Method for detecting metal particles in battery material

Abstract

The present application provides a method for detecting metal particles in a battery material. The detection method comprises: subjecting metal particles in the battery material to a chromogenic reaction with a chromogenic agent, and identifying the metal particles on the basis of the chromogenic sites of the chromogenic reaction. By means of the detection method provided in the present application, metal particles in the battery material can be effectively identified.

Description

A method for detecting metal particles in battery materials

[0001] Cross-referencing

[0002] This application references Chinese Patent Application No. 202510360587.5, filed on March 25, 2025, entitled "A Method for Detecting Metal Particles in Battery Materials," which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of secondary battery technology, and in particular to a method for detecting metal particles in battery materials. Background Technology

[0004] In recent years, rechargeable batteries have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Metal particles present in rechargeable battery materials can affect cell performance. During battery use, metal particles may puncture the separator, causing a micro-short circuit between the positive and negative electrodes, triggering self-discharge, reducing cell capacity, and potentially leading to thermal runaway, posing serious safety risks.

[0005] Therefore, there is an urgent need to develop a method for detecting metal particles in battery materials. Summary of the Invention

[0006] To address the aforementioned issues, this application provides a method for detecting metal particles in battery materials. This method can effectively detect and identify metal particles in battery materials that are difficult to identify using conventional methods, providing a basis for the detection of metal particle properties (such as size, quantity, physicochemical properties, etc.).

[0007] The first aspect of this application provides a method for detecting metal particles in a battery material, the method comprising: using a colorimetric reagent to react with the metal particles in the battery material to produce a colorimetric reaction, and identifying the metal particles based on the colorimetric sites of the colorimetric reaction.

[0008] This detection method does not rely on the luster of metal particles, which can effectively reduce equipment costs and has the characteristics of low cost.

[0009] In any embodiment, the step of using a colorimetric agent to react with the metal particles in the battery material specifically includes: enriching the impurities, including metal particles, in the battery material on the surface of the separation medium; bringing the other opposite surface of the separation medium into contact with the colorimetric agent; the colorimetric agent penetrating into the separation medium and reacting with the metal particles to produce colorimetric sites on the separation medium.

[0010] The reverse wetting colorimetric method effectively reduces metal particle slippage and colorimetric reagent crystallization, reduces the duplication of colorimetric sites in the colorimetric reaction during the identification process and the interference of impurities, thereby improving the detection rate.

[0011] In any embodiment, the separation medium includes one or more of filter membranes, permeable membranes, and filter paper.

[0012] In any embodiment, the pore size of the separation medium is 0.45μm-5μm, and can be selected as 3μm-5μm.

[0013] When the pore size of the separation medium is within the aforementioned range, the chromogenic agent can rapidly and uniformly diffuse laterally and longitudinally, and wet from bottom to top in the thickness direction, reacting quickly with metal particles to form chromogenic sites, which is beneficial for the detection and identification of metal particles. Simultaneously, the uniform lateral diffusion of the chromogenic agent does not affect the particle position, reducing the duplication of chromogenic sites caused by particle slippage and improving the detection rate.

[0014] In any embodiment, the material of the separation medium includes one or more of polyolefin materials, polyester materials, fluorinated polymer materials, and polyamide materials.

[0015] In any embodiment, the polyolefin material includes one or more of polyethylene, polypropylene, and polyvinyl chloride, and / or

[0016] The polyester material includes one or more of polyethylene terephthalate and polycarbonate, and / or

[0017] The fluorinated polymer material includes one or more of polytetrafluoroethylene and polyvinylidene fluoride, and / or

[0018] The polyamide materials include one or more of polyamide and polyetheretherketone.

[0019] The separation medium described above exhibits strong chemical stability, preventing decomposition or swelling of the material upon contact with the chromogenic agent, thus maintaining its smoothness. This smoothness and chemical stability ensure a uniform and clear distribution of chromogenic sites in the reaction, reducing background interference, facilitating the identification of metal particles, and improving the detection rate.

[0020] In any embodiment, based on the mass of the battery material, the amount of the colorimetric agent is 150 μL / kg-250 μL / kg, optionally 200 μL / kg-250 μL / kg.

[0021] Based on the mass of the battery material, using a colorimetric reagent within the above-mentioned range is beneficial for improving the colorimetric reaction effect and increasing the detection rate.

[0022] In any embodiment, based on the area of ​​the separation medium, the amount of the colorimetric reagent is 7 μL / cm². 2 -15μL / cm 2 9μL / cm can be selected. 2 -15μL / cm 2 .

[0023] Based on the area of ​​the separation medium, the amount of colorimetric reagent used within the above range is beneficial for sufficient and uniform color development, thereby improving the detection rate.

[0024] In any embodiment, the metal particles include one or more of copper particles and zinc particles.

[0025] In any embodiment, the metal particles include copper particles, and the colorimetric agent includes a colorimetric component, which includes one or more of dicyclohexanone oxaloyl dihydrazone, 2,9-dimethyl-1,10-phenanthroline, 1,10-phenanthroline, and sodium diethyldithiocarbamate.

