阅读说明：本技术 一种锂电池隔膜及其锂离子电池的制备方法 (Lithium battery diaphragm and preparation method of lithium ion battery ) 是由 程跃 王中奇 陈永乐 庄志 何方波 廖晨博 于 2019-11-15 设计创作，主要内容包括：本发明涉及一种锂电池隔膜及其锂离子电池的制备方法,隔膜包括基底层和形成在所述基底层的至少一个主面上的涂布层,涂布层包含聚偏二氟乙烯及其共聚物和无机粒子,并且所述涂布层含有微孔结构；涂布层靠近基底层侧的微孔平均直径大于涂布层表面的微孔平均直径；涂布层的微孔平均直径在0.2-10微米。本申请的有点在于：涂布层中的聚偏二氟乙烯及其共聚物具有粘结作用,可以将多孔基底和正、负极粘结起来,形成良好的界面,防止电池使用过程中发生变形,降低安全风险,提高循环性能和能量密度。(The invention relates to a lithium battery diaphragm and a preparation method of a lithium battery thereof, wherein the diaphragm comprises a substrate layer and a coating layer formed on at least one main surface of the substrate layer, the coating layer comprises polyvinylidene fluoride and copolymers thereof and inorganic particles, and the coating layer contains a microporous structure; the average diameter of micropores on the side of the coating layer close to the base layer is larger than that of micropores on the surface of the coating layer; the average diameter of micropores of the coating layer is 0.2-10 μm. The application has the advantages that: the polyvinylidene fluoride and the polyvinylidene fluoride copolymer in the coating layer have a binding effect, and can bind the porous substrate, the positive electrode and the negative electrode to form a good interface, prevent the battery from deforming in the using process, reduce the safety risk and improve the cycle performance and the energy density.)

1. A lithium battery separator comprising a base layer and a coating layer formed on at least one principal surface of the base layer;

the coating layer comprises polyvinylidene fluoride and copolymers thereof and inorganic particles, and the coating layer contains a microporous structure;

the average diameter of micropores on the coating layer side close to the base layer side is larger than that of micropores on the coating layer surface.

2. The lithium battery separator as claimed in claim 1, wherein the average diameter of the micropores of the coating layer is 0.2 to 10 μm.

3. The lithium battery separator as claimed in claim 1, wherein the substrate separator has a thickness of 3 to 30 μm.

4. The lithium battery separator as claimed in claim 1, wherein the coating layer has a thickness of 0.2 to 5 μm.

5. The lithium battery separator as claimed in claim 1, wherein the substrate layer is made of a Polyethylene (PE) single-layer film, a polypropylene (PP) single-layer film, and a PP/PE/PP multi-layer microporous film formed by compounding PP and PE.

6. A preparation method of a lithium battery diaphragm is characterized by comprising the following specific steps:

(1) mixing and dispersing polyvinylidene fluoride and copolymer thereof and solvent according to the weight ratio of 1 (0.1-99) to obtain dispersed glue solution;

(2) mixing and dispersing the dispersed glue solution and the inorganic particles according to the weight ratio of 1 (0.1-50) to obtain ceramic slurry;

(3) and uniformly coating the ceramic slurry on the surface of the base material diaphragm, extracting for three times by using an extracting agent, and drying to obtain the diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particle lithium ion battery diaphragm.

7. The method for preparing a lithium battery separator according to claim 6, wherein the solvent is one or a combination of two or more of dimethylacetamide, N-methylpyrrolidone, pentane, dichloromethane, carbon disulfide, or acetone.

8. The method of claim 6, wherein the inorganic particles are one or more of alumina, boehmite, barium titanate, cerium oxide, zirconium oxide, titanium oxide, barium sulfate, and magnesium oxide; the particle size of the inorganic particles is 0.1-10 μm.

9. The method for preparing a lithium battery separator as claimed in claim 6, wherein the mass fractions of the tertiary extractants in the step (3) are 5-30%, 1-5% and 0.1-1%, respectively.

10. A lithium battery, comprising: a positive electrode; a negative electrode; and the separator according to any one of claims 1 to 9 provided between the positive electrode and the negative electrode.

Technical Field

The invention relates to the technical field of diaphragm production, in particular to a lithium battery diaphragm and a preparation method of a lithium ion battery thereof.

Background

The lithium ion battery generally mainly comprises a positive electrode, a negative electrode, a diaphragm, an electrolyte and a battery shell. In the structure of the lithium ion battery, a diaphragm is one of key inner layer components. The performance of the diaphragm determines the interface structure, internal resistance and the like of the battery, directly influences the capacity, circulation, safety performance and other characteristics of the battery, and the diaphragm with excellent performance plays an important role in improving the comprehensive performance of the battery. The separator has a main function of separating the positive electrode and the negative electrode of the battery to prevent short circuit due to contact between the two electrodes, and also has a function of allowing electrolyte ions to pass therethrough.

