Ternary positive electrode slurry as well as preparation method and application thereof

Abstract

The invention provides ternary positive electrode slurry, and a preparation method and application thereof. The preparation method comprises the following steps: testing the residual alkali content of the ternary positive electrode material, wherein the residual alkali content comprises the content a of LiOH and the content b of Li2CO3; mixing a solvent, a fluorine-containing binder and a neutralizer for the first time, and then mixing the mixture with a conductive agent and a ternary positive electrode material in sequence to obtain ternary positive electrode slurry; the neutralizer is NH4HSO4 or NH4HSO3, and the addition amount of the neutralizer is calculated by using a specific formula. The acid neutralizer which is quantified according to the residual alkali content of the ternary positive electrode material in a specific relational expression is added in the slurry mixing process, the acid neutralizer can react with residual lithium salt in the ternary positive electrode material to prevent gelatinization of the slurry, residual alkali can be fully neutralized, and meanwhile, excessive acid neutralizer is prevented from corroding lithium oxide in the positive electrode material; meanwhile, the neutralization product can be used as surface layer point-like doping of the ternary positive electrode material, so that the electrochemical performance of a finished battery cell is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a ternary positive electrode slurry, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium-ion batteries are widely used in products in power batteries, 3C, energy storage and other related fields due to their advantages such as high energy density, long life and no memory effect. In recent years, ternary materials have always maintained a high level of competitiveness in the power battery market. The demand for long battery life and high energy has forced the material side to increase the demand for high-nickel materials (Ni ≥ 80%). Since high-nickel ternary materials usually use LiOH as a lithium source and the lithium source will be slightly excessive during the preparation process, most of their finished products are highly alkaline (pH>11), which may cause defluorination reactions of fluorinated binders such as PVDF, causing slurry gelation, increasing the risk of viscosity abnormalities, resulting in waste of resources, and affecting the electrochemical performance of the battery cell.

[0003] At present, the main methods for increasing the stability of ternary slurry include residual alkali control, moisture control, PVDF alkali resistance modification, slurry process parameter optimization, and acidic additives added during the slurry process. For example, Chinese application CN119050307A discloses a low-residual-alkali, high-nickel positive electrode material in which water washing and surface coating are carried out simultaneously, and its preparation method and application, so that the water washing step of reducing residual alkali and the surface coating step of the high-nickel positive electrode material are respectively carried out in the upper aqueous phase and the lower organic phase to obtain a low-residual-alkali, high-nickel positive electrode material. Chinese application CN118291066A discloses a method for preparing positive electrode glue, which uses the carboxyl functional group in the acrylic acid comonomer to provide more polar sites, synthesizes comonomers containing specific groups, copolymerizes and modifies PVDF, and improves the alkali corrosion resistance of PVDF. Chinese application CN119008954A discloses a method for selecting and using organic additives for positive electrode slurry, which can reduce the influence of moisture on the previous process, reduce the alkalinity of the slurry, and improve the dispersion performance of the material.

[0004] The use of acidic additives is a process option that is more suitable for mass production routes. How to simply and reasonably select and use acidic additives is an important optimization and supplementary direction for increasing the viscosity stability of the material slurry and improving the electrochemical performance. However, although the water washing method can remove most of the lithium salt residues on the surface of the material, the damage to the layered structure near the surface is slightly more serious; after the introduction of some acidic additives, they may act as impurity phases / inert phases, which have a negative impact on the battery system and energy density. Chinese application CN112234188A discloses a method for preparing a medium-high nickel ternary positive electrode material slurry, in which additives are added during slurrying, and the additives are selected from one or more of Al2O3, SiO2, TiO2, Mn2O3, P2O5, and NH4H2PO4 to improve the viscosity of the medium-high nickel ternary positive electrode material slurry and generate a coating layer in situ to improve the material performance. However, since the amount of acidic additives added is difficult to accurately control, it is easy to cause abnormal slurry viscosity or even gelation in actual large-scale industrial production processes. Moreover, although some additives can improve the fluidity of the slurry, they may increase electrochemical or electrolyte side reactions, resulting in the risk of abnormal battery cell performance during the use of the material. Summary of the Invention

[0005] The main purpose of the present invention is to provide a ternary positive electrode slurry, a preparation method and application thereof, so as to solve the problem in the prior art that the amount of acidic additives added to the ternary positive electrode slurry is difficult to accurately control, and abnormal viscosity or even gelation is prone to occur, resulting in poor battery performance.

[0006] In order to achieve the above object, according to one aspect of the present invention, a method for preparing a ternary positive electrode slurry is provided, comprising the following steps: step S1, testing the residual alkali content of the ternary positive electrode material, the residual alkali including LiOH and Li2CO3, the content of LiOH being recorded as a, and the content of Li2CO3 being recorded as b; step S2, performing a first mixing of a solvent, a fluorine-containing binder, and a neutralizing agent to obtain a first mixture; step S3, performing a second mixing of the first mixture and a conductive agent to obtain a second mixture; step S4 The second mixture is mixed with the ternary positive electrode material for a third time to obtain a ternary positive electrode slurry, the viscosity of the ternary positive electrode slurry is 3000-5500 mPa·s, and the solid content is ≥71%; wherein the neutralizer is NH4HSO4 or NH4HSO3; the amount of NH4HSO4 added is recorded as M1, M1=d*(2.40*a+1.56*b); the amount of NH4HSO3 added is recorded as M2, M2=d*(2.07*a+1.34*b); 0.5≤d≤1.2.

