CN115832289A - A kind of flexible sodium vanadium manganese phosphate/carbon composite positive electrode material for sodium ion battery and preparation method thereof - Google Patents

Abstract

The invention discloses a flexible vanadium manganese sodium phosphate/carbon composite cathode material for a sodium ion battery and a preparation method thereof. Polyvinylpyrrolidone is dissolved in a proper amount of solvent under the condition of water bath or oil bath to obtain solution A; adding a vanadium source, a manganese source, a sodium source, ammonium dihydrogen phosphate and citric acid monohydrate into deionized water to form a solution B; slowly dripping the solution B into the solution A, and stirring to obtain a spinning solution; and (3) obtaining a flexible spinning membrane from the spinning solution through an electrostatic spinning technology, drying, and calcining to obtain the flexible self-supporting composite anode material. The self-supporting anode with mechanical flexibility and certain electrochemistry is prepared through electrostatic spinning, and meanwhile, the necessity of sodium supplement to the anode and the cathode in the practical application process of the sodium-ion battery is demonstrated by combining the cathode sodium supplement strategy, so that the potential wide application of the vanadium-based vanadium manganese phosphate sodium material in the field of the sodium-ion battery is effectively promoted.

Description

A flexible sodium vanadium manganese phosphate/carbon composite positive electrode material for sodium ion batteries and its Preparation

technical field

The invention relates to the technical field of sodium ion batteries, in particular to a flexible sodium vanadium manganese phosphate/carbon composite positive electrode material for sodium ion batteries and a preparation method thereof.

Background technique

In order to reduce pollution during the use of traditional fossil energy, it is of great significance to develop new chemical batteries and high-efficiency energy storage systems. Sodium-ion batteries are considered to be the most likely to replace or supplement lithium-ion batteries and become the next generation of new energy storage batteries due to their rich sodium resources, low price, and similar working principles to lithium-ion batteries. The electrochemical performance and safety of energy storage batteries mainly depend on the electrode materials and electrolytes used. Among them, the choice of electrode materials, especially the cathode material, largely determines the output voltage, cycle performance, safety and even battery cost that the battery can provide (the cathode accounts for about 35%-40% of the entire battery cost). Currently, cathode materials for Na-ion batteries are mainly classified into the following four categories: layered transition metal oxides, polyanionic compounds, organic compounds, and Prussian blue analogues. Among them, polyanionic compounds have the advantages of stable structure, small volume strain, and fast ion diffusion, which meet the actual needs of the energy storage field. Sodium fast ion conductor (NASICON) type Na ₃ V ₂ (PO ₄ ) ₃ is considered to be a kind with great application potential because of its three-dimensional open structure, fast ion migration ability, high theoretical capacity, and appropriate working potential. positive electrode material. However, due to the high cost and toxicity of vanadium, its cost-effective advantage as a material for energy storage batteries has been weakened. In order to further reduce costs, the development of new low-vanadium phosphate cathodes with long-term cycle stability and high energy density has profound significance for large-scale energy storage applications of sodium-ion batteries. At the same time, the development of flexible devices has also put forward new requirements for energy storage components. At present, flexible sodium-ion batteries are still in the research and exploration stage. Applications in energy storage devices are necessary.

Contents of the invention

The invention provides a method for preparing a flexible sodium vanadium manganese phosphate/carbon composite positive electrode material for a sodium ion battery, comprising the following steps:

(1) Add an appropriate amount of polyvinylpyrrolidone to a certain amount of solvent to obtain solution A;

(2) Weigh vanadium source, manganese source, sodium source, ammonium dihydrogen phosphate, citric acid, add deionized water and stir to obtain solution B;

(3) Slowly add solution B dropwise to solution A, and stir to obtain spinning solution;

(4) Electrospinning the spinning solution to obtain a yellow-white flexible spinning film;

(5) Drying, pre-oxidizing and sintering the flexible spinning membrane to obtain the black vanadium manganese sodium phosphate/carbon composite positive electrode material.

Further, the solvent in the step (1) is at least one of deionized water or absolute ethanol.

