CN115842101A - Positive electrode slurry, method for producing same, positive electrode sheet, secondary battery, and electricity-using device - Google Patents
Positive electrode slurry, method for producing same, positive electrode sheet, secondary battery, and electricity-using device Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The present application relates to a method for preparing a positive electrode slurry, and a positive electrode slurry prepared by the method, a positive electrode sheet, a secondary battery and an electric device comprising the same. The preparation method can obtain the cathode slurry which is uniformly mixed and has good stability and does not generate gelation under the condition of using more than two cathode active materials.
Description
Technical Field
The application relates to the technical field of lithium batteries, in particular to a method for preparing anode slurry, the anode slurry prepared by the method, an anode pole piece comprising the anode slurry, a secondary battery and an electric device.
Background
In recent years, with the application range of lithium ion batteries becoming wider, lithium ion batteries are widely used in energy storage power systems such as hydraulic power, thermal power, wind power and solar power stations, and in a plurality of fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment and aerospace. As lithium ion batteries have been greatly developed, higher requirements are also put forward on energy density, cycle performance, safety performance and the like. With the increasing demand of the market for the performance of lithium ion batteries, the demand cannot be met by only using one positive active material in the positive pole piece, and therefore, the use of a mixture of more than two active materials in the same positive pole piece is gradually a hot spot pursued by enterprises and research and development institutions. However, in actual production, it has been found that when two or more positive electrode active materials are mixed with a binder or the like to prepare a positive electrode slurry, a problem of chemical gelation often occurs, resulting in poor slurry fluidity, easy clogging of a pipe and a filter, and in a serious case, failure in normal application of the slurry.
Therefore, how to solve the gelation occurring when two or more kinds of positive electrode active materials are used to prepare a positive electrode slurry is still a problem to be solved in the art.
Disclosure of Invention
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for preparing a positive electrode slurry, which solves the problem of gelation occurring when preparing a positive electrode slurry using two or more kinds of positive electrode active materials in the prior art.
In order to achieve the above objects, the present application provides a method of preparing a positive electrode slurry, and a positive electrode slurry prepared by the method, a positive electrode sheet and a secondary battery including the same, and an electric device.
A first aspect of the present application provides a method of preparing a positive electrode slurry, comprising the steps of:
(1) Adding a first cathode active material, a first binder and a first conductive agent and optionally other solid components in a first agitation tank and performing dry mixing; then adding the liquid component and carrying out pre-stirring; finally, performing formal stirring to obtain a first slurry S1;
(2) Adding a second positive electrode active material, a second binder and a second conductive agent and optionally other solid components in a second stirring tank and performing dry mixing; then adding the liquid component and carrying out pre-stirring; finally, performing formal stirring to obtain a second slurry S2;
(3) Mixing the first slurry S1 and the second slurry S2 in a third stirring tank to obtain positive slurry Smix with the viscosity of 8000-13000 mPa & S;
wherein, in step (1), the first binder is polyvinylidene fluoride having a number average molecular weight of 500,000 to 800,000; in step (2), the second binder is polyvinylidene fluoride having a number average molecular weight of 850,000 to 1200,000;
in any embodiment, the first positive electrode active material has a pH of 7 to 10 at standard temperature and pressure; the second positive electrode active material has a pH value of greater than 10 and equal to or less than 14 at standard temperature and pressure.
In any embodiment, the mass ratio of the first positive electrode active material to the second positive electrode active material is 1: (0.5-10), optionally 1: (0.8-9), optionally 1: (0.9-6).
In any embodiment, in step (1), the mass ratio of the first positive electrode active material to the first binder is (30-60): 1, optionally (35-50): 1; in the step (2), the mass ratio of the second positive electrode active material to the second binder is (40-120): 1, optional (50-100): 1.
in any embodiment, the first positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobaltate and modified materials thereof, and the second positive electrode active material is selected from one or more of a lithium-rich manganese-based positive electrode material, lithium nickel cobalt manganese oxide and modified materials thereof.
In any embodiment, in the steps (1) and (2), in the dry blending, the revolution speed of the stirring blade is 20 to 50rpm, the rotation speed is 600 to 1200rpm, and the stirring is performed for 10 to 20 minutes.
In any embodiment, in the steps (1) and (2), in the preliminary stirring, the revolution speed of the stirring paddle is 20 to 50rpm, the rotation speed is 200 to 600rpm, and the stirring is performed for 3 to 20 minutes.
