High-thermal-conductivity base film and preparation process thereof

Abstract

The invention discloses a high-thermal-conductivity base membrane and a preparation process thereof, and belongs to the field of lithium battery diaphragms. The high-thermal-conductivity base film comprises a polyolefin base film and a polyether-ether-ketone melt-blown film arranged on at least one side of the polyolefin base film; the polyether-ether-ketone melt-blown film has a three-dimensional network structure; the gram weight of the polyether-ether-ketone melt-blown film is 0.6 to 3.5 g / m < 2 >; the thickness of the high-thermal-conductivity base film is 8.0-11.0 mu m, and the porosity of the high-thermal-conductivity base film is 30-40%. The high-thermal-conductivity base film provided by the invention has the advantages of small thickness and excellent thermal conductivity.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery separator technology, and more specifically, relates to a high thermal conductivity base film and its preparation process. Background Technology

[0002] Lithium-ion batteries are widely used in power batteries, 3C digital products, and energy storage due to their high energy density and long lifespan. In recent years, however, new technologies such as semi-solid-state batteries, solid-state batteries, hydrogen energy, and sodium-ion batteries have emerged, posing challenges to lithium-ion batteries. Throughout their development, lithium-ion battery safety incidents have occurred frequently, not only hindering their development but, more importantly, threatening consumers' lives and property. Most lithium-ion battery safety incidents involve fires and explosions caused by thermal runaway. Therefore, preventing and suppressing thermal runaway has become a primary task for the lithium battery industry.

[0003] During normal use, lithium-ion batteries generate heat due to the electrochemical reactions of lithium ion insertion / extraction at the positive and negative electrodes, the flow of current through resistive battery materials, the voltage drop between the average terminal voltage and open-circuit voltage, and internal side reactions. This heat rises the battery temperature and can eventually induce thermal runaway. Modes that can lead to thermal runaway include: mechanical abuse, such as puncture or crushing; electrical abuse, such as external short circuits or overcharging / discharging; and thermal abuse, such as high and low temperature environments or lateral heating. Thermal runaway in individual lithium-ion battery cells can propagate through heat conduction via the battery casing and connectors, thermal convection of high-temperature gases, and thermal radiation, potentially causing fires or explosions. From the perspective of the battery pack, the propagation of thermal runaway can be suppressed through air cooling, liquid cooling, phase change cooling, high thermal conductivity materials, thermal insulation materials, or a combination of thermal management technologies. From the perspective of individual battery cells, thermal runaway can be suppressed through the electrolyte, positive and negative electrode materials, and separator materials. In electrolyte systems, methods such as adding flame retardants and using ionic liquids or polymer electrolytes can be employed. Both positive and negative electrode materials, as well as separator materials, can be modified through surface treatment to improve their high-temperature resistance. In recent years, improving the thermal conductivity of battery material systems has become a hot topic in mitigating battery thermal runaway. While there has been relevant research on positive and negative electrode materials and electrolytes, less attention has been paid to the thermal conductivity of battery separators.

[0004] Heat accumulation is one of the most serious safety concerns in battery systems. The separator, a crucial battery component, serves as both a heat carrier and a heat dissipation channel. However, most battery separators are made of polyolefin materials, a type of plastic primarily composed of polymers. Unlike metal ions in metal oxides, which can transfer energy more quickly, polymer molecules are relatively far apart, limiting the transfer speed and resulting in relatively poor thermal conductivity. Poor separator thermal conductivity prevents timely heat dissipation during use, leading to heat accumulation within the battery system. This poses a risk of thermal runaway when the separator is subjected to mechanical or thermal abuse. Existing technologies often use coatings to modify the separator, but these coatings frequently suffer from powder shedding, resulting in unstable separator performance. Some existing technologies involve using polyetheretherketone (PEEK) to improve the thermal conductivity of polyolefin-based films.

[0005] Chinese patent document publication number CN109659468A discloses a composite separator with thermal insulation function. It uses a polyolefin porous membrane as a substrate, and at least one heat-resistant coating is applied to the surface of this substrate using a phase inversion method to form a composite porous membrane. This prior art provides a composite separator for lithium-ion batteries with high heat resistance, improving battery safety. For example, in Example 5, polybenzimidazole and sulfonated polyether ether ketone are coated onto the polyolefin separator through impregnation, followed by ethanol impregnation and curing to form a porous membrane, resulting in a composite separator with a coating thickness of 5 μm. However, the improvement in thermal performance cannot be achieved by impregnation of sulfonated polyether ether ketone alone, which requires the combined use of polybenzimidazole or polyimide to achieve the claimed technical effect. The prior art has a relatively thick coating, increasing the thickness of the separator, and the ethanol impregnation step is required to create pores in the coating, making the process more complex.

[0006] Chinese patent publication CN108807822A discloses a high-safety lithium-ion battery separator, employing a polyetheretherketone / polyolefin / polyetheretherketone structure with ceramic coatings on both the top and bottom surfaces. Polyetheretherketone possesses physicochemical properties such as high temperature resistance and chemical corrosion resistance, with a melting point of 334℃ and a tensile strength of 132MPa to 148MPa. In the event of thermal runaway, the polyolefin layer melts, blocking the current. Due to the high melting point of polyetheretherketone, the polyetheretherketone layer does not melt, effectively preventing short circuits caused by contact between the positive and negative electrodes. Furthermore, the inherent flame-retardant properties, high-temperature resistance, corrosion resistance, chemical stability, and mechanical strength of polyetheretherketone significantly improve the safety performance of the battery cell. The ceramic coating layers on both the top and bottom surfaces of the separator can further improve the separator's heat resistance, wettability, and liquid absorption and retention capacity, thereby improving the battery's electrical performance. Simultaneously, the ceramic coating layer can further enhance the battery's safety performance. However, in this prior art, to achieve optimal safety performance, the minimum thickness of each of the top and bottom polyetheretherketone (PEEK) layers is 2 μm, with a total PEEK thickness of at least 4 μm. This significantly impacts the separator's thickness, resulting in an overall separator thickness of approximately 20 μm, and further ceramic layers are still needed to improve the separator's heat resistance.

