Diaphragm black spot detection method

Abstract

The application provides a diaphragm black point detection method, comprising the following steps: S1, providing a black point diaphragm with black points and a normal diaphragm without black points; S2, obtaining the total area A of all black points on the black point diaphragm; S3, respectively dissolving the black point diaphragm and the normal diaphragm to obtain a first solution and a second solution; S4, respectively testing the first solution and the second solution to obtain the concentration parameters of target elements in the first solution and the second solution; according to the concentration parameters, the mass parameter M of the target elements in the black points on the black point diaphragm is calculated; S5, according to M and A, the enrichment degree alpha of the target elements in the black points on the black point diaphragm is calculated, alpha=M / A. The diaphragm black point detection method can simply and conveniently obtain the mass of the target elements in the black points on the black point diaphragm, and the concept of the enrichment degree of the target elements is introduced, so that the quantitative analysis of the target elements is facilitated.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for detecting black spots on a separator. Background Technology

[0002] Lithium-ion batteries are important energy storage carriers, widely used in electronic devices, energy storage power stations, electric vehicles, and other fields. Abnormal black spots appear on the separators of some lithium-ion batteries. These black spots are a significant quality problem plaguing the battery manufacturing industry. At best, they affect product performance; at worst, they pose safety hazards during use.

[0003] However, the size of the black spots on the diaphragm is usually in the micrometer range and the mass is in the microgram range. Moreover, it is difficult to remove the black spots completely from the diaphragm. Even if the black spots are removed from the diaphragm, it is difficult to accurately weigh the mass of the black spots even with a high-precision balance. Therefore, this poses a great challenge to the quantitative analysis of black spots. Summary of the Invention

[0004] The purpose of this invention is to provide a method for detecting black spots on a diaphragm, which can easily and conveniently obtain the mass of target elements in black spots on the diaphragm, and introduce the concept of enrichment of target elements to facilitate quantitative analysis of target elements.

[0005] This invention provides a method for detecting black spots on a diaphragm, comprising the following steps: S1. Provides diaphragms with black spots and normal diaphragms without black spots; S2. Obtain the total area A of all black spots on the black spot membrane; S3. Digest the black spot membrane and the normal membrane respectively to obtain the corresponding first solution and second solution; S4. Perform elemental analysis on the first solution and the second solution respectively to obtain the concentration parameters of the target element in the first solution and the second solution; Based on the concentration parameter, calculate the mass parameter M of the target element in the black spot on the black spot membrane; S5. Based on M and A, calculate the enrichment degree α of the target element in the black dots on the black dot membrane, α=M / A.

[0006] In one feasible manner, in step S1 above, the black spot diaphragm and the normal diaphragm are the same size; In step S3 above, the first solution and the second solution have the same volume.

[0007] In one feasible manner, in step S4 above, the concentration parameter includes the total concentration C1 of the target element in the first solution and the total concentration C2 of the target element in the second solution, and M includes the total mass M1 of the target element in the black dots on the black dot membrane, M1=(C1-C2)*V, where V is the volume of the first solution.

[0008] In one feasible manner, in step S5 above, α includes the total mass enrichment α1 of the target elements in the black dots on the black dot diaphragm, α1=M1 / A.

[0009] In one feasible approach, in step S4 above, the concentration parameter includes the total concentration C1 of the target element in the first solution and the total concentration C2 of the target element in the second solution, and M includes the mass M2 of the target element introduced by the inactive substance in the black spots on the black spot membrane, M2=(C1-C2)*V-M3; where V is the volume of the first solution and M3 is the mass of the target element introduced by the active substance in the black spots on the black spot membrane.

[0010] In one feasible manner, in step S5 above, α includes the mass enrichment α2 of the target element introduced by the inactive substance in the black spot on the black spot membrane, α2=M2 / A.

[0011] In one feasible implementation, step S2 above further includes: Obtain the total area A1 of all reflective black spots on the black spot membrane.

