CN118603703A - Method for detecting the content of metal elemental foreign particles in positive electrode active materials - Google Patents

Abstract

The application discloses a method for detecting the content of metal simple substance foreign particles in a positive electrode active material, which comprises the following steps: uniformly mixing the positive electrode active material to be detected with a first solvent to obtain a first mixed solution; sieving the obtained first mixed solution, and collecting first solid components remained on a sieve after sieving; mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant and a corrosion inhibitor solution, and then reacting to obtain a second mixed solution; separating the obtained second mixed solution to obtain a second solid component comprising metal simple substance foreign particles; and counting the number of the metal simple substance foreign particles after the obtained second solid component is scanned by using scanning equipment, and calculating the mass of the metal simple substance foreign particles and the content of the metal simple substance foreign particles in the positive electrode active material according to the number of the metal simple substance foreign particles.

Description

Method for detecting the content of metal foreign particles in positive electrode active materials

Technical Field

The present application relates to a method for detecting the content of metal elemental foreign particles in a positive electrode active material.

Background Art

The positive electrode active materials used in batteries usually come into contact with metal parts during the production process. Due to reasons such as component wear, the prepared positive electrode active materials may contain a small amount of foreign particles such as metal elements and metal oxides. Some metal element particles will gradually dissolve metal ions during the use of the battery. After the metal ions migrate from the positive electrode to the negative electrode, they will be reduced to form metal elements on the surface of the negative electrode, and may continue to grow to form dendrites, thereby increasing the self-discharge of the battery, causing the battery capacity to decay, and affecting the service life of the battery. In severe cases, the dendrites will also pierce the isolation membrane to cause thermal runaway of the battery, reducing the reliability of the battery. Therefore, strict quantitative detection and specification control of metal element foreign particles in the positive electrode active materials are required. The above statements are only used to provide background technical information related to this application and do not necessarily constitute prior art.

Summary of the invention

The present application provides a method for detecting the content of metal single substance foreign particles in a positive electrode active material, which can perform qualitative and quantitative detection of the metal single substance foreign particles in the positive electrode active material.

The method comprises the following steps: uniformly mixing a positive electrode active material to be tested with a first solvent to obtain a first mixed liquid; sieving the obtained first mixed liquid, and collecting a first solid component remaining on the sieve after the sieving; mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution, and reacting the mixture to obtain a second mixed liquid; separating the obtained second mixed liquid to obtain a second solid component including metal elemental foreign matter particles; scanning the obtained second solid component with a scanning device, and counting the number of metal elemental foreign matter particles, and calculating the mass of the metal elemental foreign matter particles and their content in the positive electrode active material according to the number of the metal elemental foreign matter particles.

The combination of weak oxidizing acid solution, antioxidant and corrosion inhibitor solution helps to fully dissolve oxide (such as copper oxide, etc.) foreign particles and residual positive electrode active materials, eliminate the interference of oxide (such as copper oxide, etc.) foreign particles, and at the same time reduce the oxidation and dissolution of metal element foreign particles and reduce the damage to the structure of metal element foreign particles. This can improve the detection accuracy of the metal element foreign particle content in the positive electrode active material, and facilitate the accurate characterization of the particle size, morphology, etc. of the metal element foreign particles.

The detection method provided in the embodiments of the present application uses screening treatment to separate most of the positive electrode active materials from foreign particles such as copper oxide particles and metal element foreign particles, thereby reducing the amount of reaction reagents (such as weak oxidizing acid solutions, antioxidants, and corrosion inhibitor solutions) used in subsequent treatments; at the same time, the detection method provided in the embodiments of the present application does not use highly toxic chemicals such as acetaldehyde, thereby reducing environmental pollution.

In the detection method provided in the embodiments of the present application, a scanning device is used to perform qualitative and quantitative detection of metal single substance foreign particles, which can not only realize the detection of element content at the ppm level, but also the detection of element content at the ppb level, and the detection accuracy is high and the repeatability is good. The detection method provided in the embodiments of the present application can also identify the particle size and morphology of metal single substance foreign particles, thereby better performing quantitative detection and specification control of metal single substance foreign particles in positive electrode active materials.

In any embodiment of the present application, the metal single substance foreign particles include one or more of copper single substance foreign particles and stainless steel foreign particles.

In any embodiment of the present application, before the obtained first solid component is mixed with the weak oxidizing acid solution, the antioxidant, and the corrosion inhibitor solution for reaction, the step of: washing the first solid component is also included, and optionally, the cleaning agent includes water. Washing can reduce the amount of positive electrode active material remaining in the first solid component, and also help to reduce the amount of reaction reagents (such as weak oxidizing acid solution, antioxidant, corrosion inhibitor solution) used, reducing environmental pollution.

In any embodiment of the present application, before the positive electrode active material to be detected is mixed evenly with the first solvent to obtain the first mixed solution, the method further includes the steps of pre-screening the solid powder of the positive electrode active material to be detected, collecting the solid components remaining on the sieve after the pre-screening, and then mixing them evenly with the first solvent to obtain the first mixed solution. In this way, a large number of samples can be processed, and at the same time, the risk of missing samples during detection is relatively small.

In any embodiment of the present application, the pre-screening process uses a dry screener.

In any embodiment of the present application, the positive electrode active material solid powder to be detected is pre-screened using a screen with an aperture of 8 μm-25 μm, optionally 10 μm-18 μm, thereby reducing the risk of missed kills and improving the detection efficiency.

