阅读说明：本技术 一种磷酸铁锂锂离子电池正极片制备方法 (Preparation method of lithium iron phosphate lithium ion battery positive plate ) 是由 罗明 杨庆亨 胡学平 于 2020-07-01 设计创作，主要内容包括：本发明提出了一种磷酸铁锂锂离子电池正极片,包括电池正极集流体以及依次涂覆于集流体外的内涂覆层以及外涂覆层；所述内涂覆层由以下质量百分比的组分组成,96.7％LiFePO<Sub>4</Sub>,1.5％导电炭黑以及1.8聚偏氟乙烯,其中LiFePO<Sub>4</Sub>粒径D50为1.18±0.1μm；所述外涂覆层由以下质量百分比的组分组成,95.2％LiFePO<Sub>4</Sub>,3％导电剂以及1.8％聚偏氟乙烯,其中LiFePO<Sub>4</Sub>粒径D50为0.98±0.1μm,导电剂为导电炭黑、科琴黑以及碳纳米管的混合物,其中导电炭黑、科琴黑和碳纳米管的质量比为4:1:1；聚偏氟乙烯分子量在100万至200万之间；所述电池正极集流体为厚度为8μm的铝箔。本发明通过分层涂布、多次辊压的方法提高锂离子电池内部电子及离子传输速率,降低电池内部阻抗,制备方法简易。(The invention provides a lithium iron phosphate lithium ion battery positive plate, which comprises a battery positive current collector, an inner coating layer and an outer coating layer, wherein the inner coating layer and the outer coating layer are sequentially coated outside the current collector; the inner coating layer consists of 96.7 mass percent of LiFePO 4 1.5% of conductive carbon black and 1.8% of polyvinylidene fluoride, wherein the material is LiFePO 4 The grain diameter D50 is 1.18 +/-0.1 mu m; the outer coating layer consists of the following components in percentage by mass, 95.2% of LiFePO 4 3% of conductive agent and 1.8% of polyvinylidene fluoride, wherein the material is LiFePO 4 The particle diameter D50 is 0.98 + -0.1 μm, and the conductive agent is a mixture of conductive carbon black, Ketjen black and carbon nanotube, wherein the mass ratio of conductive carbon black, Ketjen black and carbon nanotubeIs 4:1: 1; the molecular weight of the polyvinylidene fluoride is between 100 and 200 ten thousand; the current collector of the battery anode is an aluminum foil with the thickness of 8 mu m. According to the invention, the transmission rate of electrons and ions in the lithium ion battery is improved by means of layered coating and multiple rolling, the internal impedance of the battery is reduced, and the preparation method is simple.)

1. The lithium iron phosphate lithium ion battery positive plate is characterized by comprising a battery positive current collector, an inner coating layer and an outer coating layer, wherein the inner coating layer and the outer coating layer are sequentially coated outside the current collector; the inner coating layer consists of 96.7 mass percent of LiFePO₄1.5% of conductive carbon black and 1.8% of polyvinylidene fluoride, wherein the material is LiFePO₄The grain diameter D50 is 1.18 +/-0.1 mu m; the outer coating layer consists of the following components in percentage by mass, 95.2% of LiFePO₄3% of conductive agent and 1.8%Polyvinylidene fluoride, of which LiFePO₄The particle size D50 is 0.98 +/-0.1 mu m, the conductive agent is a mixture of conductive carbon black, Ketjen black and carbon nanotubes, wherein the mass ratio of the conductive carbon black, the Ketjen black and the carbon nanotubes is 4:1: 1; the molecular weight of the polyvinylidene fluoride is between 100 and 200 ten thousand; the current collector of the battery anode is an aluminum foil with the thickness of 8 mu m.

2. The method for preparing the positive plate of the lithium iron phosphate lithium ion battery according to claim 1, which is characterized by comprising the following steps of:

s1, adding the slurry required by the inner coating layer and the slurry required by the outer coating layer into a stirrer respectively according to a formula ratio, and uniformly dispersing and adjusting the slurry to reach the viscosity of 3000-5000 mPa.s;

s2, coating the inner coating layer slurry obtained in the S1 on the surface of a current collector, wherein the coating surface density of the positive electrode slurry is 23.4 +/-0.2 mg/cm²Baking at 100 ℃ for 20min to form an internal coating layer of the positive electrode, and rolling to obtain a primary rolled positive plate; the compacted density of the pole piece rolled in one time is 2.3 +/-0.1 g/cm³The thickness is 124 +/-2 mu m;

s3, coating the external coating layer slurry on the primary rolling positive plate obtained in S2, wherein the surface density of the external coating layer is 10 +/-0.2 mg/cm²Baking at 105 deg.C for 30min to form an external coating layer of the positive electrode, and rolling to obtain the positive plate of the lithium ion battery with the compacted density of the plate of 2.35 + -0.1 g/cm³. The thickness of the rolled pole piece is 159 +/-2 mu m.