In any embodiment, in the steps (1) and (2), in the main stirring, the revolution speed of the stirring paddle is 20 to 50rpm, the rotation speed is 600 to 1200rpm, and the stirring is performed for 160 to 240 minutes.
In any embodiment, in step (3), the revolution speed of the stirring paddle is 10rpm to 100rpm, and the stirring is performed for 5 to 30 minutes.
In any embodiment, in step (3), slurry S1 and slurry S2 are mixed at a ratio of 1: (0.5-1.5), optionally 1: (0.8-1.2) are mixed and added into a third stirring tank.
In any embodiment, wherein the solids content of the first slurry S1 is 60 to 68 wt%; the solid content of the second slurry S2 is 65 to 75 wt%; the solid content of the positive electrode slurry Smix is 65 to 70 wt%.
In any embodiment, the Dv50 of the first positive electrode active material is 0.2 μm to 5 μm, and the Dv50 of the second positive electrode active material is 1 μm to 15 μm.
In any embodiment, in steps (1), (2) and (3), the vacuum in the stirred tank is maintained at 0 to-60 kpa while stirring, and the temperature in the stirred tank is 5 ℃ to 55 ℃, optionally 15 ℃ to 50 ℃.
A second aspect of the present application provides a positive electrode slurry prepared by the method of the first aspect of the present application.
A third aspect of the present application provides a positive electrode sheet, comprising:
a positive current collector;
a positive electrode active material layer disposed on at least one surface of the positive electrode current collector;
the positive electrode active material layer is prepared from the positive electrode slurry of the second aspect of the present application.
In any embodiment, the total mass percentage of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer is 95% to 98%, optionally 96.5% to 97%; the total mass percentage of the first binder and the second binder in the positive electrode active material layer is 0.5% to 2.2%, and optionally 1.1% to 1.5%.
A fourth aspect of the present application provides a secondary battery comprising the positive electrode sheet according to the third aspect of the present application.
A fifth aspect of the present application provides an electric device including the secondary battery described in the fourth aspect of the present application.
The preparation method can obtain the cathode slurry which is uniformly mixed and has good stability and does not generate gelation under the condition of using more than two cathode active materials.
Drawings
Fig. 1 is a schematic view of a method of preparing a positive electrode slurry according to an embodiment of the present application.
Detailed Description
Hereinafter, embodiments of a method of preparing a positive electrode slurry of the present application, a positive electrode slurry prepared by the method, a positive electrode sheet and a secondary battery including the same, and an electric device including the secondary battery are specifically disclosed in detail with reference to the accompanying drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.
The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.
All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.
All technical and optional features of the present application may be combined with each other to form new solutions, if not otherwise specified.
All steps of the present application may be performed sequentially, randomly, or alternatively sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.
The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.
As used herein, the terms "above," "below," and "including numbers, such as" more than one, "mean one or more," more than one of A and B "mean" A, "" B, "or" A and B.
In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).
Unless otherwise indicated, the contents and percentages in the context of the present application are based on mass.
Unless otherwise stated, the operations in this application are carried out at standard temperature (25 ℃) and standard pressure (1 atm).
Due to the increasing demand of the market for the performance of lithium ion batteries, the use of a mixture of two or more active materials in the same positive electrode plate is gradually a hot spot pursued by enterprises and research and development institutions. However, the two active materials are generally mixed to prepare a positive electrode slurry, which causes a problem of gelation, and the prior art generally employs a layered coating method to coat the two active materials on a current collector. However, such coating can degrade the compaction density, electrical resistance, adhesion, and shear strength of the pole piece.
Unexpectedly, the inventors found that when two positive electrode active materials are separately subjected to mixing and stirring and then subjected to combined stirring, the time during which gelation occurs can be greatly prolonged, and gelation can be even completely avoided. Without being bound by any theory, it is believed that the particle surface pH is higher and more alkaline due to excessive lithium source, and the like, in the preparation process of the cathode slurry, and particularly, the cathode material is rich in lithium and manganese. Hydroxyl on the surface of the positive active particles can chemically react with polyvinylidene fluoride (PVDF), so that the PVDF is subjected to HF removal to form double bonds, crosslinking is easier, and further, the positive slurry is gelled. In addition, some positive electrode active materials such as lithium iron phosphate often exist in the form of nanoscale primary particles with carbon-coated surfaces, and when a binder with a larger molecular weight and a longer molecular chain is used for positive electrode slurry, hydrogen bonds are easily formed between the nanoscale lithium iron phosphate particles and the binder molecules with the longer molecular chain due to small particle size and large specific surface area, and physical gelation occurs. According to the method, the positive active materials with strong alkalinity (pH is more than 10 to 14) and weak alkalinity (pH is 7 to 10) are separately and uniformly stirred, stable colloid particles are respectively formed, then the colloid particles are combined and stirred, and the charging sequence, the stirring time and the stirring speed are optimized, so that the lithium ion positive slurry which is uniformly dispersed and stable and does not gel is obtained.