[0012] In one possible implementation, A1 is obtained by scanning the black spot membrane from multiple angles using a cleanliness detection system.

[0013] In one feasible approach, step S3 above involves separately eliminating the black spot membrane and the normal membrane, specifically including: The black-spotted diaphragm and the normal diaphragm were respectively placed in a solvent for digestion and then brought to a final volume.

[0014] In one feasible approach, in step S3 above, the black spot membrane and the normal membrane are first cleaned and dried respectively before the black spot membrane and the normal membrane are digested.

[0015] In one feasible approach, in step S4 above, the elemental tests are performed on the first solution and the second solution respectively using ICP-OES.

[0016] In one possible implementation, in step S1 above, the black spot diaphragm and the normal diaphragm are selected from the same cell.

[0017] In one possible implementation, in step S1 above, the black spot with the largest area on the black spot membrane is located at the center of the black spot membrane.

[0018] The analysis of black spots on the diaphragm mainly includes the analysis of target elements within the black spots. This invention eliminates the need to first obtain the mass of the black spots to confirm the relevant data of the target elements used for analysis. Specifically, the diaphragm black spot detection method provided by this invention involves digesting the black spot diaphragm and a normal diaphragm to obtain a first solution and a second solution. The mass parameter M of the target element in the black spots on the black spot diaphragm is calculated using the concentration parameters of the target element in the first and second solutions. This eliminates the need to obtain the mass of the black spots by weighing, providing a simple and convenient way to acquire the mass of the target element in the black spots on the black spot diaphragm. Simultaneously, by measuring the total area A of all black spots on the black spot diaphragm and introducing the concept of enrichment α, the content of the target element in the black spots is evaluated based on this enrichment α, thus facilitating quantitative analysis of the black spots. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in further detail below. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. The terms "first," "second," "third," "fourth," etc. (if present) in the specification and claims of the present invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0020] This invention provides a method for detecting black spots on a diaphragm, comprising the following steps: S1. Provides diaphragms with black spots and normal diaphragms without black spots; S2. Obtain the total area A of all black spots on the black spot membrane; S3. The black spot membrane and the normal membrane are digested separately to obtain the corresponding first solution and second solution, that is, the black spot membrane is digested in the first solution and the normal membrane is digested in the second solution; S4. Perform elemental analysis on the first solution and the second solution respectively to obtain the concentration parameters of the target element (the target element is the element to be analyzed, such as a metal element) in the first solution and the second solution. Based on the concentration parameter, calculate the mass parameter M of the target element in the black spot on the black spot membrane; S5. Based on M and A, calculate the enrichment degree α of the target element in the black dots on the black dot membrane, α = M / A. Wherein, the unit of M can be μg, and the unit of A can be mm. 2 The unit of α can be μg / mm 2 .

[0021] Specifically, the analysis of black spots includes the analysis of target elements within the black spots. However, existing technologies struggle to accurately weigh the mass of black spots, making quantitative analysis of target elements difficult. This application addresses this issue by digesting a black-spotted separator and a normal separator to obtain a first solution and a second solution. The mass parameter M of the target element within the black spots on the separator is calculated using the concentration parameters of the target element in the first and second solutions. This eliminates the need for direct weighing to obtain the mass of the black spots, providing a simple and convenient way to acquire the mass of the target element within the black spots on the separator. By measuring the total area A of all black spots on the separator and introducing the concept of enrichment α, the content of the target element per unit area within the black spots is evaluated based on the enrichment α, thus achieving quantitative analysis of the black spots. This separator black spot detection method is not only applicable to the detection and analysis of separators in lithium-ion batteries but can also be used for the detection and analysis of separators in other types of batteries.

