Modified Sodium-Ion Battery Cathode Material, Its Preparation Method and Application

Abstract

The present invention belongs to the technical field of sodium batteries, and particularly relates to a modified sodium-ion battery cathode material, a preparation method thereof, and an application thereof. The preparation method includes the following steps: (1) Mix Prussian white with anhydrous oxalic acid and perform dry ball milling under vacuum conditions to obtain a mixed powder; (2) Add the mixed powder into a polytetrafluoroethylene-lined reaction kettle filled with ethanol, then seal the reaction kettle and place it in a muffle furnace for hydrothermal reaction; (3) Wash the powder obtained after the hydrothermal reaction in step (2) with a sodium carbonate solution. After the washing is completed, perform vacuum drying treatment on the powder, and the modified sodium-ion battery cathode material is obtained after drying. By using anhydrous oxalic acid as a modification additive, a stable covalent bond network and a uniform surface coating layer formed by the hydrothermal method can effectively inhibit the volume expansion and transition metal dissolution of the electrode material during charge and discharge, and extend the battery cycle life.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium batteries, and in particular relates to a modified sodium ion battery positive electrode material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries, as an emerging secondary battery technology, have rapidly become a hot topic in the field of research and application in recent years due to their significant advantages in safety, cost-effectiveness and abundance of raw materials. This type of battery stores and releases electrical energy through the reversible insertion and extraction of sodium ions between the positive and negative electrodes, providing strong support for the large-scale storage of renewable energy and the construction of smart grids. However, the development of sodium-ion batteries still faces some technical challenges, among which the environmental adaptability of the positive electrode material is one of the key issues that needs to be solved urgently.

[0003] At present, the positive electrode materials of sodium ion batteries (such as Prussian white) are very easy to absorb moisture and deteriorate in the natural environment, resulting in a significant decrease in their electrochemical performance, which seriously limits their practical application. The root of this problem is that the positive electrode materials are highly sensitive to humidity, which requires strict environmental control during their preparation, storage and use, increasing production costs and technical difficulties. Therefore, the development of a modified sodium ion battery positive electrode material with strong environmental adaptability has become an important research direction to promote the commercial application of sodium ion battery technology.

[0004] In the prior art, the modification methods for the positive electrode materials of sodium ion batteries mainly include surface coating, element doping and structural optimization. However, these methods often have problems such as complex process, high cost or limited modification effect, and it is difficult to take into account both the electrochemical performance and environmental stability of the materials. Therefore, it is urgent to develop a modification method with simple process, low cost and significant improvement of the environmental adaptability and electrochemical performance of the positive electrode materials to meet the needs of sodium ion batteries in practical applications. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a modified sodium ion battery positive electrode material. By using anhydrous oxalic acid as a modified additive, a stable covalent bond network and a uniform surface coating layer formed by a hydrothermal method can effectively inhibit the volume expansion of the electrode material during the charge and discharge process and the dissolution of transition metals, thereby extending the battery cycle life.

[0006] Another object of the present invention is to provide a preparation method and application of a modified sodium ion battery positive electrode material.

[0007] The technical solution adopted by the present invention is as follows:

[0008] The method for preparing the modified sodium ion battery positive electrode material comprises the following steps:

[0009] (1)Mix Prussian white with anhydrous oxalic acid and then perform dry ball milling under vacuum conditions to obtain a mixed powder;

[0010] (2)Add the mixed powder into a polytetrafluoroethylene-lined reactor filled with ethanol, then seal the reactor and place it in a muffle furnace for hydrothermal reaction;

[0011] (3)Wash the powder obtained after the hydrothermal reaction in step (2) with a sodium carbonate solution. After the washing is completed, perform vacuum drying on the powder. After drying, the modified cathode material for sodium-ion batteries is obtained.

[0012] In the step (1) described above, the mass ratio of Prussian white to anhydrous oxalic acid is 30:(1 - 3).

[0013] In the step (1) described above, a planetary ball mill is used for dry ball milling, agate balls are used as grinding balls, the rotation speed of dry ball milling is 150 - 200 rpm, and the time of dry ball milling is 2 - 3 h.

[0014] In the step (1) described above, the ball-to-material ratio of dry ball milling is (8 - 10):1.

[0015] In the step (2) described above, the temperature of the hydrothermal reaction is 200 - 250 °C, the time of the hydrothermal reaction is 6 - 10 h, and the heating rate is 1 - 3 °C / min.

[0016] In the step (2) described above, the mass-volume ratio of the added amount of the mixed powder to ethanol is (2 - 3):10 mg / mL.

[0017] In the step (3) described above, the concentration of the sodium carbonate solution is 1 - 3 mol / L.

