High-power long-life sodium ion battery and preparation method thereof

Abstract

The invention relates to the technical field of electrochemical energy storage, and particularly discloses a high-power long-life sodium ion battery and a preparation method thereof. The preparation method of the sodium ion battery comprises the following steps: mixing NaFePO4 with a positive electrode binder and a positive electrode conductive agent to obtain positive electrode slurry; the particle size D50 of the NaFePO4 is 0.5 to 1 [mu] m; coating a positive electrode current collector with the positive electrode slurry, and drying to obtain a positive plate; the mass ratio of the polymer solute in the positive electrode binder is 10-15%; mixing hard carbon with a negative electrode binder and a negative electrode conductive agent to obtain negative electrode slurry; coating a negative electrode current collector with the negative electrode slurry, and drying to obtain a negative electrode plate; and infiltrating the positive plate, the negative plate and the diaphragm in the electrolyte, and packaging to obtain the sodium ion battery. The small-particle-size NaFePO4 improves the de-intercalation speed of sodium ions, and the low-concentration and high-total-amount positive electrode binder is beneficial to the formation of multiple micropores and promotes the migration of sodium ions, so that the battery has higher power and longer cycle life.

Description

Technical Field

[0001] The present application relates to the field of electrochemical energy storage technology, and in particular to a high-power, long-life sodium ion battery and a preparation method thereof. Background Art

[0002] With the rapid development of the new energy industry, the demand for efficient energy storage equipment is growing. At present, the mainstream energy storage technology on the market is still dominated by lithium-ion batteries, but lithium resources are limited and prices fluctuate greatly, prompting the industry to seek alternatives. Sodium-ion batteries have attracted much attention due to their abundant resources and low costs, but early sodium-ion batteries generally have problems such as poor cycle stability and poor rate performance. With the advancement of technology, sodium-ion batteries have greatly improved in capacity and cycle life. However, at present, sodium-ion batteries have low working efficiency at high power density and slow charging speed, which makes it difficult to meet the needs of high-performance energy storage systems. Summary of the invention

[0003] In view of the fact that the current sodium-ion batteries have low working efficiency and slow charging speed at high power density, and are difficult to meet the needs of high-performance energy storage systems, this application proposes the following technical solutions.

[0004] A method for preparing a high-power and long-life sodium ion battery comprises the following steps.

[0005] NaFePO4 is uniformly mixed with a positive electrode binder and a positive electrode conductor in a mass ratio of 10:(2-3):(0.5-1.5) to obtain a positive electrode slurry; the particle size D50 of the NaFePO4 is 0.5-1 μm; the positive electrode slurry is coated on a positive electrode collector, and a positive electrode sheet is obtained after drying and curing; wherein the positive electrode binder includes a polymer solute and a solvent, and the mass proportion of the polymer solute in the positive electrode binder is 10-15%.

[0006] The hard carbon is mixed evenly with the negative electrode binder and the negative electrode conductive agent to obtain a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and dried and solidified to obtain a negative electrode sheet.

[0007] The positive electrode sheet, the negative electrode sheet and the separator are immersed in an electrolyte and packaged into a sodium ion battery.

[0008] By adopting the above technical solution, using NaFePO4 with a small particle size, so that its specific surface area is large and the sodium ions are fully exposed, it is applied to sodium ion batteries, which is conducive to improving the speed of sodium ion extraction and back-insertion into the positive electrode, thereby improving the ability to output large current in a short time and improving the working efficiency of sodium ion batteries at high power density. When the sodium ion battery is charged, the sodium ions are extracted from the positive electrode, the positive electrode potential increases, and at the same time, the sodium ions further migrate to the negative electrode surface in the electrolyte and embed into the negative electrode active material hard carbon. In this process, electrons flow from the positive electrode to the negative electrode through the external circuit, causing the negative electrode potential to decrease, thereby increasing the voltage difference between the positive and negative electrodes and realizing the charging of the sodium ion battery. This solution increases the speed of sodium ion extraction and back-insertion into the positive electrode, thereby increasing the charging and discharging speed. After the positive current collector is dried and solidified, the solvent of the positive electrode binder is evaporated, and more micropores are obtained. These micropores are conducive to the penetration of the electrolyte, thereby promoting the migration of sodium ions. The mass ratio of NaFePO4 to the positive electrode binder and the positive electrode conductor is 10:(2-3):(0.5-1.5), and the mass proportion of the polymer solute in the positive electrode binder is 10-15%. The lower concentration and higher total amount of the positive electrode binder can not only have a better adhesion effect on NaFePO4 after drying, reducing the powdering and cracking of the positive electrode material on the positive electrode sheet, but also facilitate the formation of more micropores after drying, which is conducive to the infiltration of the electrolyte and promotes the migration of sodium ions. The above design makes the sodium ion migration resistance small and the migration speed fast, so that the sodium ion battery has higher power and cycle life.

