Positive electrode slurry, preparation method thereof, positive plate containing positive electrode slurry, and sodium ion battery

Abstract

The invention discloses a positive electrode slurry, a preparation method thereof, a positive plate containing the positive electrode slurry, and a sodium ion battery. The preparation method comprises the following steps: adding a water-based binder 1 into deionized water to obtain a solution A; adding a slurry additive to obtain a solution B; adding conductive agent slurry to obtain a suspension A; adding conductive agent powder to obtain a suspension B; adding half of the active substance to obtain a suspension C; adding the other half of the active substance to obtain a suspension D; adding a water-based binder 2 to obtain a suspension E; adding a slurry additive to obtain a suspension F; and stirring and defoaming in a vacuum state to obtain the positive electrode slurry. The water-based slurry and the positive plate of the phosphorus-based polyanionic positive electrode material with excellent performance are prepared by adopting the low-cost and environment-friendly water-based binder and the deionized water solvent, and the water-based slurry and the positive plate are assembled into the sodium ion battery, so that the purposes of reducing the processing toxicity of the positive slurry and reducing the manufacturing cost of the sodium ion battery are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly to a positive electrode slurry, a preparation method thereof, a positive electrode sheet containing the same, and a sodium-ion battery. Background Art

[0002] With the large-scale application of lithium-ion batteries in fields such as electronic devices and electric vehicles, the shortage of key resources such as lithium, cobalt, and nickel has become increasingly prominent, and their costs have also been rising continuously. Since the positive electrode of sodium-ion batteries uses elements with relatively high abundances such as phosphorus, iron, manganese, sodium, and copper and has a low nickel content, it has the significant advantages of low cost and rich resources, and has become a research hotspot in the fields of emerging energy storage batteries and low-speed electric vehicles.

[0003] However, the commercialization process of current sodium-ion batteries is hindered by many factors. On the one hand, its energy density is relatively low, resulting in a large amount of positive and negative electrode materials required per watt-hour of electricity; on the other hand, the continuous decline in the cost of lithium iron phosphate batteries has further increased the cost pressure on sodium-ion batteries.

[0004] In the preparation process of traditional positive electrode slurries and positive electrode sheets for sodium-ion batteries, N-methylpyrrolidone (NMP) is usually used as a solvent and polyvinylidene fluoride (PVDF) is used as an aqueous binder. NMP is not only expensive but also has great harm to the environment and poses a poisoning risk to the human reproductive system and health. Its vapor also has the danger of explosion and combustion, so an additional vapor recovery and treatment system needs to be equipped. The PVDF aqueous binder is costly and easily gels when exposed to water, which makes the slurry coating process extremely strict with respect to the humidity of the processing environment and must be carried out in a dry room environment, thus further increasing the manufacturing cost of sodium-ion batteries. These problems limit the large-scale popularization and application of sodium-ion batteries. Summary of the Invention

[0005] The present invention aims to provide a positive electrode slurry, a preparation method thereof, a positive electrode sheet containing the same, and a sodium-ion battery to solve the problems of high cost, toxicity, and harmfulness of traditional positive electrode slurries for existing sodium-ion batteries.

[0006] The positive electrode slurry and its preparation method in this solution include the following steps:

[0007] Step 1: Weigh an aqueous binder 1 according to the slurry ratio, add it to a deionized water solvent, stir at a low speed until the aqueous binder 1 is dispersed in the deionized water, and then stir at a medium speed in a vacuum until the aqueous binder 1 is dissolved to obtain solution A;

[0008] Step 2: Add a slurry additive to solution A as needed, and then stir and dissolve it at a medium speed in a vacuum to obtain solution B. If no addition is required, directly use solution A for step 3;

[0009] Step 3: Add conductive agent slurry to Solution A or Solution B as needed, and stir at medium speed in vacuum to obtain Suspension A. If no addition is required, directly use Solution A or Solution B for Step 4;

