Method for detecting content of elemental iron in lithium iron phosphate

Abstract

The invention provides a method for detecting the content of elemental iron in lithium iron phosphate, which comprises the following steps: carrying out magnetic separation on lithium iron phosphate to obtain a magnetic material; reacting the magnetic material with an acid solution or a copper sulfate solution to form a solution containing ferrous iron; carrying out oxidation titration on the solution containing ferrous iron, and calculating the content of elemental iron in the lithium iron phosphate according to a titration result; wherein a titration reagent adopted by the oxidation titration comprises an oxidizing agent, and the oxidizing agent comprises cerium salt. According to the content detection method, the detection result is more accurate, detection instruments such as XRF and ICP do not need to be adopted, the detection cost is low, and the detection efficiency is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a method for detecting the content of elemental iron in lithium iron phosphate. BACKGROUND

[0002] In recent years, the application range of secondary batteries is more and more extensive, which is widely used in energy storage power supply systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] Lithium iron phosphate is a commonly used positive active material of secondary batteries, which has the advantages of stable structure, controllable cost and high safety. At present, the mainstream preparation route of lithium iron phosphate is solid phase sintering method. If the reducing atmosphere is too strong or the carbon source is excessive during the preparation process, the iron ions will be excessively reduced to elemental iron. In addition, if the raw material ratio is deviated or the sintering process parameters are not properly controlled, the probability of forming elemental iron will increase. Therefore, elemental iron almost inevitably exists in lithium iron phosphate. Elemental iron will be oxidized to free metal ions when the battery is charged, which will pass through the separator to the negative electrode and be finally reduced to metal particles to pierce the separator, causing internal short circuit. In order to ensure the safety and performance stability of the battery, it is necessary to accurately detect the content of elemental iron in lithium iron phosphate.

[0004] In the traditional content detection method, the displacement reaction of elemental iron and copper sulfate solution is used to detect the content of elemental iron in magnetic foreign matter. The copper ions in the solution are reduced to copper, and the elemental iron is oxidized to iron ions. Then the content of copper element in the solid state is detected by X-ray fluorescence spectrometer (XRF) or inductively coupled plasma spectrometry (ICP), and the elemental iron in the magnetic foreign matter is quantified. However, the accuracy of the detection results of this detection method needs to be further improved. In addition, this detection method relies on XRF, ICP and other detection instruments, the detection cost is high, and usually needs to be centralized for external detection, which consumes a lot of time and is not conducive to the improvement of production efficiency. SUMMARY

[0005] In view of the above problems, the present application provides a method for detecting the content of elemental iron in lithium iron phosphate, which is more accurate, and does not need to use XRF, ICP and other detection instruments, so the detection cost is low and the detection efficiency is high.

[0006] The first aspect of the present application provides a method for detecting the content of elemental iron in lithium iron phosphate, which comprises the following steps:

[0007] Magnetic separation is performed on the lithium iron phosphate to separate and obtain magnetic material;

[0008] The magnetic material is reacted with an acid solution or a copper sulfate solution to form a solution containing divalent iron;

[0009] The solution containing ferrous iron was subjected to oxidative titration, and the content of elemental iron in the lithium iron phosphate was calculated based on the titration results.

[0010] The titration reagent used in the oxidation titration includes an oxidizing agent, which includes cerium salts.

[0011] The aforementioned content detection method, after magnetic separation and reaction to form a solution containing ferrous iron in lithium iron phosphate, further titrates the solution using an oxidizing titration reagent including cerium salts. In this process: firstly, even if some elemental iron is oxidized to ferrous iron during pretreatment such as magnetic separation or material transfer and does not participate in the reaction with copper sulfate or acid, it will still be oxidized to ferric iron during the titration reaction with the oxidant, ensuring accurate detection results; secondly, research has found that using cerium salts as oxidants can selectively oxidize ferrous iron. Even if ferric phosphide reacts simultaneously or is not completely separated during the reaction with copper sulfate or acid, accurate quantification of elemental iron can still be achieved during the oxidative titration. In summary, the content detection method provided in this application can more accurately detect the elemental iron content in lithium iron phosphate. Furthermore, quantification can be achieved through commonly used laboratory titration steps, eliminating the need for XRF, ICP, and other detection instruments, reducing detection costs, saving detection time, and improving production efficiency.

[0012] In some embodiments, the cerium salt includes one or both of cerium sulfate and cerium ammonium nitrate.

