A method for detecting the content of elemental metallic particles in positive electrode active materials.

Abstract

This application discloses a method for detecting the content of elemental metal foreign particles in a positive electrode active material, comprising the following steps: mixing the positive electrode active material to be detected with a first solvent to obtain a first mixture; sieving the obtained first mixture and collecting the first solid component remaining on the sieve after sieving; mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution and reacting to obtain a second mixture; separating the obtained second mixture to obtain a second solid component including elemental metal foreign particles; scanning the obtained second solid component with a scanning device and counting the number of elemental metal foreign particles, and calculating the mass of the elemental metal foreign particles and their content in the positive electrode active material based on the number of elemental metal foreign particles.

Description

Technical Field

[0001] This application relates to a method for detecting the content of elemental metallic foreign particles in positive electrode active materials. Background Technology

[0002] The positive electrode active material used in batteries typically comes into contact with metal components during production. Due to wear and tear on these components, the prepared positive electrode active material may contain small amounts of foreign particles such as elemental metals and metal oxides. Some of these elemental metal particles gradually dissolve into metal ions during battery use. These metal ions migrate from the positive electrode to the negative electrode and are reduced to elemental metals on the negative electrode surface. They may also continue to grow, forming dendrites, which increases battery self-discharge, causes capacity decay, and affects battery lifespan. In severe cases, dendrites can even puncture the separator, leading to thermal runaway and reducing battery reliability. Therefore, strict quantitative detection and specification control of elemental metal foreign particles in the positive electrode active material are necessary. The above statements are for providing background information related to this application only and do not necessarily constitute prior art. Summary of the Invention

[0003] This application provides a method for detecting the content of elemental metal foreign particles in positive electrode active materials, which can perform qualitative and quantitative detection of elemental metal foreign particles in positive electrode active materials.

[0004] The method includes the following steps: mixing the positive electrode active material to be tested with a first solvent to obtain a first mixture; sieving the obtained first mixture and collecting the first solid component remaining on the sieve after sieving; mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution and reacting to obtain a second mixture; separating the obtained second mixture to obtain a second solid component including elemental metal particles; scanning the obtained second solid component with a scanning device and counting the number of elemental metal particles, and calculating the mass of the elemental metal particles and their content in the positive electrode active material based on the number of elemental metal particles.

[0005] The combination of weak oxidizing acid solution, antioxidant, and corrosion inhibitor solution helps to fully dissolve oxide (e.g., copper oxide) foreign particles and residual positive electrode active material, eliminating interference from oxide (e.g., copper oxide) foreign particles. At the same time, it can also reduce the oxidation and dissolution of elemental metal foreign particles and reduce the damage to the structure of elemental metal foreign particles. This can improve the accuracy of detecting the content of elemental metal foreign particles in positive electrode active material and facilitate accurate characterization of the particle size, morphology, etc. of elemental metal foreign particles.

[0006] The detection method provided in the embodiments of this application uses a sieving process to separate most of the positive electrode active material from foreign particles such as copper oxide particles and elemental metal particles. This reduces the amount of reaction reagents (such as weak oxidizing acid solutions, antioxidants, and corrosion inhibitor solutions) used in subsequent processing. At the same time, the detection method provided in the embodiments of this application does not use highly toxic chemicals such as acetaldehyde, which can further reduce environmental pollution.

[0007] The detection method provided in the embodiments of this application employs a scanning device for qualitative and quantitative detection of elemental metal foreign particles. This method can achieve elemental content detection at both the ppm and ppb levels, with high accuracy and good repeatability. Furthermore, the detection method provided in the embodiments of this application can also identify the particle size and morphology of elemental metal foreign particles, thereby enabling better quantitative detection and specification control of elemental metal foreign particles in positive electrode active materials.

[0008] In any embodiment of this application, the metallic foreign matter particles include one or more of copper foreign matter particles and stainless steel foreign matter particles.

[0009] In any embodiment of this application, before reacting the obtained first solid component with a weak oxidizing acid solution, an antioxidant solution, and a corrosion inhibitor solution, the method further includes a step of cleaning the first solid component. Optionally, the cleaning agent includes water. Cleaning can reduce the amount of residual positive electrode active material in the first solid component and also helps to reduce the amount of reaction reagents (e.g., weak oxidizing acid solution, antioxidant solution, corrosion inhibitor solution) used, thereby reducing environmental pollution.

[0010] In any embodiment of this application, before uniformly mixing the positive electrode active material to be tested with the first solvent to obtain the first mixture, the method further includes the step of: pre-sieving the solid powder of the positive electrode active material to be tested, collecting the solid components remaining on the sieve after pre-sieving, and then uniformly mixing it with the first solvent to obtain the first mixture. This allows for the processing of large quantities of samples while minimizing the risk of missed detections.

[0011] In any embodiment of this application, the pre-screening process employs a dry screening machine.

[0012] In any embodiment of this application, the sieve used for pre-sieving the positive electrode active material solid powder to be tested has a pore size of 8μm-25μm, optionally 10μm-18μm. This can reduce the risk of missed detection while improving detection efficiency.