Further, in the step (2), the vanadium source is vanadium pentoxide or ammonium metavanadate, the manganese source is manganese acetate tetrahydrate, and the sodium source is sodium acetate trihydrate.

Further, the operation of the step (4) is as follows: draw 8mL of spinning liquid, adjust the voltage of the electrospinning machine to 25-28kV, the propulsion flow rate to 0.5-1mL/h, the collection speed to 800rpm, and the needle head to and fro distance to 80- 100mm, the outer diameter of the needle is 0.4-1.0mm, and the distance between the needle and the collector is 15cm.

Further, in the step (5), the flexible spinning membrane is pre-oxidized in air at 250-300°C for 0.5-2h; the sintering temperature is 700-850°C, the sintering time is 6-12h, and the protective atmosphere is nitrogen or argon .

The invention provides a flexible sodium vanadium manganese phosphate/carbon composite cathode material for a sodium ion battery prepared by the above preparation method.

Further, the positive electrode material is a NASICON vanadium-based phosphate structure.

The invention provides a flexible sodium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is made of the above-mentioned positive electrode material, and the positive electrode or negative electrode of the battery is supplemented with sodium.

Beneficial effects of the present invention:

Through the combination of electrospinning and pre-oxidation preparation techniques, a self-supporting positive electrode with electrochemical properties and flexibility is constructed, which promotes the wide potential application of vanadium manganese vanadium manganese phosphate materials in the field of sodium ion batteries. Combined with the positive and negative sodium supplementation strategy, the necessity of sodium supplementation to the positive and negative electrodes in the practical application of sodium ion batteries is illustrated.

On the one hand, the technology of the present invention provides a flexible self-supporting positive electrode, and on the other hand, it provides the assembly application of flexible sodium-ion batteries, which is expected to promote the practical process of flexible sodium-ion batteries.

Description of drawings

Fig. 1 is the sample picture prepared by embodiment 1;

Fig. 2 is the prepared sample picture of embodiment 2;

Fig. 3 is the circular pole piece that the sample prepared in embodiment 1 is cut into;

Fig. 4 is the XRD figure of the sample prepared in embodiment 1;

Fig. 5 is the SEM figure of the sample prepared in embodiment 1;

Fig. 6 is the charge-discharge curve of the button sodium-ion half-cell composed of the composite positive electrode obtained in Example 1 in Example 5 at a rate of 0.2C;

Fig. 7 is the charge-discharge curve of embodiment 6 button sodium-ion full battery under 0.1C rate;

Fig. 8 is the charge-discharge curve of the button sodium-ion full battery of Example 7 at a rate of 0.1C;

Fig. 9 is the flexible soft pack sodium-ion battery gained in embodiment 8;

Figure 10 is the charge and discharge curve of the flexible pouch battery obtained in Example 8 at a rate of 0.2C.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention easier to understand, the present invention will be described in detail below in conjunction with specific embodiments.

In the following examples, the required reagents are commercially available products of analytical grade. The electrospinning equipment used in the examples is the nano electrospinning machine NANON-01A produced by Japan MECC.

Example 1

The preparation method of the flexible sodium vanadium manganese phosphate/carbon composite positive electrode material for the sodium ion battery of the present embodiment comprises the following steps:

(1) Weigh 0.8g of polyvinylpyrrolidone (PVP) and 4mL of absolute ethanol, and magnetically stir in an oil bath at 60°C for 1 hour to obtain solution A;

(2) Weigh 0.576g of citric acid and dissolve it in 4mL of deionized water, add 0.117g of ammonium metavanadate, 0.245g of manganese acetate, 0.345g of ammonium dihydrogen phosphate and 0.544g of sodium acetate in sequence, and stir magnetically in an oil bath at 60°C to obtain a solution b. Slowly add solution B to solution A dropwise, and stir overnight at room temperature to obtain a transparent spinning solution;

(3) Adjust the voltage of the electrospinning machine to 28kV, the propulsion flow rate to 0.5mL/h, the collection speed to 800rpm, the round-trip distance of the needle to 80mm, the outer diameter of the needle to 0.6mm, and the distance between the needle and the tin foil collector to 15cm.

