Isolating membrane, preparation method thereof, battery comprising isolating membrane and electric device

Abstract

The invention provides an isolating membrane, a preparation method of the isolating membrane, a battery comprising the isolating membrane and an electric device. The isolating membrane comprises polyphenylene sulfide, and the maximum aperture of the isolating membrane is smaller than or equal to 50 nm.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an isolation membrane and a preparation method thereof, a battery comprising the isolation membrane, and an electrical device. Background Art

[0002] Secondary batteries rely on active ions to be reciprocated between the positive and negative electrodes for charging and discharging. Secondary batteries represented by lithium-ion batteries have outstanding features such as high energy density, long cycle life, no pollution, and no memory effect. Therefore, as a clean energy, secondary batteries have gradually spread from electronic products to large-scale devices such as electric vehicles to adapt to the sustainable development strategy of the environment and energy.

[0003] With the development of electronic products, electric vehicles and other devices, people have put forward higher requirements on the reliability and cycle performance of secondary batteries. Summary of the invention

[0004] In order to achieve the above-mentioned objectives, the present application provides an isolation membrane, which can improve the reliability and cycle performance of a battery containing the isolation membrane; the present application also provides a method for preparing the isolation membrane, a battery containing the isolation membrane, and an electrical device.

[0005] An embodiment of the first aspect of the present application provides an isolation membrane, comprising polyphenylene sulfide, wherein the maximum pore size of the isolation membrane is less than or equal to 50 nm.

[0006] Without intending to be limited by any theory or explanation, the separator of the embodiment of the present application includes polyphenylene sulfide, and its maximum pore size satisfies the above range, which can make the separator have suitable air permeability, mechanical strength and good ionic conductivity. As a result, not only the electrolyte infiltration performance of the separator can be improved, but also the mechanical properties such as tensile strength of the separator can be improved. Therefore, the separator of the embodiment of the present application is applied to the battery, which can reduce the battery's withstand voltage test (Hi-pot) failure rate, reduce the battery's self-discharge, and improve the battery's cycle performance.

[0007] Therefore, the isolation membrane of the embodiment of the present application is applied to a battery to improve the reliability and cycle performance of the battery.

[0008] In any embodiment of the present application, the average pore size of the isolation membrane is 10 nm-50 nm, and can be optionally 20 nm-35 nm.

[0009] The average pore size of the isolation membrane is within the above-mentioned suitable range, and can have lower resistance and higher ion conductivity, which helps to improve the cycle performance of the battery.

[0010] In any embodiment of the present application, the porosity of the isolation membrane is 30%-60%, and can be optionally 45%-48%.

[0011] The porosity of the separator is within the above-mentioned appropriate range, which can adjust the air permeability and mechanical strength, and also make the separator have both good barrier properties and good ion conductivity, thereby helping to improve the reliability and cycle performance of the battery.

[0012] In any embodiment of the present application, the thickness of the isolation film is less than or equal to 15 μm, and can be optionally 5 μm-15 μm.

[0013] The separator of the embodiment of the present application has a suitable pore structure, and when it has the above-mentioned small thickness, it can still have good heat resistance and mechanical strength. Therefore, it can not only reduce the internal resistance of the battery and increase the energy density of the battery, but also effectively improve the high temperature cycle performance and reliability of the battery.

[0014] In any embodiment of the present application, the separator further comprises polysulfone and / or polyetheretherketone, thereby improving the transverse tensile strength and longitudinal tensile strength of the separator, thereby improving the puncture resistance of the separator, reducing the risk of the separator being punctured, and thus improving the reliability of the battery.

[0015] In any embodiment of the present application, the melt index of polyphenylene sulfide at 315° C. and 5 MPa is 100 g / 10 min-200 g / 10 min.

[0016] When the melt index of polyphenylene sulfide satisfies the given range, it is beneficial to improve the tensile strength of the separator, thereby improving the heat resistance and physical properties of the separator, thereby further improving the reliability of the battery.

[0017] In any embodiment of the present application, the sulfur content of the polyphenylene sulfide is greater than 28 wt %, and can be optionally 28 wt %-30 wt %, based on the total mass of the polyphenylene sulfide.

[0018] When the sulfur content of polyphenylene sulfide meets the given range, it is beneficial to improve the electrolyte wetting performance of the separator, thereby reducing the internal resistance of the battery and further improving the cycle performance of the battery.

[0019] In any embodiment of the present application, the transverse tensile strength of the separator is 2300 kg / cm 2 Above, 3800kg / cm2 can be selected 2 above.

[0020] In any embodiment of the present application, the longitudinal tensile strength of the separator is 2600 kg / cm 2 Above, 4200kg / cm2 is optional 2 above.

[0021] When the tensile strength of the isolation membrane meets the above conditions, the isolation membrane can have good heat resistance and physical properties, thereby further improving the reliability of the battery.

[0022] An embodiment of the second aspect of the present application provides a method for preparing an isolation membrane, comprising the following steps.

[0023] A separator substrate material is provided, wherein the separator substrate material comprises polyphenylene sulfide.

[0024] The substrate material of the isolation film is melted in a molten salt to obtain a composite molten salt including polyphenylene sulfide, wherein the cation of the molten salt includes K + and / or Na + , the anions of the molten salt include NO3 - and / or NO2 - .

[0025] The composite molten salt is prepared into a membrane to obtain a composite membrane including polyphenylene sulfide and an inorganic salt.

[0026] The composite membrane is brought into contact with a solvent to dissolve the inorganic salt in the composite membrane, thereby obtaining an isolation membrane, wherein the maximum pore size of the isolation membrane is less than or equal to 50 nm.

[0027] According to the method of the embodiment of the present application, an inorganic salt flux is used to evenly disperse the molten polyphenylene sulfide into the molten salt system to form a composite molten salt system with good fluidity, and then the composite molten salt is prepared into a composite membrane. The composite membrane includes evenly dispersed polyphenylene sulfide and inorganic salt particles. After solvent extraction, the inorganic salt particles are dissolved to form nanopores in the membrane. According to the method of the present application, the prepared isolation membrane has a uniform pore size distribution, controllable pore size, and controllable porosity. When applied to batteries, it can not only reduce the battery's withstand voltage test failure rate and reduce the battery's self-discharge, but also improve the battery's cycle performance.

[0028] Therefore, the isolation membrane prepared according to the method of the embodiment of the present application is applied to the battery, which can effectively improve the battery reliability and cycle performance.

[0029] In addition, the method of the present application is simple to operate, and the molten salt and solvent are reusable and non-toxic and harmless, which can not only reduce production costs but also reduce pollution to the environment.

[0030] In any embodiment of the present application, the molten salt includes potassium nitrate, sodium nitrite and sodium nitrate. Optionally, in the molten salt, the mass ratio of potassium nitrate, sodium nitrite and sodium nitrate is 1:(0.1-10):(0.1-10).

[0031] In any embodiment of the present application, the molten salt includes potassium nitrate and sodium nitrite. Optionally, in the molten salt, the mass ratio of potassium nitrate to sodium nitrite is 1:(0.1-10).

