A method for detecting the aluminum content in waste powder of lithium iron phosphate cathode

Abstract

The present invention provides a method for detecting the aluminum content in waste powder of lithium iron phosphate cathode, comprising the following steps: digestion of the sample; removal of phosphate; removal of metal impurity ions; determination of aluminum content. When the method of the present invention is used for the separate test of the aluminum content in the waste powder of lithium iron phosphate cathode, impurity removal treatment is carried out. Ferric chloride is added first to remove the anionic phosphate ions. Ferric chloride preferentially forms ferric phosphate precipitate with phosphate ions under weakly acidic conditions. Then sodium hydroxide solution is added to remove metal cations such as nickel, cobalt, manganese, and iron, avoiding the influence of aluminum phosphate precipitate on the test, improving the test accuracy, reducing the test cost. When excluding the interfering factor of phosphate ions, the phosphate ions can be effectively excluded, avoiding the formation of aluminum phosphate precipitate and improving the detection accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of element detection, and particularly relates to a method for determining the aluminum content in waste powder of lithium iron phosphate cathode. Background Art

[0002] In recent years, with the improvement of people's environmental protection awareness, lithium battery-powered vehicles have developed rapidly, and lithium batteries are increasingly widely used. As one of the cathode materials for lithium-ion batteries, lithium iron phosphate has attracted much attention due to its high safety. The detection of the contents of its main elements such as lithium, iron, phosphorus and impurity elements such as manganese and sodium is not only a key index for the quality of lithium iron phosphate materials, but also has an important guiding role for the adjustment and control of the production process. Therefore, it is of great significance to develop a rapid and convenient method to detect the element content in lithium iron phosphate.

[0003] At present, the sample pretreatment method for measuring aluminum mainly removes metal impurity ions in the form of masking or precipitation with a masking agent. For example, in patent document CN201310422451, sodium hydroxide + barium chloride is used to remove iron and vanadium, and there is no mention of removing anions in the sample such as phosphate ions. Under alkaline conditions, other metal impurity ions in the waste powder of lithium iron phosphate cathode are generally removed in the form of hydroxide precipitation. However, due to the presence of phosphate ions, phosphate ions and aluminum ions will form partial precipitation at this time, resulting in a decrease in the detection accuracy. At present, the full-component analysis of metal ions in the waste powder of lithium iron phosphate cathode is carried out by ICP-OES. For sample pretreatment, there is no sample pretreatment process for separately testing the aluminum ion content. Therefore, it is necessary to study a sample digestion method for the waste powder of lithium iron phosphate cathode containing aluminum, so that the detection of aluminum content in the waste powder of lithium iron phosphate cathode has the characteristics of high accuracy and good reproducibility. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies and defects in the background art, and provide a detection method for the aluminum content in the waste powder of lithium iron phosphate cathode with high accuracy and good reproducibility.

[0005] To solve the above technical problem, the technical solution proposed by the present invention is as follows:

[0006] A method for detecting the aluminum content in the waste powder of lithium iron phosphate cathode, comprising the following steps:

[0007] (1) Digestion of the sample: Add perchloric acid to the sample to be measured of the waste powder of lithium iron phosphate cathode, heat until the sample is completely digested and then cool to obtain the digested sample of the waste powder of lithium iron phosphate cathode; after digestion with perchloric acid, the initial pH is -2.5 to -3.0;

[0008] (2) Removal of phosphate: Add the lithium iron phosphate cathode waste powder sample obtained in step (1) to the ferric chloride solution, adjust the pH, and collect filtrate A; in this step, ferric chloride is added to remove the anionic phosphate ions first. Ferric chloride preferentially forms ferric phosphate precipitate with phosphate ions under weakly acidic conditions;

[0009] (3) Removal of metal impurity ions: Adjust the pH of filtrate A collected in step (2) to alkaline, collect the filtrate, make up the volume, and record it as filtrate B; in this step, sodium hydroxide solution is added to remove metal cations such as nickel, cobalt, manganese, and iron;

[0010] (4) Determination of aluminum content: Add disodium ethylenediaminetetraacetate solution to filtrate B collected in step (3), add an indicator to prepare a test solution, and use titration method to test the aluminum content, and calculate the percentage content of aluminum with the formula;

[0011] The formula is:

[0012] In the formula: w is the mass fraction of aluminum, unit: %;

[0013] V1 is the volume of lead standard solution consumed for titrating the released EDTA, unit: mL;

[0014] V0 is the volume of lead standard solution consumed for the blank sample accompanying the test sample, unit: mL;

[0015] c is the actual concentration of the lead standard solution, unit: mol / L;

[0016] m is the mass of the lithium iron phosphate cathode waste powder test sample, unit: g.

