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

Abstract

The application provides a method for detecting the content of active metal foreign matters in electrode materials, which comprises the following steps: providing a sample to be detected containing active metal foreign matters; contacting the sample to be detected with a sufficient amount of an acid solution, so that the active metal foreign matters sufficiently react with the acid at a reaction temperature to obtain a reaction product containing hydrogen; and detecting the content of hydrogen in the reaction product, so as to obtain the content of the active metal foreign matters in the sample to be detected according to the content of hydrogen in the reaction product.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a method for detecting the content of active metal foreign matter in electrode materials. Background Technology

[0002] Secondary batteries rely on the repeated insertion and extraction of active ions between the positive and negative electrodes for charging and discharging. Lithium-ion batteries, in particular, possess outstanding characteristics such as high energy density, long cycle life, and the absence of pollution and memory effect. Therefore, as a clean energy source, secondary batteries have gradually expanded from electronic products to large-scale devices such as electric vehicles, in line with sustainable development strategies for the environment and energy.

[0003] With the development of electronic products, electric vehicles, and other devices, higher demands are being placed on the performance of rechargeable batteries. During the production of electrode materials, wear and tear on machinery and pipelines, as well as the introduction of impurities from raw materials, inevitably introduce metal particles such as iron and iron-chromium-nickel. During battery charging and discharging, these metal particles undergo redox reactions between the positive and negative electrodes. When the reduced metal element accumulates to a certain level at the negative electrode, its sharp edges can pierce the separator, causing a short circuit and self-discharge, affecting the battery's lifespan and reliability. Therefore, the detection of metal particles in electrode materials is particularly important. Summary of the Invention

[0004] To achieve the above objectives, this application provides a method for detecting the content of active metal foreign matter in electrode materials, which can efficiently and accurately detect the content of active metal foreign matter in electrode materials, thereby extending the service life of the battery and improving the reliability of the battery.

[0005] This application provides a method for detecting the content of active metal foreign matter in electrode materials, including:

[0006] Provide a test sample containing reactive metallic foreign matter;

[0007] The sample to be tested is brought into contact with a sufficient amount of acid solution to allow the active metal foreign matter to react fully with the acid at the reaction temperature, thereby obtaining a reaction product containing hydrogen.

[0008] The hydrogen content in the reaction products is detected so that the content of active metal foreign matter in the sample to be tested can be determined based on the hydrogen content in the reaction products.

[0009] Not intended to be limited to any theory or explanation, the method according to embodiments of this application involves providing a sample to be tested, obtained from a sample taken from the electrode material to be tested, and contacting the sample with an acid to allow an active metal foreign substance to undergo a displacement reaction with the acid, yielding a reaction product containing hydrogen. The content of the active metal foreign substance in the sample can be determined by detecting the hydrogen content in the reaction product. The method according to embodiments of this application indirectly determines the content of active metal foreign substances through a displacement reaction between the active metal foreign substance and the acid, which has higher accuracy and detection efficiency compared to the SEM-DES detection method involved in related technologies. Furthermore, the method according to embodiments of this application obtains the content of the active metal foreign substance in the sample by the hydrogen content in the reaction product; since hydrogen is a gaseous product, the acid solution and electrode material, etc., have minimal influence on the detection of hydrogen content, thereby improving the accuracy of quantitative detection. Therefore, compared to the related technical solutions that indirectly determine the content of active metal foreign substances through a displacement reaction between copper sulfate and an active metal, the method of embodiments of this application can achieve higher accuracy.

[0010] Therefore, the method of this application embodiment, when applied to the battery field, can efficiently and accurately detect the content of active metal foreign matter in electrode materials during battery manufacturing. The method of this application embodiment has high detection efficiency, allowing the monitoring of active metal foreign matter content to be adapted to the production cycle of battery manufacturing, thereby improving battery production efficiency. The method of this application embodiment also has high accuracy, enabling precise monitoring of the content of active metal foreign matter in electrode materials, thus facilitating strict control over the metal particle content in electrode materials, reducing the risk of battery short-circuit self-discharge, extending battery life, and improving battery reliability.

[0011] In any embodiment of this application, the reactive metallic foreign object includes at least one of elemental iron or an iron-chromium-nickel alloy.

[0012] The method described in this application can detect the content of active metal foreign matter, including elemental iron and / or iron-chromium-nickel alloys. It is applicable to the detection of active metal foreign matter content in lithium iron phosphate prepared from ferrous oxalate and nickel-containing lithium transition metal oxides. This facilitates precise monitoring of the active metal foreign matter content in the aforementioned cathode active materials, thereby enabling strict control over the metal particle content in batteries using these materials, reducing the risk of short-circuit self-discharge, extending battery life, and improving battery reliability.

[0013] In any embodiment of this application, a test sample containing a reactive metallic foreign object is provided, including:

[0014] After the electrode material to be tested is stirred evenly, a predetermined mass of the electrode material to be tested is weighed to obtain the sample to be tested.

[0015] Optionally, the electrode material to be tested includes lithium iron phosphate prepared from ferrous oxalate.

[0016] According to the method in the embodiments of this application, for lithium iron phosphate materials containing multiple active metal foreign matter, samples can be directly taken from lithium iron phosphate for testing without extracting the active metal foreign matter, and the content of active metal foreign matter in the sample can be determined. This simplifies the detection process, reduces the risk of loss of active metal foreign matter, and thus improves the detection efficiency and accuracy of active metal foreign matter content.

[0017] In any embodiment of this application, the preset mass is 40g-80g, and more preferably 50g-60g. When the preset mass is within a suitable range, the proportion of active metal foreign matter in the sample to be tested can be made closer to the actual proportion of active metal foreign matter in lithium iron phosphate. This improves the accuracy of active metal foreign matter detection. Furthermore, when the preset mass is within the aforementioned suitable range, the reaction time can be shortened, improving the detection efficiency of active metal foreign matter content.

[0018] In any embodiment of this application, a test sample containing a reactive metallic foreign object is provided, including:

[0019] Provide a dispersion of the electrode material to be tested;

[0020] Magnetic materials are extracted from the dispersion using a 5000GS-6000GS magnetic rod. The magnetic materials include at least one of elemental iron or an iron-chromium-nickel alloy.

[0021] The magnetic material is enriched onto the filter membrane, washed and dried, and then placed into a water-soluble bag to obtain the sample to be tested.

[0022] Optionally, the electrode material to be tested includes nickel-containing lithium transition metal oxides.

[0023] According to the method of this application embodiment, magnetic materials are extracted from the dispersion of the electrode material to be tested using a magnetic rod. These magnetic materials are then enriched onto a filter membrane, processed, and placed in a water-soluble bag to obtain the sample to be tested. This reduces the loss of magnetic materials during filter membrane transfer, thereby improving detection accuracy. After the sample to be tested comes into contact with an acid solution, the water-soluble bag dissolves in the acid solution, allowing the magnetic materials in the sample to come into contact with the acid and react fully. This further improves reaction efficiency, thereby increasing detection efficiency.

[0024] In any embodiment of this application, the sample to be tested is contacted with a sufficient amount of acid solution to allow the active metal foreign substance to react fully with the acid at the reaction temperature, yielding a reaction product containing hydrogen gas, including:

[0025] The sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum to allow the active metal foreign substance to react fully with the acid at the first reaction temperature, thereby obtaining a reaction product containing hydrogen gas.

[0026] This can improve the accuracy of detecting the content of reactive metal foreign matter.

[0027] In any embodiment of this application, the first reaction temperature is 50°C-70°C, and can be selected as 55°C-60°C.

[0028] In any embodiment of this application, the reaction time for the active metal foreign substance and the acid to fully react at the first reaction temperature is 1.5h-2.5h.

[0029] When the first reaction temperature and / or the reaction time for the active metal foreign substance to fully react with the acid at the first reaction temperature are within the above-mentioned appropriate range, the detection time for the active metal foreign substance can be controlled within a shorter range, thereby improving the detection efficiency of the active metal foreign substance content.

[0030] In any embodiment of this application, the reactive metallic foreign object includes elemental iron.

[0031] Optionally, the electrode material to be tested includes lithium iron phosphate prepared from iron phosphate.

[0032] The method described in this application can be applied to the detection of active metal foreign matter content in lithium iron phosphate prepared from lithium iron phosphate. This facilitates precise monitoring of the active metal foreign matter content in lithium iron phosphate prepared from lithium iron phosphate, thereby enabling strict control over the metal particle content in batteries using the aforementioned lithium iron phosphate, reducing the risk of battery short-circuit self-discharge, extending battery life, and improving battery reliability.

[0033] In any embodiment of this application, a test sample containing a reactive metallic foreign object is provided, including:

[0034] Provide a dispersion of the electrode material to be tested;

[0035] Magnetic materials were extracted from the dispersion using a 5000GS-6000GS magnetic rod. The magnetic materials included elemental iron and iron phosphide impurities.