(4) Slowly peel off the spun film from the tinfoil paper, vacuum-dry the spun film at 100°C, pre-oxidize at 300°C for 2 hours, and calcinate at 700°C under nitrogen protection for 6 hours to obtain the sodium vanadium manganese phosphate/carbon composite positive electrode material (see figure 1).

Example 2

The preparation method of the flexible sodium vanadium manganese phosphate/carbon composite positive electrode material for the sodium ion battery of the present embodiment comprises the following steps:

This example is the same as Example 1, except that the pre-oxidation process is omitted in step (4), so that the sodium vanadium manganese phosphate/carbon composite positive electrode material is obtained (see FIG. 2 ).

Example 3

The preparation method of the flexible sodium vanadium manganese phosphate/carbon composite positive electrode material for the sodium ion battery of the present embodiment comprises the following steps:

(1) Weigh 3.0g of polyvinylpyrrolidone (PVP) and 15mL of deionized water, and magnetically stir in a water bath at 80°C for 2 hours to obtain solution A;

(2) Weigh 2.306g of citric acid and dissolve it in 8mL of deionized water, add 0.468g of ammonium metavanadate, 0.980g of manganese acetate, 1.380g of ammonium dihydrogen phosphate and 2.177g of sodium acetate in sequence, and stir magnetically to obtain solution B. Slowly add solution B dropwise to solution A, and stir overnight to obtain a transparent spinning solution;

(3) Install two syringes on the nozzle, absorb 8mL of spinning solution respectively, adjust the voltage of the electrospinning machine to 25kV, the propulsion flow rate to 1.0mL/h, the collection speed to 800rpm, the needle head to and fro distance to 100mm, the needle outer diameter 1.0mm, the distance between the needle and the tin foil collector is 15cm.

(4) The spun film was slowly peeled off from the tin foil paper, and the spun film was vacuum-dried at 100°C, pre-oxidized at 280°C for 1 hour, and calcined at 800°C for 8 hours under the protection of argon to obtain the sodium vanadium manganese phosphate/carbon composite positive electrode material.

Example 4

The preparation method of the flexible sodium vanadium manganese phosphate/carbon composite positive electrode material for the sodium ion battery of the present embodiment comprises the following steps:

(1) Weigh 0.5g of polyvinylpyrrolidone (PVP) and 5mL of deionized water, and magnetically stir in a water bath at 80°C for 2 hours to obtain solution A;

(2) Weigh 0.720g of citric acid and dissolve it in 15mL of deionized water, add 0.227g of vanadium pentoxide, stir magnetically in a water bath at 80°C, wait until a transparent solution is obtained, then lower the temperature to room temperature, add 0.613g of manganese acetate, 0.863 g ammonium dihydrogen phosphate and 0.820 g sodium acetate to obtain solution B. Slowly add solution B dropwise to solution A, and stir overnight to obtain a transparent spinning solution;

(3) Install two syringes on the nozzle, absorb 8mL of spinning liquid respectively, adjust the voltage of the electrospinning machine to 25kV, the propulsion flow rate to 0.8mL/h, the collection speed to 800rpm, the needle head to and fro distance to 100mm, the needle outer diameter 0.8mm, the distance between the needle and the tin foil collector is 15cm.

(4) The spun film was slowly peeled off from the tin foil paper, and the spun film was vacuum-dried at 100°C, pre-oxidized at 250°C for 2 hours, and calcined at 750°C for 12 hours under nitrogen protection to obtain the sodium vanadium manganese phosphate/carbon composite positive electrode material.

Example 5

The sodium ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is a glass cellulose membrane, the electrolyte is 1M NaClO ₄ dissolved in ethylene carbonate/propylene carbonate (EC/PC, mass ratio 1:1), and then 5% fluoroethylene carbonate (FEC) is added as additive.

