CN111628137A

CN111628137A - Negative electrode slurry and preparation method and application thereof

Info

Publication number: CN111628137A
Application number: CN202010519863.5A
Authority: CN
Inventors: 曾冬冬; 刘子文; 殷军; 芦昱; 刘金成
Original assignee: Hubei Eve Power Co Ltd
Current assignee: Hubei Eve Power Co Ltd
Priority date: 2020-06-09
Filing date: 2020-06-09
Publication date: 2020-09-04
Anticipated expiration: 2040-06-09
Also published as: CN111628137B

Abstract

The invention relates to a negative electrode slurry and a preparation method and application thereof. The method comprises the following steps: (1) mixing a dispersing agent, a conductive agent, a binder and a solvent to obtain a mixture; (2) the mixture obtained in the step (1) is divided into two parts, and one part of the mixture is added into a negative active material and mixed to obtain first slurry; (3) and (3) adding the rest part of the mixture into the first slurry obtained in the step (2), and mixing to obtain the cathode slurry. According to the method, a part of mixture is used for wetting the negative active material, and then the negative active material and the rest of mixture are dispersed, so that the negative slurry with a good dispersion effect is obtained. The method does not use a surfactant, has low requirements on equipment, short process period and higher application value.

Description

Negative electrode slurry and preparation method and application thereof

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to negative electrode slurry and a preparation method and application thereof.

Background

The lithium ion battery has the advantages of high energy density, no memory effect, long storage life, environmental friendliness and the like, and is widely applied to the fields of portable electronic equipment, instruments, new energy sources and the like. The lithium ion battery comprises a positive plate, a diaphragm and a negative plate, wherein the positive plate and the negative plate are generally prepared by coating positive slurry or negative slurry on the surface of a current collector by adopting a coating machine and performing processes such as drying, rolling, die cutting and the like, and the uniformity of slurry dispersion directly influences the subsequent manufacturing process and the performance of the positive plate and the negative plate.

At present, three main stirring processes of the negative electrode slurry exist: (1) the traditional wet process comprises the following steps: adding a conductive agent and graphite into a glue solution prepared from CMC (sodium carboxymethylcellulose) and water step by step, adjusting viscosity, and adding a binder (SBR, PAA and the like) emulsion, as shown in CN 107492628A; (2) the traditional dry process comprises the following steps: adding a glue solution prepared from CMC and water into a dry powder mixture of graphite and a conductive agent step by step, adjusting viscosity, and adding a binder emulsion, referred to CN 106159266A; (3) the improved wet process comprises the following steps: the dispersing agent and graphite are added into the conductive agent and water step by step, two steps or three steps can be carried out, and the adhesive emulsion is added after the viscosity is adjusted, see CN 107617351A.

The dry process and the wet process have the advantages and the disadvantages, the production efficiency of the dry process is high, the stirring effect is better than that of the wet process, the equipment loss is large, and the requirement on the equipment is high; the wet process is simple to operate, the equipment requirement is low, but the stability of mixing materials is poor, and the consumed time is long.

The rate type lithium ion battery generally requires low internal resistance, high proportion of conductive agent, small particle size of active substance, large specific surface area, and much larger dispersion difficulty than common energy type slurry, and the slurry prepared by the process (1) has poor stability; in the process (2), the slurry is easy to agglomerate in the stirring process, and can be stirred by high-power equipment, so that the large-scale production of a factory is severely limited; the process (3) is easy to agglomerate when the conductive agent and water are stirred, the overall dispersion of the slurry is poor, and the stability is general.

In order to further improve the dispersion uniformity and stability of the negative electrode slurry, researchers have added a surfactant to the negative electrode slurry. CN108428865A discloses a preparation method of a lithium ion battery negative electrode slurry, which comprises the following steps: a. weighing the negative electrode slurry according to the proportion of the negative electrode slurry of the lithium ion battery: an active material, a conductive agent, a thickener, a binder, a solvent, and a surfactant; b. mixing the thickening agent in the raw materials with the solvent, adding the conductive agent into the mixed solvent after fully and uniformly stirring, and continuously and uniformly stirring; c. adding a surfactant into the mixture obtained in the step b, stirring, adding active substances in three batches in an equal amount, and fully stirring for 1.5 hours again to obtain slurry a with uniform appearance; d. adding a binder into the slurry a, and adjusting the viscosity of the slurry by using a solvent in the stirring process to obtain the lithium ion battery cathode slurry; the patent adopts a step-by-step wet mixing process, the cathode slurry is uniformly dispersed, but the used surfactant reduces the content of active substances, increases the production cost, and is not friendly to the environment and human bodies.

Based on the research of the prior art, how to develop a preparation method of negative electrode slurry with low requirements on equipment and short process period can obtain negative electrode slurry with better dispersibility and stability without using a surfactant except a dispersing agent, especially obtain multiplying power type negative electrode slurry with better dispersibility and stability, and overcome the defects of poor cycle performance and low reliability of a negative electrode plate and the like caused by poor uniformity of the negative electrode slurry in the prior art.

Disclosure of Invention

In view of the problems in the prior art, the invention provides a negative electrode slurry and a preparation method and application thereof. According to the preparation method, a dispersing agent, a conductive agent, a binder and a solvent form a mixture, a part of the mixture is added into a negative electrode active material, the negative electrode active material is wetted to have good dispersibility, and then the mixture is mixed with the rest part of the mixture to obtain negative electrode slurry with good dispersibility and stability.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a method for preparing an anode slurry, the method comprising the steps of:

(1) mixing a dispersing agent, a conductive agent, a binder and a solvent to obtain a mixture;

(2) dividing the mixture obtained in the step (1) into two parts, adding one part of the mixture into a negative active material, and mixing to obtain first slurry;

(3) and (3) adding the rest part of the mixture into the first slurry obtained in the step (2), and mixing to obtain the cathode slurry.