[0036] The magnetic material is enriched onto the filter membrane, washed and dried, and then placed into a water-soluble bag to obtain the sample to be tested.

[0037] According to the method of this application embodiment, magnetic materials are extracted from the dispersion of the electrode material to be tested using a magnetic rod. These magnetic materials are then enriched onto a filter membrane, processed, and placed in a water-soluble bag to obtain the sample to be tested. This reduces the loss of magnetic materials during filter membrane transfer, thereby improving detection accuracy. After the sample to be tested comes into contact with an acid solution, the water-soluble bag dissolves in the acid solution, allowing the magnetic materials in the sample to come into contact with the acid and react fully. This further improves reaction efficiency, thereby increasing detection efficiency.

[0038] In any embodiment of this application, the sample to be tested is contacted with a sufficient amount of acid solution to allow the active metal foreign substance to react fully with the acid at the reaction temperature, yielding a reaction product containing hydrogen gas, including:

[0039] The sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum to allow the active metal foreign substance to react fully with the acid at a second reaction temperature to obtain a reaction product containing hydrogen gas. The second reaction temperature is 20℃-30℃.

[0040] The above-described embodiments can reduce the interference of reduced iron in ferric phosphide on the detection of active metal foreign matter content, thereby improving the accuracy of detection. Furthermore, according to the above embodiments, mixing the sample to be tested with a sufficient amount of acid solution in an inert atmosphere or vacuum can reduce the risk of side reactions between iron ions and elemental iron in the sample, and can also improve the accuracy of detecting hydrogen content in the reaction products. Therefore, the accuracy of detecting active metal foreign matter can be further improved.

[0041] In any embodiment of this application, the second reaction temperature is 25°C-30°C.

[0042] In any embodiment of this application, the reaction time for the active metal foreign substance and the acid to fully react at the second reaction temperature is 2h-2.5h.

[0043] When the second reaction temperature and / or the reaction time for the active metal foreign matter to fully react with the acid at the second reaction temperature are within the above-mentioned appropriate range, not only can the detection time of the active metal foreign matter be controlled within a shorter range, but the risk of iron phosphide reacting with the acid at the second reaction temperature can also be further reduced, thereby reducing the interference of reduced iron in iron phosphide on the detection of active metal foreign matter content, thus improving the detection efficiency and accuracy of active metal foreign matter content.

[0044] In any embodiment of this application, the acid solution includes at least one of a dilute sulfuric acid solution and a dilute hydrochloric acid solution. The aforementioned acid solution can exhibit a suitable reaction rate with reactive metallic foreign substances, which helps to shorten detection time and improve detection efficiency.

[0045] In any embodiment of this application, the acid solution contains F-. F- can complex with iron ions dissolved from active metal foreign substances, thereby inhibiting the reaction between iron ions and elemental iron and improving the accuracy of detecting the content of active metal foreign substances.

[0046] In any embodiment of this application, the acid solution further includes antioxidants and / or oxygen scavengers. This further reduces the risk of ferrous ions being oxidized to ferric ions, thereby reducing side reactions between ferric ions and elemental iron, and further improving the accuracy of detection.

[0047] In any embodiment of this application, the acid solution further includes a surfactant. The surfactant improves the dispersibility of the powdered test sample in the acid solution, facilitating the full reaction of reactive metallic foreign matter in the test sample with the acid. This further enhances the accuracy of the detection.

[0048] In any embodiment of this application, contacting the sample to be tested with an acid solution includes: mixing the sample to be tested and the acid solution in a closed reaction vessel, wherein the inner wall surface of the reaction vessel is coated with Teflon.

[0049] This reduces the impact of the reaction vessel on the detection results, thus helping to further improve the accuracy of the detection.

[0050] In any embodiment of this application, detecting the hydrogen content in the reaction product includes: performing gas chromatography on the reaction product to obtain the hydrogen content in the reaction product. Gas chromatography has high accuracy in detecting hydrogen content, which is beneficial for improving the accuracy of detecting the content of active metal foreign substances. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of a reaction apparatus according to one embodiment of this application.

[0052] Figure 2 This is a gas chromatogram of the gas phase components of the reaction product in sample 5 in Example 5 of this application. Detailed Implementation

[0053] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the method for detecting the content of active metal foreign matter in electrode materials according to this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0054] 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.

[0055] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0056] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0057] 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.

[0058] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0059] In this paper, an active metal can be defined as a metal that precedes hydrogen in the metal activity series; the standard electrode potential of an active metal in a neutral solution for half-reaction is less than 0.

[0060] In the embodiments of this application, the nickel-containing lithium transition metal oxide may include one or more of the nickel-containing lithium transition metal oxides and their modified compounds known in the art for use in secondary batteries. Examples of nickel-containing lithium transition metal oxides may include, but are not limited to, one or more of lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. For example, it may include, but is not limited to, LiNi 0.9 Co 0.05 Mn 0.05 (NCM9055), LiNi 0.8 Co 0.1 Mn 0.1 (NCM811), LiNi 0.7 Co 0.2 Mn 0.1 (NCM721), LiNi 0.6 Co 0.2 Mn 0.2 One or more of (NCM622).

[0061] With the development of electronic products, electric vehicles and other devices, people have put forward higher requirements for the performance of secondary batteries.

[0062] During the production of electrode materials, metal particles such as iron and iron-chromium-nickel are inevitably introduced due to wear and tear on machinery and pipelines, as well as impurities from raw materials. During battery charging and discharging, these metal particles undergo redox reactions between the positive and negative electrodes. When the reduced metal at the negative electrode accumulates to a certain level, its sharp edges can pierce the separator, causing a short circuit and self-discharge, thus affecting the battery's lifespan and reliability. Therefore, the detection of metal particles in electrode materials is particularly important.

[0063] Therefore, this application provides a method for detecting the content of active metal foreign matter in electrode materials, which can efficiently and accurately detect the residual amount of volatile substances in the sample, thereby extending the battery's service life and improving its reliability.

[0064] This application provides a method for detecting the content of active metal foreign matter in electrode materials, including the following steps S110 to S130.

[0065] S110 provides a sample to be tested containing a reactive metallic foreign object.

[0066] In step S110, the sample to be tested may include a sample taken from the electrode material to be tested. The electrode material to be tested may include the positive electrode material and / or the negative electrode material to be tested. The electrode material to be tested may be an electrode material obtained in any process before coating the electrode film layer on the electrode current collector surface, for example, it may be battery raw material powder, positive electrode slurry, negative electrode slurry, etc. The battery raw material powder may include, but is not limited to, powders used to form the positive electrode film layer and / or the negative electrode film layer, for example, it may include, but is not limited to, at least one of positive electrode active material, negative electrode active material, and conductive agent.

[0067] S120 involves contacting the sample to be tested with a sufficient amount of acid solution to allow the active metal foreign substance to react fully with the acid at the reaction temperature, thereby obtaining a reaction product containing hydrogen gas.

[0068] In step S120, the acid solution may include non-oxidizing acid solutions known in the art, and those skilled in the art can select appropriate types of acid solutions according to actual needs. Sufficient acid solution indicates that the amount of acid solution is sufficient to allow all active metal foreign matter in the test sample to react completely. The aforementioned "sufficient reaction" indicates that the active metal foreign matter in the test sample reacts completely with the acid until no more hydrogen gas is produced. "Sufficient reaction" can be determined in various ways. As an example, the test sample can be brought into sufficient contact with a sufficient amount of acid solution for a sufficiently long time, for example, the reaction time can be more than 1 hour, more than 1.5 hours, more than 2 hours, etc. Those skilled in the art can determine the appropriate reaction time based on the amount of the test sample and the reaction temperature, etc. As another example, the test sample and acid solution can be brought into contact in a closed container, and the hydrogen concentration and / or pressure in the closed container can be detected. When the hydrogen concentration and / or pressure no longer change, it can be considered that the active metal foreign matter and acid have reached a sufficient reaction state.

[0069] S130, detects the hydrogen content in the reaction product, so as to obtain the content of active metal foreign matter in the sample to be tested based on the hydrogen content in the reaction product.

[0070] In step S130, detecting the hydrogen content in the reaction products may include detecting the hydrogen content of the gaseous components in the closed reaction system. Detecting the hydrogen content in the reaction products can be achieved using equipment and methods known in the art, such as hydrogen sensors or gas chromatographs. Those skilled in the art can select appropriate testing equipment and methods based on the detection environment, accuracy requirements, etc.

