A positive electrode slurry, a method for preparing the same, and an application thereof

Abstract

The application discloses a positive electrode slurry and a preparation method and application thereof. The preparation method of the positive electrode slurry comprises the following steps: firstly, a binder and a first solvent are configured into a glue solution; secondly, the glue solution, a part of a conductive agent and a second solvent are mixed to prepare a conductive glue solution; thirdly, all positive electrode active materials and the remaining part of the conductive agent are mixed to prepare dry materials; finally, the conductive glue solution and a third solvent are added into the dry materials in batches for multiple times and stirred to realize a uniform slurry process. The application has the advantages of improving the dispersion uniformity of the positive electrode slurry and reducing the equipment loss.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a positive electrode slurry, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have long been highly valued in consumer electronics and power products due to their advantages such as high operating voltage, high energy density, long cycle life, safety, and environmental friendliness. A lithium-ion battery mainly consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The preparation of the positive electrode involves processes such as the preparation of the positive electrode slurry, coating, and rolling.

[0003] Currently, cathode slurry preparation processes are mainly divided into wet and dry methods. Wet processes result in cathode slurries with poor dispersion of the conductive agent and higher viscosity at the same solid content compared to dry processes, leading to higher internal resistance in the manufactured battery electrodes. Dry processes, on the other hand, struggle to control the optimal material state, requiring constant process adjustments, ultimately resulting in unstable slurry dispersion and viscosity, which is detrimental to mass production. Furthermore, it's worth noting that both wet and dry processes require stirring and dispersion at high solid content levels. Equipment with lower power outputs often experiences current overload, damaging the equipment. Therefore, both processes place high demands on the performance of the stirring equipment.

[0004] Therefore, there is an urgent need to study a cathode slurry preparation process that can improve the uniformity of cathode slurry dispersion while reducing the wear and tear on the stirring equipment. Summary of the Invention

[0005] In order to improve the dispersion uniformity of the cathode slurry and reduce equipment wear, this application provides a cathode slurry, its preparation method and application.

[0006] In a first aspect, this application provides a method for preparing a positive electrode slurry, which adopts the following technical solution:

[0007] A method for preparing a positive electrode slurry includes the following steps:

[0008] (1) Mix the adhesive with the first solvent to obtain an adhesive solution;

[0009] (2) Mix the adhesive solution, a portion of the conductive agent, and the second solvent to obtain a conductive adhesive solution;

[0010] (3) Dry mix the positive electrode active material and the remaining conductive agent to obtain a dry material;

[0011] (4) Mix 30wt% to 40wt% of the conductive adhesive liquid in step (2) with the dry material in step (3) and stir to obtain the first premix;

[0012] (5) Mix 30wt% to 40wt% of the conductive adhesive liquid in step (2), 70wt% to 90wt% of the third solvent, and the first premix in step (4), and stir to obtain the second premix.

[0013] (6) Mix 10wt% to 20wt% of the conductive adhesive liquid in step (2), 10wt% to 30wt% of the third solvent, and the second premix in step (5), and stir to obtain the third premix;

[0014] (7) Mix 5 wt% to 10 wt% of the conductive adhesive liquid in step (2) and the third premix in step (6), and stir to obtain the positive electrode slurry.

[0015] In the preparation of lithium-ion battery cathodes, the main materials in the cathode slurry, such as the cathode active material, binder, and conductive agent, have varying particle sizes and densities. During stirring, various contact mechanisms occur, including mixing, extrusion, friction, and agglomeration, which may ultimately lead to the formation of large particles. If the cathode active material and conductive agent particles agglomerate, forming large spheres with the binder, it will prevent stable bonding, resulting in a lack of good ion channels and conductive networks. This will severely degrade the electrochemical performance of the electrode and cause lithium plating during battery cycling, affecting battery safety. Therefore, the uniformity and stability of the cathode slurry have a significant impact on the performance of lithium-ion batteries.

