A method for characterizing the microporous structure of battery separators

Abstract

The present application discloses a method for characterizing the microporous structure of a battery separator, which belongs to the field of multi-scale structural characterization of thin film materials. The method comprises: stretching a polyolefin film to obtain a battery separator sample to be tested; placing the battery separator sample on a sample stage, and making the plane of the battery separator sample perpendicular to the direction of the neutron beam, adjusting the neutron wavelength, the distance between the battery separator sample and the detector, and the exposure time to obtain multiple different scattering vectors; through air background and empty sample box detection, correcting the sample thickness, air background, and the influence of the empty sample box, obtaining the absolute scattering intensity corresponding to each scattering vector of the battery separator sample, and obtaining a functional relationship curve between the absolute scattering intensity and the scattering vector; selecting a theoretical model to fit the functional relationship curve to obtain the structural information of the microporous structure of the battery separator sample. The present application can quantitatively characterize the structural information of the microporous structure of the battery separator sample in a non-destructive, rapid, simple, efficient, and highly accurate manner.

Description

Technical Field

[0001] The present application relates to the technical field of multi-scale structural characterization of thin film materials, and in particular to a method for characterizing the microporous structure of a battery separator. Background Art

[0002] Battery separators are functional membrane materials with microporous structures. As a key component of new energy batteries, their primary functions include isolating the positive and negative electrodes, transporting ions, and maintaining the ion-electron circuit during charge and discharge. To meet the performance requirements of batteries, the separator's microporous structure must possess micro-nanoscale pore sizes and high porosity. This ensures efficient ion transport while maintaining mechanical strength, while also providing a microporous structure that can block temperature and voltage fluctuations.

[0003] Although battery separators do not directly participate in the electrochemical reactions of batteries, their intrinsic microporous structure determines the ion transport efficiency, current density, and electrolyte storage of the battery separator, which in turn affects the battery's capacity, cycle performance, and charge and discharge current efficiency. Therefore, accurately characterizing the microporous structure of battery separators through simple and efficient detection methods is a key factor in studying the structure and performance of battery separators, providing an important reference for improving battery performance.

[0004] Conventional methods for testing the microporous structure of battery separators include scanning electron microscopy, surface area analysis, and pressure pumping. The scanning electron microscopy method first sprays the sample with gold before bombarding the separator surface with a focused high-energy electron beam. The surface or cross-section of the separator is then characterized and analyzed to determine the pore size distribution and pore size of the microporous structure. The gold spraying during sample preparation for scanning electron microscopy blocks the nanoscale pores in the separator's microporous structure, affecting the pore size statistics and leading to significant errors in the test results. Furthermore, the fibrous morphology of the separator's microporous structure is easily fractured by the heat generated by the high-energy electron beam bombardment, damaging the microporous structure and making it impossible to accurately calculate the pore size, resulting in significant errors in the test results. The pressure pumping method uses an external force to press mercury into the pores of the separator. The volume of the injected mercury is then measured to calculate the separator's pore size distribution and porosity parameters. However, in actual testing, the stress generated by the mercury injection damages the separator's microporous structure, leading to significant errors in the test results. The specific surface area method primarily uses the amount of gas adsorbed by the microporous structure of battery separators at different pressures to calculate pore size distribution and pore volume. However, due to sample drying and gas adsorption and desorption processes, sample testing can take up to 10 hours, resulting in low detection efficiency and inability to obtain geometric information on the micropore shape. Summary of the Invention

[0005] The embodiments of the present application provide a method for characterizing the microporous structure of a battery separator, which can solve the problems that existing methods for detecting the microporous structure of a battery separator may damage the microporous structure, result in large errors in the detection results, and have low detection efficiency.

[0006] In order to achieve the above-mentioned purpose, the technical solution of the embodiment of the present invention is:

[0007] An embodiment of the present invention provides a method for characterizing the microporous structure of a battery separator, comprising:

[0008] A polyolefin film is stretched to obtain a battery separator sample to be tested;

[0009] Placing the battery separator sample on the sample stage of a small-angle neutron scattering spectrometer, with the plane of the battery separator sample perpendicular to the direction of the neutron beam, and adjusting the neutron wavelength, the distance from the battery separator sample to the detector of the small-angle neutron scattering spectrometer, and the exposure time to obtain multiple different scattering vectors;

[0010] By testing with an air background and an empty sample box, the sample thickness, air background and the influence of the empty sample box are corrected to obtain the absolute scattering intensity corresponding to each scattering vector of the battery separator sample, and a functional relationship curve between the absolute scattering intensity and the scattering vector is obtained;

[0011] A theoretical model is selected to fit and analyze the functional relationship curve to obtain structural information of the microporous structure of the battery separator sample.

