An aqueous positive electrode slurry, a preparation method and application thereof

Abstract

The application discloses a kind of water-based positive electrode slurry and its preparation method and application, it is related to lithium battery technical field.The water-based positive electrode slurry of the application includes active material, binder, conductive agent and solvent, the binder is water-based PVDF emulsion, PVDF primary particle size is 10~80nm.The water-based positive electrode slurry of the application uses water-based PVDF emulsion with primary particle size of 10~80nm as binder, no longer uses NMP solvent, production process is environmentally friendly, drying temperature is low, energy consumption is low, and low primary particle size can reduce the distance between lithium iron phosphate particles, increase the contact opportunity between lithium iron phosphate particles, thereby enhance electron transmission probability, PVDF is strong, and the residual moisture is low, effectively improve the electrochemical performance of water-based lithium battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to an aqueous cathode slurry, its preparation method, and its application. Background Technology

[0002] In recent years, with the development of the new energy industry, lithium-ion batteries have experienced rapid growth. Lithium iron phosphate (LFP) batteries, due to their low cost, good cycle performance, and high safety, have gradually become the mainstream in the market. LFP batteries account for over 60% of the installed capacity of power batteries. Currently, in the manufacturing of LFP batteries, a PVDF oil-based binder system is typically used, with NMP as the dispersion solvent. However, this system has the following drawbacks: NMP is volatile, has an amine odor, and is highly toxic; it can be absorbed through the skin and inhaled, posing a significant health hazard. NMP has a boiling point of 202℃, requiring substantial energy consumption for drying during lithium battery manufacturing. To reduce environmental pollution and save production costs, NMP typically needs to be recycled, adding to the recycling costs.

[0003] Besides oil-based systems, existing technologies also disclose methods for preparing aqueous lithium iron phosphate slurries. These methods utilize two types of binders: binder A has a main chain of polyethylene glycol and branched chains of acrylates; binder B is a copolymer of acrylic acid and acrylonitrile. This invention can improve slurry stability, enhance electrode flexibility, and solve the problem of electrode cracking and powder shedding. However, these aqueous binders all contain strongly polar groups with carboxyl or hydroxyl groups. These groups have extremely strong hydrophilicity, which can easily cause moisture residue during slurry drying, thus affecting the electrochemical performance of the battery. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the poor electrochemical performance of existing aqueous lithium iron phosphate slurries, and to provide an aqueous positive electrode slurry that uses aqueous PVDF emulsion as a binder to increase the contact opportunities between lithium iron phosphate particles, and the prepared electrode has low water content, thereby improving electrochemical performance.

[0005] Another object of the present invention is to provide a method for preparing an aqueous positive electrode slurry.

[0006] Another object of the present invention is to provide an application of an aqueous cathode slurry in the preparation of lithium iron phosphate batteries.

[0007] The above-mentioned objective of this invention is achieved through the following technical solution:

[0008] An aqueous positive electrode slurry includes an active material, a binder, a conductive agent, and a solvent, wherein the binder is an aqueous PVDF emulsion, and the primary particle size of the PVDF is 10–80 nm.

[0009] It should be noted that:

[0010] The aqueous positive electrode slurry of the present invention uses an aqueous binder and an aqueous PVDF emulsion, eliminating the use of NMP solvent. The production process is environmentally friendly, with low drying temperature and low energy consumption.

[0011] The aqueous PVDF emulsion of this invention is an aqueous binder with strong hydrophobicity and low moisture residue. Furthermore, this invention uses aqueous PVDF, which has an ultra-low primary particle size of 10-80 nm, compared to the 150-350 nm primary particle size of traditional oil-based PVDF. This ultra-low primary particle size reduces the distance between lithium iron phosphate particles, increasing the contact opportunities between them, thereby enhancing electron conduction and improving electrochemical performance.

[0012] Furthermore, the primary particle size of PVDF cannot be too small. If the particle size is too small, more emulsifier is required, which is detrimental to battery performance. If the particle size is too large, it increases the contact gap between active materials and increases the internal resistance of the electrode.

[0013] The waterborne PVDF emulsion of the present invention has a PVDF weight-average molecular weight of 200,000 to 800,000.

[0014] To further optimize the electrochemical performance of the aqueous lithium iron phosphate slurry, preferably, the primary particle size of the PVDF is 20–60 nm.