The preparation method provided by the invention belongs to a dry preparation process, and the mixture is added into the negative active material step by step, so that the agglomeration of the negative active material is avoided, the negative active material is not easy to disperse, the solid content of the negative slurry is gradually reduced after the negative active material is subjected to the processes of wetting, kneading and dispersing, the preparation process is short, and the dispersion degree of the slurry is high.

In the preparation process, a part of the mixture in the step (2) mainly functions to wet the negative active material and then kneaded like a dough so that the negative active material can be well dispersed in the step (3); the effect of the rest mixture in the step (3) is mainly dispersion, and the wetted negative electrode active material and the rest mixture are dispersed together, so that the dispersion time is shortened, and the dispersion effect is good. The preparation method has low requirement on equipment and short process period, can still obtain the cathode slurry with better dispersity and stability by adjusting the mixing sequence of the dispersing agent, the conductive agent, the binder and the cathode active material under the condition of not using a surfactant except the dispersing agent, and has higher application value.

In the prior art, a negative active substance is added into a mixture at one time or step by step, the method belongs to a wet process, the negative active substance is easy to agglomerate, the solid content of the obtained negative slurry is a process of gradually increasing, the stirring time is usually long, and the viscosity of the slurry is low. According to the preparation method provided by the invention, the mixture is added into the negative active material step by step, and the solid active materials such as the negative active material are subjected to wetting, kneading and dispersing processes, so that the problems that the wet process is long in use time, the slurry viscosity is low, and the solid active materials such as the negative active material are easy to agglomerate are solved.

In the invention, the proportion of the amount of the mixture in the step (2) varies according to the physical and chemical properties of the negative electrode active material, such as the type, the particle size, the specific surface area and the like, and the type of the conductive agent, and the specific proportion is determined by taking the paste obtained finally as a standard that the paste is in a dough shape.

In the present invention, the mixing method of the remaining mixture and the negative electrode active material is not particularly limited, and may be one-step mixing or stepwise mixing, and any mixing method may be applied to the present invention as long as it can obtain a negative electrode slurry having good dispersibility and stability.

Preferably, the dispersant comprises any one or a combination of at least two of sodium carboxymethylcellulose, polyacrylic acid, sodium polyacrylate, guar gum, or acrylonitrile multipolymer, wherein typical but non-limiting combinations are: sodium carboxymethylcellulose and polyacrylic acid, polyacrylic acid and acrylonitrile multipolymer, sodium carboxymethylcellulose and guar gum and the like.

In the present invention, the acrylonitrile multipolymer is not particularly limited, and may be LA132 or LA133, and any type commonly used by those skilled in the art may be applied to the present invention.

Preferably, the conductive agent comprises any one of, or a combination of at least two of, SP carbon black, KS-6, ketjen black, carbon fibers, carbon nanotubes, or graphene, with typical but non-limiting combinations: SP carbon black and Ketjen black, carbon fibers and carbon nanotubes, KS-6 and graphene, and the like.

Preferably, the binder comprises any one of or a combination of at least two of styrene-butadiene rubber, acrylic polymer or acrylonitrile copolymer, wherein the typical but non-limiting combination: styrene-butadiene rubber and acrylonitrile copolymers, acrylic acid polymers and acrylonitrile copolymers, and the like.

Preferably, the solvent comprises water.

In the present invention, water is not particularly limited, and may be deionized water, may be ultrapure water, and any water commonly used by those skilled in the art may be used in the present invention.

Preferably, the negative active material comprises any one of elemental silicon, silica, graphite, soft carbon, hard carbon, or mesocarbon microbeads, or a combination of at least two of these, typically but not limited to: elemental silicon and silica, graphite and mesophase carbon microspheres, soft carbon and mesophase carbon microspheres, graphite, soft carbon and hard carbon, and the like.

In the invention, the preparation method has obvious advantages in the aspect of dispersion effect especially for rate type cathode slurry of a small-particle cathode active material and a high-conductivity agent system.

According to the invention, the proportion of each material in the negative electrode slurry is changed to a certain extent according to the particle size of the negative electrode active material, the selection of the conductive agent, the collocation of the dispersing agent and the binder, the difference of the application scenes of the lithium battery, the capacity of production equipment and the like, and the collocation is specifically carried out according to the actual situation. Regardless of the ratio, the invention is applicable.

In a preferred embodiment of the present invention, the dispersant may be contained in an amount of 0.3 to 3% by mass, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3% by mass, based on 100% by mass of the total of the dispersant, the conductive agent, the binder and the negative electrode active material, but the present invention is not limited to the above-mentioned values, and the present invention is also applicable as long as the values are within the above-mentioned numerical ranges.

Preferably, the content of the conductive agent is 1 to 8% by mass, for example, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 5%, 7%, 7.5%, or 8% by mass, based on 100% by mass of the total of the dispersant, the conductive agent, the binder, and the negative electrode active material, but the content is not limited to the above-mentioned values, and any value within the above-mentioned range may be used, and the content may be selected as appropriate according to the electrical property requirement of the battery cell.

Preferably, the binder is contained in an amount of 1 to 4% by mass, for example, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4% by mass based on 100% by mass of the total of the dispersant, the conductive agent, the binder, and the negative electrode active material, but the binder is not limited to the enumerated values, and is also applicable as long as the binder is within the above numerical range.

