High-flame-retardant polyolefin diaphragm and preparation method thereof

Abstract

The invention discloses a high-flame-retardant polyolefin diaphragm and a preparation method thereof, and belongs to the technical field of lithium ion batteries. The high-flame-retardant polyolefin diaphragm comprises the following raw materials in parts by weight: 88-97 parts of a high-flame-retardant PE master batch, 0.3-1.5 parts of an antioxidant and 2-10 parts of paraffin oil, and the high-flame-retardant PE master batch is prepared by blending and granulating a flame retardant and PE powder, and specifically comprises 20-35 parts of the flame retardant and 65-80 parts of the PE powder. The electronic-grade hypophosphite is mixed into the PE particles to form the flame retardant polyolefin master batch, and the flame retardant polyolefin master batch has the advantages of high flame retardant effect, high heat sensitivity and controllable thermal response temperature, so that the flame retardant can be timely and quickly released at the initial stage of thermal runaway of the battery, the diaphragm is prevented from being burnt to fire after the battery is heated, the ignition temperature of a glowing filament can reach 800 DEG C, and the service life of the battery is prolonged. The normal heating temperature of the battery is exceeded, and the high-flame-retardant diaphragm material prevents the battery from firing and exploding in a severe environment, so that the safety of the battery is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a highly flame-retardant polyolefin diaphragm and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are mainly composed of positive and negative electrode materials, electrolytes, diaphragms, and related packaging materials. The main function of the diaphragm is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and short-circuiting. In addition, it also has the function of allowing electrolyte ions to pass through. Different types of batteries use different diaphragms. The performance of the diaphragm determines the interface structure and internal resistance of the battery, and directly affects the battery's capacity, cycle, and safety performance. A diaphragm with excellent performance plays an important role in improving the overall performance of the battery.

[0003] For lithium battery series, since the electrolyte is an organic solvent system, a diaphragm material resistant to organic solvents is required, and a high-strength thin-film polyolefin porous membrane is generally used. Currently, commercial lithium battery diaphragms are mainly polyethylene (PE) diaphragms, polypropylene (PP) diaphragms, and PE and PP composite multilayer microporous membranes. Among them, PE diaphragms have high strength and a wide processing range, but poor heat resistance; PP diaphragms have high porosity, air permeability, and mechanical properties, but low strength. In addition, polyolefin diaphragms also have a very obvious disadvantage, that is, insufficient thermal stability, which poses a hidden danger to the safety of the battery. Therefore, process modification of polyolefin diaphragms has become a research and development trend.

[0004] This application is based on the above-mentioned situation and creates a highly flame-retardant polyolefin diaphragm and its preparation method, which can release flame retardants promptly and quickly at the early stage of thermal runaway of the battery, prevent the diaphragm from burning and catching fire after the battery is heated, and make the ignition temperature of the burning wire reach 800°C, effectively avoiding the battery from catching fire and exploding in harsh environments, greatly improving the safety of the battery. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a highly flame-retardant polyolefin diaphragm, which can release the flame retardant promptly and quickly at the early stage of thermal runaway of the battery, prevent the diaphragm from burning and catching fire after the battery is heated, and make the ignition temperature of the burning wire reach 800°C, effectively avoiding the battery from catching fire and exploding in harsh environments, greatly improving the safety of the battery, thereby overcoming the shortcomings of the existing polyolefin diaphragms.

[0006] In order to solve the above technical problems, the present invention provides a highly flame-retardant polyolefin diaphragm, comprising a highly flame-retardant PE masterbatch, an antioxidant and paraffin oil, and the highly flame-retardant PE masterbatch is formed by blending and granulating the flame retardant and PE powder.

[0007] As a further improvement of the present invention, the highly flame-retardant polyolefin diaphragm comprises the following raw materials in parts by weight: 88-97 parts of highly flame-retardant PE masterbatch, 0.3-1.5 parts of antioxidant and 2-10 parts of paraffin oil, wherein the highly flame-retardant PE masterbatch comprises the following raw materials in parts by weight: 20-35 parts of flame retardant and 65-80 parts of PE powder.

[0008] As a further improvement of the present invention, the highly flame-retardant polyolefin diaphragm comprises the following raw materials in parts by weight: 93 parts of highly flame-retardant PE masterbatch, 1 part of antioxidant and 6 parts of paraffin oil, wherein the highly flame-retardant PE masterbatch comprises the following raw materials in parts by weight: 30 parts of flame retardant and 70 parts of PE powder.

[0009] As a further improvement of the present invention, the flame retardant is one or more electronic grade hypophosphite flame retardants of diethyl aluminum hypophosphite, dipropyl aluminum hypophosphite, phenyl aluminum hypophosphite, methyl aluminum hypophosphite, and methylphenyl aluminum hypophosphite; the polyethylene molecular weight of the PE powder is 400,000-1.2 million.

[0010] As a further improvement, the preparation method of the highly flame-retardant PE masterbatch is as follows: the flame retardant and PE powder are mixed and polymerized in a twin-screw extruder according to the weight ratio of the raw materials, and granulated to obtain the modified highly flame-retardant PE masterbatch.

