Coating diaphragm with asymmetric structure and battery

Abstract

The utility model relates to the technical field of battery diaphragm structures, in particular to a coating diaphragm with an asymmetric structure and a battery, a first coating and a third coating are respectively arranged on two sides of a base diaphragm, and a second coating is arranged on the first coating; the first coating is made of high-temperature-resistant aromatic polyamide; the third coating comprises high-temperature-resistant aromatic polyamide and oily PVDF (Polyvinylidene Fluoride); the second coating is water-based PVDF (Polyvinylidene Fluoride); and the porosity of the first coating and the third coating is 30-70%. The thickness of the first coating is 0.5-4.0 microns, the thickness of the third coating is 0.5-4.0 microns, and the thickness of the second coating is 0.5-4.0 microns. The coating diaphragm with the asymmetric structure can meet the requirements of different binding power between the diaphragm and a positive electrode and between the diaphragm and a negative electrode, can be better matched with a battery processing technology, and improves the cycle capacity retention ratio of a battery.

Description

Technical Field

[0001] The utility model relates to an asymmetrically structured coated separator and a battery, belonging to the technical field of battery separator structures. Background Art

[0002] In the structure of a lithium battery, the separator is one of the key inner components. Among them, the separator is located between the positive electrode and the negative electrode, and its main function is to separate the positive and negative active substances to prevent short circuit due to contact between the two poles, while allowing the rapid transport of charged ions. Among them, in order to improve the heat resistance of the separator, a layer of slurry needs to be coated on the separator to improve the safety performance of the lithium battery. However, at present, the compatibility between the slurry and the separator in related prior art is poor, resulting in the slurry being easily detached from the separator, weakening the heat resistance of the separator product, and further affecting the service life of the lithium battery.

[0003] With the development of battery technology, the production efficiency of batteries has been improved. On the basis of traditional winding and lamination processes, some battery enterprises have also developed more advanced thermal composite lamination processes. Usually, for the lamination process or the thermal composite lamination process, a certain adhesiveness is required between the separator and the positive and negative electrodes to reduce the gap between the separator and the positive and negative electrodes during battery charge and discharge, and improve the charge and discharge performance of the battery. Currently, most separator enterprises adopt the method of PVDF coating on the base film. For example, Chinese Patent Application CN105552284A discloses a composite-coated lithium-ion battery separator and its preparation method, in which a PVDF coating is applied to the battery separator, and the used PVDF coating is obtained by coating and drying an aqueous PVDF slurry. In addition, Chinese Patent Application CN104993089A discloses an aramid-coated lithium-ion battery separator and its preparation method. The separator is composed of a lithium-ion battery base film and coatings on one or both sides of the base film. The coating is obtained by coating, soaking in water, and drying an aramid slurry, and the aramid slurry is composed of an aramid fiber solution, an emulsifier solution, and a polymer adhesive. Although these related technologies can effectively improve the adhesiveness between the separator and the electrode, they cannot achieve different adhesive forces between the separator and the positive and negative electrodes. For battery positive and negative electrode materials and battery processes, there are differences in the adhesive forces between the positive and negative electrodes and the separator. Therefore, it is necessary to achieve different adhesive forces between the two sides of the separator and the positive and negative electrodes, and for different electrode materials, the requirements for the adhesive performance of the separator are different.

[0004] Currently, commercial PVDF separators are mainly PVDF-coated on polyolefin separators mainly composed of polyethylene and polypropylene, including aqueous coating and oily coating, and there is the same adhesive force between the positive and negative electrodes and the separator, and it is impossible to adjust the bonding situation of the separator. Summary of the Utility Model

[0005] In view of the deficiencies existing in the prior art, the present utility model provides an asymmetrically structured coated separator and a battery, so as to overcome the defect that the adhesion between the positive and negative electrodes of the separator in the prior art cannot be made different. The present utility model can provide an asymmetrically structured separator with different and adjustable adhesion forces to the positive and negative electrodes, and can also improve the heat resistance of the separator during membrane breakage, thereby improving the safety of battery use.

