A method for preparing a sodium iron sulfate cathode material for a sodium-ion battery without calcination

Abstract

A method for preparing a sodium iron sulfate cathode material for a sodium-ion battery without calcination, which relates to a method for preparing a sodium iron sulfate cathode material. It aims to solve the problems of complex synthesis process, low production efficiency and high production cost of the existing sodium iron sulfate cathode material. Preparation method: Mix a sodium source, an iron source and a carbon-coated material, or add a flux thereto to obtain a mixture, and then perform high-energy ball milling on the mixture to obtain the sodium iron sulfate cathode material. The initial discharge specific capacity at a rate of 0.1C is 79.2-88.3 mAh / g, the initial Coulombic efficiency is 87.7%-89.4%, and the median discharge voltage is 3.7-3.8V. The method of the present invention is convenient and efficient, has low energy consumption, is suitable for batch material synthesis, and can be used in the field of sodium-ion batteries.

Description

Technical Field

[0001] The invention belongs to the technical field of battery material preparation, and specifically relates to a calcination-free preparation method and application of sodium iron sulfate positive electrode material for sodium ion batteries. Background Art

[0002] Sodium-ion batteries have become one of the most promising chemical power sources in the post-lithium-ion battery era due to their uniform distribution of sodium resources, low cost, and similar electrochemical properties to lithium-ion batteries. However, the larger ionic radius and heavier atomic mass compared to lithium ions limit the rapid movement of sodium ions in electrode materials, resulting in relatively slow reaction kinetics and low energy density in sodium-ion batteries. As a key component affecting the final performance and cost of batteries, the key to achieving the next generation of batteries lies in the development of high-quality cathodes that combine low cost and high energy density. In view of this, developing new types of cathode materials by improving battery voltage and stable capacity is the best way to develop sodium-ion batteries. Among the many sodium-ion battery cathode materials, sodium iron sulfate materials exhibit outstanding high redox potentials due to the strong inductive effect of sulfate. At the same time, the low raw material cost and environmental friendliness make this material show comprehensive superiority and broad application prospects.

[0003] Sodium iron sulfate cathode materials are generally prepared from sodium sulfate and ferrous sulfate using sol-gel method, spray drying method or solid phase ball milling method. 2+ The presence of makes it very sensitive to water and oxygen, and the use of liquid phase synthesis methods such as sol-gel and spray drying has inherent disadvantages. Relatively speaking, the solid phase ball milling method not only effectively eliminates the interference of water and air on the material, but is also more conducive to scale-up synthesis. However, the traditional solid phase ball milling method usually requires a long ball milling and inert atmosphere calcination time, low production efficiency and high cost. Therefore, it is of great significance to provide a more efficient and convenient method for preparing sodium iron sulfate positive electrode materials to reduce the time and cost of material synthesis. Summary of the invention

[0004] The present invention aims to solve the problems of complex synthesis process, low production efficiency and high production cost of existing sodium ferric sulfate positive electrode materials, and provide a calcination-free preparation method of sodium ferric sulfate positive electrode materials for sodium ion batteries. The method is convenient, efficient, low in energy consumption, and can be applied to batch material synthesis.

[0005] The calcination-free preparation method of the sodium iron sulfate positive electrode material for a sodium ion battery of the present invention is carried out according to the following steps:

[0006] Step 1: mixing a sodium source, an iron source, and a carbon-coated material, or adding a flux thereto, to obtain a mixture;

[0007] Step 2: subjecting the mixture to high-energy ball milling to obtain sodium iron sulfate positive electrode material.

[0008] Further, the sodium source described in step one is anhydrous sodium sulfate and / or sodium sulfate decahydrate.

[0009] Further, the iron source described in step one is one or more of anhydrous ferrous sulfate, ferrous sulfate monohydrate, and ferrous sulfate heptahydrate.

[0010] Further, the carbon coating material described in step one is one or more of conductive carbon black, acetylene black, Ketjen black, graphene, reduced graphene oxide, and carbon nanotubes.