[0011] As a further improvement, the particle size D50 of the highly flame-retardant PE masterbatch is ≤80 μm, which is beneficial to the processing fluidity and thermal response temperature of the highly flame-retardant PE masterbatch.

[0012] Further improvement, the preparation method of the highly flame-retardant polyolefin diaphragm is:

[0013] (1) mixing a high flame retardant PE masterbatch, an antioxidant and paraffin oil according to the weight ratio of the raw materials at a high temperature speed of a twin screw to form a high temperature molten fluid;

[0014] (2) The high-temperature molten fluid is cast through a die head and cooled to form a film. The thick film from the cast sheet is then longitudinally stretched by adjusting the roller speed difference. The longitudinally stretched film is then transversely stretched once to form a film material with uniform thickness.

[0015] (3) the film material after the transverse primary stretching passes through an extraction tank to separate the paraffin oil with an extracting liquid, wherein the extracting liquid is dichloromethane;

[0016] (4) The extracted membrane material is stretched transversely for a second time, the transverse pores are repaired uniformly at high temperature, and after heat setting, the membrane material is rolled up into a highly flame-retardant polyolefin diaphragm.

[0017] As a further improvement, the highly flame-retardant polyolefin diaphragm has a thickness of 40-100 μm and a width of 3-10 m. According to the classification of thickness, it can not only be applied to existing conventional lithium-ion battery isolation membrane materials, but also can be used in flame-retardant cover materials, air conditioning filter elements and other scenarios due to its high flame-retardant effect.

[0018] As another improvement of the present invention, the present invention also provides a method for preparing the above-mentioned highly flame-retardant polyolefin diaphragm, comprising the following steps:

[0019] S1: adding the flame retardant and PE powder into a twin-screw extruder according to the weight ratio of the raw materials, blending and polymerizing, and then granulating to obtain a modified high flame retardant PE masterbatch; the particle size D50 of the high flame retardant PE masterbatch is ≤80μm;

[0020] S2: mixing the high flame retardant PE masterbatch, antioxidant and paraffin oil obtained in step S1 according to the weight ratio of the raw materials at a high temperature speed of a twin-screw extruder to form a high-temperature molten fluid;

[0021] S3 The high-temperature molten fluid is cast through the die head and cooled to form a film, and then the thick film from the cast sheet is longitudinally stretched by adjusting the roller speed difference, and then the longitudinally stretched film is transversely stretched once to form a film material with uniform thickness;

[0022] S4 The film material after the transverse primary stretching passes through an extraction tank to separate the paraffin oil with an extracting liquid, wherein the extracting liquid is dichloromethane;

[0023] S5 performs a transverse secondary stretching on the extracted membrane material, performs high-temperature uniformity repair on the transverse pores, and after heat setting, rolls it up into a highly flame-retardant polyolefin diaphragm semi-finished membrane;

[0024] S6: subjecting the semi-finished film to a slitting device to obtain a finished film of the highly flame-retardant polyolefin diaphragm.

[0025] Further improvement, in step S2, the screw aspect ratio of the twin-screw extruder is greater than 45, the segmented temperature is 160-220°C, the filter precision is 10-50μm, the cooling film thickness is ≥100μm, and the casting roller temperature is 10-40°C;

[0026] In step S3, the stretching ratio of the longitudinal stretching is 1-15 times, the longitudinal stretching speed is 3-15 m / min, the stretching ratio of the transverse primary stretching is 6-15 times, and the transverse primary stretching speed is 8-30 m / min;

[0027] In step S4, the extraction phase separation time is controlled to be ≥ 2 min, the production speed is 10-60 m / min, and the running direction of the gas and the high barrier membrane in this step forms a convection mode;

[0028] In step S5, the stretching ratio of the transverse secondary stretching is 1-5 times, the transverse secondary stretching speed is 20-80 m / min, and the temperature of the heat setting roller is 130-180° C.;

[0029] In step S6, the primary slitting speed is controlled to be 50-150 m / min, the speed of the slitting machine is controlled to be 80-100 m / min, the unwinding tension is 25-50 N, the winding tension is 15-40 N, and the winding taper is gradually reduced at a rate of 10%.

[0030] After adopting such a design, the present invention has at least the following advantages:

[0031] The highly flame-retardant polyolefin diaphragm of the present invention forms a flame retardant polyolefin masterbatch by mixing environmentally friendly electronic-grade hypophosphite into PE particles. By utilizing the advantages of high flame retardant effect, high thermal sensitivity and controllable thermal response temperature, the flame retardant can be released promptly and quickly at the early stage of thermal runaway of the battery to prevent the diaphragm from burning and catching fire after the battery is heated. The ignition temperature of the glow wire can reach 800°C, which not only exceeds the normal heating temperature of the battery, but also the highly flame-retardant diaphragm material prevents the battery from catching fire and exploding in harsh environments, thereby greatly improving the battery safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0033] Figure 1 The present invention is a flow chart of the method for preparing the highly flame-retardant polyolefin diaphragm. DETAILED DESCRIPTION

[0034] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0035] Example 1

[0036] The highly flame-retardant polyolefin diaphragm of this embodiment includes 93 parts of highly flame-retardant PE masterbatch, 1 part of antioxidant and 6 parts of paraffin oil. The highly flame-retardant PE masterbatch includes 20 parts of flame retardant and 80 parts of PE powder. Among them, the flame retardant is electronic grade diethyl aluminum hypophosphite, the PE powder is a polyethylene material with a molecular weight of 400,000, and the antioxidant is BHT (2,6-di-tert-butyl-4-methylphenol).

