Method for detecting content of active metal foreign matters in electrode material

Abstract

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

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for detecting the content of active metallic foreign matter in an electrode material. Background Art

[0002] Secondary batteries rely on active ions to be reciprocated between the positive and negative electrodes for charging and discharging. Secondary batteries represented by lithium-ion batteries have outstanding features such as high energy density, long cycle life, no pollution, and no memory effect. Therefore, as a clean energy, secondary batteries have gradually spread from electronic products to large-scale devices such as electric vehicles to adapt to the sustainable development strategy of the environment and energy.

[0003] With the development of electronic products, electric vehicles and other devices, people have also put forward higher requirements for the performance of secondary batteries. In the production process of electrode materials, due to the wear of machine pipes and the introduction of impurities in raw materials, metal particles such as iron and iron-chromium-nickel are inevitably introduced. These metal particles will undergo redox reactions between the positive and negative electrodes of the battery during the battery charging and discharging process. When the reduced metal element at the negative electrode accumulates to a certain extent, the hard edges and corners of the metal element will pierce the diaphragm, causing the battery to short-circuit and self-discharge, affecting the battery's service life and reliability. Therefore, the detection of metal particles in electrode materials is particularly important. Summary of the invention

[0004] In order to achieve the above objectives, the present 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 to extend the service life of the battery and improve the reliability of the battery.

[0005] The present application provides a method for detecting the content of active metal foreign matter in an electrode material, comprising:

[0006] Provide a sample to be tested containing active metallic foreign matter;

[0007] The sample to be tested is contacted with a sufficient amount of acid solution so that the active metal foreign matter and the acid react fully at the reaction temperature to obtain a reaction product containing hydrogen;

[0008] The hydrogen content in the reaction product is detected to obtain the content of active metal foreign matter in the sample to be tested according to the hydrogen content in the reaction product.

[0009] Without intending to be limited by any theory or explanation, the method according to the embodiment of the present application provides a sample to be tested obtained by sampling from the electrode material to be tested, and contacts the sample to be tested with an acid so that the active metal foreign matter and the acid undergo a substitution reaction to obtain a reaction product containing hydrogen. The hydrogen content in the reaction product is detected, and the content of the active metal foreign matter in the sample to be tested can be obtained according to the hydrogen content in the reaction product. According to the method of the embodiment of the present application, the content of the active metal foreign matter is indirectly determined by the substitution reaction between the active metal foreign matter and the acid, which has higher accuracy and detection efficiency than the SEM-DES detection method involved in the related art. In addition, according to the method of the embodiment of the present application, the content of the active metal foreign matter in the sample to be tested is obtained by the hydrogen content in the reaction product; hydrogen is a gas phase product, and the influence of reactants such as acid solution and electrode material on the detection of hydrogen content is extremely low, thereby improving the accuracy of quantitative detection. Therefore, compared with the technical solution involved in the related art of indirectly determining the content of active metal foreign matter by the substitution reaction between copper sulfate and active metal, the method of the embodiment of the present application can have higher accuracy.

[0010] Therefore, the method of the embodiment of the present application is applied to the field of batteries, and can efficiently and accurately detect the content of active metal foreign matter in the electrode material during the battery preparation process. The method of the embodiment of the present application has a high detection efficiency, which can make the monitoring of the content of active metal foreign matter compatible with the production rhythm of battery preparation, thereby improving the efficiency of battery production; the method of the embodiment of the present application also has a high accuracy, and can accurately monitor the content of active metal foreign matter in the electrode material, thereby helping to strictly control the content of metal particles in the electrode material, reduce the risk of short-circuit self-discharge of the battery, extend the service life of the battery, and improve the reliability of the battery.

[0011] In any embodiment of the present application, the active metallic foreign matter includes at least one of a single substance of iron or an iron-chromium-nickel alloy.

[0012] The method of the embodiment of the present application can detect the content of active metal foreign matter including iron and / or iron-chromium-nickel alloy, and can be applied to the detection of the content of active metal foreign matter in lithium iron phosphate prepared with ferrous oxalate as raw material and nickel-containing lithium transition metal oxide. Therefore, it is conducive to accurately monitoring the content of active metal foreign matter in the above-mentioned positive electrode active material, thereby helping to strictly control the content of metal particles in the battery using the above-mentioned positive electrode active material, reduce the risk of short circuit self-discharge of the battery, extend the service life of the battery, and improve the reliability of the battery.

[0013] In any embodiment of the present application, a sample to be tested containing active metal foreign matter is provided, including:

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

[0015] Optionally, the electrode material to be tested includes lithium iron phosphate prepared using ferrous oxalate as a raw material.

[0016] According to the method of the embodiment of the present application, for lithium iron phosphate materials containing multiple active metal foreign matters, samples can be directly taken from the lithium iron phosphate for testing, and the content of active metal foreign matters in the sample to be tested can be determined without extracting the active metal foreign matters. As a result, the detection process can be simplified, the risk of loss of active metal foreign matters can be reduced, and the detection efficiency and accuracy of the content of active metal foreign matters can be improved.

[0017] In any embodiment of the present application, the preset mass is 40g-80g, and can be optionally 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. Thus, the accuracy of active metal foreign matter detection can be improved. In addition, when the preset mass is within the above-mentioned suitable range, the reaction time can also be shortened, thereby improving the detection efficiency of the active metal foreign matter content.

[0018] In any embodiment of the present application, a sample to be tested containing active metal foreign matter is provided, including:

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

[0020] Extracting magnetic material from the dispersion using a 5000GS-6000GS magnetic bar, wherein the magnetic material includes at least one of iron or an iron-chromium-nickel alloy;

[0021] The magnetic substance is enriched in the filter membrane, and after being washed and dried, it is put into a water-soluble bag to obtain a sample to be tested.

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

[0023] According to the method of the embodiment of the present application, a magnetic substance is extracted from the dispersion of the electrode material to be tested by a magnetic rod, and the magnetic substance is enriched in a filter membrane and, after treatment, is placed in a water-soluble bag to obtain a sample to be tested. Thus, the loss of magnetic substances during the transfer of the filter membrane can be reduced, thereby improving the accuracy of the detection. After the sample to be tested is in contact with the acid solution, the water-soluble bag can be dissolved in the acid solution, so that the magnetic substance in the sample to be tested is in contact with the acid and fully reacts. Thus, the reaction efficiency can also be improved, thereby improving the detection efficiency.

[0024] In any embodiment of the present application, the sample to be tested is contacted with a sufficient amount of acid solution so that the active metal foreign matter and the acid react fully at the reaction temperature to obtain a reaction product containing hydrogen, including:

[0025] The sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum, so that the active metal foreign matter and the acid react fully at a first reaction temperature to obtain a reaction product containing hydrogen.

[0026] Thereby, the accuracy of detecting the content of active metal foreign matter can be improved.

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

[0028] In any embodiment of the present application, the reaction time for the active metal foreign matter to fully react with the acid 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 matter to fully react with the acid at the first reaction temperature are within the above-mentioned appropriate range, the detection time of the active metal foreign matter detection can be controlled within a shorter range, thereby improving the detection efficiency of the active metal foreign matter content.

[0030] In any embodiment of the present application, the active metallic foreign matter includes simple iron.

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

[0032] The method of the embodiment of the present application can be applied to the detection of the content of active metal foreign matter in lithium iron phosphate prepared with iron phosphate as raw material. Therefore, it is conducive to accurately monitoring the content of active metal foreign matter in lithium iron phosphate prepared with iron phosphate as raw material, thereby helping to strictly control the content of metal particles in the battery using the above lithium iron phosphate, reduce the risk of short circuit self-discharge of the battery, extend the service life of the battery, and improve the reliability of the battery.