[0016] By mixing a portion of the conductive agent with the positive electrode active material to obtain a dry material, and mixing another portion of the conductive agent with a binder and a solution to prepare a conductive adhesive, the finer-sized conductive agent can adhere to the surface of the larger-sized positive electrode active material particles. This, to a certain extent, inhibits the water absorption of the positive electrode active material during the pulping process and reduces the probability of agglomeration. At the same time, after mixing the conductive adhesive with the dry material, the conductive agent in the conductive adhesive has excellent compatibility with the conductive agent on the surface of the positive electrode active material, allowing the positive electrode active material coated with the conductive agent to be better dispersed in the conductive adhesive. This improves the dispersibility of the positive electrode active material and the conductive agent in the positive electrode slurry and enhances the dispersion uniformity of the positive electrode slurry.

[0017] In addition, by controlling the dry mixing of the conductive agent and the positive electrode active material first, and then adding the conductive adhesive and solvent to the dry material in steps and in quantitative amounts, while controlling the stirring speed of each batch, the materials can be made to present different states. On the one hand, the production state of the positive electrode slurry can be quantitatively controlled, improving the state of the finished positive electrode slurry and the consistency and stability of its coating on the positive electrode sheet. On the other hand, it strengthens the collision and kneading between powder particles, allowing the positive electrode active material and the conductive agent to absorb the conductive adhesive simultaneously, so that the powder particles in the system are fully wetted. This results in the deposition of a uniformly dispersed conductive agent deposit layer on the surface of larger positive electrode active material particles, forming a good conductive network path. This effectively reduces the internal resistance of the cell pulse, reduces the polarization generated by the cell during charging and discharging, and improves the pulse performance of the cell.

[0018] Finally, by controlling the solvent added in step (5), the wear and tear on the equipment caused by the stirring process can be reduced, and the service life of the equipment can be extended.

[0019] Optionally, the conductive agent is a carbon black conductive agent, which includes at least one of SP, acetylene black, and Ketjen black.

[0020] By adopting the above technical solution, carbon black conductive agent has excellent conductivity, which can fill more positive electrode active material with a smaller amount, thereby improving the stability of positive electrode slurry. In addition, carbon black conductive agent has a small particle size, which can be combined with positive electrode active material to obtain dry material with low agglomeration. After the dry material is mixed with conductive adhesive, a uniform conductive agent coating layer can be formed on the surface of positive electrode active material, forming a three-dimensional network of conductive pathways, thereby further improving the dispersion uniformity and conductivity of positive electrode slurry, and thus reducing the cell pulse internal resistance.

[0021] Optionally, the weight of the conductive agent used in the conductive adhesive obtained in step (2) accounts for 30% to 50% of the total weight of the conductive agent used in steps (2) and (3). For example, it can be 30%, 33%, 35%, 40%, 45%, 48%, or 50%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] By adjusting the amount of conductive agent in the dry material and the amount of conductive agent in the conductive adhesive, the conductive agent in the dry material can form a coating layer on the surface of the positive electrode active material while reducing the probability of conductive agent agglomeration or / and positive electrode active material agglomeration. Thus, in combination with the conductive agent in the conductive adhesive, a positive electrode slurry with excellent dispersion performance can be obtained.

[0023] Optionally, the weight ratio of the adhesive to the conductive agent in the conductive adhesive obtained in step (2) is 1:(0.55~0.8), for example, it can be 1:0.55, 1:0.6, 1:0.63, 1:0.65, 1:0.7, 1:0.75, 1:0.8, but is not limited to the listed ratios. Other unlisted ratios within the range are also applicable.

[0024] By controlling the weight ratio of binder to conductive agent in the conductive adhesive, the solid content of the conductive adhesive is controlled within a certain range. After the dry material is added to the conductive adhesive in batches, it is beneficial to obtain the first premix, the second premix, and the third premix with excellent viscosity, thereby obtaining a uniformly dispersed positive electrode slurry. Furthermore, the viscosity of the positive electrode slurry is kept within a certain range, making it easy to be uniformly coated on the positive electrode sheet to form a coating with uniform thickness and stable composition.

[0025] Optionally, the solid content of the adhesive obtained in step (1) is 5% to 8%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The solid content of the conductive adhesive obtained in step (2) is 7% to 10.5%, for example, it can be 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Optionally, the ratio of the total mass of the conductive adhesive liquid in steps (4) to (7) to the total mass of the third solvent in steps (5) to (6) is (2.70-2.72):1, for example, it can be 2.70:1, 2.71:1, 2.72:1, but is not limited to the listed ratios. Other unlisted ratios within the range are also applicable.