[0026] The aforementioned chromogenic components can react with copper particles to generate a chromogenic product of a specific color. This facilitates the identification of metal particles and improves the detection rate.

[0027] In any embodiment, the concentration of the colorimetric component in the colorimetric reagent is 0.25 mg / mL to 2 mg / mL.

[0028] In any embodiment, the concentration of the colorimetric component in the colorimetric reagent is 0.25 mg / mL to 1 mg / mL.

[0029] When the concentration of the colorimetric component in the colorimetric reagent is within the above-mentioned range, the colorimetric reaction can be uniform and sufficient, reducing background interference and improving the detection rate.

[0030] In any embodiment, the pH of the colorimetric reagent is 4-9, optionally 8-9.

[0031] When the pH of the colorimetric reagent is within the above range, the colorimetric reagent can form a stable colorimetric product with a specific color with copper particles, and the colorimetric reaction is rapid, uniform and sufficient, which is beneficial to improving the colorimetric effect and increasing the detection rate.

[0032] In any embodiment, the colorimetric agent further includes a buffer component, which includes one or more of the following: acetate solution, acetic acid solution, citrate solution, ammonium acetate-sodium acetate solution, and ammonia-ammonium chloride solution.

[0033] Buffer components help maintain the pH stability of the reaction system, prevent interference from side reactions, enhance the stability of the colorimetric products, and improve the detection rate.

[0034] In any embodiment, the metal particles include zinc particles, and the color developer includes one or more of 2-carboxy-2'-hydro-5'-sulfobenzoic acid monosodium salt and [o-[2-(2-hydroxy-5-sulfobenzoazo)benzyl]hydrazinobenzoic acid].

[0035] In any embodiment, the concentration of the colorimetric reagent is 1 mg / mL to 3 mg / mL.

[0036] In any implementation, the settling time is 2h-24h, and can be selected as 2h-4h.

[0037] Allowing the colorimetric reaction to proceed within the above-mentioned time range is beneficial for ensuring a complete colorimetric reaction, stabilizing the colorimetric product, improving the colorimetric effect of the colorimetric sites, and increasing the detection rate.

[0038] In any embodiment, identifying the metal particles includes: using a microscope to identify the metal particles at the chromogenic sites, and detecting the size and number of the metal particles. Optionally, the microscope may include a CCD microscope or a cleanliness analysis microscope.

[0039] In any embodiment, the battery material includes one or more of the following: positive electrode active material, negative electrode active material, binder, electrolyte, and separator.

[0040] In any implementation, the detection method has a detection rate of 30% or greater.

[0041] In any embodiment, for metal particles with a diameter of 5μm-15μm, the detection rate of the detection method is greater than or equal to 30%, and can be optionally 50%; for metal particles with a diameter of 15μm or greater, the detection rate of the detection method is 99%-100%. The detection method provided in this application has a wide range of applications and a high detection rate. Attached Figure Description

[0042] Figure 1 is a morphology diagram of copper particles at the colorimetric sites of the colorimetric reaction observed under a microscope in Example 1 of this application. Detailed Implementation

[0043] The embodiments of the secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0044] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0046] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0047] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0048] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0049] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] During battery use, metal particles may puncture the separator, causing a micro-short circuit between the positive and negative electrodes, triggering self-discharge, reducing cell capacity, and potentially even leading to thermal runaway, posing serious safety risks. The detection of conventional magnetic metal particles (such as stainless steel and iron particles) typically employs a cleanliness inspection microscope, utilizing the difference in metallic luster exhibited by these particles under polarized light at different angles compared to other particles. However, for metal particles such as copper, zinc, and their alloys, due to their insufficient luster, they cannot be effectively detected directly using a cleanliness inspection microscope and require a cleanliness scanning electron microscope. This method suffers from high equipment maintenance costs and high testing costs.

[0051] Based on this, this application proposes a method for detecting metal particles in battery materials. The method includes: using a colorimetric reagent to react with the metal particles in the battery material to produce a colorimetric reaction, and identifying the metal particles based on the colorimetric sites of the colorimetric reaction.

[0052] The method proposed in this application can effectively detect and identify metal particles in battery materials that are difficult to identify using conventional methods, providing a basis for the detection of metal particle properties (such as size, quantity, physicochemical properties, etc.).

[0053] This method is not bound by any theoretical constraints, likely because metal particles can react with a colorimetric reagent to generate a colorimetric product with a specific color. The identification of metal particles is based on the colorimetric sites of this reaction. This detection method does not rely on the luster of the metal particles, effectively reducing equipment costs and offering the advantage of low cost.

[0054] It can be understood that battery materials refer to the materials used in the preparation of batteries, including but not limited to positive electrode active materials, negative electrode active materials, binders, electrolytes, separators, and other materials or raw materials used in their preparation process.

[0055] In some embodiments, the battery material includes a positive electrode active material, which includes one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary materials.

[0056] In the preparation process of positive electrode active materials, metal particles are inevitably introduced. These metal particles may come from impurities in raw materials (such as lithium sources, iron sources, cobalt sources, etc.) or from wear and tear on production equipment (such as ball mills and mixing equipment).

