Asymmetric diaphragm and battery

Abstract

The utility model relates to the technical field of lithium battery diaphragms, in particular to an asymmetric diaphragm and a battery, the asymmetric diaphragm comprises a base membrane, two sides of the base membrane are respectively provided with a first coating and a second coating, the pore structure of the first coating is a small pore structure, and the pore structure of the second coating is a three-dimensional network microporous structure. The micropore diameter of the first coating layer is 0.05-0.2 [mu] m, and the micropore diameter of the second coating layer is 0.08-3.0 [mu] m. The first coating and the second coating are simultaneously coated on the two sides of the base film through a phase inversion method. The asymmetric diaphragm not only can meet different binding power with a positive electrode and a negative electrode, but also can improve the heat resistance of the diaphragm so as to improve the safety performance of the battery, and the structure of the asymmetric diaphragm can realize double-sided simultaneous coating in the preparation process, so that the energy waste is greatly reduced, and the cost is reduced.

Description

Technical Field

[0001] The utility model relates to an asymmetric diaphragm and a battery, belonging to the technical field of lithium battery diaphragms. Background Art

[0002] In the structure of lithium batteries, the diaphragm is one of the key internal components. Located between the positive and negative electrodes, the diaphragm primarily separates the positive and negative active materials, preventing short circuits between the two electrodes due to contact, while allowing for the rapid transport of charged ions. To improve the heat resistance of the diaphragm, a layer of slurry is applied to the diaphragm. The slurry improves the heat resistance of the diaphragm and enhances the safety of the lithium battery. However, the compatibility between the slurry and the diaphragm in the current state of the art is poor, resulting in the slurry easily falling off the diaphragm, weakening the heat resistance of the diaphragm product and, in turn, affecting the service life of the lithium battery.

[0003] With the development of battery technology, battery production efficiency has improved. Based on the traditional winding and lamination processes, some battery companies have also developed more advanced thermal composite lamination processes. Generally, the lamination process or thermal composite lamination process requires a certain degree of adhesion between the separator and the positive and negative electrodes to reduce the gap between the separator and the positive and negative electrodes during the battery charging and discharging process, thereby improving the battery charging and discharging performance. The method currently used by separator companies is to coat the base film with PVDF. For example, Chinese patent application CN105552284A discloses a composite coated lithium-ion battery separator and a preparation method thereof, in which a PVDF coating is applied to the battery separator. The PVDF coating used 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 a preparation method thereof. The separator is composed of a lithium-ion battery base membrane and a coating on one or both sides of the base membrane. The coating is obtained by coating, soaking, and drying an aramid slurry. The aramid slurry is composed of an aramid fiber dissolving solution, an emulsifier solution, and a polymer adhesive. Although these related technologies can effectively improve the adhesion between the diaphragm and the electrode, they cannot achieve different adhesion between the diaphragm and the positive and negative electrodes. For the positive and negative electrode materials and battery processes of the battery, there are differences in the adhesion between the positive and negative electrodes and the diaphragm, so it is necessary to achieve different adhesion between the two sides of the diaphragm to the positive and negative electrodes, and for different electrode materials, the adhesion performance requirements for the diaphragm are different.

[0004] Currently, commercialized PVDF membranes are mainly PVDF coated on polyolefin membranes mainly composed of polyethylene and polypropylene, including water-based coating and oil-based coating. On the one hand, there is the same adhesion between the positive and negative electrodes and the membrane, and on the other hand, there are safety hazards caused by poor heat resistance. Moreover, it is generally necessary to coat twice to achieve adhesion on both sides of the membrane, resulting in high costs and energy waste. Utility Model Content

[0005] In response to the deficiencies in the prior art, the utility model provides an asymmetric diaphragm, which can not only meet the different bonding forces with the positive and negative electrodes, but also improve the heat resistance of the diaphragm, thereby improving the safety performance of the battery. Moreover, the structure of the asymmetric diaphragm can be coated on both sides simultaneously during the preparation process, greatly reducing energy waste and thus reducing costs.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: an asymmetric diaphragm, the asymmetric diaphragm includes a base membrane, and a first coating and a second coating are respectively provided on both sides of the base membrane, the pore structure of the first coating presents a small pore structure, and the pore structure of the second coating presents a three-dimensional network-like microporous structure.

