value consisting of any two of these values.

[0025] In the positive electrode material of the present invention, if the thickness of the first coating layer is too high, it will affect the sodium ion interfacial transport, and if it is too low, a complete coating layer cannot be formed. If the thickness of the second coating layer is too high, it will affect the sodium ion interfacial transport, and if it is too low, it does not have good hydrophobicity.

[0026] In a second aspect, some embodiments of the present invention further provide a method for manufacturing the positive electrode material, and the manufacturing method includes: mixing tannic acid, formaldehyde, ammonium ions, a first solvent, and water to obtain a precursor solution containing tannic acid; reacting Prussian blue matrix (PB) with the precursor solution containing tannic acid in a first reaction to obtain PB@TA; A step of obtaining a positive electrode material by subjecting PB@TA, a material for forming a second coating layer, and a second solvent to a second reaction is included.

[0027] In the present invention, a tannic acid precursor solution and a Prussian blue matrix are subjected to a first reaction, and tannic acid, formaldehyde, and ammonium ions undergo a Mannich reaction and condense to form a tannic acid polymer, and a uniform layer of tannic acid polymer is formed on the surface of the Prussian blue matrix to obtain a Prussian blue matrix coated with tannic acid polymer (PB@TA). Then, it is coated using a hydrophobic material. For example, octadecylamine undergoes a Michael addition reaction or a Schiff base reaction with a hydroxyl group or a carbonyl group in the tannic acid polymer, and a second coating layer is formed on the surface of PB@TA, so that a positive electrode material (PB@TA@ODA) having a double coating structure can be obtained.

[0028] In a preferred embodiment, the temperatures of the first reaction and the second reaction are each independently 25 to 80 °C, and the times of the first reaction and the second reaction are each independently 1 to 72 h. Typically but not limitedly, for example, the temperatures of the first reaction and the second reaction may each independently be 25 °C, 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, or a range value composed of any two of these values, and the times of the first reaction and the second reaction may each independently be 1 h, 10 h, 20 h, 30 h, 40 h, 50 h, 60 h, 70 h, or a range value composed of any two of these values.

[0029] In a preferred embodiment, after the first reaction, it further includes a first washing and a first drying, and after the second reaction, it further includes a second washing and a second drying. Preferably, the drying temperature is 50 to 200 °C.

[0030] In a preferred embodiment, the molar ratio of tannic acid to formaldehyde is (0.022 to 0.024):1, preferably 0.023:1.

[0031] In a preferred embodiment, the substance providing ammonium ions includes aqueous ammonia.

[0032] In a preferred embodiment, the concentration of aqueous ammonia is 20 - 30 wt%, and the usage ratio of aqueous ammonia to tannic acid is 1 mL: 0.1 - 1 mmol. Typically but not limitedly, for example, the usage ratio of aqueous ammonia to tannic acid is 1 mL: 0.1 mmol, 1 mL: 0.3 mmol, 1 mL: 0.5 mmol, 1 mL: 0.7 mmol, 1 mL: 1 mmol, or a range value composed of any two of these values.

[0033] In a preferred embodiment, the method for manufacturing the precursor solution containing tannic acid includes mixing an aqueous tannic acid solution, an aqueous formaldehyde solution, aqueous ammonia, a first solvent, and water to obtain a precursor solution containing tannic acid. Preferably, the concentration of the aqueous tannic acid solution is 0.01 - 0.02 mol / L, the concentration of the aqueous formaldehyde solution is 2 - 5 wt%, the concentration of aqueous ammonia is 20 - 30 wt%. More preferably, the volume ratio of aqueous ammonia to the aqueous tannic acid solution is 1: (15 - 25), preferably 1:20.

[0034] In a preferred embodiment, the pH value of the first reaction system is 6 - 7. Tannic acid, formaldehyde, and ammonium undergo a Mannich reaction and condense to form a polymer of tannic acid. The above-mentioned amount of aqueous ammonia can provide sufficient NH4+ to accelerate the reaction rate.

[0035] In a preferred embodiment, the mass ratio of the Prussian blue matrix to tannic acid is 1:(0.05 - 2). This is typical but not limiting. For example, the mass ratio of the Prussian blue matrix to tannic acid can be 1:0.05, 1:0.08, 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2 or a range value consisting of any two of these values. Preferably, the mass ratio of the Prussian blue matrix to tannic acid is 1:(0.15 - 0.2).