[0057] To increase the accuracy of metal particle detection, the battery material needs to be sampled in a certain quantity. Optionally, the sample quantity of the battery material is 10g-2000g. Examples include any value from 10g, 50g, 100g, 500g, 1000g, 1500g, and 2000g, or any value within a range formed by any two of the above values. The sample quantity of the battery material can further be selected as 100g-2000g.

[0058] In some embodiments, the step of using a colorimetric agent to react with the metal particles in the battery material specifically includes: enriching impurities, including metal particles, in the battery material on the surface of a separation medium; bringing the other opposing surface of the separation medium into contact with the colorimetric agent; allowing the colorimetric agent to penetrate into the separation medium and react with the metal particles to produce colorimetric sites on the separation medium.

[0059] It is understood that impurities including metal particles in battery materials can be enriched using any method known in the art. In some embodiments, methods for enriching impurities including metal particles in battery materials include one or more of physical separation, chemical separation, and electrochemical separation. In some embodiments, physical separation methods include one or more of mechanical sorting, sieving, flotation, magnetic separation, and gravity separation. Physical separation methods enrich based on differences in the size, magnetic properties, and density of metal particles. In some embodiments, chemical separation methods include at least one of chemical precipitation and solvent extraction. Chemical separation methods selectively dissolve particles and enrich the target particles. In some embodiments, electrochemical separation methods effectively separate metal particles through potential differences.

[0060] Compared to forward spraying or direct wetting of the colorimetric reagent, the reverse wetting method, which involves contacting the other surface of the separation medium containing metal particles with the colorimetric reagent, and then allowing the colorimetric reagent to penetrate into the separation medium and react with the metal particles to produce a colorimetric reaction, can effectively reduce the slippage of metal particles and crystallization of the colorimetric reagent during the detection process, reduce the misalignment of colorimetric sites and interference from impurities during the identification process, and improve the detection rate.

[0061] In some embodiments, methods for enriching impurities including metal particles in battery materials include physical separation and chemical separation. For example, a wet sieve separator can be used to sieve large quantities of battery materials, utilizing a dual-solvent system of ethanol solution and water to allow the sieved material to settle in layers, achieving effective physical separation of battery materials and additives from metal impurities, thereby obtaining impurities including metal particles.

[0062] In some embodiments, the separation medium includes, but is not limited to, devices with a certain pore size such as filter membranes, permeable membranes, and filter paper, through which liquid can pass and permeate. In some embodiments, the separation medium includes filter membranes.

[0063] In some embodiments, the separation medium is made of one or more of polyolefin materials, polyester materials, fluorinated polymer materials, and polyamide materials. In some embodiments, the polyolefin material includes one or more of polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC). In some embodiments, the polyester material includes one or more of polyethylene terephthalate (PET) and polycarbonate (PC). In some embodiments, the fluorinated polymer material includes one or more of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF). In some embodiments, the polyamide material includes one or more of polyamide (nylon) and polyetheretherketone (PEEK).

[0064] The separation medium described above exhibits strong chemical stability, preventing decomposition or swelling of the material upon contact with the chromogenic agent, thus maintaining its smoothness. This smoothness and chemical stability ensure a uniform and clear distribution of chromogenic sites in the reaction, reducing background interference, facilitating the identification of metal particles, and improving the detection rate.

[0065] In some embodiments, the separation medium is made of polyamide (nylon). Nylon has good mechanical strength and solvent resistance, which allows the colorimetric reagent solution to quickly and uniformly impregnate the particles, resulting in a clear distribution of colorimetric sites, facilitating subsequent identification of metal particles and improving the detection rate.

[0066] In some embodiments, the pore size of the separation medium is 0.45 μm-5 μm.

[0067] In some embodiments, the pore size of the separation medium is 0.45μm-3μm, 0.45μm-4μm, 0.45μm-5μm, 3μm-4μm, or 3μm-5μm. In some embodiments, the pore size of the separation medium is any value selected from 0.45μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, or 5μm, or any value within the range formed by any pair of the above values.

[0068] In this application, the term "aperture" refers to the diameter of a pore in the separation medium.

[0069] The pore size of the separation medium can be tested using any method known in the art. For example, the diameter of the pores can be directly observed and measured using an electron microscope.

[0070] When the pore size of the separation medium is within the aforementioned range, the chromogenic agent can rapidly and uniformly diffuse in both the lateral and longitudinal directions of the separation medium, and wet from bottom to top in the thickness direction. It quickly contacts and reacts with the metal particles, forming chromogenic sites for the reaction, which is beneficial for detecting and identifying metal particles. Furthermore, the uniform diffusion of the chromogenic agent in the lateral direction of the separation medium does not affect the particle position, helping to reduce the duplication of chromogenic sites caused by particle slippage and improving the detection rate.

[0071] In some embodiments, based on the mass of the battery material, the amount of colorimetric agent used is 150 μL / kg-250 μL / kg, optionally 200 μL / kg-250 μL / kg.