[0015] In a specific embodiment, the aqueous positive electrode slurry of the present invention comprises the following components by weight:

[0016] 100 parts lithium iron phosphate, 3-30 parts aqueous PVDF emulsion, 0.1-5 parts conductive agent, and 30-80 parts deionized water.

[0017] Furthermore, the aqueous cathode slurry preferably comprises the following components by weight:

[0018] 100 parts lithium iron phosphate, 10-15 parts aqueous PVDF emulsion, 0.5-1.5 parts conductive agent, and 40-60 parts deionized water.

[0019] In a specific embodiment, the solid content of the aqueous PVDF emulsion of the present invention is the same as that of conventional production, for example, 30 wt%.

[0020] In a specific embodiment, the lithium iron phosphate in the aqueous positive electrode slurry of the present invention is lithium iron phosphate particles with a particle size of 0.5 to 1.5 μm.

[0021] In specific embodiments, the conductive agent of the present invention is a conventional conductive agent in the art, such as one or more of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes and graphene.

[0022] This invention also specifically protects a method for preparing an aqueous positive electrode slurry, comprising the following steps:

[0023] S1. Mix lithium iron phosphate and a conductive agent evenly to obtain a mixed powder;

[0024] S2. Add deionized water and PVDF emulsion and stir until homogeneous, then add mixed powder and stir until homogeneous to obtain primary slurry;

[0025] S3. The primary slurry is then emulsified to obtain the aqueous positive electrode slurry, wherein the emulsification speed is 4000-10000 rpm.

[0026] The solid content of the aqueous positive electrode slurry of the present invention can reach 55-75%.

[0027] This invention also specifically protects the application of an aqueous cathode slurry in the preparation of lithium iron phosphate batteries.

[0028] This invention also specifically protects a positive electrode sheet for a lithium iron phosphate battery, which is prepared by the following method:

[0029] The aqueous cathode slurry is coated on both sides of an aluminum foil, baked, and rolled to prepare a lithium iron phosphate battery cathode sheet.

[0030] Preferably, the positive electrode of the lithium iron phosphate battery has a water content of ≤80ppm and a resistance of 1.2~1.5Ω / cm.

[0031] The present invention also specifically protects a lithium iron phosphate battery, wherein the positive electrode of the lithium iron phosphate battery is the positive electrode of the lithium iron phosphate battery.

[0032] The aqueous positive electrode slurry of this invention uses an aqueous PVDF emulsion with a primary particle size of 10-80 nm as a binder, which greatly reduces the distance between lithium iron phosphate particles, increases the contact opportunities between lithium iron phosphate particles, enhances the probability of electron conduction, and improves electrochemical performance. In addition, the electrode has a low water content, which is controlled below 80 ppm, and the low residual water content further improves the electrochemical performance. The electrode resistance can be reduced to 1.2-1.5 Ω / cm.

[0033] Based on the above-mentioned excellent performance improvements, the aqueous cathode slurry of the present invention can be widely used in the preparation of lithium iron phosphate batteries.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] The aqueous cathode slurry of this invention uses an aqueous PVDF emulsion with a primary particle size of 10-80 nm as a binder, eliminating the need for NMP solvent. The production process is environmentally friendly, with low drying temperature and low energy consumption. The low primary particle size reduces the distance between lithium iron phosphate particles, increasing the contact opportunities between them and thus enhancing electron conduction. PVDF has strong hydrophobicity and low moisture residue, effectively improving the electrochemical performance of aqueous lithium batteries.

[0036] The water-based positive electrode slurry coated with the present invention can control the water content of the positive electrode sheet to below 80 ppm, with low residual water content, and the electrode resistance can be reduced to 1.2 to 1.5 Ω / cm, exhibiting good electrochemical performance. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0038] Example 1

[0039] An aqueous positive electrode slurry, comprising the following components by weight:

[0040] 100 parts lithium iron phosphate, 20 parts aqueous PVDF emulsion, 2 parts conductive agent, 50 parts deionized water

[0041] The aqueous PVDF emulsion contains PVDF with a primary particle size of 20 nm and a molecular weight of 600,000, and has a solid content of 30%.

[0042] The particle size of lithium iron phosphate is 0.5–1.5 μm.

[0043] The conductive agent is conductive carbon black.

