Isolating membrane and preparation method thereof, secondary battery monomer and electric device

Abstract

The invention provides an isolating membrane, a preparation method of the isolating membrane, a battery monomer and a power utilization device. The isolating membrane comprises a polypropylene porous base membrane, and the average pore size of the polypropylene porous base membrane is smaller than or equal to 30 nm. According to the present invention, the average pore size of the polypropylene porous base membrane is less than or equal to 30 nm, and is smaller than the average pore size of the conventional polypropylene porous base membrane, such that the puncture resistance of the isolation membrane is substantially improved so as to improve the safety performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a separator and its preparation method, a secondary battery cell, and an electrical device. Background Technology

[0002] With the development of lithium-ion batteries in power batteries, their safety has received increasing attention from researchers. Studies have shown that because the electrolyte is an organic substance, it poses significant safety hazards in safety tests such as nail penetration, overcharging, drop, immersion, and hot box tests. The lithium battery separator is a crucial component of liquid lithium-ion batteries, not only transporting lithium ions but also isolating the positive and negative electrodes to prevent short circuits. The performance of the lithium battery separator has a decisive influence on the interface structure of the entire battery system and directly affects the battery's safety performance. Summary of the Invention

[0003] This application provides a separator, a method for preparing the separator, a secondary battery cell, and an electrical device to improve the puncture resistance of the separator.

[0004] The first aspect of this application provides a separating membrane, comprising a polypropylene porous base membrane, wherein the average pore size of the polypropylene porous base membrane is less than or equal to 30 nm.

[0005] The separator of this application includes a polypropylene porous base membrane, and the average pore size of the polypropylene porous base membrane is less than or equal to 30 nm, which is smaller than the average pore size of conventional polypropylene porous base membranes, thus greatly improving the separator's resistance to dendrite puncture.

[0006] In any embodiment of the first aspect, the average pore size of the polypropylene porous base membrane is 10 nm-30 nm; optionally, it is 15 nm-25 nm.

[0007] In any embodiment of the first aspect, the porosity of the polypropylene porous base membrane is 37%-50%, optionally 38%-43%.

[0008] In any embodiment of the first aspect, the ratio of puncture strength to thickness of the polypropylene porous base membrane is 40 gf / μm-60 gf / μm; optionally, it is 48 gf / μm-58 gf / μm.

[0009] In any embodiment of the first aspect, the puncture strength of the polypropylene porous base membrane is 250gf-400gf, optionally 280gf-380gf; and / or the thickness of the polypropylene porous base membrane is 4μm-10μm, optionally 6μm-8μm.

[0010] In any embodiment of the first aspect, the air permeability of the polypropylene porous base membrane is 150 seconds / 100mL to 300 seconds / 100mL, and optionally 170 seconds / 100mL to 280 seconds / 100mL.

[0011] In any embodiment of the first aspect, the transverse tensile strength of the polypropylene porous base membrane is 1500 kgf / cm. 2 -2000 kgf / cm 2 1600 kgf / cm² is optional. 2 -1800 kgf / cm 2 .

[0012] In any embodiment of the first aspect, the longitudinal tensile strength of the polypropylene porous base membrane is 2100 kgf / cm. 2 -2800 kgf / cm 2 2200 kgf / cm² is optional. 2 -2600 kgf / cm 2 .

[0013] In any embodiment of the first aspect, the crystallinity of the polypropylene porous base membrane is 40%-55%.

[0014] In any embodiment of the first aspect, the polypropylene in the porous polypropylene base membrane includes a first polypropylene and a second polypropylene. The first polypropylene has a weight-average molecular weight of 50w-150w and a melt index of 0.05g / 10min-1g / 10min, and the second polypropylene has a weight-average molecular weight of 20w-100w and a melt index of 0.5g / 10min-2g / 10min. Optionally, the mass ratio of the first polypropylene to the second polypropylene is 4:1-8:1.

[0015] In any embodiment of the first aspect, the separator further includes a coating disposed on one or both sides of the polypropylene porous base membrane.

[0016] In any embodiment of the first aspect, the coating includes a heat-resistant layer disposed on one or both sides of the polypropylene porous base film.

[0017] In any embodiment of the first aspect, the coating includes an adhesive layer disposed on one or both sides of the polypropylene porous base membrane; or the adhesive layer is disposed on the side of the heat-resistant layer away from the polypropylene porous base membrane.

[0018] The second aspect of this application provides a method for preparing a separator membrane, the separator membrane comprising a polypropylene porous base membrane. The preparation method includes a process for preparing the polypropylene porous base membrane, the process comprising: preparing a polypropylene casting; performing wet biaxial stretching on the polypropylene casting to obtain an initial membrane, the wet biaxial stretching comprising sequentially performing a first longitudinal stretching, a first transverse stretching, a second longitudinal stretching, and a second transverse stretching, wherein the stretching ratios of the first longitudinal stretching and the first transverse stretching are each independently 1.1-2, and the stretching ratio of the first longitudinal stretching is less than the stretching ratio of the first transverse stretching; the stretching ratios of the second longitudinal stretching and the second transverse stretching are each independently 5-13, and the stretching ratio of the second longitudinal stretching is less than the stretching ratio of the second transverse stretching; removing the solvent from the initial membrane and then performing heat setting to obtain the polypropylene porous base membrane.

[0019] In any embodiment of the second aspect, the stretching ratio of the first longitudinal stretch is 1.1-1.5; and / or, the stretching ratio of the first transverse stretch is 1.2-1.7; and / or, the stretching ratio of the second longitudinal stretch is 5-10; and / or, the stretching ratio of the second transverse stretch is 7-13.

[0020] In any embodiment of the second aspect, the process of preparing polypropylene castings includes: melting, extruding, and quenching a mixture comprising raw material polypropylene and a solvent to obtain polypropylene castings, wherein the mass ratio of raw material polypropylene to solvent is optionally 3:7-5:5.

[0021] In any embodiment of the second aspect, the mixture further includes a solubilizer, a nucleating agent, and an antioxidant; optionally, the solubilizer includes one or more polyolefins or polyolefin copolymers with a weight average molecular weight of less than 1000; optionally, the solubilizer includes polypropylene.

[0022] In any embodiment of the second aspect, the weight ratio of the raw material polypropylene to the solubilizer is (10-30):1.

[0023] In any embodiment of the second aspect, the raw material polypropylene satisfies one or more of the following (1)-(5):

[0024] (1) The weight-average molecular weight of the raw material polypropylene is 80W-130W;

[0025] (2) The raw material polypropylene includes first polypropylene and second polypropylene, and the weight-average molecular weight of first polypropylene is greater than that of second polypropylene.

