Lithium content testing method for regenerated lithium iron phosphate material and application

Abstract

This application discloses a method and application for testing the lithium content of recycled lithium iron phosphate materials, relating to the technical field of positive electrode materials for batteries. The method involves dividing the prepared recycled lithium iron phosphate filtrate into two portions, titrating the first test solution, and recording the volume of titrant consumed at the first equivalence point and the second titration volume consumed at the second equivalence point. The second test solution is then titrated, and a conversion factor is obtained by combining the fitted curve. The additional titration volume calculated by the conversion system, along with the fluoride ion concentration, is used to calculate the corrected volume. The lithium content in the recycled lithium iron phosphate is calculated by combining the corrected volume and the first titration volume. By correcting for fluoride ions in the filtrate, the accuracy of testing the lithium content in the recycled lithium iron phosphate is improved.

Description

Technical Field

[0001] This application relates to the field of cathode material technology for batteries, specifically to a method for testing the lithium content of recycled lithium iron phosphate materials and its application. Background Technology

[0002] Different lithium contents in lithium iron phosphate have different effects on the electrochemical performance of lithium-ion batteries. If the lithium content is too high, excessive lithium can easily cause over-electrolysis of the battery and even thermal runaway. If the lithium content is too low, the battery will have insufficient energy. The determination of lithium content is the basis for ensuring the performance stability of lithium iron phosphate materials.

[0003] In some related technologies, the residual lithium content in recycled lithium iron phosphate materials is currently tested using the same methods as virgin materials. However, recycled materials differ from virgin materials. Recycled lithium iron phosphate materials contain fluorine, which exists as fluoride ions in a slightly alkaline environment. During acidic titration, under acidic conditions, fluoride ions combine with hydrogen ions to form hydrofluoric acid, thus causing deviations in the detected lithium content in recycled lithium iron phosphate. Summary of the Invention

[0004] In order to solve at least one of the problems mentioned in the background art, this application provides a method and application for testing the lithium content of recycled lithium iron phosphate materials. The method involves first determining the concentration of fluoride ions in the filtrate of recycled lithium iron phosphate, and then performing a correction to obtain an accurate value of the residual lithium content in the recycled lithium iron phosphate material.

[0005] The specific technical solutions provided in this application are as follows: Firstly, a method for testing the lithium content of recycled lithium iron phosphate materials is provided, including the following steps: Prepare a regenerated lithium iron phosphate filtrate, and divide the filtrate into a first test solution and a second test solution; The first test solution is titrated, and the first titration volume of titrant consumed at the first equivalence point is recorded, as well as the second titration volume of titrant consumed at the second equivalence point is recorded. The concentration of fluoride ions in the filtrate is measured, and the conversion factor is obtained by titrating the second test solution. The additional titration volume is calculated by combining the concentration of fluoride ions and the conversion factor. The corrected volume is obtained by subtracting the additional titration volume from the second titration volume, and the lithium content of the regenerated lithium iron phosphate is calculated by combining the corrected volume and the first titration volume.

[0006] In one specific embodiment, the pH value of the titration solution at the first equivalence point is greater than the pH value of the titration solution at the second equivalence point; And / or, the pH of the titrant at the first equivalence point is 8.5; and / or, the pH of the titrant at the second equivalence point is 4.5.

[0007] In one specific embodiment, measuring the fluoride ion concentration in the filtrate specifically includes: Take a preset volume of the filtrate, adjust the pH of the filtrate to 6-8 using nitric acid solution to obtain an adjusted solution; add fluoride buffer to the adjusted solution and make up to volume, measure the fluoride ion concentration in the adjusted solution using an electrode, and calculate the fluoride ion concentration by combining the volume of the adjusted solution and the fluoride ion concentration.

[0008] In one specific embodiment, the conversion coefficient is obtained by calibrating and fitting the second test liquid, specifically including: Take a preset volume of the second test solution, titrate it with a preset concentration of hydrochloric acid standard solution, and calculate the fluoride ion concentration in the second test solution; plot a curve with the fluoride ion concentration as the independent variable and the additional titration volume as the dependent variable to obtain the fitted curve equation; The conversion coefficient is calculated by combining the fitted curve equation.

