阅读说明：本技术 隔膜及锂离子电池 (Diaphragm and lithium ion battery ) 是由 谢小缔 曾彪 颜海鹏 于 2019-09-26 设计创作，主要内容包括：本公开涉及一种隔膜,该隔膜包括基材和位于所述基材上的由聚合物形成的涂层,所述聚合物包括聚偏氟乙烯-六氟丙烯和聚丙烯酸酯；其中,所述聚偏氟乙烯-六氟丙烯的玻璃态转化温度Tg值为-30℃～0℃,熔点为80℃～110℃；所述聚丙烯酸酯的玻璃态转化温度Tg值为-40℃～0℃,软化点为0℃～60℃。本公开提供的隔膜中,形成涂层的聚偏氟乙烯-六氟丙烯具有合适的玻璃态转化温度Tg值和熔点,聚丙烯酸酯具有合适的玻璃态转化温度Tg值和软化点,使聚合物涂层在冷压条件下具有粘性,该隔膜可实现冷压压合。(The present disclosure relates to a separator including a substrate and a coating layer formed of a polymer including polyvinylidene fluoride-hexafluoropropylene and polyacrylate on the substrate; wherein the glass transition temperature Tg value of the polyvinylidene fluoride-hexafluoropropylene is-30-0 ℃, and the melting point is 80-110 ℃; the glass transition temperature Tg value of the polyacrylate is-40-0 ℃, and the softening point is 0-60 ℃. The polyvinylidene fluoride-hexafluoropropylene forming the coating layer has a proper glass transition temperature Tg value and a melting point, and the polyacrylate has a proper glass transition temperature Tg value and a softening point, so that the polymer coating layer has viscosity under the cold pressing condition, and the diaphragm can realize the cold pressing lamination.)

1. A separator comprising a substrate and a coating layer formed of a polymer on the substrate, the polymer comprising polyvinylidene fluoride-hexafluoropropylene and polyacrylate;

wherein the glass transition temperature Tg value of the polyvinylidene fluoride-hexafluoropropylene is-30-0 ℃, and the melting point is 80-110 ℃; the glass transition temperature Tg value of the polyacrylate is-40-0 ℃, and the softening point is 0-60 ℃.

2. The membrane according to claim 1, wherein said polyvinylidene fluoride-hexafluoropropylene has a glass transition temperature, Tg, value of-28 ℃ to-10 ℃ and a melting point of 90 ℃ to 105 ℃; the glass transition temperature Tg value of the polyacrylate is-30 ℃ to-10 ℃, and the softening point is 5 ℃ to 30 ℃.

3. The separator according to claim 1, wherein the weight ratio of the polyvinylidene fluoride-hexafluoropropylene to the polyacrylate is (70-90): (30-10).

4. The membrane according to claim 3, wherein the weight ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylate is (75-85): (25-15).

5. The separator according to claim 1, wherein the coating layer has a thickness of 0.5 to 2 μm and an areal density of 0.1 to 5g/m²。

6. The separator according to claim 1, wherein at least two layers of the separator can be bonded under a pressing condition of a temperature of 10 to 30 ℃ and a pressure of 0.1 to 10MPa, and a peeling force between any two layers of the separator after bonding is 0.002 to 1N; the diaphragm can be bonded with the pole piece under the pressing condition that the temperature is 10-30 ℃ and the pressure is 0.1-10 MPa, and the stripping force between the diaphragm and the pole piece after bonding is 0.002-0.5N.

7. The separator of any of claims 1-6, wherein the substrate comprises a polyolefin-based film and/or a ceramic coated lithium ion battery separator;

the polyolefin base film is made of polyethylene, polypropylene or at least one of three layers of polypropylene/polyethylene/polypropylene; the thickness of the polyolefin basal membrane is 5-25 mu m, and the porosity is 30-80%;

the ceramic-coated lithium ion battery separator has a single-sided or double-sided ceramic coating comprising at least one of alumina, boehmite, zirconia, silica, and magnesium hydroxide; the thickness of the ceramic coating lithium ion battery diaphragm is 7-35 mu m.