[0007] However, when these existing technologies use polyetheretherketone (PEEK) to improve the heat resistance of the diaphragm, on the one hand, they all require a thicker PEEK layer to improve the heat resistance of the diaphragm, or add a coating or other substances to improve the heat resistance of the diaphragm on the basis of PEEK. On the other hand, the diaphragm itself is thick, which will greatly increase the overall thickness of the diaphragm. Summary of the Invention

[0008] 1. The problem to be solved

[0009] In recent years, battery separators have been trending towards thinner and stronger designs. Major battery separator manufacturers are developing base films of 5μm, 4μm, and even 3μm. The thinner the separator, the higher the relative content of active materials that can be stored inside the battery. Currently, the base films used in 3C products are relatively thin, such as 3μm; while there is a trend towards using 5μm base films in power batteries. In actual production, thinner films are more difficult to manufacture, have a higher probability of breakage during the stretching process, and a lower yield. Furthermore, thicker separators have higher resistance, which is detrimental to the battery's charge and discharge efficiency.

[0010] Based on this, the first objective of the present invention is to address the problem that when polyetheretherketone (PEEK) is used to improve the heat resistance of a diaphragm in the prior art, the thickness of the diaphragm is greatly increased due to the thicker PEEK coating. The present invention provides a high thermal conductivity base film by hot-pressing a PEEK meltblown film with a three-dimensional network structure onto the surface of a polyolefin base film, thereby improving the thermal conductivity of the diaphragm, while the overall thickness of the diaphragm is not higher than 11 μm.

[0011] Based on the first objective of this invention, this invention further provides a process for preparing a high thermal conductivity base film. By controlling the moving speed of the polyolefin base film placed on the forming screen, a polyether ether ketone meltblown film of ideal thickness is obtained, and a high thermal conductivity base film of ideal thickness is further obtained.

[0012] 2. Technical Solution

[0013] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0014] [High thermal conductivity base film]

[0015] This technical solution utilizes a melt-blowing process to fabricate a three-dimensional network structure membrane material from polyetheretherketone (PEEK), which has high thermal conductivity, and then laminates it onto the surface of a polyolefin membrane. This lamination method results in a more stable and uniform pore structure in the separator. The melt-blowing process allows for control over the thickness of the PEEK membrane, enabling the composite separator to achieve high thermal conductivity at a relatively low thickness, thus avoiding a reduction in the relative content of active materials in the battery system due to excessive membrane thickness. In contrast, composite separators obtained by coating and modifying polyolefin membranes through impregnation often suffer from powder shedding, and the impregnation method reduces the porosity of the polyolefin membrane, which is detrimental to the electrochemical performance of the battery separator.

[0016] The first aspect of this invention provides a high thermal conductivity base film, comprising:

[0017] Polyolefin-based films; and

[0018] A polyetheretherketone meltblown film disposed on at least one side of the polyolefin-based film;

[0019] The polyetheretherketone meltblown film has a three-dimensional network structure;

[0020] The basis weight of the polyetheretherketone meltblown film is 0.6–3.5 g / m³. 2 ;

[0021] The thickness of the high thermal conductivity base film is 7.5–11.0 μm, and the porosity is 30–41%.

[0022] The inventors discovered that polyetheretherketone (PEEK) possesses high temperature resistance, high mechanical strength, and insulation properties. The thermal conductivity of PEEK can compensate for the insufficient thermal conductivity of thermoplastics, rapidly dissipating heat from the battery system and effectively preventing internal overheating, thus improving the safety of the battery separator. To improve the thermal conductivity of the separator while minimizing its thickness, this invention employs a strategy of loading a PEEK meltblown film with a three-dimensional network structure onto the surface of a polyolefin-based membrane. In the three-dimensional network structure of the PEEK meltblown film, PEEK is interwoven in a fibrous form, which both conducts heat and promotes heat dissipation, improving the thermal conductivity per unit mass of PEEK while having minimal impact on the porosity of the polyolefin separator itself. Furthermore, using the three-dimensional network structure formed by melt spinning highly thermally conductive PEEK as a composite layer of the polyolefin-based membrane avoids the problem of powder shedding from the coated separator.

[0023] As a preferred embodiment of the high thermal conductivity base film in any of the first aspects of the present invention, the fiber diameter in the three-dimensional network structure of the polyether ether ketone meltblown film is 0.5 to 0.8 μm.

[0024] Heat transfer within the battery is primarily achieved through thermal conduction, with polyetheretherketone (PEEK) fibers dissipating heat and preventing its accumulation, thus improving safety. Furthermore, the PEEK layer forms directly on the base film surface. Due to the three-dimensional network structure of the PEEK meltblown film, with fiber diameters of only 0.5–0.8 μm, it exhibits superior thermal conductivity compared to other structures. This ensures that the composite separator, within a relatively small thickness range, possesses higher thermal conductivity than polyethylene separators while simultaneously reducing the relative content of active materials within the battery.

[0025] Unlike impregnation coatings that affect porosity and air permeability, the three-dimensional network structure of the polyetheretherketone layer gives it a pore structure similar to that of polyolefin membranes, but with a larger pore size. When laminated onto the surface of a polyolefin membrane, it neither blocks the pores of the base membrane nor affects the air permeability.