[0009] In one specific embodiment, the fitting curve equation (1) is y = 91.23x, where y represents the additional titration volume and x represents the fluoride ion concentration.

[0010] In one specific embodiment, the first analyte and / or the second analyte are titrated with a standard hydrochloric acid titration solution having a concentration of 0.05 mol / L. The additional titration volume is calculated using equation (2): Equation (2) in, Indicates the additional titration volume, in mL; The value represents the fluoride ion concentration, mol / L; 21.92 represents the conversion factor; 100 represents the volume of the second test solution, mL; and 0.05 represents the concentration of the hydrochloric acid standard titration solution, mol / L.

[0011] In a specific embodiment, the lithium carbonate content and lithium hydroxide content in the regenerated lithium iron phosphate are calculated by combining the corrected volume and the first titration volume, respectively. The lithium carbonate content is calculated using formula (3): Equation (3) in, This indicates the lithium carbonate content, % . The concentration of the hydrochloric acid standard titration solution is expressed in mol / L. The volume after correction is expressed in mL. The first titration volume is indicated in mL; 300 indicates the volume of deionized water added, in mL. The value represents the mass of regenerated lithium iron phosphate in the filtrate, in g; 100 represents the volume of the first test solution, in mL; 73.89 represents the relative molecular mass of lithium carbonate. The lithium hydroxide content is calculated using formula (4): Equation (4) in, This indicates the lithium hydroxide content, % . The concentration of the hydrochloric acid standard titration solution is expressed in mol / L. The volume after correction is expressed in mL. The first titration volume is indicated in mL; 300 indicates the volume of deionized water added, in mL. The value represents the mass of regenerated lithium iron phosphate in the filtrate, in g; 100 represents the volume of the second test liquid, in mL; and 23.95 represents the relative molecular mass of lithium hydroxide.

[0012] In a specific embodiment, the alkali content in the regenerated lithium iron phosphate is calculated by formula (5) by combining the lithium carbonate content and the lithium hydroxide content; Equation (5) in, The percentage indicates the alkali content; 1.54 represents the alkali content conversion factor. This indicates the lithium carbonate content, % . This indicates the lithium hydroxide content, expressed as a percentage.

[0013] In one specific embodiment, the preparation of regenerated lithium iron phosphate filtrate specifically includes: Deionized water was added to the regenerated lithium iron phosphate and stirred until homogeneous to obtain a mixture; the mixture was then vacuum filtered to obtain the filtrate.

[0014] Secondly, the method for testing the lithium content of recycled lithium iron phosphate material as described above is provided for use in the detection of cathode materials for lithium batteries.

[0015] The embodiments of this application have the following beneficial effects: In this embodiment, the concentration of fluoride ions in the regenerated lithium iron phosphate filtrate is obtained by curve fitting. When titrating the regenerated lithium iron phosphate, the amount of hydrochloric acid consumed to react with the fluoride ions in the filtrate is corrected to obtain the corrected volume of the titration liquid. The content of lithium carbonate and lithium hydroxide in the regenerated lithium iron phosphate is calculated based on the corrected volume of the titration liquid, thereby obtaining the accurate value of the residual lithium content in the regenerated lithium iron phosphate material. Attached Figure Description

[0016] To more clearly illustrate the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of a lithium content testing method for recycled lithium iron phosphate materials provided in an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of this application.

[0019] The "range" disclosed herein is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0020] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0021] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0022] In this application, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed 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) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] This application provides a method for testing the lithium content of recycled lithium iron phosphate materials, such as... Figure 1 As shown, it includes the following steps: S1. Prepare regenerated lithium iron phosphate filtrate and divide the filtrate into a first test solution and a second test solution.

[0025] Specifically, this involves adding deionized water to regenerated lithium iron phosphate, stirring until a mixture is obtained, and then vacuum filtering the mixture to obtain a filtrate.