[0018] In the step (3) described above, the drying temperature is 90 - 120 °C, and the drying time is 8 - 12 h.

[0019] The modified cathode material for sodium-ion batteries is prepared by using the preparation method of the modified cathode material for sodium-ion batteries described above.

[0020] The application of the modified cathode material for sodium-ion batteries is used to prepare sodium-ion batteries.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The preparation method of the modified sodium-ion battery cathode material of the present invention uses anhydrous oxalic acid as a modification additive, greatly enhancing the structural stability and chemical stability of the prepared cathode material, thereby effectively suppressing the phenomenon of moisture absorption and deterioration in the air environment and ensuring the long-term stability of battery performance. In addition, the prepared cathode material exhibits excellent electrochemical performance and high specific capacity, providing a solid material basis and technical support for the development of high-stability and long-life sodium-ion batteries. Specific Embodiments

[0023] The following further illustrates the present invention in conjunction with embodiments, but it does not limit the implementation of the present invention.

[0024] The raw materials used in the examples and comparative examples are all conventional commercially available raw materials without special instructions, and the process methods used in the examples and comparative examples are all conventional methods in the art without special instructions.

[0025] Example 1

[0026] The preparation method of the modified sodium-ion battery cathode material includes the following steps:

[0027] (1) Mix Prussian white and anhydrous oxalic acid with a mass ratio of 30:1, and then carry out dry ball milling using a planetary ball mill under vacuum conditions. Use agate balls as grinding balls. The rotation speed of dry ball milling is 150 rpm, the time of dry ball milling is 2 h, and the ball-to-material ratio of dry ball milling is 8:1. After dry ball milling, a mixed powder is obtained;

[0028] (2) Add the mixed powder into a polytetrafluoroethylene-lined reaction kettle filled with ethanol. The mass-volume ratio of the added amount of the mixed powder to ethanol is 2:10 mg / mL; then seal the reaction kettle and place it in a muffle furnace for hydrothermal reaction. The temperature of the hydrothermal reaction is 200 °C, the time of the hydrothermal reaction is 6 h, and the heating rate is 1 °C / min;

[0029] (3) Wash the powder obtained after the hydrothermal reaction in step (2) with a sodium carbonate solution with a concentration of 1 mol / L. After washing, perform vacuum drying treatment on the powder. The drying temperature is 90 °C, and the drying time is 8 h. After drying, the modified sodium-ion battery cathode material is obtained.

[0030] Example 2

[0031] The preparation method of the modified sodium-ion battery cathode material includes the following steps:

[0032] (1) Mix Prussian white and anhydrous oxalic acid with a mass ratio of 30:2, and then, under vacuum conditions, perform dry ball milling using a planetary ball mill. Use agate balls as grinding balls. The rotation speed of the dry ball milling is 170 rpm, the time of the dry ball milling is 3 h, and the ball-to-material ratio of the dry ball milling is 9:1. After dry ball milling, a mixed powder is obtained;

[0033] (2) Add the mixed powder into a polytetrafluoroethylene-lined reactor filled with ethanol. The mass-volume ratio of the added amount of the mixed powder to ethanol is 3:10 mg / mL; then seal the reactor and place it in a muffle furnace for hydrothermal reaction. The temperature of the hydrothermal reaction is 220 °C, the time of the hydrothermal reaction is 8 h, and the heating rate is 2 °C / min;

[0034] (3) Wash the powder obtained after the hydrothermal reaction in step (2) with a sodium carbonate solution with a concentration of 2 mol / L. After the washing is completed, perform vacuum drying treatment on the powder. The drying temperature is 100 °C, and the drying time is 10 h. After drying, the modified sodium-ion battery cathode material is obtained.

[0035] Example 3

[0036] The preparation method of the described modified sodium-ion battery cathode material includes the following steps:

[0037] (1) Mix Prussian white and anhydrous oxalic acid with a mass ratio of 30:3, and then, under vacuum conditions, perform dry ball milling using a planetary ball mill. Use agate balls as grinding balls. The rotation speed of the dry ball milling is 150 rpm, the time of the dry ball milling is 2 h, and the ball-to-material ratio of the dry ball milling is 9:1. After dry ball milling, a mixed powder is obtained;

[0038] (2) Add the mixed powder into a polytetrafluoroethylene-lined reactor filled with ethanol. The mass-volume ratio of the added amount of the mixed powder to ethanol is 2.5:10 mg / mL; then seal the reactor and place it in a muffle furnace for hydrothermal reaction. The temperature of the hydrothermal reaction is 200 °C, the time of the hydrothermal reaction is 10 h, and the heating rate is 1 °C / min;

[0039] (3) Wash the powder obtained after the hydrothermal reaction in step (2) with a sodium carbonate solution with a concentration of 3 mol / L. After the washing is completed, perform vacuum drying treatment on the powder. The drying temperature is 120 °C, and the drying time is 8 h. After drying, the modified sodium-ion battery cathode material is obtained.