8. The separator according to any one of claims 1 to 6, wherein the coating layer formed of the polymer further contains a surfactant, the surfactant including at least one of sodium dodecylbenzenesulfonate, fatty acid glyceride and fatty alcohol-polyoxyethylene ether, and the content of the surfactant is 0.2 to 1 part by weight with respect to 100 parts by weight of the polyvinylidene fluoride-hexafluoropropylene and polyacrylate.

9. A method of making the separator of any one of claims 1-8, comprising:

coating the water system emulsion of the polymer on the surface of the base material, and drying to obtain the diaphragm;

wherein the solid content of the water-based emulsion of the polymer is 10-35%, and the viscosity is 20-500 mpa.s;

the water-based emulsion of the polymer is coated on the surface of the base material in a spraying or spot coating mode, and the coating speed of the spraying or spot coating is 30-80 m/min;

the drying mode is drying, and the drying conditions are as follows: the temperature is 50-70 ℃, and the time is 0.2-1 min.

10. Lithium ion battery, characterized in that it comprises a separator according to any one of claims 1 to 8.

Technical Field

The disclosure relates to the technical field of lithium ion batteries, in particular to a diaphragm and a lithium ion battery.

Background

The separator is one of important components of the lithium ion battery, and has the main functions of separating the positive electrode and the negative electrode of the lithium ion battery, preventing the two electrodes from contacting and short-circuiting, and enabling lithium ions to pass through. In practical application, after the battery core is assembled by the diaphragm and the battery cathode, the problems of diaphragm wrinkling, battery core loosening and the like may occur.

At present, in order to avoid the problems of wrinkling of the diaphragm and looseness of the battery core, the battery core is generally assembled by adopting a glue-coated diaphragm and a positive electrode and a negative electrode of the battery, namely, after an oil PVDF glue layer is coated on the diaphragm, the diaphragm is assembled into the battery core by combining the positive electrode and the negative electrode of the battery with hot pressing, so that the diaphragm is attached to the positive electrode and the negative electrode, the gap between the diaphragm and the positive electrode and the negative electrode is reduced, the thickness of the battery after circulation is improved, the deformation of the.

However, the battery core assembled by the glue-coated diaphragm and the positive and negative electrodes of the battery has the following problems: after the oil PVDF gluing diaphragm, the anode and the cathode are assembled into the battery core, the battery core needs to be heated to a certain temperature for pressing, and the battery core has a certain thickness, so that the heat conduction needs longer time, and the time consumption of the working procedure is increased; moreover, the outer layer reaches the set temperature before the inner layer, when the temperature between the inner layer and the outer layer of the battery cell reaches the same temperature, the time of the outer layer at the set temperature is longer than that of the inner layer, so that the pressing combination degree of the inner layer and the outer layer of the battery cell with the positive electrode and the negative electrode is different, and the cycle performance of the lithium ion battery is influenced; in addition, the diaphragm is coated by adopting oil PVDF, and the PVDF needs to be dissolved by using an organic solvent, so that the diaphragm is not environment-friendly and has high production cost.

Disclosure of Invention

The diaphragm has viscosity under normal temperature and does not need to be heated during pressing.

In order to achieve the above objects, the present disclosure provides a separator including a substrate and a coating layer formed of a polymer including polyvinylidene fluoride-hexafluoropropylene and polyacrylate on the substrate;

wherein the glass transition temperature Tg value of the polyvinylidene fluoride-hexafluoropropylene is-30-0 ℃, and the melting point is 80-110 ℃; the glass transition temperature Tg value of the polyacrylate is-40-0 ℃, and the softening point is 0-60 ℃.

Preferably, the glass transition temperature Tg value of the polyvinylidene fluoride-hexafluoropropylene is-28 ℃ to-10 ℃, and the melting point is 90 ℃ to 105 ℃; the glass transition temperature Tg value of the polyacrylate is-30 ℃ to-10 ℃, and the softening point is 5 ℃ to 30 ℃.

