Color developing solution for detecting iron metal foreign matters in lithium battery production process and detection method

Abstract

The invention relates to a color developing solution for detecting iron metal foreign matters in a lithium battery production process and a detection method, and the color developing solution comprises the following components in parts by volume: 3-4 parts of an acid solution, 1-2 parts of an oxidizing agent and 3-4 parts of a thiocyanate solution. The color developing solution is provided for detection of the iron metal foreign matter in the lithium battery production process, the iron metal foreign matter in the lithium battery production process is rapidly and qualitatively detected by utilizing a color developing reaction of ferric ions and thiocyanate ions to generate a blood red complex iron thiocyanate, and the detection sensitivity, the detection efficiency and the speed are high; the reagent of the color developing solution is nontoxic and harmless, the cost is low, the color developing solution is particularly suitable for large-batch detection on a mass production line, the detection efficiency of the production line is greatly improved, and meanwhile, high detection sensitivity is taken into account.

Description

Technical Field

[0001] This invention relates to the field of iron metal foreign object detection technology in lithium battery production, and particularly to a colorimetric solution and detection method for detecting iron metal foreign objects in lithium battery production. Background Technology

[0002] Foreign objects are a core hidden danger affecting battery performance, safety and consistency during the lithium battery production process. Metal foreign objects are inevitably mixed in the raw materials for lithium-ion battery production, and many parts of the manufacturing equipment are made of stainless steel. These factors may introduce metal foreign objects into the battery cell, causing internal short circuits, abnormal self-discharge, and affecting the battery's performance.

[0003] Therefore, strict control of foreign objects, especially metallic foreign objects, is necessary during battery production. Iron is currently the most common foreign object in lithium-ion battery production. Foreign object control requires rapid analysis of its composition. Currently, the industry commonly uses energy-dispersive X-ray spectroscopy (EDS) or atomic emission spectrometry (ICP) for detection. However, both methods require expensive equipment, complex procedures, specialized operators, poor timeliness, and high testing costs, making them unsuitable for the frequent testing demands of mass production.

[0004] Therefore, how to provide a method that is highly sensitive, efficient, fast, and easy to detect iron metal foreign objects in the lithium battery production process, adaptable to mass production line testing, and significantly improve production line testing efficiency is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a colorimetric solution and detection method for detecting ferrous metal foreign objects during lithium battery production. This invention provides a colorimetric solution for detecting ferrous metal foreign objects during lithium battery production. It utilizes the colorimetric reaction between ferric ions and thiocyanate ions to generate a blood-red complex, ferric thiocyanate, enabling rapid qualitative detection of ferrous metal foreign objects during lithium battery production. The solution offers high sensitivity, high efficiency, and fast detection speed. Furthermore, the reagents in the colorimetric solution are non-toxic, harmless, and low-cost, making it particularly suitable for high-volume testing on mass production lines. This significantly improves production line detection efficiency while maintaining high detection sensitivity.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a colorimetric solution for detecting iron metal foreign matter during the production of lithium batteries. The colorimetric solution comprises, by volume, 3-4 parts of an acid solution, such as 3 parts, 3.1 parts, 3.2 parts, 3.3 parts, 3.4 parts, 3.5 parts, 3.6 parts, 3.7 parts, 3.8 parts, 3.9 parts, or 4 parts; 1-2 parts of an oxidant, such as 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, or 2 parts; and 3-4 parts of a thiocyanate solution, such as 3 parts, 3.1 parts, 3.2 parts, 3.3 parts, 3.4 parts, 3.5 parts, 3.6 parts, 3.7 parts, 3.8 parts, 3.9 parts, or 4 parts.

[0008] The colorimetric solution for iron metal foreign matter provided by this invention comprises, by volume, 3-4 parts of acid, 1-2 parts of oxidant, and 3-4 parts of thiocyanate solution. The acid serves to maintain an acidic environment and oxidizes iron metal into divalent ferrous ions. The oxidant then further oxidizes the ferrous ions into trivalent ferric ions. The unique colorimetric reaction (red) between thiocyanate and trivalent ferric ions enables the detection of iron metal foreign matter. Combined with the aforementioned volume fractions, this solution enables rapid qualitative detection of iron metal foreign matter during lithium battery production, offering high sensitivity, high efficiency, and fast speed. Furthermore, the reagents in the colorimetric solution are non-toxic, harmless, and low-cost, making it particularly suitable for large-scale testing on mass production lines. This significantly improves production line testing efficiency while maintaining high detection sensitivity.