[0044] The specific preparation method of the aqueous positive electrode slurry in Example 1 above is as follows:

[0045] S1. Place 100 parts of lithium iron phosphate and 2 parts of conductive carbon black into a dry mixer and mix for 30 minutes to obtain a mixed powder;

[0046] S2. In a 5L high-speed disperser tank, add 30 parts of deionized water and 30 parts of PVDF emulsion and stir evenly. Then add the mixed powder to the PVDF dispersion solution and stir at high speed of 3000 rpm for 1 hour to obtain the primary slurry.

[0047] S2. Then emulsify the primary slurry using a high-speed emulsifier for 1 hour at a speed of 6000 rpm to obtain the aqueous cathode slurry.

[0048] Example 2

[0049] An aqueous positive electrode slurry, comprising the following components by weight:

[0050] 100 parts lithium iron phosphate, 20 parts aqueous PVDF emulsion, 2 parts conductive agent, 50 parts deionized water

[0051] The aqueous PVDF emulsion contains PVDF with a primary particle size of 60 nm and a molecular weight of 400,000, and has a solid content of 30%.

[0052] The particle size of lithium iron phosphate is 0.5–1.5 μm.

[0053] The conductive agent is acetylene black.

[0054] The preparation method of the aqueous positive electrode slurry in Example 2 above is as follows:

[0055] S1. Mix 100 parts lithium iron phosphate and 5 parts acetylene black in a dry mixer for 30 minutes to obtain a mixed powder;

[0056] S2. In a 5L high-speed disperser tank, add 60 parts of deionized water and 10 parts of PVDF emulsion and stir evenly. Then add the mixed powder to the PVDF dispersion solution and stir at high speed of 6000 rpm for 2 hours to obtain the primary slurry.

[0057] S2. Then emulsify the primary slurry using a high-speed emulsifier for 1 hour at a speed of 10,000 rpm to obtain the aqueous cathode slurry.

[0058] Example 3

[0059] An aqueous positive electrode slurry, comprising the following components by weight:

[0060] 100 parts lithium iron phosphate, 20 parts aqueous PVDF emulsion, 2 parts conductive agent, 50 parts deionized water

[0061] The aqueous PVDF emulsion contains PVDF with a primary particle size of 10 nm and a molecular weight of 400,000, and has a solid content of 30%.

[0062] The particle size of lithium iron phosphate is 0.5–1.5 μm.

[0063] The conductive agent is conductive graphite.

[0064] The preparation method of the aqueous positive electrode slurry in Example 3 above is as follows:

[0065] S1. Place 100 parts of lithium iron phosphate and 1 part of conductive graphite into a dry mixer and mix for 30 minutes to obtain a mixed powder;

[0066] S2. In a 5L high-speed disperser tank, add 50 parts of deionized water and 10 parts of PVDF emulsion and stir evenly. Then add the mixed powder to the PVDF dispersion solution and stir at high speed of 6000 rpm for 2 hours to obtain the primary slurry.

[0067] S2. Then emulsify the primary slurry using a high-speed emulsifier for 1 hour at a speed of 10,000 rpm to obtain the aqueous cathode slurry.

[0068] Example 4

[0069] An aqueous positive electrode slurry, comprising the following components by weight:

[0070] 100 parts lithium iron phosphate, 20 parts aqueous PVDF emulsion, 2 parts conductive agent, 50 parts deionized water

[0071] The aqueous PVDF emulsion contains PVDF with a primary particle size of 80 nm and a molecular weight of 400,000, and has a solid content of 30%.

[0072] The particle size of lithium iron phosphate is 0.5–1.5 μm.

[0073] The conductive agent is carbon nanotubes.

[0074] The preparation method of the aqueous positive electrode slurry in Example 4 above is as follows:

[0075] S1. Place 100 parts of lithium iron phosphate and 1 part of carbon nanotubes into a dry mixer and mix for 30 minutes to obtain a mixed powder;

[0076] S2. In a 5L high-speed disperser tank, add 50 parts of deionized water and 10 parts of PVDF emulsion and stir evenly. Then add the mixed powder to the PVDF dispersion solution and stir at high speed of 6000 rpm for 2 hours to obtain the primary slurry.

[0077] S2. Then emulsify the primary slurry using a high-speed emulsifier for 1 hour at a speed of 10,000 rpm to obtain the aqueous cathode slurry.

[0078] Example 5

[0079] An aqueous positive electrode slurry, comprising the following components by weight:

[0080] 100 parts lithium iron phosphate, 20 parts aqueous PVDF emulsion, 2 parts conductive agent, 50 parts deionized water

[0081] The aqueous PVDF emulsion contains PVDF with a primary particle size of 30 nm and a molecular weight of 400,000, and has a solid content of 30%.

