Method for detecting content of elemental iron in lithium iron phosphate material

Abstract

The invention discloses a method for detecting the content of elemental iron in a lithium iron phosphate material. The method comprises the following steps: separating magnetic foreign matters from the lithium iron phosphate material; the magnetic foreign matter is placed in the copper salt solution, a first solid matter is obtained through reaction, and the first solid matter comprises a copper element; and measuring the content of the copper element in the first solid substance to obtain the content of the elemental iron in the lithium iron phosphate material. According to the embodiment of the invention, the elemental iron and other iron-containing foreign matters in the magnetic foreign matters are subjected to differential treatment, and the content of the elemental iron in the lithium iron phosphate material is obtained according to the determination result of the content of the copper element obtained through the replacement reaction, so that the obtained detection result reduces the interference of non-elemental iron foreign matters on the content of the elemental iron, and the detection accuracy is improved. The detection accuracy of the content of the elemental iron in the lithium iron phosphate material is favorably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for detecting the content of elemental iron in a lithium iron phosphate material. Background Art

[0002] This section merely provides background information related to the present application and is not necessarily prior art.

[0003] Lithium iron phosphate (LIFP) is an important active material for the positive electrode of batteries, and its performance directly affects battery performance. Elemental iron is a common impurity in LFP, which can affect battery performance and increase battery risks. Summary of the Invention

[0004] In view of the technical problems existing in the background technology, the present invention aims to provide a method for detecting the elemental iron content in lithium iron phosphate material.

[0005] In order to achieve the above objectives, the first aspect of the present application provides a method for detecting the elemental iron content in a lithium iron phosphate material, comprising:

[0006] Separation of magnetic foreign matter from lithium iron phosphate materials;

[0007] placing a magnetic foreign body in a copper salt solution to react and obtain a first solid body, the first solid body including copper elements;

[0008] The content of copper in the first solid is measured, and the content of elemental iron in the lithium iron phosphate material is obtained by converting the mass of copper and iron.

[0009] The embodiments of the present application differentially process elemental iron and other iron-containing foreign matter in magnetic foreign matter, and obtain the elemental iron content in the lithium iron phosphate material based on the measurement results of the copper element content obtained by the replacement reaction. The obtained detection results reduce the interference of non-elemental iron foreign matter on the elemental iron content, which is conducive to improving the accuracy of the detection of elemental iron content in the lithium iron phosphate material.

[0010] In some embodiments, the step of placing the magnetic foreign body in a copper salt solution to react and obtain a first solid body comprises:

[0011] placing the magnetic foreign matter in a copper salt solution, treating it at a first temperature and for a first time, and reacting to obtain a first treatment system;

[0012] The first treatment system is subjected to solid-liquid separation to obtain a first solid matter.

[0013] In the embodiments of the present application, by regulating the process parameters of the replacement reaction, a replacement reaction is achieved between the iron element in the magnetic foreign matter and the copper salt. The measured copper content can be used to characterize the elemental iron content. In addition, by separating the first solid matter from the liquid system in the first treatment system, the embodiments of the present application reduce the interference of copper ions in the liquid system that do not participate in the replacement reaction on the measurement results of the copper content.

[0014] In some embodiments, the copper salt solution includes at least one of a copper sulfate solution, a copper nitrate solution, and a copper chloride solution; and / or the mass fraction of the copper salt solution includes 1% to 6%.

[0015] The embodiments of the present application achieve the replacement reaction between elemental iron and copper salt by providing a specific scheme of copper salt in the replacement reaction, and the content of elemental iron can be characterized by measuring the content of copper element.

[0016] In some embodiments, the first temperature ranges from 60° C. to 200° C.; and / or the first duration ranges from 20 min to 90 min.

[0017] The embodiments of the present application achieve a replacement reaction between elemental iron and copper salt by regulating the reaction conditions of the replacement reaction, and the content of elemental iron can be characterized by measuring the content of copper element.

[0018] In some embodiments, the step of performing solid-liquid separation on the first treatment system to obtain a first solid material includes:

[0019] The first treatment system is flushed and filtered at least once to obtain a first solid matter.

[0020] The embodiments of the present application reduce the copper ions that may remain on the surface of the first solid object through filtration and rinsing during the filtration process, thereby reducing the interference of the copper ions that may remain on the surface of the first solid object on the measurement results of the copper element content.

[0021] In some embodiments, the step of flushing the first treatment system at least once comprises:

[0022] The first treatment system is flushed at least once with a flushing liquid.

[0023] The flushing liquid includes a detergent, and the mass fraction of the detergent in the flushing liquid ranges from 0.1% to 0.5%.

[0024] In some embodiments, the mass fraction of the detergent in the rinse liquid can be 0.1%, 0.12%, 0.15%, 0.17%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.29%, 0.3%, 0.33%, 0.36%, 0.39%, 0.4%, 0.41%, 0.43%, 0.45%, 0.47%, 0.48%, 0.5%, or the like, or a range consisting of any two of the above values. For example, the mass fraction can be 0.1% to 0.18%, 0.15% to 0.24%, 0.22% to 0.33%, 0.3% to 0.39%, 0.36% to 0.43%, 0.4% to 0.45%, 0.43% to 0.48%, 0.47% to 0.5%, etc.