[0012] In one possible implementation, the neutron wavelength range is 0.4 nm to 1.3 nm, the distance from the battery diaphragm sample to the detector of the small-angle neutron scattering spectrometer is 1 m to 10 m, and the exposure time is sufficient to ensure that the total count of the detector accumulates more than 50,000.

[0013] In a possible implementation, the calculation formula for the absolute scattering intensity is:

[0014] = - ;

[0015] Where q is the scattering vector, I abs is the absolute scattering intensity of the battery separator sample, I S+C is the scattering intensity of the battery separator sample and the empty sample box, I b is the scattering intensity of the air background, I C is the scattering intensity of the empty sample box, T S+C is the transmittance of the battery separator sample and the empty sample box, T C is the transmittance of the empty sample box.

[0016] In a possible implementation, the theoretical model includes one or a combination of Guinier's law, Porod's law, and Kratky's law.

[0017] In a possible implementation, the selecting a theoretical model to fit and analyze the functional relationship curve includes:

[0018] For an anisotropic system where the functional relationship curves in both the horizontal and vertical directions satisfy the Porod law, the horizontal and vertical directions are fitted simultaneously, and the fitting formula is:

[0019] ;

[0020] ;

[0021] Where, is the equatorial scattering intensity of the battery separator sample, is the meridian scattering intensity of the battery separator sample, A is a constant coefficient, B is the incoherent scattering intensity, q is the scattering vector, m is the fractal dimension of the battery separator sample, is the size ratio of the battery separator sample in the equatorial direction to the meridian direction.

[0022] In a possible implementation, the selecting a theoretical model to fit and analyze the functional relationship curve includes:

[0023] For a battery separator sample with a one-dimensional periodic layered structure in a certain direction, the Porod model is selected to combine the shape factor to describe the geometric shape of the microporous structure of the battery separator sample, and the structure factor to describe the spatial correlation of the microporous structure of the battery separator sample for fitting analysis. The fitting formula is:

[0024] ;

[0025] ;

[0026] Where, is the equatorial scattering intensity of the battery separator sample, A is a constant coefficient, q is the scattering vector, m is the fractal dimension of the battery separator sample, B is the incoherent scattering intensity, is the meridian scattering intensity of the battery separator sample, K is a constant coefficient, P is the shape factor, and S is the structure factor.

[0027] In one possible implementation, ;

[0028] ;

[0029] ;

[0030] Where q is the scattering vector, i is the imaginary unit, r is the real space distance vector, d is the distance between the two layers of the layered battery separator sample, T is the thickness of the battery separator sample, and q z is the scattering vector component along the stretching direction, and z' is the real space distance along the stretching direction.

[0031] In one possible implementation, ;

[0032] ( , );

[0033] Where q is the scattering vector, i is the imaginary unit, d0 and v d for The distribution parameter, q z is the scattering vector component along the stretching direction, d for The standard deviation of for d is the distance between the two layers of the layered battery separator sample.

[0034] In a possible implementation, the polyolefin is one or more combinations of polyethylene, polypropylene, and poly(ethylene-propylene) copolymer.

[0035] In one possible implementation, the battery separator sample is one or more combinations of a single-layer polyethylene / polypropylene separator, a polyethylene / ceramic coated separator, a double-layer polyethylene / polypropylene separator, or a three-layer polyethylene / polypropylene / polyethylene separator.