[0022] In one implementation, in step S1 above, the black spot separator and the normal separator are selected from the same battery cell, thereby ensuring the consistency of parameters between the black spot separator and the normal separator as much as possible, that is, ensuring that the black spot separator and the normal separator are made of the same material, source, and environment. The black spot separator and the normal separator can originate from different separators within the same battery cell; of course, they can also originate from different parts of the same separator (for example, a separator may have both black spot areas and blank areas, with black spots in the black spot areas and no black spots in the blank areas; in this case, the separator can be cut so that the black spot areas become the black spot separator and the blank areas become the normal separator).

[0023] In one implementation, in step S3 above, the content of black spot membrane in the first solution (i.e., the content of black spot membrane dissolved in a unit volume of the first solution) is the same as the content of normal membrane in the second solution (i.e., the content of normal membrane dissolved in a unit volume of the second solution), which facilitates experimental operation and subsequent data calculation.

[0024] Specifically, to ensure that the content of the black-spotted membrane in the first solution is the same as the content of the normal membrane in the second solution, in step S1 above, the black-spotted membrane and the normal membrane are the same size (i.e., the selected black-spotted membrane and normal membrane have the same single-sided surface area and thickness. For example, when both the black-spotted membrane and the normal membrane are circular, their diameters and thicknesses are the same; when both the black-spotted membrane and the normal membrane are rectangular sheet structures, their lengths, widths, and thicknesses are the same); in step S3 above, the volumes of the first solution and the second solution are the same. Of course, in other embodiments, the content of the black spot membrane in the first solution may not be the same as the content of the normal membrane in the second solution. For example, the two may be multiples of each other. In this case, the data needs to be processed in subsequent calculations to make the contents of the two equal. (For example, when preparing the first solution and the second solution, the black spot membrane and the normal membrane have the same size, but the volume of the second solution is twice the volume of the first solution. In this case, the concentration parameter of the target element in the second solution needs to be multiplied by two and compared with the concentration parameter of the target element in the first solution. And when the solution volume is involved in subsequent calculations, the volume of the first solution is used.)

[0025] As one implementation method, in step S3 above, before digesting the black spot membrane and the normal membrane, the black spot membrane and the normal membrane are first cleaned and dried respectively to eliminate the influence of the internal environment of the battery cell on the test results. The cleaning step for the black spot membrane and the normal membrane can be as follows: first clean the black spot membrane and the normal membrane with a DMC (dimethyl carbonate) solution, and then clean them with ultrapure water. The drying step for the black spot membrane and the normal membrane can be as follows: place the cleaned black spot membrane and the normal membrane at room temperature to air dry.

[0026] As one implementation method, step S3 above involves digesting the black spot membrane and the normal membrane, specifically including: The black-spotted membrane and the normal membrane were respectively placed in a solvent for digestion and then brought to a final volume. The solvent could be concentrated hydrochloric acid, with a concentration of 36% to 38%.

[0027] Specifically, when digesting the black-spotted membrane and the normal membrane, the black-spotted membrane and the normal membrane can be placed in different centrifuge tubes, then concentrated hydrochloric acid can be added to the centrifuge tubes, and then the centrifuge tubes can be placed on a digestion apparatus and heated. The heating temperature can be 120°C, and the heating time can be 1 hour. After the black-spotted membrane / normal membrane in the centrifuge tube is completely digested, ultrapure water can be added to the centrifuge tube to make up the volume (for example, to make up the volume of the first solution and the second solution to 50 mL).

[0028] In one implementation, step S2 above further includes: The total area A1 of all reflective black spots and the total area A2 of all non-reflective black spots on the black spot membrane are obtained respectively; where A = A1 + A2. A1 and A2 are obtained by repeatedly scanning the black spot membrane from multiple angles using a cleanliness detection system (specifically, by repeatedly scanning the black spot membrane from multiple angles under polarized light and normal light conditions). Specifically, A1 is obtained by repeatedly scanning the black spot membrane from multiple angles using a cleanliness detection system (including repeated scanning under normal light and multi-angle polarized light conditions), while A2 can generally be obtained by scanning the black spot membrane from normal light conditions using the cleanliness detection system.