[0037] The highly flame-retardant polyolefin diaphragm of this embodiment is prepared by a unidirectional asynchronous stretching method. Figure 1 As shown, the specific steps include:

[0038] S1: Add the flame retardant and PE powder according to the weight ratio of the raw materials into a twin-screw extruder, blend and polymerize, and then granulate to obtain a modified high flame retardant PE masterbatch; the particle size D50 of the high flame retardant PE masterbatch is ≤80μm. The feeding metering is ≥100kg / h and the accuracy is ≤±0.5%.

[0039] S2: The highly flame-retardant PE masterbatch and antioxidant obtained in step S1 are mixed according to the weight ratio of the raw materials, and added into the metering main material tank through the automatic feeding system. At the same time, paraffin oil is injected through the oil inlet of the extruder. The powder and the liquid are melted at the high temperature speed of the twin screw to form a high-temperature molten fluid.

[0040] The S3 high-temperature molten fluid is cast through the die head and cooled to form a film. The thick film from the cast sheet is then longitudinally stretched by adjusting the roller speed difference. The longitudinally stretched film is then transversely stretched once to form a film material with uniform thickness.

[0041] Specifically, the extruder screw aspect ratio is 62, the segmented temperature is 185°C, the filter accuracy is 20μm, the cooling film thickness is 320μm, and the casting roller temperature is 30°C; the longitudinal stretching ratio is controlled to be 6.5 times, and the longitudinal stretching speed is 11m / min; the transverse primary stretching ratio is 10.5 times, and the transverse primary stretching speed is 23m / min.

[0042] S4 The film material after transverse one-time stretching passes through the extraction tank, and the paraffin oil is separated from the dichloromethane extraction liquid phase. Specifically, the extraction phase separation time is controlled to be 3 minutes, the production speed is 44m / min, and the gas and the running direction of the high barrier membrane form a convection mode;

[0043] S5 performs transverse secondary stretching on the extracted film material, performs high temperature uniformity repair on the transverse pores, and after heat setting, rolls it up into a highly flame-retardant polyolefin diaphragm semi-finished film. Specifically, the transverse secondary stretching ratio is controlled to be 4.3 times, the transverse secondary stretching speed is 65m / min, and the heat setting roller temperature is 142°C.

[0044] S6 processes the semi-finished film through a slitting device to obtain a finished film of a highly flame-retardant polyolefin diaphragm.

[0045] Specifically, the speed of the slitting machine is controlled to be 100 m / min, the unwinding tension is 28 N, the winding tension is 22 N, and the winding taper is gradually reduced by 10%.

[0046] Example 2

[0047] The highly flame-retardant polyolefin diaphragm of this embodiment includes 89 parts of highly flame-retardant PE masterbatch, 1 part of antioxidant and 10 parts of paraffin oil. The highly flame-retardant PE masterbatch includes 25 parts of flame retardant and 75 parts of PE powder. Among them, the flame retardant is electronic grade dipropyl aluminum hypophosphite, the PE powder is a polyethylene material with a molecular weight of 1.2 million, and the antioxidant is BHT (2,6-di-tert-butyl-4-methylphenol).

[0048] The highly flame-retardant polyolefin separator of this embodiment is prepared by a unidirectional asynchronous stretching method, and the specific preparation method is as follows:

[0049] S1: adding the flame retardant and PE powder into a twin-screw extruder according to the weight ratio of the raw materials, blending and polymerizing, and then granulating to obtain a modified high flame retardant PE masterbatch; the particle size D50 of the high flame retardant PE masterbatch is ≤80 μm.

[0050] S2: The highly flame-retardant PE masterbatch and antioxidant obtained in step S1 are mixed according to the weight ratio of the raw materials, and added into the metering main material tank through the automatic feeding system. At the same time, paraffin oil is injected through the oil inlet of the extruder. The powder and the liquid are melted at the high temperature speed of the twin screw to form a high-temperature molten fluid.

[0051] The S3 high-temperature molten fluid is cast through the die head and cooled to form a film. The thick film from the cast sheet is then longitudinally stretched by adjusting the roller speed difference. The longitudinally stretched film is then transversely stretched once to form a film material with uniform thickness.

[0052] Specifically, the extruder screw aspect ratio is 68, the segmented temperature is 205°C, the filter accuracy is 20μm, the cooling film thickness is 320μm, and the casting roller temperature is 30°C; the longitudinal stretching ratio is controlled to be 6.5 times, and the longitudinal stretching speed is 7m / min; the transverse primary stretching ratio is 6.5 times, and the transverse primary stretching speed is 10.5m / min.