Accordingly, the present application provides in a first aspect a method of preparing a positive electrode slurry comprising the steps of:
(1) Adding a first cathode active material, a first binder and a first conductive agent and optionally other solid components in a first agitation tank and performing dry mixing; then adding the liquid component and pre-stirring; finally, performing formal stirring to obtain a first slurry S1;
(2) Adding a second cathode active material, a second binder and a second conductive agent and optionally other solid components in a second agitation tank and performing dry mixing; then adding the liquid component and carrying out pre-stirring; finally, performing formal stirring to obtain a second slurry S2;
(3) Mixing the first slurry S1 and the second slurry S2 in a third stirring tank to obtain positive slurry Smix, wherein the viscosity of the positive slurry Smix is 8000-13000 mPa & S;
wherein, in step (1), the first binder is polyvinylidene fluoride having a number average molecular weight of 500,000 to 800,000, optionally 550,000 to 700,000, and further optionally 570,000 to 650,000; in step (2), the second binder is a polyvinylidene fluoride having a molecular weight of 850,000 to 1200,000, optionally 900,000 to 1,000,000, and further optionally 950,000 to 990,000.
In the present application, the term "polyvinylidene fluoride" refers to a compound having the general formula (CH) 2 CF 2 ) The polymer of n can be synthesized by polymerization of 1, 1-difluoroethylene. One skilled in the art will appreciate that the polyvinylidene fluoride described herein can also be chemically modified in a variety of ways. It is understood that n in the formula corresponds to the molecular weight.
As shown in fig. 1, a first slurry S1 including colloidal particles 1 is formed by dry mixing, preliminary stirring, and main stirring of a first positive electrode active material and a first binder in a first stirring tank. Similarly, the second positive electrode active material and the second binder form a second slurry S2 containing colloidal particles 2. Subsequently, the first slurry S1 and the second slurry S2 are mixed and stirred in the third stirring tank to form the positive electrode slurry Smix containing the colloidal particles 1 and 2.
In some embodiments, the pH of the first positive electrode active material is 7 to 10, optionally 7.5 to 9; the second positive electrode active material has a pH value of greater than 10 and equal to or less than 14, optionally 11 to 13, the pH value being measured at a standard temperature and pressure.
In the present application, the pH of the positive electrode active material is measured according to the following manner: a sample of the positive active material and deionized water are mixed into a solution in a conical flask according to a fixed mass ratio of 1. The determination of the pH is carried out at standard temperature (25 ℃) and standard pressure (1 atm), and the pH can be determined using a pH paper or a pH meter, optionally using a pH meter.
The inventors found that the gelation problem occurring when preparing a positive electrode slurry can be better solved by classifying stirring according to the alkalinity of a positive electrode active material and using a corresponding binder in combination. For example, in step (1), the first binder is a binder with a smaller molecular weight and a shorter molecular chain, such as commercially available HSV900 and GPK010; in step (2), the second binder is a binder with a relatively high molecular weight and a relatively long molecular chain, such as commercially available PVDF5130; GPK012, which is carboxyl-modified and alkali-resistant binder.
In some embodiments, the mass ratio of the first positive electrode active material to the second positive electrode active material is 1: (0.5-10), optionally 1: (0.8-9), optionally 1: (0.9-6), and further optionally 1: (1-3).
In some embodiments, the mass ratio of the first positive electrode active material to the first conductive agent is (90-150): 1, optionally (100-140): 1, optionally (110-130): 1.
in some embodiments, the first and second conductive agents may be conductive agents conventionally used in the art for preparing a positive electrode slurry, which may be the same or different, and the conductive agent is selected from at least one of conductive carbon black, conductive graphite, ketjen black, acetylene black, carbon fiber, vapor-grown carbon fiber, carbon nanotube, graphene, and graphene oxide.
In some embodiments, the mass ratio of the first conductive agent to the second conductive agent may be 1: (1-10), optionally 1: (1-3), optionally 1: (1.5-2.5).