[0013] In some embodiments, the concentration of the cerium salt in the titration reagent is 0.01 mol / L to 1 mol / L. Properly controlling the concentration of the cerium salt can improve the accuracy of the detection.

[0014] In some embodiments, the oxidative titration indicates the endpoint by a color change or potential change of an indicator; optionally, the indicator includes o-phenanthroline.

[0015] In some embodiments, in the step of forming the solution containing ferrous iron, the magnetic material is reacted with an acid solution;

[0016] Optionally, the acid in the acid solution is hydrochloric acid;

[0017] Optionally, the concentration of the acid solution is 0.05 mol / L to 0.5 mol / L;

[0018] Optionally, the ratio of the magnetic material to the acid solution is: 5 mL to 8 mL of the acid solution for every 5 mg of the magnetic material.

[0019] By converting magnetic materials into a solution containing ferrous iron using an acid solution, the time difference in the dissolution reaction of magnetic foreign matter such as elemental iron and ferric phosphide under a specific concentration of acid solution can be utilized to selectively separate elemental iron, reduce the influence of magnetic foreign matter such as ferric phosphide and iron(III) oxide on the detection results, and improve the accuracy of the detection.

[0020] In some embodiments, the conditions for reacting the magnetic material with the acid solution include one or both of the following:

[0021] (1) An ultrasonic-assisted reaction is used, and optionally, the power of the ultrasonic wave is 40W~250W;

[0022] (2) The reaction temperature is 20℃~70℃ and the reaction time is 1.5min~2.5min.

[0023] In some embodiments, in the step of forming the solution containing ferrous iron, the magnetic material is reacted with a copper sulfate solution;

[0024] Optionally, the concentration of the copper sulfate solution is 0.05 mol / L to 0.5 mol / L;

[0025] Optionally, the ratio of the magnetic material to the copper sulfate solution is: 5 mL to 8 mL of copper sulfate solution for every 5 mg of the magnetic material.

[0026] In some embodiments, the conditions for reacting the magnetic material with the copper sulfate solution include: a reaction temperature of 60°C to 200°C and a reaction time of 30 min to 100 min.

[0027] In some embodiments, the magnetic separation step includes: mixing the lithium iron phosphate, water and magnetic apparatus for adsorption treatment;

[0028] Optionally, the magnetic induction intensity of the magnetic device is 0.6T~1.2T per 1kg of the lithium iron phosphate.

[0029] In some embodiments, the adsorption process also includes a step of adding a dispersant;

[0030] Optionally, the dispersant includes one or more of polyethylene glycol trimethyl nonyl ether, X-3204 dispersant, and sodium lauroyl urate.

[0031] Details of one or more embodiments of this application are set forth in the following description. Other features, objects, and advantages of this application will become apparent from the specification and claims. Detailed Implementation

[0032] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0033] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be independently included or excluded, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this document; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, stating that a parameter is an integer ≥2 is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, stating that a parameter is an integer selected from "2~10" is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0034] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0036] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0037] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0038] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0039] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0040] Currently, the accuracy of methods for detecting elemental iron content in lithium iron phosphate needs further improvement. This is because during pretreatment (such as magnetic separation), some elemental iron is oxidized to ferrous ions (Fe2+). Since ferrous ions do not react with copper sulfate, the actual amount of elemental iron undergoing the displacement reaction is lower than expected. Directly detecting the copper obtained through this displacement reaction would lead to an underestimation of the actual value. Furthermore, to ensure accuracy, current detection methods rely on instruments such as XRF and ICP, resulting in high costs and often requiring centralized external testing, which is time-consuming and hinders production efficiency.

[0041] Meanwhile, due to factors such as fluctuations in iron source quality, abnormal phosphorus source composition, and uneven dispersion of lithium source, lithium iron phosphate also contains magnetic impurities such as iron phosphide. During the magnetic separation process, these impurities are mixed with elemental iron and are separated simultaneously. How to effectively separate elemental iron and iron phosphide is also one of the factors that determine the accuracy of elemental iron detection.

[0042] Based on this, some embodiments of this application provide a method for detecting the content of elemental iron in lithium iron phosphate, comprising the following steps:

[0043] Lithium iron phosphate is subjected to magnetic separation to obtain magnetic materials;

[0044] The magnetic material is reacted with an acid solution or a copper sulfate solution to form a solution containing ferrous iron.