[0071] In battery manufacturing, it is necessary to detect active metal foreign matter in electrode materials. To address this technical challenge, related technologies involve separating the active metal foreign matter from the electrode material before detecting its content. Methods for detecting the content of active metal foreign matter include direct determination using scanning electron microscopy (SEM-DES) and indirect determination via a displacement reaction between copper sulfate and the active metal. However, the SEM-DES method can only detect active metal foreign matter in minute areas, resulting in a lengthy process and low efficiency. Furthermore, in the indirect determination method using a displacement reaction between copper sulfate and the active metal, residual copper sulfate may interfere with the quantitative detection of the displacement reaction, further reducing the accuracy of the detection.

[0072] Not intended to be limited to any theory or explanation, the method according to embodiments of this application involves providing a sample to be tested, obtained from a sample taken from the electrode material to be tested, and contacting the sample with an acid to allow an active metal foreign substance to undergo a displacement reaction with the acid, yielding a reaction product containing hydrogen. The content of the active metal foreign substance in the sample can be determined by detecting the hydrogen content in the reaction product. The method according to embodiments of this application indirectly determines the content of active metal foreign substances through a displacement reaction between the active metal foreign substance and the acid, which has higher accuracy and detection efficiency compared to the SEM-DES detection method involved in related technologies. Furthermore, the method according to embodiments of this application obtains the content of the active metal foreign substance in the sample by the hydrogen content in the reaction product; since hydrogen is a gaseous product, the acid solution and electrode material, etc., have minimal influence on the detection of hydrogen content, thereby improving the accuracy of quantitative detection. Therefore, compared to the related technical solutions that indirectly determine the content of active metal foreign substances through a displacement reaction between copper sulfate and an active metal, the method of embodiments of this application can achieve higher accuracy.

[0073] Therefore, the method of this application embodiment, when applied to the battery field, can efficiently and accurately detect the content of active metal foreign matter in electrode materials during battery manufacturing. The method of this application embodiment has high detection efficiency, allowing the monitoring of active metal foreign matter content to be adapted to the production cycle of battery manufacturing, thereby improving battery production efficiency. The method of this application embodiment also has high accuracy, enabling precise monitoring of the content of active metal foreign matter in electrode materials, thus facilitating strict control over the metal particle content in electrode materials, reducing the risk of battery short-circuit self-discharge, extending battery life, and improving battery reliability.

[0074] In some embodiments, the reactive metallic foreign body may include at least one of elemental iron or an iron-chromium-nickel alloy.

[0075] The production process of positive electrode active materials may introduce reactive metal foreign matter such as elemental iron and iron-chromium-nickel alloys. For example, in the production process of lithium iron phosphate using ferrous oxalate as a raw material, elemental iron and / or iron-chromium-nickel alloys are inevitably present in lithium iron phosphate due to factors such as wear and tear of production equipment pipelines and the introduction of impurities from raw materials. Similarly, in the production process of nickel-containing lithium transition metal oxides, elemental iron and / or iron-chromium-nickel alloys are also inevitably present in nickel-containing lithium transition metal oxides due to factors such as wear and tear of production equipment pipelines, the introduction of impurities from raw materials, and side reactions of raw materials. The method of this application embodiment can detect the content of reactive metal foreign matter including elemental iron and / or iron-chromium-nickel alloys, and can be applied to the detection of reactive metal foreign matter content in lithium iron phosphate prepared using ferrous oxalate as a raw material and nickel-containing lithium transition metal oxides. This facilitates precise monitoring of the content of active metal foreign matter in the aforementioned positive electrode active material, thereby enabling strict control over the content of metal particles in batteries using the aforementioned positive electrode active material, reducing the risk of battery short-circuit self-discharge, extending battery life, and improving battery reliability.

[0076] In some implementations, a test sample containing a reactive metallic foreign object is provided, which may specifically include:

[0077] After the electrode material to be tested is stirred evenly, a predetermined mass of the electrode material to be tested is weighed to obtain the sample to be tested.

[0078] Optionally, the electrode material to be tested includes lithium iron phosphate prepared from ferrous oxalate.

[0079] During the production of lithium iron phosphate, due to factors such as wear and tear on production equipment and pipelines, and the introduction of impurities from raw materials, reactive metal foreign matter, such as elemental iron, iron-chromium-nickel alloys, and elemental zinc, is inevitably introduced into the lithium iron phosphate. When the content of reactive metal foreign matter in lithium iron phosphate is high, the risk of short circuit and self-discharge in the battery is increased, thereby negatively impacting the battery's lifespan and reliability.

[0080] When detecting various active metal foreign matter in lithium iron phosphate, the relevant technology typically involves adding high-purity water and lithium iron phosphate to a test bottle, placing a magnet inside, and mixing thoroughly. The magnet is then removed, and the magnetic foreign matter on it is rinsed, ultrasonically washed, and dried. The magnetic foreign matter is then adhered to adhesive tape, and the morphology and particle size of the magnetic foreign matter particles are identified using a scanning electron microscope (SEM). The chemical composition and type of the magnetic foreign matter particles are determined using energy dispersive spectroscopy (EDS). Finally, the content of active metal foreign matter in lithium iron phosphate is determined by the type, quantity, and particle size of the magnetic foreign matter particles containing active metal foreign matter.

[0081] However, when using magnets to extract magnetic materials, the small adsorption area of ​​the magnets and the collision of powder with the magnetic rod during stirring and adsorption can easily cause magnetic impurities to fall off. Furthermore, highly suspended particles on the surface of lithium iron phosphate slurry cannot be adsorbed, and adsorption during rolling is probabilistic, resulting in low extraction rates for small iron powder particles smaller than 10μm. Additionally, in some lithium iron phosphate preparation processes, such as those using ferrous oxalate as the main raw material, not only are small iron powder particles easily introduced, but also other weakly magnetic, highly reactive metal foreign particles. Using magnets to extract magnetic materials may lead to incomplete extraction of these reactive metal foreign particles, thus reducing the accuracy of detection. Moreover, the methods for magnetic material extraction, ultrasonic washing, and electron microscopy are cumbersome, have long testing procedures, and require significant manpower and time costs.

[0082] According to the method in the embodiments of this application, for lithium iron phosphate materials containing multiple active metal foreign matter, samples can be directly taken from lithium iron phosphate for testing without extracting the active metal foreign matter, and the content of active metal foreign matter in the sample can be determined. This simplifies the detection process, reduces the risk of loss of active metal foreign matter, and thus improves the detection efficiency and accuracy of active metal foreign matter content.

[0083] In some implementations, the preset weight can be 40g-80g, for example, it can be 40g, 45g, 50g, 55g, 60g, 65g, 70g, 75g, 80g, or any range of two of the above values.

[0084] Optionally, in some embodiments, the preset mass can also be 50g-60g, for example, it can be 50g, 51g, 52g, 53g, 54g, 55g, 56g, 57g, 58g, 59g, 60g, or any range of two of the above values.

[0085] When the preset mass is within the aforementioned suitable range, the sample to be tested becomes more representative. In other words, the proportion of active metal foreign matter in the sample is closer to the actual proportion of active metal foreign matter in lithium iron phosphate. This improves the accuracy of active metal foreign matter detection. Furthermore, when the preset mass is within the aforementioned suitable range, the active metal foreign matter in the sample can reach a state of full reaction with the acid in a shorter time, thereby shortening the reaction time and improving the detection efficiency of active metal foreign matter content.

[0086] In some embodiments, a test sample containing a reactive metallic foreign object is provided, which may specifically include: providing a dispersion of the electrode material to be tested; extracting a magnetic material from the dispersion using a 5000GS-6000GS magnetic rod, the magnetic material including at least one of elemental iron or an iron-chromium-nickel alloy; enriching the magnetic material onto a filter membrane, washing and drying it, and then placing it into a water-soluble bag to obtain the test sample.

[0087] Optionally, the electrode material to be tested includes nickel-containing lithium transition metal oxides.

[0088] In this embodiment, the mass of the electrode material to be tested in the dispersion can be a known quantity. The content of active metal foreign matter in the electrode material to be tested can be calculated by detecting the content of active metal foreign matter in the sample. As an example, the dispersion of the electrode material to be tested can be obtained by dispersing 0.5-1.5 kg of nickel-containing lithium transition metal oxide powder in 4-8 L of high-purity water. The water-soluble bag can include water-soluble packaging bags known in the art; as an example, the water-soluble bag can be a starch-polyvinyl chloride water-soluble bag, a polyvinyl alcohol water-soluble bag, or other water-soluble polymer bags made of water-soluble polymer materials.

[0089] In related technologies, when detecting the content of active metal foreign matter in the electrode material to be tested, the method often involves extracting magnetic substances from the electrode material by adsorption with a magnetic rod, followed by SEM-EDS testing of the extracted magnetic substances to determine the content of active metal foreign matter, or indirectly determining it through the displacement reaction between copper sulfate and the active metal. After extraction, these technologies require washing the magnetic substances and separating them through a filter membrane. During the filter membrane transfer process, there may be loss of magnetic substances, leading to a decrease in detection accuracy.