[0006] The technical solution of the present utility model for solving the above technical problems is as follows: An asymmetrically structured coated separator, the asymmetrically structured coated separator includes a base film, and a first coating and a third coating are respectively provided on both sides of the base film, and a second coating is provided on the first coating;

[0007] The first coating is a high-temperature resistant aromatic polyamide; the third coating includes a high-temperature resistant aromatic polyamide and an oily PVDF; the second coating is an aqueous PVDF;

[0008] The porosity of the first coating and the third coating is 30-70%.

[0009] Based on the above technical solution, the present utility model can also be improved as follows:

[0010] Further, the thickness of the first coating is 0.5-4.0 μm.

[0011] Further, the thickness of the third coating is 0.5-4.0 μm.

[0012] Further, the thickness of the second coating is 0.5-4.0 μm.

[0013] Further, the high-temperature resistant aromatic polyamide is meta-aramid, para-aramid, heterocyclic aramid or polyamideimide.

[0014] Further, the weight-average molecular weight of the meta-aramid is 150,000-250,000; the weight-average molecular weight of the para-aramid is 40,000-80,000; the weight-average molecular weight of the heterocyclic aramid is 200,000-400,000; the weight-average molecular weight of the polyamideimide is 100,000-300,000.

[0015] Further, the weight-average molecular weight of the oily PVDF is 400,000-800,000;

[0016] The difference in the weight-average molecular weight between the oily PVDF and the meta-aramid is not less than 250,000;

[0017] The difference in the weight-average molecular weight between the oily PVDF and the para-aramid is not less than 400,000;

[0018] The difference in the weight-average molecular weight between the oily PVDF and the heterocyclic aramid is not less than 250,000;

[0019] The difference in the weight-average molecular weight between the oily PVDF and the polyamide-imide is not less than 350,000.

[0020] Further, the base film is any one of polyethylene, polypropylene, and polypropylene / polyethylene / polypropylene materials.

[0021] The present utility model also discloses a battery, and the battery contains the asymmetric structure coated separator of the present utility model.

[0022] The beneficial effects of the present utility model are:

[0023] The asymmetric structure coated separator of the present utility model can meet the requirements of different bonding forces between the separator and the positive electrode and the negative electrode, better match the battery processing technology, and improve the battery cycle capacity retention rate. In addition, the asymmetric structure coated separator of the present utility model can specifically prepare a separator with the required hot pressing bonding force. In actual production, a separator that meets the requirements can be directly prepared according to the downstream application requirements, thereby greatly reducing the workload of exploring experimental conditions. Description of the Drawings

[0024] Figure 1 is a schematic structural diagram of the asymmetric structure coated separator of the utility model;

[0025] Figure 2 is an SEM image of the surface of the second coating of the asymmetric structure coated separator in Example 1;

[0026] Figure 3 is an SEM image of the surface of the third coating of the asymmetric structure coated separator in Example 1;

[0027] In the figure, 1 is the base film; 2 is the first coating; 3 is the third coating; 4 is the second coating. Detailed Embodiments

[0028] The following makes a detailed description of the specific embodiments of the present utility model. The present utility model can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present utility model. Therefore, the present utility model is not limited by the specific embodiments disclosed.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present utility model belongs. The terms used are only for describing the specific embodiments and are not intended to limit the present utility model.

[0030] As Figure 1 shown, an asymmetric structure coated separator, the asymmetric structure coated separator includes a base film 1, a first coating 2 and a third coating 3 are respectively arranged on both sides of the base film 1, and a second coating 4 is arranged on the first coating 2;

[0031] The first coating 2 is a heat-resistant aromatic polyamide; the third coating 3 comprises a heat-resistant aromatic polyamide and an oil-based PVDF; the second coating 4 is a water-based PVDF;

[0032] The porosity of the first coating 2 and the third coating 3 is 30-70%.

[0033] Specifically, the thickness of the first coating 2 is 0.5-4.0 μm.

[0034] Specifically, the thickness of the third coating 3 is 0.5-4.0 μm.

[0035] Specifically, the thickness of the second coating 4 is 0.5-4.0 μm.

[0036] More specifically, in the third coating 3, the mass ratio of the heat-resistant aromatic polyamide to the oil-based PVDF is 1:(1-10); the hot-pressing adhesion of the third coating 3 is 1-30 N / m 2 ; the hot-pressing adhesion of the second coating 4 is 2-12 N / m 2 .