[0009] In this invention, if the amount of acid is too high, it will dissolve other metallic foreign matter, interfering with the detection sensitivity of iron metal. Furthermore, if the colorimetric solution is too acidic, it will corrode the detection equipment. If the amount of acid is too low, the iron metal foreign matter will not dissolve sufficiently, resulting in an incomplete colorimetric reaction and reduced detection sensitivity. If the amount of oxidant is too high, it will lead to over-oxidation, producing other impurities that interfere with the colorimetric reaction. If the amount of oxidant is too low, the colorimetric reaction will be incomplete, reducing detection sensitivity. If the amount of thiocyanate solution is too high, the background color will be too dark, interfering with the detection of low-content iron metal foreign matter and reducing detection sensitivity. If the amount of thiocyanate solution is too low, the colorimetric reaction will be incomplete, reducing detection sensitivity. Therefore, a colorimetric solution comprising 3-4 parts acid, 1-2 parts oxidant, and 3-4 parts thiocyanate solution can more effectively achieve rapid qualitative detection of iron metal foreign matter during lithium battery production, offering high detection sensitivity, high detection efficiency, and fast speed.

[0010] As a preferred embodiment of the present invention, the acid solution includes at least one of hydrochloric acid solution, nitric acid solution or sulfuric acid solution.

[0011] As a preferred embodiment of the present invention, the molar concentration of the acid solution is 0.1 mol / L to 1 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L.

[0012] The present invention controls the molar concentration of the acid solution to be 0.1 mol / L-1 mol / L. If the molar concentration of the acid solution is too high, it will lead to excessive acidity, which will not only dissolve iron metal foreign matter, but also other metal foreign matter impurities, interfering with the detection results and reducing the detection sensitivity. If the molar concentration of the acid solution is too low, it will lead to insufficient acidity, slow dissolution of iron metal, delayed or weakened color reaction, reduced detection efficiency, and reduced sensitivity.

[0013] As a preferred embodiment of the present invention, the oxidant includes hydrogen peroxide solution and / or ammonium persulfate solution.

[0014] As a preferred embodiment of the present invention, the mass concentration of the oxidant is 2.7wt%-3.3wt%, for example, 2.7wt%, 2.75wt%, 2.8wt%, 2.85wt%, 2.9wt%, 2.95wt%, 3.0wt%, 3.05wt%, 3.1wt%, 3.15wt%, 3.2wt%, 3.25wt%, or 3.3wt%.

[0015] The present invention controls the mass concentration of the oxidant to be 2.7wt%-3.3wt%. If the mass concentration of the oxidant is too high, it will oxidize thiocyanate and generate bubbles that interfere with color development. If the mass concentration of the oxidant is too low, it will lead to insufficient oxidation capacity, incomplete oxidation of iron metal foreign matter, and reduced detection sensitivity.

[0016] As a preferred embodiment of the present invention, the thiocyanate solution includes potassium thiocyanate solution and / or ammonium thiocyanate solution.

[0017] As a preferred embodiment of the present invention, the molar concentration of the thiocyanate solution is 0.1 mol / L-2 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, or 2 mol / L, preferably 0.1 mol / L-0.3 mol / L.

[0018] This invention regulates the molar concentration of the thiocyanate solution to 0.1 mol / L-0.3 mol / L. If the molar concentration of the thiocyanate solution is too high, the background color will be too dark during the color development process (with large areas of red halo), and the red dot signals generated by iron metal foreign objects will be relatively weak and thus masked, reducing the signal-to-noise ratio and sensitivity of the detection. If the molar concentration of the thiocyanate solution is too low, it will not provide enough thiocyanate ions to fully react with ferric ions, resulting in insufficient color development intensity, missed detection of small iron metal foreign objects, and reduced detection sensitivity.

[0019] The colorimetric solution provided by this invention for detecting iron metal foreign matter in the lithium battery production process, with the volume fractions of acid, oxidant and thiocyanate solution combined with their respective molar / mass concentrations, will enable faster qualitative detection of iron metal foreign matter in the lithium battery production process, with high detection sensitivity and high detection efficiency.

[0020] As a preferred embodiment of the present invention, the method for preparing the colorimetric solution includes the following steps:

[0021] According to the formula, the acid solution, the oxidant, and the thiocyanate solution are mixed evenly to obtain the colorimetric solution.