In some embodiments, in step (1), the mass ratio of the first positive electrode active material to the first binder is (30-60): 1, optionally (35-50): 1, optionally (37-49): 1; in the step (2), the mass ratio of the second positive electrode active material to the second binder is (40-120): 1, optional (50-100): 1, optionally (70-95): 1.
in some embodiments, the first positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobaltate, and modified materials thereof, and the second positive electrode active material is selected from one or more of a lithium-rich manganese-based positive electrode material, lithium nickel manganese cobalt, and modified materials thereof. Here, the term "modifying material" is to be understood as a form of a coating or a dopant of the positive electrode active material.
In some embodiments, the first positive electrode active material: a first binder: the proportion of the first conductive agent is (30-60): 1: (0.1-1), optionally (35-50): 1: (0.2-0.8), optionally (37-49): 1: (0.3-0.5); in step (2), the second positive electrode active material: a second binder: the mass ratio of the second conductive agent is (40-120): 1: (0.5-5), optionally (50-100): 1: (0.8-3), optionally (70-95): 1: (1-2).
In some embodiments, in step (3), the first slurry S1 and the second slurry S2 are mixed in a ratio of 1: (0.5-9), optionally 1: (0.8-5), optionally 1: (0.9-2) in a third agitation tank.
In some embodiments, wherein the solids content of the first slurry S1 is from 60 wt% to 68 wt%; the solid content of the second slurry S2 is 65 to 75 wt%; the solid content of the positive electrode slurry Smix is 65-70 wt%.
In the present application, the solids content is determined in the following manner: and (3) putting the mass M1 slurry into an oven, and drying at 120 ℃ for 48h, wherein the mass after drying is M2. Solid content = M2/M1 × 100%.
In some embodiments, in steps (1) and (2), the liquid component may be a solvent conventionally used in the art, such as N-methylpyrrolidone. However, in some cases, the liquid component may also be in the form of a solution of other components, for example when carbon nanotubes are used, it is usually used in the form of a solution thereof (e.g. a solution of water and alcohol), in which case a solution of the conductive agent carbon nanotubes is used as the liquid component.
In some embodiments, the Dv50 of the first positive electrode active material is 0.2 μm to 5 μm, optionally 0.5 μm to 3 μm, and further optionally 0.8 μm to 2 μm, and the Dv50 of the second positive electrode active material is 1 μm to 15 μm, optionally 2 μm to 12 μm, further optionally 4 μm to 10 μm, and still further preferably 5 μm to 8 μm.
In the present application, the rotation speed and the stirring time of the paddle may be adjusted depending on the particle diameter of the solid component, particularly the particle diameter of the positive electrode active particle, and for example, when the particle diameter Dv50 of the positive electrode active particle is 0 to 1 μm, the rotation speed of the paddle may be 1100rpm to 1500rpm, for example 1200rpm, and the stirring time may be at least 200 minutes or more; when the particle diameter Dv50 of the positive electrode active particles is 1 μm to 5 μm, the rotation speed of the paddle may be 800rpm to 1100rpm, for example, 1000rpm, and the stirring time may be 150 minutes to 210 minutes; when the particle diameter Dv50 of the positive electrode active particles is greater than 5 μm, for example, 5 μm to 100 μm, the rotation speed of the paddle may be 500rpm to 900rpm, for example, 800rpm, and the stirring time may be 120 minutes to 180 minutes.
In the present application, the particle Size Dv50 of the particles may be determined using a laser particle Size analyser (e.g. Malvern Master Size 3000) with reference to standard GB/T19077.1-2016. Wherein Dv50 is physically defined as follows:
dv50: the particle size corresponding to the cumulative volume distribution percentage of the particles reaching 50 percent.
In some embodiments, the Dv50 of the first and second conductive agents is 0.2 μm to 10 μm, and optionally 0.5 μm to 5 μm.
Here, it should be understood that the stirring in the present application may be performed using a stirrer that: the agitator has a container for containing a material and an agitating blade for agitating the material, for example, the agitating blade rotates counterclockwise while revolving clockwise around the center of the container in the container.
In some embodiments, in steps (1) and (2), the stirring paddle revolves at a speed of 20 to 50rpm, optionally 22 to 40rpm, and rotates at a speed of 600 to 1200rpm, optionally 700 to 1000rpm, for 10 to 20 minutes, optionally 11 to 18 minutes, during dry mixing.
In some embodiments, in steps (1) and (2), the stirring paddle has a revolution speed of 20rpm to 50rpm, optionally 22rpm to 40rpm, and a rotation speed of 200rpm to 600rpm, optionally 250rpm to 400rpm, and is stirred for 3 minutes to 20 minutes, optionally 4 minutes to 10 minutes, while pre-stirring.