[0090] According to the method of this application embodiment, magnetic materials are extracted from the dispersion of the electrode material to be tested using a magnetic rod. These magnetic materials are then enriched onto a filter membrane, processed, and placed in a water-soluble bag to obtain the sample to be tested. This reduces the loss of magnetic materials during filter membrane transfer, thereby improving detection accuracy. After the sample to be tested comes into contact with an acid solution, the water-soluble bag dissolves in the acid solution, allowing the magnetic materials in the sample to come into contact with the acid and react fully. This further improves reaction efficiency, thereby increasing detection efficiency.

[0091] In some embodiments, the sample to be tested is contacted with a sufficient amount of acid solution to allow the active metal foreign substance to react fully with the acid at the reaction temperature, yielding a reaction product containing hydrogen gas. Specifically, this may include:

[0092] The sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum to allow the active metal foreign substance to react fully with the acid at the first reaction temperature, thereby obtaining a reaction product containing hydrogen gas.

[0093] In the above embodiments, the inert atmosphere may include an atmosphere that does not react with substances in the reaction system and does not affect the detection of hydrogen content. As an example, the inert atmosphere may include a nitrogen atmosphere, a rare gas atmosphere, or a mixture thereof. The first reaction temperature can be adjusted according to factors such as the required reaction rate and the ease of the reaction.

[0094] In this embodiment, the sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum. This isolates the sample from air, reducing the risk of ferrous ions being oxidized to ferric ions, thereby reducing the risk of side reactions between ferric ions and elemental iron in the sample and improving detection accuracy. Furthermore, the hydrogen gas generated in the reaction is dispersed in the inert gas, minimizing the presence of impurities that could affect hydrogen content detection. This reduces the difficulty of detecting hydrogen content in the reaction products and improves their accuracy. Therefore, the accuracy of detecting the content of reactive metal foreign substances can be improved.

[0095] In some embodiments, the first reaction temperature can be 50°C-70°C, for example, it can be 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 68°C, 70°C, or a range of any two of the above values.

[0096] Optionally, in some embodiments, the first reaction temperature may also be 55°C-60°C, for example, it may be 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, or any range of two of the above values.

[0097] In some embodiments, the reaction time for the active metal foreign substance and the acid to react fully at the first reaction temperature can be 1.5h-2.5h, for example, it can be 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, or any range of two of the above values.

[0098] When the first reaction temperature and / or the reaction time for the active metal foreign substance to fully react with the acid at the first reaction temperature are within the above-mentioned appropriate range, the detection time for the active metal foreign substance can be controlled within a shorter range, thereby improving the detection efficiency of the active metal foreign substance content.

[0099] In some implementations, the reactive metallic foreign object may include elemental iron.

[0100] Optionally, the electrode material to be tested may include lithium iron phosphate prepared from iron phosphate.

[0101] Iron may be introduced during the production of positive electrode active materials. For example, in the production of lithium iron phosphate using iron phosphate as a raw material, iron is inevitably generated in the lithium iron phosphate due to side reactions of iron phosphate. The method of this application embodiment can be applied to the detection of the content of active metal foreign matter in lithium iron phosphate prepared using iron phosphate as a raw material. This facilitates accurate monitoring of the content of active metal foreign matter in lithium iron phosphate prepared using iron phosphate as a raw material, thereby enabling strict control of the metal particle content in batteries using the aforementioned lithium iron phosphate, reducing the risk of battery short-circuit self-discharge, extending battery life, and improving battery reliability.

[0102] In some embodiments, a test sample containing reactive metallic foreign matter is provided, which may specifically include: providing a dispersion of the electrode material to be tested; extracting magnetic material from the dispersion using a 5000GS-6000GS magnetic rod, the magnetic material including elemental iron and iron phosphide impurities; enriching the magnetic material onto a filter membrane, washing and drying it, and then placing it into a water-soluble bag to obtain the test sample.

[0103] In this embodiment, the mass of the electrode material to be tested in the dispersion can be a known quantity. The content of active metal foreign matter in the electrode material to be tested can be calculated by detecting the content of active metal foreign matter in the sample. As an example, the dispersion of the electrode material to be tested can be obtained by dispersing 0.5-1.5 kg of lithium iron phosphate powder in 4 L-8 L of high-purity water. The water-soluble bag can include packaging bags known in the art that are water-soluble; as an example, the water-soluble bag can be a starch-polyvinyl chloride water-soluble bag, a polyvinyl alcohol water-soluble bag, or other water-soluble polymer bags made of water-soluble polymer materials.

[0104] According to the method of this application embodiment, magnetic materials are extracted from the dispersion of the electrode material to be tested using a magnetic rod. These magnetic materials are then enriched onto a filter membrane, processed, and placed in a water-soluble bag to obtain the sample to be tested. This reduces the loss of magnetic materials during filter membrane transfer, thereby improving detection accuracy. After the sample to be tested comes into contact with an acid solution, the water-soluble bag dissolves in the acid solution, allowing the magnetic materials in the sample to come into contact with the acid and react fully. This further improves reaction efficiency, thereby increasing detection efficiency.

[0105] In some embodiments, the sample to be tested is contacted with a sufficient amount of acid solution to allow the active metal foreign substance to react fully with the acid at the reaction temperature, yielding a reaction product containing hydrogen gas. Specifically, this may include:

[0106] The sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum to allow the active metal foreign substance to react fully with the acid at a second reaction temperature, yielding a reaction product containing hydrogen gas. The second reaction temperature is 20℃-30℃. For example, the second reaction temperature can be 20℃, 22℃, 25℃, 28℃, 30℃, or any range of two of the above values.

[0107] In the production process of lithium iron phosphate (LFP) using iron phosphate as a raw material, elemental iron particles may be generated through side reactions. Due to the characteristics of the process, the active metallic foreign matter in LFP produced by the iron phosphate process is mainly elemental iron. This process also generates a small amount of iron phosphide as a byproduct (0–2000 ppm). Iron phosphide is a complex compound; generally, the iron in iron phosphide has a +1 and +2 valence, making it relatively stable and having almost no impact on battery performance within a certain content range. However, some iron phosphides contain reduced iron, exhibiting reducing properties at high temperatures and possessing a certain degree of magnetism.

[0108] When detecting the content of active metal foreign matter in lithium iron phosphate produced by the iron phosphate process, related technologies involve performing cleanliness analysis (Jemosa or SEM-EDS) on the extracted magnetic material, or using copper sulfate displacement testing to determine the iron content. However, after extracting magnetic material from lithium iron phosphate materials, a significant amount of iron phosphide may be present, making cleanliness analysis or SEM-EDS testing difficult. Even if testing is performed, only trace amounts of the sample can be tested, resulting in unrepresentative samples and lengthy testing times. Furthermore, the copper sulfate displacement method for determining iron content suffers from interference from the dissolution of reduced iron from iron phosphide and residual copper sulfate, leading to low accuracy.

[0109] Studies have shown that elemental iron in the sample reacts preferentially with acid over reduced iron in ferric phosphide. In the above embodiments, the second reaction temperature, within a suitable range, satisfies the following condition: at the second reaction temperature, elemental iron can react with acid, while reduced iron in ferric phosphide does not react with acid.

[0110] Therefore, in the above embodiment, the sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum to allow the active metal foreign matter to react fully with the acid at a second reaction temperature, resulting in a reaction product containing hydrogen. By detecting the hydrogen content in the reaction product, the content of elemental iron in the sample to be tested can be obtained. This reduces the interference of reduced iron in ferric phosphide and improves the accuracy of detection. In addition, according to the above embodiment, mixing the sample to be tested with a sufficient amount of acid solution in an inert atmosphere or vacuum can, on the one hand, isolate air and reduce the risk of ferrous ions being oxidized to ferric ions, thereby reducing the risk of side reactions between iron ions and elemental iron in the sample to be tested, which helps to improve the accuracy of detection; on the other hand, the hydrogen generated in the reaction is dispersed in an inert gas or is pure hydrogen, with fewer impurity gases affecting the detection of hydrogen content, which helps to reduce the difficulty of detecting the hydrogen content in the reaction product and improve the accuracy of hydrogen content detection in the reaction product. Therefore, the accuracy of detecting active metal foreign matter can be further improved.

[0111] In some embodiments, the second reaction temperature may also be 25°C-30°C, for example, it may be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, or any range of two of the above values.

[0112] In some embodiments, the reaction time for the active metal foreign substance and the acid to react fully at the second reaction temperature can be 2h-2.5h, for example, it can be 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, or any range of two of the above values.

[0113] When the second reaction temperature and / or the reaction time for the active metal foreign matter to fully react with the acid at the second reaction temperature are within the above-mentioned appropriate range, not only can the detection time of the active metal foreign matter be controlled within a shorter range, but the risk of iron phosphide reacting with the acid at the second reaction temperature can also be further reduced, thereby reducing the interference of reduced iron in iron phosphide on the detection of active metal foreign matter content, thus improving the detection efficiency and accuracy of active metal foreign matter content.

