A highly flexible, heat-resistant composite battery separator, its preparation method and application

Abstract

This invention discloses a highly flexible, heat-resistant composite battery separator, its preparation method, and its application, belonging to the field of separator technology. It comprises a porous polymer base membrane, a flexible coating, and a high-temperature resistant coating. The raw materials for preparing the flexible coating include flexible particles, namely hydroxyl-terminated polybutadiene and carboxyl-terminated nitrile butadiene rubber. The preparation method includes the following steps: preparing the raw materials for the high-temperature resistant coating and the flexible coating into a high-temperature resistant coating and a flexible coating, respectively; sequentially coating the high-temperature resistant coating and the flexible coating onto the surface of the porous polymer base membrane, and drying to obtain the highly flexible, heat-resistant composite battery separator. This invention provides a highly flexible, heat-resistant composite battery separator with readily available raw materials and industrial feasibility by preparing self-healing flexible particles, achieving a synergistic improvement in flexibility, self-healing, and heat resistance. It effectively buffers the expansion of the positive and negative electrodes, resists lithium dendrite puncture, and reduces the risk of thermal runaway, significantly improving battery safety and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, specifically a highly flexible heat-resistant composite battery membrane, its preparation method, and its application. Background Technology

[0002] Currently, commercially available battery separators are mainly polyolefin-based membranes, which have advantages such as low cost and good air permeability. However, they have two major drawbacks: First, they have poor heat resistance. When the battery is locally overheated (e.g., above 120°C), they are prone to thermal shrinkage, which can lead to direct contact between the positive and negative electrodes, causing short circuits or even thermal runaway. Second, they lack flexibility. During the battery charge and discharge cycle, the volume expansion of the positive and negative electrodes will generate continuous mechanical stress on the separator, leading to separator rupture or coating peeling, and increasing the risk of dendrite puncture.

[0003] Currently, the industry typically improves heat resistance by coating the membrane with ceramic or high-temperature resistant polymers, which enhances the membrane's thermal stability. However, ceramic coatings are brittle, prone to peeling, and reduce the membrane's flexibility and permeability. To improve flexibility, flexible materials such as styrene-butadiene rubber and polyurethane are used for coating, which improves the membrane's impact resistance. However, these materials have poor resistance to electrolyte swelling, are prone to structural failure with long-term use, and lack self-healing capabilities, making them unable to cope with the minor damage caused by lithium dendrites. A dual-layer structure with a flexible and heat-resistant layer is also employed, but existing flexible and heat-resistant materials have poor compatibility, weak interfacial bonding, and lack a synergistic mechanism, making it difficult to simultaneously meet the multiple requirements of high flexibility, high heat resistance, and electrolyte resistance. Summary of the Invention

[0004] To overcome the aforementioned technical problems, this invention provides a highly flexible, heat-resistant composite battery separator, its preparation method, and its applications. By preparing self-healing flexible particles, this invention provides a highly flexible, heat-resistant composite battery separator with readily available raw materials and industrial feasibility. It achieves a synergistic improvement in flexibility, self-healing, and heat resistance, effectively buffering the expansion of the positive and negative electrodes, resisting lithium dendrite puncture, and reducing the risk of thermal runaway, significantly improving battery safety and cycle stability.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention discloses a highly flexible and heat-resistant composite battery separator, characterized in that it comprises: a porous polymer base membrane, a flexible coating, and a high-temperature resistant coating;

[0007] The flexible coating is prepared from flexible particles, which are hydroxyl-terminated polybutadiene and carboxyl-terminated nitrile butadiene rubber. The selection of flexible particles in this invention essentially utilizes the dynamic hydrogen bonding between hydroxyl and carboxyl groups to form a self-healing mechanism, thereby improving the membrane's flexibility.

[0008] According to some embodiments of the present invention, the porous polymer base membrane is polyethylene (PE), polypropylene (PP), polyamide (PA), polyimide (PI), or polyaramid (AR).

[0009] According to some embodiments of the present invention, the thickness of the porous polymer-based membrane is 2 micrometers to 20 micrometers.

[0010] According to some embodiments of the present invention, the porosity of the porous polymer-based membrane is 30% to 80%.