In any embodiment of the present application, the aperture of the sieve used for sieving the obtained first mixed solution is 8 μm-25 μm, and can be 10 μm-18 μm. This can reduce the risk of missed killing, and also help reduce the amount of reaction reagents (such as weak oxidizing acid solution, antioxidant, corrosion inhibitor solution) used, reducing environmental pollution.

In any embodiment of the present application, a dispersant is further added to the first mixed solution. The dispersant helps to evenly disperse the positive electrode active material, facilitates the effective separation of the positive electrode active material from oxide foreign particles, metal single substance foreign particles, etc. through the screen, reduces the amount of positive electrode active material remaining in the first solid component, reduces the amount of reaction reagents (such as weak oxidizing acid solution, antioxidant, corrosion inhibitor solution), reduces environmental pollution, and also helps to improve detection efficiency.

In any embodiment of the present application, the mass ratio of the dispersant to the positive electrode active material is less than or equal to 0.025:1, and can be optionally 0.005:1 to 0.02:1.

In any embodiment of the present application, the dispersant includes an aqueous dispersant, which may optionally include a polymer compound.

In any embodiment of the present application, the mass ratio of the antioxidant to the weak oxidizing acid solution is 1:5 to 1:40, and can be optionally 1:8 to 1:25. By adjusting the mass ratio of the antioxidant to the weak oxidizing acid solution within the above range, the oxide foreign particles and the residual positive electrode active material can be better dissolved, and the dissolution of the metal foreign particles can be reduced, thereby improving the detection accuracy of the metal foreign particles content in the positive electrode active material.

In any embodiment of the present application, the mass ratio of the antioxidant to the corrosion inhibitor solution is 1: 1 to 1: 5, and can be optionally 1: 1.15 to 1: 3. By adjusting the mass ratio of the antioxidant to the corrosion inhibitor solution within the above range, the oxidation and dissolution of the metal elemental foreign particles can be further reduced, and the detection accuracy of the metal elemental foreign particle content in the positive electrode active material can be improved.

In any embodiment of the present application, the mass fraction of the weak oxidizing acid solution is 5%-30%, and can be optionally 8%-28%. This can better dissolve the oxide foreign particles and the residual positive electrode active material, and at the same time reduce the dissolution of the metal foreign particles, thereby improving the detection accuracy of the metal foreign particles content in the positive electrode active material.

In any embodiment of the present application, the mass fraction of the corrosion inhibitor solution is 5%-15%, and can be optionally 7%-14%.

In any embodiment of the present application, the weak oxidizing acid includes an inorganic acid and/or an organic acid.

In any embodiment of the present application, the inorganic acid includes one or more of sulfuric acid, hydrochloric acid, and phosphoric acid.

In any embodiment of the present application, the organic acid includes one or more of aminosulfonic acid, citric acid, oxalic acid, acetic acid, lactic acid, malic acid, and citric acid.

In any embodiment of the present application, the mass fraction of the sulfuric acid solution is 10%-30%.

In any embodiment of the present application, the mass fraction of the hydrochloric acid solution is 5%-20%.

In any embodiment of the present application, the mass fraction of the phosphoric acid solution is 15%-30%.

In any embodiment of the present application, the corrosion inhibitor includes one or more of benzotriazole corrosion inhibitors, imidazole corrosion inhibitors, thiazole corrosion inhibitors, and thiophene corrosion inhibitors.

In any embodiment of the present application, the benzotriazole corrosion inhibitor includes one or more of benzotriazole, methylbenzotriazole, ethylbenzotriazole, propylbenzotriazole, butylbenzotriazole, and carboxybenzotriazole.

In any embodiment of the present application, the imidazole corrosion inhibitor includes one or more of benzimidazole and thiabendazole.

In any embodiment of the present application, the thiazole corrosion inhibitor includes one or more of 2-methylbenzothiazole and 2-mercaptobenzothiazole.

In any embodiment of the present application, the thiophene corrosion inhibitor includes benzothiophene.

In any embodiment of the present application, the antioxidant includes one or more of tea polyphenols, acetaldehyde oxime, ascorbic acid, acetone oxime, hydrazine hydrate, H ₂ O ₂ , Na ₂ S ₂ O ₃ , Na ₂ SO ₃ , NaHSO ₃ , and FeSO ₄ .

In any embodiment of the present application, the first solid component obtained is mixed with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution and reacted for 0.5-2 hours. By adjusting the reaction time within the above range, the oxide foreign particles and the residual positive electrode active material can be better dissolved, and the dissolution of the metal foreign particles can be reduced, thereby improving the detection accuracy of the metal foreign particles in the positive electrode active material.

In any embodiment of the present application, the temperature for reacting the obtained first solid component after mixing with the weak oxidizing acid solution, the antioxidant, and the corrosion inhibitor solution is 40° C.-80° C. By adjusting the reaction time within the above range, the oxide foreign particles and the residual positive electrode active material can be better dissolved, and the dissolution of the metal foreign particles can be reduced, thereby improving the detection accuracy of the metal foreign particles content in the positive electrode active material.

In any embodiment of the present application, the positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium-rich manganese-based materials, ternary positive electrode active materials, and their respective modified materials.

In any embodiment of the present application, the first solvent includes one or more of water, methanol, ethanol, and acetone.

In any embodiment of the present application, the mass ratio of the positive electrode active material to be detected to the first solvent is 1:2.5 to 1:30, and can be optionally 1:10 to 1:20. This can make the positive electrode active material evenly dispersed, facilitate the effective separation of the positive electrode active material from oxide foreign particles, metal single foreign particles, etc. through the screen, reduce the amount of positive electrode active material remaining in the first solid component, reduce the amount of reaction reagents (such as weak oxidizing acid solution, antioxidant, corrosion inhibitor solution), reduce environmental pollution; and also help to improve detection efficiency.

