Composite diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention provides a composite diaphragm, a preparation method thereof and a lithium ion battery. The composite diaphragm comprises a base membrane and a functional layer located on the surface of at least one side of the base membrane, and the functional layer comprises a polymer material; the polymer material comprises an olefin polymer, and the olefin polymer has a thiazole ring group, an alkylamino group and a ketone group. According to the composite diaphragm structure, under the combined action of the specific polymer material in the functional layer and the base diaphragm, the thermal stability of the diaphragm is improved, the diaphragm has excellent ion conduction performance, meanwhile, the mechanical strength is high, the interface compatibility is excellent, the wettability of an electrolyte is enhanced, the volume expansion of the negative electrode end in the battery is relieved, and the service life of the battery is prolonged. Therefore, the lithium ion battery has excellent fast charging performance while excellent performance of the diaphragm is ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and relates to a composite separator, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] With the development of lithium ion batteries to large-scale application fields such as electric vehicles and renewable energy storage systems, the endurance mileage of electric vehicles is continuously improved, the mileage anxiety is alleviated, the charging anxiety is highlighted, and the development of fast charging becomes a trend. Long endurance (400+km) and fast charging (15-30min) are two major demand directions. To achieve the development of high specific energy fast charging technology, it is necessary to improve the performance of lithium ion batteries such as energy density and power density. For this purpose, the improvement measures mainly focus on the negative electrode material, and the silicon-based negative electrode has high theoretical specific capacity and safety, which is a strong competitor of graphite negative electrode. The graphite negative electrode has approached the theoretical limit of 372mAh / g, while the silicon-based negative electrode has a theoretical specific capacity of 4200mAh / g, which is about 10 times that of the graphite negative electrode. The silicon-based negative electrode material has a lower lithium extraction potential (~0.4V vs. Li / Li+), which is slightly higher than that of graphite (~0.05V vs. Li / Li+), and can avoid the surface lithium precipitation phenomenon during fast charging.

[0003] Although the development of fast charging lithium ion batteries, the traditional polymer-based film separator has the following problems: 1) insufficient thermal stability: easy to shrink at high temperature (150℃ thermal shrinkage rate >10%), leading to positive and negative electrode contact short circuit, and unable to buffer the expansion stress of silicon-based negative electrode (expansion rate 300%), causing interface failure. 2) Low ion transport efficiency: porosity <40%, high interface impedance (>100mΩ·cm²), constant current charge-in ratio <70% at 6C fast charging, and fast charging performance is limited. 3) Poor interface compatibility: weak bonding force with silicon-based negative electrode (interface strength <30N / m), capacity retention rate <70% after 1000 cycles. 4) Weak mechanical strength: puncture resistance is only 380g, and silicon expansion easily punctures the separator, leading to lithium dendrite growth and thermal runaway.

[0004] In the prior art, high-porosity substrates are often used to solve the above problems. Although the high-porosity substrate increases the channel for ion transport, it cannot orderly control the deposition of ions, and is prone to lithium dendrite at the negative electrode, leading to safety problems such as thermal stability. It also reduces the strength of the separator, and the increase in pores also increases the risk of self-discharge, making it difficult to achieve the balance of fast charging performance and the thermal stability, interface compatibility and mechanical strength of the separator.

[0005] Therefore, it is currently necessary to explore how to ensure that the lithium ion battery fast charging performance is good, while avoiding the problems of poor thermal stability, low ion conductivity, poor interface compatibility and weak mechanical strength of the separator. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a composite separator, a preparation method thereof and a lithium ion battery. The composite separator structure of the present application improves the thermal stability of the separator under the joint action of specific polymer materials in the functional layer and the base film, has excellent ion conduction performance, has high mechanical strength, excellent interface compatibility, and also enhances the wettability of the electrolyte, relieves the volume expansion of the negative electrode end in the battery, so as to ensure excellent performance of the separator and make the lithium ion battery have excellent fast charging performance.

[0007] In order to achieve the purpose of the present application, the following technical solutions are adopted in the present application:

[0008] In the first aspect, the present application provides a composite separator, which comprises a base film and a functional layer located on at least one side surface of the base film, and the functional layer comprises a polymer material.

[0009] The polymer material comprises an olefin-based polymer, and the olefin-based polymer has a thiazole ring group, an alkylamino group and a ketone group.

[0010] The following is a preferred technical solution of the present application, but not as a limitation of the technical solutions provided by the present application. Through the following preferred technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0011] Preferably, the thickness of the functional layer is 1-5 μm.

[0012] Preferably, the functional layer further comprises a binder.

[0013] Preferably, the thickness of the base film is 6-12 μm.

[0014] Preferably, the total thickness of the composite separator is 7-16 μm.

[0015] Preferably, the porosity of the composite separator is 45-55%.

[0016] Preferably, the weight average molecular weight of the polymer material is 70,000-150,000.

[0017] Preferably, in the polymer material, the alkylamino group comprises a dimethylamino group and / or a methylamino group.

[0018] Preferably, in the polymer material, the molar ratio of the thiazole ring group, the ketone group and the alkylamino group is (0.8-1):(0.5-1):(1-2).

[0019] Preferably, the polymer material comprises poly(2E)-3-(dimethylamino)-1-[4-methyl-2-(methylamino)-5-thiazolyl]-2-propen-1-one.

[0020] Preferably, the functional layer further comprises an inorganic oxide material.

[0021] Preferably, the mass ratio of the polymer material to the inorganic oxide material is (20~35):(5~18).

[0022] Preferably, the inorganic oxide material comprises a first inorganic oxide material and a second inorganic oxide material; the median particle size D50 of the first inorganic oxide material is less than the median particle size D50 of the second inorganic oxide material.

[0023] Preferably, the median particle size D50 of the first inorganic oxide material is 5nm~15nm.

[0024] Preferably, the median particle size D50 of the second inorganic oxide material is 25nm~50nm.

[0025] Preferably, the second inorganic oxide material has a mesoporous structure with a pore size of 2nm~5nm.

[0026] Preferably, the mass ratio of the first inorganic oxide material to the second inorganic oxide material is 1:(1~2).

[0027] Preferably, the first inorganic oxide material comprises MgO and the second inorganic oxide material comprises ZnO.

[0028] In a second aspect, the application provides a preparation method of the composite separator according to the first aspect, the preparation method comprising the following steps:

[0029] providing a functional layer slurry, and coating the functional layer slurry on the surface of at least one side of the base film to obtain the composite separator.

[0030] Preferably, the functional layer slurry further comprises a binder.

[0031] Preferably, the functional layer slurry further comprises a binder.

[0032] Preferably, the functional layer slurry further comprises an auxiliary agent, and the auxiliary agent comprises a wetting agent and a dispersing agent.

[0033] Preferably, the functional layer slurry further comprises an inorganic oxide material.

[0034] Preferably, the solvent comprises water and / or an organic solvent.

[0035] Preferably, the mass ratio of the polymer material, the inorganic oxide material, the solvent, the wetting agent, the dispersant and the binder in the functional layer slurry is (20-35):(5-18):(42-71):(0.02-0.08):(0.1-0.3):(2-6).

[0036] Preferably, the coating method comprises a micro gravure printing method.

[0037] Preferably, in the micro gravure printing method, the number of lines of the anilox roller is 150 lines / cm-200 lines / cm, the coating speed is 12 m / min-32 m / min, the printing gap is 0.1 mm-0.3 mm, and the doctor blade angle is 45°-65°.