Preferably, the negative electrode active material is contained in an amount of 85 to 98% by mass, for example, 85%, 88%, 90%, 95%, or 98% by mass, based on 100% by mass of the total of the dispersant, the conductive agent, the binder, and the negative electrode active material, but the negative electrode active material is not limited to the above-mentioned values, and is also applicable as long as the value is within the above-mentioned numerical range, preferably 85 to 95%.

As a preferable embodiment of the present invention, the mixing method in the step (1) includes: the method comprises the steps of mixing a dispersing agent and a solvent for the first time to obtain a first mixed solution, and mixing a conductive agent and a binder with the first mixed solution for the second time to obtain a mixture.

In the invention, the dispersing agent is mixed with the solvent and dissolved in the solvent to form a glue solution with higher viscosity, the conductive agent is insoluble in the solvent, has small particles and large specific surface area, is easy to agglomerate in the solvent, the binder is insoluble in the solvent, and the conductive agent, the dispersing agent and the binder are simultaneously added into the solvent to have poorer dispersing effect, so that the conductive agent and the binder are added into the glue solution with higher viscosity to ensure the dispersing effect.

Preferably, the primary mixing comprises the steps of: stirring the dispersant and the solvent for the first time, scraping the materials, and stirring for the second time.

Preferably, the revolution speed of one stirring in the one mixing is 1 to 20rpm, and may be, for example, 1rpm, 3rpm, 5rpm, 10rpm, 15rpm, 18rpm or 20rpm, but is not limited to the enumerated values, and is also applicable as long as the value is within the above numerical range, and preferably 5 to 10 rpm.

Preferably, the rotation speed of the primary stirring in the primary mixing is 100-1000rpm, and may be, for example, 100rpm, 150rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, 950rpm, 1000rpm, or the like, but is not limited to the enumerated values, and is also applicable as long as the value is within the above numerical range, and is preferably 500-1000 rpm.

Preferably, the time for one stirring in the one mixing is 5 to 15min, for example, 5min, 8min, 10min, 12min, or 15min, but is not limited to the above-mentioned values, and the same is applicable as long as the value is within the above-mentioned range, and preferably 8 to 12 min.

Preferably, the revolution speed of the secondary stirring in the primary mixing is 20 to 30rpm, and may be, for example, 20rpm, 22rpm, 25rpm, 28rpm or 30rpm, but is not limited to the enumerated values, and the same applies as long as the value is within the above numerical range, and preferably 20 to 25 rpm.

Preferably, the rotation speed of the secondary stirring in the primary mixing is 1500-.

Preferably, the time of the second stirring in the first mixing is 60 to 180min, for example, 60min, 70min, 80min, 90min, 100min, 120min, 150min, 180min, or the like, but is not limited to the above-mentioned values, and the same is applicable as long as the value is within the above-mentioned range, and preferably 90 to 120 min.

Preferably, the content of the dispersant is 0.5 to 3% by mass, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 2.8%, or 3% by mass based on 100% by mass of the first mixed solution, but the content is not limited to the above-mentioned values, and the content is also applicable as long as it is within the above-mentioned numerical range, and is preferably 1 to 2%.

Preferably, the second mixing mode comprises the following steps: and adding the conductive agent into the first mixed solution, stirring for the first time, and then adding the binder and stirring for the second time.

According to the invention, the conductive agent and the binder are added into the first mixed solution step by step, so that the dispersion effect of the conductive agent and the binder is further improved.

Preferably, the primary stirring in the secondary mixing comprises the steps of: stirring for 5-15min at a first revolution speed of 1-20rpm and a first rotation speed of 100-3000 rpm, scraping, and stirring for 60-120min at a second revolution speed of 20-30rpm and a second rotation speed of 1500-3000 rpm.

In the present invention, the first revolution speed may be 1rpm, 3rpm, 5rpm, 10rpm, 15rpm, 18rpm, 20rpm, or the like; the first rotation speed may be 100rpm, 150rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, 950rpm, 1000rpm, or the like; the stirring time at the first revolution speed and the first rotation speed may be 5min, 8min, 10min, 12min, 15min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

In the present invention, the second revolution speed may be 20rpm, 22rpm, 25rpm, 28rpm, 30rpm, or the like; the second rotation speed may be 1500rpm, 1800rpm, 2000rpm, 2500rpm, 2800rpm, 3000rpm, or the like; the stirring time at the second revolution speed and the second rotation speed may be 60min, 70min, 80min, 90min, 100min, 110min, 120min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

Preferably, the primary stirring in the secondary mixing comprises the steps of: stirring for 8-12min at a first revolution speed of 5-10rpm and a first rotation speed of 500-1000rpm, scraping, and stirring for 90-120min at a second revolution speed of 20-25rpm and a second rotation speed of 1000-2500 rpm.

In the present invention, the first revolution speed may be 5rpm, 8rpm, 10rpm, 12rpm, 15rpm, or the like; the first rotation speed may be 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 750rpm, 800rpm, or the like; the stirring time at the first revolution speed and the first rotation speed may be 8min, 9min, 10min, 12min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

Preferably, the secondary stirring in the secondary mixing includes the steps of: stirring for 5-15min at a first revolution speed of 1-20rpm and a first rotation speed of 100-3000 rpm, scraping, and stirring for 30-60min at a second revolution speed of 20-30rpm and a second rotation speed of 1500-3000 rpm.

In the present invention, the second revolution speed may be 20rpm, 22rpm, 25rpm, 28rpm, 30rpm, or the like; the second rotation speed may be 1500rpm, 1800rpm, 2000rpm, 2500rpm, 2800rpm, 3000rpm, or the like; the stirring time at the second revolution speed and the second rotation speed may be 30min, 35min, 40min, 45min, 50min, 55min, 60min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

Preferably, the secondary stirring in the secondary mixing includes the steps of: stirring for 8-12min at a first revolution speed of 5-15rpm and a first rotation speed of 500-1000rpm, scraping, and stirring for 40-50min at a second revolution speed of 20-25rpm and a second rotation speed of 200-2500 rpm.