[0072] In some embodiments, based on the mass of the battery material, the amount of colorimetric agent used is 150 μL / kg-220 μL / kg, 150 μL / kg-200 μL / kg, or 150 μL / kg-180 μL / kg. In some embodiments, based on the mass of the battery material, the amount of colorimetric agent used is any value selected from 150 μL / kg, 170 μL / kg, 190 μL / kg, 210 μL / kg, 230 μL / kg, or 250 μL / kg, or any value within a range formed by any pair of the above values.

[0073] Excessive use of the colorimetric reagent can lead to excessive lateral wettability of the separation medium, causing metal particle slippage, prolonging subsequent drying time, and potentially affecting metal particle identification due to reagent crystallization. Insufficient use of the colorimetric reagent results in insufficient wettability, incomplete colorimetric reaction, and poor colorimetric effect. Therefore, using the colorimetric reagent within the above-mentioned range is beneficial for improving the colorimetric effect and increasing the detection rate.

[0074] In some embodiments, the amount of colorimetric reagent used is 7 μL / cm², based on the area of ​​the separation medium. 2 -15μL / cm 2 .

[0075] In some embodiments, based on the area of ​​the separation medium, the amount of the colorimetric reagent is 9 μL / cm². 2 -13μL / cm 2 9μL / cm 2 -15μL / cm 2 In some embodiments, the amount of colorimetric reagent used is 7 μL / cm², based on the area of ​​the separation medium. 2 8μL / cm 2 9μL / cm 2 10μL / cm 2 11μL / cm 2 12μL / cm2 13μL / cm 2 14μL / cm 2 Or 15 μL / cm 2 Any value in the range or any value within the range formed by any pair of the above values.

[0076] In this application, the term "area of ​​the separation medium" refers to the area of ​​a surface of the separation medium in contact with the colorimetric agent.

[0077] In this application, based on the area of ​​the separation medium, the amount of colorimetric agent used is calculated as follows: total volume of colorimetric agent required to wet the separation medium / area of ​​the separation medium.

[0078] Based on the area of ​​the separation medium, the amount of colorimetric reagent used within the above range is beneficial to ensure that the separation medium is completely wetted, so that all metal particles included in the separation medium can come into contact with the colorimetric reagent as much as possible, resulting in sufficient and uniform color development and improving the detection rate.

[0079] In some embodiments, the metal particles include one or more of copper particles and zinc particles.

[0080] In some embodiments, the metal particles include copper particles, and the colorimetric agent includes a colorimetric component, which includes one or more of dicyclohexanone oxaloyl dihydrazone, 2,9-dimethyl-1,10-phenanthroline, 1,10-phenanthroline, and sodium diethyldithiocarbamate.

[0081] In this application, the term "color-developing component" refers to the component in the color-developing agent that can react with metal particles to generate a color-developing product.

[0082] In some embodiments, the metal particles include copper particles, and the colorimetric component includes dicyclohexanone oxaloyl dihydrazone.

[0083] The surface of the metallic copper particles in the battery material has an oxide layer, and the copper ions (Cu) in the oxide layer... 2+ It reacts with the chromogenic component to produce a chromogenic product with a specific color, forming chromogenic sites on the surface of the separation medium. As an example, dicyclohexanone oxalyl dihydrazone reacts with divalent copper to form a blue complex Cu(BCO)2.

[0084] In some embodiments, the concentration of the colorimetric component in the colorimetric reagent is 0.25 mg / mL to 2 mg / mL.

[0085] In some embodiments, the concentration of the chromogenic component in the chromogenic reagent is 0.25 mg / mL-1.5 mg / mL or 0.25 mg / mL-1 mg / mL. In some embodiments, the concentration of the chromogenic component in the chromogenic reagent is any value selected from 0.25 mg / mL, 0.5 mg / mL, 0.7 mg / mL, 0.9 mg / mL, 1.1 mg / mL, 1.3 mg / mL, 1.5 mg / mL, or 2 mg / mL, or any value within the range formed by any pair of the above values.

[0086] Excessive concentration of the chromogenic component in the developer can increase background interference, cause uneven color development, and even crystallization, thus reducing the detection rate. Conversely, insufficient concentration of the chromogenic component will result in an incomplete color development reaction, affecting the color development effect and potentially leading to missed detection of metal particles, further reducing the detection rate. Maintaining the concentration of the chromogenic component within the aforementioned range ensures a uniform and sufficient color development reaction, reduces background interference on the color development sites, and improves the detection rate.

[0087] In some embodiments, the colorimetric reagent has a pH of 4-9.

[0088] In some embodiments, the pH of the colorimetric reagent is 4-8, 4-7, 4-6, 4-5, 5-8, 5-7, 5-6, 6-7, 6-8, 6-9, 7-8, 7-9, 4-7, or 8-9. In some embodiments, the pH of the colorimetric reagent is any value among 4, 5, 6, 7, 8, or 9, or any value within a range formed by any pair of the above values.