[0036] In a preferred embodiment, the mass ratio of PB@TA to the material forming the second coating layer is 1:(0.1 - 5). This is typical but not limiting. For example, the mass ratio of PB@TA to the material forming the second coating layer can be 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or a range value consisting of any two of these values. Preferably, the mass ratio of PB@TA to the material of the second coating layer is 1:(0.8 - 1.2). In a preferred embodiment, the first solvent contains ethanol.

[0037] In a preferred embodiment, the mass ratio of tannic acid to the first solvent is 1:(45 - 50).

[0038] In a preferred embodiment, the volume ratio of the first solvent to water is (0.01 - 1):1.

[0039] In a preferred embodiment, the second solvent contains at least one of methanol, ethanol, ethylene glycol, acetone, and tetrahydrofuran.

[0040] In a preferred embodiment, the mass ratio of the material of the second coating layer to the second solvent is 1:(50 - 55).

[0041] In a preferred embodiment, the method for manufacturing the Prussian blue matrix includes a liquid phase method or a solid phase method.

[0042] In a preferred embodiment, the method for manufacturing a Prussian blue matrix includes reacting an aqueous solution of Na4Fe(CN)6 with an aqueous solution of a soluble metal salt, and then obtaining a Prussian blue matrix, wherein the soluble metal salt includes sodium citrate and at least one of Ni salt, Cu salt, Fe salt, Mn salt, Co salt and Zn salt.

[0043] In a preferred embodiment, the method for manufacturing a Prussian blue matrix includes ball-milling Na4Fe(CN)6 and a metal salt to obtain a Prussian blue matrix, wherein the metal salt includes at least one of Ni salt, Cu salt, Fe salt, Mn salt, Co salt and Zn salt.

[0044] In a third aspect, some embodiments of the present invention further provide a sodium-ion battery including the above positive electrode material.

[0045] By using the positive electrode material of the present invention in a sodium-ion battery, it is based on ensuring that the sodium-ion battery has excellent cycle performance and rate performance, and the storage performance of the sodium-ion battery at normal temperature, normal pressure and high humidity can be improved. Hereinafter, the embodiments of the present invention will be described in detail together with examples. However, those skilled in the art will understand that the following examples are only used to explain the present invention and should not be regarded as limiting the scope of the present invention. When specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. When the manufacturer is not specified for the reagents or equipment used, they are all conventional products that can be purchased on the market.

Examples

[0046] Example 1 The method for manufacturing the positive electrode material provided in this example is 4 mmol of Na4Fe(CN)6·10H2O was dissolved in 200 mL of deionized water to form solution A, 6 mmol of FeSO4·7H2O and 15 g of sodium citrate were dissolved in 200 mL of deionized water to form solution B, solution A was added to solution B, and then after standing at room temperature (25 °C) for 6 h, solid-liquid separation was carried out to obtain a filter cake. The filter cake was centrifugally washed 3 times each with deionized water and absolute ethanol, and then dried in a blowing drying box at 80 °C for 12 h to obtain Prussian blue matrix (PB) Na 1.54 Fe[Fe(CN)6]·0.96H2O in step S1, 2 mL of tannic acid aqueous solution with a concentration of 0.015 M, 1 mL of formaldehyde aqueous solution (3.7 wt%), 0.1 mL of ammonia water (concentration 25 wt%) and 3 mL of ethanol were added to 13 mL of deionized water and mixed well to obtain a tannic acid precursor solution. 0.3 g of Na1.54Fe[Fe(CN)6]·0.96H2O was added to the tannic acid precursor solution, and stirring was continued at room temperature (25 °C) for 24 h. After filtration, it was dried under vacuum at 80 °C to obtain PB@TA in step S2, 0.3 g of octadecylamine was added to 20 mL of ethanol and dissolved well to obtain an octadecylamine precursor solution. 0.3 g of PB@TA was added to the octadecylamine precursor solution, and stirring was continued at room temperature (25 °C) for 24 h. After filtration, it was dried under vacuum at 80 °C to obtain a positive electrode material (PB@TA@ODA) in step S3, including.