Optionally, the weight ratio of the polyvinylidene fluoride-hexafluoropropylene to the polyacrylate is (70-90): (30-10).

Preferably, the weight ratio of the polyvinylidene fluoride-hexafluoropropylene to the polyacrylate is (75-85): (25-15).

Optionally, the thickness of the coating is 0.5-2 μm, and the surface density is 0.1-5 g/m²。

Optionally, at least two layers of the diaphragms can be bonded under the pressing condition that the temperature is 10-30 ℃ and the pressure is 0.1-10 MPa, and the peeling force between any two layers of the diaphragms after bonding is 0.002-1N; the diaphragm can be bonded with the pole piece under the pressing condition that the temperature is 10-30 ℃ and the pressure is 0.1-10 MPa, and the stripping force between the diaphragm and the pole piece after bonding is 0.002-0.5N.

Optionally, the substrate comprises a polyolefin-based film and/or a ceramic coated lithium ion battery separator;

the polyolefin base film is made of polyethylene, polypropylene or at least one of three layers of polypropylene/polyethylene/polypropylene; the thickness of the polyolefin basal membrane is 5-25 mu m, and the porosity is 30-80%;

the ceramic-coated lithium ion battery separator has a single-sided or double-sided ceramic coating comprising at least one of alumina, boehmite, zirconia, silica, and magnesium hydroxide; the thickness of the ceramic coating lithium ion battery diaphragm is 7-35 mu m.

Optionally, the coating layer formed by the polymer further contains a surfactant, the surfactant comprises at least one of sodium dodecyl benzene sulfonate, fatty glyceride and fatty alcohol-polyoxyethylene ether, and the content of the surfactant is 0.2-1 part by weight relative to 100 parts by weight of polyvinylidene fluoride-hexafluoropropylene and polyacrylate.

The present disclosure also provides a method of making a separator as described in any of the above, comprising:

coating the water system emulsion of the polymer on the surface of the base material, and drying to obtain the diaphragm;

wherein the solid content of the water-based emulsion of the polymer is 10-35%, and the viscosity is 20-500 mpa.s;

the water-based emulsion of the polymer is coated on the surface of the base material in a spraying or spot coating mode, and the coating speed of the spraying or spot coating is 30-80 m/min;

the drying mode is drying, and the drying conditions are as follows: the temperature is 50-70 ℃, and the time is 0.2-1 min.

The present disclosure also provides a lithium ion battery comprising the separator of any one of the above.

Through the technical scheme, the diaphragm provided by the disclosure comprises a base material and a coating layer which is positioned on the base material and is formed by a polymer, wherein polyvinylidene fluoride-hexafluoropropylene in the polymer has a proper glass transition temperature Tg value and a melting point, and polyacrylate has a proper glass transition temperature Tg value and a softening point, so that the coating layer formed by the polymer has viscosity under the cold pressing condition, and the diaphragm can realize cold pressing.

Additional features and advantages of the disclosure will be set forth in the detailed description which follows.

Detailed Description

The following describes in detail specific embodiments of the present disclosure. It should be understood that the detailed description and specific examples, while indicating the present disclosure, are given by way of illustration and explanation only, not limitation.

A first aspect of the present disclosure provides a separator including a substrate and a coating layer formed of a polymer including polyvinylidene fluoride-hexafluoropropylene and polyacrylate on the substrate;

wherein the glass transition temperature Tg value of the polyvinylidene fluoride-hexafluoropropylene is-30-0 ℃, and the melting point is 80-110 ℃; the glass transition temperature Tg value of the polyacrylate is-40-0 ℃, and the softening point is 0-60 ℃.