[0007] On the basis of the above technical solution, the present invention can also be improved as follows:

[0008] Furthermore, the diameter of the micropores of the first coating layer is 0.05-0.2 μm, and the diameter of the micropores of the second coating layer is 0.08-3.0 μm.

[0009] Furthermore, the thickness of the first coating layer is 0.5-4.0 μm, and the thickness of the second coating layer is 0.5-4.0 μm.

[0010] Furthermore, the porosity of the first coating layer is 30%-70%, and the porosity of the second coating layer is 30%-70%.

[0011] Furthermore, the first coating layer and the second coating layer are simultaneously coated on both sides of the base film through a phase inversion method.

[0012] Furthermore, the base film is made of any one of polyethylene, polypropylene and polypropylene / polyethylene / polypropylene.

[0013] Furthermore, the material of the first coating layer includes high-temperature resistant aromatic polyamide and PVDF; the material of the second coating layer includes high-temperature resistant aromatic polyamide and PVDF;

[0014] The high temperature resistant aromatic polyamide is one or two of meta-aromatic polyamide, para-aromatic polyamide, heterocyclic aramid, and polyamide-imide.

[0015] Furthermore, the weight average molecular weight of the PVDF is 400,000-800,000; 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; and the weight average molecular weight of the polyamideimide is 100,000-300,000.

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

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

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

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

[0020] The utility model also discloses a battery, wherein the battery contains the asymmetric diaphragm of the utility model.

[0021] The beneficial effects of the utility model are:

[0022] The asymmetric diaphragm described in this utility model can meet the different requirements for the bonding strength between the diaphragm and the positive and negative electrodes. This reduces the lithium ion migration path during the charge and discharge process of the lithium battery, improves the battery cycle performance, better matches the battery processing technology, and improves the battery cycle capacity retention rate. It also improves the heat resistance of the diaphragm, increases the pass rate of battery safety tests such as needle penetration, extrusion, and hot box, and improves the safety performance of lithium batteries.

[0023] The first coating and the second coating of the asymmetric diaphragm of the utility model have the same component category, the raw material composition is simple, and the coatings on both sides can be applied simultaneously. The operation is simple, the processing is convenient, the coating thickness is controllable, and the bonding force between the diaphragm and the positive and negative electrodes is controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of the asymmetric diaphragm of the present invention;

[0025] Figure 2 This is an SEM image of the first coating surface of the asymmetric coating membrane in Example 1;

[0026] Figure 3 This is an SEM image of the second coating surface of the asymmetric coating diaphragm in Example 1;

[0027] In the figure, 1, base film; 2, first coating; 3, second coating. DETAILED DESCRIPTION

[0028] The following is a detailed description of the specific embodiments of the present invention. The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

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

[0030] like Figure 1 As shown, an asymmetric diaphragm includes a base membrane 1, and a first coating 2 and a second coating 3 are respectively provided on both sides of the base membrane 1. The pore structure of the first coating 2 presents a small pore structure, and the pore structure of the second coating 3 presents a three-dimensional network-like microporous structure.

[0031] Specifically, the diameter of the micropores of the first coating layer 2 is 0.05-0.2 μm, and the diameter of the micropores of the second coating layer 3 is 0.08-3.0 μm.

[0032] Specifically, the thickness of the first coating 2 is 0.5-4.0 μm, the thickness of the second coating 3 is 0.5-4.0 μm; the hot pressing bonding force of the first coating 2 is 10-30 N / m 2 ; The hot pressing bonding force of the second coating 3 is 1-12N / m 2 .

[0033] Specifically, the porosity of the first coating layer 2 is 30%-70%, and the porosity of the second coating layer 3 is 30%-70%.

[0034] Specifically, the first coating layer 2 and the second coating layer 3 are simultaneously coated on both sides of the base film 1 through a phase inversion method.

[0035] Specifically, the base film 1 is made of any one of polyethylene, polypropylene, and polypropylene / polyethylene / polypropylene.

[0036] Specifically, the material of the first coating layer 2 includes high-temperature resistant aromatic polyamide and PVDF; the material of the second coating layer 3 includes high-temperature resistant aromatic polyamide and PVDF;

[0037] The high temperature resistant aromatic polyamide is one or two of meta-aromatic polyamide, para-aromatic polyamide, heterocyclic aramid, and polyamide-imide.

