阅读说明：本技术 一种隔膜及其制备方法和应用 (Diaphragm and preparation method and application thereof ) 是由 汪杰 曹勇 赵伟 苏峰 宣健 王从周 于 2021-08-27 设计创作，主要内容包括：本发明提供了一种隔膜及其制备方法和应用,该隔膜包括：基膜；以及若干相互平行且隔开的涂覆条纹,所述涂覆条纹由胶液涂覆在所述基膜的表面形成,其中,所述涂覆条纹平行于所述基膜的TD方向,垂直于所述基膜的MD方向排布。该隔膜能够显著降低卷绕式锂离子电池或圆柱型锂离子电池的K值,改善卷绕式锂离子电池或圆柱型锂离子电池的自放电行为,提高电池安全性和一致性。(The invention provides a diaphragm and a preparation method and application thereof, wherein the diaphragm comprises the following components: a base film; and a plurality of coating stripes which are parallel to each other and are separated from each other, wherein the coating stripes are formed by coating glue solution on the surface of the base film, and the coating stripes are parallel to the TD direction of the base film and are arranged perpendicular to the MD direction of the base film. The diaphragm can obviously reduce the K value of a coiled lithium ion battery or a cylindrical lithium ion battery, improve the self-discharge behavior of the coiled lithium ion battery or the cylindrical lithium ion battery, and improve the safety and consistency of the battery.)

1. A membrane, characterized in that it comprises:

a base film;

and a plurality of coating stripes which are parallel to each other and are separated from each other, wherein the coating stripes are formed by coating glue solution on the surface of the base film, and the coating stripes are parallel to the TD direction of the base film and are arranged perpendicular to the MD direction of the base film.

2. The separator of claim 1, wherein the base film is selected from a polyolefin film or a polyolefin film coated with ceramic.

3. The separator of claim 1 wherein said coating stripes have a coating areal density of 0.5 to 4g/m²。

4. The separator of claim 1, wherein the coating stripes have a thickness of 0.5-2 μm.

5. The separator of claim 1, wherein the width of the coating stripe is 4mm or less.

6. The separator of claim 1 wherein the coated stripes are all equally spaced.

7. The separator of claim 6 wherein the coated stripes are spaced apart by a distance of 0.5mm or less.

8. A method of making a membrane according to any of claims 1 to 7, comprising the steps of:

providing a glue solution;

and coating the glue solution on the surface of the base film, extracting the solvent, forming mesh holes on the coating stripes, and drying to obtain the diaphragm.

9. The method of claim 8, wherein the coating is carried out by a micro-gravure roll coating, and wherein the micro-gravure roll is a zebra-stripe micro-gravure roll.

10. Use of a separator according to any of claims 1 to 7 in a wound lithium ion battery or a cylindrical lithium ion battery.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a diaphragm and a preparation method and application thereof.

Background

The lithium ion battery is a secondary batteryIt mainly works by means of lithium ion movement between the positive and negative electrodes. In particular, during charging and discharging, Li⁺Intercalation and deintercalation to and from two electrodes: upon charging, Li⁺The lithium ion battery is extracted from the positive electrode and is inserted into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the process is reversed during discharging.

Among the performance parameters of the lithium ion battery, the self-discharge capability is one of the important parameters for measuring the battery state, and the self-discharge is the charge retention capability of the battery, which means the retention capability of the stored electricity of the lithium ion battery in a certain environment under the open circuit state. The lithium ion battery is damaged to a certain extent due to the fact that the self-discharge rate of the lithium ion battery is too high, for example, the service life of the lithium ion battery is shortened, the service life of the battery is shortened, the charged quantity in a battery pack is uneven, and the like. In the past, the deterioration degree of the battery was further increased, and the cycle life of the battery pack was significantly reduced.

The self-discharge behavior of the lithium ion battery is improved, the service life and the performance of the lithium ion battery can be improved, the self-discharge behavior of the lithium ion battery is generally related to the performance of materials and the storage environment, and researches show that the self-discharge rate of the ternary battery is higher than that of a lithium cobalt oxide battery, so that the improvement of the materials of the lithium ion battery is an effective breakthrough direction.