In any embodiment of the present application, the second mixed liquid is separated by suction filtration to obtain a second solid component including metal elemental foreign matter particles.

In any embodiment of the present application, the first mixed liquid is sieved using a sieving device, and a wet sieving device may be used.

In any embodiment of the present application, the scanning device comprises a scanning electron microscope, thereby enabling qualitative and quantitative detection of metal foreign particles at the same time.

DETAILED DESCRIPTION

The following detailed description specifically discloses the implementation method of the method for detecting the content of metal single substance foreign particles in the positive electrode active material of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art.

"Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If not otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form a new technical solution, and such a technical solution should be deemed to be included in the disclosure of the present application.

If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

If not otherwise specified, in this application, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

In the present application, the terms "plurality" and "multiple" refer to two or more.

In the present application, the term "weakly oxidizing acid solution" generally refers to an acid that can only exhibit weak oxidizing properties of hydrogen ions in chemical reactions, while the central elements in the acid other than hydrogen and oxygen will not exhibit strong oxidizing properties in chemical reactions, for example, an acid that will not oxidize copper into copper ions.

In the present application, the term "weak oxidizing acid solution" includes non-oxidizing acids.

If not specifically stated, the terms used in this application have the commonly known meanings generally understood by those skilled in the art.

Unless otherwise specified, the values of the parameters mentioned in this application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in this application. Unless otherwise specified, the temperature used for testing each parameter is 25°C.

The embodiments of the present application provide a method for detecting the content of metal elemental foreign particles in a positive electrode active material.

The detection method includes the following steps: uniformly mixing the positive electrode active material to be detected with a first solvent to obtain a first mixed liquid; sieving the obtained first mixed liquid, and collecting the first solid component remaining on the sieve after the sieving; mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution, and reacting the mixture to obtain a second mixed liquid; separating the obtained second mixed liquid to obtain a second solid component including metal elemental foreign matter particles; scanning the obtained second solid component with a scanning device, and counting the number of metal elemental foreign matter particles, and calculating the mass of the metal elemental foreign matter particles and their content in the positive electrode active material according to the number of the metal elemental foreign matter particles.

The metal single substance foreign matter particles include one or more of copper single substance foreign matter particles and stainless steel foreign matter particles.

At present, the method for quantitative detection of foreign particles such as copper in positive electrode active materials is usually the inductively coupled plasma method (ICP method for short). However, the object of the ICP method is the copper element in the test liquid, and the foreign particles of oxides (such as copper oxide, etc.) contained in the positive electrode active material will interfere with the detection results, resulting in low detection accuracy of the content of foreign particles such as copper in the positive electrode active material. At the same time, the detection limit of the ICP method is relatively high, and it can be used to detect the element content at the ppm level; however, when the content of foreign particles such as copper in the positive electrode active material is very small, for example, when the content of copper is at the ppb level, the detection signal is easily masked by noise. At this time, when the ICP method is used to detect the test liquid, it is difficult to detect copper elements, etc.

In the detection method provided in the embodiments of the present application, the positive electrode active material to be detected is evenly mixed with the first solvent and sieving. The sieve can separate most of the positive electrode active material from foreign particles of oxides (such as copper oxide, etc.), foreign particles of metal elements (such as copper element, stainless steel, etc.), etc. Thus, the first solid component remaining on the sieve mainly includes foreign particles of oxides (such as copper oxide, etc.), foreign particles of metal elements (such as copper element, stainless steel, etc.), etc., and inevitably contains positive electrode active materials (hereinafter referred to as residual positive electrode active materials).

The step of mixing the first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution and then reacting them is mainly used to fully dissolve the oxide foreign particles (such as copper oxide, etc.) and the residual positive electrode active material in the first solid component, while reducing the oxidation and dissolution of metal element foreign particles (such as copper element, stainless steel, etc.) to separate the oxide foreign particles and the metal element foreign particles, thereby facilitating the subsequent qualitative and quantitative detection of the metal element foreign particles using scanning equipment.

The use of a weak oxidizing acid solution can dissolve the oxide (e.g., copper oxide, etc.) foreign particles in the first solid component and the residual positive electrode active material, while also avoiding the dissolution of metal single substance foreign particles (e.g., copper single substance, stainless steel, etc.). The high-valent metal ions (e.g., Ni ³⁺ , Co ³⁺ , Mn ³⁺ , etc.) in the residual positive electrode active material will promote the oxidation of the metal single substance foreign particles, and the oxide layer formed on the surface of the metal single substance foreign particles after oxidation will dissolve in an acidic environment, thereby reducing the detection accuracy of the metal single substance foreign particles in the positive electrode active material. The antioxidant can reduce the high-valent metal ions (e.g., Ni ³⁺ , Co ³⁺ , Mn ³⁺ , etc.) in the residual positive electrode active material into low-valent metal ions (e.g., Ni ²⁺ , Co ²⁺ , Mn ²⁺ , etc.), thereby destroying the structure of the residual positive electrode active material and promoting the dissolution of the residual positive electrode active material in the weak oxidizing acid solution. After adding the antioxidant, the high-valent metal ions can be reduced to low-valent metal ions, thereby reducing the oxidation of metal single foreign particles and improving the detection accuracy. The corrosion inhibitor can form covalent bonds and coordination bonds with atoms in the metal single substance (such as copper atoms, etc.), and alternately form chain polymers, thereby forming a protective film on the surface of the metal single foreign particles, further reducing the oxidation of the metal single foreign particles, further reducing the dissolution of the metal single foreign particles, and improving the detection accuracy of the metal single foreign particles in the positive electrode active material.