[0114] In some embodiments, the sample to be tested is contacted with a sufficient amount of acid solution to allow the active metal foreign substance to react fully with the acid at a reaction temperature to obtain a reaction product containing hydrogen. Specifically, this may include: mixing the sample to be tested with a sufficient amount of acid solution in an inert atmosphere or vacuum to allow the active metal foreign substance to react fully with the acid at a second reaction temperature to obtain a first reaction product containing hydrogen, wherein the second reaction temperature is 20°C-30°C.

[0115] Optionally, after obtaining the first reaction product containing hydrogen, the method may further include: separating the gaseous components in the first reaction product; heating the remaining sample to be tested and the acid solution to allow the iron phosphide impurities to react fully with the acid at a third reaction temperature to obtain a second reaction product containing hydrogen, wherein the third reaction temperature is higher than the second reaction temperature; and detecting the hydrogen content in the second reaction product to determine the content of reduced iron in the iron phosphide impurities contained in the sample to be tested based on the hydrogen content in the second reaction product.

[0116] As mentioned above, iron phosphide is a complex compound. Generally, the iron in iron phosphide has a +1 and +2 valence, making it relatively stable and having almost no impact on battery performance within a certain content range. However, some iron phosphides contain reduced iron, which exhibits reducing properties at high temperatures and may affect the battery's high-temperature performance. Therefore, it is necessary to monitor the elemental iron in the magnetic material extracted from lithium iron phosphate and the reduced iron in iron phosphide separately to obtain the content of elemental iron in lithium iron phosphate and the content of reduced iron in iron phosphide.

[0117] Related technologies involve separately monitoring elemental iron and the reduced iron contained in ferric phosphide. This typically requires extracting elemental iron and ferric phosphide separately, and then separately determining the content of elemental iron and the content of reduced iron in ferric phosphide. As an example, lithium iron phosphate powder can be mixed evenly with deionized water to obtain a dispersion. A magnetic rod with a heat-shrink tubing is used for two-dimensional stirring and adsorption to extract magnetic substances from the dispersion. The magnetic substances are transferred to a beaker, water is added and mixed evenly, and then the magnetic substances are extracted again using a magnet. This process is repeated multiple times, followed by filtration using a filter membrane. The cleanliness of the filter membrane loaded with magnetic substances is analyzed using a cleanliness microscope, and the number of metal particles is tested for size. The filter membrane is then immersed in N-methylpyrrolidone (NMP) to obtain an NMP dispersion of the magnetic substances. The NMP dispersion is then extracted a second time using a magnetic rod, and the extract is tested to determine the content of elemental iron remaining after removing ferric phosphide.

[0118] However, iron phosphide and elemental iron have similar magnetic properties, making it impossible to remove through secondary extraction. Furthermore, during cleanliness analysis, iron phosphide is not only difficult to identify but also masks the presence of elemental iron. This results in low accuracy in the detected elemental iron content. In addition, secondary extraction not only increases the risk of magnetic material loss but also complicates the detection process, leading to a decrease in both accuracy and efficiency.

[0119] According to the above embodiments of this application, after extracting magnetic materials from lithium iron phosphate to obtain a test sample, the elemental iron in the test sample is first reacted with acid at a lower second reaction temperature, and then the reduced iron contained in ferric phosphide in the test sample is reacted with acid at a higher third reaction temperature. By detecting the hydrogen content in the first reaction product and the hydrogen content in the second reaction product, the content of elemental iron in lithium iron phosphate and the content of reduced iron contained in ferric phosphide are obtained. According to the above embodiments of this application, by utilizing the difference in reactivity between elemental iron and reduced iron contained in ferric phosphide with acid, elemental iron and reduced iron contained in ferric phosphide react with acid sequentially in the same reaction system, thereby allowing the determination of the content of elemental iron in lithium iron phosphate and the content of reduced iron contained in ferric phosphide separately. This not only simplifies the detection process, reduces detection costs, and improves detection efficiency, but also improves detection accuracy. In some embodiments, the spiked recovery rate of elemental iron according to the above embodiments can reach more than 80%. In addition, according to the above implementation method, magnetic materials only need to be extracted once, which not only greatly reduces the risk of loss of magnetic materials, but also simplifies the extraction process, thereby further improving detection efficiency and accuracy.

[0120] In some embodiments, the third reaction temperature can be 60°C-80°C, for example, it can be 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, or a range of any two of the above values.

[0121] Optionally, in some embodiments, the third reaction temperature may also be 65°C-75°C, for example, it may be 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 73°C, 75°C, or a range of any two of the above values.

[0122] In some embodiments, the reaction time between the iron phosphide impurity and the acid at the third reaction temperature can be 1.5h-2.5h, for example, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, or any range of two of the above values.

[0123] When the third reaction temperature and / or the reaction time of the iron phosphide impurity and the acid at the third reaction temperature are within the above-mentioned appropriate range, the detection time of the reduced iron content in the iron phosphide impurity can be controlled within a shorter range, thereby improving the detection efficiency of the reduced iron content in the iron phosphide impurity.

[0124] In some embodiments, the acid solution may include at least one of a dilute sulfuric acid solution and a dilute acid solution. The acid solution may include at least one of a dilute sulfuric acid solution and a dilute hydrochloric acid solution. When the acid solution includes a dilute hydrochloric acid solution, since hydrochloric acid has a certain degree of volatility, the gaseous components of the reaction system can be filtered through a hydrochloric acid filter before detecting the hydrogen content in the reaction products.

[0125] Alternatively, in some embodiments, the acid solution may be a dilute sulfuric acid solution.

[0126] The acid solution described above can react with active metal foreign substances at a suitable rate, which helps to shorten the detection time and improve the detection efficiency.

[0127] In some embodiments, the acid solution may contain F - F - It can be made by F - F is obtained by dissolving the source in an acid solution. - The source may include, but is not limited to, sources containing F - Inorganic salts (e.g., NaF), HF. F - It can complex with iron ions dissolved from active metal foreign substances, thereby inhibiting the reaction between iron ions and elemental iron and improving the accuracy of detecting the content of active metal foreign substances.

[0128] In some embodiments, the acid solution may further include antioxidants and / or oxygen scavengers. Antioxidants may be selected from those known in the art, such as, but not limited to, one or more of vitamin C antioxidants and tea polyphenol antioxidants; oxygen scavengers may be selected from those known in the art, such as, but not limited to, acetone oxime. This further reduces the risk of ferrous ions being oxidized to ferric ions, thereby reducing side reactions between ferric ions and elemental iron, and further improving the accuracy of detection.

[0129] In some embodiments, the acid solution may also include a surfactant. The surfactant may be selected from ionic and / or nonionic surfactants known in the art, such as, but not limited to, Huntsman X3204. In some embodiments, when the surfactant includes a foaming surfactant, an antifoaming agent may also be added to the acid solution. Surfactants can improve the dispersibility of the powdered test sample in the acid solution, facilitating the full reaction of reactive metallic foreign matter in the test sample with the acid. This can further improve the accuracy of the detection.

[0130] In some implementations, the sample to be tested is contacted with an acid solution, which may specifically include:

[0131] The sample to be tested is mixed with an acid solution in a closed reaction vessel, the inner wall of which is coated with Teflon.

[0132] Teflon is reactive to active metallic foreign substances, iron phosphide, and acids. Therefore, it can reduce the influence of the reaction vessel on the detection results, thereby helping to further improve the accuracy of the detection.

[0133] In some implementations, the sample to be tested and the acid solution can be reacted in a manner such as... Figure 1 The mixture is stirred in the reaction apparatus shown to allow the active metal foreign acid to react.

[0134] like Figure 1 As shown, the reaction apparatus may include: a stirring motor 1, a quantitative storage tank for the reaction liquid (made of polypropylene) 2, a hose connecting the reaction liquid storage tank to the reaction vessel 3, a movable switch stopcock 4, a sealing ring between the vessel lid and the reaction flask 5, a gas outlet stopper 6, a reactor 7, a stainless steel stirring paddle (coated with polytetrafluoroethylene) 8, an ultrasonic heating device 9, and a miniature vacuum pump 10. Both the reaction apparatus and the gas path are coated with Teflon to inhibit metal contamination and acid corrosion.