3. The method for preparing the positive plate of the lithium iron phosphate lithium ion battery according to claim 2, wherein the inner coating layer consists of 96.7 mass percent of LiFePO₄1.5% of conductive carbon black and 1.8% of polyvinylidene fluoride, wherein the material is LiFePO₄The grain diameter D50 is 1.18 +/-0.1 mu m; the outer coating layer consists of the following components in percentage by mass, 95.2% of LiFePO₄3% of conductive agent and 1.8% of polyvinylidene fluoride, wherein the material is LiFePO₄The grain diameter D50 is 0.98 +/-0.1 mu m, and the conductive agent is a mixture of conductive carbon black, Ketjen black and carbon nano tubes; the molecular weight of the polyvinylidene fluoride is between 100 and 200 ten thousand; the batteryThe positive electrode current collector is an aluminum foil with a thickness of 8 μm.

4. The method for preparing the positive plate of the lithium iron phosphate lithium ion battery according to claim 2, wherein the homogenization dispersion adjustment is performed in S1 by using N-methylpyrrolidone.

Technical Field

The invention relates to the field of lithium ion battery preparation, in particular to a preparation method of a lithium iron phosphate lithium ion battery positive plate.

Background

Lithium ions have the advantages of high energy density, light weight, high voltage, environmental protection and the like, so the lithium ions are widely applied to devices such as mobile phones, digital cameras, UPS power supplies, electric automobiles and the like. The lithium iron phosphate battery has stable voltage platform, good cycle performance and abundant raw materials, and becomes the most promising positive electrode material at present. However, the unique olivine structure of the lithium iron phosphate battery has low electron and ion transmission rates, the pore size distribution state of the pole piece is difficult to control during coating, and the difference of the pore size state after rolling further aggravates polarization in the battery circulation process and affects the circulation performance. The patent documents of improving the rate capability and the cycle performance of the lithium iron phosphate battery anode by relevant modification mainly relate to carbon coating, conductive agent addition, material nanocrystallization and the like, and the improvement related to coating and rolling is relatively limited.

For example, chinese patent No. CN107742709A discloses a method for preparing a lithium iron phosphate positive plate, in which active materials on a current collector are divided into two layers: the active material comprises a first active layer and a second active layer coated on the first active layer; the first active layer comprises 7.5 parts of SP, 82.5 parts of lithium iron phosphate and 10 parts of polyvinylidene fluoride, and the second active layer comprises 2.5 parts of SP, 87.5 parts of lithium iron phosphate and 10 parts of polyvinylidene fluoride; the rate performance of the obtained lithium iron phosphate positive plate is obviously improved, but the content of active substances of the plate is reduced due to the addition of a large amount of conductive agents and adhesives, the energy density of the battery is reduced, and the application cost is increased.

Chinese patent No. CN109546080A discloses a method for preparing a positive plate of a nickel cobalt aluminum acid lithium battery, wherein active materials on a current collector are divided into two layers: the coating comprises a first coating layer and a second coating layer coated on the first coating layer, wherein the first coating layer comprises 97 parts of lithium nickel cobalt aluminate, 2 parts of carbon nano tubes, 1 part of polyvinylidene fluoride, 97 parts of lithium nickel cobalt aluminate, 2 parts of conductive carbon black and 1 part of polyvinylidene fluoride; the rate capability and the capacity retention rate of the lithium ion battery in the previous 50 weeks are improved, but the method is only limited to the replacement of a conductive agent, and the pore size distribution of a coating layer pole piece is not improved.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, and provides a method for preparing a positive plate of a lithium iron phosphate lithium ion battery.