[0026] (3) The raw material polypropylene includes first polypropylene and second polypropylene, and the melt index of first polypropylene is less than that of second polypropylene.

[0027] (4) The raw material polypropylene includes a first polypropylene, the weight average molecular weight of the first polypropylene is 50w-150w, and / or the melt index of the first polypropylene is 0.05g / 10min-1g / 10min, and / or the mass percentage of the first polypropylene in the raw material polypropylene is greater than or equal to 80%.

[0028] (5) The raw material polypropylene includes a second polypropylene, the weight average molecular weight of the second polypropylene is 20w-100w, and / or the melt index of the second polypropylene is 0.5g / 10min-2g / 10min, and / or the mass percentage of the second polypropylene in the raw material polypropylene is less than or equal to 20%.

[0029] In any embodiment of the second aspect, the temperature of the quenching roller is 20°C-30°C.

[0030] The third aspect of this application provides a secondary battery cell, including an electrode assembly, which includes a positive electrode, a negative electrode, and a separator. The separator is disposed between the positive electrode and the negative electrode. The separator includes any of the separators provided in the first aspect or any separator prepared by any of the preparation methods provided in the second aspect.

[0031] The fourth aspect of this application provides an electrical device comprising one or more of the secondary battery cells provided in the third aspect above. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0034] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0035] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0036] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0037] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0038] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0039] The accompanying drawings are not drawn to scale.

[0040] Explanation of reference numerals in the attached figures:

[0041] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Casing; 52 Electrode assembly; 53 End cap. Detailed Implementation

[0042] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0043] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the separator, its preparation method, secondary battery cell, and power supply device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0044] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0046] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0047] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0048] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0049] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] [Isolation membrane]

[0051] Currently, polypropylene separators have poor puncture resistance. To address this issue, this application provides a separator comprising a porous polypropylene base membrane, wherein the average pore size of the porous polypropylene base membrane is less than or equal to 30 nm.

[0052] The polypropylene porous membrane of this application has an average pore size of less than or equal to 30 nm, which is smaller than that of conventional polypropylene porous membranes. This significantly improves the membrane's resistance to dendrite penetration and its resistance to penetration by particles and electrode burrs in the electrode assembly. Although the mechanism is unclear, this application also finds that surface lithium deposition is effectively controlled in polypropylene porous membranes with the aforementioned average pore size.

[0053] The above-mentioned average aperture test method can be referred to the following method:

[0054] The average pore size of the polypropylene porous membrane was tested using a water pressure tester (such as the AAQ-3K-A-1 model from PMI Instruments, USA). Water can be used as the test solution.

[0055] In some embodiments, the average pore size of the polypropylene porous base membrane is 10nm-30nm, optionally 15nm-25nm, and further optionally 15nm-22nm.

[0056] In order to improve the wettability of the electrolyte in the separator membrane, given that the average pore size of the polypropylene porous membrane is relatively small, in some embodiments the porosity of the polypropylene porous membrane is 37%-50%, and can be selected as 38%-43%.

[0057] The porosity mentioned above was tested using a gravimetric method.

[0058] The pre-cut polypropylene porous membrane sample was die-cut into rectangular samples of a certain area (e.g., 100mm × 50mm). The length L and width W of the rectangular sample were measured. Then, the thickness was measured using a 0.1μm micrometer at five points: four at the edges and one in the middle. The average of the five measurements was taken as the final thickness, denoted as T. The weighed rectangular sample was then weighed using an analytical balance with an accuracy of 0.0001g, and the weight was recorded as ML. The measured length L, width W, thickness T, and the material density p of the polypropylene porous membrane (0.905g / cm³) were used to determine the final thickness. 3 The theoretical weight of the polypropylene porous membrane was calculated and denoted as M2: M2 = L × W × T × p. Porosity = (1 - M1 / M2) × 100%.

[0059] In some embodiments, the ratio of puncture strength to thickness of the polypropylene porous base membrane is 40 gf / μm to 60 gf / μm; optionally, it is 48 gf / μm to 58 gf / μm. The polypropylene porous base membrane has high puncture strength per unit thickness, thus maintaining high puncture capability while reducing thickness, thereby increasing the energy density of the battery cell by reducing the thickness of the separator.

[0060] In some embodiments, the puncture strength of the polypropylene porous base membrane is 250 gf-400 gf, optionally 280 gf-380 gf, and further optionally 350 gf-380 gf. The polypropylene porous base membrane of this application has a high overall puncture strength, indicating that the polypropylene material is relatively uniformly distributed in the polypropylene porous base membrane.

[0061] In some embodiments, the thickness of the polypropylene porous base membrane is 4μm-10μm, optionally 6μm-8μm, and further optionally 6.5μm-7μm. Polypropylene porous base membranes with the above thickness ranges have uniform thickness and small thickness differences across the entire membrane extension surface, thus providing relatively uniform puncture strength and air permeability.

[0062] Puncture strength test method:

[0063] Cut the polypropylene porous membrane into strips, with a width greater than 10cm. Place the strips in a specially designed clamp (inner clamp diameter 10mm), ensuring the membrane's flatness during placement. Ventilate the clamp to ensure it grips the membrane firmly. Turn on the universal testing instrument, setting the needle movement speed to 50mm / min (needle tip diameter 1mm, semi-circular tip shape). When the needle pierces the membrane, read the puncture strength test result; the maximum value is the puncture strength of the polypropylene porous membrane. To improve accuracy, the average of multiple measurements (e.g., 3) can be used as the final puncture strength.

[0064] The thickness of a porous polypropylene membrane can be tested using equipment and methods known in the art. The thickness of a porous polypropylene membrane is typically measured using a CP image. The testing procedure is as follows: The porous polypropylene membrane is cut into a sample of a specific size (e.g., 6mm × 6mm). The sample is sandwiched between two conductive and thermally conductive sheets (e.g., copper foil). The sample is then glued to the sheets using adhesive (e.g., double-sided tape). A flat iron block of a certain weight (e.g., approximately 400g) is used to press the sample for a certain period (e.g., 1 hour) to minimize the gap between the sample and the copper foil. The edges are then trimmed with scissors and the sample is adhered to a sample stage with conductive adhesive, with the sample slightly protruding from the edge of the stage. The sample is polished using an argon ion section polisher (e.g., IB-19500CP), and the ion-polished cross-sectional morphology (CP) image of the sample is obtained using a scanning electron microscope (e.g., ZEISS Sigma 300). The thickness of the porous polypropylene membrane is marked on the CP image. For accuracy, the average of multiple thickness measurements (e.g., 5) can be taken as the final thickness value.