[0038] Preferably, the coated film layer structure is subjected to a drying process, and the air speed in the drying process is 12 m / s-25 m / s, and the winding tension after the drying process is 10 N / m-15 N / m.

[0039] In a third aspect, the application further provides a lithium ion battery, which comprises a positive electrode, a negative electrode, an electrolyte and a composite separator as described in the first aspect or prepared by the preparation method as described in the second aspect.

[0040] Preferably, the negative active material in the negative electrode comprises a silicon-based active material.

[0041] Preferably, the electrolyte comprises an organic solvent and a main lithium salt.

[0042] Preferably, the electrolyte further comprises an auxiliary lithium salt and / or an electrolyte additive.

[0043] Preferably, the auxiliary lithium salt comprises a lithium sulfonylimide lithium salt, and the mass ratio of the auxiliary lithium salt in the electrolyte is 1%-3%.

[0044] Preferably, the electrolyte additive comprises a phosphate ester additive and / or a low impedance additive, and the mass ratio of the electrolyte additive in the electrolyte is 0.1%-1.5%.

[0045] Compared with the prior art, the application has the following beneficial effects:

[0046] The application is based on a base film, and a functional layer of a specific polymer material is compounded. The olefin polymer main chain cooperates with the thiazole ring group, the alkyl amino group and the ketone group, has multiple advantages, first, the polymer material plays a bonding and buffering role, the thiazole heterocycle provides a rigid skeleton and thermal stability, and coordinates with Li+ through the lone pair of electrons of sulfur and nitrogen atoms, promotes lithium salt dissociation and ion conduction; the alkyl amino polar group enhances the wettability of the electrolyte through hydrogen bonding, and the strong polarity of the alkyl amino group can adsorb free Li+ in the electrolyte, shorten the ion transport path; in addition, the alkyl amino group and the hydroxyl group on the surface of the negative active material of the battery anode form a hydrogen bond, buffer volume expansion, and the binding force with the negative electrode is enhanced, and the interface compatibility is improved; so that the composite diaphragm is suitable for the structure of the fast charging battery, and has excellent thermal stability, ion conductivity, interface compatibility and mechanical strength, and improves the fast charging performance, cycle performance and initial efficiency of the battery. DETAILED DESCRIPTION

[0047] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application, and should not be regarded as specific limitations of the present application.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the present application are intended to cover non-exclusive inclusion.

[0049] In the description of the present application, the technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0050] In one embodiment, the first aspect of the present application provides a composite diaphragm, the composite diaphragm comprising a base film and a functional layer located on at least one side surface of the base film, the functional layer comprising a polymer material;

[0051] The polymer material comprises an olefin polymer, and the olefin polymer has a thiazole ring group, an alkyl amino group and a ketone group.

[0052] The application is based on a base film, and a functional layer of a specific polymer material is compounded. The main chain of the olefin polymer cooperates with the thiazole ring group, the alkyl amino group and the ketone group, has multiple advantages, first, the polymer material plays a bonding and buffering role, the thiazole heterocycle provides a rigid skeleton and thermal stability, and the lone pair electrons of the sulfur and nitrogen atoms are coordinated with Li + , promoting the dissociation and ion conduction of the lithium salt; the alkyl amino polar group enhances the wettability of the electrolyte through hydrogen bonding, and the strong polarity of the alkyl amino group can adsorb free Li + in the electrolyte, shortening the ion transport path; in addition, the alkyl amino group and the hydroxyl group on the surface of the negative active material of the negative electrode form a hydrogen bond, buffer volume expansion, and the binding force with the negative electrode is enhanced, and the interface compatibility is improved; so that the composite diaphragm is suitable for fast charging battery structure, and has excellent thermal stability, ion conductivity, interface compatibility and mechanical strength, improving the fast charging performance, cycle performance and initial efficiency of the battery.

[0053] The following is a preferred technical solution of the application, but is not a limitation on the technical solutions provided by the application. Through the following preferred technical solution, the technical purpose and beneficial effects of the application can be better achieved and realized.

[0054] In some embodiments, the thickness of the functional layer is 1-5 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, etc., but is not limited to the listed values, and other values not listed in this range are also applicable.

[0055] The thickness of the functional layer is controlled to be 1-5 μm, which on the one hand ensures uniform and complete coverage of the base film, so as to provide sufficient buffering and protection for the volume expansion of the negative electrode, and on the other hand improves the thermal stability and ion conductivity of the composite diaphragm, ensuring that the diaphragm has appropriate air permeability and electrolyte wetting effect, avoiding the reduction of battery energy density and power density caused by excessive thickness, affecting the play of fast charging performance and additional cost.

[0056] In some embodiments, the functional layer further comprises a bonding agent.

[0057] The polymer material itself can play a bonding role, realizing the close adhesion of the functional layer and the base film, and on this basis, a conventional bonding agent can be further added to further improve the adhesion of the base film and the functional layer, avoiding the shedding of the functional layer and affecting the performance.

[0058] In some embodiments, the thickness of the base film is 6 μm to 12 μm, for example 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0059] In some embodiments, the total thickness of the composite separator is 7 μm to 16 μm, for example 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or 16 μm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0060] In some embodiments, the porosity of the composite separator is 45% to 55%, for example 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, or 55%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0061] For the composite separator of the present application, the specific material of the base film is not additionally limited by the present application, and all types of base films suitable for the battery separator system are applicable in principle without deviating from the inventive concept of the present application; for example, the base film can be a single-layer olefin base film such as a polyethylene (PE) base film or a polypropylene (PP base film), or a multi-layer composite olefin base film such as a PP / PE / PP laminated combination layer structure.

[0062] Further, the thickness of the suitable base film is 6 μm to 12 μm and the total thickness of the suitable separator is 7 μm to 16 μm, which can better play the synergistic effect of the functional layer and the base film and improve the battery performance.

[0063] At the same time, the total porosity of the composite separator is ensured to be 45% to 55%, which is more conducive to the coefficient of the electrolyte and is also beneficial to further improve the mechanical strength and thermal shrinkage rate of the separator.

[0064] In some embodiments, the weight average molecular weight of the polymer material affects the film forming effect, interface adhesion, and mechanical strength of the functional layer, and the weight average molecular weight of the polymer material is preferably 70,000 to 150,000, which further enhances the film forming uniformity of the functional layer, realizes the simultaneous improvement of thermal stability and mechanical strength, and also ensures the advantage of interface adhesion, for example 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, or 150,000, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0065] In some embodiments, the alkylamino group in the polymer material comprises a dimethylamino group and / or a methylamino group.

[0066] In some embodiments, the molar ratio of the thiazole ring group, the keto group and the alkylamino group in the polymer material is (0.8-1):(0.5-1):(1-2), such as 1:1:2, 0.8:1:2, 0.8:0.5:2, 0.8:0.5:1 or 1:1:1, but not limited to the listed values, and other values not listed in the range are also applicable.

[0067] The various functional groups in the polymer material cooperate with each other to jointly regulate the molar ratio of the thiazole ring group, the keto group and the alkylamino group to be (0.8-1):(0.5-1):(1-2), which can better exert the advantages of the functional layer in thermal stability, mechanical strength, electrolyte absorption effect and interface bonding effect.

[0068] In some embodiments, the polymer material comprises poly(2E)-3-(dimethylamino)-1-[4-methyl-2-(methylamino)-5-thiazolyl]-2-propen-1-one.