[0026] Weigh a certain mass of regenerated lithium iron phosphate sample and place it in a beaker, recording the mass of the sample. Add deionized water to the beaker, place a magnetic stir bar inside, seal the beaker with sealing film, and place it on a magnetic stirrer. Set the stirring speed to 700 r / min~900 r / min and stir for 4 min~6 min. After stirring, use a vacuum filtration device to filter the solution. After filtration, transfer the filtrate to other beakers and divide it into a first test solution and a second test solution. The first test solution is used for hydrochloric acid titration to obtain the titration volume, and the second test solution is used to detect the fluoride ion concentration in the filtrate and the additional titration volume consumed to obtain fluoride ions.

[0027] Specifically, weigh 50g-100g of sample into a 500mL beaker and record the sample mass m1. Add 300mL of deionized water to the beaker, place a magnetic stir bar inside, seal the beaker with sealing film, and stir on a magnetic stirrer. After stirring, filter the solution using a vacuum filtration device. After filtration, transfer the filtrate to a 500mL beaker, of which 100mL of filtrate is used for titration and 100mL of filtrate is used for fluoride ion content testing.

[0028] S2. Titrate the first test solution and record the first titration volume of titrant consumed when titrating to the first equivalence point, and the second titration volume of titrant consumed when titrating to the second equivalence point.

[0029] The pH value of the titrant at the first equivalence point is greater than the pH value of the titrant at the second equivalence point; the pH of the titrant at the first equivalence point is 8.5; and the pH of the titrant at the second equivalence point is 4.5.

[0030] First, rinse the pipette three times with the filtrate. Then, transfer the predetermined volume of filtrate into a beaker, add a magnetic stir bar, place the beaker on a point titrator, and titrate using hydrochloric acid as the standard solution. Record the volume of hydrochloric acid consumed at two equivalence points, Ep1 (pH=8.5) and Ep2 (pH=4.5), which are the first titration volume and the second titration volume, respectively.

[0031] It should be noted that during the lithium iron phosphate recovery process, the common alkaline residues in the filtrate mainly include LiOH and Li2CO. 3‌ These two substances will undergo a neutralization reaction with hydrochloric acid in stages during the titration process: CO3 2- +H + →HCO3 - Therefore, during the first stage of neutralization, lithium carbonate gradually hydrolyzes in water, first converting into lithium bicarbonate (LiHCO3). The equivalence point of this process corresponds to a pH of approximately 8.5, which is the first equivalence point. At this point, OH... - and CO3 2- The first step of protonation is completed: simultaneously, the free LiOH is also completely neutralized: OH - +H + →H2O, therefore, the amount of hydrochloric acid consumed at Ep1 (pH=8.5) mainly reflects the total amount of the first-step reaction involving both LiOH and lithium carbonate. Continue adding hydrochloric acid for the second-stage neutralization, HCO3... - It is further neutralized to H2CO3, and H2CO3 further decomposes into CO2 and H2O. The equivalence point of this reaction occurs at pH ≈ 4.5: HCO3 - +H +→H2CO3→CO2↑+H2O, thus confirming that the pH of the titrant at the first equivalence point is 8.5; and the pH of the titrant at the second equivalence point is 4.5.

[0032] Specifically, transfer 100 ml of the above filtrate into a 250 ml beaker and titrate it using a potentiometric titrator. Record the volume of hydrochloric acid consumed at two equivalence points, Ep1 (pH=8.5) and Ep2 (pH=4.5), and denote them as V1 and V2, respectively.

[0033] S3. Measure the fluoride ion concentration in the filtrate, perform titration fitting on the second test solution to obtain the conversion factor, and calculate the additional titration volume by combining the fluoride ion concentration and the conversion factor.

