Diaphragm with high voltage resistance, preparation method thereof and electrochemical device

Abstract

The invention provides a high-voltage-resistant diaphragm and a preparation method thereof, an electrochemical device and the technical field of design of electrochemical elements, the diaphragm comprises polyolefin and a base film formed by dielectric elastomer particles dispersed in the polyolefin, the voltage resistance of the base film is not lower than 250V / mu m, while the voltage resistance of a current micron-sized common diaphragm is generally lower than 200V / mu m; wherein the diaphragm containing the dielectric elastomer particles can generate elastic deformation under the instantaneous voltage not lower than 500V. The invention also provides a preparation method of the diaphragm with high voltage resistance and an electrochemical device using the diaphragm. According to the high-voltage-resistant diaphragm, the preparation method thereof and the electrochemical device provided by the invention, the defect that a lithium battery diaphragm in the prior art is easy to break down under instantaneous high voltage is overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical elements, and in particular to a high-voltage withstand diaphragm and a preparation method thereof, and an electrochemical device. Background Art

[0002] Lithium battery is a common electrochemical element that provides energy. During the production and use of lithium battery separators and lithium-ion batteries, the separators are often broken down due to insufficient insulation performance, resulting in high scrap rates or battery short circuits, wherein short circuits can cause lithium batteries to burn and explode. Therefore, the voltage resistance of the separator in the lithium battery is also closely related to the safety of the lithium battery. In order to improve the voltage resistance of the separator, a variety of improvement methods have been developed in the prior art, such as applying an inorganic coating on the surface of the separator and refining the degree of crystallization of the separator. However, the breakdown voltage of the separator of the lithium battery is still relatively low, which is difficult to meet the performance requirements of high voltage resistance. Summary of the invention

[0003] One of the purposes of the present application is to provide a high voltage-resistant diaphragm to improve the defect of lithium battery diaphragms in the prior art that they are easily broken down under high voltage.

[0004] Another object of the present application is to provide a method for preparing a high voltage withstand diaphragm.

[0005] Another object of the present application is to provide an electrochemical device.

[0006] In the prior art, the diaphragms formed by the wet or dry method have the following problems: when the thickness decreases and the porosity of the diaphragm increases, the voltage resistance of the diaphragm will decrease rapidly. This is because there is air in the micropores of the diaphragm, and small molecules such as air and solvents are prone to form bridges under the action of the electric field, which in turn causes the small molecules such as air and solvents to be ionized and discharge, which in turn causes the diaphragm to be broken down and damaged. Therefore, the means to improve the voltage resistance of the diaphragm usually fall on: (1) increasing the thickness of the diaphragm, such as applying a coating; (2) increasing the crystallinity of the diaphragm; (3) restricting the free movement of molecules in the diaphragm, etc. However, the diaphragms obtained by the above means are difficult to meet the voltage resistance requirements under high voltage, especially high voltage above 1000V.

[0007] Based on the above problems, the inventors of the present application have proposed a new high-voltage resistant diaphragm, in which a small amount of dielectric elastomer particles that can undergo elastic deformation under a driving voltage are added to the base film of the diaphragm, so that the tortuosity of the micropores in the diaphragm increases under high pressure, thereby improving the degree of occlusion of the micropores, thereby improving the voltage resistance of the diaphragm under high pressure; in addition, this diaphragm can also restore the structure of its micropores after reducing the applied pressure or removing the voltage, maintaining its porosity and permeability, and is reversible.

[0008] The specific plan is as follows:

[0009] In a first aspect, the present application discloses a high withstand voltage diaphragm, comprising a base film formed by polyolefin and dielectric elastomer particles dispersed in the polyolefin, wherein the withstand voltage of the base film is not less than 2.5 kV;

[0010] Wherein, the deformed porosity of the base film at a voltage of 500 V is not less than 95% of the original porosity of the base film.

[0011] Furthermore, in some embodiments of the present application, the deformed porosity of the base membrane at a voltage of 1000V is not higher than 50% of the original porosity of the base membrane, and the deformed permeability value of the base membrane at a voltage of 1000V is not lower than 20 times the original permeability value of the base membrane.

[0012] Furthermore, in some embodiments of the present application, the dielectric elastomer particles account for 2% to 10% by mass in the base film. Preferably, the dielectric elastomer particles account for 4% to 7% by mass in the base film.