[0026] As a preferred embodiment of the high thermal conductivity base film in any of the first aspects of the present invention, the thickness of the polyetheretherketone meltblown film is 1.0 to 3.5 μm.

[0027] Preferably, the thickness of the polyetheretherketone meltblown film is selected from the group consisting of:

[0028] 1.0~3.4μm, 1.0~3.2μm, 1.0~3.0μm, 1.0~2.8μm, 1.0~2.5μm, 1.0~2.2μm, 1.0~2.0μm, 1.0~1.8μm, 1.0~1.5μm;

[0029] 1.2~3.4μm, 1.2~3.2μm, 1.2~3.0μm, 1.2~2.8μm, 1.2~2.5μm, 1.2~2.2μm, 1.2~2.0μm, 1.2~1.8μm, 1.2~1.5μm;

[0030] 1.5~3.4μm, 1.5~3.2μm, 1.5~3.0μm, 1.5~2.8μm, 1.5~2.5μm, 1.5~2.2μm, 1.5~2.0μm, 1.5~1.8μm;

[0031] 1.8~3.4μm, 1.8~3.2μm, 1.8~3.0μm, 1.8~2.8μm, 1.8~2.5μm, 1.8~2.2μm, 1.8~2.0μm;

[0032] 2.0~3.4μm, 2.0~3.2μm, 2.0~3.0μm, 2.0~2.8μm, 2.0~2.5μm, 2.0~2.2μm;

[0033] 2.2~3.4μm, 2.2~3.2μm, 2.2~3.0μm, 2.2~2.8μm, 2.2~2.5μm;

[0034] 2.5~3.4μm, 2.5~3.2μm, 2.5~3.0μm, 2.5~2.8μm;

[0035] 2.8~3.4μm, 2.8~3.2μm, 2.8~3.0μm.

[0036] Most preferably, the thickness of the polyetheretherketone meltblown film is selected from 1.0 to 2.0 μm, 1.0 to 1.8 μm, and 1.0 to 1.5 μm.

[0037] The polyetheretherketone (PEEK) layer is a three-dimensional network structure formed by fibers with a small diameter and is formed directly on the surface of the base film. Therefore, even if its thickness is thin, for example, 1.0 to 2.0 μm, it still has high thermal conductivity.

[0038] As a preferred embodiment of the high thermal conductivity base film in any aspect of the present invention, the ratio of the thickness of the polyolefin base film to the thickness of the polyether ether ketone meltblown film is (5-10):(0.1-4), preferably (5-10):(1-4), more preferably (6-8):(1-4), and even more preferably (7-8):(1-3.5). Due to the excellent thermal conductivity of polyetheretherketone (PEEK), increasing the thickness of the PEEK meltblown film is beneficial to improving the thermal conductivity of the high thermal conductivity base film. Furthermore, because PEEK has high strength and low thermal shrinkage, increasing the thickness of the PEEK meltblown film also helps to improve the puncture strength, MD tensile strength, and TD tensile strength of the high thermal conductivity base film, and helps to reduce the MD and TD thermal shrinkage rates of the high thermal conductivity base film. However, increasing the thickness of the PEEK meltblown film will adversely affect the porosity and air permeability of the base film. Therefore, provided that the porosity and air permeability of the high thermal conductivity base film are within an acceptable range, a higher thickness of the PEEK meltblown film results in better thermal conductivity of the high thermal conductivity base film.

[0039] As a preferred embodiment of the high thermal conductivity base film in any aspect of the present invention, the weight ratio of the polyolefin base film to the polyetheretherketone meltblown film is (3-5):(0.1-3.6), more preferably (4-5):(0.5-3.2). Generally, the weight of the polyetheretherketone meltblown film is positively correlated with its thickness; the thicker the polyetheretherketone meltblown film, the heavier the weight per square meter. However, since excessive thickness of the polyetheretherketone meltblown film will adversely affect the porosity and permeability of the high thermal conductivity base film, while pursuing a high thermal conductivity base film, the weight ratio of the polyolefin base film to the polyetheretherketone meltblown film should be limited to a certain range, taking into account porosity and permeability.

[0040] Preferred high thermal conductivity base film as any embodiment of the first aspect of the present invention:

[0041] The polyolefin-based film is a polyethylene-based film;

[0042] The polyethylene-based film has a thickness of 6.5–7.5 μm;

[0043] The porosity of the polyethylene-based film is 35-41%.

[0044] Preferred high thermal conductivity base film as any embodiment of the first aspect of the present invention:

[0045] The basis weight of the high thermal conductivity base film is 4.8 g / m³. 2 ~7.5g / m 2 ; and / or

[0046] The thermal conductivity of the high thermal conductivity base film is not less than 0.06 W / (m·K); and / or

[0047] The air permeability of the high thermal conductivity base film is 150–200 sec / 100cc; and / or

[0048] The high thermal conductivity base film has a MD thermal shrinkage rate of no more than 2.0% and a TD thermal shrinkage rate of no more than 1.5%; and / or

[0049] The high thermal conductivity base film has a MD tensile strength of not less than 3000 kgf and a TD tensile strength of not less than 3000 kgf; and / or

[0050] The puncture strength of the high thermal conductivity base film is not less than 400 gf.

[0051] As a preferred embodiment of the high thermal conductivity base film in any of the first aspects of the present invention, the polyetheretherketone meltblown film uses polyetheretherketone manufactured by Shandong Junhao, with product model PEEK5600CF30 particles.

[0052] As a preferred embodiment of the high thermal conductivity base film in any of the first aspects of the present invention, the polyolefin base film is a polyethylene base film; preferably, the viscosity-average molecular weight of the polyethylene raw material of the polyethylene base film is 1 million to 2 million; preferably, the viscosity-average molecular weight of the polyethylene raw material of the polyethylene base film is 1.3 million to 1.5 million.

