Pole piece surface density measurement method based on double-index model

Abstract

The invention discloses a pole piece surface density measurement method based on a double-index model, which comprises the following steps: firstly, starting an X-ray source, and measuring the ray intensity when a pole piece is not placed; secondly, replacing standard to-be-measured pole pieces with different surface densities, and measuring ray intensity; obtaining mass attenuation coefficients corresponding to different coating surface densities according to an attenuation formula, and performing double-index model correction on the mass attenuation coefficients according to the calibration data; and finally, measuring the intensity of rays passing through the pole piece to be measured, and measuring the surface density of the pole piece according to a ray intensity attenuation model and the calibrated mass attenuation coefficient. According to the method, the surface density of the pole piece is measured by using a method for correcting the quality attenuation coefficient of the pole piece through the double-index model, and compared with a method for directly calibrating the measured ray intensity and the standard surface density value, the problem that the measurement of the surface density of the pole piece coating is affected by X-ray beam hardening and Compton scattering is solved; and the surface density measurement precision of the pole piece is improved.

Description

Technical Field

[0001] The invention relates to the field of lithium battery pole piece surface density measurement, and in particular to a method for measuring the pole piece surface density by calibrating the mass attenuation coefficient of a lithium battery pole piece using a double exponential model. Background Art

[0002] The uniformity of the surface density of the lithium battery electrode will directly affect the internal resistance, capacity and safety of the lithium battery, so the surface density of the electrode coating needs to be precisely controlled. X-ray surface density measuring instrument, using After the ray penetrates the object, the ray intensity is attenuated to a certain extent relative to the incident ray intensity. The attenuation ratio is in a negative exponential relationship with the surface density of the penetrated object. The surface density of the object can be calculated by measuring the ray intensity. Therefore, most of the current lithium battery electrode surface density testers use the method of directly fitting the detected ray intensity value with the actual surface density value of the electrode coating. However, in actual applications, due to The energy distribution of the ray is continuous, and when it interacts with the electrode to be measured, beam hardening will occur, resulting in the mass attenuation coefficient not being a fixed constant, but a variable. Therefore, the current measurement method does not consider the impact of the change in the mass attenuation coefficient on the surface density detection, thereby affecting the accuracy of the surface density measurement. Summary of the invention

[0003] In order to overcome the shortcomings of the prior art, the present invention provides a pole piece surface density measurement method based on a double exponential model, so as to reduce the influence of radiation hardening on surface density measurement, thereby improving the accuracy and reliability of lithium battery pole piece surface density measurement.

[0004] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme:

[0005] The present invention provides a pole piece surface density measurement method based on a double exponential model, which is applied to the lithium battery pole piece surface density detector and includes: a high voltage power supply, Radiation source, ionization chamber, host computer, lithium battery electrode to be tested, A lithium battery electrode to be calibrated, and the ionization chamber is The radiation sources are symmetrically arranged; wherein the lithium battery pole piece is composed of a substrate and a coating; wherein the surface density of the substrate is a known quantity, the surface density of the coating is the surface density of the lithium battery pole piece, and the surface density of the lithium battery pole to be calibrated is a known quantity, is a positive integer not less than 6, wherein the measuring method comprises the following steps:

[0006] Step 1: The high voltage power supply is respectively supplied to the The anode input of the radiation source is used to control The DC high voltage of the ray intensity The cathode input of the radiation source is used to control The adjustable alternating current of the ray energy spectrum distribution; thereby making the The ray source outputs an initial voltage that matches the high voltage power supply. ray;

[0007] Step 2: The ionization chamber obtains the initial The intensity of the rays and the The ray source passes through After the lithium battery electrode to be calibrated The intensity of the ray is detected and transmitted to the host computer;

[0008] Step 3: The host computer The intensity of the rays and after The intensity of the radiation behind the lithium battery electrode to be calibrated is constructed using formula (1) Ray intensity model;

[0009] (1)