[0011] According to some embodiments of the present invention, the air permeability of the porous polymer-based membrane is 100 sec / 100 mL to 150 sec / 100 mL.

[0012] According to some embodiments of the present invention, the flexible coating comprises, by mass percentage, the following raw materials: 5%–40% flexible particles, 3%–10% additives, and the balance water;

[0013] According to some embodiments of the present invention, the high-temperature resistant coating comprises, by weight percentage: 1%–20% high-temperature resistant fiber, 5%–20% inorganic filler, 3%–10% additives, and the balance being water. The high-temperature resistant fiber forms a supporting skeleton, and the filler fills the gaps in the skeleton, ensuring both the coating's air permeability and improving its heat resistance.

[0014] According to some embodiments of the present invention, the mass ratio of the hydroxyl-terminated polybutadiene to the carboxyl-terminated nitrile rubber is 1~5:1, preferably 1~3:1.

[0015] According to some embodiments of the present invention, the hydroxyl value of the hydroxyl-terminated polybutadiene is 0.5 mmol / g to 0.7 mmol / g.

[0016] According to some embodiments of the present invention, the number-average molecular weight of the hydroxyl-terminated polybutadiene is 3000-4600.

[0017] According to some embodiments of the present invention, the viscosity of the hydroxyl-terminated polybutadiene is ≤8.5 Pa·s at 40°C.

[0018] According to some embodiments of the present invention, the carboxyl content of the terminal carboxyl nitrile rubber is 0.5 mmol / g to 0.65 mmol / g.

[0019] According to some embodiments of the present invention, the number average molecular weight of the carboxyl-terminated butadiene-acrylonitrile rubber is 2000~3500.

[0020] According to some embodiments of the present invention, the viscosity of the carboxyl-terminated nitrile rubber is 7 Pa·s to 50 Pa·s at 40°C.

[0021] According to some embodiments of the present invention, the acrylonitrile content of the carboxyl-terminated butadiene-acrylonitrile rubber is 8% to 20%.

[0022] According to some embodiments of the present invention, the high-temperature resistant fiber is alumina nanofiber, silicon carbide nanofiber, boron nitride nanofiber, silica nanofiber, chitin / chitosan nanofiber, cellulose fiber or aramid fiber; preferably, the high-temperature resistant fiber is silicon carbide nanofiber or boron nitride nanofiber.

[0023] According to some embodiments of the present invention, the average particle size of the high-temperature resistant fiber is 10nm~80nm, preferably 10nm~50nm.

[0024] According to some embodiments of the present invention, the inorganic filler is at least one selected from alumina, silicon dioxide, molecular sieve, hydrotalcite, diatomaceous earth, montmorillonite, titanium dioxide, and magnesium oxide; preferably alumina or silicon dioxide.

[0025] According to some embodiments of the present invention, the particle size of the inorganic filler is 20 nm to 100 nm.

[0026] According to some embodiments of the present invention, the additive is a wetting agent, a binder, a thickener, and a dispersant.

[0027] According to some embodiments of the present invention, the wetting agent is at least one of polyacrylate, polyether-modified silane surfactant, and fatty alcohol polyether wetting agent.

[0028] According to some embodiments of the present invention, the adhesive is polyvinylidene fluoride, polyvinyl alcohol, polyvinyl butyral, or polyvinylidene fluoride. One of the following: hexafluoropropylene, sodium alginate, lithium alginate, polymethacrylic acid, acrylic acid, carboxymethyl chitosan, polyethylene oxide, and styrene-butadiene rubber.

[0029] According to some embodiments of the present invention, the thickener is at least one of sodium cellulose, lithium cellulose, and polyvinylamide.

[0030] According to some embodiments of the present invention, the dispersant is one of lithium polyacrylate, sodium polyacrylate, and ammonium polyacrylate.

[0031] According to some embodiments of the present invention, the flexible coating comprises, by mass percentage, the following raw materials: 5% to 40% flexible particles, 1% to 4% binder, 1% to 4% thickener, 0.05% to 1% dispersant, 0.05% to 1% wetting agent, and the balance being water.