[0013] Furthermore, in some embodiments of the present application, the average particle size of the dielectric elastomer particles is 1 to 500 nm, preferably, the average particle size of the dielectric elastomer particles is 1 to 100 nm; more preferably, the average particle size of the dielectric elastomer particles is 1 to 10 nm.

[0014] Furthermore, in some embodiments of the present application, the original porosity of the base film is not less than 25%; the original air permeability of the base film is not higher than 300s / 100cc.

[0015] Furthermore, in some embodiments of the present application, the deformation permeability value of the base film at a voltage of 1000V is not less than 5000s / 100cc.

[0016] Furthermore, in some embodiments of the present application, the dielectric elastomer particles include at least one of modified or unmodified PVDF particles, PVDF and PE blend particles, silicone rubber particles, silicone resin particles, polyurethane particles, nitrile rubber particles, acrylic particles, natural rubber particles, polystyrene-butadiene-styrene based elastomers, polyurethane and acrylate copolymers, and vinyl trifluoride particles.

[0017] In a second aspect, the present application further provides a method for preparing the high withstand voltage diaphragm according to the first aspect, comprising:

[0018] Provide dielectric elastomer particles, polyolefins, and pore formers;

[0019] The dielectric elastomer particles, polyolefin and pore-forming agent are mixed and kneaded to obtain a melt;

[0020] Extruding the melt by an extrusion process to obtain a cast sheet;

[0021] The cast sheet is stretched by a stretching process to obtain an oil film;

[0022] removing the pore-forming agent in the oil film and shaping it by a heat setting process to obtain a diaphragm;

[0023] The solid content of the melt is not less than 15.3% by mass; the proportion of the polyolefin in the melt is not less than 15% by mass.

[0024] Further, in some embodiments of the present application, the cast sheet is stretched using a stretching process, comprising:

[0025] The temperature of the cast sheet does not exceed 120° C., and the temperature difference between different points in the temperature field of the stretching area is less than 0.5° C.; the stretching rate of the stretching process is not less than 30 m / min.

[0026] Furthermore, in some embodiments of the present application, the setting temperature in the heat setting treatment process is 120-140°C.

[0027] In a third aspect, the present application further provides an electrochemical device comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and the high-voltage-withstand diaphragm described in the first aspect or the high-voltage-withstand diaphragm obtained by the preparation method described in the second aspect.

[0028] Beneficial effects of this application:

[0029] The present application provides a high voltage-resistant diaphragm, in which a small amount of dielectric elastomer particles that undergo reversible deformation under high pressure are uniformly dispersed in polyolefin, and the deformation of the dielectric elastomer particles under high pressure is utilized to increase the degree of micropore occlusion in the diaphragm, thereby improving the voltage-resistant capability of the diaphragm under high pressure, reducing the risk of the diaphragm being broken down under high pressure, and effectively improving the yield rate of the diaphragm and the safety of the battery using the diaphragm. The diaphragm provided in the present application is suitable for lithium batteries with an overcharge voltage of more than 500V, and is particularly suitable for lithium batteries with an overcharge voltage of more than 1000V.

[0030] The present application also provides a method for preparing a high-voltage-resistant diaphragm. The preparation method has simple steps, is easy to promote and use, and has a high yield rate for the obtained diaphragm product.

[0031] The present application also provides an electrochemical device, which uses a base film that can reversibly increase the degree of micropore occlusion under high pressure as a diaphragm, so that the voltage resistance of the electrochemical device under high pressure is significantly improved, and the safety performance under high pressure of at least 500V is significantly improved, reducing the risk of short circuit caused by the breakdown of the diaphragm of the electrochemical device under high pressure, while also reducing the high-voltage deformation of the electrochemical device and extending the service life of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic structural diagram of a lithium battery separator provided in Example 1 of the present application;

[0033] Among them, 10 is a base film, 11 is a dielectric elastomer particle, and 12 is a micropore. DETAILED DESCRIPTION

[0034] In order to better explain the present invention, the following description will be given in detail with reference to the embodiments of the present invention, and the main contents of the present invention will be further clarified in conjunction with specific examples. However, the contents of the present invention are not limited to the following examples.