In some embodiments, in the steps (1) and (2), in the formal stirring, the revolution speed of the stirring paddle is 20rpm to 50rpm, optionally 22rpm to 40rpm, the rotation speed is 600rpm to 1200rpm, optionally 700rpm to 1000rpm, and the stirring is performed for 160 minutes to 240 minutes, optionally 165 minutes to 230 minutes.
In some embodiments, in step (3), the revolution speed of the stirring paddle is 10rpm to 100rpm, optionally 22rpm to 80rpm, further optionally 25rpm to 50rpm, and the stirring is performed for 5 minutes to 30 minutes, optionally 7 minutes to 20 minutes. In this application, it should be noted that in the step (3), during the mixing of the two slurries S1 and S2, the stable colloidal particles that have been formed may be destroyed by too fast revolution speed or too long revolution time, thereby causing gelation.
In some embodiments, in step (3), the paddle does not spin.
In the present application, the agitation tanks used in the respective steps may have the same configuration, and for convenience of expression, they are referred to as a first agitation tank, a second agitation tank, and a third agitation tank. It will be understood by those skilled in the art that step (1) conducted in the first stirred tank and step (2) conducted in the second stirred tank may be conducted sequentially or simultaneously and then metered into a third stirred tank simultaneously, where the third stirred tank may have a larger capacity than the first and second stirred tanks.
In some embodiments, in step (3), slurry S1 and slurry S2 are mixed at a ratio of 1: (0.5-1.5), optionally 1: (0.8-1.2) are mixed and added into a third stirring tank. Here, the specific flow rate value is not particularly limited, and the addition time depends on the amount of the slurry, and the mixing may be optionally completed in 1 minute to 5 minutes. The addition in this way can ensure that the colloidal particles in the two slurries are distributed more uniformly in the third slurry tank, further reducing the time for gelation to occur. Here, the above-mentioned mixing addition may be carried out in the following manner: the slurry S1 and the slurry S2 are pre-mixed before being added into a third slurry tank, and then the mixed slurry is added into the third slurry tank; alternatively, the slurry S1 and the slurry S2 are mixed in the above flow ratio directly in the third slurry tank. Optionally, while mixing, stirring is also simultaneously performed in the third stirred tank.
In some embodiments, in steps (1), (2) and (3), the agitation tank is maintained at a vacuum level of 0kpa to-60 kpa, optionally-10 kpa to-50 kpa, while agitating, and the temperature within the agitation tank is 5 ℃ to 55 ℃, optionally 15 ℃ to 50 ℃, and optionally 30 ℃ to 46 ℃.
In the present application, it is understood that other solid components than the first cathode active material, the conductive agent, etc. may be used in steps (1) and (2), and the proportion of their total amount in the final cathode slurry may be adjusted according to conventional contents known to those skilled in the art. In addition, if not explicitly stated, the addition amount of the components other than the positive electrode active material in steps (1) and (2) may be adjusted accordingly, for example, the same as the ratio of the first positive electrode active material to the second positive electrode active material. If other liquid components are used, their use in each step is similar to the solid case described above.
Further, it is also understood by those skilled in the art that in the case of using three or more kinds of positive electrode active materials, mixing may be performed in two kinds according to their alkaline condition. Of course, it is also possible to mix three or more kinds of positive electrode active materials separately (using a certain ratio of the binder, the conductive agent, the solvent, and the like, respectively) and then mix them together.
In some embodiments, in steps (1) and (2), the viscosity of each of the slurry S1 and the slurry S2 is 8000mPa · S to 15000mPa · S, optionally 8500mPa · S to 14000mPa · S, and further optionally 9000mPa · S to 13000mPa · S.
A second aspect of the present application provides a positive electrode slurry prepared by the method of the first aspect of the present application.
In some embodiments, the positive electrode slurry has a viscosity of 8000 to 13000 mPa-s, optionally 8500 to 12000 mPa-s.
In some embodiments, the solid content of the cathode slurry is 65 to 70 wt%.
In the present application, the viscosity is measured according to the standard GB/T10247-2008 using the rotary method. The specific operation is as follows: use the rotational viscometer, select the rotor according to sample viscosity, use the viscometer crane, make the viscometer slowly descend, the rotor submergence is in the thick liquids, mark and liquid level on until the rotor are equal, test temperature: 25 ℃, rotation speed: and (5) starting measurement at 12rpm by pressing a measurement key, and reading the viscosity value after the data are kept stable after 5 min.