[0038] More specifically, the mass content of the high-temperature resistant aromatic polyamide in the first coating is 0-20%; the mass content of the high-temperature resistant aromatic polyamide in the second coating is 50-75%.

[0039] Specifically, the weight average molecular weight of the PVDF is 400,000-800,000; 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; and the weight average molecular weight of the polyamideimide is 100,000-300,000.

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

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

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

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

[0044] A battery comprises the asymmetric diaphragm of the utility model.

[0045] The following example is about the preparation of an asymmetric separator, wherein the base membrane 1 used is a 7 μm PE membrane.

[0046] Example 1

[0047] (1) A meta-aramid polymer solution (weight-average molecular weight of 210,000) and PVDF (weight-average molecular weight of 600,000) were mixed in DMAc at a certain solid content and mechanically stirred at 20°C for 0.5 h. After complete dissolution, a casting solution A was obtained. The slurry viscosity of the casting solution A was 20 mPa·s, and the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A was 2 wt%. The mass ratio of PVDF to meta-aramid was 4 / 1.

[0048] (2) A meta-aramid polymer solution (weight-average molecular weight of 210,000) and PVDF (weight-average molecular weight of 600,000) were mixed in DMAc at a certain solid content, and a pore-forming agent, PVP K30, was added. The mixture was mechanically stirred at 20°C for 0.5 h, and after complete dissolution, a casting solution B was obtained. The mass content of the pore-forming agent in the casting solution B was 10%, the slurry viscosity of the casting solution B was 5000 mPa·s, and the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B was 10 wt%. The mass ratio of meta-aramid to PVDF was 1 / 1.

[0049] (3) The casting liquid A and the casting liquid B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 30 seconds, and then placed in a drying oven at 40°C for drying, and then rolled up after drying;

[0050] The first coagulation bath is a DMAc aqueous solution with a mass concentration of 30% and a temperature of 30°C.

[0051] The second coagulation bath is an aqueous solution of DMAc with a mass concentration of 5% and a temperature of 20°C;

[0052] The thickness of the first coating layer is 0.5 μm, and the thickness of the second coating layer is 4.0 μm.

[0053] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 20%; the mass content of the PVDF in the first coating is 80%;

[0054] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 50%; the mass content of PVDF in the second coating layer is 50%.

[0055] Among them, the SEM image of the first coating surface is as follows Figure 2 As shown, the SEM image of the second coating surface is as follows Figure 3 As shown, from Figure 2 and Figure 3 It can be seen that the pore structure of the first coating is mostly smaller pores, and the second coating is a three-dimensional network microporous structure. The advantages of this structure are: the small pores of the first coating make the diaphragm surface have more PVDF, and the effective bonding cotton provided during the hot pressing process with the electrode is larger; the three-dimensional network microporous structure of the second coating has a high porosity, which can increase the ion migration rate and improve the battery cycle performance.

[0056] Example 2

[0057] (1) PVDF (weight-average molecular weight of 600,000) was mixed with DMAc at a certain solid content, a pore-forming agent PVP K30 was added, and mechanical stirring was performed at 20°C for 0.5 h. After complete dissolution, a casting solution A was obtained; the mass content of the pore-forming agent in the casting solution A was 10%, the slurry viscosity of the casting solution A was 120 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A was 0 wt%, and the mass fraction of PVDF was 10%.

[0058] (2) A meta-aramid polymer solution (weight-average molecular weight of 210,000) and PVDF (weight-average molecular weight of 600,000) were mixed in DMAc at a certain solid content, and a pore-forming agent, PVP K30, was added. The mixture was mechanically stirred at 20°C for 0.5 h, and after complete dissolution, a casting solution B was obtained. The mass content of the pore-forming agent in the casting solution B was 0%, the slurry viscosity of the casting solution B was 60 mPa·s, and the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B was 2 wt%. The mass ratio of meta-aramid to PVDF was 3 / 1.

[0059] (3) The casting liquid A and the casting liquid B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 30 seconds, and then placed in a drying oven at 40°C for drying, and then rolled up after drying;

[0060] The first coagulation bath is a DMAc aqueous solution with a mass concentration of 60% and a temperature of 60°C.