[0022] It should be noted that the present invention does not impose specific requirements or special limitations on the mixing method and mixing parameters, as long as the raw materials are mixed evenly. Those skilled in the art can make adaptive selections and adjustments according to actual conditions.

[0023] Secondly, the present invention also provides a method for detecting iron metal foreign objects during the lithium battery production process, the detection method comprising the following steps:

[0024] Metal foreign matter from the lithium battery production process is collected and filtered using a solution to obtain the metal foreign matter to be tested.

[0025] An adhesive material is used to make the metallic foreign object to be detected adhere to the surface of the adhesive material;

[0026] The pretreated filter membrane is impregnated with the color-developing solution described in the first aspect, and then the impregnated filter membrane is covered on the surface of the adhesive material. Red dots appear on the surface of the impregnated filter membrane, indicating the presence of iron metal foreign matter during the lithium battery production process.

[0027] The detection method of the present invention first filters the collected solution containing metal foreign objects to remove metal foreign objects that are too small and other impurities, which can effectively improve the sensitivity and efficiency of subsequent detection.

[0028] It should be noted that in the step of collecting and filtering metallic foreign matter in the lithium battery production process using a solution, there are no specific requirements or special limitations on the solution, as long as it can collect metallic foreign matter from, for example, positive and negative electrode slurry conveying pipes, electrolyte conveying pipes, rolling components, die-cutting components, and winding components. For example, it can be pure water, ethanol, isopropanol, or a mixture thereof. There are no specific requirements or special limitations on the filter membrane used for filtration. Commonly used filter membranes in the art are applicable to this invention, such as nylon filter membranes, polyvinylidene fluoride filter membranes, or polytetrafluoroethylene filter membranes.

[0029] As a preferred technical solution of the present invention, after the filtration, the particle size of the metal foreign object to be detected is ≥1μm, such as 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 4μm, 5μm, 10μm, 50μm or 100μm, etc.

[0030] Preferably, the pretreatment step includes: washing the filter membrane with an acid washing solution to obtain a pretreated filter membrane.

[0031] Preferably, the pickling solution includes at least one of hydrochloric acid solution, nitric acid solution, sulfuric acid solution or citric acid solution.

[0032] Preferably, the molar concentration of the pickling solution is 0.1 mol / L to 1 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L.

[0033] Preferably, the filtration includes negative pressure filtration.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] This invention provides a colorimetric solution for detecting iron metal foreign objects during lithium battery production. It utilizes a colorimetric reaction between ferric ions and thiocyanate ions to generate a blood-red complex, ferric thiocyanate, enabling rapid qualitative detection of iron metal foreign objects during lithium battery production. The solution boasts high sensitivity, high efficiency, and fast detection speed. Furthermore, the reagents in the colorimetric solution are non-toxic, harmless, and low-cost, making it particularly suitable for high-volume testing on mass production lines. This significantly improves production line testing efficiency while maintaining high detection sensitivity. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the negative pressure filtration device used to filter foreign objects collected inside the pipe, as provided in Embodiment 1 of the present invention.

[0037] Among them, 1-Eragonal bottle, 2-Sand core filter, 3-Nylon filter membrane, 4-Glass funnel, 5-Vacuum exhaust pipe and 6-Vacuum pump.

[0038] Figure 2 This is an optical photograph of a metallic foreign object adhering to the surface of adhesive paper, as provided in Embodiment 1 of the present invention.

[0039] Figure 3 This is a colorimetric optical photograph showing the presence of ferrous metal foreign matter after the impregnated nylon filter membrane provided in Embodiment 1 of the present invention is covered on the surface of the adhesive paper. Detailed Implementation

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0041] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0042] In the specific implementation section of this invention, all detected metallic foreign objects originate from the same positive and negative electrode slurry conveying pipeline, and the presence of ferrous metal foreign objects is determined.

[0043] Example 1

[0044] This embodiment provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. By volume, the colorimetric solution comprises 4 parts of dilute hydrochloric acid solution (molar concentration of 0.1 mol / L), 2 parts of hydrogen peroxide aqueous solution (mass concentration of 3 wt%), and 4 parts of potassium thiocyanate solution (molar concentration of 0.2 mol / L).