[0025] The embodiment of the present application uses a flushing liquid to flush the first treatment system at least once, which is beneficial to reducing the metal ions that may remain on the surface of the first solid object and reducing the interference of the copper ions that may remain on the surface of the first solid object on the measurement results of the copper element content.

[0026] In some embodiments, the detergent comprises one or more of disodium edetate, sodium glutamate diacetate, caprylhydroxamic acid, and sodium hexametaphosphate.

[0027] The embodiments of the present application can have a better flushing effect by providing a specific flushing agent, which is beneficial to reducing the copper ions that may remain on the surface of the first solid object and reducing the interference of the copper ions that may remain on the surface of the first solid object on the measurement results of the copper element content.

[0028] In some embodiments, the step of determining the copper content in the first solid object includes:

[0029] Transferring the first solid matter into a digestion solution, treating the solid matter at a second temperature for a second time, and reacting to obtain a second treatment system;

[0030] performing solid-liquid separation on the second treatment system to obtain a second liquid;

[0031] The concentration of the copper element in the second liquid is measured, and the mass of the copper element in the first solid is obtained according to the concentration of the copper element in the second liquid.

[0032] The embodiments of the present application utilize a digestion reaction between elemental copper and a digestion solution to convert the copper element in the first solid object into copper ions. By measuring the content of the copper ions, the content of the elemental copper obtained by elemental iron replacement is obtained, and the content of elemental iron in the magnetic foreign matter is further converted based on the mass of copper and iron. This method easily allows the content of copper ions to be accurately determined, which is conducive to the determination of the content of copper in the first solid object with high accuracy.

[0033] In some embodiments, the digestion solution includes at least one of nitric acid solution, sulfuric acid solution, hydrogen peroxide, and aqua regia.

[0034] In the embodiment of the present application, the digestion solution provided undergoes a digestion reaction with the copper element in the first solid object, so that the copper element in the first solid object is converted into copper ions, which facilitates simplifying the process of measuring the copper element content in the first solid object and improves the accuracy of the measurement result of the copper element content in the first solid object.

[0035] In some embodiments, the second temperature ranges from 150° C. to 200° C.; and / or the second duration ranges from 20 min to 60 min.

[0036] The embodiments of the present application achieve a digestion reaction between the copper element in the first solid object and the digestion solution by regulating the reaction conditions of the digestion reaction, so that the copper element in the first solid object is converted into copper ions, which facilitates the simplification of the measurement process of the copper element content in the first solid object and improves the accuracy of the measurement result of the copper element content in the first solid object.

[0037] In some embodiments, the step of separating magnetic foreign matter from the lithium iron phosphate material includes:

[0038] Use magnetic materials to absorb magnetic foreign matter from lithium iron phosphate materials.

[0039] In the embodiment of the present application, magnetic foreign matter in the lithium iron phosphate material is adsorbed by a magnetic substance, thereby achieving separation of the lithium iron phosphate material from the magnetic foreign matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0041] Figure 1 It is a flow chart of a method for detecting the elemental iron content in lithium iron phosphate material provided in an embodiment of the present application. DETAILED DESCRIPTION

[0042] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0043] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0044] In the description herein, unless otherwise indicated, the term "or" is inclusive. That is, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0045] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” include the number itself, and “several” in “one or several” means two or more.

[0046] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0047] Lithium iron phosphate material is a positive electrode active material for lithium-ion batteries. Its crystal has an olivine structure and its chemical formula is LiFePO4. Its foreign name is Ferrous lithium phosphate, abbreviated as LFP.

[0048] During the sintering process to form lithium iron phosphate material, due to factors such as the imbalance of the lithium-iron-phosphorus ratio, the reducing atmosphere, and the excessively high sintering temperature, part of the lithium iron phosphate is over-reduced to iron phosphide and iron elemental phase when the lithium iron phosphate crystallizes.

[0049] Elemental iron is prone to self-discharge in the early stages of the battery cycle, causing the battery voltage drop to drop too quickly per unit time (i.e., a poor K value phenomenon), resulting in a large capacity loss. Elemental iron is easily dissolved into iron ions under high pressure. After passing through the diaphragm, the iron ions are reduced at the negative electrode to form deposited iron with sharp edges. When the deposited iron accumulates to a certain extent, its sharp edges can easily pierce the diaphragm, causing a micro-short circuit between the positive and negative electrodes.

[0050] Iron phosphide can increase the conductivity of lithium iron phosphate to a certain extent, that is, the iron phosphide content can be used normally within a certain range, but too high a content will affect the capacity. Therefore, the elemental iron and iron phosphide in the lithium iron phosphate material need to be treated differently.

[0051] Therefore, detecting the elemental iron content in lithium iron phosphate materials is of great significance for monitoring the quality of lithium iron phosphate materials and reducing the battery risks of lithium iron phosphate-type lithium-ion batteries (such as poor K value, cycle attenuation deterioration, etc.).

[0052] The technical solution described in the embodiment of this application is applicable to the method for detecting the elemental iron content in lithium iron phosphate materials. The method disclosed in this application can be used for single lithium-ion batteries and lithium-ion battery components, and this application does not limit it.

[0053] See also Figure 1 , Figure 1 It is a flow chart of a method for detecting the elemental iron content in lithium iron phosphate material provided in an embodiment of the present application.