[0010] Step 4: Add conductive agent powder to Suspension A or Solution A or Solution B, stir at low speed until the conductive powder is dispersed, and then stir evenly at medium speed in vacuum to obtain Suspension B;

[0011] Step 5: Add half of the active material to Suspension B, stir at low speed until the active material is dispersed, and then stir evenly at high speed in vacuum to obtain Suspension C;

[0012] Step 6: Add the other half of the active material to Suspension C, stir at low speed until the active material is dispersed, then stir evenly at high speed in vacuum, and then add deionized water thereto, and stir evenly at high speed in vacuum to obtain Suspension D;

[0013] Step 7: Add aqueous binder 2 to Suspension D as needed, and stir at low to medium speed in vacuum to obtain Suspension E. If no addition is required, directly use Suspension D for Step 8;

[0014] Step 8: Add slurry additive to Suspension E or Suspension D as needed, and then add deionized water thereto, and stir at low to medium speed in vacuum to obtain Suspension F. If no addition is required, directly use Suspension D or Suspension E for Step 9;

[0015] Step 9: Turn off the dispersion impeller, adjust the stirring impeller to medium speed, and stir to defoam in vacuum to obtain the final positive electrode slurry; in the above steps, the low-speed stirring means: the stirring impeller rotates at 500 - 1000 rpm, and the dispersion impeller rotates at 500 - 1000 rpm; the medium-speed stirring means: the stirring impeller rotates at 1000 - 1500 rpm, and the dispersion impeller rotates at 1000 - 2000 rpm; the high-speed stirring means: the stirring impeller rotates at 1500 - 3000 rpm, and the dispersion impeller rotates at 1000 - 3000 rpm.

[0016] Further, in Steps 1 to 8, the addition amounts of all materials are weighed according to the slurry ratio, and the slurry ratio is: active material∶conductive agent∶total of aqueous binder 1 and aqueous binder 2∶slurry additive = (90 - 96)∶(0.5 - 8.5)∶(2 - 6)∶(0 - 0.5).

[0017] Preferably, the stirring parameters in Steps 1 to 8 are as follows:

[0018] Low-speed stirring: The stirring paddle rotates at 500 - 1000 rpm, the dispersing paddle rotates at 500 - 1000 rpm, and the stirring time is 10 - 30 minutes; Medium-speed stirring: The stirring paddle rotates at 1000 - 1500 rpm, the dispersing paddle rotates at 1000 - 2000 rpm, and the stirring time is 30 - 180 minutes; High-speed stirring: The stirring paddle rotates at 1500 - 3000 rpm, the dispersing paddle rotates at 1000 - 3000 rpm, the vacuum degree is -80 - 95 kPa, and the stirring time is 30 - 180 minutes.

[0019] Further, in the step 1, the aqueous binder 1 includes one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium polyacrylate, lithium polyacrylate, and sodium alginate.

[0020] Further, in the steps 2 and 8, the slurry additives include one or more of polyvinylpyrrolidone, carboxymethyl starch, hydrolyzed acrylonitrile starch, condensed alkyl benzene ether sulfate, ethylene carbonate, propylene carbonate, polyvinyl alcohol, ethanol, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyoxyethylene polyoxypropylene ether, and polyvinyl ether.

[0021] Preferably, the slurry additives in the steps 2 and 8 may or may not be added. If the slurry additives need to be added, they can be added all at once in the step 2 or step 8.

[0022] Further, in the step 3, the conductive agent slurry includes one or more of single-walled carbon nanotube dispersion, graphene dispersion, and reduced graphene oxide dispersion.

[0023] Further, in the step 4, the conductive agent powder includes one or more of conductive carbon black SP, acetylene black, Ketjen black, multi-walled carbon nanotubes, carbon nanofibers, and conductive graphite.

[0024] Further, in the steps 5 and 6, the active materials include one or more of sodium vanadium phosphate, sodium fluorovanadium phosphate, sodium iron pyrophosphate phosphate, sodium fluorophosphate iron, sodium fluorophosphate pyrophosphate iron, sodium vanadium iron phosphate, and sodium iron manganese phosphate.