[0029] Specifically, a cleanliness testing system is a professional analytical system capable of automatically scanning the size, quantity, and type (such as metal and non-metal) of contaminants on the surface of a tested item. During measurement, a black spot diaphragm is clamped onto the fixture of the cleanliness testing system, and then the diaphragm is scanned under polarized light and normal light conditions (polarized light and normal light scanning are built-in functions of the cleanliness testing system). The cleanliness testing system automatically analyzes parameters such as the particle size, quantity, and area of ​​reflective black spots (metal) and non-reflective black spots (non-metal or fiber, etc.) to obtain A, A1, and A2. The total area A of all black spots on the diaphragm is the sum of the total area A1 of reflective black spots and the total area A2 of non-reflective black spots.

[0030] In the analysis of black spot impurities, the state of the metal elements is crucial because the harmfulness of most metal elements (such as Fe and Cu) in their elemental form is far greater than that in their combined form. Most valence state analysis methods and component analysis techniques are destructive tests, making the analysis process complex and inefficient when multiple metal elements need to be analyzed. This application employs a non-destructive cleanliness detection method to scan the area of ​​black spots on the black spot diaphragm. During the cleanliness analysis, both normal and polarized light conditions are used to identify whether the black spots contain elemental metal particles (utilizing the principle that elemental metals cannot be extinct under orthogonal polarized light). This allows for the determination of the number, size, and area of ​​black spots containing elemental metals. This not only accurately obtains the total area A1 of all reflective black spots, facilitating the analysis of elemental metals (generally, a larger A1 indicates more severe metal contamination), but also avoids damaging the black spot diaphragm during measurement, thus preventing the acquisition of subsequent quality parameters M.

[0031] In one implementation, in step S1 above, the black spot with the largest area on the black spot membrane is located at the center of the black spot membrane, thus making the sampling of the black spot membrane more representative. For example, when the black spot membrane is circular, the black spot with the largest area on the black spot membrane is located at the center of the black spot membrane.

[0032] In one implementation, in step S1 above, the black spot separator is obtained by cutting a first test separator (i.e., the first original separator). The first test separator has black spots, and the black spot separator contains the largest black spot on the first test separator. That is, when cutting the first test separator, the largest black spot on the first test separator is retained on the black spot separator, thus making the sampling of the black spot separator more representative. The normal separator is obtained by cutting a second test separator, which has no black spots. The first test separator and the second test separator are selected from the same cell. The first test separator and the second test separator can be the same separator, and the black spot separator and the normal separator can come from different parts of the same separator.

[0033] Specifically, in this embodiment, the black spot diaphragm is obtained by cutting the first test diaphragm twice, and the normal diaphragm is obtained by cutting the second test diaphragm twice. Specifically, the first and second test diaphragms can be cut once each to obtain a first intermediate diaphragm sample and a second intermediate diaphragm sample. Then, the first and second intermediate diaphragm samples are cleaned and dried. Next, the first intermediate diaphragm sample is clamped onto the fixture of the cleanliness detection system. After the cleanliness detection system scans the first intermediate diaphragm sample (the cleanliness detection system only scans the black spots within the area covered by the fixture), the first intermediate diaphragm sample is cut a second time along the edge of the fixture of the cleanliness detection system to obtain the black spot diaphragm. The shape and size of the black spot diaphragm are similar to those of the clamp (wherein, in order to place the largest black spot on the black spot diaphragm at the center of the black spot diaphragm, the first intermediate diaphragm sample is clamped on the clamp of the cleanliness detection system with the largest black spot in the selected area of ​​the first intermediate diaphragm sample as the center, so that after the second cutting, the largest black spot is located at the center of the black spot diaphragm); the second intermediate diaphragm sample is clamped on the clamp of the cleanliness detection system, and then the second intermediate diaphragm sample is cut again along the edge of the clamp of the cleanliness detection system to obtain a normal diaphragm.