[0045] The solution containing ferrous iron was subjected to oxidative titration, and the content of elemental iron in the lithium iron phosphate was calculated based on the titration results.

[0046] The titration reagent used in the oxidation titration includes an oxidizing agent, which includes cerium salts.

[0047] The aforementioned content detection method, after magnetic separation and reaction to form a solution containing ferrous iron in lithium iron phosphate, further titrates the solution using an oxidizing titration reagent including cerium salts. In this process: firstly, even if some elemental iron is oxidized to ferrous iron during pretreatment such as magnetic separation or material transfer and does not participate in the reaction with copper sulfate or acid, it will still be oxidized to ferric iron during the titration reaction with the oxidant, ensuring accurate detection results; secondly, research has found that using cerium salts as oxidants can selectively oxidize ferrous iron. Even if ferric phosphide reacts simultaneously or is not completely separated during the reaction with copper sulfate or acid, accurate quantification of elemental iron can still be achieved during the oxidative titration. In summary, the content detection method provided in this application can more accurately detect the elemental iron content in lithium iron phosphate. Furthermore, quantification can be achieved through commonly used laboratory titration steps, eliminating the need for XRF, ICP, and other detection instruments, reducing detection costs, saving detection time, and improving production efficiency.

[0048] In addition, cerium salts are safer and more environmentally friendly than reagents such as potassium dichromate and potassium permanganate, which are commonly used in oxidation titrations.

[0049] Without restriction, the reaction equation for the oxidative titration process is as follows:

[0050] Ce 4+ +Fe 2+ →Ce 3+ +Fe 3+ .

[0051] Without limitation, the cerium salt includes one or both of cerium sulfate and cerium ammonium nitrate.

[0052] In some embodiments, the concentration of the cerium salt in the titration reagent is 0.01 mol / L to 0.01 mol / L. Appropriately controlling the concentration of the cerium salt can improve the accuracy of the detection. Specifically, the concentration of the cerium salt includes, but is not limited to: 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1 mol / L, or any range between the foregoing.

[0053] In some embodiments, 20 mL to 25 mL of the solution containing ferrous iron is used for oxidative titration. Appropriately controlling the volume of the titrated sample can improve the accuracy of the detection. Specifically, the volume of the solution containing ferrous iron includes, but is not limited to: 20 mL, 21 mL, 22 mL, 23 mL, 24 mL, 25 mL, or any range between the foregoing.

[0054] Without limitation, the endpoint of the oxidative titration is indicated by a color change or potential change of an indicator. Further, the indicator may include o-phenanthroline, and a sulfuric acid masking agent may be added to improve the accuracy of the indication. The concentration of the sulfuric acid masking agent is 0.1 mol / L to 0.5 mol / L. Specifically, the concentration of the sulfuric acid masking agent includes, but is not limited to: 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, or any range between the foregoing.

[0055] Without limitation, prior to the oxidative titration, the container holding the solution containing ferrous iron is rinsed with an aqueous solution of a metal ion complexing agent to ensure adequate transfer, followed by a final volume titration. Examples of the metal ion complexing agent include, for instance, an aqueous solution of EDTA-2Na. Further, the concentration of the aqueous solution of the metal ion complexing agent is 0.1% to 0.5%. Specifically, the concentration of the aqueous solution of the metal ion complexing agent includes, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any range between the foregoing.

[0056] In some embodiments, the magnetic material is reacted with an acid solution in the step of forming the solution containing ferrous iron. By converting the magnetic material into a solution containing ferrous iron using an acid solution, the time difference in the dissolution reaction of magnetic foreign matter such as elemental iron and ferric phosphide under a specific concentration of acid solution can be utilized to selectively separate elemental iron, reduce the influence of magnetic foreign matter such as ferric phosphide and magnetite on the detection results, and improve the accuracy of the detection.

[0057] Furthermore, the acid in the acid solution is hydrochloric acid.

[0058] Further, the concentration of the acid solution is 0.05 mol / L to 0.5 mol / L. Specifically, the concentration of the acid solution includes, but is not limited to: 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, or any range between the foregoing.

[0059] Further, the ratio of the magnetic material to the acid solution is: 5 mL to 8 mL of the acid solution for every 5 mg of the magnetic material. Specifically, the volume of the acid solution includes, but is not limited to, 5 mL, 5.5 mL, 6 mL, 6.5 mL, 7 mL, 7.5 mL, 8 mL, or any combination thereof.