[0053] S4 The film material after transverse one-time stretching passes through the extraction tank, and the paraffin oil is separated by dichloromethane extraction liquid phase. Specifically, the extraction phase separation time is controlled to be 5min, the production speed is 31m / min, and the gas and the running direction of the high barrier membrane form a convection mode;

[0054] S5 performs transverse secondary stretching on the extracted film material, performs high temperature uniformity repair on the transverse pores, and after heat setting, rolls it up into a highly flame-retardant polyolefin diaphragm semi-finished film. Specifically, the transverse secondary stretching ratio is controlled to be 3.5 times, the transverse secondary stretching speed is 41m / min, and the heat setting roller temperature is 150°C.

[0055] S6 processes the semi-finished film through a slitting device to obtain a finished film of a highly flame-retardant polyolefin diaphragm.

[0056] Specifically, the speed of the slitting machine is controlled to be 80 m / min, the unwinding tension is 28 N, the winding tension is 22 N, and the winding taper is gradually reduced by 10%.

[0057] Example 3

[0058] The highly flame-retardant polyolefin diaphragm of this embodiment includes 93 parts of highly flame-retardant PE masterbatch, 1 part of antioxidant and 6 parts of paraffin oil. The highly flame-retardant PE masterbatch includes 30 parts of flame retardant and 70 parts of PE powder. Among them, the flame retardant is electronic grade phenyl aluminum hypophosphite, the PE powder is a polyethylene material with a molecular weight of 1.2 million, and the antioxidant is BHT (2,6-di-tert-butyl-4-methylphenol).

[0059] The highly flame-retardant polyolefin separator of this embodiment is prepared by a unidirectional asynchronous stretching method, and the specific preparation method is as follows:

[0060] S1: adding the flame retardant and PE powder into a twin-screw extruder according to the weight ratio of the raw materials, blending and polymerizing, and then granulating to obtain a modified high flame retardant PE masterbatch; the particle size D50 of the high flame retardant PE masterbatch is ≤80 μm.

[0061] S2: The highly flame-retardant PE masterbatch and antioxidant obtained in step S1 are mixed according to the weight ratio of the raw materials, and added into the metering main material tank through the automatic feeding system. At the same time, paraffin oil is injected through the oil inlet of the extruder. The powder and the liquid are melted at the high temperature speed of the twin screw to form a high-temperature molten fluid.

[0062] The S3 high-temperature molten fluid is cast through the die head and cooled to form a film. The thick film from the cast sheet is then longitudinally stretched by adjusting the roller speed difference. The longitudinally stretched film is then transversely stretched once to form a film material with uniform thickness.

[0063] Specifically, the extruder screw aspect ratio is 68, the segmented temperature is 205°C, the filter accuracy is 20μm, the cooling film thickness is 320μm, and the casting roller temperature is 30°C; the longitudinal stretching ratio is controlled to be 6.5 times, and the longitudinal stretching speed is 7m / min; the transverse primary stretching ratio is 6.5 times, and the transverse primary stretching speed is 10.5m / min.

[0064] S4 The film material after transverse one-time stretching passes through the extraction tank, and the paraffin oil is separated by dichloromethane extraction liquid phase. Specifically, the extraction phase separation time is controlled to be 5min, the production speed is 31m / min, and the gas and the running direction of the high barrier membrane form a convection mode;

[0065] S5 performs transverse secondary stretching on the extracted film material, performs high temperature uniformity repair on the transverse pores, and after heat setting, rolls it up into a highly flame-retardant polyolefin diaphragm semi-finished film. Specifically, the transverse secondary stretching ratio is controlled to be 3.5 times, the transverse secondary stretching speed is 41m / min, and the heat setting roller temperature is 150°C.

[0066] S6 processes the semi-finished film through a slitting device to obtain a finished film of a highly flame-retardant polyolefin diaphragm.

[0067] Specifically, the speed of the slitting machine is controlled to be 100 m / min, the unwinding tension is 28 N, the winding tension is 22 N, and the winding taper is gradually reduced by 10%.

[0068] Example 4

[0069] The highly flame-retardant polyolefin diaphragm of this embodiment includes 97 parts of highly flame-retardant PE masterbatch, 0.5 parts of antioxidant and 2.5 parts of paraffin oil. The highly flame-retardant PE masterbatch includes 35 parts of flame retardant and 65 parts of PE powder. Among them, the flame retardant is electronic grade phenyl aluminum hypophosphite, the PE powder is a polyethylene material with a molecular weight of 400,000, and the antioxidant is BHT (2,6-di-tert-butyl-4-methylphenol).

[0070] The highly flame-retardant polyolefin separator of this embodiment is prepared by a unidirectional asynchronous stretching method, and the specific preparation method is as follows:

[0071] S1: adding the flame retardant and PE powder into a twin-screw extruder according to the weight ratio of the raw materials, blending and polymerizing, and then granulating to obtain a modified high flame retardant PE masterbatch; the particle size D50 of the high flame retardant PE masterbatch is ≤80 μm.