[0007] The technical solution of the present invention is applied, and an acidic neutralizer is used to improve the stability of the ternary positive electrode material slurry. During the slurrying process, an acidic neutralizer is added according to the residual alkali content of the ternary positive electrode material in a quantitative manner according to a specific relationship. The acidic neutralizer can react with the residual lithium salt in the ternary positive electrode material to reduce the residual alkali content, inhibit the occurrence of defluorination reaction of the fluorine-containing binder, prevent the slurry from gelling, and improve the fluidity of the slurry. At the same time, the surface residual alkali generates LiSO4 or LiSO3 after the reaction. The neutralization product can be used as a point doping on the surface of the ternary positive electrode material to inhibit the side reaction between the surface of the positive electrode material and the electrolyte, and improve the electrochemical performance of the finished battery cell. At the same time, the present invention determines the amount of the neutralizer added according to the specific relationship based on the residual alkali content of the ternary positive electrode material. While fully neutralizing the residual alkali, it can avoid excessive acidic neutralizer from corroding the lithium oxide inside the positive electrode material, thereby avoiding a decrease in capacity. The ternary positive electrode slurry prepared by the method of the present invention has good process stability, and the soft-pack battery cell assembled therewith has a higher capacity retention rate under charge and discharge cycles.

[0008] Furthermore, the general structural formula of the ternary cathode material is Li m Ni x Co y Mn z O2, of which 1 <m<1.05,x+y+z=1,0.8≤x<1,0<y<0.2,0<z<0.2。上述高镍三元正极材料更有利于协同本发明的酸性中和剂精确调控方法,提高电芯的能量密度、容量保持率和循环性能。

[0009] Furthermore, in step S2, the solvent is NMP; and / or the fluorinated binder includes PVDF and / or PTFE; and / or the weight ratio of the fluorinated binder to the solvent is (0.02 to 0.07):1. Adding the fluorinated binder and the solvent according to the above ratio, combined with the quantitative use of the acidic neutralizer of the present invention, can more accurately control the alkaline substances in the slurry, inhibit the defluorination reaction of PVDF, thereby effectively preventing slurry gelation, reducing the risk of abnormal viscosity, improving slurry fluidity, and improving the process stability during the battery cell manufacturing process and the electrochemical performance of the final product.

[0010] Furthermore, in step S3, the conductive agent includes SP, 4% multi-walled carbon nanotubes, and 0.4% single-walled carbon nanotubes; and / or the weight ratio of the conductive agent to the solvent is (1-1.1):1. The above addition conditions also facilitate uniform dispersion of the conductive agent in the slurry and improve the stability of the slurry.

[0011] Furthermore, in step S3, the weight ratio of SP, 4% multi-walled carbon nanotubes, and 0.4% single-walled carbon nanotubes in the conductive agent is 1:(25-35):(5-15). When the amount of the ternary positive electrode material added is within the above range, it is beneficial to maximize the actual capacity of the battery while promoting its full dissolution, which is beneficial to improving the energy density of the battery cell.

[0012] Furthermore, in step S4, the weight ratio of the ternary cathode material to the solvent is (4-6): 1. Under the above ratio, the conductive agent can be evenly distributed among the ternary cathode materials, effectively reducing the electron transfer resistance between the particles.

[0013] Furthermore, in step S4, the ternary cathode material is evenly divided into two parts, namely a first ternary cathode material and a second ternary cathode material; the second mixture is first intermediately mixed with the first ternary cathode material to obtain an intermediate mixture, and then the intermediate mixture is thirdly mixed with the second ternary cathode material to obtain a ternary cathode slurry; the intermediate mixing includes intermediate vacuum stirring for 20 to 40 minutes. The stepwise mixing of the cathode materials helps improve the uniformity and stability of the slurry and reduces the risk of abnormalities caused by gelation.

[0014] According to another aspect of the present invention, a ternary positive electrode slurry is provided, which is obtained using the above-mentioned preparation method of the ternary positive electrode slurry of the present invention, and has significantly improved slurry stability, including viscosity stability and solid content stability.

[0015] According to another aspect of the present invention, a positive electrode plate is provided, comprising a current collector and a ternary positive electrode slurry coated on at least one surface of the current collector. The ternary positive electrode slurry is the ternary positive electrode slurry described above in the present invention, which has significantly improved plate stability and significantly increased cycle performance.

[0016] According to another aspect of the present invention, a secondary battery is provided, comprising the above-mentioned positive electrode plate of the present invention, which has significantly improved capacity performance and cycle performance, and significantly reduced risk of abnormal electrical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0018] Figure 1 The viscosity change curves of the ternary positive electrode slurries according to Example 1, Example 2 and Comparative Example 1 of the present invention over 48 hours are shown;

[0019] Figure 2 The solid content change curves of the ternary positive electrode slurry according to Example 1, Example 2 and Comparative Example 1 of the present invention over 48 hours are shown;

[0020] Figure 3 The capacity retention curves of 100 cycles of 1C / 1C at room temperature according to Example 1, Example 2 and Comparative Example 1 of the present invention are shown. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0022] Unless otherwise specified, the instruments and materials used in the present invention can be purchased commercially or prepared using conventional methods in the art.