[0032] According to some embodiments of the present invention, the high-temperature resistant coating comprises, by mass percentage, the following raw materials: 1%~20% high-temperature resistant fiber, 5%~20% inorganic filler, 1%~4% binder, 1%~4% thickener, 0.05%~1% dispersant, 0.05%~1% wetting agent, and the balance being water.

[0033] According to some embodiments of the present invention, the flexible coating and the high-temperature resistant coating are located on the same side or opposite side of the porous polymer base film.

[0034] According to some embodiments of the present invention, when the flexible coating and the high-temperature resistant coating are located on the same side of the porous polymer base film, the layers from top to bottom are the porous polymer base film, the high-temperature resistant coating, and the flexible coating. When arranged on opposite sides, the flexible coating faces the negative electrode to buffer lithium dendrite penetration, and the high-temperature resistant coating faces the positive electrode to resist high-temperature shrinkage. When arranged on the same side, the high-temperature resistant coating forms the base layer, and the flexible coating covers it, also ensuring that the outermost flexible coating faces the negative electrode. The high-temperature resistant coating provides heat resistance support, and the flexible coating imparts surface elasticity, adapting to different battery structure requirements.

[0035] According to some embodiments of the present invention, the thickness of the flexible coating is 0.2 micrometers to 4 micrometers, preferably 0.5 micrometers to 2 micrometers;

[0036] According to some embodiments of the present invention, the thickness of the high-temperature resistant coating is 0.2 micrometers to 4 micrometers, preferably 0.5 micrometers to 2 micrometers.

[0037] According to some embodiments of the present invention, the air permeability of the highly flexible heat-resistant composite battery separator is ≥140 s / 100mL;

[0038] According to some embodiments of the present invention, at 180°C, the longitudinal thermal shrinkage rate of the highly flexible heat-resistant composite battery separator is ≤3.0%, preferably 2.0%~2.5%;

[0039] According to some embodiments of the present invention, at 180°C, the lateral thermal shrinkage rate of the highly flexible heat-resistant composite battery separator is ≤0.6%, preferably 0.4%~0.5%;

[0040] According to some embodiments of the present invention, the puncture strength of the highly flexible heat-resistant composite battery separator is ≥600gf, preferably 610gf~635gf.

[0041] This invention also discloses a method for preparing the aforementioned highly flexible heat-resistant composite battery separator, comprising the following steps:

[0042] The raw materials for preparing high-temperature resistant coatings and flexible coatings are respectively formulated into high-temperature resistant coatings and flexible coatings;

[0043] High-temperature resistant coating and flexible coating are sequentially applied to the surface of a porous polymer base membrane, and after drying, a highly flexible and heat-resistant composite battery separator is obtained.

[0044] The present invention also discloses the application of the aforementioned highly flexible heat-resistant composite battery separator or the highly flexible heat-resistant composite battery separator prepared by the aforementioned preparation method in secondary batteries, especially in lithium batteries.

[0045] Furthermore, the lithium battery includes a positive electrode, a separator, and a negative electrode, which are stacked or wound into a core in sequence, and then an electrolyte is injected into the core and sealed.

[0046] According to some embodiments of the present invention, when the flexible coating and the high-temperature resistant coating are located on opposite sides of the porous polymer base film, the flexible coating is connected to the negative electrode of the lithium battery, and the high-temperature resistant coating is connected to the positive electrode of the lithium battery.

[0047] According to some embodiments of the present invention, when the flexible coating and the high-temperature resistant coating are located on the same side of the porous polymer base film, they are arranged from top to bottom as the porous polymer base film, the high-temperature resistant coating, and the flexible coating.

[0048] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] This invention utilizes dynamic hydrogen bonds formed by the hydroxyl groups of hydroxyl-terminated polybutadiene and the carboxyl groups of carboxyl-terminated nitrile butadiene rubber. These hydrogen bonds can recombine after damage from external forces, achieving self-healing of the flexible coating. The flexible layer possesses high flexibility, self-healing properties, and electrolyte resistance, solving the problem of the traditional incompatibility between flexibility and stability in diaphragms. High-temperature resistant fibers form a supporting skeleton, and fillers fill the gaps in the skeleton, ensuring both the coating's air permeability and improved heat resistance.