[0034] The advantages of obtaining the black-spotted diaphragm and normal diaphragm through secondary cutting include: 1. The shapes of the black-spotted diaphragm and normal diaphragm obtained after secondary cutting are more regular, ensuring that the size of the black-spotted diaphragm and normal diaphragm immersed in the solvent during digestion in step S3 remains consistent, thereby reducing the difference in test benchmarks between different samples; 2. The regular area is beneficial for subsequent data processing, such as making it easier to calculate the impurity content within the diaphragm sheet centered on the largest black spot (while primary cutting is usually for ease of cleaning, clamping, etc., and the shape of the diaphragm after primary cutting can be irregular); 3. Ensuring that the total area A of the black spots measured in the final measurement corresponds to the same measured area as the mass parameter M. Of course, in other embodiments, the black-spotted diaphragm and normal diaphragm can also be obtained through primary cutting, or without cutting.

[0035] As one implementation method, in step S4 above, ICP-OES (Inductively Coupled Plasma Emission Spectrometer) is used to perform elemental analysis on the first solution and the second solution respectively, thereby obtaining the concentration of each element in the first solution and the second solution.

[0036] In one implementation, in step S4 above, the concentration parameter includes the total concentration C1 of the target element in the first solution and the total concentration C2 of the target element in the second solution, and M includes the total mass M1 of the target element in the black spots on the black spot membrane, M1=(C1-C2)*V, where V is the volume of the first solution; at this time, in step S5 above, the enrichment α includes the total mass enrichment α1 of the target element in the black spots on the black spot membrane, α1=M1 / A, and α1 can be used to evaluate the total content of the target element in the black spots on the black spot membrane per unit area.

[0037] Specifically, in step S4 above, when performing elemental tests on the first solution and the second solution, the total concentration C1 of the target element in the first solution and the total concentration C2 of the target element in the second solution are obtained respectively. Then, based on the difference between C1 and C2, the concentration of the target element in the black spots on the black spot membrane is obtained. Then, based on the product of the difference between C1 and C2 and the volume V of the first solution, the total mass of the target element in the black spots on the black spot membrane can be obtained. The sources of the target elements in the black spots mainly include: electrolyte, battery internal environment, separator substrate (e.g., the raw materials of the separator itself contain the target elements), active materials (e.g., active materials on the positive and / or negative electrode plates of the battery detach and adhere to the separator, participating in the formation of black spots), external process environment (e.g., foreign matter on the production equipment adheres to the separator during the manufacturing process), and introduction during the experimental process (e.g., target elements on the testing instruments or tools adhere to the separator during the testing process). By setting a normal separator as a blank sample for control, the normal separator and the black spot separator are selected from the same battery cell, and the normal separator and the black spot separator undergo the same cleaning, drying, cutting, and digestion actions. In this way, the influence of electrolyte, battery internal environment, separator substrate, and experimental process introduction on the content of target elements in the black spots can be eliminated, and the total mass of target elements in the black spots on the black spot separator can be obtained (this total mass includes the mass of active materials and target elements introduced into the black spots by the external process environment).

[0038] In another implementation, in step S4 above, the concentration parameter includes the total concentration C1 of the target element in the first solution and the total concentration C2 of the target element in the second solution. M includes the mass M2 of the target element introduced by the inactive substance in the black spots on the black spot membrane (i.e., M2 is mainly the mass of the target element introduced into the black spots by the external process environment), M2=(C1-C2)*V-M3, where V is the volume of the first solution and M3 is the mass of the target element introduced by the active substance in the black spots on the black spot membrane. In this case, in step S5 above, the enrichment α includes the mass enrichment α2 of the target element introduced by the inactive substance in the black spots on the black spot membrane, α2=M2 / A. α2 can be used to evaluate the content of the target element introduced by the inactive substance in the black spots on the black spot membrane per unit area.