[0054] To achieve the above purpose, see Figure 1 The first aspect of the present application provides a method for detecting the elemental iron content in a lithium iron phosphate material, comprising:

[0055] S1, separating magnetic foreign matter from lithium iron phosphate material.

[0056] Because the positive electrode material contains a large amount of lithium iron phosphate, which also contains a large amount of iron, without this step, the test sample would be larger, requiring more testing resources and easily adversely affecting the accuracy of the test results. Through the magnetic screening method of this step, most of the lithium iron phosphate material is separated from the detection system, and only the separated magnetic foreign matter is detected, which helps to reduce the detection resources used in the detection process, improve detection efficiency, and enhance the accuracy of the test results.

[0057] The magnetic foreign matter separated in this step may include elemental iron or iron phosphide. It's also possible that, due to the weak magnetic properties of the lithium iron phosphate material, some of the lithium iron phosphate material may be magnetized and incorporated into the magnetic foreign matter. If the iron content of the magnetic foreign matter in this step is directly used as the elemental iron content of the lithium iron phosphate material, interference from the iron phosphide and / or iron in the lithium iron phosphate material can easily lead to significant deviations in the elemental iron content detection. Specifically, this can easily result in an overly high elemental iron content.

[0058] S2, placing the magnetic foreign body in a copper salt solution to react to obtain a first solid body, wherein the first solid body includes copper element.

[0059] The purpose of setting up this step is to utilize the fact that elemental iron can undergo a replacement reaction with the copper salt solution, while compounded iron (such as iron phosphide and / or lithium iron phosphate material) does not undergo a replacement reaction with the copper salt solution, so as to achieve differentiated treatment of elemental iron and other foreign matter in magnetic foreign matter. This can easily reduce the interference of non-elemental iron impurities in magnetic foreign matter on the detection results of elemental iron content, and improve the accuracy of the detection results of elemental iron content in lithium iron phosphate material.

[0060] During the reaction, elemental iron and copper salt undergo a replacement reaction, the elemental iron in the magnetic foreign matter is converted into iron ions, and the copper ions in the copper salt are converted into elemental copper. The chemical equation for the replacement reaction between elemental iron and copper salt is:

[0061] Fe+Cu 2+ =Fe 2+ +Cu.

[0062] During the reaction, the amount of elemental iron in the reaction system gradually decreases until it disappears, while the amount of elemental copper in the reaction system gradually increases and stops increasing after reaching a certain amount.

[0063] The first treatment system obtained in this step may be a solid-liquid mixture. In some embodiments, the first treatment system may include elemental copper, iron compounds (such as iron phosphide and / or lithium iron phosphate materials), iron ions, and unreacted copper ions.

[0064] In some embodiments, before placing the magnetic foreign matter in the copper salt solution, the magnetic foreign matter may be rinsed at least once, which is beneficial for reducing impurities in the system.

[0065] S3, measuring the content of copper element in the first solid to obtain the content of elemental iron in the lithium iron phosphate material.

[0066] Among them, since the copper element appearing in the first solid object is replaced by elemental iron, the content of elemental iron in the first solid object can be indirectly known based on the content of the copper element appearing in the first solid object. This method can reduce the interference of non-elemental iron magnetic foreign matter (such as iron phosphide and / or lithium iron phosphate material) on the elemental iron content detection results, which is beneficial to reduce the deviation of the elemental iron content detection in the lithium iron phosphate material and improve the accuracy of the elemental iron content detection results in the lithium iron phosphate material.

[0067] The content of copper in the first solid object can be measured by methods and instruments known in the art.

[0068] For example, the copper content in the first solid object can be detected by an X-ray fluorescence spectrometer (XRF). The detection principle is: based on the nature of the interaction between X-rays and matter, the fluorescence emitted by the substance to be tested is analyzed to obtain the composition information of the substance to be tested. The detection process can include the following steps: preparing the first solid object into a sample to be tested, detecting the sample to be tested by an X-ray fluorescence spectrometer (XRF), and obtaining the copper content in the sample to be tested. There are many ways to prepare the first solid object into a sample to be tested. For example, the sample to be tested can be placed in a sample cup, the cup mouth is covered with a PVC (polyvinyl chloride) film, and the diameter of the sample cup is less than 10nm; or the first solid object can be mixed with a binder powder and then pressed to form a pellet as the sample to be tested; or the first solid object can be mixed with a flux and transferred to a crucible, heated to melt the sample, and then cooled and pressed to form a pellet, which is used as the sample to be tested.

[0069] For example, the content of copper in the first solid object can be detected by laser induced breakdown spectrometry (LIBS). The detection principle is: the laser is focused on the surface of the sample to be tested through a lens. When the energy density of the laser pulse is greater than the breakdown threshold energy, plasma will be generated locally, which is called laser induced plasma. Since the local energy density and temperature of this plasma are quite high, it can be used for sampling, atomization, excitation and ionization. The emission line signal generated by the plasma on the sample surface is directly collected by a spectrometer, and quantitative analysis is performed based on the intensity of the emission spectrum. The detection process may include the following steps: paraffin powder is used as a binder to mix with the first solid object and then compressed to prepare a tablet sample, the tablet sample to be tested is detected by laser induced breakdown spectrometry (LIBS), the emission line signal generated by the plasma on the surface of the tablet sample is collected, and the content of copper in the first solid object is obtained based on the element characteristic peak intensity of the emission spectrum.