[0069] It can be understood that the polymer material in the present application is an olefin-based structure polymer, and the specific preparation process of the polymer material is not further limited in detail. In principle, any conventional method that can achieve the preparation of the polymer material of the present application is applicable to the present application without deviating from the inventive concept of the present application.

[0070] Exemplarily, the present application provides a preparation method of poly(2E)-3-(dimethylamino)-1-[4-methyl-2-(methylamino)-5-thiazolyl]-2-propen-1-one, which comprises:

[0071] Mixing (2E)-3-(dimethylamino)-1-[4-methyl-2-(methylamino)-5-thiazolyl]-2-propen-1-one monomer, solvent and initiator to perform polymerization reaction. During the polymerization reaction, free radicals attack C=C double bonds to form an olefin-based carbon chain polymer.

[0072] Optionally, the initiator comprises AIBN (azobisisobutyronitrile) or benzoyl peroxide (BPO).

[0073] Optionally, the solvent comprises at least one of N,N-dimethylformamide (DMF), tetrahydrofuran (THF) or toluene.

[0074] Optionally, the temperature of the polymerization reaction is 50-100°C, such as 50°C, 60°C, 70°C, 80°C, 90°C or 100°C, etc.

[0075] Optionally, the monomer structure of the poly(2E)-3-(dimethylamino)-1-[4-methyl-2-(methylamino)-5-thiazolyl]-2-propen-1-one is (2E)-3-(dimethylamino)-1-[4-methyl-2-(methylamino)-5-thiazolyl]-2-propen-1-one, and the CAS number thereof is 1469881-09-1.

[0076] In addition, it should be further pointed out that the polymer materials in the present application can be obtained by conventional polymerization reaction or can be directly purchased by commercial means, that is, the acquisition channel of the polymer materials in the present application is not unique, as long as it is obtained by reasonable and compliant means.

[0077] In some embodiments, the functional layer further comprises an inorganic oxide material.

[0078] The functional layer of the present application is based on the polymer material, and the inorganic oxide material is added synergistically, the inorganic oxide material is dispersed in the polymer material, forming an organic-inorganic network in which the polymer material wraps the inorganic oxide material; the polymer material provides bonding and stress buffering, the inorganic particles provide rigid support and thermal barrier, and synergistically resist high-temperature thermal shrinkage and expansion stress of the negative electrode.

[0079] In some embodiments, the mass ratio of the polymer material to the inorganic oxide material is (20-35):(5-18), for example, 20:5, 20:10, 20:18, 25:5, 25:10, 25:18, 35:5, 35:10 or 35:18, etc., but not limited to the listed values, and other values not listed in this range are also applicable.

[0080] In the present application, the mass ratio of the polymer material to the inorganic oxide material is preferably limited to (20-35):(5-18), which is more conducive to achieving complete wrapping of the polymer material on the inorganic oxide material, and further improving the adhesion of the coating, and also better ensuring the advantages of rigid support and puncture resistance of the inorganic oxide material, and achieving a good balance between ion transmission and thermal stability.

[0081] In some embodiments, the inorganic oxide material comprises a first inorganic oxide material and a second inorganic oxide material; the median particle size D50 of the first inorganic oxide material is smaller than the median particle size D50 of the second inorganic oxide material.

[0082] The application further comprises the first inorganic oxide material with relatively small particle size and high surface energy, which enhances the hydrogen bonding with the alkylamino group in the polymer material and also can adsorb HF in the electrolyte to inhibit the interface side reaction, and the second inorganic oxide material with relatively large particle size, which has good thermal stability and also improves the rigid strength of the functional layer.

[0083] In some embodiments, the first inorganic oxide material has a median particle size D50 of 5 nm to 15 nm, such as 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm or 15 nm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0084] In some embodiments, the second inorganic oxide material has a median particle size D50 of 25 nm to 50 nm, such as 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0085] In some embodiments, the second inorganic oxide material has a mesoporous structure with a pore size of 2 nm to 5 nm, such as 2 nm, 3 nm, 4 nm or 5 nm, but not limited to the listed values, and other values not listed in the range are also applicable.

[0086] The second inorganic oxide material with a mesoporous structure can also increase the adsorption capacity of the electrolyte, thereby enhancing the wettability of the electrolyte and improving the ion transport effect.

[0087] In some embodiments, the mass ratio of the first inorganic oxide material to the second inorganic oxide material is 1:(1-2), such as 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, but not limited to the listed values, and other values not listed in the range are also applicable.

[0088] By adjusting the mass ratio of the first inorganic oxide material to the second inorganic oxide material to be 1:(1-2), the application can also at least partially fill the first inorganic oxide material in the voids of the second inorganic oxide material to form a close-packed structure, thereby better improving the puncture resistance of the composite separator.

[0089] In some embodiments, the first inorganic oxide material comprises MgO and the second inorganic oxide material comprises ZnO.

[0090] In the present application, the combination of MgO and ZnO materials is selected, MgO fills the gap between ZnO particles, forming a "ZnO skeleton-MgO filling-polymer bonding" composite network. In addition to the effect of improving rigid support and thermal barrier, the synergistic effect of MgO and ZnO also increases the interfacial action, better provides stress buffering for the polymer material, and further improves the puncture resistance.

[0091] In one embodiment, the second aspect of the present application provides a preparation method of the composite separator as described in the first aspect, the preparation method comprising the following steps:

[0092] providing a functional layer slurry, and coating the functional layer slurry on the surface of at least one side of the base film to obtain the composite separator;

[0093] The functional layer slurry comprises a polymer material and a solvent.

[0094] In the preparation method of the present application, a simple coating process can obtain a composite separator structure with excellent performance, and the base film and the functional layer are tightly combined.

[0095] In some embodiments, the functional layer slurry further comprises a binder.

[0096] In some embodiments, the functional layer slurry further comprises an auxiliary agent, and the auxiliary agent comprises a wetting agent and a dispersing agent.

[0097] It can be understood that the specific types of the binder, the wetting agent, the dispersing agent and the solvent in the functional layer slurry of the present application are selected according to conventional techniques, and any substance suitable for the functional layer slurry of the separator within the reasonable range of the skilled person without deviating from the inventive concept of the present application is applicable.

[0098] For example, the binder includes but is not limited to at least one of carboxymethyl cellulose (CMC) / hydroxypropyl methyl cellulose (HPMC) or polyvinyl alcohol (PVA), etc.

[0099] For example, the wetting agent includes but is not limited to at least one of sodium hexametaphosphate, sodium tripolyphosphate or sodium pyrophosphate, and the main function of the wetting agent is to reduce the surface tension and enhance the flowability of the slurry.

[0100] For example, the dispersing agent includes but is not limited to at least one of silicate dispersing agent, sodium polyacrylate or sodium citrate.

[0101] In some embodiments, the functional layer slurry further comprises an inorganic oxide material.

[0102] In some embodiments, the solvent comprises water and / or an organic solvent.

[0103] In some embodiments, the mass ratio of the polymer material, the inorganic oxide material, the solvent, the wetting agent, the dispersant and the binder in the functional layer slurry is (20-35):(5-18):(42-71):(0.02-0.08):(0.1-0.3):(2-6), for example, 20:18:42:0.02:0.1:2, 35:18:71:0.08:0.3:6, 20:18:71:0.08:0.3:6, 35:18:42:0.02:0.1:2, or 25:15:60:0.04:0.2:4, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0104] It should be noted that the preparation process of the functional slurry is not unique, and a slurry system suitable for coating can be obtained.