[0013] In any embodiment of this application, the sieve used for sieving the obtained first mixture has a mesh size of 8μm-25μm, optionally 10μm-18μm. This reduces the risk of missed detection and also helps to reduce the amount of reaction reagents (e.g., weak oxidizing acid solutions, antioxidants, corrosion inhibitor solutions), thus reducing environmental pollution.

[0014] In any embodiment of this application, a dispersant is also added to the first mixture. The dispersant helps to disperse the positive electrode active material uniformly, facilitating the effective separation of the positive electrode active material from oxide foreign particles, elemental metal foreign particles, etc., through a sieve, reducing the amount of residual positive electrode active material in the first solid component, reducing the amount of reaction reagents (e.g., weak oxidizing acid solution, antioxidant, corrosion inhibitor solution), reducing environmental pollution; and also helps to improve detection efficiency.

[0015] In any embodiment of this application, the mass ratio of the dispersant to the positive electrode active material is less than or equal to 0.025:1, and may be selected as 0.005:1 to 0.02:1.

[0016] In any embodiment of this application, the dispersant includes an aqueous dispersant, which may optionally include a polymeric compound.

[0017] In any embodiment of this application, the mass ratio of the antioxidant to the weak oxidizing acid solution is 1:5 to 1:40, optionally 1:8 to 1:25. Adjusting the mass ratio of the antioxidant to the weak oxidizing acid solution within the above range can better dissolve oxide foreign particles and residual positive electrode active material, while reducing the dissolution of elemental metal foreign particles, thereby improving the accuracy of detecting the content of elemental metal foreign particles in the positive electrode active material.

[0018] In any embodiment of this application, the mass ratio of the antioxidant to the corrosion inhibitor solution is 1:1 to 1:5, and optionally 1:1.15 to 1:3. Adjusting the mass ratio of the antioxidant to the corrosion inhibitor solution within the above range can further reduce the oxidation and dissolution of elemental metal particles, and improve the detection accuracy of elemental metal particle content in the positive electrode active material.

[0019] In any embodiment of this application, the mass fraction of the weak oxidizing acid solution is 5%-30%, optionally 8%-28%. This allows for better dissolution of oxide foreign particles and residual positive electrode active material, while reducing the dissolution of elemental metal foreign particles, thereby improving the accuracy of detecting the content of elemental metal foreign particles in the positive electrode active material.

[0020] In any embodiment of this application, the mass fraction of the corrosion inhibitor solution is 5%-15%, optionally 7%-14%.

[0021] In any embodiment of this application, the weak oxidizing acid includes inorganic acids and / or organic acids.

[0022] In any embodiment of this application, the inorganic acid includes one or more of sulfuric acid, hydrochloric acid, and phosphoric acid.

[0023] In any embodiment of this application, the organic acid includes one or more of aminosulfonic acid, citric acid, oxalic acid, acetic acid, lactic acid, malic acid, and citric acid.

[0024] In any embodiment of this application, the sulfuric acid solution has a mass fraction of 10%-30%.

[0025] In any embodiment of this application, the hydrochloric acid solution has a mass fraction of 5%-20%.

[0026] In any embodiment of this application, the mass fraction of the phosphoric acid solution is 15%-30%.

[0027] In any embodiment of this application, the corrosion inhibitor includes one or more of benzotriazole corrosion inhibitors, imidazole corrosion inhibitors, thiazole corrosion inhibitors, and thiophene corrosion inhibitors.

[0028] In any embodiment of this application, the benzotriazole corrosion inhibitor includes one or more of benzotriazole, methylbenzotriazole, ethylbenzotriazole, propylbenzotriazole, butylbenzotriazole, and carboxybenzotriazole.

[0029] In any embodiment of this application, the imidazole corrosion inhibitor includes one or more of benzimidazole and thiabendazole.

[0030] In any embodiment of this application, the thiazole corrosion inhibitor includes one or more of 2-methylbenzothiazole and 2-mercaptobenzothiazole.

[0031] In any embodiment of this application, the thiophene-based corrosion inhibitor includes benzothiophene.

[0032] In any embodiment of this application, the antioxidant includes one or more of the following: tea polyphenols, acetaldehyde oxime, ascorbic acid, acetone oxime, hydrazine hydrate, H2O2, Na2S2O3, Na2SO3, NaHSO3, and FeSO4.

[0033] In any embodiment of this application, the reaction time after mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution is 0.5-2 hours. Adjusting the reaction time within the above range can better dissolve oxide foreign particles and residual positive electrode active material, while reducing the dissolution of elemental metal foreign particles, thereby improving the accuracy of detecting the content of elemental metal foreign particles in the positive electrode active material.

[0034] In any embodiment of this application, the reaction temperature after mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution is 40°C-80°C. Adjusting the reaction time within the above range can better dissolve oxide foreign particles and residual positive electrode active material, while reducing the dissolution of elemental metal foreign particles, thereby improving the accuracy of detecting the content of elemental metal foreign particles in the positive electrode active material.

[0035] In any embodiment of this 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.

[0036] In any embodiment of this application, the first solvent includes one or more of water, methanol, ethanol, and acetone.

[0037] In any embodiment of this 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 optionally 1:10 to 1:20. This allows the positive electrode active material to be uniformly dispersed, facilitating effective separation of the positive electrode active material from oxide foreign particles, elemental metal foreign particles, etc., through a sieve, reducing the amount of residual positive electrode active material in the first solid component, reducing the amount of reaction reagents (e.g., weak oxidizing acid solution, antioxidant, corrosion inhibitor solution), reducing environmental pollution, and also helping to improve detection efficiency.