[0023] As described in the background technology of the present invention, the existing technology has the problem that the amount of acidic additives added to the ternary positive electrode slurry is difficult to accurately control, and viscosity anomalies or even gelation are prone to occur, resulting in poor battery cell performance and high abnormality risks. In order to solve the above problems, in a typical embodiment of the present invention, a method for preparing a ternary positive electrode slurry is provided, comprising the following steps: Step S1, testing the residual alkali content of the ternary positive electrode material, the residual alkali includes LiOH and Li2CO3, the content of LiOH is recorded as a, and the content of Li2CO3 is recorded as b; Step S2, first mixing the solvent, fluorine-containing binder and neutralizing agent to obtain a first mixture; Step S3, second mixing the first mixture with the conductive agent to obtain a second mixture; Step S4, mixing the second mixture with the ternary positive electrode material. Perform the third mixing to obtain a ternary positive electrode slurry, the viscosity of the ternary positive electrode slurry is 3000-5500 mPa·s, and the solid content is ≥71%; wherein, the neutralizer is NH4HSO4 or NH4HSO3; the amount of NH4HSO4 added is recorded as M1, M1=d*(2.40*a+1.56*b); the amount of NH4HSO3 added is recorded as M2, M2=d*(2.07*a+1.34*b); 0.5≤d≤1.2, preferably, 0.5≤d≤1.0; preferably, the solid content of the ternary positive electrode slurry is 72±1%.

[0024] First, before preparing the ternary positive electrode slurry, the residual alkali content of the ternary positive electrode material is tested in advance, with the LiOH content recorded as a and the Li2CO3 content recorded as b. During the preparation process, since the fluorine-containing binder generally has a relatively large molecular weight, if all materials are added together, there may be uneven dispersion. Therefore, the solvent, fluorine-containing binder and neutralizer are first mixed to obtain a first mixture, i.e., a glue solution containing a neutralizer. Among them, the amount of neutralizer added is calculated based on the content a of LiOH and the content b of Li2CO3 according to the following formula: the amount of NH4HSO4 added = M1 = d*(2.40*a+1.56*b), the amount of NH4HSO3 added = M2 = d*(2.07*a+1.34*b), wherein 0.5≤d≤1.2. The present invention determines the amount of neutralizer added according to the residual alkali content of the ternary positive electrode material using a specific relationship, which can fully neutralize the residual alkali while avoiding excessive acidic neutralizer from corroding the lithium oxide inside the positive electrode material, thereby avoiding a decrease in capacity and improving the preparation capacity retention rate.

[0025] The first mixture is then mixed with the conductive agent for a second time to obtain a second mixture; the second mixture is mixed with the ternary positive electrode material for a third time, and the dissolution and dispersion effect of the raw materials is improved by mixing in stages until the slurry viscosity is 3000-5500mPa·s and the solid content is ≥71%. The mixture is passed through a double-layer 200-mesh sieve and the ternary positive electrode slurry is obtained. Among them, the discharge viscosity of the ternary positive electrode slurry generally needs to reach ≤6500mPa·s to maintain good slurry fluidity and stability. The viscosity of the ternary positive electrode slurry of this application is 3000-5500mPa·s, which is easier to discharge while having better slurry stability and subsequent processing performance.

[0026] The present invention adds an appropriate amount of acidic neutralizer during the slurrying process, which can react with the residual lithium salt in the ternary positive electrode material, reduce the residual alkali content, inhibit the defluorination reaction of the fluorine-containing binder, prevent the slurry from gelling, improve the slurry fluidity, and increase the slurry stability. The slurry stability is reflected by comparing the viscosity and solid content of the ternary positive electrode slurry with the viscosity and solid content of the slurry after standing for 48 hours. The smaller the degree of change, the better the slurry stability. After the slurry of the present invention is prepared and stood for 48 hours, the viscosity is ≤15000mPa·s, the 48-hour viscosity change is ≤150%, and the solid content change is ≤1%. At the same time, the surface residual alkali generates LiSO4 or LiSO3 after the reaction. The neutralization product can be used as a point doping on the surface of the ternary positive electrode material, inhibiting the side reaction between the surface of the positive electrode material and the electrolyte, and improving the electrochemical performance of the finished battery cell. At the same time, determining the amount of neutralizer added by a specific relationship can fully neutralize the residual alkali while avoiding excessive acidic neutralizer from corroding the lithium oxide inside the positive electrode material, thereby improving the retention rate of the buckle capacity.