At present, the lithium ion battery diaphragm which is commercially used is generally a polyethylene or polypropylene diaphragm, and the diaphragm has the performances of better acid and alkali resistance, higher tensile strength, higher porosity and the like. However, the conventional polyolefin separator is limited by the limitation of raw materials, and has poor thermal stability, a melting point of PE of about 135 degrees and a PP of about 150 degrees. In order to solve the technical problem that the diaphragm shrinks seriously along the MD/TD direction when the temperature is 100 ℃, extensive researchers do a great deal of work on the modification treatment of the traditional polyolefin diaphragm, mainly from two aspects, firstly, inorganic or organic fillers are mixed in the preparation process of the polyolefin diaphragm, and secondly, a heat-resistant layer is coated on the surface of the finished polyolefin diaphragm. The second method is mature, and the research and application of various companies are mainly focused on coating a ceramic layer and a polymer layer, the ceramic coating can play a role in resisting heat, improving the self-discharge of the thin diaphragm and increasing the electrochemical stability and the liquid absorption of the diaphragm, and the polymer coating can play a role in enhancing the adhesion of the positive and negative pole pieces and preventing the deformation of the battery. However, the polyolefin separator surface layer is coated to cause pore blocking so that the internal resistance and self-discharge performance of the separator become large, thereby causing a problem of degradation of battery characteristics.

Therefore, it is desirable to provide a lithium battery separator which can improve the heat resistance of the separator and enhance the adhesion of positive and negative electrode plates without affecting the internal resistance and self-discharge performance of the separator.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a lithium battery diaphragm and a preparation method of a lithium battery.

The purpose of the invention is realized by the following technical scheme:

a lithium battery separator comprising a base layer and a coating layer formed on at least one main surface of the base layer,

the coating layer comprises polyvinylidene fluoride and copolymers thereof and inorganic particles, and the coating layer contains a microporous structure;

the average diameter of micropores on the side of the coating layer close to the base layer is larger than that of micropores on the surface of the coating layer;

the polyvinylidene fluoride and the polyvinylidene fluoride copolymer in the coating layer have a binding effect, and can bind the porous substrate, the positive electrode and the negative electrode to form a good interface, prevent the battery from deforming in the using process, reduce the safety risk and improve the cycle performance and the energy density.

The average diameter of micropores of the coating layer is 0.2-10 μm.

The thickness of the base material diaphragm is 3-30 microns.

The thickness of the coating layer is 0.2-5 microns.

The base layer is made of a Polyethylene (PE) single-layer film, a polypropylene (PP) single-layer film and a PP/PE/PP multi-layer microporous film compounded by PP and PE.

A preparation method of a lithium battery diaphragm comprises the following specific steps:

(1) mixing and dispersing polyvinylidene fluoride and copolymer thereof and solvent according to the weight ratio of 1 (0.1-99) to obtain dispersed glue solution;

(2) mixing and dispersing the dispersed glue solution and the inorganic particles according to the weight ratio of 1 (0.1-50) to obtain ceramic slurry;

(3) and uniformly coating the ceramic slurry on the surface of the base material diaphragm, extracting for three times by using an extracting agent, and drying to obtain the diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particle lithium ion battery diaphragm.

The solvent is one or the combination of more than two of dimethylacetamide, N-methylpyrrolidone, pentane, dichloromethane, carbon disulfide or acetone.

The inorganic particles are one or more of alumina, boehmite, barium titanate, cerium oxide, zirconia, titanium oxide, barium sulfate and magnesium oxide.

The particle size of the inorganic particles is 0.1-10 microns.

In the step (3), the mass fractions of the three extractants are respectively 5-30%, 1-5% and 0.1-1%.

A lithium battery includes: a positive electrode; a negative electrode; and a separator disposed between the positive electrode and the negative electrode.

Compared with the prior art, the invention has the following positive effects:

the separator of the present application includes a base layer and a coating layer formed on at least one main surface of the base layer, the coating layer including polyvinylidene fluoride and copolymers thereof and inorganic particles, and the coating layer containing a large amount of microporous structures, the average diameter of micropores of the coating layer near the base layer side being larger than the average diameter of micropores of the coating layer surface, the average diameter of micropores of the coating layer being 0.2 to 10 μm. The average diameter of micropores on the coating layer side of the diaphragm close to the substrate layer is larger than that of micropores on the surface of the coating layer, so that the internal resistance and self-discharge performance of the diaphragm can be effectively reduced, and the ventilation value is increased by less than 80s compared with that of the substrate layer. And the polyvinylidene fluoride and the copolymer thereof in the coating layer of the isolating membrane have a binding effect, so that the porous substrate, the positive electrode and the negative electrode can be bound to form a good interface, the deformation of the battery in the use process is prevented, the safety risk is reduced, and the cycle performance and the energy density are improved.