[0051] The highly flexible, heat-resistant composite battery separator enhances its puncture resistance and toughness through a highly flexible coating. This ensures the separator remains intact under mechanical pressure during cell charging and discharging, as well as lithium dendrite extrusion, preventing thermal runaway. A high-temperature resistant coating further improves the separator's temperature resistance, ensuring it does not shrink at higher temperatures and thus preventing internal short circuits caused by separator thermal shrinkage.

[0052] The same-side / opposite-side layout of flexible coating and high-temperature resistant coating can synergistically improve heat resistance and mechanical strength to meet the needs of different battery structures.

[0053] During battery charging and discharging, the highly flexible coating can enhance the contact between the positive and negative electrodes due to its good toughness, which is beneficial to the transport of lithium ions and thus improves the battery's cycle performance. Attached Figure Description

[0054] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0055] Figure 1 This is a schematic diagram of the structure of the highly flexible heat-resistant composite battery separator in Example 1.

[0056] Figure 2 This is a schematic diagram of the structure of the highly flexible heat-resistant composite battery separator in Example 4.

[0057] Explanation of reference numerals in the attached figures:

[0058] 10: High-temperature resistant coating; 11: Porous polymer base film; 12: Flexible coating. Detailed Implementation

[0059] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0060] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0061] The raw material information used in the following examples is as follows:

[0062] Porous polymer-based membrane—polyethylene diaphragm, purchased from Yunnan Enjie New Material Co., Ltd., with a thickness of 7.6 micrometers, a porosity of 41%, and an air permeability of 140 sec / 100mL;

[0063] Hydroxyl-terminated polybutadiene was purchased from Hongyuan New Materials. Its hydroxyl value was 0.54 mmol / g to 0.64 mmol / g, viscosity at 40℃ was ≤8.5 Pa·s, and number-average molecular weight was 3300 to 4100.

[0064] The carboxyl-terminated nitrile butadiene rubber was purchased from Hongyuan New Materials. Its carboxyl value was 0.50 mmol / g to 0.65 mmol / g, its viscosity at 40℃ was 7 Pa·s to 10 Pa·s, and its number average molecular weight was 2000 to 3000.

[0065] The silicon carbide nanofibers were purchased from Bohuas Nanotechnology (Ningbo) Co., Ltd., and their average particle size (diameter) was 25±5nm.

[0066] Boron nitride nanofibers (sheet-like) were purchased from Suzhou Napo Materials Technology Co., Ltd., with an average particle size (thickness) of 10 nm.

[0067] The average particle size of alumina is 50 nm;

[0068] The silica was purchased from Hangzhou Jiupeng New Materials Co., Ltd., with an average particle size of 30±10 nm and a specific surface area of ​​150~300 m². 2 / g;

[0069] This includes, but is not limited to, the models from the above manufacturers.

[0070] Example 1

[0071] The highly flexible and heat-resistant composite battery separator of this embodiment consists of a 7.6-micron porous polymer base film 11, a 1-micron flexible coating 12, and a 2-micron high-temperature resistant coating 10; the flexible coating 12 and the high-temperature resistant coating 11 are located on both sides of the porous polymer base film 11, respectively. See [link to specific structure] for details. Figure 1 Schematic diagram.

[0072] The porous polymer-based membrane is a polyethylene diaphragm.

[0073] The raw materials for preparing the flexible coating, by mass percentage, are: 30% flexible particles, 2% binder, 2% thickener, 0.05% dispersant, 0.05% wetting agent, and the balance water.

[0074] The flexible particles are composed of hydroxyl-terminated polybutadiene and carboxyl-terminated nitrile butadiene rubber, wherein the ratio of hydroxyl-terminated polybutadiene to carboxyl-terminated nitrile butadiene rubber is 3:2.

[0075] The raw materials for preparing the high-temperature resistant coating, by mass percentage, are: 15% high-temperature resistant fiber (silicon carbide nanofiber), 15% inorganic filler (alumina), 2% binder, 2% thickener, 0.05% dispersant, 0.05% wetting agent, and the balance being water.

[0076] In this embodiment, the adhesive is polymethyl methacrylate;

[0077] In this embodiment, the dispersant is sodium polyacrylate (Guangzhou Rongdong New Materials).