[0061] The second coagulation bath is an aqueous solution of DMAc with a mass concentration of 20% and a temperature of 50°C;

[0062] The thickness of the first coating layer is 4.0 μm; the thickness of the second coating layer is 0.5 μm.

[0063] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 0%; the mass content of the PVDF in the first coating is 100%;

[0064] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 75%; the mass content of PVDF in the second coating layer is 25%.

[0065] Example 3

[0066] (1) A meta-aramid polymer solution (weight-average molecular weight of 150,000) and PVDF (weight-average molecular weight of 400,000) were mixed in DMAc at a certain solid content, and a pore-forming agent, PVP K30, was added. The mixture was mechanically stirred at 20°C for 0.5 h, and after complete dissolution, a casting solution A was obtained. The pore-forming agent content in the casting solution A was 5%, the slurry viscosity of the casting solution A was 45 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A was 5 wt%, and the mass ratio of PVDF to meta-aramid was 9 / 1.

[0067] (2) A meta-aramid polymer solution (weight-average molecular weight of 150,000) and PVDF (weight-average molecular weight of 400,000) were mixed in DMAc at a certain solid content, and a pore-forming agent, PVP K30, was added. The mixture was mechanically stirred at 20°C for 0.5 h, and after complete dissolution, a casting solution B was obtained. The pore-forming agent content in the casting solution B was 5% by weight, the slurry viscosity of the casting solution B was 80 mPa·s, and the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B was 5% by weight. The mass ratio of meta-aramid to PVDF was 1.86 / 1.

[0068] (3) The casting liquid A and the casting liquid B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 30 seconds, and then placed in a drying oven at 40°C for drying, and then rolled up after drying;

[0069] The first coagulation bath is a DMAc aqueous solution with a mass concentration of 40% and a temperature of 40°C.

[0070] The second coagulation bath is an aqueous solution of DMAc with a mass concentration of 10% and a temperature of 30°C;

[0071] The thickness of the first coating layer is 1.0 μm; the thickness of the second coating layer is 2.0 μm.

[0072] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 10%; the mass content of the PVDF in the first coating is 90%;

[0073] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 65%; the mass content of PVDF in the second coating layer is 35%.

[0074] Example 4

[0075] (1) Meta-aramid polymer solution (weight average molecular weight of 250,000) and PVDF (weight average molecular weight of 800,000) were mixed in DMAc at a certain solid content, pore former PVP K30 was added, and mechanical stirring was carried out at 40°C for 2 hours. After complete dissolution, a casting solution A was obtained; the mass content of the pore former in the casting solution A was 5%, the slurry viscosity of the casting solution A was 110 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A was 5wt%, and the mass ratio of PVDF / meta-aramid was 9 / 1.

[0076] (2) Meta-aramid polymer solution (weight average molecular weight of 250,000) and PVDF (weight average molecular weight of 800,000) were mixed in DMAc at a certain solid content, pore former PVP K30 was added, and mechanical stirring was carried out at 40°C for 2 hours. After complete dissolution, a casting solution B was obtained; the mass content of the pore former in the casting solution B was 5%, the slurry viscosity of the casting solution B was 2500 mPa·s, and the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B was 5 wt%. The mass ratio of meta-aramid to PVDF was 1.86 / 1.

[0077] (3) The casting solution A and the casting solution B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 60 seconds, and then placed in a drying oven at 50°C for drying, and then rolled up after drying;

[0078] The first coagulation bath is a DMAc aqueous solution with a mass concentration of 40% and a temperature of 30°C.

[0079] The second coagulation bath is an aqueous solution of DMAc with a mass concentration of 20% and a temperature of 20°C;

[0080] The thickness of the first coating layer is 1.0 μm; the thickness of the second coating layer is 1.0 μm.

[0081] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 10%; the mass content of the PVDF in the first coating is 90%;

[0082] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 65%; the mass content of PVDF in the second coating layer is 35%.

[0083] Example 5

[0084] (1) Para-aramid polymer solution (weight average molecular weight of 40,000) and PVDF (weight average molecular weight of 600,000) were mixed in NMP at a certain solid content, pore former PVP K30 was added, and mechanical stirring was carried out at 40°C for 2 hours. After complete dissolution, a casting solution A was obtained; the mass content of the pore former in the casting solution A was 10%, the slurry viscosity of the casting solution A was 125 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A was 2 wt%, and the mass ratio of PVDF / para-aramid was 19 / 1.