In some embodiments, the positive electrode slurry comprises: 50 to 70 mass%, optionally 57 to 67.9 mass% of a positive electrode active material; 0.3 to 3 mass%, optionally 0.48 to 1.54 mass% of a binder; 0.5 to 3 mass%, optionally 0.84 to 1.75 mass% of a conductive agent and 25 to 40 mass%, optionally 30 to 35 mass% of a solvent, the sum of the mass percentages of the components being 100 mass%. The positive electrode active material, the binder, the conductive agent, and the solvent are as described above.
A third aspect of the present application provides a positive electrode sheet, comprising:
a positive current collector;
a positive electrode active material layer disposed on at least one surface of the positive electrode current collector;
the positive electrode active material layer is prepared from the positive electrode slurry of the second aspect of the present application.
In some embodiments, the first positive electrode active material and the second positive electrode active material together account for 95% to 98%, optionally 96.5% to 97.5% of the mass of the positive electrode active material layer; the first binder and the second binder together account for 0.5 to 2.2 mass%, optionally 1.1 to 1.7 mass%, of the positive electrode active material layer.
As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material layer is provided on either or both of the two surfaces opposite to the positive electrode current collector.
In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In some embodiments, the positive electrode sheet may be prepared by: the positive pole piece can be obtained by coating the positive pole slurry prepared according to the first aspect of the invention on a positive pole current collector and carrying out the working procedures of drying, cold pressing and the like.
A fourth aspect of the present application provides a secondary battery comprising the positive electrode sheet according to the third aspect of the present application.
In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.
A fifth aspect of the present application provides an electric device including the secondary battery described in the fourth aspect of the present application.
The electric device of the present application may be a mobile device (e.g., a mobile phone, a notebook computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.
Examples
Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Example 1:
step (1): 63.05% by mass of lithium iron phosphate (LiFePO) 4 ) A positive electrode material (particle diameter Dv50=0.96 μm, pH = 8.64), 1.43 mass% of a binder HSV900 (number average molecular weight 640,000), and 0.52 mass% of conductive carbon black SP were sequentially added to a first stirring tank, and dry-blended first, with a stirring paddle revolving at 25rpm, rotating at 800rpm, and stirring for 15min, to obtain a solid mixture.
Adding 35 mass% of solvent N-methylpyrrolidone (NMP) into the obtained solid mixture, then pre-stirring, wherein the revolution speed of a stirring paddle is 25rpm, the rotation speed is 300rpm, the stirring time is 5min, the vacuum degree in a stirring tank is-50 kpa, and the temperature in the stirring tank is controlled at 40 ℃ to obtain a solid-liquid mixture; formal stirring, wherein the revolution speed of a stirring paddle is 25rpm, the rotation speed of the stirring paddle is 900rpm, the stirring time is 220min, the vacuum degree in the stirring tank is-50 kpa, the temperature in the stirring tank is controlled at 40 ℃, and the slurry S1 with the solid content of 65 percent by weight is prepared.
Step (2): 67.9 mass% of a lithium-rich manganese-based positive electrode material (particle diameter Dv50=6.82 μm, pH = 11.70), 0.77 mass% of binder PVDF5130 (molecular weight 960,000), and 1.05 mass% of conductive carbon black SP were sequentially added to the second stirring tank, and dry-mixed first, with a stirring paddle revolving at 25rpm, rotating at 800rpm, and stirring for 15min, to obtain a solid mixture.
Adding 30 mass% of solvent NMP into the obtained solid mixture, and then pre-stirring, wherein the revolution speed of a stirring paddle is 25rpm, the rotation speed is 300rpm, the stirring time is 5min, the vacuum degree in a stirring tank is-50 kpa, and the temperature in the stirring tank is controlled at 40 ℃ to obtain a solid-liquid mixture A; adding 0.28 mass percent of conductive carbon nanotube solution (the mass of the conductive carbon nanotube accounts for 4 percent) into the obtained solid-liquid mixture A while stirring, wherein the revolution speed of a stirring paddle is 25rpm, the rotation speed is 500rpm, the stirring time is 15min, the vacuum degree in a stirring tank is-50 kpa, and the temperature in the stirring tank is controlled at 40 ℃ to obtain a solid-liquid mixture B; and (3) stirring formally, wherein the revolution speed of a stirring paddle is 25rpm, the rotation speed is 800rpm, the stirring time is 170min, the vacuum degree in the stirring tank is-50 kpa, the temperature in the stirring tank is controlled at 40 ℃, and the slurry S2 with the solid content of 70 weight percent is prepared.