[0033] In any embodiment of the present application, a sample to be tested containing active metal foreign matter is provided, including:

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

[0035] Use a 5000GS-6000GS magnetic bar to extract magnetic substances from the dispersion, including iron and iron phosphide impurities;

[0036] The magnetic substance is enriched in the filter membrane, and after being washed and dried, it is put into a water-soluble bag to obtain a sample to be tested.

[0037] According to the method of the embodiment of the present application, a magnetic substance is extracted from the dispersion of the electrode material to be tested by a magnetic rod, and the magnetic substance is enriched in a filter membrane and, after treatment, is placed in a water-soluble bag to obtain a sample to be tested. Thus, the loss of magnetic substances during the transfer of the filter membrane can be reduced, thereby improving the accuracy of the detection. After the sample to be tested is in contact with the acid solution, the water-soluble bag can be dissolved in the acid solution, so that the magnetic substance in the sample to be tested is in contact with the acid and fully reacts. Thus, the reaction efficiency can also be improved, thereby improving the detection efficiency.

[0038] In any embodiment of the present application, the sample to be tested is contacted with a sufficient amount of acid solution so that the active metal foreign matter and the acid react fully at the reaction temperature to obtain a reaction product containing hydrogen, including:

[0039] The sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum, so that the active metal foreign matter and the acid react fully at the second reaction temperature to obtain a reaction product containing hydrogen. The second reaction temperature is 20°C-30°C.

[0040] The above-mentioned implementation can reduce the interference of reduced iron in iron phosphide on the detection of active metal foreign matter content, and improve the accuracy of detection. In addition, according to the above-mentioned implementation, the sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum, which can reduce the risk of side reactions between iron ions and iron in the sample to be tested, and can also improve the accuracy of hydrogen content detection in the reaction product. Thus, the accuracy of active metal foreign matter detection can be further improved.

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

[0042] In any embodiment of the present application, the reaction time for the active metal foreign matter to fully react with the acid 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 is within the above-mentioned appropriate range, not only can the detection time of the active metal foreign matter detection be controlled within a shorter range, but also the risk of the iron phosphide reacting with the acid at the second reaction temperature can be further reduced, thereby reducing the interference of the reduced iron in the iron phosphide on the detection of the active metal foreign matter content, thereby improving the detection efficiency and accuracy of the active metal foreign matter content.

[0044] In any embodiment of the present application, the acid solution includes at least one of a dilute sulfuric acid solution and a dilute hydrochloric acid solution. The acid solution can have a suitable reaction rate with the active metal foreign matter, which helps to shorten the detection time and improve the detection efficiency.

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

[0046] In any embodiment of the present application, the acid solution further comprises an antioxidant and / or an oxygen scavenger. Thus, the risk of ferrous ions being oxidized to ferric ions can be further reduced, thereby reducing the side reaction between ferric ions and elemental iron, and further improving the accuracy of detection.

[0047] In any embodiment of the present application, the acid solution further comprises a surfactant. The surfactant can improve the dispersibility of the powdered sample to be tested in the acid solution, and is conducive to the full reaction of the active metal foreign matter in the sample to be tested with the acid. Thus, the accuracy of the detection can be further improved.

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

[0049] Thereby, the influence of the reaction container on the detection result can be reduced, thereby facilitating further improving the accuracy of the detection.

[0050] In any embodiment of the present 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 a high accuracy in detecting the hydrogen content, which is conducive to improving the accuracy of detecting the content of active metal foreign matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic diagram of a reaction device according to one embodiment of the present application.

[0052] Figure 2 This is a gas chromatogram of the gas phase component of the reaction product in sample 5 in Example 5 of the present application. DETAILED DESCRIPTION

[0053] Hereinafter, the implementation method of the method for detecting the content of active metal foreign matter in the electrode material of the present application is specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0054] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0056] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0057] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0058] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0059] In this article, active metals can refer to metals that are located before hydrogen in the metal activity series; the standard electrode potential of the half reaction of active metals in neutral solution is less than 0.

[0060] In the embodiment of the present 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 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 (NCM622) one or more.

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

[0062] In the production process of electrode materials, due to wear of machine pipes and the introduction of impurities in raw materials, metal particles such as iron and iron-chromium-nickel are inevitably introduced. These metal particles will undergo redox reactions between the positive and negative electrodes of the battery during the battery charging and discharging process. When the reduced metal element at the negative electrode accumulates to a certain extent, the hard edges of the metal element will pierce the diaphragm, causing the battery to short-circuit and self-discharge, affecting the battery's service life and reliability. Therefore, the detection of metal particles in electrode materials is particularly important.

[0063] In view of this, an embodiment of the present application provides a method for detecting the content of active metal foreign matter in an electrode material, which can efficiently and accurately detect the residual amount of volatile substances in a sample to extend the service life of the battery and improve the reliability of the battery.

[0064] The embodiment of the present application proposes a method for detecting the content of active metal foreign matter in an electrode material, comprising the following steps S110 to S130.

[0065] S110, providing a sample to be tested containing active metallic foreign matter.

[0066] In step S110, the sample to be tested may include the sample to be tested obtained by sampling from the electrode material to be tested. The electrode material to be tested may include the positive electrode material to be tested 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 the electrode film layer is coated on the surface of the electrode current collector, for example, it may be a battery raw material powder, or it may be a positive electrode slurry, a negative electrode slurry, and the like. The battery raw material powder may include but is not limited to powder for forming a positive electrode film layer and / or a negative electrode film layer, for example, it may include but is not limited to at least one of a positive electrode active material, a negative electrode active material, and a conductive agent.

[0067] S120, contacting the sample to be tested with a sufficient amount of acid solution so that the active metal foreign matter and the acid fully react at a reaction temperature to obtain a reaction product containing hydrogen.

[0068] In step S120, the acid solution may include a non-oxidizing acid solution known in the art, and those skilled in the art may select an appropriate type of acid solution according to actual needs. A sufficient amount of acid solution may indicate that the amount of the acid solution is sufficient to completely react all active metal foreign matters in the sample to be tested. The above-mentioned "sufficient reaction" may indicate that the active metal foreign matters in the sample to be tested react completely with the acid until no more hydrogen is produced. "Sufficient reaction" may be determined in a variety of ways. As an example, the sample to be tested may be fully contacted with a sufficient amount of acid solution for a sufficiently long time to react, for example, the reaction time may be more than 1 hour, more than 1.5 hours, more than 2 hours, and so on. Those skilled in the art may determine a suitable reaction time according to the amount of the sample to be tested and the reaction temperature, etc. As another example, the sample to be tested may be contacted with the acid solution in a closed container, and the hydrogen concentration and / or pressure in the closed container may be detected. When the hydrogen concentration and / or pressure no longer change, it may be considered that the active metal foreign matters and the acid have reached a fully reactive state.

[0069] S130, detecting the hydrogen content in the reaction product to obtain the content of active metal foreign matter in the sample to be tested according to the hydrogen content in the reaction product.

[0070] In step S130, detecting the hydrogen content in the reaction product may include detecting the hydrogen content of the gaseous component in the closed reaction system. Detecting the hydrogen content in the reaction product may be achieved by equipment and methods known in the art, for example, the hydrogen content in the reaction product may be measured by a hydrogen sensor, a gas chromatograph, etc. Those skilled in the art may select appropriate testing equipment and methods according to the detection environment, accuracy requirements, etc.