[0032] In any embodiment of the present application, the molten salt includes potassium nitrate, potassium nitrite and sodium nitrate. Optionally, in the molten salt, the mass ratio of potassium nitrate, potassium nitrite and sodium nitrate is 1:(0.1-10):(0.1-10).

[0033] When the molten salt has the above composition, a fluid with good fluidity can be formed at the melting temperature of the isolation membrane substrate. The fluid has good solubility in the isolation membrane substrate raw material, which is conducive to the isolation membrane substrate being uniformly melted in the molten salt to form a composite molten salt system with good fluidity. As a result, it is helpful to evenly distribute the inorganic salt particles in the composite membrane, thereby improving the uniformity of the pore size distribution of the isolation membrane, as well as the controllability of the pore size and porosity.

[0034] In any embodiment of the present application, melting the isolation membrane substrate raw material in molten salt includes: melting the isolation membrane substrate raw material in molten salt at 285° C.-300° C.

[0035] At the above temperature, on the one hand, the separator substrate material can be thermally deformed and melted, and on the other hand, the molten salt can have good fluidity. Therefore, it is beneficial for the separator substrate material to be fully melted in the molten salt to form a uniform composite molten salt, thereby helping to improve the uniformity of the pore size distribution of the separator, as well as the controllability of the pore size and porosity.

[0036] Optionally, the mass ratio of the isolation membrane substrate raw material to the molten salt is 1:(3-7).

[0037] By controlling the mass ratio of the separator substrate material to the molten salt within the above-mentioned appropriate range, the content of inorganic salt particles in the composite membrane can be appropriate, which helps to form a separator with a specific pore structure. As a result, the separator can have appropriate air permeability, mechanical strength and good ionic conductivity, thereby improving the reliability and cycle performance of the battery.

[0038] In any embodiment of the present application, the melting point of the molten salt is 140°C-150°C.

[0039] In any embodiment of the present application, the viscosity of the molten salt at 150° C. ranges from 5 mPa·s to 20 mPa·s.

[0040] In any embodiment of the present application, the viscosity of the molten salt at 280° C.-300° C. ranges from 2 mPa·s to 4 mPa·s.

[0041] When the melting point and / or viscosity of the molten salt meet the above conditions, it is helpful to form a fluid with good fluidity at the melting temperature of the isolation membrane substrate, thereby facilitating the isolation membrane substrate to melt evenly in the molten salt, forming a composite molten salt system with good fluidity. This helps the inorganic salt particles to be evenly distributed in the composite membrane, thereby improving the uniformity of the pore size distribution of the isolation membrane, as well as the controllability of the pore size and porosity, so that the isolation membrane has a smaller pore size and a suitable porosity.

[0042] In any embodiment of the present application, preparing the composite molten salt into a film comprises:

[0043] The composite molten salt is prepared into a composite membrane with a thickness less than or equal to 15 μm through a tape casting membrane forming process or a wet membrane forming process.

[0044] The separator prepared by the method of the embodiment of the present application has a suitable pore structure, and when it has the above-mentioned small thickness, it can still have good heat resistance and mechanical strength. Therefore, it can not only reduce the internal resistance of the battery and increase the energy density of the battery, but also effectively improve the high temperature cycle performance and reliability of the battery.

[0045] In any embodiment of the present application, the isolation film contains K + 、Na + 、NO3 - or NO2 - At least one of .

[0046] An embodiment of the third aspect of the present application provides a battery, comprising the isolation membrane of the first aspect, or an isolation membrane prepared according to the method of the second aspect.

[0047] An embodiment of a fourth aspect of the present application provides an electrical device, comprising the battery of the third aspect.

[0048] The electric device according to the embodiment of the present application comprises the battery of the third aspect, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of an implementation of a battery cell of the present application.

[0050] Figure 2 yes Figure 1 An exploded view of an embodiment of a battery cell of the present application is shown.

[0051] Figure 3 It is a schematic diagram of an embodiment of a battery module of the present application.

[0052] Figure 4 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0053] Figure 5 yes Figure 4 An exploded view of an embodiment of a battery pack of the present application is shown.

[0054] Figure 6 It is a schematic diagram of an implementation of an electrical device of the present application, and the electrical device may include a battery pack or a battery module according to an embodiment of the present application as a power source.

[0055] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0056] Hereinafter, the isolation membrane and its preparation method, the battery and the electric device containing the isolation membrane of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0057] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0058] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0059] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0060] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0061] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0062] Unless otherwise specified, the ratio parameters involved in this application are compared in the same unit. For example, the thickness ratio of A to B is 1.2:1, and the thickness units of A and B are the same.

[0063] With the development of electronic products, electric vehicles and other devices, people have put forward higher requirements on the reliability and cycle performance of secondary batteries.

[0064] Generally, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The separator is arranged between the positive electrode sheet and the negative electrode sheet, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting. Polyolefin separators dominate the separator market due to their stable chemical properties, low cost, and uniform pore size distribution. However, polyolefin separators also have disadvantages such as poor wettability to electrolytes and poor thermal stability.

[0065] In view of this, an embodiment of the present application provides an isolation membrane, which can enable a battery containing the isolation membrane to have both high reliability and good cycle performance; the present application also provides a method for preparing the isolation membrane, a battery containing the isolation membrane, and an electrical device.

[0066] Isolation film

[0067] The embodiment of the first aspect of the present application proposes an isolation membrane, which includes polyphenylene sulfide. The maximum pore size of the isolation membrane is less than or equal to 50nm. For example, the maximum pore size of the isolation membrane can be 50nm, 45nm, 30nm, 35nm, 30nm, 25nm, 20nm, 15nm, 10nm, or a range consisting of any two of the above values. As an example, the pore size distribution of the isolation membrane can be 1nm-50nm, 5nm-50nm, 10nm-50nm, 20nm-50nm, 30nm-50nm, 40nm-50nm, 10nm-40nm, 20nm-40nm, 30nm-40nm, 10nm-30nm, 20nm-30nm, and so on.

[0068] Polyphenylene sulfide (PPS) is a polymer containing repeating structural units of paraphenylene sulfide in its molecules. The heat deformation temperature of PPS is above 260°C, the starting temperature of thermal decomposition is above 450°C, the oxygen index is as high as 46%-53%, the thermal stability is higher than that of polyolefins, and it has good heat resistance, excellent chemical corrosion resistance and flame retardancy. Therefore, compared with polyolefin separators, polyphenylene sulfide separators can withstand higher temperatures during the baking process of battery cells, thereby improving the baking efficiency and reducing the water content of battery cells; during the charge and discharge cycle, the probability of the risk of the separator being closed, ruptured, and the battery short circuit caused by the heat shrinkage of the polyphenylene sulfide separator is also lower. In addition, PPS contains a benzene ring structure and a sulfur bond (-S-), wherein the benzene ring has a certain rigidity, which can improve the puncture strength of the separator, thereby reducing the risk of the separator being pierced by metal dendrites, reducing the self-discharge of the battery, and improving the reliability and cycle performance of the battery; the sulfur bond can improve the electrolyte wetting performance of the separator, thereby reducing the internal resistance of the battery and improving the cycle performance of the battery.