And (3): adding the positive electrode slurry S1 and the positive electrode slurry S2 into a third stirring tank (a mixing stirring tank for mixing the slurries S1 and S2, wherein the slurry S1 and the slurry S2 are added into the third stirring tank at a flow rate of 1; after stirring, a slurry Smix was obtained with a viscosity of 11400mPa · s and a solids content of 67.5 wt%.
Example 2:
the preparation method was substantially the same as that of example 1, except that the revolution speed was 30rpm and the stirring time was 30min in the preparation of the positive electrode slurry Smix.
Example 3:
the preparation method was substantially the same as that of example 1, except that the revolution speed was 60rpm and the stirring time was 10min in the preparation of the positive electrode slurry Smix.
Example 4:
the preparation method was substantially the same as that of example 1, except that the revolution speed was 60rpm and the stirring time was 30min in the preparation of the positive electrode slurry Smix.
Comparative example 1:
preparation of positive electrode slurry Smix: adding 32.74 mass% of lithium iron phosphate positive electrode material (particle diameter Dv50=0.96 μm, pH = 8.64), 32.74 mass% of lithium-rich manganese-based positive electrode material (particle diameter Dv50=6.82 μm, pH = 11.70), 0.74 mass% of binder HSV900, and 1.00 mass% of conductive carbon black SP into a stirring tank in sequence, and performing dry mixing first, wherein the revolution speed of a stirring paddle is 25rpm, the rotation speed is 800rpm, and the stirring time is 15min, so as to obtain a solid mixture; adding 32.5 mass% of solvent NMP into the obtained solid mixture, then pre-stirring, wherein the revolution speed of a stirring paddle is 25rpm, the rotation speed is 300rpm, the stirring time is 5min, the vacuum degree in a stirring tank is-50 kpa, and the temperature in the stirring tank is controlled at 40 ℃ to obtain a solid-liquid mixture A; adding 0.28 mass percent of conductive carbon nanotube solution (the mass of the conductive carbon nanotube accounts for 4 percent) into the obtained solid-liquid mixture A while stirring, wherein the revolution speed of a stirring paddle is 25rpm, the rotation speed is 500rpm, the stirring time is 15min, the vacuum degree in a stirring tank is-50 kpa, and the temperature in the stirring tank is controlled at 40 ℃ to obtain a solid-liquid mixture B; formally stirring, wherein the revolution speed of a stirring paddle is 25rpm, the rotation speed is 1200rpm, the stirring time is 220min, the vacuum degree in the stirring tank is-50 kpa, and the temperature in the stirring tank is controlled at 40 ℃ to prepare the positive electrode slurry Smix.
Comparative example 2:
substantially the same as the preparation method of comparative example 1 except that PVDF5130 was used as the binder.
Comparative example 3
The same preparation method as that of example 1 was followed except that the kinds of the binders in step (1) and step (2) were exchanged with each other.
The viscosity data of the positive electrode slurry Smix prepared in each example at 0, 2, 4, 8, 16, 32, 48 hours after shipment were measured using a Brookfield viscosity tester (model Brookfield DV2TLV, rotor # 61, range 1-6M mPa · s) as shown in table 1 below. When the viscosity of the slurry at rest exceeded 50000 mPas, it was considered that the slurry had gelled (the slurry had very poor fluidity and appeared in a jelly-like state), and it was verified that the slurry was picked up with a stirring bar.
TABLE 1
As can be seen from table 1, the positive active material, the binder, the conductive agent and the solvent with different alkalis are separately stirred to form stable colloidal particles, and then the slurry containing the strongly alkaline and weakly alkaline positive active materials is prepared by mixing the positive active material, the binder, the conductive agent and the solvent uniformly in a tank, and the problem of gelation caused by the simultaneous use of the strongly alkaline and weakly alkaline positive active materials is solved by controlling the stirring speed and the stirring time, so that the obtained lithium ion battery positive slurry has the advantages of good dispersibility, good stability and no gelation phenomenon.
The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are all included in the technical scope of the present application. Various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, which are configured by combining some of the constituent elements in the embodiments without departing from the scope of the present application.