[0071] During the battery preparation process, it is necessary to detect active metal foreign matter in the electrode material. In order to solve this technical problem, the relevant technology involves separating the active metal foreign matter in the electrode material and then detecting the content of the active metal foreign matter. The method for detecting the content of active metal foreign matter may include direct measurement by energy spectrum scanning electron microscopy (SEM-DES), indirect measurement by the replacement reaction of copper sulfate and active metals, etc. The SEM-DES detection method involved in the related technology can only detect active metal foreign matter in a small area, and the detection process is long and the detection efficiency is low. In addition, in the technical solution of indirectly determining the content of active metal foreign matter by the replacement reaction of copper sulfate and active metals, the residual copper sulfate may affect the quantitative detection of the replacement reaction, further reducing the accuracy of the detection.

[0072] Without intending to be limited by any theory or explanation, the method according to the embodiment of the present application provides a sample to be tested obtained by sampling from the electrode material to be tested, and contacts the sample to be tested with an acid so that the active metal foreign matter and the acid undergo a substitution reaction to obtain a reaction product containing hydrogen. The hydrogen content in the reaction product is detected, and the content of the active metal foreign matter in the sample to be tested can be obtained according to the hydrogen content in the reaction product. According to the method of the embodiment of the present application, the content of the active metal foreign matter is indirectly determined by the substitution reaction between the active metal foreign matter and the acid, which has higher accuracy and detection efficiency than the SEM-DES detection method involved in the related art. In addition, according to the method of the embodiment of the present application, the content of the active metal foreign matter in the sample to be tested is obtained by the hydrogen content in the reaction product; hydrogen is a gas phase product, and the influence of reactants such as acid solution and electrode material on the detection of hydrogen content is extremely low, thereby improving the accuracy of quantitative detection. Therefore, compared with the technical solution involved in the related art of indirectly determining the content of active metal foreign matter by the substitution reaction between copper sulfate and active metal, the method of the embodiment of the present application can have higher accuracy.

[0073] Therefore, the method of the embodiment of the present application is applied to the field of batteries, and can efficiently and accurately detect the content of active metal foreign matter in the electrode material during the battery preparation process. The method of the embodiment of the present application has a high detection efficiency, which can make the monitoring of the content of active metal foreign matter compatible with the production rhythm of battery preparation, thereby improving the efficiency of battery production; the method of the embodiment of the present application also has a high accuracy, and can accurately monitor the content of active metal foreign matter in the electrode material, thereby helping to strictly control the content of metal particles in the electrode material, reduce the risk of short-circuit self-discharge of the battery, extend the service life of the battery, and improve the reliability of the battery.

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

[0075] Active metal foreign bodies such as simple iron and iron-chromium-nickel alloy may be introduced in the production process of positive electrode active materials. For example, in the production process of preparing lithium iron phosphate using ferrous oxalate as raw material, due to the presence of wear of production equipment pipelines, introduction of impurities in raw materials, etc., it is inevitable that simple iron and / or iron-chromium-nickel alloy will be present in lithium iron phosphate. For example, in the production process of nickel-containing lithium transition metal oxides, due to the presence of wear of production equipment pipelines, introduction of impurities in raw materials, and side reactions of raw materials, it is also inevitable that simple iron and / or iron-chromium-nickel alloy will be present in nickel-containing lithium transition metal oxides. The method of the embodiment of the present application can be used to detect the content of active metal foreign bodies including simple iron and / or iron-chromium-nickel alloy, and can be applied to the detection of active metal foreign bodies in lithium iron phosphate prepared using ferrous oxalate as raw material and nickel-containing lithium transition metal oxides. This is conducive to accurately monitoring the content of active metal foreign matter in the above-mentioned positive electrode active materials, thereby helping to strictly control the content of metal particles in batteries using the above-mentioned positive electrode active materials, reduce the risk of battery short circuit self-discharge, extend the service life of the battery, and improve the reliability of the battery.

[0076] In some embodiments, providing a sample to be tested containing active metallic foreign matter may specifically include:

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

[0078] Optionally, the electrode material to be tested includes lithium iron phosphate prepared using ferrous oxalate as a raw material.

[0079] In the production process of lithium iron phosphate, due to the wear of production equipment pipelines and the introduction of impurities in raw materials, active metal foreign matter will inevitably be introduced into lithium iron phosphate, such as iron, iron-chromium-nickel alloy, zinc, etc. When the content of active metal foreign matter in lithium iron phosphate is high, the risk of short circuit self-discharge of the battery will also increase, thereby having a negative impact on the service life and reliability of the battery.

[0080] When related technologies are used to detect various active metal foreign matter in lithium iron phosphate, high-purity water and lithium iron phosphate are usually added to a test bottle, a magnet is placed in, and the mixture is evenly mixed; the magnet is then taken out, and the magnetic foreign matter on the magnet is rinsed, ultrasonically cleaned, and dried; the magnetic foreign matter is then adhered to a dispensing tape, and the morphology and particle size of the magnetic foreign matter particles are identified by a scanning electron microscope (SEM), and the chemical composition and type of the magnetic foreign matter particles are determined by energy spectrum analysis (EDS), and then 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 the active metal foreign matter.

[0081] However, when using a magnet to extract magnetic materials, the adsorption area of ​​the magnet is small, and the collision of the powder with the magnetic bar during the stirring and adsorption process can easily cause the magnetic impurities to fall off. In addition, the highly suspended particles on the surface of the lithium iron phosphate slurry cannot be adsorbed, and there is a probability of adsorption during rolling, resulting in a low extraction rate for small iron powder particles below 10μm. In addition, in some preparation processes of lithium iron phosphate, for example, the preparation process of lithium iron phosphate with ferrous oxalate as the main raw material, it is not only easy to introduce small iron powder particles, but also easy to introduce other active metal foreign particles with weaker magnetism; using a magnet to extract magnetic materials may lead to incomplete extraction of active metal foreign matter, thereby reducing the accuracy of detection. In addition, the extraction of magnetic materials, ultrasonic washing, and electron microscope scanning methods are cumbersome to operate, the test process is long, and it requires high labor and time costs.

[0082] According to the method of the embodiment of the present application, for lithium iron phosphate materials containing multiple active metal foreign matters, samples can be directly taken from the lithium iron phosphate for testing, and the content of active metal foreign matters in the sample to be tested can be determined without extracting the active metal foreign matters. As a result, the detection process can be simplified, the risk of loss of active metal foreign matters can be reduced, and the detection efficiency and accuracy of the content of active metal foreign matters can be improved.

[0083] In some embodiments, the preset mass may be 40g-80g, for example, 40g, 45g, 50g, 55g, 60g, 65g, 70g, 75g, 80g, or a range consisting of any 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 a range consisting of any two of the above values.

[0085] When the preset mass is within the above-mentioned appropriate range, the sample to be tested can be made more representative. In other words, 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. Thus, the accuracy of active metal foreign matter detection can be improved. In addition, when the preset mass is within the above-mentioned appropriate range, the state in which the active metal foreign matter in the sample to be tested fully reacts with the acid can be achieved in a relatively short time, thereby shortening the reaction time and improving the detection efficiency of the active metal foreign matter content.

[0086] In some embodiments, providing a sample to be tested containing active metal foreign matter can specifically include: providing a dispersion of the electrode material to be tested; extracting magnetic substances from the dispersion using a 5000GS-6000GS magnetic bar, wherein the magnetic substances include at least one of iron element or iron-chromium-nickel alloy; enriching the magnetic substances to a filter membrane, and after washing and drying, placing the enriched magnetic substances in a water-soluble bag to obtain a sample to be tested.