Polyvinylidene fluoride-hexafluoropropylene having the above-mentioned glass transition temperature Tg value and melting point is non-tacky at normal temperature but is compressible; the polyacrylate with the glass transition temperature Tg value and the softening point has stronger viscosity at normal temperature; the polyvinylidene fluoride-hexafluoropropylene and polyacrylate are combined to be used as the coating of the lithium ion battery diaphragm, so that the coating formed by the coating has viscosity and compressibility under the cold pressing condition, and the pressing can be realized without heating. The polymer coating of the diaphragm disclosed by the invention contains the polyvinylidene fluoride-hexafluoropropylene and the polyacrylate at the same time, so that the diaphragm has viscosity at normal temperature and under certain pressure, normal rolling can be realized, and self-adhesion cannot occur between diaphragm layers during rolling; the diaphragm can realize the lamination between diaphragm layers or between the diaphragm layers and the positive plate and the negative plate under the cold pressing condition, and the problem that the electrochemical performance of the battery cell is influenced due to different lamination combination degrees of the diaphragm of the inner layer and the outer layer of the battery cell and the negative electrode caused by the temperature difference between the inner layer and the outer layer of the battery cell during hot pressing can be solved; meanwhile, the cold pressing and laminating are not required to be carried out with heating treatment, so that the time consumption of the working procedure can be reduced, the production efficiency is improved, and the energy consumption is saved.

According to the disclosure, in order to further improve the viscosity and compressibility of the diaphragm during cold pressing at normal temperature, the glass transition temperature Tg value of the polyvinylidene fluoride-hexafluoropropylene can be-28 ℃ to-10 ℃, and the melting point can be 90 ℃ to 105 ℃; the glass transition temperature Tg value of the polyacrylate can be-30 ℃ to-10 ℃, and the softening point can be 5 ℃ to 30 ℃.

According to the present disclosure, the weight ratio of the polyvinylidene fluoride-hexafluoropropylene and the polyacrylate in the polymer coating can be changed in a wide range, for example, the weight ratio of the polyvinylidene fluoride-hexafluoropropylene and the polyacrylate can be (70-90): (30-10). Preferably, the weight ratio of the polyvinylidene fluoride-hexafluoropropylene to the polyacrylate can be (75-85): (25-15). Under the preferable condition, the polyvinylidene fluoride-hexafluoropropylene and the polyacrylate are in proper weight proportion, so that the coated diaphragm has better viscosity at a certain pressure at normal temperature and can be normally rolled, and self-adhesion between diaphragm layers can not occur during rolling.

According to the disclosure, theThe thickness and surface density of the coating layer in the separator may vary within a wide range, for example, the thickness of the coating layer may be 0.5 to 2 μm, and the surface density may be 0.1 to 5g/m². Preferably, the thickness of the coating can be 1-2 μm, and the surface density can be 0.3-1 g/m²Within the preferable range, the conduction rate of lithium ions in the separator is higher, the internal resistance of the battery is lower, and the performance of the lithium ion battery containing the separator is better.

According to the present disclosure, the separator has the following features: at least two layers of the diaphragms can be bonded under the pressing condition that the temperature is 10-30 ℃ and the pressure is 0.1-10 MPa, and the peeling force between any two layers of the diaphragms after bonding is 0.002-1N; the diaphragm can be bonded with the pole piece under the pressing condition that the temperature is 10-30 ℃ and the pressure is 0.1-10 MPa, and the stripping force between the diaphragm and the pole piece after bonding is 0.002-0.5N. The above-mentioned test method for the peel force may be a conventional test method in the art, and may be, for example, the method specified in GB 2792-1998.

The type and material of the substrate may vary widely in accordance with the present disclosure, for example, the substrate may comprise a polyolefin-based film and/or a ceramic-coated lithium ion battery separator;

the material of the polyolefin base film can be selected from polyethylene, polypropylene or one of at least three layers of polypropylene/polyethylene/polypropylene; the thickness of the polyolefin basal membrane can be 5-25 mu m, and the porosity can be 30-80%;

the ceramic coated lithium ion battery separator has a single or double-sided ceramic coating, which may include at least one of alumina, boehmite, zirconia, silica, and magnesium hydroxide; the thickness of the ceramic-coated lithium ion battery diaphragm can be 7-35 mu m.