[0025] Further, in the step 7, the aqueous binder 2 is styrene-butadiene rubber emulsion.

[0026] Further, in the step 8, the addition amount of deionized water is controlled within the range of 30% - 60% of the slurry solid content, and the slurry viscosity is controlled to be 3000 - 10000 Pa·s.

[0027] Further, in the step 9, the defoaming vacuum degree is -80 - 95 kPa, the stirring paddle rotation speed is 500 - 3000 rpm, and the defoaming duration is 10 - 60 minutes.

[0028] A positive electrode slurry is prepared by the method according to the above steps.

[0029] A positive electrode sheet is obtained by applying a positive electrode paste onto the surface of an aluminum current collector through methods such as extrusion coating or blade coating, followed by vacuum drying, rolling, and cutting.

[0030] Furthermore, the aluminum current collector includes one of a pure aluminum foil current collector, a novel composite aluminum current collector, and a carbon-coated current collector. The thickness of the current collector is 3 - 15 μm, and the coating thickness is 90 - 500 μm.

[0031] Furthermore, the vacuum drying temperature is 60 - 140 °C, the vacuum pressure is 20 - 1000 Pa, and the drying duration is 12 - 48 hours.

[0032] Preferably, the cutting process includes one or more of die cutting with a tool, slitting with a tool, and laser die cutting.

[0033] A sodium-ion battery is assembled by winding or laminating the positive electrode sheet.

[0034] Furthermore, the sodium-ion battery includes a soft-pack battery, a cylindrical battery, and a square aluminum-shell battery.

[0035] Furthermore, the tabs of the sodium-ion battery include a single-tab and a multi-tab structure.

[0036] The working principle and beneficial effects of this solution:

[0037] Cost reduction: Deionized water is used as a solvent in the present invention, and sodium alginate, sodium carboxymethyl cellulose, sodium polyacrylate, and styrene-butadiene rubber are used as aqueous binders. Compared with traditional N-methylpyrrolidone solvent and polyvinylidene fluoride aqueous binder, the process cost of the positive electrode paste and positive electrode sheet of the sodium-ion battery is significantly reduced, thereby reducing the manufacturing cost of the sodium-ion battery.

[0038] Environmental protection and health: Avoiding the use of toxic and harmful N-methylpyrrolidone solvent reduces environmental pollution and harm to human health, and better meets the requirements of environmental protection and health.

[0039] Excellent performance: Electrochemical performance tests show that the electrode sheet prepared by the method of the present invention has excellent electrochemical performance. Description of the Drawings

[0040] Figure 1 SEM image of the positive electrode sheet for Example 2;

[0041] Figure 2 1C rate cycling performance of the coin-type half-cells of the positive electrode sheets for Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3;

[0042] Figure 3The rate performance of the coin half-cells of the positive electrodes of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 at different rates such as 0.2C, 0.5C, 1C, 2C, 5C, 10C, and 0.2C;

[0043] Figure 4 The 1C cycle stability of the positive electrode prepared in Example 2 for the hard carbon soft-pack battery. Specific Embodiments

[0044] The following is a further detailed description through specific embodiments:

[0045] Example 1

[0046] ① Weigh 0.8 g of sodium polyacrylate (aqueous binder 1) according to the ratio of active material∶carbon black conductive agent∶carbon nanotube conductive agent∶aqueous binder 1 = 93∶1.5∶1.5∶4, and pour 30 g of deionized water into the stirring tank. Stir at a low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) to disperse the sodium polyacrylate in the deionized water, and stir at a medium speed in a vacuum (-88 kPa) (stirring paddle 1500 rpm, dispersing paddle 2000 rpm) for more than 30 minutes until the sodium polyacrylate is dissolved to obtain solution A;