[0034] The measurement of fluoride ion concentration in the filtrate specifically includes: taking a predetermined volume of filtrate, adjusting the pH of the filtrate to 6-8 using nitric acid solution to obtain an adjusted solution; adding fluoride buffer solution to the adjusted solution and making up to volume; measuring the fluoride ion concentration in the adjusted solution using a fluoride ion selective electrode; and calculating the fluoride ion concentration by combining the adjusted solution volume and the fluoride ion concentration. Then, transferring 100 mL of the above filtrate to a 250 mL beaker, measuring the fluoride ion content in the filtrate using a fluoride ion selective electrode, and recording it as c. (F - ) .

[0035] The conversion coefficients were obtained by calibrating and fitting the second test solution, specifically including: Take a preset volume of the second test solution, titrate it with a preset concentration of hydrochloric acid standard solution, and calculate the fluoride ion concentration in the second test solution; plot a curve with the fluoride ion concentration as the independent variable and the additional titration volume as the dependent variable to obtain the fitted curve equation; calculate the conversion factor based on the fitted curve equation.

[0036] The fitting curve equation (1) is y = 91.23x, where y represents the extra titration volume and x represents the fluoride ion concentration.

[0037] In one specific embodiment, the conversion factor is calculated as follows: taking the fluoride ion concentration in 100 mL of filtrate as 2 × 10⁻⁶. -3 Taking the standardization using 0.05M hydrochloric acid standard titration solution as an example: the amount of fluoride ions in the filtrate: n = 2 × 10 -3 ×0.1=2×10 -4 The acid dissociation constant pK of hydrofluoric acid a =3.17.

[0038] At pH 8.5, fluoride is produced by the presence of fluoride ions ( ). It exists in the form of ) when pH is 4.5, according to the Henderson–Hasselbalch equation: pH = pK a +log We can obtain the following equation: 4.5 = 3.17 + log Therefore, it can be calculated that = 21.38, total fluoride concentration c=[F - ]+[HF].

[0039] Among them, F - Mole fraction: = =0.955=95.5%, the mole fraction of HF: 1-0.955=0.045=4.5%.

[0040] Further calculations can be performed to obtain: The amount of HF produced at the titration endpoint is n = 0.045 × 2 × 10⁻⁶. -4 =9×10 -6 The amount of hydrogen ions consumed in the titration to generate HF is n = 9 × 10⁻⁶. -6 The volume of 0.05M hydrochloric acid standard titration solution consumed: V= =0.18mL.

[0041] With fluoride ion concentrations of 0 and 1×10⁻⁶ respectively in the filtrate -3 M, 2×10 -3 M, 3×10 -3 M and 5×10 -3 M is the independent variable. The volume of hydrochloric acid standard titration solution theoretically consumed by fluoride ions in 100 ml of filtrate and the volume of hydrochloric acid standard solution actually consumed by fluoride ions in filtrate are calculated respectively. The relevant test results are shown in Table 1.

[0042] Table 1. Test results of fluoride ion related parameters

[0043] Based on the data in Table 1, the concentration of fluoride ions in the filtrate was taken as the independent variable x, and the volume of hydrochloric acid standard titration solution actually consumed by the fluoride ions was taken as the dependent variable y. The fitting equation (1) was obtained: y = 91.23x.

[0044] In a specific embodiment, assuming the conversion factor is A, the volume of the filtrate is 100 mL, and the concentration of the hydrochloric acid standard titration solution is 0.05 M, the following equation (2) can be obtained: Equation (2) Corresponding to equation (2) above, Set to y, Setting it to x, the above formula can be converted to... , can be obtained =91.23, and the conversion factor A is calculated to be 21.92.

[0045] The first and / or second analytes are titrated with a standard hydrochloric acid titration solution, and the additional titration volume is calculated using equation (3): Equation (3) in, Indicates the additional titration volume, in mL; The value represents the fluoride ion concentration, mol / L; 21.92 represents the conversion factor; 100 represents the volume of the second test solution, mL; and 0.05 represents the concentration of the hydrochloric acid standard titration solution, mol / L.

[0046] S4. Subtract the additional titration volume from the second titration volume to obtain the corrected volume. Combine the corrected volume with the first titration volume to calculate the lithium content of the regenerated lithium iron phosphate.