[0035] In order to improve the technical problem that the voltage resistance of lithium battery separators under high pressure in the prior art is difficult to meet the use requirements, the inventors proposed a high voltage resistance separator, such as Figure 1 As shown, a base film 10 is formed by a polyolefin and dielectric elastomer particles 11 dispersed in the polyolefin, and the withstand voltage of the base film 1 is not less than 250V / μm; wherein the deformation porosity of the base film 10 at a voltage of 500V is not less than 95% of the original porosity of the base film 10, that is, the base film containing the dielectric elastomer particles 11 will not undergo relatively obvious elastic deformation at a voltage lower than 500V.

[0036] The base film containing the dielectric elastomer particles 11 can be elastically deformed at a voltage not less than 500V, which can be understood as the driving voltage of the piezoelectric deformation of the dielectric elastomer particles 11 is not less than 500V or close to 500V.

[0037] In the present application, "piezoelectric deformation driving voltage" refers to the lowest voltage that causes the material or structure to which the voltage is applied to deform. Before the voltage is lower than this voltage, the material or structure to which the voltage is applied does not deform substantially or does not deform significantly. "Deformation porosity" should be understood as the porosity of the material or structure to which the voltage is applied after it is deformed at a voltage not lower than the driving voltage. "Original porosity" should be understood as the porosity of the material or structure before the voltage is applied or when a voltage lower than the driving voltage is applied. "Deformation permeability value" should be understood as the permeability value of the material or structure to which the voltage is applied after it is deformed at a voltage not lower than the driving voltage. "Original permeability value" should be understood as the permeability value of the material or structure before the voltage is applied or when a voltage lower than the driving voltage is applied. "Deformation thickness" should be understood as the thickness of the material or structure to which the voltage is applied after it is deformed at a voltage not lower than the driving voltage. "Original thickness" should be understood as the thickness of the material or structure before the voltage is applied or when a voltage lower than the driving voltage is applied. In the present application, the driving voltage of the piezoelectric deformation of the dielectric elastomer particles 11 is such that at or above this voltage, the dielectric elastomer particles dispersed in the base film 10 undergo relatively obvious deformation, blocking the micropores 12 in the base film 10, rapidly decreasing the porosity and rapidly increasing the air permeability, thereby increasing the breakdown voltage of the base film 10 under high pressure, reducing the possibility of the base film 10 being broken down under this high pressure, and thus improving the safety of the battery based on the base film 10. After the applied voltage drops to the driving voltage or after the voltage is no longer applied, the deformation of the dielectric elastomer particles 11 is restored, the micropores 12 in the base film 10 are opened, the porosity and air permeability are restored to the original porosity and original air permeability levels, and the battery performance is restored.

[0038] It should be noted that in the present application, the base membrane containing the dielectric elastomer particles 11 can undergo elastic deformation at a voltage of not less than 500V, which does not exclude the possibility that the base membrane may undergo slight deformation at a voltage below 500V, such as 450V. It is just that at a voltage below 500V, the deformation is relatively subtle and has no obvious effect on the porosity, air permeability, etc. of the base membrane.

[0039] Furthermore, the deformation porosity of the base membrane at a voltage of 1000V is not higher than 50% of the original porosity of the base membrane, and the deformation permeability value of the base membrane at a voltage of 1000V is not less than 20 times the original permeability value of the base membrane. When the voltage is applied to deform, the thickness of the diaphragm decreases. In the present application, the thickness of the base membrane will also decrease at a voltage of 1000V, such as a decrease of about 30%. More preferably, the deformation porosity of the base membrane at a voltage of 1000V is not higher than 40% of the original porosity of the base membrane, and the deformation permeability value of the base membrane at a voltage of 1000V is not less than 30 times the original permeability value of the base membrane.

[0040] In some embodiments, the proportion of the dielectric elastomer particles in the base film is 2% to 10% by mass, preferably, the proportion of the dielectric elastomer particles in the base film is 4% to 7% by mass. The amount of the dielectric elastomer particles added should not be too high or too low. Too high an amount will affect the electrical properties of the base film, and too low an amount will make it difficult to achieve significant deformation and achieve a significant improvement in voltage resistance.

[0041] In some embodiments, the average particle size of the dielectric elastomer particles is 1 to 500 nm. Preferably, the average particle size of the dielectric elastomer particles is 1 to 100 nm. More preferably, the average particle size of the dielectric elastomer particles is 1 to 10 nm.