[0089] If the pH is too low (strongly acidic conditions), the coordination ability of the chromogenic reagent will be weakened, leading to incomplete colorimetric reaction and poor colorimetric effect. If the pH is too high (alkaline conditions), the generated chromogenic product is easily decomposed, causing the color to fade. When the pH of the chromogenic reagent is within the above-mentioned range, the chromogenic reagent can form a stable chromogenic product with a specific color with the metal particles, and the colorimetric reaction is rapid, uniform, and complete, which is beneficial to improving the colorimetric effect and increasing the detection rate.

[0090] In some embodiments, the colorimetric agent further includes a buffer component, which includes one or more of the following: acetate solution, acetic acid solution, citrate solution, ammonium acetate-sodium acetate solution, and ammonia-ammonium chloride solution.

[0091] In this application, the term "buffer component" refers to a chemical substance capable of maintaining a relatively stable pH value of a solution, typically composed of a weak acid and its conjugate base or a weak base and its conjugate acid. Its function is to resist significant changes in pH value by neutralizing small amounts of added acid or base, thereby maintaining the acid-base balance of the solution.

[0092] The buffer component helps maintain the pH stability of the reaction system, optimizes the sensitivity and selectivity of the colorimetric reaction, prevents interference from side reactions, and enhances the stability of the colorimetric product, thereby making the colorimetric sites of the colorimetric reaction uniform and clear, and improving the detection rate.

[0093] In some embodiments, the metal particles include copper particles, the colorimetric agent includes dicyclohexanone oxaloyl dihydrazone, and the buffer component includes an ammonium acetate-sodium acetate solution.

[0094] In some embodiments, the volume ratio of the colorimetric component to the buffer component is (0.7-1.5):1.

[0095] In some embodiments, the volume ratio of the colorimetric component to the buffer component is 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, or it can be any ratio within the range of (0.7-1.5):1.

[0096] When the volume ratio of the chromogenic component to the buffer component is within the above range, it is beneficial to maintain the pH stability of the reaction system and enhance the stability of the chromogenic product, thereby making the chromogenic sites of the chromogenic reaction uniform and clear, and improving the detection rate.

[0097] In some embodiments, the buffer component is prepared on the day of testing and stored in a way that protects it from light.

[0098] In some embodiments, the metal particles include zinc particles, and the colorimetric agent includes one or more of 2-carboxy-2'-hydro-5'-sulfobenzoic acid monosodium salt and [o-[2-(2-hydroxy-5-sulfobenzoazo)benzylidene]hydrazinobenzoic acid].

[0099] The zinc particles in the battery material have an oxide layer on their surface, and the zinc ions (Zn) in the oxide layer... 2+ It reacts with a colorimetric reagent to produce a colorimetric product with a specific color, forming colorimetric sites on the surface of the separation medium. As an example, monosodium 2-carboxy-2'-hydro-5,-sulfobenzoate reacts with divalent zinc to form a blue complex.

[0100] In some embodiments, the concentration of the colorimetric reagent is 1 mg / mL to 3 mg / mL. In some embodiments, the concentration of the colorimetric reagent is 1 mg / mL to 1.5 mg / mL, 1 mg / mL to 2 mg / mL, 1 mg / mL to 2.5 mg / mL, 2 mg / mL to 3 mg / mL, or 2.5 mg / mL to 3 mg / mL. In some embodiments, the concentration of the colorimetric reagent is any value selected from 1 mg / mL, 1.2 mg / mL, 1.5 mg / mL, 1.7 mg / mL, 1.9 mg / mL, 2 mg / mL, 2.2 mg / mL, 2.5 mg / mL, 2.7 mg / mL, 2.9 mg / mL, or 3 mg / mL, or any value within a range formed by any pair of the above values.

[0101] In some implementations, the settling time is 2h-24h.

[0102] In some embodiments, the settling time is 2h-20h, 2h-18h, 2h-16h, 2h-12h, 2h-10h, 2h-8h, 2h-6h, or 2h-4h. In some embodiments, the settling time is any value among 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h, or any value within the range formed by any pair of the above values.

[0103] In this application, the term "standing time" refers to the reaction time during which the color developer permeates into the separation medium and reacts with the metal particles to produce a color development reaction.

[0104] Excessive standing time will cause the colorimetric reagent to volatilize or decompose, resulting in poor color development at the colorimetric sites. Conversely, insufficient standing time will lead to incomplete reaction between the colorimetric reagent and the metal particles, also resulting in poor color development at the colorimetric sites. Standing time within the above range is beneficial for a complete colorimetric reaction, stable colorimetric products, improved color development at the colorimetric sites, and increased detection rate.

[0105] In some embodiments, a drying step is also included in the process of allowing the colorimetric agent to permeate into the separation medium and react with the metal particles.

[0106] The drying method used in this application can be any drying method known in the art. For example, oven drying, vacuum drying, and natural air drying.

[0107] The drying step helps to shorten the detection time, improve the color development effect, and increase the detection rate and detection efficiency.

[0108] In some embodiments, the drying temperature is 20°C-60°C.