[0047] Example 2 The manufacturing method of the positive electrode material provided by this example is Under an inert atmosphere, 5 mmol of MnCl2·4H2O and 5 mmol of Na4Fe(CN)6·10H2O were added to an agate ball mill bottle, the ball-to-material ratio was 1:20, and after ball milling at a speed of 300 r / min for 12 h, a mixture was obtained. The mixture was first centrifugally washed 3 times with absolute ethanol, then centrifugally washed 3 times with deionized water, and then dried in a vacuum oven at 80 °C for 12 h to obtain Prussian blue matrix (PB) Na 1.63 Mn[Fe(CN)6]·1.41H2O in step S1, 2 mL of tannic acid aqueous solution with a concentration of 0.015 M, 1 mL of formaldehyde aqueous solution (3.7 wt%), 0.1 mL of ammonia water (concentration 25 wt%), and 3 mL of ethanol were added to 13 mL of deionized water, and mixed well to obtain a tannic acid precursor solution. 0.15 g of Na 1.63 Mn[Fe(CN)6]·1.41H2O was added to the tannic acid precursor solution, and stirring was continued at 40 °C for 24 h. After filtration, it was dried under vacuum at 80 °C to obtain PB@TA in step S2, 0.3 g of octadecylamine was added to 20 mL of ethanol and dissolved well to obtain an octadecylamine precursor solution. 0.15 g of PB@TA was added to the octadecylamine precursor solution, and stirring was continued at 60 °C for 24 h. After filtration, it was dried under vacuum at 80 °C to obtain a positive electrode material (PB@TA@ODA) in step S3, and it includes

[0048] Example 3 The method for manufacturing the positive electrode material provided by this example refers to Example 1. In step S2, the only difference is that the mass of Na 1.54 Fe[Fe(CN)6]·0.96H2O is 1 g.

[0049] Example 4 The method for manufacturing the positive electrode material provided by this example refers to Example 1. In step S2, the only difference is that the mass of Na 1.54 Fe[Fe(CN)6]·0.96H2O is 0.025 g.

[0050] Example 5 The method for manufacturing the positive electrode material provided by this example refers to Example 1. In step S3, the only difference is that the mass of PB@TA is 3 g.

[0051] Example 6 The method for manufacturing the positive electrode material provided by this example refers to Example 1. In step S3, the only difference is that the mass of PB@TA is 0.06 g.

[0052] Example 7 The method for manufacturing the positive electrode material provided by this example refers to Example 1. In step S2, the only difference is that the mass of Na1.54 The mass of Fe[Fe(CN)6]·0.96H2O is 0.1 g, and in step S3, only the point that the mass of PB@TA is 0.1 g is different.

[0053] Example 8 The method for manufacturing the positive electrode material provided by this example refers to Example 1, and in step S3, only the point that octadecylamine is replaced with octadecylphosphonic acid is different.

[0054] Example 9 The method for manufacturing the positive electrode material provided by this example refers to Example 1, and in step S3, only the point that octadecylamine is replaced with 1H,1H,2H,2H-perfluorodecanethiol is different.

[0055] Example 10 The method for manufacturing the positive electrode material provided by this example refers to Example 1, and in step S3, only the point that octadecylamine is replaced with N-phenyltrifluoromethanesulfonimide is different.

[0056] Comparative Example 1 The method for manufacturing the positive electrode material provided by this comparative example refers to Example 1, and in step S2, only the point that an aqueous formaldehyde solution and aqueous ammonia are not added is different.

[0057] Comparative Example 2 The method for manufacturing the positive electrode material provided by this comparative example refers to Example 1, steps S1 and S2 are removed, and step S3 is directly performed on the Prussian blue matrix (PB) Na in Example 1 1.54 to obtain the sample PB@ODA, only this point is different.

[0058] Test Example 1 XRD tests were performed on PB and PB@TA@ODA in Example 1, and the results are as shown in Figure 1.

[0059] As can be seen from Figure 1, the structure of PB@TA@ODA has not changed significantly compared to the structure of PB and still has a pure cubic Prussian blue structure.

[0060] The PB@TA@ODA in Example 1 was tested with a scanning electron microscope, and the results are as shown in Figure 2.