[0042] In some embodiments, the average pore size of the inner pores in the base film is no greater than 35 nm.

[0043] In some embodiments, the original porosity of the base film is not less than 25%; the original air permeability of the base film is not higher than 300s / 100cc. The base film provided by the present application has a small average pore size of the inner pores and a high porosity, and has good ion conductivity under the working voltage; and under high pressure, the micropores can be quickly closed, the porosity is significantly reduced, and the voltage resistance is rapidly and significantly improved.

[0044] In some embodiments, the deformation permeability value of the base film at a voltage of 1000V is not less than 5000s / 100cc.

[0045] In certain embodiments, the dielectric elastomer particles include modified or unmodified PVDF particles, PVDF and PE blend particles, silicone rubber particles, silicone resin particles, polyurethane particles, nitrile rubber particles, acrylic particles, natural rubber particles, polystyrene-butadiene-styrene-based elastomers, polyurethane and acrylate copolymers, and vinylene trifluoride ethylene particles. It should be noted that in the present application, the dielectric elastomer particles can be modified or unmodified dielectric elastomer particles. Exemplarily, the dielectric elastomer particles used in the present application can be acrylate rubber, or acrylate rubber modified by aluminum oxide ceramic powder. In the present application, the component used to modify the dielectric elastomer particles can be inorganic nano-ceramic particles or nano-composite materials.

[0046] In some embodiments, the ultra-high molecular weight polyethylene used in the present application may be one or more. When one ultra-high molecular weight polyethylene is used, its viscosity average molecular weight is not less than 1.3 million, preferably not less than 2 million. When two or more ultra-high molecular weight polyethylenes are used, the overall viscosity average molecular weight is not less than 1.3 million, preferably not less than 2 million. When the polyolefin uses two or more ultra-high molecular weight polyethylenes, it usually uses an ultra-high molecular weight polyethylene with a lower molecular weight and an ultra-high molecular weight polyethylene with a higher molecular weight, such as using an ultra-high molecular weight polyethylene with a viscosity average molecular weight of 500,000 to 600,000 and an ultra-high molecular weight polyethylene with a viscosity average molecular weight of 2 million to 2.5 million.

[0047] In some embodiments, the base film further comprises an antioxidant, and the antioxidant accounts for 0 to 0.5% by mass in the base film. The antioxidant used in the present application can be one or more of the antioxidants in the conventional base film on the market, such as: antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant 1098, ethanolamine, isohydroxy acid, tert-butyl hydroquinone, sorbitol, dilauryl thiodipropionate, distearate thiodipropionate, etc., one or more of these amines, phenols, thioester antioxidants, and phosphite antioxidants.

[0048] In a second aspect, the present application further provides a method for preparing the high withstand voltage diaphragm according to the first aspect, comprising:

[0049] Provide dielectric elastomer particles, polyolefins, and pore formers;

[0050] The dielectric elastomer particles, polyolefin and pore-forming agent are mixed and kneaded to obtain a melt;

[0051] Extruding the melt by an extrusion process to obtain a cast sheet;

[0052] The cast sheet is stretched by a stretching process to obtain an oil film;

[0053] removing the pore-forming agent in the oil film and shaping it by a heat setting process to obtain a diaphragm;

[0054] Among them, the solid content in the melt is not less than 15.3% by mass, so that the viscosity of the obtained melt is suitable for processing and is beneficial to the pore size of the inner pores of the formed base film; the proportion of the polyolefin in the melt is not less than 15% by mass.

[0055] In some embodiments, the cast sheet is stretched using a stretching process, comprising:

[0056] The temperature of the cast sheet does not exceed 120° C., such as 115° C., and the temperature difference between different points in the temperature field of the stretching area is less than 0.5° C.; the stretching rate of the stretching process is not less than 30 m / min.

[0057] In some embodiments, the setting temperature in the heat setting treatment process is 125-140°C.

[0058] In some embodiments, the mass ratio of the dielectric elastomer particles, polyolefin, and pore former is 0.3% to 3.5%: 15% to 35%: 61.5% to 83.7%.

[0059] It should be noted that the pore-forming agent in the present application can be a commercially available pore-forming agent for a diaphragm, such as paraffin oil, and therefore they are not listed one by one in the present application.

