Prussian blue sodium battery positive electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a Prussian blue sodium battery positive electrode material and a preparation method thereof.The preparation method comprises the steps that anhydrous sodium ferrocyanide, anhydrous manganese sulfate and a NaA molecular sieve are mixed and preliminarily ground, and a precursor mixture is obtained; placing the precursor mixture in a planetary ball mill for ball milling to obtain a primary reaction product; and washing the preliminary reaction product, and carrying out vacuum drying to obtain the Prussian blue sodium battery positive electrode material. The method is low in material loss and short in generation period, and the prepared Prussian blue sodium battery positive electrode material is low in crystal water content and has good cycle stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a Prussian blue type sodium electric positive electrode material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of battery energy storage technology, the problems of increasing exploitation cost and insufficient reserves of lithium resources required by lithium ion batteries (LIBs) are becoming increasingly serious. Therefore, it is crucial to develop new energy storage batteries with abundant raw material resources, low development cost, safety, environmental protection and excellent performance. Among the current candidate energy storage technologies, sodium ion batteries have a similar working principle to lithium ion batteries and are also a "rocking chair battery". The charging and discharging is realized by the intercalation and deintercalation of sodium ions between the positive and negative electrode materials. A sodium ion battery mainly consists of a positive electrode material, a negative electrode material, a battery shell, an electrolyte, a separator, positive and negative electrode current collectors and the like. Among them, in a sodium ion full battery, the positive electrode material is the main sodium storage part in the sodium ion battery, and the sodium content and the level of the electric potential directly determine the level of the energy storage capacity of the sodium ion battery system. At the same time, the positive electrode material of the sodium ion battery provides the channel for the intercalation and deintercalation of sodium ions, and the cycle life and high-rate performance of the battery are also inseparable from the positive electrode material.

[0003] Prussian blue type positive electrode materials (PBAs) have become one of the research hotspots of sodium ion battery positive electrode materials in recent years due to their large ion transmission channel of open framework structure, high voltage platform, low cost, simple preparation and the like. The chemical general formula of Prussian blue and its derivatives (PBAs) is A x M1[M2(CN)6]y·zH2O (A represents Li, Na, K and the like alkali metal ions, M1 and M2 represent Fe, Co, Ni, Mn, Cu, Zn and the like transition metals, 0≤x≤2, y≤1). The structural stability of Prussian blue is very good, and the optimization and modification of the chemical composition will not cause the destruction of the overall crystal structure.

[0004] However, the Prussian blue type materials in the prior art are generally synthesized by a traditional liquid phase method. For example, when a coprecipitation method is used, a low-concentration precursor solution is first pumped into a reaction container by a peristaltic pump, then a reaction synthesis is carried out in a high-temperature aqueous solution, and then filtering, washing and drying are carried out. The sample feeding process and the reaction synthesis process are both slow, and the whole preparation process is complicated, which leads to a long period of preparing PBAs materials. The coprecipitation method commonly used in the synthesis of PBAs is extremely easy to cause lattice defects and introduce crystal water. On the other hand, too fast reaction speed will cause incomplete crystal growth, form vacancies, water molecules fill in, and large particles or agglomerates are easily formed, and the interaction between ions may be too strong, leading to structural defects or amorphous state formation. In the process of synthesizing PBAs, improper pH adjustment or poor temperature control will promote Fe³ +hydrolysis, generating iron hydroxide colloid, and water molecules can enter the interstitial space of the crystal lattice. The reaction environment is basically in a low concentration aqueous solution. The reaction in the low concentration aqueous solution can slow down the reaction speed, make the nucleation and growth process more controllable, and thus obtain more uniform nanostructures. Meanwhile, it is also beneficial to the slow diffusion of ions, forming a more complete crystal structure. This is easy to make the PBAs material form [Fe(CN)6] 4- The vacancies are occupied by water molecules to form crystalline water which is difficult to remove. These crystalline waters fill the vacancies in the crystal lattice, not only competing with sodium ions for space and thus reducing the capacity utilization of the material, but also causing material structure defects, leading to the collapse of the crystal structure of the material and the decomposition of the electrolyte during the charging and discharging process, affecting the cycle performance of the battery. Since the sample is a low concentration precursor solution each time, and the material loss is large during the preparation process of the liquid phase method, the amount of material produced per cycle is very small.