[0039] M3 can be calculated in the following way: Method 1: M3 = C3 * V, where C3 is the concentration of the target element introduced by the active substance in the first solution. C3 is calculated based on the concentration C4 of other elements in the first solution that form the active substance with the target element. C4 is obtained by elemental testing of the first solution.

[0040] Method 2: M3 is calculated based on the mass M4 of other elements in the first solution that form the active substance with the target element. M4 = C4 * V, where C4 is the concentration of other elements in the first solution that form the active substance with the target element. C4 is obtained by elemental testing of the first solution.

[0041] Specifically, the composition of black spots on the separator is not necessarily entirely due to external process environment. They could also be formed after active materials from the positive and / or negative electrode sheets detach and mix with foreign matter from the external process environment. In such cases, when both the active materials and the external process environment may introduce a particular element, the source of that element cannot be determined. For example, if the active materials contain Fe (in lithium iron phosphate batteries), and the separator manufacturing process extensively uses production equipment containing Fe, the source of the Fe cannot be determined without additional measures. In this situation, quantitative analysis of the Fe within the black spots becomes extremely important.

[0042] Taking Fe as the target element and lithium iron phosphate (LiFePO4) as the active material, after the lithium iron phosphate detaches, it adheres to the membrane in the form of a compound, participating in the formation of black spots. To obtain the mass M3 of Fe introduced by the active material into the black spots on the membrane, the concentration C4 of phosphorus (P) in the first solution (i.e., the other elements that constitute the active material with the target element mentioned above are P) can be measured. Based on the ratio of P to Fe in lithium iron phosphate, the concentration C3 of Fe introduced by the active material in the first solution can be calculated. Then, M3 can be calculated using M3 = C3 * V. Alternatively, the concentration C4 of P in the first solution can be measured, and the mass M4 of P in the first solution can be calculated using M4 = C4 * V. Then, M3 can be calculated using the mass ratio of Fe to P in lithium iron phosphate.

[0043] The above embodiment is an example of how to obtain the mass of the impurity element of interest contained in the active substance (i.e., the mass of the target element Fe in the active substance). If it is necessary to analyze impurity elements that are not present in the active substance (such as copper, aluminum, zinc, chromium, etc., which are usually not present in the active substance), then the total concentration C1 of the target element in the first solution and the total concentration C2 of the target element in the second solution can be obtained according to step S4 above. The mass of the target element can be obtained according to M1=(C1-C2)*V, where V is the volume of the first solution and the second solution, and the volumes of the first solution and the second solution are the same.

[0044] After obtaining the mass M3 of Fe element introduced by the active material in the black spots on the black spot separator, the total mass of Fe element in the black spots on the black spot separator is subtracted from M3 to obtain the mass M2 of Fe element introduced by the inactive material in the black spots on the black spot separator, i.e., M2=(C1-C2)*V-M3. This eliminates the influence of electrolyte, battery internal environment, separator substrate, experimental process introduction, and active material on the Fe element content in the black spots, and finally obtains the influence of external process environment on the Fe element content in the black spots. This facilitates the quantitative analysis of the source of the target element (for example, when the analysis results show that the external process environment has a large influence on the Fe element content in the black spots, the external process environment can be improved; when the analysis results show that the active material has a large influence on the Fe element content in the black spots, the anti-detachment performance of the active material on the positive electrode and / or negative electrode can be improved).

[0045] Depending on the actual analysis needs, M1 and α1 or M2 and α2 can be calculated separately, or M1, α1, M2 and α2 can be calculated simultaneously.

[0046] The following example illustrates the specific operating steps of this diaphragm black spot detection method: Equipment and tools: Cleanliness testing system, ICP-OES, ceramic scissors, digestion apparatus.

[0047] Materials: First test diaphragm containing black spots, second test diaphragm without black spots, DMC solution, ultrapure water, concentrated hydrochloric acid.

[0048] 1. One-time cutting: Take the first test diaphragm containing black spots and the second test diaphragm without black spots from the same battery cell, and cut the first test diaphragm and the second test diaphragm with ceramic scissors to obtain the first intermediate diaphragm sample and the second intermediate diaphragm sample with approximately the same size.