[0009] A preferred solution of the preparation method of the high-power and long-life sodium ion battery is that the polymer solute is polyvinylidene fluoride; the molecular weight of the polyvinylidene fluoride is 500,000 to 1,000,000.

[0010] By adopting the above technical scheme, small-particle NaFePO4 and large-molecule polyvinylidene fluoride cooperate with each other. The large-molecule polyvinylidene fluoride is dispersed in NaFePO4 to form more gaps, which is conducive to the formation of more micropores after the solvent dries. In addition, polyvinylidene fluoride is uncharged, has low adsorption force on sodium ions, and has little binding effect on sodium ions. Sodium ions can easily leave the positive electrode and enter the electrolyte. The above together improve the charging and discharging speed.

[0011] A preferred solution of the preparation method of the high-power and long-life sodium-ion battery is that before coating the positive electrode slurry on the positive electrode collector, the positive electrode collector is first heated to a temperature above the melting point and below the boiling point of the polymer solute, and the heating temperature is lower than the melting point of the positive electrode collector, and then the positive electrode slurry is coated on the positive electrode collector.

[0012] By adopting the above technical solution, at the contact surface between the positive electrode slurry and the positive electrode collector, the polymer solute melts on the surface of the positive electrode collector, thereby enhancing the mutual bonding force, reducing the contact resistance between the positive electrode material and the positive electrode collector, and improving the power density and charging speed of the battery.

[0013] A preferred solution of the preparation method of the high-power and long-life sodium-ion battery is that the electrolyte is an aqueous electrolyte; and the negative electrode binder is a polymer material with a negative charge on the surface in water.

[0014] By adopting the above technical solution, the negative electrode binder has an attractive effect on sodium ions, thereby increasing the speed at which sodium ions are embedded in the negative electrode during charging, thereby increasing the charging speed.

[0015] A preferred solution of the preparation method of the high-power and long-life sodium-ion battery is that the negative electrode binder is a carboxymethyl cellulose solution or a hydroxyethyl cellulose solution.

[0016] By adopting the above technical solution, these celluloses contain groups such as uronic acid groups and polar hydroxyl groups. These groups are usually negatively charged on the surface in water. These groups will adsorb positive charges, such as sodium ions, in aqueous solution, and accelerate the embedding of sodium ions into the negative electrode.

[0017] A preferred solution of the preparation method of the high-power and long-life sodium ion battery is that the mass concentration of the polymer material in the negative electrode binder is 0.5-1%. The hard carbon, the negative electrode binder and the negative electrode conductive agent are mixed in a mass ratio of 8: (0.5-1.5): (0.5-1.5).

[0018] By adopting the above technical solution, the negative electrode binder with a lower proportion and lower concentration is not easy to block the nanopore structure of the hard carbon, thereby protecting the hard carbon's good ability to store sodium ions, maintaining the hard carbon's higher reversible specific capacity, and improving the battery's cycle performance.

[0019] A preferred solution of the preparation method of the high-power and long-life sodium-ion battery is that the raw materials for preparing the positive electrode slurry also include N-phthalylglycine; NaFePO4 is evenly mixed with the positive electrode binder, the positive electrode conductor, and N-phthalylglycine in a mass ratio of 10:(2-3):(0.5-1.5):(0.1-0.2) to obtain the positive electrode slurry.

[0020] By adopting the above technical scheme, N-phthaloylglycine is doped in the positive electrode. The hydrophilic carboxyl group in N-phthaloylglycine promotes the wetting effect of the electrolyte on the microporous surface of the positive electrode. The benzene heterocycle has a water-repellent effect, which reduces the excessive penetration of water into the bonding structure, reduces the damage to the positive electrode structure caused by battery charging and discharging, and improves the battery's cycle capacity retention rate and power density.