[0005] A solid phase ball milling method for synthesizing a Prussian blue type sodium electric positive electrode material is disclosed in Chinese patent document CN111029572A. The basic principle is to control the water content in the material by using different metal salts, and to combine the ball milling method to synthesize the material in an environment without a large amount of water, thereby reducing the water content in the product and increasing the sodium content in the Prussian blue type positive electrode material. Although the solid phase ball milling method is carried out in a solid phase environment, the water contained in the metal salt raw material will also occupy the vacancies in the crystal lattice during the reaction process, causing material structure defects. Moreover, in the high-speed ball milling process, the metal salt materials are directly contacted, mixed and ground, quickly forming the target product, resulting in more structure defects in the material crystal compared with the positive electrode material prepared by the liquid phase method. SUMMARY

[0006] The purpose of the present application is to provide a Prussian blue type sodium electric positive electrode material and a preparation method thereof. The method has small material loss and short generation cycle, and the Prussian blue type sodium electric positive electrode material prepared has less crystalline water content and good cycle stability.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: On the one hand, the present application provides a preparation method of a Prussian blue type sodium electric positive electrode material, comprising the following steps: (1) mixing anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve to carry out preliminary grinding to obtain a precursor mixture; (2) placing the precursor mixture in a planetary ball mill to carry out ball milling to obtain a preliminary reaction product; (3) washing and vacuum drying the preliminary reaction product to obtain a Prussian blue type sodium electric positive electrode material.

[0008] The molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate in step (1) is 1:0.5-1:3; preferably 1:1-1:1.5.

[0009] The mass ratio of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate in step (1) is 2:1-5:1, preferably 4:1-5:1.

[0010] The ball-to-material ratio in step (2) is 1:10-1:50; preferably 1:10-1:30.

[0011] The ball milling speed in step (2) is 300-800 r / min; preferably 400-600 r / min.

[0012] The ball milling time in step (2) is 4-20 h; preferably 10-15 h.

[0013] The vacuum drying temperature in step (3) is 100-200℃; preferably 100-150℃.

[0014] The vacuum drying time in step (3) is 6 - 16 h; preferably 8 - 14 h.

[0015] In another aspect, the application also provides a Prussian blue type sodium battery cathode material, which is prepared by the above method.

[0016] Compared with the prior art, the technical scheme of the application has the following beneficial effects: (1) The preparation method of the Prussian blue type sodium battery cathode material disclosed in the application uses anhydrous sodium ferrocyanide and anhydrous manganese sulfate as raw materials, the water content in the raw materials is low, the formation of structural defects of the cathode material in the preparation process is reduced, and the cycle stability of the cathode material is improved.

[0017] (2) The preparation method of the Prussian blue type sodium electric positive electrode material disclosed in the application adds NaA molecular sieve in the process of ball milling and mixing of raw materials. The NaA molecular sieve has three effects. Firstly, in the process of ball milling and mixing, the molecular sieve can adsorb water in the raw materials to prevent the water from occupying the lattice vacancies in the product material, and the water adsorbed on the molecular sieve is removed through the subsequent vacuum drying process, thereby improving the dehydration efficiency of the vacuum drying, finally reducing the content of crystal water in the material and reducing the structural defects of the material. Secondly, the NaA molecular sieve reduces the contact area between the metal salt raw materials in the process of raw material mixing and grinding, delays the reaction speed, provides sufficient time for the crystal growth of the material, reduces the structural defects of the material, and improves the specific charge and discharge capacity of the product material. Thirdly, the NaA molecular sieve serves as a skeleton, so that the metal salt raw materials are uniformly distributed in the three-dimensional network cavity of the molecular sieve, thereby improving the structural stability of the product material.