[0027] In a preferred embodiment, the general structural formula of the ternary cathode material is Li m Ni x Co y Mn z O2, of which 1 <m<1.05,x+y+z=1,0.8≤x<1,0<y<0.2,0<z<0.2。上述高镍三元正极材料更有利于协同本发明的酸性中和剂精确调控方法,能够在有效解决浆料凝胶化问题、改善浆料稳定性的同时,提高电芯的能量密度、容量保持率和循环性能。

[0028] The fluorine-containing binder can maintain the structural stability of the electrode during the charge and discharge process. In a preferred embodiment, in step S2, the solvent is NMP (N-methylpyrrolidone); and / or the fluorine-containing binder includes PVDF (polyvinylidene fluoride) and / or PTFE (polytetrafluoroethylene); and / or the weight ratio of the fluorine-containing binder to the solvent is (0.02 to 0.07): 1. The above types and addition amounts are conducive to making the concentration of the binder in the slurry system moderate, providing sufficient bonding force to prevent the active material from falling off, and not causing defluorination due to excessive concentration and accelerating the gelation process of the slurry. The above solvents not only help to fully dissolve the fluorine-containing binder and the neutralizer, but also can further effectively adjust the viscosity and fluidity of the slurry, making it easy to carry out the coating process. By adding the fluorine-containing binder and the solvent in the above-mentioned proportions, combined with the quantitative use of the acidic neutralizer of the present invention, the alkaline substances in the slurry can be more accurately controlled, and the defluorination reaction of PVDF can be inhibited, thereby effectively preventing the gelation of the slurry, reducing the risk of abnormal viscosity, improving the fluidity of the slurry, and improving the process stability during the battery cell manufacturing process and the electrochemical performance of the final product.

[0029] SP can provide a good electronic conductive network, while carbon nanotubes can further enhance the conductivity and mechanical strength while optimizing the rheological properties of the slurry. In a preferred embodiment, in step S3, the conductive agent includes SP (carbon black), 4% multi-walled carbon nanotubes and 0.4% single-walled carbon nanotubes; and / or the weight ratio of the conductive agent to the solvent is (1 to 1.1): 1. Wherein 4% multi-walled carbon nanotubes refers to a multi-walled carbon nanotube solution with an effective solid content of 4% of multi-walled carbon nanotubes, and the solvent is NMP; 0.4% single-walled carbon nanotubes refers to a single-walled carbon nanotube solution with an effective solid content of 0.4% of single-walled carbon nanotubes, and the solvent is NMP. Multi-walled carbon nanotubes and single-walled carbon nanotubes can use conventional products in the art, such as multi-walled carbon nanotubes with a diameter of 7 to 100 nm and an aspect ratio of 50 to 4000, such as single-walled carbon nanotubes with a diameter of 1 to 2 nm and an aspect ratio of 5000 to 10000. The above addition amount conditions are also conducive to the uniform dispersion of the conductive agent in the slurry and improve the stability of the slurry.

[0030] In a preferred embodiment, in step S4, the weight ratio of the ternary cathode material to the solvent is (4-6):1. When the amount of the ternary cathode material added is within the above range, it is beneficial to maximize the actual capacity of the battery while promoting its full dissolution, which is beneficial to improving the energy density of the battery cell. The appropriate amount of solvent helps to cooperate with the quantitative neutralizer to maintain the fluidity and stability of the slurry, and better prevent the slurry from being too high in viscosity or gelling.

[0031] In a preferred embodiment, in step S3, in the conductive agent, the weight ratio of SP, 4% multi-walled carbon nanotubes and 0.4% single-walled carbon nanotubes is 1: (25-35): (5-15). The reasonable ratio of the conductive agent is conducive to the formation of an efficient conductive network. SP, as the main conductive agent, can provide a high-density conductive path; multi-walled carbon nanotubes and single-walled carbon nanotubes, with their high aspect ratio and excellent conductivity, can construct a cross-scale conductive skeleton to make up for the limitations of SP in geometry and electrical properties. Under the above ratio, the conductive agent can be evenly distributed between the ternary positive electrode materials, effectively reducing the electron transfer resistance between particles. At the same time, a moderate ratio of carbon black and carbon nanotubes is more conducive to achieving the best balance between electrochemical performance and processing performance.

[0032] In a preferred embodiment, in step S4, the ternary positive electrode material is evenly divided into two parts, namely a first ternary positive electrode material and a second ternary positive electrode material; the second mixture is first intermediately mixed with the first ternary positive electrode material to obtain an intermediate mixture, and then the intermediate mixture is thirdly mixed with the second ternary positive electrode material to obtain a ternary positive electrode slurry; the intermediate mixing includes intermediate vacuum stirring, and the stirring time is 20 to 40 minutes. The step-by-step mixing of the positive electrode materials helps to improve the uniformity and stability of the slurry. The intermediate vacuum stirring is conducive to the uniform dispersion of the ternary positive electrode materials in the slurry, reducing the local high concentration and viscosity mutation caused by the addition of a large amount of positive electrode material at one time, thereby further reducing the occurrence of gelation, improving the process adaptability of the slurry and the uniformity of the electrode, and ultimately improving the electrochemical performance of the battery cell and reducing the risk of abnormalities caused by gelation.

[0033] In order to further promote the thorough mixing of the binder, solvent and quantitative acidic neutralizer to form a uniform glue solution, in a preferred embodiment, in step S2, the first mixing includes a first vacuum stirring and a vacuum defoaming performed sequentially; the height of the slurry liquid surface above the stirring paddle is 2 to 5 cm, the revolution speed of the first vacuum stirring is 10 to 100 rpm, the rotation speed is 50 to 500 rpm, and the stirring time is 3 to 6 hours; and / or the vacuum defoaming time is 1 to 3 hours; and / or the temperature of the first mixing is ≤60°C; and / or in step S3, the second mixing includes a second vacuum stirring; the revolution speed of the second vacuum stirring is 10 to 100 rpm, the rotation speed is 2000 to 3000 rpm, and the stirring time is 1 to 3 hours.