[0037] Specifically, the heat-resistant aromatic polyamide is meta-aramid, para-aramid, heterocyclic aramid or polyamide-imide.

[0038] Specifically, the weight-average molecular weight of the meta-aramid is 150,000-250,000; the weight-average molecular weight of the para-aramid is 40,000-80,000; the weight-average molecular weight of the heterocyclic aramid is 200,000-400,000; the weight-average molecular weight of the polyamide-imide is 100,000-300,000.

[0039] Specifically, the weight-average molecular weight of the oil-based PVDF is 400,000-800,000;

[0040] The difference in the weight-average molecular weight between the oil-based PVDF and the meta-aramid is not less than 250,000;

[0041] The difference in the weight-average molecular weight between the oil-based PVDF and the para-aramid is not less than 400,000;

[0042] The difference in the weight-average molecular weight between the oil-based PVDF and the heterocyclic aramid is not less than 250,000;

[0043] The difference in the weight-average molecular weight between the oil-based PVDF and the polyamide-imide is not less than 350,000.

[0044] Specifically, the base film 1 is any one of polyethylene, polypropylene and polypropylene / polyethylene / polypropylene materials.

[0045] A battery, wherein the battery contains the asymmetric structure coated separator of the present invention.

[0046] Example 1

[0047] (1) Dissolve the meta-aramid polymerization solution (weight-average molecular weight of 200,000) in N,N-dimethylacetamide to obtain the casting solution A; the mass fraction of meta-aramid in the casting solution A is 5wt%, and the slurry viscosity of the casting solution A is 80 mpas;

[0048] Mix the meta-aramid polymerization solution (weight-average molecular weight of 200,000) and oil-based PVDF (weight-average molecular weight of 630,000) in N,N-dimethylacetamide according to a certain solid content, and mechanically stir at 20 °C for 0.5 h. After complete dissolution, obtain the casting solution B; in the casting solution B, the mass ratio of meta-aramid to PVDF is 1:5, and the slurry viscosity of the casting solution B is 95 mpas;

[0049] (2) Simultaneously coat the casting solution A and the casting solution B on both sides of the base film 1 through a micro-embossing roll to form the first coating 2 and the third coating 3 respectively, and then sequentially enter the first-stage coagulation bath and the second-stage coagulation bath, wash with water for 30 s, and then enter the drying oven for drying at 40 °C, and wind up after drying;

[0050] Among them, the first-stage coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 40%, and the temperature of the first-stage coagulation bath is 40 °C;

[0051] The second-stage coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 5%, and the temperature of the second-stage coagulation bath is 20 °C;

[0052] The thickness of the first coating 2 is 2.0 μm, and the thickness of the third coating 3 is 1.0 μm.

[0053] (3) Coat the aqueous PVDF slurry on the first coating 2 to obtain the second coating 4, and the thickness of the second coating 4 is 1.0 μm. Dry at 60 °C and wind up to obtain the asymmetric structure coated separator.

[0054] Among them, the SEM image of the surface of the second coating 4 is as shown in Figure 2 shown, the SEM image of the surface of the third coating 3 is as shown in Figure 3 shown, from Figure 2 and Figure 3 it can be seen that the second coating 4 is a mixed coating of high-temperature resistant polyamide and oil-based PVDF, and the microscopic morphology presents a small hole morphology, Figure 3 and the third coating 3 in

[0055] Example 2

[0056] (1) Dissolve the meta-aramid polymerization solution (weight-average molecular weight of 150,000) in N,N-dimethylformamide, and add the pore-forming agent PVP K30 to obtain casting solution A; the mass fraction of meta-aramid in casting solution A is 10 wt%, and the slurry viscosity of casting solution A is 3150 mPa·s; the mass content of the pore-forming agent in casting solution A is 10%;