[0018] (3) The planetary ball mill is used to ball mill the precursor mixture. The planetary ball mill generates high-frequency impact force, friction force and extrusion effect on the material through the combined motion of revolution and rotation of the grinding tank, so that the anhydrous ferrocyanide, anhydrous copper sulfate sodium and NaA molecular sieve can be quickly crushed to a superfine particle size. The NaA molecular sieve is a porous material, and the three-dimensional motion mode of the planetary ball mill can avoid the damage to the structure of the molecular sieve, thereby protecting the water absorption and the complete skeleton structure of the molecular sieve during the ball milling process.

[0019] (4) The traditional liquid phase method for preparing the Prussian blue type sodium electric positive electrode material has complicated steps, a long production cycle, and a large amount of waste liquid generated in the synthesis process, and does not have the conditions for large-scale production. The mechanical solid-phase ball milling method of the application has simple and reliable preparation process, and does not need to consider the concentration of reactants, has less material loss, generates little waste liquid, and can be further used for industrial large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Reference standard Prussian blue type sodium electric positive electrode material X-ray diffraction (XRD) pattern. See page 27 of "Co-precipitation method for preparing manganese-based Prussian blue type sodium ion battery positive electrode material and electrochemical performance research", Zhejiang University, 2019.

[0021] Figure 2 Prussian blue type sodium electric positive electrode material X-ray diffraction (XRD) pattern prepared in Example 1 of the application.

[0022] Figure 3 0.1C charge-discharge curve of the Prussian blue type sodium electric positive electrode material prepared in Example 1 of the application and the iron-manganese-based Prussian blue type sodium electric positive electrode material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0023] In order to make the present application more apparent, the technical solutions of the present application are further described and explained in the following embodiments in conjunction with the drawings, but are not used to limit the protection scope of the present application.

[0024] Unless otherwise specified, the raw materials used in the embodiments of the present application are commercially available materials; unless otherwise specified, all technical and scientific terms used in the present application have the same meanings as generally understood by those skilled in the art.

[0025] NaA molecular sieve is a sodium ion exchange type A molecular sieve, which belongs to silicate-aluminate microporous crystal material, has a regular pore structure and excellent adsorption and separation performance.

[0026] Chemical formula: Na2O·Al2O4·2SiO2·4.5H2O, which is formed by connecting SiO4 and AlO4 tetrahedrons through oxygen bridges to form a three-dimensional framework structure, and sodium ions (Na + ) in the framework are used to balance the negative charge of AlO4 tetrahedron238.

[0027] Pore size characteristics: natural pore size is about 4Å (0.4nm), so it is called 4A molecular sieve. The pore size can be adjusted by ion exchange: if Na + is replaced by K + , the pore size is reduced to 3Å (3A type); if it is partially replaced by Ca 2+ , the pore size is expanded to 5Å (5A type)245.

[0028] Crystal structure: belongs to cubic crystal system, and the beta cage (composed of six-membered ring and four-membered ring) is connected through four-membered ring to form alpha cage (pore size is about 1.14nm), and eight-membered ring is the main channel entrance.

[0029] The NaA molecular sieve used in the embodiments of the present application is purchased from Shanghai Jiuzhou Chemical Co., Ltd.

[0030] The planetary ball mill used in the embodiments of the present application is Retsch PM - 100 type, from Guining (Shanghai) Experimental Instrument Co., Ltd. Example 1

[0031] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:1.2, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 4.5:1. The above materials were preliminarily ground to obtain a precursor mixture, and then the precursor mixture was added to a corundum ball mill jar, 5-15 mm corundum ball milling beads were used, and the ball mill jar was sealed. The ball mill jar was installed in a planetary ball mill, the ball milling speed was set to 500 r / min, and the ball milling time was 12 h.