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

[0088] In this embodiment, the mass of the electrode material to be tested in the dispersion can be a known amount. The content of active metal foreign matter in the sample to be tested can be detected to calculate the content of active metal foreign matter in the electrode material to be tested. 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 4L-8L of high-purity water. The water-soluble bag can include a water-soluble packaging bag 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 the like made of a water-soluble polymer material.

[0089] In the related art, when faced with the detection of the content of active metal foreign matter in the electrode material to be tested, the magnetic substance in the electrode material to be tested is usually extracted by adsorption by a magnetic rod, and then the extracted magnetic substance is subjected to SEM-EDS testing to determine the content of active metal foreign matter, or indirectly determined by the replacement reaction between copper sulfate and active metal. After the magnetic substance is extracted, the related art needs to wash the magnetic substance and separate the magnetic substance through a filter membrane. During the transfer process of the filter membrane, there may be a loss of magnetic substance, resulting in reduced detection accuracy.

[0090] According to the method of the embodiment of the present application, a magnetic substance is extracted from the dispersion of the electrode material to be tested by a magnetic rod, and the magnetic substance is enriched in a filter membrane and, after treatment, is placed in a water-soluble bag to obtain a sample to be tested. Thus, the loss of magnetic substances during the transfer of the filter membrane can be reduced, thereby improving the accuracy of the detection. After the sample to be tested is in contact with the acid solution, the water-soluble bag can be dissolved in the acid solution, so that the magnetic substance in the sample to be tested is in contact with the acid and fully reacts. Thus, the reaction efficiency can also be improved, thereby improving the detection efficiency.

[0091] In some embodiments, the sample to be tested is contacted with a sufficient amount of acid solution so that the active metal foreign matter and the acid react fully at the reaction temperature to obtain a reaction product containing hydrogen, which may specifically include:

[0092] The sample to be tested is mixed with a sufficient amount of acid solution in an inert atmosphere or vacuum, so that the active metal foreign matter and the acid react fully at a first reaction temperature to obtain a reaction product containing hydrogen.

[0093] In the above-mentioned embodiment, the inert atmosphere may include an atmosphere that does not react with the substances in the reaction system and does not affect the detection of the hydrogen content. As an example, the inert atmosphere may include a nitrogen atmosphere, a rare gas atmosphere, or a mixed atmosphere thereof. The first reaction temperature may be adjusted according to factors such as the demand for the reaction rate and the difficulty 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, which can isolate the air on the one hand, reduce the risk of ferrous ions being oxidized to ferric ions, thereby reducing the risk of side reactions between iron ions and the iron element in the sample to be tested, and help improve the accuracy of detection; on the other hand, the hydrogen generated by the reaction is dispersed in the inert gas, and the impurity gas that affects the detection of hydrogen content is less, which helps to reduce the difficulty of hydrogen content detection in the reaction product and improve the accuracy of hydrogen content detection in the reaction product. Thus, the accuracy of detection of active metal foreign matter content can be improved.

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

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

[0097] In some embodiments, the reaction time for the active metal foreign body to fully react with the acid 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 a range consisting of any two of the above values.

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

[0099] In some embodiments, the reactive metallic foreign matter may include elemental iron.

[0100] Optionally, the electrode material to be tested may include lithium iron phosphate prepared using iron phosphate as a raw material.

[0101] Iron may be introduced in the production process of positive electrode active materials. For example, in the production process of lithium iron phosphate prepared with iron phosphate as raw material, iron will inevitably be produced in the lithium iron phosphate due to side reactions of iron phosphate and the like. The method of the embodiment of the present application can be applied to the detection of the content of active metal foreign matter in lithium iron phosphate prepared with iron phosphate as raw material. Thus, it is conducive to accurately monitoring the content of active metal foreign matter in lithium iron phosphate prepared with iron phosphate as raw material, which is conducive to strictly controlling the content of metal particles in the battery using the above-mentioned lithium iron phosphate, reducing the risk of short circuit self-discharge of the battery, extending the service life of the battery, and improving the reliability of the battery.

[0102] In some embodiments, providing a sample to be tested containing active metal foreign matter can specifically include: providing a dispersion of the electrode material to be tested; extracting magnetic substances from the dispersion using a 5000GS-6000GS magnetic bar, wherein the magnetic substances include elemental iron and iron phosphide impurities; enriching the magnetic substances to a filter membrane, and after washing and drying, placing the filtered substances into a water-soluble bag to obtain a sample to be tested.

[0103] In this embodiment, the mass of the electrode material to be tested in the dispersion can be a known amount. The content of active metal foreign matter in the sample to be tested can be detected to calculate the content of active metal foreign matter in the electrode material to be tested. 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 4L-8L of high-purity water. The water-soluble bag may include a water-soluble packaging bag known in the art. As an example, the water-soluble bag may be a starch polyvinyl chloride water-soluble bag, a polyvinyl alcohol water-soluble bag, or the like made of a water-soluble polymer material.

[0104] According to the method of the embodiment of the present application, a magnetic substance is extracted from the dispersion of the electrode material to be tested by a magnetic rod, and the magnetic substance is enriched in a filter membrane and, after treatment, is placed in a water-soluble bag to obtain a sample to be tested. Thus, the loss of magnetic substances during the transfer of the filter membrane can be reduced, thereby improving the accuracy of the detection. After the sample to be tested is in contact with the acid solution, the water-soluble bag can be dissolved in the acid solution, so that the magnetic substance in the sample to be tested is in contact with the acid and fully reacts. Thus, the reaction efficiency can also be improved, thereby improving the detection efficiency.

[0105] In some embodiments, the sample to be tested is contacted with a sufficient amount of acid solution so that the active metal foreign matter and the acid react fully at the reaction temperature to obtain a reaction product containing hydrogen, which may specifically include:

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

[0107] In the process of producing lithium iron phosphate using iron phosphate as raw material, iron particles may be generated through side reactions. Due to the characteristics of the process, the active metal foreign matter in lithium iron phosphate produced by the iron phosphate process is mainly iron. The process also generates a small amount of iron phosphide byproduct (0-2000ppm). Iron phosphide is a complex. Generally speaking, the iron in iron phosphide is +1 and +2 valent, and its properties are relatively stable. It has almost no effect on battery performance within a certain content range. However, some iron phosphides contain reduced iron, which is reducible at high temperatures and has certain magnetism.

[0108] When detecting the content of active metal foreign matter in lithium iron phosphate produced by the iron phosphate process, the related technology involves conducting a cleanliness analysis Jemosa or SEM-EDS test on the extracted magnetic material, or performing a copper sulfate replacement test on the iron content. However, after the magnetic material is extracted from the lithium iron phosphate material, there may be a lot of iron phosphide in the magnetic material, which makes it difficult to perform a cleanliness analysis or SEM-EDS test; even if the test is performed, only a trace amount of the sample to be tested can be taken for testing, which has problems such as the sample to be tested is not representative and the test time is long. The method of copper sulfate replacement to test the iron content is subject to interference from the dissolution of reduced iron in iron phosphide and the residual copper sulfate element, resulting in low detection accuracy.

[0109] It has been found that the iron in the sample to be tested can react with the acid preferentially over the reduced iron in the iron phosphide. In the above embodiment, the second reaction temperature is within a suitable range, which satisfies: at the second reaction temperature, the iron can react with the acid, while the reduced iron in the iron phosphide does not react with the acid.