[0060] Furthermore, an ultrasonic-assisted reaction is employed. Optionally, the power of the ultrasonic waves is 40W to 250W. Specifically, the power of the ultrasonic waves includes, but is not limited to: 40W, 45W, 50W, 55W, 60W, 65W, 70W, 75W, 80W, 85W, 90W, 100W, 110W, 130W, 150W, 170W, 200W, 230W, 250W, or any range between the foregoing.

[0061] Furthermore, the reaction temperature is 20℃~70℃, and the reaction time is 1.5min~2.5min. Specifically, the reaction temperature includes, but is not limited to: 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, or any two of the foregoing; the reaction time includes, but is not limited to: 1.5min, 2min, 2.5min, or any two of the foregoing.

[0062] Without limitation, the process of reacting the magnetic material with the acid solution is as follows:

[0063] 1. Elemental iron (Fe) (dissolution rate > 95%):

[0064] Fe + 2HCl → FeCl2 + H2↑.

[0065] Phenomenon: Bubbles are rapidly generated, and the solution turns light green (Fe). 2+ ).

[0066] 2. Iron phosphide Fe2P / Fe3P (dissolution rate <5%):

[0067] Fe2P + 6HCl → 2FeCl2 + PH3↑;

[0068] Fe3P + 9HCl → 3FeCl2 + PH3↑.

[0069] Phenomenon: The black particles dissolve, releasing PH3 gas with a garlic smell, and the solution turns light green.

[0070] 3. Iron(III) oxide (Fe3O4) (dissolution rate <2%):

[0071] Fe3O4+8HCl→FeCl2+2FeCl3+4H2O.

[0072] Phenomenon: The black solid gradually dissolves, and the solution turns yellowish-green (Fe). 2+ / Fe 3+ mix).

[0073] In some other embodiments, in the step of forming the solution containing ferrous iron, the magnetic material is reacted with a copper sulfate solution. The solution containing ferrous iron is formed by the displacement reaction of copper sulfate with elemental iron, as shown in the following reaction formula:

[0074] Fe + CuSO4 → Cu + FeSO4.

[0075] Further, the concentration of the copper sulfate solution is 0.05 mol / L to 0.5 mol / L. Specifically, the concentration of the copper sulfate solution includes, but is not limited to: 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, or any range between the foregoing.

[0076] Further, the ratio of the magnetic material to the copper sulfate solution is: 5 mL to 8 mL of copper sulfate solution for every 5 mg of the magnetic material. Specifically, the volume of the copper sulfate solution includes, but is not limited to, 5 mL, 5.5 mL, 6 mL, 6.5 mL, 7 mL, 7.5 mL, 8 mL, or any combination thereof.

[0077] Furthermore, the reaction conditions include: a reaction temperature of 60℃ to 200℃ and a reaction time of 30 min to 100 min. Specifically, the reaction temperature includes, but is not limited to: 60℃, 80℃, 100℃, 120℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, or any range between two of the foregoing; the reaction time includes, but is not limited to: 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 70 min, 80 min, 90 min, 100 min, or any range between two of the foregoing.

[0078] Without limitation, the magnetic separation step includes: mixing the lithium iron phosphate, water, and magnetic apparatus for adsorption treatment.

[0079] In some embodiments, the magnetic induction intensity of the magnetic device is 0.6T to 1.2T per 1kg of lithium iron phosphate. Specifically, the magnetic induction intensity of the magnetic device includes, but is not limited to, 0.6T, 0.7T, 0.8T, 0.9T, 1T, 1.1T, 1.2T, or any range between the foregoing.

[0080] In some embodiments, the adsorption process further includes the addition of a dispersant. Without limitation, the dispersant includes one or more of polyethylene glycol trimethyl nonyl ether (e.g., TMN-6 dispersant), X-3204 dispersant, and sodium lauroyl ether.

[0081] Without limitation, the steps for separating and obtaining magnetic materials include: collecting the magnetic device after adsorption treatment, rinsing the magnetic device with a solvent, collecting the mixture of magnetic material and solvent, and then performing solid-liquid separation to obtain the magnetic material.

[0082] In some embodiments, solid-liquid separation is achieved using a microporous membrane for negative pressure filtration. Optionally, the pore size of the microporous membrane is 0.3 μm to 1 μm. Specifically, the pore size of the microporous membrane includes, but is not limited to, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or any range between the foregoing.