[0017] Preferably, in step (1), the mass of the lithium iron phosphate cathode waste powder test sample is 1.000 ± 0.2000 g, and the solid-liquid ratio of the lithium iron phosphate cathode waste powder test sample to perchloric acid is 1:(30 - 60).

[0018] Preferably, in step (1), the heating is carried out on a hot plate to 90 - 110 °C, and the heating time is 0.5 - 1 h.

[0019] Preferably, in step (2), the concentration of the ferric chloride solution is 2 - 4 mol / L, the addition amount of the ferric chloride solution is 10 - 30 mL, and the molar ratio of ferric chloride to the lithium iron phosphate cathode waste powder is (5 - 10):1.

[0020] Preferably, in step (2), the pH is adjusted to 1 - 2, the adjusting solution for adjusting the pH is sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 3 - 6 mol / L.

[0021] Preferably, the pH adjusted to alkaline in step (3) is 12 - 14; the pH adjusted to acidic is 2 - 3.

[0022] Preferably, the adjusting solution for adjusting pH in step (3) is a mixed solution of hydrochloric acid and water with a volume ratio of 1:(1 - 5).

[0023] Preferably, the device for suction filtration is a glass sand core crucible, and the pore size of the suction filtration filter membrane is < 1 μm.

[0024] Preferably, the volume fixing in step (3) is to fix the volume of the filtrate to 500 mL.

[0025] Preferably, the specific operation for aluminum content determination in step (4) is as follows: Take 50 mL of the solution after volume fixing, add 40 mL of 0.01 mol / L disodium ethylenediaminetetraacetate solution, heat in a water bath to 60 - 70 °C, add 2 drops of 1 g / L bromophenol blue indicator, add 5% ammonia water solution until the solution turns blue and is in excess by two drops, continue to heat in the water bath to above 88 °C and keep for 5 minutes, take out and cool to room temperature, then add 20 mL of pH 5.5 acetic acid - sodium acetate buffer solution and 6 drops of 5 g / L xylenol orange ethanol with a volume ratio of 1:1, titrate with 0.01 mol / L lead acetate standard solution until the solution turns into a stable red - purple color, add 1 g of ammonium fluoride, heat to boiling on a hot plate for 3 minutes, cool to room temperature, then add 20 mL of pH 5.5 acetic acid - sodium acetate buffer solution and 2 drops of 5 g / L xylenol orange ethanol indicator, titrate with 0.01 mol / L lead acetate standard solution until the solution turns into a stable red - purple color as the end point, record the reading, and calculate the percentage content of aluminum according to the formula. Aluminum ions have a blocking effect on xylenol orange. Disodium ethylenediaminetetraacetate (EDTA - 2Na) is used to completely complex aluminum ions. Aluminum ions are prone to hydrolysis to form polyhydroxy complexes and react slowly with EDTA - 2Na. When the pH is 3 - 4, boiling and excessive EDTA - 2Na can fully cooperate with aluminum ions; when the pH is 3 - 4.6, the bromophenol blue indicator changes from yellow to blue, and the addition of two drops of excessive ammonia water is to keep the solution pH at 3 - 4. Heating to 88 °C and keeping for 5 minutes is to complete the reaction between EDTA - 2Na and aluminum ions; under boiling conditions, the addition of 1 g of ammonium fluoride is to release aluminum ions from the EDTA complex to form aluminum fluoride complex, and the content of aluminum ions is obtained by testing the reaction between the released EDTA and lead ions.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. At present, the detection of aluminum content in lithium iron phosphate mainly relies on ICP-OES, which is used to test other metal elements such as nickel, cobalt, and manganese simultaneously. The testing process is complex, and the sample pretreatment only involves heating and digestion with nitric acid without further impurity removal. When the method of the present invention is used for the separate testing of aluminum content in the waste powder of lithium iron phosphate cathode, impurity removal treatment is carried out. Ferric chloride is added first to remove the anionic phosphate ions. Under weakly acidic conditions, ferric chloride preferentially forms iron phosphate precipitate with phosphate ions. Then, sodium hydroxide solution is added to remove metal cations such as nickel, cobalt, manganese, and iron, avoiding the influence of aluminum phosphate precipitate on the test, improving the test accuracy, reducing the test cost, effectively removing phosphate ions when excluding interfering factors, avoiding the formation of aluminum phosphate precipitate, and improving the accuracy of detection.