[0135] As an example, the sample to be tested can be placed in reactor 7, and reactor 7 can be assembled with the lid and the sealing ring 5 of the reaction flask. A vacuum is then applied to the reaction apparatus using a micro vacuum pump 10 to eliminate interference from gases such as oxygen and hydrogen in the air. Then, the movable switch valve 4 is opened to connect the quantitative storage tank 2 of the reaction solution to reactor 7, allowing the acid solution in the quantitative storage tank 2 to automatically enter reactor 7. Once the amount of acid solution is sufficient, the movable switch valve 4 is closed. The stirring motor 1 is turned on to stir the substances in reactor 7 using a stainless steel stirring paddle. The reactor 7 is ultrasonically heated for 1.5-2.5 hours using an ultrasonic heating device 9. When the pressure in reactor 7 is lower than atmospheric pressure at room temperature, air or nitrogen is introduced through the gas inlet stopper 6 by inserting a disposable syringe needle to equalize the internal pressure to atmospheric pressure. When the pressure in reactor 7 is higher than atmospheric pressure, the pressure value is recorded for calculating the amount of hydrogen generated. The hydrogen content generated by the reaction is detected by gas chromatography to determine the content of active metal foreign matter in the sample.

[0136] In some embodiments, the reaction time for the active metal foreign substance to fully react with the acid can be 1.5h-2.5h, and the hydrogen content in the reaction product is detected by gas chromatography. The detection time of gas chromatography is less than 5min (about 3min), which greatly saves testing time and testing cost and improves detection efficiency.

[0137] In some embodiments, the method of this application can achieve a spiked recovery rate of over 80% for reactive metallic foreign matter.

[0138] In the embodiments of this application, the spiked recovery rate has a meaning known in the art. As an example, a quantitative standard active metal foreign object sample can be added to the electrode material matrix without the active metal foreign object to be tested to obtain the sample to be tested. The active metal foreign object content of the sample to be tested is determined according to the method of the embodiments of this application, and the ratio of the active metal foreign object content test result to the theoretical value is the spiked recovery rate of the method of the embodiments of this application.

[0139] In some embodiments, detecting the hydrogen content in the reaction products may specifically include: performing gas chromatography on the reaction products to obtain the hydrogen content in the reaction products.

[0140] Gas chromatography has high accuracy in detecting hydrogen content, which is beneficial for improving the accuracy of detecting active metal foreign matter content.

[0141] It should be noted that in the methods of this application embodiment, gas chromatography detection can be implemented using equipment and methods known in the art. As an example, a gas chromatography device, such as an Agilent 7890, can be used to determine the chromatogram of gas phase components using nitrogen or helium as the carrier gas. The test parameters are as follows: a molecular sieve gas component testing column is used, the nitrogen carrier gas flow rate is 25 mL / min, valve injection is used, the test is conducted at a constant temperature of 60°C, and a thermal conductivity detector (TCD detector) is used with a detector temperature of 250°C.

[0142] Example

[0143] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0144] Example 1

[0145] Five samples (lithium iron phosphate powder prepared from ferrous oxalate, purchased from Fulim Precision Machinery, with an iron content of less than 0.2 ppm) were weighed, each sample weighing 50 g. Each sample was spiked with an active metal foreign substance to obtain spiked samples, designated as Sample 1 to Sample 5. The types of active metal foreign substances added and their amounts are shown in Table 1-1.

[0146] Table 1-1

[0147] Sample 1 Fe 1.51 Sample 2 Fe 3.55 Sample 3 Fe 5.30 Sample 4 Fe 5.59 Sample 5 Fe 5.56

[0148] Samples 1-5 were placed in a reactor, evacuated, and then a sufficient amount of acid solution was injected. The acid solution was prepared by mixing 300 mL of 50% dilute sulfuric acid solution, 8 g of surfactant X3204, and 5 mL of HF. Stirring was started, and the mixture was ultrasonically heated to the first reaction temperature of 55℃ and reacted for 1.5 h to obtain the reaction product. The mixture was cooled to room temperature and then purged with nitrogen to equilibrate to atmospheric pressure. The hydrogen content of the reaction product was detected by gas chromatography with the following test parameters: a molecular sieve gas composition test column was used, the nitrogen carrier gas flow rate was 25 mL / min, valve injection was used, the test was conducted at a constant temperature of 60℃, and a TCD detector was used with a detector temperature of 250℃. The content of active metal foreign matter in the spiked test sample was calculated based on the hydrogen content of the reaction product.

[0149] The detection results of active metal foreign matter content and their spiked recovery rates for samples 1 to 5 of Example 1 are shown in Tables 1-2, respectively. The spiked recovery rate of active metal foreign matter for samples 1 to 5 of Example 1 is calculated as [active metal foreign matter content (mg) / spiked amount (mg)] × 100%.

[0150] Table 1-2

[0151] Sample 1 1.28 85％ Sample 2 3.13 88％ Sample 3 4.71 89％ Sample 4 5.09 91％ Sample 5 4.99 90％

[0152] Example 2

[0153] The detection procedure is the same as in Example 1, except that 4g of acetone oxime is also dissolved in the acid solution.

[0154] The types of active metal foreign matter spiked in samples 1 to 5 of Example 2 and their spiked amounts are shown in Table 2-1, and the detection results of the active metal foreign matter content and their spiked recovery rates in samples 1 to 5 are shown in Table 2-2. The spiked recovery rate of active metal foreign matter in samples 1 to 5 of Example 2 is calculated as: [Active metal foreign matter content (mg) / spiked amount (mg)] × 100%.

[0155] Table 2-1

[0156] Sample 1 Fe 1.17 Sample 2 Fe 3.05 Sample 3 Fe 6.41 Sample 4 Fe 5.62 Sample 5 Fe 5.77

[0157] Table 2-2

[0158] Sample 1 1.09 93％ Sample 2 2.89 95％ Sample 3 5.97 93％ Sample 4 5.29 94％ Sample 5 5.13 89％

[0159] Example 3

[0160] The detection process is the same as in Example 1, except that the first reaction temperature is 50°C and the reaction time is 2.5h.

[0161] The types of active metal foreign matter spiked in samples 1 to 5 of Example 3 and their spiked amounts are shown in Table 3-1, and the detection results of the active metal foreign matter content and their spiked recovery rates in samples 1 to 5 are shown in Table 3-2. The spiked recovery rate of active metal foreign matter in samples 1 to 5 of Example 3 is calculated as: [Active metal foreign matter content (mg) / spiked amount (mg)] × 100%.

[0162] Table 3-1

[0163] Sample 1 Fe 1.21 Sample 2 Fe 2.95 Sample 3 Fe 4.46 Sample 4 Fe 5.09 Sample 5 Fe 5.54

[0164] Table 3-2

[0165] Sample 1 1.09 90％ Sample 2 2.64 89％ Sample 3 4.23 95％ Sample 4 4.46 88％ Sample 5 5.2 94％

[0166] Example 4

[0167] The detection process is the same as in Example 1, except that the first reaction temperature is 70°C and the reaction time is 2 hours.

[0168] The types of active metal foreign matter spiked in samples 1 to 5 of Example 4 and their spiked amounts are shown in Table 4-1, and the detection results of the active metal foreign matter content and their spiked recovery rates in samples 1 to 5 are shown in Table 4-2. The spiked recovery rate of active metal foreign matter in samples 1 to 5 of Example 4 is calculated as: [Active metal foreign matter content (mg) / spiked amount (mg)] × 100%.

[0169] Table 4-1

[0170] Sample 1 Fe 1.38 Sample 2 Fe 2.53 Sample 3 Fe 4.63 Sample 4 Fe 5.44 Sample 5 Fe 5.57

[0171] Table 4-2

[0172] Sample 1 1.15 83％ Sample 2 2.25 89％ Sample 3 4.31 93％ Sample 4 4.88 90％ Sample 5 5.14 92％

[0173] Example 5

[0174] 1 kg of lithium iron phosphate powder (purchased from Hunan Yuneng) prepared from iron phosphate was mixed evenly with 6 L of high-purity water to obtain an aqueous dispersion of lithium iron phosphate. Magnetic material in the dispersion was extracted using a 6000GS heat-shrink tubing magnetic rod. After cleaning the magnetic material from the heat-shrink tubing, a 50% dilute sulfuric acid solution was added and stirred at 25°C for 2 hours to remove elemental iron from the magnetic material. Subsequently, the magnetic material was magnetically adsorbed and rinsed three times with water to remove residual sulfuric acid. The mixture was then filtered through a filter membrane, dried, and spiked (an active metal foreign object was weighed and added to the magnetic material). The filter membrane loaded with the spiked magnetic material was transferred to a starch-polyvinyl chloride water-soluble bag and sealed to obtain the spiked test sample. Five spiked test samples were prepared according to the above steps, and these were designated as Sample 1 to Sample 5. The types and masses of the spiked active metal foreign objects are shown in Table 5-1.