[0011] Further, the flux described in step one is a halide flux. The halide flux is one or more of aluminum fluoride, aluminum chloride, magnesium fluoride, magnesium chloride, lithium fluoride, lithium chloride, sodium fluoride, sodium chloride, potassium fluoride, potassium chloride, barium fluoride, barium chloride, calcium fluoride, calcium chloride, stannous chloride, stannous fluoride, tin chloride, tin fluoride, gallium chloride, gallium fluoride, ammonium fluoride, and ammonium chloride. The halide flux has a low melting point itself or can generate a molten substance during heating. The purpose of adding the flux is mainly to reduce the reaction temperature and make it easier for the material to be generated by the mechanical heat release of ball milling.

[0012] Further, the molar ratio of the sodium source to the iron source described in step one is (1 - 2):1. If the molar ratio of the sodium source to the iron source is too high or too low, it is easy to generate impurity phases and affect the performance of the product. Under the molar ratio conditions set in the present invention, the obtained product is purer.

[0013] Further, the flux accounts for 1wt% - 7wt% of the total material. Adding a certain amount of flux in the mixing formula can effectively reduce the reaction temperature, improve production efficiency, and reduce reaction energy consumption. However, too high a flux ratio may reduce the purity and discharge specific capacity of the product. Therefore, the present invention makes the above limitation on the flux addition amount.

[0014] Further, the mass ratio of the carbon coating material described in step one is 2wt% - 10wt% of the total material. Appropriate carbon addition can effectively improve the electronic conductivity of the material. However, in order to minimize the introduction of electrochemically inert carbon components, the present invention makes the above limitation on the addition amount of the carbon source.

[0015] Further, the ball mill described in step two is a planetary ball mill, the ball milling speed is 200rpm - 500rpm, and the ball milling time is 10h - 55h. If the ball milling speed is too slow or the ball milling time is too short, it will lead to uneven mixing of raw materials, incomplete crushing, and insufficient heat generation in the ball mill tank, resulting in a higher impurity content in the product; if the ball milling speed is too fast or the ball milling time is too long, it will lead to excessive heat generation in the ball mill tank, causing the material to be overburned, generating impurity phases or decomposition.

[0016] Furthermore, the atmosphere of ball milling described in step 2 is an inert atmosphere or air.

[0017] The technical solution of the present invention has the following advantages compared with the prior art:

[0018] (1) The preparation method of the present invention does not require calcination in an inert atmosphere, has a short time cycle for material synthesis, high production efficiency, low energy consumption, low cost, simple process, easy to realize industrialization, and has good economic benefits and operability.

[0019] (2) In the preparation method of the present invention, a certain amount of flux can be added to the raw materials. The melting point of the flux is relatively low, which can effectively reduce the reaction temperature and make it easier for the material to be generated by the mechanical heat release of ball milling; the added flux can melt in advance during the ball milling process, acting as a flux and a reaction medium, enabling the reaction raw materials to fully contact and mix, effectively shortening the ball milling time; the added flux can also form a coating layer on the surface of the material, isolating the contact between the sodium iron sulfate material and oxygen and moisture; the added flux has reducibility, which can effectively prevent the oxidation of Fe 2+ in the material; the added flux has strong conductivity, which can effectively improve the electronic conductivity of the material and improve the electrochemical performance of the material; the added flux has redox activity, which can further increase the discharge specific capacity of the cathode material. The sodium iron sulfate cathode material prepared with stannous chloride as the flux has the formula Na x Fe y Sn z (SO4)3Cl m / C compound, where 2 ≤ x ≤ 3, 1.5 ≤ y ≤ 2, 0 < z ≤ 0.40, 0 < m ≤ 0.80; the values of x, y, z, and m satisfy the charge balance of the chemical formula. The initial discharge specific capacity of the sodium iron sulfate cathode material of the present invention at a rate of 0.1C is 79.2 - 88.3 mAh / g, the initial Coulomb efficiency is 87.7% - 89.4%, and the discharge median voltage is 3.7 - 3.8V. This sodium iron sulfate cathode material can be used in the field of sodium-ion batteries. Description of the Drawings