[0065] In some embodiments, to improve the heat resistance of the separator, the rupture temperature of the polypropylene porous base membrane is 160°C-180°C, optionally 170°C-180°C. When the temperature of the battery cell rises, the polypropylene porous base membrane with the above-mentioned rupture temperature is less likely to rupture and cause a short circuit in the electrode assembly, thus controlling the risk of thermal runaway of the battery cell.

[0066] The test method for the above-mentioned membrane rupture temperature is as follows:

[0067] According to the shape requirements of the test fixture, the polypropylene porous base membrane to be tested was cut to an appropriate size (length 10mm) and shape. The sample was placed in a differential scanning calorimeter (DSC) with the heating rate set to 5℃ / min, the heating temperature range to 50-250℃, and the load force to 0.1N. Heating was then performed. By analyzing the relationship curve between sample size change and temperature, the membrane rupture temperature was identified as the temperature at which the size suddenly increased on the curve.

[0068] In some embodiments, the melting point of the polypropylene porous base membrane is 165°C-180°C, giving it high thermal stability.

[0069] The method for testing the melting point is as follows:

[0070] A polypropylene porous membrane sample was placed in a differential scanning calorimeter (DSC) crucible, leveled, and the crucible lid was closed. Parameter settings: nitrogen atmosphere, purge gas 60 mL / min, protective gas 20 mL / min; temperature rise program: heating rate 10 °C / min. The differential scanning calorimeter curve, i.e., the DSC curve, was obtained. The melting point of the polypropylene porous membrane was determined using the DSC curve.

[0071] In some embodiments, the air permeability of the polypropylene porous membrane is 150 seconds / 100mL to 300 seconds / 100mL, optionally 170 seconds / 100mL to 280 seconds / 100mL, and further optionally 190 seconds / 100mL to 280 seconds / 100mL. The polypropylene porous membrane with the above air permeability exhibits good electrolyte wettability, thus improving the cycle performance of the battery cell to some extent. Furthermore, the air permeability of the polypropylene porous membrane varies little at different locations and is all within the above range, indicating that the pore locations in the polypropylene porous membrane are relatively uniformly distributed.

[0072] Air permeability test: Polypropylene porous base membrane was cut into 5cm squares. Using an air permeability meter, a pressure of 1.21kPa was applied, and the test showed that 100mL of air permeated 6.45cm. 2 The time required for the polypropylene porous base membrane to breathe is expressed as its air permeability value, measured in seconds per 100 mL. A higher air permeability value indicates poorer air permeability of the polypropylene porous base membrane.

[0073] In some embodiments, the transverse tensile strength of the polypropylene porous base membrane is 1500 kgf / cm. 2 -2000kgf / cm 2 1600 kgf / cm² is optional. 2 -1800 kgf / cm 2 A further option is 1680 kgf / cm². 2 -1760kgf / cm 2 Based on improvements in puncture resistance through pore size and porosity, the polypropylene porous base membrane exhibits high transverse tensile strength, thereby further enhancing its puncture resistance.

[0074] In some embodiments, the longitudinal tensile strength of the polypropylene porous base membrane is 2100 kgf / cm². 2 -2800 kgf / cm 2 2200 kgf / cm² is optional. 2-2600 kgf / cm 2 A further option is 2430 kgf / cm². 2 -2550 kgf / cm 2 The high longitudinal tensile strength of the polypropylene porous base membrane is also beneficial for further improving its puncture resistance.

[0075] The tensile strength mentioned above can be tested according to standard GB / T 36363-2018. The following operating steps can be used as a reference: Prepare a standard sample of polypropylene porous base film, and then perform a tensile test on it using a tensile testing machine until the sample breaks. The maximum tensile force obtained from the test is taken as the tensile strength of the polypropylene porous base film. The tensile rate is 50 mm / min.

[0076] In some embodiments, the crystallinity of the polypropylene porous base membrane is 40%-55%, optionally 45%-52%. The high crystallinity of this polypropylene porous base membrane is beneficial for improving the uniformity of pore distribution, thereby improving puncture resistance.

[0077] Crystallinity is tested using differential scanning calorimetry (DSC), for example:

[0078] The polypropylene porous membrane was placed in a DSC instrument. A first heating scan was performed to eliminate the thermal history of the polypropylene porous membrane, followed by a second heating scan, recording the enthalpy of the melting peak. The crystallinity of the polypropylene porous membrane was calculated using the following formula: Crystallinity Xc = ΔHf / Hf × 100%, where ΔHf is the melting enthalpy of the polypropylene porous membrane, corresponding to the integral of the area enclosed by the melting peak and the baseline of the DSC curve, and Hf is the enthalpy of complete crystallization.

[0079] To obtain a high molecular weight polypropylene porous membrane and to facilitate the preparation method of the polypropylene porous membrane, in some embodiments, the polypropylene in the polypropylene porous membrane includes a first polypropylene and a second polypropylene. The first polypropylene has a weight-average molecular weight of 50w-150w (optionally 100w-150w) and a melt index of 0.05g / 10min-1g / 10min (optionally 0.05g / 10min-0.12g / 10min). The second polypropylene has a weight-average molecular weight of 20w-100w (optionally 20w-50w) and a melt index of 0.5g / 10min-2g / 10min (optionally 0.7g / 10min-2g / 10min). Optionally, the mass ratio of the first polypropylene to the second polypropylene is 4:1-8:1. By mixing polypropylenes with different weight-average molecular weights, the high molecular weight of the first polypropylene can improve the strength of the formed polypropylene porous membrane, while the low molecular weight of the second polypropylene can improve the flowability of the polypropylene mixture during preparation and accelerate the extrusion efficiency.

[0080] The aforementioned porous polypropylene base membrane can be used directly as a separator, or different functional coatings can be applied to the porous polypropylene base membrane to improve its application performance. In some embodiments, the separator membrane further includes a coating, which is disposed on one or both sides of the porous polypropylene base membrane.

[0081] The coating can be a single layer or multiple layers. When the coating is multiple layers, it can be a combination of coatings with a single function, such as a heat-resistant layer and / or an adhesive layer. When the coating is a single layer, it can be a combination of heat-resistant material and adhesive material, that is, the coating is formed by mixing heat-resistant material and adhesive material.