[0038] In any embodiment of this application, the second mixture is separated by filtration to obtain a second solid component comprising metallic foreign particles.

[0039] In any embodiment of this application, a sieving device is used when the obtained first mixture is sieved, which may be a wet sieve separator.

[0040] In any embodiment of this application, the scanning device includes a scanning electron microscope. This allows for simultaneous qualitative and quantitative detection of metallic foreign particles. Detailed Implementation

[0041] The following detailed description discloses embodiments of the method for detecting the content of elemental metal particles in a positive electrode active material according to this application. However, unnecessary details 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.

[0042] 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.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0045] 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.

[0046] 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.

[0047] 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).

[0048] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0049] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0050] In this application, the term "weakly oxidizing acid solution" generally refers to an acid that exhibits only the weak oxidizing property of hydrogen ions in a chemical reaction, while the central element in the acid, other than hydrogen and oxygen, does not exhibit strong oxidizing property in a chemical reaction. For example, an acid that does not oxidize elemental copper to copper ions.

[0051] In this application, the term "weakly oxidizing acid solution" includes non-oxidizing acids.

[0052] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0053] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, such as the testing methods provided in this application. Unless otherwise specified, the temperature for testing each parameter is 25°C.

[0054] The embodiments of this application provide a method for detecting the content of elemental metal particles in a positive electrode active material.

[0055] The detection method includes the following steps: mixing the positive electrode active material to be detected with a first solvent to obtain a first mixture; sieving the obtained first mixture and collecting the first solid component remaining on the sieve after sieving; mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution and reacting to obtain a second mixture; separating the obtained second mixture to obtain a second solid component including elemental metal particles; scanning the obtained second solid component with a scanning device and counting the number of elemental metal particles, and calculating the mass of the elemental metal particles and their content in the positive electrode active material based on the number of elemental metal particles.

[0056] The metallic foreign matter particles include one or more of copper foreign matter particles and stainless steel foreign matter particles.

[0057] Currently, the common method for quantitative detection of foreign particles such as elemental copper in cathode active materials is inductively coupled plasma (ICP). However, ICP detects copper and other elements in the test solution, while oxide particles (such as copper oxide) in the cathode active material can interfere with the detection results, leading to low accuracy in detecting the content of elemental copper and other foreign particles in the cathode active material. Furthermore, while ICP has a high detection limit, allowing for the detection of elemental content at the ppm level, when the content of elemental copper and other foreign particles in the cathode active material is very low—for example, at the ppb level—the detection signal is easily masked by noise, making it difficult to detect copper and other foreign particles using ICP in such cases.

[0058] In the detection method provided in the embodiments of this application, the positive electrode active material to be detected is mixed evenly with the first solvent and then sieved. The sieve can separate most of the positive electrode active material from oxide (e.g., copper oxide) foreign particles and metal element (e.g., copper, stainless steel) foreign particles. Thus, the first solid component remaining on the sieve mainly includes oxide (e.g., copper oxide) foreign particles and metal element (e.g., copper, stainless steel) foreign particles, and inevitably also contains positive electrode active material (hereinafter referred to as residual positive electrode active material).

[0059] The step of reacting the first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution is mainly used to fully dissolve the oxide (e.g., copper oxide) foreign particles and residual positive electrode active material in the first solid component, while reducing the oxidation and dissolution of elemental metal (e.g., copper, stainless steel) foreign particles, so as to separate oxide foreign particles and elemental metal foreign particles. This facilitates the subsequent qualitative and quantitative detection of elemental metal foreign particles using scanning equipment.

[0060] Using a weak oxidizing acid solution can dissolve oxide (e.g., copper oxide) foreign particles and residual positive electrode active material in the first solid component, while avoiding the dissolution of elemental metal foreign particles (e.g., elemental copper, stainless steel, etc.). High-valence metal ions (e.g., Ni) in the residual positive electrode active material can also be dissolved. 3+ Co 3+ Mn 3+ Antioxidants (such as Ni) can promote the oxidation of metallic foreign particles. The oxide layer formed on the surface of these particles after oxidation dissolves in an acidic environment, thus reducing the accuracy of detecting the content of metallic foreign particles in the positive electrode active material. Antioxidants can neutralize residual high-valence metal ions (such as Ni) in the positive electrode active material. 3+ Co 3+ Mn 3+ (etc.) reduced to lower valence metal ions (such as Ni) 2+ Co 2+ Mn 2+ (etc.), thereby disrupting the structure of residual positive electrode active material and promoting its dissolution in weakly oxidizing acid solutions. Adding antioxidants can reduce high-valence metal ions to low-valence metal ions, thus reducing the oxidation of elemental metal particles and improving detection accuracy. Corrosion inhibitors can form covalent and coordinate bonds with atoms in elemental metals (such as copper atoms), alternating to form chain-like polymers. This forms a protective film on the surface of elemental metal particles, further reducing their oxidation and dissolution, and improving the accuracy of detecting the content of elemental metal particles in the positive electrode active material.