[0021] A preferred solution of the preparation method of the high-power and long-life sodium-ion battery is that the positive electrode conductive agent is acetylene black, carbon nanotubes or Ketjen black; the negative electrode conductive agent is acetylene black, carbon nanotubes or Ketjen black; the D50 particle size of the acetylene black is 30 to 45 nm; the D50 length of the carbon nanotubes is 10 to 30 μm; and the D50 particle size of the Ketjen black is 20 to 100 nm.

[0022] By adopting the above technical solution, acetylene black, carbon nanotubes or Ketjen black of this size have good conductivity and stability.

[0023] A preferred solution of the preparation method of the high-power and long-life sodium-ion battery is that the solute of the electrolyte is NaPF6, and the solvent is a mixture of monomethyl acrylate, ethylene glycol dimethyl ether and methanol; the concentration of NaPF6 in the electrolyte is 0.5M to 1.5M; hydroquinone monomethyl ether is also added to the electrolyte, and the mass concentration of hydroquinone monomethyl ether in the electrolyte is 0.05 to 0.15%.

[0024] By adopting the above technical solution, hydroquinone monomethyl ether can effectively inhibit the oxidative decomposition of the electrolyte under high voltage, thereby improving the cycle life of the battery. A high-power and long-life sodium ion battery is prepared according to the above preparation method.

[0025] By adopting the above technical solution, the sodium ions of the battery can quickly detach from the positive electrode during charging, thereby increasing its power. The cycle life of the battery can be increased by designing a suitable raw material ratio, adding N-phthalylglycine, etc.

[0026] In summary, the high-power and long-life sodium ion battery and its preparation method of the present application have the following beneficial effects: by designing the ratio of NaFePO4 to the positive electrode binder and the positive electrode conductive agent, a positive electrode with a stable structure and rich in micropores is formed, which is conducive to the penetration of the electrolyte into the positive electrode and the formation of a thicker SEI film during the first charge and discharge, thereby facilitating the rapid detachment and embedding of sodium ions into the electrode, improving the cycle stability and service life of the positive electrode, thereby improving the rate performance and power density of the battery. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the following embodiments, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0028] Example 1 In this embodiment, a high-power and long-life sodium ion battery is prepared by the following steps.

[0029] Preparation of positive electrode slurry: NaFePO4 is evenly mixed with positive electrode binder and positive electrode conductor in a mass ratio of 10:2.5:1 to obtain positive electrode slurry. Among them, the particle size D50 of NaFePO4 is 0.8μm. The positive electrode binder includes a polymer solute and a solvent. The polymer solute is polyvinylidene fluoride. DMF (tetrahydrofuran) is used as the solvent. The mass proportion of polyvinylidene fluoride in the positive electrode binder is 12%, and complete dissolution is achieved by heating. The molecular weight of polyvinylidene fluoride is 700,000. The positive electrode conductor is acetylene black, and the D50 particle size of acetylene black is 38nm.

[0030] Preparation of positive electrode sheet: The positive electrode slurry is coated on the positive electrode current collector, and the positive electrode sheet is obtained after drying and curing. The positive electrode current collector is an aluminum foil with a thickness of 0.1 mm. The coating thickness of the positive electrode slurry on the positive electrode current collector is 50 μm.

[0031] Preparation of negative electrode slurry: Hard carbon, negative electrode binder and negative electrode conductor are mixed evenly in a mass ratio of 8:1:1 to obtain negative electrode slurry. The D50 particle size of hard carbon is 46nm. The negative electrode binder is a carboxymethyl cellulose aqueous solution, and the mass proportion of carboxymethyl cellulose in the negative electrode binder is 0.7%. The negative electrode conductor is carbon nanotubes, and the D50 length of the carbon nanotubes is 22μm.

[0032] Preparation of negative electrode sheet: The negative electrode slurry is coated on the negative electrode current collector, baked at 155°C for 1 hour, and dried and solidified to obtain the negative electrode sheet. The coating thickness of the negative electrode slurry on the negative electrode current collector is 50 μm. The negative electrode current collector is an aluminum foil with a thickness of 0.1 mm.