Drawings

FIG. 1 polyvinylidene and its copolymers and inorganic particle coated separator;

the labels in the figures are:

1 a coating layer,

2, a substrate.

Detailed Description

The following provides specific embodiments of a lithium battery separator and a preparation method of a lithium battery thereof.

Example 1

As shown in fig. 1, a lithium battery separator coated with polyvinylidene fluoride and its copolymer and inorganic particles, the separator comprising a substrate layer and a coating layer formed on at least one major surface of the substrate layer; the coating layer comprises a polyvinylidene fluoride and copolymer thereof, an inorganic particle coating layer 1 and a polyolefin film layer substrate 2 from top to bottom, wherein the coating layer contains a large number of micropore structures, the average diameter of micropores of the coating layer close to the substrate layer side is larger than the average diameter of micropores of the coating layer surface, and the average diameter of micropores of the coating layer is 0.2-10 mu m. The coated separator is prepared by the following steps:

taking a polyethylene diaphragm as a base material, wherein the thickness of the base material is 14 mu m, mixing polyvinylidene fluoride and a copolymer thereof with N-methyl pyrrolidone according to the weight ratio of 1:2, and grinding and dispersing to obtain a dispersion glue solution; mixing and dispersing the dispersed glue solution and alumina particles according to the weight ratio of 1:5 to obtain coating slurry, wherein the particle size of the alumina is 500 mu m; the coating slurry was uniformly applied to both surfaces of the substrate separator by means of gravure coating. The thickness of the coating layer is 3 mu m, and the prepared extracting agents with the concentration of 10 percent, 3 percent and 0.5 percent are extracted for three times and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Example 2

Taking a polyethylene diaphragm as a base material, wherein the thickness of the base material is 9 mu m, mixing polyvinylidene fluoride and a copolymer thereof with dimethylacetamide according to a weight ratio of 1:1, and grinding and dispersing to obtain a dispersed glue solution; mixing and dispersing the dispersed glue solution and boehmite particles according to the weight ratio of 1:10 to obtain coating slurry, wherein the particle size of boehmite is 800 mu m; the coating slurry was uniformly applied to both surfaces of the substrate separator by means of gravure coating. The thickness of the coating layer is 2 mu m, and the prepared extracting agents with the concentration of 15 percent, 4 percent and 0.2 percent are extracted for three times and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Example 3

Mixing polyvinylidene fluoride and copolymer thereof with pentane according to the weight ratio of 1:3, grinding and dispersing to obtain a dispersion glue solution, wherein the polypropylene diaphragm is used as a base material, the thickness of the base material is 9 mu m; mixing and dispersing the dispersed glue solution and barium titanate particles according to the weight ratio of 1:15 to obtain coating slurry, wherein the particle size of barium titanate is 100 nm; the coating slurry is uniformly applied to both surfaces of the substrate separator by means of gravure printing. The thickness of the coating layer is 1 mu m, and the prepared extracting agents with the concentration of 20 percent, 3 percent and 0.1 percent are extracted for three times and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Example 4

Mixing polyvinylidene fluoride and copolymer thereof with carbon disulfide according to the weight ratio of 1:10, grinding and dispersing to obtain a dispersed glue solution, wherein the polypropylene diaphragm is used as a base material, the thickness of the base material is 9 microns; mixing and dispersing the dispersed glue solution and cerium oxide particles according to the weight ratio of 1:20 to obtain coating slurry, wherein the particle size of cerium oxide is 30 nm; the coating slurry is uniformly coated on two surfaces of the substrate membrane in a dip coating mode. The thickness of the coating layer is 2 mu m, and the prepared extracting agents with the concentration of 15 percent, 3 percent and 0.1 percent are extracted for three times and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Example 5

Taking a diaphragm compounded by polyethylene and polypropylene as a base material, wherein the thickness of the base material is 9 mu m, mixing polyvinylidene fluoride and copolymer thereof with pentane according to the weight ratio of 1:5, and grinding and dispersing to obtain a dispersion glue solution; mixing and dispersing the dispersed glue solution and zirconia particles according to the weight ratio of 1:15 to obtain coating slurry, wherein the particle size of zirconia is 200 nm; the coating slurry was uniformly applied to both surfaces of the substrate separator by means of gravure coating. The thickness of the coating layer is 1.5 mu m, and the prepared extracting agents with the concentration of 20 percent, 3 percent and 0.1 percent are extracted for three times and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Example 6