[0040] Example 4

[0041] The preparation method of the described modified sodium-ion battery cathode material includes the following steps:

[0042] (1) Mix Prussian white and anhydrous oxalic acid with a mass ratio of 30:2, and then, under vacuum conditions, perform dry ball milling using a planetary ball mill. Use agate balls as grinding balls. The rotation speed of the dry ball milling is 200 rpm, the time of the dry ball milling is 2 h, and the ball-to-material ratio of the dry ball milling is 10:1. After dry ball milling, a mixed powder is obtained;

[0043] (2) Add the mixed powder into a polytetrafluoroethylene-lined reaction kettle filled with ethanol. The mass-volume ratio of the added amount of the mixed powder to ethanol is 2:10 mg / mL; then seal the reaction kettle and place it in a muffle furnace for hydrothermal reaction. The temperature of the hydrothermal reaction is 250 °C, the time of the hydrothermal reaction is 10 h, and the heating rate is 3 °C / min;

[0044] (3) Wash the powder obtained after the hydrothermal reaction in step (2) with a sodium carbonate solution with a concentration of 1 mol / L. After the washing is completed, perform vacuum drying treatment on the powder. The drying temperature is 100 °C, the drying time is 12 h, and the modified sodium-ion battery cathode material is obtained after drying.

[0045] Example 5

[0046] The preparation method of the described modified sodium-ion battery cathode material includes the following steps:

[0047] (1) Mix Prussian white and anhydrous oxalic acid with a mass ratio of 30:1, and then, under vacuum conditions, perform dry ball milling using a planetary ball mill. Use agate balls as grinding balls. The rotation speed of the dry ball milling is 150 rpm, the time of the dry ball milling is 3 h, and the ball-to-material ratio of the dry ball milling is 10:1. After dry ball milling, a mixed powder is obtained;

[0048] (2) Add the mixed powder into a polytetrafluoroethylene-lined reaction kettle filled with ethanol. The mass-volume ratio of the added amount of the mixed powder to ethanol is 3:10 mg / mL; then seal the reaction kettle and place it in a muffle furnace for hydrothermal reaction. The temperature of the hydrothermal reaction is 220 °C, the time of the hydrothermal reaction is 6 h, and the heating rate is 2 °C / min;

[0049] (3) Wash the powder obtained after the hydrothermal reaction in step (2) with a sodium carbonate solution with a concentration of 2 mol / L. After the washing is completed, perform vacuum drying treatment on the powder. The drying temperature is 120 °C, the drying time is 10 h, and the modified sodium-ion battery cathode material is obtained after drying.

[0050] Comparative Example 1

[0051] The difference from Example 1 is that anhydrous oxalic acid is not added in step (1).

[0052] Comparative Example 2

[0053] The difference from Example 2 is that in step (2), the mixed powder is put into a vacuum drying oven, and under vacuum conditions, it is heated to 220°C at a rate of 2°C / min, and the heat preservation time is 8 h.

[0054] The CR2032 coin cells and soft-pack sodium-ion batteries were respectively assembled using the positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-2, as follows:

[0055] The assembly process of the CR2032 coin cell is as follows:

[0056] Using the positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-2 as the positive electrode, sodium foil as the negative electrode, and a GF / A glass fiber separator with a thickness of 290 μm; using NaPF6 as the solute and a mixed solution of EC, DMC, and DEC with a volume ratio of 1:1:1 as the solvent, a NaPF6 solution with a concentration of 1 mol / L was prepared as the electrolyte, and the CR2032 coin cell was assembled. After assembly, it was left standing for 12 h. Under the condition of a current density of 0.1C, it was charged to 4.0V and then discharged to 1.5V to test the specific capacity (mAh / g) of the CR2032 coin cell.

[0057] The assembly process of the soft-pack sodium-ion battery is as follows:

[0058] Using the positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-2 as the positive electrode and hard carbon as the negative electrode, positive electrode sheets with a size of 96 mm×81 mm and negative electrode sheets with a size of 98 mm×83 mm were respectively prepared; using NaPF6 as the solute and a mixed solution of EC, DMC, and DEC with a volume ratio of 1:1:1 as the solvent, a NaPF6 solution with a concentration of 1 mol / L was prepared as the electrolyte; a ceramic separator was used to assemble the soft-pack sodium-ion battery, and the NP ratio was 1.1:1; after assembly, it was left standing for 12 h. Under the condition of a current density of 1C, it was charged to 4.0V and then discharged to 1.5V as one charge-discharge cycle. The capacity retention rate (%) of the soft-pack sodium-ion battery after 50 charge-discharge cycles was tested, and the appearance of the soft-pack sodium-ion battery after 50 charge-discharge cycles was observed.