[0083] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following will provide a more detailed description of this application in conjunction with embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0084] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0085] Example 1

[0086] This embodiment provides a method for detecting the content of elemental iron in lithium iron phosphate, the steps of which are as follows:

[0087] (1) Magnetic separation enrichment

[0088] 1.1 Weigh 1 kg of LiFePO4 powder into a roller mill barrel, add 2 L of deionized water and 50 mL of TMN-6 dispersant to the roller mill barrel, and use a 1T magnetic rod covered with a plastic diaphragm to adsorb the powder in the roller for 30 min.

[0089] 1.2 Remove all the magnetic rods and rinse the magnetic phase on the plastic diaphragm three times with 50 mL of anhydrous ethanol into a beaker to obtain magnetic phase filter residue.

[0090] 1.3 Weigh a 0.5μm microporous filter membrane and record its mass as m1. Use the 0.5μm microporous filter membrane to perform negative pressure filtration of the filter residue and weigh the mass of the filtered residue as m2.

[0091] 1.4 After filtering, the filter membrane is placed in a beaker, and the mass of the filter residue is m_mag = m2 - m1 = 50 mg.

[0092] (2) Selective dissolution of weak acids

[0093] 2.1 Add 50.0 mL of 0.05 mol / L HCl aqueous solution pre-cooled to 25 °C to the beaker containing the filtered membrane from step (1).

[0094] 2.2 Ultrasonic assisted treatment for 2 minutes (power 50W, constant temperature water bath 25℃).

[0095] The dissolution rate of elemental iron (Fe) within 2 minutes is >95 wt%; the dissolution rate of Fe2P is <5 wt%; and the dissolution rate of Fe3O4 is <2 wt%.

[0096] 2.3 Immediately remove any undissolved residue with a magnetic rod, transfer the solution to a 100mL volumetric flask, rinse the beaker twice with a 0.1% EDTA-2Na aqueous solution, and then dilute to the mark with pure water (V_total = 100mL).

[0097] (3) Titration of elemental iron with cerium sulfate

[0098] 3.1 Take 20.00 mL of the solution after dilution in step (2) into a 100 mL beaker.

[0099] 3.2 Add 2 drops of sulfuric acid-phosphoric acid masking agent (prepared according to the ratio of concentrated sulfuric acid: phosphoric acid: pure water = 13.9 mL: 100 mL: 386.1 mL) and 2 drops of o-phenanthroline indicator.

[0100] 3.3 Titrate with 0.01 mol / L Ce(SO4)2 aqueous solution. Visually observe the transition from orange-red to light blue as the endpoint, and record the volume V_sample.

[0101] (4) Blanks and Calculations

[0102] 4.1 Blank: Direct titration with 20 mL of 0.05 mol / L HCl aqueous solution, volume V_blank (usually <0.05 mL).

[0103] 4.2 Calculation:

[0104] Elemental iron (Fe) (ppm) = [C × (V_sample - V_blank) × 55.845 × 1000] / (M_sample × 1000 × 20 / 100),

[0105] Where C is the Ce(SO4)2 concentration; M_sample is the original 1kg powder mass.

[0106] The lithium iron phosphate samples (from Hunan Yuneng New Energy Battery Materials Co., Ltd.) of the batch to be tested were tested according to the above content detection method. Specifically:

[0107] Original powder mass: M_sample=1000g;

[0108] The volume of the weak acid was adjusted to a final volume of 100 mL.

[0109] Aliquot the titration volume: 20.00 mL;

[0110] Ce(SO4)2 concentration: C = 0.01 mol / L;

[0111] Sample consumption volume: V_sample = 0.42 mL;

[0112] Blank volume: V_blank = 0.02 mL.

[0113] Substitute into the formula:

[0114] Elemental iron (Fe) (ppm) = [C × (V_sample - V_blank) × 55.845 × 1000] / (M_sample × 1000 × 20 / 100)

[0115] =[0.01×0.40×55.845×1000] / (1000×0.20)≈1.12ppm.

[0116] Example 2

[0117] This embodiment provides a method for detecting the content of elemental iron in lithium iron phosphate. The steps are the same as in embodiment 1, but the main difference is that the weak acid selective leaching in step (2) is replaced by copper sulfate leaching.

[0118] Specifically, step (2) is as follows:

[0119] 2.1 Add 50.0 mL of 0.1 mol / L anhydrous copper sulfate aqueous solution to the beaker containing the filtered membrane from step (1).

