Positive electrode slurry and preparation method thereof as well as positive electrode plate and battery applying positive electrode slurry

Abstract

The invention specifically discloses a positive electrode slurry and a preparation method thereof, and a positive electrode plate and a battery using the positive electrode slurry. The positive pole piece comprises a positive active material layer, and the positive active material layer comprises a first positive active material, a second positive active material and a modified dispersant; the first positive electrode active material comprises at least one of a ternary material and a lithium iron manganese phosphate material, and the second active material comprises at least one of a lithium iron phosphate material, a lithium manganate material and a lithium-rich manganese-based material; the modified dispersant comprises a solid carrier and a surfactant; the solid carrier comprises at least one of mesoporous silica microspheres, a metal organic framework, a covalent organic framework, a hydrogen bond organic framework and porous polymer microspheres; the surface active agent comprises at least one of a cationic surface active agent, an anionic surface active agent and a nonionic surface active agent. The positive pole piece disclosed by the invention can keep excellent cycle performance while giving consideration to high energy density.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a positive electrode slurry, a method for preparing the same, and positive electrode sheets and batteries using the same. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, high power density, and long lifespan, occupy an important position in portable electronics, transportation, and large-scale energy storage. The currently booming market for household electric vehicles urgently needs products with higher energy density, longer cycle life, and improved safety performance. For mainstream lithium iron phosphate batteries, after decades of development, energy density is nearing its limit. The most direct way to explore higher energy density lithium batteries is to combine low-energy-density positive electrode active materials with high-energy-density positive electrode active materials, which will help produce power batteries that better meet future development trends.

[0003] However, research has found that when different types of positive electrode active materials with significant differences in particle size, morphology and surface properties are mixed, they are prone to agglomeration due to the mismatch of their physical properties. Agglomeration will cause uneven dispersion of positive electrode active materials in the slurry, and then uneven distribution in the positive electrode active material layer formed after coating, resulting in deterioration of the electrode microstructure, which is not conducive to improving the cycle performance and high energy density of lithium batteries. Summary of the Invention

[0004] In order to solve the technical problems in the prior art, this application provides a positive electrode slurry, a method for preparing the same, and a positive electrode sheet and battery using the same.

[0005] In a first aspect, this application provides a positive electrode sheet, which adopts the following technical solution: A positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer comprising a first positive electrode active material, a second positive electrode active material, and a modified dispersant; the particle size of the first positive electrode active material is larger than the particle size of the second positive electrode active material; the first positive electrode active material comprises at least one of ternary materials and lithium manganese iron phosphate materials, and the second active material comprises at least one of lithium iron phosphate materials, lithium manganese oxide materials, and lithium-rich manganese-based materials; The modified dispersant comprises a solid carrier and a surfactant; the solid carrier comprises at least one of mesoporous silica microspheres, metal-organic frameworks, covalent organic frameworks, hydrogen-bonded organic frameworks, and porous polymer microspheres; the surfactant comprises at least one of cationic surfactants, anionic surfactants, and nonionic surfactants.

[0006] In this application, by adding a modified dispersant, large-particle first positive electrode active material and small-particle second positive electrode active material can be uniformly dispersed in the positive electrode active material layer of the positive electrode sheet. This indirectly optimizes the conductive network distribution in the positive electrode active material layer, helps reduce the internal resistance of the positive electrode sheet, and improves its cycle performance. Furthermore, the small-particle second positive electrode active material can effectively fill the spaces between the large-particle first positive electrode active material, forming a dense positive electrode active material layer. This allows the electrode to carry a higher active material loading at the same thickness. At this time, the dual continuous transport path of "second positive electrode active material ion channel + first positive electrode active material electronic conductive network" in the positive electrode sheet significantly reduces electrode polarization, especially improving the electron transport bottleneck of the second positive electrode active material. This allows the specific capacity of both positive electrode active materials to approach the theoretical value, all of which contribute to improving the energy density of the positive electrode sheet. This results in a lithium battery with excellent cycle performance and high energy density.

[0007] Preferably, the mass ratio of the solid carrier to the surfactant is (10-30):1, and / or the surfactant includes at least one of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, Span series surfactants, and Tween series surfactants.

[0008] Preferably, the positive electrode active material layer is formed from a positive electrode slurry, and the preparation method of the positive electrode slurry includes the following steps: S1, prepare a first slurry including the first positive electrode active material, a second slurry including the second positive electrode active material, and a dispersion solution including the modified dispersant, for later use; S2, the first portion of the first slurry is mixed with the dispersion solution to obtain a premixed slurry; the premixed slurry is mixed with the second slurry to obtain a half-step slurry; the half-step slurry is mixed with the remaining portion of the first slurry to obtain the positive electrode slurry.

[0009] Preferably, the modified dispersant is prepared by a method comprising the following steps: A1. The solid carrier is mixed with the solvent and stirred. The pH of the mixture is adjusted to 4-5, and stirring is continued to obtain a mixed solution. A2, the surfactant is mixed with the mixed solution, the reaction temperature is adjusted to 40-60℃ and stirred, and the resulting reaction product is subjected to solid-liquid separation to obtain the modified dispersant.

[0010] Preferably, the solvent in A1 includes ethanol; the first stirring time in A1 is 20-40 min, and the second stirring time is 10-20 min.

[0011] Preferably, the pH value of the mixture is adjusted by using dilute hydrochloric acid with a concentration of 0.08-0.12 mol / L in A1.

[0012] Preferably, each 100 mL of the solvent in A1 is mixed with 2-4 g of the solid carrier.

[0013] Preferably, adjusting the reaction temperature in A2 refers to placing the surfactant and the mixed solution in an oil bath at 40-60°C; the stirring time is 3-5 hours, and the stirring speed is 400-600 rpm.

[0014] Preferably, the dispersion solution includes the modified dispersant and a solvent, wherein the mass percentage of the modified dispersant in the dispersion solution is 1%-10%; and the solvent is the same as the solvent used in the first slurry and / or the second slurry.

[0015] Preferably, in the positive electrode slurry, the mass ratio of the first slurry to the second slurry is (6-9):(1-4); the ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is (3-9):1.

[0016] Preferably, the mass of the first portion of the first slurry accounts for 10%-50% of the total mass of the first slurry.

[0017] Preferably, the absolute value of the viscosity difference between the first slurry and the second slurry is less than or equal to 2000 mPa·s.

[0018] The first mixing method includes a first stirring, wherein the revolution speed of the first stirring is 10-25 rpm and the stirring time is 20-30 min; The second mixing method includes a second stirring, wherein the revolution speed in the second stirring is 10-25 rpm, the rotation speed is 1000-1800 rpm, and the stirring time is 10-40 min; the third mixing method includes a third stirring and a fourth stirring. The revolution speed in the third stirring process is 10-25 rpm, the rotation speed is 1800-2400 rpm, and the stirring time is 100-130 min; the temperature is maintained at 30-40℃ and the vacuum degree is 60-80 kPa during the third stirring process. The fourth stirring is in the opposite direction of the third stirring; the fourth stirring has a rotation speed of 10-25 rpm and a stirring time of 10-60 min; the vacuum degree is maintained at 60-80 kPa during the fourth stirring process.