[0057] Mix the meta-aramid polymerization solution (weight-average molecular weight of 150,000) and oily PVDF (weight-average molecular weight of 400,000) in N,N-dimethylformamide according to a certain solid content, add the pore-forming agent PVP K30, and mechanically stir at 40 °C for 1.0 h. After complete dissolution, obtain casting solution B; in casting solution B, the mass ratio of meta-aramid to PVDF is 1:1, and the slurry viscosity of casting solution B is 500 mPa·s; the mass content of the pore-forming agent in casting solution B is 10%;

[0058] (2) Simultaneously coat casting solution A and casting solution B on both sides of the base film 1 through a micro-embossing roll to form a first coating 2 and a third coating 3 respectively, and then sequentially enter the first-stage coagulation bath and the second-stage coagulation bath. After washing with water for 50 s, enter the drying oven and dry at 50 °C, and then wind up after drying;

[0059] Among them, the first-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 30%, and the temperature of the first-stage coagulation bath is 30 °C;

[0060] The second-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 5%, and the temperature of the second-stage coagulation bath is 20 °C;

[0061] The thickness of the first coating 2 is 4.0 μm, and the thickness of the third coating 3 is 4.0 μm.

[0062] (3) Coat the aqueous PVDF slurry on the first coating 2 to obtain a second coating 4, and the thickness of the second coating 4 is 0.5 μm. Dry at 40 °C and wind up to obtain the asymmetrically structured coated separator.

[0063] Example 3

[0064] (1) Dissolve the meta-aramid polymerization solution (weight-average molecular weight of 250,000) in N-methylpyrrolidone, and add the pore-forming agent PVP K30 to obtain casting solution A; the mass content of meta-aramid in casting solution A is 2%, and the slurry viscosity of casting solution A is 90 mPa·s; the mass content of the pore-forming agent in casting solution A is 5%;

[0065] Mix the meta-aramid polymerization solution (weight-average molecular weight of 250,000) and oily PVDF (weight-average molecular weight of 800,000) at a certain solid content in N-methylpyrrolidone, add the pore-forming agent PVP K30, and mechanically stir for 0.5 h at 40 °C. After complete dissolution, casting solution B is obtained; in casting solution B, the mass ratio of meta-aramid to PVDF is 1:10, and the slurry viscosity of casting solution B is 63 mPa·s; the mass content of the pore-forming agent in casting solution B is 5%.

[0066] (3) Simultaneously coat casting solution A and casting solution B on both sides of the base film 1 through a micro-embossing roll to form the first coating 2 and the third coating 3 respectively, and then sequentially enter the first-stage coagulation bath and the second-stage coagulation bath, wash with water for 300 s, and then enter a drying oven for drying at 80 °C. After drying, wind up.

[0067] Among them, the first-stage coagulation bath is an aqueous solution of N-methylpyrrolidone with a mass concentration of 45%, and the temperature of the first-stage coagulation bath is 60 °C;

[0068] The second-stage coagulation bath is an aqueous solution of N-methylpyrrolidone with a mass concentration of 15%, and the temperature of the second-stage coagulation bath is 50 °C;

[0069] The thickness of the first coating 2 is 3.0 μm, and the thickness of the third coating 3 is 1.0 μm.

[0070] (3) Coat an aqueous PVDF slurry on the first coating 2 to obtain the second coating 4, and the thickness of the second coating 4 is 4 μm. Dry at 40 °C and wind up to obtain the asymmetrically structured coated separator.

[0071] Example 4

[0072] (1) Dissolve the para-aramid polymerization solution (weight-average molecular weight of 80,000) in N,N-dimethylacetamide, and add the pore-forming agent PVP K30 to obtain casting solution A; the mass content of para-aramid in casting solution A is 2%, and the slurry viscosity of casting solution A is 400 mPa·s; the mass content of the pore-forming agent in casting solution A is 2%.

[0073] Mix the para-aramid polymerization solution (weight-average molecular weight of 80,000) and oily PVDF (weight-average molecular weight of 700,000) at a certain solid content in N,N-dimethylacetamide, add the pore-forming agent PVP K30, and mechanically stir for 1.0 h at 30 °C. After complete dissolution, casting solution B is obtained; in casting solution B, the mass ratio of para-aramid to PVDF is 1:4, and the slurry viscosity of casting solution B is 240 mPa·s; the mass content of the pore-forming agent in casting solution B is 2%.