[0028] 2. The detection method of the present invention uses a small amount of acid, mainly perchloric acid, and the amount of hydrochloric acid used is extremely small. The analysis cost is low, the operation is simple, and the repeatability and reproducibility of the detection data are good. The precision level of the method reaches 98%. Specific Embodiments

[0029] For the convenience of understanding the present invention, the following will describe the present invention more comprehensively and meticulously in combination with preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0031] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0032] Example 1:

[0033] A method for detecting the aluminum content in the waste powder of lithium iron phosphate cathode, comprising the following steps:

[0034] (1) Digestion of the sample: Weigh 1.0003 g of the waste powder of lithium iron phosphate cathode to be tested, add 30 mL of perchloric acid, heat on an electric hot plate to 100 °C and keep it for 0.5 - 1 h until the sample is completely digested, then remove it and cool it down, and add 50 mL of pure water to rinse the cup wall;

[0035] (2) Removal of phosphate ion interference: After cooling to room temperature, add 40 mL of 2 mol / L ferric chloride solution, dropwise add 3 mol / L sodium hydroxide solution to adjust the pH to 1, filter with a glass sand core crucible, the pore size of the filter membrane for filtration is <1 micron, wash the beaker and the precipitate 3 - 4 times, and reserve the filtrate;

[0036] (3) Removal of interference from metal impurity ions such as iron: The filtrate in step (2) is dropped with 3 mol / L sodium hydroxide solution to adjust the pH to 12, then filtered by suction. The beaker and the precipitate are washed 3 - 4 times. The filtrate is adjusted to pH = 2 with hydrochloric acid, and then the filtrate is made up to 500 mL;

[0037] (4) Determination of aluminum content: Pipette 50 mL of the filtrate into a 300 ml conical flask, add 40 mL of EDTA solution, heat in a water bath to 60 - 70 °C, add 2 drops of bromophenol blue indicator, add ammonia water (5%) until the solution turns blue and is in excess by two drops, continue to heat to gentle boiling for 5 minutes, remove and cool. Add 20 mL of buffer solution, 6 drops of xylenol orange indicator, and titrate with 0.01 mol / L lead acetate standard solution until the solution turns stable red-violet. Add 1 g of ammonium fluoride, heat to boiling on an electric hot plate for 3 minutes, remove and cool. Add 20 mL of buffer solution, 2 drops of xylenol orange indicator, and titrate with 0.01 mol / L lead acetate standard solution until the solution turns stable red-violet, and record the reading;

[0038] (5) Blank experiment: Analyze simultaneously with the sample, and the determination method is the same as the above steps;

[0039] (6) Calculation of aluminum content: Calculate the percentage content of aluminum using the formula,

[0040]

[0041] In the formula:

[0042] w --- mass fraction of aluminum, unit: %;

[0043] V1 --- volume of the lead standard solution consumed for titrating the released EDTA, unit: milliliter (mL);

[0044] V0 --- volume of the lead standard solution consumed for the blank along with the sample, unit: milliliter (mL);

[0045] c --- actual concentration of the lead standard solution, unit: mole per liter (mol / L);

[0046] m --- mass of the test sample, unit: gram (g);

[0047] 0.02698 --- amount of aluminum equivalent to 1.00 ml of lead standard solution [c(Pb) = 1.0000 mol / L], unit: gram per mole (g / mol).

[0048] The concentration of the lead acetate standard solution is 0.0105 mol / L, the volume of the lead standard solution consumed for titrating the released EDTA is 10.06 mL, and the volume of the lead standard solution consumed for titrating the blank is 0.00 mL.