[0019] Secondly, this application provides a battery, which adopts the following technical solution: A battery includes a negative electrode and a positive electrode as described above. Detailed Implementation

[0020] To better understand and implement this application, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only some of the embodiments of this application, and not all of them.

[0021] 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 application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0022] 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.

[0023] 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.

[0024] The word “and / or” as used in this article refers to one or all of the elements mentioned.

[0025] 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.

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] The first aspect of this application provides a positive electrode sheet, including a positive electrode active material layer, the positive electrode active material layer including a first positive electrode active material, a second positive electrode active material and a modified dispersant; The particle size of the first positive electrode active material is larger than that of the second positive electrode active material; The first positive electrode active material includes at least one of ternary materials and lithium manganese iron phosphate materials, and the second active material includes at least one of lithium iron phosphate materials, lithium manganese oxide materials, and lithium-rich manganese-based materials. The modified dispersant comprises a solid carrier and a surfactant; the solid carrier comprises at least one of mesoporous silica microspheres, metal-organic frameworks, covalent organic frameworks, hydrogen-bonded organic frameworks, and porous polymer microspheres; the surfactant comprises at least one of cationic surfactants, anionic surfactants, and nonionic surfactants.

[0028] In this application, the addition of a modified dispersant enables the uniform dispersion of large-particle first positive electrode active material and small-particle second positive electrode active material within the positive electrode active material layer of the positive electrode sheet. This indirectly optimizes the conductive network distribution within the positive electrode active material layer, helping to reduce the internal resistance of the positive electrode sheet and improve its cycle performance. Furthermore, the small-particle second positive electrode active material effectively fills the spaces between the large-particle first positive electrode active material, forming a dense positive electrode active material layer. This allows the electrode to carry a higher active material loading at the same thickness. Moreover, the dual continuous transport path of "second positive electrode active material ion channels + first positive electrode active material electronic conductive network" in the positive electrode sheet significantly reduces electrode polarization, particularly improving the electron transport bottleneck of the second positive electrode active material. This allows the specific capacity of both positive electrode active materials to approach the theoretical value, all of which contribute to improving the energy density of the positive electrode sheet and resulting in a lithium battery with excellent cycle performance and high energy density.

[0029] In one embodiment of this application, the mass ratio of the solid carrier to the surfactant is (10-30):1, and / or the surfactant includes at least one of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, Span series surfactants, and Tween series surfactants. Exemplarily, the mass ratio of the solid carrier to the surfactant is any one of 10:1, 15:1, 20:1, 25:1, 28:1, or 30:1, or any ratio within the range formed by any pairwise ratios of the above.

[0030] The solid carrier in the modified dispersant can disperse the modified dispersant into the gaps between the large particles of the first positive electrode active material and the small particles of the second positive electrode active material through the forced movement of physical particles. This improves the dispersion uniformity of the modified dispersant in the positive electrode active material layer, reduces the possibility of active material agglomeration in the positive electrode active material layer, and thus improves the stability of the positive electrode sheet using the mixed positive electrode active material, providing a basis for the positive electrode sheet to achieve high energy density and excellent cycle performance.

[0031] In one embodiment of this application, the positive electrode active material layer is formed from a positive electrode slurry, and the preparation method of the positive electrode slurry includes the following steps: S1, prepare a first slurry including the first positive electrode active material, a second slurry including the second positive electrode active material, and a dispersion solution including the modified dispersant, for later use; S2, the first portion of the first slurry is mixed with the dispersion solution to obtain a premixed slurry; the premixed slurry is mixed with the second slurry to obtain a half-step slurry; the half-step slurry is mixed with the remaining portion of the first slurry to obtain the positive electrode slurry.

[0032] In this application, the positive electrode slurry is prepared by adopting the above steps. First, a portion of the first slurry is mixed with the dispersion solution so that the modified dispersant can be pre-adsorbed and coated on the surface of the large-particle first positive electrode active material. This achieves the "activation" pretreatment of the large-particle first positive electrode active material, creating favorable interface conditions for the subsequent introduction of small-particle second positive electrode active material, and avoiding the agglomeration of the large-particle first positive electrode active material due to its high surface energy. Secondly, the first slurry, which has undergone "activation" pretreatment, is mixed with all of the second slurry. Since the surface of the large particles of the first positive electrode active material has been pre-coated with the modified dispersant, when the small particles of the second positive electrode active material are added, the modified dispersant can more effectively act as a "bridge" and "isolate" between the first and second positive electrode active materials. By reducing the system disorder and interfacial energy, it greatly promotes the filling and uniform distribution of the second positive electrode active material in the gaps between the first positive electrode active materials, forming a stable "nested large and small particles" structure. This fundamentally avoids the separation and agglomeration caused by differences in particle size and density when different positive electrode active materials are mixed, significantly improving the compaction density of the positive electrode sheet and the proportion of active material, laying the foundation for the high energy density of the battery. Finally, the remaining portion of the first slurry is added to the above system, ensuring that all positive electrode active materials undergo the optimal dispersion path, thereby achieving final homogenization of the mixed slurry. The resulting system, where the first and second positive electrode active materials are in close contact and uniformly dispersed, helps to construct a continuous and efficient ion and electron transport network in the positive electrode active material layer, reducing the internal resistance of the electrode and thus improving the cycle performance of the lithium battery. Simultaneously, because the dispersion solution has been added in the early stages, the viscosity of the entire mixing process is effectively and precisely controlled, avoiding the need to temporarily add large amounts of N-methylpyrrolidone due to abnormal viscosity increases in the middle of mixing. This ensures that the solid content of the final positive electrode slurry can be maintained at a level close to that of a single-material slurry, contributing to improved production efficiency.

[0033] In one embodiment of this application, the first slurry is prepared by a method comprising the following steps: B1. Weigh out the ternary material, polyvinylidene fluoride binder, conductive carbon black, and conductive CNTs according to the mass ratio of (95-98.5):(1-1.5):(0.5-1.5):(0.5-1.5) and set aside. The ternary material, the binder, the conductive carbon black, and the conductive CNT are mixed and stirred continuously at 20-40°C at a revolution speed of 10-30 rpm and a rotation speed of 500-800 rpm for 10-40 minutes to obtain a dry mixture. B2, the dry mixture is mixed with N-methylpyrrolidone accounting for 15%-25% of the total mass of the dry mixture, and stirred continuously for 60-100 minutes at 30-40°C and vacuum degree of 60-80kPa with a revolution speed of 10-30 rpm and a rotation speed of 800-1200 rpm to obtain the first premixed slurry; B3, the first premixed slurry is mixed with N-methylpyrrolidone accounting for 10%-20% of the total mass of the dry mixture, and stirred continuously for 100-130 min at 30-40℃ and vacuum degree of 60-80kPa with a revolution speed of 10-30 rpm and a rotation speed of 1500-2400 rpm to obtain the first mixed slurry; B4. The viscosity of the first mixed slurry was adjusted to 5000-12000 mpa.s using N-methylpyrrolidone; then the slurry was reverse-stirred and stirred at a speed of 10-30 rpm under a vacuum of 60-80 kPa for 10-60 min, and then sieved to obtain the first positive electrode slurry.