[0045] This embodiment provides a method for detecting ferrous metal foreign objects during lithium battery production. The detection method includes the following steps:

[0046] Figure 1 The diagram shows a negative pressure filtration device for filtering foreign matter collected inside a pipe, as provided in Embodiment 1 of the present invention. The device includes a triangular bottle 1, a sand core filter 2, a nylon filter membrane 3, a glass funnel 4, a vacuum exhaust pipe 5, and a vacuum pump 6.

[0047] Pure water is added to the positive and negative electrode slurry conveying pipelines to collect metal foreign objects in the pipelines. The pure water containing metal foreign objects is then added to a glass funnel 4. A nylon filter membrane 3 (pore size of 0.22μm) is placed between the glass funnel 4 and the sand core filter 2. The vacuum pump 6 is started to draw a vacuum for filtration. Some impurities in the pure water are retained on the nylon filter membrane, and the metal foreign objects to be detected (adhered to the surface of the nylon filter membrane) are obtained.

[0048] The nylon filter membrane with the metal foreign object to be tested attached is picked off with tweezers, and the impurities on the surface are peeled off with adhesive paper, so that the metal foreign object in it adheres to the surface of the adhesive paper.

[0049] Take another nylon filter membrane and clean it with dilute hydrochloric acid (molar concentration of 0.1 mol / L). Then, soak the acid-washed nylon filter membrane with the color developing solution provided in this embodiment. After that, cover the surface of the adhesive paper with the soaked nylon filter membrane and observe whether red dots appear.

[0050] The detection reaction principle is as follows: Fe + 2HCl = FeCl2 + H2↑; 2FeCl2 + H2O2 + 2HCl = 2FeCl3 + 2H2O; FeCl3 + 3KSCN = 3KCl + Fe(SCN)3.

[0051] Figure 2 An optical photograph of a metallic foreign object adhering to the surface of adhesive paper, as provided in Embodiment 1 of the present invention, is shown. As can be seen from the figure, there is a clear presence of a metallic foreign object.

[0052] Figure 3 The image shows a colorimetric optical photograph of the presence of iron metal foreign matter after the nylon filter membrane provided in Embodiment 1 of the present invention is covered on the surface of the adhesive paper. As can be seen from the figure, the colorimetric solution provided in this embodiment can successfully perform qualitative detection of iron metal foreign matter.

[0053] Example 2

[0054] This embodiment provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. By volume, the colorimetric solution comprises 3.5 parts of dilute hydrochloric acid solution (molar concentration of 0.5 mol / L), 1.5 parts of hydrogen peroxide aqueous solution (mass concentration of 2.7 wt%), and 3.5 parts of potassium thiocyanate solution (molar concentration of 0.1 mol / L).

[0055] This embodiment provides a method for detecting iron metal foreign objects during lithium battery production. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Embodiment 2 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0056] Example 3

[0057] This embodiment provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. By volume, the colorimetric solution comprises 3 parts dilute hydrochloric acid solution (molar concentration of 1 mol / L), 1 part hydrogen peroxide aqueous solution (mass concentration of 3.3 wt%), and 3 parts potassium thiocyanate solution (molar concentration of 0.3 mol / L).

[0058] This embodiment provides a method for detecting iron metal foreign objects during lithium battery production. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Embodiment 3 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0059] Example 4

[0060] This embodiment provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. The difference between this colorimetric solution and that of Example 1 is that the molar concentration of the dilute hydrochloric acid solution is 1.2 mol / L, while the other components and parameters remain the same as in Example 1.

[0061] This embodiment provides a method for detecting iron metal foreign objects during the lithium battery production process. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Embodiment 4 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0062] Example 5

[0063] This embodiment provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. The difference between this colorimetric solution and that of Example 1 is that the mass concentration of the hydrogen peroxide aqueous solution is 3.5 wt%, while the remaining components and parameters are the same as those of Example 1.

[0064] This embodiment provides a method for detecting iron metal foreign objects during the lithium battery production process. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Embodiment 5 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0065] Example 6

[0066] This embodiment provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. The difference between this colorimetric solution and that of Example 1 is that the molar concentration of potassium thiocyanate solution is 0.5 mol / L, while the remaining components and parameters are the same as in Example 1.