[0060] In some embodiments, when it is necessary to add an antioxidant or other additive, the antioxidant or other additive is mixed and kneaded together with the dielectric elastomer particles, polyolefin, and pore-forming agent to obtain a melt.

[0061] In a third aspect, the present application further provides an electrochemical device comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and the high-voltage-withstand diaphragm described in the first aspect or the high-voltage-withstand diaphragm obtained by the preparation method described in the second aspect.

[0062] The electrochemical device can be a lithium ion primary battery, a lithium ion secondary battery, a sodium ion battery, a semi-solid battery, a solid-state battery, etc., or can be any electronic product containing the above electrochemical devices, such as mobile electronic devices such as mobile phones, lighting equipment, UPS, electric vehicles, etc.

[0063] In some embodiments, the diaphragm provided in the present application can be directly used as a diaphragm in an electrochemical device, or can be used as an isolation membrane in an electrochemical device as a whole after coating the surface.

[0064] Hereinafter, the present invention will be described by referring to several embodiments, but the present invention is not intended to be limited to these embodiments.

[0065] Embodiment 1:

[0066] The present invention provides a method for preparing a high-voltage withstand diaphragm, which specifically includes the following steps:

[0067] 1% of acrylic rubber (AR840, Japan Zeon), 15.5% by weight of ultra-high molecular weight polyethylene powder (GUR2122, Ticona Celanese), and 83.5% by weight of paraffin oil (60#, Zhejiang Zhengxin) were used. 0.3 parts by weight of antioxidant (Irg1010 (Ciba Specialty Chemicals BASF)) and 0.1 parts by weight of antioxidant (P168 (Ciba Specialty Chemicals Co., Ltd.)) were added to 100 parts by weight of the high molecular weight polyethylene and paraffin oil in total, and they were mixed in order. The ultra-high molecular weight polyethylene material after mixing the auxiliary agent was put into a twin-screw extruder together with the paraffin oil for mixing. The average particle size of the acrylic rubber particles after mixing was 5 to 10 nm, and a mixture melt gel was finally prepared.

[0068] The gel was extruded using a T-die, the extruded melt temperature was controlled below 220°C, and then rapidly cooled on a thermostatic metal pair of rollers with a surface temperature of 15°C and rolled into a cast sheet with a thickness of 1.5 mm.

[0069] The cast sheet is pulled and stretched. Rapid stretching is performed at 115°C at a speed of 40m / min, with both the longitudinal (MD) and transverse (TD) stretching ratios of 6.5. The uniformity of the temperature field needs to be controlled during stretching, and the temperature difference between different points in the temperature field in the stretching area is less than 0.3°C. After stretching, an oil film is obtained. The oil film is pulled into the extraction to extract the paraffin oil in the oil film. Then, the dichloromethane remaining in the diaphragm is taken out by constant temperature hot air at 40°C, and then a high voltage withstand diaphragm 1 is obtained after a heat setting treatment at 129°C.

[0070] Example 2

[0071] Alumina ceramic powder (nano-alumina, 99.9%, gamma, J&K) with a particle size of less than 30 nm and acrylic rubber (THIXON 715, DuPont) were blended at a mass ratio of 5:95 at 200° C. using an internal mixer, and granulated to control the particle size to be less than 200 μm; 1 wt % of the granulated mixture, 14 wt % of ultra-high molecular weight polyethylene powder (GUR2122, Ticona Celanese), 5 wt % of high-density polyethylene powder (GUR4116, Ticona Celanese), and 80 wt % of paraffin oil (60#, Zhejiang Zhengxin) were added, with respect to a total of 100 wt % of the high molecular weight polyethylene and the paraffin oil, 0.3 wt % of antioxidant (Irg1010 (Ciba Specialty Chemicals BASF)) and 0.1 wt % of antioxidant (P168 (manufactured by Ciba Specialty Chemicals Co., Ltd.)) were added, and they were mixed in this order. The ultra-high molecular weight polyethylene material after mixing with the additives is put into a twin-screw extruder together with paraffin oil for mixing, and the average particle size of the acrylic rubber particles is controlled not to exceed 30nm, and finally a mixture melt gel is prepared.

[0072] The gel was extruded using a T-die, the extruded melt temperature was controlled below 220°C, and then rapidly cooled on a thermostatic metal pair of rollers with a surface temperature of 15°C and rolled into a cast sheet with a thickness of 1.5 mm.

