Preparation method of sodium ion battery positive electrode sheet

Abstract

The application relates to a preparation method of a sodium ion battery positive plate, and belongs to the technical field of new energy batteries. The specific scheme comprises the following steps: step one, uniformly dispersing Prussian blue positive materials and organic solvents to obtain slurry A; the organic solvents comprise a combination of one or more of N-methyl pyrrolidone, polyvinyl pyrrolidone and nitriles; step two, adding a binder into the slurry A and uniformly stirring to obtain slurry B; step three, adding a conductive agent into the slurry B and uniformly stirring to obtain slurry C; removing bubbles from the slurry C and adjusting the viscosity to obtain slurry D; step four, coating the slurry D on a positive current collector, baking, rolling, cutting and obtaining the sodium ion battery positive plate. The application can prevent subsequent glue liquid from entering Prussian blue cavities, can effectively guarantee the adhesive glue amount attached to the surface of active materials, can prevent positive electrode cold pressing and formation demolding, and can solve the problem of the battery cell manufacturing process.

Description

Technical Field

[0001] This invention belongs to the field of new energy battery technology, specifically relating to a method for preparing a sodium-ion battery cathode sheet. Background Technology

[0002] In recent years, the cost of lithium-ion batteries has increased significantly. In contrast, low-cost sodium-ion batteries have a clear advantage. The working principle and manufacturing process of sodium-ion batteries are similar to those of lithium-ion batteries, and sodium ore resources are abundant and inexpensive. Sodium-ion battery cathode materials are mainly divided into three types: Prussian blue series, layered oxide series, and polyanion and its derivative series. Prussian blue cathode materials are inexpensive, have high specific capacity, high energy density, and are simple to synthesize. However, Prussian blue cathode materials are synthesized in an aqueous dispersion system, making them prone to absorbing water, resulting in a certain proportion of crystal water inside the material, which seriously affects the cell's cycle performance. High-temperature baking of the synthesized powder to remove the crystal water is one method, but this leaves voids. During the preparation of the cathode slurry, the adhesive can enter these voids, reducing the amount of adhesive on the cathode material surface. This leads to severe delamination of the Prussian blue cathode sheet during cold pressing and formation, making battery production impossible. The invention patent with publication number CN109065883A discloses a modification method for Prussian blue and its analogues and a sodium-ion battery. Specifically, it discloses that Prussian blue and its analogues are baked at high temperature to remove moisture, and then the vacancies are filled with isopropanol and glacial acetic acid vapor. This improves the sodium storage electrochemical performance of Prussian blue and its analogues while preventing the material from absorbing water in subsequent processes, thereby improving its storage stability. Summary of the Invention

[0003] To address the issues of cold pressing and formation demolding of Prussian blue cathode slurry, this invention provides a method for preparing sodium-ion battery cathode sheets.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing a sodium-ion battery positive electrode includes the following steps:

[0006] Step 1: Disperse the Prussian blue cathode material evenly with an organic solvent to obtain slurry A; the organic solvent includes one or more combinations of N-methylpyrrolidone, polyvinylpyrrolidone, and nitrile compounds;

[0007] Step 2: Add binder to slurry A and stir until homogeneous to obtain slurry B;

[0008] Step 3: Add conductive agent to slurry B and stir evenly to obtain slurry C; defoam slurry C and adjust viscosity to obtain slurry D;

[0009] Step 4: Coat slurry D onto the positive electrode current collector, bake, roll, and cut to obtain the sodium-ion battery positive electrode sheet.

[0010] Furthermore, in step one, the weight ratio of the Prussian blue cathode material to the organic solvent is 10-70:30-90.

[0011] Furthermore, the general formula of the nitriles is R-CN, where R is a hydrocarbon group.

[0012] Furthermore, the nitrile includes one or a combination of several of acetonitrile, acrylonitrile, malononitrile, butadionitrile, and 1,2-dicyanoacetylene.

[0013] Furthermore, in step two, the adhesive is one or more of polyvinylidene fluoride, polyethylene oxide, polyvinyl alcohol, polyolefins, and hydrogenated nitrile butadiene oxide.

[0014] Furthermore, in step three, the conductive agent is one or more of the following: conductive carbon black, carbon nanotubes, conductive graphite, graphene, carbon fiber, acetylene black, and Ketjen black.

[0015] Furthermore, in step one, the moisture content of the Prussian blue cathode material is 0.001%-25%.

[0016] Furthermore, in step three, the slurry C is vacuumed and reversed to defoam the slurry.

[0017] Furthermore, in step three, the viscosity of slurry C is adjusted to 4000-7000 Pa·s.

[0018] Furthermore, after adding the binder, stir at a speed of 1000-5000 rpm for 20-90 minutes; after adding the conductive agent, stir at a speed of 1000-5000 rpm for 30-180 minutes.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] In the preparation of the slurry, compared with the traditional cathode slurry process, the cathode powder is pre-saturated with an appropriate amount of non-aqueous methylpyrrolidone and / or nitrile organic solvent before adding the binder. The binder is then added and the mixture is homogenized and stirred. The organic solvent occupies the vacancies left after the water of crystallization is baked, preventing the binder from entering the Prussian blue cavities. This effectively ensures the amount of binder adhering to the surface of the active material, preventing cold pressing and formation-induced film removal of the cathode, thus solving cell manufacturing process problems. The nitrile solvent with -CN used for pre-saturation has stronger compatibility with Prussian blue due to the presence of nitrile groups. Furthermore, nitrogen (N) has a lower electronegativity than oxygen (O), and contains only one lone pair of electrons, making its electron-donating ability stronger than that of oxygen. It forms a stronger complex with ferrous ions within the vacancy, resulting in a more stable solvated complex structure and better pre-saturation effect. The pre-saturated solvent is slowly released during battery use. Both ketone and nitrile solvents have been proven to be mature and stable in battery systems and do not pose any potential safety risks. Attached Figure Description

[0021] Figure 1 This invention provides a sodium-ion battery positive electrode sheet.