[0085] (2) A para-aramid polymer solution (weight-average molecular weight of 40,000) and PVDF (weight-average molecular weight of 600,000) were mixed in NMP at a certain solid content, a pore-forming agent PVP K30 was added, and mechanical stirring was performed at 40°C for 2 hours. After complete dissolution, a casting solution B was obtained; the mass content of the pore-forming agent in the casting solution B was 10%, the slurry viscosity of the casting solution B was 85 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B was 2 wt%, and the mass ratio of para-aramid to PVDF was 1 / 1.

[0086] (3) The casting liquid A and the casting liquid B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 30 seconds, and then placed in a drying oven at 40°C for drying, and then rolled up after drying;

[0087] The first coagulation bath is an aqueous solution of NMP with a mass concentration of 40% and a temperature of 60°C.

[0088] The second coagulation bath is an aqueous solution of NMP with a mass concentration of 10% and a temperature of 40°C;

[0089] The thickness of the first coating layer is 2.0 μm; the thickness of the second coating layer is 2.0 μm.

[0090] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 5%; the mass content of the PVDF in the first coating is 95%;

[0091] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 50%; the mass content of PVDF in the second coating layer is 50%.

[0092] Example 6

[0093] (1) Para-aramid polymer solution (weight average molecular weight of 80,000) and PVDF (weight average molecular weight of 750,000) were mixed in NMP at a certain solid content, pore former PVP K30 was added, and mechanical stirring was carried out at 40°C for 2 hours. After complete dissolution, a casting solution A was obtained; the mass content of the pore former in the casting solution A was 5%, the slurry viscosity of the casting solution A was 8800 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A was 10 wt%, and the mass ratio of PVDF / para-aramid was 4 / 1.

[0094] (2) A para-aramid polymer solution (weight-average molecular weight of 80,000) and PVDF (weight-average molecular weight of 750,000) were mixed in NMP at a certain solid content, a pore-forming agent PVP K30 was added, and mechanical stirring was performed at 40°C for 2 hours. After complete dissolution, a casting solution B was obtained; the mass content of the pore-forming agent in the casting solution B was 5%, the slurry viscosity of the casting solution B was 9775 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B was 10 wt%, and the mass ratio of para-aramid to PVDF was 3 / 1.

[0095] (3) The casting liquid A and the casting liquid B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 30 seconds, and then placed in a drying oven at 40°C for drying, and then rolled up after drying;

[0096] The first coagulation bath is an aqueous solution of NMP with a mass concentration of 60% and a temperature of 30°C.

[0097] The second coagulation bath is an aqueous solution of NMP with a mass concentration of 20% and a temperature of 20°C;

[0098] The thickness of the first coating layer is 4.0 μm; the thickness of the second coating layer is 4.0 μm.

[0099] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 20%; the mass content of the PVDF in the first coating is 80%;

[0100] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 75%; the mass content of PVDF in the second coating layer is 25%.

[0101] Example 7

[0102] (1) Polyamide-imide (weight-average molecular weight of 100,000) and PVDF (weight-average molecular weight of 800,000) were mixed in N-methylpyrrolidone at a certain solid content, a pore-forming agent PVP K30 was added, and mechanical stirring was performed at 60° C. for 4 h. After complete dissolution, a casting solution A was obtained; the mass content of the pore-forming agent in the casting solution A was 10%, the slurry viscosity of the casting solution A was 3000 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A was 10 wt%, and the mass ratio of PVDF / polyamide-imide was 19 / 1.

[0103] (2) Polyamide-imide (weight-average molecular weight of 100,000) and PVDF (weight-average molecular weight of 800,000) were mixed in N-methylpyrrolidone at a certain solid content, pore-forming agent PVP K30 was added, and mechanical stirring was performed at 60° C. for 4 h. After complete dissolution, a casting solution B was obtained; the mass content of the pore-forming agent in the casting solution B was 10%, the slurry viscosity of the casting solution B was 4000 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B was 10 wt%, and the mass ratio of polyamide-imide / PVDF was 1.5 / 1.

[0104] (3) The casting solution A and the casting solution B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 60 seconds, and then entered into a drying oven at 60°C for drying, and then rolled up after drying;

[0105] The first coagulation bath is an aqueous solution of N-methylpyrrolidone with a mass concentration of 50% and a temperature of 40°C.