[0034] At a moderate speed and for sufficient stirring time, the fluorine-containing binder can be dissolved more fully, the shear force can be more appropriate and the damage to the structure of the fluorine-containing binder can be reduced. The glue can reach its optimal state under mild conditions, maintain good fluidity and dispersibility, and effectively reduce gelation. Within the above-mentioned vacuum defoaming parameter range, the tiny bubbles generated during the stirring process can be effectively removed, the phenomenon of bubbles forming gel cores in the slurry can be reduced, the stability of the slurry can be improved, and the bubbles generated during the coating process that affect the quality of the electrode can be reduced. Temperature ≤60°C can further reduce the thermal curing of the fluorine-containing binder at high temperature and the resulting increase in the slurry viscosity. When the second vacuum stirring parameter is within the above range, the conductive agent can be quickly and evenly dispersed in the glue. The combination of high-speed rotation and lower revolution speed can create a more suitable shear environment, which not only promotes the full dispersion of the conductive agent, but also reduces the mechanical damage to the positive electrode material, which is more conducive to the improvement of electrochemical activity.

[0035] In order to further promote the deep integration of the positive electrode material and the slurry and form a stable and uniform slurry, in a preferred embodiment, in step S4, the third mixing includes a third vacuum stirring; the revolution speed of the third vacuum stirring is 10 to 100 rpm, the rotation speed is 3000 to 4500 rpm, and the stirring time is 3 to 5 hours. High-speed rotation can generate strong shear force, which helps to refine the positive electrode material particles and uniformly cover the slurry on the particle surface; while the lower revolution speed helps to carry out the overall mixing gently, reduce the damage of shear stress to the positive electrode material, and maintain its electrochemical activity. Appropriate stirring time ensures sufficient reaction and that the slurry is in the optimal state of fluidity and operability, reducing slurry aging and performance degradation caused by excessive stirring time.

[0036] In another typical embodiment of the present invention, a ternary positive electrode slurry is provided, which is obtained using the above-mentioned preparation method of the present invention and has significantly improved slurry stability, including viscosity stability and solid content stability.

[0037] In another typical embodiment of the present invention, a positive electrode plate is also provided, including a current collector and a ternary positive electrode slurry coated on at least one surface of the current collector. The ternary positive electrode slurry is the above-mentioned ternary positive electrode slurry of the present invention, which has significantly improved plate stability and significantly increased cycle performance.

[0038] In another typical embodiment of the present invention, a secondary battery is provided, comprising the above-mentioned positive electrode plate of the present invention, which has significantly improved capacity performance and cycle performance, and significantly reduced risk of abnormal electrical performance.

[0039] Typically but not limitatively, the viscosity of the ternary positive electrode slurry is 3000mPa·s, 3200mPa·s, 3500mPa·s, 3800mPa·s, 4000mPa·s, 4200mPa·s, 4500mPa·s, 4800mPa·s, 5000mPa·s, 5200mPa·s, 5500mPa·s or a range value consisting of any two of them.

[0040] Typically, but not limited to, d is 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, or a range consisting of any two of these values.

[0041] Typically, but not limited to, the weight ratio of the fluorine-containing binder to the solvent is 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, or a range consisting of any two of these values.

[0042] Typically, but not limited to, the weight ratio of the conductive agent to the solvent is 1:1, 1.02:1, 1.05:1, 1.08:1, 1.1:1, or a range consisting of any two of these values.

[0043] Typically but not limitatively, in the conductive agent, when the weight portion of SP is 1, the weight portion of 4% multi-walled carbon nanotubes is 25, 26, 28, 30, 32, 34, 35 or a range consisting of any two of their values, and the weight portion of 0.4% single-walled carbon nanotubes is 5, 6, 8, 10, 12, 14, 15 or a range consisting of any two of their values.

[0044] Typically but not limitatively, the weight ratio of the ternary cathode material to the solvent is 4:1, 2.2:1, 4.5:1, 4.8:1, 5.0:1, 5.2:1, 5.5:1, 5.8:1, 6:1 or a range consisting of any two of these values.

[0045] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0046] Example 1

[0047] The ternary cathode material is Li 1.038 Ni 0.92 Co 0.07 Mn 0.01 O2.

[0048] Step S1, testing the residual alkali content of the ternary positive electrode material, performing three parallel tests and taking the average value, wherein the content of LiOH is recorded as a, and the content of Li2CO3 is recorded as b;

[0049] Step S2, adding NMP, PVDF and NH4HSO4 to the glue tank, and performing first vacuum stirring and vacuum defoaming in sequence; the weight ratio of PVDF to NMP is 0.05:1, and the amount of NH4HSO4 added is M1; the height of the liquid surface above the stirring paddle is 4 cm, the revolution speed of the first vacuum stirring is 50 rpm, the rotation speed is 300 rpm, the stirring time is 5 hours, the vacuum defoaming time is 2 hours, and the material temperature is controlled to be ≤60°C to obtain a first mixed material;