According to the present disclosure, in order to increase workability in applying the polymer and forming a coating layer, it is preferable that the coating layer formed of the polymer may further contain a surfactant, and the kind and content of the surfactant may vary within a wide range, for example, the surfactant may include at least one of sodium dodecylbenzenesulfonate, fatty acid glyceride and fatty alcohol polyoxyethylene ether, and the content of the surfactant may be 0.2 to 1 part by weight with respect to 100 parts by weight of the polyvinylidene fluoride-hexafluoropropylene and polyacrylate. The surfactant can wet the surface of the substrate and help the polymer coating lay more evenly on the surface of the substrate.

A second aspect of the present disclosure provides a method of preparing the separator of any one of the above, the method comprising:

coating the water system emulsion of the polymer on the surface of the base material, and drying to obtain the diaphragm;

wherein the solid content of the water-based emulsion of the polymer is 10-35%, and the viscosity is 20-500 mpa.s;

the water-based emulsion of the polymer is coated on the surface of the base material in a spraying or spot coating mode, and the coating speed of the spraying or spot coating is 30-80 m/min;

the drying mode is drying, and the drying conditions are as follows: the temperature is 50-70 ℃, and the time is 0.2-1 min.

The method disclosed by the invention is simple in process and easy to control, and the base material is coated by the water-based emulsion of the polymer, so that the use of an organic solvent is avoided, the method is safe, non-toxic, environment-friendly, low in requirements on production workshops and equipment, and the production cost is saved. The solid content and viscosity condition of the aqueous polymer emulsion help the aqueous polymer emulsion to be more easily coated on the surface of the substrate, and the coating thickness and the surface density can be better controlled.

The present disclosure also provides a lithium ion battery comprising the separator of any one of the above.

After the lithium ion battery disclosed by the invention is subjected to a cycle test for 100 circles, the capacity retention rate is still not lower than 90%, so that the performance of the lithium ion battery is relatively stable, and the lithium ion battery can be used in various application occasions.

The present disclosure is further illustrated by the following examples, but is not to be construed as being limited thereby.

The materials, reagents, instruments and equipment used in the examples of the present disclosure are commercially available, unless otherwise specified.

Example 1

Uniformly mixing the polyvinylidene fluoride-hexafluoropropylene water system emulsion and the polyacrylate water system emulsion to obtain the polymer water system emulsion. The polymer water system emulsion is coated on two sides of a ceramic coating diaphragm with the thickness of 9+3 mu m in a spraying mode, the spraying speed is 60m/min, and then the ceramic coating diaphragm is dried at the temperature of 60 ℃ to obtain the diaphragm of the embodiment, wherein the thickness of a dried polymer coating is 1 mu m, and the surface density is 0.5g/m². The diaphragm of the embodiment has viscosity and can be normally rolled under the conditions that the temperature is 25 ℃ and the pressure is 1.5MPa, and self-adhesion between diaphragm layers can not occur during rolling.

In this example, in the aqueous polymer emulsion, the weight ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylate was 80: 20; the glass transition temperature Tg value of the polyvinylidene fluoride-hexafluoropropylene is-25 ℃, and the melting point is 95 ℃; the glass transition temperature Tg value of the polyacrylate is-22 ℃ and the softening point is 10 ℃.

Examples 2 to 9

Membranes of examples 2-9 were prepared according to the method of example 1, except that: the glass transition temperature Tg and melting point of PVDF-HFP and the glass transition temperature Tg and softening point of polyacrylate are different from those of example 1, and are specifically shown in Table 1.

TABLE 1

The diaphragms of the embodiments 1 to 9 have viscosity under the conditions that the temperature is 25 ℃ and the pressure is 1.5MPa, can be normally rolled, and can not be self-adhered to each other when being rolled.

Example 10

A separator was prepared according to the method of example 1, except that: in the polymer water system emulsion, the weight ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylate is 75: 25. the diaphragm of the embodiment has viscosity and can be normally rolled under the conditions that the temperature is 25 ℃ and the pressure is 1.5MPa, and self-adhesion between diaphragm layers can not occur during rolling.