[0010] In formula (1), For the The radiation intensity behind the lithium battery electrode to be calibrated, Not greater than A positive integer, For the The mass attenuation coefficient of the lithium battery electrode to be calibrated, For the The density of the coating of the lithium battery electrode to be calibrated, For the The thickness of the coating of the lithium battery electrode to be calibrated, For the The surface density of the coating of the lithium battery electrode to be calibrated, Indicates the density of the substrate of the lithium battery pole piece. Indicates the thickness of the substrate of the lithium battery electrode. is the surface density of the substrate of the lithium battery pole piece, is a natural constant;

[0011] Step 4: According to The ray intensity model is obtained The mass attenuation coefficient of the lithium battery electrode to be calibrated ;

[0012] Step 5: Correction is performed to obtain the corrected mass attenuation coefficient ;

[0013] Step 6: Measure the lithium battery electrode to be tested, and obtain the intensity value of the ray after passing through the lithium battery electrode to be tested. ;

[0014] Step 7: Use formula (2) to obtain the coating surface density of the lithium battery electrode to be tested: :

[0015] (2)

[0016] In formula (2), is the density of the coating of the lithium battery electrode to be tested, is the thickness of the coating of the lithium battery electrode to be tested, is the surface density of the coating on the lithium battery electrode to be tested.

[0017] The method for measuring the pole piece surface density based on the double exponential model described in the present invention is also characterized in that step 5 comprises:

[0018] Step 5.1: Use formula (3) to get The total surface density of the lithium battery electrode to be calibrated :

[0019] (3)

[0020] In formula (3), for The thickness of the coating of the lithium battery electrode to be calibrated; express The density value of the lithium battery electrode to be calibrated, express The thickness of the lithium battery electrode to be calibrated;

[0021] Step 5.2: Use the double exponential model described in formula (4) to The mass attenuation coefficient of the lithium battery electrode to be calibrated Correction is performed to obtain the corrected mass attenuation coefficient :

[0022] (4)

[0023] In formula (4), There are 6 calibration parameters.

[0024] An electronic device of the present invention includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the pole piece surface density measurement method, and the processor is configured to execute the program stored in the memory.

[0025] The present invention provides a computer-readable storage medium, wherein a computer program is stored on the computer-readable storage medium, and the computer program executes the steps of the pole piece surface density measurement method when the computer program is executed by a processor.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. Compared with the traditional surface density detector calibration, which requires manual stamping sampling to determine the surface density value of the sample, the method of using the standard surface density pole piece to be calibrated improves the timeliness of the calibration method and saves the pole piece surface density measurement time and labor costs;

[0028] 2. Compared with the measurement method of directly performing linear fitting on the relationship between the radiation intensity attenuation value and the surface density, the present invention takes into account the influence of the radiation hardening phenomenon on the mass attenuation coefficient during the calibration process, corrects its influence on the measurement results of the surface density of the pole piece, and improves the reliability of the surface density detection;

[0029] 3. Compared with the calibration method of the polynomial fitting model for the relationship between the ray intensity attenuation value and the surface density, the present invention requires relatively few parameters, which is convenient for solving the calibration parameters;

[0030] 4. The present invention uses a double exponential model to calibrate the mass attenuation coefficient of the electrode to be measured, which effectively reduces the multi-energy The influence of the interaction between rays and matter on the measurement results of the pole piece surface density is reduced, so it has higher measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the lithium battery pole piece surface density detector of the present invention;

[0032] Figure 2 It is a schematic diagram of the process of the present invention;

[0033] Figure 3 This is a schematic diagram of the radiation hardening effect;

[0034] Figure 4 It is a schematic diagram of the radiation hardening effect curve in the surface density detection of the present invention. DETAILED DESCRIPTION