[0020] Figure 1 is the XRD pattern of the sodium iron sulfate cathode material prepared in Example 1;

[0021] Figure 2 is the first charge-discharge curve of the sodium iron sulfate cathode material prepared in Example 1 at a rate of 0.1C;

[0022] Figure 3 is the first charge-discharge curve of the sodium iron sulfate cathode material prepared in Comparative Example 1 at a rate of 0.1C;

[0023] Figure 4 XRD pattern of the sodium iron sulfate cathode material prepared in Example 2

[0024] Figure 5 First charge-discharge curve of the sodium iron sulfate cathode material prepared in Example 2 at a rate of 0.1C Specific Embodiments

[0025] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, so that those skilled in the art can better understand the present invention and be able to implement it. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the examples given do not limit the content and protection scope of the present invention. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0026] Example 1: The method for preparing the sodium iron sulfate cathode material of the sodium-ion battery in this example is carried out according to the following steps:

[0027] I. Take 0.4259 g of sodium sulfate, 0.4562 g of ferrous sulfate, and 0.0557 g of graphene and mix them evenly to obtain a mixture;

[0028] II. Place the mixture in the ball mill tank of the Retsch PM100 planetary ball mill, fill the tank with nitrogen gas for protection, ball mill at a speed of 400 rpm for 24 h, and after natural cooling, obtain the sodium iron sulfate cathode material.

[0029] The XRD pattern of the sodium iron sulfate cathode material prepared in this example is as Figure 1 shown. From Figure 1 it can be seen that the obtained product maintains the typical sodium iron sulfate structure, but due to the mechanical heat generation during ball milling, it is difficult to maintain a high reaction temperature, and there are still some obvious impurity peaks in the product, indicating that the phase purity of the product is not high enough.

[0030] Mix the sodium iron sulfate cathode material of the sodium-ion battery prepared in this example with the conductive agent Super P and the binder polyvinylidene fluoride dissolved in N-methylpyrrolidone in a mass ratio of 7:2:1, coat it on the current collector aluminum foil, and prepare the sodium iron sulfate electrode. Assemble the obtained sodium iron sulfate cathode and the metal sodium anode to simulate a sodium-ion battery, and conduct electrochemical performance tests in the range of 2.0 - 4.5 V. The first charge-discharge curve of the sodium iron sulfate cathode material prepared in Example 1 at a rate of 0.1C is as Figure 2 shown. From Figure 2 it can be seen that the first discharge specific capacity at a rate of 0.1C is 79.2 mAh / g, the Coulomb efficiency is 87.7%, and the discharge median voltage is 3.7 V.

[0031] Comparative Example 1: The difference between this comparative example and Example 1 is that graphene carbon is not added in Step 1, and the other steps and parameters are the same as those in Example 1, obtaining a sodium iron sulfate cathode material.

[0032] Using the same method as in Example 1, the sodium iron sulfate cathode material prepared in the comparative example was assembled with a sodium metal anode to simulate a sodium-ion battery, and electrochemical performance tests were carried out in the range of 2.0 - 4.5 V. The first charge-discharge curve of the obtained sodium iron sulfate cathode material at a rate of 0.1C is as Figure 3 shown. Due to the lack of improvement in the electronic conductivity of the material by conductive carbon, the electrochemical performance of the material is poor. The first discharge specific capacity at a rate of 0.1C is 54.79 mAh / g, the Coulomb efficiency is 87.7%, and the median discharge voltage is 3.6 V.

[0033] Example 2: The method for preparing a sodium iron sulfate cathode material for a sodium-ion battery in this example is carried out according to the following steps:

[0034] I. Weigh 0.3435 g of sodium sulfate, 0.5214 g of ferrous sulfate, 0.0464 g of carbon nanotubes, and 0.0173 g of stannous chloride, mix them evenly to obtain a mixture;

[0035] II. Place the mixture in the ball milling tank of a RETSCH PM100 planetary ball mill, fill the tank with nitrogen gas for protection, ball mill at a speed of 400 rpm for 24 h, and after natural cooling, obtain a sodium iron sulfate cathode material.