In the present invention, the first revolution speed may be 5rpm, 8rpm, 10rpm, 12rpm, 15rpm, or the like; the first rotation speed may be 500rpm, 550rpm, 600rpm, 700rpm, 750rpm, 800rpm, 850rpm, 900rpm, or the like; the stirring time at the first revolution speed and the first rotation speed may be 8min, 10min, 12min, 15min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

In the present invention, the second revolution speed may be 25rpm, 26rpm, 27rpm, 28rpm, or the like; the second rotation speed may be 2000rpm, 2300rpm, 2500rpm, 2800rpm, 2900rpm, or the like; the stirring time at the second revolution speed and the second rotation speed may be 40min, 42min, 45min, 48min, 50min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

Preferably, in the step (2), the mass percentage of the portion of the mixture is 30 to 60% based on 100% by mass of the mixture, and may be, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or the like, but is not limited to the enumerated values, and the same applies as long as the values are within the above numerical ranges. The mixture of the mass percentages may wet the negative electrode active material.

Preferably, the mixing in step (2) comprises stirring.

Preferably, the stirring comprises the steps of: stirring for 5-10min at a first revolution speed of 1-10rpm and a first rotation speed of 100-1000rpm, scraping, and stirring for 30-60min at a second revolution speed of 10-20rpm and a second rotation speed of 500-1500 rpm.

In the present invention, the first revolution speed may be 1rpm, 3rpm, 5rpm, 8rpm, 10rpm, or the like; the first rotation speed may be 100rpm, 150rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, 950rpm, 1000rpm, or the like; the stirring time at the first revolution speed and the first rotation speed may be 5min, 6min, 7min, 8min, 10min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

In the present invention, the second revolution speed may be 10rpm, 12rpm, 15rpm, 18rpm, 20rpm, or the like; the second rotation speed may be 500rpm, 800rpm, 1000rpm, 1200rpm, 1300rpm, 1500rpm, or the like; the stirring time at the second revolution speed and the second rotation speed may be 30min, 35min, 40min, 45min, 50min, 55min, 60min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

Preferably, the stirring comprises the steps of: stirring for 6-8min at a first revolution speed of 3-8rpm and a first rotation speed of 200-700rpm, scraping, and stirring for 40-50min at a second revolution speed of 12-18rpm and a second rotation speed of 800-1200 rpm.

In the present invention, the first revolution speed may be 3rpm, 5rpm, 7rpm, 8rpm, or the like; the first rotation speed may be 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, or the like; the stirring time at the first revolution speed and the first rotation speed may be 6min, 7min, 8min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

In the present invention, the second revolution speed may be 12rpm, 15rpm, 17rpm, 18rpm, or the like; the second rotation speed may be 800rpm, 900rpm, 1000rpm, 1100rpm, 1200rpm, or the like; the stirring time at the second revolution speed and the second rotation speed may be 40min, 42min, 45min, 48min, 50min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

Preferably, the mixing in step (3) comprises stirring;

preferably, the stirring comprises the steps of: stirring for 5-15min at a first revolution speed of 1-10rpm and a first rotation speed of 100-3000 rpm, scraping, and stirring for 60-120min at a second revolution speed of 20-30rpm and a second rotation speed of 1500-3000 rpm.

In the present invention, the first revolution speed may be 1rpm, 3rpm, 5rpm, 8rpm, 10rpm, or the like; the first rotation speed may be 100rpm, 150rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, 950rpm, 1000rpm, or the like; the stirring time at the first revolution speed and the first rotation speed may be 5min, 8min, 10min, 12min, 15min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

Preferably, the stirring comprises the steps of: stirring for 8-12min at a first revolution speed of 5-10rpm and a first rotation speed of 500-1000rpm, scraping, and stirring for 70-110min at a second revolution speed of 20-25rpm and a second rotation speed of 2000-2500 rpm.

In the present invention, the first revolution speed may be 3rpm, 5rpm, 7rpm, 8rpm, or the like; the first rotation speed may be 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, or the like; the stirring time at the first revolution speed and the first rotation speed may be 8min, 9min, 10min, 12min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

In the present invention, the second revolution speed may be 22rpm, 25rpm, 27rpm, 28rpm, or the like; the second rotation speed may be 1800rpm, 1900rpm, 2000rpm, 2200rpm, 2500rpm, 2700rpm, 2900rpm, or the like; the stirring time at the second revolution speed and the second rotation speed may be 70min, 75min, 80min, 90min, 100min, 110min, or the like. However, the values are not limited to the enumerated values, and the values within the above numerical ranges are also applicable.

Preferably, the method further comprises: and (3) performing viscosity adjustment and/or defoaming treatment on the negative electrode slurry.

In the invention, the process of adjusting the viscosity and defoaming treatment is the prior art, and the process of adjusting the viscosity can be stirring for 30-60min at the revolution speed of 10-20rpm and the rotation speed of 1000-2000 rpm; the defoaming treatment process can be a process of standing under the vacuum degree of less than or equal to-80 kPa. Any technique for adjusting viscosity and defoaming treatment, which is commonly used by those skilled in the art, is applicable to the present invention.

In the present invention, the solid content and viscosity of the negative electrode slurry are not specifically limited, and in practical applications, the solid content and viscosity of the negative electrode slurry need to be determined according to the stability of the slurry and the capability of subsequent coating equipment, and any solid content and viscosity commonly used by those skilled in the art are suitable for the present invention.