In order to solve the technical problems, the invention adopts the technical scheme that: the lithium iron phosphate lithium ion battery positive plate comprises a battery positive current collector, an inner coating layer and an outer coating layer, wherein the inner coating layer and the outer coating layer are sequentially coated outside the current collector; the inner coating layer consists of 96.7 mass percent of LiFePO₄1.5% of conductive carbon black and 1.8% of polyvinylidene fluoride, wherein the material is LiFePO₄The grain diameter D50 is 1.18 +/-0.1 mu m; the outer coating layer consists of the following components in percentage by mass, 95.2% of LiFePO₄3% of conductive agent and 1.8% of polyvinylidene fluoride, wherein the material is LiFePO₄The particle size D50 is 0.98 +/-0.1 mu m, the conductive agent is a mixture of conductive carbon black, Ketjen black and carbon nanotubes, wherein the mass ratio of the conductive carbon black, the Ketjen black and the carbon nanotubes is 4:1: 1; the molecular weight of the polyvinylidene fluoride is between 100 and 200 ten thousand; the current collector of the battery anode is an aluminum foil with the thickness of 8 mu m.

A preparation method of a lithium iron phosphate lithium ion battery positive plate comprises the following steps:

s1, adding the slurry required by the inner coating layer and the slurry required by the outer coating layer into a stirrer respectively according to a formula ratio, and uniformly dispersing and adjusting the slurry to reach the viscosity of 3000-5000 mPa.s;

s2, coating the inner coating layer slurry obtained in the S1 on the surface of a current collector, wherein the coating surface density of the positive electrode slurry is 23.4 +/-0.2 mg/cm²Baking at 100 ℃ for 20min to form an internal coating layer of the positive electrode, and rolling to obtain a primary rolled positive plate; the compacted density of the pole piece rolled in one time is 2.3 +/-0.1 g/cm³The thickness is 124 +/-2 mu m;

s3, coating the external coating layer slurry on the primary rolling positive plate obtained in S2, wherein the surface density of the external coating layer is 10 +/-0.2 mg/cm²Baking at 105 deg.C for 30min to form anode coatingCoating and rolling to obtain the lithium ion battery positive plate with the compacted density of 2.35 +/-0.1 g/cm³. The thickness of the rolled pole piece is 159 +/-2 mu m.

Further, the inner coating layer consists of 96.7 mass percent of LiFePO₄1.5% of conductive carbon black and 1.8% of polyvinylidene fluoride, wherein the material is LiFePO₄The grain diameter D50 is 1.18 +/-0.1 mu m; the outer coating layer consists of the following components in percentage by mass, 95.2% of LiFePO₄3% of conductive agent and 1.8% of polyvinylidene fluoride, wherein the material is LiFePO₄The grain diameter D50 is 0.98 +/-0.1 mu m, and the conductive agent is a mixture of conductive carbon black, Ketjen black and carbon nano tubes; the molecular weight of the polyvinylidene fluoride is between 100 and 200 ten thousand; the current collector of the battery anode is an aluminum foil with the thickness of 8 mu m.

Further, in S1, N-methylpyrrolidone is used for homogenization dispersion adjustment.

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

(1) the preparation method is simple, and the discharge capacity of the battery can be effectively improved.

(2) The battery discharge efficiency can be effectively improved.

(3) The internal aperture of the pole piece is controlled, and the lithium ion transfer impedance in the battery is obviously reduced.

(4) The direct current internal resistance of the battery is obviously reduced, and the cycle stability of the battery can be improved.

Drawings

The disclosure of the present invention is illustrated with reference to the accompanying drawings. It is to be understood that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention. In the drawings, like reference numerals are used to refer to like parts. Wherein:

FIG. 1 is a schematic sectional view of a positive electrode sheet according to an embodiment.

FIG. 2 is a graph showing the AC impedance at 25 ℃ and a frequency of 0.01 to 4000Hz in examples and comparative examples.

FIG. 3 is a graph showing the AC impedance at a frequency of 0.002 to 4000Hz at-20 ℃ in the examples and comparative examples.

FIG. 4 is a graph of testing the discharge DC internal resistance at room temperature for examples and comparative examples.

FIG. 5 is a graph showing the charging DC internal resistance at room temperature for the examples and comparative examples.

Reference numbers in the figures: 1-positive current collector, 2-inner coating layer and 3-outer coating layer.

Detailed Description

It is easily understood that according to the technical solution of the present invention, a person skilled in the art can propose various alternative structures and implementation ways without changing the spirit of the present invention. Therefore, the following detailed description and the accompanying drawings are merely illustrative of the technical aspects of the present invention, and should not be construed as all of the present invention or as limitations or limitations on the technical aspects of the present invention.