[0036] In this example, stannous chloride was added as a flux. The chemical formula of the obtained sodium iron sulfate cathode material is Na 2.48 Fe 1.76 Sn 0.09 (SO4)3Cl 0.18 / C, and its XRD pattern is as Figure 3 shown. The obtained product shows the characteristic peaks of sodium iron sulfate. Due to the effective reduction of the reaction temperature by the flux, the mechanical heat release during ball milling well maintains the reaction temperature, making the crystallization state of the product good, and showing a sharper peak shape compared with Example 1.

[0037] Using the same method as in Example 1, the sodium iron sulfate cathode material prepared in the comparative example was assembled with a sodium metal anode to simulate a sodium-ion battery, and electrochemical performance tests were carried out in the range of 2.0 - 4.5 V. The first charge-discharge curve of the obtained sodium iron sulfate cathode material at a rate of 0.1C is as Figure 3 shown. Due to the lack of improvement in the electronic conductivity of the material by conductive carbon, the electrochemical performance of the material is poor. The first discharge specific capacity at a rate of 0.1C is 54.79 mAh / g, the Coulomb efficiency is 87.7%, and the median discharge voltage is 3.6 V.

[0038] Using the same method as in Example 1, the sodium iron sulfate cathode material prepared in this example was assembled with a sodium metal anode to simulate a sodium-ion battery, and the electrochemical performance was tested in the range of 2.0 - 4.5 V. The first charge-discharge curve of the sodium iron sulfate cathode material prepared in Example 2 at a rate of 0.1C is as Figure 4 shown. The addition of stannous chloride flux effectively reduced the reaction temperature, improved the electronic conductivity and stability of the material, and the redox activity of Sn 2+ also further enhanced the discharge specific capacity of the material. Therefore, the sodium iron sulfate cathode material prepared in Example 2 exhibited excellent electrochemical performance, with a first discharge specific capacity of 88.3 mAh / g, a first Coulombic efficiency of 89.4%, and a discharge median voltage of 3.8 V at a rate of 0.1C.

[0039] Example 3: The method for preparing the sodium iron sulfate cathode material of the sodium-ion battery in this example is carried out according to the following steps:

[0040] 1. Weigh 0.3435 g of sodium sulfate, 0.5214 g of ferrous sulfate, 0.0464 g of conductive carbon black, and 0.0173 g of ammonium chloride, and mix them evenly to obtain a mixture;

[0041] 2. Place the mixture in the ball mill tank of the Retsch PM100 planetary ball mill, fill the tank with inert gas for protection, and ball mill at a speed of 350 rpm for 50 h. After natural cooling, the sodium iron sulfate cathode material is obtained.

[0042] Using the same method as in Example 1, the sodium iron sulfate cathode material prepared in Example 3 was assembled with a sodium metal anode to simulate a sodium-ion battery, and the electrochemical performance was tested in the range of 2.0 - 4.5 V. The first discharge specific capacity of the obtained cathode at a rate of 0.1C was 83.0 mAh / g, the Coulombic efficiency was 85.1%, and the discharge median voltage was 3.7 V.

[0043] Example 4: The method for preparing the sodium iron sulfate cathode material of the sodium-ion battery in this example is carried out according to the following steps:

[0044] 1. Weigh 0.3572 g of sodium sulfate, 0.5068 g of ferrous sulfate, 0.0464 g of graphene, and 0.0173 g of stannous chloride, and mix them evenly to obtain a mixture;

[0045] 2. Place the mixture in the ball mill tank of the Retsch PM100 planetary ball mill, fill the tank with inert gas for protection, and ball mill at a speed of 300 rpm for 48 h. After natural cooling, the sodium iron sulfate cathode material is obtained.