[0035] In this embodiment, a pole piece surface density measurement method based on a double exponential model is applied to a lithium battery pole piece surface density detector, such as Figure 1As shown, including: high voltage power supply, Radiation source, ionization chamber, host computer, lithium battery electrode to be tested, The lithium battery electrode to be calibrated, and the ionization chamber and The radiation source is symmetrically arranged; wherein the lithium battery pole piece is composed of a substrate and a coating; wherein the surface density of the substrate is a known quantity, the surface density of the coating is the surface density of the lithium battery pole piece, and the surface density of the lithium battery pole to be calibrated is a known quantity, is a positive integer not less than 6. The measuring method is to calibrate the surface density value of the lithium battery pole piece to be calibrated and the measured radiation intensity value during the calibration process of the surface density detector, so as to correct the mass attenuation coefficient of the lithium battery pole piece to be calibrated by a double exponential model, and then use the calibrated mass attenuation coefficient and the measured radiation intensity value of the pole piece to be measured to calculate the surface density value of the pole piece to be measured; specifically, Figure 2 As shown, the method is performed in the following steps:

[0036] Step 1: High voltage power supply to The anode input of the radiation source is used to control The DC high voltage of the ray intensity The cathode input of the radiation source is used to control Adjustable AC current for ray energy spectrum distribution; thus The ray source output matches the initial high voltage power supply ray;

[0037] Step 2: Ionization chamber obtains initial The intensity of the rays as well as The ray source passes through After the lithium battery electrode to be calibrated The intensity of the ray is then transmitted to the host computer. The intensity attenuation of the ray is used to indirectly measure the surface density of the pole piece. The intensity of the ray can avoid the interference of the measuring environment ray and ensure the accuracy of the measurement to the greatest extent.

[0038] Step 3: The host computer is based on the initial The intensity of the rays and after The intensity of the radiation behind the lithium battery electrode to be calibrated is constructed using formula (1) Ray intensity model;

[0039] (1)

[0040] In formula (1), For the The radiation intensity behind the lithium battery electrode to be calibrated, Not greater than A positive integer, For the The mass attenuation coefficient of the lithium battery electrode to be calibrated, For the The density of the coating of the lithium battery electrode to be calibrated, For the The thickness of the coating of the lithium battery electrode to be calibrated, For the The surface density of the coating of the lithium battery electrode to be calibrated, Indicates the density of the substrate of the lithium battery pole piece. Indicates the thickness of the substrate of the lithium battery electrode. is the surface density of the substrate of the lithium battery pole piece, where is a known value, is a natural constant. That is, the corresponding ray intensity under the lithium battery electrode to be calibrated with known surface density can be obtained, preparing for the subsequent correction of the mass attenuation coefficient.

[0041] exist The theoretical basis for correcting the mass attenuation coefficient in the X-ray surface density meter is: , is a measure of the absorption probability per gram of absorbing material per square centimeter of radiation beam. In the ray surface density measurement system, It can be expressed as:

[0042] (2)

[0043] In formula (2): is the electron density of the object, is the photoelectric effect cross section of electrons, is the Compton effect cross section of the electron, is the density of the object.

[0044] The electron density of an object and object density Not following The photoelectric effect cross section varies with the energy of the photon, but and Compton effect cross section All follow As the photon energy increases, the total cross section decreases. Follow The mass line attenuation coefficient decreases with the increase of photon energy. Follow The energy of photons increases with the increase of photon energy. Photons are more likely to interact with electrons in objects. When the rays hit an object, low energy Photons are easily absorbed by objects, which reduces the proportion of low-energy photons and increases the proportion of high-energy photons in the transmitted photons. The average energy of the beam increases, and the energy spectrum peak shifts to the right (the energy spectrum becomes hard), which produces a beam hardening effect, such as Figure 3 shown.

[0045] Under ideal conditions, the mass attenuation coefficient of the substance being measured is It can be expressed as:

[0046] (3)

[0047] In formula (3), represents Avogadro's constant, is Planck's constant, The speed of light, is the relative atomic mass, is a constant, is the atomic number of the absorbing element, is the wavelength of the incident ray, is the energy of the incident ray. Due to the beam hardening effect, the transmitted The energy of the rays increases and the wavelength decreases, resulting in a mass attenuation coefficient Therefore, when measuring the surface density of the pole piece, the mass attenuation coefficient must be Only by calibrating it can more accurate measurement results be obtained.