[0033] Prepare electrolyte: the solute of the electrolyte is NaPF6, and the solvent is a mixture of monomethyl acrylate, ethylene glycol dimethyl ether and methanol in a volume ratio of 1:1:1; the concentration of NaPF6 in the electrolyte is 1M; hydroquinone monomethyl ether is also added to the electrolyte, and the mass concentration of hydroquinone monomethyl ether in the electrolyte is 0.1%.

[0034] Prepare the battery: immerse the positive electrode sheet, negative electrode sheet and polyethylene separator in the electrolyte and encapsulate them into a sodium ion battery.

[0035] Example 2 In this embodiment, a high-power and long-life sodium ion battery is prepared by the following steps.

[0036] Preparation of positive electrode slurry: NaFePO4 is evenly mixed with positive electrode binder and positive electrode conductor in a mass ratio of 10:2:1.5 to obtain positive electrode slurry. Among them, the particle size D50 of NaFePO4 is 0.5μm. The positive electrode binder includes a polymer solute and a solvent. The polymer solute is polyvinylidene fluoride. DMF (tetrahydrofuran) is used as the solvent. The mass proportion of polyvinylidene fluoride in the positive electrode binder is 10%, and complete dissolution is achieved by heating. The molecular weight of polyvinylidene fluoride is 500,000. The positive electrode conductor is acetylene black, and the D50 particle size of acetylene black is 38nm.

[0037] Preparation of positive electrode sheet: The positive electrode slurry is coated on the positive electrode current collector, and the positive electrode sheet is obtained after drying and curing. The positive electrode current collector is an aluminum foil with a thickness of 0.1 mm. The coating thickness of the positive electrode slurry on the positive electrode current collector is 50 μm.

[0038] Preparation of negative electrode slurry: Hard carbon, negative electrode binder and negative electrode conductor are mixed evenly in a mass ratio of 8:1:1 to obtain negative electrode slurry. The D50 particle size of hard carbon is 46nm. The negative electrode binder is a carboxymethyl cellulose aqueous solution, and the mass proportion of carboxymethyl cellulose in the negative electrode binder is 0.5%. The negative electrode conductor is carbon nanotubes, and the D50 length of the carbon nanotubes is 22μm.

[0039] Preparation of negative electrode sheet: The negative electrode slurry is coated on the negative electrode current collector, baked at 155°C for 1 hour, and dried and solidified to obtain the negative electrode sheet. The coating thickness of the negative electrode slurry on the negative electrode current collector is 50 μm. The negative electrode current collector is an aluminum foil with a thickness of 0.1 mm.

[0040] Prepare electrolyte: the solute of the electrolyte is NaPF6, and the solvent is a mixture of monomethyl acrylate, ethylene glycol dimethyl ether and methanol in a volume ratio of 1:1:1; the concentration of NaPF6 in the electrolyte is 1M; hydroquinone monomethyl ether is also added to the electrolyte, and the mass concentration of hydroquinone monomethyl ether in the electrolyte is 0.1%.

[0041] Prepare the battery: immerse the positive electrode sheet, negative electrode sheet and polyethylene separator in the electrolyte and encapsulate them into a sodium ion battery.

[0042] Example 3 In this embodiment, a high-power and long-life sodium ion battery is prepared by the following steps.

[0043] Preparation of positive electrode slurry: NaFePO4 is evenly mixed with positive electrode binder and positive electrode conductor in a mass ratio of 10:3:0.5 to obtain positive electrode slurry. Among them, the particle size D50 of NaFePO4 is 1μm. The positive electrode binder includes a polymer solute and a solvent. The polymer solute is polyvinylidene fluoride. DMF (tetrahydrofuran) is used as the solvent. The mass proportion of polyvinylidene fluoride in the positive electrode binder is 15%, and complete dissolution is achieved by heating. The molecular weight of polyvinylidene fluoride is 1 million. The positive electrode conductor is acetylene black, and the D50 particle size of acetylene black is 38nm.

[0044] Preparation of positive electrode sheet: The positive electrode slurry is coated on the positive electrode current collector, and the positive electrode sheet is obtained after drying and curing. The positive electrode current collector is an aluminum foil with a thickness of 0.1 mm. The coating thickness of the positive electrode slurry on the positive electrode current collector is 50 μm.