[0061] As can be seen from Figure 2, PB@TA@ODA still maintains a cubic shape.

[0062] Thermogravimetric tests were performed on PB, PB-7D, PB@TA@ODA, and PB@TA@ODA-7D in Example 1, and the results are as shown in Figures 3 and 4. Here, PB-7D indicates that PB was left standing at room temperature, normal pressure, and 80% humidity for 7 days, and PB@TA@ODA-7D indicates that PB was left standing at room temperature, normal pressure, and 80% humidity for 7 days.

[0063] As can be seen from Figures 3 and 4, the sample PB-7D shows significant weight loss at 150 °C and 250 °C, and the adsorbed water and interstitial water in the material have increased significantly. On the other hand, the TG curve of PB@TA@ODA-7D shows little change compared to PB@TA@ODA, indicating excellent moisture absorption inhibition ability.

[0064] Test Example 2 The method for manufacturing the positive electrode plate is Weighing a positive electrode material, a conductive agent (Ketjen Black and Super P with a mass ratio of 1:1) and polyvinylidene fluoride (PVDF) at a mass ratio of 7:2:1 respectively, adding a certain amount of N-methylpyrrolidone (NMP) as a solvent, and grinding them to form a uniform slurry; Uniformly coating the above slurry on an aluminum foil, and then baking it at 70 °C for 24 h; Finally, cutting it into small discs with a diameter of 8 mm to obtain a positive electrode plate with a loading amount of 1.6 - 2.4 mg / cm2.

[0065] The manufacturing method of the sodium-ion battery is as follows: Placing the above positive electrode tab into a 2032-type battery shell, using a sodium piece as the negative electrode, glass fiber as the separator, and foamed nickel as the support piece; Dissolving 1 mol / L of NaClO4 in EC (ethylene carbonate) and DEC (diethyl carbonate) with a volume ratio of 1:1, and adding 5% of FEC (fluorinated ethylene carbonate) to obtain an electrolyte; Assembling inside a glove box filled with argon, and strictly controlling the moisture content inside the glove box to be less than 0.01 ppm and the oxygen content to be less than 0.05 ppm to obtain a sodium-ion battery.

[0066] Leave the packaged sodium battery at room temperature for 8 h, conduct a charge-discharge test using a CT2001 charge-discharge tester from Wuhan Blue Electric Co., and set the charge-discharge voltage to 2.0 V - 4.2 V. In the cycle performance test, conduct the test at a rate of 1 C (1 C = 170 mA g-1).

[0067] Use PB and PB@TA@ODA in Example 1 as the positive electrode materials respectively, manufacture the positive electrode tab according to the manufacturing method of the above positive electrode tab, and test the contact angle of the positive electrode tab. The results are as shown in FIGS. 5 and 6.

[0068] As can be seen from FIGS. 5 and 6, FIG. 5 shows the contact angle of the positive electrode tab made of PB, and the contact angle is 108°. FIG. 6 shows the contact angle of the positive electrode tab made of PB@TA@ODA, and the contact angle is 127°, which is much larger than that of the positive electrode tab made of PB. From this, it can be seen that PB@TA@ODA has good hydrophobicity.

[0069] In Example 1, PB, PB-7D, PB@TA@ODA, and PB@TA@ODA-7D were used as the cathode materials respectively, and sodium batteries were manufactured according to the manufacturing method of the above sodium-ion battery. Charge-discharge and cycle tests were performed on the sodium-ion battery, and the results are as shown in FIGS. 7, 8, 9, and 10. Here, PB-7D indicates that PB was left standing for 7 days at room temperature, normal pressure, and 80% humidity, and PB@TA@ODA-7D indicates that PB was left standing for 7 days at room temperature, normal pressure, and 80% humidity.

[0070] As can be seen from FIGS. 7 and 8, the initial discharge capacities of the sodium-ion batteries manufactured using PB and PB@TA@ODA respectively are 142 mAh g-1 and 150 mAh g-1, respectively, with no significant difference, and the cycle performances are relatively similar.