[0072] S2: The highly flame-retardant PE masterbatch and antioxidant obtained in step S1 are mixed according to the weight ratio of the raw materials, and added into the metering main material tank through the automatic feeding system. At the same time, paraffin oil is injected through the oil inlet of the extruder. The powder and the liquid are melted at the high temperature speed of the twin screw to form a high-temperature molten fluid.

[0073] The S3 high-temperature molten fluid is cast through the die head and cooled to form a film. The thick film from the cast sheet is then longitudinally stretched by adjusting the roller speed difference. The longitudinally stretched film is then transversely stretched once to form a film material with uniform thickness.

[0074] Specifically, the extruder screw aspect ratio is 62, the segmented temperature is 185°C, the filter accuracy is 20μm, the cooling film thickness is 320μm, and the casting roller temperature is 30°C; the longitudinal stretching ratio is controlled to be 6.5 times, and the longitudinal stretching speed is 11m / min; the transverse primary stretching ratio is 10.5 times, and the transverse primary stretching speed is 23m / min.

[0075] S4 The film material after transverse one-time stretching passes through the extraction tank, and the paraffin oil is separated from the dichloromethane extraction liquid phase. Specifically, the extraction phase separation time is controlled to be 3 minutes, the production speed is 44m / min, and the gas and the running direction of the high barrier membrane form a convection mode;

[0076] S5 performs transverse secondary stretching on the extracted film material, performs high temperature uniformity repair on the transverse pores, and after heat setting, rolls it up into a highly flame-retardant polyolefin diaphragm semi-finished film. Specifically, the transverse secondary stretching ratio is controlled to be 4.3 times, the transverse secondary stretching speed is 65m / min, and the heat setting roller temperature is 142°C.

[0077] S6 processes the semi-finished film through a slitting device to obtain a finished film of a highly flame-retardant polyolefin diaphragm.

[0078] Specifically, the speed of the slitting machine is controlled to be 100 m / min, the unwinding tension is 28 N, the winding tension is 22 N, and the winding taper is gradually reduced by 10%.

[0079] Comparative Example 1

[0080] The highly flame-retardant polyolefin diaphragm of this embodiment includes 30 parts of highly flame-retardant PE masterbatch, 7 parts of antioxidant and 63 parts of paraffin oil. The highly flame-retardant PE masterbatch includes 30 parts of flame retardant and 70 parts of PE powder. Among them, the flame retardant is electronic grade phenyl aluminum hypophosphite, the PE powder is a polyethylene material with a molecular weight of 1.2 million, and the antioxidant is BHT (2,6-di-tert-butyl-4-methylphenol).

[0081] The highly flame-retardant polyolefin separator of this embodiment is prepared by a unidirectional asynchronous stretching method, and the specific preparation method is as follows:

[0082] S1: adding the flame retardant and PE powder into a twin-screw extruder according to the weight ratio of the raw materials, blending and polymerizing, and then granulating to obtain a modified high flame retardant PE masterbatch; the particle size D50 of the high flame retardant PE masterbatch is ≤80 μm.

[0083] S2: The highly flame-retardant PE masterbatch and antioxidant obtained in step S1 are mixed according to the weight ratio of the raw materials, and added into the metering main material tank through the automatic feeding system. At the same time, paraffin oil is injected through the oil inlet of the extruder. The powder and the liquid are melted at the high temperature speed of the twin screw to form a high-temperature molten fluid.

[0084] The S3 high-temperature molten fluid is cast through the die head and cooled to form a film. The thick film from the cast sheet is then longitudinally stretched by adjusting the roller speed difference. The longitudinally stretched film is then transversely stretched once to form a film material with uniform thickness.

[0085] Specifically, the extruder screw aspect ratio is 62, the segmented temperature is 185°C, the filter accuracy is 20μm, the cooling film thickness is 320μm, and the casting roller temperature is 30°C; the longitudinal stretching ratio is controlled to be 6.5 times, and the longitudinal stretching speed is 11m / min; the transverse primary stretching ratio is 10.5 times, and the transverse primary stretching speed is 23m / min.

[0086] S4 The film material after transverse one-time stretching passes through the extraction tank, and the paraffin oil is separated from the dichloromethane extraction liquid phase. Specifically, the extraction phase separation time is controlled to be 3 minutes, the production speed is 44m / min, and the gas and the running direction of the high barrier membrane form a convection mode;

[0087] S5 performs transverse secondary stretching on the extracted film material, performs high temperature uniformity repair on the transverse pores, and after heat setting, rolls it up into a highly flame-retardant polyolefin diaphragm semi-finished film. Specifically, the transverse secondary stretching ratio is controlled to be 4.3 times, the transverse secondary stretching speed is 65m / min, and the heat setting roller temperature is 142°C.

[0088] S6 processes the semi-finished film through a slitting device to obtain a finished film of a highly flame-retardant polyolefin diaphragm.