[0061] Therefore, the combination of weak oxidizing acid solution, antioxidant, and corrosion inhibitor solution helps to fully dissolve oxide (e.g., copper oxide) foreign particles and residual positive electrode active material, eliminate the interference of oxide (e.g., copper oxide) foreign particles, and at the same time reduce the oxidation and dissolution of elemental metal foreign particles, reducing the damage to the structure of elemental metal foreign particles. This can improve the accuracy of detecting the content of elemental metal foreign particles in positive electrode active material, and also facilitate the accurate characterization of the particle size, morphology, etc. of elemental metal foreign particles.

[0062] The detection method provided in the embodiments of this application uses a sieving process to separate most of the positive electrode active material from foreign particles such as copper oxide particles and elemental metal particles. This reduces the amount of reaction reagents (such as weak oxidizing acid solutions, antioxidants, and corrosion inhibitor solutions) used in subsequent processing. At the same time, the detection method provided in the embodiments of this application does not use highly toxic chemicals such as acetaldehyde, which can further reduce environmental pollution.

[0063] The detection method provided in the embodiments of this application employs a scanning device for qualitative and quantitative detection of elemental metal foreign particles. This method can achieve elemental content detection at both the ppm and ppb levels, with high accuracy and good repeatability. Furthermore, the detection method provided in the embodiments of this application can also identify the particle size and morphology of elemental metal foreign particles, thereby enabling better quantitative detection and specification control of elemental metal foreign particles in positive electrode active materials.

[0064] 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, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.9 Co 0.05 Mn 0.025 O2, LiNi 0.85 Co 0.15 Al 0.05 O2, and one or more of their respective modifying materials. Modification methods may include doping modification and / or surface coating modification. Optionally, the material constituting the coating layer is soluble in a weak oxidizing acid solution.

[0065] In some embodiments, before reacting the obtained first solid component with a weak oxidizing acid solution, an antioxidant solution, and a corrosion inhibitor solution, the method further includes a step of cleaning the first solid component. Optionally, the cleaning agent includes water (e.g., ultrapure water). Cleaning can reduce the amount of residual positive electrode active material in the first solid component and also helps to reduce the amount of reaction reagents (e.g., weak oxidizing acid solution, antioxidant solution, corrosion inhibitor solution) used, thereby reducing environmental pollution.

[0066] In some embodiments, before uniformly mixing the positive electrode active material to be tested with the first solvent to obtain a first mixture, the method may further include the step of: pre-sieving the solid powder of the positive electrode active material to be tested, collecting the solid components remaining on the sieve after pre-sieving, and then uniformly mixing it with the first solvent to obtain a first mixture.

[0067] The industry often needs to process large quantities of samples. When using the ICP method for detection, the sample mass weighed each time is small (usually less than 500g), making it difficult to quantitatively monitor all the metal elemental foreign particles contained in the positive electrode active material. Therefore, when using the ICP method to detect the content of metal elemental foreign particles in the positive electrode active material, there is a high risk of missed detection.

[0068] In the detection method provided in the embodiments of this application, before the positive electrode active material is mixed evenly with the first solvent, the positive electrode active material is subjected to dry sieving, which can process a large number of samples, such as up to 100 kg of solid powder of the positive electrode active material to be tested. At the same time, the risk of missed detection is relatively small.

[0069] In some embodiments, the detection method includes the following steps: pre-sieving the solid powder of the positive electrode active material to be detected, collecting the solid components remaining on the sieve after pre-sieving, and then mixing it evenly with a first solvent to obtain a first mixture; sieving the obtained first mixture, collecting the first solid components remaining on the sieve after sieving; cleaning the first solid components with a cleaning agent, drying the cleaned first solid components, and then reacting them with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution to obtain a second mixture; separating the obtained second mixture to obtain a second solid component including elemental metal particles; scanning the obtained second solid component with a scanning device to count the number of elemental metal particles, and calculating the mass of the elemental metal particles and their content in the positive electrode active material based on the number of elemental metal particles. This reduces the risk of missed detection and improves detection accuracy.

[0070] In some embodiments, a dry sieving machine, such as a dry vibrating sieve, can be used to pre-sieve the solid powder of the positive electrode active material to be tested.

[0071] When pre-sieving the solid powder of the positive electrode active material to be tested, a suitable sieve can be selected according to the required control specifications to reduce the risk of missed detection and improve detection accuracy. Furthermore, a suitable sieve can be selected based on the volume distribution and particle size of the positive electrode active material to improve detection efficiency.

[0072] When pre-sieving large quantities of solid powdered positive electrode active materials, selecting a suitable sieve can reduce the risk of missed detection and improve detection accuracy, while effectively reducing the amount of positive electrode active material remaining on the sieve. This also helps to reduce the amount of reaction reagents (such as weak oxidizing acid solutions, antioxidants, and corrosion inhibitor solutions) used, thus reducing environmental pollution.

[0073] In some embodiments, the pore size of the sieve used for pre-sieving the positive electrode active material solid powder to be detected can be 8μm-25μm, specifically 9μm-22μm, 9μm-20μm, 10μm-18μm, or 10μm-15μm. This can reduce the risk of missed detection while improving detection efficiency.