[0082] In some embodiments, the heat-resistant material includes one or more of inorganic heat-resistant particles or organic heat-resistant particles.

[0083] In some embodiments, the inorganic heat-resistant particles include one or more of boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (SrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2).

[0084] In some embodiments, the organic heat-resistant particles include one or more of phenolic resin, polystyrene, polyethylene, polypropylene, polyimide, cellulose, polyester, polyphenylene sulfide, polyarylamide, polyamide-imide, and polyimide.

[0085] In some embodiments, the adhesive material includes one or more of the following: polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorinated alkenyl monomer units, copolymers of fluorinated alkenyl monomer units and olefin monomer units, copolymers of fluorinated alkenyl monomer units and acrylic monomer units, copolymers of fluorinated alkenyl monomer units and acrylate monomer units, copolymers of acrylate monomer units and styrene monomer units, copolymers of acrylic monomer units-acrylate monomer units-styrene monomer units, copolymers of styrene monomer units and unsaturated nitrile monomer units, and copolymers of styrene monomer units-olefin monomer units-unsaturated nitrile monomer units. These adhesive materials are typically granular, allowing for some space within the battery, which helps to further address the battery expansion problem.

[0086] [Preparation method of the separating membrane]

[0087] The second embodiment of this application provides a method for preparing a separator membrane, the separator membrane comprising a polypropylene porous base membrane, the preparation method comprising a polypropylene porous base membrane preparation process, the preparation process comprising:

[0088] Preparation of polypropylene castings;

[0089] The initial film is obtained by wet biaxial stretching of polypropylene casting sheets. The wet biaxial stretching includes sequentially performing a first longitudinal stretch, a first transverse stretch, a second longitudinal stretch, and a second transverse stretch. The stretching ratios of the first longitudinal stretch and the first transverse stretch are each independently 1-2, and the stretching ratio of the first longitudinal stretch is less than that of the first transverse stretch. The stretching ratios of the second longitudinal stretch and the second transverse stretch are each independently 5-13, and the stretching ratio of the second longitudinal stretch is less than that of the second transverse stretch.

[0090] After removing the solvent from the initial membrane, heat setting is performed to obtain a porous polypropylene base membrane.

[0091] In preparing the polypropylene porous membrane, this application employs a wet biaxial stretching process. This process not only results in a more regular molecular chain arrangement in both the longitudinal and transverse directions, but also increases the transverse and longitudinal tensile strength of the polypropylene porous membrane. Furthermore, the more regular the molecular chain arrangement, the more uniform the pore size and location distribution within the polypropylene porous membrane. Simultaneously, wet biaxial stretching allows for a uniform reduction in the thickness of the polypropylene porous membrane, enabling the production of a high-strength membrane even with a thinner profile. Further control of the stretching ratio during the wet biaxial stretching process, particularly the high stretching ratios in the second transverse and second longitudinal stretching, reduces the pore size to an average pore size below 30 nm and imparts a higher porosity to the polypropylene porous membrane, thereby improving its puncture resistance and tensile strength.

[0092] In some embodiments, the stretching ratio of the first longitudinal stretch is 1.1-1.5, optionally 1.1-1.3, and further optionally 1.2-1.3.

[0093] In some embodiments, the stretching ratio of the first transverse stretch is 1.2-1.7, and optionally 1.5-1.6.

[0094] In some embodiments, the stretching ratio of the second longitudinal stretch is 5-10, optionally 5-7.

[0095] In some embodiments, the stretching ratio of the second transverse stretch is 7-13, optionally 7-10.

[0096] Furthermore, by controlling the stretching ratio, the uniformity of pore dispersion and the control of pore size can be improved, thereby enhancing the puncture resistance and tensile strength of the polypropylene porous base film.

[0097] To improve stretching efficiency, in some embodiments, wet biaxial stretching has one or more of the following characteristics: high-temperature air is used for heating during the wet biaxial stretching process, with the temperature of the high-temperature air being 150℃-165℃; the film surface temperature during wet biaxial stretching is 130℃-150℃; and the stretching speed during wet biaxial stretching is 20m / min-40m / min. Using the aforementioned high-temperature air to heat the film during the wet biaxial stretching process facilitates film stretching while preventing excessively high temperatures that make it difficult to control the degree of film stretching.

[0098] The polypropylene castings described above can be prepared using conventional casting methods, such as wet casting. In some embodiments, the process for preparing the polypropylene castings includes:

[0099] A mixture comprising raw material polypropylene and solvent is melted, extruded, and cooled by quenching rollers to obtain polypropylene cast sheets.

[0100] Dispersing the raw polypropylene in a solvent improves the uniformity of the polypropylene.

[0101] Polypropylene, a common raw material, has a high molecular weight, making it difficult to achieve rapid and uniform dispersion in solvents. In some embodiments, the mixture also includes a solubilizer.

[0102] In some embodiments, the solubilizer includes one or more polyolefins or polyolefin copolymers with a weight-average molecular weight of less than 1000; optionally, the solubilizer includes polypropylene with a weight-average molecular weight of less than 1000. By selecting the aforementioned low-molecule polyolefin as the solubilizer, and utilizing the principle of similar compatibility, the solubilizer can optimize the dispersion rate and uniformity of the raw material polypropylene in the solvent. This is beneficial for improving the uniformity of pore size distribution, pore position distribution, and thickness distribution during stretching in the polypropylene porous membrane, thereby uniformly improving the air permeability and tensile strength of the polypropylene porous membrane at all locations.

[0103] Solvents can improve the dispersion uniformity of raw polypropylene, but due to their small molecular weight, they can affect the strength of the polypropylene porous membrane. In some embodiments, in order to control the influence of the solvent on the strength of the polypropylene porous membrane, the weight ratio of raw polypropylene to solvent is (10-30):1; and / or the weight ratio of raw polypropylene to solvent is 3:7-5:5.

[0104] In some embodiments, the raw material polypropylene satisfies one or more of the following (1)-(5):

[0105] (1) The weight-average molecular weight of the raw material polypropylene is 80W-130W;

[0106] (2) The raw material polypropylene includes first polypropylene and second polypropylene, and the weight-average molecular weight of first polypropylene is greater than that of second polypropylene.

[0107] (3) The raw material polypropylene includes first polypropylene and second polypropylene, and the melt index of first polypropylene is less than that of second polypropylene.