[0036] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0037] The method for characterizing the microporous structure of a battery separator provided in an embodiment of the present invention first stretches a polyolefin film to obtain a battery separator sample to be tested. The battery separator sample is then placed on the sample stage of a small-angle neutron scattering spectrometer, with the plane of the battery separator sample perpendicular to the direction of the neutron beam. The neutron wavelength, the distance between the battery separator sample and the detector of the small-angle neutron scattering spectrometer, and the exposure time are adjusted to obtain multiple different scattering vectors. Subsequently, the sample thickness, air background, and the effects of the empty sample box are corrected by testing with an air background and an empty sample box to obtain the absolute scattering intensity corresponding to each scattering vector of the battery separator sample, and a functional relationship curve between the absolute scattering intensity and the scattering vector is obtained. Finally, a theoretical model is selected to fit and analyze the functional relationship curve to obtain structural information about the microporous structure of the battery separator sample. The method provided in an embodiment of the present invention detects structural information about the microporous structure of the battery separator sample using the method of small-angle neutron scattering. The battery separator sample does not require special pretreatment, ensuring non-destructive testing of the battery separator sample. By fitting a selected theoretical model, one or more structural information, including fractal dimension, orientation, pore size, and interpore spacing, can be obtained for battery separator samples, improving the stability and accuracy of characterization results. This method enables non-destructive, rapid, simple, efficient, and highly accurate quantitative characterization of the microporous structure of battery separator samples, providing an important test and characterization method for controlling microporous structure processing and establishing the relationship between microporous structure and performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 A flowchart of a method for characterizing the microporous structure of a battery separator provided in an embodiment of the present application;

[0040] Figure 2 The absolute scattering intensity curves of the A-PE@film sample in the meridian and equatorial directions in Example 1 of the present application are shown in the figure. The middle illustration is the two-dimensional scattering diagram of small-angle neutron scattering in Example 1.

[0041] Figure 3 The absolute scattering intensity curves of the B-PE@film sample in the meridian and equatorial directions in Example 2 of the present application are shown in the figure. The middle illustration is the two-dimensional scattering diagram of small-angle neutron scattering in Example 2.

[0042] Figure 4The absolute scattering intensity curves in the meridian and equatorial directions of the Al2O3 / PE@film battery separator in Example 3 of the present application are shown in the figure. The middle illustration is a two-dimensional scattering diagram of small-angle neutron scattering in Example 3.

[0043] Figure 5 This is a schematic diagram of the calculation provided in the embodiment of the present application. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0045] An embodiment of the present invention provides a method for characterizing the microporous structure of a battery separator, comprising:

[0046] Step 1: Stretch a polyolefin film to obtain a battery separator sample to be tested.

[0047] The polyolefin is one or more combinations of polyethylene, polypropylene and poly(ethylene-propylene) copolymer.

[0048] The stretching is one or more combinations of wet uniaxial stretching, wet biaxial stretching, dry uniaxial stretching and dry biaxial stretching.

[0049] The battery separator sample is one or more combinations of a single-layer polyethylene / polypropylene separator, a polyethylene / ceramic coated separator, a double-layer polyethylene / polypropylene separator, or a three-layer polyethylene / polypropylene / polyethylene separator. The method for characterizing the microporous structure of the battery separator in the embodiment of the present application has good applicability to battery separator samples of various forms.

[0050] The ceramic is one or more combinations of aluminum oxide, silicon dioxide, titanium dioxide, etc.

[0051] Step 2: Place the battery separator sample on the sample stage of the small-angle neutron scattering spectrometer, and make the plane of the battery separator sample perpendicular to the direction of the neutron beam. Adjust the neutron wavelength, the distance from the battery separator sample to the detector of the small-angle neutron scattering spectrometer, and the exposure time to obtain multiple different scattering vectors.

[0052] The neutron wavelength range is 0.4nm~1.3nm, the distance between the battery separator sample and the detector of the small-angle neutron scattering spectrometer is 1m~10m, and the exposure time is sufficient to meet the total detector count accumulation of more than 50,000, so that the q value range of the scattering vector can be quickly adjusted to 0.02nm -1 ~6.3nm -1Therefore, it is possible to quickly conduct detection and obtain accurate data.

[0053] Step 3: Through air background and empty sample box detection, correct the sample thickness, air background and empty sample box effects, obtain the absolute scattering intensity corresponding to each scattering vector of the battery separator sample, and obtain the functional relationship curve of absolute scattering intensity and scattering vector.

[0054] The measurement area for battery separator samples is calculated by multiplying the spot diameter of a neutron beam with a spot diameter of 4mm to 8mm through the sample and calculating the corresponding volume. The air background is used for testing without any sample placed in the background.