[0089] Specifically, the speed of the slitting machine is controlled to be 100 m / min, the unwinding tension is 28 N, the winding tension is 22 N, and the winding taper is gradually reduced by 10%.

[0090] Comparative Example 2

[0091] The highly flame-retardant polyolefin diaphragm of this embodiment includes 93 parts of highly flame-retardant PE masterbatch, 1 part of antioxidant and 6 parts of paraffin oil. The highly flame-retardant PE masterbatch includes 15 parts of flame retardant and 85 parts of PE powder. Among them, the flame retardant is electronic grade phenyl aluminum hypophosphite, the PE powder is a polyethylene material with a molecular weight of 1.2 million, and the antioxidant is BHT (2,6-di-tert-butyl-4-methylphenol).

[0092] The highly flame-retardant polyolefin separator of this embodiment is prepared by a unidirectional asynchronous stretching method, and the specific preparation method is as follows:

[0093] S1: adding the flame retardant and PE powder into a twin-screw extruder according to the weight ratio of the raw materials, blending and polymerizing, and then granulating to obtain a modified high flame retardant PE masterbatch; the particle size D50 of the high flame retardant PE masterbatch is ≤80 μm.

[0094] S2: The highly flame-retardant PE masterbatch and antioxidant obtained in step S1 are mixed according to the weight ratio of the raw materials, and added into the metering main material tank through the automatic feeding system. At the same time, paraffin oil is injected through the oil inlet of the extruder. The powder and the liquid are melted at the high temperature speed of the twin screw to form a high-temperature molten fluid.

[0095] The S3 high-temperature molten fluid is cast through the die head and cooled to form a film. The thick film from the cast sheet is then longitudinally stretched by adjusting the roller speed difference. The longitudinally stretched film is then transversely stretched once to form a film material with uniform thickness.

[0096] Specifically, the extruder screw aspect ratio is 62, the segmented temperature is 185°C, the filter accuracy is 20μm, the cooling film thickness is 320μm, and the casting roller temperature is 30°C; the longitudinal stretching ratio is controlled to be 6.5 times, and the longitudinal stretching speed is 11m / min; the transverse primary stretching ratio is 10.5 times, and the transverse primary stretching speed is 23m / min.

[0097] S4 The film material after transverse one-time stretching passes through the extraction tank, and the paraffin oil is separated from the dichloromethane extraction liquid phase. Specifically, the extraction phase separation time is controlled to be 3 minutes, the production speed is 44m / min, and the gas and the running direction of the high barrier membrane form a convection mode;

[0098] S5 performs transverse secondary stretching on the extracted film material, performs high temperature uniformity repair on the transverse pores, and after heat setting, rolls it up into a highly flame-retardant polyolefin diaphragm semi-finished film. Specifically, the transverse secondary stretching ratio is controlled to be 4.3 times, the transverse secondary stretching speed is 65m / min, and the heat setting roller temperature is 150°C.

[0099] S6 processes the semi-finished film through a slitting device to obtain a finished film of a highly flame-retardant polyolefin diaphragm.

[0100] Specifically, the speed of the slitting machine is controlled to be 100 m / min, the unwinding tension is 28 N, the winding tension is 22 N, and the winding taper is gradually reduced by 10%.

[0101] Comparative Example 3

[0102] The highly flame-retardant polyolefin diaphragm of this embodiment includes 93 parts of highly flame-retardant PE masterbatch, 1 part of antioxidant and 6 parts of paraffin oil. The highly flame-retardant PE masterbatch includes 40 parts of flame retardant and 60 parts of PE powder. Among them, the flame retardant is electronic grade phenyl aluminum hypophosphite, the PE powder is a polyethylene material with a molecular weight of 1.2 million, and the antioxidant is BHT (2,6-di-tert-butyl-4-methylphenol).

[0103] The highly flame-retardant polyolefin separator of this embodiment is prepared by a unidirectional asynchronous stretching method, and the specific preparation method is as follows:

[0104] S1: adding the flame retardant and PE powder into a twin-screw extruder according to the weight ratio of the raw materials, blending and polymerizing, and then granulating to obtain a modified high flame retardant PE masterbatch; the particle size D50 of the high flame retardant PE masterbatch is ≤80 μm.

[0105] S2: The highly flame-retardant PE masterbatch and antioxidant obtained in step S1 are mixed according to the weight ratio of the raw materials, and added into the metering main material tank through the automatic feeding system. At the same time, paraffin oil is injected through the oil inlet of the extruder. The powder and the liquid are melted at the high temperature speed of the twin screw to form a high-temperature molten fluid.

[0106] The S3 high-temperature molten fluid is cast through the die head and cooled to form a film. The thick film from the cast sheet is then longitudinally stretched by adjusting the roller speed difference. The longitudinally stretched film is then transversely stretched once to form a film material with uniform thickness.

[0107] Specifically, the extruder screw aspect ratio is 62, the segmented temperature is 185°C, the filter accuracy is 20μm, the cooling film thickness is 320μm, and the casting roller temperature is 30°C; the longitudinal stretching ratio is controlled to be 6.5 times, and the longitudinal stretching speed is 11m / min; the transverse primary stretching ratio is 10.5 times, and the transverse primary stretching speed is 23m / min.