Therefore, the combination of weak oxidizing acid solution, antioxidant, and corrosion inhibitor solution helps to fully dissolve oxide (such as copper oxide, etc.) foreign particles and residual positive electrode active materials, eliminate the interference of oxide (such as copper oxide, etc.) foreign particles, and at the same time reduce the oxidation and dissolution of metal elemental foreign particles, and reduce the damage to the structure of metal elemental foreign particles. This can improve the detection accuracy of the metal elemental foreign particle content in the positive electrode active material, and also facilitate the accurate characterization of the particle size, morphology, etc. of the metal elemental foreign particles.

The detection method provided in the embodiments of the present application uses screening treatment to separate most of the positive electrode active materials from foreign particles such as copper oxide particles and metal element foreign particles, thereby reducing the amount of reaction reagents (such as weak oxidizing acid solutions, antioxidants, and corrosion inhibitor solutions) used in subsequent treatments; at the same time, the detection method provided in the embodiments of the present application does not use highly toxic chemicals such as acetaldehyde, thereby reducing environmental pollution.

In the detection method provided in the embodiments of the present application, a scanning device is used to perform qualitative and quantitative detection of metal single substance foreign particles, which can not only realize the detection of element content at the ppm level, but also the detection of element content at the ppb level, and the detection accuracy is high and the repeatability is good. The detection method provided in the embodiments of the present application can also identify the particle size and morphology of metal single substance foreign particles, thereby better performing quantitative detection and specification control of metal single substance foreign particles in positive electrode active materials.

In some embodiments, the positive electrode active material may include one or more of lithium cobalt oxide _, lithium nickel oxide, lithium manganese oxide, lithium-rich manganese-based materials, ternary positive electrode active materials, and their respective modified materials. For example _, the positive _electrode active material may _{include LiCoO2} , _{LiNiO2 , LiMnO2 , LiMn2O4 , LiNi1 /} 3Co1/ _3Mn1 / _3O2 (NCM333 _{) ,} LiNi0.5Co0.2Mn0.3O2 ₍ NCM523 ₎ , LiNi0.6Co0.2Mn0.2O2 _{( NCM622 )} , _{LiNi0.8Co0.1Mn0.1O2} ( _{NCM811 )} , _{LiNi0.9Co0.05Mn0.025O2 , LiNi0.85Co0.15Al0.05O2} , and _their respective modified materials. The modification may include doping modification and/or surface coating modification. Optionally, the material constituting the coating layer is soluble in a weak oxidizing acid solution.

In some embodiments, before mixing the obtained first solid component with the weak oxidizing acid solution, the antioxidant, and the corrosion inhibitor solution for reaction, the step of: washing the first solid component is further included. Optionally, the cleaning agent includes water (e.g., ultrapure water). Washing can reduce the amount of positive electrode active material remaining in the first solid component, and also help reduce the amount of reaction reagents (e.g., weak oxidizing acid solution, antioxidant, corrosion inhibitor solution) used, reducing environmental pollution.

In some embodiments, before the positive electrode active material to be tested is mixed evenly with the first solvent to obtain a first mixed liquid, the step of pre-screening the solid powder of the positive electrode active material to be tested, collecting the solid components remaining on the sieve after the pre-screening, and then mixing them evenly with the first solvent to obtain a first mixed liquid can also be included.

The industry also often needs to process large quantities of samples. When the ICP method is used for testing, the mass of the sample weighed each time is small (for example, usually less than 500g), which makes it difficult to quantitatively monitor all the metal foreign particles contained in the positive electrode active material. Therefore, when the ICP method is used to detect the content of metal foreign particles in the positive electrode active material, the risk of missing is relatively high.

In the detection method provided in the embodiments of the present application, before the positive electrode active material is evenly mixed with the first solvent, a large number of samples can be processed by dry screening the positive electrode active material. For example, the solid powder of the positive electrode active material to be detected can be as high as 100 kg. At the same time, the risk of missing during detection is relatively small.

In some embodiments, the detection method includes the steps of: pre-screening the solid powder of the positive electrode active material to be detected, collecting the solid components remaining on the screen after the pre-screening, and then mixing them evenly with the first solvent to obtain a first mixed solution; screening the obtained first mixed solution, collecting the first solid components remaining on the screen after the screening; using a cleaning agent to clean the first solid component, drying the cleaned first solid component and mixing it with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution to react to obtain a second mixed solution; separating the obtained second mixed solution to obtain a second solid component including metal elemental foreign particles; scanning the obtained second solid component with a scanning device to count the number of metal elemental foreign particles, and calculating the mass of the metal elemental foreign particles and their content in the positive electrode active material according to the number of metal elemental foreign particles. In this way, the risk of missing can be reduced and the detection accuracy can be improved.

In some embodiments, a dry sieving machine, such as a dry vibrating sieving machine, may be used to pre-screen the solid powder of the positive electrode active material to be tested.

When pre-screening the solid powder of the positive electrode active material to be tested, a suitable screen can be selected according to the required control specifications to reduce the risk of missed kills and improve the detection accuracy. A suitable screen can also be selected according to the volume distribution particle size of the positive electrode active material to improve the detection efficiency.