[0034] In one embodiment of this application, the second slurry is prepared by a method comprising the following steps: C1, weigh out lithium iron phosphate material, polyvinylidene fluoride binder, and sodium carboxymethyl cellulose dispersant according to the mass ratio (95.5-98.5):(1-2.5):(0.5-2), and set aside; Lithium iron phosphate and polyvinylidene fluoride binder are mixed and stirred continuously at 20-40℃ with an orbital speed of 10-30 rpm and a rotational speed of 500-800 rpm for 10-40 minutes to obtain a dry powder mixture. C2, the dry powder mixture is mixed with N-methylpyrrolidone accounting for 15%-25% of the total mass of the dry powder mixture, and stirred continuously for 60-100 min at 30-40℃ and vacuum degree of 60-80kPa with a revolution speed of 10-30 rpm and a rotation speed of 800-1200 rpm to obtain the second premixed slurry; C3, the second premixed slurry is mixed with all the dispersant and N-methylpyrrolidone accounting for 10%-20% of the total mass of the dry powder mixture, and stirred continuously for 100-130 min at 30-40℃ and vacuum degree 60-80kPa with a revolution speed of 10-30 rpm and a rotation speed of 1500-2400 rpm to obtain the second mixed slurry; C4, using N-methylpyrrolidone to adjust the viscosity of the second mixed slurry to 5000-12000 mpa.s; then reverse stirring of the slurry, under vacuum of 60-80 kPa and a revolution speed of 10-30 rpm for 10-60 min, and sieve to obtain the second positive electrode slurry.

[0035] In one embodiment of this application, the modified dispersant is prepared by a method comprising the following steps: A1. The solid carrier is mixed with the solvent and stirred. The pH value of the mixture is adjusted to 4-5, and stirring is continued to obtain a mixed solution. For example, the pH value of the mixture is any value of 4, 4.3, 4.5, 4.7, 4.9, 5 or any value within the range of any two of the above values. A2, the surfactant is mixed with the mixed solution, the reaction temperature is adjusted to 40-60℃ and stirred, and the resulting reaction product is subjected to solid-liquid separation to obtain the modified dispersant. Exemplarily, the reaction temperature is any value selected from 40℃, 45℃, 50℃, 53℃, 58℃, and 60℃, or any value within the range formed by any two of the above values.

[0036] Preferably, the solvent in A1 includes ethanol; the first stirring time in A1 is 20-40 min, and the second stirring time is 10-20 min; for example, the first stirring time includes any value of 20 min, 30 min, 40 min or any value within the range of any two of the above values, and the second stirring time is any value of 10 min, 20 min, 30 min or any value within the range of any two of the above values.

[0037] Preferably, in A1, dilute hydrochloric acid with a concentration of 0.08-0.12 mol / L is used to adjust the pH value of the mixed system; for example, the concentration of dilute hydrochloric acid is any value among 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, or any value within the range of any two of the above values.

[0038] Preferably, 2-4g of the solid carrier is mixed with every 100mL of the solvent in A1; exemplaryly, the mass of the solid carrier mixed in every 100mL of the solvent is any value of 2g, 3g, or 4g, or any value within the range of any two of the above values.

[0039] Preferably, adjusting the reaction temperature in A2 refers to placing the surfactant and the mixed solution in an oil bath at 40-60°C; the stirring time is 3-5 hours, and the stirring speed is 400-600 rpm; for example, the oil bath temperature is any value among 40°C, 50°C, and 60°C, or any value within the range of any two of the above values; the stirring time is any value among 3 hours, 4 hours, and 5 hours, or any value within the range of any two of the above values; and the stirring speed is any value among 400 rpm, 500 rpm, and 600 rpm, or any value within the range of any two of the above values.

[0040] Preferably, the modified dispersant is obtained by further performing solid-liquid separation on the obtained reaction product and then proceeding to washing and drying steps.

[0041] The modified dispersant prepared using the method described in this application can protonate functional groups such as -COOH and -OH on the surface of the solid support under weakly acidic conditions, thereby enhancing its surface charge and reactivity and creating conditions for subsequent chemical adsorption or strong interactions. At the same time, surfactant molecules are more likely to bind tightly to the "activated" solid support through hydrogen bonds, ionic bonds, or chemical bonds under these conditions. This makes the final modified dispersant no longer a simple physical adsorption, but rather a strong anchoring on the surface of the positive electrode active material, making it difficult for the modified dispersant to desorb from the particle surface, thus ensuring the long-term effect of dispersion and process stability.

[0042] In one embodiment of this application, the dispersion solution includes the modified dispersant and a solvent, wherein the mass percentage of the modified dispersant in the dispersion solution is 1%-10%; and the solvent is the same as the solvent used in the first slurry and / or the second slurry. Exemplarily, the mass percentage of the modified dispersant in the dispersion solution is any value selected from 1%, 3%, 4%, 6%, 7%, 8%, and 10%, or any value within a range formed by any pair of the above values.

[0043] In this application, a dispersion solution is prepared by mixing a modified dispersant with N-methylpyrrolidone, and then the dispersion solution is added to the positive electrode slurry. On the one hand, this helps to improve the full dispersion of the modified dispersant in the positive electrode slurry. On the other hand, the N-methylpyrrolidone in the dispersion solution acts as a supplementary solvent to adjust the viscosity of the mixed slurry, which can avoid the sudden drop in the solid content of the positive electrode slurry due to the temporary addition of a large amount of N-methylpyrrolidone. Furthermore, by adjusting the mass ratio of the modified dispersant in the dispersion solution, it can also be ensured that the modified dispersant in the dispersion solution acts uniformly between the large particles of the first positive electrode active material and the small particles of the second positive electrode active material, fundamentally promoting the uniform dispersion of the first positive electrode active material and the second positive electrode active material and preventing agglomeration. If the mass ratio of the modified dispersant is too low, it cannot fully coat the surface of the large particles of the first positive electrode active material in subsequent mixing, forming sufficient steric hindrance and electrostatic repulsion. This will not effectively "reduce the surface energy of the system" and "reduce the disorder of the system," resulting in poor dispersion and the risk of agglomeration and increased viscosity of the positive electrode slurry. If the mass ratio of the modified dispersant is too high, it may lead to excessive inactive components in the slurry or the formation of an excessively thick adsorption layer on the surface of the positive electrode active material particles. This may affect the rheological properties, coating performance, and the compaction density and energy density of the final positive electrode sheet.

[0044] In one embodiment of this application, the mass ratio of the first slurry to the second slurry in the positive electrode slurry is (6-9):(1-4); exemplarily, the mass ratio of the first slurry to the second slurry is any one of 6:4, 9:4, 6:2, 6:1, 8:1, 9:1, or any ratio within the range formed by any pair of the above ratios; the ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is (3-9):1; the ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is any one of 3:1, 4:1, 5:1, 6:1, 8:1, 9:1, or any ratio within the range formed by any pair of the above ratios.

