阅读说明：本技术 一种正极厚极片及其制备方法，锂离子电池 (Thick positive pole piece, preparation method thereof and lithium ion battery ) 是由 汪正兵 孙玉龙 郭娜娜 白科 彭小河 汪依水 于 2021-07-30 设计创作，主要内容包括：本发明属于锂离子电池技术领域,具体是一种正极厚极片的制备方法,包括如下步骤：S1.将正极活性材料、炭黑导电剂、粘结剂和保液剂进行干混,再加入分散剂和溶剂,混合搅拌均匀,达到黏度5000～8000mPa·s、固含量70～80％,制成正极浆料；S2通过涂布机在涂碳铝箔上涂覆所述正极浆料,烘干,得到厚度300μm以上的正极厚极片。本发明通过在正极配方中添加大量碳黑类导电剂和保液剂,可在电池充放电循环中存储和保住电解液,离子传输有介质,从而提升寿命。本发明通过对正极制备工艺方法的改进,提供了一种能量密度高、倍率性能优异,安全、成本低、寿命长的锂离子电池。(The invention belongs to the technical field of lithium ion batteries, and particularly relates to a preparation method of a thick positive pole piece, which comprises the following steps: s1, dry-mixing an anode active material, a carbon black conductive agent, a binder and a liquid retention agent, adding a dispersant and a solvent, uniformly mixing and stirring to reach the viscosity of 5000-8000 mPa & s and the solid content of 70-80%, and preparing anode slurry; and S2, coating the positive electrode slurry on the carbon-coated aluminum foil through a coating machine, and drying to obtain a positive electrode thick pole piece with the thickness of more than 300 mu m. According to the invention, a large amount of carbon black conductive agent and liquid retention agent are added in the positive electrode formula, so that the electrolyte can be stored and retained in the charge-discharge cycle of the battery, and the electrolyte has a medium for ion transmission, thereby prolonging the service life. The invention provides the lithium ion battery with high energy density, excellent rate capability, safety, low cost and long service life by improving the preparation process of the anode.)

1. A preparation method of a thick positive pole piece is characterized by comprising the following steps:

s1, dry-mixing an anode active material, a carbon black conductive agent, a binder and a liquid retention agent, adding a dispersant and a solvent, uniformly mixing and stirring to reach the viscosity of 5000-8000 mPa & s and the solid content of 70-80%, and preparing anode slurry;

and S2, coating the positive electrode slurry on the carbon-coated aluminum foil through a coating machine, and drying to obtain a positive electrode thick pole piece with the thickness of more than 300 mu m.

2. The method for preparing the thick positive pole piece according to claim 1, wherein the liquid retention agent is one of polyacrylate, polymethyl methacrylate, polyacrylonitrile, polyacrylamide and polystyrene.

3. The method for preparing the thick positive pole piece according to claim 2, wherein the positive active material is lithium iron phosphate, the carbon black conductive agent is one selected from acetylene black, ketjen black and 350G, VGCF, and the binder is PVDF.

4. The method for preparing the thick positive pole piece according to claim 3, wherein the weight percentage of the positive active material, the carbon black conductive agent, the binder and the liquid retention agent is 94-95.6: 2-4: 1-3: 0.1-0.3.

5. The method for preparing the thick positive pole piece according to claim 4, wherein the weight percentage of the positive active material, the acetylene black, the binder and the liquid retention agent is 94.8: 3: 2: 0.2.

6. The method for preparing the thick positive pole piece according to claim 1, wherein the dispersing agent is one of ethanol or isopropanol, and the solvent is N-methylpyrrolidone.

7. A thick positive pole piece prepared by the preparation method of any one of claims 1-6.

8. A lithium ion battery, which is characterized by comprising a positive plate, a negative plate, a diaphragm and electrolyte, wherein the positive plate adopts the positive thick plate of claim 7.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a thick positive pole piece and a lithium ion battery.

Background

Under the pressure of energy crisis and environmental pollution problems, safety, environmental protection and energy conservation become the subjects of current automobile development, and new energy automobiles are highly valued and strongly supported by traffic and energy departments due to the advantages of energy conservation, environmental protection and no pollution. The power battery plays a very important role as the key of the new energy automobile. The power battery is used as a power source of the electric automobile and is a key component of the electric automobile. In recent years, power batteries are expensive and have short endurance mileage, which is a constraint point of industry development, and therefore, cost reduction and energy density improvement are required.