[0108] (4) The raw material polypropylene includes a first polypropylene, the first polypropylene having a weight average molecular weight of 50w-150w (optionally 100w-150w), and / or, the first polypropylene having a melt index of 0.05g / 10min-1g / 10min (optionally 0.05g / 10min-0.12g / 10min), and / or, the first polypropylene having a mass percentage of greater than or equal to 80% in the raw material polypropylene;

[0109] (5) The raw material polypropylene includes a second polypropylene, the weight average molecular weight of the second polypropylene is 20w-100w (optionally 20w-50w), and / or the melt index of the second polypropylene is 0.5g / 10min-2g / 10min (optionally 0.7g / 10min-2g / 10min), and / or the mass percentage of the second polypropylene in the raw material polypropylene is less than or equal to 20%.

[0110] By mixing polypropylene raw materials with different weight-average molecular weights, the higher molecular weight first polypropylene can improve the strength of the formed porous polypropylene membrane, while the lower molecular weight second polypropylene can improve the flowability of the polypropylene mixture during preparation and accelerate extrusion efficiency. However, when mixing the first and second polypropylene materials with different molecular weights, although the higher molecular weight is beneficial for improving the strength of the porous polypropylene membrane, the difficulty of achieving uniform mixing of the two types of polypropylene increases with the increase of molecular weight, making it difficult for the higher molecular weight to fully exert its strength-improving effect. When using polypropylene raw materials with different molecular weights, the use of the aforementioned solubilizer further helps to improve the uniformity of mixing of the polypropylene raw materials with different molecular weights. This results in a more significant improvement in the uniformity of pore size distribution, pore position distribution, and thickness distribution during stretching in the porous polypropylene membrane, thereby leading to a more uniform improvement in the puncture strength, air permeability, and tensile strength of the porous polypropylene membrane at all locations.

[0111] Weight-average molecular weight test method:

[0112] The polypropylene sample was dissolved in trichlorobenzene solvent and analyzed using a high-temperature GPC (high-temperature gel permeation chromatography) instrument. For specific implementation, please refer to the ASTM D6474 standard.

[0113] In some embodiments, to improve extrusion efficiency, extrusion is performed using a twin-screw extrusion process, and the extrusion process meets one or more of the following conditions: screw temperature of 200°C-230°C; twin-screw speed of 70-100 rpm; melt channel temperature of 190°C-220°C; and die temperature of 180°C-210°C.

[0114] When the extruded film is cooled using a quench roll, the temperature of the quench roll affects the crystallinity of the polypropylene wafer. In some embodiments, the temperature of the quench roll is 20°C-30°C. This improves the crystallinity of the polypropylene wafer, enhances the uniformity of pore dispersion during subsequent wet biaxial stretching, and controls the pore size.

[0115] The heat setting process can further optimize the uniformity of pore size. In some embodiments, heat setting includes: performing a third transverse stretch on the initial film after solvent removal, optionally with a stretching ratio of 1.1-1.3 times; controlling the film layer after the third transverse stretch to shrink to 1.05-1.15 times the size of the initial film before heat setting, with a heat setting temperature of 125-145°C and a forward speed of 40-80 m / min during the heat setting process. The above heat setting process further improves the uniformity of pore size distribution, thereby improving the puncture resistance and tensile strength of the polypropylene porous film.

[0116] In some embodiments, the mixture further includes nucleating agents or antioxidants. The use of nucleating agents can improve the crystallinity of the polypropylene porous membrane; antioxidants can enhance the oxidation resistance of the polypropylene porous membrane at high temperatures, further improving its strength.

[0117] This application does not have any special requirements for the solvents, nucleating agents and antioxidants mentioned above, and commonly used solvents, nucleating agents and antioxidants in the field can be used.

[0118] In some embodiments, the solvent may include one or more of white oil, phthalates, and aromatic ethers.

[0119] In some embodiments, the nucleating agent may include bis(3,4-dimethylbenzyl)sorbitol.

[0120] In some embodiments, the antioxidant may include one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris[2,4-di-tert-butylphenyl] phosphite.

[0121] [Battery cell]

[0122] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0123] The battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and the embodiments of this application are not limited to this.

[0124] The third embodiment of this application provides a battery cell, which includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, an electrolyte, and a separator. The separator includes any of the separators provided in the first embodiment or any of the separators prepared by the preparation method of the second embodiment.

[0125] During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. A separator is placed between the positive and negative electrodes to prevent short circuits while allowing active ions to pass through.

[0126] The isolation membrane of this application can achieve high puncture resistance.

[0127] In some embodiments, the positive electrode may include a positive current collector and a positive active material disposed on at least one surface of the positive current collector.

[0128] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0129] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0130] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As an example, when the secondary battery is a lithium-ion secondary battery, the positive electrode active material may include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of the following: (O2) and its modified compounds. Examples of lithium phosphates include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0131] When the secondary battery is a sodium-ion secondary battery, as an example, the positive electrode active material of the sodium-ion secondary battery may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0132] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0133] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0134] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n-A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0135] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0136] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO4) y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0137] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0138] In some embodiments, the positive electrode active material includes one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. When the battery cell is a sodium-ion battery cell, the separator of this application has a better suppression effect on sodium dendrites.

[0139] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0140] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0141] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0142] [Negative electrode plate]

[0143] In some embodiments, the negative electrode may include a negative current collector.

[0144] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0145] As an example, the negative electrode sheet may include a negative current collector and a negative active material disposed on at least one surface of the negative current collector.

[0146] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0147] As an example, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0148] In some embodiments, the negative electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not have a negative electrode active material.

[0149] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0150] In some embodiments, the positive current collector may be made of aluminum, and the negative current collector may be made of copper. In some embodiments, the negative electrode may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0151] In some embodiments, the negative electrode may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0152] In some embodiments, the negative electrode may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0153] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0154] [Electrolytes]

[0155] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0156] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0157] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0158] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0159] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0160] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0161] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0162] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0163] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium-germanium-phosphorus-sulfur, sulfosilium-germanium), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0164] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes. The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0165] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0166] In some implementations, the electrode assembly is a stacked structure.

[0167] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0168] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0169] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0170] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0171] As an example, the separator can be continuously installed between any adjacent positive or negative electrode plates by folding or rolling.

[0172] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0173] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0174] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0175] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0176] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more. Figure 1 The example shown is a square-structured battery cell 5.

[0177] In some implementations, refer to Figure 2 The outer casing may include a housing 51 and an end cap 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the end cap 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single secondary battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0178] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0179] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0180] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0181] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0182] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0183] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0184] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0185] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of the separator, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0186] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0187] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0188] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0189] Figure 3 This is battery module 4 as an example. (See reference...) Figure 3 In the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other way. Furthermore, these multiple secondary battery cells 5 can be fixed in place using fasteners.