[0045] Preparation of negative electrode slurry: Hard carbon, negative electrode binder and negative electrode conductive agent are mixed evenly in a mass ratio of 8:1:1 to obtain negative electrode slurry. The D50 particle size of hard carbon is 46nm. The negative electrode binder is a hydroxyethyl cellulose aqueous solution, and the mass proportion of hydroxyethyl cellulose in the negative electrode binder is 1%. The negative electrode conductive agent is carbon nanotubes, and the D50 length of the carbon nanotubes is 22μm.

[0046] Preparation of negative electrode sheet: The negative electrode slurry is coated on the negative electrode current collector, baked at 155°C for 1 hour, and dried and solidified to obtain the negative electrode sheet. The coating thickness of the negative electrode slurry on the negative electrode current collector is 50 μm. The negative electrode current collector is an aluminum foil with a thickness of 0.1 mm.

[0047] Prepare electrolyte: the solute of the electrolyte is NaPF6, and the solvent is a mixture of monomethyl acrylate, ethylene glycol dimethyl ether and methanol in a volume ratio of 1:1:1; the concentration of NaPF6 in the electrolyte is 1M; hydroquinone monomethyl ether is also added to the electrolyte, and the mass concentration of hydroquinone monomethyl ether in the electrolyte is 0.1%.

[0048] Prepare the battery: immerse the positive electrode sheet, negative electrode sheet and polyethylene separator in the electrolyte and encapsulate them into a sodium ion battery.

[0049] Example 4 This embodiment adopts a technical scheme substantially similar to that of Embodiment 1 to prepare a sodium ion battery, the only difference being that before the positive electrode slurry is coated on the positive electrode collector, the positive electrode collector is first heated to 200° C., and then the positive electrode slurry is coated on the positive electrode collector.

[0050] Example 5 This embodiment adopts the same technical scheme as that of embodiment 1 to prepare a sodium ion battery, the only difference being that the raw material for preparing the positive electrode slurry also includes N-phthalylglycine (melting point 198° C.). NaFePO4 is uniformly mixed with a positive electrode binder, a positive electrode conductor, and N-phthalylglycine in a mass ratio of 10:2:0.5:0.2 to obtain a positive electrode slurry.

[0051] Example 6 This embodiment adopts the same technical scheme as that of embodiment 1 to prepare a sodium ion battery, the only difference being that the raw material for preparing the positive electrode slurry also includes N-phthalylglycine (melting point 198° C.). NaFePO4 is uniformly mixed with the positive electrode binder, the positive electrode conductor, and N-phthalylglycine in a mass ratio of 10:3:1.5:0.1 to obtain a positive electrode slurry.

[0052] Comparative Example 1 This comparative example adopts substantially the same technical scheme as Example 1 to prepare a sodium ion battery, the only difference being that the particle size D50 of NaFePO4 is 0.2 μm.

[0053] Comparative Example 2 This comparative example adopts substantially the same technical scheme as Example 1 to prepare a sodium ion battery, the only difference being that the particle size D50 of NaFePO4 is 2 μm.

[0054] Comparative Example 3 This comparative example adopts a technical scheme substantially the same as that of Example 1 to prepare a sodium ion battery, the only difference being that when preparing the positive electrode slurry, NaFePO4 is evenly mixed with the positive electrode binder and the positive electrode conductor in a mass ratio of 10:1:1, and the mass proportion of polyvinylidene fluoride in the positive electrode binder is 30%.

[0055] The sizes of the positive electrode sheets and negative electrode sheets prepared in the above embodiments and comparative examples are the same, and other objects in the battery are also the same. The following electrical performance tests are carried out.

[0056] Test Example 1 1. Test capacity retention rate under the same conditions: Table 1 Number of 5C charge and discharge cycles and capacity retention at 45°C The sodium ion batteries prepared in Examples 1-6 have good capacity retention and long cycle life under high-power charge and discharge conditions. The NaFePO4 particle size of Comparative Example 1 is too small, resulting in a decrease in the retention of the positive electrode structure strength, which reduces the cycle capacity of the battery. The NaFePO4 particle size of Comparative Example 2 is too large, resulting in a small specific surface area, which makes the positive electrode structure less regular, and the strength also decreases, which reduces the cycle capacity of the battery. The concentration of polyvinylidene fluoride in the positive electrode binder of Comparative Example 3 is large, and the overall amount of positive electrode binder is small, which reduces the uniformity of the dispersion of polyvinylidene fluoride, weakens the adhesion to other materials, and reduces the strength of the positive electrode structure, thereby reducing the cycle capacity of the battery.