[0070] For example, the copper content in a first solid object can be detected using a laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). The detection principle is to combine laser ablation technology with inductively coupled plasma mass spectrometry technology, using laser ablation technology to remove molecules from the surface of the sample to be tested, and then using inductively coupled plasma to ionize and analyze them. The detection process can include the following steps: preparing the first solid object into a sample to be tested, and detecting the sample to be tested using a laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) to obtain the copper content in the sample to be tested. There are various ways to prepare the first solid object into a sample to be tested. For example, the first solid object can be mixed with a binder powder and then pressed to form a pellet as the sample to be tested; or the first solid object can be mixed with a flux and then transferred to a crucible, heated to melt the sample, then cooled and pressed to form a pellet, and the pellet can be used as the sample to be tested; or the first solid object can be transferred to a crucible, heated to melt the sample, then cooled and pressed to form a pellet, and the pellet can be used as the sample to be tested.

[0071] The embodiments of the present application differentially process elemental iron and other iron-containing foreign matter in magnetic foreign matter, and obtain the elemental iron content in the lithium iron phosphate material based on the measurement results of the copper element content obtained by the replacement reaction. The obtained detection results reduce the interference of non-elemental iron foreign matter on the elemental iron content, which is conducive to improving the accuracy of the detection of elemental iron content in the lithium iron phosphate material.

[0072] In some embodiments, the step S2 of placing the magnetic foreign body in a copper salt solution to react and obtain a first solid body comprises:

[0073] S21, placing the magnetic foreign matter in a copper salt solution, treating it at a first temperature for a first time, and reacting to obtain a first treatment system.

[0074] The purpose of this step is to achieve a replacement reaction between the iron element in the magnetic foreign matter and the copper salt. The replacement reaction is smoothly carried out by regulating the reaction temperature and treatment time.

[0075] Among them, copper ions that did not participate in the replacement reaction may remain in the liquid phase system of the first treatment system. If these copper ions remain on the first solid matter, it is easy to cause the measurement result of the copper element content in step S3 to be too high, and then it is easy to cause the result of the elemental iron content in the lithium iron phosphate material to be too high.

[0076] S22, performing solid-liquid separation on the first treatment system to obtain a first solid.

[0077] In this step, the copper ions in the liquid system of the first treatment system are removed from the detection system by solid-liquid separation, thereby reducing the interference of these copper ions on the determination result of the elemental copper content in step S3.

[0078] The first solid separated in this step may include elemental copper and / or iron compounds (such as iron phosphide and / or lithium iron phosphate materials).

[0079] In the embodiments of the present application, by regulating the process parameters of the replacement reaction, the iron in the magnetic foreign matter undergoes a replacement reaction with the copper salt, and the measured copper content can be used to characterize the elemental iron content. In addition, in the embodiments of the present application, by separating the first solid matter from the liquid system in the first treatment system, the interference of copper ions in the liquid system that do not participate in the replacement reaction on the measurement result of the copper content in step S3 is reduced.

[0080] In some embodiments, in step S2 and / or step S21, the copper salt solution includes at least one of a copper sulfate [CuSO4] solution, a copper nitrate [Cu(NO3)2] solution, and a copper chloride [CuCl2] solution. In some embodiments, the solute of the copper salt solution is water.

[0081] In some embodiments, in step S2 and / or step S21, the mass fraction of the copper salt solution includes 1% to 6%. In some embodiments, the mass fraction of the copper salt solution can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.7%, 3.9%, 4%, 4.1%, 4.4%, 4.6%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, or the like, or a range consisting of any two of the above values. For example, it can be 1% to 2%, 1.5% to 2.5%, 2% to 3%, 2.5% to 3.7%, 3% to 4%, 3.4% to 4.4%, 4% to 5%, 4.4% to 5.5%, 5% to 6%, or the like.

[0082] The embodiments of the present application achieve the replacement reaction of elemental iron with copper salt by providing a specific scheme of copper salt in the replacement reaction of step S2 and / or step S21, and the content of elemental iron can be characterized by measuring the content of copper element.

[0083] In some embodiments, the value range of the first temperature in step S21 includes 60° C. to 200° C. In some embodiments, the value of the first temperature can be 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., 90° C., 95° C., 100° C., 105° C., 110° C., 115° C., 120° C., 125° C., 130° C., 135° C., 140° C., 145° C., 150° C., 155° C., 160° C., 165° C., 170° C., 172° C., 174° C., 175° C., 178° C., 180° C., 182° C., 184° C., 185° C., 187° C., 188° C., 190° C., 195° C., 200° C., etc., or a range consisting of any two of the above values. For example, the temperature may be 100°C to 120°C, 115°C to 150°C, 145°C to 170°C, 165°C to 188°C, 175°C to 190°C, 187°C to 195°C, 185°C to 200°C, etc.

[0084] In some embodiments, the first duration in step S21 ranges from 20 minutes to 90 minutes. In some embodiments, the first duration can be 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, 90 minutes, or a range consisting of any two of the above values. For example, the first duration can be 20 minutes to 40 minutes, 30 minutes to 50 minutes, 40 minutes to 60 minutes, 50 minutes to 70 minutes, 60 minutes to 80 minutes, 70 minutes to 90 minutes, or the like.