[0069] Without intending to be limited by any theory or explanation, the separator of the embodiment of the present application includes polyphenylene sulfide, and its maximum pore size satisfies the above range, which can make the separator have suitable air permeability, mechanical strength and good ionic conductivity. As a result, not only the electrolyte infiltration performance of the separator can be improved, but also the mechanical properties such as tensile strength of the separator can be improved. Therefore, the separator of the embodiment of the present application is applied to the battery, which can reduce the battery's withstand voltage test (Hi-pot) failure rate, reduce the battery's self-discharge, and improve the battery's cycle performance.

[0070] Therefore, the isolation membrane of the embodiment of the present application is applied to a battery to improve the reliability and cycle performance of the battery.

[0071] In some embodiments, the average pore size of the isolation membrane may be 10 nm-50 nm. For example, the average pore size of the isolation membrane may be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or a range consisting of any two of the above values.

[0072] Optionally, in some embodiments, the average pore size of the isolation membrane may be 20 nm-35 nm. For example, the average pore size of the isolation membrane may be 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 32 nm, 34 nm, 35 nm, or a range consisting of any two of the above values.

[0073] The average pore size of the isolation membrane is within the above-mentioned suitable range, and can have lower resistance and higher ion conductivity, which helps to improve the cycle performance of the battery.

[0074] The maximum pore size and average pore size of the isolation membrane have well-known meanings in the art and can be measured using equipment and methods known in the art. As an example, the fully automatic specific surface area and micropore size analyzer of the American PMI instrument can be used for determination by gas adsorption method. Specifically, an appropriate amount of isolation membrane sample (about 100 mg) can be taken, the sample can be placed in a sample tube, and its mass is recorded as m1 mg; the sample tube is loaded into a degassing station, the sample is heated and vacuum degassed to remove the gas adsorbed on the surface of the isolation membrane, and then the sample is cooled to room temperature and backfilled with helium to normal pressure; the mass of the sample tube is weighed and recorded as m2 mg, (m2-m1) is the weight of the sample after degassing; refer to the test standard GB / T 19587-2017, the sample tube is placed in a liquid nitrogen environment, and after the sample tube is evacuated, helium is added to the sample tube and the gas is evacuated, and the adsorption amount at each partial pressure point, the adsorption-desorption isotherm and the BET surface area A of the sample are measured. Based on the adsorption-desorption isotherm, the capillary radius rk at which capillary condensation occurs corresponding to the horizontal coordinate P / P0 (P is the gas adsorption equilibrium pressure, and P0 is the saturated vapor pressure of the gas at the adsorption temperature) is calculated using the Kelvin formula. Under this P / P0 condition, all pores with a value smaller than rk are filled with adsorbates by capillary condensation. Therefore, the adsorption volume Vr corresponding to this relative pressure P / P0 on the adsorption isotherm is the total volume of all pores with a radius less than or equal to this rk; a Vr-rk relationship curve is drawn, which is the integral distribution curve of the pore volume versus the pore radius; a graphical method is used on the integral distribution curve to obtain the volume ΔVr that increases in the adsorption amount when the pore radius increases by Δr, and ΔVr / Δr is calculated, and a plot of ΔVr / Δr versus rk is drawn, which is the differential distribution curve of the pore radius; the pore diameter value corresponding to the maximum point on the horizontal coordinate in the differential distribution curve is the maximum pore diameter of the isolation membrane. Using the multi-molecular layer adsorption theory (BET theory), the average pore size of the isolation membrane can be calculated using the formula d=4V / A, where d represents the average pore size, V represents the total pore volume (the volume of adsorbed gas converted into liquid), and A represents the BET surface area of ​​the sample.

[0075] In some embodiments, the porosity of the isolation membrane may be 30%-60%. For example, the porosity of the isolation membrane may be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range consisting of any two of the above values.

[0076] Optionally, in some embodiments, the porosity of the isolation membrane may be 45%-48%. For example, the porosity of the isolation membrane may be 45%, 46%, 47%, 48%, or a range consisting of any two of the above values.

[0077] The porosity of the separator is within the above-mentioned appropriate range, which can adjust the air permeability and mechanical strength, and also make the separator have both good barrier properties and good ion conductivity, thereby helping to improve the reliability and cycle performance of the battery.

[0078] The porosity of the isolation membrane has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, the porosity of the isolation membrane can be calculated by weight method with reference to the test standard GB / T 21650-2008. Specifically, a 100mm×100mm standard size isolation membrane sample can be weighed, and the actual weight is recorded as W, the volume of the isolation membrane sample is V, and the density of the isolation membrane resin is ρ. The porosity calculation formula is as follows: Porosity % = [1-W / (V×ρ)]×100%.

[0079] In some embodiments, the thickness of the isolation film may be less than or equal to 15 μm. For example, the thickness of the isolation film may be 15 μm, 12 μm, 10 μm, 8 μm, 6 μm, 4 μm, or a range consisting of any two of the above values.

[0080] Optionally, in some embodiments, the thickness of the isolation film may be 5 μm-15 μm. For example, the thickness of the isolation film may be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range consisting of any two of the above values.

[0081] Without intending to be limited by any theory or explanation, the separator of the embodiment of the present application has a suitable pore structure, and when it has the above-mentioned small thickness, it can still have good heat resistance and mechanical strength. Therefore, it can not only reduce the internal resistance of the battery and increase the energy density of the battery, but also effectively improve the high temperature cycle performance and reliability of the battery.

[0082] The thickness of the isolation film has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, six groups of parallel samples can be taken, and the thickness of each group of samples at different positions can be measured using a micrometer thickness gauge, and at least 20 positions of each group of samples can be measured, and the average value of the thickness of the six groups of samples is taken as the thickness of the sample.

[0083] In some embodiments, the separator may further include polysulfone and / or polyetheretherketone, thereby improving the transverse tensile strength and longitudinal tensile strength of the separator, thereby improving the puncture resistance of the separator, reducing the risk of the separator being punctured, and thus improving the reliability of the battery.

[0084] In some embodiments, the melt index of polyphenylene sulfide at 315°C and 5 MPa can be 100 g / 10min-200 g / 10min, for example, 100 g / 10min, 110 g / 10min, 120 g / 10min, 130 g / 10min, 140 g / 10min, 150 g / 10min, 160 g / 10min, 170 g / 10min, 180 g / 10min, 190 g / 10min, 200 g / 10min, or a range consisting of any two of the above values.

[0085] Without intending to be limited by any theory or explanation, when the melt index of polyphenylene sulfide satisfies the given range, it is beneficial to improve the tensile strength of the separator, thereby improving the heat resistance and physical properties of the separator, thereby further improving the reliability of the battery.