[0108] S4 The film material after transverse one-time stretching passes through the extraction tank, and the paraffin oil is separated from the dichloromethane extraction liquid phase. Specifically, the extraction phase separation time is controlled to be 3 minutes, the production speed is 44m / min, and the gas and the running direction of the high barrier membrane form a convection mode;

[0109] S5 performs transverse secondary stretching on the extracted film material, performs high temperature uniformity repair on the transverse pores, and after heat setting, rolls it up into a highly flame-retardant polyolefin diaphragm semi-finished film. Specifically, the transverse secondary stretching ratio is controlled to be 4.3 times, the transverse secondary stretching speed is 65m / min, and the heat setting roller temperature is 150°C.

[0110] S6 processes the semi-finished film through a slitting device to obtain a finished film of a highly flame-retardant polyolefin diaphragm.

[0111] Specifically, the speed of the slitting machine is controlled to be 100 m / min, the unwinding tension is 28 N, the winding tension is 22 N, and the winding taper is gradually reduced by 10%.

[0112] Test Example 1

[0113] The thickness and air permeability of the finished films of the highly flame-retardant polyolefin diaphragms obtained in the above Examples 1-4 and Comparative Examples 1-3 were tested, and the results are shown in Table 1 below.

[0114] Table 1 Thickness and air permeability test results of each test piece

[0115]

[0116]

[0117] As can be seen from Table 1, the thickness of the highly flame-retardant polyolefin diaphragms obtained in Examples 1-4 is greater than 40 μm, forming a thick film with air permeability that meets the requirements. The film obtained in Comparative Example 1 is thicker and has lower air permeability, and meets the requirements for battery diaphragms.

[0118] Test Example 2

[0119] The finished films of highly flame-retardant polyolefin diaphragms obtained in the above-mentioned Examples 1-4 and Comparative Examples 1-3, as well as conventional PE / PP diaphragms currently on the market, were tested according to the test method of national standard GBT2408 "Horizontal and vertical methods for testing the combustion performance of plastics".

[0120] The specific test method is: take the same length of each embodiment of the diaphragm as the diaphragm test piece. Clamp one end of each diaphragm test piece horizontally, take an iron mesh and fix it horizontally 10±1mm below the test piece, move the Bunsen burner (flame height of about 20mm) to the other end of the test piece at 45 degrees, contact the test piece sample 6mm, stay for 2±0.5s, and then immediately remove the flame to observe the burning duration of each diaphragm test piece. The results are shown in Table 2 below.

[0121] Table 2 Combustion performance test results of each test piece

[0122]

[0123]

[0124] As can be seen from Table 2, the highly flame-retardant polyolefin diaphragms obtained in Examples 1-4 can meet the national flame-retardant film UL94 standard and meet the flame retardant grade requirements under the 800°C Bunsen burner test conditions. In addition, from the comparison of the burning time, it can be seen that increasing the proportion of the flame retardant content can increase the burning duration and better ensure the safety of the battery. However, the conventional PE diaphragms on the market will melt at 170°C, and will dissolve rapidly when the temperature reaches 300°C. The burning time is less than 1s, which cannot meet the requirements for use as battery diaphragm materials. From the results of Comparative Examples 1 and 2, it can be seen that a reduction in the flame retardant content or a small diaphragm thickness will significantly reduce the burning time, and the effect of using it as a battery diaphragm material is poor. From the results of Comparative Example 3, it can be seen that the burning time of the diaphragm obtained in Comparative Example 3 is lower than that of Example 3, indicating that further increasing the flame retardant content cannot more effectively extend the burning time, and also leads to an increase in the cost of the diaphragm.

[0125] The results show that the present invention mixes the environmentally friendly material electronic-grade hypophosphite into PE particles, forms a film through melt extrusion and stretching, and utilizes the advantages of high flame retardant effect, high thermal sensitivity and controllable thermal response temperature to release the flame retardant promptly and quickly at the early stage of thermal runaway of the battery to prevent the diaphragm from burning and catching fire after the battery is heated. The ignition temperature of the glow wire can reach 800°C, which not only exceeds the normal heating temperature of the battery, but also the high flame retardant diaphragm material prevents the battery from catching fire and exploding in harsh environments, thereby greatly improving the safety of the battery, controlling costs, and facilitating market promotion.

[0126] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A highly flame-retardant polyolefin diaphragm, characterized in that: The invention comprises a highly flame-retardant PE masterbatch, an antioxidant and paraffin oil, and the highly flame-retardant PE masterbatch is formed by blending and granulating the flame retardant and PE powder.

2. The highly flame-retardant polyolefin diaphragm according to claim 1, characterized in that: The method comprises the following raw materials in parts by weight: 88-97 parts of high flame retardant PE masterbatch, 0.3-1.5 parts of antioxidant and 2-10 parts of paraffin oil, wherein the high flame retardant PE masterbatch comprises the following raw materials in parts by weight: 20-35 parts of flame retardant and 65-80 parts of PE powder.