[0047] ② Weigh 0.3 g of carbon black conductive agent SP and 0.3 g of carbon nanotube conductive agent CNTs powder and pour them into solution A. Stir at a low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the conductive agent powder, and then stir at a medium speed in a vacuum (stirring paddle 1500 rpm, dispersing paddle 2000 rpm) for 30 minutes to obtain suspension A;

[0048] ③ Weigh 9.3 g of sodium vanadium phosphate cathode material and pour it into suspension A. Stir at a low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the sodium vanadium phosphate cathode material powder, and stir at a high speed in a vacuum (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) for 30 minutes to obtain suspension B;

[0049] ④ Weigh the remaining 9.3 g of sodium vanadium phosphate cathode material and pour it into suspension B. Stir at a low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the sodium vanadium phosphate cathode material powder, and stir at a high speed in a vacuum (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) for 30 minutes to obtain suspension C;

[0050] ⑤ Observe whether the viscosity of the slurry is appropriate. If it is too viscous, add an appropriate amount of deionized water, and then stir at a high speed in a vacuum (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) for 30 minutes.

[0051] ⑥Turn off the dispersing impeller, adjust the stirring impeller to medium speed (stirring impeller at 1500 rpm, dispersing impeller at 1500 rpm), and stir for 30 minutes under vacuum to defoam and obtain the final positive electrode paste.

[0052] ⑦Perform coating by the doctor blade coating method. Use a pure aluminum current collector with a thickness of 12 μm for the current collector, a coating thickness of 120 μm, and then dry it by blowing air.

[0053] ⑧Dry the electrode sheet at 110 °C under a vacuum of 100 Pa for 24 hours, roll press the electrode sheet to a compaction density of 1.6 g / cm3, and cut it into strip-shaped electrode sheets using a cutter.

[0054] ⑨Assemble a coin-type half-cell to test the performance of the electrode sheet, and use the winding process to fabricate a soft-pack battery.

[0055] Comparative Example 1

[0056] The preparation method of the sodium vanadium phosphate positive electrode sheet is the same as that of Example 1, and the slurry ratio is changed to active material∶carbon black conductive agent∶carbon nanotube conductive agent∶aqueous binder = 91∶2∶2∶5.

[0057] Comparative Example 2

[0058] The preparation method of the sodium vanadium phosphate positive electrode sheet is the same as that of Example 1, and the slurry ratio is changed to active material∶carbon black conductive agent∶carbon nanotube conductive agent∶aqueous binder = 92∶1.5∶1.5∶5.

[0059] Comparative Example 3

[0060] The preparation method of the sodium vanadium phosphate positive electrode sheet is the same as that of Example 1, and the slurry ratio is changed to active material∶carbon black conductive agent∶carbon nanotube conductive agent∶aqueous binder = 93∶1∶1∶5.

[0061] Example 2

[0062] ①Weigh 0.7 g of sodium polyacrylate (aqueous binder 1) and 30 g of deionized water according to the ratio of active material∶single-walled carbon nanotube∶carbon black conductive agent∶carbon nanotube conductive agent∶aqueous binder 1∶slurry additive = 93∶0.1∶1.45∶1.45∶3.5∶0.5, pour them into a stirring tank, and stir at low speed (stirring impeller at 1000 rpm, dispersing impeller at 1000 rpm) to disperse sodium polyacrylate in deionized water. Stir at medium speed (stirring impeller at 1500 rpm, dispersing impeller at 2000 rpm) under vacuum (-88 kPa) for more than 30 minutes until sodium polyacrylate is dissolved to obtain Solution A;

[0063] ②Weigh 5 g of single-walled carbon nanotube slurry (the solid content of the single-walled carbon nanotube slurry is 0.4%) and pour it into Solution A, and stir at medium speed (stirring impeller at 1500 rpm, dispersing impeller at 2000 rpm) under vacuum for 30 minutes to obtain Suspension A;