[0105] Exemplarily, the present application provides a preparation process of a functional slurry:

[0106] The dispersant and water are first mixed, and then the inorganic oxide material is added for second mixing to obtain a second mixed solution; the remaining raw materials such as the polymer material, the binder and the additives are added to the second mixed solution for third mixing to obtain the functional layer slurry.

[0107] Optionally, all the mixing processes can be simultaneously subjected to ultrasonic treatment.

[0108] In addition, the parameters in the mixing process can be adaptively selected and adjusted by those skilled in the art according to actual needs.

[0109] In some embodiments, the coating method comprises a microgravure printing method.

[0110] The microgravure printing method is used for coating the functional layer slurry, which can further improve the thickness uniformity and better improve the cycle performance of the battery.

[0111] In some embodiments, in the microgravure printing method, the line number of the anilox roller is 150-200 lines / cm, for example, 150 lines / cm, 160 lines / cm, 170 lines / cm, 180 lines / cm, 190 lines / cm or 200 lines / cm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0112] In some embodiments, the microgravure printing method has a coating speed of 12 m / min to 32 m / min, such as 12 m / min, 15 m / min, 18 m / min, 20 m / min, 23 m / min, 25 m / min, 28 m / min, 30 m / min, or 32 m / min, and the like, but not limited to the listed values, and other values not listed in the range are also applicable.

[0113] In some embodiments, the microgravure printing method has a printing gap of 0.1 mm to 0.3 mm, such as 0.1 mm, 0.2 mm, or 0.3 mm, and the like, but not limited to the listed values, and other values not listed in the range are also applicable.

[0114] In some embodiments, the microgravure printing method has a doctor blade angle of 45° to 65°, such as 45°, 50°, 55°, 60°, or 65°, and the like, but not limited to the listed values, and other values not listed in the range are also applicable.

[0115] During the microgravure printing process, the various parameters are controlled to better achieve the coating of the functional layer and improve the coating effect.

[0116] In some embodiments, the coated film layer structure is subjected to a drying process, and the drying process has a wind speed of 12 m / s to 25 m / s, such as 12 m / s, 15 m / s, 18 m / s, 20 m / s, 23 m / s, or 25 m / s, and the like, but not limited to the listed values, and other values not listed in the range are also applicable.

[0117] In some embodiments, the drying process has a winding tension of 10 N / m to 15 N / m, such as 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, or 15 N / m, and the like, but not limited to the listed values, and other values not listed in the range are also applicable.

[0118] In one embodiment, the third aspect of the present application further provides a lithium ion battery, which comprises a positive electrode, a negative electrode, an electrolyte, and a composite separator as described in the first aspect or prepared by the preparation method as described in the second aspect.

[0119] In some embodiments, the negative active material in the negative electrode comprises a silicon-based active material.

[0120] The silicon-based negative electrode material is more suitable for fast-charging batteries, but the volume expansion of the silicon-based active material during charging and discharging can cause the performance of the battery to deteriorate. The composite separator structure of the application can effectively solve the problem of volume expansion of the silicon-based negative electrode active material and improve the interfacial compatibility between the composite separator and the negative electrode.

[0121] It can be understood that the silicon-based negative electrode material described in the application is a conventional silicon system negative electrode material, such as pure silicon material, silicon-carbon negative electrode material, and silicon-oxygen negative electrode material, and the source of the silicon-based negative electrode material can be prepared by a conventional technical solution or purchased directly from the market.

[0122] In some embodiments, the electrolyte includes an organic solvent and a main lithium salt.

[0123] In some embodiments, the organic solvent can include at least one of a carbonate compound, a carboxylic ester compound, an ether compound, and a sulfone compound. As an example, the solvent can include, but is not limited to, at least one of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone, sulfobutane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), methylsulfobutane, dimethyl sulfoxide, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl ether, diethyl ether, nitromethane, and N,N-dimethylformamide. The above-mentioned solvents can be used alone or simultaneously with two or more.

[0124] In some embodiments, the main lithium includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenate (LiAsF6). The above-mentioned electrolyte salts can be used alone or simultaneously with two or more.

[0125] In some embodiments, the electrolyte further includes an auxiliary lithium salt and / or an electrolyte additive.

[0126] In some embodiments, the auxiliary lithium salt comprises a lithium sulfonylimide lithium salt, and the mass percentage of the auxiliary lithium salt in the electrolyte is 1% to 3%, for example, 1%, 2%, or 3%, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0127] The addition of a lithium sulfonylimide lithium salt, such as lithium bis(fluorosulfonyl)imide LiFSI or lithium bis(trifluoromethanesulfonyl)imide LiTFSI, and the like, in the electrolyte further reduces the interface impedance of the battery and has a synergistic effect with the composite separator.

[0128] In some embodiments, the electrolyte additive comprises a phosphate ester additive and / or a low-impedance additive, and the mass percentage of the electrolyte additive in the electrolyte is 0.1% to 1.5%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0129] On the premise of the base electrolyte, the electrolyte additive, the phosphate ester additive, and / or the low-impedance additive can also be added to further improve the rate performance of the battery in combination with the composite separator.

[0130] Specifically, the phosphate ester additive includes but is not limited to tris(4-nitrophenyl) phosphate, and the low-impedance additive includes but is not limited to lithium bis(oxalato)borate LiBOB.

[0131] In some embodiments, the positive electrode can comprise a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector.

[0132] In some embodiments, the shape of the positive electrode current collector can be a plate or a foil, and the present application is not limited thereto.

[0133] In some embodiments, the material of the positive electrode current collector is not particularly limited and can be selected from materials having electronic conductivity. For example, a simple substance or an alloy containing at least one element selected from C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, Al (for example, stainless steel, etc.) can be used.

[0134] From the viewpoint of high conductivity, high stability in the electrolyte, and good oxidation resistance, a C layer, an Al foil, a stainless steel foil, and the like are optional. From the viewpoint of further reducing production costs, an Al foil is more preferred. Those skilled in the art can make adaptive adjustments and selections according to actual conditions.

[0135] The positive electrode active material layer includes a positive electrode active material, which can be selected from materials capable of absorbing and releasing lithium.

[0136] The specific type of the positive electrode active material is not particularly limited and can be selected as needed. As an example, the positive electrode active material can include, but is not limited to, at least one of lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), iron pyrophosphate (Li2FeP2O7), lithium cobaltate (LiCoO2), spinel lithium manganate (LiMn2O4), spinel lithium nickel manganate, layered lithium manganate (LiMnO2), lithium nickelate (LiNiO2), lithium niobate (LiNbO2), lithium ferrate (LiFeO2), lithium magnesiumate (LiMgO2), lithium calciumate (LiCaO2), lithium copperate (LiCuO2), lithium zincate (LiZnO2), lithium molybdate (LiMoO2), lithium tantalate (LiTaO2), lithium tungstate (LiWO2), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium-rich material (e.g., lithium-rich nickel cobalt manganese oxide), manganese oxide (MnO2), vanadium oxide, sulfur oxide, silicate oxide, and a modified compound of each thereof. These materials can be used alone or in combination with two or more.

[0137] Optionally, the positive electrode active material can include at least one of lithium iron phosphate (LiFePO4), lithium manganese iron phosphate, lithium cobaltate (LiCoO2), lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, spinel lithium nickel manganate, and a modified compound of each thereof.