[0053] [Preparation process of high thermal conductivity base film]

[0054] The second aspect of this invention provides a process for preparing the high thermal conductivity substrate film according to any one of the first aspects of this invention, comprising the following steps:

[0055] S1 provides polyolefin-based films;

[0056] S2 Place the polyolefin-based film on a forming curtain, the forming curtain moving at a speed of 3-10 m / min, and the polyolefin-based film moving with the forming curtain; provide a polyetheretherketone meltblown film on the moving polyolefin-based film;

[0057] S3 involves calendering the polyolefin-based film and the polyether ether ketone meltblown film to obtain a high thermal conductivity base film.

[0058] The preparation process of the present invention fixes the prepared polyolefin-based film on a forming screen, and collects the refined polyether ether ketone fibers directly on the surface of the polyolefin-based film on the forming screen, and forms a mesh-like polyether ether ketone meltblown film by relying on the self-adhesion of the polyether ether ketone fibers.

[0059] As a preferred embodiment of the high thermal conductivity base film preparation process of the second aspect of the present invention, the step of providing the polyetheretherketone meltblown film in S2 includes the following steps:

[0060] S2.1 A twin-screw extruder is used to melt high thermal conductivity polyetheretherketone to obtain a melt;

[0061] S2.2 A metering pump is used to quantitatively deliver the melt to the die head;

[0062] S2.3 The melt is passed through the spinneret holes on the surface of the die head spinneret to form a melt stream. Under the action of the stretching airflow, the melt is refined into fibers. The fibers form a polyether ether ketone meltblown film with a three-dimensional network structure on the moving polyolefin base film.

[0063] Preferred process for preparing the high thermal conductivity base film according to any embodiment of the second aspect of the present invention:

[0064] In step S2.1, the high thermal conductivity polyetheretherketone is gradually and fully melted through a temperature gradient:

[0065] The twin-screw extruder has a total temperature range of 220–400℃. Specifically, it features gradient temperature zones: Feeding Zone 1: 220–240℃, Zone 2: 240–260℃, Zone 3: 260–280℃, ensuring uniform entry of high thermal conductivity polyetheretherketone (PEEK) into the extruder without melting, thus preventing feed clogging and backflow; Melt mixing zone: Zone 4: 320–340℃, Zone 5: 340–360℃, Zone 6: 360–380℃, Zone 7: 380–400℃, Zone 8: 380–400℃, Zone 9: 380–400℃, Zone 10: 380–400℃; Filtration device: 380–400℃.

[0066] The filtration device can remove impurities from the melt to prevent clogging of the spinneret orifice. The pressure of the melt after filtration is 1.5 MPa to 3.0 MPa.

[0067] Preferably, in step S2.1:

[0068] The twin-screw extruder is set with gradient temperature ranges as follows: Feeding section: Zone 1: 220℃, Zone 2: 250℃, Zone 3: 250℃, to ensure that the high thermal conductivity polyether ether ketone enters the extruder evenly and does not melt, avoiding material blockage and backflow at the feed inlet; Melt mixing section: Zone 4: 320℃, Zone 5: 340℃, Zone 6: 360℃, Zones 7-10: 380℃; Filtering device: 380℃.

[0069] Preferably, in step S2.1, the pressure of the melt after filtration by the filtration device is 1.6 MPa.

[0070] As a preferred embodiment of the high thermal conductivity base film preparation process according to any aspect of the second aspect of the present invention, in step S2.2:

[0071] The metering pump temperature is 380~400℃, and the metering pump speed is 15~20r / min.

[0072] Preferably, in step S2.2, the metering pump temperature is 380℃ and the metering pump speed is 15 r / min.

[0073] As a preferred embodiment of the high thermal conductivity base film preparation process according to any aspect of the second aspect of the present invention, in step S2.3:

[0074] Die head: 380~400℃; Distance from die head to receiving screen: 10~20cm.

[0075] Preferably, in step S2.3, the die head temperature is 380°C.

[0076] Preferably, in step S2.3: the receiving distance from the mold head to the net curtain is 15cm, and the suction frequency under the net is 30Hz.

[0077] More preferably, the forming speed of the screen is 3 to 9.5 m / min to obtain a high thermal conductivity polyether ether ketone meltblown film.

[0078] Most preferably, the forming speed of the net curtain is selected from the group consisting of:

[0079] 3~9m / min, 3~8m / min, 3~7m / min, 3~6m / min, 3~5m / min, 3~4m / min;

[0080] 4~9m / min, 4~8m / min, 4~7m / min, 4~6m / min, 4~5m / min;

[0081] 5~9m / min, 5~8m / min, 5~7m / min, 5~6m / min;

[0082] 6~9m / min, 6~8m / min, 6~7m / min;

[0083] 7~9m / min, 7~8m / min

[0084] 8~9m / min.

[0085] As a preferred embodiment of the high thermal conductivity base film preparation process of any aspect of the present invention, in step S3:

[0086] Calendering temperature: 120℃~150℃, pressure: 1MPa to 1.5MPa, calendering speed: 3~5m / min.

[0087] Preferably, in step S3, the calendering temperature is 120°C, the pressure is 1.5 MPa, and the calendering speed is 3 m / min.

[0088] As a preferred embodiment of the high thermal conductivity base film preparation process in any of the second aspects of the present invention, the polyetheretherketone meltblown film uses polyetheretherketone produced by Shandong Junhao, with product model PEEK5600CF30 particles.

[0089] As a preferred embodiment of the preparation process of the high thermal conductivity base film in any of the second aspects of the present invention, the polyetheretherketone has a melting point of 334±5℃.