[0086] Melt index has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, reference can be made to ASTMD 1238 and a melt index tester can be used for testing. Specifically, the test can be carried out according to the following steps: (1) Dry or vacuum dry the polyphenylene sulfide sample; (2) Adjust the melt index tester to a horizontal position; (3) Place the standard die into the barrel, insert the piston rod, and start heating. After reaching 315°C, keep the temperature constant for at least 15 minutes; (4) Weigh the sample and add it to the barrel; (5) Preheat the sample for 4 minutes, return the furnace temperature to the specified temperature, apply a pressure load of 5 kg, and press the piston down by hand until the lower ring mark is 5mm-10mm away from the barrel mouth. Step ( 5) The operation time should not exceed 1 min; (6) When the piston drops to the level of the lower ring mark and the barrel mouth, cut off the outflowing sample and start formal cutting. Keep three bubble-free sample strips cut continuously. When the piston drops to the level of the lower ring mark and the barrel mouth, stop cutting; (7) After the sample strips are cooled, place them on a balance and weigh them separately. Take the average value as the mass m of the sample strip, in g; (8) Calculate the melt index MFR of polyphenylene sulfide = (600×m) / t, in g / 10min.

[0087] In some embodiments, the sulfur content of the polyphenylene sulfide may be greater than 28 wt%, and may be 28 wt%-30 wt%, based on the total weight of the polyphenylene sulfide. For example, it may be 28 wt%, 28.1 wt%, 28.5 wt%, 28.7 wt%, 29 wt%, 29.2 wt%, 29.4 wt%, 29.8%, 30 wt%, or a range consisting of any two of the above values.

[0088] Without intending to be limited by any theory or explanation, when the sulfur content of polyphenylene sulfide meets the given range, it is beneficial to improve the electrolyte wetting performance of the separator, thereby reducing the internal resistance of the battery and further improving the cycle performance of the battery.

[0089] The sulfur content of polyphenylene sulfide has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, it can be measured using an HCS-140 infrared carbon-sulfur analyzer. Specifically, the sulfur in a polyphenylene sulfide sample can be heated at a high temperature of 1000°C under oxygen-rich conditions to oxidize the sample and generate a mixed gas containing carbon dioxide and sulfur dioxide; the gas enters a corresponding absorption cell after treatment, absorbs infrared radiation of a corresponding wavelength, is forwarded by a detector as a signal, and outputs the sulfur content after being processed by a computer.

[0090] In some embodiments, the tensile strength of the separator in transverse direction (TD) may be 2300 kg / cm 2 Above, 3800kg / cm2 can be selected 2 above.

[0091] In some embodiments, the longitudinal tensile strength of the separator may be 2600 kg / cm 2 Above, 4200kg / cm2 is optional 2 above.

[0092] When the tensile strength of the isolation membrane meets the above conditions, the isolation membrane can have good heat resistance and physical properties, thereby further improving the reliability of the battery.

[0093] The transverse tensile strength and longitudinal tensile strength of the isolation membrane have well-known meanings in the art, and can be measured using equipment and methods known in the art. For example, a tensile tester can be used for testing with reference to GB / T 1040-2006. Specifically, each membrane sample can be made into a sample with a size of 3cm*15cm, and stretched using a tensile tester, with a stretching speed of 50mm / min and a stretching spacing of 40mm. When the isolation membrane sample is broken, the tensile strength of each isolation membrane sample is recorded, and the average tensile strength of 5 samples is taken as the tensile strength of the isolation membrane. By adjusting the stretching direction during the test, the transverse (TD) tensile strength and longitudinal (MD) tensile strength of the isolation membrane can be obtained respectively.

[0094] In some embodiments, the isolation film may contain K + 、Na + 、NO3 - 、NO2 - At least one of .

[0095] In some embodiments, the isolation film contains 0.01 ppm to 10 ppm of K+ , 0.1ppm-10ppm Na + , 0.1ppm-10ppm NO3 - , 0.1ppm-10ppm NO2 - At least one of .

[0096] Isolation film K + 、Na + 、NO3 - and NO2 - The content of can be determined by equipment and methods known in the art. For example, it can be measured by inductively coupled plasma emission spectroscopy (ICP). Specifically, the elemental analysis of K in the isolation film can be performed by inductively coupled plasma emission spectroscopy (ICP, Ametek, model: SPECTROARCOSICP-OES) with reference to standards YS / T1006.2-2014, GB / T23367.2-2009 or YS / T1028.5-2015 to determine the content of K in the isolation film. + And Na + The content of NO3 in the isolation membrane can be determined by ion chromatography test (iCR1500 intelligent ion chromatograph) according to the standard GB / T 39305-2020. - and NO2 - The content.

[0097] Preparation method

[0098] In a second aspect, an embodiment of the present application provides a method for preparing an isolation membrane, comprising the following steps S10 to S40.

[0099] S10, providing a base material for an isolation film, wherein the base material for the isolation film includes polyphenylene sulfide.

[0100] S20, melting the separator substrate raw material in a molten salt to obtain a composite molten salt including polyphenylene sulfide, wherein the cations of the molten salt include K + and / or Na + , the anions of the molten salt include NO3 - and / or NO2 - .

[0101] In step S20, the insulating film substrate raw material and the molten salt can be mixed evenly, and then heated to melt the insulating film substrate raw material and the molten salt; the insulating film substrate raw material can also be contacted with the molten salt in a molten state and mixed evenly, so that the insulating film substrate raw material is melted and evenly dispersed in the molten salt system. The temperature at which the insulating film substrate raw material is melted in the molten salt can be adjusted according to actual needs, for example, it can be adjusted according to the melting temperature at which the insulating film substrate raw material reaches a molten state. The molten salt in step S20 has the above-mentioned composition, can have good fluidity at the melting temperature of the insulating film substrate raw material, and has good solubility in the insulating film substrate raw material. Thereby, it is conducive to the uniform mixing of the insulating film substrate raw material and the molten salt to obtain a composite molten salt including polyphenylene sulfide.

[0102] S30, preparing the composite molten salt into a membrane to obtain a composite membrane including polyphenylene sulfide and an inorganic salt.

[0103] In step S30, the composite molten salt may be prepared into a membrane by a process known in the art. The composite membrane may include a polyphenylene sulfide substrate and inorganic salt particles uniformly distributed in the substrate.

[0104] S40, contacting the composite membrane with a solvent to dissolve the inorganic salt in the composite membrane to obtain an isolation membrane, wherein the maximum pore size of the isolation membrane is less than or equal to 50 nm.

[0105] In step S40, the composite membrane is contacted with a solvent, and the solvent can dissolve the inorganic salt in the composite membrane, thereby extracting the inorganic salt from the composite membrane. After the inorganic salt is dissolved, nanoscale micropores can be formed in the composite membrane, so that the isolation membrane has a suitable pore structure. In some embodiments, the amount and composition of the inorganic salt can be adjusted to adjust the pore structure of the isolation membrane. In some embodiments, after the inorganic salt in the composite membrane is dissolved by a solvent, an inorganic salt solution can be obtained, and the inorganic salt solution can be recycled to obtain an inorganic salt and a solvent. In step S40, the solvent may include a solvent known in the art that can dissolve inorganic salts and does not dissolve polyphenylene sulfide. In some embodiments, the solvent may include, but is not limited to, one or more of water, ethanol, polyethylene glycol, and methanol.