[0048] For the continuous spectrum The intensity of the rays should be:

[0049] (4)

[0050] In formula (4), For the incident The spectrum of rays, is the peak energy, and the calculation is Initial Ray intensity.

[0051] The logarithmic attenuation of the ray intensity during the measurement process can be expressed as:

[0052] (5)

[0053] in, is the density of the object being measured, Indicates the thickness of the object being measured. Represents the surface density of the object being measured, is its mass attenuation coefficient, After the object to be tested The ray intensity is as follows: From the above formula, we can know that the logarithmic attenuation of the ray intensity is the surface density A monotonically increasing function of The increase of logarithmic decay The larger the surface density is. Taking the derivative we get:

[0054] (6)

[0055] The logarithmic attenuation of the ray intensity can be obtained as a function of the surface density. is a monotonically decreasing function, that is, as the surface density of the object being measured increases The increase of logarithmic decay The increase gradually decreases, such as Figure 4 shown.

[0056] From formula (1), we can see that the slope of the curve of the logarithmic attenuation value of the ray intensity versus the surface density represents the mass attenuation coefficient of the electrode to be tested. Affected by the change of surface density, that is, the influence of radiation hardening during the measurement process, which leads to the change of mass attenuation coefficient. Therefore, for surface density detection, The existence of the radiation hardening phenomenon causes photons of different energies to show different decay rates when penetrating objects, that is, low-energy photons decay faster when penetrating thicker materials, while high-energy photons decay relatively slowly. This different decay rate can be described by a double exponential decay model, that is, two different decay constants and their corresponding amplitudes are considered in the model to more accurately reflect the physical phenomena in the actual detection process.

[0057] Therefore, in order to satisfy the above equations (5) and (6) for the continuous spectrum Based on the theoretical derivation of the variation of ray intensity with surface density and the ray hardening phenomenon that occurs when photons of different energies penetrate an object, a double exponential model correction method for the mass attenuation coefficient is proposed, namely:

[0058] (7)

[0059] In formula (7), Represent the decay constant and amplitude values ​​of lower energy photons and higher energy photons respectively.

[0060] Step 4: According to The ray intensity model is obtained , that is, The mass attenuation coefficient of the lithium battery electrode to be calibrated ;

[0061] Step 5: Correction is performed to obtain the corrected mass attenuation coefficient ;

[0062] Step 5.1: Use formula (8) to get The total surface density of the lithium battery electrode to be calibrated :

[0063] (8)

[0064] In formula (8), for The thickness of the coating of the lithium battery electrode to be calibrated; express The density value of the lithium battery electrode to be calibrated, express The thickness of the lithium battery electrode to be calibrated.

[0065] Step 5.2: Use the double exponential model of formula (9) to The mass attenuation coefficient of the lithium battery electrode to be calibrated Compared with directly obtaining The calibration data of the group ray intensity and the corresponding surface density are used to calibrate the surface density and ray intensity, and the mass attenuation coefficient is The correction method takes into account the influence of radiation hardening on the mass attenuation coefficient, corrects its influence on the measurement results, and improves the reliability of surface density detection. The corrected mass attenuation coefficient :

[0066] (9)

[0067] In formula (9), There are 6 correction parameters, representing the decay constant and amplitude value of lower energy photons and higher energy photons respectively;

[0068] Mass decay coefficient for the double exponential model The parameter solution of is the problem of nonlinear curve fitting. The mass attenuation coefficient data corresponding to the group surface density is substituted into the double exponential model formula (9), and the optimal solution is found by iteratively searching the parameter space, that is, minimizing the sum of squares of the residuals, thereby obtaining the attenuation constants and amplitude parameters of lower energy photons and higher energy photons: .