[0090] In a preferred embodiment of the high thermal conductivity base film preparation process of the second aspect of the present invention, the polyolefin base film is a polyethylene base film; preferably, the viscosity-average molecular weight of the polyethylene raw material of the polyethylene base film is 1 million to 2 million; preferably, the viscosity-average molecular weight of the polyethylene raw material of the polyethylene base film is 1.3 million to 1.5 million.

[0091] Preferably, the polyethylene raw material of the polyethylene-based film can be a mixture of polyethylene with a viscosity-average molecular weight of 1 million to 2 million and polyethylene with a viscosity-average molecular weight of 300,000 to 700,000, wherein the mass ratio of polyethylene with a viscosity-average molecular weight of 1 million to 2 million to polyethylene with a viscosity-average molecular weight of 300,000 to 700,000 is (20 to 80): (80 to 20).

[0092] As a preferred embodiment of the high thermal conductivity base film of the second aspect of the present invention, the method for preparing the polyethylene base film is as follows:

[0093] (1) Add polyethylene (PE) powder with a viscosity-average molecular weight of 1.3 million to 1.5 million into the feeding equipment and preheat the white oil temperature to 50 to 60°C.

[0094] (2) PE powder is uniformly melted using a twin-screw extruder and extruded into cast sheets. The twin-screw extruder temperature settings are as follows: Zone 1 (feeding zone): 20–40℃; Zone 2 (first white oil inlet zone): 80–100℃; Zone 3 (second white oil inlet zone): 80–100℃; Zones 4–5: 120–140℃; Zone 6: 150–170℃; Zones 7–11: 180–200℃; Die zone 3: 200–220℃. The extrusion feed rate is set to 1–1.5 kg / h. White oil enters the twin-screw extruder through Zones 2 and 3 and is mixed and melted with the PE powder. Extruder speed: 60-70 rpm, melt pump speed: 15-20 rpm, pre-screen pressure: -0.5 MPa to -0.2 MPa, pre-pump pressure: 0.4 MPa to 0.8 MPa, post-pump pressure: 4.5 MPa to 6 MPa, melt temperature: 210-230℃, PE feed screw speed: 7-8 rpm;

[0095] (3) The die head extrudes the molten and uniformly mixed melt through the die lip, casting it into sheets, which are then cooled by the quench roller to form cast sheets. The quench roller cooling source temperature is 10-15℃, the cast sheet thickness is 700-1000 micrometers, and the solid content is 18%-22%.

[0096] (4) Use a static synchronous biaxial stretching apparatus to stretch the casting into an oil film. The stretching ratio is 7 times for both longitudinal and transverse stretching. Preheating temperature: 120~130℃, preheating time: 100~120s, stretching temperature: 120~130℃, stretching time: 100~120s.

[0097] (5) Fix the oil film after double pulling, put it into the first part of dichloromethane for 2-4 min, and then put it into the second part of dichloromethane for 2-4 min. During the process, keep the dichloromethane flowing to ensure that the oil film is fully extracted by the dichloromethane and remove the white oil in the oil film.

[0098] (6) Set the oven temperature to 120-135℃ and stabilize for 3-8 minutes. Then put the extracted membrane into the oven and heat-set for 3-8 minutes to obtain a polyethylene film.

[0099] 3. Beneficial effects

[0100] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0101] (1) The high thermal conductivity base film of the present invention comprises a polyetheretherketone meltblown film with a three-dimensional network structure on a polyolefin base film; the basis weight of the polyetheretherketone meltblown film is 0.6-3.5 g / m³. 2 The thickness of the high thermal conductivity base film is 8.0 to 11.0 μm, achieving high thermal conductivity in a relatively thin membrane with a thickness of no more than 11 μm.

[0102] (2) The fiber diameter in the polyether ether ketone three-dimensional network structure of the present invention is 0.5 to 0.8 μm, which has higher thermal conductivity. When forming a polyether ether ketone meltblown film, a good thermal conductivity can be achieved when the thickness is only 1.0 to 3.5 μm. Therefore, the overall thickness of the high thermal conductivity base film can be controlled at a low level.

[0103] (3) The present invention uses polyetheretherketone with high thermal conductivity to melt-blown spin film formation. The polyetheretherketone melt-blown film is directly formed on a polyolefin base film placed on a forming curtain at a certain speed, and then hot-pressed to obtain a composite diaphragm (high thermal conductivity base film). The thickness of the polyetheretherketone melt-blown film in the composite diaphragm formed by this method is controllable. By controlling the forming curtain speed at 3 to 10 m / min, a thin composite diaphragm with excellent thermal conductivity can be formed. Compared with the impregnation and pore-forming method of the prior art, the pores formed by melt-blown spinning are more stable, controllable and more uniform.

[0104] (4) The high temperature resistance and good mechanical strength of polyetheretherketone itself can improve the thermal shrinkage, tensile strength and puncture strength of PE separator; the high thermal conductivity of polyetheretherketone can improve the poor thermal conductivity of PE separator, which helps to increase the power density of lithium-ion battery, extend battery life and reduce safety risks; it can improve the performance of battery during high power discharge, conduct heat generated inside the battery system more quickly, avoid excessive heat accumulation and reduce temperature rise. Detailed Implementation

[0105] The terms “upper,” “lower,” “left,” “right,” and “middle” used in this specification are merely for clarity of description and are not intended to limit the scope of implementation. Any changes or adjustments to their relative relationships, without substantially altering the technical content, shall also be considered within the scope of the present invention.

[0106] 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 invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0107] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0108] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0109] Velocity, quantity, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0110] The present invention will be further described below with reference to specific embodiments.