[0106] Polyphenylene sulfide isolation membrane has good heat resistance, excellent chemical corrosion resistance and flame retardancy. The relevant technology involves using diluents such as phenyl sulfone, benzophenone, diphenyl ether or polyether sulfone, or solvents such as dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide or N,N-dimethylformamide, dioctyl phthalate to dissolve polyphenylene sulfide to prepare polyphenylene sulfide isolation membrane. However, the above diluents and solvents cannot effectively dissolve polyphenylene sulfide, resulting in uneven pore size distribution, uncontrollable pore size and porosity of the polyphenylene sulfide isolation membrane, and easily forming pore sizes of tens to hundreds of microns, which seriously affects the performance of the isolation membrane. In addition, the above diluents and solvents are highly toxic and easily pollute the environment.

[0107] According to the method of the embodiment of the present application, an inorganic salt flux is used to evenly disperse the molten polyphenylene sulfide into the molten salt system to form a composite molten salt system with good fluidity, and then the composite molten salt is prepared into a composite membrane. The composite membrane includes evenly dispersed polyphenylene sulfide and inorganic salt particles. After solvent extraction, the inorganic salt particles are dissolved to form nanopores in the membrane. According to the method of the present application, the prepared isolation membrane has a uniform pore size distribution, controllable pore size, and controllable porosity. When applied to batteries, it can not only reduce the battery's withstand voltage test failure rate and reduce the battery's self-discharge, but also improve the battery's cycle performance.

[0108] Therefore, the isolation membrane prepared according to the method of the embodiment of the present application is applied to the battery, which can effectively improve the battery reliability and cycle performance.

[0109] In addition, the method of the present application is simple to operate, and the molten salt and solvent are reusable and non-toxic and harmless, which can not only reduce production costs but also reduce pollution to the environment.

[0110] In some embodiments, based on the total mass of the isolation membrane substrate material, the mass percentage of polyphenylene sulfide can be greater than or equal to 80%, for example, it can be 80%, 85%, 90%, 95%, 100%, or a range consisting of any two of the above values.

[0111] Optionally, in some embodiments, based on the total mass of the separator substrate raw material, the mass percentage of polyphenylene sulfide can also be greater than or equal to 90%, for example, it can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or a range consisting of any two of the above values. In some embodiments, the separator substrate raw material can also include polysulfone and / or polyetheretherketone.

[0112] In some embodiments, the molten salt may include potassium nitrate, sodium nitrite, and sodium nitrate.

[0113] Optionally, in the molten salt, the mass ratio of potassium nitrate, sodium nitrite and sodium nitrate can be 1:(0.1-10):(0.1-10). For example, the mass ratio of potassium nitrate, sodium nitrite and sodium nitrate can be 1:0.1:0.1, 1:0.5:0.5, 1:1:1, 1:2:2, 1:5:5, 1:8:8, 1:10:10, 1:0.1:0.5, 1:0.1:1, 1:0.1:2, 1:0.1:5, 1:0.1:8, 1:0.1:10, 1:0.5:0.1, 1:1:0.1, 1:2:0.1, 1:5:0.1, 1:8:0.1, 1:10:0.1, and the like.

[0114] In some embodiments, the molten salt may include potassium nitrate and sodium nitrite.

[0115] Optionally, in the molten salt, the mass ratio of potassium nitrate to sodium nitrite may be 1:(0.1-10). For example, the mass ratio of potassium nitrate to sodium nitrite may be 1:0.1, 1:0.5, 1:1, 1:2, 1:5, 1:8, 1:10, and the like.

[0116] In some embodiments, the molten salt may include potassium nitrate, potassium nitrite and sodium nitrate. Optionally, in the molten salt, the mass ratio of potassium nitrate, potassium nitrite and sodium nitrate may be 1:(0.1-10):(0.1-10). For example, the mass ratio of potassium nitrate, potassium nitrite and sodium nitrate may be 1:0.1:0.1, 1:0.5:0.5, 1:1:1, 1:2:2, 1:5:5, 1:8:8, 1:10:10, 1:0.1:0.5, 1:0.1:1, 1:0.1:2, 1:0.1:5, 1:0.1:8, 1:0.1:10, 1:0.5:0.1, 1:1:0.1, 1:2:0.1, 1:5:0.1, 1:8:0.1, 1:10:0.1, and the like.

[0117] Without intending to be limited by any theory or explanation, when the molten salt has the above composition, a fluid with good fluidity can be formed at the melting temperature of the isolation membrane substrate. The fluid has good solubility in the isolation membrane substrate raw material, which is conducive to the isolation membrane substrate being uniformly melted in the molten salt to form a composite molten salt system with good fluidity. As a result, it is helpful to evenly distribute the inorganic salt particles in the composite membrane, thereby improving the uniformity of the pore size distribution of the isolation membrane, as well as the controllability of the pore size and porosity.

[0118] In some embodiments, melting the isolation film substrate raw material in molten salt may specifically include: melting the isolation film substrate raw material in molten salt at 285° C.-300° C.

[0119] At the above temperature, on the one hand, the separator substrate material can be thermally deformed and melted, and on the other hand, the molten salt can have good fluidity. Therefore, it is beneficial for the separator substrate material to be fully melted in the molten salt to form a uniform composite molten salt, thereby helping to improve the uniformity of the pore size distribution of the separator, as well as the controllability of the pore size and porosity.

[0120] Optionally, in some embodiments, the mass ratio of the isolation membrane substrate raw material to the molten salt can be 1:(3-7), for example, it can be 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, or a range consisting of any two of the above values.

[0121] By controlling the mass ratio of the separator substrate material to the molten salt within the above-mentioned appropriate range, the content of inorganic salt particles in the composite membrane can be appropriate, which helps to form a separator with a specific pore structure. As a result, the separator can have appropriate air permeability, mechanical strength and good ionic conductivity, thereby improving the reliability and cycle performance of the battery.

[0122] In some embodiments, the melting point of the molten salt may be 140°C-150°C, for example, 140°C, 142°C, 144°C, 146°C, 148°C, 150°C, or a range consisting of any two of the above values.

[0123] The melting point of a molten salt has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, the test can be performed with reference to GB / T 21781-2008.

[0124] In some embodiments, the viscosity of the molten salt at 150°C can range from 5 mPa·s to 20 mPa·s, for example, 5 mPa·s, 7 mPa·s, 9 mPa·s, 10 mPa·s, 12 mPa·s, 14 mPa·s, 16 mPa·s, 18 mPa·s, 20 mPa·s, or a range consisting of any two of the above values.

[0125] In some embodiments, the viscosity of the molten salt at 280°C-300°C can range from 2mPa·s to 4mPa·s, for example, 2mPa·s, 2.2mPa·s, 2.5mPa·s, 2.8mPa·s, 3mPa·s, 3.1mPa·s, 3.3mPa·s, 3.7mPa·s, 4mPa·s, or a range consisting of any two of the above values.