[0085] In the embodiment of the present application, the replacement reaction between elemental iron and copper salt is achieved by regulating the reaction conditions of the replacement reaction in step S21, and the content of elemental iron can be characterized by measuring the content of copper element.

[0086] In some embodiments, step S22 of performing solid-liquid separation on the first treatment system to obtain a first solid material includes:

[0087] S221, flushing and filtering the first treatment system at least once to obtain a first solid matter.

[0088] Flushing refers to the process of washing the filtrate. Filtration is the process of using a vacuum pump to reduce the pressure in the filtration bottle to achieve the effect of solid-liquid separation.

[0089] In this step, the first treatment system is flushed at least once so that the copper ions that may remain in the first treatment system are flushed into the filtered liquid phase system and separated from the detection system, thereby reducing the interference of the copper ions in the liquid system that do not participate in the replacement reaction on the determination result of the copper element content in step S3.

[0090] It is understandable that the flushing process in S221 may further include the steps of flushing the container carrying the filtrate and filtering the flushing liquid together with the filtrate.

[0091] The embodiment of the present application reduces the copper ions that may remain on the surface of the first solid object by filtration and rinsing during the filtration process, thereby reducing the interference of the copper ions that may remain on the surface of the first solid object on the measurement result of the copper element content in step S3.

[0092] In some embodiments, in S221, the step of flushing the first treatment system at least once includes:

[0093] S2211, flushing the first treatment system at least once with a flushing liquid.

[0094] The flushing liquid includes a detergent, and the mass fraction of the detergent in the flushing liquid ranges from 0.1% to 0.5%.

[0095] The term "rinsing liquid" refers to the liquid phase used to rinse the filtrate. In some embodiments, the rinsing liquid comprises water, which improves the fluidity of the rinsing liquid. The detergent refers to the active ingredient in the rinsing liquid, which is used to improve the rinsing effect.

[0096] In some embodiments, the mass fraction of the detergent in the rinse liquid can be 0.1%, 0.12%, 0.15%, 0.17%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.29%, 0.3%, 0.33%, 0.36%, 0.39%, 0.4%, 0.41%, 0.43%, 0.45%, 0.47%, 0.48%, 0.5%, or the like, or a range consisting of any two of the above values. For example, the mass fraction can be 0.1% to 0.18%, 0.15% to 0.24%, 0.22% to 0.33%, 0.3% to 0.39%, 0.36% to 0.43%, 0.4% to 0.45%, 0.43% to 0.48%, 0.47% to 0.5%, etc.

[0097] The embodiment of the present application uses a flushing liquid to flush the first treatment system at least once, which is beneficial to reducing the metal ions that may remain on the surface of the first solid object and reducing the interference of the copper ions that may remain on the surface of the first solid object on the measurement result of the copper element content in step S3.

[0098] In some embodiments, the detergent includes disodium ethylenediaminetetraacetate (EDTA-2Na, chemical formula C 10 H 14N2Na2O8, molecular weight 336.206), glutamic acid diacetic acid sodium salt (GLDA.Na4, molecular formula C9H9NO8Na4, molecular weight 351.1), octanoylhydroxamic acid (chemical formula C8H 17 NO2, molecular weight 159.23), sodium hexametaphosphate (chemical formula (NaPO3)6, molecular weight 611.77) or more.

[0099] The embodiments of the present application can have a better flushing effect by providing a specific flushing agent, which is beneficial to reducing the copper ions that may remain on the surface of the first solid object and reducing the interference of the copper ions that may remain on the surface of the first solid object on the measurement results of the copper element content in step S3.

[0100] In some embodiments, in S3, the step of determining the copper content in the first solid object includes:

[0101] S31, transferring the first solid matter into a digestion solution, treating the solid matter at a second temperature for a second time, and reacting to obtain a second treatment system.

[0102] The digestion solution refers to a liquid with strong oxidizing properties. The purpose of this step is to utilize the elemental copper in the first solid object to undergo a digestion reaction with the digestion solution, so that the elemental copper is converted into copper ions to obtain a copper salt solution, thereby simplifying the determination process of the copper content in the first solid object and improving the accuracy of the determination result of the copper content in the first solid object.

[0103] S32, performing solid-liquid separation on the second treatment system to obtain a second liquid product.

[0104] Among them, there may be solid impurities such as undigested magnetic foreign matter in the second treatment system. By performing solid-liquid separation on the second treatment system to obtain the second liquid, it is beneficial to reduce the adverse effect of solid impurities on the copper element determination result in the second liquid.

[0105] S33, measuring the concentration of the copper element in the second liquid, and obtaining the mass of the copper element in the first solid according to the concentration of the copper element in the second liquid.

[0106] In some embodiments, in S33, the step of obtaining the mass of the copper element in the first solid according to the concentration of the copper element in the second liquid may be:

[0107] S331, measuring the volume of the second liquid.

[0108] S332: Obtain a molar amount of the copper element in the second liquid according to the product of the concentration of the copper element in the second liquid and the volume of the second liquid.

[0109] S333, obtaining the mass of the copper element in the first solid object according to the product of the molar amount of the copper element in the second liquid object and the relative atomic mass of elemental copper.