[0138] Embodiment 1

[0139] The present embodiment provides a composite separator including a PE base having a thickness of 8 μm and a functional layer on both sides of the base film, the thickness of the functional layer on each side being 3 μm, i.e., the total thickness of the composite separator being 14 μm, and the total porosity of the composite separator being 50%;

[0140] The functional layer has a polymer material poly(2E)-3-(dimethylamino)-1-[4-methyl-2-(methylamino)-5-thiazolyl]-2-propen-1-one having a weight average molecular weight of 100,000, first inorganic oxide material nanoparticles Mg (D50 being 10 nm), and second inorganic oxide material ZnO having a mesoporous structure (D50 being 40 nm, mesopore size being 5 nm), and the functional layer further has a binder CMC;

[0141] In the polymer material, the molar ratio of the thiazole ring group, the ketone group, and the alkylamino group is 1:1:2;

[0142] The mass ratio of the polymer material and the inorganic oxide material is 25:10, the mass ratio of MgO and ZnO is 1:1.5, MgO is filled in the gap of ZnO particles to form a close-packed structure.

[0143] The preparation method of the composite diaphragm is as follows:

[0144] (1) First, the dispersing agent sodium polyacrylate and the solvent pure water are once stirred and blended at a speed of 2000 r / min, then the first inorganic oxide material and the second inorganic oxide material are twice stirred and blended at a speed of 2000 r / min to obtain a mixed solution, and ultrasonic is performed at the same time in the process of the above-mentioned twice stirring and blending. After the twice stirring, the solvent isopropyl alcohol, CMC, the polymer material and the wetting agent sodium hexametaphosphate are added to the mixed solution and vacuum oscillation stirring and blending is performed to prepare a functional layer slurry;

[0145] Among them, the mass fraction ratio of the polymer material, all inorganic oxide materials, pure water, wetting agent, dispersing agent, isopropyl alcohol and CMC is 25:10:50:0.06:0.2:3:4;

[0146] (2) The functional layer slurry of step (1) is used to perform functional layer wet film coating on the double-sided surface of the base film by using a double-sided micro-gravure printing process. In the coating process, the line number of the anilox roll is 180 lines / cm, the coating speed is 25 m / min, the printing gap is 0.2 mm, and the doctor blade angle is 55°;

[0147] (3) The functional layer wet film obtained in step (2) is dried at 80℃, the wind speed in the drying process is 20 m / s, and the winding tension after drying is 13 N / m to obtain the composite diaphragm.

[0148] Example 2

[0149] The embodiment provides a composite diaphragm, which comprises a PE base with a thickness of 6 μm and a functional layer on the double-sided surface of the base film, the thickness of the functional layer on each side is 5 μm, that is, the total thickness of the composite diaphragm is 16 μm, and the total porosity of the composite diaphragm is 45%;

[0150] The functional layer has a polymer material poly(2E)-3-(dimethylamino)-1-[4-methyl-2-(methylamino)-5-thiazolyl]-2-propylene-1-ketone with a weight average molecular weight of 70000, a first inorganic oxide material nano-particle Mg (D50 is 5 nm) and a second inorganic oxide material mesoporous ZnO (D50 is 25 nm, mesoporous pore size is 3 nm), and the functional layer also has a binder CMC;

[0151] The mass ratio of the polymer material to the inorganic oxide material is 20:5, the mass ratio of MgO to ZnO is 1:2, MgO is filled in the voids of ZnO particles to form a close-packed structure.

[0152] The preparation method of the composite separator is as follows:

[0153] (1) First, the dispersing agent sodium polyacrylate and the solvent pure water are once stirred and blended at a speed of 3000 r / min, then the first inorganic oxide material and the second inorganic oxide material are twice stirred and blended at a speed of 3000 r / min to obtain a mixed solution, and ultrasonic is performed simultaneously during the above-mentioned twice stirring and blending. After the twice stirring, the solvent isopropyl alcohol, CMC, the polymer material and the wetting agent sodium hexametaphosphate are added to the mixed solution and vacuum oscillation stirring and blending is performed to prepare a functional layer slurry;

[0154] Among them, the mass fraction ratio of the polymer material, all inorganic oxide materials, pure water, wetting agent, dispersing agent, isopropyl alcohol and CMC is 20:5:40:0.02:0.1:2:2;

[0155] (2) The functional layer slurry of step (1) is used to perform functional layer wet film coating on the double-sided surfaces of the base film by using a double-sided micro-gravure printing process. During the coating process, the line number of the anilox roll is 150 lines / cm, the coating speed is 12 m / min, the printing gap is 0.3 mm, and the doctor blade angle is 45°;

[0156] (3) The functional layer wet film obtained in step (2) is dried at 40℃, the wind speed during the drying process is 25 m / s, and the winding tension after drying is 10 N / m to obtain the composite separator.

[0157] Example 3

[0158] The present embodiment provides a composite separator, which comprises a PE base with a thickness of 6 μm and a functional layer on the double-sided surfaces of the base film, the thickness of the functional layer on each side is 1 μm, that is, the total thickness of the composite separator is 8 μm, and the total porosity of the composite separator is 55%;

[0159] The functional layer has a polymer material poly(2E)-3-(dimethylamino)-1-[4-methyl-2-(methylamino)-5-thiazolyl]-2-propen-1-one with a weight average molecular weight of 150000, a first inorganic oxide material nano-particle Mg (D50 is 15 nm) and a second inorganic oxide material ZnO with a mesoporous structure (D50 is 50 nm, mesoporous pore size is 1 nm), and the functional layer also has a binder CMC;

[0160] In the polymer material, the molar ratio of the thiazole ring group, the ketone group and the alkylamino group is 1:1:2;

[0161] The mass ratio of the polymer material to the inorganic oxide material is 35:18, the mass ratio of MgO to ZnO is 1:1.5, MgO is filled in the voids of ZnO particles to form a close-packed structure.

[0162] The preparation method of the composite diaphragm is as follows:

[0163] (1) First, the dispersing agent sodium citrate and the solvent pure water are once stirred and blended at a speed of 2500 r / min, then the first inorganic oxide material and the second inorganic oxide material are twice stirred and blended at a speed of 2500 r / min to obtain a mixed solution, and ultrasonic is performed at the same time in the process of the above-mentioned twice stirring and blending. After the twice stirring, the solvent isopropyl alcohol, PVA, the polymer material and the wetting agent sodium tripolyphosphate are added to the mixed solution and vacuum oscillation stirring and blending is performed to prepare a functional layer slurry;

[0164] Among them, the mass fraction ratio of the polymer material, all inorganic oxide materials, pure water, wetting agent, dispersing agent, isopropyl alcohol and CMC is 35:18:66:0.08:0.3:5:6;

[0165] (2) The functional layer slurry of step (1) is used to perform functional layer wet film coating on the double-sided surface of the base film by using a double-sided micro-gravure printing process. In the coating process, the line number of the anilox roller is 200 lines / cm, the coating speed is 12 m / min, the printing gap is 0.1 mm, and the doctor blade angle is 65°;

[0166] (3) The functional layer wet film obtained in step (2) is dried at 60°C. In the drying process, the air speed is 25 m / s, and the drying after rolling tension is 15 N / m to obtain the composite diaphragm.

[0167] Example 4

[0168] The difference between this embodiment and Example 1 is that the weight average molecular weight of the polymer material in this embodiment is 70000.

[0169] The rest of the conditions remain the same as in Example 1.