[0069] Step 6: Measure the lithium battery electrode to be tested, and obtain the intensity value of the ray after passing through the lithium battery electrode to be tested. ;

[0070] Step 7: Use formula (10) to obtain the coating surface density of the lithium battery electrode to be tested: :

[0071] (10)

[0072] In formula (10), is the density of the coating of the lithium battery electrode to be tested, is the thickness of the coating of the lithium battery electrode to be tested, is the surface density of the coating on the lithium battery electrode to be tested.

[0073] In this embodiment, an electronic device includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the above method, and the processor is configured to execute the program stored in the memory.

[0074] In this embodiment, a computer-readable storage medium stores a computer program on the computer-readable storage medium, and the computer program executes the steps of the above method when executed by a processor.

Claims

1. A method for measuring the surface density of a pole piece based on a double exponential model is applied to the lithium battery pole piece surface density detector and comprises: High voltage power supply, Radiation source, ionization chamber, host computer, lithium battery electrode to be tested, A lithium battery electrode to be calibrated, and the ionization chamber is The radiation sources are symmetrically arranged; wherein the lithium battery pole piece is composed of a substrate and a coating; wherein the surface density of the substrate is a known quantity, the surface density of the coating is the surface density of the lithium battery pole piece, and the surface density of the lithium battery pole to be calibrated is a known quantity, is a positive integer not less than 6, characterized in that the measuring method comprises the following steps: Step 1: The high voltage power supply is respectively supplied to the The anode input of the radiation source is used to control The DC high voltage of the ray intensity The cathode input of the X-ray source is used to control The adjustable alternating current of the ray energy spectrum distribution; thereby making the The ray source outputs an initial voltage that matches the high voltage power supply. ray; Step 2: The ionization chamber obtains the initial The intensity of the rays and the The ray source passes through After the lithium battery electrode to be calibrated The intensity of the ray is detected and transmitted to the host computer; Step 3: The host computer The intensity of the rays and after The intensity of the radiation behind the lithium battery electrode to be calibrated is constructed using formula (1) Ray intensity model; (1) In formula (1), For the The radiation intensity behind the lithium battery electrode to be calibrated, Not greater than A positive integer, For the The mass attenuation coefficient of the lithium battery electrode to be calibrated, For the The density of the coating of the lithium battery electrode to be calibrated, For the The thickness of the coating of the lithium battery electrode to be calibrated, For the The surface density of the coating of the lithium battery electrode to be calibrated, Indicates the density of the substrate of the lithium battery pole piece. Indicates the thickness of the substrate of the lithium battery pole piece. is the surface density of the substrate of the lithium battery pole piece, is a natural constant; Step 4: According to The ray intensity model is obtained The mass attenuation coefficient of the lithium battery electrode to be calibrated ; Step 5: Correction is performed to obtain the corrected mass attenuation coefficient ; Step 6: Measure the lithium battery electrode to be tested, and obtain the intensity value of the ray after passing through the lithium battery electrode to be tested. ; Step 7: Use formula (2) to obtain the coating surface density of the lithium battery electrode to be tested: : (2) In formula (2), is the density of the coating of the lithium battery electrode to be tested, is the thickness of the coating of the lithium battery electrode to be tested, is the surface density of the coating on the lithium battery electrode to be tested.

2. A method for measuring the surface density of a pole piece based on a double exponential model according to claim 1, characterized in that: The step 5 comprises: Step 5.1: Use formula (3) to get The total surface density of the lithium battery electrode to be calibrated : (3) In formula (3), for The thickness of the coating of the lithium battery electrode to be calibrated; express The density value of the lithium battery electrode to be calibrated, express The thickness of the lithium battery electrode to be calibrated; Step 5.2: Use the double exponential model described in formula (4) to The mass attenuation coefficient of the lithium battery electrode to be calibrated Correction is performed to obtain the corrected mass attenuation coefficient : (4) In formula (4), There are 6 calibration parameters.

3. An electronic device, comprising a memory and a processor, characterized in that: The memory is used to store a program that supports the processor to execute the pole piece surface density measurement method according to claim 1 or 2, and the processor is configured to execute the program stored in the memory.

4. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the pole piece surface density measurement method according to claim 1 or 2 are executed.

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