[0082] The particle size of lithium iron phosphate is 0.5–1.5 μm.

[0083] The conductive agent is conductive carbon black.

[0084] The specific preparation method of the aqueous positive electrode slurry in Example 5 above is as follows:

[0085] S1. Mix 100 parts of lithium iron phosphate and 1 part of conductive carbon black in a dry mixer for 30 minutes to obtain a mixed powder;

[0086] S2. In a 5L high-speed disperser tank, add 50 parts of deionized water and 10 parts of PVDF emulsion and stir evenly. Then add the mixed powder to the PVDF dispersion solution and stir at high speed of 6000 rpm for 2 hours to obtain the primary slurry.

[0087] S2. Then emulsify the primary slurry using a high-speed emulsifier for 1 hour at a speed of 10,000 rpm to obtain the aqueous cathode slurry.

[0088] Example 6

[0089] An aqueous positive electrode slurry, comprising the following components by weight:

[0090] 100 parts lithium iron phosphate, 12 parts aqueous PVDF emulsion, 2 parts conductive agent, 50 parts deionized water

[0091] The aqueous PVDF emulsion contains PVDF with a primary particle size of 30 nm and a molecular weight of 400,000, and has a solid content of 30%.

[0092] The particle size of lithium iron phosphate is 0.5–1.5 μm.

[0093] The conductive agent is conductive carbon black.

[0094] The specific preparation method of the aqueous positive electrode slurry in Example 6 above is as follows:

[0095] S1. Mix 100 parts of lithium iron phosphate and 1 part of conductive carbon black in a dry mixer for 30 minutes to obtain a mixed powder;

[0096] S2. In a 5L high-speed disperser tank, add 50 parts of deionized water and 12 parts of PVDF emulsion and stir evenly. Then add the mixed powder to the PVDF dispersion solution and stir at high speed (6000 rpm) for 2 hours to obtain the primary slurry.

[0097] S2. Then emulsify the primary slurry using a high-speed emulsifier for 1 hour at a speed of 10,000 rpm to obtain the aqueous cathode slurry.

[0098] Comparative Example 1

[0099] An aqueous positive electrode slurry, comprising the following components by weight:

[0100] 100 parts lithium iron phosphate, 20 parts aqueous PVDF emulsion, 2 parts conductive agent, 50 parts deionized water

[0101] The aqueous PVDF emulsion contains PVDF with a primary particle size of 280 nm and a molecular weight of 600,000, and has a solid content of 30%.

[0102] The particle size of lithium iron phosphate is 0.5–1.5 μm.

[0103] The conductive agent is conductive carbon black.

[0104] The specific preparation method of the aqueous positive electrode slurry in Example 1 above is as follows:

[0105] S1. Mix 100 parts of lithium iron phosphate and 1 part of conductive carbon black in a dry mixer for 30 minutes to obtain a mixed powder;

[0106] S2. In a 5L high-speed disperser tank, add 30 parts of deionized water and 10 parts of PVDF emulsion and stir evenly. Then add the mixed powder to the PVDF dispersion solution and stir at high speed of 3000 rpm for 1 hour to obtain the primary slurry.

[0107] S2. Then emulsify the primary slurry using a high-speed emulsifier for 1 hour at a speed of 6000 rpm to obtain the aqueous cathode slurry.

[0108] Comparative Example 2

[0109] An aqueous positive electrode slurry, comprising the following components by weight:

[0110] 100 parts lithium iron phosphate, 3 parts PAA type binder, 2 parts conductive agent, 50 parts deionized water.

[0111] The particle size of lithium iron phosphate is 0.5–1.5 μm.

[0112] The conductive agent is conductive carbon black.

[0113] The specific preparation method of the aqueous positive electrode slurry in Example 1 above is as follows:

[0114] S1. Mix 100 parts of lithium iron phosphate and 1 part of conductive carbon black in a dry mixer for 30 minutes to obtain a mixed powder;

[0115] S2. In a 5L high-speed disperser tank, add 45 parts of deionized water and 3 parts of PAA binder and stir evenly. Then add the mixed powder to the PVDF dispersion solution and stir at high speed of 3000 rpm for 1 hour to obtain the primary slurry.

[0116] S2. Then emulsify the primary slurry using a high-speed emulsifier for 1 hour at a speed of 6000 rpm to obtain the aqueous cathode slurry.