[0111] Example 1

[0112] I. Preparation of Polyolefin Membranes

[0113] PE powder with a molecular weight of 1.5 million is fed into the feeding equipment, and the white oil temperature is preheated to 55°C. The PE powder is uniformly melted through a twin-screw extruder and extruded into cast sheets.

[0114] Twin-screw extruder temperature settings: Zone 1 (feeding zone): 30℃; Zone 2 (first white oil inlet zone): 80℃; Zone 3 (second white oil inlet zone): 100℃; Zones 4-5: 120℃; Zone 6: 150℃; Zones 7-11: 180℃; Die 3: 210℃; Extrusion feed rate setting: 1kg / h.

[0115] White oil enters the twin-screw extruder through zones two and three, where it is mixed and melted with PE powder.

[0116] Extruder speed: 69 rpm, melt pump speed: 18 rpm, screen pressure: -0.4 MPa, pump pressure: 0.6 MPa, pump pressure: 6 MPa, melt temperature: 223℃, PE feed screw speed: 7.98 rpm.

[0117] The die head extrudes the molten and uniformly mixed melt through the die lip, casting it into a sheet, which is then cooled by a chilling roller to form a cast sheet. Chilling roller temperature: 12℃; cast sheet thickness: 815 micrometers; solid content: 20.63%.

[0118] The cast sheet was stretched into an oil film using a static synchronous biaxial stretching apparatus. The stretching ratio was 7 times in both the longitudinal and transverse directions. The preheating temperature was 120℃, the preheating time was 100s, the stretching temperature was 120℃, and the stretching time was 120s.

[0119] After double-stretching, fix the oil film and extract it in the first portion of dichloromethane for 3 minutes, then extract it in the second portion of dichloromethane for 3 minutes. During the process, keep the dichloromethane flowing to ensure that the oil film is fully extracted by the dichloromethane and remove the white oil from the oil film.

[0120] The oven temperature was set to 130℃. After stabilizing for 5 minutes, the extracted membrane was placed in the oven and heat-set for 5 minutes to obtain a polyethylene-based membrane.

[0121] II. Preparation of Polyetheretherketone Meltblown Film

[0122] The polyetheretherketone (PEEK) is manufactured by Shandong Junhao, and the product model is PEEK5600CF30 particles.

[0123] A twin-screw extruder is used to fully melt high thermal conductivity polyetheretherketone (PEEK). The entire temperature range of the twin-screw extruder is 220–400℃. Based on the different functional zones of the twin-screw, a gradient temperature range is set: Feeding zone 1: 220℃, Zone 2: 250℃, Zone 3: 250℃, ensuring that the PEEK enters the extruder uniformly without melting, avoiding feed port blockage and backflow; Melting and mixing zone: Zone 4: 320℃, Zone 5: 340℃, Zone 6: 360℃, Zones 7–10: 380℃; Filtering device: 380℃. This gradient temperature ensures the PEEK melts gradually and fully, and the filtration device removes impurities from the melt, preventing clogging of the spinneret orifices. The post-filtration pressure is 1.6 MPa.

[0124] The melt is metered and delivered to the die head via a metering pump. The metering pump temperature is 380℃ and the metering pump speed is 15 r / min. The die head passes the melt through a spinneret to form a fine melt stream. Under the action of the stretching airflow, the melt is refined into fibers. The die head temperature is 380℃.

[0125] The prepared PE film (polyethylene film) is fixed on a forming screen. The refined fibers are directly collected on the surface of the PE film on the forming screen, forming a mesh sheet through the adhesion of the fibers themselves. The receiving distance from the die head to the forming screen is 15 cm, the suction frequency under the screen is 30 Hz, and the forming screen speed is 3 m / min, resulting in a high thermal conductivity polyetheretherketone meltblown film. The high thermal conductivity polyetheretherketone meltblown film has a three-dimensional mesh structure, with fiber diameters of approximately 0.5–0.8 μm.

[0126] III. Preparation of Composite Separators

[0127] Polyetheretherketone meltblown film and polyolefin film materials were calendered at a temperature of 120℃, a pressure of 1.5MPa, and a calendering speed of 3m / min to obtain a composite diaphragm, namely a high thermal conductivity base film.

[0128] Example 2

[0129] This embodiment is basically the same as Embodiment 1, except that the forming speed of the polyetheretherketone meltblown film is 5m / min.

[0130] Polyetheretherketone meltblown film and polyolefin film materials were calendered at a temperature of 120℃, a pressure of 1.5MPa, and a calendering speed of 3m / min to obtain a composite diaphragm, namely a high thermal conductivity base film.

[0131] Example 3

[0132] This embodiment is basically the same as Embodiment 1, except that the forming speed of the polyetheretherketone meltblown film is 7m / min.

[0133] Polyetheretherketone meltblown film and polyolefin film materials were calendered at a temperature of 120℃, a pressure of 1.5MPa, and a calendering speed of 3m / min to obtain a composite diaphragm, namely a high thermal conductivity base film.

[0134] Example 4

[0135] This embodiment is basically the same as Embodiment 1, except that the forming speed of the polyetheretherketone meltblown film is 9m / min.

[0136] Polyetheretherketone meltblown film and polyolefin film materials were calendered at a temperature of 120℃, a pressure of 1.5MPa, and a calendering speed of 3m / min to obtain a composite diaphragm, namely a high thermal conductivity base film.

[0137] Comparative Example 1

[0138] This comparative example is the polyethylene-based film prepared in Example 1.

[0139] Comparative Example 2

[0140] This comparative example is basically the same as Example 1, except that the forming speed of the polyetheretherketone meltblown film is 1m / min.