When pre-screening large quantities of solid powder of positive electrode active materials, choosing a suitable screen can effectively reduce the amount of positive electrode active materials remaining on the screen while reducing the risk of missing and improving detection accuracy. This also helps to reduce the amount of reaction reagents (such as weak oxidizing acid solutions, antioxidants, and corrosion inhibitor solutions) used and reduce environmental pollution.

In some embodiments, the sieve used for pre-screening the positive electrode active material solid powder to be detected may have an aperture of 8 μm-25 μm, optionally 9 μm-22 μm, 9 μm-20 μm, 10 μm-18 μm, 10 μm-15 μm, thereby reducing the risk of missed kills and improving the detection efficiency.

When the first mixed solution is sieved, a suitable sieve can be selected according to the required control specifications to reduce the risk of missed kills and improve the detection accuracy. A suitable sieve can also be selected according to the volume distribution particle size of the positive electrode active material to improve the detection efficiency.

In some embodiments, the aperture of the sieve used for sieving the obtained first mixed solution may be 8 μm-25 μm, optionally 9 μm-22 μm, 9 μm-20 μm, 10 μm-18 μm, 10 μm-15 μm. This can reduce the risk of missed kills, improve detection efficiency, and also help reduce the amount of reaction reagents (such as weak oxidizing acid solution, antioxidant, corrosion inhibitor solution) and reduce environmental pollution.

In some embodiments, the first solvent may include one or more of water (eg, ultrapure water), methanol, ethanol, and acetone, which is not limited in this embodiment of the present application.

In some embodiments, in the step of uniformly mixing the positive electrode active material to be detected with the first solvent to obtain the first mixed solution, the mass ratio of the positive electrode active material to be detected to the first solvent may be 1:2.5 to 1:30, and may be 1:10 to 1:20. This allows the positive electrode active material to be evenly dispersed, facilitates the effective separation of the positive electrode active material from oxide foreign particles, metal element foreign particles, etc. through the screen, reduces the amount of positive electrode active material remaining in the first solid component, reduces the amount of reaction reagents (such as weak oxidizing acid solution, antioxidant, corrosion inhibitor solution), reduces environmental pollution, and also helps to improve detection efficiency.

In some embodiments, a dispersant may be added to the first mixed solution. The dispersant helps to evenly disperse the positive electrode active material, facilitates the effective separation of the positive electrode active material from oxide foreign particles, metal foreign particles, etc. through the screen, reduces the amount of positive electrode active material remaining in the first solid component, reduces the amount of reaction reagents (such as weak oxidizing acid solution, antioxidant, corrosion inhibitor solution), reduces environmental pollution, and also helps to improve detection efficiency.

In some embodiments, the mass ratio of the dispersant to the positive electrode active material may be less than or equal to 0.025:1, and may be 0.005:1 to 0.02:1.

"Dispersant" means a substance added to a suspension to improve particle separation and prevent particle sedimentation or agglomeration. In some embodiments, the dispersant may include an aqueous dispersant, which may optionally include a polymer compound, such as a comb-type polymer compound, a block polymer compound, etc., and may further be a non-ionic polymer compound.

For example, the dispersant may include, but is not limited to, one or more of polyvinyl pyrrolidone (PVP), polyethylene glycol, ethyl cellulose, waterborne polyurethane, waterborne acrylic resin, and branched secondary alcohol polyoxyethylene ether. As an example, the dispersant may include polyvinyl pyrrolidone (PVP), polyethylene glycol, ethyl cellulose, Huntsman's JEFFSPERSE series dispersants (such as JEFFSPERSE X-3202, X-3204, X-3202RF, etc.), Ruigu New Energy (Shanghai) Materials Technology Co., Ltd.'s water-based dispersants (such as LIB-D200, LIB-D300, etc.), Dow's TERGITOL series dispersants (such as TMN-6, TMN-10, etc.) One or more. In some embodiments, a screening device may be used when the first mixed solution is screened, and a wet sieving device may be used.

This helps to effectively separate the positive electrode active material from oxide foreign particles, metal element foreign particles, etc., reduce the amount of positive electrode active material remaining in the first solid component, reduce the amount of reaction reagents (such as weak oxidizing acid solution, antioxidant, corrosion inhibitor solution), and reduce environmental pollution; it also helps to improve detection efficiency.

In some embodiments, the total amount of the weak oxidizing acid solution, antioxidant, and corrosion inhibitor solution added is preferably sufficient to immerse the first solid component and fully dissolve the residual positive electrode active material and oxide foreign particles therein.

In some embodiments, the mass ratio of the antioxidant to the weak oxidizing acid solution may be 1:5 to 1:40, optionally 1:6 to 1:30, 1:8 to 1:25, 1:8 to 1:20. By adjusting the mass ratio of the antioxidant to the weak oxidizing acid solution within the above range, the oxide foreign particles and the residual positive electrode active material can be better dissolved, and the dissolution of the metal foreign particles can be reduced, thereby improving the detection accuracy of the content of the metal foreign particles in the positive electrode active material.

In some embodiments, the mass ratio of the antioxidant to the corrosion inhibitor solution may be 1: 1 to 1: 5, and may be 1: 1.1 to 1: 4, 1: 1.15 to 1: 3. By adjusting the mass ratio of the antioxidant to the corrosion inhibitor solution within the above range, the oxidation and dissolution of the metal elemental foreign particles can be further reduced, and the detection accuracy of the metal elemental foreign particle content in the positive electrode active material can be improved.

In some embodiments, the weak oxidizing acid may include an inorganic acid and/or an organic acid.

In some embodiments, the inorganic acid may include one or more of sulfuric acid, hydrochloric acid, and phosphoric acid.