[0106] The second coagulation bath is an aqueous solution of N-methylpyrrolidone with a mass concentration of 20% and a temperature of 20°C;

[0107] The thickness of the first coating layer is 4.0 μm; the thickness of the second coating layer is 4.0 μm.

[0108] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 5%; the mass content of the PVDF in the first coating is 95%;

[0109] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 60%; the mass content of PVDF in the second coating layer is 40%.

[0110] Example 8

[0111] (1) Polyamide-imide (weight-average molecular weight of 300,000) and PVDF (weight-average molecular weight of 800,000) were mixed in N,N-dimethylacetamide at a certain solid content, pore-forming agent PVP K30 was added, and mechanical stirring was performed at 60°C for 4 hours. After complete dissolution, a casting solution A was obtained; the mass content of the pore-forming agent in the casting solution A was 10%, the slurry viscosity of the casting solution A was 284 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A was 2 wt%, and the mass ratio of PVDF / polyamide-imide was 4 / 1.

[0112] (2) Polyamide-imide (weight-average molecular weight of 300,000) and PVDF (weight-average molecular weight of 800,000) were mixed in N,N-dimethylacetamide at a certain solid content, pore-forming agent PVP K30 was added, and mechanical stirring was carried out at 60°C for 4 hours. After complete dissolution, a casting solution B was obtained; the mass content of the pore-forming agent in the casting solution B was 10%, the slurry viscosity of the casting solution B was 5600 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B was 10 wt%, and the mass ratio of polyamide-imide / PVDF was 1 / 1.

[0113] (3) The casting solution A and the casting solution B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 60 seconds, and then entered into a drying oven at 60°C for drying, and then rolled up after drying;

[0114] The first coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 30% and a temperature of 30°C.

[0115] The second coagulation bath is an aqueous solution of N,N-dimethylacetamide with a mass concentration of 5% and a temperature of 50°C;

[0116] The thickness of the first coating layer is 2.0 μm; the thickness of the second coating layer is 2.0 μm.

[0117] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 20%; the mass content of the PVDF in the first coating is 80%;

[0118] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 50%; the mass content of PVDF in the second coating layer is 50%.

[0119] Example 9

[0120] (1) A heterocyclic aramid polymer solution (the heterocyclic aramid is aromatic III with a weight-average molecular weight of 200,000) and PVDF (weight-average molecular weight of 700,000) are mixed in N-methylpyrrolidone at a certain solid content, a pore-forming agent PVP K30 is added, and mechanical stirring is carried out at 30° C. for 1 hour. After complete dissolution, a casting solution A is obtained; the mass content of the pore-forming agent in the casting solution A is 3%, the slurry viscosity of the casting solution A is 180 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A is 6 wt%, and the mass ratio of PVDF / heterocyclic aramid is 4 / 1.

[0121] (2) A heterocyclic aramid polymer solution (the heterocyclic aramid is aromatic III with a weight-average molecular weight of 200,000) and PVDF (weight-average molecular weight of 700,000) are mixed in N-methylpyrrolidone at a certain solid content, a pore-forming agent PVP K30 is added, and mechanical stirring is carried out at 30° C. for 1 hour. After complete dissolution, a casting solution B is obtained; the mass content of the pore-forming agent in the casting solution B is 3%, the slurry viscosity of the casting solution B is 350 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B is 6 wt%, and the mass ratio of heterocyclic aramid to PVDF is 1 / 1.

[0122] (3) The casting solution A and the casting solution B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 60 seconds, and then entered into a drying oven at 60°C for drying, and then rolled up after drying;

[0123] The first coagulation bath is an aqueous solution of N-methylpyrrolidone with a mass concentration of 35% and a temperature of 60°C.

[0124] The second coagulation bath is an aqueous solution of N-methylpyrrolidone with a mass concentration of 10% and a temperature of 45°C;

[0125] The thickness of the first coating layer is 2.0 μm; the thickness of the second coating layer is 2.0 μm.

[0126] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 20%; the mass content of the PVDF in the first coating is 80%;

[0127] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 50%; the mass content of PVDF in the second coating layer is 50%.