[0109] In some embodiments, the drying temperature is 30℃-60℃, 30℃-50℃, or 30℃-45℃. In some embodiments, the drying temperature is any value among 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, or 60℃, or any value within a range formed by any pair of the above values. Excessively high drying temperatures may cause decomposition of the colorimetric reagent or oxidation of metal particles, affecting the colorimetric effect; excessively low drying temperatures may prolong the drying time, leading to uneven color development or enhanced background signal; while suitable temperatures can improve the stability of the colorimetric reagent and metal particles, making the colorimetric reaction rapid, uniform, and complete, thus improving the detection rate.

[0110] In some embodiments, identifying the metal particles includes: using a microscope to identify the metal particles at the chromogenic sites, and detecting the size and number of the metal particles.

[0111] In some embodiments, the microscope includes any microscope known in the art for observing particle size or morphology. In some embodiments, the microscope includes a CCD microscope or a cleanliness analysis microscope. In some embodiments, the microscope includes a CCD microscope. Observation using a charge-coupled device (CCD) microscope can quickly and accurately determine the number and size of chromogenic metal particles.

[0112] In some embodiments, for metal particles with a diameter of 5 μm to 15 μm, the zoom ratio of the microscope is 4 to 6, and the scale bar of the microscope is 1 μm / Fxl to 1.5 μm / Fxl.

[0113] In this application, the zoom ratio of a microscope refers to the percentage change in the combined magnification of the objective lens and eyepiece when the magnification of the microscope is adjusted.

[0114] In this application, Fxl refers to a unit of length in an image, typically representing a pixel in the image. μm / Fxl represents the actual length (in micrometers) corresponding to 1 Fxl in the image.

[0115] In some embodiments, for metal particles with a diameter of 5 μm to 15 μm, the zoom ratio of the microscope is 4, 5, or 6, or any value within the range of 4 to 6. In some embodiments, the scale bar of the microscope is 1 μm / Fxl, 1.2 μm / Fxl, or 1.5 μm / Fxl, or any value within the range of 1 μm / Fxl to 1.5 μm / Fxl.

[0116] In some embodiments, for metal particles with a diameter greater than or equal to 15 μm, the zoom ratio of the microscope is 1-2.5, and the scale bar of the microscope is 2.5 μm / Fxl-5 μm / Fxl.

[0117] In some embodiments, for metal particles with a diameter greater than or equal to 15 μm, the magnification ratio of the microscope is 1, 1.5, 2, or 2.5, or any value within the range of 1-2.5. In some embodiments, the scale bar of the microscope is 2.5 μm / Fxl, 3 μm / Fxl, 3.5 μm / Fxl, 4 μm / Fxl, 4.5 μm / Fxl, or 5 μm / Fxl, or any value within the range of 2.5 μm / Fxl-5 μm / Fxl.

[0118] The scale of different particle sizes can be adjusted within the above range as needed until the metal particle boundaries are clear and the morphology is distinct, which is beneficial to improving the detection rate.

[0119] In some implementations, any known image recognition software in the art can also be used to automatically identify and analyze the colorimetric sites.

[0120] In some implementations, the detection method has a detection rate of 30% or greater.

[0121] In some embodiments, the detection method has a detection rate of 40% or higher, 50% or higher, 60% or higher, 70% or higher, 80% or higher, or 90% or higher.

[0122] In some embodiments, the detection method has a detection rate of ≥30% for metal particles with a particle size of 5μm-15μm. In some embodiments, the detection method has a detection rate of ≥40%, ≥50%, ≥60%, or ≥80% for metal particles with a particle size of 5μm-15μm.

[0123] In some embodiments, the detection rate of the detection method for metal particles with a particle size greater than or equal to 15 μm is 99%-100%. In some embodiments, the detection rate of the detection method for metal particles with a particle size greater than or equal to 15 μm is 99.2%-100%, 99.5%-100%, 99.7%-100%, or 99.9%-100%. In some embodiments, the detection rate of the detection method for metal particles with a particle size greater than or equal to 15 μm is any value selected from 99%, 99.25%, 99.5%, 99.75%, 99.95%, or 100%, or any value within the range of any pair of the above values. The detection method for metal particles in battery materials provided in this application has a high detection rate.

[0124] Example

[0125] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0126] I. Implementation Methods

[0127] 1. Positive spiking verification

[0128] The detection rate of the method was validated in positive electrode active material powders with known metal particle quantity and size.

[0129] Example 1

[0130] (1) Enriching impurities, including metal particles, in the separation medium

[0131] Weigh 1 kg of nickel-cobalt-manganese ternary cathode active material powder, add 10 L of pure water, and stir thoroughly until homogeneous. Sieve the material using a wet sieve separator, repeating the process until all material is sieved. Rinse the remaining powder and metal particles on the sieve with water into a beaker, vacuum filter to the surface of the filter membrane, and rinse and dry. Add the dried sieve residue to 50 mL of a 65% (v / v) ethanol aqueous solution, sonicate and stir until homogeneous. Transfer the sieve mixture to a dual-solvent system consisting of a 65% (v / v) ethanol aqueous solution and water for sedimentation. Collect the metal particles at the bottom of the aqueous solution using vacuum filtration onto a polyamide-nylon filter membrane (Shanghai Xingya, 5 μm pore size). Add copper particles according to the following specifications: 6 copper particles of 5 μm-15 μm, 2 copper particles of 15 μm-25 μm, 1 copper particle of 25 μm-50 μm, and 1 copper particle of 50 μm-100 μm. Mix thoroughly and then dry. (Note: The spiked particles have regular shapes, and their morphological differences can be used to identify them as spiked particles.)