[0078] In this embodiment, the thickener is sodium cellulose;

[0079] In this embodiment, the wetting agent is a polyether-modified silane surfactant (Cayman additive).

[0080] The preparation method of the highly flexible heat-resistant composite battery separator is as follows:

[0081] (1) Pretreatment of the base membrane: The porous polymer base membrane was ultrasonically cleaned in a 20% ethanol aqueous solution and then vacuum dried at 65~70℃ until the water content of the base membrane was ≤0.4%;

[0082] (2) Coating preparation: According to the above formula, the raw materials for the preparation of high temperature resistant coating and the raw materials for the preparation of flexible coating are mixed at 1500 rpm for 15 min, and then passed through a 1300 mesh nylon filter to obtain high temperature resistant coating and flexible coating respectively.

[0083] (3) Coating: A gravure coating machine is used to coat the flexible coating on one side of the pretreated base film at a coating speed of 6 m / min and a coating pressure of 0.4 MPa. The film is then dried with hot air at 85℃ for 20 min, and the moisture content of the flexible coating is controlled to be ≤0.9%. The high-temperature resistant coating is then coated on the other side of the pretreated base film at a coating speed of 6 m / min and a coating pressure of 0.4 MPa. The film is then dried with hot air at 100℃ for 20 min, and the moisture content of the high-temperature resistant coating is controlled to be ≤0.7%.

[0084] (4) Hot pressing curing: The diaphragm coated in (3) is hot pressed at 90℃ and 0.6MPa for 4 minutes, and then heated to 120℃ and 1.0MPa for 5 minutes; during the hot pressing process, argon gas protection at a flow rate of 5L / min is required.

[0085] Example 2

[0086] The difference between this embodiment and Embodiment 1 is as follows:

[0087] In this embodiment, the ratio of hydroxyl-terminated polybutadiene to carboxyl-terminated butadiene-acrylonitrile rubber is 2:1;

[0088] The other raw materials, steps and parameters are the same as in Example 1.

[0089] Example 3

[0090] The difference between this embodiment and Embodiment 1 is as follows:

[0091] In this embodiment, the ratio of hydroxyl-terminated polybutadiene to carboxyl-terminated butadiene-acrylonitrile rubber is 5:1.

[0092] The other raw materials, steps and parameters are the same as in Example 1.

[0093] Example 4

[0094] The difference between this embodiment and Embodiment 1 is as follows:

[0095] The raw materials for preparing the high-temperature resistant coating, by mass percentage, are: 15% high-temperature resistant fiber (boron nitride nanofiber), 15% inorganic filler (silicon oxide), 2% binder, 2% thickener, 0.05% dispersant, 0.05% wetting agent, and the balance being water.

[0096] The other raw materials, steps and parameters are the same as in Example 1.

[0097] Example 5

[0098] The difference between this embodiment and Embodiment 1 is as follows:

[0099] A schematic diagram of the highly flexible, heat-resistant composite battery separator in this embodiment is shown below. Figure 2 Its structure consists of a porous polymer base membrane 11, a high-temperature resistant coating 10, and a flexible coating 12, from top to bottom; the flexible coating 12 and the high-temperature resistant coating 10 are located on the same side of the porous polymer base membrane 11.

[0100] In this embodiment, during the coating process in step (3): a gravure coating machine is used to coat the high-temperature resistant coating onto one side of the pretreated base film at a coating speed of 6 m / min and a coating pressure of 0.4 MPa. The coating is then dried with hot air at 85°C for 20 min, and the moisture content of the high-temperature resistant coating is controlled to be ≤0.9%. A flexible coating is then coated onto the surface of the high-temperature resistant coating at a coating speed of 6 m / min and a coating pressure of 0.4 MPa. The coating is then dried with hot air at 100°C for 20 min, and the moisture content of the flexible coating is controlled to be ≤0.7%.

[0101] The other raw materials, steps and parameters are the same as in Example 1.

[0102] Example 6

[0103] The difference between this embodiment and Embodiment 1 is as follows:

[0104] The final thickness of the flexible coating is 2 micrometers, and the final thickness of the high-temperature resistant coating is 1 micrometer.

