Method for rapidly determining content of phosphorus in sodium ferric phosphate-based material
By adding carbon quantum dots to sodium iron phosphate-based materials and using quinomolybdate reagent, the error problem in phosphorus content detection was solved, enabling rapid and accurate phosphorus content determination, reducing errors and improving operability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUNAN JINGGONG INSPECTION SERVICE CO LTD
- Filing Date
- 2026-01-22
- Publication Date
- 2026-04-21
AI Technical Summary
In the acid dissolution process of existing sodium iron phosphate materials, the valence state of iron and coexisting ions may interfere with the precipitation of phosphate ions, resulting in large errors in the phosphorus content detection results. There is a lack of an accurate, reliable and interference-resistant determination method.
Carbon quantum dots were mixed with sodium iron phosphate-based materials and dissolved in an acid solution. The various functional groups of carbon quantum dots were used to improve the dispersion effect. Then, an excess of quinomolybdate reagent was added under specific conditions to carry out the reaction, and the phosphorus content was calculated.
The method enables rapid and accurate determination of phosphorus content in sodium iron phosphate-based materials with an error within 0.05%, and is highly resistant to interference and easy to operate.
Smart Images
Figure CN121899326A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of analytical chemistry and electrode material detection technology, and more specifically, to a method for rapidly determining the phosphorus content in sodium iron phosphate-based materials. Background Technology
[0002] Sodium iron phosphate (SOF) is an important cathode material for sodium-ion batteries, widely used due to its high safety, long cycle life, and environmental friendliness. Phosphorus, as one of its key structural elements, directly determines the stoichiometry, crystal structure integrity, and final electrochemical performance of the material. Therefore, establishing an accurate, reliable, and precise method for determining phosphorus content is crucial for the research and development, production quality control, and product certification of sodium-ion battery cathode materials.
[0003] Currently, there are various methods for determining phosphorus content, such as spectrophotometry, inductively coupled plasma optical emission spectrometry (ICP-OES / MS), and gravimetric methods. Among them, the quinoline phosphomolybdate weighing method, as a classic method, has advantages such as reliable principle, no need for expensive instruments, and high accuracy, and has been adopted by multiple standards. Existing standard methods, such as YS / T 1028.3—2015, provide a basic operational framework.
[0004] However, in practical applications, it has been found that during the acid dissolution process of sodium iron phosphate, the valence state of iron and coexisting ions may potentially interfere with the precipitation of phosphate, leading to a significant error between the detection results and the instrument detection results.
[0005] Therefore, there is an urgent need in this field to establish a phosphorus content determination method specifically for sodium iron phosphate materials that is highly resistant to interference, easy to operate, cost-effective, and provides accurate and reliable results. Summary of the Invention
[0006] In view of the above-mentioned technical problems existing in the prior art, the present invention provides a method for rapidly determining the phosphorus content in sodium iron phosphate-based materials. This method can effectively and rapidly determine the phosphorus content in sodium iron phosphate-based materials, and the results are accurate and reliable.
[0007] To achieve the above objectives, the technical solution of the present invention is as follows:
[0008] A rapid method for determining the phosphorus content in sodium iron phosphate-based materials includes the following steps:
[0009] S1. Weigh out a sample of sodium iron phosphate based material with mass m, add carbon quantum dots, grind and mix evenly to obtain a mixed powder;
[0010] S2. Add the mixed powder to the hydrochloric acid solution, heat to dissolve, cool and filter to obtain the test solution, the volume of the test solution is V0;
[0011] S3. Take a volume of V from the solution to be tested, add nitric acid solution, heat up, and while stirring, add excess quinomolybdate reagent while the solution is in a state of slight boiling. Keep warm and age, then cool to room temperature, separate the solid and liquid, and obtain the first precipitate.
[0012] S4. Wash the first precipitate with water until neutral, dry it to constant weight, and weigh it to obtain the mass of the first precipitate after drying as m1.
[0013] S5. Following the order of steps S1-S4, without adding sodium iron phosphate-based materials, perform a blank experiment to obtain the second precipitate. The mass of the dried second precipitate is m2.