Preferably, the solid content of the anode slurry in the step (2) is 45 to 58%, for example, 45%, 48%, 50%, 55%, 58% or the like, but is not limited to the enumerated values, and the same is true as long as the values are within the above numerical range.

Preferably, the viscosity of the anode slurry in the step (2) is 1000-. For example, 1000 mPa.s, 1500 mPa.s, 2000 mPa.s, 3000 mPa.s, 4000 mPa.s, 5000 mPa.s, 5500 mPa.s or 6000 mPa.s may be mentioned, but the values are not limited to the above-mentioned values, and any values within the above-mentioned numerical range may be used.

In the invention, in each operation step, the revolution speed and the rotation speed after scraping have great influence on the dispersion effect of the negative electrode slurry, and the dispersion effect of the negative electrode slurry is improved through the mutual matching of the revolution speed and the rotation speed in each operation step. Generally, under the condition that the stirring time and the dispersing effect are the same, the revolution speed is slow, and the rotation speed can be fast; the revolution speed is high, and the rotation speed can be slow.

As a further preferred embodiment of the present invention, the method comprises the steps of:

(1) mixing a dispersing agent and a solvent, stirring for 5-15min at a first revolution speed of 1-20rpm and a first rotation speed of 100-1000rpm, scraping, and stirring for 60-180min at a second revolution speed of 20-30rpm and a second rotation speed of 1500-3000rpm to obtain a first mixed solution;

(2) adding a conductive agent into the first mixed solution obtained in the step (1), stirring for 5-15min at a first revolution speed of 1-20rpm and a first rotation speed of 100-1000rpm, scraping, and stirring for 60-120min at a second revolution speed of 20-30rpm and a second rotation speed of 1500-3000rpm to obtain a second mixed solution;

(3) adding an adhesive into the second mixed solution obtained in the step (2), stirring for 5-15min at a first revolution speed of 1-20rpm and a first rotation speed of 100-3000 rpm, scraping, and stirring for 30-60min at a second revolution speed of 20-30rpm and a second rotation speed of 1500-3000rpm to obtain a third mixed solution;

(4) dividing the third mixture obtained in the step (3) into two parts by mass, adding 30-60% of the mixture by mass percent into a negative active material, stirring for 5-10min at a first revolution speed of 1-10rpm and a first rotation speed of 100-1000rpm, scraping, and stirring for 30-60min at a second revolution speed of 10-20rpm and a second rotation speed of 500-1500rpm to obtain a first slurry;

(5) adding the rest part of the mixture in the step (4) into the first slurry, stirring for 5-15min at a first revolution speed of 1-10rpm and a first rotation speed of 100-.

In a second aspect, the present invention provides an anode slurry prepared by the method of the first aspect.

In a third aspect, the present invention provides a negative electrode sheet made of the negative electrode slurry of the second aspect.

In a fourth aspect, the present invention provides a lithium ion battery comprising the negative electrode sheet according to the third aspect.

Compared with the prior art, the invention has the beneficial effects that:

(1) according to the preparation method of the cathode slurry, the mixture prepared by the dispersing agent, the conductive agent, the binder and the solvent is added into the cathode active material step by step, one part of the mixture is used for wetting the cathode active material, and the rest part of the mixture is used for dispersing, so that the cathode slurry with good dispersibility is obtained; the preparation method has short process flow and good dispersion effect;

(2) according to the preparation method of the cathode slurry, the uniformity and the stability of the cathode slurry are further improved by regulating and controlling the mass percentage content of the cathode active substance, the dispersing agent, the conductive agent and the binder, and the revolution speed and the rotation speed in each mixing process, and particularly, the dispersing effect of the multiplying power type cathode slurry can be obviously improved.

Drawings

Fig. 1 is a flow chart of a method for preparing a negative electrode slurry according to the present invention.

Fig. 2 is an SEM image of the negative electrode slurry obtained in example 2.

FIG. 3 is a graph comparing the cycle performance of example 2 with that of comparative example 1.

Detailed Description

The technical solution of the present invention will be further described with reference to the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

The embodiment of the invention provides a preparation method of negative electrode slurry, and a flow chart of the method is shown in fig. 1. Mixing sodium carboxymethylcellulose (CMC) with water to prepare a first mixed solution, adding a conductive agent into the first mixed solution, stirring to obtain a second mixed solution, adding a binder into the second mixed solution, and stirring to obtain a mixture. Then, the mixture was divided into two parts by mass, and a part of the mixture at 40% by mass was added to the negative electrode active material, wetted, and mixed with the remaining part of the mixture (at 60% by mass). And adding water to adjust the viscosity, defoaming and discharging to obtain the cathode slurry.

Example 1

The embodiment provides a preparation method of anode slurry, which comprises the following steps:

(1) mixing sodium carboxymethylcellulose, SP carbon black, styrene butadiene rubber and water, and stirring for 180min at a revolution speed of 100rpm and a rotation speed of 1500rpm to obtain a mixture;

(2) dividing the mixture into two parts by mass, adding 40% of the mixture into graphite, stirring for 10min at a first revolution speed of 8rpm and a first rotation speed of 800rpm, adding the rest of the mixture, stirring for 100min at a second revolution speed of 25rpm and a second rotation speed of 2500rpm, and obtaining negative electrode slurry with a solid content of 45% and a viscosity of 1000mpa & s;

the mass percentage of the sodium carboxymethylcellulose is 0.3%, the mass percentage of the SP carbon black is 1%, the mass percentage of the styrene butadiene rubber is 1%, and the mass percentage of the graphite is 97.7%, wherein the mass percentages of the sodium carboxymethylcellulose, the SP carbon black, the styrene butadiene rubber and the graphite are 100%.