The preparation method of this sodium ion battery comprises the steps:

(1) The sodium vanadium manganese phosphate/carbon composite material obtained in Examples 1-4 was directly cut into an electrode with a diameter of 12 mm by a punching machine to obtain a positive electrode sheet.

(2) The counter electrode is a metal sodium sheet with a diameter of 14 mm, and a button sodium ion battery is assembled according to the button battery assembly method in the prior art.

Example 6

The sodium ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The diaphragm is polyethylene film (PE), the electrolyte is 1M NaPF ₆ dissolved in ethylene carbonate/diethyl carbonate (EC/DEC, mass ratio 1:1), and then 5% fluoroethylene carbonate ( FEC) as an additive.

(1) The positive electrode is the sodium vanadium manganese phosphate/carbon composite material obtained in Example 1, and the composite material is cut into electrodes with a diameter of 12 mm to obtain a positive electrode sheet.

(2) The flexible carbon nanofiber cloth is also cut into an electrode with a diameter of 12 mm to obtain a negative electrode sheet.

The above-mentioned flexible carbon nanofiber cloth is prepared by a method comprising the following steps:

Dissolve 1.0 g of polyacrylonitrile (PAN) in 10 mL of N,N-dimethylformamide (DMF), and stir at 60 ^o C overnight to obtain a transparent solution. The PAN electrospun fiber cloth was prepared by electrospinning, the working voltage was 18kV, and the product was received by tin foil. The collected PAN electrospun fiber cloth was pre-oxidized in air at 280 °C for 1 h to obtain a relatively stable structure, and then carbonized in a tube furnace under nitrogen to obtain a flexible carbon nanofiber cloth.

(3) With the above-mentioned positive and negative electrodes as the positive and negative electrodes, 1M NaPF ₆ solution as the electrolyte, and PE as the separator, a button sodium-ion full battery was assembled according to the assembly method of the button battery in the prior art.

Example 7

The sodium ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The diaphragm is polyethylene film (PE), the electrolyte is 1M NaPF ₆ dissolved in ethylene carbonate/diethyl carbonate (EC/DEC, mass ratio 1:1), and then 5% fluoroethylene carbonate ( FEC) as an additive.

(1) The positive electrode is the sodium vanadium manganese phosphate/carbon composite material obtained in Example 1, and a certain concentration of Na ₂ C ₂ O ₄ solution is added dropwise on one side of the material, vacuum dried and rolled, and finally the composite material is punched into a diameter of 12mm electrode to make a positive electrode sheet.

(2) The flexible carbon nanofiber cloth was also punched into an electrode with a diameter of 12 mm to prepare a negative electrode sheet.

The above-mentioned flexible carbon nanofiber cloth is obtained according to Example 6.

(3) Use the above-mentioned positive electrode sheet and negative electrode sheet as the positive electrode and the negative electrode respectively, use 1M NaPF ₆ solution as the electrolyte, and PE as the separator, and assemble button sodium-ion batteries according to the assembly method of button batteries in the prior art.

Example 8

The sodium ion battery of this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The diaphragm is polypropylene film (PP), the electrolyte is 1M NaClO ₄ dissolved in ethylene carbonate/diethyl carbonate (EC/DEC, mass ratio 1:1), and then 2% fluoroethylene carbonate ( FEC) as an additive.

(1) The positive electrode is the sodium vanadium manganese phosphate/carbon composite material obtained in Example 1, and the composite material is cut into rectangular pieces with a size of 1×2 cm ² to obtain the positive electrode piece.

(2) The flexible carbon nanofiber cloth is also cut into a rectangular sheet with a size of 1 × 2 cm ² , and the negative electrode sheet is obtained after dropping the electrolyte on the sheet and directly shorting the metal sodium sheet.

The above-mentioned flexible carbon nanofiber cloth is obtained according to Example 6.

(3) Use the above-mentioned positive electrode sheet and negative electrode sheet as the positive electrode and the negative electrode respectively, and use double-sided conductive copper foil tape as the positive and negative electrode lugs, use 1M NaClO ₄ solution as the electrolyte, and use PP as the diaphragm. According to the existing technology The flexible sodium-ion battery is assembled by the aluminum-plastic film soft pack assembly method.