[0128] Example 10

[0129] (1) A heterocyclic aramid polymer solution (the heterocyclic aramid is aromatic III with a weight-average molecular weight of 400,000) and PVDF (weight-average molecular weight of 800,000) are mixed in N,N-dimethylformamide according to a certain solid content, a pore-forming agent PVP K30 is added, and mechanical stirring is carried out at 30°C for 1 hour. After complete dissolution, a casting solution A is obtained; the mass content of the pore-forming agent in the casting solution A is 3%, the slurry viscosity of the casting solution A is 240 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution A is 6 wt%, and the mass ratio of PVDF / heterocyclic aramid is 4 / 1.

[0130] (2) A heterocyclic aramid polymer solution (the heterocyclic aramid is aromatic III with a weight-average molecular weight of 400,000) and PVDF (weight-average molecular weight of 800,000) are mixed in N,N-dimethylformamide according to a certain solid content, a pore-forming agent PVP K30 is added, and mechanical stirring is carried out at 30°C for 1 hour. After complete dissolution, a casting solution B is obtained; the mass content of the pore-forming agent in the casting solution B is 3%, the slurry viscosity of the casting solution B is 410 mPa·s, the mass fraction of the high-temperature resistant aromatic polyamide in the casting solution B is 6 wt%, and the mass ratio of heterocyclic aramid to PVDF is 1 / 1.

[0131] (3) The casting solution A and the casting solution B obtained in steps (1) and (2) are simultaneously coated on both sides of the base film through a micro-concave roller, and then enter the first stage coagulation bath and the second stage coagulation bath in sequence, washed with water for 60 seconds, and then entered into a drying oven at 60°C for drying, and then rolled up after drying;

[0132] The first coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 30% and a temperature of 50°C.

[0133] The second coagulation bath is an aqueous solution of N,N-dimethylformamide with a mass concentration of 5% and a temperature of 35°C;

[0134] The thickness of the first coating layer is 3.0 μm; the thickness of the second coating layer is 4.0 μm.

[0135] The mass content of the high-temperature resistant aromatic polyamide in the first coating is 20%; the mass content of the PVDF in the first coating is 80%;

[0136] The mass content of high-temperature resistant aromatic polyamide in the second coating layer is 50%; the mass content of PVDF in the second coating layer is 50%.

[0137] The performance of the diaphragms prepared in the above examples was tested, and the specific results are shown in Table 1 below.

[0138] The detection methods involved are:

[0139] The hot-pressing bonding strength testing method comprises the following steps:

[0140] (1) Fold the basement membrane in half along the midline and place it between two sheets of silicone oil paper;

[0141] (2) Turn on the plastic sealing heat press (U-H6330T) and set the parameters: temperature to 120°C and speed to 2700 mm / min;

[0142] (3) Place the membrane sample in the laminator from one side, take it out from the other side, and lay it flat on the cutting pad;

[0143] (4) Use a 15 mm cutter to cut a coated membrane sample with a width of 15.0 mm and a length greater than 18 cm;

[0144] (5) Turn on the electronic tensile testing machine and test the peel strength of the sample. For specific operations, refer to the provisions of 6.5.6 in T / CPPIA10-2021.

[0145] The test method for film rupture temperature is as follows: in accordance with GB / T 36800.1, the sample size is 8.0 × 4.0 mm in length × width. The specific test method is as follows:

[0146] 1) Cut the sample into strips with a length × width of 8 × 4 mm in the MD and TD directions respectively, and fix them in the fixture of the instrument;

[0147] 2) Select a thin film probe and quartz platform, place the sample on the sample stage, set the test parameters: preload force to 0.03N, high-purity nitrogen flow rate to 40mL / min, temperature range 50-300°C, rate 5°C / min, and start measurement;

[0148] 3) The measured value is used as the test result.

[0149] Table 1 Diaphragm performance test

[0150]

[0151] It can be seen from the above data that the separators of Examples 1 to 10 can meet the different hot pressing bonding strengths of the positive and negative electrodes, have air permeability values ≤ 400s / 100cc, and membrane rupture temperatures ≥ 220°C.

[0152] Application Examples 1-10

[0153] The diaphragm obtained in the above embodiment was assembled into a 4Ah 811 system ternary lithium battery using a lamination process.

[0154] The batteries assembled with the separators of the above embodiments 1-10 correspond to application examples 1-10 respectively.