Example 2

(1) mixing sodium carboxymethylcellulose with water, stirring for 15min at a first revolution speed of 1rpm and a first rotation speed of 100rpm, scraping, and stirring for 60min at a second revolution speed of 20rpm and a second rotation speed of 1500rpm to obtain a first mixed solution;

the mass percentage of the sodium carboxymethylcellulose is 0.5% based on 100% of the mass of the first mixed solution;

(2) adding SP carbon black into the first mixed solution obtained in the step (1), stirring for 15min at a first revolution speed of 1rpm and a first rotation speed of 100rpm, scraping, and stirring for 120min at a second revolution speed of 20rpm and a second rotation speed of 1500rpm to obtain a second mixed solution;

(3) adding styrene butadiene rubber into the second mixed solution obtained in the step (2), stirring for 15min at a first revolution speed of 1rpm and a first rotation speed of 100rpm, scraping, and stirring for 60min at a second revolution speed of 20rpm and a second rotation speed of 1500rpm to obtain a mixture;

(4) dividing the mixture obtained in the step (3) into two parts by mass, adding 30% of the mixture into graphite by mass percent, stirring for 10min at a first revolution speed of 1rpm and a first rotation speed of 100rpm, scraping, and then stirring for 60min at a second revolution speed of 10rpm and a second rotation speed of 500rpm to obtain first slurry;

by taking the mass of the sodium carboxymethylcellulose, the SP carbon black, the styrene butadiene rubber and the graphite as 100%, the mass percentage of the sodium carboxymethylcellulose is 0.3%, the mass percentage of the SP carbon black is 1%, the mass percentage of the styrene butadiene rubber is 1%, and the mass percentage of the graphite is 97.7%;

(5) adding the rest part of the mixture in the step (4) into the first slurry, stirring for 15min at a first revolution speed of 1rpm and a first rotation speed of 100rpm, scraping, then stirring for 120min at a second revolution speed of 20rpm and a second rotation speed of 1500rpm, adjusting the viscosity to be 1000mpa & s by using water, and defoaming to obtain the cathode slurry with the solid content of 45%.

The negative electrode slurry obtained in this example is coated on the surface of a copper foil, and SEM characterization is performed, and the characterization result is shown in fig. 2, which shows that the negative electrode slurry has good dispersibility.

Example 3

(1) mixing polyacrylic acid with water, stirring for 10min at a first revolution speed of 10rpm and a first rotation speed of 600rpm, scraping, and stirring for 120min at a second revolution speed of 22rpm and a second rotation speed of 2200rpm to obtain a first mixed solution;

the polyacrylic acid accounts for 1.5 percent by mass based on 100 percent by mass of the first mixed solution;

(2) adding Ketjen black into the first mixed solution obtained in the step (1), stirring for 10min at a first revolution speed of 10rpm and a first rotation speed of 600rpm, scraping, and stirring for 90min at a second revolution speed of 25rpm and a second rotation speed of 2200rpm to obtain a second mixed solution;

(3) adding acrylonitrile multipolymer LA133 into the second mixed solution obtained in the step (2), stirring for 10min at a first revolution speed of 10rpm and a first rotation speed of 600rpm, scraping, and stirring for 45min at a second revolution speed of 25rpm and a second rotation speed of 2200rpm to obtain a mixture;

(4) dividing the mixture obtained in the step (3) into two parts by mass, adding 45% of the mixture into soft carbon, stirring for 8min at a first revolution speed of 5rpm and a first rotation speed of 600rpm, scraping, and stirring for 45min at a second revolution speed of 15rpm and a second rotation speed of 1000rpm to obtain first slurry;

by taking the mass of the polyacrylic acid, the Ketjen black and the acrylonitrile copolymer LA133 and the soft carbon as 100%, the mass percentage of the polyacrylic acid is 1.5%, the mass percentage of the Ketjen black is 4%, the mass percentage of the acrylonitrile copolymer is 2.5%, and the mass percentage of the soft carbon is 92%;

(5) adding the rest part of the mixture in the step (4) into the first slurry, stirring for 10min at a first revolution speed of 5rpm and a first rotation speed of 600rpm, scraping, then stirring for 90min at a second revolution speed of 25rpm and a second rotation speed of 2200rpm, adjusting the viscosity to 3500mpa & s by using water, and defoaming to obtain the cathode slurry with the solid content of 52%.

Example 4

(1) mixing guar gum with water, stirring for 5min at a first revolution speed of 20rpm and a first rotation speed of 1000rpm, scraping, and stirring for 60min at a second revolution speed of 30rpm and a second rotation speed of 3000rpm to obtain a first mixed solution;

the mass percentage of the guar gum is 1.5% based on 100% of the mass of the first mixed solution;

(2) adding carbon nanotubes into the first mixed solution obtained in the step (1), stirring for 5min at a first revolution speed of 20rpm and a first rotation speed of 1000rpm, scraping, and stirring for 60min at a second revolution speed of 30rpm and a second rotation speed of 3000rpm to obtain a second mixed solution;

(3) adding sodium polyacrylate into the second mixed solution obtained in the step (2), stirring for 5min at a first revolution speed of 20rpm and a first rotation speed of 1000rpm, scraping, and stirring for 30min at a second revolution speed of 30rpm and a second rotation speed of 3000rpm to obtain a mixture;

(4) dividing the mixture obtained in the step (3) into two parts by mass, adding 60% of the mixture into mesocarbon microbeads by mass percent, stirring for 5min at a first revolution speed of 10rpm and a first rotation speed of 1000rpm, scraping, and then stirring for 30min at a second revolution speed of 20rpm and a second rotation speed of 1500rpm to obtain first slurry;

by taking the mass of the guar gum, the carbon nano tube, the sodium polyacrylate and the mesocarbon microbeads as 100%, the mass percentage of the guar gum is 3%, the mass percentage of the carbon nano tube is 8%, the mass percentage of the sodium polyacrylate is 4%, and the mass percentage of the mesocarbon microbeads is 85%;

(5) adding the rest part of the mixture in the step (4) into the first slurry, stirring for 5min at a first revolution speed of 10rpm and a first rotation speed of 1000rpm, scraping, then stirring for 60min at a second revolution speed of 30rpm and a second rotation speed of 3000rpm, adjusting the viscosity to 6000mpa & s by using water, and defoaming to obtain the negative electrode slurry with the solid content of 58%.