[0073] The cast sheet is pulled and stretched. Rapid stretching is performed at 119°C at a speed of 40m / min, with both the longitudinal (MD) and transverse (TD) stretching ratios of 6.5. The uniformity of the temperature field needs to be controlled during stretching, and the temperature difference between different points in the temperature field in the stretching area is less than 0.3°C. An oil film is obtained after stretching. The oil film is pulled into the extraction to extract the paraffin oil in the oil film. Then, the dichloromethane remaining in the diaphragm is taken out by constant temperature hot air at 40°C, and then a high voltage withstand diaphragm 2 is obtained after a heat setting treatment at 129°C.

[0074] Example 3

[0075] 5% ethylene-trifluoride copolymer (6514, Solvay) and PVDF (1006, Solvay) were melt-blended at 220°C and granulated to a particle size of no more than 300 μm; the granulated mixture was mixed with 4% by weight of polyethylene powder (GUR2122, Ticona Celanese), 10% by weight of high-density polyethylene powder (VH200U, KPIC), 5% by weight of polyethylene powder (VH035, KPIC), and 80% by weight of paraffin oil (60#, Zhejiang Zhengxin), and an antioxidant was added to 100 parts by weight of the solid mixture and the paraffin oil.

[0076] 0.3 parts by weight of Irg1010 (Ciba Specialty Chemicals BASF) and 0.1 parts by weight of antioxidant (P168 (Ciba Specialty Chemicals Co., Ltd.)) are mixed in order. The ultra-high molecular weight polyethylene material after mixing the auxiliary agent is put into a twin-screw extruder together with paraffin oil for mixing, and the average particle size of the dielectric elastomer particles is controlled to be about 5-10nm, and finally a mixture melt gel is prepared.

[0077] The gel was extruded using a T-die, the extruded melt temperature was controlled below 220°C, and then rapidly cooled on a thermostatic metal pair of rollers with a surface temperature of 15°C and rolled into a sheet with a thickness of 1.5 mm.

[0078] The sheet is pulled and stretched. Rapid stretching is performed at 116°C at a speed of 40m / min, with both the longitudinal (MD) and transverse (TD) stretching ratios of 6.5. The uniformity of the temperature field needs to be controlled during stretching, and the temperature difference between different points in the temperature field in the stretching area is less than 0.3°C. An oil film is obtained after stretching. The oil film is pulled into the extraction to extract the paraffin oil in the oil film. Then, the dichloromethane remaining in the diaphragm is taken out by constant temperature hot air at 40°C, and then a high voltage withstand diaphragm 3 is obtained after a heat setting treatment at 129°C.

[0079] Comparative Example 1

[0080] Compared with Example 1, no dielectric elastomer particles were added in this comparative example, and the remaining steps were the same as those in Example 1 to obtain a comparative diaphragm 1.

[0081] Comparative Example 2

[0082] Compared with Example 1, the amount of dielectric elastomer particles added in this comparative example is 0.2% by weight, and the remaining steps are the same as those in Example 1, to obtain a comparative diaphragm 2.

[0083] Comparative Example 3

[0084] Compared with Example 1, the amount of dielectric elastomer particles added in this comparative example is 5 parts by weight, and the remaining steps are the same as those in Example 1, to obtain a comparative diaphragm 3.

[0085] Comparative Example 4

[0086] Compared with Example 1, the elastomer particles added in this comparative example are EPDM (4725P, Dow), and the elastomer particles do not have piezoelectric deformation performance. The remaining steps are the same as those in Example 1, and a comparative diaphragm 4 is obtained.

[0087] Comparative Example 5

[0088] Compared with Example 1, in the stretching process of this comparative example, the cast sheet is pulled and stretched, and rapid stretching is performed at 125° C. at a speed of 40 m / min. The remaining steps are the same as those of Example 1, and a comparative diaphragm 5 is obtained.

[0089] In order to further verify the high withstand voltage performance of the diaphragm provided in the present application, the inventors also verified the performance of comparative diaphragms obtained at a non-heat setting temperature, specifically, the preparation comparative examples 6 to 10 of the comparative diaphragms.