[0055] The calculation formula for absolute scattering intensity is:

[0056] = - ;

[0057] Where q is the scattering vector, I abs is the absolute scattering intensity of the battery separator sample, I S+C is the scattering intensity of the battery separator sample and the empty sample box, I b is the scattering intensity of the air background, I C is the scattering intensity of the empty sample box, T S+C is the transmittance of the battery separator sample and the empty sample box, T C is the transmittance of the empty sample box.

[0058] Step 4: Select a theoretical model to fit the analysis function relationship curve to obtain structural information of the microporous structure of the battery separator sample. The structural information includes one or more of fractal dimension, orientation, pore size, and pore spacing.

[0059] Optionally, the theoretical model includes one or a combination of Guinier's law, Porod's law, and Kratky's law.

[0060] Optionally, select a theoretical model to fit the analytical function relationship curve, including:

[0061] For an anisotropic system whose horizontal and vertical function relationship curves both satisfy Porod's law, the horizontal and vertical directions are fitted simultaneously, and the fitting formula is:

[0062] ;

[0063] ;

[0064] Where, is the equatorial scattering intensity of the battery separator sample, is the meridian scattering intensity of the battery separator sample, A is a constant coefficient, B is the incoherent scattering intensity, q is the scattering vector, m is the fractal dimension of the battery separator sample (also known as the Porod factor), is the size ratio of the battery separator sample in the equatorial direction to the meridian direction.

[0065] The size of m can reflect the morphological characteristics of the battery separator sample. If m = 1, it is a long rod-shaped battery separator sample. m = 2, it is a two-dimensional smooth battery separator sample. 3 < m < 4, it is a three-dimensional battery separator sample with a rough surface. m = 4, it is a three-dimensional battery separator sample with a smooth surface.

[0066] like =1 (isotropic), ≠1 (anisotropy), and finally the morphological characteristics and orientation information of the microporous structure of the battery separator sample are calculated.

[0067] For the estimation of the microscopic deformation of the above-mentioned self-similar system in the vertical direction, , the proof is as follows:

[0068] Coherent scattering intensity , where b(r) is the coherent scattering length of the atom at r, i is the imaginary unit, q is the scattering vector, and r is the real space position vector.

[0069] , where n is the scatterer number density, is the contrast, i is the imaginary unit, q is the scattering vector, r is the real space position vector, r x is the x-direction component of r, r y is the y-direction component of r, r z is the z-direction component of r.

[0070] , where n is the scatterer number density, is the contrast, i is the imaginary unit, q is the scattering vector, r is the real space position vector, r x is the x-direction component of r, r y is the y-direction component of r, r z is the z-direction component of r.

[0071] For the similar structures in the z and x (y) directions, the size ratio of the equatorial direction to the meridian direction of the battery separator sample is The battery separator samples :

[0072] ( The points limit is the same , The points limit is the same )

[0073] Therefore: .

[0074] Optionally, select a theoretical model to fit the analytical function relationship curve, including:

[0075] For a battery separator sample with a one-dimensional periodic layered structure in a certain direction, the Porod model is selected to combine the shape factor to describe the geometric shape of the microporous structure of the battery separator sample, and the structure factor to describe the spatial correlation of the microporous structure of the battery separator sample for fitting analysis. The fitting formula is:

[0076] ;

[0077] ;

[0078] Where, is the equatorial scattering intensity of the battery separator sample, A is a constant coefficient, q is the scattering vector, m is the fractal dimension of the battery separator sample, B is the incoherent scattering intensity, is the meridian scattering intensity of the battery separator sample, K is a constant coefficient, P is the shape factor, and S is the structure factor.

[0079] Furthermore, ;

[0080] ;

[0081] ;

[0082] Where q is the scattering vector, i is the imaginary unit, r is the real space distance vector, T is the thickness of the battery separator sample, and q z is the scattering vector component along the stretching direction, and z' is the real space distance along the stretching direction.

[0083] The shape factor P describes the geometric shape of the microporous structure of the battery separator sample, such as Figure 5 As shown, the proof is as follows:

[0084] Average shape factor of sheet battery separator samples: , where q is the scattering vector, R is the radius of the battery separator sample, and T is the thickness of the battery separator sample.