Mixing polyvinylidene fluoride and copolymer thereof with pentane according to the weight ratio of 1:5, grinding and dispersing to obtain a dispersion glue solution, wherein the polypropylene diaphragm is used as a base material, the thickness of the base material is 10 mu m; mixing and dispersing the dispersed glue solution and barium sulfate particles according to the weight ratio of 1:10 to obtain coating slurry, wherein the particle size of barium sulfate is 500 mu m; the coating slurry is uniformly applied to both surfaces of the substrate separator by means of gravure printing. The thickness of the coating layer is 2 mu m, and the prepared extracting agents with the concentration of 10 percent, 3 percent and 0.1 percent are extracted for three times and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Example 7

Taking a polyethylene diaphragm as a base material, wherein the thickness of the base material is 16 mu m, mixing polyvinylidene fluoride and copolymer thereof with acetone according to the weight ratio of 1:10, and grinding and dispersing to obtain a dispersed glue solution; mixing and dispersing the dispersed glue solution and magnesium oxide particles according to the weight ratio of 1:15 to obtain coating slurry, wherein the particle size of barium sulfate is 30 microns; the coating slurry is uniformly applied to both surfaces of the substrate separator by means of gravure printing. The thickness of the coating layer is 1.5 mu m, and the prepared extracting agents with the concentration of 10 percent, 3 percent and 0.1 percent are extracted for three times and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Comparative example 1

Taking a polyethylene diaphragm as a base material, wherein the thickness of the base material is 14 mu m, mixing polyvinylidene fluoride and a copolymer thereof with N-methyl pyrrolidone according to the weight ratio of 1:2, and grinding and dispersing to obtain a dispersion glue solution; mixing and dispersing the dispersed glue solution and alumina particles according to the weight ratio of 1:5 to obtain coating slurry, wherein the particle size of the alumina is 500 mu m; the coating slurry was uniformly applied to both surfaces of the substrate separator by means of gravure coating. The thickness of the coating layer is 3 mu m, and an extracting agent with the concentration of 40% is prepared, and the coating layer is extracted and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particle lithium ion battery diaphragm, and the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particle lithium ion battery diaphragm.

Comparative example 2

Taking a polyethylene diaphragm as a base material, wherein the thickness of the base material is 9 mu m, mixing polyvinylidene fluoride and a copolymer thereof with dimethylacetamide according to a weight ratio of 1:1, and grinding and dispersing to obtain a dispersed glue solution; mixing and dispersing the dispersed glue solution and boehmite particles according to the weight ratio of 1:10 to obtain coating slurry, wherein the particle size of boehmite is 800 mu m; the coating slurry was uniformly applied to both surfaces of the substrate separator by means of gravure coating. And (3) drying the coating layer with the thickness of 2 mu m to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Comparative example 3

Mixing polyvinylidene fluoride and copolymer thereof with pentane according to the weight ratio of 1:3, grinding and dispersing to obtain a dispersion glue solution, wherein the polypropylene diaphragm is used as a base material, the thickness of the base material is 10 mu m; mixing and dispersing the dispersed glue solution and barium titanate particles according to the weight ratio of 1:15 to obtain coating slurry, wherein the particle size of barium titanate is 100 nm; the coating slurry is uniformly applied to both surfaces of the substrate separator by means of gravure printing. The thickness of the coating layer is 1 mu m, and an extracting agent with the concentration of 40% is prepared, and the coating layer is extracted and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Comparative example 4

Mixing polyvinylidene fluoride and copolymer thereof with carbon disulfide according to the weight ratio of 1:10, grinding and dispersing to obtain a dispersed glue solution, wherein the polypropylene diaphragm is used as a base material, the thickness of the base material is 9 microns; mixing and dispersing the dispersed glue solution and cerium oxide particles according to the weight ratio of 1:20 to obtain coating slurry, wherein the particle size of cerium oxide is 30 nm; the coating slurry is uniformly coated on two surfaces of the substrate membrane in a dip coating mode. The thickness of the coating layer is 2 mu m, and the prepared extractant with the concentration of 40 percent is extracted and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Comparative example 5