[0074] When sieving the obtained first mixture, a suitable screen can be selected according to the required control specifications to reduce the risk of missed detection and improve detection accuracy. Furthermore, a suitable screen can be selected based on the volume distribution and particle size of the positive electrode active material to improve detection efficiency.

[0075] In some embodiments, the sieve used for sieving the obtained first mixture can have a pore size of 8μm-25μm, specifically 9μm-22μm, 9μm-20μm, 10μm-18μm, or 10μm-15μm. This can reduce the risk of missed detection, improve detection efficiency, and also help reduce the amount of reaction reagents (e.g., weak oxidizing acid solutions, antioxidants, corrosion inhibitor solutions), thus reducing environmental pollution.

[0076] In some embodiments, the first solvent may include one or more of water (e.g., ultrapure water), methanol, ethanol, and acetone, but this application embodiment is not limited to this.

[0077] In some embodiments, in the step of uniformly mixing the positive electrode active material to be detected with a first solvent to obtain a first mixture, the mass ratio of the positive electrode active material to be detected to the first solvent can be from 1:2.5 to 1:30, and optionally from 1:10 to 1:20. This allows for uniform dispersion of the positive electrode active material, facilitating effective separation of the positive electrode active material from oxide foreign particles, elemental metal foreign particles, etc., through a sieve. It also reduces the amount of residual positive electrode active material in the first solid component, reduces the amount of reaction reagents (e.g., weak oxidizing acid solutions, antioxidants, corrosion inhibitor solutions), and reduces environmental pollution; furthermore, it helps improve detection efficiency.

[0078] In some embodiments, a dispersant may also be added to the first mixture. The dispersant helps to disperse the positive electrode active material uniformly, facilitating the effective separation of the positive electrode active material from oxide foreign particles, elemental metal foreign particles, etc., through a sieve, reducing the amount of residual positive electrode active material in the first solid component, reducing the amount of reaction reagents (e.g., weak oxidizing acid solution, antioxidant, corrosion inhibitor solution), reducing environmental pollution; and also helps to improve detection efficiency.

[0079] 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 selected as 0.005:1 to 0.02:1.

[0080] "Dispersant" refers to a class of substances added to a suspension to improve particle separation and prevent particle sedimentation or agglomeration. In some embodiments, the dispersant may include an aqueous dispersant, optionally including a polymer compound such as a comb-type polymer compound, a block polymer compound, etc., and more preferably a nonionic polymer compound.

[0081] For example, the dispersant may include, but is not limited to, one or more of polyvinylpyrrolidone (PVP), polyethylene glycol, ethyl cellulose, waterborne polyurethane, waterborne acrylic resin, and branched secondary alcohol polyoxyethylene ether. As an example, the dispersant may include one or more of polyvinylpyrrolidone (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 waterborne dispersants (such as LIB-D200, LIB-D300, etc.), and Dow Chemical's TERGITOL series dispersants (such as TMN-6, TMN-10, etc.). In some embodiments, the obtained first mixture may be sieved using a sieving device, optionally a wet sieve separator.

[0082] This helps to effectively separate the positive electrode active material from oxide foreign particles and elemental metal foreign particles, reducing the amount of residual positive electrode active material in the first solid component, reducing the amount of reaction reagents (such as weak oxidizing acid solutions, antioxidants, and corrosion inhibitor solutions), and reducing environmental pollution; it also helps to improve detection efficiency.

[0083] In some embodiments, the total amount of the weak oxidizing acid solution, antioxidant, and corrosion inhibitor solution added is sufficient to submerge the first solid component and fully dissolve the residual positive electrode active material and oxide foreign particles therein.

[0084] In some embodiments, the mass ratio of the antioxidant to the weak oxidizing acid solution can be 1:5 to 1:40, preferably 1:6 to 1:30, 1:8 to 1:25, or 1:8 to 1:20. Adjusting the mass ratio of the antioxidant to the weak oxidizing acid solution within the above range can better dissolve oxide foreign particles and residual positive electrode active material, while reducing the dissolution of elemental metal foreign particles, thereby improving the accuracy of detecting the content of elemental metal foreign particles in the positive electrode active material.

[0085] In some embodiments, the mass ratio of the antioxidant to the corrosion inhibitor solution can be 1:1 to 1:5, preferably 1:1.1 to 1:4, or 1:1.15 to 1:3. Adjusting the mass ratio of the antioxidant to the corrosion inhibitor solution within the above range can further reduce the oxidation and dissolution of elemental metal particles, thereby improving the accuracy of detecting the content of elemental metal particles in the positive electrode active material.

[0086] In some embodiments, the weak oxidizing acid may include inorganic acids and / or organic acids.

[0087] In some embodiments, the inorganic acid may include one or more of sulfuric acid, hydrochloric acid, and phosphoric acid.

[0088] In some embodiments, the organic acid may include one or more of aminosulfonic acid, citric acid, oxalic acid, acetic acid, lactic acid, malic acid, and citric acid.

[0089] In some embodiments, the mass fraction of the weak oxidizing acid solution can be 5%-30%, optionally 8%-28%, with the remainder being water. This allows for better dissolution of oxide foreign particles and residual positive electrode active material, while reducing the dissolution of elemental metal foreign particles, thereby improving the accuracy of detecting the content of elemental metal foreign particles in the positive electrode active material.

[0090] 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% or 14%-22%.