[0050] Step S3, placing the first mixture in a stirring tank, adding a conductive agent and performing a second vacuum stirring; the conductive agent includes SP, 4% multi-walled carbon nanotubes and 0.4% single-walled carbon nanotubes (weight ratio is 1:30:10), and the weight ratio of the conductive agent to NMP is 1.08:1; the second vacuum stirring is performed at a revolution speed of 50 rpm, a rotation speed of 2500 rpm, and a stirring time of 2 hours to obtain a second mixture;

[0051] Step S4: The second mixture and half of the ternary cathode material are subjected to intermediate vacuum stirring for 30 minutes to obtain an intermediate mixture, and then the intermediate mixture and the other half of the ternary cathode material are subjected to a third vacuum stirring; the weight ratio of the total weight of the ternary cathode material to NMP is 5:1; the revolution speed of the third vacuum stirring is 50 rpm, the rotation speed is 4200 rpm, and the stirring time is 4 hours. The viscosity and solid content of the slurry are tested to see if they meet the standards, and the slurry is passed through a double-layer 200-mesh sieve to obtain a ternary cathode slurry. Record the viscosity and solid content of the ternary cathode slurry after standing for 2 hours, 6 hours, 12 hours, 24 hours, and 48 hours.

[0052] Example 2

[0053] The difference from Example 1 is that NH4HSO3 is used as the neutralizer, and the addition amount is M2.

[0054] Example 3

[0055] The difference from Example 1 is that d is 1.0.

[0056] Example 4

[0057] The difference from Example 2 is that d is 1.0.

[0058] Example 5

[0059] The difference from Example 1 is that in step S2, the weight ratio of PVDF to NMP is 0.02:1; and d is 0.5.

[0060] Example 6

[0061] The difference from Example 1 is that in step S2, the weight ratio of PVDF to NMP is 0.07:1; and d is 1.2.

[0062] Example 7

[0063] The difference from Example 1 is that in step S3, the conductive agent includes SP, 4% multi-walled carbon nanotubes and 0.4% single-walled carbon nanotubes (weight ratio is 1:25:15), and the weight ratio of the conductive agent to NMP is 1:1.

[0064] Example 8

[0065] The difference from Example 1 is that in step S3, the conductive agent includes SP, 4% multi-walled carbon nanotubes and 0.4% single-walled carbon nanotubes (weight ratio is 1:35:5), and the weight ratio of the conductive agent to NMP is 1.1:1.

[0066] Example 9

[0067] The difference from Example 1 is that the ternary cathode material is Li 1.033 Ni 0.80 Co 0.10 Mn 0.10 The weight ratio of O2, ternary cathode material and NMP is 4:1.

[0068] Example 10

[0069] The difference from Example 1 is that the ternary cathode material is Li 1.045 Ni 0.95 Co 0.03 Mn 0.02 The weight ratio of O2, ternary cathode material and NMP is 6:1.

[0070] Comparative Example 1

[0071] The difference from Example 1 is that no neutralizer was used. The viscosity of the prepared slurry was 6834 mPa·s, which was too high to meet the discharge requirements. NMP was added in portions of 40 g for 3 times to adjust the viscosity until the slurry viscosity was less than 5500 mPa·s before discharge. After adjustment, the slurry viscosity was 5396 mPa·s and the solids content was 70.24%.

[0072] Comparative Example 2

[0073] The difference from Example 1 is that d is 0.4. The viscosity of the prepared slurry is too high to meet the discharge requirements. It is necessary to add NMP in batches of 40 g twice to adjust the viscosity until the slurry viscosity is less than 5500 mPa·s before discharge. The slurry viscosity and solid content before and after viscosity adjustment are shown in Table 4.

[0074] Comparative Example 3

[0075] The difference from Example 1 is that d is 1.3. The viscosity of the prepared slurry is too high to meet the discharge requirements, and additional NMP needs to be added in batches of 40 g × 2 times to adjust the viscosity until the slurry viscosity is less than 5500 mPa·s before discharge. The slurry viscosity and solid content before and after viscosity adjustment are shown in Table 4.

[0076] Test method:

[0077] Residual alkali of ternary positive electrode material: Weigh 5g of ternary positive electrode material, dissolve it in 100mL of deionized water, stir and disperse it at 800rpm for 5min, separate the sample from the water with a vacuum filtration device, and record the mass of the filtrate as m. Place the filtrate in a potentiometric titrator and titrate it with a 0.1mol / L hydrochloric acid standard titration solution. Ep1 (pH≈8.5) and Ep2 (pH≈4.5) are two equivalence points. The volumes of hydrochloric acid consumed at the equivalence points are recorded as V1 and V2, respectively; the residual Li2CO3 mass fraction ω Li2CO3 =[0.1*(V2-V1)*100*73.89] / (1000*5*m)*100%; residual LiOH mass fraction ω LiOH =[0.1*V2-2(V2-V1)*100*23.95] / (1000*5*m)*100%; repeat the measurement three times in parallel and record the results, and take the average value.

[0078] Slurry viscosity: About 300 ml of the middle slurry was placed in a beaker and measured using a LAMY-RM100 rotational viscometer (Lamy). Spindle No. 3 was selected, the speed was 10 rpm, the torque was set to 45%, and the measurement time was 90 s. Each sample was measured three times in parallel and the results were recorded to take the average value.

[0079] Solid content of slurry: Take about 2 to 3 g of the middle slurry and spread it evenly on an empty aluminum foil. Use JFGHL-120A battery slurry solid content tester (Jingfan) for testing. Set the drying temperature to 170°C. Record the solid content reading when the instrument automatically stops. Repeat the measurement three times for each sample and record the results, taking the average value.