[0110] In the embodiments of the present application, a digestion reaction is performed between elemental copper and a digestion solution, converting the copper element in the first solid object into copper ions. By measuring the copper ion content, the content of elemental copper obtained by elemental iron replacement is obtained to obtain the elemental iron content in the magnetic foreign matter. This method easily allows the copper ion content to be accurately measured, which is beneficial for achieving a high degree of accuracy in the determination of the copper content in the first solid object.

[0111] In some embodiments, the digestion solution includes at least one of nitric acid (HNO 3 ) solution, sulfuric acid (H 2 SO 4 ) solution, hydrogen peroxide (H 2 O 2 ), and aqua regia.

[0112] In some embodiments, the nitric acid (HNO 3 ) solution includes a concentrated nitric acid solution. In some embodiments, the mass fraction of the concentrated nitric acid solution is greater than or equal to 65%.

[0113] In some embodiments, the sulfuric acid (H2SO4) solution includes a concentrated sulfuric acid solution. In some embodiments, the mass fraction of the concentrated sulfuric acid solution is greater than or equal to 70%.

[0114] In some embodiments, the mass fraction of hydrogen peroxide is greater than or equal to 10%.

[0115] Aqua regia, also known as royal acid or nitrohydrochloric acid, is a highly corrosive liquid that produces a yellow mist. It is a mixture of concentrated hydrochloric acid (HCl) and concentrated nitric acid (HNO3) in a 3:1 volume ratio. In some embodiments, the mass fraction of concentrated hydrochloric acid is greater than or equal to 20%, and in some embodiments, the mass fraction of concentrated nitric acid is greater than or equal to 65%.

[0116] In the embodiment of the present application, the digestion solution provided undergoes a digestion reaction with the copper element in the first solid object, so that the copper element in the first solid object is converted into copper ions, which facilitates simplifying the process of measuring the copper element content in the first solid object and improves the accuracy of the measurement result of the copper element content in the first solid object.

[0117] In some embodiments, the second temperature in S31 ranges from 150°C to 200°C. In some embodiments, the second temperature can be 150°C, 155°C, 160°C, 165°C, 170°C, 172°C, 174°C, 175°C, 178°C, 180°C, 182°C, 184°C, 185°C, 187°C, 188°C, 190°C, 195°C, 200°C, or a range consisting of any two of the above values. For example, the second temperature can be 150°C to 170°C, 165°C to 188°C, 175°C to 190°C, 187°C to 195°C, 185°C to 200°C, or the like.

[0118] In some embodiments, the second duration in S31 ranges from 20 minutes to 60 minutes. In some embodiments, the second duration can be 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, or a range consisting of any two of the above values. For example, the second duration can be 20 minutes to 30 minutes, 25 minutes to 35 minutes, 30 minutes to 40 minutes, 35 minutes to 45 minutes, 40 minutes to 50 minutes, 45 minutes to 55 minutes, 50 minutes to 60 minutes, or the like.

[0119] In the embodiment of the present application, by regulating the reaction conditions of the digestion reaction in step S31, the copper element in the first solid object undergoes a digestion reaction with the digestion solution, so that the copper element in the first solid object is converted into copper ions, thereby simplifying the process of measuring the copper element content in the first solid object and improving the accuracy of the measurement result of the copper element content in the first solid object.

[0120] In some embodiments, in S1, the step of separating magnetic foreign matter from the lithium iron phosphate material includes:

[0121] Use magnetic materials to absorb magnetic foreign matter from lithium iron phosphate materials.

[0122] In some embodiments, the magnetic material is a magnetic rod. In some embodiments, the magnetic flux density of the magnetic rod may range from 6000 GS to 10000 GS, where GS refers to Gauss, a unit of magnetic flux density. In some embodiments, the magnetic flux density of the magnetic rod may be 6000 GS, 6200 GS, 6400 GS, 6500 GS, 6700 GS, 6800 GS, 7000 GS, 7200 GS, 7500 GS, 7800 GS, 8000 GS, 8300 GS, 8500 GS, 8700 GS, 8900 GS, 9000 GS, 9100 GS, 9300 GS, 9500 GS, 9600 GS, 9800 GS, 10000 GS, or a range consisting of any two of the foregoing values. For example, it may be 6000GS to 7000GS, 6500GS to 7500GS, 7000GS to 8000GS, 7500GS to 8500GS, 8000GS to 9000GS, 8500GS to 9500GS, 9000GS to 10000GS, etc.

[0123] It should be noted that the magnetic material can also be a magnetic filter or an electromagnetic filter.

[0124] In some embodiments, a magnetic rod can be used to directly absorb magnetic foreign matter in the lithium iron phosphate material. In some embodiments, the lithium iron phosphate material can be first dispersed in a liquid phase system to form a slurry, and then the magnetic rod can be used to absorb the magnetic material in the slurry. In some embodiments, the liquid phase system can include water and other solvents, such as anhydrous ethanol.

[0125] In the embodiment of the present application, magnetic foreign matter in the lithium iron phosphate material is adsorbed by a magnetic substance, thereby achieving separation of the lithium iron phosphate material from the magnetic foreign matter.