[0120] 2.2 Place the beaker on a heating plate and heat at 180°C for 50 minutes.

[0121] 2.3 Use a 0.5μm microporous membrane for negative pressure filtration and collect the filtrate into a 100mL volumetric flask.

[0122] 2.4 First, rinse the beaker twice with a 0.1% EDTA-2Na aqueous solution, then dilute to the mark with pure water (V_total = 100mL).

[0123] Example 3

[0124] This embodiment provides a method for detecting the content of elemental iron in lithium iron phosphate. The steps are the same as in embodiment 1, but the main difference is that in step (3), during the titration of elemental iron with cerium sulfate, the concentration of the Ce(SO4)2 aqueous solution is 0.05 mol / L.

[0125] Example 4

[0126] This embodiment provides a method for detecting the content of elemental iron in lithium iron phosphate. The steps are the same as in embodiment 1, but the main difference is that in step (3), during the titration of elemental iron with cerium sulfate, the concentration of the Ce(SO4)2 aqueous solution is 0.25 mol / L.

[0127] Example 5

[0128] This embodiment provides a method for detecting the content of elemental iron in lithium iron phosphate. The steps are the same as in embodiment 1, but the main difference is that in step (3), during the titration of elemental iron with cerium sulfate, the concentration of the Ce(SO4)2 aqueous solution is 1 mol / L.

[0129] Example 6

[0130] This embodiment provides a method for detecting the content of elemental iron in lithium iron phosphate. The steps are the same as in embodiment 1, but the main difference is that in step (2) the concentration of the HCl aqueous solution is 0.1 mol / L, the reaction temperature is 70℃, and the reaction time is 1.5 min.

[0131] Example 7

[0132] This embodiment provides a method for detecting the content of elemental iron in lithium iron phosphate. The steps are the same as in embodiment 1, but the main difference is that in step (2) the concentration of the HCl aqueous solution is 0.5 mol / L, the reaction temperature is 40℃, and the reaction time is 2.5 min.

[0133] Example 8

[0134] This embodiment provides a method for detecting the content of elemental iron in lithium iron phosphate. The steps are the same as in Embodiment 2, with the main difference being that the concentration of the anhydrous copper sulfate aqueous solution is 0.05 mol / L, and it is heated at 200°C for 30 min.

[0135] Example 9

[0136] This embodiment provides a method for detecting the content of elemental iron in lithium iron phosphate. The steps are the same as in embodiment 2, with the main difference being that the concentration of the anhydrous copper sulfate aqueous solution is 0.5 mol / L, and it is heated at 60°C for 100 min.

[0137] Comparative Example 1

[0138] This comparative example provides a method for detecting the content of elemental iron in lithium iron phosphate. The steps are the same as in Example 1, but the main difference is that in step (3), during the titration of elemental iron with cerium sulfate, ammonium persulfate is used to replace Ce(SO4)2 at the same concentration.

[0139] Accuracy assessment of test cases:

[0140] (1) Interference test of iron phosphide:

[0141] Preparation of standard samples: A certain amount (15 mg, 50 mg) of iron phosphate was added to 1 kg of lithium iron phosphate sample (from Hunan Yuneng New Energy Battery Materials Co., Ltd.).

[0142] The content was detected according to the method provided in Example 1, and the results are shown in Table 1 below:

[0143] Table 1

[0144]

[0145] Note: Ferric phosphide precipitation rate = Ferric phosphide titration result / Ferric phosphide addition amount × 100%.

[0146] As shown in Table 1, the precipitation results of different amounts of iron phosphide added to the lithium iron phosphate samples were all less than 3%, indicating that the amount of iron phosphide that could be titrated was less than 3%, which confirms that the interference of iron phosphide on the test results is very small.

[0147] (2) Deviation test for elemental iron:

[0148] Standard sample preparation: 1 mg, 5 mg, and 15 mg of elemental iron were added to 1 kg of lithium iron phosphate sample (from Hunan Yuneng New Energy Battery Materials Co., Ltd.).

[0149] The content detection method provided in Example 1 was used for testing, and the results are shown in Table 2 below:

[0150] Table 2

[0151]

[0152] Note: Test deviation rate = (1 - titration result of elemental iron / amount of elemental iron added) × 100%.