In some embodiments, the organic acid may include one or more of sulfamic acid, citric acid, oxalic acid, acetic acid, lactic acid, malic acid, and citric acid.

In some embodiments, the mass fraction of the weak oxidizing acid solution may be 5%-30%, optionally 8%-28%, and the remainder is solvent water. This can better dissolve oxide foreign particles and residual positive electrode active materials, and at the same time reduce the dissolution of metal foreign particles, thereby improving the detection accuracy of the content of metal foreign particles in the positive electrode active material.

In some embodiments, the weak oxidizing acid solution may be a sulfuric acid solution, and the mass fraction of the sulfuric acid solution may be 10%-30%, optionally 12%-25%, 14%-22%.

In some embodiments, the weak oxidizing acid solution may be a hydrochloric acid solution, and the mass fraction of the hydrochloric acid solution may be 5%-20%, optionally 5%-18%, 8%-18%.

In some embodiments, the weak oxidizing acid solution may be a phosphoric acid solution, and the mass fraction of the phosphoric acid solution may be 15%-30%, optionally 16%-28%, 16%-26%.

In some embodiments, the corrosion inhibitor may include one or more of a benzotriazole corrosion inhibitor, an imidazole corrosion inhibitor, a thiazole corrosion inhibitor, and a thiophene corrosion inhibitor.

In some embodiments, the benzotriazole corrosion inhibitor may include one or more of benzotriazole (BTA), methyl benzotriazole, ethyl benzotriazole, propyl benzotriazole, butyl benzotriazole, and carboxy benzotriazole.

In some embodiments, the imidazole corrosion inhibitor may include one or more of benzimidazole and thiabendazole.

In some embodiments, the thiazole corrosion inhibitor may include one or more of 2-methylbenzothiazole and 2-mercaptobenzothiazole.

In some embodiments, the thiophene-based corrosion inhibitor may include benzothiophene.

In some embodiments, the corrosion inhibitor solution can be prepared according to the following steps: uniformly mixing the corrosion inhibitor, alkali and solvent water to prepare the corrosion inhibitor solution. Optionally, the alkali includes sodium hydroxide.

In some embodiments, the mass fraction of the corrosion inhibitor in the corrosion inhibitor solution may be 5%-15%, and optionally 7%-14%.

In some embodiments, the antioxidant may include one or more of tea polyphenols, acetaldehyde oxime, ascorbic acid, acetone oxime, hydrazine hydrate, H ₂ O ₂ , Na ₂ S ₂ O ₃ , Na ₂ SO ₃ , NaHSO ₃ , and FeSO ₄ .

In some embodiments, the first solid component obtained is mixed with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution and reacted for a time of 0.5-2 hours. Adjusting the reaction time within the above range can better dissolve the oxide foreign particles and the residual positive electrode active material, and at the same time can reduce the dissolution of the metal foreign particles, thereby improving the detection accuracy of the metal foreign particles in the positive electrode active material.

In some embodiments, the temperature for reacting the obtained first solid component after mixing with the weak oxidizing acid solution, the antioxidant, and the corrosion inhibitor solution can be 40° C.-80° C. By adjusting the reaction time within the above range, the oxide foreign particles and the residual positive electrode active material can be better dissolved, and the dissolution of the metal foreign particles can be reduced, thereby improving the detection accuracy of the metal foreign particles content in the positive electrode active material.

In some embodiments, the heating method for mixing the obtained first solid component with the weak oxidizing acid solution, the antioxidant, and the corrosion inhibitor solution for reaction can be water bath heating, which is not limited in the embodiments of the present application.

In some embodiments, the second mixed liquid can be separated by filtration (such as vacuum filtration) to obtain a second solid component including metal elemental foreign particles. Of course, other solid-liquid separation methods known in the art can also be used, and the embodiments of the present application are not limited to this.

In some embodiments, the scanning device may include a scanning electron microscope, such as a Phenomenon scanning electron microscope, so that the metal foreign particles can be qualitatively and quantitatively detected at the same time.

Example

The following examples describe the disclosure of the present application in more detail, and these examples are only for illustrative purposes, as it is obvious to those skilled in the art that various modifications and variations are made within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

Example 1-1

Weigh 0.1g of the positive electrode active material NCM523 and add about 5mg of the Cu standard. Prepare a reaction solution with 50ml of dilute sulfuric acid aqueous solution (mass fraction 20%), 5g of ascorbic acid powder and 5ml of benzotriazole sodium hydroxide solution (mass fraction of benzotriazole is 11%, mass fraction of sodium hydroxide is 5.5%), and the volume _V1 is recorded as 55ml. Add the positive electrode active material containing the Cu standard to the reaction solution, and let it stand in a 50℃ water bath for 1-2h to react until the positive electrode active material is completely dissolved.

Take 1 mL of the liquid after the reaction and dilute it 50 times with ultrapure water to obtain the liquid to be tested. Take an appropriate amount of the liquid to be tested, use an inductively coupled plasma emission spectrometer to determine the content of copper in the liquid to be tested, and calculate the recovery rate of copper. The results are shown in Table 1.

Example 1-2 to Example 1-18

Except for the type and/or mass of the positive electrode active material and the type and mass of the standard product, the other parameters are the same as those of Example 1-1. Specific parameters are shown in Table 1.

In Table 1, the recovery rate of copper element (%) = [(the content of copper element in the liquid to be tested × V ₁ × 50) / the mass of copper element in the standard / 1000] × 100%. The unit of the content of copper element in the liquid to be tested is mg/L, and V ₁ is 55ml. When the standard is copper oxide, the mass of copper element in the standard = the mass of copper oxide standard × 0.8, in mg.