[0032] Figure 2 The X-ray diffraction (XRD) pattern of the Prussian blue type sodium electric positive electrode material was compared with the main characteristic peaks of the iron-manganese-based Prussian blue type sodium electric positive electrode material of Figure 1 The position matched, proving that the Prussian blue prepared in the embodiment maintained the original crystal structure. In addition, the peak near 24° was split into two peaks, indicating that the iron-manganese-based Prussian blue type sodium electric positive electrode material prepared in the embodiment was a monoclinic phase structure with a small amount of water. Example 2

[0033] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:0.5, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 5:1. The above materials were preliminarily ground and mixed uniformly, and then the materials were added to a corundum ball mill jar, 5-15 mm corundum ball milling beads were used, and the ball mill jar was sealed. The ball mill jar was installed in a planetary ball mill, the ball milling speed was set to 600 r / min, and the ball milling time was 11 h. Example 3

[0034] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:3, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 4:1. The above materials were preliminarily ground and uniformly mixed, and then the materials were added to a corundum ball mill tank, corundum grinding beads were put in according to a ball-to-material ratio of 1:30, and the ball mill tank was sealed. The ball mill tank was installed in a planetary ball mill, the ball milling speed was set to 400 r / min, and the ball milling time was 13 h. The mixture obtained after ball milling was washed with deionized water and anhydrous ethanol for 3 times, and then the washed product was placed in a vacuum oven and vacuum dried at 130°C for 8 h to obtain a Prussian blue type sodium electric positive electrode material. Example 4

[0035] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:2, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 3:1. The above materials were preliminarily ground and uniformly mixed, and then the materials were added to a corundum ball mill tank, corundum grinding beads were put in according to a ball-to-material ratio of 1:40, and the ball mill tank was sealed. The ball mill tank was installed in a planetary ball mill, the ball milling speed was set to 700 r / min, and the ball milling time was 15 h. The mixture obtained after ball milling was washed with deionized water and anhydrous ethanol for 3 times, and then the washed product was placed in a vacuum oven and vacuum dried at 100°C for 10 h to obtain a Prussian blue type sodium electric positive electrode material. Example 5

[0036] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:1.5, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 2:1. The above materials were preliminarily ground and uniformly mixed, and then the materials were added to a corundum ball mill tank, corundum grinding beads were put in according to a ball-to-material ratio of 1:50, and the ball mill tank was sealed. The ball mill tank was installed in a planetary ball mill, the ball milling speed was set to 800 r / min, and the ball milling time was 10 h. The mixture obtained after ball milling was washed with deionized water and anhydrous ethanol for 3 times, and then the washed product was placed in a vacuum oven and vacuum dried at 150°C for 14 h to obtain a Prussian blue type sodium electric positive electrode material. Example 6

[0037] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:1, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the sodium ferrocyanide and the manganese sulfate was 2.5:1. The above materials were preliminarily ground and uniformly mixed, and then the raw materials were added to a corundum ball mill tank, 15 - mm corundum milling beads were put in the ball mill tank according to a ball-to-material ratio of 1:50, and the ball mill tank was sealed. The ball mill tank was installed in a planetary ball mill, the ball milling speed was set to 300 r / min, and the ball milling time was 5 h. The mixture obtained after ball milling was washed with deionized water and anhydrous ethanol for 3 times respectively, and then the washed product was placed in a vacuum oven and vacuum dried at 140°C for 9 h to obtain a Prussian blue type sodium electric positive electrode material. Comparative Example 1

[0038] The difference from Example 1 is that no NaA molecular sieve was added.

[0039] A certain amount of anhydrous sodium ferrocyanide and anhydrous manganese sulfate were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:1.2. The above materials were preliminarily ground and uniformly mixed, and then the materials were added to a corundum ball mill tank, 5-15 mm corundum milling beads were put in the ball mill tank according to a ball-to-material ratio of 1:20, and the ball mill tank was sealed. The ball mill tank was installed in a planetary ball mill, the ball milling speed was set to 500 r / min, and the ball milling time was 12 h. The mixture obtained after ball milling was washed with deionized water and anhydrous ethanol for 3 times respectively, and then the washed product was placed in a vacuum oven and vacuum dried at 120°C for 12 h to obtain a Prussian blue type sodium electric positive electrode material without NaA molecular sieve. Comparative Example 2

[0040] The difference from Example 1 is that a shaking ball mill was used instead of a planetary ball mill for ball milling.