[0049] 2. Cleaning: First, clean the first and second intermediate septum samples with DMC solution, and then clean the first and second intermediate septum samples with ultrapure water.

[0050] 3. Drying: Air dry the first and second intermediate septum samples after cleaning at room temperature.

[0051] 4. Cleanliness Detection System Scanning: Clamp the first intermediate septum sample containing black spots onto the fixture of the cleanliness detection system (centered on the largest possible black spot). Scan under both normal and polarized light conditions. The cleanliness detection system will automatically analyze the particle size, number, and area of ​​reflective particles (metal) and non-reflective particles (non-metallic or fiber, etc.), thereby automatically calculating the total area A1 (in mm) of all reflective black spots. 2 The total area A2 of all non-reflective black dots (in mm)2 ) and the total area A of all black dots (in mm) 2 ).

[0052] 5. Secondary Cutting: The first intermediate septum sample is cut along the circular edge of the fixture of the cleanliness detection system (this can be done by tracing the circular edge of the fixture with a carbon pen after scanning and then cutting it with ceramic scissors) to obtain a circular black spot septum. Similarly, the second intermediate septum sample is clamped on the fixture of the cleanliness detection system, and then the second intermediate septum sample is cut along the circular edge of the fixture of the cleanliness detection system to obtain a circular normal septum. The normal septum is the same size as the black spot septum.

[0053] 6. Digestion and Volume Adjustment: Digest the black-spotted membrane and the normal membrane separately in concentrated hydrochloric acid and then adjust the volume to obtain a first solution containing the black-spotted membrane and a second solution containing the normal membrane. The specific steps are as follows: Place the black-spotted membrane and the normal membrane in separate centrifuge tubes, then add concentrated hydrochloric acid to the centrifuge tubes. Place the centrifuge tubes on a digester and heat at 120°C for 1 hour. After the black-spotted / normal membranes in the centrifuge tubes have completely digested, add ultrapure water to adjust the volume (e.g., to 50 mL). The concentrated hydrochloric acid was commercially available and of analytical grade.

[0054] 7. Elemental analysis: ICP-OES was used to analyze the concentration of each element in the black spot membrane and the normal membrane to obtain the total concentration of the target element C1 (in mg / L) in the first solution and the total concentration of the target element C2 (in mg / L) in the second solution.

[0055] 8. Calculation: Based on C1, C2, and A, calculate M (in μg) and α (in μg / mm²). 2 M = (C1 - C2) * V, where V is the volume of the first solution; α = M / A.

[0056] The advantages of the diaphragm black spot detection method in this embodiment include: 1. By digesting the black spot membrane and the normal membrane, a first solution and a second solution are obtained. The target elements in the first solution and the second solution are analyzed by ICP-OES to obtain the concentration parameters of the target elements in the first solution and the second solution. Based on the concentration parameters, the mass parameter M of the target elements in the black spots on the black spot membrane can be calculated, thus obtaining the mass of the target elements in the black spots on the black spot membrane simply and conveniently.

[0057] 2. A non-destructive cleanliness testing method is used to scan the black spots on the black spot diaphragm, and the total area A of all black spots on the black spot diaphragm is measured. The concept of enrichment α is introduced, and the content of the target element in the black spot per unit area is evaluated based on the enrichment α, which facilitates the quantitative analysis of black spots and cleverly avoids the problem of needing to weigh the actual quality of black spots.

[0058] 3. Scanning is performed under both normal and polarized light conditions to identify whether the black spots contain metallic particles (based on the principle that metallic particles cannot be extinct under orthogonal polarized light). This allows us to obtain the number, size, and area of ​​the black spots containing metallic particles, which facilitates the analysis of elemental metals.