[0105] The other raw materials, steps and parameters are the same as in Example 1.

[0106] Comparative Example 1

[0107] The difference between this comparative example and Example 1 is as follows:

[0108] It does not contain a high-temperature resistant coating, therefore the coating process in step (3) does not involve applying a high-temperature resistant coating;

[0109] The other raw materials, steps and parameters are the same as in Example 1.

[0110] Comparative Example 2

[0111] The difference between this comparative example and Example 1 is as follows:

[0112] Since it does not contain a flexible coating, the coating process in step (3) also does not apply a flexible coating.

[0113] The other raw materials, steps and parameters are the same as in Example 1.

[0114] Comparative Example 3

[0115] The difference between this comparative example and Example 1 is as follows:

[0116] The raw materials for preparing the high-temperature resistant coating, by mass percentage, are: 15% high-temperature resistant fiber (boron nitride nanofiber), 2% binder, 2% thickener, 0.05% dispersant, 0.05% wetting agent, and the balance water.

[0117] The other raw materials, steps and parameters are the same as in Example 1.

[0118] Comparative Example 4

[0119] The difference between this comparative example and Example 1 is as follows:

[0120] The raw materials for preparing the high-temperature resistant coating, by mass percentage, are: 15% inorganic filler (silicon oxide), 2% binder, 2% thickener, 0.05% dispersant, 0.05% wetting agent, and the balance being water.

[0121] The other raw materials, steps and parameters are the same as in Example 1.

[0122] Test Example 1—Diaphragm Performance Test

[0123] The diaphragms prepared in the above embodiments and comparative examples were subjected to the following tests, and the test results are shown in Table 1.

[0124] (1) Air permeability test of diaphragm at different temperatures

[0125] Place the diaphragm in an oven at the set temperature for 5 minutes, then cut 3 pieces of the diaphragm, each sample measuring 100mm × 100mm. Place the diaphragm in the test head of an air permeability meter with a suitable test range for air permeability testing, and take the average of the 3 test results as the air permeability of the diaphragm.

[0126] (2) Test of the heat shrinkage performance of the diaphragm

[0127] Mark the longitudinal and transverse lengths of the diaphragm, measure the longitudinal and transverse lengths of the sample respectively, then place the diaphragm flat in a forced-air constant temperature chamber and maintain it at 180℃ for 1 hour. Measure the longitudinal (MD) and transverse (TD) lengths of the sample again, and use the formula S(%)=(L) i -L f ) / L i The thermal shrinkage rate of the diaphragm sample is calculated by multiplying by 100%, where S is the thermal shrinkage rate and L is the thermal shrinkage rate. i L is the length of the diaphragm before heat treatment. f This refers to the length of the diaphragm after heat treatment.

[0128] (3) Test of the needle penetration strength of the diaphragm

[0129] The diaphragm is fixed in the fixture, and a certain puncture rate (50 mm / min) is set to test the diaphragm puncture strength. A 100 mm × 100 mm diaphragm sample is cut and fixed flat on the test fixture (fixture hole diameter 20 mm). The equipment is started, and the puncture needle punctures the diaphragm vertically. The maximum force value during the puncture process is recorded in gf. Each sample is tested at least 5 different positions. After removing outliers, the average value is taken as the final result.

[0130]

[0131] Test Example 2—Performance Testing of Assembled Batteries

[0132] The highly flexible, heat-resistant composite battery separators prepared in the above embodiments and comparative examples were used to fabricate 280Ah lithium-ion square aluminum-cased batteries using a winding process. The positive electrode material was lithium iron phosphate, and the negative electrode was artificial graphite. During fabrication, the flexible coating faced the negative electrode. The positive electrode sheet, separator, and negative electrode sheet were stacked sequentially, with the separator positioned between the positive and negative electrodes for isolation, and then wound to obtain a bare cell. The bare cell was placed in an outer packaging, injected with prepared electrolyte, and then subjected to processes such as encapsulation, electrolyte injection, formation, and venting to obtain the battery. The safety performance of the above battery was tested, and the test results are shown in Table 2.