[0074] (2) The casting solutions A and B are simultaneously coated on both sides of the base film 1 through a gravure roll to form a first coating 2 and a third coating 3 respectively, and then enter the first-stage coagulation bath and the second-stage coagulation bath in sequence. After washing with water for 30 s, they enter a drying oven for drying at 40 °C, and are wound up after drying;

[0075] Among them, the first-stage coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 40%, and the temperature of the first-stage coagulation bath is 50 °C;

[0076] The second-stage coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 10%, and the temperature of the second-stage coagulation bath is 30 °C;

[0077] The thickness of the first coating 2 is 1.0 μm, and the thickness of the third coating 3 is 3.0 μm.

[0078] (3) An aqueous PVDF slurry is coated on the first coating 2 to obtain a second coating 4, and the thickness of the second coating 4 is 2.0 μm. After drying at 50 °C and winding up, the asymmetrically structured coated separator is obtained.

[0079] Example 5

[0080] (1) Dissolve the para-aramid polymerization solution (weight average molecular weight of 40,000) in N,N-dimethylformamide, and add the pore-forming agent PVP K30 to obtain the casting solution A; the mass content of para-aramid in the casting solution A is 10%, and the slurry viscosity of the casting solution A is 5000 mpas; the mass content of the pore-forming agent in the casting solution A is 4%.

[0081] Mix the para-aramid polymerization solution (weight average molecular weight of 40,000) and the oily PVDF (weight average molecular weight of 550,000) in N,N-dimethylformamide according to a certain solid content, add the pore-forming agent PVP K30, and mechanically stir at 30 °C for 1.0 h. After complete dissolution, obtain the casting solution B; in the casting solution B, the mass ratio of para-aramid to PVDF is 1:6, and the slurry viscosity of the casting solution B is... 8900 mpas; the mass content of the pore-forming agent in the casting solution B is 4%.

[0082] (2) The casting solutions A and B are simultaneously coated on both sides of the base film 1 through a gravure roll to form a first coating 2 and a third coating 3 respectively, and then enter the first-stage coagulation bath and the second-stage coagulation bath in sequence. After washing with water for 30 s, they enter a drying oven for drying at 40 °C, and are wound up after drying;

[0083] Among them, the first-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 45%, and the temperature of the first-stage coagulation bath is 45 °C;

[0084] The second-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 10%, and the temperature of the second-stage coagulation bath is 20 °C;

[0085] The thickness of the first coating 2 is 2.0 μm, and the thickness of the third coating 3 is 2.0 μm.

[0086] (3) Apply an aqueous PVDF slurry on the first coating 2 to obtain the second coating 4 with a thickness of 1.0 μm. Dry at 50 °C and wind up to obtain the asymmetrically structured coated separator.

[0087] Example 6

[0088] (1) Dissolve a polyamide-imide polymerization solution (weight-average molecular weight of 100,000) in N,N-dimethylacetamide, and add a pore-forming agent PVP K90 to obtain a casting solution A; the mass content of polyamide-imide in the casting solution A is 10%, the slurry viscosity of the casting solution A is 2100 mpas; the mass content of the pore-forming agent in the casting solution A is 1%.

[0089] Mix a polyamide-imide polymerization solution (weight-average molecular weight of 100,000) and an oily PVDF (weight-average molecular weight of 500,000) at a certain solid content in N,N-dimethylacetamide, add a pore-forming agent PVP K90, and mechanically stir at 40 °C for 1.0 h. After complete dissolution, obtain a casting solution B; in the casting solution B, the mass ratio of polyamide-imide to PVDF is 1:2, the slurry viscosity of the casting solution B is 150 mpas; the mass content of the pore-forming agent in the casting solution B is 1%.

[0090] (2) Simultaneously coat the casting solution A and the casting solution B on both sides of the base film 1 through a microgravure roll to respectively form the first coating 2 and the third coating 3, then sequentially enter the first-stage coagulation bath and the second-stage coagulation bath, wash with water for 30 s, and then enter a drying oven for drying at 40 °C, and wind up after drying;

[0091] Among them, the first-stage coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 35% and a temperature of 50 °C;

[0092] The second-stage coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 5% and a temperature of 30 °C;

[0093] The thickness of the first coating 2 is 2.0 μm, and the thickness of the third coating 3 is 3.0 μm.