[0190] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple secondary battery cells 5 are received.

[0191] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0192] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0193] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0194] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0195] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0196] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0197] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0198] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0199] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0200] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0201] [Example]

[0202] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0203] Example 1 of membrane preparation

[0204] 1. Preparation of polypropylene porous base membrane:

[0205] (1) Casting: A mixture is obtained by melting and plasticizing raw polypropylene, solubilizer, solvent, nucleating agent, and antioxidant. The raw polypropylene consists of a first polypropylene and a second polypropylene in a weight ratio of 4:1. The first polypropylene has a weight-average molecular weight of 150W and a melt index of approximately 0.05 g / 10 min, while the second polypropylene has a weight-average molecular weight of 20W and a melt index of approximately 2 g / min. The solvent is white oil, the solubilizer is polypropylene with a weight-average molecular weight of approximately 3000, the nucleating agent is sorbitol, and the antioxidant is... The chemical additive is bis(3,4-dimethylbenzyl)sorbitol. The weight ratio of raw material polypropylene to solvent is 4:6, and the weight ratio of raw material polypropylene to solubilizer is 20:1. The mass percentage of nucleating agent and antioxidant in the mixture is 0.5%. The mixture is extruded by twin-screw extrusion followed by thermally induced phase separation to obtain cast sheets. During twin-screw extrusion, the screw temperature is 220℃, the twin-screw speed is 80 rpm, the melt pipe temperature is 200℃, and the die temperature is 190℃. After casting, the sheets are cooled by a chiller roller at a temperature of 20℃.

[0206] (2) Wet biaxial stretching: The cast film cooled by the chiller rollers is sequentially stretched by the first longitudinal stretching MD1, the first transverse stretching TD1, the second longitudinal stretching MD2, and the second transverse stretching TD2 to obtain the initial film. High-temperature air is used for heating during stretching. The stretching conditions are recorded in Table 1.

[0207] (3) Extraction: The initial membrane obtained by stretching is extracted using dichloromethane as the extractant. After passing through 9 extraction tanks, it is dried in an oven at 110°C and 130°C.

[0208] (4) Heat setting: After drying to remove excess dichloromethane, the film undergoes a third transverse stretching with a stretching ratio of 1.2, a heat setting temperature of 135℃, and a film advance speed of 60m / min. Finally, the film is wound up using a take-up roller to obtain a polypropylene porous base film 1.

[0209] 2. Coating preparation:

[0210] (1) Preparation of coating slurry 1: Inorganic particles of aluminum oxide (Al2O3), polymethyl methacrylate binder, dispersant sodium carboxymethyl cellulose (CMC-Na), and wetting agent organosilicon modified polyether are mixed evenly in an appropriate amount of solvent deionized water at a mass ratio of 93:6:0.5:0.5 to obtain coating slurry 1;

[0211] (2) Preparation of coating slurry 2: Commercially available polyvinylidene fluoride particles, binder polyacrylate, dispersant sodium carboxymethyl cellulose, and ether-based surfactants are mixed evenly in deionized water at a solid content mass ratio of 87:8:3:2 to obtain coating slurry 2.

[0212] (3) Coating slurry 1 is applied to the two surfaces of polypropylene porous base membrane 1 to form a heat-resistant coating, and coating slurry 2 is sprayed onto the two surfaces of the heat-resistant coating to form an adhesive coating. After drying, cutting and other processes, the isolation membrane 1 is obtained.

[0213] Separator preparation examples 2-7 and comparative preparation examples 1-2

[0214] The preparation processes of isolation membrane preparation examples 2-7 and isolation membrane comparative preparation examples 1-2 are similar to those of isolation membrane preparation example 1, except that the preparation process of the polypropylene porous base membrane is adjusted, as detailed in Table 1.

[0215] The average pore size, porosity, and puncture strength of the polypropylene porous base membrane were tested according to the method described above, and the test results are recorded in Table 1.

[0216] Table 1

[0217] As can be seen from the data in Tables 1 and 6, when the separator includes a polypropylene porous base membrane and the pore size of the polypropylene porous base membrane is controlled below 30nm, the puncture strength of the separator can be improved, thereby improving the safety performance of the battery.

[0218] The following investigation examines the influence of the composition of the raw material polypropylene on the performance of polypropylene porous membranes.

[0219] The polypropylene compositions of Preparation Examples 8 to 13 are recorded in Table 2. The remaining preparation processes were the same as in Preparation Example 2. The test results of the polypropylene porous base membranes are recorded in Table 2. The mass ratios in Table 2 represent the mass ratios of the first polypropylene and the second polypropylene.

[0220] Table 2

[0221] As shown in Table 2, adjusting the molecular weight composition and melt index of the raw polypropylene within the aforementioned range affects the puncture strength of the polypropylene porous membrane. Specifically, in Preparation Examples 2, 8, and 9, the increase in the molecular weight of the second polypropylene from 20W to 100W may affect the uniformity of the mixture, making it more difficult to achieve uniform pore distribution in the resulting polypropylene porous membrane. Consequently, the puncture strength of the polypropylene porous membrane did not increase with the increase in molecular weight. Compared to Preparation Examples 2, 10, and 11, the decrease in the molecular weight of the first polypropylene from 150W to 50W leads to a reduction in the high-molecular-weight polypropylene in the polypropylene porous membrane, thus affecting its puncture strength. Compared to Preparation Examples 8 and 12, the decrease in the molecular weight of the first polypropylene also leads to a reduction in the high-molecular-weight polypropylene in the polypropylene porous membrane, further reducing its puncture strength. Because the content of the first polypropylene increased in Preparation Example 13, although the puncture strength increased compared to Preparation Examples 8 to 12, the puncture strength of the polypropylene porous base film decreased compared to Preparation Example 2 due to the poor mixing uniformity of the two polypropylenes and the uneven thickness or molecular weight distribution of polypropylene in some locations.

[0222] The following investigation examines the effect of the solubilizer addition ratio on the performance of polypropylene porous membranes.

[0223] The mass ratio of polypropylene and solubilizer in Examples 14 and 15 is recorded in Table 3. The remaining preparation process is the same as in Example 2. The test results of the polypropylene porous membrane are recorded in Table 3. The mass ratio in Table 3 is the mass ratio of polypropylene and solubilizer.