[0110] Therefore, the above-mentioned embodiment mixes the sample to be tested with a sufficient acid solution in an inert atmosphere or vacuum, so that the active metal foreign matter and the acid fully react at the second reaction temperature to obtain a reaction product containing hydrogen; By detecting the hydrogen content in the reaction product, the content of the iron element in the sample to be tested can be obtained. Thus, the interference of reduced iron in iron phosphide can be reduced, and the accuracy of detection can be improved. In addition, according to the above-mentioned embodiment, the sample to be tested is mixed with a sufficient acid solution in an inert atmosphere or vacuum, on the one hand, air can be isolated, the risk of ferrous ions being oxidized to ferric ions can be reduced, thereby reducing the risk of side reactions between iron ions and the iron element in the sample to be tested, which helps to improve the accuracy of detection; on the other hand, the hydrogen generated by the reaction is dispersed in an inert gas or is pure hydrogen, and the impurity gas that affects the detection of hydrogen content is less, which helps to reduce the difficulty of hydrogen content detection in the reaction product and improve the accuracy of hydrogen content detection in the reaction product. Thus, the accuracy of active metal foreign matter detection can be further improved.

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

[0112] In some embodiments, the reaction time for the active metal foreign body to fully react with the acid 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 a range consisting of any 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 is within the above-mentioned appropriate range, not only can the detection time of the active metal foreign matter detection be controlled within a shorter range, but also the risk of the iron phosphide reacting with the acid at the second reaction temperature can be further reduced, thereby reducing the interference of the reduced iron in the iron phosphide on the detection of the active metal foreign matter content, thereby improving the detection efficiency and accuracy of the active metal foreign matter content.

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

[0115] Optionally, after obtaining a first reaction product containing hydrogen, the method may further include: separating a gaseous component in the first reaction product; heating the remaining sample to be tested and the acid solution so that the iron phosphide impurities react fully with the acid at a third reaction temperature to obtain a second reaction product containing hydrogen, the third reaction temperature being higher than the second reaction temperature; detecting the hydrogen content in the second reaction product to obtain 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. Generally speaking, the iron in iron phosphide is +1 and +2 valent, and its properties are relatively stable. It has almost no effect on battery performance within a certain content range. However, some iron phosphides contain reduced iron, which is reducible at high temperatures and may affect the high-temperature performance of the battery. Therefore, it is necessary to monitor the iron in the magnetic material extracted from lithium iron phosphate and the reduced iron contained in the iron phosphide separately to obtain the content of iron in lithium iron phosphate and the content of reduced iron in the iron phosphide.

[0117] When the related technology involves separately monitoring the iron element and the reduced iron contained in the iron phosphide, it is usually necessary to extract the iron element and the iron phosphide separately, and determine the iron element content and the reduced iron content contained in the iron phosphide separately. As an example, the lithium iron phosphate powder can be mixed evenly with deionized water to obtain a dispersion; a magnetic rod covered with a heat shrink tube is used for two-dimensional stirring adsorption to extract the magnetic substance in the dispersion; the magnetic substance is transferred to a beaker, water is added and mixed evenly, and then the magnetic substance is extracted with a magnet, and after repeating this process for many times, it is filtered with a filter membrane; the filter membrane loaded with the magnetic substance is analyzed for cleanliness with a cleanliness microscope, and the metal particles are tested for the particle size; the filter membrane is then placed in N-methylpyrrolidone (NMP) to obtain an NMP dispersion of the magnetic substance; the NMP dispersion is extracted twice with a magnetic rod, and the extract is tested to determine the content of the remaining iron element after the iron phosphide is removed.

[0118] However, iron phosphide has a magnetic property similar to that of iron, and cannot be removed by secondary extraction. In addition, during the cleanliness analysis, iron phosphide is not only difficult to identify, but also masks the iron. As a result, the accuracy of the iron content detected is low. In addition, secondary extraction not only increases the risk of loss of magnetic materials, but also complicates the detection process, resulting in a decrease in the accuracy and efficiency of the detection.

[0119] According to the above embodiment of the present application, after extracting the magnetic substance in the lithium iron phosphate to obtain the sample to be tested, the iron element in the sample to be tested is first reacted with the acid at a lower second reaction temperature, and then the reduced iron contained in the iron phosphide in the sample to be tested is reacted with the acid at a higher third reaction temperature; by respectively detecting the hydrogen content in the first reaction product and the hydrogen content in the second reaction product, the content of the iron element in the lithium iron phosphate and the content of the reduced iron contained in the iron phosphide are obtained. According to the above embodiment of the present application, the difference in the reactivity of the iron element and the reduced iron contained in the iron phosphide with the acid is utilized, and the iron element and the reduced iron contained in the iron phosphide are reacted with the acid successively in the same reaction system, so that the content of the iron element in the lithium iron phosphate and the content of the reduced iron contained in the iron phosphide can be determined respectively, thereby not only simplifying the detection process, reducing the detection cost, and improving the detection efficiency, but also improving the detection accuracy. In some embodiments, the spiked recovery rate of the iron element according to the above embodiment can reach more than 80%. In addition, according to the above-mentioned implementation, the magnetic material only needs to be extracted once, which not only greatly reduces the risk of magnetic material loss, but also simplifies the process of magnetic material extraction, thereby further improving the detection efficiency and detection accuracy.

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

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

[0122] In some embodiments, the time for the iron phosphide impurity to fully react with 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 a range consisting of any two of the above values.

[0123] When the third reaction temperature and / or the reaction time for the iron phosphide impurity to fully react with the acid at the third reaction temperature is within the above-mentioned appropriate range, the detection time for detecting 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 volatility, before detecting the hydrogen content in the reaction product, the gas phase components of the reaction system may be filtered through a hydrochloric acid filter.

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

[0126] The above acid solution can have a suitable reaction rate with active metal foreign matter, which helps to shorten the detection time and improve the detection efficiency.

[0127] In some embodiments, the acid solution may include F - . F - Can be made by F - The source is dissolved in an acid solution, F - The source may include but is not limited to F - Inorganic salts (such as NaF), HF. - It can complex with the iron ions dissolved from active metal foreign matter, thereby inhibiting the reaction between iron ions and elemental iron and improving the accuracy of active metal foreign matter content detection.

[0128] In some embodiments, the acid solution may further include an antioxidant and / or a scavenger. The antioxidant may be selected from antioxidants known in the art, for example, including but not limited to one or more of vitamin C antioxidants and tea polyphenol antioxidants; the scavenger may be selected from scavengers known in the art, for example, including but not limited to acetone oxime. Thus, the risk of ferrous ions being oxidized to ferric ions can be further reduced, thereby reducing the side reaction of ferric ions with elemental iron, and further improving the accuracy of detection.

[0129] In some embodiments, the acid solution may further include a surfactant. The surfactant may be selected from ionic surfactants and / or nonionic surfactants known in the art, for example, including but not limited to the surfactant Huntsman X3204. In some embodiments, when the surfactant includes a foaming surfactant, a defoamer may also be added to the acid solution. The surfactant may improve the dispersibility of the powdered sample to be tested in the acid solution, which is conducive to the full reaction of the active metal foreign matter in the sample to be tested with the acid. Thus, the accuracy of the detection can be further improved.

[0130] In some embodiments, contacting the sample to be tested with the acid solution may specifically include:

[0131] The sample to be tested is mixed with an acid solution in a closed reaction container, and the inner wall surface of the reaction container includes a Teflon coating.

[0132] Teflon is inert to active metal foreign matter, iron phosphide and acid, which can reduce the impact of the reaction container on the test results, thereby helping to further improve the accuracy of the test.

[0133] In some embodiments, the sample to be tested and the acid solution can be mixed in a Figure 1 The mixture is mixed in the reaction device shown to react the active metal foreign acid.