[0141] Polyetheretherketone meltblown film and polyolefin film materials were calendered at a temperature of 120℃, a pressure of 1.5MPa, and a calendering speed of 3m / min to obtain a composite diaphragm, namely a high thermal conductivity base film.

[0142] Comparative Example 3

[0143] This comparative example is basically the same as Example 1, except that the forming speed of the polyetheretherketone meltblown film is 12m / min.

[0144] Polyetheretherketone meltblown film and polyolefin film materials were calendered at a temperature of 120℃, a pressure of 1.5MPa, and a calendering speed of 3m / min to obtain a composite diaphragm, namely a high thermal conductivity base film.

[0145] Test case

[0146] The diaphragms prepared in Examples 1-4 and Comparative Examples 1-3 were tested for basis weight, thickness, porosity, air permeability, tensile strength, puncture strength and thermal stability.

[0147] For the gram weight test, the diaphragm is cut into 10cm×10cm pieces, folded twice in opposite directions, and weighed using an electronic balance (Mettler-Toledo Instruments (Shanghai) Co., Ltd., ME204E / 02). The resulting value is the gram weight (area density).

[0148] For thickness testing, the diaphragm was cut into 10cm×10cm pieces, and the thickness of the sample was measured at the four corners and the middle position using a Mahr thickness gauge (C1202). The average value was then taken.

[0149] Porosity testing involved cutting 10cm x 10cm samples and measuring their thickness (Mahr thickness gauge, C1202) and mass (electronic balance, Mettler Toledo Instruments (Shanghai) Co., Ltd., ME204E / 02). Calculate the porosity, where p is the porosity of the sample in %, and d is the thickness of the sample in cm.

[0150] For the air permeability test, a 10cm wide sample was taken, and the air permeability of 5 points was tested using a Wang Yanshi air permeability meter (ASAHI Corporation, EG01-55-1MR), and the average value was taken.

[0151] Tensile strength was tested according to GB / T 1040.3-2006. A 2.5cm × 20cm specimen was cut and marked with the MD / TD direction of the diaphragm. The specimen was tested using a tensile testing machine (Jinan Sike Testing Technology Co., Ltd., TSL-1002). The specimen was fixed between the upper and lower clamps of the tensile testing machine (the distance between the clamps was 100±5mm). The specimen was ensured to be flat and wrinkle-free, and vertical and not skewed. The tensile speed was 250mm / min. Based on the width and thickness of the specimen, the test was performed 3 times and the average value was taken as the tensile strength (MPa) in the MD / TD direction.

[0152] For the puncture strength test, a 500*100mm diaphragm was cut along the TD direction and fixed on the sample fixture of the puncture testing machine (model: AI-3000-S, High-speed Rail Testing Instruments (Dongguan) Co., Ltd.). A steel needle with a diameter of 1.0mm was used to puncture the diaphragm at a speed of 300mm / min. The maximum load of the steel needle penetrating the diaphragm was read. The test was performed more than 5 times and the arithmetic mean was taken.

[0153] Thermal stability testing was conducted according to the requirements of GB / T36363-2018. A 10cm × 10cm sample was cut, and the transverse (TD) and longitudinal (MD) widths were marked on the sample. The transverse and longitudinal widths were measured using a fully automatic image measuring projector (Kunshan Gaopin Precision Instruments Co., Ltd., GP-300C). The sample was then sandwiched between two sealed A4 sheets of paper and placed in a 105℃ oven for 1 hour. After the sample returned to room temperature, the transverse and longitudinal widths were measured again using the fully automatic image measuring projector. Three measurements were taken, and the average value was recorded.

[0154] Table 1 Physical properties of composite membranes

[0155]

[0156] As shown in Table 1, compared with the pure PE separator of Comparative Example 1, the tensile strength, puncture strength, and heat shrinkage performance of Examples 1-4 and Comparative Examples 2 and 3 are significantly improved. This is due to the incorporation of a high thermal conductivity polyetheretherketone (PEEK) meltblown film, which offers better high-temperature resistance and mechanical strength. Furthermore, Examples 1-4 show that as the content of the high thermal conductivity PEEK meltblown film increases, the tensile strength, puncture strength, and heat shrinkage performance all tend to be higher. However, the thickness, basis weight, porosity, and air permeability of the composite separator are also affected by the content of the high thermal conductivity PEEK meltblown film. Higher content leads to a significant increase in the thickness, basis weight, and air permeability of the composite separator, while the porosity decreases. For battery separators, while ensuring other performance characteristics, the thickness should be as thin as possible to help improve battery capacity. Excessively low porosity affects the battery's cycle performance. Therefore, among Examples 1-4, the composite membrane obtained in Example 3 has the best physical properties. Compared with Comparative Example 2, although its high thermal conductivity polyetheretherketone meltblown film content is lower, its thickness, porosity, and air permeability are better. Compared with Comparative Example 3, the polyetheretherketone content in Example 4 is relatively higher, and its puncture strength, tensile strength, and heat shrinkage performance are better.