3. The highly flame-retardant polyolefin diaphragm according to claim 2, characterized in that: The method comprises the following raw materials in parts by weight: 93 parts of high flame retardant PE masterbatch, 1 part of antioxidant and 6 parts of paraffin oil, wherein the high flame retardant PE masterbatch comprises the following raw materials in parts by weight: 30 parts of flame retardant and 70 parts of PE powder.

4. The highly flame-retardant polyolefin diaphragm according to claim 2, characterized in that: The flame retardant is one or more electronic grade hypophosphite flame retardants of diethyl aluminum hypophosphite, dipropyl aluminum hypophosphite, phenyl aluminum hypophosphite, methyl aluminum hypophosphite, and methylphenyl aluminum hypophosphite; the polyethylene molecular weight of the PE powder is 400,000-1.2 million.

5. The highly flame-retardant polyolefin diaphragm according to claim 4, characterized in that: The preparation method of the highly flame-retardant PE masterbatch comprises: mixing the flame retardant and the PE powder according to the weight ratio of the raw materials, polymerizing them in a twin-screw extruder, and granulating them to obtain the modified highly flame-retardant PE masterbatch.

6. The highly flame-retardant polyolefin diaphragm according to claim 5, characterized in that: The particle size D50 of the highly flame-retardant PE masterbatch is ≤80 μm.

7. The highly flame-retardant polyolefin separator according to claim 6, characterized in that: The preparation method of the highly flame-retardant polyolefin diaphragm is as follows: (1) mixing a high flame retardant PE masterbatch, an antioxidant and paraffin oil according to the weight ratio of the raw materials at a high temperature speed of a twin screw to form a high temperature molten fluid; (2) The high-temperature molten fluid is cast through a die head and cooled to form a film. The thick film from the cast sheet is then longitudinally stretched by adjusting the roller speed difference. The longitudinally stretched film is then transversely stretched once to form a film material with uniform thickness. (3) the film material after the transverse primary stretching passes through an extraction tank to separate the paraffin oil with an extracting liquid, wherein the extracting liquid is dichloromethane; (4) The extracted membrane material is stretched transversely for a second time, the transverse pores are repaired uniformly at high temperature, and after heat setting, the membrane material is rolled up into a highly flame-retardant polyolefin diaphragm.

8. The highly flame-retardant polyolefin separator according to claim 7, characterized in that: The thickness of the highly flame-retardant polyolefin separator is 40-100 μm.

9. A method for preparing a highly flame-retardant polyolefin diaphragm according to any one of claims 1 to 8, characterized in that: The steps include: S1: adding the flame retardant and PE powder into a twin-screw extruder according to the weight ratio of the raw materials, blending and polymerizing, and then granulating to obtain a modified high flame retardant PE masterbatch; the particle size D50 of the high flame retardant PE masterbatch is ≤80μm; S2: mixing the high flame retardant PE masterbatch, antioxidant and paraffin oil obtained in step S1 according to the weight ratio of the raw materials at a high temperature speed of a twin-screw extruder to form a high-temperature molten fluid; S3 The high-temperature molten fluid is cast through the die head and cooled to form a film, and then the thick film from the cast sheet is longitudinally stretched by adjusting the roller speed difference, and then the longitudinally stretched film is transversely stretched once to form a film material with uniform thickness; S4 The film material after the transverse primary stretching passes through an extraction tank to separate the paraffin oil with an extracting liquid, wherein the extracting liquid is dichloromethane; S5 performs a transverse secondary stretching on the extracted membrane material, performs high-temperature uniformity repair on the transverse pores, and after heat setting, rolls it up into a highly flame-retardant polyolefin diaphragm semi-finished membrane; S6: subjecting the semi-finished film to a slitting device to obtain a finished film of the highly flame-retardant polyolefin diaphragm.

10. The method for preparing a highly flame-retardant polyolefin diaphragm according to claim 9, characterized in that: In step S2, the screw aspect ratio of the twin-screw extruder is greater than 45, the segmented temperature is 160-220°C, the filter precision is 10-50 μm, the cooling film thickness is ≥100 μm, and the casting roller temperature is 10-40°C; In step S3, the longitudinal stretching ratio is 1-15 times, the longitudinal stretching speed is 3-15 m / min, the transverse primary stretching ratio is 6-15 times, and the transverse primary stretching speed is 8-30 m / min; In step S4, the extraction phase separation time is controlled to be ≥ 2 min, the production speed is 10-60 m / min, and the running direction of the gas and the high barrier membrane in this step forms a convection mode; In step S5, the stretching ratio of the transverse secondary stretching is 1-5 times, the transverse secondary stretching speed is 20-80 m / min, and the temperature of the heat setting roller is 130-180° C.; In step S6, the primary slitting speed is controlled to be 50-150 m / min, the speed of the slitting machine is controlled to be 80-100 m / min, the unwinding tension is 25-50 N, the winding tension is 15-40 N, and the winding taper is gradually reduced at a rate of 10%.

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