[0094] (3) Apply an aqueous PVDF slurry on the first coating 2 to obtain the second coating 4 with a thickness of 1.0 μm. Dry at 50 °C and wind up to obtain the asymmetrically structured coated separator.

[0095] Example 7

[0096] (1) Dissolve the polyamide-imide polymerization solution (weight-average molecular weight of 300,000) in N,N-dimethylformamide, and add the pore-forming agent PVP K90 to obtain the casting solution A; the mass content of polyamide-imide in the casting solution A is 2%, and the slurry viscosity of the casting solution A is 120 mPas; the mass content of the pore-forming agent in the casting solution A is 3%.

[0097] Mix the polyamide-imide polymerization solution (weight-average molecular weight of 300,000) and the oily PVDF (weight-average molecular weight of 800,000) in N,N-dimethylformamide according to a certain solid content, add the pore-forming agent PVP K90, and mechanically stir at 40 °C for 1.0 h. After complete dissolution, obtain the casting solution B; in the casting solution B, the mass ratio of polyamide-imide to PVDF is 1:2, and the slurry viscosity of the casting solution B is 45 mPas; the mass content of the pore-forming agent in the casting solution B is 3%.

[0098] (2) Simultaneously coat the casting solution A and the casting solution B on both sides of the base film 1 through a micro-embossing roll to respectively form the first coating 2 and the third coating 3, and then sequentially enter the first-stage coagulation bath and the second-stage coagulation bath, wash with water for 100 s, and then enter the drying oven for drying at 40 °C, and wind up after drying;

[0099] Among them, the first-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 45% and a temperature of 40 °C;

[0100] The second-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 10% and a temperature of 25 °C;

[0101] The thickness of the first coating 2 is 1.0 μm, and the thickness of the third coating 3 is 2.0 μm.

[0102] (3) Coat the aqueous PVDF slurry on the first coating 2 to obtain the second coating 4, and the thickness of the second coating 4 is 1.0 μm. Dry at 40 °C and wind up to obtain the asymmetrically structured coated separator.

[0103] Example 8

[0104] (1) Dissolve the heterocyclic aramid polymerization solution (the heterocyclic aramid is Aramid III, weight-average molecular weight of 200,000) in N,N-dimethylformamide, and add the pore-forming agent PVP K30 to obtain the casting solution A; the mass content of heterocyclic aramid in the casting solution A is 10%, and the slurry viscosity of the casting solution A is 4500 mPas; the mass content of the pore-forming agent in the casting solution A is 2%.

[0105] The heterocyclic aramid polymerization solution (the heterocyclic aramid is Aramid III with a weight-average molecular weight of 200,000) and oily PVDF (weight-average molecular weight of 600,000) are mixed in N,N-dimethylformamide at a certain solid content, and the pore-forming agent PVP K30 is added. After mechanical stirring at 40 °C for 1.0 h and complete dissolution, the casting solution B is obtained; in the casting solution B, the mass ratio of heterocyclic aramid to PVDF is 1:6, and the slurry viscosity of the casting solution B is 350 mPa·s; the mass content of the pore-forming agent in the casting solution B is 2%.

[0106] (2) The casting solution A and the casting solution B are simultaneously coated on both sides of the base film 1 through a micro-gravure roll to form the first coating 2 and the third coating 3 respectively, and then successively enter the first-stage coagulation bath and the second-stage coagulation bath, and are washed with water for 100 s and then enter a drying oven for drying at 40 °C, and are wound up after drying;

[0107] Among them, the first-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 45%, and the temperature of the first-stage coagulation bath is 55 °C;

[0108] The second-stage coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 5%, and the temperature of the second-stage coagulation bath is 25 °C;

[0109] The thickness of the first coating 2 is 2.0 μm, and the thickness of the third coating 3 is 3.0 μm.

[0110] (3) An aqueous PVDF slurry is coated on the first coating 2 to obtain the second coating 4, and the thickness of the second coating 4 is 1.0 μm. After drying at 40 °C and winding up, the asymmetric structure coated separator is obtained.