Table 1

As shown in Table 1, after adding the copper oxide standard, the recovery rate of the copper element is around 100%, while after adding the copper standard, the recovery rate of the copper element is very low, such as less than 5%. This shows that the reaction solution provided by the present application can completely dissolve the positive electrode active material and the copper oxide foreign particles, and almost does not dissolve the copper single substance foreign particles.

Next, the inventors examined the applicability and effectiveness of the detection method provided in the embodiments of the present application for the positive electrode active material remaining on the sieve.

Take 1000g of positive electrode active material (volume distribution particle size Dv50 is 6μm) and mix it evenly with 10g of dispersant and 15Kg of solvent water. After sieving with a wet sieving instrument (the mesh size can be 10μm-15μm), the mass of the positive electrode active material remaining on the mesh is less than 1.0g. In Examples 2-1 to 2-9, the inventor weighed 0.5g of positive electrode active material to simulate the positive electrode active material remaining on the mesh, and added a small amount of copper elemental particles to perform a spiked recovery experiment.

Example 2-1 to Example 2-9

Weigh 0.5g of the positive electrode active material NCM523, and add copper particles of different volume distribution particle size Dv50, different number of particles, and different morphologies (see Table 2 for specific parameters). 50ml of dilute sulfuric acid aqueous solution (mass fraction of 20%), 5g of ascorbic acid powder and 5ml of benzotriazole sodium hydroxide solution (mass fraction of benzotriazole is 11%, and mass fraction of sodium hydroxide is 5.5%) are prepared into a reaction solution, and the volume _V1 is recorded as 55ml. The above-mentioned positive electrode active material containing copper particles is added to the reaction solution, and the reaction is allowed to stand in a 50°C water bath for 1-2h until the positive electrode active material is completely dissolved. The reacted liquid is filtered, and then the filter membrane is removed. After sufficient drying, the number of copper particles on the filter membrane is counted using a Phi-nano scanning electron microscope, and the results are shown in Table 2.

In Table 2, the recovery rate of copper elemental particles=(the number of copper elemental particles detected/the number of copper elemental particles added)×100%.

Table 2

As can be seen from Table 2, the detection method provided in the embodiments of the present application can effectively collect copper particles of various particle sizes, various morphologies and a small number of particles (such as ppb level), the recovery rate of copper particles is above 80%, and the repeatability of the detection results is good.

In Comparative Examples 1 to 9, the inventors weighed 0.5 g of the positive electrode active material remaining on the positive electrode active material simulation sieve, and added Cu standard, CuO standard and a small amount of copper elemental particles to conduct a spiked recovery experiment.

Comparative Example 1 to Comparative Example 3

Weigh 0.5g of positive electrode active material NCM523, NCM622 or NCM811 respectively, add about 5mg of Cu standard, then stir the reaction at 25°C for 1h in an ammonium chloride-ammonia water mixed solution (the mass ratio of ammonium chloride to ammonia water is 1:50), filter, and collect the filtrate. The filtrate was concentrated to 10mL at 300°C, then fixed to 100mL with ultrapure water, and then diluted 50 times with ultrapure water to obtain 5L of the liquid to be tested. Take an appropriate amount of the liquid to be tested, and use an inductively coupled plasma emission spectrometer to determine the content of copper in the liquid to be tested, and calculate the recovery of copper. The results are shown in Table 3.

Comparative Examples 4 to 6

Except that the standard product is CuO standard product, the other parameters are the same as those of Comparative Examples 1 to 3. See Table 3 for specific parameters.

Comparative Examples 7 to 9

Except that the standard product uses copper single substance particles (spherical particles, volume distribution particle size Dv50 is 20 μm), the other parts are the same as Comparative Examples 1 to 3. Specific parameters are shown in Table 3.

In Table 3, the recovery rate of copper element (%) = [(content of copper element in the liquid to be tested × volume of the liquid to be tested) / mass of copper element in the standard] × 100%. The unit of the content of copper element in the liquid to be tested is mg/L, and the volume of the liquid to be tested is 5 L. When the standard is copper oxide, the mass of copper element in the standard = the mass of copper oxide standard × 0.8, in mg.

Table 3

It can be seen from Comparative Examples 1 to 3 that the ICP method has a good detection capability for copper elemental particles at the ppm level.

It can be seen from Comparative Examples 4 to 6 that after adding copper oxide standard, the recovery rate of copper element is relatively high, which indicates that some copper oxide will also react, so when performing ICP detection, copper oxide foreign particles will interfere with the detection results of copper element foreign particles, resulting in low detection accuracy.

It can be seen from Comparative Examples 7 to 9 that when the content of copper element particles is relatively low (eg, the copper element content is at the ppb level), the copper element cannot be detected in the test solution due to the detection limit of the instrument itself.

It can also be seen from Table 1 and Table 2 that the detection method provided in the embodiment of the present application can perform qualitative and quantitative detection of foreign particles such as copper in the positive electrode active material, and the detection result has high accuracy and good repeatability. The detection method provided in the embodiment of the present application can also identify the particle size and morphology of foreign particles such as copper in the positive electrode active material. The detection method provided in the embodiment of the present application uses fewer reaction reagents and can also reduce environmental pollution.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims (12)

1. A method for detecting the content of elemental foreign particles of metal in a positive electrode active material, comprising the steps of:

Uniformly mixing the positive electrode active material to be detected with a first solvent to obtain a first mixed solution;

Sieving the obtained first mixed solution, and collecting first solid components remained on a sieve after sieving;

Mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant and a corrosion inhibitor solution, and then reacting to obtain a second mixed solution;

Separating the obtained second mixed solution to obtain a second solid component comprising metal simple substance foreign particles;

And counting the number of the metal simple substance foreign particles after the obtained second solid component is scanned by using scanning equipment, and calculating the mass of the metal simple substance foreign particles and the content of the metal simple substance foreign particles in the positive electrode active material according to the number of the metal simple substance foreign particles.