[0126] When the melting point and / or viscosity of the molten salt meet the above conditions, it is helpful to form a fluid with good fluidity at the melting temperature of the isolation membrane substrate, thereby facilitating the isolation membrane substrate to melt evenly in the molten salt, forming a composite molten salt system with good fluidity. This helps the inorganic salt particles to be evenly distributed in the composite membrane, thereby improving the uniformity of the pore size distribution of the isolation membrane, as well as the controllability of the pore size and porosity, so that the isolation membrane has a smaller pore size and a suitable porosity.

[0127] The viscosity range of the molten salt has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, it can be measured using a BROOKFIELD viscometer from the United States. Specifically, the molten salt can be heated to a predetermined temperature, and after the temperature is constant, the viscosity of the molten salt at the predetermined temperature can be measured using a viscometer.

[0128] In some embodiments, preparing the composite molten salt into a film may specifically include: preparing the composite molten salt into a composite film having a thickness less than or equal to 15 μm through a tape casting film forming process or a wet film forming process.

[0129] As an example of the tape casting process, the composite molten salt can be made to flow from the lower part of the hopper to the film carrier (conveyor belt) of the tape casting machine, and the film thickness can be controlled by a scraper, and the composite film can be obtained after cooling.

[0130] As an example of a wet film forming process, the composite molten salt can be cooled and then cast into a sheet, which can be stretched to obtain a composite film. In some embodiments, after the composite film is formed through a wet film forming process, the composite film is contacted with a solvent to dissolve the inorganic salt in the composite film, and then the composite film can be stretched again and cut to obtain a separator.

[0131] The separator prepared by the method of the embodiment of the present application has a suitable pore structure, and when it has the above-mentioned small thickness, it can still have good heat resistance and mechanical strength. Therefore, it can not only reduce the internal resistance of the battery and increase the energy density of the battery, but also effectively improve the high temperature cycle performance and reliability of the battery.

[0132] In some embodiments, the isolation film may contain K + 、Na + 、NO3 - 、NO2 - At least one of .

[0133] In some embodiments, the isolation film contains 0.01 ppm to 10 ppm of K + , 0.1ppm-10ppm Na + , 0.1ppm-10ppm NO3 - , 0.1ppm-10ppm NO2 -At least one of .

[0134] In some embodiments, the average pore size of the isolation membrane prepared by the method of the embodiment of the present application can be 10nm-50nm. For example, the average pore size of the isolation membrane can be 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, or a range consisting of any two of the above values.

[0135] Optionally, in some embodiments, the average pore size of the isolation membrane prepared by the method of the embodiment of the present application can be 20nm-35nm. For example, the average pore size of the isolation membrane can be 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, 32nm, 34nm, 35nm, or a range consisting of any two of the above values.

[0136] In some embodiments, the porosity of the isolation membrane prepared by the method of the embodiment of the present application can be 30%-60%. For example, the porosity of the isolation membrane can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range consisting of any two of the above values.

[0137] Optionally, in some embodiments, the porosity of the isolation membrane prepared by the method of the embodiment of the present application can also be 45%-48%. For example, the porosity of the isolation membrane can be 45%, 46%, 47%, 48%, or a range consisting of any two of the above values.

[0138] In some embodiments, the thickness of the isolation film prepared by the method of the embodiment of the present application may be less than or equal to 15 μm. For example, the thickness of the isolation film may be 15 μm, 12 μm, 10 μm, 8 μm, 6 μm, 4 μm, or a range consisting of any two of the above values.

[0139] Optionally, in some embodiments, the thickness of the isolation film prepared by the method of the embodiment of the present application can also be 5 μm-15 μm. For example, the thickness of the isolation film can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range consisting of any two of the above values.

[0140] In some embodiments, the transverse direction (TD) tensile strength of the isolation film prepared according to the method of the embodiment of the present application can be 2300 kg / cm 2 Above, 3800kg / cm2 can be selected 2 above.

[0141] In some embodiments, the longitudinal tensile strength of the separator prepared by the method of the embodiment of the present application can be 2600 kg / cm 2 Above, 4200kg / cm2 is optional 2 above.

[0142] Battery

[0143] The battery mentioned in the embodiments of the present application may include one or more battery cells to provide a single physical module with higher voltage and capacity. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel or in mixed connection through a busbar component.

[0144] Typically, a battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. During the charge and discharge process of the battery cell, active ions (such as lithium ions) are embedded and removed back and forth between the positive electrode and the negative electrode. The separator is arranged between the positive electrode and the negative electrode to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte plays the role of conducting active ions between the positive electrode plate and the negative electrode plate.

[0145] The battery cell provided in the embodiments of the present application includes an isolation membrane as in the embodiments of the first aspect of the present application or an isolation membrane prepared according to the method of the embodiments of the second aspect of the present application, which can improve the reliability and cycle performance of the battery.

[0146] [Positive electrode]

[0147] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0148] When the battery cell is a lithium-ion battery, the positive electrode active material may include, but is not limited to, at least one of lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0149] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material for the lithium ion battery may include a general formula of Li a Nib Co c M d O e A f At least one of lithium transition metal oxides and modified compounds thereof. 0<a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 0<e≤2, 0≤f≤1, M is selected from at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from at least one of N, F, S and Cl.

[0150] As an example, the positive electrode active material for lithium ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.8 Co 0.15 Al 0.05 At least one of O2, LiFePO4, and LiMnPO4.

[0151] When the battery cell is a sodium ion battery, the positive electrode active material may include but is not limited to at least one of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0152] As an example, the positive electrode active material for sodium ion batteries may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2、NaNi 1 / 2 Mn 1 / 2 O2、Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2、NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials, general formula X p M' q (PO4)r O x Y 3-x In the general formula X p M' q (PO4) r O x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X is selected from H + , Li + 、Na + , K + and NH4 + At least one of, M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, optionally at least one of F, Cl and Br.

[0153] The modified compounds of the above-mentioned positive electrode active materials may be the ones that undergo doping modification and / or surface coating modification on the positive electrode active materials.

[0154] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application has no particular restrictions on the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0155] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The present application has no particular restrictions on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0156] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base and a metal material layer formed on at least one surface of the polymer material base. As an example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0157] The positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0158] [Negative electrode]

[0159] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0160] The negative electrode active material may adopt the negative electrode active material for battery cells known in the art. As an example, the negative electrode active material may include but is not limited to at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite and silicon alloy material. The tin-based material may include at least one of elemental tin, tin oxide and tin alloy material.

[0161] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. The present application has no particular restrictions on the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0162] In some embodiments, the negative electrode film layer may further include a negative electrode binder. The present application has no particular restrictions on the type of the negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-based unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0163] In some embodiments, the negative electrode film layer may further include other additives. As an example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0164] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0165] The negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliary agents in a solvent and stirring them evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0166] The negative electrode plate does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode plate also includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In some embodiments, the negative electrode plate of the present application also includes a protective layer covering the surface of the negative electrode film layer.