[0049] Example 2:

[0050] A method for detecting the aluminum content in lithium iron phosphate cathode waste powder, comprising the following steps:

[0051] (1) Digestion of the sample: Weigh 0.8013 g of the lithium iron phosphate cathode waste powder to be tested, add 40 mL of perchloric acid, heat on a hot plate to 100 °C and maintain for 0.5 - 1 h until the sample is completely digested, then remove and cool, and add 50 mL of pure water;

[0052] (2) Removal of phosphate ion interference: After cooling to room temperature, add 30 mL of 3 mol / L ferric chloride solution, dropwise add 6 mol / L sodium hydroxide solution to adjust the pH to 2, filter with a glass sand core crucible, the pore size of the filter membrane for filtration is <1 μm, wash the beaker and the precipitate 3 - 4 times, and reserve the filtrate;

[0053] (3) Removal of interference from iron and other metal impurity ions: Dropwise add 6 mol / L sodium hydroxide solution to the filtrate in step (2) to adjust the pH to 13, filter, wash the beaker and the precipitate 3 - 4 times, add hydrochloric acid to the filtrate to adjust the pH to 2.5, and make the volume of the filtrate constant to 500 mL;

[0054] (4) Determination of aluminum content: The same as in Example 1;

[0055] (5) Blank experiment: The same as in Example 1;

[0056] (6) Calculation of aluminum content: The same as in Example 1.

[0057] The concentration of the lead acetate standard solution is 0.0105 mol / L, the volume of the lead standard solution consumed for titrating the released EDTA is 9.19 mL, and the volume of the lead standard solution consumed for titrating the blank is 0.00 mL.

[0058] Example 3:

[0059] A method for detecting the aluminum content in lithium iron phosphate cathode waste powder, comprising the following steps:

[0060] (1) Digestion of the sample: Weigh 1.1013 g of the lithium iron phosphate cathode waste powder to be tested, add 60 mL of perchloric acid, heat on a hot plate to 100 °C and maintain for 0.5 - 1 h until the sample is completely digested, then remove and cool, and add 50 mL of pure water;

[0061] (2) Removal of phosphate ion interference: After cooling to room temperature, add 20 mL of 4 mol / L ferric chloride solution, dropwise add 6 mol / L sodium hydroxide solution to adjust the pH to 1, filter with a glass sand core crucible, the pore size of the filter membrane for filtration is <1 μm, wash the beaker and the precipitate 3 - 4 times, and reserve the filtrate;

[0062] (3) Removal of interference from metal impurity ions such as iron: The filtrate in step (2) is adjusted to pH = 14 by dropping 6 mol / L sodium hydroxide solution, and then filtered by suction. The beaker and the precipitate are washed 3 - 4 times. The filtrate is adjusted to pH 3.0 with hydrochloric acid, and then the filtrate is made up to 500 mL.

[0063] (4) Determination of aluminum content: The same as in Example 1;

[0064] (5) Blank experiment: The same as in Example 1;

[0065] (6) Calculation of aluminum content: The same as in Example 1.

[0066] The concentration of the lead acetate standard solution is 0.0105 mol / L. The volume of the lead standard solution consumed for titrating the released EDTA is 13.92 mL, and the volume of the lead standard solution consumed for titrating the blank is 0.00 mL.

[0067] Method comparison experiment: The data of this method is compared with the ICP-MS method commonly used in the current industry. The comparison data is shown in Table 1.

[0068] Table 1: Data comparison between this method and ICP-MS method

[0069] Sample Measured value by this method Measured value by ICP-MS Difference Specimen 1 2.94 3.01 -0.07 Specimen 2 3.16 3.32 -0.16 Specimen 3 3.51 3.40 +0.11

[0070] It can be seen from the comparison data in Table 1 that the data of the two methods do not differ much, indicating that this method has good accuracy.

[0071] Method precision experiment: The lithium iron phosphate cathode waste powder is continuously measured 10 times according to the steps of Example 1, Example 2, and Example 3 to evaluate the precision level of this method. The specific data is shown in Tables 2 - 4.

[0072] Table 2: Method precision experiment of Example 1 (n = 10)

[0073]

[0074] Table 3: Method precision experiment of Example 2 (n = 10)

[0075]

[0076] Table 4: Method precision experiment of Example 3 (n = 10)

[0077]

[0078]

[0079] It can be seen from the data in Tables 2 - 4 that the relative standard deviations of this method are not high, indicating that it has high precision.