The purposes of improving the energy density, the quick charge performance and the safety performance and reducing the cost are targets of the lithium ion battery industry, the loading capacity of the active substances of the pole piece is increased, the use amount of the positive and negative current collectors and the diaphragms with higher weight is reduced, the energy density can be improved, and the purpose of reducing the cost can be achieved; however, a series of problems are also caused by thick pole pieces, the polarization of the battery is large, the pole pieces of the battery are thick, the paths of lithium ions and electrons are increased, and the heterogeneity of the internal and external polarization in the thickness direction of the pole pieces is intensified; if the compaction density of the pole piece is large, the porosity is lower, and the path of lithium ion movement in the thickness direction of the pole piece is longer; in addition, the contact area between the material and the electrolyte is reduced, the electrolyte is difficult to soak, the reaction sites of the electrodes are reduced, the internal resistance of the battery is increased, and the problems of increased temperature of the battery, poor rate capability and cycle performance and the like are caused.

The prior patent CN109148820A discloses a preparation method of a thick pole piece and a high-energy density soft package lithium ion battery thereof, which describe the preparation method and the formula of the thick pole piece, but have the problems of difficult electrolyte infiltration, large battery polarization and the like; another prior patent CN107093701A discloses a method for preparing a thick electrode with excellent electrochemical performance and a lithium ion battery, which describes a method for preparing an electrode with a thickness greater than 300 μm, but still does not solve the problems of large polarization, difficult electrolyte infiltration and the like of the thick electrode under high compaction. In addition, the prior art has the following disadvantages: (1) the addition of substances such as surfactants, porous active substances and the like leads to high cost; (2) the thick electrode is difficult to realize high compaction, and the energy density cannot be further improved under low compaction; (3) the polarization of the thick electrode is large, the electrolyte is difficult to infiltrate, and the electrochemical performance is poor; (4) it is difficult to realize mass production.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a thick positive pole piece, so that the lithium ion battery has excellent high-temperature cycle and normal-temperature cycle performance, high energy density, high safety, long service life and low cost.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a preparation method of a thick positive pole piece comprises the following steps:

s1, dry-mixing an anode active material, a carbon black conductive agent, a binder and a liquid retention agent, adding a dispersant and a solvent, uniformly mixing and stirring to reach the viscosity of 5000-8000 mPa & s and the solid content of 70-80%, and preparing anode slurry;

and S2, coating the positive electrode slurry on the carbon-coated aluminum foil through a coating machine, and drying to obtain a positive electrode thick pole piece with the thickness of more than 300 mu m.

Preferably, the liquid retention agent is one of polyacrylate, polymethyl methacrylate, polyacrylonitrile, polyacrylamide and polystyrene.

Preferably, the positive electrode active material is lithium iron phosphate, the carbon black conductive agent is one selected from acetylene black, ketjen black and 350G, VGCF, and the binder is PVDF.

Preferably, the weight percentage of the positive active material, the carbon black conductive agent, the binder and the liquid retention agent is 94-95.6: 2-4: 1-3: 0.1-0.3.

Preferably, the weight percentage of the positive active material, the acetylene black, the binder and the liquid retention agent is 94.8: 3: 2: 0.2.

Preferably, the dispersant is one of ethanol or isopropanol, and the solvent is N-methylpyrrolidone.

Based on a general inventive concept, another object of the present invention is to protect the thick positive electrode sheet prepared by the above preparation method and a lithium ion battery comprising the thick positive electrode sheet as a positive electrode sheet, the lithium ion battery further comprises a negative electrode sheet, a separator and an electrolyte, the negative electrode sheet can adopt the prior art, for example, artificial graphite is adopted as a negative electrode; and selecting a Celgard 2400 membrane as a diaphragm, and assembling into a battery cell according to the prior art to obtain the lithium ion battery.