[0167] [Isolation film]

[0168] The isolation film is arranged between the positive electrode sheet and the negative electrode sheet to play an isolating role. The isolation film included in the battery of the embodiment of the present application includes the isolation film of the first aspect of the embodiment of the present application, or the isolation film prepared according to the method of the second aspect of the embodiment of the present application. The embodiments of the isolation film have been described and explained in detail above, and will not be repeated here. It can be understood that the battery of the embodiment of the present application can achieve the beneficial effects of any of the above embodiments of the isolation film of the embodiment of the present application.

[0169] [Electrolytes]

[0170] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application embodiment has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid or gel.

[0171] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0172] When the battery cell is a lithium ion battery, as an example, the electrolyte salt may include but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0173] When the battery cell is a sodium ion battery, as an example, the electrolyte salt may include but is not limited to at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0174] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0175] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature power performance.

[0176] In some embodiments, the positive electrode sheet, the separator and the negative electrode sheet can be made into an electrode assembly by a winding process and / or a lamination process. The negative electrode sheet can face the second bonding layer in the separator, so that there can be a smaller gap between the negative electrode sheet and the separator, thereby delaying the growth of lithium dendrites and improving the reliability of the battery. It can be understood that the separator of the present application includes both a first base film and a second base film, and the first base film or the second base film can be optionally facing the positive electrode sheet or the negative electrode sheet. For example, the first base film faces the positive electrode sheet, and the second base film faces the negative electrode sheet; or the first base film faces the negative electrode sheet, and the second base film faces the positive electrode sheet.

[0177] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0178] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0179] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0180] In some embodiments, Figure 2 As shown, the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to demand.

[0181] The preparation method of battery cells is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, the separator and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with electrolyte, and then vacuum packaged, left to stand, formed, shaped and other processes are performed to obtain a battery cell.

[0182] In some embodiments, the battery cells according to the present application may be assembled into a battery module. The battery module may contain multiple battery cells, and the specific number may be adjusted according to the application and capacity of the battery module.

[0183] Figure 3 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 3 As shown, in the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0184] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0185] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0186] Figure 4 and Figure 5 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0187] Electrical devices

[0188] The embodiment of the present application also provides an electric device, the electric device includes a battery cell provided in the embodiment of the present application, and the battery cell is used to provide electrical energy. The battery cell can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0189] As the electrical device, a battery cell, a battery module including a plurality of battery cells, or a battery pack may be selected according to its usage requirements.

[0190] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirements of the power consumption device for high power and high energy density, a battery pack or a battery module can be used.

[0191] As another example, the power-consuming device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a battery cell may be used as a power source.

[0192] Example

[0193] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0194] Example 1

[0195] Preparation of isolation membrane

[0196] The raw material of the isolation membrane substrate, polyphenylene sulfide (PPS, the melt index at 315°C and 5MPa is 125g / 10min, and the sulfur content is 28.5wt%), is dispersed in a molten salt (mass ratio of potassium nitrate: sodium nitrite: sodium nitrate = 1:1:1), and then melted at a preset temperature of 295°C to form a uniform composite molten salt, wherein the mass ratio A of the isolation membrane substrate raw material to the molten salt is 1:3; the composite molten salt is extruded through a twin-screw extruder, and is transported to a T-die head at a certain rotation speed through a metering gear pump, and then extruded from the T-die to form a thin film sheet with a thickness of 0.1mm and a width of 200mm; the temperature is controlled to be 100°C, and longitudinal stretching and then shaping are performed, the stretching ratio is between 3.5, and the stretching speed is 45m / min, to prepare a composite film with a thickness d0 of 10μm; after the composite film is cooled, the composite film is washed with deionized water to dissolve the inorganic salt in the composite film to obtain an isolation membrane. The maximum pore size, average pore size, porosity, thickness d, transverse (TD) tensile strength and longitudinal (MD) tensile strength of the isolation membrane were tested according to the method described in the specification of this application. The test results are shown in Table 1 and Table 2 respectively.

[0197] Preparation of positive electrode

[0198] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a proper amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.2:2.7:1.1 to obtain positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting.

[0199] Preparation of negative electrode

[0200] The negative electrode active material artificial graphite, the conductive agent carbon black (Super P), the binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) are mixed uniformly in a proper amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained through the processes of drying, cold pressing, slitting and cutting.

[0201] Preparation of electrolyte

[0202] Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:30:40 to obtain an organic solvent, and fully dried LiPF6 is dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0203] Preparation of secondary batteries

[0204] The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in an outer package, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a secondary battery is obtained.

[0205] Example 2-22

[0206] Based on the preparation process of the isolation membrane in Example 1, the preparation parameters such as the type of isolation membrane substrate raw material, molten salt composition, mass ratio A of the isolation membrane substrate raw material to the molten salt, preset temperature, thickness d of the composite film, etc. are adjusted as shown in Table 1 to prepare the isolation membranes of Examples 2-22.

[0207] The preparation of the positive electrode sheet, negative electrode sheet, electrolyte and secondary battery of Examples 2-22 is the same as that of Example 1.

[0208] Comparative Example 1

[0209] Preparation of isolation membrane

[0210] Polyphenylene sulfide (PPS, melt index of 125 g / 10 min at 315°C and 5 MPa, sulfur content of 28.5 wt%) was dissolved in dioctyl phthalate (DOP) at 290°C to prepare a homogeneous solution with a mass percentage of 30%; the solution was prepared into a film by a cast film process; the residual DOP was cleaned with butyl acetate, and after drying and stretching, an isolation film with a thickness d0 of 10 μm was obtained.

[0211] The preparation of the positive electrode sheet, negative electrode sheet, electrolyte and secondary battery of Comparative Example 1 is the same as that of Example 1.

[0212] Test Section

[0213] Self-discharge test

[0214] Ten batteries were taken from each example or comparative example, and charged at a constant current of 0.5C until the voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the current reached 0.05C. The voltage at this time was measured and recorded as OCV0.

[0215] The 10 batteries were placed at 25°C and the voltages were measured on the 14th and 90th days, respectively, and recorded as OCV1, OCV 长期 , in mV. Then the self-discharge performance K1=(OCV0-OCV1) / (14×24h); K 长期 =(OCV0-OCV 长期 ) / (90×24h), K1 and K 长期 The unit is mV / h.

[0216] Cyclic performance test

[0217] At 25°C, the batteries of the above embodiments and comparative examples are charged at 1C constant current to a voltage of 4.2V, then charged at 4.2V constant voltage to a current ≤ 0.05C, and then discharged at 1C constant current to a voltage of 2.8V. This is a charge and discharge process, and the discharge capacity at this time is recorded as the discharge capacity of the first cycle of the battery. Repeat the charge and discharge cycles in this way, and record the discharge capacity D0 of the first cycle and the discharge capacity D of the 500th cycle. 500 . Cycle capacity retention rate P of secondary battery 500 =D 500 / D0×100%.

[0218] Hi-pot test

[0219] The test was conducted using an LST-212 insulation resistance tester. Within 2 seconds, the tester was used to apply voltage to the battery from 0 to the set value U = 100V; the voltage U was continued to be applied for 2 seconds; after the test was completed, the test voltage was cut off to short-circuit the stray capacitance formed by the positive and negative electrodes of the battery to discharge; the current value of the leakage current was detected to determine the corresponding insulation resistance value. When the insulation resistance value was above 1 megohm (MΩ), the battery was considered to have passed the withstand voltage test. 100 batteries were taken for testing in each group of embodiments or comparative examples, and the Hi-pot yield = the number of batteries that passed the test / 100 × 100%.