[0057] 2. Test power density under the same conditions: Table 2 Power density test data Power density / (kW / kg) Example 1 6.53 Example 2 6.29 Example 3 6.41 Example 4 6.76 Example 5 6.84 Example 6 6.95 Comparative Example 1 6.08 Comparative Example 2 5.87 Comparative Example 3 5.95 The power density of the battery prepared in Examples 1-6 is relatively large. The raw materials for preparing the positive electrode slurry in Examples 5 and 6 also include N-phthalylglycine. The hydrophilic carboxyl group in N-phthalylglycine promotes the wetting of the electrolyte on the surface of the positive electrode micropores, increases the speed of sodium ions leaving the positive electrode and re-embedding the positive electrode, and the benzene heterocycle has a water-repellent effect, reduces excessive water penetration into the bonding structure, reduces the damage to the positive electrode structure during battery charging and discharging, and increases the power density of the battery.

[0058] The NaFePO4 particle size of Comparative Example 1 is too small. Although the specific surface area is increased, the holes formed are also small, which is not conducive to the infiltration of electrolyte and the formation of a thicker SEI film, which reduces the sodium ion migration rate and the power density. The NaFePO4 particle size of Comparative Example 2 is too large, which makes the specific surface area of ​​NaFePO4 smaller, reduces the amount of sodium ions released, reduces the rate of sodium ions released, and reduces the power density. The polyvinylidene fluoride concentration of Comparative Example 3 is large, and the overall amount of positive electrode binder is small, that is, the amount of solvent is reduced, the space occupied by the solvent is reduced, and the holes formed after the solvent evaporates are reduced, which is not conducive to the infiltration of the electrolyte and the formation of a thicker SEI film, and reduces the migration efficiency of effective sodium ions, thereby reducing the power density of the battery.

[0059] 3. Test the charging speed under the same conditions Table 3 Charging speed test The batteries prepared in Examples 1 to 6 have a relatively fast charging speed. Example 4 has the fastest charging speed because the positive electrode current collector is heated to 200° C. before the positive electrode slurry is applied to the positive electrode current collector, and then the positive electrode slurry is applied to the positive electrode current collector, which reduces the contact resistance and thus improves the charging speed.

[0060] The particle size of NaFePO4 in Comparative Example 1 is too small. Although the specific surface area is increased, the holes formed are also small, which is not conducive to the infiltration of electrolyte and the formation of a thicker SEI film, which reduces the migration rate of sodium ions and reduces the charging speed. The particle size of NaFePO4 in Comparative Example 2 is too large, which makes the specific surface area of ​​NaFePO4 smaller, reduces the amount of sodium ions released, reduces the rate of sodium ion release, and reduces its charging speed. The positive electrode of Comparative Example 3 has few holes, which is not conducive to the infiltration of electrolyte and the formation of a thicker SEI film, reduces the migration efficiency of effective sodium ions, and thus reduces the charging speed of the battery.

[0061] The present application controls the NaFePO4 particle size to be moderately small, increases its specific surface area, increases the amount and speed of sodium ion release, controls the positive electrode binder with a larger molecular weight, is conducive to creating more and larger pores, is conducive to the penetration of the electrolyte, and is conducive to the migration of sodium ions. In addition, it also controls the addition of a larger volume but lower concentration of positive electrode binder, which on the one hand promotes the dispersion of polymer solutes in NaFePO4 particles, and on the other hand, increases the amount of solvent so that more pores can be formed by solvent evaporation, which is conducive to the penetration of the electrolyte, improves the sodium ion mobility, and improves the cycle performance, power performance and charging speed of the battery. The present application also heats the current collector to above the melting point and outside the boiling point of the polymer solute, so that after the positive electrode slurry is coated on the current collector, the polymer solute melts on the current collector, increases the contact area, reduces the contact resistance, and thus improves the power density and charging speed of the battery. The present application also adds N-phthaloylglycine to the positive electrode slurry. The hydrophilic carboxyl group in N-phthaloylglycine promotes the wetting effect of the electrolyte on the microporous surface of the positive electrode, increases the speed at which sodium ions leave the positive electrode and re-embed into the positive electrode, and the benzene heterocycle has a water-repellent effect, reduces excessive penetration of water into the bonding structure, reduces the damage to the positive electrode structure caused by battery charging and discharging, and improves the power density and cycle life of the battery.