[0085] , where q is the scattering vector, i is the imaginary unit, r is the real space distance vector, R is the radius of the battery separator sample, and T is the thickness of the battery separator sample. and They are The component perpendicular to and parallel to the disk normal.

[0086] For a sheet-like battery separator sample with nearly infinite diameter, ;

[0087] , where q z is the scattering vector component along the stretching direction, T is the thickness of the battery separator sample, i is the imaginary unit, z' is the real space distance along the stretching direction, = , is the angle between the scattering vector q and the z' axis (e.g. Figure 5 shown).

[0088] Furthermore, , It is an infinite one-dimensional periodic arrangement.

[0089] ( , );

[0090] Where q is the scattering vector, i is the imaginary unit, d0 and v d for The distribution parameter, q z is the scattering vector component along the stretching direction, d for The standard deviation of for d is the distance between the two layers of the layered battery separator sample.

[0091] The structure factor S describes the spatial correlation of the microporous structure of the battery separator sample, which is demonstrated as follows:

[0092] according to Approximately, the effective structure factor of the polydisperse battery separator sample is:

[0093] ;

[0094] , where q is the scattering vector, R is the radius of the micropores of the battery separator sample, T is the thickness of the battery separator sample, and F(q) is the Fourier transform of the scatterer density distribution.

[0095] For monodisperse systems: , .

[0096] One-dimensional periodic structure factor: Where N is the number of periodically arranged scatterers, i is the imaginary unit, q is the scattering vector, and Rj is the real space position vector of the jth scatterer, R j＇ For the The real space position vector of each scatterer, d is the center distance between adjacent scatterers.

[0097] ( , ), where q z is the scattering vector component along the stretching direction, i is the imaginary unit, d0 and v d for The distribution parameters of d for The standard deviation of for d is the distance between the two layers of the layered battery separator sample.

[0098] The method for characterizing the microporous structure of a battery separator provided in an embodiment of the present invention first stretches a polyolefin film to obtain a battery separator sample to be tested. The battery separator sample is then placed on the sample stage of a small-angle neutron scattering spectrometer, with the plane of the battery separator sample perpendicular to the direction of the neutron beam. The neutron wavelength, the distance between the battery separator sample and the detector of the small-angle neutron scattering spectrometer, and the exposure time are adjusted to obtain multiple different scattering vectors. Subsequently, the sample thickness, air background, and the effects of the empty sample box are corrected by testing with an air background and an empty sample box to obtain the absolute scattering intensity corresponding to each scattering vector of the battery separator sample, and a functional relationship curve between the absolute scattering intensity and the scattering vector is obtained. Finally, a theoretical model is selected to fit and analyze the functional relationship curve to obtain structural information about the microporous structure of the battery separator sample. The method provided in an embodiment of the present invention detects structural information about the microporous structure of the battery separator sample using the method of small-angle neutron scattering. The battery separator sample does not require special pretreatment, ensuring non-destructive testing of the battery separator sample. By fitting a selected theoretical model, one or more structural information, including fractal dimension, orientation, pore size, and interpore spacing, can be obtained for battery separator samples, improving the stability and accuracy of characterization results. This method enables non-destructive, rapid, simple, efficient, and highly accurate quantitative characterization of the microporous structure of battery separator samples, providing an important test and characterization method for controlling microporous structure processing and establishing the relationship between microporous structure and performance.

[0099] The method for characterizing the microporous structure of a battery separator provided in an embodiment of the present invention can be applied to battery separator detection.

[0100] In order to make the above implementation details and operations of this application clearly understood by those skilled in the art, and to significantly reflect the progressiveness of the method for characterizing the microporous structure of the battery separator in the embodiment of this application, the above technical solution is illustrated by multiple embodiments below.

[0101] Example 1

[0102] The polyolefin film was uniaxially stretched to obtain the polyethylene battery separator (A-PE@film) sample to be tested.

[0103] The A-PE@film sample was placed on the sample stage of the small-angle neutron scattering spectrometer, and the plane of the A-PE@film sample was perpendicular to the direction of the neutron beam. The neutron wavelength was adjusted to 0.5 nm, the distance from the A-PE@film sample to the detector of the small-angle neutron scattering spectrometer was adjusted to 6 m, and the exposure time was adjusted to 600 s to obtain multiple different scattering vectors.