Disclosure of Invention

In view of the above, the present invention provides a separator and a method for preparing the same, wherein a plurality of coating stripes that are parallel to each other and spaced apart are formed on a surface of a base film, the coating stripes are parallel to a TD direction of the base film and are arranged perpendicular to an MD direction of the base film.

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

the present invention provides a separator, comprising:

a base film;

and a plurality of coating stripes which are parallel to each other and are separated from each other, wherein the coating stripes are formed by coating glue solution on the surface of the base film, and the coating stripes are parallel to the TD direction of the base film and are arranged perpendicular to the MD direction of the base film.

Further, the base film is selected from a polyolefin film or a polyolefin film coated with ceramic.

Further, the coating surface density of the coating stripes is 0.5-4g/m²。

Further, the thickness of the coating stripe is 0.5-2 μm.

Furthermore, the width of the coating stripes is less than or equal to 4 mm.

Further, the coating stripes are all spaced at equal distances.

Furthermore, the distance between the coating stripes is less than or equal to 0.5 mm.

The invention further provides a preparation method of the diaphragm, which comprises the following steps:

providing a glue solution;

and coating the glue solution on the surface of the base film, extracting the solvent, forming mesh holes on the coating stripes, and drying to obtain the diaphragm.

Further, the coating mode adopts micro-concave roller coating, wherein the micro-concave roller is a zebra-stripe micro-concave roller.

The invention also provides application of the diaphragm in a coiled lithium ion battery or a cylindrical lithium ion battery.

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

the diaphragm of the invention is provided with a plurality of coating stripes which are parallel to each other and are separated from each other on the surface of the base film, the coating stripes are parallel to the TD direction of the base film and are arranged in the direction vertical to the MD direction of the base film, the diaphragm obviously reduces the K value of a winding type lithium ion battery or a cylindrical lithium ion battery and improves the self-discharge behavior of the winding type lithium ion battery or the cylindrical lithium ion battery, thereby avoiding the abnormal capacity exertion of the battery, more importantly, the grouping risk is reduced, the consistency of the battery is promoted, and the inconsistent terminal voltage of each single battery caused by the inconsistent self-discharge of each single battery in the battery pack is avoided, so that the phenomenon of over-charge or over-discharge of individual batteries in the module can be caused.

In addition, the diaphragm is applied to a winding type lithium ion battery or a cylindrical lithium ion battery, after thermal compounding, a channel is formed in an interval area among the coating stripes, and the direction of the channel is consistent with the infiltration direction of electrolyte, so that a siphon channel of the electrolyte is formed, the entry of the electrolyte is accelerated, and the problem of slow infiltration of the electrolyte is solved. And the diaphragm also has the effect of reducing the internal resistance of the battery, thereby reducing the capacity loss of the lithium ion battery and improving the first effect of the lithium ion battery.

Drawings

FIG. 1 is a schematic diagram of a diaphragm 10 according to a preferred embodiment of the present invention;

FIG. 2 is a schematic diagram of a wound lithium ion battery assembled by using the separator 10 in FIG. 1;

fig. 3 is a schematic diagram of a cylindrical lithium ion battery assembled by using the separator 10 in fig. 1.

In the figure: 10-membrane, 101-base film, 102-coated stripes, 103-uncoated areas.

Detailed Description

In order that the invention may be more fully understood, reference will now be made to the specific embodiments illustrated. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

The present invention provides, in a first aspect, a separator comprising:

a base film;

the coating stripes are formed by coating glue solution on the surface of the base film, and are parallel to the TD direction of the base film and arranged perpendicular to the MD direction of the base film.