[0014] S6. Calculate the phosphorus content in sodium iron phosphate-based materials using the following formula:
[0015] ;
[0016] Among them, w p The values represent the percentage of phosphorus content, m1 is the mass of the first precipitate, m2 is the mass of the second precipitate, m is the mass of the sample to be tested, V0 is the total volume of the solution to be tested, V is the volume of the test solution taken, and 0.014 is the factor for converting quinoline phosphomolybdate to phosphorus.
[0017] In some embodiments, the mass of the carbon quantum dots is 1-6% of the sodium iron phosphate sample to be tested.
[0018] In some embodiments, the hydrochloric acid solution is hydrochloric acid (1+1), which is prepared by mixing concentrated hydrochloric acid with a concentration of 36-38 wt% and deionized water in a 1:1 volume ratio.
[0019] In some embodiments, the nitric acid solution is nitric acid (1+1), which is prepared by mixing concentrated nitric acid with a concentration of 65-68 wt% and deionized water in a 1:1 volume ratio.
[0020] In some embodiments, in step S2, the temperature is increased to dissolve the mixed powder in a state of slight boiling of the solvent.
[0021] In some embodiments, in step S4, the first precipitate is washed with warm water at 30-45°C.
[0022] In some embodiments, the preparation method of the quinomolybdate reagent includes the following steps:
[0023] Preparation of solution A: Dissolve sodium molybdate dihydrate in water and disperse evenly to obtain a sodium molybdate solution with a concentration of 0.7 g / mL;
[0024] Preparation of solution B: Dissolve citric acid monohydrate in water to obtain a citric acid aqueous solution with a concentration of 0.6 g / mL. Then mix concentrated nitric acid with a concentration of 65-68 wt% with the above citric acid aqueous solution at a volume ratio of 0.85:1 to obtain solution B.
[0025] To prepare solution C: Slowly add solution A to solution B while stirring, mix thoroughly, and you will get solution C.
[0026] Preparation of solution D: Mix concentrated nitric acid (65-68 wt%) with water at a volume ratio of 0.35:1, then add quinoline at a volume ratio of 1:7 to concentrated nitric acid, and stir until clear to obtain solution D;
[0027] Preparation of the final precipitant: Slowly add solution D to solution C, mix well, let stand overnight in the dark, filter through a glass frit funnel, add acetone to the filtrate, dilute with water to 1000 mL, store in a brown polyethylene bottle, and store in the dark at 20-25℃.
[0028] In some embodiments, during the preparation of solution C, the rate at which solution A is added to solution B is 5-10 mL / min.
[0029] In some embodiments, during the final precipitant preparation process, solution D is added to solution C at a rate of 5-10 mL / min.
[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0031] The method for determining the phosphorus content in sodium iron phosphate-based materials of the present invention involves first grinding the sample to be tested with carbon quantum dots until homogeneous, and then dissolving it in acid. The various functional groups on the surface of carbon quantum dots are utilized to improve the dispersion effect of the sample in acid and the reaction effect between the sample to be tested and acid, thereby improving the accuracy of the results. Then, a portion of the solution after dissolving the sample to be tested is added to nitric acid, and then an excess of quinomolybdate reagent is added under specific conditions to carry out the reaction. Finally, the phosphorus content is calculated.
[0032] The method of this invention can effectively and rapidly determine the phosphorus content in sodium iron phosphate-based materials, with an error within 0.05%, demonstrating high accuracy. Furthermore, this method is highly resistant to interference and easy to operate. Attached Figure Description
[0033] Figure 1 The images show the states of carbon quantum dots, a mixture of composite sodium iron phosphate and carbon quantum dots, and the state of the composite sodium iron phosphate before and after heating and dissolving in hydrochloric acid solution. Detailed Implementation
[0034] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0035] 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0036] The hydrochloric acid (1+1) used in the following examples is a hydrochloric acid solution prepared by mixing concentrated hydrochloric acid with a concentration of 36-38wt% and deionized water in a volume ratio of 1:1; the nitric acid (1+1) is a nitric acid solution prepared by mixing concentrated nitric acid with a concentration of 65-68wt% and deionized water in a volume ratio of 1:1.
[0037] Example 1: Acid solubility test of composite sodium iron phosphate sample with or without the addition of carbon quantum dots.
[0038] (1) Sample pretreatment and dispersion
[0039] Take a 40mL centrifuge tube, add 0.0060g of carbon quantum dot powder, and then add 10.00mL of hydrochloric acid (1+1), labeled 1#.