According to the invention, a large amount of carbon black conductive agent and liquid retention agent are added in the positive electrode formula, so that the electrolyte can be stored and retained in the charge-discharge cycle of the battery, and the electrolyte has a medium for ion transmission, thereby prolonging the service life. The invention provides the lithium ion battery with high energy density, excellent rate capability, safety, low cost and long service life by improving the preparation process of the anode.

Detailed Description

The present invention will be further described with reference to specific embodiments for making the objects, technical solutions and advantages of the present invention more apparent, but the present invention is not limited to these examples. It should be noted that, without conflict, any combination between the embodiments or technical features described below may form a new embodiment. In the invention, all parts and percentages are mass units, and the adopted equipment, raw materials and the like can be purchased from the market or are commonly used in the field. The methods in the following examples are conventional in the art unless otherwise specified.

Example 1

The preparation method of the thick positive pole piece of the embodiment adopts the following steps:

s1, performing dry mixing on 94.8g of lithium iron phosphate, 3g of acetylene black, 2g of PVDF and 0.2g of polyacrylonitrile, adding 1g of dispersing agent-ethanol (the dispersing agent is volatilized after drying) and a solvent NMP, uniformly mixing and stirring to reach the viscosity of 6500mPa & s and the solid content of 75%, and preparing anode slurry;

s2, coating the positive electrode slurry on the carbon-coated aluminum foil through a coating machine, and drying to obtain a positive electrode thick pole piece with the thickness of 450 mu m.

The lithium ion battery of the embodiment adopts the positive plate of the embodiment, takes artificial graphite as a negative electrode, takes the Celgard 2400 membrane as a diaphragm, and the positive plate and the negative plate are rolled and laser cut, and then are wound, assembled, baked, injected, formed and formed by air extraction with the diaphragm to obtain the 15Ah soft-packaged thick electrode lithium ion battery.

Button cell: the positive electrode used was the positive electrode sheet of the above example, the mating electrode was a Li sheet, and the positive electrode, separator, Li sheet, electrolyte and battery case were assembled into a button cell (CR2032) in a glove box.

Example 2

The preparation method of the thick positive pole piece of the embodiment adopts the following steps:

s1, performing dry mixing on 95.6g of lithium iron phosphate, 1.6g of Ketjen black ECP600JD, 2.5g of PVDF and 0.3g of polyacrylamide, adding 1g of dispersing agent-isopropanol (the dispersing agent is volatilized after drying) and a solvent NMP, uniformly mixing and stirring to reach the viscosity of 7800mPa & s and the solid content of 80%, and preparing into anode slurry;

s2, coating the positive electrode slurry on the carbon-coated aluminum foil through a coating machine, and drying to obtain a positive electrode thick pole piece with the thickness of 450 mu m.

The lithium ion battery of the embodiment adopts the positive plate of the embodiment, takes artificial graphite as a negative electrode, takes the Celgard 2400 membrane as a diaphragm, and the positive plate and the negative plate are rolled and laser cut, and then are wound, assembled, baked, injected, formed and formed by air extraction with the diaphragm to obtain the 15Ah soft-packaged thick electrode lithium ion battery.

Button cell: the positive electrode used was the positive electrode sheet of the above example, the mating electrode was a Li sheet, and the positive electrode, separator, Li sheet, electrolyte and battery case were assembled into a button cell (CR2032) in a glove box.

Example 3

The preparation method of the thick positive pole piece of the embodiment adopts the following steps:

s1, dry-mixing 94.2G of lithium iron phosphate, 3.8G of 350G, 1.7G of PVDF and 0.3G of polyacrylate, adding 1G of dispersing agent-ethanol (the dispersing agent is volatilized after drying) and a solvent NMP, mixing and stirring uniformly to reach the viscosity of 6500mPa & s and the solid content of 75 percent, and preparing anode slurry;

s2, coating the positive electrode slurry on the carbon-coated aluminum foil through a coating machine, and drying to obtain a positive electrode thick pole piece with the thickness of 450 mu m.

The lithium ion battery of the embodiment adopts the positive plate of the embodiment, takes artificial graphite as a negative electrode, takes the Celgard 2400 membrane as a diaphragm, and the positive plate and the negative plate are rolled and laser cut, and then are wound, assembled, baked, injected, formed and formed by air extraction with the diaphragm to obtain the 15Ah soft-packaged thick electrode lithium ion battery.