[0067] This embodiment provides a method for detecting iron metal foreign objects during the lithium battery production process. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Embodiment 6 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0068] Comparative Example 1

[0069] This comparative example provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. The difference between the colorimetric solution and that of Example 1 is that the volume fraction of the dilute hydrochloric acid solution is 5 parts, the volume fraction of the hydrogen peroxide aqueous solution is 1.7 parts, and the volume fraction of the potassium thiocyanate solution is 3.3 parts. The remaining components and parameters are the same as those of Example 1.

[0070] This embodiment provides a method for detecting iron metal foreign objects during the lithium battery production process. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Comparative Example 1 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0071] Comparative Example 2

[0072] This comparative example provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. The difference between the colorimetric solution and that of Example 1 is that the volume fraction of the dilute hydrochloric acid solution is 2 parts, the volume fraction of the hydrogen peroxide aqueous solution is 2.6 parts, and the volume fraction of the potassium thiocyanate solution is 5.4 parts. The remaining components and parameters are the same as those of Example 1.

[0073] This embodiment provides a method for detecting iron metal foreign objects during the lithium battery production process. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Comparative Example 2 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0074] Comparative Example 3

[0075] This comparative example provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. The difference between the colorimetric solution and that of Example 1 is that the volume fraction of the dilute hydrochloric acid solution is 3.5 parts, the volume fraction of the hydrogen peroxide aqueous solution is 3 parts, and the volume fraction of the potassium thiocyanate solution is 3.5 parts. The remaining components and parameters are the same as those of Example 1.

[0076] This embodiment provides a method for detecting iron metal foreign objects during the lithium battery production process. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Comparative Example 3 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0077] Comparative Example 4

[0078] This comparative example provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. The difference between the colorimetric solution and that of Example 1 is that the volume fraction of the dilute hydrochloric acid solution is 4.75 parts, the volume fraction of the hydrogen peroxide aqueous solution is 0.5 parts, and the volume fraction of the potassium thiocyanate solution is 4.75 parts. The remaining components and parameters are the same as those of Example 1.

[0079] This embodiment provides a method for detecting iron metal foreign objects during the lithium battery production process. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Comparative Example 4 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0080] Comparative Example 5

[0081] This comparative example provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. The difference between the colorimetric solution and that of Example 1 is that the volume fraction of the dilute hydrochloric acid solution is 5.4 parts, the volume fraction of the hydrogen peroxide aqueous solution is 2.6 parts, and the volume fraction of the potassium thiocyanate solution is 2 parts. The remaining components and parameters are the same as those of Example 1.

[0082] This embodiment provides a method for detecting iron metal foreign objects during the lithium battery production process. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Comparative Example 5 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0083] Comparative Example 6

[0084] This comparative example provides a colorimetric solution for detecting iron metal foreign matter during lithium battery production. The difference between the colorimetric solution and that of Example 1 is that the volume fraction of the dilute hydrochloric acid solution is 3.3 parts, the volume fraction of the hydrogen peroxide aqueous solution is 1.7 parts, and the volume fraction of the potassium thiocyanate solution is 5 parts. The remaining components and parameters are the same as those of Example 1.

[0085] This embodiment provides a method for detecting iron metal foreign objects during the lithium battery production process. The difference between this method and that of Embodiment 1 is that the colorimetric solution provided in Comparative Example 6 is used for detection, while the other detection methods and parameters remain the same as those in Embodiment 1.

[0086] The time it took for the red dots to fully appear in Examples 1-6 and Comparative Examples 1-6 (from the start of appearance until they stopped increasing) and the number of red dots were determined (the average value of 3 tests was taken for both). The specific test results are shown in Table 1.

[0087] Examples 2-6 and Comparative Examples 1-6 of the present invention have relatively stable consistency in the composition of the metal foreign matter to be detected with that provided in Example 1. This is mainly achieved by thoroughly ultrasonically dispersing and uniformly stirring the pure water containing the same metal foreign matter before filtration, and by using the same batch and specification of nylon filter membrane and the same filtration parameters.

[0088] Table 1

[0089]

[0090] The test results show that:

[0091] (1) As can be seen from Examples 1 to 3, the present invention provides a colorimetric solution for the detection of iron metal foreign matter in the lithium battery production process. It utilizes the colorimetric reaction between ferric ions and thiocyanate ions to generate a blood-red complex, ferric thiocyanate, thereby achieving rapid qualitative detection of iron metal foreign matter in the lithium battery production process. The solution exhibits high sensitivity, high efficiency, and fast speed. Furthermore, the reagents in the colorimetric solution are non-toxic, harmless, and low in cost, making it particularly suitable for large-scale detection on mass production lines. This significantly improves production line detection efficiency while maintaining high detection sensitivity. Specifically, the time for the red dots to fully appear is 4-6 seconds.

