Method for representing microporous structure of battery diaphragm

Abstract

The invention discloses a method for characterizing a microporous structure of a battery diaphragm, and belongs to the field of thin film material multi-scale structure characterization. The method comprises the following steps: stretching a polyolefin film to obtain a battery diaphragm sample to be detected; placing the battery diaphragm sample on a sample table, enabling the plane of the battery diaphragm sample to be perpendicular to the neutron beam direction, and adjusting the neutron wavelength, the distance from the battery diaphragm sample to a detector and the exposure time to obtain a plurality of different scattering vectors; detecting through an air back bottom and an empty sample box, correcting the influence of the sample thickness, the air back bottom and the empty sample box, obtaining the absolute scattering intensity corresponding to each scattering vector of the battery diaphragm sample, and obtaining a function relation curve of the absolute scattering intensity and the scattering vector; and selecting a theoretical model to fit and analyze the function relation curve to obtain the structure information of the microporous structure of the battery diaphragm sample. According to the method, the structural information of the microporous structure of the battery diaphragm sample can be quantitatively characterized in a lossless, rapid, simple, efficient and high-accuracy manner.

Description

Technical Field

[0001] This application relates to the technical field of multi-scale structure characterization of thin film materials, and particularly to a method for characterizing the microporous structure of battery separators. Background Art

[0002] A battery separator is a functional membrane material with a microporous structure. As a key component of new energy batteries, its main functions include: isolating the positive and negative electrodes of the battery, transporting ions, and maintaining the ion-electron circuit during charge and discharge. To meet the performance requirements of battery operation, the microporous structure of the battery separator must have the characteristics of micro-nano scale pore size and high porosity, realizing efficient ion transport while ensuring mechanical strength, and at the same time having the microporous structure locking function under abnormal temperature / voltage.

[0003] Although the battery separator does not directly participate in the electrochemical reaction of the battery, its intrinsic microporous structure determines the ion transport efficiency, current density, and electrolyte storage of the battery separator, thereby affecting the capacity, cycle performance, charge and discharge current efficiency, etc. of the battery. Therefore, accurately characterizing the microporous structure of the battery separator through simple and efficient detection means is a key factor in studying the structure and performance of the battery separator, providing an important reference for improving battery performance.

[0004] Existing conventional detection methods for the microporous structure of battery separators include scanning electron microscopy, specific surface area method, mercury intrusion method, etc. In the scanning electron microscopy method, the sample is first sputter-coated with gold for sample preparation, and then the surface of the battery separator is bombarded with a focused high-energy electron beam. After that, the morphology of the surface or cross-section of the battery separator is characterized and analyzed to obtain the pore size distribution and pore size of the microporous structure. When preparing samples by scanning electron microscopy, the sample is sputter-coated with gold, resulting in the nanopore size of the microporous structure of the battery separator being blocked, affecting the statistical results of the pore size, and resulting in large errors in the detection results. In addition, the fiber morphology of the microporous structure of the battery separator is extremely easy to break under the heat generated by the bombardment of the high-energy electron beam, damaging the microporous structure and unable to accurately count the pore size, resulting in large errors in the detection results. The mercury intrusion method is to use external force to press mercury into the pores of the battery separator, and then measure the volume of the injected mercury to calculate the pore size distribution and porosity parameters of the separator. However, in actual tests, stress will be generated when mercury is pressed into the battery separator, damaging the microporous structure of the battery separator and resulting in large errors in the detection results. The specific surface area method mainly uses the gas adsorption amount of the microporous structure of the battery separator at different pressures to calculate the pore size distribution and pore volume. Due to processes such as sample drying, gas adsorption and desorption, the sample test takes up to more than ten hours, with low detection efficiency, and the geometric information of the micropore shape cannot be obtained. 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 the existing detection methods for the microporous structure of a battery separator can damage the microporous structure, the detection results have large errors, and the detection efficiency is low.