[0045] In this application, by controlling the mass ratio of the first slurry to the second slurry, and the total mass of the first and second slurries to the mass ratio of the dispersion solution, the number of large particles of the first positive electrode active material in the positive electrode slurry is ensured to be sufficient, and there are enough "active sites" on the surface to guide and accommodate the uniform distribution of small particles of the second positive electrode active material. This avoids the agglomeration of small particles of the second positive electrode active material due to excess, thereby realizing the nested structure of the first and second positive electrode active materials. This helps to form a positive electrode active material layer with a more continuous and stable conductive network and ion transport channels, which is beneficial to improving the cycle stability and energy density of the lithium battery.

[0046] In one embodiment of this application, the mass of the first portion of the first slurry accounts for 10%-50% of the total mass of the first slurry. For example, the mass of the first portion of the first slurry accounts for any value among 10%, 15%, 20%, 28%, 30%, 40%, and 50% of the total mass of the first slurry, or any value within the range of any pair of the above values.

[0047] In this application, adjusting the amount of the first portion of the first slurry helps the dispersion solution to fully "activate" the pretreated first positive electrode active material. This ensures that the modified dispersant molecules are fully adsorbed on the surface of the large particles of the first positive electrode active material at the optimal concentration, forming a complete coating layer. This creates the best "anchoring point" and dispersion interface for the subsequent introduction of small particles of the second positive electrode active material. If too much first slurry is added in the pretreatment stage, the modified dispersant may not be able to completely coat all the large particles of the first positive electrode active material due to insufficient dosage, resulting in some large particles of the first positive electrode active material not being effectively activated. This may lead to a sharp increase in viscosity during the subsequent mixing with the entire second slurry.

[0048] In one embodiment of this application, the absolute value of the viscosity difference between the first slurry and the second slurry is less than or equal to 2000 mPa·s. Exemplarily, the absolute value of the viscosity difference between the first slurry and the second slurry is any value selected from 100 mPa·s, 300 mPa·s, 800 mPa·s, 1100 mPa·s, 1500 mPa·s, and 2000 mPa·s, or any value within the range formed by any pair of the aforementioned values.

[0049] This application achieves uniform mixing of the first and second slurries by controlling the absolute value of the viscosity difference between the two slurries during the mixing process to meet the above conditions. When the viscosity of the first slurry containing large particles of the first positive electrode active material is too high, it will cause the second slurry to gel rapidly, and the modified dispersant will be difficult to uniformly fill the spaces between the positive electrode active materials. When the viscosity of the second slurry containing small particles of the second positive electrode active material is too high, the positive electrode slurry obtained after stirring is prone to sedimentation. In addition, due to the high specific surface area of ​​the second positive electrode active material, excessive modified dispersant will be adsorbed on its surface, which will reduce the effective contact area between the positive electrode active material particles and is detrimental to the cycle performance of the positive electrode sheet.

[0050] In one embodiment of this application, the first mixing method includes a first stirring, wherein the revolution speed of the first stirring is 10-25 rpm and the stirring time is 20-30 min; for example, the revolution speed of the first stirring is any value of 10 rpm, 13 rpm, 18 rpm, 20 rpm, 25 rpm or any value within the range of any two of the above values, and the stirring time is any value of 20 min, 22 min, 25 min, 28 min, 30 min or any value within the range of any two of the above values; The second mixing method includes a second stirring, wherein the revolution speed of the second stirring is 10-25 rpm, the rotation speed is 1000-1800 rpm, and the stirring time is 10-40 min; the revolution speed of the second stirring is any value of 10 rpm, 13 rpm, 18 rpm, 20 rpm, 25 rpm or any value within the range of any two of the above values, the rotation speed is any value of 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm or any value within the range of any two of the above values, and the stirring time is any value of 10 min, 20 min, 25 min, 30 min, 40 min or any value within the range of any two of the above values; The third mixing method includes a third stirring and a fourth stirring; The revolution speed in the third stirring process is 10-25 rpm, the rotation speed is 1800-2400 rpm, and the stirring time is 100-130 min. During the third stirring process, the temperature is maintained at 30-40℃ and the vacuum degree is 60-80 kPa. The revolution speed in the third stirring process is any value from 10 rpm, 13 rpm, 18 rpm, 20 rpm, 25 rpm, or any value within any range of any two of the above values; the rotation speed is any value from 1800 rpm, 2000 rpm, 2300 rpm, 2400 rpm, or any value within any range of any two of the above values; the stirring time is any value from 100 min, 110 min, 115 min, 120 min, 130 min, or any value within any range of any two of the above values; the temperature is any value from 30℃, 35℃, 40℃, or any value within any range of any two of the above values; and the vacuum degree is 60 kPa or 70 kPa. Any value in 80 kPa or any value within the range of any two of the above values; The fourth stirring is in the opposite direction of revolution to the third stirring; the revolution speed of the fourth stirring is 10-25 rpm, and the stirring time is 10-60 min; the vacuum degree is maintained at 60-80 kPa during the fourth stirring process; the revolution speed of the fourth stirring is any value of 10 rpm, 13 rpm, 18 rpm, 20 rpm, 25 rpm or any value within the range of any two of the above values; the stirring time is any value of 10 min, 20 min, 30 min, 40 min, 50 min, 60 min or any value within the range of any two of the above values; the vacuum degree is any value of 60 kPa, 70 kPa, 80 kPa or any value within the range of any two of the above values.

[0051] The first stirring in this application uses low-shear, long-term, gentle mixing to ensure that the modified dispersant is fully wetted and coated on the surface of the large-particle first positive electrode active material, laying the foundation for subsequent dispersion. The second stirring, under low revolution and high rotation conditions, introduces high-intensity shear force to efficiently break up the agglomerates of small-particle second positive electrode active material and uniformly embed them into the network of activated first positive electrode active material. The third stirring further increases the rotation speed and extends the mixing time, which helps to completely eliminate the micro-agglomeration phenomenon in the mixed slurry. The fourth stirring uses reverse, low-speed revolution to eliminate the internal stress and mixing dead zones in the mixed slurry without introducing new shear, significantly improving the stability and coating consistency of the finally prepared positive electrode slurry.

[0052] A second aspect of this application provides a battery including a negative electrode and a positive electrode as described above.

[0053] The following describes the implementation methods of this application. The implementation methods described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the implementation methods, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents, materials, or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0054] Example 1 1. Preparation of modified dispersants The modified dispersant was prepared by a method comprising the following steps: A1. Mix 3g of solid support (mesoporous silica microspheres) with 100mL of solvent (ethanol) and stir for 30min. Adjust the pH of the mixture to 4.5 with 0.1mol / L dilute hydrochloric acid and continue stirring for 15min to obtain a mixed solution. A2, 0.3g of surfactant (hexadecyltrimethylammonium bromide) was mixed with the above mixed solution, the oil bath reaction temperature was adjusted to 45℃ and stirred at 600rpm for 4h, and the resulting reaction product was subjected to solid-liquid separation, washing and drying (60℃) to obtain the modified dispersant.