Taking a diaphragm compounded by polyethylene and polypropylene as a base material, wherein the thickness of the base material is 9 mu m, mixing polyvinylidene fluoride and copolymer thereof with pentane according to the weight ratio of 1:5, and grinding and dispersing to obtain a dispersion glue solution; mixing and dispersing the dispersed glue solution and zirconia particles according to the weight ratio of 1:15 to obtain coating slurry, wherein the particle size of zirconia is 200 nm; the coating slurry was uniformly applied to both surfaces of the substrate separator by means of gravure coating. The thickness of the coating layer is 1.5 mu m, and the prepared extractant with the concentration of 40 percent is extracted and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Comparative example 6

Mixing polyvinylidene fluoride and copolymer thereof with pentane according to the weight ratio of 1:5, grinding and dispersing to obtain a dispersion glue solution, wherein the polypropylene diaphragm is used as a base material, the thickness of the base material is 10 mu m; mixing and dispersing the dispersed glue solution and barium sulfate particles according to the weight ratio of 1:10 to obtain coating slurry, wherein the particle size of barium sulfate is 500 mu m; the coating slurry is uniformly applied to both surfaces of the substrate separator by means of gravure printing. The thickness of the coating layer is 2 mu m, and the prepared extractant with the concentration of 40 percent is extracted and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

Comparative example 7

Taking a polyethylene diaphragm as a base material, wherein the thickness of the base material is 16 mu m, mixing polyvinylidene fluoride and copolymer thereof with acetone according to the weight ratio of 1:10, and grinding and dispersing to obtain a dispersed glue solution; mixing and dispersing the dispersed glue solution and magnesium oxide particles according to the weight ratio of 1:15 to obtain coating slurry, wherein the particle size of barium sulfate is 30 microns; the coating slurry is uniformly applied to both surfaces of the substrate separator by means of gravure printing. The thickness of the coating layer is 1.5 mu m, and the prepared extractant with the concentration of 40 percent is extracted and dried to obtain the lithium ion battery diaphragm coated with the polyvinylidene fluoride and the copolymer thereof and the inorganic particles.

The present invention also provides a nonaqueous electrolyte secondary battery including: positive pole, negative pole, diaphragm, electrolyte and outside encapsulation shell. The separator was the separators in the above examples and comparative examples, and the coating layer of the separator contained a large number of fine pores, the average diameter of the fine pores of the coating layer on the side close to the base layer was larger than the average diameter of the fine pores of the surface of the coating layer, and the average diameter of the fine pores of the coating layer was 0.2 to 10 μm.

Performance testing of the separator

The following performance tests were performed on the separators of examples 1 to 7 and comparative examples 1 to 7:

(1) air permeability: air permeability may also be characterized by a Gurley value, which refers to the time required for a particular amount of air to pass through a particular area of membrane at a particular pressure (standard Gruley: the time for 100mL of gas to pass through a 1 square inch membrane at a 4.88 inch water column pressure). The permeability increase is the permeability of the coating layer membrane minus the permeability of the base film.

(2) Internal resistance: the alternating current impedance method (EIS) is more commonly used for testing the resistance of the separator, and the Nm value, i.e., the MacMullini constant, is obtained by testing the resistance of the separator in an electrolyte solution as compared with the resistance of the electrolyte solution. And applying a sinusoidal alternating voltage signal to a measuring device, and analyzing data by using an equivalent circuit through measuring impedance values with different frequencies in a certain range to obtain the information of the diaphragm ionic resistance.

(3) A relationship curve of pressure and gas flow rate is measured for different commercial lithium ion battery diaphragms by using a capillary flow Aperture gauge (CFP) and a non-volatile fluorine-containing organic liquid as a medium. The pore size of the membrane can be obtained from the formula P ═ CT/d, T represents the surface tension of the test liquid, C is the capillary constant, P is the gas pressure, and d is the pore size.

The results of the separator performance tests of comparative examples 1 to 7 and examples 1 to 7 are shown in table 1 below.

TABLE 1

Through the test results, the pore diameters of the coating layers of the samples 1 to 7 are in step change because the three-stage extraction mode is adopted and the concentrations of the three-stage extraction agents are respectively 5 to 30 percent, 1 to 5 percent and 0.1 to 1 percent, so that the difference between the maximum pore diameter and the average pore diameter is large. In comparative examples 1 to 7, however, since only one extraction was performed and the concentration of the extractant was 40% higher, a step-like distribution of the microporous structure was not formed and the values of the maximum pore diameter and the average pore diameter were close to each other. In addition, the air permeability was increased by less than 80s in examples 1 to 7, which passed the air permeability test, while the air permeability was increased by more than 80s in comparative examples 1 to 7, and the internal resistance of the separators in examples 1 to 7 was smaller than that in comparative examples 1 to 7.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and decorations can be made without departing from the concept of the present invention, and these modifications and decorations should also be regarded as being within the protection scope of the present invention.