[0133] (1) Battery internal short circuit performance test: The blunt needle test method is used to test the battery cell. A blunt needle with a diameter of 1 / 4 inch is used to squeeze the cell until a 500 mV drop in the cell open circuit voltage is detected. Record whether the cell has thermal runaway and the highest temperature reached during thermal runaway.

[0134] (2) Cyclic performance and energy efficiency testing:

[0135] Step 1: Let the battery stand at 25°C for 30 minutes, discharge it to 2.5V at 0.5P, and let it stand at 25°C for 30 minutes.

[0136] Step 2: Charge the battery to 3.65V at a constant power of 0.5P, let it rest for 30 minutes at 25℃, then discharge it to 2.5V at a constant power of 0.5P, and let it rest for 30 minutes at 25℃. Repeat Step 2 for 1000 cycles, and record the cycle capacity retention and energy efficiency of the battery after 1000 cycles.

[0137] The capacity retention rate CR (%) after n battery cycles = discharge capacity of the nth cycle / discharge capacity of the first cycle × 100%.

[0138]

[0139] Based on the above test results, we can conclude that:

[0140] In Comparative Example 1, when the separator only has a highly flexible coating and no high-temperature resistant coating as thermal support, the flexible coating alone causes slight blockage of the pores; the thermal shrinkage rate of the separator increases significantly and the thermal shrinkage performance deteriorates. When the battery is punctured, the separator will shrink at a relatively low temperature, causing a short circuit between the positive and negative electrodes and triggering thermal runaway of the battery. The highest temperature of thermal runaway reaches over 400°C.

[0141] In Comparative Example 2, when the separator only has a high-temperature resistant coating and no high-flexibility coating, the puncture resistance of the separator deteriorates significantly. When the battery is punctured, the battery temperature reaches over 400°C, resulting in thermal runaway. Furthermore, during the cycle, the positive and negative electrode contacts deteriorate due to the expansion and contraction of the positive and negative electrode plates, leading to poor battery cycle performance.

[0142] Comparative Examples 3 and 4 show that when the high-temperature resistant coating of the separator contains only nano high-temperature resistant fiber components or only porous inorganic material components, the thermal shrinkage performance of the separator will also deteriorate. When the battery is punctured, the battery temperature reaches above 390°C, and thermal runaway occurs.

[0143] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this invention. It should be understood that the above descriptions are merely specific embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A highly flexible, heat-resistant composite battery separator, characterized in that, include: Porous polymer-based membranes, flexible coatings, and high-temperature resistant coatings; The raw materials for preparing the flexible coating include flexible particles, which are hydroxyl-terminated polybutadiene and carboxyl-terminated butadiene-acrylonitrile rubber.

2. The highly flexible, heat-resistant composite battery separator as described in claim 1, characterized in that, The porous polymer base membrane is made of polyethylene, polypropylene, polyamide, polyimide, or polyaramid. And / or, the thickness of the porous polymer-based membrane is 2 micrometers to 20 micrometers; And / or, the porosity of the porous polymer-based membrane is 30% to 80%; And / or, the air permeability of the porous polymer-based membrane is 100~150 sec / 100 ml.

3. The highly flexible, heat-resistant composite battery separator as described in claim 2, characterized in that, The flexible coating comprises, by weight percentage, the following raw materials: 5%–40% flexible particles, 3%–10% additives, and the balance water; And / or, by mass percentage, the high-temperature resistant coating comprises the following raw materials: 1%–20% high-temperature resistant fiber, 5%–20% inorganic filler, 3%–10% additives, and the balance being water.