[0055] 2. Preparation of positive electrode slurry 2.1 Preparation of the first slurry The first slurry was prepared using a method comprising the following steps: B1. Ternary materials (lithium nickel cobalt manganese oxide), polyvinylidene fluoride binder, conductive carbon black, and conductive CNTs are mixed in a mass ratio of 96.5:1.5:1.5:0.5 and stirred continuously at 35°C with a revolution speed of 15 rpm and a rotation speed of 800 rpm for 30 minutes to obtain a dry mixture. B2, the above dry mixture is mixed with N-methylpyrrolidone at 18% of the mass of the dry mixture, and stirred continuously for 90 minutes at 40°C and 80 kPa vacuum with a revolution speed of 25 rpm and a rotation speed of 1000 rpm to obtain the first premixed slurry; B3. The first premixed slurry is mixed with N-methylpyrrolidone at 10% of the mass of the dry mixture, and stirred continuously for 120 minutes at 40°C and 80 kPa vacuum with a revolution speed of 25 rpm and a rotation speed of 2000 rpm to obtain the first mixed slurry. B4, the viscosity of the first mixed slurry was adjusted to 8000 mPa·s using N-methylpyrrolidone; then the slurry was reverse-stirred and stirred at 20 rpm for 30 min in a vacuum environment of 80 kPa. The resulting slurry was passed through a 150-mesh sieve to obtain the first positive electrode slurry.

[0056] 2.2 Preparation of the second slurry The second slurry was prepared using a method comprising the following steps: C1, weigh out lithium iron phosphate material, polyvinylidene fluoride binder and sodium carboxymethyl cellulose dispersant in a mass ratio of 96.5:2.5:1.0, and set aside; Lithium iron phosphate material and polyvinylidene fluoride binder were mixed and stirred continuously at 32°C with a revolution speed of 15 rpm and a rotation speed of 800 rpm for 30 minutes to obtain a dry powder mixture. C2, the above dry powder mixture is mixed with N-methylpyrrolidone accounting for 20% of the total mass of the dry powder mixture, and stirred continuously for 90 minutes at 40°C and 80 kPa with a revolution speed of 25 rpm and a rotation speed of 1000 rpm to obtain the second premixed slurry; C3, the above second premixed slurry is mixed with sodium carboxymethyl cellulose dispersant and N-methylpyrrolidone accounting for 15% of the total mass of the dry powder mixture, and stirred continuously for 120 min at 40°C and vacuum degree of 80 kPa with a revolution speed of 25 rpm and a rotation speed of 2000 rpm to obtain the second mixed slurry; C4, using N-methylpyrrolidone to adjust the viscosity of the second mixed slurry to 8500 mpa.s; then reverse stirring of the slurry, in an environment with a vacuum degree of 80 kPa, at a revolution speed of 20 rpm for 30 min, the resulting slurry is passed through a 150 mesh sieve to obtain the second positive electrode slurry.

[0057] 2.3 The positive electrode slurry was prepared using a method comprising the following steps: S1, Weigh the first slurry prepared in 2.1 and the second slurry prepared in 2.2 above according to the mass ratio of the first slurry to the second slurry of 7:3, and set them aside; The modified dispersant was mixed with N-methylpyrrolidone to obtain a dispersion solution with a modified dispersant mass ratio of 5%, which was then set aside. S2, mix the first part of the first slurry (accounting for 30% of the total mass of the first slurry) with the dispersion solution (the ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is 6:1), and stir at a revolution speed of 15 rpm for 25 min to obtain the premixed slurry; The premixed slurry was mixed with the second slurry and stirred for 30 minutes at a revolution speed of 25 rpm and a rotation speed of 1500 rpm to obtain a semi-step slurry. The above-mentioned semi-step slurry is mixed with the remaining part of the first slurry (accounting for 70% of the total mass of the first slurry), and stirred for 120 minutes at 40°C and 80 kPa with a revolution speed of 25 rpm and a rotation speed of 2000 rpm. Then the stirring paddle is reversed and stirred for 30 minutes at 80 kPa with a revolution speed of 20 rpm. The mixture is then passed through a 150-mesh sieve to obtain the positive electrode slurry.

[0058] 3. Preparation of the positive electrode sheet The positive electrode slurry prepared in step 2 was coated onto the positive electrode current collector by transfer coating. After drying, a positive electrode roll was obtained, which was then rolled to obtain a positive electrode sheet. The coating weight of the positive electrode sheet was 0.4 g / 1540.25 mm. 2 The coating thickness is 0.216 mm.

[0059] 4. Preparation of lithium batteries The positive electrode, separator, and negative electrode are arranged in sequence, wound and assembled, and the electrolyte is injected into the dry cell. After formation and capacity testing, a lithium-ion soft-pack battery is obtained.

[0060] The negative electrode sheet is prepared using the following steps: The negative electrode active material (hard carbon surface coated with soft carbon material): conductive agent: binder = 95.5:2.5:2 is weighed, mixed and stirred evenly, and deionized water is added with continued stirring to obtain a negative electrode slurry. This negative electrode slurry is then coated onto a negative electrode current collector using a transfer coating method. After drying, a negative electrode roll is obtained, which is then rolled to obtain the negative electrode sheet. The coating weight of the negative electrode sheet is 0.187 g / 1540.25 mm. 2 The coating thickness is 0.16 mm.

[0061] The separator is made of polypropylene base film with a thickness of 9μm, coated with PVDF with a thickness of 3μm on both sides, and then coated with 3μm of alumina by gravure.

[0062] The electrolyte consists of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 1.5:1:0.5 as solvents, and also contains LiPF6 at a concentration of 1.2 mol / L.

[0063] Example 2 The difference between this embodiment and Example 1 is that the preparation of the modified dispersant and the positive electrode slurry are different; The modified dispersant was prepared by a method comprising the following steps: A1. Mix 2g of solid support (metal-organic framework) with 100mL of solvent (ethanol) and stir for 40min. Adjust the pH of the mixture to 5 with 0.08mol / L dilute hydrochloric acid and continue stirring for 10min to obtain a mixed solution. A2. Mix 0.1g of surfactant (Span series surfactant) with the above mixed solution, adjust the oil bath reaction temperature to 60℃ and stir at 600rpm for 3h. Separate the solid and liquid components of the resulting reaction product, wash and dry (60℃) to obtain the modified dispersant.

[0064] The positive electrode slurry is prepared by a method including the following steps: S1, Weigh the first slurry prepared in 2.1 and the second slurry prepared in 2.2 above according to the mass ratio of the first slurry to the second slurry of 6:4, and set them aside; The modified dispersant was mixed with N-methylpyrrolidone to obtain a dispersion solution with a modified dispersant mass ratio of 1%, which was then set aside. S2, mix the first part of the first slurry (accounting for 10% of the total mass of the first slurry) with the dispersion solution (the ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is 9:1), and stir at a revolution speed of 10 rpm for 30 min to obtain the premixed slurry; The above premixed slurry was mixed with the second slurry and stirred for 40 minutes at a revolution speed of 10 rpm and a rotation speed of 1000 rpm to obtain a semi-step slurry. The above-mentioned semi-step slurry is mixed with the remaining part of the first slurry (accounting for 90% of the total mass of the first slurry), and stirred for 100 minutes at 40°C and 80 kPa vacuum with a revolution speed of 25 rpm and a rotation speed of 2400 rpm. Then the stirring paddle is reversed and stirred for 10 minutes at 80 kPa vacuum with a revolution speed of 25 rpm. The mixture is then passed through a 150-mesh sieve to obtain the positive electrode slurry.