Example 5

The difference from example 2 is only that the second spinning speed in step (2) was replaced with 2000 rpm.

Example 6

The difference from example 2 is only that the second spinning speed in step (3) was replaced with 2000 rpm.

Example 7

The difference from example 2 is only that the second spinning speed in step (4) is replaced with 500 rpm.

Example 8

Compared with example 2, the difference is only that the mass percentage of the mixture in step (4) is replaced by 20%.

Example 9

The only difference compared to example 2 is that the mass percentage of the mixture in step (4) is replaced by 70%.

Example 10

The difference from example 2 is only that the second spinning speed in step (5) was replaced with 2000 rpm.

Comparative example 1

Compared with example 2, the difference is only that the mixture is added into graphite in step (4) to be mixed in one step, and negative electrode slurry is obtained.

The negative electrode slurry prepared by the comparative example is coated on the surface of copper foil to obtain a negative electrode plate, the negative electrode plate, a diaphragm and a positive electrode plate are assembled into a battery, and the nickel cobalt lithium manganate, the acetylene black and the polyvinylidene fluoride in the positive electrode plate are mixed according to the mass ratio of 8:1: 1. The cycle performance was tested at a voltage range of 3.0-4.2V and a current density of 1C, and the test curve is shown in FIG. 3. With the increase of the cycle number, the battery corresponding to the example 2 shows good cycle performance, and the capacity retention rate after 1000 cycles is 94.5%.

Evaluation of negative electrode slurry properties:

carrying out solid content tests of an upper layer and a lower layer on the cathode slurry obtained in each embodiment and each comparative example after 24 hours, and performing interpolation representation of solid content and comparing the stability of the slurry; and secondly, coating the slurry, and testing the resistance of the pole piece so as to compare the dispersion effect of the slurry.

The test results are shown in table 1.

TABLE 1

The following points can be seen from table 1:

(1) compared with the embodiment 1, the stability of the cathode slurry obtained in the embodiments 2 to 7 is better, and the difference of the solid contents of the upper layer and the lower layer of the slurry after 24 hours is small, because the material required by the mixture of the embodiment 1 is added at one time, the stability of the mixture prepared in the step 1 is poor, and the dispersion of the subsequent cathode active material and the stability of the whole cathode slurry are influenced;

(2) compared with the embodiment 2, the negative electrode slurry obtained in the embodiment 5 has better dispersibility and small resistance value of the electrode sheet, because the second rotation speed adopted in the step (2) in the embodiment 2 is lower, and the dispersing effect of the conductive agent is poorer;

(3) compared with the embodiment 2, the negative electrode slurry obtained in the embodiment 6 has better dispersibility and small resistance of the electrode sheet, because the second rotation speed adopted in the step (3) in the embodiment 2 is lower and the dispersion effect of the binder is poorer;

(4) compared with the example 2, the negative electrode slurry obtained in the example 7 has better dispersibility and small resistance of the electrode sheet, because the second rotation speed adopted in the step (4) in the example 2 is lower, and the wetting effect of the negative electrode active material is poorer;

(5) compared with the embodiment 2, the dispersibility of the negative electrode slurry obtained in the embodiment 8 and the embodiment 9 is poor, and the resistance value of the electrode plate is large, because the mass percentage of the mixture adopted in the step (4) in the embodiment 2 is proper, and the dispersion effect of the negative electrode active material is good;

(6) compared with example 2, the negative electrode slurry obtained in example 10 has better dispersibility and small resistance of the electrode sheet, because the second rotation speed adopted in the step (5) in example 2 is lower and the dispersion effect of the negative electrode active material is poorer;

(7) compared with the embodiment 2, the negative electrode slurry obtained in the comparative example 1 has poor stability and dispersibility and large resistance value of a pole piece, and the difference of the solid contents of the upper layer and the lower layer of the slurry after 24 hours is large, because the slurry does not reach the complete dispersion and the stable state after the mixture is added into graphite and mixed for the same time in the comparative example 1.

In summary, according to the preparation method of the negative electrode slurry provided by the invention, the mixture prepared from the dispersing agent, the conductive agent, the binder and the solvent is added to the negative electrode active material step by step, the negative electrode active material is wetted firstly, and then is mixed with the rest of the mixture for dispersing, so that the negative electrode slurry with a good dispersing effect is obtained. The uniformity and stability of the cathode slurry are further improved by further regulating and controlling the mixing process of the cathode active material, the dispersing agent, the conductive agent and the binder, and particularly the dispersing effect of the multiplying power type cathode slurry can be obviously improved.

The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. A method for preparing anode slurry, comprising the steps of:

2. The method of claim 1, wherein the dispersant comprises any one or a combination of at least two of sodium carboxymethylcellulose, polyacrylic acid, sodium polyacrylate, guar gum, or acrylonitrile multipolymer;

preferably, the conductive agent comprises any one or a combination of at least two of SP carbon black, KS-6, Ketjen black, carbon fiber, carbon nanotube or graphene;

preferably, the binder comprises any one of styrene-butadiene rubber, acrylic polymer or acrylonitrile copolymer or a combination of at least two of the same;

preferably, the solvent comprises water;

preferably, the negative active material includes any one of elemental silicon, silicon monoxide, graphite, soft carbon, hard carbon, or mesocarbon microbeads or a combination of at least two of the foregoing.