[0157] This invention controls the thickness and basis weight of the polyetheretherketone (PEEK) meltblown film formed on a polyolefin-based membrane by changing the speed of the forming screen, and investigates the effect of PEEK content on the performance of the composite membrane. The forming screen speeds in Examples 1-4 were 3 m / min, 5 m / min, 7 m / min, and 9 m / min, respectively, while the forming screen speeds in Comparative Examples 2 and 3 were 1 m / min and 12 m / min, respectively. In these examples, as the forming screen speed increased, the thickness and basis weight of the film formed on the receiving screen decreased; the thickness of the PEEK meltblown film decreased from 3.4 μm to 1 μm, and the basis weight decreased from 3.1 g / m³. 2 Reduced to 0.6 g / m 2 Under the same parameter conditions as the PE-based film, as the forming speed of the web in Examples 1-4 increased, the thickness and basis weight of the composite diaphragm after hot pressing also decreased. The thickness decreased from 10.5 μm to 8.1 μm, and the basis weight decreased from 7.3 g / m³. 2 Reduced to 4.8g / m 2Meanwhile, the thermal conductivity also decreased from 0.084 W / (m·K) to 0.065 W / (m·K). Although a lower forming speed results in a thicker polyetheretherketone meltblown film and a higher thermal conductivity, the porosity decreased from 36% to 32%. Therefore, while ensuring an improvement in thermal conductivity, it is desirable to keep the thickness of the polyetheretherketone meltblown film as low as possible to prevent the porosity from becoming too low. From the basic requirements of polyolefin-based films, the polyolefin-based films in Examples 1-4 all meet the basic requirements, but Example 3 is the most preferred option. Compared with Comparative Example 1, Example 3 shows a significant improvement in thermal conductivity; compared with Comparative Example 2, Example 3 has a higher porosity; and compared with Comparative Example 3, Example 3 has better thermal conductivity and mechanical strength.

[0158] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. A high thermal conductivity base film, characterized in that, include: Polyolefin-based film; and A polyetheretherketone meltblown film disposed on at least one side of the polyolefin-based film; The polyetheretherketone meltblown film has a three-dimensional network structure; The basis weight of the polyetheretherketone meltblown film is 0.6–3.5 g / m³. 2 ; The thickness of the high thermal conductivity base film is 7.5–11.0 μm, and the porosity is 30–41%.

2. The high thermal conductivity base film according to claim 1, characterized in that, The fiber diameter in the three-dimensional network structure of the polyetheretherketone meltblown film is 0.5 to 0.8 μm, and the thickness of the polyetheretherketone meltblown film is 1.0 to 3.5 μm.

3. The high thermal conductivity base film according to claim 1, characterized in that, The ratio of the thickness of the polyolefin-based film to the thickness of the polyether ether ketone layer is (5-10):(0.1-4), preferably (5-10):(1-4), more preferably (6-8):(1-4), and even more preferably (7-8):(1-3.5).

4. The high thermal conductivity base film according to claim 1, characterized in that, The ratio of the basis weight of the polyolefin-based film to the basis weight of the polyetheretherketone layer is (3-5):(0.1-3.6), more preferably (4-5):(0.5-3.2).

5. The high thermal conductivity substrate film according to claim 1, characterized in that: The polyolefin-based film is a polyethylene-based film; The polyethylene-based film has a thickness of 6.5–7.5 μm; The porosity of the polyethylene-based film is 35-41%.

6. The high thermal conductivity substrate film according to claim 1, characterized in that: The basis weight of the high thermal conductivity base film is 4.8 g / m³. 2 ~7.5g / m 2 ; and / or The thermal conductivity of the high thermal conductivity base film is not less than 0.06 W / (m·K); and / or The air permeability of the high thermal conductivity base film is 150–200 sec / 100cc; and / or The high thermal conductivity base film has a MD thermal shrinkage rate of no more than 2.0% and a TD thermal shrinkage rate of no more than 1.5%; and / or The high thermal conductivity base film has a MD tensile strength of not less than 3000 kgf and a TD tensile strength of not less than 3000 kgf; and / or The puncture strength of the high thermal conductivity base film is not less than 400 gf.

7. The preparation process of the high thermal conductivity substrate film according to any one of claims 1 to 6, characterized in that... Includes the following steps: S1 provides polyolefin-based films; S2 Place the polyolefin-based film on a forming curtain, the forming curtain moving at a speed of 3-10 m / min, and the polyolefin-based film moving with the forming curtain; provide a polyetheretherketone meltblown film on the moving polyolefin-based film; S3 involves calendering the polyolefin-based film and the polyether ether ketone meltblown film to obtain a high thermal conductivity base film.

8. The preparation process of the high thermal conductivity substrate film according to claim 7, characterized in that, The step of providing the polyetheretherketone meltblown film in S2 includes the following steps: S2.1 A twin-screw extruder is used to melt high thermal conductivity polyetheretherketone to obtain a melt; S2.2 A metering pump is used to quantitatively deliver the melt to the die head; S2.3 The melt is passed through the spinneret holes on the surface of the die head spinneret to form a melt stream. Under the action of the stretching airflow, the melt is refined into fibers. The fibers form a polyether ether ketone meltblown film with a three-dimensional network structure on the moving polyolefin base film.

9. The preparation process of the high thermal conductivity substrate film according to claim 7, characterized in that: In step S2.1: The twin-screw extruder has a total temperature range of 220–400℃. Specifically, it features gradient temperature zones: Feeding Zone 1: 220–240℃, Zone 2: 240–260℃, Zone 3: 260–280℃, ensuring uniform entry of high thermal conductivity polyetheretherketone (PEEK) into the extruder without melting, thus preventing feed blockage and backflow; Melt mixing zone: Zone 4: 320–340℃, Zone 5: 340–360℃, Zone 6: 360–380℃, Zone 7: 380–400℃, Zone 8: 380–400℃, Zone 9: 380–400℃, Zone 10: 380–400℃; Filtration device: 380–400℃. The pressure of the melt after filtration by the filtration device is 1.5 MPa to 3.0 MPa; and / or In step S2.2: The metering pump temperature is 380–400℃, and the metering pump speed is 15–20 r / min; and / or In step S2.3: Die head: 380~400℃; Distance from die head to receiving screen: 10~20cm.

10. The preparation process of the high thermal conductivity substrate film according to claim 7, characterized in that, The calendering temperature in S3 is 120-150℃, the pressure is 1MPa to 1.5MPa, and the calendering speed is 3-5m / min.

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