[0091] 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% or 8%-18%.

[0092] 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% or 16%-26%.

[0093] In some embodiments, the corrosion inhibitor may include one or more of benzotriazole corrosion inhibitors, imidazole corrosion inhibitors, thiazole corrosion inhibitors, and thiophene corrosion inhibitors.

[0094] In some embodiments, the benzotriazole corrosion inhibitor may include one or more of benzotriazole (BTA), methylbenzotriazole, ethylbenzotriazole, propylbenzotriazole, butylbenzotriazole, and carboxybenzotriazole.

[0095] In some embodiments, the imidazole corrosion inhibitor may include one or more of benzimidazole and thiabendazole.

[0096] In some embodiments, the thiazole corrosion inhibitor may include one or more of 2-methylbenzothiazole and 2-mercaptobenzothiazole.

[0097] In some embodiments, the thiophene-based corrosion inhibitor may include benzothiophene.

[0098] In some embodiments, the corrosion inhibitor solution can be prepared by mixing a corrosion inhibitor, an alkali, and water solvent evenly to form a corrosion inhibitor solution. Optionally, the alkali includes sodium hydroxide.

[0099] In some embodiments, the mass fraction of the corrosion inhibitor in the corrosion inhibitor solution may be 5%-15%, preferably 7%-14%.

[0100] In some embodiments, the antioxidant may include one or more of the following: tea polyphenols, acetaldehyde oxime, ascorbic acid, acetone oxime, hydrazine hydrate, H2O2, Na2S2O3, Na2SO3, NaHSO3, and FeSO4.

[0101] In some embodiments, the reaction time after mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution can be 0.5-2 hours. Adjusting the reaction time within the above range can better dissolve oxide foreign particles and residual positive electrode active material, while reducing the dissolution of elemental metal foreign particles, thereby improving the accuracy of detecting the content of elemental metal foreign particles in the positive electrode active material.

[0102] In some embodiments, the reaction temperature after mixing the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution can be 40°C-80°C. Adjusting the reaction time within the above range can better dissolve oxide foreign particles and residual positive electrode active material, while reducing the dissolution of elemental metal foreign particles, thereby improving the accuracy of detecting the content of elemental metal foreign particles in the positive electrode active material.

[0103] In some embodiments, the heating method for reacting the obtained first solid component with a weak oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution can be water bath heating, and this application embodiment does not limit this.

[0104] In some embodiments, the second mixture can be separated by filtration (such as vacuum filtration) to obtain a second solid component including metallic foreign particles. Of course, other solid-liquid separation methods known in the art can also be used, and the embodiments of this application are not limited in this regard.

[0105] In some embodiments, the scanning device may include a scanning electron microscope, such as a Phenom scanning electron microscope. This allows for simultaneous qualitative and quantitative detection of metallic foreign particles.

[0106] Example

[0107] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0108] Example 1-1

[0109] Weigh 0.1g of the positive electrode active material NCM523 and add approximately 5mg of Cu standard. Prepare a reaction solution (V1) by mixing 50ml of dilute sulfuric acid aqueous solution (20% by mass), 5g of ascorbic acid powder, and 5ml of benzotriazole sodium hydroxide solution (11% by mass of benzotriazole and 5.5% by mass of sodium hydroxide). Add the positive electrode active material containing Cu standard to the reaction solution and allow it to react in a 50℃ water bath for 1-2 hours until the positive electrode active material is completely dissolved.

[0110] Take 1 mL of the reaction liquid and dilute it 50 times with ultrapure water to obtain the test solution. Take an appropriate amount of the test solution and determine the copper content in the test solution using inductively coupled plasma atomic emission spectrometry (ICP-AES), and calculate the copper recovery rate. The results are shown in Table 1.

[0111] Examples 1-2 to Examples 1-18

[0112] Except for the type and / or quality of the positive electrode active material and the type and quality of the standard, everything else is the same as in Examples 1-1. Specific parameters are detailed in Table 1.

[0113] In Table 1, the recovery rate of copper (%) is calculated as follows: [(Copper content in the test solution × V1 × 50) / Mass of copper in the standard / 1000] × 100%. The unit for the copper content in the test solution is mg / L, and V1 is 55 ml. When the standard is copper oxide, the mass of copper in the standard is calculated as: Mass of copper oxide standard × 0.8, in mg.

[0114] Table 1

[0115]

[0116] As shown in Table 1, the recovery rate of copper element was around 100% after adding copper oxide standard, while the recovery rate of copper element was very low, such as below 5%, after adding copper standard. This indicates that the reaction solution provided in this application can completely dissolve the positive electrode active material and copper oxide foreign particles, while hardly dissolving the copper element foreign particles.

[0117] The inventors then examined the applicability and effectiveness of the detection method provided in the embodiments of this application for residual positive electrode active material on the sieve.

[0118] 1000g of positive electrode active material (volume distribution particle size Dv50 of 6μm) was mixed evenly with 10g of dispersant and 15kg of solvent water. After being sieved using a wet sieve separator (sieve aperture can be 10μm-15μm), the mass of positive electrode active material remaining on the sieve was less than 1.0g. In Examples 2-1 to 2-9, the inventors weighed 0.5g of positive electrode active material to simulate the positive electrode active material remaining on the sieve and added a small amount of elemental copper particles to conduct a spiked recovery experiment.