Test case

(1) Physical property test

1) Flexible detection

Compare the flexibility of the vanadium manganese sodium manganese phosphate/carbon composite positive electrode material prepared in Examples 1 and 2. It can be seen from the picture that the sample obtained in Example 1 is more flexible than Example 2, and the sample in Example 1 can be punched into diameter It is a 12mm electrode sheet (see Figure 3), and the edge of the sample in Example 2 is easy to drop during the punching process.

2) XRD test

The sodium vanadium manganese phosphate/carbon composite positive electrode prepared in Example 1 was tested by XRD, and the results are shown in FIG. 4 . It can be seen from Figure 4 that the product is mainly the characteristic peak of sodium vanadium manganese phosphate, and the broad peak between 15-25 ^° is the characteristic peak of amorphous carbon, indicating that the prepared material is sodium vanadium manganese phosphate/carbon composite material, and the TG The analyzed carbon content is about 18%.

3) SEM test

The sodium vanadium manganese phosphate/carbon composite positive electrode prepared in Example 1 was tested by SEM, and the test results are shown in FIG. 5 . It can be seen from the figure that the composite positive electrode material forms a porous network structure. Its one-dimensional structure facilitates electron transport, and the porous structure facilitates the extraction and insertion of sodium ions. The three-dimensional network structure makes the material flexible.

(2) Electrochemical performance test

1) Half-cell performance test

Table 1 The electrochemical performance test results of the sodium ion half-cell composed of the materials obtained in Examples 1-4

Discharge specific capacity (mAh/g) First Coulombic Efficiency (%) Example 1 90 96.0 Example 2 84 95.5 Example 3 87 95.7 Example 4 91 95.3

At room temperature, the button half-cell prepared in Example 5 was used for charge and discharge test. The charge and discharge current was 0.2C (22mA/g), the charge cut-off voltage was 3.8V, and the discharge cut-off voltage was 2.5V. The test results are shown in Table 1 shown. As can be seen from the table, the sodium ion half-cell discharge specific capacity made by the composite positive electrode made in Examples 1, 3 and 4 is basically 90mAh/g, and the carbon content is about 18% by the aforementioned thermogravimetric analysis, so that the active material can be calculated The capacity of sodium vanadium manganese phosphate is about 110mAh/g, basically close to its theoretical capacity of 111mAh/g. At the same time, it can be seen that the first charge and discharge coulombic efficiencies of the materials obtained in Examples 1-4 are relatively high, all above 95%, and high coulombic efficiency is an important indicator that the materials have practical applications. In addition, the first three charge and discharge curves of the sodium ion battery obtained in Example 1 are shown in Figure 6. It can be seen from the figure that the first three charge curves of the battery are almost coincident, and the first three discharge curves are also almost coincident. The obtained composite cathode material has good structural stability and flexibility. The low discharge specific capacity of the material obtained in Example 2 is due to the poor flexibility of the composite positive electrode material due to the omission of the pre-oxidation process, and the quality error caused by the easy drop of the edge of the electrode sheet during the battery manufacturing process. The higher discharge specific capacity of the composite positive electrode material obtained in Example 4 is due to the higher crystallinity of the material caused by the higher sintering temperature and longer sintering time. For battery materials, high crystallinity is beneficial to the capacity of the material, but if the temperature is too high and the heating time is too long, the flexibility of the material will deteriorate.