As shown in fig. 1, which shows a schematic structural view of a separator 10 according to a preferred embodiment of the present invention, the separator 10 includes a base film 101, a plurality of coating stripes 102 formed on a surface of the base film 101 in parallel and spaced apart from each other, and an uncoated region 103 formed between adjacent coating stripes 102. The K value of the coiled lithium ion battery can be obviously reduced through the diaphragm structure, so that the self-discharge behavior of the lithium ion battery is improved. And after thermal compounding, the uncoated region 103 can form a siphon channel, thereby increasing the infiltration speed of the electrolyte; in addition, the diaphragm 10 simultaneously improves the internal resistance problem of the lithium ion battery and reduces the capacity loss of the lithium ion battery. It is understood that the glue solution described herein refers to a binder slurry that is conventional in the art, mainly includes a binder and an organic solvent, and may further include additives that are conventional in the art, such as a dispersing agent, a wetting agent, etc., and since the composition of the glue solution is conventional in the art, and may be adjusted as needed, it will not be specifically described herein, and in one or more embodiments of the present invention, the glue solution is prepared by mixing P (VDF-HFP) powder and an organic solvent NMP in a weight ratio of (10-30): 100.

Further, the kind or thickness of the base film described herein is not particularly limited and may be conventionally selected in the art, and in one or more embodiments of the present invention, the base film is selected from a polyolefin film or a polyolefin film coated with ceramic, and specific examples that may be mentioned include, but are not limited to, a polyethylene film, a polypropylene film, a polyethylene film coated with alumina ceramic, and the like.

Further, the coating surface density of the separator in the present invention can be adjusted according to actual needs and performance parameters of the lithium ion battery, and is not particularly limited, and in one or more embodiments of the present invention, the coating surface density of the coating stripes is 0.5 to 4g/m²。

Further, the thickness of the coating stripe in the present invention can refer to the conventional coating thickness of the glue layer in the art, and can be adjusted according to actual needs, and in one or more embodiments of the present invention, the thickness of the coating stripe is 0.5-2 μm.

Further, in one or more embodiments of the present invention, the width of the coating stripe is less than or equal to 4mm, so that the wetting speed of the electrolyte can be further increased, the wetting time of the electrolyte can be reduced, and the coating stripe is too small, which may cause the texture of the coating roller to be difficult to prepare, and therefore, preferably, the width of the coating stripe is between 1mm and 4 mm.

Further, in order to improve the uniformity of the electrolyte wetting, in one or more embodiments of the present invention, the coating stripes are equally spaced apart.

Further, in one or more embodiments of the present invention, the distance between the coated stripes is less than or equal to 0.5mm, and preferably, the width of the uncoated area is between 0.2mm and 0.5mm, all together with the selection of cost, wetting speed and adhesion.

In a second aspect, the present invention provides a method for preparing the separator according to any one of the first aspect of the present invention, comprising the steps of:

providing a glue solution;

and coating the glue solution on the surface of the base film, extracting the solvent, forming mesh holes on the coating stripes, and drying to obtain the diaphragm.

Further, the coating mode adopts micro-concave roller coating, wherein the micro-concave roller is a zebra-stripe micro-concave roller.

The third aspect of the invention provides the use of the separator according to any one of the first aspect of the invention in a wound lithium ion battery or a cylindrical lithium ion battery. Fig. 2 and 3 show the use of the separator 10 in a wound lithium ion battery and a cylindrical lithium ion battery, respectively.

The technical solution of the present invention will be further clearly and completely described below with reference to specific embodiments.

Example 1

Adding 40kg of P (VDF-HFP) powder into 200kg of NMP, and fully stirring and dissolving to obtain a glue solution;

then coating the glue solution on the surface of a PE (polyethylene) base film with the thickness of 9 mu m by a zebra-line type micro-concave roller, wherein the coating stripes are parallel to the TD direction of the diaphragm and are arranged in the direction vertical to the MD direction of the diaphragm, the coating thickness of the stripes is 1 mu m, the width of the coating stripes is 4mm, and the width of an uncoated area is 0.5 mm;

then extracting solvent NMP, forming mesh holes on the coating stripes, drying to obtain the oil-system coating lithium ion battery diaphragm with the coating surface density of 0.9g/m²。

Example 2

The present example adopts the same embodiment as example 2, except that: the stripe coating thickness was 1 μm, the width of the coated stripes was 1mm, the width of the uncoated regions was 0.1mm, and the coated areal density was 1.2g/m²。