[0134] like Figure 1 As shown, the reaction device may include: a stirring motor 1, a reaction liquid quantitative storage tank (polypropylene material) 2, a reaction liquid storage tank hose and a reaction kettle interface 3, a movable switch cock 4, a kettle cover and a reaction bottle sealing ring 5, a gas inlet plug 6, a reactor 7, a stainless steel stirring paddle (externally coated with polytetrafluoroethylene) 8, an ultrasonic heating device 9, and a micro vacuum pump 10. The reaction device and the gas path are both coated with Teflon coating to inhibit metal pollution reactions and acid corrosion.

[0135] As an example, the sample to be tested can be placed in the reactor 7, and the reactor 7, the kettle cover and the reaction bottle sealing ring 5 are assembled; the reaction device is evacuated by a micro vacuum pump 10 to eliminate the interference of gases such as oxygen and hydrogen in the air; then the movable switch cock 4 is opened to connect the reaction liquid quantitative storage tank 2 and the reactor 7, so that the acid solution in the reaction liquid quantitative storage tank 2 automatically enters the reactor 7, and when the amount of acid solution is sufficient, the movable switch cock 4 is closed; the stirring motor 1 is turned on to stir the substance in the reactor 7 through the stainless steel stirring paddle; the ultrasonic heating device 9 is used to ultrasonically heat the reactor 7 for 1.5h-2.5h; at room temperature, when the pressure in the reactor 7 is lower than the atmospheric pressure, the needle of a disposable syringe is inserted into the air inlet rubber plug 6 to fill air, or nitrogen is filled through the air inlet rubber plug 6 to balance the internal pressure of the reactor to atmospheric pressure; when the pressure in the reactor 7 is higher than the atmospheric pressure, the pressure value is recorded for the calculation of the amount of substance generating hydrogen; the hydrogen content generated by the reaction is detected by gas chromatography to obtain the content of active metal foreign matter in the sample to be tested according to the hydrogen content.

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

[0137] In some embodiments, the method of the embodiments of the present application can achieve a spike recovery rate of more than 80% for active metal foreign matter.

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

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

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

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

[0142] Example

[0143] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0144] Example 1

[0145] Weigh 5 samples to be tested (lithium iron phosphate powder prepared with ferrous oxalate as raw material, purchased from Fulin Precision, iron content less than 0.2ppm), each of which has a mass of 50g. Each sample to be tested is spiked, and active metal foreign matter is added to obtain spiked samples to be tested, which are recorded as samples 1 to 5. The types of active metal foreign matter added and their spiked amounts are shown in Table 1-1.

[0146] Table 1-1

[0147] serial number Active metal foreign matter Added amount / mg 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 to 5 were placed in a reactor respectively, and after evacuation, a sufficient amount of acid solution was injected, wherein the acid solution was obtained by mixing 300 mL of 50% dilute sulfuric acid solution, 8 g of surfactant X3204 and 5 mL of HF; stirring was started, ultrasonic heating was performed to a first reaction temperature of 55°C, and the reaction was performed for 1.5 hours to obtain a reaction product; the reaction product was cooled to room temperature, and nitrogen was charged to balance to normal pressure; the hydrogen content of the reaction product was detected by a gas chromatograph, and the test parameters were as follows: a molecular sieve gas composition test column was used, a nitrogen carrier gas flow rate of 25 mL / min, valve injection was used, the test was performed at a constant temperature of 60°C, a TCD detector was used, and the detector temperature was 250°C; the content of active metal foreign matter in the spiked sample to be tested was calculated according to the hydrogen content of the reaction product.

[0149] The detection results of active metal foreign matter content of samples 1 to 5 of Example 1 and their spiked recovery rates are shown in Table 1-2. Spiked recovery rate of active metal foreign matter of samples 1 to 5 of Example 1 = [active metal foreign matter content (mg) / specified amount (mg)] × 100%.

[0150] Table 1-2

[0151] serial number Active metal foreign matter content / mg Spike recovery 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 process is the same as that of Example 1, except that 4 g 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, respectively, and the active metal foreign matter content detection results and spiked recovery rates of samples 1 to 5 are shown in Table 2-2, respectively. Spiked recovery rates of active metal foreign matter in samples 1 to 5 of Example 2 = [active metal foreign matter content (mg) / specified amount (mg)] × 100%.

[0155] Table 2-1

[0156] serial number Active metal foreign matter Added amount / mg 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] serial number Active metal foreign matter content / mg Spike recovery 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 that of Example 1, except that the first reaction temperature is 50° C. and the reaction time is 2.5 h.

[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, respectively, and the active metal foreign matter content detection results and spiked recovery rates of samples 1 to 5 are shown in Table 3-2, respectively. Spiked recovery rates of active metal foreign matter in samples 1 to 5 of Example 3 = [active metal foreign matter content (mg) / specified amount (mg)] × 100%.

[0162] Table 3-1

[0163] serial number Active metal foreign matter Added amount / mg 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] serial number Active metal foreign matter content / mg Spike recovery 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 that of Example 1, except that the first reaction temperature is 70° C. and the reaction time is 2 h.

[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, respectively, and the detection results of active metal foreign matter content in samples 1 to 5 and their spiked recoveries are shown in Table 4-2, respectively. Spiked recoveries of active metal foreign matter in samples 1 to 5 of Example 4 = [active metal foreign matter content (mg) / specified amount (mg)] × 100%.

[0169] Table 4-1

[0170] serial number Active metal foreign matter Added amount / mg 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] serial number Active metal foreign matter content / mg Spike recovery 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] Take 1kg of lithium iron phosphate powder prepared with iron phosphate as raw material (purchased from Hunan Yuneng), mix it evenly with 6L of high-purity water to obtain an aqueous dispersion of lithium iron phosphate; use a 6000GS heat shrink tube magnetic rod to extract the magnetic substance in the dispersion; after cleaning the magnetic substance on the heat shrink tube, add 50% dilute sulfuric acid solution and stir at 25°C for 2h to remove the iron element contained in the magnetic substance itself; then adsorb the magnetic substance on the magnetic block and rinse it with water 3 times to remove the remaining sulfuric acid; filter it with a filter membrane, dry it, and then add a spike (weigh the active metal foreign matter and add it to the magnetic substance); transfer the filter membrane loaded with the spiked magnetic substance to a starch polyvinyl chloride water-soluble bag, and seal it to obtain the spiked sample to be tested. Prepare 5 samples to be tested with the above steps to obtain the spiked samples to be tested, which are recorded as samples 1 to 5. The types and masses of the active metal foreign matter added are shown in Table 5-1.

[0175] Table 5-1

[0176] serial number Active metal foreign matter Added amount / mg 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] Put samples 1 to 5 into a flask filled with sufficient acid solution respectively, evacuate the flask, and then fill it with acid solution, which is obtained by mixing 150mL of 50% dilute sulfuric acid solution and 0.3g of NaF; stir the reaction at the second reaction temperature of 25°C for 2h to obtain a reaction product, and fill it with nitrogen to atmospheric pressure; detect the hydrogen content in the reaction product by gas chromatograph, and the test parameters are as follows: use a molecular sieve gas composition test column, a nitrogen carrier gas flow rate of 25mL / min, valve injection, constant temperature 60°C test, TCD detector, and detector temperature 250°C; calculate the content of iron element in the spiked sample to be tested based on the hydrogen content of the reaction product. As an example, Figure 2 The gas chromatogram of the gas phase components of the reaction products in sample 5. Analysis Figure 2 H 2 The characteristic peak (t=1.05 min) can be used to calculate the hydrogen content of the reaction product in sample 5, and then the content of the iron element in the spiked sample to be tested can be calculated.