[0153] In addition, the content detection methods of Examples 2-9 and Comparative Example 1 were used to detect the content of a standard sample containing a determined amount (5 mg), and the results are shown in Table 3 below:

[0154] Table 3

[0155]

[0156] As can be seen, this application, by using cerium salt as an oxidant for titration, can more accurately detect the content of elemental iron in lithium iron phosphate. Furthermore, it eliminates the need for detection instruments such as XRF and ICP, resulting in low detection cost and high detection efficiency.

[0157] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0158] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0159] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification can be used to interpret the scope of the claims.

Claims

1. A method for detecting the content of elemental iron in lithium iron phosphate, characterized by, The method comprises the following steps: magnetic separation of lithium iron phosphate to separate magnetic material; reacting the magnetic material with an acid solution or a copper sulfate solution to form a solution containing divalent iron; oxidative titration of the solution containing divalent iron to calculate the content of elemental iron in the lithium iron phosphate according to the titration result; The titration reagent used in the oxidative titration comprises an oxidizing agent, and the oxidizing agent comprises a cerium salt.

2. The method of claim 1, wherein the content of elemental iron in lithium iron phosphate is detected by the method, characterized in that, The cerium salt comprises one or both of cerium sulfate and cerium ammonium nitrate.

3. The method for detecting the content of elemental iron in lithium iron phosphate according to claim 1 or 2, characterized in that, The concentration of the cerium salt in the titration reagent is 0.01 mol / L to 1 mol / L.

4. The method for detecting the content of elemental iron in lithium iron phosphate according to claim 1 or 2, characterized in that, The end point of the oxidative titration is indicated by a change in color or potential of an indicator.

5. The method of claim 4, wherein the content of elemental iron in the lithium iron phosphate is detected by the following steps of: The indicator comprises o-phenanthroline. ​ 6. The method for detecting the content of elemental iron in lithium iron phosphate according to claim 1 or 2, characterized in that, In the step of forming the solution containing divalent iron, the magnetic material is reacted with an acid solution.

7. The method of claim 6, wherein the content of elemental iron in the lithium iron phosphate is detected by the following steps of: The acid solution has one or more of the following characteristics: ​ (1) the acid in the acid solution is hydrochloric acid; (2) the concentration of the acid solution is 0.05 mol / L to 0.5 mol / L; (3) the ratio of the magnetic material to the acid solution is 5 mL to 8 mL of the acid solution per 5 mg of the magnetic material.

8. The method for detecting the content of elemental iron in lithium iron phosphate according to claim 1 or 2, characterized in that, The conditions for reacting the magnetic material with the acid solution include one or both of the following: (1) ultrasonic assistance is used for the reaction; (2) the reaction temperature is 20°C to 70°C, and the reaction time is 1.5 min to 2.5 min.

9. The method of claim 8, wherein the content of elemental iron in the lithium iron phosphate is detected by the following steps of: The power of the ultrasonic wave is 40 W to 250 W. ​ 10. The method for detecting the content of elemental iron in lithium iron phosphate according to claim 1 or 2, characterized in that, In the step of forming the solution containing divalent iron, the magnetic material is reacted with a copper sulfate solution.

11. The method of claim 10, wherein the elemental iron content of the lithium iron phosphate is determined by the method comprising: The copper sulfate solution has one or both of the following characteristics: ​ (1) the concentration of the copper sulfate solution is 0.05 mol / L to 0.5 mol / L; (2) the ratio of the magnetic material to the copper sulfate solution is 5 mL to 8 mL of the copper sulfate solution per 5 mg of the magnetic material.

12. The method for detecting the content of elemental iron in lithium iron phosphate according to claim 1 or 2, characterized in that, The conditions for reacting the magnetic material with the copper sulfate solution include a reaction temperature of 60°C to 200°C and a reaction time of 30 min to 100 min.

13. The method for detecting the content of elemental iron in lithium iron phosphate as described in claim 1 or 2, characterized in that, The step of magnetic separation comprises mixing the lithium iron phosphate, water, and a magnetic device for adsorption treatment.

14. The method of claim 13, wherein the content of elemental iron in the lithium iron phosphate is detected by the method comprising: The magnetic induction intensity of the magnetic device is 0.6 T to 1.2 T per 1 kg of the lithium iron phosphate. ​ 15. The method of claim 13, wherein the content of elemental iron in the lithium iron phosphate is detected by the method comprising: The adsorption treatment further comprises a step of adding a dispersant; the dispersant comprises one or more of polyethylene glycol trimethyl nonyl ether, X-3204 dispersant, and sodium lauroyl amino acid. ​

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