[0224] Table 3

[0225] The data comparison in Table 3 shows that as the ratio of raw polypropylene to solubilizer increases within the range of 10:1 to 30:1, the amount of solubilizer decreases, and the puncture strength of the polypropylene porous base membrane first increases and then decreases. This indicates that an appropriate amount of solubilizer is beneficial for the uniform mixing of the first and second polypropylene, which in turn helps the first polypropylene to improve the puncture strength.

[0226] The following investigation examines the effect of solvent addition ratio on the performance of polypropylene porous membranes.

[0227] The mass ratios of solvent to polypropylene in Examples 16 and 17 are recorded in Table 4. The remaining preparation process is the same as in Example 2. The test results of the polypropylene porous membrane are recorded in Table 4. The mass ratios in Table 4 are the mass ratios of the raw material polypropylene and the solvent.

[0228] Table 4

[0229] As shown in Table 4, with the increase of the mass ratio of polypropylene to solvent in the range of 3:7-5:5, the tensile resistance of the polypropylene porous membrane increases, thus reducing the average pore size and porosity. Furthermore, with the increase of polypropylene content, the puncture strength of the polypropylene porous membrane first increases and then decreases. This may be because a suitable polypropylene to solvent ratio is beneficial for improving the dispersion uniformity of polypropylene, thereby facilitating the obtaining of a porous membrane with uniform pore size and pore size distribution, and ultimately improving its puncture strength.

[0230] The following examines the effect of quench roll temperature on polypropylene porous base film.

[0231] The temperature of the chilled roller in Example 18 is recorded in Table 5. The rest of the preparation process is the same as in Example 2. The test results of the polypropylene porous base film are recorded in Table 5.

[0232] Table 5

[0233] The data comparison in Table 5 shows that when the temperature of the chilling roller increases, the crystallinity of polypropylene in the polypropylene porous base film decreases, the pore size increases, and the puncture strength decreases.

[0234] In addition, the test results of the polypropylene porous base film prepared in the above preparation example, which were tested according to the test method described above, including thickness, puncture strength to thickness ratio, air permeability, transverse tensile strength, longitudinal tensile strength, MD heat shrinkage rate (105℃ / 1h) and TD heat shrinkage rate (105℃ / 1h), are recorded in Table 6.

[0235] Table 6

[0236] [Example 1]

[0237] The manufacturing process of a secondary battery cell is as follows:

[0238] Production of positive electrode sheets:

[0239] According to the mass ratio, the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2: Conductive carbon black: PVDF binder is mixed in a ratio of 8:1:1 and then N-methylpyrrolidone solvent is added. The mixture is coated on both sides of aluminum foil, and after cold pressing and cutting, a positive electrode sheet is obtained.

[0240] Preparation of negative electrode sheet:

[0241] Artificial graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC-Na) binder, and deionized water are mixed evenly in a weight ratio of 95:2:3. The mixture is then coated on both sides of a copper foil and cold-pressed and cut to obtain the negative electrode sheet.

[0242] Separating membrane: The separating membrane prepared in Example 1 above was selected.

[0243] Electrolyte preparation:

[0244] Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1. LiPF6 was dissolved in the mixture, and fluoroethylene carbonate (FEC) was added to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1.2 mol / L, and the mass fraction of FEC was 3%.

[0245] Assembly of secondary battery cells:

[0246] The positive electrode sheet, the polyethylene porous base film of Preparation Example 1 above, and the negative electrode sheet are stacked and wound in sequence to obtain a wound electrode assembly. The wound electrode assembly is placed in a square aluminum shell outer packaging, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and shaping processes, a secondary battery cell is obtained.

[0247] Examples 2-18 and Comparative Examples 1-2 are similar to the preparation steps of Battery Example 1, except that the separators used are different (the separators of Preparation Examples 2-18 and Comparative Examples 1-2 are used in sequence). That is, Example 2 uses the separator of Preparation Example 2, and so on; Comparative Example 1 uses the separator of Comparative Example 1, and Comparative Example 2 uses the separator of Comparative Example 2.

[0248] Hipot loss test: Under a certain pressure (e.g., 5 MPa), take a number of the wound electrode assemblies from each of the above embodiments and comparative examples (e.g., 1000 for each embodiment and comparative example) and test their insulation resistance at 100V. When the resistance is ≤2MΩ, it is considered to be a failure. Calculate the proportion of electrode assemblies that have not failed and record it in Table 7.

[0249] Lithium plating resistance test:

[0250] The positive electrode, negative electrode, and separator of each preparation example were slit and stacked sequentially to obtain a stacked electrode assembly. The stacked electrode assembly was placed in an aluminum-plastic bag for packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, and formation processes, a secondary battery cell was obtained. A fixture was installed with an initial clamping force of 3000N. The battery was charged at 1C to 100% SOC with a cutoff voltage of 4.2V, and then discharged at 1C to 0% SOC with a cutoff voltage of 2.5V for cyclic charge-discharge testing. During cycling, excess positive electrode material led to lithium plating, forming lithium dendrites that easily punctured the separator. When a short circuit occurred between the positive and negative electrodes, it indicated that the separator was punctured and the electrode assembly failed. A confocal microscope was used to observe the process of lithium dendrites puncturing the separator, and the number of charge-discharge cycles at which the electrode assembly failed was recorded.

[0251] The test results are recorded in Table 7.

[0252] Table 7 Separating membrane Process domain resistance without loss of efficiency Lithium plating resistance test / circle Example 1 Preparation Example 1 99.9％ 39 Example 2 Preparation Example 2 99.9％ 35 Example 3 Preparation Example 3 99.5％ 28 Example 4 Preparation Example 4 98.8％ 22 Example 5 Preparation Example 5 99.9％ 43 Example 6 Preparation Example 6 99.9％ 37 Example 7 Preparation Example 7 96.8％ 16 Example 8 Preparation Example 8 99.1％ 33 Example 9 Preparation Example 9 96.7％ 31 Example 10 Preparation Example 10 95.1％ 35 Example 11 Preparation Example 11 95.4％ 35 Example 12 Preparation Example 12 96.4％ 34 Example 13 Preparation Example 13 99.8％ 33 Example 14 Preparation Example 14 95.2％ 33 Example 15 Preparation Example 15 97.1％ 31 Example 16 Preparation Example 16 99.3％ 28 Example 17 Preparation Example 17 99.4％ 36 Example 18 Preparation Example 18 99.8％ 20 Comparative Example 1 Comparative Preparation Example 1 93.7％ 11 Comparative Example 2 Comparative Preparation Example 2 91.0％ 6

[0253] Based on the data of polypropylene porous membranes mentioned above, it can be seen that the smaller the average pore size of the polypropylene porous membrane, the stronger its puncture resistance, which effectively improves the safety performance of secondary batteries.