[0071] As can be seen from FIG. 9, after PB7 was left standing for a day, its initial discharge capacity decayed to 116 mAh g-1, and its sodium storage performance decreased significantly. On the other hand, PB@TA@ODA-7D still has an initial discharge capacity of 145 mAh g-1 or more, showing almost no capacity decay compared with PB@TA@ODA, and better storage stability under the environment of room temperature, normal pressure, and high humidity.

[0072] As can be seen from FIG. 10, PB@TA@ODA-7D, as the cathode of the sodium-ion battery, still has very stable cycle stability, shows high initial efficiency and high specific capacity, and excellent hydrophobic performance.

[0073] The cathode materials manufactured in Examples 1 to 10 and Comparative Examples 1 to 2 and the cathode materials after being left standing for 7 days were used respectively, and sodium batteries were manufactured according to the manufacturing method of the above sodium-ion battery. Charge-discharge and cycle tests were performed on the sodium-ion battery, and the results were recorded in Table 1.

[0074]

Table 1

[0075] As can be seen from Table 1, when Prussian blue is double-coated with an appropriate amount of tannic acid polymer and the second layer coating material, it can exhibit excellent electrochemical performance while showing good environmental storage performance.

[0076] Although the present invention has been described with specific examples, it should be noted that the above examples are only used to explain the technical solutions of the present invention and do not limit them. Those skilled in the art can modify the technical solutions described in each of the above examples or equivalently substitute some or all of their technical features without departing from the spirit and scope of the present invention. It should be understood that these modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the scope of the technical solutions of each example of the present invention. Therefore, it means that all such substitutions and modifications belonging to the scope of the present invention are included in the appended claims.

Claims

1. A positive electrode material comprising a Prussian blue matrix and a first coating layer and a second coating layer sequentially coated on the surface of the Prussian blue matrix, wherein the material for forming the first coating layer contains a polymer of tannic acid, and the material for forming the second coating layer contains at least one of hexadecylamine, octadecylamine, octadecylphosphonic acid, N-phenyltrifluoromethanesulfonimide, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and 1H,1H,2H,2H-perfluorodecanethiol.

2. The chemical formula of the Prussian blue matrix is Na x M a M’ b (CN) 6 ・zH 2 O, where M and M’ are each independently selected from at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < x < 2, 0 < a < 1, 0 < b < 1, and z > 0. The positive electrode material according to claim 1, wherein the particle size of the positive electrode material is 200-300 nm, and / or.

3. The positive electrode material according to claim 1, wherein the thickness of the first coating layer is 3-4 nm.

4. The positive electrode material according to claim 1, wherein the thickness of the second coating layer is 1-2 nm.

5. Mixing tannic acid, formaldehyde, ammonium ions, a first solvent, and water to obtain a precursor solution containing tannic acid; First reacting a Prussian blue matrix with the precursor solution containing tannic acid to obtain a Prussian blue matrix coated with a polymer of tannic acid (PB@TA); A method for manufacturing a positive electrode material according to any one of claims 1 to 4, comprising: second reacting the PB@TA, a material for forming a second coating layer, and a second solvent to obtain the positive electrode material.

6. The temperature of the first reaction and the second reaction are each independently 25-80 °C, and / or the time of the first reaction and the second reaction are each independently 1-72 h. A method for manufacturing a positive electrode material according to claim 5, characterized in that.

7. Feature (1): The molar ratio of the tannic acid to the formaldehyde is (0.022-0.024):1; Feature (2): The substance providing the ammonium ions contains aqueous ammonia; Feature (3): The concentration of the aqueous ammonia is 20-30 wt%, and the usage ratio of the aqueous ammonia to the tannic acid is 1 mL:0.1-1 mmol. A method for manufacturing a positive electrode material according to claim 5, characterized by including at least one of the above features.

8. The mass ratio of the Prussian blue matrix to the tannic acid is 1:(0.05 to 2), and / or the mass ratio of the PB@TA to the material forming the second coating layer is 1:(0.1 to 5). The method for manufacturing a positive electrode material according to claim 5, characterized by the above.

9. The first solvent contains ethanol, and / or the second solvent contains at least one of methanol, ethanol, ethylene glycol, acetone, and tetrahydrofuran. The method for manufacturing a positive electrode material according to claim 5, characterized by the above.

10. A sodium ion battery comprising the positive electrode material according to any one of claims 1 to 4.

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