[0064] ③ Weigh 0.29 g of carbon black conductive agent SP and 0.29 g of carbon nanotube conductive agent CNTs powder into suspension A respectively, stir at a low speed (stirring paddle at 1000 rpm, dispersing paddle at 1000 rpm) for 15 minutes to disperse the conductive agent powder, and then stir at a medium speed in vacuum (stirring paddle at 1500 rpm, dispersing paddle at 2000 rpm) for 30 minutes to obtain suspension B;

[0065] ④ Weigh 9.3 g of sodium vanadium phosphate cathode material and pour it into suspension B, stir at a low speed (stirring paddle at 1000 rpm, dispersing paddle at 1000 rpm) for 15 minutes to disperse the sodium vanadium phosphate cathode material powder, and stir at a high speed in vacuum (stirring paddle at 2000 rpm, dispersing paddle at 3000 rpm) for 30 minutes to obtain suspension C;

[0066] ⑤ Weigh the remaining 9.3 g of sodium vanadium phosphate cathode material and pour it into suspension C, stir at a low speed (stirring paddle at 1000 rpm, dispersing paddle at 1000 rpm) for 15 minutes to disperse the sodium vanadium phosphate cathode material powder, and stir at a high speed in vacuum (stirring paddle at 2000 rpm, dispersing paddle at 3000 rpm) for 30 minutes to obtain suspension D;

[0067] ⑥ Add 0.1 g of slurry additive ethylene carbonate to suspension D, observe whether the viscosity of the slurry is appropriate, add an appropriate amount of deionized water if it is too viscous, and then stir at a high speed in vacuum (stirring paddle at 2000 rpm, dispersing paddle at 3000 rpm) for 30 minutes.

[0068] ⑦ Turn off the dispersing paddle, adjust the stirring paddle to medium speed (stirring paddle at 1500 rpm, dispersing paddle at 1500 rpm), and stir for 30 minutes in vacuum to defoam and obtain the final cathode slurry.

[0069] ⑧ Perform coating by the doctor blade coating method, use a pure aluminum current collector, the thickness of the current collector is 12 μm, the coating thickness is 300 μm, and then dry it by blowing air.

[0070] ⑨ Dry the electrode sheet at 110 °C under a vacuum of 100 Pa for 24 hours, roll press the electrode sheet to a compaction density of 1.6 g / cm3, and cut it into strip-shaped electrode sheets using a cutter.

[0071] ⑩ Fabricate a soft-pack battery using the winding process.

[0072] Among them, the aqueous binder 1 plays roles such as suspension, adhesion, and dispersion, and the aqueous binder 2 plays a role in enhancing the adhesion and the strength of the electrode sheet. When it is necessary to enhance the adhesion and the strength of the electrode sheet, add the aqueous binder 2 by yourself.

[0073] Table 1 shows the statistical data of the electrical performance of the coin-type half-cells of the positive electrode sheets of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 in the first 3 weeks of charge and discharge at a rate of 0.1C.

[0074]

[0075] Judging from the data of the examples, under different charge and discharge rate conditions, the positive electrode sheets of Example 1 and Example 2 showed good charge and discharge capacities and initial efficiency in the first 3 weeks of charge and discharge at a rate of 0.1C, and were stable in the 1C rate cycle performance test, having the potential for large-scale application.

[0076] Through the research and analysis of the examples and comparative examples, the effectiveness and advantages of the preparation method provided by the present invention in optimizing the performance of sodium-ion batteries were further verified.