Claims

1. A method for detecting the aluminum content in waste powder of lithium iron phosphate cathode, characterized in that, It includes the following steps: (1) Digestion of the sample: Add perchloric acid to the waste powder sample of lithium iron phosphate cathode to be measured, heat it until the sample is completely digested and then cool it to obtain the digested waste powder sample of lithium iron phosphate cathode; (2) Removal of phosphate: Add the waste powder sample of lithium iron phosphate cathode obtained in step (1) to the ferric chloride solution, adjust the pH to 1 - 2, and collect filtrate A; (3) Removal of metal impurity ions: Adjust the pH of filtrate A collected in step (2) to alkaline, collect the filtrate, adjust the pH to acidic and then make a constant volume, denoted as filtrate B; (4) Determination of aluminum content: Add disodium ethylenediaminetetraacetate solution to filtrate B collected in step (3), add an indicator to prepare the test solution, use titration method to test the aluminum content, and calculate the percentage content of aluminum with the formula; The formula is as follows: , In the formula: w is the mass fraction of aluminum, with the unit of %; V1 is the volume of the lead standard solution consumed for titrating the released EDTA, with the unit of mL; V0 is the volume of the lead standard solution consumed for the blank of the sample, with the unit of mL; c is the actual concentration of the lead standard solution, with the unit of mol / L; m is the mass of the waste powder sample of lithium iron phosphate cathode to be measured, with the unit of g.

2. The detection method according to claim 1, wherein In step (1), the mass of the waste powder sample of lithium iron phosphate cathode to be measured is 1.000 ± 0.2000 g, and the solid - liquid ratio of the waste powder sample of lithium iron phosphate cathode to be measured to perchloric acid is 1∶(30 - 60).

3. The detection method according to claim 1, wherein In step (1), the heating is carried out on a hot plate to 90 - 110 °C, and the heating time is 0.5 - 1 h.

4. The detection method according to claim 1, characterized in that, In step (2), the concentration of the ferric chloride solution is 2 - 4 mol / L, the addition amount of the ferric chloride solution is 10 - 40 mL, and the molar ratio of ferric chloride to the waste powder of lithium iron phosphate cathode is (5 - 10)∶1.

5. The detection method according to claim 1, characterized in that, In step (2), the adjusting solution for adjusting the pH is sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 3 - 6 mol / L.

6. The detection method according to claim 1, characterized in that, In step (3), the pH for adjusting to alkaline is 12 - 14; the pH for adjusting to acidic is 2 - 3.

7. The detection method according to claim 1, wherein In step (3), the adjusting solution for adjusting the pH is a mixed solution with a volume ratio of hydrochloric acid to water of 1∶(1 - 5).

8. The detection method according to claim 1, characterized in that, The method for collecting the filtrate is suction filtration, the suction filtration device is a glass sand - core crucible, and the pore diameter of the suction filtration filter membrane is < 1 μm.

9. The detection method according to claim 1, characterized in that, In step (3), the constant volume is to make the filtrate have a constant volume of 500 mL.

10. The detection method according to claim 1, wherein The specific operation of testing the aluminum content by titration method described in step (4) is as follows: Take 50 mL of the fixed-volume solution, add 40 mL of 0.01 mol / L disodium ethylenediaminetetraacetate solution, heat it in a water bath to 60 - 70 °C, add 2 drops of 1 g / L bromophenol blue indicator, add 5% ammonia water solution until the solution turns blue and is in excess by two drops, continue to heat in the water bath to above 88 °C and keep for 5 minutes. After taking it out and cooling to room temperature, add 20 mL of pH 5.5 acetic acid - sodium acetate buffer solution and 6 drops of 5 g / L xylenol orange ethanol with a volume ratio of 1:1, titrate with 0.01 mol / L lead acetate standard solution until the solution turns into a stable red-violet color, add 1 g of ammonium fluoride, heat it on a hot plate until boiling for 3 minutes, after cooling to room temperature, add 20 mL of pH 5.5 acetic acid - sodium acetate buffer solution and 2 drops of 5 g / L xylenol orange ethanol indicator, titrate with 0.01 mol / L lead acetate standard solution until the solution turns into a stable red-violet color as the end point, record the reading, and calculate the percentage content of aluminum according to the formula.

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