[0104] A neutron beam with a spot diameter of 5 mm was used to detect different positions of the air background and A-PE@film samples. By detecting the air background and the empty sample box, the influence of the sample thickness, air background and the empty sample box was corrected, and the absolute scattering intensity corresponding to each scattering vector of the battery separator sample was obtained. The functional relationship curve between the absolute scattering intensity and the scattering vector was obtained.

[0105] The calculation formula for absolute scattering intensity is:

[0106] = - ;

[0107] Where q is the scattering vector, I abs is the absolute scattering intensity of the battery separator sample, I S+C is the scattering intensity of the battery separator sample and the empty sample box, I b is the scattering intensity of the air background, I C is the scattering intensity of the empty sample box, T S+C is the transmittance of the battery separator sample and the empty sample box, T C is the transmittance of the empty sample box.

[0108] The theoretical model was selected to fit the analysis function relationship curve to obtain the structural information of the microporous structure of the A-PE@film sample, which includes fractal dimension and orientation structure information. Specifically, for an anisotropic system where the function relationship curves in both the horizontal and vertical directions satisfy the Porod law, the horizontal and vertical directions were fitted simultaneously, and the fitting formula is:

[0109] ;

[0110] ;

[0111] Where, is the scattering intensity in the equatorial direction, is the scattering intensity in the meridian direction, A is a constant coefficient, B is the incoherent scattering intensity, q is the scattering vector, m is the fractal dimension of the battery separator sample, The ratio of the size in the equatorial direction to the meridian direction.

[0112] In the first embodiment of the present application, a theoretical model is selected to fit the analysis function relationship curve as shown in FIG. Figure 2 As shown, the surface of the A-PE@film sample is rough (m=3.7) and anisotropic ( =1.2).

[0113] Example 2

[0114] The polyolefin film was biaxially stretched to obtain the polyethylene battery separator (B-PE@film) sample to be tested.

[0115] The B-PE@film sample was placed on the sample stage of the small-angle neutron scattering spectrometer, and the plane of the B-PE@film sample was perpendicular to the direction of the neutron beam. The neutron wavelength was adjusted to 0.5 nm, the distance from the B-PE@film sample to the detector of the small-angle neutron scattering spectrometer was adjusted to 6 m, and the exposure time was adjusted to 600 s to obtain multiple different scattering vectors.

[0116] A neutron beam with a spot diameter of 5 mm was used to detect different positions of the air background and B-PE@film samples. By detecting the air background and an empty sample box, the influence of sample thickness, air background and empty sample box was corrected, and the absolute scattering intensity corresponding to each scattering vector of the battery separator sample was obtained. The functional relationship curve of the absolute scattering intensity and the scattering vector was obtained.

[0117] The calculation formula for absolute scattering intensity is:

[0118] = - ;

[0119] Where q is the scattering vector, I abs is the absolute scattering intensity of the battery separator sample, I S+C is the scattering intensity of the battery separator sample and the empty sample box, I b is the scattering intensity of the air background, I C is the scattering intensity of the empty sample box, T S+C is the transmittance of the battery separator sample and the empty sample box, T C is the transmittance of the empty sample box.

[0120] The theoretical model was selected to fit the functional relationship curve and obtain the structural information of the microporous structure of the B-PE@film sample, including fractal dimension, orientation, pore size, and pore space structure information. Specifically, for a layered structure with one-dimensional periodicity in a certain direction, the Porod model was selected in combination with the shape factor to describe the geometry of the microporous structure of the battery separator sample, and the structure factor to describe the spatial correlation of the microporous structure of the battery separator sample. The fitting analysis was performed, and the fitting formula was:

[0121] ;

[0122] ;

[0123] Where, is the equatorial scattering intensity of the battery separator sample, A is a constant coefficient, q is the scattering vector, m is the fractal dimension of the battery separator sample, B is the incoherent scattering intensity, is the meridian scattering intensity of the battery separator sample, K is a constant coefficient, P is the shape factor, and S is the structure factor.