[0254] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A separating membrane comprising a polypropylene porous base membrane, wherein the average pore size of the polypropylene porous base membrane is less than or equal to 30 nm.

2. The separator according to claim 1, wherein, The average pore size of the polypropylene porous base membrane is 10nm-30nm; optionally, it is 15nm-25nm.

3. The separator according to claim 1 or 2, wherein, The porosity of the polypropylene porous base membrane is 37%-50%; optionally 38%-43%.

4. The separator according to any one of claims 1 to 3, wherein, The ratio of puncture strength to thickness of the polypropylene porous base membrane is 40 gf / μm-60 gf / μm; optionally, it is 48 gf / μm-58 gf / μm.

5. The separator according to any one of claims 1 to 4, wherein, The puncture strength of the polypropylene porous base membrane is 250gf-400gf, optionally 280gf-380gf; and / or, the thickness of the polypropylene porous base membrane is 4μm-10μm, optionally 6μm-8μm.

6. The separator according to any one of claims 1 to 5, wherein, The air permeability of the polypropylene porous base membrane is 150 seconds / 100mL-300 seconds / 100mL, and can be selected as 170 seconds / 100mL-280 seconds / 100mL.

7. The separator according to any one of claims 1 to 6, wherein, The transverse tensile strength of the polypropylene porous base membrane is 1500 kgf / cm. 2 -2000kgf / cm 2 1600 kgf / cm² is optional. 2 -1800 kgf / cm 2 .

8. The separator according to any one of claims 1 to 7, wherein, The longitudinal tensile strength of the polypropylene porous base membrane is 2100 kgf / cm. 2 -2800 kgf / cm 2 2200 kgf / cm² is optional. 2 -2600 kgf / cm 2 .

9. The separator according to any one of claims 1 to 8, wherein, The crystallinity of the polypropylene porous base membrane is 40%-55%.

10. The separator membrane according to any one of claims 1 to 9, wherein, The polypropylene porous base membrane comprises a first polypropylene and a second polypropylene. The first polypropylene has a weight-average molecular weight of 50w-150w and a melt index of 0.05g / 10min-1g / 10min. The second polypropylene has a weight-average molecular weight of 20w-100w and a melt index of 0.5g / 10min-2g / 10min. Optionally, the mass ratio of the first polypropylene to the second polypropylene is 4:1-8:

1.

11. The separator membrane according to any one of claims 1 to 10, wherein, The separator also includes a coating, which is disposed on one or both sides of the polypropylene porous base membrane.

12. The separator according to claim 11, wherein, The coating includes a heat-resistant layer disposed on one or both sides of the polypropylene porous base film.

13. The separator according to claim 11 or 12, wherein, The coating includes an adhesive layer disposed on one or both sides of the polypropylene porous base film; or the adhesive layer is disposed on the side of the heat-resistant layer away from the polypropylene porous base film.

14. A method for preparing a separator membrane, the separator membrane comprising a polypropylene porous base membrane, the preparation method comprising a preparation process of the polypropylene porous base membrane, the preparation process comprising: Preparation of polypropylene castings; The polypropylene casting is subjected to wet biaxial stretching to obtain an initial film. The wet biaxial stretching includes sequentially performing a first longitudinal stretch, a first transverse stretch, a second longitudinal stretch, and a second transverse stretch. The stretching ratios of the first longitudinal stretch and the first transverse stretch are each independently 1.1-2. Furthermore, the stretching ratio of the first longitudinal stretch is less than the stretching ratio of the first transverse stretch. The stretching ratios of the second longitudinal stretch and the second transverse stretch are each independently 5-13. Furthermore, the stretching ratio of the second longitudinal stretch is less than the stretching ratio of the second transverse stretch; After removing the solvent from the initial membrane, heat setting is performed to obtain the polypropylene porous base membrane.

15. The preparation method according to claim 14, wherein, The first longitudinal stretching has a stretching ratio of 1.1-1.5; and / or, The first transverse stretching has a stretching ratio of 1.2-1.7; and / or, The stretching ratio of the second longitudinal stretching is 5-10; and / or, The stretching ratio of the second transverse stretching is 7-13.

16. The preparation method according to claim 14 or 15, wherein, The process for preparing polypropylene castings includes: The mixture comprising raw material polypropylene and solvent is melted, extruded, and cooled by quenching rollers to obtain the polypropylene casting sheet; optionally, the mass ratio of raw material polypropylene to solvent is 3:7-5:

5.

17. The preparation method according to claim 16, wherein, The mixture also includes a solubilizer; Optionally, the solubilizer includes one or more of polyolefins or polyolefin copolymers with a weight average molecular weight of less than 5000; Optionally, the solubilizer comprises polypropylene with a weight-average molecular weight of less than 5000.

18. The preparation method according to claim 17, wherein, The weight ratio of the raw material polypropylene to the solubilizer is (10-30):

1.

19. The preparation method according to any one of claims 14 to 18, wherein, The raw material polypropylene satisfies one or more of the following (1)-(5): (1) The weight-average molecular weight of the raw material polypropylene is 80W-130W; (2) The raw material polypropylene includes a first polypropylene and a second polypropylene, wherein the weight-average molecular weight of the first polypropylene is greater than that of the second polypropylene. (3) The raw material polypropylene includes a first polypropylene and a second polypropylene, wherein the melt index of the first polypropylene is less than the melt index of the second polypropylene; (4) The raw material polypropylene includes a first polypropylene, the first polypropylene having a weight-average molecular weight of 50w-150w, and / or having a melt index of 0.05g / 10min-1g / 10min, and / or having a mass percentage of the first polypropylene in the raw material polypropylene greater than or equal to 80%. (5) The raw material polypropylene includes a second polypropylene, the second polypropylene having a weight-average molecular weight of 20w-100w, and / or having a melt index of 0.5g / 10min-2g / 10min, and / or having a mass percentage of the second polypropylene in the raw material polypropylene of less than or equal to 20%.

20. The preparation method according to any one of claims 15 to 19, wherein, The temperature of the cooling roller is 20℃-30℃.

21. A secondary battery cell, comprising an electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator, the separator being disposed between the positive electrode and the negative electrode, wherein, The isolation membrane comprises the isolation membrane according to any one of claims 1 to 12 or the isolation membrane prepared by the preparation method according to any one of claims 13 to 20.

22. An electrical device comprising one or more secondary battery cells as described in claim 20.

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