Claims (17)
1. A method of preparing a positive electrode slurry, comprising the steps of:
(1) Adding a first positive electrode active material, a first binder and a first conductive agent and optionally other solid components in a first stirring tank and performing dry mixing; then adding the liquid component and carrying out pre-stirring; finally, performing formal stirring to obtain a first slurry S1;
(2) Adding a second positive electrode active material, a second binder and a second conductive agent and optionally other solid components in a second stirring tank and performing dry mixing; then adding the liquid component and carrying out pre-stirring; finally, performing formal stirring to obtain a second slurry S2;
(3) Mixing the first slurry S1 and the second slurry S2 in a third stirring tank to obtain positive slurry Smix, wherein the viscosity of the positive slurry Smix is 8000-13000 mPa & S;
wherein, in step (1), the first binder is polyvinylidene fluoride having a number average molecular weight of 500,000 to 800,000; in step (2), the second binder is polyvinylidene fluoride having a number average molecular weight of 850,000 to 1200,000;
wherein the first positive electrode active material has a pH value of 7 to 10 at standard temperature and pressure; the second positive electrode active material has a pH value of greater than 10 and equal to or less than 14 at standard temperature and pressure.
2. The method according to claim 1, wherein a mass ratio of the first positive electrode active material to the second positive electrode active material is 1: (0.5-10), optionally 1: (0.8-9), optionally 1: (0.9-6).
3. The method according to claim 1 or 2, wherein in step (1), the mass ratio of the first positive electrode active material to the first binder is (30-60): 1, optional (35-50): 1; in the step (2), the mass ratio of the second positive electrode active material to the second binder is (40-120): 1, optional (50-100): 1.
4. the method according to claim 1 or 2, wherein the first positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobaltate, and a modified material thereof, and the second positive electrode active material is selected from one or more of a lithium-rich manganese-based positive electrode material, lithium nickel manganese cobalt, and a modified material thereof.
5. The method according to claim 1 or 2, wherein in the steps (1) and (2), in the dry blending, the revolution speed of the stirring paddle is 20rpm to 50rpm, the rotation speed is 600rpm to 1200rpm, and the stirring is performed for 10 to 20 minutes.
6. The method according to claim 1 or 2, wherein in the steps (1) and (2), in the preliminary stirring, the revolution speed of the stirring paddle is 20rpm to 50rpm, the rotation speed is 200rpm to 600rpm, and the stirring is performed for 3 to 20 minutes.
7. The method according to claim 1 or 2, wherein in the steps (1) and (2), the revolution speed of the stirring paddle is 20rpm to 50rpm, the rotation speed is 600rpm to 1200rpm, and the stirring is performed for 160 to 240 minutes at the time of formal stirring.
8. The method according to claim 1 or 2, wherein in the step (3), the revolution speed of the paddle is 10rpm to 100rpm, and the stirring is carried out for 5 to 30 minutes.
9. The method according to claim 1 or 2, wherein in step (3), slurry S1 and slurry S2 are mixed in a ratio of 1: (0.5-1.5), optionally 1: (0.8-1.2) are mixed and added into a third stirring tank.
10. The process according to claim 1 or 2, wherein the solids content of the first slurry S1 is from 60 to 68 wt%; the solid content of the second slurry S2 is 65 to 75 wt%; the solid content of the positive electrode slurry Smix is 65 to 70 wt%.
11. The method according to claim 1 or 2, wherein the Dv50 of the first positive electrode active material is 0.2 μ ι η to 5 μ ι η, and the Dv50 of the second positive electrode active material is 1 μ ι η to 15 μ ι η.
12. A process according to claim 1 or 2, wherein in steps (1), (2) and (3) the agitation tank is maintained at a vacuum of from 0 to-60 kpa while stirring and the temperature within the agitation tank is from 5 ℃ to 55 ℃, optionally from 15 ℃ to 50 ℃.
13. A positive electrode slurry prepared according to the method of any one of claims 1 to 12.
14. A positive electrode sheet, comprising:
a positive current collector;
a positive electrode active material layer disposed on at least one surface of the positive electrode current collector;
the positive electrode active material layer is prepared from the positive electrode slurry according to claim 13.
15. The positive electrode sheet according to claim 14, wherein the mass percentage of the first positive electrode active material and the second positive electrode active material in total in the positive electrode active material layer is 95% to 98%, optionally 96.5% to 97%; the total mass percentage of the first binder and the second binder in the positive electrode active material layer is 0.5% to 2.2%, and optionally 1.1% to 1.5%.
16. A secondary battery comprising the positive electrode sheet of claim 14 or 15.
17. An electric device comprising the secondary battery according to claim 16.
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