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

[0179] Table 5-2

[0180] serial number Active metal foreign matter content / mg Spike recovery 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 that of Example 5, except that 0.5 g of tea polyphenols is 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, respectively, and the active metal foreign matter content detection results and spiked recovery rates of samples 1 to 5 are shown in Table 6-2, respectively. Spiked recovery rates of active metal foreign matter in samples 1 to 5 of Example 6 = [active metal foreign matter content (mg) / specified amount (mg)] × 100%.

[0184] Table 6-1

[0185] serial number Active metal foreign matter Added amount / mg 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] serial number Active metal foreign matter content / mg Spike recovery 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 that of 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, respectively, and the detection results of active metal foreign matter content in samples 1 to 5 and their spiked recovery rates are shown in Table 7-2, respectively. Spiked recovery rates of active metal foreign matter in samples 1 to 5 of Example 7 = [active metal foreign matter content (mg) / specified amount (mg)] × 100%.

[0191] Table 7-1

[0192] serial number Active metal foreign matter Added amount / mg 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] serial number Active metal foreign matter content / mg Spike recovery 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 that of 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, respectively, and the detection results of active metal foreign matter content in samples 1 to 5 and their spiked recoveries are shown in Table 8-2, respectively. Spiked recoveries of active metal foreign matter in samples 1 to 5 of Example 8 = [active metal foreign matter content (mg) / specified amount (mg)] × 100%.

[0198] Table 8-1

[0199] serial number Active metal foreign matter Added amount / mg 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] serial number Active metal foreign matter content / mg Spike recovery 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 1kg LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NCM622) ternary powder is mixed evenly with 6L high-purity water to obtain an aqueous dispersion of the ternary powder; the magnetic substance in the dispersion is extracted with a 6000GS heat shrink tube magnetic rod; after cleaning the magnetic substance on the heat shrink tube, a 50% dilute sulfuric acid solution is added and stirred at 70°C for 2h to remove the stainless steel contained in the magnetic substance itself; the magnetic substance is then rinsed with magnetic block adsorption water for 3 times to remove the remaining sulfuric acid; filtered with a filter membrane, dried and then spiked (active metal foreign matter is weighed and added to the magnetic substance); the filter membrane loaded with the spiked magnetic substance is transferred to a starch polyvinyl chloride water-soluble bag and sealed to obtain the spiked sample to be tested. Five spiked samples to be tested are prepared according to the above steps to obtain spiked samples to be tested, which are recorded as samples 1 to 5. The spiked active metal foreign matter is austenitic stainless steel (component Fe 66wt％ Cr 17wt％ Ni 13wt％ , 1 mol of Fe can react with acid to generate 1 mol of H 2 , 1 mol Cr can react with acid to generate 1.5 mol H 2 , 1 mol Ni can react with acid to generate 1 mol H 2 ), the spiked amounts of each sample are shown in Table 9-1.

[0204] Table 9-1

[0205] serial number Active metal foreign matter Added amount / mg 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 to 5 were respectively put into a flask filled with a sufficient amount of acid solution. After evacuation, nitrogen was filled in to balance the pressure. The acid solution was obtained by mixing 150 mL of a 50% dilute sulfuric acid solution and 0.3 g of NaF. The reaction was stirred at a first reaction temperature of 55°C for 1.5 hours to obtain a reaction product. The hydrogen content in the reaction product was detected by a gas chromatograph. The test parameters were as follows: 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 performed at a constant temperature of 60°C, a TCD detector was used, and the detector temperature was 250°C; the content of active metal foreign matter in the spiked sample to be tested was calculated based on the hydrogen content of the reaction product.

[0207] The test results of active metal foreign matter content of samples 1 to 5 of Example 9 and their spiked recovery rates are shown in Table 9-2. Spiked recovery rates of active metal foreign matter of samples 1 to 5 of Example 9 = [active metal foreign matter content (mg) / specified amount (mg)] × 100%.

[0208] Table 9-2

[0209]

[0210]

[0211] Comparative Example 1

[0212] 1 kg of lithium iron phosphate powder prepared with ferrous oxalate as raw material (purchased from Fulin Seiko) was taken and mixed evenly with 6 L of high-purity water to obtain an aqueous dispersion of lithium iron phosphate; the magnetic substance in the dispersion was extracted 3 times using a 6000GS heat shrink tube magnetic rod, and the magnetic substance was rinsed with water, filtered to a filter membrane, and then dried to scan the number of magnetic particles with a cleanliness analyzer. In the magnetic substance extracted for the last time, the total content of magnetic particles was less than 10; a spike treatment was performed: active metal foreign matter iron powder was dispersed in water, part of the iron powder was taken with a pipette, dispersed and filtered onto a filter membrane, and after scanning with a cleanliness analyzer, the number and particle size of iron elemental particles on the surface of the filter membrane were recorded; the filter membrane was then ultrasonically immersed in water, added to the aqueous dispersion of lithium iron phosphate and stirred evenly; the magnetic substance in the dispersion was extracted again using a 6000GS heat shrink tube magnetic rod, and after transferring the magnetic substance to a beaker, the bottom of the beaker was adsorbed with a magnet, the magnetic substance was rinsed with pure water, filtered onto a 5-micron filter membrane, and dried to scan with a cleanliness analyzer. The particle size of the spiked active metal foreign matter and its spiked amount, the detection results of the active metal foreign matter content and its spiked recovery rate are shown in Table 10. Comparative Example 1 The spiked recovery rate of active metal foreign matter in each particle size range = [active metal foreign matter content (particles) / specified amount (particles)] × 100%.

[0213] Table 10

[0214] Active metal foreign matter Particle size / μm Added amount / particle Active metal foreign matter content / particle Spike recovery 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 1kg of the sample to be tested (lithium iron phosphate powder prepared with iron phosphate as raw material, purchased from Hunan Yuneng), mix it evenly with 6L of high-purity water to obtain an aqueous dispersion of lithium iron phosphate; use a 6000GS heat shrink tube magnetic bar to extract the magnetic substance in the dispersion; after cleaning the magnetic substance on the heat shrink tube, add 50% sulfuric acid aqueous solution and stir for 2h to remove the iron element contained in the magnetic substance itself; then perform a spike treatment (weigh active metal foreign matter and add it to the magnetic substance) to obtain a spiked sample to be tested; add 0.2% copper sulfate solution and react at 140°C for 1h , so that the replacement reaction between the iron element and the copper ion is completed; after cooling to room temperature, the solid remaining after the reaction is filtered and washed onto the filter membrane, the filter membrane is removed and placed in a beaker, 10 ml of water and 10 ml of concentrated nitric acid are added, and heated at 180°C for digestion for 1 h; the filtrate is filtered and the copper ion content is measured (the filtrate is diluted to a 50 mL volumetric flask, 1 ml is taken and diluted to 50 mL again, and the copper ion content Cu content is tested by inductively coupled plasma emission spectrometer, the unit is μg), and the replacement iron content Fe (mg) is converted to [(Cu content / 64)×56]×10 -3 , and obtain the detection results of active metal foreign matter content.

[0217] According to the above steps, 5 samples to be tested were prepared with spikes, which were recorded as samples 1 to 5. The types of active metal foreign matter spiked in samples 1 to 5 and their spiked amounts are shown in Table 11-1, respectively, and the test results of active metal foreign matter content in samples 1 to 5 and their spiked recoveries are shown in Table 11-2, respectively. Comparative Example 1 Spiked recovery rate of active metal foreign matter in each particle size range = [active metal foreign matter content (mg) / specified amount (mg)] × 100%.