[0047] Specifically, the corrected volume is calculated using the following formula (4), which is the volume of hydrochloric acid consumed at the second equivalence point during the titration process minus the additional titration volume of acid consumed due to fluoride ions.

[0048] Equation (4) in, The volume after correction is expressed in mL. The volume of the second titration is expressed in mL. Indicates the additional titration volume, in mL.

[0049] In one specific embodiment, the lithium content of the regenerated lithium iron phosphate is calculated by combining the corrected volume and the first titration volume, specifically including: calculating the lithium carbonate content and lithium hydroxide content in the regenerated lithium iron phosphate by combining the corrected volume and the first titration volume, respectively.

[0050] The lithium carbonate content is calculated using formula (5): Equation (5) in, This indicates the lithium carbonate content, % . The concentration of the hydrochloric acid standard titration solution is expressed in mol / L. The volume after correction is expressed in mL. The first titration volume is indicated in mL; 300 indicates the volume of deionized water added, in mL. The value represents the mass of regenerated lithium iron phosphate in the filtrate, in g; 100 represents the volume of the first test solution, in mL; 73.89 represents the relative molecular mass of lithium carbonate. The lithium hydroxide content is calculated using formula (6). Equation (6) in, This indicates the lithium hydroxide content, % . The concentration of the hydrochloric acid standard titration solution is expressed in mol / L. The volume after correction is expressed in mL. The first titration volume is indicated in mL; 300 indicates the volume of deionized water added, in mL. The value represents the mass of regenerated lithium iron phosphate in the filtrate, in g; 100 represents the volume of the second test liquid, in mL; and 23.95 represents the relative molecular mass of lithium hydroxide.

[0051] Furthermore, combining the lithium carbonate content and lithium hydroxide content, the alkali content in the recycled lithium iron phosphate is calculated using formula (7); Equation (7) in, The percentage indicates the alkali content; 1.54 represents the alkali content conversion factor. This indicates the lithium carbonate content, % . This indicates the lithium hydroxide content, expressed as a percentage.

[0052] The presence of fluorine in the recycled lithium iron phosphate material increases the amount of hydrochloric acid consumed at the second equivalence point, resulting in a much higher test result for the residual lithium content than the actual value. Therefore, to more accurately determine the residual lithium content in the recycled lithium iron phosphate material, this application obtains an accurate value for the residual lithium content by first measuring the concentration of fluoride ions in the residual alkali test solution and then performing correction.

[0053] Corresponding to the above embodiments, this application provides a lithium content testing method based on recycled lithium iron phosphate material, which is used in the detection of cathode materials for lithium batteries.

[0054] Example 1 This invention provides a method for detecting the residual lithium content in recycled lithium iron phosphate materials, the method comprising the following steps: S1. Preparation of test solution for regenerated lithium iron phosphate material Weigh 60.0 g of sample into a 500 mL beaker and record the sample mass m1. Add 300 mL of deionized water to the beaker, place a magnetic stir bar inside, seal the beaker with sealing film, and place it on a magnetic stirrer. Stir at 800 rpm for 5 min. After stirring, filter the solution using a vacuum filtration device. After filtration, transfer the filtrate to a 500 mL beaker, of which 100 mL is used for titration and 100 mL is used for fluoride ion content testing.

[0055] S2, Titration process First, rinse the 100mL pipette three times with the filtrate. Then, transfer 100mL of the filtrate into a 200mL beaker, add a magnetic stir bar, and place the beaker on a potentiometric titrator for titration. Record the volume of hydrochloric acid consumed at two equivalence points, Ep1 (pH=8.5) and Ep2 (pH=4.5), and denote them as V1 and V2, respectively.

[0056] S3, Fluorine content test Transfer 100 mL of the filtrate to a 200 mL beaker using a pipette. Adjust the pH of the solution to approximately 6-8 with nitric acid or sodium hydroxide solution. Transfer the solution to a 250 mL volumetric flask, add 4 mL of TISAB (fluoride buffer), and bring the volume to a final volume. Measure the fluoride ion content in the liquid using a fluoride ion-selective electrode and record it as c. (F - ) Calculate the additional acid volume consumed due to fluoride ions using the formula above, V. (F - ) .