[0059] The test data are shown in Table 1.

[0060] Table 1 Performance test results

[0061]

[0062] As can be seen from the data in Table 1, the specific capacity of the CR2032 coin cells assembled with the cathode materials prepared in Examples 1-5 is relatively high. After 50 charge-discharge cycles, the capacity retention rate of the pouch sodium-ion batteries assembled with the cathode materials prepared in Examples 1-5 is above 97%, and there is no obvious swelling phenomenon on the appearance of the pouch sodium-ion batteries after 50 charge-discharge cycles.

[0063] Compared with Example 1, in Comparative Example 1, due to the absence of anhydrous oxalic acid, the specific capacity of the CR2032 coin cells assembled with the cathode material of Comparative Example 1 is significantly lower than that of Example 1. After 50 charge-discharge cycles at a current density of 1C, the swelling phenomenon of the pouch sodium-ion batteries assembled with the cathode material of Comparative Example 1 is more obvious, and the capacity retention rate after 50 charge-discharge cycles is lower than that of Example 1. The main reason for this phenomenon is that the addition of anhydrous oxalic acid plays a key role in Example 1: the oxalate forms a complex with the transition metal in Prussian white, inhibiting the formation of the cubic structure of Prussian white, thereby reducing the possibility of water molecules entering the vacancies of the cubic structure and avoiding the formation of Prussian white with crystal water. Therefore, the cathode material in Example 1 exhibits higher structural stability and electrochemical performance in the electrochemical reaction. In Comparative Example 1, due to the lack of this effect of anhydrous oxalic acid, the material structure is unstable, and side reactions are more likely to occur during cycling, generating gas and thus causing an obvious swelling phenomenon.

[0064] Compared with Example 2, in Comparative Example 2, since the hydrothermal reaction was not carried out in step (2), but direct vacuum heating was used for the reaction, the specific capacity of the CR2032 coin cells assembled with the cathode material of Comparative Example 2 is lower than that of Example 2, and the capacity retention rate of the pouch sodium-ion batteries assembled with the cathode material of Comparative Example 2 after 50 charge-discharge cycles is also lower than that of Example 2. This is because the hydrothermal method can provide a high-pressure environment, promoting the more effective formation of stable covalent bonds between the oxalate and the transition metal in Prussian white, thereby optimizing the structure and electrochemical performance of the material. Due to the lack of high-pressure conditions in the direct vacuum heating method, the binding efficiency of the oxalate and the transition metal is low, resulting in poor structural integrity of the material, which in turn affects the overall performance of the battery.

Claims

1. A method for preparing a modified sodium ion battery positive electrode material, characterized in that: The following steps are involved: (1) Prussian white and anhydrous oxalic acid are mixed and dry-milled under vacuum conditions to obtain a mixed powder; (2) adding the mixed powder into a polytetrafluoroethylene-lined reactor filled with ethanol, then sealing the reactor and placing it in a muffle furnace for hydrothermal reaction; (3) washing the powder obtained after the hydrothermal reaction in step (2) with a sodium carbonate solution, and after washing, vacuum drying the powder to obtain a modified sodium ion battery positive electrode material; In the step (1), the mass ratio of Prussian white to anhydrous oxalic acid is 30:(1-3); In the step (2), the temperature of the hydrothermal reaction is 200-250°C, the time of the hydrothermal reaction is 6-10h, and the heating rate is 1-3°C / min; In the step (2), the mass volume ratio of the mixed powder and the added amount of ethanol is (2-3): 10 mg / mL.

2. The method for preparing the modified sodium ion battery positive electrode material according to claim 1, characterized in that: In the step (1), the rotation speed of the dry ball milling is 150-200 rpm, and the time of the dry ball milling is 2-3 hours.

3. The method for preparing the modified sodium ion battery positive electrode material according to claim 1, characterized in that: In the step (1), the ball-to-material ratio of dry ball milling is (8-10):

1.

4. The method for preparing the modified sodium ion battery positive electrode material according to claim 1, characterized in that: In the step (3), the concentration of the sodium carbonate solution is 1-3 mol / L.

5. The method for preparing the modified sodium ion battery positive electrode material according to claim 1, characterized in that: In the step (3), the drying temperature is 90-120°C and the drying time is 8-12 hours.

6. A modified sodium ion battery positive electrode material, characterized in that: The modified sodium ion battery positive electrode material is prepared by the preparation method of any one of claims 1 to 5.

7. An application of the modified sodium ion battery positive electrode material according to claim 6, characterized in that: Used to prepare sodium ion batteries.

Images