Button cell: the positive electrode used was the positive electrode sheet of the above example, the mating electrode was a Li sheet, and the positive electrode, separator, Li sheet, electrolyte and battery case were assembled into a button cell (CR2032) in a glove box.

Comparative example 1

The preparation method of the positive electrode sheet of the comparative example includes the following steps:

s1, dry-mixing 94.8g of lithium iron phosphate, 3g of acetylene black and 2.2g of PVDF, adding 1g of dispersing agent-ethanol (the dispersing agent is volatilized after drying) and a solvent NMP, mixing and stirring uniformly to reach the viscosity of 6500mPa & s and the solid content of 75%, and preparing into anode slurry;

s2, coating the positive electrode slurry on the carbon-coated aluminum foil through a coating machine, and drying to obtain a positive electrode thick pole piece with the thickness of 450 mu m.

The lithium ion battery of the embodiment adopts the positive plate of the embodiment, takes artificial graphite as a negative electrode, takes the Celgard 2400 membrane as a diaphragm, and the positive plate and the negative plate are rolled and laser cut, and then are wound, assembled, baked, injected, formed and formed by air extraction with the diaphragm to obtain the 15Ah soft-packaged thick electrode lithium ion battery.

Button cell: the positive electrode used was the positive electrode sheet of the comparative example, the mating electrode was a Li sheet, and the positive electrode, separator, Li sheet, electrolyte solution and battery case were assembled into a button cell (CR2032) in a glove box.

Comparative example 2

The preparation method of the positive plate of the embodiment adopts the following steps:

s1, dry-mixing 94.8g of lithium iron phosphate, 0.5g of acetylene black, 4.2g of PVDF and 0.5g of polyacrylonitrile, adding 1g of dispersing agent-ethanol (the dispersing agent is volatilized after drying) and a solvent NMP, mixing and stirring uniformly to reach the viscosity of 6500mPa & s and the solid content of 75 percent, and preparing anode slurry;

s2, coating the positive electrode slurry on the carbon-coated aluminum foil through a coating machine, and drying to obtain a positive electrode thick pole piece with the thickness of 450 mu m.

The lithium ion battery of the embodiment adopts the positive plate of the embodiment, takes artificial graphite as a negative electrode, takes the Celgard 2400 membrane as a diaphragm, and the positive plate and the negative plate are rolled and laser cut, and then are wound, assembled, baked, injected, formed and formed by air extraction with the diaphragm to obtain the 15Ah soft-packaged thick electrode lithium ion battery.

The electrolyte used in the injection solutions of examples 1 to 3 and comparative examples 1 to 2 was prepared by the following method:

mixing LiPF₆(1.2mol/L) and an additive VC (1%) are dissolved in a mixed solvent of PC (propylene carbonate)/EC (ethylene carbonate)/DMC (dimethyl carbonate) of 3: 1: 2 (volume ratio) to form an electrolyte.

Button cell: the positive electrode used was the positive electrode sheet of the comparative example, the mating electrode was a Li sheet, and the positive electrode, separator, Li sheet, electrolyte solution and battery case were assembled into a button cell (CR2032) in a glove box.

Test example 1

The performance of the lithium ion batteries prepared in examples 1 to 3 and comparative examples 1 to 2 was measured, and the measurement method is shown in table 1 below. The button cell is adopted for testing the discharge specific capacity, and the flexible package lithium ion battery is adopted for other detection items. The results of the performance tests are shown in table 2 below.

TABLE 1 Performance test method

Table 2 results of performance testing

Note: in the results of the overcharge, pin puncture, and hot box tests in the above table, "1/3" indicates that 3 batteries were tested, 1 passed the test, and so on.

As can be seen from the above table 2, the lithium ion battery prepared by using the thick pole piece prepared by the invention as the positive pole piece has excellent comprehensive performance, the discharge specific capacity and the mass energy density of the lithium ion battery are both greatly improved, the average voltage and the cycle life are better, and the safety performance is better.

The above embodiments are merely preferred embodiments of the present invention, and any simple modification, modification and substitution changes made to the above embodiments according to the technical spirit of the present invention are within the scope of the technical solution of the present invention.