[0220] The test results are shown in Table 3.

[0221] Table 1

[0222]

[0223] Table 2

[0224]

[0225] Table 3

[0226] Serial number <![CDATA[K1 / (mV / h)]]> <![CDATA[K 长期 (mV / h)]]> <![CDATA[Capacity retention rate P 500 > Hi-pot yield Example 1 0.015 0.012 98.90％ 99％ Example 2 0.013 0.012 99.10％ 100％ Example 3 0.012 0.011 99.30％ 100％ Example 4 0.015 0.013 98.50％ 99％ Example 5 0.016 0.013 98.80％ 100％ Example 6 0.017 0.014 97.90％ 99％ Example 7 0.011 0.010 98.60％ 99％ Example 8 0.016 0.012 97.50％ 98％ Example 9 0.014 0.012 97.60％ 98％ Example 10 0.015 0.013 98.50％ 99％ Embodiment 11 0.013 0.011 98.20％ 99％ Example 12 0.013 0.011 98.10％ 99％ Embodiment 13 0.015 0.012 97.70％ 98％ Embodiment 14 0.016 0.013 97.50％ 98％ Embodiment 15 0.015 0.012 97.90％ 99％ Example 16 0.016 0.014 98.50％ 99％ Embodiment 17 0.013 0.011 98.60％ 100％ Embodiment 18 0.015 0.013 98.70％ 100％ Embodiment 19 0.013 0.011 98.50％ 99％ Embodiment 20 0.016 0.013 98.30％ 99％ Embodiment 21 0.013 0.010 99.20％ 100％ Embodiment 22 0.012 0.011 99.50％ 100％ Comparative Example 1 0.250 0.210 93.50％ 93％

[0227] From the test results of Tables 1 to 3, it can be seen that the isolation membranes prepared in Examples 1-22 according to the method of the embodiments of the present application have good pore structures, and the pore sizes are all within the range specified in the embodiments of the present application. As a result, the self-discharge of the battery is effectively suppressed, the cycle capacity retention rate and Hi-pot yield of the battery are improved, and the cycle performance and reliability of the battery are improved.

[0228] In contrast, in Comparative Example 1, dioctyl phthalate (DOP) was used to dissolve polyphenylene sulfide (PPS), and DOP had poor solubility in PPS, resulting in the pore structure of the separator of Comparative Example 1 being difficult to control, the pore size distribution being large, and the maximum pore size reaching 1 μm. As a result, the battery of Comparative Example 1 not only had a serious self-discharge phenomenon, but also had a cycle capacity retention rate and Hi-pot yield rate far lower than those of Examples 1-22.

[0229] For some compounds given but not listed in the embodiments, since their chemical properties and reaction properties when participating in electrochemical reactions are similar to those of the compounds listed in the embodiments, they are all suitable for the technical scheme of the present invention and are therefore not listed one by one here.

[0230] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A separator comprising polyphenylene sulfide, wherein: The maximum pore size of the isolation membrane is less than or equal to 50 nm.

2. The isolation film according to claim 1, wherein: The average pore size of the isolation membrane is 10nm-50nm, and can be optionally 20nm-35nm.

3. The isolation film according to claim 1 or 2, wherein: The porosity of the isolation film is 30%-60%, and can be optionally 45%-48%.

4. The isolation film according to any one of claims 1 to 3, wherein: The thickness of the isolation film is less than or equal to 15 μm, and can be optionally 5 μm-15 μm.

5. The isolation film according to any one of claims 1 to 4, wherein: The isolation membrane further comprises polysulfone and / or polyetheretherketone.

6. The isolation film according to any one of claims 1 to 5, wherein: The melt index of the polyphenylene sulfide at 315° C. and 5 MPa is 100 g / 10 min-200 g / 10 min; and / or, The sulfur content of the polyphenylene sulfide is greater than 28 wt %, and can be selected from 28 wt % to 30 wt %, based on the total mass of the polyphenylene sulfide.

7. The isolation film according to any one of claims 1 to 6, wherein: The transverse tensile strength of the isolation film is 2300 kg / cm 2 Above, 3800kg / cm2 can be selected 2 above; and / or, The longitudinal tensile strength of the isolation film is 2600 kg / cm 2 Above, 4200kg / cm2 is optional 2 above.

8. A method for preparing an isolation film, comprising: Providing a separator substrate material, wherein the separator substrate material comprises polyphenylene sulfide; The isolation film substrate raw material is melted in a molten salt to obtain a composite molten salt including polyphenylene sulfide, wherein the cation of the molten salt includes K + and / or Na + , the anions of the molten salt include NO3 - and / or NO2 - ; The composite molten salt is prepared into a membrane to obtain a composite membrane including polyphenylene sulfide and an inorganic salt; The composite membrane is brought into contact with a solvent to dissolve the inorganic salt in the composite membrane, thereby obtaining an isolation membrane, wherein the maximum pore size of the isolation membrane is less than or equal to 50 nm.

9. The method according to claim 8, wherein: The molten salt comprises potassium nitrate, sodium nitrite and sodium nitrate. Optionally, in the molten salt, the mass ratio of potassium nitrate, sodium nitrite and sodium nitrate is 1:(0.1-10):(0.1-10); and / or, The molten salt comprises potassium nitrate and sodium nitrite. Optionally, in the molten salt, the mass ratio of potassium nitrate to sodium nitrite is 1:(0.1-10); and / or, The molten salt includes potassium nitrate, potassium nitrite and sodium nitrate. Optionally, in the molten salt, the mass ratio of potassium nitrate, potassium nitrite and sodium nitrate is 1:(0.1-10):(0.1-10).

10. The method according to claim 8 or 9, wherein: The step of melting the isolation film substrate raw material in molten salt comprises: Melting the isolation film substrate raw material in molten salt at 285° C.-300° C.; Optionally, the mass ratio of the isolation membrane substrate raw material to the molten salt is 1:(3-7).

11. The method according to any one of claims 8 to 10, wherein: The melting point of the molten salt is 140°C-150°C; and / or, The viscosity of the molten salt at 150° C. is in the range of 5 mPa·s to 20 mPa·s; and / or, The viscosity of the molten salt at 280° C.-300° C. ranges from 2 mPa·s to 4 mPa·s.

12. The method according to any one of claims 8 to 11, wherein: The step of preparing the composite molten salt into a film comprises: The composite molten salt is prepared into a composite membrane with a thickness less than or equal to 15 μm by a tape casting membrane forming process or a wet membrane forming process.

13. The method according to any one of claims 8 to 12, wherein: The isolation film contains K + 、Na + 、NO3 - or NO2 - At least one of .

14. A battery comprising the separator according to any one of claims 1 to 7, or the separator prepared by the method according to any one of claims 8 to 13.

15. An electrical device comprising the battery according to claim 14.

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