[0111] Example 9

[0112] (1) The heterocyclic aramid polymerization solution (the heterocyclic aramid is Aramid III with a weight-average molecular weight of 400,000) is dissolved in N,N-dimethylacetamide, and the pore-forming agent PVP K30 is added to obtain the casting solution A; the mass content of heterocyclic aramid in the casting solution A is 2%, and the slurry viscosity of the casting solution A is 300 mPa·s; the mass content of the pore-forming agent in the casting solution A is 3%.

[0113] The heterocyclic aramid polymerization solution (the heterocyclic aramid is Aramid III with a weight-average molecular weight of 400,000) and oily PVDF (weight-average molecular weight of 800,000) are mixed in N,N-dimethylacetamide at a certain solid content, and the pore-forming agent PVP K30 is added. After mechanical stirring at 40 °C for 1.0 h and complete dissolution, the casting solution B is obtained; in the casting solution B, the mass ratio of heterocyclic aramid to PVDF is 1:3, and the slurry viscosity of the casting solution B is 100 mPa·s; the mass content of the pore-forming agent in the casting solution B is 3%.

[0114] (2) Coating casting solution A and casting solution B on both sides of the base film 1 simultaneously through a gravure roll to form a first coating 2 and a third coating 3 respectively, then successively entering a first-stage coagulation bath and a second-stage coagulation bath, washing with water for 100 s and then entering a drying oven for drying at 40 °C, and winding up after drying;

[0115] Among them, the first-stage coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 45%, and the temperature of the first-stage coagulation bath is 60 °C;

[0116] The second-stage coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 10%, and the temperature of the second-stage coagulation bath is 30 °C;

[0117] The thickness of the first coating 2 is 2.0 μm, and the thickness of the third coating 3 is 4.0 μm.

[0118] (3) Coating an aqueous PVDF slurry on the first coating 2 to obtain a second coating 4 with a thickness of 3.0 μm. Drying at 40 °C and winding up to obtain the asymmetric structure coated separator.

[0119] Performing performance tests on the separators prepared in the above examples, and the specific results are shown in Table 1 below.

[0120] The detection methods involved are:

[0121] The test method for the hot pressing bonding force includes the following steps:

[0122] (1) Folding the base film 1 along the midline and placing it between two pieces of silicon oil paper;

[0123] (2) Turning on the plastic sealing hot press (Youmashi U-H6330T) and setting the parameters: the temperature is 120 °C and the speed is 2700 mm / min;

[0124] (3) Putting the separator sample into the plastic sealer from one side and taking it out from the other side, and laying it flat on the cutting backing plate;

[0125] (4) Using a 15 mm cutter to cut a coated separator sample with a width of 15.0 mm and a length > 18 cm;

[0126] (5) Turning on the switch of the electronic tensile testing machine and testing the peel strength of the sample, and the specific operation is carried out with reference to the provisions in 6.5.6 of T / CPPIA10-2021.

[0127] The test method for the film-breaking temperature is: carried out in accordance with the provisions of GB / T 36800.1, where the sample size is length × width = 8.0 × 4.0 mm, and the specific test method is as follows:

[0128] 1) Cutting the samples into strips with a size of length × width = 8 × 4 mm in the MD and TD directions respectively, and fixing them in the fixed fixture of the instrument;

[0129] 2) Select a thin film probe and a quartz platform, place the sample on the sample stage, and set the test parameters: the preloading force is 0.03 N, the high-purity nitrogen gas flow rate is 40 mL / min, the temperature range for heating is 50 - 300 °C, and the rate is 5 °C / min. Then start the measurement;

[0130] 3) Take the measured value as the test result.

[0131] Table 1 Diaphragm Performance Data

[0132]

[0133] It can be seen from the above data that the diaphragms prepared by the preparation method described in Examples 1 - 9 of the present invention can meet the different hot pressing adhesion forces of the positive and negative electrodes, with an air permeability value ≤ 300 s / 100 cc and a film breaking temperature ≥ 250 °C.

[0134] Application Examples 1 - 9

[0135] Assemble the diaphragms obtained in the above examples into a 4 Ah 811 system ternary lithium battery by using a stacking process.