Example 11

A separator was prepared according to the method of example 1, except that: in the polymer water system emulsion, the weight ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylate is 85: 15. the diaphragm of the embodiment has viscosity and can be normally rolled under the conditions that the temperature is 25 ℃ and the pressure is 1.5MPa, and self-adhesion between diaphragm layers can not occur during rolling.

Example 12

A separator was prepared according to the method of example 1, except that: in the polymer water system emulsion, the weight ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylate is 70: 30. the diaphragm of the embodiment has viscosity and can be normally rolled under the conditions that the temperature is 25 ℃ and the pressure is 1.5MPa, and self-adhesion between diaphragm layers can not occur during rolling.

Example 13

A separator was prepared according to the method of example 1, except that: in the polymer water system emulsion, the weight ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylate is 90: 10. the diaphragm of the embodiment has viscosity and can be normally rolled under the conditions that the temperature is 25 ℃ and the pressure is 1.5MPa, and self-adhesion between diaphragm layers can not occur during rolling.

Example 14

A separator was prepared according to the method of example 1, except that: the aqueous polymer emulsion further contained a surfactant (sodium dodecylbenzenesulfonate) in an amount of 0.4 part by weight per 100 parts by weight of polyvinylidene fluoride-hexafluoropropylene and polyacrylate. The diaphragm of the embodiment has viscosity and can be normally rolled under the conditions that the temperature is 25 ℃ and the pressure is 1.5MPa, and self-adhesion between diaphragm layers can not occur during rolling.

Example 15

A separator was prepared according to the method of example 1, except that: in the polymer water system emulsion, the weight ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylate is 95: 5. the separator of the present example had a small adhesive force under the conditions of a temperature of 25 ℃ and a pressure of 1.5 MPa.

Example 16

A separator was prepared according to the method of example 1, except that: in the polymer water system emulsion, the weight ratio of polyvinylidene fluoride-hexafluoropropylene to polyacrylate is 60: 40. the separator of this example exhibited strong self-adhesion at a temperature of 25 c.

Comparative example 1

A separator was prepared according to the method of example 1, except that: the aqueous polymer emulsion contains only polyvinylidene fluoride-hexafluoropropylene. The separator of this comparative example had no tackiness at a temperature of 25 ℃ and a pressure of 1.5 MPa.

Comparative example 2

A separator was prepared according to the method of example 1, except that: the aqueous polymer emulsion contains only polyacrylate. The diaphragm of the comparative example has extremely strong self-adhesion at the temperature of 25 ℃, and can not be normally rolled.

Comparative example 3

A separator was prepared according to the method of example 1, except that: the glass transition temperature Tg value of the polyvinylidene fluoride-hexafluoropropylene is 10 ℃, and the melting point is 120 ℃; the glass transition temperature Tg value of the polyacrylate is 10 ℃ and the softening point is 70 ℃. The separator of this comparative example was poor in adhesiveness at a temperature of 25 ℃ and a pressure of 1.5 MPa.

Comparative example 4

A separator was prepared according to the method of example 1, except that: the glass transition temperature Tg value of the polyvinylidene fluoride-hexafluoropropylene is-40 ℃, and the melting point is 70 ℃; the glass transition temperature Tg value of the polyacrylate is-50 ℃ and the softening point is-10 ℃. The diaphragm of the comparative example has strong self-adhesion property at the temperature of 25 ℃, and can not be normally rolled.

Test example 1

The separators prepared in examples 1 to 16 and comparative examples 1 to 4 were respectively wound or laminated with the positive plate and the negative plate to form a structure in which the negative plate, the separator and the positive plate were arranged at intervals, and then cold pressing and lamination were performed at a temperature of 25 ℃, a pressure of 1.5MPa, and a lamination time of 50s to obtain a cell as a test experiment. Meanwhile, the oil PVDF gluing membrane, the positive plate and the negative plate are subjected to hot pressing under the conditions that the temperature is 95 ℃, the pressure is 1.5MPa and the pressing time is 50s to obtain the battery cell which is used as a contrast experiment. The thickness of each cell before and after lamination is respectively tested, the thickness difference is calculated, the stripping force between the diaphragm and between the diaphragm and the pole piece in each cell is tested by adopting the method specified in GB2792-1998, and the test result is shown in Table 2.