[0041] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:1.2, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the sodium ferrocyanide and the manganese sulfate was 4.5:1. After uniform mixing, the raw materials were added to a shaking ball mill tank, 5-15 mm corundum milling beads were put in the ball mill tank according to a ball-to-material ratio of 1:20, and the ball mill tank was sealed. The ball mill tank was installed in a shaking ball mill, the ball milling speed was set to 500 r / min, and the ball milling time was 12 h. The mixture obtained after ball milling was washed with deionized water and anhydrous ethanol for 3 times respectively, and then the washed product was placed in a vacuum oven and vacuum dried at 120°C for 12 h to obtain a molecular sieve coated Prussian blue sodium electric positive electrode material. Comparative Example 3

[0042] The difference from Example 1 is that the ball-to-material ratio is adjusted to 1:10.

[0043] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve are weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate is 1:1.2, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate is 4.5:1. Then the materials are added to a agate ball mill jar, and 5-15 mm agate ball milling beads are used and the ball mill jar is sealed. The ball mill jar is installed in a planetary ball mill, the ball milling speed is set to 500 r / min, and the ball milling time is 12 h. The mixture obtained after ball milling is washed with deionized water and anhydrous ethanol for 3 times respectively, and then the washed product is placed in a vacuum oven, vacuum dried at 120°C for 12 h to obtain a Prussian blue type sodium electric positive electrode material. Comparative Example 4

[0044] The difference from Example 1 is that the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate is 3.5:1.

[0045] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve are weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate is 1:1.2, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate is 3.5:1. The materials are first ground and mixed uniformly in an agate mortar, and then the raw materials are added to an agate ball mill jar, 5-15 mm agate ball milling beads are used according to a ball-to-material ratio of 1:20, and the ball mill jar is sealed. The ball mill jar is installed in a planetary ball mill, the ball milling speed is set to 500 r / min, and the ball milling time is 12 h. The mixture obtained after ball milling is washed with deionized water and anhydrous ethanol for 3 times respectively, and then the washed product is placed in a vacuum oven, vacuum dried at 120°C for 12 h to obtain a Prussian blue type sodium electric positive electrode material. Comparative Example 5

[0046] The difference from Example 1 is that the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate is 5.5:1.

[0047] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:1.2, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the sodium ferrocyanide and the manganese sulfate was 5.5:1. The above materials were preliminarily ground and uniformly mixed, and then the materials were added to a corundum ball mill tank, 5-15 mm corundum ball milling beads were used, and the ball mill tank was sealed. The ball mill tank was installed in a planetary ball mill, the ball milling speed was set to 500 r / min, and the ball milling time was 12 h. The mixture obtained after ball milling was washed with deionized water and anhydrous ethanol for 3 times, and then the washed product was placed in a vacuum oven and vacuum dried at 120°C for 12 h to obtain a Prussian blue type sodium electric positive electrode material. Comparative Example 6

[0048] The difference from Example 1 is that tenhydrate sodium ferrocyanide is used instead of anhydrous sodium ferrocyanide.

[0049] A certain amount of tenhydrate sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:1.2, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the sodium ferrocyanide and the manganese sulfate was 4.5:1. The above materials were preliminarily ground and uniformly mixed, and then the materials were added to a corundum ball mill tank, 5-15 mm corundum ball milling beads were used, and the ball mill tank was sealed. The ball mill tank was installed in a planetary ball mill, the ball milling speed was set to 500 r / min, and the ball milling time was 12 h. The mixture obtained after ball milling was washed with deionized water and anhydrous ethanol for 3 times, and then the washed product was placed in a vacuum oven and vacuum dried at 120°C for 12 h to obtain a Prussian blue type sodium electric positive electrode material. Comparative Example 7

[0050] The difference from Example 1 is that the anhydrous sodium ferrocyanide, the anhydrous manganese sulfate and the NaA molecular sieve are mixed without preliminary ball milling, and are directly sent to the planetary ball mill for ball milling.