[0170] Example 5

[0171] The difference between this embodiment and Example 1 is that the weight average molecular weight of the polymer material in this embodiment is 150000.

[0172] The rest of the conditions remain the same as in Example 1.

[0173] Example 6

[0174] The difference between this embodiment and Example 1 is that the mass ratio of the first inorganic oxide material to the second inorganic oxide material in this embodiment is 1:1.

[0175] The rest of the conditions are consistent with Example 1.

[0176] Example 7

[0177] The difference between this example and Example 1 is that the mass ratio of the first inorganic oxide material MgO to the second inorganic oxide material ZnO in this example is 1:2.

[0178] The rest of the conditions are consistent with Example 1.

[0179] Example 8

[0180] The difference between this example and Example 1 is that the weight average molecular weight of the polymer material in this example is 200000.

[0181] The rest of the conditions are consistent with Example 1.

[0182] Example 9

[0183] The difference between this example and Example 1 is that the weight average molecular weight of the polymer material in this example is 50000.

[0184] The rest of the conditions are consistent with Example 1.

[0185] Example 10

[0186] The difference between this example and Example 1 is that the thickness of the functional layer in this example is 8μm.

[0187] The rest of the conditions are consistent with Example 1.

[0188] Example 11

[0189] The difference between this example and Example 1 is that this example only contains the first inorganic oxide material MgO.

[0190] The rest of the conditions are consistent with Example 1.

[0191] Example 12

[0192] The difference between this example and Example 1 is that this example only contains the second inorganic oxide material ZnO.

[0193] The rest of the conditions are consistent with Example 1.

[0194] Example 13

[0195] The difference between this example and Example 1 is that the second inorganic oxide material ZnO in this example does not contain a pore structure.

[0196] The rest of the conditions are consistent with Example 1.

[0197] Example 14

[0198] The difference between this example and Example 1 is that the D50 of the first inorganic oxide material MgO and the second inorganic oxide material ZnO in this example are both 10 nm.

[0199] The rest of the conditions are kept the same as Example 1.

[0200] Example 15

[0201] The difference between this example and Example 1 is that the D50 of the first inorganic oxide material MgO and the second inorganic oxide material ZnO in this example are both 40 nm.

[0202] The rest of the conditions are kept the same as Example 1.

[0203] Example 16

[0204] The difference between this example and Example 1 is that the mass ratio of the first inorganic oxide material MgO and the second inorganic oxide material ZnO in this example is 1:0.5.

[0205] The rest of the conditions are kept the same as Example 1.

[0206] Example 17

[0207] The difference between this example and Example 1 is that the mass ratio of the first inorganic oxide material MgO and the second inorganic oxide material ZnO in this example is 1:2.5.

[0208] The rest of the conditions are kept the same as Example 1.

[0209] Example 18

[0210] The difference between this example and Example 1 is that the functional layer in this example does not contain the first inorganic oxide material MgO, nor does it contain the second inorganic oxide material ZnO, i.e., it does not contain any inorganic oxide material.

[0211] The rest of the conditions are kept the same as Example 1.

[0212] Comparative Example 1

[0213] The difference between this comparative example and Example 1 is that the functional layer in this comparative example does not contain a polymeric material.

[0214] The rest of the conditions are kept the same as Example 1.

[0215] Comparative Example 2

[0216] The difference between the present comparative example and Example 1 is that the polymer material in the functional layer of the present comparative example is modified polyacrylic acid, which is obtained by graft copolymerization of 4-methyl-5-vinylthiazole and acrylic acid, specifically including:

[0217] 4-methyl-5-vinylthiazole and acrylic acid were added to ethanol, and then mercaptoacetic acid and ammonium persulfate were slowly added under a nitrogen atmosphere, and the mixture was heated to 45°C, and then reacted at 65°C for 3h. A 30wt% sodium hydroxide solution was added to adjust the pH to 7, and then extracted and dried to obtain the modified polyacrylic acid; wherein the molar ratio of 4-methyl-5-vinylthiazole to acrylic acid is 1:1; the mass-volume ratio of acrylic acid to ethanol is 1g:6mL; the mass ratio of acrylic acid to mercaptoacetic acid is 1:0.12; and the mass ratio of acrylic acid to ammonium persulfate is 1:0.05.

[0218] The remaining conditions are the same as those in Example 1.

[0219] Comparative Example 3

[0220] The difference between the present comparative example and Example 1 is that the polymer material in the present comparative example is poly(N,N-dimethylacrylamide) (CAS No.: 26793-34-0).

[0221] The remaining conditions are the same as those in Example 1.

[0222] Comparative Example 4

[0223] The difference between the present comparative example and Example 1 is that the polymer material in the present comparative example is poly(ethylene methyl ketone) (CAS No.: 25038-87-3).

[0224] The remaining conditions are the same as those in Example 1.

[0225] Comparative Example 5

[0226] The difference between the present comparative example and Example 1 is that the composite separator in the present comparative example is the PE-based film in Example 1.

[0227] The composite separators provided in Examples 1-18 and Comparative Examples 1-5 were used to prepare batteries, specifically as follows:

[0228] Application Example 1

[0229] The present application example provides a lithium ion battery, and the preparation method of the lithium ion battery is as follows:

[0230] (1) Preparation of the positive electrode sheet:

[0231] The ternary material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1O2) positive active material, binder PVDF (polyvinylidene fluoride), conductive agent SP (conductive carbon black Super-P), SWCNT (single-walled carbon nanotube), mixed and stirred uniformly in a mass ratio of 96:2:1.9:0.1 to obtain a positive electrode slurry, then the positive electrode slurry is coated on an aluminum foil through a coating process, dried, and cold-pressed to obtain a positive electrode sheet;

[0232] (2) Preparation of a negative electrode sheet

[0233] The silicon-carbon negative electrode material, conductive agent SP (conductive carbon black Super-P), SWCNT (single-walled carbon nanotube), binder PAA (polyacrylic acid), and SBR are mixed and stirred uniformly in a mass ratio of 90:2:0.5:5:2.5 to obtain a negative electrode slurry, with a solid content of 30%, then the negative electrode slurry is coated on a copper foil current collector through a coating process, vacuum dried, and cold-pressed to obtain a negative electrode sheet.

[0234] (3) Selection of an electrolyte

[0235] The organic solvents ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, diethyl carbonate DEC, and fluoroethylene carbonate are mixed in a mass ratio of 15:20:25:30:10, then LiPF6 is added to make the concentration 1 mol / L, to obtain an electrolyte.

[0236] (4) Selection of a separator

[0237] The composite separator provided in Example 1 is used as the separator.

[0238] (5) Preparation of a lithium ion battery

[0239] The above positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, then wound to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried, and then injected with the electrolyte, and then subjected to vacuum packaging, standing, formation, shaping, and other processes to obtain a lithium ion battery.

[0240] Application Example 2-18

[0241] The difference between Application Example 2-18 and Application Example 1 is that the composite separator provided in Example 2-18 is used as the separator, respectively.

[0242] The remaining conditions are the same as those in Application Example 1.

[0243] Application Example 19

[0244] The difference between this application example and Application Example 1 is that the negative active material in the negative electrode sheet of this application example is artificial graphite material.

[0245] The other conditions are the same as in Application Example 1.

[0246] Comparative Application Examples 1-5

[0247] The difference between Comparative Application Examples 1-5 and Application Example 1 is that the composite separator provided in Comparative Examples 1-5 is used as the isolation film, respectively.