4. The highly flexible, heat-resistant composite battery separator as described in claim 3, characterized in that, The mass ratio of the hydroxyl-terminated polybutadiene to the carboxyl-terminated butyronitrile rubber is 1~5:1; And / or, the hydroxyl value of the terminal hydroxyl polybutadiene is 0.5 mmol / g to 0.7 mmol / g; And / or, the number-average molecular weight of the hydroxyl-terminated polybutadiene is 3000~4600; And / or, at 40°C, the viscosity of the hydroxyl-terminated polybutadiene is ≤8.5 Pa·s; And / or, the carboxyl content of the terminal carboxyl acrylonitrile rubber is 0.5 mmol / g to 0.65 mmol / g; And / or, the number average molecular weight of the terminal carboxyl acrylonitrile rubber is 2000~3500; And / or, at 40°C, the viscosity of the end-carboxyl nitrile rubber is 7 Pa·s to 50 Pa·s; And / or, the acrylonitrile content of the carboxyl-terminated butadiene-acrylonitrile rubber is 8%~20%; And / or, the high-temperature resistant fiber is alumina nanofiber, silicon carbide nanofiber, boron nitride nanofiber, silicon oxide nanofiber, chitin / chitosan nanofiber, cellulose fiber or aramid fiber; And / or, the average particle size of the high-temperature resistant fiber is 10nm~80nm; And / or, the inorganic filler is at least one of alumina, silica, molecular sieve, hydrotalcite, diatomaceous earth, montmorillonite, titanium dioxide and magnesium oxide; And / or, the particle size of the inorganic filler is 20nm~100nm.

5. The highly flexible, heat-resistant composite battery separator as described in claim 4, characterized in that, The additives are wetting agents, binders, thickeners, and dispersants; And / or, the wetting agent is at least one of polyacrylate, polyether-modified silane surfactant, and fatty alcohol polyether wetting agent; And / or, the adhesive is polyvinylidene fluoride, polyvinyl alcohol, polyvinyl butyral, or polyvinylidene fluoride. One of the following: hexafluoropropylene, sodium alginate, lithium alginate, polymethacrylic acid, acrylic acid, carboxymethyl chitosan, polyethylene oxide, and styrene-butadiene rubber; And / or, the thickener is at least one of sodium cellulose, lithium cellulose, and polyvinylamide; And / or, the dispersant is one of lithium polyacrylate, sodium polyacrylate, and ammonium polyacrylate.

6. The highly flexible, heat-resistant composite battery separator as described in claim 5, characterized in that, The flexible coating comprises, by weight percentage, the following raw materials: 5%~40% flexible particles, 1%~4% binder, 1%~4% thickener, 0.05%~1% dispersant, 0.05%~1% wetting agent, and the balance being water; The high-temperature resistant coating comprises, by weight percentage, the following raw materials: 1%~20% high-temperature resistant fiber, 5%~20% inorganic filler, 1%~4% binder, 1%~4% thickener, 0.05%~1% dispersant, 0.05%~1% wetting agent, and the balance being water.

7. The highly flexible, heat-resistant composite battery separator as described in claim 1, characterized in that, The flexible coating and the high-temperature resistant coating are located on the same side or opposite side of the porous polymer base film; And / or, when the flexible coating and the high-temperature resistant coating are located on the same side of the porous polymer base film, they are arranged in the following order: porous polymer base film, high-temperature resistant coating, and flexible coating; And / or, the thickness of the flexible coating is 0.2 micrometers to 4 micrometers; And / or, the thickness of the high-temperature resistant coating is 0.2 micrometers to 4 micrometers.

8. The highly flexible, heat-resistant composite battery separator as described in claim 1, characterized in that, At least one of the following conditions a to d must be met: a. The air permeability of the highly flexible heat-resistant composite battery separator is ≥140s / 100mL; b. At 180℃, the longitudinal thermal shrinkage rate of the highly flexible heat-resistant composite battery separator is ≤3.0%; c. At 180℃, the lateral thermal shrinkage rate of the highly flexible heat-resistant composite battery separator is ≤0.6%; d. The puncture strength of the highly flexible heat-resistant composite battery separator is ≥600gf.

9. A method for preparing a highly flexible, heat-resistant composite battery separator, characterized in that, The method for preparing the highly flexible, heat-resistant composite battery separator as described in any one of claims 1 to 8 comprises the following steps: The raw materials for preparing high-temperature resistant coatings and flexible coatings are respectively formulated into high-temperature resistant coatings and flexible coatings; High-temperature resistant coating and flexible coating were respectively applied to the surface of a porous polymer base membrane, and after drying, a highly flexible and heat-resistant composite battery separator was obtained.

10. The application of the highly flexible heat-resistant composite battery separator as described in any one of claims 1 to 8 or the highly flexible heat-resistant composite battery separator prepared by the preparation method as described in claim 9 in secondary batteries.

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