[0080] Button battery assembly and testing: The prepared slurry is placed on a coater, coated with 400μm carbon-coated aluminum foil, placed in a 90℃ oven for drying, and then placed in a 120℃ vacuum oven for drying overnight; a 12mm puncher is used to take the sheet and assembled with a metal lithium sheet into a button half-cell, using a conventional ceramic diaphragm (9+1.5+1.5)μm, 1M LiPF6 electrolyte (solvent is EC:DMC=1:1), and the operating voltage range is set to 2.8~4.35V. The 0.2C first cycle charge and discharge specific capacity, first efficiency, charge and discharge curve, and capacity retention rate after 1C / 1C cycle 100 cycles are tested and recorded.

[0081] The residual alkali content parallel determination results are shown in Table 1 (taking Example 1 as an example), and the slurry viscosity and solid content parallel determination results of the positive electrode outfeed (ternary positive electrode slurry) of Example 1, Example 2 and Comparative Example 1 are shown in Tables 2-3.

[0082] The LiOH content a, Li2CO3 content b, d, the addition amount M1 of the neutralizer NH4HSO4, the addition amount M2 of the neutralizer NH4HSO3, the slurry viscosity and solid content of the ternary positive electrode slurry (i.e. the positive electrode outfeed) prepared by each example and comparative example are shown in Table 4, and the electrochemical performance results of the ternary positive electrode slurry (i.e. the positive electrode outfeed, which is adjusted after the adjustment in the comparative examples) are shown in Table 5.

[0083] Table 1

[0084]

[0085] Table 2

[0086]

[0087]

[0088] Table 3

[0089] Positive electrode discharge solid content (%) Test Result 1 Test Result 2 Test Result 3 mean Example 1 72.30 72.33 72.28 72.30 Example 2 72.26 72.23 72.17 72.22 Comparative Example 1 (before viscosity adjustment) 72.31 72.39 72.36 72.35 Comparative Example 1 (after viscosity adjustment) 70.14 70.25 70.32 70.24

[0090] Table 4

[0091]

[0092]

[0093] Table 5

[0094] Buckle power (2.8-4.35V) First charge capacity (mAh / g) First discharge capacity (mAh / g) First effect (%) Example 1 245.4 217.2 88.51 Example 2 244.8 216.6 88.48 Example 3 243.9 215.8 88.48 Example 4 243.6 215.5 88.46 Example 5 243.4 215.2 88.41 Example 6 243.5 215.2 88.38 Example 7 244.0 215.6 88.36 Example 8 243.9 215.7 88.44 Example 9 239.3 211.7 88.47 Example 10 250.7 221.8 88.47 Comparative Example 1 242.3 211.8 87.41 Comparative Example 2 243.2 213.0 87.58 Comparative Example 3 242.7 212.2 87.43

[0095] From Table 1, it can be seen that the three measurement data of the residual alkali test method are consistent.

[0096] From Table 2, it can be seen that the slurry outfeed viscosity of Example 1 and Example 2 is obviously lower due to the addition of NH4HSO4 and NH4HSO3 respectively, and there is no need to use NMP for later adjustment; while the outfeed viscosity of Comparative Example 1 is higher, and after adding NMP 40g for 3 times for adjustment, the outfeed viscosity standard can be reached.

[0097] From Table 3, it can be seen that the final slurry solid content of Example 1 and Example 2 is >72% due to no use of NMP for later adjustment; while the solid content of Comparative Example 1 is obviously reduced to about 70.2% due to the use of NMP for 3 times for adjustment, although the outfeed viscosity meets the requirements.

[0098] As can be seen from Table 5, in Example 1 and Example 2, since excess residual alkali is consumed by adding NH4HSO4 and NH4HSO3 respectively, the side reactions consume less active lithium and the interface is less converted to the rock salt phase. The charge specific capacity, discharge specific capacity and first efficiency are all higher than those of Comparative Example 1.

[0099] The viscosity change curves of the ternary positive electrode slurry of Example 1, Example 2 and Comparative Example 1 (after viscosity adjustment) for 48 hours are shown in FIG. Figure 1 .Depend on Figure 1 It can be seen that the viscosity of the slurry in Comparative Example 1 remains basically stable after 24 hours, but the viscosity is close to 25000 mPa·s, and there is a greater risk of gelation; in Example 1 and Example 2, since most of the residual alkali in the slurry is consumed by adding NH4HSO4 and NH4HSO3 respectively, the viscosity stability of the slurry is improved, and it remains basically stable after 24 hours, and the viscosity is <15000 mPa·s at 48 hours, and the improvement effect is obvious.

[0100] The solid content change curves of the ternary positive electrode slurry of Example 1, Example 2 and Comparative Example 1 (after viscosity adjustment) for 48 hours are shown in FIG. Figure 2 .Depend on Figure 2 It can be seen that in Example 1 and Example 2, since most of the residual alkali in the slurry is consumed by adding NH4HSO4 and NH4HSO3 respectively, the viscosity stability of the slurry is improved, and the corresponding solid content fluctuates less within 48 hours; the viscosity of the slurry in Comparative Example 1 fluctuates slightly within 48 hours, and the corresponding solid content level is lower.