[0065] All other steps and parameter settings are consistent with those in Example 1.

[0066] Example 3 The difference between this embodiment and Example 1 is that the preparation of the modified dispersant and the positive electrode slurry are different; The modified dispersant was prepared by a method comprising the following steps: A1. Mix 3g of solid support (covalent organic framework) with 100mL of solvent (ethanol) and stir for 20min. Adjust the pH of the mixture to 4 with 0.12mol / L dilute hydrochloric acid and continue stirring for 20min to obtain a mixed solution. A2, 0.1g of surfactant (hexadecyltrimethylammonium bromide) was mixed with the above mixed solution, the oil bath reaction temperature was adjusted to 40℃ and stirred at 600rpm for 5h, and the resulting reaction product was subjected to solid-liquid separation, washing and drying (60℃) to obtain the modified dispersant.

[0067] The positive electrode slurry is prepared by a method including the following steps: S1, Weigh the first slurry prepared in 2.1 and the second slurry prepared in 2.2 above according to the mass ratio of the first slurry to the second slurry of 9:1, and set them aside; The modified dispersant was mixed with (N-methylpyrrolidone) to obtain a dispersion solution with a modified dispersant mass ratio of 10, which was then set aside. S2, mix the first part of the first slurry (accounting for 50% of the total mass of the first slurry) with the dispersion solution (the ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is 5:1), and stir at a revolution speed of 25 rpm for 20 min to obtain the premixed slurry; The above premixed slurry is mixed with the second slurry and stirred for 10 minutes at a revolution speed of 25 rpm and a rotation speed of 1800 rpm to obtain a semi-step slurry; The above-mentioned semi-step slurry is mixed with the remaining part of the first slurry (accounting for 50% of the total mass of the first slurry), and stirred for 130 minutes at 40°C and 80 kPa vacuum with a revolution speed of 10 rpm and a rotation speed of 1800 rpm. Then the stirring paddle is reversed and stirred for 60 minutes at 80 kPa vacuum with a revolution speed of 10 rpm. The mixture is then passed through a 150-mesh sieve to obtain the positive electrode slurry.

[0068] All other steps and parameter settings are consistent with those in Example 1.

[0069] Example 4 The difference between this embodiment and Example 1 is that the surfactant in the modified dispersant is sodium dodecyl sulfate; all other steps and parameter settings are consistent with Example 1.

[0070] Example 5 The difference between this embodiment and Embodiment 1 is that the ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is 2:1; all other steps and parameter settings are consistent with Embodiment 1.

[0071] Example 6 The difference between this embodiment and Embodiment 1 is that the ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is 12:1; all other steps and parameter settings are consistent with Embodiment 1.

[0072] Example 7 The difference between this embodiment and Embodiment 1 is that the first part of the first slurry accounts for 60% of the total mass of the first slurry; the other steps and parameter settings are consistent with Embodiment 1.

[0073] Example 8 The difference between this embodiment and Embodiment 1 is that the first part of the first slurry accounts for 5% of the total mass of the first slurry; the other steps and parameter settings are consistent with Embodiment 1.

[0074] Example 9 The difference between this embodiment and Embodiment 1 is that the viscosity difference between the first slurry and the second slurry is 2500 mPa·s; all other steps and parameter settings are consistent with Embodiment 1.

[0075] Example 10 The difference between this embodiment and Embodiment 1 is that the viscosity difference between the second slurry and the first slurry is 2500 mPa·s; all other steps and parameter settings are consistent with Embodiment 1.

[0076] Example 11 The difference between this embodiment and Embodiment 1 is that, in the preparation process of the positive electrode slurry, the modified dispersant is directly mixed with the first part of the first slurry; the other steps and parameter settings are consistent with Embodiment 1.

[0077] Example 12 The difference between this embodiment and Embodiment 1 is that the positive electrode slurry is prepared using the following steps: S1, Weigh the first slurry prepared in 2.1 and the second slurry prepared in 2.2 above according to the mass ratio of the first slurry to the second slurry of 7:3, and set them aside; The modified dispersant was mixed with N-methylpyrrolidone to obtain a dispersion solution with a modified dispersant mass ratio of 5%, which was then set aside. S2, mix the first part of the second slurry (accounting for 30% of the total mass of the second slurry) with the dispersion solution (the ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is 6:1), and stir at a revolution speed of 15 rpm for 25 min to obtain a premixed slurry; The above premixed slurry was mixed with the first slurry and stirred for 30 minutes at 40°C and 80 kPa vacuum with a revolution speed of 25 rpm and a rotation speed of 1500 rpm to obtain a semi-step slurry. The above-mentioned semi-step slurry is mixed with the remaining part of the second slurry (accounting for 70% of the total mass of the second slurry), and stirred at a vacuum of 80 kPa with a revolution speed of 25 rpm and a rotation speed of 2000 rpm for 120 min. Then the stirring paddle is reversed and stirred at a vacuum of 80 kPa with a revolution speed of 20 rpm for 30 min. The mixture is then passed through a 150-mesh sieve to obtain the positive electrode slurry.

[0078] All other steps and parameter settings are consistent with those in Example 1.

[0079] Comparative Example 1 The difference between this comparative example and Example 1 is that no modified dispersant is used in the positive electrode slurry; specifically, the positive electrode slurry is prepared by a method including the following steps: Specifically, the first slurry prepared in section 2.1 and the second slurry prepared in section 2.2 are weighed according to a mass ratio of 7:3. The first slurry is directly added to the second slurry, and the mixture is stirred for 120 minutes at a stirring temperature of 40℃, a vacuum degree of 80kPa, a revolution speed of 25rpm, and a rotation speed of 2000rpm. Then, the stirring paddle is reversed and stirred for 30 minutes at a revolution speed of 20rpm under 80kPa. The mixture is then passed through a 150-mesh sieve to obtain the positive electrode slurry.

[0080] All other steps and parameter settings are consistent with those in Example 1.