[0126] In some embodiments, the process of detecting the copper content in the second treatment system may be:

[0127] The second treatment system is filtered, and the filtered system is transferred to a first volumetric flask, and the volume is adjusted to the first volume by rinsing to obtain a first fixed volume system; a certain amount of stock solution is drawn from the first fixed volume system, and transferred to a second volumetric flask, and the volume is diluted to the second volume to obtain a second fixed volume system.

[0128] The concentration of copper ions in the second constant volume system was detected by electron coupled optical emission spectrometry (ICP-OES). The dilution factor and constant volume were input, and the detection result of the mass of the elemental copper element was recorded. The mass of the elemental iron was calculated based on the mass ratio of copper to iron.

[0129] The mass ratio of elemental iron to the lithium iron phosphate material in S1 in the above step is the elemental iron content in the lithium iron phosphate material.

[0130] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0131] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0132] The examples of the present application use a spiked experiment to verify the accuracy of the method for detecting the elemental iron content in the lithium iron phosphate material provided in the present application.

[0133] Example 1

[0134] Preparation of elemental iron content in lithium iron phosphate material:

[0135] (1) Accurately weigh 20.8 mg of elemental iron and 50 mg of iron phosphide, respectively, and add 20.8 mg of elemental iron and 50 mg of iron phosphide to 1 kg of pure lithium iron phosphate material to obtain a mixture, which is dispersed in a liquid phase system to form a slurry.

[0136] (2) Use a magnetic rod with a magnetic induction intensity of 8000GS to absorb magnetic foreign matter in the slurry.

[0137] (3) The adsorbed magnetic foreign matter is transferred to a beaker containing 50 mL of a 2% copper sulfate solution, and treated at a first temperature of 180° C. for a first time of 60 min to obtain a first treatment system. Here, 1 g of copper sulfate is dissolved in 49 mL of water, and the mass fraction of copper sulfate in the resulting copper sulfate solution is 2%. Therefore, the mass of copper sulfate in the 50 mL of the 2% copper sulfate solution in this step is slightly greater than 1 g, and the molar amount of copper sulfate is slightly greater than 6.25 mmol.

[0138] (4) The first treatment system is subjected to a first filtration, and the solid matter obtained by solid-liquid separation is retained on the filter membrane of the filtration device, and the solid matter retained on the filter membrane is the first filtrate; the first filtrate is rinsed for the first time with an EDTA-2Na solution with a mass fraction of 0.1%, and the solid matter obtained is the first solid matter.

[0139] (5) Directly measuring the copper content of the first solid obtained in step (4). The specific testing process is as follows: placing the first solid in a sample cup, covering the cup mouth with a PVC (polyvinyl chloride) film, the diameter of the sample cup is less than 10 nm, forming a sample to be tested, and detecting the sample to be tested by an X-ray fluorescence spectrometer (XRF) to obtain the copper content in the sample to be tested.

[0140] (6) The copper content of the first solid obtained by measuring the step (5) is used to obtain the molar amount of the copper element of the first solid, and the molar ratio of copper to iron in the replacement reaction is 1:1, and the corresponding molar amount of iron is obtained. According to the calculated molar amount of iron and the relative atomic mass, the detected mass of elemental iron is obtained, and the percentage of the ratio of the detected mass of elemental iron to the added mass of elemental iron in step (1) is used as the detection rate of elemental iron. The deviation value between the detection rate and the theoretical detection rate is used to characterize the detection accuracy of the method for detecting the content of elemental iron in the lithium iron phosphate material of the present application. The smaller the deviation value, the higher the accuracy of the method for detecting the content of elemental iron in the lithium iron phosphate material of the present application, and the larger the deviation value, the lower the accuracy of the method for detecting the content of elemental iron in the lithium iron phosphate material of the present application.

[0141] Example 2 is similar to Example 1, except that the mass of elemental iron weighed in step (1) is 20.7 mg; after step (4), the first solid obtained in step (4) is transferred to a beaker containing 10 mL of concentrated nitric acid with a mass fraction of 68%, and treated at 180° C. for 30 min to obtain a second treatment system.

[0142] Transfer the second treatment system to a 100 ml first volumetric flask through a funnel filter, rinse the beaker three times, and dilute to 100 ml; use a pipette to draw 1 ml of the stock solution, dilute and dilute to a 50 ml second volumetric flask.

[0143] The concentration of copper element was tested by ICP-OES (inductively coupled plasma optical emission spectrometer), and the dilution multiple and constant volume were input to obtain the mass of elemental copper. The molar amount of elemental copper was obtained based on the mass of elemental copper. The molar ratio of copper to iron in the displacement reaction was 1:1, and the corresponding molar amount of iron was obtained. The detected mass of elemental iron was obtained based on the calculated molar amount of iron and the relative atomic mass. The percentage of the ratio of the detected mass of elemental iron to the added mass of elemental iron in step (1) was used as the detection rate of elemental iron.

[0144] Example 3 is similar to Example 2, except that: the mass of elemental iron weighed in step (1) is 21.2 mg; and in step (4), after the first filtration, the inner wall of the beaker is rinsed with a 0.1% EDTA-2Na solution, and the resulting dispersion is also poured on the first filtrate, and the first filtration is rinsed together.