[0218] Table 11-1

[0219] serial number Active metal foreign matter Added amount / mg 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] serial number Active metal foreign matter content / mg Spike recovery 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 1kg LiNi 0.6 Mn 0.2 Co 0.2 O 2(NCM622) ternary powder is mixed evenly with 6L high-purity water to obtain an aqueous dispersion of the ternary powder; the magnetic substance in the dispersion is extracted 3 times with a 6000GS heat shrink tube magnetic rod, and the magnetic substance is rinsed with water, filtered to a filter membrane, and then dried to scan the number of magnetic particles with a cleanliness analyzer. The total content of magnetic metal particles is less than 10 for the last time; a spike treatment is performed: about 500-1000 mesh magnetic austenitic stainless steel (composition Fe66wt%Cr17wt%Ni13wt%) particles are dispersed in water, a portion of the stainless steel particles is taken with a pipette, dispersed and filtered onto a filter membrane, and after scanning with a cleanliness analyzer, the number and particle size of the stainless steel particles on the filter membrane surface are recorded; the filter membrane is ultrasonically immersed in water, added to the aqueous dispersion of the ternary powder and stirred evenly; the magnetic substance in the dispersion is extracted again with a 6000GS heat shrink tube magnetic rod, the magnetic substance is transferred to a beaker, the bottom of the beaker is adsorbed with a magnet, and the magnetic substance is rinsed with pure water; it is filtered onto a 5-micron filter membrane, and the cleanliness analyzer is scanned after drying. The particle size of the spiked active metal foreign matter and its spiked amount, the detection results of the active metal foreign matter content and its spiked recovery rate are shown in Table 12. Comparative Example 3 The spiked recovery rate of active metal foreign matter in each particle size range = [active metal foreign matter content (particles) / specified amount (particles)] × 100%.

[0224] Table 12

[0225] Active metal foreign matter Particle size / μm Added amount / particle Metal foreign matter content / particles Spike recovery 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 detection process according to the method of the embodiment of the present application is simple, and can more accurately detect the content of active metal foreign matter in the electrode material, and can have both high detection efficiency and accuracy.

[0227] In contrast, in Comparative Examples 1 and 3, magnetic substances in the aqueous dispersion of lithium iron phosphate powder are extracted with a magnetic rod, and then a cleanliness analysis scan is performed. Compared with the treatment method of directly mixing the powder with the acid solution in Examples 1-4, the pre-treatment process of Comparative Example 1 is more complicated; compared with the gas chromatography detection of Examples 1-4 and 9, the cleanliness analysis scan operation of Comparative Examples 1 and 3 is also more complicated. In addition, Comparative Examples 1 and 3 have a lower accuracy in the detection of the content of active metal foreign matter with a particle size of less than 100 μm. The overall spiked recovery rate of Comparative Example 1 is far less than that of Examples 1-4, and the overall spiked recovery rate of Comparative Example 3 is far less than that of Example 9. Comparative Example 2 uses a magnetic rod to extract the magnetic substance in the aqueous dispersion of lithium iron phosphate powder, and then replaces the active metal foreign matter in the magnetic substance with copper sulfate. Copper sulfate may affect the quantitative detection of the replacement reaction. Therefore, the detection accuracy of the active metal foreign matter content in Comparative Example 2 is much lower than that of Examples 5-8.

[0228] For some compounds given but not listed in the embodiments, since their chemical properties and reaction properties when participating in electrochemical reactions are similar to those of the compounds listed in the embodiments, they are all suitable for the technical scheme of the present invention and are therefore not listed one by one here.

[0229] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for detecting the content of active metallic foreign matter in electrode materials, include: Provide a sample to be tested containing active metallic foreign matter; The sample to be tested is contacted with a sufficient amount of acid solution so that the active metal foreign matter and the acid react fully at the reaction temperature to obtain a reaction product containing hydrogen; The hydrogen content in the reaction product is detected to obtain the content of active metal foreign matter in the sample to be tested according to the hydrogen content in the reaction product.

2. The method according to claim 1, in, The active metallic foreign matter includes at least one of a single substance of iron or an iron-chromium-nickel alloy.

3. The method according to claim 2, in, The method of providing a sample to be tested containing active metallic foreign matter comprises: After the electrode material to be tested is stirred evenly, a preset mass of the electrode material to be tested is weighed to obtain the sample to be tested; Optionally, the electrode material to be tested includes lithium iron phosphate prepared using ferrous oxalate as a raw material; Optionally, the preset mass is 40g-80g, and more optionally 50g-60g.

4. The method according to claim 2, in, The method of providing a sample to be tested containing active metallic foreign matter comprises: Providing a dispersion of the electrode material to be tested; Extracting magnetic material from the dispersion using a 5000GS-6000GS magnetic bar, wherein the magnetic material includes at least one of iron or an iron-chromium-nickel alloy; The magnetic substance is enriched in the filter membrane, and after being washed and dried, it is put into a water-soluble bag to obtain the sample to be tested; Optionally, the electrode material to be tested includes a lithium transition metal oxide containing nickel.

5. The method according to any one of claims 2 to 4, in, The method of contacting the sample to be tested with a sufficient amount of acid solution so that the active metal foreign matter and the acid fully react at a reaction temperature to obtain a reaction product containing hydrogen includes: 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 matter and the acid react fully at a first reaction temperature to obtain a reaction product containing hydrogen.

6. The method according to claim 5, in, The first reaction temperature is 50°C-70°C, optionally 55°C-60°C; and / or The reaction time for the active metal foreign matter to fully react with the acid at the first reaction temperature is 1.5h-2.5h.

7. The method according to claim 1, in, The active metallic foreign matter includes iron element; Optionally, the electrode material to be tested includes lithium iron phosphate prepared using iron phosphate as raw material.

8. The method according to claim 7, in, The method of providing a sample to be tested containing active metallic foreign matter comprises: Providing a dispersion of the electrode material to be tested; Extracting magnetic substances from the dispersion using a 5000GS-6000GS magnetic bar, wherein the magnetic substances include iron and iron phosphide impurities; The magnetic substance is enriched in the filter membrane, and after being washed and dried, it is put into a water-soluble bag to obtain the sample to be tested.

9. The method according to claim 7 or 8, in, The method of contacting the sample to be tested with a sufficient amount of acid solution so that the active metal foreign matter and the acid fully react at a reaction temperature to obtain a reaction product containing hydrogen includes: 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 matter and the acid fully react at a second reaction temperature to obtain a reaction product containing hydrogen, wherein the second reaction temperature is 20° C.-30° C.; Optionally, the second reaction temperature is 25°C-30°C; Optionally, the reaction time for the active metal foreign matter to fully react with the acid at the second reaction temperature is 2h-2.5h.

10. The method according to any one of claims 1 to 9, in, The acid solution includes at least one of a dilute sulfuric acid solution and a dilute hydrochloric acid solution; Optionally, the acid solution contains F - ; Optionally, the acid solution further comprises an antioxidant and / or a deoxidizer; Optionally, the acid solution further comprises a surfactant.

11. The method according to any one of claims 1 to 10, in, The test sample is contacted with an acid solution, comprising: The sample to be tested is mixed with the acid solution in a closed reaction container, and the inner wall surface of the reaction container includes a Teflon coating.

12. The method according to any one of claims 1 to 11, in, The detecting of the hydrogen content in the reaction product comprises: The reaction product is subjected to gas chromatography detection to obtain the hydrogen content in the reaction product.

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