[0248] The other conditions are the same as in Application Example 1.

[0249] Performance test

[0250] ①The composite separator structure provided in the examples and comparative examples is tested for thermal shrinkage, and the standard test method (GB / T36363) is referred to. Under the specified temperature (such as 150°C) and time (30 min), the size change of the separator sample in the free state is measured, and the thermal shrinkage in the transverse direction (TD) and the longitudinal direction (MD) is calculated. The test conditions are as follows:

[0251] 1) The composite separator sample is placed in an environment of 23±2°C and humidity of 50±5%RH for 24 hours. After placement, the edge of the composite separator is cut by 10mm, and a 100mm×100mm test composite separator is obtained;

[0252] 2) The initial size of the composite separator is measured using an optical projector, and a cross line is drawn on the surface of the sample. The initial length L0 in the transverse direction (TD) and the longitudinal direction (MD) is recorded (accurate to 0.1mm);

[0253] 3) Then the test composite separator with initial size in step 2) is fixed with a stainless steel frame clamp and placed in the center of a preheated high-temperature furnace at 150°C, ensuring that the sample does not contact the furnace wall; after constant temperature for 30 min, the clamp is quickly taken out and cooled at room temperature for 10 min;

[0254] 4) The cross line length L1 of the sample after cooling is measured (TD and MD directions are measured respectively), 3 parallel samples are tested for each sample, and the average value is taken. The thermal shrinkage in the transverse and longitudinal directions is calculated based on the initial size and the sample after cooling. The calculation formula is: thermal shrinkage (%) = (L0-L1) / L0×100%, and the data results are recorded in Table 1.

[0255] Table 1

[0256] 150°C / 30 min heat shrinkage rate-TD (%) 150°C / 30 min heat shrinkage rate-MD (%) Example 1 0.6 0.9 Example 2 0.7 1.0 Example 3 0.8 1.1 Example 4 0.9 1.2 Example 5 1.0 1.3 Example 6 1.1 1.4 Example 7 1.2 1.5 Example 8 1.8 2.2 Example 9 2.0 2.5 Example 10 2.8 3.3 Example 11 2.8 3.3 Example 12 3.0 3.5 Example 13 2.2 2.6 Example 14 2.4 2.8 Example 15 2.6 3.1 Example 16 3.2 3.8 Example 17 3.5 4.0 Example 18 2.1 2.4 Comparative Example 1 8.5 10.0 Comparative Example 2 9.0 11.5 Comparative Example 3 7.5 9.2 Comparative Example 4 8.0 10.5 Comparative Example 5 10.2% 12.8%

[0257] ②Tested on the LAND battery test system of Wuhan Jinuo Electronics Co., Ltd. at room temperature (25°C), and the specific test conditions are as follows:

[0258] a) First coulombic efficiency

[0259] The lithium ion battery was charged at 0.33C rate to 4.2V at 25°C, and then discharged at 0.33C rate to 2.5V, and the first coulombic efficiency of the lithium ion battery was calculated.

[0260] First coulombic efficiency (%) = lithium ion battery 0.33C first discharge total capacity / lithium ion battery 0.33C first charge total capacity x 100%.

[0261] b) Capacity retention rate at room temperature 1C / 2C cycle for 1000 times

[0262] The lithium ion battery was charged at 1C rate to 4.2V at 25°C, and then discharged at 2C rate to 2.5V, and the capacity retention rate of the lithium ion battery after 1C / 2C charge-discharge cycle for 1000 times was calculated.

[0263] The capacity retention rate of the lithium ion battery after N cycles (%) = (discharge capacity of the Nth cycle / first discharge capacity) x 100%, and N was the cycle number of the lithium ion battery.

[0264] c) Room temperature 6C rate performance - constant current charge ratio

[0265] The lithium ion battery was discharged at 1C rate to 2.5V at 25°C, and then charged at 6C rate to 4.2V, and the constant current charge capacity Q1 and the constant voltage charge total capacity Q2 of the lithium ion battery were recorded, and the 6C rate charge constant current charge ratio was calculated according to the following formula: 6C rate charge constant current charge ratio = constant current charge capacity Q1 / constant voltage charge total capacity Q2 x 100%.

[0266] d) Room temperature 1C / 8C discharge capacity retention rate

[0267] The lithium ion battery after the separation was charged at 1C rate to 4.2V at 25℃, and the cutoff current was 0.05C; it was rested for 10min; then the lithium ion battery was discharged at 1C rate to 2.5V, and its discharge capacity Q1C was recorded as the initial discharge capacity; then the lithium ion battery was charged at 1C rate to 4.2V at 25℃, and the cutoff current was 0.05C; it was rested for 10min; then the fully charged battery was discharged at 8C rate to 2.5V, and its discharge capacity Q8C was recorded; the discharge capacity retention rate (%) of the lithium ion battery at 1C / 8C rate was calculated as Q8C at 8C rate / Q1C at 1C rate x 100%.

[0268] e) Cell thermal runaway ARC test: start ARC adiabatic thermal runaway test (test sample in the cavity from room temperature to 45±2ºC, after 90min, detect the change of battery temperature rise rate, if the temperature rise is more than 0.2ºC in 10min (i.e. SHR>0.02ºC / min), it is considered that the self-heat reaction occurs inside the battery, and the adiabatic environment is maintained until the battery thermal runaway occurs; if the temperature rise is not more than 0.2ºC in 10min (i.e. SHR≤0.02ºC / min), continue to the next step temperature rise test; 5ºC at each temperature step, repeat the steps at each step, the ARC test temperature range is 45℃~300℃, the self-heat generation starting temperature is T1 (temperature rise rate SHR>0.02ºC / min), and the thermal runaway starting temperature T2 (temperature rise rate SHR>1ºC / min).

[0269] The above battery performance test results are shown in Table 2.

[0270] Table 2

[0271] 0.33C initial efficiency (%) Ambient 1C / 2C cycle 1000 cycles capacity retention rate (%) Ambient 6C constant current charge ratio (%) Ambient 1C / 8C discharge capacity retention rate (%) Self-heat starting temperature T1 (°C) thermal runaway starting temperature T2 (°C) Application Example 1 84.8 83.1 79.3 74.5 108.6 168.0 Application Example 2 84.5 82.8 79.0 76.5 108.2 167.5 Application Example 3 85.0 83.5 79.5 77.2 109.0 169.0 Application Example 4 84.2 82.5 78.8 76.2 108.0 167.0 Application Example 5 83.8 82.2 78.5 76.0 107.8 166.5 Application Example 6 83.5 82.0 78.0 75.8 107.5 166.0 Application Example 7 84.0 82.3 78.2 76.1 107.6 166.2 Application Example 8 82.0 80.0 76.0 74.0 106.5 165.0 Application Example 9 81.5 79.5 75.5 73.5 106.0 164.5 Application Example 10 80.0 78.0 74.0 72.5 105.5 164.0 Application Example 11 79.5 77.5 73.5 72.0 105.0 163.5 Application Example 12 79.0 77.0 73.0 71.5 104.8 163.0 Application Example 13 81.0 79.0 75.0 73.0 105.8 164.2 Application Example 14 80.5 78.5 74.5 72.8 105.6 164.0 Application Example 15 80.2 78.2 74.2 72.6 105.4 163.8 Application Example 16 78.5 76.0 72.0 71.0 104.5 163.2 Application Example 17 78.0 75.0 71.0 70.5 104.0 162.5 Application Example 18 81.8 80.5 76.5 74.5 106.2 165.5 Application Example 19 80.0 78.5 74.0 73.2 105.0 163.0 Comparative Application Example 1 75.0 68.0 66.0 64.5 102.0 148.0 Comparative Application Example 2 74.5 67.0 65.5 64.0 101.5 147.0 Comparative Application Example 3 73.0 65.0 64.0 62.5 100.0 145.0 Comparative Application Example 4 72.0 64.0 63.0 61.5 99.5 144.0 Comparative Application Example 5 77.9 60.1 67.3 65.0 105.3 140.9

[0272] From Tables 1-2, it can be seen that:

[0273] In Examples 1, 4, 5, 8 and 9, the weight average molecular weight of the polymer material of the functional layer affected the film forming effect, interface adhesion and mechanical strength of the functional layer, and located in a suitable numerical range, so that the various properties of the functional layer reached a balance, greatly improved the thermal shrinkage rate of the composite separator, and further improved the electrochemical performance of the battery.