[0155] Comparative Application Example 1

[0156] The battery was assembled using the same method as in Application Example 1, except that the separator was replaced with a commercially available 7 μm PE-based film.

[0157] Application Comparative Example 2

[0158] The battery was assembled using the same method as in Application Example 1, except that the separator was replaced with a commercially available (1+2+7+2+1) μm PE / ceramic / PVDF coating membrane, where 2 is the ceramic coating thickness, 1 is the coating thickness of the water-based roller-coated PVDF, and 7 is the PE base membrane thickness.

[0159] The batteries of the above application examples and comparative application examples were subjected to performance tests, and the specific test results are shown in Table 2 below.

[0160] Table 2 Battery performance test results

[0161]

[0162] It can be seen from the data in the above table that the battery separators of application examples 1-10, compared with the PE base film of application comparison example 1 and the PE / ceramic / PVDF coating film of application comparison example 2, have improved capacity retention rates after 100 cycles, all of which are above 90%, which can effectively improve the battery cycle life. In the Arc (accelerating calorimeter) test, application comparison example 1 does not have a high-temperature resistant coating layer, and the measured Arc temperature is 739°C. The Arc temperature of application comparison example 2 with a high-temperature resistant ceramic coating is reduced to 620°C. The high-temperature resistant aromatic polyamides in application examples 5-6 and application examples 9-10 respectively use para-aramid and aromatic III with better heat resistance, and the Arc temperature of the batteries prepared with their separators is also the lowest, at 412°C and 434°C, respectively. It can be seen from this that the separator described in the utility model has good application performance in batteries.

[0163] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0164] For ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the utility model, which all fall within the scope of protection of the utility model. The scope of protection of the utility model shall be based on the attached claims.

Claims

1. An asymmetric diaphragm, characterized in that: The asymmetric diaphragm comprises a base membrane (1), wherein a first coating (2) and a second coating (3) are respectively provided on both sides of the base membrane (1), wherein the pore structure of the first coating (2) presents a small pore structure, and the pore structure of the second coating (3) presents a three-dimensional network-like microporous structure.

2. The asymmetric diaphragm according to claim 1, characterized in that: The micropore diameter of the first coating (2) is 0.05-0.2 μm, and the micropore diameter of the second coating (3) is 0.08-3.0 μm.

3. The asymmetric diaphragm according to claim 1, characterized in that: The thickness of the first coating layer (2) is 0.5-4.0 μm, and the thickness of the second coating layer (3) is 0.5-4.0 μm.

4. The asymmetric diaphragm according to claim 1, characterized in that: The porosity of the first coating (2) is 30%-70%, and the porosity of the second coating (3) is 30%-70%.

5. The asymmetric diaphragm according to claim 1, characterized in that: The first coating (2) and the second coating (3) are simultaneously coated on both sides of the base film (1) through a phase inversion method.

6. The asymmetric diaphragm according to claim 1, characterized in that: The base film (1) is made of any one of polyethylene, polypropylene and polypropylene / polyethylene / polypropylene.

7. The asymmetric diaphragm according to claim 1, characterized in that: The material of the first coating (2) includes high-temperature resistant aromatic polyamide and PVDF; the material of the second coating (3) includes high-temperature resistant aromatic polyamide and PVDF; The high temperature resistant aromatic polyamide is one or two of meta-aromatic polyamide, para-aromatic polyamide, heterocyclic aramid, and polyamide-imide.

8. The asymmetric diaphragm according to claim 7, characterized in that: The weight average molecular weight of the PVDF is 400,000-800,000; the weight average molecular weight of the meta-aromatic polyamide is 150,000-250,000; the weight average molecular weight of the para-aromatic polyamide is 40,000-80,000; the weight average molecular weight of the heterocyclic aramid is 200,000-400,000; and the weight average molecular weight of the polyamideimide is 100,000-300,000. The difference in weight average molecular weight between the PVDF and the meta-aromatic polyamide is not less than 250,000; The difference in weight average molecular weight between the PVDF and the para-aromatic polyamide is not less than 400,000; The difference in weight average molecular weight between the PVDF and the heterocyclic aramid is not less than 250,000; The difference in weight average molecular weight between the PVDF and the polyamide-imide is not less than 350,000.

9. A battery, characterized in that: The battery contains the asymmetric separator according to any one of claims 1 to 8.

Images