[0119] Examples 2-1 to 2-9

[0120] Weigh 0.5g of the positive electrode active material NCM523 and add copper elemental particles with different volume distribution particle sizes (Dv50), different particle numbers, and different morphologies (specific parameters are detailed in Table 2). Prepare a reaction solution by mixing 50ml of dilute sulfuric acid aqueous solution (20% by mass), 5g of ascorbic acid powder, and 5ml of benzotriazole sodium hydroxide solution (benzotriazole mass fraction 11%, sodium hydroxide mass fraction 5.5%), with a volume V1 recorded as 55ml. Add the above-mentioned positive electrode active material containing copper elemental particles to the reaction solution and let it react in a 50℃ water bath for 1-2 hours until the positive electrode active material is completely dissolved. Filter the reaction liquid, then remove the filter membrane, and after it is fully dried, count the number of copper elemental particles on the filter membrane using a Phenom scanning electron microscope. The results are shown in Table 2.

[0121] In Table 2, the recovery rate of elemental copper particles = (number of elemental copper particles detected / number of elemental copper particles added) × 100%.

[0122] Table 2

[0123]

[0124] As shown in Table 2, the detection method provided by the embodiments of this application can effectively collect copper elemental particles of various sizes, morphologies, and small particle numbers (such as ppb level). The recovery rate of copper elemental particles is above 80%, and the repeatability of the detection results is good.

[0125] In Comparative Examples 1 to 9, the inventors weighed 0.5g of the positive electrode active material remaining on the simulated sieve and added Cu standard, CuO standard and a small amount of copper elemental particles to conduct a spiked recovery experiment.

[0126] Comparative Examples 1 to 3

[0127] Weigh 0.5 g of positive electrode active material NCM523, NCM622, or NCM811 respectively, add approximately 5 mg of Cu standard, and then react in a mixed solution of ammonium chloride and ammonia (mass ratio of ammonium chloride to ammonia is 1:50) at 25 °C for 1 h with stirring. Filter and collect the filtrate. Concentrate the filtrate to 10 mL at 300 °C, then dilute to 100 mL with ultrapure water, and then dilute 50 times with ultrapure water to obtain 5 L of test solution. Take an appropriate amount of the test solution and determine the copper content in the test solution using inductively coupled plasma atomic emission spectrometry (ICP-AES), and calculate the copper recovery rate. The results are shown in Table 3.

[0128] Comparative Examples 4 to 6

[0129] Except for the use of CuO standard, all other parameters are the same as those in Comparative Examples 1 to 3. See Table 3 for specific parameters.

[0130] Comparative Examples 7 to 9

[0131] Except for the standard sample, which uses elemental copper particles (spherical particles with a volume distribution particle size Dv50 of 20 μm), all other parameters are the same as those in Comparative Examples 1 to 3. Specific parameters are detailed in Table 3.

[0132] In Table 3, the recovery rate of copper (%) is calculated as follows: [(Copper content in the test solution × Volume of the test solution) / Mass of copper in the standard] × 100%. The unit for the copper content in the test solution is mg / L, and the volume of the test solution is 5L. When the standard is copper oxide, the mass of copper in the standard = mass of copper oxide standard × 0.8, in mg.

[0133] Table 3

[0134]

[0135] Comparative Examples 1 to 3 show that the ICP method has good detection capability for copper elemental particles at the ppm level.

[0136] Comparative Examples 4 to 6 show that the copper recovery rate is higher after adding copper oxide standard. This indicates that some copper oxide also reacts, and therefore, during ICP testing, copper oxide foreign particles can interfere with the detection results of elemental copper foreign particles, leading to lower detection accuracy.

[0137] As can be seen from Comparative Examples 7 to 9, when the content of copper elemental particles is low (such as the copper element content is at the ppb level), copper cannot be detected in the test solution due to the limitation of the instrument's own detection limit.

[0138] As can be seen from Tables 1 and 2, the detection method provided in the embodiments of this application can perform qualitative and quantitative detection of foreign particles such as elemental copper in the positive electrode active material, and the detection results are highly accurate and repeatable. The detection method provided in the embodiments of this application can also identify the particle size and morphology of foreign particles such as elemental copper in the positive electrode active material. The detection method provided in the embodiments of this application uses fewer reaction reagents and can also reduce environmental pollution.

[0139] 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 for detecting the content of metal elemental foreign particles in a positive electrode active material, comprising the following steps: mixing the positive electrode active material to be detected with a first solvent uniformly to obtain a first mixture; performing a sieving treatment on the obtained first mixture to collect a first solid component remaining on a sieve after the sieving treatment; mixing the obtained first solid component with a weakly oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution to perform a reaction, to obtain a second mixture; separating the obtained second mixture to obtain a second solid component comprising 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 the content of the metal elemental foreign particles in the positive electrode active material according to the number of the metal elemental foreign particles. The metal elemental foreign particles comprise one or more of copper elemental foreign particles and stainless steel foreign particles. Before the step of mixing the obtained first solid component with a weakly oxidizing acid solution, an antioxidant, and a corrosion inhibitor solution to perform a reaction, the method further comprises the step of: cleaning the first solid component with a cleaning agent. The cleaning agent comprises water. Before the step of mixing the positive electrode active material to be detected with a first solvent uniformly to obtain a first mixture, the method further comprises the step of: performing a pre-sieving treatment on a solid powder of the positive electrode active material to be detected, collecting a solid component remaining on a sieve after the pre-sieving treatment, and then mixing the solid component with a first solvent uniformly to obtain a first mixture. 6.The method of claim 5, wherein the pre-sieving treatment is performed using a dry sieving machine; and / or the pre-sieving treatment is performed using a sieve with a pore size of 8-25 μm.