[0051] A certain amount of anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve were weighed, wherein the molar ratio of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate was 1:1.2, and the mass ratio of the mass of the NaA molecular sieve to the total mass of the sodium ferrocyanide and the manganese sulfate was 4.5:1. The raw materials were directly added to a corundum ball mill jar, corundum milling beads were put in according to a ball-to-material ratio of 1:20, 5-15 mm corundum milling beads were used, and the ball mill jar was sealed. The ball mill jar was installed in a planetary ball mill, the ball milling speed was set to 500 r / min, and the ball milling time was 12 h. The mixture obtained after ball milling was washed with deionized water and anhydrous ethanol for 3 times, and then the washed product was placed in a vacuum oven, vacuum dried at 120°C for 12 h to obtain a Prussian blue type sodium electric positive electrode material. Application Example

[0052] The Prussian blue type sodium electric positive electrode material prepared by using the examples and comparative examples was used as an active material to prepare a positive electrode sheet, which was used for the assembly test of a sodium ion battery.

[0053] The positive electrode sheet was prepared as follows: the Prussian blue type sodium electric positive electrode material was used as an active material, Ketjen black was used as a conductive agent, and a 20 mg / ml polyvinylidene fluoride (PVDF) solution in N-methyl pyrrolidone (NMP) was used as a binder. The active material, the conductive agent and the polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1, and then ground into a slurry with a suitable viscosity. Subsequently, the slurry was uniformly coated on a carbon-coated aluminum foil. The coated electrode sheet was dried in a vacuum drying oven at 120°C for 10 hours. After complete drying, it was punched into small round sheets with a diameter of 12 mm by a punching machine, and finally placed in a glove box in an argon atmosphere for battery assembly. - The methyl pyrrolidone (NMP) solution was used as a binder, and the active material, the conductive agent and the polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 7:2:1, and then ground into a slurry with a suitable viscosity. Subsequently, the slurry was uniformly coated on a carbon-coated aluminum foil. The coated electrode sheet was dried in a vacuum drying oven at 120°C for 10 hours. After complete drying, it was punched into small round sheets with a diameter of 12 mm by a punching machine, and finally placed in a glove box in an argon atmosphere for battery assembly.

[0054] The battery assembly process was as follows: the prepared positive electrode sheet was used as a positive electrode, a metal sodium sheet was used as a negative electrode, a glass fiber separator was used as a separator, 200 μL of a sodium perchlorate electrolyte with a concentration of 1 mol / L was added, a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 was used as an electrolyte solvent, and 5% fluoroethylene carbonate (FEC) was added as an additive in the electrolyte. A half battery was assembled in the order of a negative electrode shell, a spring, a gasket, a sodium sheet, a separator, a positive electrode and a positive electrode shell, and finally packaged using a button cell sealing machine.

[0055] The assembled button cell half battery was subjected to corresponding electrochemical performance tests in a constant current charge and discharge mode in a voltage range of 2.0-4.0 V.

[0056] The electrochemical performance test results are shown in Table 1.

[0057]

[0058] Figure 3 The first charge-discharge curve of the Prussian blue type sodium battery positive electrode material prepared in Example 1 and the Prussian blue type sodium battery positive electrode material prepared in Comparative Example 1 can be seen by comparison, and it can be seen that the 0.1C discharge capacity and the first cycle coulombic efficiency of the material of Example 1 are much higher than those of Comparative Example 1. This can indicate that the molecular sieve used in the technical solution can specifically adsorb water in the Prussian blue type sodium battery positive electrode material, and the prepared material has less lattice defects and interstitial water content, has greater reversible charge specific capacity, and has relatively better electrochemical performance.

[0059] Example 1 is obviously superior to Comparative Example 1 in terms of discharge specific capacity and cycle ratio, indicating that after adding NaA molecular sieve in Example 1, sufficient time is provided for material crystal growth, reducing structural defects in the material, improving the charge-discharge specific capacity of the product material, and making the metal salt raw material uniformly distributed in the three-dimensional network cavity of the NaA molecular sieve, improving the structural stability of the product material. In addition, its mesoporous structure can provide an additional sodium ion transmission channel to improve the sodium storage capacity, and the optimization of electrical conductivity (such as the introduction of metal ion doping) can reduce the interface impedance.