[0046] Example 5: The method for preparing the sodium iron sulfate cathode material of a sodium-ion battery in this example without calcination is carried out according to the following steps:

[0047] 1. Weigh 0.3435 g of sodium sulfate, 0.5214 g of ferrous sulfate, 0.0464 g of conductive carbon black, and 0.0173 g of aluminum fluoride, mix them evenly to obtain a mixture;

[0048] 2. Place the mixture in the ball milling tank of the Retsch PM100 planetary ball mill. The gas filled in the tank is air. Ball mill at a speed of 450 rpm for 30 h. After natural cooling, the sodium iron sulfate cathode material is obtained.

[0049] Example 6: The method for preparing the sodium iron sulfate cathode material of a sodium-ion battery in this example without calcination is carried out according to the following steps:

[0050] 1. Weigh 0.3267 g of sodium sulfate, 0.5394 g of ferrous sulfate, 0.0464 g of graphene, and 0.0173 g of ammonium fluoride, mix them evenly to obtain a mixture;

[0051] 2. Place the mixture in the ball milling tank of the Retsch PM100 planetary ball mill. Fill the tank with an inert gas for protection. Ball mill at a speed of 500 rpm for 10 h. After natural cooling, the sodium iron sulfate cathode material is obtained.

Claims

1. A calcination-free preparation method for sodium iron sulfate positive electrode material of sodium ion battery, characterized in that The method proceeds as follows: Step 1: mixing a sodium source, an iron source, and a carbon-coated material, or adding a flux thereto, to obtain a mixture; wherein the flux is one or more of aluminum fluoride, aluminum chloride, magnesium fluoride, magnesium chloride, lithium fluoride, lithium chloride, sodium fluoride, sodium chloride, potassium fluoride, potassium chloride, barium fluoride, barium chloride, calcium fluoride, calcium chloride, stannous chloride, stannous fluoride, stannous chloride, stannous fluoride, gallium chloride, gallium fluoride, ammonium fluoride, and ammonium chloride; Step 2: subjecting the mixture to high-energy ball milling to obtain sodium iron sulfate positive electrode material.

2. The calcination-free preparation method of sodium iron sulfate positive electrode material for sodium ion battery according to claim 1, characterized in that: The sodium source described in step 1 is anhydrous sodium sulfate and / or sodium sulfate decahydrate.

3. The calcination-free preparation method of sodium iron sulfate positive electrode material for sodium ion battery according to claim 1 or 2, characterized in that: The iron source described in step 1 is one or more of anhydrous ferrous sulfate, ferrous sulfate monohydrate and ferrous sulfate heptahydrate.

4. The calcination-free preparation method of a sodium iron sulfate positive electrode material for a sodium ion battery according to claim 1 or 2, characterized in that: The carbon coating material described in step 1 is one or more of conductive carbon black, acetylene black, Ketjen black, graphene, redox graphene and carbon nanotubes.

5. The calcination-free preparation method of sodium iron sulfate positive electrode material for sodium ion battery according to claim 1 or 2, characterized in that: The molar ratio of the sodium source to the iron source in step 1 is (1-2):

1.

6. The calcination-free preparation method of sodium iron sulfate positive electrode material for sodium ion battery according to claim 1 or 2, characterized in that: The flux described in step 1 accounts for 1wt% to 7wt% of the total material.

7. The calcination-free preparation method of sodium iron sulfate positive electrode material for sodium ion battery according to claim 1 or 2, characterized in that: The mass proportion of the carbon coating material described in step 1 is 2wt% to 10wt% of the total material.

8. The calcination-free preparation method of sodium iron sulfate positive electrode material for sodium ion battery according to claim 1 or 2, characterized in that: The ball mill described in step 2 is a planetary ball mill, the ball milling speed is 200 rpm to 500 rpm, and the ball milling time is 10 h to 55 h.

9. The calcination-free preparation method of sodium iron sulfate positive electrode material for sodium ion battery according to claim 1 or 2, characterized in that: The ball milling atmosphere in step 2 is an inert atmosphere or air.

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