[0077] The above are only the embodiments of the present invention, and common knowledge such as the specific structures and characteristics known in the art are not described in detail herein. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicability of the patent. The protection scope required by this application shall be subject to the content of its claims, and the specific implementation manners described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a positive electrode slurry, characterized in that: The following steps are involved: Step 1: according to the slurry ratio, weigh the water-based binder 1 and add it to the deionized water solvent, stir at a low speed until the water-based binder 1 is dispersed in the deionized water, and then stir at a medium speed in a vacuum until the water-based binder 1 is dissolved to obtain solution A; Step 2: Add slurry additives to solution A as needed, and then stir and dissolve in a vacuum to obtain solution B. If no addition is required, directly use solution A to proceed to step 3; Step 3: Add conductive agent slurry to solution A or solution B as needed, and stir at medium speed in vacuum to obtain suspension A. If no addition is required, directly use solution A or solution B to proceed to step 4; Step 4: Add the conductive agent powder to the suspension A or solution A or solution B, stir at a low speed until the conductive powder is dispersed, and then stir at a medium speed in a vacuum to obtain a suspension B; Step 5: add half of the active substance to suspension B, stir at a low speed until the active substance is dispersed, and then stir at a high speed in a vacuum to obtain suspension C; Step 6: Add the other half of the active substance to the suspension C, stir at a low speed until the active substance is dispersed, and then stir at a high speed in a vacuum to obtain a suspension D. Then, add deionized water, and stir at a high speed in a vacuum to obtain a suspension D. Step 7: Add water-based binder 2 to suspension D as needed, and stir at a low speed in a vacuum to obtain suspension E. If no addition is required, directly use suspension D to proceed to step 8; Step 8: Add slurry additives to suspension E or suspension D as needed, then add deionized water thereto, and stir at a low speed in a vacuum to obtain suspension F. If no addition is required, directly use suspension D or suspension E to proceed to step 9; Step 9: Turn off the dispersing paddle, adjust the stirring paddle to medium speed, and stir and defoam under vacuum to obtain the final positive electrode slurry; the low-speed stirring described in the above steps: stirring paddle 500-1000rpm, dispersing paddle 500-1000rpm; medium-speed stirring: stirring paddle 1000-1500rpm, dispersing paddle 1000-2000rpm; high-speed stirring: stirring paddle 1500-3000rpm, dispersing paddle 1000-3000rpm.

2. The method for preparing the positive electrode slurry according to claim 1, characterized in that: In the steps 1 to 8, the amount of each material added is weighed according to the slurry ratio, and the slurry ratio is: active material: conductive agent: the sum of water-based binder 1 and water-based binder 2: slurry additive = (90-96): (0.5-8.5): (2-6): (0-0.5).

3. The method for preparing the positive electrode slurry according to claim 2, characterized in that: In the step 1, the water-based binder 1 includes one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium polyacrylate, lithium polyacrylate, and sodium alginate.

4. The method for preparing the positive electrode slurry according to claim 3, characterized in that: The slurry additives in step 2 and step 8 include one or more of polyvinyl pyrrolidone, carboxymethyl starch, hydrolyzed acrylonitrile starch, condensed alkyl benzene ether sulfate, ethylene carbonate, propylene carbonate, polyvinyl alcohol, ethanol, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyoxyethylene polyoxypropylene ether, and polyvinyl ether.

5. The method for preparing the positive electrode slurry according to claim 4, characterized in that: The conductive agent slurry in step 3 includes one or more of a single-walled carbon nanotube dispersion, a graphene dispersion, and a reduced oxide graphene dispersion.

6. The method for preparing the positive electrode slurry according to claim 5, characterized in that: The conductive agent powder in step 4 includes one or more of conductive carbon black SP, acetylene black, Ketjen black, single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, and conductive graphite.

7. The method for preparing the positive electrode slurry according to claim 6, characterized in that: The active substances in step 5 and step 6 include one or more of sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium ferric phosphate pyrophosphate, sodium ferric fluorophosphate, sodium ferric pyrophosphate fluorophosphate, sodium ferric vanadium phosphate, and sodium ferric manganese phosphate.

8. A positive electrode slurry, characterized in that: Prepared according to the method according to any one of claims 1 to 7.

9. A positive electrode sheet, characterized in that: The positive electrode slurry according to any one of claims 1 to 7 is applied to the surface of the aluminum current collector by extrusion coating or doctor blade coating, and then vacuum dried, rolled and cut to obtain the final positive electrode sheet.

10. A sodium ion battery, characterized in that: The positive electrode sheet according to claim 9 is included, and the positive electrode sheet is assembled into a sodium ion battery by winding or laminating.

Images