[0022] Figure 2 It is a sodium-ion battery cathode sheet prepared using traditional processes. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] Example 1:

[0025] A method for preparing a sodium-ion battery positive electrode includes the following steps:

[0026] Step 1: Add N-methylpyrrolidone and Prussian blue cathode material to the mixing tank at a weight ratio of 1:2 and stir slowly for 30 minutes;

[0027] Step 2: Add polyvinylidene fluoride with a certain solid content to the mixing system of Step 1 and stir until homogeneous;

[0028] Step 3: Add a certain proportion of conductive agent to the slurry in Step 2 and stir evenly at an appropriate speed;

[0029] Step 4: Adjust viscosity and remove bubbles;

[0030] Step 5: Coat the above slurry onto the surface of aluminum foil, and then dry, roll, cut, and prepare the positive electrode sheet;

[0031] Example 2

[0032] The only difference from Example 1 is that the weight ratio of N-methylpyrrolidone to Prussian blue cathode material in step one is 1:1, and the other steps are the same as in Example 1.

[0033] Example 3

[0034] The only difference from Example 1 is that acetonitrile is mixed with Prussian blue cathode material.

[0035] Example 4

[0036] The only difference from Example 2 is that polyvinylpyrrolidone is mixed with Prussian blue cathode material.

[0037] Comparative Example 1:

[0038] The difference from Example 1 is that in step one of Comparative Example 1, only Prussian blue cathode material was used, and no other solvents were used.

[0039] Comparative Example 2:

[0040] The difference between Comparative Example 2 and Example 1 is that N-methylpyrrolidone in step one of Example 1 is replaced with isopropanol and glacial acetic acid, and the mass ratio of isopropanol to glacial acetic acid is 1:1.

[0041] Battery assembly:

[0042] The above-mentioned positive electrode / separator / hard carbon negative electrode are stacked in sequence, electrolyte is injected, and a battery is prepared by formation. Physical and electrochemical tests are then performed.

[0043] Test method:

[0044] 25℃ Cyclic Test: At 25℃, after resting for 10 minutes, charge at 1C constant current and constant voltage to 3.70V; after resting for 10 minutes, discharge at 1C constant current to 2.0V;

[0045]

[0046] in conclusion:

[0047] Compared to Comparative Example 1, all four examples showed significantly improved peel strength, and no film detachment occurred during formation. Therefore, the solvent pre-saturation method used in this invention has a significant effect on solving the problems of cold pressing and formation film detachment of the positive electrode sheet. In comparison, Comparative Example 2 showed better capacity retention (800T) at 25°C than Comparative Example 1, indicating that the use of N-methylpyrrolidone, polyvinylpyrrolidone, and nitrile compounds in this invention is significantly more effective than isopropanol and glacial acetic acid. Glacial acetic acid contains a large number of hydrogen ions, which can easily combine with hexafluorophosphate in the electrolyte to form hydrofluoric acid, posing a risk of battery degradation.

[0048] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a sodium-ion battery positive electrode, characterized in that, Includes the following steps: Step 1: Baking the Prussian blue cathode material removes the water of crystallization and creates vacancies. The treated Prussian blue cathode material is then evenly dispersed with an organic solvent, allowing the organic solvent to occupy the vacancies, resulting in slurry A. The organic solvent includes one or more combinations of N-methylpyrrolidone and nitrile compounds, including acetonitrile, acrylonitrile, malononitrile, butadienenitrile, and 1,2-dicyanoacetylene. The weight ratio of the Prussian blue cathode material to the organic solvent is 10-70:30-90. Step 2: Add binder to slurry A and stir until homogeneous to obtain slurry B; Step 3: Add conductive agent to slurry B and stir evenly to obtain slurry C; defoam slurry C and adjust viscosity to obtain slurry D; Step 4: Coat slurry D onto the positive electrode current collector, bake, roll, and cut to obtain the sodium-ion battery positive electrode sheet.

2. The preparation method according to claim 1, characterized in that: In step two, the adhesive is one or more of polyvinylidene fluoride, polyethylene oxide, polyvinyl alcohol, and hydrogenated nitrile butadiene.

3. The preparation method according to claim 1, characterized in that: In step three, the conductive agent is one or more of the following: conductive carbon black, carbon nanotubes, conductive graphite, graphene, and carbon fiber.

4. The preparation method according to claim 1, characterized in that: In step one, the moisture content of the Prussian blue cathode material is 0.001%.

5. The preparation method according to claim 1, characterized in that: In step three, the slurry C is vacuumed and reversed to remove bubbles.

6. The preparation method according to claim 1, characterized in that: In step three, the viscosity of slurry C is adjusted to 4000-7000 Pa·s.

7. The preparation method according to claim 1, characterized in that: After adding the binder, stir at 1000-5000 rpm for 20-90 minutes; after adding the conductive agent, stir at 1000-5000 rpm for 30-180 minutes.

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