[0027] By controlling the solid content of the conductive adhesive, the conductive adhesive can be added to the dry material in batches to form a premix with a viscosity and solid content within a certain range. This makes the premix easier to stir and reduces equipment wear, resulting in a positive electrode slurry that is easy to coat on the positive electrode surface and has stable electrochemical performance.

[0028] Optionally, in the dry mixing process of step (3), the material is stirred for 10 to 30 minutes at a revolution speed of 10 to 20 rpm and a dispersion speed of 100 to 400 rpm to obtain the dry material; in the stirring process of step (4), the material is stirred for 10 to 30 minutes at a revolution speed of 10 to 15 rpm and then stirred for 60 to 90 minutes at a revolution speed of 20 to 30 rpm and a dispersion speed of 100 to 400 rpm to obtain the first premix.

[0029] Optionally, in step (5), during the stirring process, after stirring at a revolution speed of 10-15 rpm for 10-30 min, the mixture is stirred at a revolution speed of 20-30 rpm and a dispersion speed of 100-400 rpm for 90-120 min to obtain the second premix; in step (6), during the stirring process, after stirring at a revolution speed of 10-15 rpm and a dispersion speed of 400-700 rpm for 18-23 min, the mixture is stirred at a revolution speed of 15-30 rpm and a dispersion speed of 1500-2500 rpm for 90-120 min to obtain the third premix.

[0030] Optionally, in the stirring process of step (7), after stirring for 18 to 23 minutes at a revolution speed of 10 to 15 rpm and a dispersion speed of 1000 to 2000 rpm, the mixture is stirred for 120 to 150 minutes at a revolution speed of 20 to 25 rpm and a dispersion speed of 1500 to 2500 rpm to obtain the fourth premix.

[0031] By performing the low-speed wetting, low-speed stirring and high-speed stirring operations in steps (4) to (7), the slurry can be guaranteed to have good flow characteristics, and the state, appearance and fineness of the slurry can meet the requirements, so that the slurry is less likely to clog the screen during filtration and the coating is stable.

[0032] Optionally, the binder includes at least one of polyvinylidene fluoride and styrene-butadiene rubber; the first solvent, the second solvent, and the third solvent are independently selected from at least one of N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; the positive electrode active material includes at least one of nickel-cobalt-manganese ternary materials and / or nickel-cobalt-aluminum ternary materials.

[0033] Secondly, this application provides a positive electrode slurry, which adopts the following technical solution:

[0034] A positive electrode slurry, said positive electrode slurry being prepared by any of the methods described above.

[0035] Thirdly, this application provides a positive electrode sheet, which adopts the following technical solution:

[0036] A positive electrode sheet comprising the positive electrode slurry as described above.

[0037] Fourthly, this application provides a battery that adopts the following technical solution:

[0038] A battery includes a negative electrode, a separator, and a positive electrode as described above. Detailed Implementation

[0039] To better understand and implement this invention, the technical solution will be clearly and completely described below with reference to the embodiments.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0041] Unless otherwise stated, all numerical values ​​for the amounts of expressed components, reaction conditions, etc., used in the specification and claims are to be understood as being modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values ​​that can be varied to obtain the desired performance.

[0042] The word “and / or” as used in this article refers to one or all of the elements mentioned.

[0043] The terms "include" and "contain" as used in this article cover both cases where only the mentioned elements exist and cases where other unmentioned elements exist in addition to the mentioned elements.

[0044] All percentages in this invention are weight percentages, unless otherwise stated.

[0045] Unless otherwise stated, the terms “a,” “an,” “an,” and “the” as used in this specification are intended to include “at least one” or “one or more.” For example, “a component” refers to one or more components, and therefore more than one component may be considered and may be employed or used in the implementation of the described embodiments.

[0046] Example

[0047] Example 1

[0048] 1. Preparation of positive electrode slurry

[0049] (1) Styrene-butadiene rubber is mixed with dimethylformamide as the first solvent to prepare a rubber solution with a solid content of 6%;

[0050] (2) Mix the adhesive solution, acetylene black accounting for 40% of the total weight of the conductive agent, and dimethylformamide as the second solvent to obtain a conductive adhesive solution with a weight ratio of styrene-butadiene rubber to acetylene black of 1:0.7 and a solid content of 8.5% in the conductive adhesive solution.