[0136] The batteries assembled with the diaphragms of Examples 1 - 9 above respectively correspond to Application Examples 1 - 10.

[0137] Application Comparative Example 1

[0138] Assemble the battery by using the same method as in Application Example 1, except that the diaphragm is replaced with a commercially available PE / Ceramic / PVDF coated film of (1 + 2 + 7 + 2 + 1) μm, where 2 is the thickness of the ceramic coating, 1 is the thickness of the aqueous roll-coated PVDF coating, and 7 is the thickness of the PE base film.

[0139] Perform performance tests on the batteries of the above application examples and application comparative examples, and the specific test results are shown in Table 2 below.

[0140] Table 2 Battery Performance Test Results

[0141]

[0142] As can be seen from the above table data, for the diaphragms prepared by the preparation method of the present invention in the batteries of Application Examples 1-9, compared with the PE / ceramic / PVDF coated films, the capacity retention rates after 100 cycles are all improved, all above 90%, which can effectively improve the battery cycle life. In the Arc (accelerated calorimeter) test, there is no high-temperature resistant polyamide coating layer in Comparative Application Example 1, and the measured Arc temperature is 686 °C. For Application Examples 1-8 with high-temperature resistant aromatic polyamide coating layers, their Arc temperatures are all reduced to below 600 °C. Among them, in Application Examples 4-5 and Application Examples 8-9, the high-temperature resistant aromatic polyamides are respectively para-aramid and Aramid III with better heat resistance, and the Arc temperatures of the batteries prepared with their diaphragms are also the lowest, which are 435, 415 °C and 425, 420 °C respectively. It can be seen from this that the asymmetric structure coated diaphragm prepared by the preparation method of the present invention has good application performance in the battery.

[0143] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above-described embodiments are exhausted. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0144] For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. An asymmetrically structured coated separator, characterized in that, The asymmetrically structured coated separator includes a base film (1), with a first coating (2) and a third coating (3) provided on both sides of the base film (1), and a second coating (4) provided on the first coating (2); The first coating (2) is a heat-resistant aromatic polyamide; the third coating (3) includes a heat-resistant aromatic polyamide and an oil-based PVDF; the second coating (4) is a water-based PVDF; The porosity of the first coating (2) and the third coating (3) is 30 - 70%.

2. The asymmetrically structured coated separator according to claim 1, wherein, The thickness of the first coating (2) is 0.5 - 4.0 μm.

3. The asymmetric structure coating diaphragm according to claim 1, characterized in that, The thickness of the third coating (3) is 0.5 - 4.0 μm.

4. The asymmetric structure coating diaphragm according to claim 1, wherein The thickness of the second coating (4) is 0.5 - 4.0 μm.

5. The asymmetrically structured coated separator according to claim 1, wherein The heat-resistant aromatic polyamide is meta-aramid, para-aramid, heterocyclic aramid or polyamide-imide.

6. The asymmetrically structured coated separator according to claim 5, wherein The weight-average molecular weight of the meta-aramid is 150,000 - 250,000; the weight-average molecular weight of the para-aramid is 40,000 - 80,000; the weight-average molecular weight of the heterocyclic aramid is 200,000 - 400,000; the weight-average molecular weight of the polyamide-imide is 100,000 - 300,000.

7. The asymmetric structure coated diaphragm according to claim 6, characterized in that, The weight-average molecular weight of the oil-based PVDF is 400,000 - 800,000; The difference in weight-average molecular weight between the oil-based PVDF and the meta-aramid is not less than 250,000; The difference in weight-average molecular weight between the oil-based PVDF and the para-aramid is not less than 400,000; The difference in weight-average molecular weight between the oil-based PVDF and the heterocyclic aramid is not less than 250,000; The difference in weight-average molecular weight between the oil-based PVDF and the polyamide-imide is not less than 350,000.

8. The asymmetrically structured coated separator according to claim 1, wherein, The base film (1) is any one of polyethylene, polypropylene, and polypropylene / polyethylene / polypropylene materials.

9. A battery, characterized in that, The battery contains the asymmetrically structured coated separator according to any one of claims 1 - 8.

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