[0062] Although the present application has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a high-power and long-life sodium-ion battery, characterized in that: include: NaFePO4 is mixed evenly with a positive electrode binder and a positive electrode conductor in a mass ratio of 10:(2-3):(0.5-1.5) to obtain a positive electrode slurry; the particle size D50 of the NaFePO4 is 0.5-1 μm; the positive electrode slurry is coated on a positive electrode current collector, and a positive electrode sheet is obtained after drying and curing; wherein the positive electrode binder includes a polymer solute and a solvent, and the mass proportion of the polymer solute in the positive electrode binder is 10-15%; The hard carbon is mixed with a negative electrode binder and a negative electrode conductive agent to obtain a negative electrode slurry; the negative electrode slurry is coated on a negative electrode current collector, and dried and solidified to obtain a negative electrode sheet; The positive electrode sheet, the negative electrode sheet and the separator are immersed in an electrolyte and packaged into a sodium ion battery.

2. The method for preparing a high-power and long-life sodium-ion battery according to claim 1, characterized in that: The polymer solute is polyvinylidene fluoride; the molecular weight of the polyvinylidene fluoride is 500,000 to 1,000,000.

3. The method for preparing a high-power and long-life sodium-ion battery according to claim 1, characterized in that: Before coating the positive electrode slurry on the positive electrode collector, the positive electrode collector is first heated to a temperature above the melting point and below the boiling point of the polymer solute, the heating temperature being lower than the melting point of the positive electrode collector, and then the positive electrode slurry is coated on the positive electrode collector.

4. The method for preparing a high-power and long-life sodium-ion battery according to claim 1, characterized in that: The electrolyte is an aqueous electrolyte; the negative electrode binder is a polymer material with negative charge on the surface in water.

5. The method for preparing a high-power and long-life sodium-ion battery according to claim 4, characterized in that: The negative electrode binder is a carboxymethyl cellulose solution or a hydroxyethyl cellulose solution.

6. The method for preparing a high-power and long-life sodium-ion battery according to claim 5, characterized in that: The mass concentration of the polymer material in the negative electrode binder is 0.5-1%; the hard carbon, the negative electrode binder and the negative electrode conductive agent are mixed in a mass ratio of 8: (0.5-1.5): (0.5-1.5).

7. The method for preparing a high-power and long-life sodium-ion battery according to claim 1, characterized in that: The raw materials for preparing the positive electrode slurry also include N-phthalylglycine (melting point 198° C.); NaFePO4 is evenly mixed with a positive electrode binder, a positive electrode conductor, and N-phthalylglycine in a mass ratio of 10: (2~3): (0.5~1.5): (0.1~0.2) to obtain the positive electrode slurry.

8. The method for preparing a high-power and long-life sodium-ion battery according to claim 1, characterized in that: The positive electrode conductive agent is acetylene black, carbon nanotubes or Ketjen black; the negative electrode conductive agent is acetylene black, carbon nanotubes or Ketjen black; the D50 particle size of the acetylene black is 30~45nm; the D50 length of the carbon nanotubes is 10~30μm; the D50 particle size of the Ketjen black is 20~100nm.

9. The method for preparing a high-power and long-life sodium-ion battery according to claim 1, characterized in that: The solute of the electrolyte is NaPF6, and the solvent is a mixture of monomethyl acrylate, ethylene glycol dimethyl ether and methanol; the concentration of NaPF6 in the electrolyte is 0.5M~1.5M; hydroquinone monomethyl ether is also added to the electrolyte, and the mass concentration of hydroquinone monomethyl ether in the electrolyte is 0.05~0.15%.

10. A high-power and long-life sodium-ion battery, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 9.

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