[0006] To achieve the above object, the technical solution of the embodiments of the present invention is as follows:

[0007] The embodiments of the present invention provide a method for characterizing the microporous structure of a battery separator, including:

[0008] Stretching a film made of polyolefin to obtain a battery separator sample to be measured;

[0009] Placing the battery separator sample on the sample stage of a small-angle neutron scattering spectrometer, and making the plane of the battery separator sample perpendicular to the neutron beam direction. 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 a plurality of different scattering vectors;

[0010] Through air background and empty sample cell detection, correct the influence of sample thickness, air background and empty sample cell, obtain the absolute scattering intensity corresponding to each scattering vector of the battery separator sample, and obtain a function relationship curve between the absolute scattering intensity and the scattering vector;

[0011] Select a theoretical model to fit and analyze the function relationship curve to obtain the structural information of the microporous structure of the battery separator sample.

[0012] In a possible implementation, the neutron wavelength range is 0.4 nm to 1.3 nm, the distance from the battery separator sample to the detector of the small-angle neutron scattering spectrometer is 1 m to 10 m, and the exposure time is such 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] In the formula, 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 cell, I b is the scattering intensity of the air background, I C is the scattering intensity of the empty sample cell, T S+C is the transmittance of the battery separator sample and the empty sample cell, T C is the transmittance of the empty sample cell.

[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 selection of the theoretical model to fit and analyze the functional relationship curve includes:

[0018] For an anisotropic system where the functional relationship curve satisfies Porod's law in both the horizontal and vertical directions, simultaneous fitting is performed for the horizontal and vertical directions, and the fitting formula is:

[0019] ;

[0020] ;

[0021] In the formula, is the scattering intensity in the equatorial direction of the battery separator sample, is the scattering intensity in the meridional direction 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 between the equatorial direction and the meridional direction of the battery separator sample.

[0022] In a possible implementation, the selection of the 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 describe the geometric shape of the microporous structure of the battery separator sample in combination with the shape factor, and the structure factor is used to describe the spatial correlation of the microporous structure of the battery separator sample for fitting analysis. The fitting formula is:

[0024] ;

[0025] ;

[0026] In the formula, is the scattering intensity in the equatorial direction 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 scattering intensity in the meridional direction of the battery separator sample, K is a constant coefficient, P is the shape factor, and S is the structure factor.

[0027] In a possible implementation, ;

[0028] ;

[0029] ;

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

[0031] In a possible implementation, ;

[0032] ( , )

[0033] In the formula, q is the scattering vector, i is the imaginary unit, d 0 and v d are 's distribution parameters, q z is the component of the scattering vector along the stretching direction, d is 's standard deviation, is 's average value, and d is the distance between two layers of the layered battery separator sample.

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

[0035] In a possible implementation, the battery separator sample is one or a combination of more than one of a single-layer polyethylene / polypropylene separator, a polyethylene / ceramic-coated separator, a double-layer polyethylene / polypropylene separator, and 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 by an embodiment of the present invention first subjects a film made of polyolefin to stretching to obtain a battery separator sample to be measured. Then, the battery separator sample is placed on the sample stage of a small-angle neutron scattering spectrometer, and the plane of the battery separator sample is perpendicular to the neutron beam direction. The neutron wavelength, the distance from the battery separator sample to the detector of the small-angle neutron scattering spectrometer, and the exposure time are adjusted to obtain a plurality of different scattering vectors. After that, through air background and empty sample cell detection, the influences of sample thickness, air background, and empty sample cell are corrected, the absolute scattering intensity corresponding to each scattering vector of the battery separator sample is obtained, and a function relationship curve between the absolute scattering intensity and the scattering vector is obtained. Finally, a theoretical model is selected to fit and analyze the function relationship curve to obtain the structural information of the microporous structure of the battery separator sample. The method provided by the embodiment of the present invention detects the structural information of the microporous structure of the battery separator sample by 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 selecting a theoretical model for fitting, one or more structural information such as the fractal dimension, orientation, pore size, and pore gap of the battery separator sample are obtained, improving the stability of the characterization result and the accuracy of the detection result. It can realize non-destructive, fast, simple, efficient, and highly accurate quantitative characterization of the structural information of the microporous structure of the battery separator sample, providing an important test and characterization method for realizing the processing control of the microporous structure and establishing the relationship between the microporous structure and performance. Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for description in the embodiments of the present invention. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

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

[0040] Figure 2 It is the absolute scattering intensity curve in the meridian and equatorial directions of the A-PE@film sample in Embodiment 1 of the present application. The middle inset is the two-dimensional scattering diagram of small-angle neutron scattering in Embodiment 1;