[0132] (2) The color developer reacts with the metal particles through backwetting.

[0133] A 2 mg / mL dicyclohexanone oxaloyl dihydrazone ethanol solution was mixed with a buffer (0.2 g / mL ammonium acetate + 0.5 g / mL sodium acetate) at a 1:1 volume ratio to obtain a colorimetric reagent. 200 μL of the reagent was evenly added to a 50 mm thick acrylic slide. Using ceramic tweezers, the nylon filter membrane (50 mm in diameter) was gently placed onto the slide containing the reagent. After observing that the membrane was completely wetted by the reagent, it was allowed to stand at room temperature for 2 hours.

[0134] (3) Identifying metal particles

[0135] After the colorimetric reaction is complete, place the slide under a cleanliness analysis light microscope, count the size and number of the colorimetric particles, and calculate the detection rate. The formula for calculating the detection rate is: number of extracted metal particles / number of spiked particles.

[0136] Example 2-11

[0137] Examples 2-11 are similar to the method in Example 1, except that the parameters in the detection process are adjusted, as shown in Table 1.

[0138] Examples 12-14

[0139] Examples 12-14 are similar to the method in Example 1, except that the spiked particles in step (1) are zinc particles and the amount of spiked particles are adjusted, and the colorimetric agent in step (2) is 2-carboxy-2'-hydro-5,-sulfobenzoic acid monosodium salt. Specific parameters are shown in Table 2.

[0140] Examples 15-16

[0141] Example 15 is similar to the steps of Examples 1-11, except that step (2) is adjusted as follows: use a spray bottle containing a color developer to press and spray the color developer on the filter membrane until the filter membrane is completely wetted by the color developer, and then let it stand at room temperature for 2 hours. Specific parameters are shown in Table 1.

[0142] Example 16 is similar to Example 15 in terms of steps, except that the spiked particles in step (1) are zinc particles and the color reagent in step (2) is 2-carboxy-2'-hydro-5,-sulfobenzoic acid monosodium salt. Specific parameters are shown in Table 2.

[0143] Comparative Example 1

[0144] The process is consistent with step (1) of Example 1, except that step (2) is deleted and the cleanliness scanning electron microscope is used directly to detect the type and number of particles.

[0145] Table 1 Preparation parameters of Examples 1-11 and Example 15

[0146] Table 2 Preparation parameters for Examples 12-14 and Example 16

[0147] II. Test Results of Each Embodiment and Comparative Example

[0148] Compared to Comparative Example 1, which uses a cleanliness scanning electron microscope to detect particles, the colorimetric method used in this embodiment can save on instrument costs and greatly reduce detection costs.

[0149] Table 3 Test Results of Examples

[0150] As can be seen from the data in the embodiments, the detection method provided in this application can effectively detect and identify metal particles in battery materials.

[0151] As can be seen from the comparison of Examples 15 and 16 with other examples, under the same test conditions, the detection method of reverse wetting in the present application is more efficient in detecting metal particles than the detection method of forward spraying of colorimetric agent under the same conditions.

[0152] As shown in Examples 1 and 4, the pore size of the separation medium is 0.45 μm-5 μm, which can effectively detect and identify metal particles in battery materials. This is likely because the pore size of the separation medium is within this range, allowing the colorimetric agent to diffuse rapidly and uniformly in the lateral and longitudinal directions of the separation medium, and to wet from bottom to top in the thickness direction. This allows for rapid contact and reaction with the metal particles, forming colorimetric sites that facilitate the detection and identification of metal particles, thus improving the detection rate.

[0153] As shown in Examples 5-6, based on the mass of the battery material, the amount of colorimetric reagent used is 150 μL / kg-250 μL / kg, which can effectively detect and identify metal particles in the battery material. This may be because the amount of colorimetric reagent within the above range is beneficial to improving the colorimetric reaction effect and increasing the detection rate.

[0154] As shown in Examples 1 and 7, the settling time of 2-24 hours can effectively detect and identify metal particles in battery materials. This is likely because a settling time within this range allows for a complete colorimetric reaction, stable colorimetric products, improved colorimetric effects at the colorimetric sites, and increased detection rate.

[0155] As shown in Examples 1 and 8-11, the pH of the colorimetric reagent is 8-9, which can effectively detect and identify metal particles in battery materials. This is likely because when the pH of the colorimetric reagent is within the above range, it can form a stable colorimetric product with a specific color with copper particles. Furthermore, the colorimetric reaction is rapid, uniform, and thorough, which helps to improve the colorimetric effect and increase the detection rate.

[0156] As can be seen from Examples 12-14, the detection method provided in this application is applicable to the detection of different types of metal particles, and the detection rate of the detection method is greater than or equal to 30%.