[0175] Table 5-1

[0176] Sample 1 Fe 2.59 Sample 2 Fe 5.31 Sample 3 Fe 10.44 Sample 4 Fe 9.87 Sample 5 Fe 10.13

[0177] Samples 1 through 5 were placed into flasks containing sufficient acid solution. After evacuation, the flasks were filled with the acid solution, which was prepared by mixing 150 mL of 50% dilute sulfuric acid solution and 0.3 g of NaF. The mixture was stirred at a second reaction temperature of 25 °C for 2 h to obtain the reaction product. Nitrogen gas was then introduced to atmospheric pressure. The hydrogen content in the reaction product was detected by gas chromatography with the following parameters: a molecular sieve gas composition analysis column was used, the nitrogen carrier gas flow rate was 25 mL / min, valve injection was used, the temperature was kept constant at 60 °C, and a TCD detector was used at a detector temperature of 250 °C. The iron content in the spiked sample was calculated based on the hydrogen content of the reaction product. As an example, Figure 2 The image shows the gas chromatogram of the gas phase components of the reaction product in sample 5. Analysis Figure 2 The hydrogen content of the reaction product in sample 5 can be calculated from the H2 characteristic peak (t = 1.05 min), and then the iron content in the spiked test sample can be calculated.

[0178] The results of the detection of active metal foreign matter content and their spiked recovery rates for samples 1 to 5 of Example 5 are shown in Table 5-2. The spiked recovery rate of active metal foreign matter for samples 1 to 5 of Example 5 = [active metal foreign matter content (mg) / spiked amount (mg)] × 100%.

[0179] Table 5-2

[0180] Sample 1 2.26 87％ Sample 2 4.93 93％ Sample 3 9.20 88％ Sample 4 9.22 93％ Sample 5 9.48 94％

[0181] Example 6

[0182] The detection process is the same as in Example 5, except that 0.5g of tea polyphenols are also dissolved in the acid solution.

[0183] The types of active metal foreign matter spiked in samples 1 to 5 of Example 6 and their spiked amounts are shown in Table 6-1, and the detection results of the active metal foreign matter content and their spiked recovery rates in samples 1 to 5 are shown in Table 6-2. The spiked recovery rate of active metal foreign matter in samples 1 to 5 of Example 6 is calculated as: [Active metal foreign matter content (mg) / spiked amount (mg)] × 100%.

[0184] Table 6-1

[0185] Sample 1 Fe 2.30 Sample 2 Fe 4.98 Sample 3 Fe 9.46 Sample 4 Fe 10.34 Sample 5 Fe 11.37

[0186] Table 6-2

[0187] Sample 1 2.19 95％ Sample 2 4.65 93％ Sample 3 9.17 97％ Sample 4 9.88 95％ Sample 5 10.65 94％

[0188] Example 7

[0189] The detection process is the same as in Example 5, except that the second reaction temperature is 20°C and the reaction time at the second reaction temperature is 2.5 h.

[0190] The types of active metal foreign matter spiked in Samples 1 to 5 of Example 7 and their spiked amounts are shown in Table 7-1, and the detection results of the active metal foreign matter content and their spiked recovery rates in Samples 1 to 5 are shown in Table 7-2. The spiked recovery rate of active metal foreign matter in Samples 1 to 5 of Example 7 is calculated as: [Active metal foreign matter content (mg) / Spiked amount (mg)] × 100%.

[0191] Table 7-1

[0192] Sample 1 Fe 2.75 Sample 2 Fe 6.00 Sample 3 Fe 9.66 Sample 4 Fe 11.77 Sample 5 Fe 11.63

[0193] Table 7-2

[0194] Sample 1 2.34 85％ Sample 2 5.40 90％ Sample 3 8.98 93％ Sample 4 10.59 90％ Sample 5 10.47 90％

[0195] Example 8

[0196] The detection process is the same as in Example 5, except that the second reaction temperature is 30°C.

[0197] The types of active metal foreign matter spiked in samples 1 to 5 of Example 8 and their spiked amounts are shown in Table 8-1, and the detection results of the active metal foreign matter content and their spiked recovery rates in samples 1 to 5 are shown in Table 8-2. The spiked recovery rate of active metal foreign matter in samples 1 to 5 of Example 8 is calculated as: [Active metal foreign matter content (mg) / spiked amount (mg)] × 100%.

[0198] Table 8-1

[0199] Sample 1 Fe 2.64 Sample 2 Fe 4.93 Sample 3 Fe 10.81 Sample 4 Fe 9.76 Sample 5 Fe 11.70

[0200] Table 8-2

[0201] Sample 1 2.32 88％ Sample 2 4.39 89％ Sample 3 9.95 92％ Sample 4 9.08 93％ Sample 5 10.41 89％

[0202] Example 9

[0203] Take 1 kg of LiNi 0.6 Mn 0.2 Co 0.2 O2 (NCM622) ternary powder was mixed evenly with 6L of high-purity water to obtain an aqueous dispersion of the ternary powder. Magnetic material in the dispersion was extracted using a 6000GS heat-shrink tubing magnetic rod. After cleaning the magnetic material from the heat-shrink tubing, a 50% dilute sulfuric acid solution was added, and the mixture was stirred at 70℃ for 2 hours to remove the stainless steel contained in the magnetic material. Subsequently, the magnetic material was rinsed three times with water adsorbed by a magnetic block to remove residual sulfuric acid. After filtration through a filter membrane and drying, a spiked treatment was performed (an active metal foreign object was weighed and added to the magnetic material). The filter membrane loaded with the spiked magnetic material was transferred to a starch-polyvinyl chloride water-soluble bag and sealed to obtain the spiked test sample. Five spiked test samples were prepared according to the above steps, and these were designated as Sample 1 to Sample 5. The spiked active metal foreign object was austenitic stainless steel (composition Fe). 66wt％ Cr 17wt％ Ni 13wt％ (1 mol Fe can react with acid to produce 1 mol H2, 1 mol Cr can react with acid to produce 1.5 mol H2, and 1 mol Ni can react with acid to produce 1 mol H2. The amount of spiking for each sample is shown in Table 9-1.)

[0204] Table 9-1

[0205] Sample 1 Austenitic stainless steel 1.05 Sample 2 Austenitic stainless steel 2.64 Sample 3 Austenitic stainless steel 3.44 Sample 4 Austenitic stainless steel 3.79 Sample 5 Austenitic stainless steel 3.07

[0206] Samples 1 through 5 were placed into flasks containing sufficient acid solution. After evacuation, nitrogen gas was introduced to balance the pressure. The acid solution was prepared by mixing 150 mL of 50% dilute sulfuric acid solution and 0.3 g of NaF. The mixture was stirred at the first reaction temperature of 55 °C for 1.5 h to obtain the reaction product. The hydrogen content in the reaction product was detected by gas chromatography with the following test parameters: a molecular sieve gas composition test column was used, the nitrogen carrier gas flow rate was 25 mL / min, valve injection was used, the test was conducted at a constant temperature of 60 °C, and a TCD detector was used with a detector temperature of 250 °C. The content of active metal foreign matter in the spiked test sample was calculated based on the hydrogen content of the reaction product.

[0207] The detection results of active metal foreign matter content and their spiked recovery rates for samples 1 to 5 of Example 9 are shown in Table 9-2. The spiked recovery rate of active metal foreign matter for samples 1 to 5 of Example 9 is calculated as [active metal foreign matter content (mg) / spiked amount (mg)] × 100%.

[0208] Table 9-2

[0209]

[0210]

[0211] Comparative Example 1

[0212] Take 1 kg of lithium iron phosphate powder (purchased from Fulim Precision) prepared from ferrous oxalate, mix it evenly with 6 L of high-purity water to obtain an aqueous dispersion of lithium iron phosphate; use a 6000GS heat shrink tubing magnetic rod to extract magnetic substances from the dispersion three times. After rinsing with water, the magnetic substances are filtered onto a filter membrane and dried. The cleanliness analyzer is used to scan the number of magnetic particles. In the last extraction, the total content of magnetic particles is less than 10. Spiking treatment is then performed: take active metal foreign matter iron powder and disperse it in water. Use a pipette to take a portion of the iron powder, disperse it and filter it onto a filter membrane. After scanning with a cleanliness analyzer, record the number and particle size of iron particles on the filter membrane surface; then sonicate the filter membrane into water, add it to the aqueous dispersion of lithium iron phosphate and stir evenly; use a 6000GS heat shrink tubing magnetic rod to extract magnetic substances from the dispersion again, transfer the magnetic substances to a beaker, use a magnet to attract the bottom of the beaker, add pure water to rinse the magnetic substances, filter onto a 5-micron filter membrane, dry it, and scan with a cleanliness analyzer. The particle size, spiking amount, content of active metal foreign matter, and spike recovery rate of the spiked particles are shown in Table 10. Comparative Example 1: Spiking recovery rate of active metal foreign matter in each particle size range = [Active metal foreign matter content (particles) / Spiking amount (particles)] × 100%.