[0051] (3) The nickel-cobalt-aluminum ternary material and acetylene black accounting for 60% of the total weight of the conductive agent were dry mixed and stirred for 20 minutes at a revolution speed of 15 rpm and a dispersion speed of 250 rpm to obtain a dry material with a mass ratio of nickel-cobalt-aluminum ternary material to acetylene black of 92.5:2.5.

[0052] (4) Add 40wt% of the prepared conductive adhesive to the dry material, stir at 12rpm for 20min, and then stir at 25rpm and 250rpm for 80min to obtain the first premix.

[0053] (5) Add 40wt% of the prepared conductive adhesive and 80wt% of the third solvent dimethylformamide to the first premix, stir at a revolution speed of 13 rpm for 20 min, and then stir at a revolution speed of 25 rpm and a dispersion speed of 250 rpm for 110 min to obtain the second premix.

[0054] (6) Add 11 wt% of the prepared conductive adhesive and 20 wt% of the third solvent dimethylformamide to the second premix, stir for 20 min at a revolution speed of 12 rpm and a dispersion speed of 550 rpm, and then stir for 100 min at a revolution speed of 23 rpm and a dispersion speed of 2000 rpm to obtain the third premix.

[0055] (7) Add 9 wt% of the prepared conductive adhesive to the third premix, stir for 20 min at a revolution speed of 12 rpm and a dispersion speed of 1500 rpm, and then stir for 130 min at a revolution speed of 22 rpm and a dispersion speed of 2000 rpm to obtain the positive electrode slurry; wherein, the ratio of the total mass of the conductive adhesive used in steps (4) to (7) to the total mass of the third solvent dimethylformamide used in steps (5) to (6) is 2.70:1.

[0056] 2. Cathode Preparation

[0057] The above-mentioned positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil twice, once on one side and once on both sides, using a coating machine. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a positive electrode semi-finished product is obtained. Then, the positive electrode semi-finished product is cold-pressed and cut to obtain the positive electrode sheet to be assembled.

[0058] 3. Anode Preparation

[0059] The negative electrode slurry was prepared as follows: artificial graphite, conductive agent acetylene black, thickener CMC, and binder SBR were added to a vacuum mixer in a mass ratio of 96.4:1:1.2:1.4 and mixed. Then, deionized water was added to the resulting mixture and the mixture was stirred in a vacuum mixer until it became homogeneous, thus obtaining the negative electrode slurry of this embodiment.

[0060] The above-mentioned negative electrode slurry is uniformly coated on both surfaces of the negative electrode current collector copper foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a negative electrode semi-finished product is obtained. Then, the negative electrode semi-finished product is cold-pressed and cut to obtain the negative electrode sheet to be assembled.

[0061] 4. Battery Assembly

[0062] Commercially available polyethylene film is used as the separator for the lithium-ion battery, and a commercially available electrolyte suitable for 4.2V (upper charging voltage) battery system is used as the electrolyte. The above-mentioned positive electrode sheet, negative electrode sheet and separator are wound together to obtain bare cell. The bare cell is then packaged, injected with electrolyte, left to stand, formed and tested for capacity to obtain the finished battery.

[0063] Example 2

[0064] The difference from Example 1 lies in the preparation of the positive electrode slurry.

[0065] A positive electrode slurry is prepared by the following steps:

[0066] (1) Polyvinylidene fluoride is mixed with dimethylacetamide as the first solvent to prepare a glue solution with a solid content of 5%.

[0067] (2) Mix the adhesive, SP (30% of the total weight of the conductive agent) and dimethylacetamide as the second solvent to obtain a conductive adhesive with a polyvinylidene fluoride to SP weight ratio of 1:0.8 and a solid content of 7%.

[0068] (3) The nickel-cobalt-manganese ternary material and SP, which account for 70% of the total weight of the conductive agent, are dry mixed and stirred for 30 minutes at a revolution speed of 10 rpm and a dispersion speed of 400 rpm to obtain a dry material with a mass ratio of nickel-cobalt-manganese ternary material to SP of 92.5:2.5.

[0069] (4) Add 30wt% of the prepared conductive adhesive liquid to the dry material, stir at a revolution speed of 15rpm for 30min, and then stir at a revolution speed of 30rpm and a dispersion speed of 100rpm for 90min to obtain the first premix.