[0041] Figure 3 It is the absolute scattering intensity curve in the meridian and equatorial directions of the B-PE@film sample in Embodiment 2 of the present application. The middle inset is the two-dimensional scattering diagram of small-angle neutron scattering in Embodiment 2;

[0042] Figure 4 For Al in Embodiment 3 of the present application 2 O 3Absolute scattering intensity curves in the meridional and equatorial directions of the / PE@film battery separator, and the middle inset shows the two-dimensional small-angle neutron scattering pattern of Example III;

[0043] Figure 5 This is a schematic diagram for calculation provided by an embodiment of the present application. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

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

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

[0047] Among them, the polyolefin is one or a combination of polyethylene, polypropylene, and poly(ethylene-propylene) copolymer.

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

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

[0050] The ceramic is one or a combination 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 neutron beam direction. 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 0.4 nm to 1.3 nm, the distance from the battery separator sample to the detector of the small-angle neutron scattering spectrometer is 1 m to 10 m, and the exposure time is such that the total count of the detector accumulates more than 50,000, so as to quickly adjust the q value range of the scattering vector to be 0.02 nm -1 ~6.3 nm -1Thereby, rapid detection can be carried out, and accurate data can be obtained.

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

[0054] The measurement area of the battery separator sample is the corresponding volume calculated by the product of the spot diameter and the thickness of the battery separator sample through which a neutron beam with a spot diameter of 4 mm to 8 mm passes. The air background is detected without placing any samples.

[0055] Among them, the calculation formula of the absolute scattering intensity is:

[0056] = - ;

[0057] In the formula, 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 and analyze the function relationship curve to obtain the structural information of the microporous structure of the battery separator sample. The structural information includes one or more of the fractal dimension, orientation, pore size, and pore gap.

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

[0060] Optionally, selecting a theoretical model to fit and analyze the function relationship curve includes:

[0061] For an anisotropic system where the function relationship curves in the horizontal and vertical directions both satisfy the Porod law, simultaneous fitting is performed on the horizontal and vertical directions, and the fitting formula is:

[0062] ;

[0063] ;

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

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

[0066] If = 1 (isotropic), ≠ 1 (anisotropic), 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 system with self-similarity in the above 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 a battery separator sample with similar structures in the z, x (y) directions and the size ratio of the equatorial direction to the meridional direction being , let : ( The integration limits of are the same as those of , The integration limits of are the same as those of )

[0072] Therefore, we have: .

[0073] Optionally, select a theoretical model to fit the analytical function relationship curve, including:

[0074] For a battery separator sample with a one-dimensional periodic layered structure in a certain direction, select the Porod model combined with a shape factor to describe the geometry of the microporous structure of the battery separator sample, and a structure factor to describe the spatial correlation of the microporous structure of the battery separator sample for fitting analysis. The fitting formula is:

[0075] ;

[0076] ;

[0077] In the formula, is the scattering intensity in the equatorial direction 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 scattering intensity in the meridional direction of the battery separator sample, K is a constant coefficient, P is the shape factor, and S is the structure factor.

[0078] Furthermore, ;

[0079] ;

[0080] ;

[0081] In the formula, 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, q z is the component of the scattering vector along the stretching direction, and z' is the real-space distance along the stretching direction.

[0082] For the shape factor P to describe the geometry of the microporous structure of the battery separator sample, as shown in Figure 5 as follows:

[0083] Average shape factor of the flake battery separator sample: , 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.

[0084] , 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, T is the thickness of the battery separator sample, and are respectively the vertical and parallel components to the normal of the disk surface in

[0085] For a sheet-like battery separator sample with an approximately infinite diameter, ;

[0086] , where q z is the component of the scattering vector along the stretching direction, T is the thickness of the battery separator sample, i is the imaginary unit, and z' is the real-space distance along the stretching direction. = , is the angle between the scattering vector q and the z'-axis (as shown in Figure 5 ).

[0087] Furthermore, , is an infinite one-dimensional periodic arrangement.

[0088] ( , );

[0089] where q is the scattering vector, i is the imaginary unit, d 0 and v d are the distribution parameters of , q z is the component of the scattering vector along the stretching direction, d is the standard deviation of is the average value of , and d is the distance between two layers of the layered battery separator sample.