[0040] Accurately weigh 0.2000 g of each of the composite sodium iron phosphate sample that has been dried at 105℃ for 2 h. Add 0.0060 g of carbon quantum dot powder to one sample and grind it in an agate mortar for 5 min to mix it evenly; leave the other sample untreated.
[0041] (2) Sample pretreatment
[0042] The two pretreated samples were placed in two separate 40 mL centrifuge tubes. The tube containing the mixture of carbon quantum dots and sodium iron phosphate was numbered 2#, and the tube containing only the sodium iron phosphate sample was numbered 3#. Each tube was moistened with 0.5 mL of water, and then 10.00 mL of hydrochloric acid (1+1) was added. The tubes were capped, and the initial state of the three tubes was recorded (e.g., ...). Figure 1 As shown in Figure A), the three centrifuge tubes were heated on a hot plate until they were just about to boil and the samples were no longer dispersed. The time required for the samples in each centrifuge tube to dissolve and their respective dissolution states were recorded.
[0043] (3) Observation of results
[0044] After processing according to the above steps, the resulting three centrifuge tubes are as follows: Figure 1 As shown in Figure B:
[0045] It can be observed that the carbon quantum dot acid solution in tube 1 is a pale yellow transparent liquid. Before heating, the samples in tubes 2 and 3 are in a dispersed state. After heating, the color distribution in tube 2 is uniform, indicating that the sample is still uniformly dispersed. In tube 3, some samples agglomerated and settled, causing the supernatant to become lighter in color. Based on this phenomenon and the time required for the dissolution process, the following table 1 shows the results.
[0046] Table 1
[0047]
[0048] It can be seen that the acid dissolution rate is accelerated by 40%-50% after the addition of carbon quantum dots. Therefore, this treatment can speed up the testing efficiency. More importantly, the sample is more evenly dispersed after the addition of carbon quantum dots, which reduces the problem of insufficient dissolution caused by agglomeration, thereby improving the pretreatment efficiency and the consistency of the measurement.
[0049] Example 2: Determination of phosphorus content in a batch of compound sodium iron phosphate.
[0050] (1) Reagent preparation
[0051] Preparation of quinomolybdate precipitant:
[0052] Preparation of solution A: Dissolve 70g of sodium molybdate dihydrate in 100mL of water and disperse evenly to obtain solution A;
[0053] Preparation of solution B: Dissolve 60g of citric acid monohydrate in 100mL of water, then add 85mL of concentrated nitric acid (65-68%), disperse evenly, and obtain solution B;
[0054] To prepare solution C: Slowly add solution A to solution B while stirring (5 mL / min), mix well, and you will get solution C.
[0055] Preparation of solution D: Mix 35 mL of concentrated nitric acid (65-68 wt%) with 100 mL of water, then add 5 mL of quinoline and stir until clear to obtain solution D;
[0056] Preparation of precipitant: Slowly add solution D (5 mL / min) to solution C, mix well, let stand overnight in the dark, filter through a glass frit funnel, add 280 mL of acetone to the filtrate, then dilute with water to 1000 mL, store in a brown polyethylene bottle, and store in the dark at 20-25 °C.
[0057] (2) Sample pretreatment and dispersion
[0058] Accurately weigh 0.2001 g (m) of the ferric phosphate sample that has been dried at 105℃ for 2 hours. Add 0.0060 g of carbon quantum dot powder to the sample and grind it in an agate mortar for 5 min to mix it evenly.
[0059] (3) Sample pretreatment
[0060] All pretreated samples were placed in a 250mL beaker, moistened with a small amount of water, and then 20.00mL of hydrochloric acid (1+1) was added. A watch glass was placed on top, and the mixture was heated on a hot plate until it reached a gentle boil. The mixture was kept at a gentle boil for about 3 minutes until it was completely dissolved. The beaker was then removed and cooled to room temperature. The inner wall of the watch glass was rinsed with a small amount of water to return the adhering material to the solution. The solution was then filtered through a 150mL glass funnel using quantitative slow-speed filter paper. The original beaker and filter paper were washed six times with warm water at 30-45℃. All filtrates were collected in a 250mL volumetric flask (V0), diluted to the mark with water, and shaken well before use.