[0124] Furthermore, ;

[0125] ;

[0126] ;

[0127] Where q is the scattering vector, i is the imaginary unit, r is the real space distance vector, T is the thickness of the battery separator sample, and q z is the scattering vector component along the stretching direction, and z' is the real space distance along the stretching direction.

[0128] Furthermore, ;

[0129] ( , );

[0130] Where q is the scattering vector, i is the imaginary unit, d0 and v d for The distribution parameter, q z is the scattering vector component along the stretching direction, d for The standard deviation of for d is the distance between the two layers of the layered battery separator sample.

[0131] In the second embodiment of the present application, the theoretical model is selected to fit the analysis function relationship curve as shown in FIG. Figure 3 As shown, the B-PE@film sample is substituted into the above theoretical model formula and calculated to have a two-dimensional surface roughness (m=2.7) and anisotropy ( =1.5), pore size 35 nm, pore gap 10 nm.

[0132] Example 3

[0133] The film coated with aluminum oxide / polyethylene ceramics was stretched to obtain the aluminum oxide / polyethylene ceramics coated battery separator (Al2O3 / PE@film) sample to be tested.

[0134] The Al2O3 / PE@film sample was placed on the sample stage of the small-angle neutron scattering spectrometer, and the plane of the Al2O3 / PE@film sample was perpendicular to the direction of the neutron beam. The neutron wavelength was adjusted to 0.5 nm, the distance from the Al2O3 / PE@film sample to the detector of the small-angle neutron scattering spectrometer was 6 m, and the exposure time was 600 s to obtain multiple different scattering vectors.

[0135] A neutron beam with a spot diameter of 5 mm was used to detect different positions of the air background and Al2O3 / PE@film sample. By detecting the air background and the empty sample box, the influence of sample thickness, air background and the empty sample box was corrected, and the absolute scattering intensity corresponding to each scattering vector of the battery separator sample was obtained. The functional relationship curve of the absolute scattering intensity and the scattering vector was obtained.

[0136] The calculation formula for absolute scattering intensity is:

[0137] = - ;

[0138] Where q is the scattering vector, I abs is the absolute scattering intensity of the battery separator sample, I S+C is the scattering intensity of the battery separator sample and the empty sample box, I b is the scattering intensity of the air background, I C is the scattering intensity of the empty sample box, T S+C is the transmittance of the battery separator sample and the empty sample box, T C is the transmittance of the empty sample box.

[0139] A theoretical model was selected to fit the functional relationship curve and obtain structural information of the microporous structure of the Al2O3 / PE@film sample, including fractal dimension, orientation, pore size, and pore space structure information. Specifically, for a layered structure with one-dimensional periodicity in a certain direction, the Porod model was selected in combination with the shape factor to describe the geometry of the microporous structure of the battery separator sample, and the structure factor to describe the spatial correlation of the microporous structure of the battery separator sample. The fitting analysis was performed, and the fitting formula was:

[0140] ;

[0141] ;

[0142] Where, is the equatorial scattering intensity of the battery separator sample, A is a constant coefficient, q is the scattering vector, m is the fractal dimension of the battery separator sample, B is the incoherent scattering intensity, is the meridian scattering intensity of the battery separator sample, K is a constant coefficient, P is the shape factor, and S is the structure factor.

[0143] Furthermore, ;

[0144] ;

[0145] ;

[0146] Where q is the scattering vector, i is the imaginary unit, r is the real space distance vector, T is the thickness of the battery separator sample, and q z is the scattering vector component along the stretching direction, and z' is the real space distance along the stretching direction.

[0147] Furthermore, ;

[0148] ( , );

[0149] Where q is the scattering vector, i is the imaginary unit, d0 and v d for The distribution parameter, q z is the scattering vector component along the stretching direction, d for The standard deviation of for d is the distance between the two layers of the layered battery separator sample.

[0150] In the third embodiment of the present application, the theoretical model is selected to fit the analysis function relationship curve as shown in FIG. Figure 4 As shown, the Al2O3 / PE@film sample is substituted into the above theoretical model formula and calculated to have a smooth three-dimensional surface (m=4) and isotropic ( =1), pore size 60 nm, pore gap 40 nm.