[0090] For the structure factor S to describe the spatial correlation of the microporous structure of the battery separator sample, the proof is as follows:

[0091] According to approximation, the effective structure factor of the polydisperse battery separator sample is:

[0092] ;

[0093] , 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.

[0094] For a monodisperse system: , .

[0095] One-dimensional periodic structure factor: . Where N is the number of scatterers in the periodic arrangement, i is the imaginary unit, q is the scattering vector, R jis the real-space position vector of the j-th scatterer, R j＇ is the real-space position vector of the scatterer, and d is the center-to-center spacing between adjacent scatterers.

[0096] ( , ) where q z is the component of the scattering vector along the stretching direction, i is the imaginary unit, d 0 and v d are the distribution parameters of , d is the standard deviation of is the average value of , and d is the spacing between two layers of the layered battery separator sample.

[0097] The method for characterizing the microporous structure of a battery separator provided by an embodiment of the present invention first subjects a film made of polyolefin to stretching to obtain a battery separator sample to be measured. Then, the battery separator sample is placed on the sample stage of a small-angle neutron scattering spectrometer, and the plane of the battery separator sample is perpendicular to the neutron beam direction. The neutron wavelength, the distance from the battery separator sample to the detector of the small-angle neutron scattering spectrometer, and the exposure time are adjusted to obtain a plurality of different scattering vectors. Then, through air background and empty sample cell detection, the influences of sample thickness, air background, and empty sample cell are corrected, and the absolute scattering intensity corresponding to each scattering vector of the battery separator sample is obtained, and a function relationship curve between the absolute scattering intensity and the scattering vector is obtained. Finally, a theoretical model is selected to fit and analyze the function relationship curve to obtain the structural information of the microporous structure of the battery separator sample. The method provided by the embodiment of the present invention detects the structural information of the microporous structure of the battery separator sample by the method of small-angle neutron scattering. The battery separator sample does not require special pretreatment, ensuring non-destructive detection of the battery separator sample. By selecting a theoretical model for fitting, one or more structural information such as the fractal dimension, orientation, pore size, and pore gap of the battery separator sample are obtained, improving the stability of the characterization result and the accuracy of the detection result. It can realize non-destructive, fast, simple and efficient, and highly accurate quantitative characterization of the structural information of the microporous structure of the battery separator sample, providing an important test and characterization method for realizing the processing control of the microporous structure and establishing the relationship between the microporous structure and performance.

[0098] The method for characterizing the microporous structure of a battery separator provided by an embodiment of the present invention can be applied to battery separator detection.

[0099] To enable those skilled in the art to clearly understand the above implementation details and operations of the present application, and to significantly reflect the progressiveness of the method for characterizing the microporous structure of a battery separator in the embodiments of the present application, the following uses multiple embodiments to illustrate the above technical solutions.

[0100] Example 1

[0101] A polyethylene battery separator (A-PE@film) sample to be measured was obtained by uniaxially stretching a film made of polyolefin.

[0102] The A-PE@film sample was placed on the sample stage of a small-angle neutron scattering spectrometer, and the plane of the A-PE@film sample was perpendicular to the neutron beam direction. 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 6 m, and the exposure time was 600 s to obtain a plurality of different scattering vectors.

[0103] A neutron beam with a spot diameter of 5 mm was used to detect different positions of the air background and the A-PE@film sample respectively. Through the detection of the air background and the empty sample cell, the influence of the sample thickness, air background and empty sample cell was corrected, and the absolute scattering intensity corresponding to each scattering vector of the battery separator sample was obtained, and the function relationship curve between the absolute scattering intensity and the scattering vector was obtained.

[0104] The calculation formula for the absolute scattering intensity is:

[0105] = - ;

[0106] In the formula, 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 cell, I b is the scattering intensity of the air background, I C is the scattering intensity of the empty sample cell, T S+C is the transmittance of the battery separator sample and the empty sample cell, T C is the transmittance of the empty sample cell.

[0107] A theoretical model fitting analysis function relationship curve was selected to obtain the structural information of the microporous structure of the A-PE@film sample. This structural information includes the fractal dimension and the orientation structure information. Specifically, for an anisotropic system where the function relationship curves in the horizontal and vertical directions both satisfy the Porod law, simultaneous fitting was performed on the horizontal and vertical directions, and the fitting formula is:

[0108] ;

[0109] ;

[0110] In the formula, 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, is the size ratio in the equatorial direction to the meridian direction.