[0057] S4, Calculation of Free Lithium Content The corrected hydrochloric acid consumption at the second equivalence point is calculated using the above formula, which is: the hydrochloric acid consumption at the second equivalence point during titration minus the volume of additional acid consumed due to fluoride ions. Using the above method, the lithium content in the lithium iron phosphate recycled from different batches of raw materials was tested. The residual lithium carbonate content in the sample was calculated using the above formula (5); the residual lithium hydroxide content in the sample was calculated using the above formula (6); and the residual alkali content in the sample was calculated using the above formula (7). The calculation results are shown in Table 2. Wherein, V1 represents the first titration volume consumed when titrating to the first equivalence point. The second titration volume consumed when titrating the solution to the first equivalence point is indicated. Sample 1, Sample 2 and Sample 3 represent three batches of regenerated lithium iron phosphate material, respectively.

[0058] Table 2 Test results of three recycled lithium iron phosphate samples corresponding to the scheme in Example 1

[0059] Comparative Example Corresponding to Example 1 above, the difference between this comparative example and Example 1 is that the presence of fluoride ions in the recycled lithium iron phosphate material is not considered, and the residual lithium content in the recycled lithium iron phosphate is directly titrated.

[0060] The titration process and calculation results of the three batches of recycled lithium iron phosphate material used in Example 1 and Comparative Example 1 are shown in Table 3. Sample 1, Sample 2, and Sample 3 represent the three batches of recycled lithium iron phosphate material, respectively.

[0061] Table 3 Test results of three recycled lithium iron phosphate samples corresponding to the comparative scheme

[0062] Combining the data in Tables 2 and 3, it can be seen that when using recycled lithium iron phosphate material of the same mass and specifications as samples, the corrected volume of the hydrochloric acid standard solution used in the titration test method of this scheme for the recycled lithium iron phosphate is significantly lower than the volume of hydrochloric acid standard solution consumed in the comparative example. Although the batches of recycled lithium iron phosphate are different, the trend of the content of lithium carbonate, lithium hydroxide, etc. in the recycled lithium iron phosphate is the same, all showing that the lithium carbonate content is significantly higher than the lithium hydroxide content. At the same time, the difference in the volume of the hydrochloric acid standard solution before and after correction is based on the fact that the presence of fluorine in the recycled lithium iron phosphate material increases the amount of hydrochloric acid consumed at the second equivalence point, resulting in the test result of residual lithium content being much higher than the actual value. Therefore, this invention obtains the accurate value of residual lithium content in recycled lithium iron phosphate material by first measuring the concentration of fluoride ions in the residual alkali test solution and then performing correction.

[0063] Although preferred embodiments have been described in this application, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of this application.

[0064] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for testing the lithium content of recycled lithium iron phosphate materials, characterized in that, Includes the following steps: Prepare a regenerated lithium iron phosphate filtrate, and divide the filtrate into a first test solution and a second test solution; Titrate the first test solution and record the first titration volume of titrant consumed when titrating to the first equivalence point, and the second titration volume of titrant consumed when titrating to the second equivalence point. The concentration of fluoride ions in the filtrate is measured, and the conversion factor is obtained by titrating the second test solution. The additional titration volume is calculated by combining the concentration of fluoride ions and the conversion factor. The corrected volume is obtained by subtracting the additional titration volume from the second titration volume, and the lithium content of the regenerated lithium iron phosphate is calculated by combining the corrected volume and the first titration volume.

2. The method for testing the lithium content of recycled lithium iron phosphate material according to claim 1, characterized in that, The pH value of the titration solution at the first equivalence point is greater than the pH value of the titration solution at the second equivalence point; And / or, the pH of the titrant at the first equivalence point is 8.5; And / or, the pH of the titrant at the second equivalence point is 4.

5.