[0157] Table 4 Test results of Examples 1-3 and 12-14

[0158] As shown in Table 4, the detection method provided in this application has a detection rate of 50% or higher for metal particles with a particle size of 5μm-15μm, and a detection rate of 99%-100% for metal particles with a particle size of 15μm or higher.

[0159] Figure 1 illustrates, by way of example, the morphology of copper particles at the colorimetric sites of the colorimetric reaction observed under a microscope in Embodiment 1 of this application.

[0160] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method of detecting metal particles in a battery material, wherein, The detection method includes: A colorimetric reaction is initiated between a colorimetric agent and the metal particles in the battery material; The metal particles are identified based on the colorimetric sites of the colorimetric reaction.

2. The detection method according to claim 1, wherein, The specific steps of using a colorimetric agent to react with the metal particles in the battery material to produce a colorimetric reaction include: Impurities, including metal particles, in the battery material are enriched on the surface of the separation medium; This allows the other opposing surface of the separation medium to come into contact with the colorimetric agent; The colorimetric agent permeates into the separation medium and reacts with the metal particles to produce colorimetric sites on the separation medium.

3. The detection method according to claim 1 or 2, wherein, The separation medium includes one or more of filter membranes, permeable membranes, and filter paper.

4. The detection method according to any one of claims 1 to 3, wherein, The separation medium includes at least one of the following conditions: (1) The pore size of the separation medium is 0.45μm-5μm, and can be selected as 3μm-5μm; (2) The material of the separation medium includes one or more of polyolefin materials, polyester materials, fluorinated polymer materials and polyamide materials.

5. The detection method according to claim 4, wherein, The polyolefin materials include one or more of polyethylene, polypropylene, and polyvinyl chloride, and / or The polyester material includes one or more of polyethylene terephthalate and polycarbonate, and / or The fluorinated polymer material includes one or more of polytetrafluoroethylene and polyvinylidene fluoride, and / or The polyamide materials include one or more of polyamide and polyetheretherketone.

6. The detection method according to any one of claims 1 to 5, wherein, The colorimetric agent satisfies at least one of the following conditions: (1) Based on the mass of the battery material, the amount of the colorimetric agent is 150μL / kg-250μL / kg, and can be selected as 200μL / kg-250μL / kg; (2) Based on the area of ​​the separation medium, the amount of the colorimetric reagent used is 7 μL / cm². 2 -15μL / cm 2 9μL / cm can be selected. 2 -15μL / cm 2 .

7. The assay method according to any one of claims 1 to 6, wherein, The metal particles include one or more of copper particles and zinc particles.

8. The detection method according to any one of claims 1 to 7, wherein, The metal particles include copper particles, and the colorimetric agent includes a colorimetric component, which includes one or more of dicyclohexanone oxaloyl dihydrazone, 2,9-dimethyl-1,10-phenanthroline, 1,10-phenanthroline, and sodium diethyldithiocarbamate.

9. The detection method according to claim 8, wherein, The concentration of the colorimetric component in the colorimetric reagent is 0.25 mg / mL to 2 mg / mL.

10. The detection method according to claim 8 or 9, wherein, The concentration of the colorimetric component in the colorimetric reagent is 0.25 mg / mL to 1 mg / mL.

11. The detection method according to any one of claims 8 to 10, wherein, The pH of the colorimetric reagent is 4-9, and can be selected as 8-9.

12. The detection method according to any one of claims 8 to 11, wherein, The colorimetric agent also includes a buffer component, which includes one or more of the following: acetate solution, acetic acid solution, citrate solution, ammonium acetate-sodium acetate solution, and ammonia-ammonium chloride solution.

13. The assay method according to any one of claims 1 to 7, wherein, The metal particles include zinc particles, and the colorimetric agent includes one or more of 2-carboxy-2'-hydro-5'-sulfobenzoic acid monosodium salt and [o-[2-(2-hydroxy-5-sulfobenzoazo)benzylidene]hydrazinobenzoic acid].

14. The detection method according to claim 13, wherein, The concentration of the colorimetric reagent is 1 mg / mL to 3 mg / mL.

15. The assay method according to any one of claims 1 to 14, wherein, The settling time is 2h-24h, and can be selected as 2h-4h.

16. The assay method according to any one of claims 1 to 15, wherein, The identification of the metal particles includes: using a microscope to identify the metal particles at the chromogenic sites, and detecting the size and number of the metal particles. Optionally, the microscope may include a CCD microscope or a cleanliness analysis microscope.

17. The assay method according to any one of claims 1 to 16, wherein, The battery materials include one or more of the following: positive electrode active material, negative electrode active material, binder, electrolyte, and separator.

18. The assay method according to any one of claims 1 to 17, wherein, The detection rate of the detection method is greater than or equal to 30%.

19. The assay method according to any one of claims 1 to 18, wherein, For metal particles with a diameter of 5μm-15μm, the detection rate of the detection method is greater than or equal to 30%, and can be selected as 50%. For metal particles with a diameter of 15 μm or greater, the detection rate of the method is 99%-100%.

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