Example 3

Adding 20kg of P (VDF-HFP) powder into 200kg of NMP, and fully stirring and dissolving to obtain a glue solution;

coating the glue solution on the surface of a PE (polyethylene) base film with the thickness of 9 mu m by a zebra-stripe type micro-concave roller, wherein the coating stripes are parallel to the TD direction of the diaphragm and are arranged in the MD direction of the diaphragm, the coating thickness of the stripes is 0.5 mu m, the width of the coating stripes is 2mm, and the width of an uncoated area is 0.2 mm;

then extracting solvent NMP, forming mesh holes on the coating stripes, drying to obtain the oil-system coating lithium ion battery diaphragm with the coating surface density of 0.5g/m²。

Example 4

Adding 60kg of P (VDF-HFP) powder into 200kg of NMP, and fully stirring and dissolving to obtain a glue solution;

coating the glue solution on the surface of a PE (polyethylene) base film with the thickness of 9 mu m by a zebra-type micro-concave roller, wherein the coating stripes are parallel to the TD direction of the diaphragm and are arranged in the direction vertical to the MD direction of the diaphragm, and then extracting a solvent NMP (N-methyl pyrrolidone) to form a net-shaped cavity; drying the oil-system coated lithium ion battery separator by using an oven to obtain an oil-system coated lithium ion battery separator, wherein the coating thickness of the stripes is 2 mu m, the width of the coated stripes is 4mm, and the width of the uncoated area is 0.05 mm;

then extracting solvent NMP, forming mesh holes on the coating stripes, drying to obtain the oil-system coating lithium ion battery diaphragm with the coating surface density of 4g/m²。

Comparative example 1

Adding 40kg of P (VDF-HFP) powder into 200kg of NMP, and fully stirring and dissolving to obtain a glue solution;

then coating the glue solution on the surface of a PE base film with the thickness of 1 mu m by a micro-concave roller;

then extracting solvent NMP, forming mesh holes on the coating stripes, drying to obtain the oil-system coating lithium ion battery diaphragm with the coating surface density of 0.9g/m²。

Comparative example 2

This comparative example uses the same embodiment as example 1 except that: the coating stripes are arranged parallel to the membrane MD direction and perpendicular to the membrane TD direction.

Test example

1. The lithium ion diaphragms prepared in the examples 1 to 4 and the comparative examples 1 to 2 are respectively assembled into a cylindrical lithium ion battery, and a soaking test is carried out, wherein the method specifically comprises the following steps: an equal amount of electrolyte (commercially available, main components: EC, EMC, DMC, LiPF)₆) And injecting the electrolyte into the assembled cylindrical lithium ion battery, standing for 1, 2, 3 and 5 days at normal temperature, disassembling, testing the quality of the residual electrolyte after soaking for 1 day, 2 days, 3 days and 5 days at normal temperature and normal pressure respectively, and testing the wettability of the cylindrical lithium ion battery.

TABLE 1 comparison of residual electrolyte in cylindrical lithium ion batteries

	1 day	2 days	3 days	5 days
					Example 1	6g	1.7g	1.8g	1.8g
Example 2	1.1g	1.5g	0.5g	0.9g
					Comparative example 1	25g	21g	18g	17.6g
Comparative example 2	20g	16g	14g	10g

As can be seen from the test results in table 1, the electrolyte of the wound lithium ion battery assembled by the separators of examples 1 and 2 can completely infiltrate in 2 days at most, even example 2 can completely infiltrate in 1 day, while the separator of the comparative example still retains about 10g of the electrolyte after 5 days, which shows that the separator of the present invention has a great effect of promoting the infiltration of the electrolyte.

2. The assembled wound lithium ion battery was subjected to normal temperature K value and other parameter tests, and the results are shown in table 2.

TABLE 2 comparison of basic Performance of cylindrical lithium ion batteries

As can be seen from the test results in table 2, the inventors surprisingly found that the use of the separator in the present invention allows the K value of the cylindrical lithium ion battery to be significantly reduced. And the ACR and DCIR of the diaphragm prepared by the invention are obviously smaller than those of a comparative example, which shows that the diaphragm prepared by the invention has the function of reducing the internal resistance of the battery, and the capacity loss is reduced due to the reduction of the internal resistance, so that the first effect of the cylindrical lithium ion battery is improved.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.