[0090] Comparative Example 6

[0091] Compared with Example 1, this comparative example does not add dielectric elastomer particles, and the stretching process adopted is rapid stretching at 123°C and a speed of 40m / min; the shaping process adopted is: heat setting treatment at 130°C, and the remaining steps are the same as Example 1, to obtain a comparative diaphragm 6.

[0092] Comparative Example 7

[0093] Compared with Example 6, the shaping process adopted in this comparative example is: heat-setting treatment at 133° C., and the remaining steps are the same as those in Example 6, to obtain a comparative diaphragm 7.

[0094] Comparative Example 8

[0095] Compared with Example 6, the shaping process adopted in this comparative example is: heat-setting treatment at 135° C., and the remaining steps are the same as those in Example 6, to obtain a comparative diaphragm 8.

[0096] Comparative Example 9

[0097] Compared with Example 6, the shaping process adopted in this comparative example is: heat-setting treatment at 136° C., and the remaining steps are the same as those in Example 6, to obtain a comparative diaphragm 9.

[0098] Comparative Example 10

[0099] Compared with Example 6, the shaping process adopted in this comparative example is: after heat shaping treatment at 138° C., the remaining steps are the same as those in Example 6, and a comparative diaphragm 10 is obtained.

[0100] experiment

[0101] The physical parameters and performance parameters of the diaphragms obtained in the above-mentioned Examples 1 to 3 and Comparative Examples 1 to 10 were tested respectively by the following test methods, and the specific test methods are as follows:

[0102] Test method:

[0103] 1-Porosity

[0104] The porosity ε of the diaphragm is calculated according to the following calculation method:

[0105] Assume that the constituent materials of the diaphragm are a, b, c...n, and the mass of each constituent material is W a , W b , W c …W n (g / cm 2 ), the true density of each constituent material is ρ a , b , c …ρ n (g / cm 3 ), when the membrane thickness is recorded as t (cm), the porosity ε (%) is calculated using the following formula:

[0106] ε={1(W a / ρ a +W b / ρ b +W c / ρ c +…+W n / ρ n ) / t}×100.

[0107] 2- Withstand voltage of diaphragm (DC)

[0108] Cut a circular diaphragm sample with a diameter of 60 mm, place it on a square aluminum plate with a side length of 150 mm, place a brass cylindrical electrode with a diameter of 50 mm, a height of 30 mm, and a weight of 500 g on it, and connect it to the TOS5051A dielectric breakdown tester made by Kikusui Electronics Industry. Apply a DC voltage at a boost rate of 0.15 KV / sec, set the current to 2 mA, and read the voltage V when the sample breaks down. The withstand voltage was measured 15 times and the average value was obtained.

[0109] 3- Membrane air permeability

[0110] Cut a 100mm×100mm membrane sample and use the American Gurley 4110N air permeability tester to test it using the 100cc test gas mode. Record the time it takes for the test gas to pass through the membrane sample, which is the membrane air permeability value R. 2 .

[0111] 4-Film thickness

[0112] The thickness d of the diaphragm is measured using a micrometer.

[0113] The test results are shown in Table 1:

[0114] Table 1

[0115] d(μm) <![CDATA[R 2 (s / 100cc)]]> ε(%) V(Kv) Example 1 10 173 44.5 2.5 Example 2 10 180 44.5 2.6 Example 3 10 190 44.8 3.1 Comparative Example 1 10 155 44.5 1.5 Comparative Example 2 10 157 44.5 1.5 Comparative Example 3 10 600 45.3 2.8 Comparative Example 4 10 246 42.5 1.3 Comparative Example 5 10 135 48.3 2.2 Comparative Example 6 10 160 45 1.7 Comparative Example 7 7.2 600 23.2 1.8 Comparative Example 8 6.1 4300 10.2 2.2 Comparative Example 9 6 5900 8.2 2.6 Comparative Example 10 5.9 6000 6.8 5

[0116] As can be seen from Table 1, the diaphragm provided by the present application has significantly improved voltage resistance performance without significantly increasing the thickness of the diaphragm, the porosity, or even significantly reducing the permeability, and the voltage resistance performance is good and can reach more than 2.5 kV. At the same time, it can be seen from the measurement results of the porosity, permeability, and voltage resistance of the diaphragms of Examples 6 to 10 that although a higher voltage resistance can be obtained by using a higher heat setting, the porosity of the diaphragm obtained is significantly reduced and the permeability is also significantly increased, which is not conducive to the ion conductivity of the diaphragm.