2. The method of claim 1, wherein the elemental metal foreign particles comprise one or more of elemental copper foreign particles, stainless steel foreign particles.

3. The method according to claim 1 or 2, wherein before mixing the obtained first solid component with the weak oxidizing acid solution, the antioxidant, the corrosion inhibitor solution for reaction, further comprising the steps of: the first solid component is washed, optionally the washing agent comprises water.

4. The method according to any one of claims 1 to 3, wherein before uniformly mixing the positive electrode active material to be detected with the first solvent to obtain the first mixed solution, further comprising the step of: and (3) carrying out pre-screening treatment on the solid powder of the positive electrode active material to be detected, collecting solid components remained on the screen after the pre-screening treatment, and then uniformly mixing with a first solvent to obtain a first mixed solution.

5. The method of claim 4, wherein,

The pre-sieving treatment adopts a dry sieving machine; and/or the number of the groups of groups,

The positive electrode active material solid powder to be detected is subjected to a pre-screening treatment using a screen having a pore diameter of 8 μm to 25 μm, optionally 10 μm to 18 μm.

6. The method according to any one of claims 1 to 5, wherein the first mixture obtained is subjected to a sieving treatment with a sieve having a pore size of 8 μm to 25 μm, optionally 10 μm to 18 μm.

7. The method according to any one of claims 1 to 6, wherein,

A dispersing agent is also added into the first mixed solution;

Optionally, the mass ratio of the dispersant to the positive electrode active material is 0.025:1 or less, optionally 0.005:1 to 0.02:1;

alternatively, the dispersant comprises an aqueous dispersant, more alternatively a polymeric compound.

8. The method according to any one of claims 1 to 7, wherein,

The mass ratio of the antioxidant to the weak oxidizing acid solution is 1:5 to 1:40, optionally 1:8 to 1:25; and/or the number of the groups of groups,

The mass ratio of the antioxidant to the corrosion inhibitor solution is 1:1 to 1:5, optionally 1:1.15 to 1:3; and/or the number of the groups of groups,

The mass fraction of the weak oxidizing acid solution is 5% -30%, and optionally 8% -28%; and/or the number of the groups of groups,

The mass fraction of the corrosion inhibitor solution is 5% -15%, and optionally 7% -14%.

9. The method according to any one of claims 1-8, wherein,

The weak oxidizing acid includes an inorganic acid and/or an organic acid; and/or the number of the groups of groups,

The corrosion inhibitor comprises one or more of benzotriazole corrosion inhibitor, imidazole corrosion inhibitor, thiazole corrosion inhibitor and thiophene corrosion inhibitor; and/or the number of the groups of groups,

The antioxidant comprises one or more of tea polyphenols, aldoxime, ascorbic acid, acetoxime, and hydrazine hydrate 、H₂O₂、Na₂S₂O₃、Na₂SO₃、NaHSO₃、FeSO₄.

10. The method of claim 9, wherein,

The inorganic acid comprises one or more of sulfuric acid, hydrochloric acid and phosphoric acid, wherein the mass fraction of the sulfuric acid solution is 10% -30%, the mass fraction of the hydrochloric acid solution is 5% -20%, and the mass fraction of the phosphoric acid solution is 15% -30%; and/or the number of the groups of groups,

The organic acid comprises one or more of sulfamic acid, citric acid, oxalic acid, acetic acid, lactic acid, malic acid and citric acid; and/or the number of the groups of groups,

The benzotriazole corrosion inhibition the agent comprises benzotriazole the agent comprises benzo triazole(s) propyl benzotriazol butyl benzotriazol butylbenzo triazole(s); and/or the number of the groups of groups,

The imidazole corrosion inhibitor comprises one or more of benzimidazole and thiabendazole; and/or the number of the groups of groups,

The thiazole corrosion inhibitor comprises one or more of 2-methylbenzothiazole and 2-mercaptobenzothiazole; and/or the number of the groups of groups,

The thiophene corrosion inhibitor comprises benzothiophene.

11. The method according to any one of claims 1-10, wherein,

Mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant and a corrosion inhibitor solution, and reacting for 0.5-2h; and/or the number of the groups of groups,

The temperature at which the obtained first solid component is reacted after being mixed with the weak oxidizing acid solution, the antioxidant and the corrosion inhibitor solution is 40-80 ℃.

12. The method according to any one of claims 1-11, wherein the method satisfies at least one of the following conditions (1) to (6):

(1) The positive electrode active material comprises one or more of lithium cobaltate, lithium nickelate, lithium manganate, lithium-rich manganese-based material, ternary positive electrode active material and respective modified materials thereof;

(2) The first solvent comprises one or more of water, methanol, ethanol and acetone;

(3) The mass ratio of the positive electrode active material to be detected to the first solvent is 1:2.5 to 1:30, and is optionally 1:10 to 1:20;

(4) The second mixed solution is separated through suction filtration to obtain a second solid component comprising metal simple substance foreign particles;

(5) Screening the obtained first mixed solution by adopting screening equipment, and optionally adopting a wet screening instrument;

(6) The scanning device comprises a scanning electron microscope.