[0092] (2) As can be seen from Examples 1 and 4-6, by further controlling the molar concentration of the acid solution to 0.1 mol / L-1 mol / L, the mass concentration of the oxidant to 2.7 wt%-3.3 wt%, and the molar concentration of the thiocyanate solution to 0.1 mol / L-0.3 mol / L, the present invention can achieve better detection results for ferrous metal foreign objects, with higher detection sensitivity and efficiency. In Examples 4-6, the time for the red dots to fully appear reached 5s-8s, and the number of red dots was less than that in Example 1, resulting in a relatively lower detection sensitivity (the composition of the metal foreign object to be detected has a relatively stable consistency).

[0093] (3) As can be seen from Example 1 and Comparative Examples 1-6, by further adjusting the volume fraction of the colorimetric solution to include 3-4 parts of acid, 1-2 parts of oxidant, and 3-4 parts of thiocyanate solution, the present invention can achieve better detection results for iron metal foreign objects, with higher detection sensitivity and efficiency. The time for the red dots to fully develop in Comparative Examples 1-6 is as high as 7-10 seconds, and the number of red dots is also less than that in Example 1, resulting in lower detection sensitivity (the composition of the metal foreign object to be detected has relatively stable consistency).

[0094] In summary, this invention provides a colorimetric solution for detecting iron metal foreign objects during lithium battery production. It utilizes the colorimetric reaction between ferric ions and thiocyanate ions to generate a blood-red complex, ferric thiocyanate, enabling rapid qualitative detection of iron metal foreign objects during lithium battery production. This solution offers high sensitivity, high efficiency, and fast detection speed. Furthermore, the reagents in the colorimetric solution are non-toxic, harmless, and low-cost, making it particularly suitable for high-volume testing on mass production lines. This significantly improves production line testing efficiency while maintaining high detection sensitivity.

[0095] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A colorimetric solution for detecting iron metal foreign matter during lithium battery production, characterized in that, The colorimetric solution comprises, by volume, 3-4 parts of acid, 1-2 parts of oxidant, and 3-4 parts of thiocyanate solution.

2. The colorimetric solution according to claim 1, characterized in that, The acid solution includes at least one of hydrochloric acid solution, nitric acid solution, or sulfuric acid solution.

3. The colorimetric solution according to claim 1 or 2, characterized in that, The molar concentration of the acid solution is 0.1 mol / L to 1 mol / L.

4. The colorimetric solution according to any one of claims 1-3, characterized in that, The oxidant includes hydrogen peroxide solution and / or ammonium persulfate solution.

5. The colorimetric solution according to any one of claims 1-4, characterized in that, The mass concentration of the oxidant is 2.7wt%-3.3wt%.

6. The colorimetric solution according to any one of claims 1-5, characterized in that, The thiocyanate solution includes potassium thiocyanate solution and / or ammonium thiocyanate solution.

7. The colorimetric solution according to any one of claims 1-6, characterized in that, The molar concentration of the thiocyanate solution is 0.1 mol / L to 2 mol / L, preferably 0.1 mol / L to 0.3 mol / L.

8. The colorimetric solution according to any one of claims 1-7, characterized in that, The preparation method of the colorimetric solution includes the following steps: According to the formula, the acid solution, the oxidant, and the thiocyanate solution are mixed evenly to obtain the colorimetric solution.

9. A method for detecting ferrous metal foreign objects during lithium battery production, characterized in that, The detection method includes the following steps: Metal foreign matter from the lithium battery production process is collected and filtered using a solution to obtain the metal foreign matter to be tested. An adhesive material is used to make the metallic foreign object to be detected adhere to the surface of the adhesive material; The pretreated filter membrane is impregnated with the color-developing solution according to any one of claims 1-8, and then the impregnated filter membrane is covered on the surface of the adhesive material. Red dots appear on the surface of the impregnated filter membrane, indicating the presence of iron metal foreign matter in the lithium battery production process.

10. The detection method according to claim 9, characterized in that, After filtration, the particle size of the metal foreign object to be detected is ≥1μm; Preferably, the pretreatment step includes: washing the filter membrane with an acid washing solution to obtain a pretreated filter membrane.

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