[0061] (4) Precipitation and aging
[0062] Accurately pipette 25.00 mL (V) of the above test solution into a 500 mL beaker. Add 10.0 mL of nitric acid (1+1) and dilute with water to approximately the 100 mL mark. Cover with a watch glass and heat on a hot plate until the solution gently boils. Turn on the mechanical stirrer and adjust the speed to create a stable vortex. Measure 22 mL of quinomolybdate precipitant using a graduated cylinder and pour it evenly into the boiling test solution over 30 seconds. Continue to maintain the temperature and stir for 2.5 min. Remove the beaker, stop heating, continue stirring for 0.5 min, and then allow it to cool naturally to room temperature (approximately 50 min).
[0063] (5) Filtration and washing
[0064] The G4 glass frit crucible, dried to constant weight at 180℃, was removed and placed in a desiccator to cool to room temperature. After weighing (mass 35.2465 g, m²), it was installed on a vacuum filtration apparatus. The supernatant was first filtered by decantation. Then, the precipitate was washed three times by decantation with approximately 10 mL of warm water at 25-30℃ in a wash bottle. All the precipitate in the beaker was carefully transferred quantitatively to the crucible, and the inner wall of the crucible and the precipitate were washed five more times with warm water (a total of eight washes). The mixture was then dried under vacuum.
[0065] (6) Drying and weighing
[0066] The crucible containing the precipitate was placed in a forced convection drying oven preheated to 180℃±2℃. After drying for 1.5 hours, it was removed and cooled in a desiccator to room temperature for 0.5 hours. The weight was then recorded as 35.5455 g (m1). The crucible was then placed back into the drying oven for another 0.5 hours, cooled, and weighed. The weight was 35.5452 g. The difference between the two weights was 0.0003 g, indicating that constant weight had been achieved.
[0067] (7) Blank test
[0068] Except for the absence of a sample, all other steps were identical, using the same batch of reagents. The difference between the mass of the precipitate and crucible (m3) in the blank test and the mass of the empty crucible (m4) was measured to be 0.0008 g.
[0069] (8) Calculation of results
[0070] Substitute the obtained data into the formula:
[0071] .
[0072] Calculations showed that the phosphorus content of this batch of iron phosphate samples was 20.84% using this method. This result was not significantly different from the phosphorus content value (20.83%) indicated in the product specifications for this batch, proving that the method is effective.
[0073] Example 3: Method Precision Validation Experiment
[0074] For the same homogeneous composite sodium iron phosphate sample (theoretical value is 19.5%), eight independent determinations were performed using the method of this invention.
[0075] The measured values (%) were 19.47, 19.51, 19.48, 19.53, 19.46, 19.50, 19.49, and 19.52, respectively.
[0076] Calculated mean: 19.495%, standard deviation: 0.025%.
[0077] According to the repeatability limit formula, the repeatability limit (r) of this method at this content level is much lower than 0.10%, which proves the excellent reproducibility of the method of the present invention.
[0078] Example 4: Comparative verification of the accuracy and precision of carbon quantum dots in measurement
[0079] Three composite sodium iron phosphate samples with known phosphorus content were selected, and two pretreatment methods were used: one without carbon quantum dots and the other with 0.0060g of carbon quantum dots. Each method was measured 6 times independently, and the statistical results are shown in Table 2 below.
[0080] Table 2
[0081]
[0082] The experimental results clearly show that the method of this invention for determining the phosphorus content in sodium iron phosphate materials has the following advantages:
[0083] 1. Improved accuracy: After adding carbon quantum dots, the mean value of all samples measured is closer to the theoretical value. The absolute error decreased from 0.07%-0.09% to 0.01%, and the relative error decreased from about -0.4% to -0.05%, improving the accuracy by an order of magnitude.
[0084] 2. Improved precision: After adding carbon quantum dots, the standard deviation (SD) of six parallel measurements of each sample was significantly reduced (by an average of about 50%), indicating that the method precision and repeatability were further improved.
[0085] Therefore, the introduction of carbon quantum dots, by improving sample dispersibility, ensures rapid and complete acid dissolution, fundamentally reducing systematic and random errors caused by uneven sample dissolution, thereby simultaneously achieving a comprehensive improvement in analytical speed, accuracy, and precision.
[0086] In summary, the method provided by this invention is complete, standardized in operation, and reliable in data, offering a powerful analytical tool for the quality control and basic research of composite sodium iron phosphate materials.