[0111] In Example 1 of this application, the theoretical model fitting analysis function relationship curve is selected as Figure 2 shown. Substituting into the above theoretical model formula, it is calculated that the surface of the A-PE@film sample is rough (m = 3.7) and anisotropic ( = 1.2).

[0112] Example 2

[0113] The film made of polyolefin is biaxially stretched to obtain the sample of the polyethylene battery separator to be measured (B-PE@film).

[0114] The B-PE@film sample is placed on the sample stage of the small-angle neutron scattering spectrometer, and the plane of the B-PE@film sample is perpendicular to the neutron beam direction. The neutron wavelength is adjusted to 0.5 nm, the distance from the B-PE@film sample to the detector of the small-angle neutron scattering spectrometer is 6 m, and the exposure time is 600 s to obtain a plurality of different scattering vectors.

[0115] The neutron beam with a spot diameter of 5 mm is used to detect different positions of the air background and the B-PE@film sample respectively. Through the detection of the air background and the empty sample box, the influences of the sample thickness, air background and empty sample box are corrected, and the absolute scattering intensity corresponding to each scattering vector of the battery separator sample is obtained, and the function relationship curve between the absolute scattering intensity and the scattering vector is obtained.

[0116] The calculation formula of the absolute scattering intensity is:

[0117] = - ;

[0118] In the formula, 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.

[0119] Select a theoretical model to fit and analyze the functional relationship curve to obtain the structural information of the microporous structure of the B-PE@film sample. This structural information includes the fractal dimension, orientation, pore size, and pore gap structure information. Specifically, for a layered structure with one-dimensional periodicity in a certain direction, select the Porod model combined with 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, and perform fitting analysis. The fitting formula is:

[0120] ;

[0121] ;

[0122] wherein, is the scattering intensity in the equatorial direction 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 scattering intensity in the meridional direction of the battery separator sample, K is a constant coefficient, P is the shape factor, and S is the structure factor.

[0123] Furthermore, ;

[0124] ;

[0125] ;

[0126] wherein, 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, q z is the scattering vector component along the stretching direction, and z' is the real space distance along the stretching direction.

[0127] Furthermore, ;

[0128] ( , );

[0129] wherein, q is the scattering vector, i is the imaginary unit, d 0 and v d are the distribution parameters of , q z is the scattering vector component along the stretching direction, d is the standard deviation of , is the average value of , and d is the distance between two layers of the layered battery separator sample.

[0130] In Example 2 of the present application, the theoretical model fitting analysis function relationship curve is as follows Figure 3 shown. Substituting into the above theoretical model formula, it is calculated that the B-PE@film sample has a two-dimensional surface roughness (m = 2.7) and shows anisotropy ( = 1.5), with a pore size of 35 nm and a pore gap of 10 nm.

[0131] Example 3

[0132] The film coated with alumina / polyethylene ceramic is stretched to obtain a battery separator diaphragm (Al 2 O 3 / PE@film) sample to be measured.

[0133] The Al 2 O 3 / PE@film sample is placed on the sample stage of the small-angle neutron scattering spectrometer, and the plane of the Al 2 O 3 / PE@film sample is perpendicular to the neutron beam direction. The neutron wavelength is adjusted to 0.5 nm, the distance from the Al 2 O 3 / PE@film sample to the detector of the small-angle neutron scattering spectrometer is 6 m, and the exposure time is 600 s to obtain a plurality of different scattering vectors.

[0134] The neutron beam with a spot diameter of 5 mm is used to detect different positions of the air background and the Al 2 O 3 / PE@film sample respectively. Through the detection of the air background and the empty sample box, the influence of the sample thickness, air background and empty sample box is corrected, and the absolute scattering intensity corresponding to each scattering vector of the battery separator diaphragm sample is obtained, and the function relationship curve between the absolute scattering intensity and the scattering vector is obtained.

[0135] The calculation formula for the absolute scattering intensity is:

[0136] = - ;

[0137] In the formula, q is the scattering vector, I abs is the absolute scattering intensity of the battery separator diaphragm sample, I S+C is the scattering intensity of the battery separator diaphragm 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 diaphragm sample and the empty sample box, and T C is the transmittance of the empty sample box.