3. The method according to claim 1 or 2, wherein the mass percentage of the dispersant is 0.3 to 3% based on 100% of the total mass of the dispersant, the conductive agent, the binder and the negative electrode active material;

preferably, the mass percentage of the conductive agent is 1-8% based on 100% of the total mass of the dispersant, the conductive agent, the binder and the negative electrode active material;

preferably, the mass percentage of the binder is 1-4% based on 100% of the total mass of the dispersant, the conductive agent, the binder and the negative electrode active material;

preferably, the mass percentage of the negative electrode active material is 85 to 98%, preferably 85 to 95%, based on 100% of the total mass of the dispersant, the conductive agent, the binder and the negative electrode active material.

4. The method according to any one of claims 1 to 3, wherein the mixing means of step (1) comprises: mixing a dispersant and a solvent for the first time to obtain a first mixed solution, and mixing a conductive agent and a binder with the first mixed solution for the second time to obtain a mixture;

preferably, the primary mixing comprises the steps of: stirring the dispersing agent and the solvent for the first time, scraping the materials, and stirring for the second time;

preferably, the revolution speed of one stirring in the one mixing is 1 to 20rpm, preferably 5 to 10 rpm;

preferably, the rotation speed of the primary stirring in the primary mixing is 100-;

preferably, the time for one stirring in the first mixing is 5-15min, preferably 8-12 min;

preferably, the revolution speed of the secondary stirring in the primary mixing is 20 to 30rpm, preferably 20 to 25 rpm;

preferably, the rotation speed of the secondary stirring in the primary mixing is 1500-;

preferably, the time of the secondary stirring in the primary mixing is 60-180min, preferably 90-120 min;

preferably, the mass percentage of the dispersant is 0.5-3%, preferably 1-2%, based on 100% of the mass of the first mixed solution;

preferably, the second mixing mode comprises the following steps: adding a conductive agent into the first mixed solution, stirring for the first time, and then adding a binder and stirring for the second time;

preferably, the primary stirring in the secondary mixing comprises the steps of: stirring for 5-15min at a first revolution speed of 1-20rpm and a first rotation speed of 100-;

preferably, the primary stirring in the secondary mixing comprises the steps of: stirring for 8-12min at a first revolution speed of 5-10rpm and a first rotation speed of 500-1000rpm, scraping, and stirring for 90-120min at a second revolution speed of 20-25rpm and a second rotation speed of 2000-2500 rpm;

preferably, the secondary stirring in the secondary mixing includes the steps of: stirring for 5-15min at a first revolution speed of 1-20rpm and a first rotation speed of 100-;

preferably, the secondary stirring in the secondary mixing includes the steps of: stirring for 8-12min at a first revolution speed of 5-15rpm and a first rotation speed of 500-1000rpm, scraping, and stirring for 40-50min at a second revolution speed of 20-25rpm and a second rotation speed of 2000-2500 rpm.

5. The method according to any one of claims 1 to 4, wherein in the step (2), the mass percentage of the portion of the mixture is 30 to 60% based on 100% by mass of the mixture;

preferably, the mixing in step (2) comprises stirring;

preferably, the stirring comprises the steps of: stirring for 5-10min at a first revolution speed of 1-10rpm and a first rotation speed of 100-1000rpm, scraping, and stirring for 30-60min at a second revolution speed of 10-20rpm and a second rotation speed of 500-1500 rpm;

6. The method according to any one of claims 1 to 5, wherein the manner of mixing in step (3) comprises stirring;

preferably, the stirring comprises the steps of: stirring for 5-15min at a first revolution speed of 1-10rpm and a first rotation speed of 100-3000 rpm, scraping, and stirring for 60-120min at a second revolution speed of 20-30rpm and a second rotation speed of 1500-3000 rpm;

preferably, the stirring comprises the steps of: stirring for 8-12min at a first revolution speed of 5-10rpm and a first rotation speed of 500-1000rpm, scraping, and stirring for 70-110min at a second revolution speed of 20-25rpm and a second rotation speed of 2000-2500 rpm;

preferably, the method further comprises: adjusting the viscosity and/or defoaming the negative electrode slurry;

preferably, the solid content of the anode slurry in the step (3) is 45-58%;

preferably, the viscosity of the anode slurry in the step (3) is 1000-.

7. Method according to any of claims 1-6, characterized in that the method comprises the steps of:

(3) adding an adhesive into the second mixed solution obtained in the step (2), stirring for 5-15min at a first revolution speed of 1-20rpm and a first rotation speed of 100-1000rpm, scraping, and stirring for 30-60min at a second revolution speed of 20-30rpm and a second rotation speed of 1500-3000rpm to obtain a third mixed solution;

(4) dividing the third mixture obtained in the step (3) into two parts by mass, adding the mixture with the mass percentage of 30-60% into a negative active material, stirring for 5-10min at a first revolution speed of 1-10rpm and a first rotation speed of 100-1000rpm, scraping, and stirring for 30-60min at a second revolution speed of 10-20rpm and a second rotation speed of 500-1500rpm to obtain a first slurry;

8. An anode slurry, characterized in that it is prepared by the method of any one of claims 1 to 7.

9. A negative electrode sheet, characterized in that the negative electrode sheet is made of the negative electrode slurry according to claim 8.

10. A lithium ion battery comprising the negative electrode sheet according to claim 9.