2) Full battery performance test

The button sodium ion full battery assembled in Example 6 was charged and discharged at a current density of 0.1C, and the charge and discharge cut-off voltage was 2.5-4.0V. The obtained charge and discharge curves are shown in FIG. 7 . It can be seen from the figure that the initial voltage of the full battery is low, the initial reversible capacity is about 81mAh/g, and the initial charge and discharge Coulombic efficiency is low, only 79%. Extreme efficiency matching problem. The button full battery assembled in Example 7 is also charged and discharged at a current density of 0.1C. The first charge cut-off voltage is 4.3V, and the discharge cut-off voltage is 2.5V. Afterwards, the charge-discharge cut-off voltage is 2.5-4.0V. The discharge curve is shown in Figure 8. It can be seen from the figure that the first charge and discharge coulombic efficiency of the full battery is very low, which is mainly caused by the oxidative decomposition of the sodium supplement material sodium oxalate at a higher voltage. Compared with Example 6, the gram capacity of the material is slightly increased, and the first reversible capacity is about 85mAh/g, which shows that adding sodium supplement material to the positive electrode material has a certain capacity improvement effect. The flexible sodium ion full battery assembled in Example 8 (see Figure 9) was charged and discharged at a current density of 0.2C, and the charge and discharge cut-off voltage was 2.4-3.8V. The obtained charge and discharge curves are shown in Figure 10. It can be seen from the figure that the first-time Coulombic efficiency of the full battery is about 92%, which is mainly due to the pre-sodium treatment of the negative electrode, which improves the first-time efficiency of the whole battery. In addition, the first three charge-discharge curves of flexible full batteries are in good agreement, indicating good cycle stability, which also reveals that sodium supplementation measures for negative or positive electrodes should be considered in the practical application of sodium-ion batteries.

Claims (8)

1. A preparation method of a flexible vanadium manganese phosphate sodium/carbon composite positive electrode material for a sodium ion battery is characterized by comprising the following steps:

(1) Adding a proper amount of polyvinylpyrrolidone into a certain amount of solvent to obtain a solution A;

(2) Weighing a vanadium source, a manganese source, a sodium source, ammonium dihydrogen phosphate and citric acid, adding deionized water and stirring to obtain a solution B;

(3) Slowly dripping the solution B into the solution A, and stirring to obtain a spinning solution;

(4) Electrostatic spinning is carried out on the spinning solution to obtain a yellow-white flexible spinning film;

(5) And drying, pre-oxidizing and sintering the flexible spinning membrane at high temperature to obtain the black vanadium manganese sodium phosphate/carbon composite anode material.

2. The method for preparing the flexible vanadium manganese phosphate sodium/carbon composite cathode material for the sodium-ion battery according to claim 1, wherein the solvent in the step (1) is at least one of deionized water or absolute ethyl alcohol.

3. The method for preparing the flexible vanadium manganese phosphate sodium/carbon composite cathode material for the sodium-ion battery according to claim 1, wherein in the step (2), the vanadium source is vanadium pentoxide or ammonium metavanadate, the manganese source is manganese acetate tetrahydrate, and the sodium source is sodium acetate trihydrate.

4. The preparation method of the flexible vanadium manganese sodium phosphate/carbon composite cathode material for the sodium-ion battery, according to claim 1, is characterized in that the operation of the step (4) is as follows: sucking 8mL of spinning solution, adjusting the voltage of an electrostatic spinning machine to be 25-28kV, the propelling flow rate to be 0.5-1mL/h, the collecting rotation speed to be 800rpm, the needle reciprocating distance to be 80-100mm, the needle outer diameter to be 0.4-1.0mm, and the distance between the needle and the collector to be 15cm.

5. The preparation method of the flexible vanadium manganese sodium phosphate/carbon composite cathode material for the sodium-ion battery as claimed in claim 1, wherein in the step (5), the flexible spinning membrane is pre-oxidized in air at 250-300 ℃ for 0.5-2h; the sintering temperature is 700-850 ℃, the sintering time is 6-12h, and the atmosphere is nitrogen or argon.

6. A flexible vanadium manganese phosphate sodium/carbon composite anode material for a sodium ion battery is characterized in that: the positive electrode material is produced by the production method according to any one of claims 1 to 5.

7. The flexible vanadium manganese sodium phosphate/carbon composite positive electrode material for the sodium ion battery as claimed in claim 6, wherein the positive electrode material is of NASICON type vanadium-based phosphate structure.

8. A flexible sodium-ion battery, which comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, and is characterized in that the positive electrode of the battery is made of the positive electrode material of claim 7, and the positive electrode or the negative electrode of the battery is subjected to sodium supplement measures.

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