[0081] Comparative Example 2 The difference between this comparative example and Example 1 is that no modified dispersant is used in the positive electrode slurry; specifically, the positive electrode slurry is prepared by a method including the following steps: A1. Weigh out lithium iron phosphate material, lithium nickel cobalt manganese oxide material, polyvinylidene fluoride binder, conductive carbon black, conductive CNTs, and sodium carboxymethyl cellulose dispersant in a mass ratio of 67.6:29.0:1.5:1.0:0.5:0.4, and set aside. A2, mix lithium iron phosphate material, lithium nickel cobalt manganese oxide material, polyvinylidene fluoride binder and conductive carbon black, and pre-stir at 40°C with a revolution speed of 15 rpm and a rotation speed of 800 rpm for 30 minutes to obtain a dry mixture; A3. Add conductive CNTs and N-methylpyrrolidone accounting for 20% of the total weight of the dry mixture to the above dry mixture, and stir at 40°C and 80 kPa with an orbital speed of 25 rpm and a rotational speed of 1000 rpm for 90 min to obtain a premix. A4. Add sodium carboxymethyl cellulose dispersant and N-methylpyrrolidone accounting for 20% of the total weight of the dry mixture to the above premix, and stir for 120 minutes at 40°C and vacuum of 80 kPa with a revolution speed of 25 rpm and a rotation speed of 2000 rpm to form a premixed slurry. A5, the viscosity of the above premixed slurry was adjusted to 8000 mpa·s using N-methylpyrrolidone; A6. Reverse the stirring paddle and stir the slurry obtained in A5 at a vacuum of 80 kPa and a revolution speed of 20 rpm for 30 minutes. Pass it through a 150-mesh sieve to obtain the positive electrode slurry.

[0082] All other steps and parameter settings are consistent with those in Example 1.

[0083] Comparative Example 3 The difference between this comparative example and Example 1 is that an equal weight of hexadecyltrimethylammonium bromide was used instead of the modified dispersant in the preparation of the positive slurry; all other steps and parameter settings were consistent with those in Example 1.

[0084] Comparative Example 4 The difference between this comparative example and Example 1 is that the positive electrode sheet does not contain a modified dispersant, and the positive electrode active material in the positive electrode slurry is lithium iron phosphate.

[0085] Comparative Example 5 The difference between this comparative example and Example 1 is that the positive electrode sheet does not contain a modified dispersant, and the positive electrode active material in the positive electrode slurry is lithium nickel cobalt manganese oxide.

[0086] Test methods I. Lithium-ion battery discharge capacity test 1. The specific steps for testing the discharge capacity of lithium iron phosphate batteries are as follows: Let the battery stand at 25℃ for 1 hour, discharge it at a constant current of 0.33C to 2.5V, let it stand for 30 minutes, then charge it at a constant current of 0.33C to 3.65V, then charge it at a constant voltage of 3.65V until the current is less than or equal to 0.05C, let it stand for 30 minutes, then discharge it at a constant current of 1C to 2.5V, and then discharge it at a constant voltage of 2.5V until the current is 0.05C. Record the discharge capacity at this time.

[0087] 2. The specific test steps for the discharge capacity of the ternary lithium battery and the lithium batteries in the embodiments and comparative examples of this application are as follows: The battery is left to stand at 25°C for 1 hour, discharged at a constant current of 0.33C to 2.5V, left to stand for 30 minutes, charged at a constant current of 0.33C to 4.25V, charged at a constant voltage of 4.25V until the current is less than or equal to 0.05C, left to stand for 30 minutes, discharged at a constant current of 1C to 2.5V, and discharged at a constant voltage of 2.5V until the current is 0.05C. The discharge capacity at this time is recorded.

[0088] II. Lithium-ion battery cycle performance test 1. The specific steps for the cycle performance test of lithium iron phosphate batteries are as follows: In a 25℃ chamber, charge the battery at a constant current rate of 0.33C to 3.65V, then charge at a constant voltage of 3.65V until the current cutoff is 0.05C. After resting for 30 minutes, discharge at a constant current rate of 0.33C to 2.5V, let it rest, and cycle the battery for three cycles. The capacity of the last cycle is taken as the actual battery capacity C0. Charge and discharge the battery using 1C / 1C cycles, comparing the capacity of each cycle with the first cycle to obtain the cycle capacity retention rate. Stop cycling when the capacity reaches 0.8*C0, and record the number of cycles.

[0089] 2. The specific steps for the cycle performance test of the ternary lithium battery and the lithium batteries in the embodiments and comparative examples of this application are as follows: Pure ternary and ternary lithium iron phosphate batteries: Charged at a constant current rate of 0.33C to 4.25V in a 25℃ chamber, then charged at a constant voltage of 4.25V until the current cutoff is 0.05C. After resting for 30 minutes, discharged at a constant current rate of 0.33C to 2.5V, and then rested. The battery was cycled for three cycles, and the capacity of the last cycle was taken as the actual battery capacity C0. The battery was charged and discharged using 1C / 1C, and the capacity of each cycle was compared with the first cycle to obtain the cycle capacity retention rate. Cycling was stopped when the capacity reached 0.8*C0, and the number of cycles was recorded.

[0090] III. Lithium-ion battery AC internal resistance test The internal resistance data of a lithium battery (50% SOC) was tested using an internal resistance tester at an environment of 25℃.

[0091] Table 1

[0092] Based on Examples 1-4, Comparative Examples 1-2, and Table 1, it can be seen that this application, by introducing a modified dispersant into the positive electrode slurry through the addition of a dispersion solution during the preparation process, can significantly improve the cycle life of lithium batteries and promote the high energy density of lithium batteries. This is because the addition of the modified dispersant can uniformly disperse large particles of lithium nickel cobalt manganese oxide and small particles of lithium iron phosphate in the positive electrode active material layer, and the small particles of lithium iron phosphate can fill the spaces between the large particles of lithium nickel cobalt manganese oxide, which helps to form a dense positive electrode active material layer, improves the distribution of the conductive network in the positive electrode active material layer, and significantly improves the cycle performance of lithium batteries; at the same time, it makes the specific capacity of both lithium nickel cobalt manganese oxide and lithium iron phosphate close to the theoretical value, which all contributes to improving the energy density of the positive electrode sheet.

[0093] Based on Example 1, Comparative Example 3, and Table 1, it can be seen that for the blending system of lithium nickel cobalt manganese oxide slurry and lithium iron phosphate slurry, if hexadecyltrimethylammonium bromide is used instead of the modified dispersant, its long-term stability on the surface of the positive electrode active material decreases, and the long-term effect and stability of the dispersion cannot be guaranteed. This will lead to uneven dispersion of the two positive electrode active materials in the blending system, resulting in a lower specific capacity of the lithium battery and a significant increase in internal resistance.

[0094] Based on Example 1, Comparative Examples 4-5 and Table 1, it can be seen that the lithium-ion battery of this application can maintain excellent cycle performance while achieving high energy density.

[0095] Based on Examples 1, 5-6, and Table 1, it can be seen that when the mass of the dispersion solution added to the positive electrode slurry is high, there is a large amount of modified dispersant in the system. However, the number of cycles of the lithium battery decreases and the internal resistance increases. This is because excessive modified dispersant will agglomerate in the positive electrode slurry system, which is detrimental to the stability of the positive electrode slurry system and has a certain deteriorating effect on the long-term cycling of the lithium battery. When the mass of the dispersion solution added to the positive electrode slurry is low, the number of cycles of the lithium battery decreases and the internal resistance increases. This is because there is too little modified dispersant in the system, which is not conducive to the formation of a stable "nested large and small particles" structure in the positive electrode slurry and is also not conducive to the homogenization of the positive electrode slurry.