[0070] (5) Add 40wt% of the prepared conductive adhesive and 70wt% of the third solvent N-methylpyrrolidone to the first premix, stir for 10min at a revolution speed of 10rpm, and then stir for 120min at a revolution speed of 20rpm and a dispersion speed of 400rpm to obtain the second premix.

[0071] (6) Add 20wt% of the prepared conductive adhesive and 30wt% of the third solvent N-methylpyrrolidone to the second premix, stir for 23min at a revolution speed of 15rpm and a dispersion speed of 400rpm, and then stir for 120min at a revolution speed of 15rpm and a dispersion speed of 2500rpm to obtain the third premix.

[0072] (7) Add 10wt% of the prepared conductive adhesive to the third premix, stir for 23min at a revolution speed of 10rpm and a dispersion speed of 1000rpm, and then stir for 150min at a revolution speed of 25rpm and a dispersion speed of 2500rpm to obtain the positive electrode slurry; wherein, the ratio of the total mass of the conductive adhesive used in steps (4) to (7) to the total mass of the third solvent N-methylpyrrolidone used in steps (5) to (6) is 2.72:1.

[0073] Example 3

[0074] The difference from Example 1 lies in the preparation of the positive electrode slurry.

[0075] A positive electrode slurry is prepared by the following steps:

[0076] (1) Polyvinylidene fluoride is mixed with dimethylformamide as the first solvent to prepare a glue solution with a solid content of 8%;

[0077] (2) Mix the adhesive solution, 50% of the total weight of the conductive agent, Ketjen black, and the second solvent dimethylformamide to obtain a conductive adhesive solution with a weight ratio of polyvinylidene fluoride to Ketjen black of 1:0.55 and a solid content of 10.5% in the conductive adhesive solution.

[0078] (3) Dry mix the nickel-cobalt-manganese ternary material and Ketjen black, which accounts for 50% of the total weight of the conductive agent, and stir for 10 minutes at a revolution speed of 20 rpm and a dispersion speed of 100 rpm to obtain a dry material with a mass ratio of nickel-cobalt-manganese ternary material to Ketjen black of 92.5:2.5.

[0079] (4) Add 40wt% of the prepared conductive adhesive to the dry material, stir at 10rpm for 10min, and then stir at 20rpm and 400rpm for 60min to obtain the first premix.

[0080] (5) Add 40wt% of the prepared conductive adhesive and 90wt% of the third solvent dimethylacetamide to the first premix, stir at 15rpm for 30min, then stir at 30rpm and 100rpm for 90min to obtain the second premix.

[0081] (6) Add 15wt% of the prepared conductive adhesive and 10wt% of the third solvent dimethylacetamide to the second premix, stir for 18min at a revolution speed of 10rpm and a dispersion speed of 700rpm, and then stir for 90min at a revolution speed of 30rpm and a dispersion speed of 1500rpm to obtain the third premix.

[0082] (7) Add 5 wt% of the prepared conductive adhesive to the third premix, stir for 18 min at a revolution speed of 15 rpm and a dispersion speed of 2000 rpm, and then stir for 120 min at a revolution speed of 20 rpm and a dispersion speed of 1500 rpm to obtain the positive electrode slurry; wherein, the ratio of the total mass of the conductive adhesive used in steps (4) to (7) to the total mass of the third solvent dimethylacetamide used in steps (5) to (6) is 2.72:1.

[0083] Example 4

[0084] The difference from Example 1 is that, in the process of preparing the positive electrode slurry, the weight of the conductive agent used in step (2) accounts for 25% of the total weight of the conductive agent used in steps (2) and (3).

[0085] Example 5

[0086] The difference from Example 1 is that, in the process of preparing the positive electrode slurry, the weight of the conductive agent used in step (2) accounts for 55% of the total weight of the conductive agent used in steps (2) and (3).

[0087] Example 6

[0088] The difference from Example 1 is that, in the process of preparing the positive electrode slurry, the weight ratio of binder to conductive agent in the conductive adhesive obtained in step (2) is 1:0.5.

[0089] Example 7

[0090] The difference from Example 1 is that, in the process of preparing the positive electrode slurry, the weight ratio of binder to conductive agent in the conductive adhesive obtained in step (2) is 1:0.85.