[0213] Table 10

[0214] Fe >100 5 5 100％ Fe 50-100 28 20 71％ Fe 25-50 57 20 75％ Fe 15-25 101 20 61％ Fe 5-15 243 20 57％

[0215] Comparative Example 2

[0216] Take 1 kg of the sample to be tested (lithium iron phosphate powder prepared from iron phosphate, purchased from Hunan Yuneng), mix it evenly with 6 L of high-purity water to obtain an aqueous dispersion of lithium iron phosphate; extract the magnetic material in the dispersion using a 6000GS heat shrink tubing magnetic rod; after cleaning the magnetic material on the heat shrink tubing, add 50% sulfuric acid aqueous solution and stir for 2 h to remove the elemental iron contained in the magnetic material itself; then perform spiking treatment (weighing an active metal foreign object and adding it to the magnetic material) to obtain the spiked sample to be tested; add 0.2% copper sulfate solution and react at 140℃ for 1 h. To ensure the displacement reaction between elemental iron and copper ions is complete, the remaining solid after cooling to room temperature is filtered and washed onto a filter membrane. The filter membrane is then removed and placed in a beaker, where 10 mL of water and 10 mL of concentrated nitric acid are added. The mixture is heated at 180 °C for 1 hour to digest. The filtrate is then diluted to a final volume to determine the copper ion content (the filtrate is diluted to a 50 mL volumetric flask, 1 mL is taken, and the volume is adjusted again to 50 mL; the copper ion content (Cu content) is measured using inductively coupled plasma atomic emission spectrometry (ICP-AES), in μg). The displacement iron content (Fe (mg)) is calculated as: [(Cu content / 64) × 56] × 10. -3 The results of the detection of active metal foreign matter content were obtained.

[0217] Five spiked samples were prepared according to the above steps, designated as Sample 1 to Sample 5. The types of active metal foreign matter spiked in Samples 1 to 5 and their spiking amounts are shown in Table 11-1, and the detection results of the active metal foreign matter content and their spiked recoveries in Samples 1 to 5 are shown in Table 11-2. The spiked recoveries of active metal foreign matter in Comparative Example 1 for each particle size range are calculated as follows: [Active metal foreign matter content (mg) / Spiked amount (mg)] × 100%.

[0218] Table 11-1

[0219] Sample 1 Fe 1.28 Sample 2 Fe 3.60 Sample 3 Fe 5.39 Sample 4 Fe 5.87 Sample 5 Fe 5.40

[0220] Table 11-2

[0221] Sample 1 1.79 70％ Sample 2 3.45 82％ Sample 3 4.05 75％ Sample 4 4.33 74％ Sample 5 4.29 79％

[0222] Comparative Example 3

[0223] Take 1 kg of LiNi 0.6 Mn 0.2 Co 0.2O2 (NCM622) ternary powder was mixed evenly with 6L of high-purity water to obtain an aqueous dispersion of the ternary powder. Magnetic materials in the dispersion were extracted three times using a 6000GS heat-shrinkable tubing magnetic rod. After rinsing with water, the magnetic materials were filtered onto a filter membrane and dried. The cleanliness of the filter membrane was then analyzed to determine the number of magnetic particles. The final analysis showed a total magnetic metal particle content of less than 10 particles. Spiking was then performed: approximately 500-1000 mesh magnetic austenitic stainless steel particles (Fe 66wt%, Cr 17wt%, Ni 13wt%) were dispersed in water. A portion of the stainless steel particles was collected using a pipette and dispersed onto a filter membrane. After scanning with a cleanliness analyzer, the number and size of the stainless steel particles on the filter membrane surface were recorded. The filter membrane was then ultrasonically immersed in water, and the aqueous dispersion of the ternary powder was added and stirred evenly. Magnetic materials in the dispersion were extracted again using a 6000GS heat-shrinkable tubing magnetic rod. The magnetic materials were transferred to a beaker, attracted to the bottom of the beaker with a magnet, and rinsed with pure water. The mixture was then filtered onto a 5-micron filter membrane, dried, and scanned with a cleanliness analyzer. The particle size and spiking amount of the spiked active metal foreign matter, the detection results of the active metal foreign matter content, and the spiking recovery rate are shown in Table 12. The spiking recovery rate of active metal foreign matter in Comparative Example 3 for each particle size range is calculated as [active metal foreign matter content (particles) / spiking amount (particles)] × 100%.

[0224] Table 12

[0225] Austenitic stainless steel >100 8 6 75％ Austenitic stainless steel 50-100 46 25 54％ Austenitic stainless steel 25-50 113 72 64％ Austenitic stainless steel 15-25 345 203 59％ Austenitic stainless steel 5-15 544 341 63％

[0226] Based on the test results of Examples 1-9, it can be seen that the method according to the embodiments of this application has a simple detection process and can detect the content of active metal foreign matter in the electrode material relatively accurately, and can have both high detection efficiency and accuracy.

[0227] In contrast, Comparative Examples 1 and 3 used magnetic rods to extract magnetic substances from the aqueous dispersion of lithium iron phosphate powder before performing cleanliness analysis. Compared to the method of directly mixing powder and acid solution in Examples 1-4, the pretreatment process of Comparative Example 1 is more cumbersome; compared to the gas chromatography detection in Examples 1-4 and 9, the cleanliness analysis scans of Comparative Examples 1 and 3 are also more complex. Furthermore, Comparative Examples 1 and 3 have lower accuracy in detecting the content of active metal foreign matter with a particle size below 100 μm. The overall spiked recovery rate of Comparative Example 1 is far lower than that of Examples 1-4, and the overall spiked recovery rate of Comparative Example 3 is far lower than that of Example 9. In Comparative Example 2, after extracting magnetic substances from the aqueous dispersion of lithium iron phosphate powder with a magnetic rod, copper sulfate was used to replace the active metal foreign matter in the magnetic substances. Copper sulfate may affect the quantitative detection of the replacement reaction; therefore, the detection accuracy of active metal foreign matter content in Comparative Example 2 is far lower than that in Examples 5-8.

[0228] For the compounds given but not listed in the examples, since their chemical properties and electrochemical reaction properties are similar to those of the compounds listed in the examples, they are all applicable to the technical solutions of the present invention, and therefore will not be listed here.

[0229] 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 active metal foreign matter in electrode materials, comprising: Provide a test sample containing reactive metallic foreign matter; The sample to be tested is brought into contact with a sufficient amount of acid solution to allow the active metal foreign matter to react fully with the acid at the reaction temperature, thereby obtaining a reaction product containing hydrogen. The hydrogen content in the reaction products is detected to determine the content of active metal foreign matter in the sample to be tested. in, The sample to be tested includes magnetic materials, which include elemental iron and iron phosphide impurities. The active metal foreign matter includes elemental iron. The electrode material to be tested includes lithium iron phosphate prepared from iron phosphate. The step involves contacting the sample to be tested with a sufficient amount of acid solution to allow the active metal foreign substance to react fully with the acid at the reaction temperature, yielding a reaction product containing hydrogen gas, including: The sample to be tested is mixed with a sufficient amount of the acid solution in an inert atmosphere or vacuum, so that the active metal foreign substance reacts fully with the acid at a second reaction temperature to obtain a reaction product containing hydrogen gas. The second reaction temperature is 20°C - 30°C.

2. The method according to claim 1, wherein, The active metallic foreign matter also includes iron-chromium-nickel alloys.

3. The method according to claim 2, wherein, The provision of a test sample containing an active metallic foreign object includes: After the electrode material to be tested is stirred evenly, a predetermined mass of the electrode material to be tested is weighed to obtain the sample to be tested.

4. The method according to claim 3, wherein, The preset weight is 40g-80g.

5. The method according to claim 4, wherein, The preset weight is 50g-60g.

6. The method according to claim 1, wherein, The provision of a test sample containing an active metallic foreign object includes: Provide a dispersion of the electrode material to be tested; Magnetic substances were extracted from the dispersion using a 5000GS-6000GS magnetic rod; The magnetic material is enriched onto the filter membrane, washed and dried, and then placed into a water-soluble bag to obtain the sample to be tested.

7. The method according to claim 1, wherein, The second reaction temperature is 25℃-30℃.

8. The method according to claim 7, wherein, The reaction time for the active metal foreign substance to fully react with the acid at the second reaction temperature is 2h-2.5h.

9. The method according to any one of claims 1-7, wherein, The acid solution includes at least one of dilute sulfuric acid solution and dilute hydrochloric acid solution.

10. The method according to claim 9, wherein, The acid solution contains F - .

11. The method according to claim 9, wherein, The acid solution also includes antioxidants and / or oxygen scavengers.

12. The method according to claim 9, wherein, The acid solution also includes a surfactant.

13. The method according to any one of claims 1-8, wherein, Contacting the sample to be tested with an acid solution includes: The sample to be tested is mixed with the acid solution in a closed reaction vessel, the inner wall surface of which is coated with Teflon.

14. The method according to any one of claims 1-8, wherein, The detection of hydrogen content in the reaction product includes: The hydrogen content in the reaction products was determined by gas chromatography.

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