[0117] Result detection

[0118] Positive electrode preparation

[0119] The slurry was evenly coated on both sides of a 12µm thick carbon-coated aluminum foil using a scraper, and then baked in a forced-air oven at 100℃ for 30 minutes. The surface density of the coating on one side was 185g / m². 2 The surface density of both sides is 370 g / m³. 2 Then, the positive electrode sheet is obtained by rolling it at 180°C using a roller press.

[0120] Positive electrode moisture content test

[0121] The positive electrode sheet was cut into a circle with a diameter of 1 cm, and then the water content was tested using a Karl Fischer moisture analyzer. The heating temperature was 120℃ and the heating time was 10 min.

[0122] Positive electrode resistance measurement

[0123] Cut the positive electrode into a 1 square centimeter circle using a mold, and then test the resistance using a resistance tester.

[0124] The specific test results are as follows:

[0125] Serial Number Electrode moisture content / ppm Electrode resistance / Ω / cm Example 1 62 2.4 Example 2 78 1.5 Example 3 74 2.2 Example 4 76 2.8 Example 5 68 0.8 Example 6 64 1.0 Comparative Example 1 85 7.6 Comparative Example 2 186 2.8

[0126] As can be seen from the table above, within the scope of the embodiments of the present invention, the prepared positive electrode sheets have extremely low water content, all controlled at 78 ppm or below. The low residual water effectively improves the electrochemical performance of aqueous lithium batteries. Furthermore, combined with the low primary particle size of the aqueous PVDF emulsion in the specific aqueous positive electrode slurry of the present invention, the distance between lithium iron phosphate particles can be reduced, increasing the contact opportunities between lithium iron phosphate particles and thus enhancing the probability of electron conduction. The electrode resistance of the positive electrode substrate is controlled at 2.8 Ω / cm or below, exhibiting good conductivity.

[0127] A comparison of Examples 1-2 and Examples 3-4 above shows that the preferred PVDF primary particle size distribution is more beneficial for improving the moisture content and electrode resistance of the positive electrode sheet.

[0128] As can be seen from the comparison between Comparative Example 1 and Example 1, the primary particle size of PVDF in the aqueous PVDF emulsion is 280 nm, which exceeds the range of extremely low primary particle size of PVDF in this invention. This not only increases the water content of the positive electrode, but also increases the distance between lithium iron phosphate particles, reducing the contact opportunities between lithium iron phosphate particles. As a result, the resistance of the positive electrode increases significantly to 7.6 Ω / cm, and it does not have good electrochemical performance.

[0129] As can be seen from the comparison between Comparative Example 2 and Example 1, the PAA type binder of the prior art significantly increases the moisture content of the electrode to 186 ppm, but still cannot achieve the technical effect of the present invention.

[0130] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An aqueous positive electrode slurry, characterized in that, By weight, it comprises the following components: 100 parts lithium iron phosphate, 10-20 parts aqueous PVDF emulsion, 0.5-2 parts conductive agent, and 40-60 parts deionized water; The PVDF has a primary particle size of 20-60 nm; the aqueous PVDF emulsion has a solid content of 30 wt%.

2. The aqueous positive electrode slurry as described in claim 1, characterized in that, The lithium iron phosphate particles have a particle size of 0.5~1.5μm.

3. The aqueous positive electrode slurry as described in claim 1, characterized in that, The conductive agent is one or more of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, and graphene.

4. A method for preparing the aqueous positive electrode slurry according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Mix lithium iron phosphate and a conductive agent evenly to obtain a mixed powder; S2. Add deionized water and PVDF emulsion and stir until homogeneous, then add mixed powder and stir until homogeneous to obtain primary slurry; S3. The primary slurry is then emulsified to obtain the aqueous positive electrode slurry, wherein the emulsion rotation speed is 4000~10000 rpm.

5. The application of the aqueous cathode slurry as described in any one of claims 1 to 3 in the preparation of lithium iron phosphate batteries.

6. A positive electrode sheet for a lithium iron phosphate battery, characterized in that, The positive electrode sheet is prepared by the following method: coating the aqueous positive electrode slurry of any one of claims 1 to 3 onto aluminum foil on both sides, baking, and rolling to prepare the positive electrode sheet for lithium iron phosphate batteries.

7. A lithium iron phosphate battery, characterized in that, The positive electrode of the lithium iron phosphate battery is the positive electrode of the lithium iron phosphate battery as described in claim 6.