[0091] Example 8

[0092] The difference from Example 1 is that, in the process of preparing the positive electrode slurry, the solid content of the conductive adhesive liquid obtained in step (2) is 6%.

[0093] Example 9

[0094] The difference from Example 1 is that, in the process of preparing the positive electrode slurry, the solid content of the conductive adhesive liquid obtained in step (2) is 12%.

[0095] Example 10

[0096] The difference from Example 1 is that, in the process of preparing the positive electrode slurry, the dispersion speed is 1000 rpm during the stirring process after stirring for 20 minutes in step (6).

[0097] Example 11

[0098] The difference from Example 1 is that, in the process of preparing the positive electrode slurry, the dispersion speed is 3000 rpm during the stirring process after stirring for 20 minutes in step (6).

[0099] Comparative Example 1

[0100] The difference from Example 1 is that, in the process of preparing the positive electrode slurry, all the acetylene black was used in the preparation of the conductive adhesive in step (2), and the dry material in step (3) was only nickel-cobalt-aluminum ternary material.

[0101] Comparative Example 2

[0102] The difference from Example 1 is that step (2) is omitted in the preparation of the positive electrode slurry, and all the acetylene black is used in the preparation of the dry material in step (3).

[0103] Comparative Example 3

[0104] The difference from Example 1 is that in the process of preparing the positive electrode slurry, step (5) adds 40 wt% of the prepared conductive adhesive and 65 wt% of the third solvent dimethylformamide to the first premix; and step (6) adds 11 wt% of the prepared conductive adhesive and 35 wt% of the third solvent dimethylformamide to the second premix.

[0105] Comparative Example 4

[0106] The difference from Example 1 is that in the process of preparing the positive electrode slurry, step (5) adds 40 wt% of the prepared conductive adhesive and 95 wt% of the third solvent dimethylformamide to the first premix; step (6) adds 11 wt% of the prepared conductive adhesive and 5 wt% of the third solvent dimethylformamide to the second premix.

[0107] Comparative Example 5

[0108] The difference from Example 1 is that step (2) is omitted in the preparation of the positive electrode slurry, and acetylene black accounting for 100% of the total conductive agent is used when preparing the dry material in step (3); in addition, the mixing process of the adhesive and the dry material is as follows:

[0109] (1) Add 30wt% of the prepared adhesive solution and 10wt% of dimethylformamide to the dry material, stir at 15rpm for 30min, and then stir at 20rpm and 1500rpm for 90min to obtain the first premix.

[0110] (2) Add 20wt% of the prepared adhesive solution and 10wt% of dimethylformamide to the first premix, stir at 10rpm for 15min, then stir at 20rpm and 300rpm for 90min to obtain the second premix.

[0111] (3) Add 30wt% of the prepared adhesive solution and 30wt% of dimethylformamide to the second premix, stir at 15rpm for 30min, and then stir at 25rpm and 600rpm for 90min to obtain the third premix.

[0112] (4) Add 20wt% of the prepared adhesive solution and 10wt% of dimethylformamide to the third premix, stir for 23min at a revolution speed of 10rpm and a dispersion speed of 1000rpm, and then stir for 150min at a revolution speed of 25rpm and a dispersion speed of 2500rpm to obtain the fourth premix.

[0113] (5) Add 40 wt% of dimethylformamide to the fourth premix, stir for 120 min at a revolution speed of 15 rpm and a dispersion speed of 1500 rpm, and then stir for 30 min at a revolution speed of 15 rpm and a dispersion speed of 200 rpm to obtain the positive electrode slurry.

[0114] Detection methods

[0115] I. DCR Test

[0116] The internal resistance of the lithium batteries prepared in Examples 1-11 and Comparative Examples 1-5 was tested. The test method is as follows: under 50% SOC conditions, constant current discharge was performed for 10s at temperatures of -20℃, 0℃, 25℃ and 45℃ respectively. The measured DCR values ​​are recorded in Table 1.

[0117] II. Cell Pulse Discharge Power Performance Test

[0118] The cell pulse discharge power of the lithium batteries prepared in Examples 1-11 and Comparative Examples 1-5 was tested. The test method is as follows: the cell was adjusted to 50% SOC at 25℃ and 1C, and the constant power test lasted for 10s (discharge: cutoff voltage at 25℃ is 2.8V); the measured start voltage and cutoff voltage values ​​are recorded in Table 1.