TABLE 2

Therefore, the diaphragm provided by the disclosure can be pressed with the positive plate and the negative plate to form a battery cell under a cold pressing condition, and the thickness difference before and after pressing of each battery cell is basically the same as that of the hot-pressed diaphragm formed by pressing of the positive plate and the negative plate under a hot pressing condition, which indicates that the battery cell formed by pressing of the diaphragm with the positive plate and the negative plate under the cold pressing condition can be normally assembled into a lithium ion battery shell; the diaphragm can be pressed and bonded with a pole piece at normal temperature, the bonded stripping force is proper, and particularly when the glass transition temperature Tg value of polyvinylidene fluoride-hexafluoropropylene is-28 ℃ to-10 ℃, and the melting point is 90 ℃ to 105 ℃; the glass transition temperature Tg value of the polyacrylate is-30 ℃ to-10 ℃, and the softening point is 5 ℃ to 30 ℃; the weight ratio of the polyvinylidene fluoride-hexafluoropropylene to the polyacrylate is (75-85): (25-15), the peeling force is more preferable. The peel force of comparative example 2 and comparative example 4 was too high, and the adhesion between the separator layers was tight, affecting the cycle performance of the battery.

Test example 2

The separators prepared in examples 1 to 16 and comparative examples 1 to 4 were laminated with the positive plate and the negative plate, respectively, to form a structure in which the negative plate, the separator, and the positive plate were arranged at intervals, and then cold-pressed at a temperature of 25 ℃, a pressure of 1.5MPa, and a pressing time of 50s, to obtain a cell, which was used as a test experiment. Meanwhile, the oil PVDF gluing membrane, the positive plate and the negative plate are subjected to hot pressing under the conditions that the temperature is 95 ℃, the pressure is 1.5MPa and the pressing time is 50s to obtain the battery cell which is used as a contrast experiment. The test experiment battery cells and the control experiment battery cells are assembled into the soft-pack laminated lithium ion battery according to the same method, all the lithium ion batteries are subjected to 1C cycle test for 100 circles at the temperature of 23 +/-2 ℃, the capacity retention rate of each lithium ion battery is tested, and the test results are shown in table 3.

TABLE 3

Test object	Capacity retention ratio/%)
		Control experiment	80.6
Example 1	95.3
		Example 2	92.4
Example 3	93.1
		Example 4	91.8
Example 5	93.9
		Example 6	90.9
Example 7	90.6
		Example 8	89.5
Example 9	89.3
		Example 10	91.5
Example 11	92.0
		Example 12	90.1
Example 13	90.4
		Example 14	95.3
Example 15	88.5
		Example 16	88.4
Comparative example 1	Short circuit of wrinkling of diaphragm in battery
		Comparative example 2	83.1
Comparative example 3	Short circuit of wrinkling of diaphragm in battery
		Comparative example 4	82.7

Therefore, after the oil-based PVDF gluing membrane, the positive plate and the negative plate are subjected to hot pressing and laminating under the conditions that the temperature is 95 ℃, the pressure is 1.5MPa and the laminating time is 50s to obtain the battery cell, the laminating and combining degree of the inner layer and the outer layer of the battery cell and the negative plate is different due to different retention times of the inner layer and the outer layer of the battery cell at 95 ℃, and the cycle performance of the lithium ion battery is poor; the diaphragm disclosed by the invention does not need to be heated, the pressing degree is uniform, and the influence on the cycle performance of the lithium ion battery is small, so that the lithium ion battery adopting the diaphragm disclosed by the invention has good cycle performance and more stable cycle performance.

The preferred embodiments of the present disclosure have been described in detail above, however, the present disclosure is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present disclosure within the technical idea of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

It should be noted that, in the foregoing embodiments, various features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various combinations that are possible in the present disclosure are not described again.

In addition, any combination of various embodiments of the present disclosure may be made, and the same should be considered as the disclosure of the present disclosure, as long as it does not depart from the spirit of the present disclosure.