[0117] In order to further verify the improvement of the withstand voltage of the diaphragm provided in the present application, the inventors also measured the porosity, air permeability and thickness of the diaphragm provided in Example 1 of the present application at different voltages, and the test results obtained are shown in Table 2.

[0118] Table 2

[0119]

[0120] As can be seen from Table 2, the membrane provided in Example 1 of the present application has a low air permeability when no voltage is applied, and when the applied voltage reaches 500V, the thickness of the membrane decreases and the air permeability increases significantly. It can be seen that at this time, the dielectric elastomer particles in the membrane have been deformed, causing the micropores in the membrane to be partially closed; and as the applied voltage increases to 2000V, the thickness of the membrane decreases, the porosity decreases to 8%, and the air permeability increases to 7000s / 100cc. It can be seen that the membrane provided by the present application has closed micropores under high pressure, the porosity and thickness decrease significantly, the air permeability increases significantly, and the electrical resistance is significantly improved.

[0121] The present invention can be implemented in other forms than those described above without departing from the spirit and scope of the present invention. The embodiments disclosed in the present application are examples and are not limited to these.

Claims

1. A high withstand voltage diaphragm, characterized in that: A base film comprising polyolefin and dielectric elastomer particles dispersed in the polyolefin, wherein the base film has a withstand voltage of not less than 250V / μm; Wherein, the deformed porosity of the base film at a voltage of 500 V is not less than 95% of the original porosity of the base film.

2. The high withstand voltage diaphragm according to claim 1, characterized in that: The deformed porosity of the base film at a voltage of 1000V is not higher than 50% of the original porosity of the base film, and the deformed permeability value of the base film at a voltage of 1000V is not lower than 20 times the original permeability value of the base film.

3. The high withstand voltage diaphragm according to claim 1, characterized in that: The dielectric elastomer particles account for 2% to 10% by mass in the base film. Preferably, the dielectric elastomer particles account for 4% to 7% by mass in the base film.

4. The high withstand voltage diaphragm according to claim 1, characterized in that: The average particle size of the dielectric elastomer particles is 1 to 500 nm. Preferably, the average particle size of the dielectric elastomer particles is 1 to 100 nm. More preferably, the average particle size of the dielectric elastomer particles is 1 to 10 nm.

5. The high withstand voltage diaphragm according to claim 2, characterized in that: The original porosity of the base film is not less than 25%; the original air permeability of the base film is not higher than 300s / 100cc.

6. The high withstand voltage diaphragm according to claim 5, characterized in that: The deformation permeability value of the base film under a voltage of 1000V is not less than 5000s / 100cc.

7. The high withstand voltage diaphragm according to claim 1, characterized in that: The dielectric elastomer particles include at least one of modified or unmodified PVDF particles, PVDF and PE blend particles, silicone rubber particles, silicone resin particles, polyurethane particles, nitrile rubber particles, acrylic particles, natural rubber particles, polystyrene-butadiene-styrene based elastomers, polyurethane and acrylate copolymers, and vinylidene trifluoride particles.

8. The method for preparing a high withstand voltage diaphragm according to any one of claims 1 to 7, characterized in that: include: Provide dielectric elastomer particles, polyolefins, and pore formers; The dielectric elastomer particles, polyolefin and pore-forming agent are mixed and kneaded to obtain a melt; Extruding the melt by an extrusion process to obtain a cast sheet; The cast sheet is stretched by a stretching process to obtain an oil film; removing the pore-forming agent in the oil film and shaping it by a heat setting process to obtain a diaphragm; The solid content of the melt is not less than 15.3% by mass; the proportion of the polyolefin in the melt is not less than 15% by mass.

9. The method for preparing a high withstand voltage diaphragm according to claim 8, characterized in that: The cast sheet is stretched by a stretching process, comprising: The temperature of the cast sheet does not exceed 120°C, and the temperature difference between different points in the temperature field of the stretching area is less than 0.5°C; the stretching rate of the stretching process is not less than 30m / min; and / or The setting temperature in the heat setting treatment process is 120°C to 140°C.

10. An electrochemical device, characterized in that: The invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte and a high-voltage-withstanding membrane according to any one of claims 1 to 7 or a high-voltage-withstanding membrane obtained by the preparation method according to any one of claims 8 to 9.

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