[0119] Table 1

[0120]

[0121]

[0122] Combining Examples 1-3, Comparative Examples 1-5, and Table 1, it can be seen that during the preparation of the positive electrode slurry, mixing the conductive agent with the positive electrode active material to obtain a dry material, and then mixing the dry material with a conductive adhesive containing the conductive agent, has a very positive impact on the dispersion uniformity of the obtained positive electrode slurry. The cell in Example 1 has the lowest pulse internal resistance and the highest cutoff voltage, meaning the usable energy of the cell is increased. This is because, during the process of mixing the conductive agent with the active material to obtain the dry material, the conductive agent, due to its much smaller particle size and larger specific surface area than the positive electrode active material, can coat the surface of the positive electrode active material. By first mixing a portion of the conductive agent with the positive electrode active material... The materials are dry-mixed to obtain a dry material, and then conductive adhesive is added to it in batches. On the one hand, this reduces the adverse effect of the positive electrode active material on the viscosity of the positive electrode slurry during the preparation process. On the other hand, the combination with the conductive adhesive containing conductive agent can increase the compatibility and suitability between the dry material and the conductive adhesive. A conductive agent layer with a three-dimensional network conductive pathway is generated on the surface of the positive electrode active material, which further improves the dispersion uniformity of the conductive agent and active material with large particle size differences. This improves the dispersion uniformity of the positive electrode slurry, reduces the pulse internal resistance of the battery cell, reduces the polarization generated by the battery cell during charging and discharging, and thus improves the pulse performance of the battery cell.

[0123] When the amount of the third solvent used in step (5) is too much or too little, it is not conducive to obtaining a positive electrode slurry with high uniformity. A certain degree of agglomeration will occur in the slurry, thereby reducing the electrochemical performance of the battery cell.

[0124] Combining Examples 1, 4-5 and Table 1, it can be seen that when the proportion of conductive agent in the conductive adhesive to the total weight of conductive agent is too high or too low, the internal resistance of the cell pulse increases and the cutoff voltage decreases. This is because, by controlling the percentage of the weight of conductive agent used in step (2) to the total weight of conductive agent used in steps (2) and (3), on the one hand, a sufficient amount of conductive agent in the conductive adhesive is used to cooperate with the binder, so that a uniform conductive agent coating layer can be formed during the later mixing process with the dry material. On the other hand, it reduces the occurrence of conductive agent agglomeration caused by too much conductive agent in the dry material or the situation where the conductive agent is too little and cannot be uniformly coated on the positive electrode active material, thereby improving the uniformity of the positive electrode slurry and thus improving the various pulse performance of the cell.

[0125] Based on Examples 1, 6-7, and Table 1, it can be seen that when the ratio of binder to conductive agent in the conductive adhesive is too high or too low, the internal resistance of the cell pulse increases and the cutoff voltage decreases. This is because when the amount of binder is too high or too low, the binder and conductive agent in the conductive adhesive cannot be uniformly dispersed in the solvent. During the later mixing process with the dry material, the unstable dispersion of the binder will negatively affect the uniformity and stability of the conductive agent layer formed on the surface of the positive electrode active material, thereby reducing the dispersion uniformity of the positive electrode active material and conductive agent in the positive electrode active slurry and decreasing the dispersion uniformity of the positive electrode slurry.

[0126] Based on Examples 1, 8-9, and Table 1, it can be seen that both excessively high and excessively low solid content of the conductive adhesive are detrimental to obtaining a uniformly dispersed positive electrode slurry, leading to an increase in the pulse internal resistance of the battery cell and a decrease in the cutoff voltage. This is because, by controlling the solid content of the conductive adhesive, after the conductive adhesive is mixed with dry materials and various premixes in batches, the slurry has better high-speed flow characteristics, which allows the positive electrode active material and conductive agent particles to be fully wetted, achieving thorough mixing of positive electrode active materials and conductive agents with large differences in specific surface areas, thereby improving the dispersion performance of the positive electrode slurry.

[0127] Combining Examples 1, 10-11 and Table 1, it can be seen that during the high-speed stirring process in step (6), both excessively high and excessively low dispersion speeds will affect the dispersion uniformity of the positive electrode active slurry, thereby negatively impacting the DCR value or pulse performance of the battery cell.