3. The method for testing the lithium content of recycled lithium iron phosphate materials according to claim 1 or 2, characterized in that, Measuring the fluoride ion concentration in the filtrate specifically includes: Take a predetermined volume of the filtrate and adjust the pH of the filtrate to 6-8 using nitric acid solution to obtain the adjusted solution; Fluoride buffer solution was added to the adjusted solution and the volume was adjusted. The concentration of fluoride ions in the adjusted solution was measured using an electrode. The concentration of fluoride ions was calculated by combining the volume of the adjusted solution and the concentration of fluoride ions.

4. The method for testing the lithium content of recycled lithium iron phosphate materials according to claim 1 or 2, characterized in that, The conversion coefficients are obtained by calibrating and fitting the second test solution, specifically including: Take a preset volume of the second test solution, titrate it with a preset concentration of hydrochloric acid standard solution, and calculate the fluoride ion concentration in the second test solution; A curve was plotted with the fluoride ion concentration as the independent variable and the additional titration volume as the dependent variable to obtain the fitted curve equation. The conversion coefficient is calculated by combining the fitted curve equation.

5. The method for testing the lithium content of recycled lithium iron phosphate material according to claim 4, characterized in that, The fitting curve equation (1) is y=91.23x, where y represents the additional titration volume and x represents the fluoride ion concentration.

6. The method for testing the lithium content of recycled lithium iron phosphate materials according to claim 1 or 2, characterized in that, The first analyte and / or the second analyte are titrated with a standard hydrochloric acid titration solution of 0.05 mol / L. The additional titration volume is calculated using equation (2): Equation (2) in, Indicates the additional titration volume, in mL; The value represents the fluoride ion concentration, mol / L; 21.92 represents the conversion factor; 100 represents the volume of the second test solution, mL; and 0.05 represents the concentration of the hydrochloric acid standard titration solution, mol / L.

7. The method for testing the lithium content of recycled lithium iron phosphate materials according to claim 1 or 2, characterized in that, The lithium carbonate content and lithium hydroxide content in the regenerated lithium iron phosphate were calculated by combining the corrected volume and the first titration volume, respectively. The lithium carbonate content is calculated using formula (3): Equation (3) in, This indicates the lithium carbonate content, % . The concentration of the hydrochloric acid standard titration solution is expressed in mol / L. The volume after correction is expressed in mL. The first titration volume is indicated in mL; 300 indicates the volume of deionized water added, in mL. The value represents the mass of regenerated lithium iron phosphate in the filtrate, in g; 100 represents the volume of the first test solution, in mL; 73.89 represents the relative molecular mass of lithium carbonate. The lithium hydroxide content is calculated using formula (4): Equation (4) in, This indicates the lithium hydroxide content, % . The concentration of the hydrochloric acid standard titration solution is expressed in mol / L. The volume after correction is expressed in mL. The first titration volume is indicated in mL; 300 indicates the volume of deionized water added, in mL. The value represents the mass of regenerated lithium iron phosphate in the filtrate, in g; 100 represents the volume of the second test liquid, in mL; and 23.95 represents the relative molecular mass of lithium hydroxide.

8. The method for testing the lithium content of recycled lithium iron phosphate material according to claim 7, characterized in that, The alkali content in the recycled lithium iron phosphate is calculated by formula (5) based on the lithium carbonate content and the lithium hydroxide content. Equation (5) in, The percentage indicates the alkali content; 1.54 represents the alkali content conversion factor. This indicates the lithium carbonate content, % . This indicates the lithium hydroxide content, expressed as a percentage.

9. The method for testing the lithium content of recycled lithium iron phosphate materials according to claim 1 or 2, characterized in that, The preparation of regenerated lithium iron phosphate filtrate specifically includes: Deionized water was added to the regenerated lithium iron phosphate, and the mixture was stirred until homogeneous to obtain a solution. The mixture is subjected to vacuum filtration to obtain the filtrate.

10. The application of a method for testing the lithium content of recycled lithium iron phosphate material according to any one of claims 1 to 9 in the detection of cathode materials for lithium batteries.

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