[0060] Example 1 is compared with Comparative Example 2, and the high shear force of the planetary ball mill is more conducive to the uniform compounding of the molecular sieve and the metal salt, avoiding the blockage of the molecular sieve channel, while optimizing and reducing the crystallization water and reducing the particle size. Secondly, the three-dimensional motion mode can avoid the destruction of the structure of the NaA molecular sieve, while achieving uniform distribution of particle size and improving the subsequent electrochemical performance of the material.

[0061] Example 1 is compared with Comparative Example 3, and the material with a ball-to-material ratio of 1:20 has a more complete structure, and the high ball-to-material ratio material has a more unobstructed sodium ion transmission path, which optimizes and reduces Fe(CN)6 vacancies. In addition, more grinding media bring higher mechanical energy input, thereby more effectively breaking particles, reducing crystallization water, and improving the uniformity of the material.

[0062] Example 1 is compared with Comparative Example 4, and Comparative Example 5, the NaA molecular sieve can effectively capture free water molecules in the reaction system through channel adsorption, reducing the crystallization water content in the Prussian blue lattice (from 5000 ppm to below 2000 ppm). However, excessive use can cause blockage of the molecular sieve channel, thereby hindering the coordination reaction of transition metal ions (Fe 2+ , Mn 2+ ) and cyanide (CN - ), increasing the Fe(CN)6 vacancy defect rate from 5% to more than 10%. When the amount of NaA molecular sieve is too small, particles are easily agglomerated due to local supersaturation differences caused by free water (specific surface area from 45 m 2 / g to 30 m 2 / g), the residual crystal water will interfere with the sodium ion deintercalation process by hydrogen bonding, resulting in a lag in the discharge platform voltage. Then it is not possible to effectively control the crystal water and defects, reducing the specific capacity and cycle stability of the material.

[0063] Example 1 compared with Comparative Example 6, sodium ferrocyanide contains a large amount of crystal water (about 40% mass fraction), which is difficult to completely remove during synthesis, resulting in residual crystal water (typical value 4700-6000 ppm) in the Prussian blue material. These crystal waters will occupy the sodium ion transmission channel, reduce the specific capacity, and trigger the electrolyte decomposition side reaction, shorten the cycle life. The activity of sodium ferrocyanide is low, and it cannot be preferentially combined with Mn 2+ Combined, it is not possible to effectively repair the [Fe(CN)6] vacancy defects in the Prussian blue framework.

[0064] Example 1 compared with Comparative Example 7, the electrochemical performance is better, which shows that compared with one-step grinding, two-step grinding can more effectively remove crystal water, also inhibit particle agglomeration, and more accurately repair Fe(CN)6 vacancy defects by segmented energy input, significantly improve the specific capacity, rate performance and cycle life.

[0065] The above specific embodiments further illustrate the present application, but these descriptions cannot be understood as limiting the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a sodium electrode material of Prussian blue type, characterized in that, The method comprises the following steps: (1) mixing anhydrous sodium ferrocyanide, anhydrous manganese sulfate and NaA molecular sieve to perform preliminary grinding to obtain a precursor mixture; (2) placing the precursor mixture in a planetary ball mill to perform ball milling to obtain a preliminary reaction product; (3) washing and vacuum drying the preliminary reaction product to obtain a Prussian blue type sodium electric positive electrode material.

2. The method for preparing a Prussian blue sodium cathode material according to claim 1, characterized in that, In the step (1), the molar ratio of the anhydrous sodium ferrocyanide to the anhydrous manganese sulfate is 1:0.5-1:3; the mass ratio of the mass of the NaA molecular sieve to the total mass of the anhydrous sodium ferrocyanide and the anhydrous manganese sulfate is 2:1-5:

1.

3. The method for preparing a Prussian blue sodium cathode material according to claim 1, characterized in that, In the step (2), the ball-to-material ratio is 1:10-1:50, the rotation speed of the ball milling is 300-800 r / min, and the ball milling time is 4-20 h.

4. The method for preparing a Prussian blue sodium cathode material according to claim 1, characterized in that, The vacuum drying temperature in the step (3) is 100-200℃, and the vacuum drying time is 6 - 16h.

5. A Prussian blue-based sodium electro-positive electrode material, characterized in that, The Prussian blue type sodium electric positive electrode material is prepared by the method according to any one of claims 1-4.

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