[0274] In Examples 1 and 10, when the thickness of the functional layer was relatively thick, the synergistic effect of various groups in the polymer material was reduced, which led to the decline of the performance of the composite separator, thereby affecting the electrochemical performance of the battery.

[0275] In Embodiment 1, Embodiment 11, Embodiment 12, Embodiment 13 and Embodiment 18, two different types and different structures of inorganic oxide materials are selected and combined in the functional layer, which is more conducive to realizing the function of organic-inorganic functional network on the basis of ensuring the performance of the polymer material, thereby improving the thermal shrinkage rate of the composite separator and the electrochemical performance of the battery.

[0276] In Embodiment 1, Embodiment 14 and Embodiment 15, when the particle sizes of the two inorganic oxide materials in the functional layer are consistent, the synergistic effect with the polymer material can still be played to a certain extent, but due to the influence of the particle size, the connection effect with each group in the polymer material is poor, which leads to the difficulty in eliminating the interface side reaction when contacting with the electrolyte, greatly affecting the performance of the composite separator and the final battery.

[0277] In Embodiment 1, Embodiment 6, Embodiment 7, Embodiment 16 and Embodiment 17, when the functional layer has two different inorganic oxide materials, the performance of the composite separator is more excellent, and the electrochemical performance of the battery is also significantly improved.

[0278] On the basis of Embodiment 1, in Application Example 1 and Application Example 19, when the negative electrode of the battery is a silicon-based negative electrode material, the composite separator of the present application further plays a role in inhibiting the expansion of silicon, and the interface compatibility between the separator and the negative electrode is more excellent.

[0279] In Embodiment 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 and Comparative Example 5, only when the composite separator has a functional layer and the functional layer contains a polymer material with a specific group combination, can the thermal shrinkage rate of the separator be effectively improved, the thermal stability thereof can be improved, and the performance of the battery can be greatly increased.

[0280] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and all such changes or replacements fall within the protection scope and disclosure scope of the present application.

Claims

1. A composite separator, characterized by, The composite diaphragm comprises a base film and a functional layer on at least one side surface of the base film, and the functional layer comprises a polymer material; The polymer material comprises an olefin polymer, and the olefin polymer comprises a thiazole ring group, an alkyl amino group and a ketone group.

2. The composite separator of claim 1, wherein The thickness of the functional layer is 1 μm to 5 μm; Preferably, the functional layer further comprises a binder; Preferably, the thickness of the base film is 6 μm to 12 μm; Preferably, the total thickness of the composite diaphragm is 7 μm to 16 μm; Preferably, the porosity of the composite diaphragm is 45% to 55%.

3. The composite separator of claim 1, wherein The weight average molecular weight of the polymer material is 70,000 to 150,000; Preferably, in the polymer material, the alkyl amino group comprises a dimethyl amino group and / or a methyl amino group; Preferably, in the polymer material, the molar ratio of the thiazole ring group, the ketone group and the alkyl amino group is (0.8 to 1):(0.5 to 1):(1 to 2). Preferably, the polymer material comprises poly(2E)-3-(dimethyl amino)-1-[4-methyl-2-(methyl amino)-5-thiazolyl]-2-propen-1-one.

4. The composite separator according to claim 1 or 3, characterized by The functional layer further comprises an inorganic oxide material; Preferably, the mass ratio of the polymer material to the inorganic oxide material is (20 to 35):(5 to 18).

5. The composite separator of claim 4, wherein The inorganic oxide material comprises a first inorganic oxide material and a second inorganic oxide material; the median particle size D50 of the first inorganic oxide material is smaller than the median particle size D50 of the second inorganic oxide material; Preferably, the median particle size D50 of the first inorganic oxide material is 5 nm to 15 nm; Preferably, the median particle size D50 of the second inorganic oxide material is 25 nm to 50 nm; Preferably, the second inorganic oxide material has a mesoporous structure, and the pore size of the mesoporous structure is 2 nm to 5 nm; Preferably, the mass ratio of the first inorganic oxide material to the second inorganic oxide material is 1:(1 to 2). Preferably, the first inorganic oxide material comprises MgO, and the second inorganic oxide material comprises ZnO.

6. A method of producing a composite separator as claimed in any one of claims 1 to 5, characterized in that, The preparation method comprises the following steps: Providing a functional layer slurry, and coating the functional layer slurry on at least one side surface of a base film to obtain the composite diaphragm; The functional layer slurry comprises a polymer material and a solvent.

7. The production method according to claim 6, characterized by, The functional layer slurry further comprises a binder; Preferably, the functional layer slurry further comprises an auxiliary agent, and the auxiliary agent comprises a wetting agent and a dispersing agent; Preferably, the functional layer slurry further comprises an inorganic oxide material; Preferably, the solvent comprises water and / or an organic solvent; Preferably, in the functional layer slurry, the mass ratio of the polymer material, the inorganic oxide material, the solvent, the wetting agent, the dispersing agent and the binder is (20 to 35):(5 to 18):(42 to 71):(0.02 to 0.08):(0.1 to 0.3):(2 to 6).

8. The production method according to claim 6 or 7, characterized by, The coating method comprises a microgravure printing method. Preferably, in the microgravure printing method, the line number of the anilox roller is 150 lines / cm to 200 lines / cm, the coating speed is 12 m / min to 32 m / min, the printing gap is 0.1 mm to 0.3 mm, and the doctor blade angle is 45° to 65°. Preferably, the coated film layer structure is subjected to a drying process, and the air speed in the drying process is 12 m / s to 25 m / s, and the winding tension after the drying process is 10 N / m to 15 N / m.

9. A lithium-ion battery, characterized by The lithium ion battery comprises a positive electrode, a negative electrode, an electrolyte and the composite separator according to any one of claims 1-5 or prepared by the preparation method according to any one of claims 6-8.

10. The lithium-ion battery of claim 9, wherein, The negative active material in the negative electrode comprises a silicon-based active material. Preferably, the electrolyte comprises an organic solvent and a main lithium salt. Preferably, the electrolyte further comprises an auxiliary lithium salt and / or an electrolyte additive. Preferably, the auxiliary lithium salt comprises a lithium sulfonylimide salt, and the mass percentage of the auxiliary lithium salt in the electrolyte is 1% to 3%. Preferably, the electrolyte additive comprises a phosphate additive and / or a low-resistance additive, and the mass percentage of the electrolyte additive in the electrolyte is 0.1% to 1.5%.