2. The method of claim 1, wherein, The pre-sieving treatment is performed using a sieve with a pore size of 10-18 μm.

3. The method of claim 1, wherein, The sieving treatment on the first mixture is performed using a sieve with a pore size of 8-25 μm.

4. The method of claim 3, wherein, The sieving treatment on the first mixture is performed using a sieve with a pore size of 10-18 μm.

5. The method of claim 1, wherein, 10.The method of claim 1, wherein a dispersing agent is further added to the first mixture. The mass ratio of the dispersing agent to the positive electrode active material is less than or equal to 0.025:

1. The mass ratio of the dispersing agent to the positive electrode active material is 0.005:1 to 0.02:

1. The dispersing agent comprises an aqueous dispersing agent.

7. The method of claim 6, wherein, The dispersing agent comprises a high molecular compound.

8. The method of claim 1, wherein, 15.The method of claim 1, wherein the mass ratio of the antioxidant to the weakly oxidizing acid solution is 1:5 to 1:40; and / or the mass ratio of the antioxidant to the corrosion inhibitor solution is 1:1 to 1:5; and / or the mass fraction of the weakly oxidizing acid solution is 5%-30%; and / or the mass fraction of the corrosion inhibitor solution is 5%-15%.

9. The method of claim 8, wherein, 16.The method of claim 15, wherein the mass ratio of the antioxidant to the weakly oxidizing acid solution is 1:8 to 1:25; and / or the mass ratio of the antioxidant to the corrosion inhibitor solution is 1:1.15 to 1:3; and / or ​ ​ 11. The method of claim 10, wherein, ​ 12. The method of claim 11, wherein, ​ 13. The method of claim 10, wherein, ​ 14. The method of claim 13, wherein, ​ ​ ​ ​ ​ ​ ​ ​ ​ The mass fraction of the weak oxidizing acid solution is 8%-28%; and / or, The mass fraction of the corrosion inhibitor solution is 7%-14%.

17. The method of claim 1, wherein, The weak oxidizing acid comprises inorganic acid and / or organic acid; and / or, The corrosion inhibitor comprises one or more of benzotriazole corrosion inhibitor, imidazole corrosion inhibitor, thiazole corrosion inhibitor, thiophene corrosion inhibitor; and / or, The antioxidant comprises one or more of tea polyphenol, acetaldoxime, ascorbic acid, acetone oxime, hydrazine hydrate, H2O2, Na2S2O3, Na2SO3, NaHSO3, FeSO4.

18. The method of claim 17, wherein, The inorganic acid comprises one or more of sulfuric acid, hydrochloric acid, phosphoric acid; and / or, The organic acid comprises one or more of sulfamic acid, citric acid, oxalic acid, acetic acid, lactic acid, malic acid, citric acid; and / or, The benzotriazole corrosion inhibitor comprises one or more of benzotriazole, methyl benzotriazole, ethyl benzotriazole, propyl benzotriazole, butyl benzotriazole, carboxyl benzotriazole; and / or, The imidazole corrosion inhibitor comprises one or more of benzimidazole, thio benzimidazole; and / or, The thiazole corrosion inhibitor comprises one or more of 2-methyl benzothiazole, 2-mercaptobenzothiazole; and / or, The thiophene corrosion inhibitor comprises benzothiophene.

19. The method of claim 1, wherein, The weak oxidizing acid solution is a sulfuric acid solution, and the mass fraction of the sulfuric acid solution is 10%-30%.

20. The method of claim 1, wherein, The weak oxidizing acid solution is a hydrochloric acid solution, and the mass fraction of the hydrochloric acid solution is 5%-20%.

21. The method of claim 1, wherein, The weak oxidizing acid solution is a phosphoric acid solution, and the mass fraction of the phosphoric acid solution is 15%-30%.

22. The method of claim 1, wherein, The time for the obtained first solid component to react after being mixed with the weak oxidizing acid solution, the antioxidant, and the corrosion inhibitor solution is 0.5-2h; and / or, The temperature for the obtained first solid component to react after being mixed with the weak oxidizing acid solution, the antioxidant, and the corrosion inhibitor solution is 40℃-80℃.

23. The method of any one of claims 1-22, 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 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; (4) The second mixed solution is separated by suction filtration to obtain a second solid component comprising metal elemental foreign object particles; (5) A screening device is used when the obtained first mixed solution is subjected to screening treatment; (6) The scanning device comprises a scanning electron microscope.

24. The method of claim 23, wherein, The mass ratio of the positive electrode active material to be detected to the first solvent is 1:10 to 1:

20.

25. The method of claim 23, wherein, A wet screening instrument is used when the obtained first mixed solution is subjected to screening treatment.

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