[0096] Based on Examples 1, 7-8, and Table 1, it can be seen that when the amount of lithium nickel cobalt manganese oxide slurry added during mixing with the dispersion solution is excessive, the specific capacity of the lithium battery is significantly reduced and the internal resistance increases. This is because excessive large-particle lithium nickel cobalt manganese oxide material will preemptively adsorb most of the modified dispersant, resulting in insufficient uniform dispersion of the subsequently added lithium iron phosphate slurry by the remaining modified dispersant, leading to a viscosity rebound phenomenon in the cathode slurry after 5 hours. When the amount of lithium nickel cobalt manganese oxide slurry added during mixing with the dispersion solution is insufficient, although the remaining modified dispersant can uniformly disperse the lithium manganese iron phosphate material during subsequent mixing with the lithium iron phosphate slurry, the stability of the lithium nickel cobalt manganese oxide slurry is significantly compromised due to the excessive addition of lithium nickel cobalt manganese oxide, making it prone to gelation and leading to deterioration of lithium battery performance.

[0097] Combining Examples 1, 9-10, and Table 1, it can be seen that when the absolute value of the viscosity difference between the two slurries is greater than 2000 mPa·s, the cycle number of the lithium battery decreases and the internal resistance increases. This is because when the viscosity of the lithium nickel cobalt manganese oxide slurry is too high, it will cause the lithium iron phosphate slurry to gel rapidly, and the modified dispersant will also be difficult to uniformly fill between the lithium nickel cobalt manganese oxide active material and the lithium iron phosphate active material. When the viscosity of the lithium iron phosphate slurry is too high, the positive electrode slurry obtained after stirring is prone to sedimentation. In addition, due to the high specific surface area of ​​the lithium iron phosphate positive electrode active material, it will cause excessive adsorption of modified dispersant on its surface, which will reduce the effective contact area between the positive electrode active material particles and is not conducive to the performance of the lithium battery.

[0098] Based on Examples 1 and 11 and Table 1, it can be seen that when the modified dispersant is directly added to the lithium nickel cobalt manganese oxide slurry, the modified dispersant is not sufficiently dispersed. During the slurry stirring process, the modified dispersant is prone to agglomeration or enrichment on the surface of the lithium nickel cobalt manganese oxide material. Therefore, for the lithium iron phosphate slurry subsequently added to the lithium nickel cobalt manganese oxide slurry, the amount of modified dispersant that can play a dispersing role decreases sharply. At this time, the amount of modified dispersant in the mixed system is insufficient to alleviate the slurry gelation problem, resulting in a low specific capacity of the lithium battery and an increased internal resistance.

[0099] Based on Examples 1 and 12 and Table 1, it can be seen that the specific capacity and cycle performance of the lithium battery are slightly reduced. This is because, when the lithium iron phosphate slurry is mixed with the dispersion solution in advance, although the modified dispersant can be dispersed between small particles of lithium iron phosphate material, the gaps between the lithium iron phosphate materials are small. The large particles of lithium nickel cobalt manganese oxide material added to the second slurry cannot be "embedded" between the lithium iron phosphate materials. The "bridging" role of the modified dispersant between the lithium iron phosphate material and the lithium nickel cobalt manganese oxide material cannot be fully utilized. It is impossible to effectively avoid the separation and agglomeration of the positive electrode active material in the mixed slurry due to the difference in particle size and density, which reduces the uniformity of the final positive electrode slurry and is not conducive to improving the cycle performance and fully utilizing the energy density of the lithium battery.

[0100] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application, but such modifications or substitutions are all within the scope of protection of this application.

Claims

1. A positive electrode plate, characterized in that: It includes a positive electrode active material layer, wherein the positive electrode active material layer comprises a first positive electrode active material, a second positive electrode active material, and a modified dispersant; The particle size of the first positive electrode active material is larger than that of the second positive electrode active material; The first positive electrode active material includes at least one of ternary materials and lithium manganese iron phosphate materials, and the second active material includes at least one of lithium iron phosphate materials, lithium manganese oxide materials, and lithium-rich manganese-based materials. The modified dispersant comprises a solid carrier and a surfactant; the solid carrier comprises at least one of mesoporous silica microspheres, metal-organic frameworks, covalent organic frameworks, hydrogen-bonded organic frameworks, and porous polymer microspheres; the surfactant comprises at least one of cationic surfactants, anionic surfactants, and nonionic surfactants.

2. The positive electrode sheet according to claim 1, characterized in that: The mass ratio of the solid carrier to the surfactant is (10-30):1, and / or the surfactant includes at least one of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, Span series surfactants, and Tween series surfactants.

3. The positive electrode sheet according to any one of claims 1-2, characterized in that: The positive electrode active material layer is formed from a positive electrode slurry, and the preparation method of the positive electrode slurry includes the following steps: S1, prepare a first slurry including the first positive electrode active material, a second slurry including the second positive electrode active material, and a dispersion solution including the modified dispersant, for later use; S2, the first portion of the first slurry is mixed with the dispersion solution to obtain a premixed slurry; the premixed slurry is then mixed with the second slurry to obtain a semi-step slurry; The half-step slurry is mixed with the remaining portion of the first slurry in a third mixing process to obtain the positive electrode slurry.

4. The positive electrode sheet according to claim 3, characterized in that: The modified dispersant is prepared by a method comprising the following steps: A1. The solid carrier is mixed with the solvent and stirred. The pH of the mixture is adjusted to 4-5, and stirring is continued to obtain a mixed solution. A2, the surfactant is mixed with the mixed solution, the reaction temperature is adjusted to 40-60℃ and stirred, and the resulting reaction product is subjected to solid-liquid separation to obtain the modified dispersant.

5. The positive electrode sheet according to claim 3, characterized in that: The dispersion solution includes the modified dispersant and a solvent, wherein the mass percentage of the modified dispersant in the dispersion solution is 1%-10%. The solvent is the same as the solvent used in the first slurry and / or the second slurry.

6. The positive electrode sheet according to claim 3, characterized in that: In the positive electrode slurry, the mass ratio of the first slurry to the second slurry is (6-9):(1-4). The ratio of the total mass of the first slurry and the second slurry to the mass of the dispersion solution is (3-9):

1.

7. The positive electrode sheet according to claim 3, characterized in that: The mass of the first portion of the first slurry accounts for 10%-50% of the total mass of the first slurry.

8. The positive electrode sheet according to claim 3, characterized in that: The absolute value of the viscosity difference between the first slurry and the second slurry is less than or equal to 2000 mPa·s.

9. The positive electrode sheet according to claim 3, characterized in that: The first mixing method includes a first stirring, wherein the revolution speed of the first stirring is 10-25 rpm and the stirring time is 20-30 min; The second mixing method includes a second stirring, wherein the revolution speed in the second stirring is 10-25 rpm, the rotation speed is 1000-1800 rpm, and the stirring time is 10-40 min; The third mixing method includes a third stirring and a fourth stirring; The revolution speed in the third stirring process is 10-25 rpm, the rotation speed is 1800-2400 rpm, and the stirring time is 100-130 min. The fourth stirring motion is in the opposite direction to the third stirring motion; the fourth stirring motion rotates at a speed of 10-25 rpm and lasts for 10-60 minutes.

10. A battery, characterized in that: It includes a negative electrode and a positive electrode as described in any one of claims 1-9.

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