[0101] The capacity retention curves of Example 1, Example 2 and Comparative Example 1 (after viscosity adjustment) after 100 cycles of 1C / 1C at room temperature are shown in FIG. Figure 3 .Depend on Figure 3 It can be seen that the capacity retention of Examples 1 and 2 after 100 cycles is higher (about 97.5%), and the improvement effect is basically the same; while the capacity retention rate of Comparative Example 1 is lower (about 96.5%) due to slightly more residual alkali and slightly greater loss of active lithium.

[0102] As can be seen from the above, compared with the comparative example, each embodiment of the present invention uses an acidic neutralizer to improve the stability of the ternary positive electrode material slurry. The acidic neutralizer is added in a quantitative manner according to the residual alkali content of the ternary positive electrode material in the slurrying process, which can react with the residual lithium salt in the ternary positive electrode material, reduce the residual alkali content, inhibit the occurrence of defluorination reaction of the fluorine-containing binder, prevent the slurry from gelling, and improve the fluidity of the slurry. At the same time, the surface residual alkali generates LiSO4 or LiSO3 after the reaction. The neutralization product can be used as a point doping on the surface of the ternary positive electrode material to inhibit the side reaction between the surface of the positive electrode material and the electrolyte, and improve the electrochemical performance of the finished battery cell. At the same time, the present invention determines the amount of the neutralizer added according to the specific relationship based on the residual alkali content of the ternary positive electrode material, which can fully neutralize the residual alkali while avoiding excessive acidic neutralizers from corroding the lithium oxide inside the positive electrode material, thereby avoiding a decrease in capacity. The ternary positive electrode slurry prepared by the method of the present invention has good process stability, and the soft-pack battery cell assembled therewith has a higher capacity retention rate under charge and discharge cycles.

[0103] In addition, it can be seen that when all process parameters are within the preferred range of the present invention, the overall effect is better.

[0104] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a ternary positive electrode slurry, characterized in that: The following steps are involved: Step S1, testing the residual alkali content of the ternary positive electrode material, wherein the residual alkali includes LiOH and Li2CO3, the content of LiOH is recorded as a, and the content of Li2CO3 is recorded as b; Step S2, performing a first mixing of the solvent, the fluorine-containing binder and the neutralizer to obtain a first mixture; Step S3, performing a second mixing of the first mixed material and the conductive agent to obtain a second mixed material; Step S4, performing a third mixing of the second mixed material and the ternary positive electrode material to obtain the ternary positive electrode slurry, wherein the ternary positive electrode slurry has a viscosity of 3000 to 5500 mPa·s and a solid content of ≥71%; Wherein, the neutralizing agent is NH4HSO4 or NH4HSO3; The amount of NH4HSO4 added is recorded as M1, M1 = d*(2.40*a+1.56*b); The amount of NH4HSO3 added is recorded as M2, M2 = d*(2.07*a+1.34*b); 0.5≤d≤1.2。 2. The method for preparing the ternary positive electrode slurry according to claim 1, characterized in that: The general structural formula of the ternary cathode material is Li m Ni x Co y Mn z O2, of which 1 <m<1.05,x+y+z=1,0.8≤x<1,0<y<0.2,0<z<0.2。 3. The method for preparing the ternary positive electrode slurry according to claim 1 or 2, characterized in that: In the step S2, the solvent is NMP; and / or The fluorine-containing binder includes PVDF and / or PTFE; and / or The weight ratio of the fluorine-containing binder to the solvent is (0.02-0.07):

1.

4. The method for preparing a ternary positive electrode slurry according to claim 1 or 2, wherein: In step S3, the conductive agent includes SP, 4% multi-walled carbon nanotubes and 0.4% single-walled carbon nanotubes; and / or the weight ratio of the conductive agent to the solvent is (1-1.1):

1.

5. The method for preparing the ternary positive electrode slurry according to claim 4, characterized in that: In the step S3, the weight ratio of SP, the 4% multi-walled carbon nanotubes, and the 0.4% single-walled carbon nanotubes in the conductive agent is 1:(25-35): (5～15)。 6. The method for preparing the ternary positive electrode slurry according to claim 1 or 2, characterized in that: In the step S4, the weight ratio of the ternary cathode material to the solvent is (4-6):

1.

7. The method for preparing a ternary positive electrode slurry according to claim 1 or 2, characterized in that: In step S4, the ternary positive electrode material is evenly divided into two parts, namely a first ternary positive electrode material and a second ternary positive electrode material; the second mixture is firstly intermediately mixed with the first ternary positive electrode material to obtain an intermediate mixture, and then the intermediate mixture is thirdly mixed with the second ternary positive electrode material to obtain the ternary positive electrode slurry; the intermediate mixing includes intermediate vacuum stirring, and the stirring time is 20 to 40 minutes.

8. A ternary positive electrode slurry, characterized in that: The method for preparing the ternary positive electrode slurry according to any one of claims 1 to 7 is used.

9. A positive electrode sheet comprising a current collector and a ternary positive electrode slurry coated on at least one surface of the current collector, characterized in that: The ternary positive electrode slurry is the ternary positive electrode slurry according to claim 8.

10. A secondary battery, characterized in that: Including the positive electrode sheet according to claim 9.

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