[0145] Example 4 is similar to Example 2, except that the mass of elemental iron weighed in step (1) is 19.5 mg; and step (4) further includes a second rinsing and filtration of the solid matter obtained from the first filtration and washing. The solid matter obtained by solid-liquid separation is retained on the filter membrane of the filtration device, and the solid matter retained on the filter membrane is the second filtrate. The rinsing liquid used in the second rinsing is still a 0.1% by mass EDTA-2Na solution.

[0146] Examples 5 to 13 are similar to Example 4, except that the mass of elemental iron weighed in step (1) is slightly different from that in Example 4; and at least one of the first temperature and the first duration in step (3) is different from that in Example 4.

[0147] Table 1: Test results of elemental iron content of Examples 1 to 13

[0148]

[0149] Note: The theoretical detection rate is 100%.

[0150] The results show that the deviation between the detection rate of the elemental iron content in the lithium iron phosphate material obtained in Examples 1 to 13 and the theoretical detection rate is in the range of -8% to +10.1%, indicating that the method for detecting the elemental iron content in the lithium iron phosphate material provided in this application has good application prospects and is expected to provide reliable elemental iron content monitoring in the field of lithium iron phosphate lithium-ion batteries.

[0151] From Examples 1 to 2, it can be seen that the detection rate of the elemental iron content in the lithium iron phosphate material in Example 2 deviates greatly from the theoretical detection rate. This may be because there are more copper ions (from the copper sulfate solution) that do not participate in the replacement reaction remaining in the liquid phase system of the first treatment system in Example 2, resulting in a large deviation in the measurement results.

[0152] From Examples 2 to 4, it can be seen that increasing the number of flushing and filtration during the detection process is beneficial to reducing the copper ions that may remain on the surface of the first solid object and reducing the detection deviation of the elemental iron content.

[0153] From Examples 4 to 13, it can be seen that the deviation between the detection rate of the elemental iron content in the lithium iron phosphate material of each example and the theoretical detection rate fluctuates within a small range, indicating that the first temperature and the first duration have a certain influence on the detection result. Therefore, the detection effect can be regulated by adjusting the first temperature and / or the first duration.

[0154] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for detecting the elemental iron content in lithium iron phosphate material, characterized in that: include: Separation of magnetic foreign matter from lithium iron phosphate materials; placing the magnetic foreign body in a copper salt solution to react and obtain a first solid body, wherein the first solid body includes copper element; The content of the copper element in the first solid object is measured to obtain the content of elemental iron in the lithium iron phosphate material.

2. The method for detecting the elemental iron content in the lithium iron phosphate material according to claim 1, characterized in that: The step of placing the magnetic foreign body in a copper salt solution to react and obtain a first solid body comprises: placing the magnetic foreign matter in a copper salt solution, treating it at a first temperature and for a first time, and reacting to obtain a first treatment system; The first treatment system is subjected to solid-liquid separation to obtain a first solid matter.

3. The method for detecting the elemental iron content in the lithium iron phosphate material according to claim 1 or 2, characterized in that: The copper salt solution includes at least one of copper sulfate solution, copper nitrate solution, and copper chloride solution; and / or the mass fraction of the copper salt solution includes 1% to 6%.

4. The method for detecting the elemental iron content in the lithium iron phosphate material according to claim 2 or 3, characterized in that: The first temperature ranges from 60° C. to 200° C.; and / or the first duration ranges from 20 min to 90 min.

5. The method for detecting the elemental iron content in the lithium iron phosphate material according to any one of claims 2 to 4, characterized in that: The step of performing solid-liquid separation on the first treatment system to obtain a first solid object includes: The first treatment system is rinsed and filtered at least once to obtain a first solid.

6. The method for detecting the elemental iron content in the lithium iron phosphate material according to claim 5, characterized in that: The step of flushing the first treatment system at least once comprises: flushing the first treatment system at least once with a flushing liquid; The flushing liquid includes a detergent, and the mass fraction of the detergent in the flushing liquid ranges from 0.1% to 0.5%.

7. The method for detecting the elemental iron content in the lithium iron phosphate material according to claim 6, characterized in that: The detergent comprises one or more of disodium ethylenediaminetetraacetate, sodium glutamate diacetate, caprylhydroxamic acid, and sodium hexametaphosphate.

8. The method for detecting the elemental iron content in the lithium iron phosphate material according to any one of claims 1 to 7, characterized in that: The step of determining the content of copper in the first solid object comprises: transferring the first solid matter into a digestion solution, treating the solid matter at a second temperature for a second time, and reacting to obtain a second treatment system; performing solid-liquid separation on the second treatment system to obtain a second liquid; The concentration of the copper element in the second liquid is measured, and the mass of the copper element in the first solid is obtained according to the concentration of the copper element in the second liquid.

9. The method for detecting the elemental iron content in the lithium iron phosphate material according to claim 8, characterized in that: The digestion solution includes at least one of nitric acid solution, sulfuric acid solution, hydrogen peroxide and aqua regia.

10. The method for detecting the elemental iron content in the lithium iron phosphate material according to claim 8 or 9, characterized in that: The second temperature ranges from 150° C. to 200° C.; and / or the second duration ranges from 20 min to 60 min.

11. The method for detecting the elemental iron content in the lithium iron phosphate material according to any one of claims 1 to 10, characterized in that: The step of separating magnetic foreign matter from the lithium iron phosphate material comprises: Magnetic foreign matter in the lithium iron phosphate material is adsorbed by a magnetic substance.

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