[0128] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a positive electrode slurry, characterized in that: Includes the following steps: (1) The adhesive is mixed with the first solvent to obtain the adhesive solution; (2) The adhesive solution, a portion of the conductive agent, and the second solvent are mixed to obtain a conductive adhesive solution; (3) Dry mix the positive electrode active material and the remaining conductive agent to obtain a dry material; (4) Mix 30wt% to 40wt% of the conductive adhesive liquid in step (2) with the dry material in step (3) and stir to obtain the first premix; (5) Mix 30wt% to 40wt% of the conductive adhesive liquid in step (2), 70wt% to 90wt% of the third solvent, and the first premix in step (4), and stir to obtain a second premix; (6) Mix 10wt% to 20wt% of the conductive adhesive liquid in step (2), 10wt% to 30wt% of the third solvent, and the second premix in step (5), and stir to obtain the third premix; (7) Mix 5 wt% to 10 wt% of the conductive adhesive liquid in step (2) and the third premix in step (6), and stir to obtain a positive electrode slurry; The ratio of the total mass of the conductive adhesive liquid in steps (4) to (7) to the total mass of the third solvent in steps (5) to (6) is (2.70-2.72):1; The conductive agent is carbon black, and the solid content of the conductive adhesive obtained in step (2) is 7% to 10.5%. In the dry mixing process of step (3), the mixture is stirred for 10 to 30 minutes at a revolution speed of 10 to 20 rpm and a dispersion speed of 100 to 400 rpm to obtain the dry material; in the stirring process of step (4), the mixture is stirred for 10 to 30 minutes at a revolution speed of 10 to 15 rpm and then stirred for 60 to 90 minutes at a revolution speed of 20 to 30 rpm and a dispersion speed of 100 to 400 rpm to obtain the first premix. In step (5), the mixing process is carried out at a revolution speed of 10-15 rpm for 10-30 minutes, followed by mixing at a revolution speed of 20-30 rpm and a dispersion speed of 100-400 rpm for 90-120 minutes to obtain the second premix; in step (6), the mixing process is carried out at a revolution speed of 10-15 rpm and a dispersion speed of 400-700 rpm for 18-23 minutes, followed by mixing at a revolution speed of 15-30 rpm and a dispersion speed of 1500-2500 rpm for 90-120 minutes to obtain the third premix; In step (7), during the stirring process, the mixture is stirred for 18 to 23 minutes at a revolution speed of 10 to 15 rpm and a dispersion speed of 1000 to 2000 rpm, and then stirred for 120 to 150 minutes at a revolution speed of 20 to 25 rpm and a dispersion speed of 1500 to 2500 rpm to obtain the fourth premix.

2. The method for preparing a positive electrode slurry according to claim 1, characterized in that: The carbon black conductive agent includes at least one of SP, acetylene black, and Ketjen black.

3. A method for preparing a positive electrode slurry according to any one of claims 1 or 2, characterized in that: The weight of the conductive agent used in the conductive adhesive obtained in step (2) accounts for 30% to 50% of the total weight of the conductive agent used in steps (2) and (3).

4. A method for preparing a positive electrode slurry according to any one of claims 1 or 2, characterized in that: The weight ratio of the binder to the conductive agent in the conductive adhesive obtained in step (2) is 1:(0.55~0.8).

5. A method for preparing a positive electrode slurry according to any one of claims 1 or 2, characterized in that: The solid content of the adhesive obtained in step (1) is 5% to 8%.

6. The method for preparing a positive electrode slurry according to claim 1, characterized in that: The adhesive comprises at least one of polyvinylidene fluoride and styrene-butadiene rubber; the first solvent, the second solvent, and the third solvent are independently selected from N... At least one of methylpyrrolidone, dimethylformamide, and dimethylacetamide; the positive electrode active material includes at least one of nickel-cobalt-manganese ternary materials and / or nickel-cobalt-aluminum ternary materials.

7. A positive electrode slurry, characterized in that: The positive electrode slurry is prepared by the method described in any one of claims 1-6.

8. A positive electrode plate, characterized in that: The positive electrode sheet includes the positive electrode slurry as described in claim 7.

9. A battery, characterized in that: It includes a negative electrode, a separator, and a positive electrode as described in claim 8.

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