[0138] Select a theoretical model to fit and analyze the functional relationship curve to obtain Al 2 O 3 / PE@film sample's microporous structure information, which includes fractal dimension, orientation, pore size, and pore gap structure information. Specifically, for a layered structure with one-dimensional periodicity in a certain direction, select the Porod model combined with 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, and perform fitting analysis. The fitting formula is:

[0139] ;

[0140] ;

[0141] In the formula, is the scattering intensity in the equatorial direction 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 scattering intensity in the meridian direction of the battery separator sample, K is a constant coefficient, P is the shape factor, and S is the structure factor.

[0142] Furthermore, ;

[0143] ;

[0144] ;

[0145] In the formula, 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, q z is the component of the scattering vector along the stretching direction, and z' is the real-space distance along the stretching direction.

[0146] Furthermore, ;

[0147] ( , );

[0148] In the formula, q is the scattering vector, i is the imaginary unit, d 0 and v d are the distribution parameters of , q z is the component of the scattering vector along the stretching direction, d is the standard deviation of , is the average value of , and d is the distance between two layers of the layered battery separator sample.

[0149] In the third embodiment of the present application, the function relationship curve of the selected theoretical model fitting analysis is as Figure 4 shown. Substituting into the above theoretical model formula, Al 2 O 3 / PE@film sample has a three-dimensional smooth surface (m = 4) and is isotropic ( = 1), with a pore size of 60 nm and a pore gap of 40 nm.

[0150] Table 1 Structural information of the microporous structure of the battery separator sample obtained by fitting with the theoretical model

[0151] Although the present application provides method operation steps such as in the embodiments or flowcharts, based on routine or non-creative labor, there may be more or fewer operation steps. The step sequence listed in this embodiment is only one way among the execution sequences of numerous steps and does not represent the only execution sequence. In practice, it can be executed in the method sequence shown in this embodiment or the accompanying drawings or executed in parallel.

[0152] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, reference can be made to each other. The key points of each embodiment are the differences from other embodiments. The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application.

Claims

1. A method for characterizing the microporous structure of a battery separator, characterized in that: include: A film made of polyolefin is stretched to obtain a battery separator sample to be tested; Placing the battery diaphragm sample on a sample stage of a neutron small-angle scattering spectrometer, and making the plane of the battery diaphragm sample perpendicular to the direction of the neutron beam, adjusting the neutron wavelength, the distance from the battery diaphragm sample to the detector of the neutron small-angle scattering spectrometer, and the exposure time to obtain a plurality of different scattering vectors; By testing with air background and empty sample box, the sample thickness, air background and empty sample box influence are corrected, the absolute scattering intensity corresponding to each scattering vector of the battery separator sample is obtained, and a functional relationship curve between the absolute scattering intensity and the scattering vector is obtained; 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.

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

3. The method for characterizing the microporous structure of a battery separator according to claim 1, characterized in that: 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, characterized in that: The theoretical model includes one or a combination of Guinier's law, Porod's law, and Kratky's law.

5. The method for characterizing the microporous structure of a battery separator according to claim 1, characterized in that: The selecting theoretical model to fit and analyze the functional relationship curve includes: For an anisotropic system in which the functional relationship curves in the horizontal and vertical directions satisfy the Porod law, the horizontal and vertical directions are fitted simultaneously, and the fitting formula is: ； ； In the formula, is the equatorial scattering intensity of the battery separator sample, is the scattering intensity of the battery separator sample 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, It is the size ratio between the equatorial direction and the meridian direction of the battery separator sample.

6. The method for characterizing the microporous structure of a battery separator according to claim 1, characterized in that: The selecting theoretical model to fit and analyze the functional relationship curve includes: For the 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. The fitting analysis is performed, and the fitting formula is: ； ； In the formula, is the scattering intensity in the equatorial direction 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 a shape factor, and S is a structure factor.

7. The method for characterizing the microporous structure of a battery separator according to claim 6, characterized in that: ； ； ； 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.

8. The method for characterizing the microporous structure of a battery separator according to claim 6, characterized in that: ； ( , )； 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 is the average value of , and d is the distance between the two layers of the layered battery separator sample.

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

10. The method for characterizing the microporous structure of a battery separator according to claim 1, characterized in that: 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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