[0087] 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.
[0088] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.
Claims
1. A method for rapidly determining the phosphorus content in sodium iron phosphate-based materials, characterized in that, Includes the following steps: S1. Weigh out a sample of sodium iron phosphate based material with mass m, add carbon quantum dots, grind and mix evenly to obtain a mixed powder; S2. Add the mixed powder to the hydrochloric acid solution, heat to dissolve, cool and filter to obtain the test solution, the volume of the test solution is V0; S3. Take a volume of V from the solution to be tested, add nitric acid solution, heat up, and while stirring, add excess quinomolybdate reagent while the solution is in a state of slight boiling. Keep warm and age, then cool to room temperature, separate the solid and liquid, and obtain the first precipitate. S4. Wash the first precipitate with water until neutral, dry it to constant weight, and weigh it to obtain the mass of the first precipitate after drying as m1. S5. Following the order of steps S1-S4, without adding sodium iron phosphate-based materials, perform a blank experiment to obtain the second precipitate. The mass of the dried second precipitate is m2. S6. Calculate the phosphorus content in sodium iron phosphate-based materials using the following formula: ； Among them, w p The values represent the percentage of phosphorus content, m1 is the mass of the first precipitate, m2 is the mass of the second precipitate, m is the mass of the sample to be tested, V0 is the total volume of the solution to be tested, V is the volume of the test solution taken, and 0.014 is the factor for converting quinoline phosphomolybdate to phosphorus.
2. The method for rapidly determining the phosphorus content in sodium iron phosphate-based materials according to claim 1, characterized in that, The mass of the carbon quantum dots is 1-6% of the sodium iron phosphate sample to be tested.
3. The method for rapidly determining the phosphorus content in sodium iron phosphate-based materials according to claim 1, characterized in that, The hydrochloric acid solution is prepared by mixing concentrated hydrochloric acid (36-38 wt%) with deionized water in a 1:1 volume ratio.
4. The method for rapidly determining the phosphorus content in sodium iron phosphate-based materials according to claim 1, characterized in that, The nitric acid solution is prepared by mixing concentrated nitric acid (65-68 wt%) with deionized water in a 1:1 volume ratio.
5. The method for rapidly determining the phosphorus content in sodium iron phosphate-based materials according to claim 1, characterized in that, In step S2, the temperature is increased to dissolve the mixed powder in a state of slight boiling in the solvent.
6. The method for rapidly determining the phosphorus content in sodium iron phosphate-based materials according to claim 1, characterized in that, In step S4, the first precipitate is washed with warm water at 30-45℃.
7. The method for rapid determination of phosphorus content in sodium iron phosphate-based materials according to any one of claims 1-6, characterized in that, The preparation method of the quinomolybdate reagent includes the following steps: Preparation of solution A: Dissolve sodium molybdate dihydrate in water and disperse evenly to obtain a sodium molybdate solution with a concentration of 0.7 g / mL; Preparation of solution B: Dissolve citric acid monohydrate in water to obtain a citric acid aqueous solution with a concentration of 0.6 g / mL. Then mix concentrated nitric acid with a concentration of 65-68 wt% with the above citric acid aqueous solution at a volume ratio of 0.85:1 to obtain solution B. To prepare solution C: Slowly add solution A to solution B while stirring, mix thoroughly, and you will get solution C. Preparation of solution D: Mix concentrated nitric acid (65-68 wt%) with water at a volume ratio of 0.35:1, then add quinoline at a volume ratio of 1:7 to concentrated nitric acid, and stir until clear to obtain solution D; Preparation of the final precipitant: Slowly add solution D to solution C, mix well, let stand overnight in the dark, filter through a glass frit funnel, add acetone to the filtrate, dilute with water to 1000 mL, store in a brown polyethylene bottle, and store in the dark at 20-25℃.
8. The method for rapidly determining the phosphorus content in sodium iron phosphate-based materials according to claim 7, characterized in that, During the preparation of solution C, the rate at which solution A is added to solution B is 5-10 mL / min.
9. The method for rapidly determining the phosphorus content in sodium iron phosphate-based materials according to claim 7, characterized in that, In the final precipitant preparation process, the rate at which solution D is added to solution C is 5-10 mL / min.