[0059] 4. By calculating the concentration / mass of other elements that make up the active substance with the target element in the black spot, the mass of the target element introduced by the active substance can be obtained. Then, the mass of the target element introduced by the inactive substance in the black spot on the black spot membrane can be calculated (mass of the target element in the black spot on the black spot membrane minus the mass of the target element introduced by the active substance). This facilitates the quantitative analysis of the source of the target element.

[0060] The above method can be used to easily and accurately measure and analyze indicators such as the composition, size, area, and source of black spots.

[0061] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for detecting black spots on a diaphragm, characterized in that, Includes the following steps: S1. Provides diaphragms with black spots and normal diaphragms without black spots; S2. Obtain the total area A of all black spots on the black spot membrane; S3. Digest the black spot membrane and the normal membrane respectively to obtain the corresponding first solution and second solution; S4. Perform elemental analysis on the first solution and the second solution respectively to obtain the concentration parameters of the target element in the first solution and the second solution; calculate the mass parameter M of the target element in the black spot on the black spot membrane based on the concentration parameters. S5. Based on M and A, calculate the enrichment degree α of the target element in the black dots on the black dot membrane, α=M / A.

2. The method for detecting black spots on a diaphragm as described in claim 1, characterized in that, In step S1 above, the black-spotted diaphragm and the normal diaphragm are the same size; In step S3 above, the first solution and the second solution have the same volume.

3. The method for detecting black spots on a diaphragm as described in claim 2, characterized in that, In step S4 above, the concentration parameter includes the total concentration of the target element C1 in the first solution and the total concentration of the target element C2 in the second solution, and M includes the total mass M1 of the target element in the black dots on the black dot membrane, M1=(C1-C2)*V, where V is the volume of the first solution.

4. The method for detecting black spots on a diaphragm as described in claim 3, characterized in that, In step S5 above, α includes the total mass enrichment α1 of the target elements in the black dots on the black dot membrane, α1=M1 / A.

5. The method for detecting black spots on a diaphragm as described in claim 2, characterized in that, In step S4 above, the concentration parameter includes the total concentration of the target element C1 in the first solution and the total concentration of the target element C2 in the second solution. M includes the mass M2 of the target element introduced by the inactive substance in the black spot on the black spot membrane, M2=(C1-C2)*V-M3; where V is the volume of the first solution and M3 is the mass of the target element introduced by the active substance in the black spot on the black spot membrane.

6. The method for detecting black spots on a diaphragm as described in claim 5, characterized in that, In step S5 above, α includes the mass enrichment α2 of the target element introduced by the inactive substance in the black spot on the black spot membrane, where α2 = M2 / A.

7. The method for detecting black spots on a diaphragm as described in claim 1, characterized in that, The above S2 step also includes: Obtain the total area A1 of all reflective black spots on the black spot membrane.

8. The method for detecting black spots on a diaphragm as described in claim 7, characterized in that, A1 is obtained by scanning the black spot membrane from multiple angles using a cleanliness detection system.

9. The method for detecting black spots on a diaphragm as described in claim 1, characterized in that, In step S3 above, the black spot membrane and the normal membrane are respectively digested, specifically including: The black-spotted diaphragm and the normal diaphragm were respectively placed in a solvent for digestion and then brought to a final volume.

10. The method for detecting black spots on a diaphragm as described in claim 1, characterized in that, In step S3 above, before digesting the black spot membrane and the normal membrane, the black spot membrane and the normal membrane are first cleaned and dried respectively.

11. The method for detecting black spots on a diaphragm as described in claim 1, characterized in that, In step S4 above, ICP-OES is used to perform the elemental tests on the first solution and the second solution, respectively.

12. The method for detecting black spots on a diaphragm as described in claim 1, characterized in that, In step S1 above, the black spot diaphragm and the normal diaphragm are selected from the same battery cell.

13. The method for detecting black spots on a diaphragm as described in any one of claims 1-12, characterized in that, In step S1 above, the black spot with the largest area on the black spot membrane is located at the center of the black spot membrane.