[0151] Table 1 Structural information of the microporous structure of the battery separator sample obtained after fitting the theoretical model

[0152]

[0153] Although this application provides method operation steps such as embodiments or flow charts, more or fewer operation steps may be included based on conventional or non-creative work. The order of steps listed in this embodiment is only one way of executing the steps among many steps and does not represent the only execution order. In practice, the method can be executed in the order shown in this embodiment or the accompanying drawings or in parallel.

[0154] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments. The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the aforementioned embodiments, it should be understood by those skilled in the art that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions from the scope of the technical solutions of this application.

Claims

1. A method for characterizing the microporous structure of a battery separator, characterized in that: include: A polyolefin film is stretched to obtain a battery separator sample to be tested; Placing the battery separator sample on the sample stage of a small-angle neutron scattering spectrometer, with the plane of the battery separator sample perpendicular to the direction of the neutron beam, and adjusting the neutron wavelength, the distance from the battery separator sample to the detector of the small-angle neutron scattering spectrometer, and the exposure time to obtain multiple different scattering vectors; By testing with an air background and an empty sample box, the sample thickness, air background and the influence of the empty sample box are corrected to obtain the absolute scattering intensity corresponding to each scattering vector of the battery separator sample, and a functional relationship curve between the absolute scattering intensity and the scattering vector is obtained; Selecting a theoretical model to fit and analyze the functional relationship curve to obtain structural information of the microporous structure of the battery separator sample; The selecting theoretical model to fit and analyze the functional relationship curve includes: For an anisotropic system where the functional relationship curves in both the horizontal and vertical directions satisfy the Porod law, the horizontal and vertical directions are fitted simultaneously, and the fitting formula is: ； ； Where, is the equatorial scattering intensity of the battery separator sample, is the meridian scattering intensity of the battery separator sample, A is a constant coefficient, B is the incoherent scattering intensity, q is the scattering vector, m is the fractal dimension of the battery separator sample, is the size ratio of the battery separator sample in the equatorial direction to the meridian direction; For a battery separator sample with a one-dimensional periodic layered structure in a certain direction, the Porod model is selected to combine the shape factor to describe the geometric shape of the microporous structure of the battery separator sample, and the structure factor to describe the spatial correlation of the microporous structure of the battery separator sample for fitting analysis. The fitting formula is: ； ； Where, is the equatorial scattering intensity of the battery separator sample, A is a constant coefficient, q is the scattering vector, m is the fractal dimension of the battery separator sample, B is the incoherent scattering intensity, is the meridian scattering intensity of the battery separator sample, K is the constant coefficient, P is the shape factor, and S is the structure factor; ； ； ； Where q is the scattering vector, i is the imaginary unit, r is the real space distance vector, T is the thickness of the battery separator sample, and q z is the scattering vector component along the stretching direction, z' is the real space distance along the stretching direction; ； ； Where q is the scattering vector, i is the imaginary unit, d0 and v d for The distribution parameter, q z is the scattering vector component along the stretching direction, d for The standard deviation of for d is the distance between the two layers of the layered battery separator sample.

2. The method for characterizing the microporous structure of a battery separator according to claim 1, wherein: The neutron wavelength range is 0.4nm~1.3nm, the distance between the battery diaphragm sample and the detector of the small-angle neutron scattering spectrometer is 1m~10m, and the exposure time is sufficient to meet the total count of the detector of more than 50,000.

3. The method for characterizing the microporous structure of a battery separator according to claim 1, wherein: The calculation formula of the absolute scattering intensity is: ； Where q is the scattering vector, I abs is the absolute scattering intensity of the battery separator sample, I S+C is the scattering intensity of the battery separator sample and the empty sample box, I b is the scattering intensity of the air background, I C is the scattering intensity of the empty sample box, T S+C is the transmittance of the battery separator sample and the empty sample box, T C is the transmittance of the empty sample box.

4. The method for characterizing the microporous structure of a battery separator according to claim 1, wherein: The polyolefin is one or more combinations of polyethylene, polypropylene and poly(ethylene-propylene) copolymer.

5. The method for characterizing the microporous structure of a battery separator according to claim 1, wherein: The battery separator sample is one or more combinations of a single-layer polyethylene / polypropylene separator, a polyethylene / ceramic coated separator, a double-layer polyethylene / polypropylene separator, or a three-layer polyethylene / polypropylene / polyethylene separator.

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